Abstract

Summarizes information on wood as an engineering material.

Presents properties of wood and wood-based products of

particular concern to the architect and engineer. Includes

discussion of designing with wood and wood-based products

along with some pertinent uses.

Keywords: wood structure, physical properties (wood),

mechanical properties (wood), lumber, wood-based

composites, plywood, panel products, design, fastenings,

wood moisture, drying, gluing, fire resistance, finishing,

decay, sandwich construction, preservation, and woodbased products

March 1999

Forest Products Laboratory. 1999. Wood handbook—Wood as an

engineering material. Gen. Tech. Rep. FPL–GTR–113. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest Products

Laboratory. 463 p.

A limited number of free copies of this publication are available to the

public from the Forest Products Laboratory, One Gifford Pinchot Drive,

Madison, WI 53705–2398. Laboratory publications are sent to hundreds

of libraries in the United States and elsewhere. This publication may

also be viewed on the FPL website at www.fpl.fs.fed.us/.

The Forest Products Laboratory is maintained in cooperation with the

University of Wisconsin.

The use of trade or firm names is for information only and does not imply

endorsement by the U.S. Department of Agriculture of any product or

service.

The United States Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national

origin, gender, religion, age, disability, political beliefs, sexual orientation,

or marital or familial status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (braille, large print, audiotape, etc.)

should contact the USDA’s TARGET Center at (202) 720–2600 (voice and

TDD). To file a complaint of discrimination, write USDA, Director, Office

of Civil Rights, Room 326-W, Whitten Building, 14th and Independence

Avenue, SW, Washington, DC 20250–9410, or call (202) 720–5964

(voice and TDD). USDA is an equal employment opportunity employer.

On the cover: (Left to right, top to bottom)

1. Research at the Forest Products Laboratory,

Madison, Wisconsin, contributes to maximizing

benefits of the Nation’s timber resource.

2. Testing the behavior of wood in fire helps

enhance fire safety.

3. The all-wood, 162-m (530-ft ) clear-span Tacoma

Dome exemplifies the structural and esthetic

potential of wood construction (photo courtesy of

Western Wood Structures, Inc., Tualatin,

Oregon).

4. Bending tests are commonly used to determine

the engineering properties of wood.

5. Engineered wood trusses exemplify research

that has led to more efficient use of wood.

6. The Teal River stress-laminated deck bridge is

located in Sawyer County, Wisconsin.

7. Kiln drying of wood is an important procedure

during lumber manufacturing.

8. Legging adhesive (photo courtesy of Air Products

and Chemicals, Inc., Allentown Pennsylvania). 

Adhesive bonding is a critical component in the

performance of many wood products.

 Pesticide Precautionary Statement

This publication reports research involving pesticides.

It does not contain recommendations for their use, nor

does it imply that the uses discussed here have been

registered. All uses of pesticides must be registered by

appropriate State and/or Federal agencies before they

can be recommended.

Caution: Pesticides can be injurious to humans,

domestic animals, desirable plants, and fish or other

wildlife, if they are not handled or applied properly.

Use all pesticides selectively and carefully. Follow

recommended practices for the disposal of surplus

pesticides and pesticide containers.
Wood Handbook

Wood as an Engineering Material

Forest Products Laboratory

USDA Forest Service

Madison, Wisconsin
 iii

Contents

Preface v

Acknowledgments vii

Contributors xi

1 Characteristics and Availability of

Commercially Important Wood

Timber Resources and Uses 1–2

Species Descriptions 1–3

U.S. Wood Species 1–3

Imported Woods 1–17

References 1–34

2 Structure of Wood

Bark, Wood, Branches, and Cambium 2–1

Sapwood and Heartwood 2–2

Growth Rings 2–2

Wood Cells 2–3

Chemical Composition 2–3

Species Identification 2–4

References 2–4

3 Physical Properties and Moisture Relations

of Wood

Appearance 3–1

Moisture Content 3–5

Shrinkage 3–7

Weight, Density, and Specific Gravity 3–11

Working Qualities 3–15

Decay Resistance 3–15

Thermal Properties 3–15

Electrical Properties 3–21

Coefficient of Friction 3–22

Nuclear Radiation 3–23

References 3–23

4 Mechanical Properties of Wood

Orthotropic Nature of Wood 4–1

Elastic Properties 4–2

Strength Properties 4–3

Vibration Properties 4–25

Mechanical Properties of Clear Straight-Grained

 Wood 4–26

Natural Characteristics Affecting Mechanical

 Properties 4–27

Effects of Manufacturing and Service

 Environments 4–34

References 4–44

5 Commercial Lumber

Hardwood Lumber 5–1

Softwood Lumber 5–7

Purchase of Lumber 5–12

Commonly Used Lumber Abbreviations 5–18

References 5–20

6 Lumber Stress Grades and Design Properties

Responsibilities and Standards for Stress

 Grading 6–2

Visually Graded Structural Lumber 6–3

Machine-Graded Structural Lumber 6–7

Adjustment of Properties for Design Use 6–11

References 6–14

7 Fastenings

Nails 7–2

Spikes 7–8

Staples 7–8

Drift Bolts 7–9

Wood Screws 7–9

Lag Screws 7–11

Bolts 7–14

Connector Joints 7–18

Multiple-Fastener Joints 7–24

Metal Plate Connectors 7–25

Fastener Head Embedment 7–26

References 7–27

8 Structural Analysis Equations

Deformation Equations 8–1

Stress Equations 8–4

Stability Equations 8–8

References 8–11

9 Adhesive Bonding of Wood Materials

Adhesion to Wood 9–1

Surface Properties of Wood Adherends 9–2

Physical Properties of Wood Adherends 9–6

Adhesives 9–9

Bonding Process 9–15

Bonded Joints 9–18

Testing and Performance 9–20

References 9–23
iv

10 Wood-Based Composites and Panel Products

Scope 10–2

Types of Conventional Composite

 Materials 10–3

Adhesive Considerations 10–3

Additives 10–4

General Manufacturing Issues 10–4

Standards for Wood–Based Panels 10–4

Plywood 10–6

Particle and Fiber Composites 10–13

Wood–Nonwood Composites 10–24

References 10–30

11 Glued Structural Members

Structural Composite Lumber 11–1

Glulam 11–3

Glued Members With Lumber and

 Panels 11–12

Structural Sandwich Construction 11–16

References 11–21

12 Drying and Control of Moisture Content

and Dimensional Changes

Determination of Moisture Content 12–1

Recommended Moisture Content 12–3

Drying of Wood 12–5

Moisture Control During Transit and

 Storage 12–14

Dimensional Changes in Wood 12–15

Design Factors Affecting Dimensional

 Change 12–18

Wood Care and Installation During

 Construction 12–18

References 12–20

13 Biodeterioration of Wood

Fungus Damage and Control 13–1

Bacteria 13–8

Insect Damage and Control 13–8

Marine Borer Damage and Control 13–13

References 13–15

14 Wood Preservation

Wood Preservatives 14–2

Preservative Effectiveness 14–12

Effect of Species on Penetration 14–12

Preparation of Timber for Treatment 14–17

Application of Preservatives 14–19

Handling and Seasoning of Timber After

 Treatment 14–24

Quality Assurance for Treated Wood 14–25

References 14–26

15 Finishing of Wood

Factors Affecting Finish Performance 15–1

Control of Water or Moisture in Wood 15–9

Types of Exterior Wood Finishes 15–14

Application of Wood Finishes 15–19

Finish Failure or Discoloration 15–24

Finishing of Interior Wood 15–30

Finishes for Items Used for Food 15–32

Wood Cleaners and Brighteners 15–33

Paint Strippers 15–33

Lead-Based Paint 15–35

References 15–36

16 Use of Wood In Building and Bridges

Light-Frame Buildings 16–1

Post-Frame and Pole Buildings 16–4

Log Buildings 16–6

Heavy Timber Buildings 16–6

Timber Bridges 16–9

Considerations for Wood Buildings 16–10

References 16–14

17 Fire Safety

Fire Safety Design and Evaluation 17–1

Fire Performance Characteristics of Wood 17–6

Flame-Retardant Treatments 17–12

References 17–13

18 Round Timbers and Ties

Standards and Specifications 18–1

Material Requirements 18–1

Availability 18–2

Form 18–3

Weight and Volume 18–5

Durability 18–6

Strength Properties 18–7

References 18–8

19 Specialty Treatments

Plasticizing Wood 19–1

Modified Woods 19–4

Paper-Based Plastic Laminates 19–12

References 19–14

Glossary G–1

Index I–1
 v

Efficient use of our nation’s timber resource is a vital concern. Because a major use of wood in the United States is in

construction, particularly housing construction, good practice in this endeavor can have a profound impact on the resource. This

handbook is intended as an aid to more efficient use of wood as a construction material. It provides engineers, architects, and

others with a source of information on the physical and mechanical properties of wood and how these properties are affected by

variations in the wood itself. Continuing research and evaluation techniques hold promise for wider and more efficient utilization

of wood and for more advanced industrial, structural, and decorative uses.

This handbook was prepared by the Forest Products Laboratory (FPL), a unit of the research organization of the Forest Service,

U.S. Department of Agriculture. The Laboratory, established in 1910, is maintained at Madison, Wisconsin, in cooperation

with the University of Wisconsin. It was the first institution in the world to conduct general research on wood and its

utilization. The accumulation of information that has resulted from its engineering and allied investigations of wood and

wood products over nine decades—along with knowledge of everyday construction practices and problems—is the chief basis

for this handbook.

The Wood Handbook was first issued in 1935, and slightly revised in 1939, as an unnumbered publication. Further revisions

in 1955, 1974, and 1987 were published by the U.S. Department of Agriculture as Agriculture Handbook No. 72. This current

work is a complete revision of the 1987 edition. This revision was necessary to reflect more recent research accomplishments

and technological changes.

The audience for the Wood Handbook is fairly broad. Therefore, the coverage of each chapter is aimed at providing a general

discussion of the topic, with references included for additional information. Past versions of the Wood Handbook tended to report

only the findings and applications of FPL research. Although the handbook is not intended to be a state-of-the-art review, this

approach would now leave significant gaps in some important areas. The current edition has broadened the sources of

information to provide better coverage of important topics.

The organization of this version of the Wood Handbook is similar to previous ones, with some modifications:

• Plywood (chapter 11 in the previous version), insulation board, hardboard, medium-density fiberboard (part of chapter 21

in the previous version), and wood-based particle panel materials (chapter 22 in the previous version) are now included

in a new chapter on wood-based composites and panel products.

• Structural sandwich construction (chapter 12 in the previous version) is now included in the chapter on glued structural

members.

• Moisture movement and thermal insulation in light-frame structures (chapter 20 in the previous version) are now part of

a new chapter on use of wood in buildings and bridges.

• Bent wood members (chapter 13 in the previous version), modified woods, and paper-based laminates (chapter 23 in the

previous version) are now included in a chapter on specialty treatments.

Consistent with movement by many U.S. standards agencies and industry associations toward use of metric units and nearuniversal implementation of metric usage in the international community, units of measurement in this version of the handbook

are provided primarily in metric units, with customary inch–pound equivalents as secondary units. All conversions in this

handbook to metric units, including conversions of empirically derived equations, are direct (or soft) conversions from

previously derived inch–pound values. At some future time, metric expressions may need to be derived from a reevaluation

of original research.

Preface
 vii

Acknowledgments

We gratefully acknowledge the extraordinary effort of the following individuals in their review of the final draft of this

entire volume. Their effort has substantially enhanced the clarity, consistency, and coverage of the Wood Handbook.

Donald Bender

Wood Materials & Engineering Laboratory

Washington State University

Pullman, Washington

Arthur Brauner

Forest Products Society

Madison, Wisconsin

Bradford Douglas

American Forest & Paper Association

Washington, DC

David Green

USDA Forest Service, Forest Products Laboratory

Madison, Wisconsin

Michael Hunt

Department of Forestry and Natural Resources

Purdue University

West Lafayette, Indiana

Thomas McLain

Department of Forest Products

Oregon State University

Corvallis, Oregon

Russell Moody

Madison, Wisconsin

Michael O’Halloran

APA—The Engineered Wood Association

Tacoma, Washington

Erwin Schaffer

Sun City West, Arizona

Contributors to the Wood Handbook are indebted to the following individuals and organizations for their early

technical review of chapter manuscripts.

Terry Amburgey

Forest Products Laboratory

Mississippi State University

Mississippi State, Mississippi

Jon Arno

Troy, Minnesota

B. Alan Bendtsen

Madison, Wisconsin

A. William Boehner

Trus Joist MacMillan

Boise, Idaho

R. Michael Caldwell

American Institute of Timber Construction

Englewood, Colorado

Donald Carr

NAHB—National Research Center

Upper Marlboro, Maryland

Richard Caster

Weyerhaeuser Company

Tacoma, Washington

Kevin Cheung

Western Wood Products Association

Portland, Oregon

Stephen Clark

Northeastern Lumber Manufacturers Association

Cumberland Center, Maine

Richard Cook

National Casein Company

Santa Ana, California

William Crossman

Atlanta Wood Industries

Savannah, Georgia
viii

Thomas Daniels

Energy Products of Idaho

Coeur D’Alene, Idaho

Donald DeVisser

West Coast Lumber Inspection Bureau

Portland, Oregon

Bradford Douglas

American Forest and Paper Association

Washington, DC

Stan Elberg

National Oak Flooring Manufacturers Association

Memphis, Tennessee

Paul Foehlich

Southern Cypress Manufacturers Association

Pittsburgh, Pennsylvania

Barry Goodell

Forest Products Laboratory

University of Maine

Orono, Maine

Kevin Haile

HP&VA

Reston, Virginia

Daniel Hare

The Composite Panel Association

Gaithersburg, Maryland

R. Bruce Hoadley

Forestry Department

University of Massachusetts

Amherst, Massachusetts

David Hon

Department of Forest Resources

Clemson University

Clemson, South Carolina

Robert Hunt

Western Wood Products Association

Portland, Oregon

Lisa Johnson

Southern Pine Inspection Bureau

Pensacola, Florida

Tom Jones

Southern Pine Inspection Bureau

Pensacola, Florida

Charles Jourdain

California Redwood Association

Novato, California

John Kressbach

Gillette, New Jersey

Robert Kundrot

Nestle Resins Corporation

Springfield, Oregon

Steven Lawser

Wood Component Manufacturers Association

Marietta, Georgia

Phillip Line

American Forest & Paper Association

Washington, DC

Joseph Loferski

Brooks Forest Products Center

Blacksburg, Virginia

Maple Flooring Manufacturers Association

Northbrook, Illinois

Thomas McLain

Department of Forest Products

Oregon State University

Corvallis, Oregon

David McLean

Civil Engineering Department

Washington State University

Pullman, Washington

Rodney McPhee

Canadian Wood Council

Ottawa, Ontario, Canada

Michael Milota

Oregon State University

Corvallis, Oregon

Jeffrey Morrell

Department of Forest Products

Oregon State University

Corvallis, Oregon

National Hardwood Lumber Association

Memphis, Tennessee

Darrel Nicholas

Forest Products Laboratory

Mississippi State University

Mississippi State, Mississippi

Michael O’Halloran

APA—The Engineered Wood Association

Tacoma, Washington
 ix

Perry Peralta

Department of Wood and Paper Science

North Carolina State University

Raleigh, North Carolina

David Plackett

Forintek Canada Corporation

Vancouver, British Columbia, Canada

David Pollock

Civil Engineering Department

Washington State University

Pullman, Washington

Redwood Inspection Service

Mill Valley, California

Alan Ross

Kop–Coat Inc.

Pittsburgh, Pennsylvania

Thomas Searles

American Lumber Standards Committee

Germantown, Maryland

James Shaw

Weyerhaeuser Company

Tacoma, Washington

Bradley Shelley

West Coast Lumber Inspection Bureau

Portland, Oregon

Ramsey Smith

Louisiana Forest Products Laboratory

Baton Rouge, Louisiana

William Smith

SUNY–ESF

Wood Products Engineering

Syracuse, New York

Edward Starostovic

PFS/TECO Corporations

Madison, Wisconsin

Louis Wagner

American Hardwood Association

Palatine, Illinois

Eugene Wengert

Department of Forestry

University of Wisconsin

Madison, Wisconsin

Michael Westfall

Red Cedar Shingle & Handsplit Shake Bureau

Bellevue, Washington

Borjen Yeh

APA—The Engineered Wood Association

Tacoma, Washington
 xi

Contributors

The following staff of the Forest Products Laboratory contributed to the writing, revision, and compilation of information

contained in the Wood Handbook.

Mark A. Dietenberger

Research General Engineer

David W. Green

Supervisory Research General Engineer

David E. Kretschmann

Research General Engineer

Roland Hernandez

Research General Engineer

Terry L. Highley

Supervisory Research Plant Pathologist (retired)

Rebecca E. Ibach

Chemist

Jen Y. Liu

Research General Engineer

Kent A. McDonald

Research Forest Products Technologist (retired)

Regis B. Miller

Botanist

Russell C. Moody

Supervisory Research General Engineer (retired)

Roger M. Rowell

Supervisory Research Chemist

William T. Simpson

Research Forest Products Technologist

Lawrence A. Soltis

Research General Engineer

Anton TenWolde

Research Physicist

Ronald W. Wolfe

Research General Engineer

Charles B. Vick

Research Forest Products Technologist

Robert H. White

Supervisory Wood Scientist

R. Sam Williams

Supervisory Research Chemist

Jerrold E. Winandy

Research Forest Products Technologist

John A. Youngquist

Supervisory Research General Engineer
1–1

Chapter 1

Characteristics and Availability of

Commercially Important Woods

Regis B. Miller

Contents

Timber Resources and Uses 1–2

Hardwoods and Softwoods 1–2

Commercial Sources of Wood Products 1–2

Use Classes and Trends 1–3

Species Descriptions 1–3

U.S. Wood Species 1–3

Hardwoods 1–3

Softwoods 1–10

Imported Woods 1–17

Hardwoods 1–17

Softwoods 1–33

References 1–34

hroughout history, the unique characteristics and

comparative abundance of wood have made it a

natural material for homes and other structures,

furniture, tools, vehicles, and decorative objects. Today, for

the same reasons, wood is prized for a multitude of uses.

All wood is composed of cellulose, lignin, hemicelluloses,

and minor amounts (5% to 10%) of extraneous materials

contained in a cellular structure. Variations in the characteristics and volume of these components and differences in cellular structure make woods heavy or light, stiff or flexible, and

hard or soft. The properties of a single species are relatively

constant within limits; therefore, selection of wood by species alone may sometimes be adequate. However, to use

wood to its best advantage and most effectively in engineering applications, specific characteristics or physical properties

must be considered.

Historically, some species filled many purposes, while other

less available or less desirable species served only one or two

needs. For example, because white oak is tough, strong, and

durable, it was highly prized for shipbuilding, bridges,

cooperage, barn timbers, farm implements, railroad crossties,

fence posts, and flooring. Woods such as black walnut and

cherry were used primarily for furniture and cabinets. Hickory

was manufactured into tough, hard, and resilient striking-tool

handles, and black locust was prized for barn timbers. What

the early builder or craftsman learned by trial and error became the basis for deciding which species were appropriate

for a given use in terms of their characteristics. It was commonly accepted that wood from trees grown in certain locations under certain conditions was stronger, more durable,

more easily worked with tools, or finer grained than wood

from trees in other locations. Modern research on wood has

substantiated that location and growth conditions do

significantly affect wood properties.

The gradual reductions in use of old-growth forests in the

United States has reduced the supply of large clear logs for

lumber and veneer. However, the importance of high-quality

logs has diminished as new concepts of wood use have been

introduced. Second-growth wood, the remaining old-growth

forests, and imports continue to fill the needs for wood in the

quality required. Wood is as valuable an engineering material as ever, and in many cases, technological advances have

made it even more useful.

T
 1–2

The inherent factors that keep wood in the forefront of raw

materials are many and varied, but a chief attribute is its

availability in many species, sizes, shapes, and conditions to

suit almost every demand. Wood has a high ratio of strength

to weight and a remarkable record for durability and performance as a structural material. Dry wood has good insulating

properties against heat, sound, and electricity. It tends to

absorb and dissipate vibrations under some conditions of

use, and yet it is an incomparable material for such musical

instruments as the violin. The grain patterns and colors of

wood make it an esthetically pleasing material, and its

appearance may be easily enhanced by stains, varnishes,

lacquers, and other finishes. It is easily shaped with tools

and fastened with adhesives, nails, screws, bolts, and dowels. Damaged wood is easily repaired, and wood structures

are easily remodeled or altered. In addition, wood resists

oxidation, acid, saltwater, and other corrosive agents, has

high salvage value, has good shock resistance, can be treated

with preservatives and fire retardants, and can be combined

with almost any other material for both functional and

esthetic uses.

Timber Resources and Uses

In the United States, more than 100 wood species are available to the prospective user, but all are unlikely to be available in any one locality. About 60 native woods are of major

commercial importance. Another 30 species are commonly

imported in the form of logs, cants, lumber, and veneer for

industrial uses, the building trade, and crafts.

A continuing program of timber inventory is in effect in the

United States through the cooperation of Federal and State

agencies, and new information on wood resources is published in State and Federal reports. Two of the most valuable

sourcebooks are An Analysis of the Timber Situation in the

United States 1989–2040 (USDA 1990) and The 1993 RPA

Timber Assessment Update (Haynes and others 1995).

Current information on wood consumption, production,

imports, and supply and demand is published periodically

by the Forest Products Laboratory (Howard 1997) and is

available from the Superintendent of Documents, U.S.

Government Printing Office, Washington, DC.

Hardwoods and Softwoods

Trees are divided into two broad classes, usually referred to

as hardwoods and softwoods. These names can be confusing

since some softwoods are actually harder than some hardwoods, and conversely some hardwoods are softer than some

softwoods. For example, softwoods such as longleaf pine and

Douglas-fir are typically harder than the hardwoods basswood

and aspen. Botanically, hardwoods are Angiosperms; the

seeds are enclosed in the ovary of the flower. Anatomically,

hardwoods are porous; that is, they contain vessel elements.

A vessel element is a wood cell with open ends; when vessel

elements are set one above another, they form a continuous

tube (vessel), which serves as a conduit for transporting water

or sap in the tree. Typically, hardwoods are plants with

broad leaves that, with few exceptions in the temperate region, lose their leaves in autumn or winter. Most imported

tropical woods are hardwoods. Botanically, softwoods are

Gymnosperms or conifers; the seeds are naked (not enclosed

in the ovary of the flower). Anatomically, softwoods are

nonporous and do not contain vessels. Softwoods are usually

cone-bearing plants with needle- or scale-like evergreen

leaves. Some softwoods, such as larches and baldcypress,

lose their needles during autumn or winter.

Major resources of softwood species are spread across the

United States, except for the Great Plains where only small

areas are forested. Softwood species are often loosely grouped

in three general regions, as shown in Table 1–1. Hardwoods

also occur in all parts of the United States, although most

grow east of the Great Plains. Hardwood species are shown

by region in Table 1–2.

Commercial Sources

of Wood Products

Softwoods are available directly from the sawmill, wholesale

and retail yards, or lumber brokers. Softwood lumber and

plywood are used in construction for forms, scaffolding,

framing, sheathing, flooring, moulding, paneling, cabinets,

poles and piles, and many other building components. Softwoods may also appear in the form of shingles, sashes,

doors, and other millwork, in addition to some rough products such as timber and round posts.

Hardwoods are used in construction for flooring, architectural

woodwork, interior woodwork, and paneling. These items

are usually available from lumberyards and building supply

dealers. Most hardwood lumber and dimension stock are

remanufactured into furniture, flooring, pallets, containers,

dunnage, and blocking. Hardwood lumber and dimension

Table 1–1. Major resources of U.S. softwoods according

to region

Western Northern Southern

Incense-cedar Northern white-cedar Atlantic white-cedar

Port-Orford-cedar Balsam fir Baldcypress

Douglas-fir Eastern hemlock Fraser fir

White firs Fraser fir Southern Pine

Western hemlock Jack pine Eastern redcedar

Western larch Red pine

Lodgepole pine Eastern white pine

Ponderosa pine Eastern redcedar

Sugar pine Eastern spruces

Western white pine Tamarack

Western redcedar

Redwood

Engelmann spruce

Sitka spruce

Yellow-cedar
1–3

stock are available directly from the manufacturer, through

wholesalers and brokers, and from some retail yards.

Both softwood and hardwood products are distributed

throughout the United States. Local preferences and the

availability of certain species may influence choice, but a

wide selection of woods is generally available for building

construction, industrial uses, remanufacturing, and home use.

Use Classes and Trends

The production and consumption levels of some of the many

use-classifications for wood are increasing with the overall

national economy, and others are holding about the same.

The most vigorously growing wood-based industries are

those that convert wood to thin slices (veneer), particles

(chips, flakes), or fiber pulps and reassemble the elements to

produce various types of engineered panels such as plywood,

particleboard, strandboard, veneer lumber, paper, paperboard,

and fiberboard products. Another growing wood industry is

the production of laminated wood. For a number of years, the

lumber industry has produced almost the same volume of

wood per year. Modest increases have occurred in the production of railroad crossties, cooperage, shingles, and shakes.

Species Descriptions

In this chapter, each species or group of species is described

in terms of its principal location, characteristics, and uses.

More detailed information on the properties of these and

other species is given in various tables throughout this

handbook. Information on historical and traditional uses is

provided for some species. Common and botanical names

follow the Checklist of United States Trees (Little 1979).

U.S. Wood Species

Hardwoods

Alder, Red

Red alder (Alnus rubra) grows along the Pacific coast between Alaska and California. It is the principal hardwood for

commercial manufacture of wood products in Oregon and

Washington and the most abundant commercial hardwood

species in these two states.

The wood of red alder varies from almost white to pale

pinkish brown, and there is no visible boundary between

heartwood and sapwood. Red alder is moderately light in

weight and intermediate in most strength properties but low

in shock resistance. It has relatively low shrinkage.

The principal use of red alder is for furniture, but it is also

used for sash and door panel stock and other millwork.

Ash (White Ash Group)

Important species of the white ash group are American white

ash (Fraxinus americana), green ash (F. pennsylvanica), blue

ash (F. quadrangulata), and Oregon ash (F. latifolia). The

first three species grow in the eastern half of the United

States. Oregon ash grows along the Pacific Coast.

The heartwood of the white ash group is brown, and the

sapwood is light-colored or nearly white. Second-growth

trees are particularly sought after because of the inherent

qualities of the wood from these trees: it is heavy, strong,

hard, and stiff, and it has high resistance to shock. Oregon

ash has somewhat lower strength properties than American

white ash, but it is used for similar purposes on the West

Coast.

American white ash is used principally for nonstriking tool

handles, oars, baseball bats, and other sporting and athletic

goods. For handles of the best grade, some handle specifications call for not less than 2 nor more than 7 growth rings

per centimeter (not less than 5 nor more than 17 growth

rings per inch). The additional weight requirement of

690 kg/m3

 (43 lb/ft3) or more at 12% moisture content ensures high quality material. Principal uses for the white ash

group are decorative veneer, cabinets, furniture, flooring,

millwork, and crates.

Table 1–2. Major resources of U.S. hardwoods according

to region

Southern

Northern and

Appalachia Western

Ash Ash Red alder

Basswood Aspen Oregon ash

American beech Basswood Aspen

Butternut Buckeye Black cottonwood

Cottonwood Butternut California black oak

Elm American beech Oregon white oak

Hackberry Birch Bigleaf maple

Pecan hickory Black cherry Paper birch

True hickory American chestnuta Tanoak

Honeylocust Cottonwood

Black locust Elm

Magnolia Hackberry

Soft maple True hickory

Red oaks Honeylocust

White oaks Black locust

Sassafras Hard maple

Sweetgum Soft maple

American sycamore Red oaks

Tupelo White oaks

Black walnut American sycamore

Black willow Black walnut

Yellow-poplar Yellow-poplar

a

American chestnut is no longer harvested, but chestnut

 lumber from salvaged timbers can still be found on the

 market.
 1–4

Ash (Black Ash Group)

The black ash group includes black ash (F. nigra) and

pumpkin ash (F. profunda). Black ash grows in the Northeast and Midwest, and pumpkin ash in the South.

The heartwood of black ash is a darker brown than that of

American white ash; the sapwood is light-colored or nearly

white. The wood of the black ash group is lighter in weight

(basic specific gravity of 0.45 to 0.48) than that of the white

ash group (>0.50). Pumpkin ash, American white ash, and

green ash that grow in southern river bottoms, especially in

areas frequently flooded for long periods, produce buttresses

that contain relatively lightweight and brash wood.

Principal uses for the black ash group are decorative veneer,

cabinets, millwork, furniture, cooperage, and crates.

Aspen

Aspen is a generally recognized name that is applied to

bigtooth (Populus grandidentata) and quaking

(P. tremuloides) aspen. Aspen does not include balsam

poplar (P. balsamifera) and the other species of Populus that

are included in the cottonwoods. In lumber statistics of the

U.S. Bureau of the Census, however, the term cottonwood

includes all the preceding species. Also, the lumber of aspen

and cottonwood may be mixed in trade and sold as either

popple or cottonwood. The name popple should not be

confused with yellow-poplar (Liriodendron tulipifera), also

known in the trade as poplar. Aspen lumber is produced

principally in the Northeastern and Lake States, with some

production in the Rocky Mountain States.

The heartwood of aspen is grayish white to light grayish

brown. The sapwood is lighter colored and generally merges

gradually into the heartwood without being clearly marked.

Aspen wood is usually straight grained with a fine, uniform

texture. It is easily worked. Well-dried aspen lumber does

not impart odor or flavor to foodstuffs. The wood of aspen is

lightweight and soft. It is low in strength, moderately stiff,

and moderately low in resistance to shock and has moderately high shrinkage.

Aspen is cut for lumber, pallets, boxes and crating, pulpwood, particleboard, strand panels, excelsior, matches, veneer, and miscellaneous turned articles. Today, aspen is one

of the preferred species for use in oriented strandboard, a

panel product that is increasingly being used as sheathing.

Basswood

American basswood (Tilia americana) is the most important

of the native basswood species; next in importance is white

basswood (T. heterophylla), and no attempt is made to

distinguish between these species in lumber form. In commercial usage, “white basswood” is used to specify the white

wood or sapwood of either species. Basswood grows in the

eastern half of the United States from the Canadian provinces

southward. Most basswood lumber comes from the Lake,

Middle Atlantic, and Central States.

The heartwood of basswood is pale yellowish brown with

occasional darker streaks. Basswood has wide, creamy white

or pale brown sapwood that merges gradually into heartwood. When dry, the wood is without odor or taste. It is

soft and light in weight, has fine, even texture, and is

straight grained and easy to work with tools. Shrinkage in

width and thickness during drying is rated as high; however,

basswood seldom warps in use.

Basswood lumber is used mainly in venetian blinds, sashes

and door frames, moulding, apiary supplies, wooden ware,

and boxes. Some basswood is cut for veneer, cooperage,

excelsior, and pulpwood, and it is a favorite of wood carvers.

Beech, American

Only one species of beech, American beech (Fagus

grandifolia), is native to the United States. It grows in the

eastern one-third of the United States and adjacent Canadian

provinces. The greatest production of beech lumber is in the

Central and Middle Atlantic States.

In some beech trees, color varies from nearly white sapwood

to reddish-brown heartwood. Sometimes there is no clear

line of demarcation between heartwood and sapwood. Sapwood may be roughly 7 to 13 cm (3 to 5 in.) wide. The

wood has little figure and is of close, uniform texture. It has

no characteristic taste or odor. The wood of beech is classed

as heavy, hard, strong, high in resistance to shock, and

highly suitable for steam bending. Beech shrinks substantially and therefore requires careful drying. It machines

smoothly, is an excellent wood for turning, wears well, and

is rather easily treated with preservatives.

Most beech is used for flooring, furniture, brush blocks,

handles, veneer, woodenware, containers, and cooperage.

When treated with preservative, beech is suitable for

railway ties.

Birch

The three most important species are yellow birch (Betula

alleghaniensis), sweet birch (B. lenta), and paper birch

(B. papyrifera). These three species are the source of most

birch lumber and veneer. Other birch species of some commercial importance are river birch (B. nigra), gray birch

(B. populifolia), and western paper birch (B. papyrifera var.

commutata). Yellow, sweet, and paper birch grow principally

in the Northeast and the Lake States; yellow and sweet birch

also grow along the Appalachian Mountains to northern

Georgia.

Yellow birch has white sapwood and light reddish-brown

heartwood. Sweet birch has light-colored sapwood and dark

brown heartwood tinged with red. For both yellow and sweet

birch, the wood is heavy, hard, and strong, and it has good

shock-resisting ability. The wood is fine and uniform in

texture. Paper birch is lower in weight, softer, and lower in

strength than yellow and sweet birch. Birch shrinks considerably during drying.
1–5

Yellow and sweet birch lumber is used primarily for the

manufacture of furniture, boxes, baskets, crates, wooden ware,

cooperage, interior woodwork, and doors; veneer plywood is

used for flush doors, furniture, paneling, cabinets, aircraft,

and other specialty uses. Paper birch is used for toothpicks,

tongue depressors, ice cream sticks, and turned products,

including spools, bobbins, small handles, and toys.

Buckeye

Buckeye consists of two species, yellow buckeye (Aesculus

octandra) and Ohio buckeye (A. glabra). These species

range from the Appalachians of Pennsylvania, Virginia, and

North Carolina westward to Kansas, Oklahoma, and Texas.

Buckeye is not customarily separated from other species

when manufactured into lumber and can be used for the same

purposes as aspen (Populus), basswood (Tilia), and sapwood

of yellow-poplar (Liriodendron tulipifera).

The white sapwood of buckeye merges gradually into the

creamy or yellowish white heartwood. The wood is uniform

in texture, generally straight grained, light in weight, weak

when used as a beam, soft, and low in shock resistance. It is

rated low on machinability such as shaping, mortising,

boring, and turning.

Buckeye is suitable for pulping for paper; in lumber form, it

has been used principally for furniture, boxes and crates,

food containers, wooden ware, novelties, and planing mill

products.

Butternut

Also called white walnut, butternut (Juglans cinerea) grows

from southern New Brunswick and Maine west to Minnesota. Its southern range extends into northeastern Arkansas

and eastward to western North Carolina.

The narrow sapwood is nearly white and heartwood is light

brown, frequently modified by pinkish tones or darker brown

streaks. The wood is moderately light in weight (about the

same as eastern white pine), rather coarse textured, moderately weak in bending and endwise compression, relatively

low in stiffness, moderately soft, and moderately high in

shock resistance. Butternut machines easily and finishes

well. In many ways, butternut resembles black walnut especially when stained, but it does not have the same strength

or hardness.

Principal uses are for lumber and veneer, which are further

manufactured into furniture, cabinets, paneling, interior

woodwork, and miscellaneous rough items.

Cherry, Black

Black cherry (Prunus serotina) is sometimes known as

cherry, wild black cherry, and wild cherry. It is the only

native species of the genus Prunus of commercial importance

for lumber production. Black cherry is found from southeastern Canada throughout the eastern half of the United States.

Production is centered chiefly in the Middle Atlantic States.

The heartwood of black cherry varies from light to dark

reddish brown and has a distinctive luster. The nearly white

sapwood is narrow in old-growth trees and wider in secondgrowth trees. The wood has a fairly uniform texture and very

good machining properties. It is moderately heavy, strong,

stiff, and moderately hard; it has high shock resistance and

moderately high shrinkage. Black cherry is very dimensionally stable after drying.

Black cherry is used principally for furniture, fine veneer

panels, and architectural woodwork. Other uses include

burial caskets, wooden ware, novelties, patterns, and

paneling.

Chestnut, American

American chestnut (Castanea dentata) is also known as

sweet chestnut. Before this species was attacked by a blight

in the 1920s, it grew in commercial quantities from New

England to northern Georgia. Practically all standing chestnut has been killed by blight, and most supplies of the

lumber come from salvaged timbers. Because of the species’

natural resistance to decay, standing dead trees in the Appalachian Mountains continued to provide substantial quantities of lumber for several decades after the blight, but this

source is now exhausted.

The heartwood of chestnut is grayish brown or brown and

darkens with age. The sapwood is very narrow and almost

white. The wood is coarse in texture; growth rings are made

conspicuous by several rows of large, distinct pores at the

beginning of each year’s growth. Chestnut wood is moderately light in weight, moderately hard, moderately low in

strength, moderately low in resistance to shock, and low in

stiffness. It dries well and is easy to work with tools.

Chestnut was once used for poles, railroad crossties, furniture, caskets, boxes, shingles, crates, and corestock for veneer

panels. At present, it appears most frequently as wormy

chestnut for paneling, interior woodwork, and picture frames.

Cottonwood

Cottonwood includes several species of the genus Populus.

Most important are eastern cottonwood (P. deltoides and

varieties), also known as Carolina poplar and whitewood;

swamp cottonwood (P. heterophylla), also known as

cottonwood, river cottonwood, and swamp poplar; black

cottonwood (P. trichocarpa); and balsam poplar

(P. balsamifera). Eastern and swamp cottonwood grow

throughout the eastern half of the United States. Greatest

production of lumber is in the Southern and Central States.

Black cottonwood grows on the West Coast and in western

Montana, northern Idaho, and western Nevada. Balsam

poplar grows from Alaska across Canada and in the northern

Great Lakes States.

The heartwood of cottonwood is grayish white to light

brown. The sapwood is whitish and merges gradually with

the heartwood. The wood is comparatively uniform in texture and generally straight grained. It is odorless when well

dried. Eastern cottonwood is moderately low in bending and
 1–6

compressive strength, moderately stiff, moderately soft, and

moderately low in ability to resist shock. Most strength

properties of black cottonwood are slightly lower than those

of eastern cottonwood. Both eastern and black cottonwood

have moderately high shrinkage. Some cottonwood is

difficult to work with tools because of its fuzzy surface, which

is mainly the result of tension wood (see discussion of Reaction Wood in Ch. 4).

Cottonwood is used principally for lumber, veneer, pulpwood, excelsior, and fuel. Lumber and veneer are used

primarily for boxes, crates, baskets, and pallets.

Elm

Six species of elm grow in the eastern United States:

American (Ulmus americana), slippery (U. rubra), rock

(U. thomasii), winged (U. alata), cedar (U. crassifolia), and

September (U. serotina) elm. American elm is also known

as white, water, and gray elm; slippery elm as red elm; rock

elm as cork and hickory elm; winged elm as wahoo; cedar

elm as red and basket elm; and September elm as red elm.

American elm is threatened by two diseases, Dutch Elm

disease and phloem necrosis, which have killed hundreds of

thousands of trees.

Sapwood of elm is nearly white and heartwood light brown,

often tinged with red. Elm may be divided into two general

classes, soft and hard, based on the weight and strength of

the wood. Soft elm includes American and slippery elm. It is

moderately heavy, has high shock resistance, and is moderately hard and stiff. Hard elm includes rock, winged, cedar,

and September elm. These species are somewhat heavier than

soft elm. Elm has excellent bending qualities.

Historically, elm lumber was used for boxes, baskets, crates,

and slack cooperage; furniture; agricultural supplies and

implements; caskets and burial boxes; and wood components

in vehicles. Today, elm lumber and veneer are used mostly

for furniture and decorative panels. Hard elm is preferred for

uses that require strength.

Hackberry

Hackberry (Celtis occidentalis) and sugarberry (C. laevigata)

supply the lumber known in the trade as hackberry. Hackberry grows east of the Great Plains from Alabama, Georgia,

Arkansas, and Oklahoma northward, except along the Canadian boundary. Sugarberry overlaps the southern part of the

hackberry range and grows throughout the Southern and

South Atlantic States.

Sapwood of both species varies from pale yellow to greenish

or grayish yellow. The heartwood is commonly darker. The

wood resembles elm in structure. Hackberry lumber is moderately heavy. It is moderately strong in bending, moderately

weak in compression parallel to grain, moderately hard to

very hard, and high in shock resistance, but low in stiffness.

Hackberry has high shrinkage but keeps its shape well during

drying.

Most hackberry is cut into lumber; small amounts are used

for furniture parts, dimension stock, and veneer.

Hickory (Pecan Group)

Species of the pecan hickory group include bitternut hickory

(Carya cordiformis), pecan (C. illinoensis), water hickory

(C. aquatica), and nutmeg hickory (C. myristiciformis).

Bitternut hickory grows throughout the eastern half of the

United States; pecan hickory, from central Texas and

Louisiana to Missouri and Indiana; water hickory, from

Texas to South Carolina; and nutmeg hickory, in Texas

and Louisiana.

The sapwood of this group is white or nearly white and

relatively wide. The heartwood is somewhat darker. The

wood is heavy and sometimes has very high shrinkage.

Heavy pecan hickory is used for tool and implement handles

and flooring. The lower grades are used for pallets. Many

higher grade logs are sliced to provide veneer for furniture

and decorative paneling.

Hickory (True Group)

True hickories are found throughout the eastern half of the

United States. The species most important commercially are

shagbark (Carya ovata), pignut (C. glabra), shellbark

(C. laciniosa), and mockernut (C. tomentosa). The greatest

commercial production of the true hickories for all uses is in

the Middle Atlantic and Central States, with the Southern

and South Atlantic States rapidly expanding to handle nearly

half of all hickory lumber.

The sapwood of the true hickory group is white and usually

quite wide, except in old, slow-growing trees. The heartwood is reddish. The wood is exceptionally tough, heavy,

hard, and strong, and shrinks considerably in drying. For

some purposes, both rings per centimeter (or inch) and

weight are limiting factors where strength is important.

The major use for high quality hickory is for tool handles,

which require high shock resistance. It is also used for ladder

rungs, athletic goods, agricultural implements, dowels,

gymnasium apparatuses, poles, and furniture. Lower grade

hickory is not suitable for the special uses of high quality

hickory because of knottiness or other growth features and

low density. However, the lower grade is useful for pallets

and similar items. Hickory sawdust, chips, and some solid

wood are used to flavor meat by smoking.

Honeylocust

The wood of honeylocust (Gleditsia triacanthos) has many

desirable qualities, such as attractive figure and color, hardness, and strength, but it is little used because of its scarcity.

Although the natural range of honeylocust has been extended

by planting, this species is found most commonly in the

eastern United States, except for New England and the South

Atlantic and Gulf Coastal Plains.
1–7

Sapwood is generally wide and yellowish, in contrast to the

light red to reddish-brown heartwood. The wood is very

heavy, very hard, strong in bending, stiff, resistant to shock,

and durable when in contact with the ground.

When available, honeylocust is primarily used locally for

fence posts and general construction. It is occasionally used

with other species in lumber for pallets and crating.

Locust, Black

Black locust (Robinia pseudoacacia) is sometimes called

yellow or post locust. This species grows from Pennsylvania

along the Appalachian Mountains to northern Georgia and

Alabama. It is also native to western Arkansas and southern

Missouri. The greatest production of black locust timber is

in Tennessee, Kentucky, West Virginia, and Virginia.

Locust has narrow, creamy white sapwood. The heartwood,

when freshly cut, varies from greenish yellow to dark brown.

Black locust is very heavy, very hard, very resistant to

shock, and very strong and stiff. It has moderately low

shrinkage. The heartwood has high decay resistance.

Black locust is used for round, hewed, or split mine timbers

as well as fence posts, poles, railroad crossties, stakes, and

fuel. Other uses are for rough construction, crating, and mine

equipment. Historically, black locust was important for the

manufacture of insulator pins and wooden pegs used in the

construction of ships, for which the wood was well adapted

because of its strength, decay resistance, and moderate

shrinkage and swelling.

Magnolia

Commercial magnolia consists of three species: southern

magnolia (Magnolia grandiflora), sweetbay (M. virginiana),

and cucumbertree (M. acuminata). Other names for southern

magnolia are evergreen magnolia, big laurel, bull bay, and

laurel bay. Sweetbay is sometimes called swamp magnolia.

The lumber produced by all three species is simply called

magnolia. The natural range of sweetbay extends along the

Atlantic and Gulf Coasts from Long Island to Texas, and

that of southern magnolia extends from North Carolina to

Texas. Cucumbertree grows from the Appalachians to the

Ozarks northward to Ohio. Louisiana leads in the production

of magnolia lumber.

Sapwood of southern magnolia is yellowish white, and

heartwood is light to dark brown with a tinge of yellow or

green. The wood, which has close, uniform texture and is

generally straight grained, closely resembles yellow-poplar

(Liriodendron tulipifera). It is moderately heavy, moderately

low in shrinkage, moderately low in bending and compressive strength, moderately hard and stiff, and moderately high

in shock resistance. Sweetbay is much like southern magnolia. The wood of cucumbertree is similar to that of yellowpoplar (L. tulipifera); cucumbertree that grows in the yellowpoplar range is not separated from that species on the market.

Magnolia lumber is used principally in the manufacture of

furniture, boxes, pallets, venetian blinds, sashes, doors,

veneer, and millwork.

Maple, Hard

Hard maple includes sugar maple (Acer saccharum) and

black maple (A. nigrum). Sugar maple is also known as hard

and rock maple, and black maple as black sugar maple.

Maple lumber is manufactured principally in the Middle

Atlantic and Great Lake States, which together account for

about two-thirds of production.

The heartwood is usually light reddish brown but sometimes

considerably darker. The sapwood is commonly white with a

slight reddish-brown tinge. It is roughly 7 to 13 cm or more

(3 to 5 in. or more) wide. Hard maple has a fine, uniform

texture. It is heavy, strong, stiff, hard, and resistant to shock

and has high shrinkage. The grain of sugar maple is generally straight, but birdseye, curly, or fiddleback grain is often

selected for furniture or novelty items.

Hard maple is used principally for lumber and veneer. A

large proportion is manufactured into flooring, furniture,

cabinets, cutting boards and blocks, pianos, billiard cues,

handles, novelties, bowling alleys, dance and gymnasium

floors, spools, and bobbins.

Maple, Soft

Soft maple includes silver maple (Acer saccharinum), red

maple (A. rubrum), boxelder (A. negundo), and bigleaf maple

(A. macrophyllum). Silver maple is also known as white,

river, water, and swamp maple; red maple as soft, water,

scarlet, white, and swamp maple; boxelder as ash-leaved,

three-leaved, and cut-leaved maple; and bigleaf maple as

Oregon maple. Soft maple is found in the eastern United

States except for bigleaf maple, which comes from the

Pacific Coast.

Heartwood and sapwood are similar in appearance to hard

maple: heartwood of soft maple is somewhat lighter in color

and the sapwood, somewhat wider. The wood of soft maple,

primarily silver and red maple, resembles that of hard maple

but is not as heavy, hard, and strong.

Soft maple is used for railroad crossties, boxes, pallets,

crates, furniture, veneer, wooden ware, and novelties.

Oak (Red Oak Group)

Most red oak comes from the Eastern States. The principal

species are northern red (Quercus rubra), scarlet (Q. coccinea), Shumard (Q. shumardii), pin (Q. palustris), Nuttall

(Q. nuttallii), black (Q. velutina), southern red (Q. falcata),

cherrybark (Q. falcata var. pagodaefolia), water (Q. nigra),

laurel (Q. laurifolia), and willow (Q. phellos) oak.

The sapwood is nearly white and roughly 2 to 5 cm

(1 to 2 in.) wide. The heartwood is brown with a tinge of

red. Sawn lumber of the red oak group cannot be separated

by species on the basis of wood characteristics alone.
 1–8

Red oak lumber can be separated from white oak by the size

and arrangement of pores in latewood and because it generally lacks tyloses in the pores. The open pores of red oak

make this species group unsuitable for tight cooperage,

unless the barrels are lined with sealer or plastic. Quartersawn lumber of the oaks is distinguished by the broad and

conspicuous rays. Wood of the red oaks is heavy. Rapidly

grown second-growth wood is generally harder and tougher

than finer textured old-growth wood. The red oaks have fairly

high shrinkage in drying.

The red oaks are primarily cut into lumber, railroad crossties, mine timbers, fence posts, veneer, pulpwood, and

fuelwood. Ties, mine timbers, and fence posts require preservative treatment for satisfactory service. Red oak lumber is

remanufactured into flooring, furniture, general millwork,

boxes, pallets and crates, agricultural implements, caskets,

wooden ware, and handles. It is also used in railroad cars

and boats.

Oak (White Oak Group)

White oak lumber comes chiefly from the South, South

Atlantic, and Central States, including the southern Appalachian area. Principal species are white (Quercus alba), chestnut (Q. prinus), post (Q. stellata), overcup (Q. lyrata),

swamp chestnut (Q. michauxii), bur (Q. macrocarpa),

chinkapin (Q. muehlenbergii), swamp white (Q. bicolor),

and live (Q. virginiana) oak.

The sapwood of the white oaks is nearly white and roughly

2 to 5 cm or more (1 to 2 in. or more) wide. The heartwood

is generally grayish brown. Heartwood pores are usually

plugged with tyloses, which tend to make the wood impenetrable by liquids. Consequently, most white oaks are suitable for tight cooperage. Many heartwood pores of chestnut

oak lack tyloses. The wood of white oak is heavy, averaging

somewhat greater in weight than red oak wood. The heartwood has good decay resistance.

White oaks are usually cut into lumber, railroad crossties,

cooperage, mine timbers, fence posts, veneer, fuelwood, and

many other products. High-quality white oak is especially

sought for tight cooperage. Live oak is considerably heavier

and stronger than the other oaks, and it was formerly used

extensively for ship timbers. An important use of white oak

is for planking and bent parts of ships and boats; heartwood

is often specified because of its decay resistance. White oak is

also used for furniture, flooring, pallets, agricultural implements, railroad cars, truck floors, furniture, doors, and

millwork.

Sassafras

Sassafras (Sassafras albidum) ranges through most of the

eastern half of the United States, from southeastern Iowa and

eastern Texas eastward.

Sassafras is easily confused with black ash, which it resembles in color, grain, and texture. Sapwood is light yellow,

and heartwood varies from dull grayish brown to dark brown,

sometimes with a reddish tinge. Freshly cut surfaces have the

characteristic odor of sassafras. The wood is moderately

heavy, moderately hard, moderately weak in bending and

endwise compression, quite high in shock resistance, and

resistant to decay.

Sassafras was highly prized by the Indians for dugout canoes,

and some sassafras lumber is still used for small boats.

Locally, sassafras is used for fence posts and rails and for

general millwork.

Sweetgum

Sweetgum (Liquidambar styraciflua) grows from southwestern Connecticut westward into Missouri and southward to

the Gulf Coast. Almost all lumber is produced in the Southern and South Atlantic States.

The lumber from sweetgum is usually marked as sap gum

(the light-colored sapwood) or redgum (the reddish-brown

heartwood). Sweetgum often has a form of cross grain called

interlocked grain, and it must be dried slowly. When quartersawn, interlocked grain produces a ribbon-type stripe that

is desirable for interior woodwork and furniture. The wood is

moderately heavy and hard. It is moderately strong, moderately stiff, and moderately high in shock resistance.

Sweetgum is used principally for lumber, veneer, plywood,

slack cooperage, railroad crossties, fuel, pulpwood, boxes

and crates, furniture, interior moulding, and millwork.

Sycamore, American

American sycamore (Platanus occidentalis) is known as

sycamore and sometimes as buttonwood, buttonball-tree, and

in the United Kingdom, planetree. Sycamore grows from

Maine to Nebraska, southward to Texas, and eastward to

Florida.

The heartwood of sycamore is reddish brown; the sapwood is

lighter in color and from 4 to 8 cm (1-1/2 to 3 in.) wide.

The wood has a fine texture and interlocked grain. It has

high shrinkage in drying; is moderately heavy, moderately

hard, moderately stiff, and moderately strong; and has good

resistance to shock.

Sycamore is used principally for lumber, veneer, railroad

crossties, slack cooperage, fence posts, and fuel. The lumber

is used for furniture, boxes (particularly small food containers), pallets, flooring, handles, and butcher blocks. Veneer is

used for fruit and vegetable baskets and some decorative

panels and door skins.

Tanoak

Tanoak (Lithocarpus densiflorus) has recently gained some

commercial value, primarily in California and Oregon. It is

also known as tanbark–oak because high-grade tannin was

once obtained from the bark in commercial quantities. This

species is found in southwestern Oregon and south to

Southern California, mostly near the coast but also in the

Sierra Nevadas.
1–9

Sapwood of tanoak is light reddish brown when first cut and

turns darker with age to become almost indistinguishable

from heartwood, which also ages to dark reddish brown. The

wood is heavy and hard; except for compression perpendicular to grain, the wood has roughly the same strength properties as those of eastern white oak. Tanoak has higher shrinkage during drying than does white oak, and it has a tendency

to collapse during drying. Tanoak is quite susceptible to

decay, but the sapwood takes preservatives easily. Tanoak

has straight grain, machines and glues well, and takes stains

readily.

Because of its hardness and abrasion resistance, tanoak is

excellent for flooring in homes or commercial buildings.

It is also suitable for industrial applications such as truck

flooring. Tanoak treated with preservative has been used for

railroad crossties. The wood has been manufactured into

baseball bats with good results, and it is also suitable for

veneer, both decorative and industrial, and for high quality

furniture.

Tupelo

The tupelo group includes water (Nyssa aquatica), black

(N. sylvatica), swamp (N. sylvatica var. biflora), and

Ogeechee (N. ogeche) tupelo. Water tupelo is also known as

tupelo gum, swamp tupelo, and sourgum; black tupelo, as

blackgum and sourgum; swamp tupelo, as swamp blackgum,

blackgum, and sourgum; and Ogeechee tupelo, as sour tupelo, gopher plum, and Ogeechee plum. All except black

tupelo grow principally in the southeastern United States.

Black tupelo grows in the eastern United States from Maine

to Texas and Missouri. About two-thirds of the production

of tupelo lumber is from Southern States.

Wood of the different tupelo species is quite similar in

appearance and properties. The heartwood is light brownish

gray and merges gradually into the lighter-colored sapwood,

which is generally many centimeters wide. The wood has

fine, uniform texture and interlocked grain. Tupelo wood is

moderately heavy, moderately strong, moderately hard and

stiff, and moderately high in shock resistance. Buttresses of

trees growing in swamps or flooded areas contain wood that

is much lighter in weight than that from upper portions of

the same trees. Because of interlocked grain, tupelo lumber

requires care in drying.

Tupelo is cut principally for lumber, veneer, pulpwood, and

some railroad crossties and slack cooperage. Lumber goes

into boxes, pallets, crates, baskets, and furniture.

Walnut, Black

Black walnut (Juglans nigra), also known as American black

walnut, ranges from Vermont to the Great Plains and southward into Louisiana and Texas. About three-quarters of

walnut wood is grown in the Central States.

The heartwood of black walnut varies from light to dark

brown; the sapwood is nearly white and up to 8 cm (3 in.)

wide in open-grown trees. Black walnut is normally straight

grained, easily worked with tools, and stable in use. It is

heavy, hard, strong, and stiff, and has good resistance to

shock. Black walnut is well suited for natural finishes.

Because of its good properties and interesting grain pattern,

black walnut is much valued for furniture, architectural

woodwork, and decorative panels. Other important uses are

gunstocks, cabinets, and interior woodwork.

Willow, Black

Black willow (Salix nigra) is the most important of the

many willows that grow in the United States. It is the only

willow marketed under its own name. Most black willow

comes from the Mississippi Valley, from Louisiana to southern Missouri and Illinois.

The heartwood of black willow is grayish brown or light

reddish brown and frequently contains darker streaks. The

sapwood is whitish to creamy yellow. The wood is uniform

in texture, with somewhat interlocked grain, and light in

weight. It has exceedingly low strength as a beam or post, is

moderately soft, and is moderately high in shock resistance.

It has moderately high shrinkage.

Black willow is principally cut into lumber. Small amounts

are used for slack cooperage, veneer, excelsior, charcoal,

pulpwood, artificial limbs, and fence posts. The lumber is

remanufactured principally into boxes, pallets, crates, caskets, and furniture.

Yellow-Poplar

Yellow-poplar (Liriodendron tulipifera) is also known as

poplar, tulip-poplar, and tulipwood. Sapwood from yellowpoplar is sometimes called white poplar or whitewood.

Yellow-poplar grows from Connecticut and New York

southward to Florida and westward to Missouri. The greatest

commercial production of yellow-poplar lumber is in the

South and Southeast.

Yellow-poplar sapwood is white and frequently several centimeters wide. The heartwood is yellowish brown, sometimes streaked with purple, green, black, blue, or red. These

colorations do not affect the physical properties of the wood.

The wood is generally straight grained and comparatively

uniform in texture. Slow-grown wood is moderately light in

weight and moderately low in bending strength, moderately

soft, and moderately low in shock resistance. The wood has

moderately high shrinkage when dried from a green condition, but it is not difficult to dry and is stable after drying.

Much of the second-growth wood is heavier, harder, and

stronger than that of older trees that have grown more

slowly.

The lumber is used primarily for furniture, interior moulding, siding, cabinets, musical instruments, and structural

components. Boxes, pallets, and crates are made from lowergrade stock. Yellow-poplar is also made into plywood for

paneling, furniture, piano cases, and various other special

products.
 1–10

Softwoods

Baldcypress

Baldcypress or cypress (Taxodium distichum) is also known

as southern-cypress, red-cypress, yellow-cypress, and whitecypress. Commercially, the terms tidewater red-cypress, gulfcypress, red-cypress (coast type), and yellow-cypress (inland

type) are frequently used. About half of the cypress lumber

comes from the Southern States and about a fourth from the

South Atlantic States (Fig. 1–1). Old-growth baldcypress is

no longer readily available, but second-growth wood is

available.

Sapwood of baldcypress is narrow and nearly white. The

color of heartwood varies widely, ranging from light yellowish brown to dark brownish red, brown, or chocolate.

The wood is moderately heavy, moderately strong, and

moderately hard. The heartwood of old-growth baldcypress

is one of the most decay resistant of U.S. species, but second-growth wood is only moderately resistant to decay.

Shrinkage is moderately low but somewhat higher than that

of the cedars and lower than that of Southern Pine. The wood

of certain baldcypress trees frequently contains pockets or

localized areas that have been attacked by a fungus. Such

wood is known as pecky cypress. The decay caused by this

fungus is stopped when the wood is cut into lumber and

dried. Pecky cypress is therefore durable and useful where

water tightness is unnecessary, appearance is not important,

or a novel effect is desired.

When old-growth wood was available, baldcypress was used

principally for building construction, especially where resistance to decay was required. It was also used for caskets,

sashes, doors, blinds, tanks, vats, ship and boat building,

and cooling towers. Second-growth wood is used for siding

and millwork, including interior woodwork and paneling.

Pecky cypress is used for paneling in restaurants, stores, and

other buildings.

Douglas-Fir

Douglas-fir (Pseudotsuga menziesii) is also known locally as

red-fir, Douglas-spruce, and yellow-fir. Its range extends from

the Rocky Mountains to the Pacific Coast and from Mexico

to central British Columbia.

Sapwood of Douglas-fir is narrow in old-growth trees but

may be as much as 7 cm (3 in.) wide in second-growth trees

of commercial size. Young trees of moderate to rapid growth

have reddish heartwood and are called red-fir. Very narrowringed heartwood of old-growth trees may be yellowish

brown and is known on the market as yellow-fir. The wood

of Douglas-fir varies widely in weight and strength. When

lumber of high strength is needed for structural uses, selection can be improved by selecting wood with higher density.

Douglas-fir is used mostly for building and construction

purposes in the form of lumber, marine fendering (Fig. 1–2),

piles, and plywood. Considerable quantities are used for

railroad crossties, cooperage stock, mine timbers, poles, and

fencing. Douglas-fir lumber is used in the manufacture of

various products, including sashes, doors, laminated beams,

general millwork, railroad-car construction, boxes, pallets,

and crates. Small amounts are used for flooring, furniture,

ship and boat construction, and tanks. Douglas-fir plywood

has found application in construction, furniture, cabinets,

marine use, and other products.

Firs, True (Eastern Species)

Balsam fir (Abies balsamea) grows principally in New England, New York, Pennsylvania, and the Great Lake States.

Fraser fir (A. fraseri) grows in the Appalachian Mountains of

Virginia, North Carolina, and Tennessee.

The wood of the eastern true firs, as well as the western true

firs, is creamy white to pale brown. The heartwood and

sapwood are generally indistinguishable. The similarity of

wood structure in the true firs makes it impossible to distinguish the species by examination of the wood alone. Balsam

and Fraser firs are lightweight, have low bending and compressive strength, are moderately low in stiffness, are soft,

and have low resistance to shock.

The eastern firs are used mainly for pulpwood, although

some lumber is produced for structural products, especially

in New England and the Great Lake States.

Firs, True (Western Species)

Six commercial species make up the western true firs: subalpine fir (Abies lasiocarpa), California red fir (A. magnifica),

grand fir (A. grandis), noble fir (A. procera), Pacific silver fir

(A. amabilis), and white fir (A. concolor). The western true

firs are cut for lumber primarily in Washington, Oregon,

California, western Montana, and northern Idaho, and they

are marketed as white fir throughout the United States.

Figure 1–1. Cypress-tupelo swamp near New Orleans,

LA. Species include baldcypress (Taxodium distichum)),

tupelo (Nyssa), ash (Fraxinus), willow (Salix), and elm

(Ulmus). Swollen buttresses and “knees” are typically

present in cypress.
1–11

The wood of the western true firs is similar to that of the

eastern true firs, which makes it impossible to distinguish

the true fir species by examination of the wood alone. Western true firs are light in weight but, with the exception of

subalpine fir, have somewhat higher strength properties than

does balsam fir. Shrinkage of the wood is low to moderately

high.

Lumber of the western true firs is primarily used for building

construction, boxes and crates, planing-mill products,

sashes, doors, and general millwork. In house construction,

the lumber is used for framing, subflooring, and sheathing.

Some western true fir lumber is manufactured into boxes and

crates. High-grade lumber from noble fir is used mainly for

interior woodwork, moulding, siding, and sash and door

stock. Some of the highest quality material is suitable for

aircraft construction. Other special uses of noble fir are venetian blinds and ladder rails.

Hemlock, Eastern

Eastern hemlock (Tsuga canadensis) grows from New England to northern Alabama and Georgia, and in the Great Lake

States. Other names are Canadian hemlock and hemlock–

spruce. The production of hemlock lumber is divided fairly

evenly among the New England States, Middle Atlantic

States, and Great Lake States.

The heartwood of eastern hemlock is pale brown with a

reddish hue. The sapwood is not distinctly separated from

the heartwood but may be lighter in color. The wood is

coarse and uneven in texture (old trees tend to have considerable shake); it is moderately lightweight, moderately hard,

moderately low in strength, moderately stiff, and moderately

low in shock resistance.

Eastern hemlock is used principally for lumber and pulpwood. The lumber is used primarily in building construction

(framing, sheathing, subflooring, and roof boards) and in the

manufacture of boxes, pallets, and crates.

Figure 1–2. Wood is favored for waterfront structures, particularly fendering, because of its shock-absorbing qualities.

The fendering on this dock in Key West, FL, is made of creosote-treated Douglas-fir (Pseudotsuga menziesii). Some

tropical species are resistant to attack by decay fungi and marine borers and are used for marine construction

without preservative treatment.
 1–12

Hemlock, Western and Mountain

Western hemlock (Tsuga heterophylla) is also known as

West Coast hemlock, Pacific hemlock, British Columbia

hemlock, hemlock–spruce, and western hemlock–fir. It grows

along the Pacific coast of Oregon and Washington and in the

northern Rocky Mountains north to Canada and Alaska. A

relative of western hemlock, mountain hemlock (T. mertensiana) grows in mountainous country from central California

to Alaska. It is treated as a separate species in assigning

lumber properties.

The heartwood and sapwood of western hemlock are almost

white with a purplish tinge. The sapwood, which is sometimes lighter in color than the heartwood, is generally not

more than 2.5 cm (1 in.) wide. The wood often contains

small, sound, black knots that are usually tight and dimensionally stable. Dark streaks are often found in the lumber;

these are caused by hemlock bark maggots and generally do

not reduce strength. Western hemlock is moderately light in

weight and moderate in strength. It is also moderate in

hardness, stiffness, and shock resistance. Shrinkage of western hemlock is moderately high, about the same as that of

Douglas-fir (Pseudotsuga menziesii). Green hemlock lumber

contains considerably more water than does Douglas-fir and

requires longer kiln-drying time. Mountain hemlock has

approximately the same density as that of western hemlock

but is somewhat lower in bending strength and stiffness.

Western hemlock and mountain hemlock are used principally

for pulpwood, lumber, and plywood. The lumber is used

primarily for building material, such as sheathing, siding,

subflooring, joists, studding, planking, and rafters, as well as

in the manufacture of boxes, pallets, crates, flooring, furniture, and ladders.

Incense-Cedar

Incense-cedar (Calocedrus decurrens (synonym Libocedrus

decurrens)) grows in California, southwestern Oregon, and

extreme western Nevada. Most incense-cedar lumber comes

from the northern half of California.

Sapwood of incense-cedar is white or cream colored, and

heartwood is light brown, often tinged with red. The wood

has a fine, uniform texture and a spicy odor. Incense-cedar is

light in weight, moderately low in strength, soft, low in

shock resistance, and low in stiffness. It has low shrinkage

and is easy to dry, with little checking or warping.

Incense-cedar is used principally for lumber and fence posts.

Nearly all the high-grade lumber is used for pencils and

venetian blinds; some is used for chests and toys. Much

incense-cedar wood is more or less pecky; that is, it contains

pockets or areas of disintegrated wood caused by advanced

stages of localized decay in the living tree. There is no further development of decay once the lumber is dried. This

low-quality lumber is used locally for rough construction

where low cost and decay resistance are important. Because

of its resistance to decay, incense-cedar is well suited for

fence posts. Other uses are railroad crossties, poles, and split

shingles.

Larch, Western

Western larch (Larix occidentalis) grows in western Montana, northern Idaho, northeastern Oregon, and on the eastern

slope of the Cascade Mountains in Washington. About twothirds of the lumber of this species is produced in Idaho and

Montana and one-third in Oregon and Washington.

The heartwood of western larch is yellowish brown and the

sapwood, yellowish white. The sapwood is generally not

more than 2.5 cm (1 in.) wide. The wood is stiff, moderately

strong and hard, moderately high in shock resistance, and

moderately heavy. It has moderately high shrinkage. The

wood is usually straight grained, splits easily, and is subject

to ring shake. Knots are common but generally small and

tight.

Western larch is used mainly for rough dimension wood in

building construction, small timbers, planks and boards, and

railroad crossties and mine timbers. It is used also for piles,

poles, and posts. Some high-grade material is manufactured

into interior woodwork, flooring, sashes, and doors. The

properties of western larch are similar to those of Douglas-fir

(Pseudotsuga menziesii), and these species are sometimes

sold mixed.

Pine, Eastern White

Eastern white pine (Pinus strobus) grows from Maine to

northern Georgia and in the Great Lake States. It is also

known as white pine, northern white pine, Weymouth pine,

and soft pine. About one-half the production of eastern white

pine lumber occurs in New England, about one-third in the

Great Lake States, and most of the remainder in the Middle

Atlantic and South Atlantic States.

The heartwood of eastern white pine is light brown, often

with a reddish tinge. It turns darker on exposure to air. The

wood has comparatively uniform texture and is straight

grained. It is easily kiln dried, has low shrinkage, and ranks

high in stability. It is also easy to work and can be readily

glued. Eastern white pine is lightweight, moderately soft,

moderately low in strength, low in shock resistance, and low

in stiffness.

Practically all eastern white pine is converted into lumber,

which is used in a great variety of ways. A large proportion,

mostly second-growth knotty wood or lower grades, is used

for structural lumber. High-grade lumber is used for patterns

for castings. Other important uses are sashes, doors, furniture, interior woodwork, knotty paneling, caskets, shade and

map rollers, and toys.

Pine, Jack

Jack pine (Pinus banksiana), sometimes known as scrub,

gray, and black pine in the United States, grows naturally in

the Great Lake States and in a few scattered areas in New

England and northern New York. Jack pine lumber is sometimes not separated from the other pines with which it

grows, including red pine (Pinus resinosa) and eastern white

pine (Pinus strobus).
1–13

Sapwood of jack pine is nearly white; heartwood is light

brown to orange. Sapwood may constitute one-half or more

of the volume of a tree. The wood has a rather coarse texture

and is somewhat resinous. It is moderately lightweight,

moderately low in bending strength and compressive

strength, moderately low in shock resistance, and low in

stiffness. It also has moderately low shrinkage. Lumber from

jack pine is generally knotty.

Jack pine is used for pulpwood, box lumber, and pallets.

Less important uses include railroad crossties, mine timber,

slack cooperage, poles, posts, and fuel.

Pine, Jeffrey (see Pine, Ponderosa)

Pine, Lodgepole

Lodgepole pine (Pinus contorta), also known as knotty,

black, and spruce pine, grows in the Rocky Mountain and

Pacific Coast regions as far northward as Alaska. Wood for

lumber and other products is produced primarily in the

central Rocky Mountain States; other producing regions are

Idaho, Montana, Oregon, and Washington.

The heartwood of lodgepole pine varies from light yellow to

light yellow-brown. The sapwood is yellow or nearly white.

The wood is generally straight grained with narrow growth

rings. The wood is moderately lightweight, is fairly easy to

work, and has moderately high shrinkage. It is moderately

low in strength, moderately soft, moderately stiff, and moderately low in shock resistance.

Lodgepole pine is used for lumber, mine timbers, railroad

crossties, and poles. Less important uses include posts and

fuel. Lodgepole pine is being used increasingly for framing,

siding, millwork, flooring, and cabin logs.

Pine, Pitch

Pitch pine (Pinus rigida) grows from Maine along the mountains to eastern Tennessee and northern Georgia.

The heartwood is brownish red and resinous; the sapwood is

wide and light yellow. The wood of pitch pine is moderately

heavy to heavy, moderately strong, stiff, and hard, and

moderately high in shock resistance. Shrinkage ranges from

moderately low to moderately high.

Pitch pine is used for lumber, fuel, and pulpwood. The

lumber is classified as a minor species in grading rules for

the Southern Pine species group.

Pine, Pond

Pond pine (Pinus serotina) grows in the coastal region from

New Jersey to Florida. It occurs in small groups or singly,

mixed with other pines on low flats.

Sapwood of pond pine is wide and pale yellow; heartwood is

dark orange. The wood is heavy, coarse grained, and resinous. Shrinkage is moderately high. The wood is moderately

strong, stiff, moderately hard, and moderately high in shock

resistance.

Pond pine is used for general construction, railway crossties,

posts, and poles. The lumber of this species is also graded

as a minor species in grading rules for the Southern Pine

species group.

Pine, Ponderosa

Ponderosa pine (Pinus ponderosa) is also known as ponderosa, western soft, western yellow, bull, and blackjack pine.

Jeffrey pine (P. jeffreyi), which grows in close association

with ponderosa pine in California and Oregon, is usually

marketed with ponderosa pine and sold under that name.

Major ponderosa pine producing areas are in Oregon, Washington, and California (Fig. 1–3). Other important producing

areas are in Idaho and Montana; lesser amounts come from

the southern Rocky Mountain region, the Black Hills of

South Dakota, and Wyoming.

The heartwood of ponderosa pine is light reddish brown, and

the wide sapwood is nearly white to pale yellow. The wood

of the outer portions of ponderosa pine of sawtimber size is

generally moderately light in weight, moderately low in

strength, moderately soft, moderately stiff, and moderately

low in shock resistance. It is generally straight grained and

has moderately low shrinkage. It is quite uniform in texture

and has little tendency to warp and twist.

Ponderosa pine is used mainly for lumber and to a lesser

extent for piles, poles, posts, mine timbers, veneer, and

railroad crossties. The clear wood is used for sashes, doors,

blinds, moulding, paneling, interior woodwork, and built-in

cases and cabinets. Low-grade lumber is used for boxes and

crates. Much intermediate- or low-grade lumber is used for

sheathing, subflooring, and roof boards. Knotty ponderosa

pine is used for interior woodwork.

Figure 1–3. Ponderosa pine (Pinus ponderosa) growing

in an open or park-like habitat.
 1–14

Pine, Red

Red pine (Pinus resinosa) is frequently called Norway pine

and occasionally known as hard pine and pitch pine. This

species grows in New England, New York, Pennsylvania,

and the Great Lake States.

The heartwood of red pine varies from pale red to reddish

brown. The sapwood is nearly white with a yellowish tinge

and is generally from 5 to 10 cm (2 to 4 in.) wide. The

wood resembles the lighter weight wood of the Southern

Pine species group. Latewood is distinct in the growth rings.

Red pine is moderately heavy, moderately strong and stiff,

moderately soft, and moderately high in shock resistance. It

is generally straight grained, not as uniform in texture as

eastern white pine (Pinus strobus), and somewhat resinous.

The wood has moderately high shrinkage, but it is not

difficult to dry and is dimensionally stable when dried.

Red pine is used principally for lumber, cabin logs, and

pulpwood, and to a lesser extent for piles, poles, posts, and

fuel. The lumber is used for many of the same purposes as for

eastern white pine (Pinus strobus). Red pine lumber is used

primarily for building construction, including treated lumber

for decking, siding, flooring, sashes, doors, general millwork, and boxes, pallets, and crates.

Pine, Southern

A number of species are included in the group marketed as

Southern Pine lumber. The four major Southern Pine species

and their growth ranges are as follows: (a) longleaf pine

(Pinus palustris), eastern North Carolina southward into

Florida and westward into eastern Texas; (b) shortleaf pine

(P. echinata), southeastern New York and New Jersey

southward to northern Florida and westward into eastern

Texas and Oklahoma; (c) loblolly pine (P. taeda), Maryland

southward through the Atlantic Coastal Plain and Piedmont

Plateau into Florida and westward into eastern Texas; (d)

slash pine (P. elliottii), Florida and southern South Carolina, Georgia, Alabama, Mississippi, and Louisiana east of

the Mississippi River. Lumber from these four species is

classified as Southern Pine by the grading standards of the

industry. These standards also classify lumber produced from

the longleaf and slash pine species as longleaf pine if the

lumber conforms to the growth-ring and latewood requirements of such standards. Southern Pine lumber is produced

principally in the Southern and South Atlantic States. Georgia, Alabama, North Carolina, Arkansas, and Louisiana lead

in Southern Pine lumber production.

The wood of these southern pines is quite similar in appearance. Sapwood is yellowish white and heartwood, reddish

brown. The sapwood is usually wide in second-growth

stands. The heartwood begins to form when the tree is about

20 years old. In old, slow-growth trees, sapwood may be

only 2 to 5 cm (1 to 2 in.) wide.

Longleaf and slash pine are classified as heavy, strong, stiff,

hard, and moderately high in shock resistance. Shortleaf and

loblolly pine are usually somewhat lighter in weight than is

longleaf. All the southern pines have moderately high

shrinkage but are dimensionally stable when properly dried.

To obtain heavy, strong wood of the southern pines for

structural purposes, a density rule has been written that

specifies a certain percentage of latewood and growth rates for

structural timbers.

The denser and higher strength southern pines are extensively used in the form of stringers in construction of factories, warehouses, bridges, trestles, and docks, and also for

roof trusses, beams, posts, joists, and piles. Lumber of lower

density and strength is also used for building material, such

as interior woodwork, sheathing, and subflooring, as well as

boxes, pallets, and crates. Southern Pine is used also for

tight and slack cooperage. When used for railroad crossties,

piles, poles, mine timbers, and exterior decking, it is usually

treated with preservatives. The manufacture of structuralgrade plywood from Southern Pine is a major wood-using

industry, as is the production of preservative-treated lumber.

Pine, Spruce

Spruce pine (Pinus glabra), also known as cedar, poor,

Walter, and bottom white pine, is classified as a minor

species in the Southern Pine species group. Spruce pine

grows most commonly on low moist lands of the coastal

regions of southeastern South Carolina, Georgia, Alabama,

Mississippi, and Louisiana, and northern and northwestern

Florida.

The heartwood of spruce pine is light brown, and the wide

sapwood is nearly white. Spruce pine wood is lower in most

strength values than the wood of the major Southern Pine

species group. Spruce pine compares favorably with the

western true firs in important bending properties, crushing

strength (perpendicular and parallel to grain), and hardness.

It is similar to denser species such as coast Douglas-fir

(Pseudotsuga menziesii) and loblolly pine (Pinus taeda)

in shear parallel to grain.

In the past, spruce pine was principally used locally for

lumber, pulpwood, and fuelwood. The lumber reportedly

was used for sashes, doors, and interior woodwork because

of its low specific gravity and similarity of earlywood and

latewood. In recent years, spruce pine has been used for

plywood.

Pine, Sugar

Sugar pine (Pinus lambertiana), the world’s largest species

of pine, is sometimes called California sugar pine. Most

sugar pine lumber grows in California and southwestern

Oregon.

The heartwood of sugar pine is buff or light brown, sometimes tinged with red. The sapwood is creamy white. The

wood is straight grained, fairly uniform in texture, and easy

to work with tools. It has very low shrinkage, is readily

dried without warping or checking, and is dimensionally

stable. Sugar pine is lightweight, moderately low in

strength, moderately soft, low in shock resistance, and low

in stiffness.
1–15

Sugar pine is used almost exclusively for lumber products.

The largest volume is used for boxes and crates, sashes,

doors, frames, blinds, general millwork, building construction, and foundry patterns. Like eastern white pine (Pinus

strobus), sugar pine is suitable for use in nearly every part

of a house because of the ease with which it can be cut, its

dimensional stability, and its good nailing properties.

Pine, Virginia

Virginia pine (Pinus virginiana), also known as Jersey and

scrub pine, grows from New Jersey and Virginia throughout

the Appalachian region to Georgia and the Ohio Valley.

It is classified as a minor species in the grading rules for

the Southern Pine species group.

The heartwood is orange, and the sapwood is nearly white

and relatively wide. The wood is moderately heavy, moderately strong, moderately hard, and moderately stiff and has

moderately high shrinkage and high shock resistance.

Virginia pine is used for lumber, railroad crossties, mine

timbers, and pulpwood.

Pine, Western White

Western white pine (Pinus monticola) is also known as

Idaho white pine or white pine. About four-fifths of the wood

for lumber from this species is from Idaho and Washington;

small amounts are cut in Montana and Oregon.

The heartwood of western white pine is cream colored to

light reddish brown and darkens on exposure to air. The

sapwood is yellowish white and generally from 2 to 8 cm

(1 to 3 in.) wide. The wood is straight grained, easy to

work, easily kiln-dried, and stable after drying. This species

is moderately lightweight, moderately low in strength,

moderately soft, moderately stiff, and moderately low in

shock resistance and has moderately high shrinkage.

Practically all western white pine is sawn into lumber, which

is used mainly for building construction, matches, boxes,

patterns, and millwork products, such as sashes and door

frames. In building construction, lower-grade boards are used

for sheathing, knotty paneling, and subflooring. High-grade

material is made into siding of various kinds, exterior and

interior woodwork, and millwork. Western white pine has

practically the same uses as eastern white pine (Pinus

strobus) and sugar pine (Pinus lambertiana).

Port-Orford-Cedar

Port-Orford-cedar (Chamaecyparis lawsoniana) is sometimes

known as Lawson-cypress, Oregon-cedar, and white-cedar. It

grows along the Pacific Coast from Coos Bay, Oregon,

southward to California. It does not extend more than

64 km (40 mi) inland.

The heartwood of Port-Orford-cedar is light yellow to pale

brown. The sapwood is narrow and hard to distinguish from

the heartwood. The wood has fine texture, generally straight

grain, and a pleasant spicy odor. It is moderately lightweight, stiff, moderately strong and hard, and moderately

resistant to shock. Port-Orford-cedar heartwood is highly

resistant to decay. The wood shrinks moderately, has little

tendency to warp, and is stable after drying.

Some high-grade Port-Orford-cedar was once used in the

manufacture of storage battery separators, matchsticks, and

specialty millwork. Today, other uses are archery supplies,

sash and door construction, stadium seats, flooring, interior

woodwork, furniture, and boats.

Redcedar, Eastern

Eastern redcedar (Juniperus virginiana) grows throughout the

eastern half of the United States, except in Maine, Florida,

and a narrow strip along the Gulf Coast, and at the higher

elevations in the Appalachian Mountain Range. Commercial

production is principally in the southern Appalachian and

Cumberland Mountain regions. Another species, southern

redcedar (J. silicicola), grows over a limited area in the

South Atlantic and Gulf Coastal Plains.

The heartwood of redcedar is bright or dull red, and the

narrow sapwood is nearly white. The wood is moderately

heavy, moderately low in strength, hard, and high in shock

resistance, but low in stiffness. It has very low shrinkage and

is dimensionally stable after drying. The texture is fine and

uniform, and the wood commonly has numerous small

knots. Eastern redcedar heartwood is very resistant to decay.

The greatest quantity of eastern redcedar is used for fence

posts. Lumber is manufactured into chests, wardrobes, and

closet lining. Other uses include flooring, novelties, pencils,

scientific instruments, and small boats. Southern redcedar

is used for the same purposes. Eastern redcedar is reputed

to repel moths, but this claim has not been supported by

research.

Redcedar, Western

Western redcedar (Thuja plicata) grows in the Pacific

Northwest and along the Pacific Coast to Alaska. It is also

called canoe-cedar, giant arborvitae, shinglewood, and Pacific

redcedar. Western redcedar lumber is produced principally in

Washington, followed by Oregon, Idaho, and Montana.

The heartwood of western redcedar is reddish or pinkish

brown to dull brown, and the sapwood is nearly white. The

sapwood is narrow, often not more than 2.5 cm (1 in.) wide.

The wood is generally straight grained and has a uniform but

rather coarse texture. It has very low shrinkage. This species

is lightweight, moderately soft, low in strength when used as

a beam or posts, and low in shock resistance. The heartwood

is very resistant to decay.

Western redcedar is used principally for shingles, lumber,

poles, posts, and piles. The lumber is used for exterior

siding, decking, interior woodwork, greenhouse construction, ship and boat building, boxes and crates, sashes,

and doors.
 1–16

Redwood

Redwood (Sequoia sempervirens) grows on the coast of

California and some trees are among the tallest in the world.

A closely related species, giant sequoia (Sequoiadendron

giganteum), is volumetrically larger and grows in a limited

area in the Sierra Nevadas of California, but its wood is used

in very limited quantities. Other names for redwood are coast

redwood, California redwood, and sequoia. Production of

redwood lumber is limited to California, but the market is

nationwide.

The heartwood of redwood varies from light “cherry” red to

dark mahogany. The narrow sapwood is almost white. Typical old-growth redwood is moderately lightweight, moderately strong and stiff, and moderately hard. The wood is easy

to work, generally straight grained, and shrinks and swells

comparatively little. The heartwood from old-growth trees

has high decay resistance; heartwood from second-growth

trees generally has low to moderate decay resistance.

Most redwood lumber is used for building. It is remanufactured extensively into siding, sashes, doors, blinds, millwork, casket stock, and containers. Because of its durability,

redwood is useful for cooling towers, decking, tanks, silos,

wood-stave pipe, and outdoor furniture. It is used in agriculture for buildings and equipment. Its use as timbers and large

dimension in bridges and trestles is relatively minor. Redwood splits readily and plays an important role in the

manufacture of split products, such as posts and fence

material. Some redwood veneer is produced for decorative

plywood.

Spruce, Eastern

The term eastern spruce includes three species: red (Picea

rubens), white (P. glauca), and black (P. mariana). White

and black spruce grow principally in the Great Lake States

and New England, and red spruce grows in New England

and the Appalachian Mountains.

The wood is light in color, and there is little difference

between heartwood and sapwood. All three species have

about the same properties, and they are not distinguished

from each other in commerce. The wood dries easily and is

stable after drying, is moderately lightweight and easily

worked, has moderate shrinkage, and is moderately strong,

stiff, tough, and hard.

The greatest use of eastern spruce is for pulpwood. Eastern

spruce lumber is used for framing material, general millwork,

boxes and crates, and piano sounding boards.

Spruce, Engelmann

Engelmann spruce (Picea engelmannii) grows at high elevations in the Rocky Mountain region of the United States.

This species is also known as white spruce, mountain

spruce, Arizona spruce, silver spruce, and balsam. About

two-thirds of the lumber is produced in the southern Rocky

Mountain States and most of the remainder in the northern

Rocky Mountain States and Oregon.

The heartwood of Engelmann spruce is nearly white, with a

slight tinge of red. The sapwood varies from 2 to 5 cm

(3/4 to 2 in.) in width and is often difficult to distinguish

from the heartwood. The wood has medium to fine texture

and is without characteristic odor. Engelmann spruce is rated

as lightweight, and it is low in strength as a beam or post. It

is also soft and low in stiffness, shock resistance, and shrinkage. The lumber typically contains many small knots.

Engelmann spruce is used principally for lumber and for

mine timbers, railroad crossties, and poles. It is used also in

building construction in the form of dimension lumber,

flooring, and sheathing. It has excellent properties for pulp

and papermaking.

Spruce, Sitka

Sitka spruce (Picea sitchensis) is a large tree that grows

along the northwestern coast of North America from California to Alaska. It is also known as yellow, tideland, western,

silver, and west coast spruce. Much Sitka spruce timber is

grown in Alaska, but most logs are sawn into cants for

export to Pacific Rim countries. Material for U.S. consumption is produced primarily in Washington and Oregon.

The heartwood of Sitka spruce is a light pinkish brown. The

sapwood is creamy white and shades gradually into the

heartwood; the sapwood may be 7 to 15 cm (3 to 6 in.) wide

or even wider in young trees. The wood has a comparatively

fine, uniform texture, generally straight grain, and no distinct

taste or odor. It is moderately lightweight, moderately low

in bending and compressive strength, moderately stiff, moderately soft, and moderately low in resistance to shock. It has

moderately low shrinkage. On the basis of weight, Sitka

spruce rates high in strength properties and can be obtained

in long, clear, straight-grained pieces.

Sitka spruce is used principally for lumber, pulpwood, and

cooperage. Boxes and crates account for a considerable

amount of the remanufactured lumber. Other important uses

are furniture, planing-mill products, sashes, doors, blinds,

millwork, and boats. Sitka spruce has been by far the most

important wood for aircraft construction. Other specialty uses

are ladder rails and sounding boards for pianos.

Tamarack

Tamarack (Larix laricina), also known as eastern larch and

locally as hackmatack, is a small to medium tree with a

straight, round, slightly tapered trunk. It grows from Maine

to Minnesota, with the bulk of the stand in the Great Lake

States.

The heartwood of tamarack is yellowish brown to russet

brown. The sapwood is whitish, generally less than 2.5 cm

(1 in.) wide. The wood is coarse in texture, without odor or

taste, and the transition from earlywood to latewood is

abrupt. The wood is intermediate in weight and in most

mechanical properties.

Tamarack is used principally for pulpwood, lumber, railroad

crossties, mine timbers, fuel, fence posts, and poles. Lumber
1–17

is used for framing material, tank construction, and boxes,

pallets, and crates. The production of tamarack lumber has

declined in recent years.

White-Cedar, Northern and Atlantic

Two species of white-cedar grow in the eastern part of the

United States: northern white-cedar (Thuja occidentalis) and

Atlantic white-cedar (Chamaecyparis thyoides). Northern

white-cedar is also known as arborvitae or simply as cedar.

Atlantic white-cedar is also known as southern white-cedar,

swamp-cedar, and boat-cedar. Northern white-cedar grows

from Maine along the Appalachians and westward through

the northern part of the Great Lake States. Atlantic whitecedar grows near the Atlantic Coast from Maine to northern

Florida and westward along the Gulf Coast to Louisiana. It

is strictly a swamp tree. Production of northern white-cedar

lumber is greatest in Maine and the Great Lake States. Production of Atlantic white-cedar centers in North Carolina and

along the Gulf Coast.

The heartwood of white-cedar is light brown, and the sapwood is white or nearly so. The sapwood is usually narrow.

The wood is lightweight, rather soft, and low in strength and

shock resistance. It shrinks little in drying. It is easily

worked and holds paint well, and the heartwood is highly

resistant to decay. Northern and Atlantic white-cedar are used

for similar purposes, primarily for poles, cabin logs, railroad

crossties, lumber, posts, and decorative fencing. White-cedar

lumber is used principally where a high degree of durability

is needed, as in tanks and boats, and for wooden ware.

Yellow-Cedar

Yellow-cedar (Chamaecyparis nootkatensis) grows in the

Pacific Coast region of North America from southeastern

Alaska southward through Washington to southern Oregon.

The heartwood of yellow-cedar is bright, clear yellow. The

sapwood is narrow, white to yellowish, and hardly distinguishable from the heartwood. The wood is fine textured and

generally straight grained. It is moderately heavy, moderately

strong and stiff, moderately hard, and moderately high in

shock resistance. Yellow-cedar shrinks little in drying and is

stable after drying, and the heartwood is very resistant to

decay. The wood has a mild, distinctive odor.

Yellow-cedar is used for interior woodwork, furniture, small

boats, cabinetwork, and novelties.

Imported Woods

This section does not purport to describe all the woods that

have been at one time or another imported into the United

States. It includes only those species that at present are

considered to be commercially important. The same species

may be marketed in the United States under other common

names. Because of the variation in common names, many

cross-references are included. Text information is necessarily

brief, but when used in conjunction with the shrinkage and

strength data tables (Ch. 3 and 4), a reasonably good picture

may be obtained of a particular wood. The references at the

end of this chapter contain information on many species not

described in this section.

Hardwoods

Afara (see Limba)

Afrormosia

Afrormosia or kokrodua (Pericopsis elata), a large West

African tree, is sometimes used as a substitute for teak

(Tectona grandis).

The heartwood is fine textured, with straight to interlocked

grain. The wood is brownish yellow with darker streaks and

moderately hard and heavy, weighing about 700 kg/m3

(43 lb/ft3) at 15% moisture content. The wood strongly

resembles teak in appearance but lacks its oily nature and has

a different texture. The wood dries readily with little degrade

and has good dimensional stability. It is somewhat heavier

and stronger than teak. The heartwood is highly resistant to

decay fungi and termite attack and is extremely durable under

adverse conditions.

Afrormosia is often used for the same purposes as teak, such

as boat construction, joinery, flooring, furniture, interior

woodwork, and decorative veneer.

Albarco

Albarco, or jequitiba as it is known in Brazil, is the common name applied to species in the genus Cariniana. The

10 species are distributed from eastern Peru and northern

Bolivia through central Brazil to Venezuela and Colombia.

The heartwood is reddish or purplish brown and sometimes

has dark streaks. It is usually not sharply demarcated from

the pale brown sapwood. The texture is medium and the

grain straight to interlocked. Albarco can be worked satisfactorily with only slight blunting of tool cutting edges because

of the presence of silica. Veneer can be cut without difficulty.

The wood is rather strong and moderately heavy, weighing

about 560 kg/m3

 (35 lb/ft3) at 12% moisture content. In

general, the wood has about the same strength as that of U.S.

oaks (Quercus spp.). The heartwood is durable, particularly

the deeply colored material. It has good resistance to drywood termite attack.

Albarco is primarily used for general construction and carpentry wood, but it can also be used for furniture components,

shipbuilding, flooring, veneer for plywood, and turnery.

Amaranth (see Purpleheart)

Anani (see Manni)

Anaura (see Marishballi)

Andiroba

Because of the widespread distribution of andiroba (Carapa

guianensis) in tropical America, the wood is known under a

variety of names, including cedro macho, carapa, crabwood,
 1–18

and tangare. These names are also applied to the related

species Carapa nicaraguensis, whose properties are generally inferior to those of C. guianensis.

The heartwood varies from medium to dark reddish brown.

The texture is like that of true mahogany (Swietenia macrophylla), and andiroba is sometimes substituted for true mahogany. The grain is usually interlocked but is rated easy to

work, paint, and glue. The wood is rated as durable to very

durable with respect to decay and insects. Andiroba is heavier than true mahogany and accordingly is markedly superior

in all static bending properties, compression parallel to

grain, hardness, shear, and durability.

On the basis of its properties, andiroba appears to be suited

for such uses as flooring, frame construction in the tropics,

furniture and cabinetwork, millwork, utility and decorative

veneer, and plywood.

Angelin (see Sucupira)

Angelique

Angelique (Dicorynia guianensis) comes from French

Guiana and Suriname.

Because of the variability in heartwood color between different trees, two forms are commonly recognized by producers.

The heartwood that is russet-colored when freshly cut and

becomes superficially dull brown with a purplish cast is

referred to as “gris.” The heartwood that is more distinctly

reddish and frequently shows wide purplish bands is called

“angelique rouge.” The texture of the wood is somewhat

coarser than that of black walnut (Juglans nigra), and the

grain is generally straight or slightly interlocked. In strength,

angelique is superior to teak (Tectona grandis) and white

oak (Quercus alba), when green or air dry, in all properties

except tension perpendicular to grain. Angelique is rated as

highly resistant to decay and resistant to marine borer attack.

Machining properties vary and may be due to differences in

density, moisture content, and silica content. After the wood

is thoroughly air or kiln dried, it can be worked effectively

only with carbide-tipped tools.

The strength and durability of angelique make it especially

suitable for heavy construction, harbor installations, bridges,

heavy planking for pier and platform decking, and railroad

bridge ties. The wood is also suitable for ship decking,

planking, boat frames, industrial flooring, and parquet blocks

and strips.

Apa (see Wallaba)

Apamate (see Roble)

Apitong (see Keruing)

Avodire

Avodire (Turraeanthus africanus) has a rather extensive

range in Africa, from Sierra Leone westward to the Congo

region and southward to Zaire and Angola. It is most common in the eastern region of the Ivory Coast and is scattered

elsewhere. Avodire is a medium-size tree of the rainforest

where it forms fairly dense but localized and discontinuous

timber stands.

The wood is cream to pale yellow with high natural luster; it

eventually darkens to a golden yellow. The grain is sometimes straight but more often wavy or irregularly interlocked,

which produces an unusual and attractive mottled figure

when sliced or cut on the quarter. Although avodire weighs

less than northern red oak (Quercus rubra), it has almost

identical strength properties except that it is lower in shock

resistance and shear. The wood works fairly easily with hand

and machine tools and finishes well in most operations.

Figured material is usually converted into veneer for use in

decorative work, and it is this kind of material that is chiefly

imported into the United States. Other uses include furniture,

fine joinery, cabinetwork, and paneling.

Azobe (Ekki)

Azobe or ekki (Lophira alata) is found in West Africa and

extends into the Congo basin.

The heartwood is dark red, chocolate-brown, or purple–

brown with conspicuous white deposits in the pores

(vessels). The texture is coarse, and the grain is usually

interlocked. The wood is strong, and its density averages

about 1,120 kg/m3

 (70 lb/ft3) at 12% moisture content. It is

very difficult to work with hand and machine tools, and tools

are severely blunted if the wood is machined when dry.

Azobe can be dressed to a smooth finish, and gluing properties are usually good. Drying is very difficult without excessive degrade. The heartwood is rated as very durable against

decay but only moderately resistant to termite attack. Azobe

is very resistant to acid and has good weathering properties.

It is also resistant to teredo attack. The heartwood is

extremely resistant to preservative treatment.

Azobe is excellent for heavy construction work, harbor construction, heavy-duty flooring, and railroad crossties.

Bagtikan (see Seraya, White)

Balata

Balata or bulletwood (Manilkara bidentata) is widely distributed throughout the West Indies, Central America, and

northern South America.

The heartwood of balata is light to dark reddish brown and

not sharply demarcated from the pale brown sapwood. Texture is fine and uniform, and the grain is straight to occasionally wavy or interlocked. Balata is a strong and very heavy

wood; density of air-dried wood is 1,060 kg/m3 (66 lb/ft3

). It

is generally difficult to air dry, with a tendency to develop

severe checking and warp. The wood is moderately easy to

work despite its high density, and it is rated good to excellent in all machining operations. Balata is very resistant to

attack by decay fungi and highly resistant to subterranean

termites but only moderately resistant to dry-wood termites.
1–19

Balata is suitable for heavy construction, textile and pulpmill

equipment, furniture parts, turnery, tool handles, flooring,

boat frames and other bentwork, railroad crossties, violin

bows, billiard cues, and other specialty uses.

Balau

Balau, red balau, and selangan batu constitute a group of

species that are the heaviest of the 200 Shorea species. About

45 species of this group grow from Sri Lanka and southern

India through southeast Asia to the Philippines.

The heartwood is light to deep red or purple–brown, and it

is fairly distinct from the lighter and yellowish- to reddishor purplish-brown sapwood. The texture is moderately fine

to coarse, and the grain is often interlocked. The wood

weighs more than 750 kg/m3

 (47 lb/ft3) at 12% moisture

content. Balau is a heavy, hard, and strong timber that dries

slowly with moderate to severe end checks and splits. The

heartwood is durable to moderately durable and very resistant

to preservative treatments.

Balau is used for heavy construction, frames of boats, decking, flooring, and utility furniture.

Balau, Red (see Balau)

Balsa

Balsa (Ochroma pyramidale) is widely distributed throughout tropical America from southern Mexico to southern

Brazil and Bolivia, but Ecuador has been the principal source

of supply since the wood gained commercial importance. It

is usually found at lower elevations, especially on bottomland soils along streams and in clearings and cutover forests.

Today, it is often cultivated in plantations.

Several characteristics make balsa suitable for a wide variety

of uses. It is the lightest and softest of all woods on the

market. The lumber selected for use in the United States

weighs, on the average, about 180 kg/m3

 (11 lb/ft3) when dry

and often as little as 100 kg/m3 (6 lb/ft3). The wood is readily recognized by its light weight; nearly white or oatmeal

color, often with a yellowish or pinkish hue; and unique

velvety feel.

Because of its light weight and exceedingly porous composition, balsa is highly efficient in uses where buoyancy, insulation against heat or cold, or low propagation of sound and

vibration are important. Principal uses are for life-saving

equipment, floats, rafts, corestock, insulation, cushioning,

sound modifiers, models, and novelties.

Banak (Cuangare)

Various species of banak (Virola) occur in tropical America,

from Belize and Guatemala southward to Venezuela, the

Guianas, the Amazon region of northern Brazil, and southern

Brazil, and on the Pacific Coast to Peru and Bolivia. Most of

the wood known as banak is V. koschnyi of Central America

and V. surinamensis and V. sebifera of northern South

America. Botanically, cuangare (Dialyanthera) is closely

related to banak, and the woods are so similar that they are

generally mixed in the trade. The main commercial supply of

cuangare comes from Colombia and Ecuador. Banak and

cuangare are common in swamp and marsh forests and may

occur in almost pure stands in some areas.

The heartwood of both banak and cuangare is usually pinkish

or grayish brown and is generally not differentiated from the

sapwood. The wood is straight grained and is of a medium

to coarse texture. The various species are nonresistant to

decay and insect attack but can be readily treated with preservatives. Machining properties are very good, but when

zones of tension wood are present, machining may result in

surface fuzziness. The wood finishes readily and is easily

glued. Strength properties of banak and cuangare are similar

to those of yellow-poplar (Liriodendron tulipifera).

Banak is considered a general utility wood for lumber, veneer, and plywood. It is also used for moulding, millwork,

and furniture components.

Benge (Ehie, Bubinga)

Although benge (Guibourtia arnoldiana), ehie or ovangkol

(Guibourtia ehie), and bubinga (Guibourtia spp.) belong to

the same West African genus, they differ rather markedly in

color and somewhat in texture.

The heartwood of benge is pale yellowish brown to medium

brown with gray to almost black stripes. Ehie heartwood

tends to be more golden brown to dark brown with gray to

almost black stripes. Bubinga heartwood is pink, vivid red,

or red–brown with purple streaks, and it becomes yellow or

medium brown with a reddish tint upon exposure to air. The

texture of ehie is moderately coarse, whereas that of benge

and bubinga is fine to moderately fine. All three woods are

moderately hard and heavy, but they can be worked well

with hand and machine tools. They are listed as moderately

durable and resistant to preservative treatment. Drying may

be difficult, but with care, the wood dries well.

These woods are used in turnery, flooring, furniture components, cabinetwork, and decorative veneers.

Brown Silverballi (see Kaneelhart)

Bubinga (see Benge)

Bulletwood (see Balata)

Carapa (see Andiroba)

Cativo

Cativo (Prioria copaifera) is one of the few tropical American species that occur in abundance and often in nearly pure

stands. Commercial stands are found in Nicaragua, Costa

Rica, Panama, and Colombia.

Sapwood may be very pale pink or distinctly reddish, and it

is usually wide. In trees up to 76 cm (30 in.) in diameter,

heartwood may be only 18 cm (7 in.) in diameter. The grain

is straight and the texture of the wood is uniform, comparable with that of true mahogany (Swietenia macrophylla). On

flat-sawn surfaces, the figure is rather subdued as a result of
 1–20

exposure of the narrow bands of parenchyma tissue. The

wood can be dried rapidly and easily with very little degrade.

Dimensional stability is very good—practically equal to that

of true mahogany. Cativo is classified as a nondurable wood

with respect to decay and insects. It may contain appreciable

quantities of gum. In wood that has been properly dried,

however, the aromatics in the gum are removed and there is

no difficulty in finishing.

Considerable quantities of cativo are used for interior woodwork, and resin-stabilized veneer is an important pattern

material. Cativo is widely used for furniture and cabinet

parts, lumber core for plywood, picture frames, edge banding

for doors, joinery, and millwork.

Cedro (see Spanish-Cedar)

Cedro Macho (see Andiroba)

Cedro-Rana (see Tornillo)

Ceiba

Ceiba (Ceiba pentandra) is a large tree, which grows to

66 m (200 ft) in height with a straight cylindrical bole 13 to

20 m (40 to 60 ft) long. Trunk diameters of 2 m (6 ft) or

more are common. Ceiba grows in West Africa, from the

Ivory Coast and Sierra Leone to Liberia, Nigeria, and the

Congo region. A related species is lupuna (Ceiba samauma)

from South America.

Sapwood and heartwood are not clearly demarcated. The

wood is whitish, pale brown, or pinkish brown, often with

yellowish or grayish streaks. The texture is coarse, and the

grain is interlocked or occasionally irregular. Ceiba is very

soft and light; density of air-dried wood is 320 kg/m3

(20 lb/ft3). In strength, the wood is comparable with basswood (Tilia americana). Ceiba dries rapidly without marked

deterioration. It is difficult to saw cleanly and dress smoothly

because of the high percentage of tension wood. It provides

good veneer and is easy to nail and glue. Ceiba is very

susceptible to attack by decay fungi and insects. It requires

rapid harvest and conversion to prevent deterioration. Treatability, however, is rated as good.

Ceiba is available in large sizes, and its low density combined with a rather high degree of dimensional stability make

it ideal for pattern and corestock. Other uses include blockboard, boxes and crates, joinery, and furniture components.

Chewstick (see Manni)

Courbaril (Jatoba)

The genus Hymenaea consists of about 25 species that occur

in the West Indies and from southern Mexico through Central America into the Amazon basin of South America. The

best-known and most important species is H. courbaril,

which occurs throughout the range of the genus. Courbaril is

often called jatoba in Brazil.

Sapwood of courbaril is gray–white and usually quite wide.

The heartwood, which is sharply differentiated from the

sapwood, is salmon red to orange–brown when freshly cut

and becomes russet or reddish brown when dried. The heartwood is often marked with dark streaks. The texture is medium to rather coarse, and the grain is mostly interlocked.

The wood is hard and heavy (about 800 kg/m3 (50 lb/ft3

) at

12% moisture content). The strength properties of courbaril

are quite high and very similar to those of shagbark hickory

(Carya ovata), a species of lower specific gravity. Courbaril

is rated as moderately to very resistant to attack by decay

fungi and dry-wood termites. The heartwood is not treatable,

but the sapwood is treatable with preservatives. Courbaril is

moderately difficult to saw and machine because of its high

density, but it can be machined to a smooth surface. Turning, gluing, and finishing properties are satisfactory. Planing,

however, is somewhat difficult because of the interlocked

grain. Courbaril compares favorably with white oak (Quercus

alba) in steam bending behavior.

Courbaril is used for tool handles and other applications that

require good shock resistance. It is also used for steam-bent

parts, flooring, turnery, furniture and cabinetwork, veneer and

plywood, railroad crossties, and other specialty items.

Crabwood (see Andiroba)

Cristobal (see Macawood)

Cuangare (see Banak)

Degame

Degame or lemonwood (Calycophyllum candidissimum)

grows in Cuba and ranges from southern Mexico through

Central America to Colombia and Venezuela. It may grow in

pure stands and is common on shaded hillsides and along

waterways.

The heartwood of degame ranges from light brown to oatmeal-colored and is sometimes grayish. The sapwood is

lighter in color and merges gradually with the heartwood.

The texture is fine and uniform. The grain is usually straight

or infrequently shows shallow interlocking, which may

produce a narrow and indistinct stripe on quartered faces. In

strength, degame is above the average for woods of similar

density; density of air-dried wood is 817 kg/m3 (51 lb/ft3

).

Tests show degame superior to persimmon (Diospyros

virginiana) in all respects but hardness. Natural durability is

low when degame is used under conditions favorable to

stain, decay, and insect attack. However, degame is reported

to be highly resistant to marine borers. Degame is moderately difficult to machine because of its density and hardness,

although it does not dull cutting tools to any extent. Machined surfaces are very smooth.

Degame is little used in the United States, but its characteristics have made it particularly adaptable for shuttles, picker

sticks, and other textile industry items that require resilience

and strength. Degame was once prized for the manufacture of

archery bows and fishing rods. It is also suitable for tool

handles and turnery.
1–21

Determa

Determa (Ocotea rubra) is native to the Guianas, Trinidad,

and the lower Amazon region of Brazil.

The heartwood is light reddish brown with a golden sheen

and distinct from the dull gray or pale yellowish brown

sapwood. The texture is rather coarse, and the grain is interlocked to straight. Determa is a moderately strong and heavy

wood (density of air-dried wood is 640 to 720 kg/m3 (40 to

45 lb/ft3)); this wood is moderately difficult to air dry. It can

be worked readily with hand and machine tools with little

dulling effect. It can be glued readily and polished fairly well.

The heartwood is durable to very durable in resistance to

decay fungi and moderately resistant to dry-wood termites.

Weathering characteristics are excellent, and the wood is

highly resistant to moisture absorption.

Uses for determa include furniture, general construction, boat

planking, tanks and cooperage, heavy marine construction,

turnery, and parquet flooring.

Ehie (see Benge)

Ekki (see Azobe)

Ekop

Ekop or gola (Tetraberlinia tubmaniana) grows only in

Liberia.

The heartwood is light reddish brown and is distinct from

the lighter colored sapwood, which may be up to 5 cm

(2 in.) wide. The wood is medium to coarse textured, and

the grain is interlocked, with a narrow striped pattern on

quartered surfaces. The wood weighs about 735 kg/m3

(46 lb/ft3) at 12% moisture content. It dries fairly well but

with a marked tendency to end and surface checks. Ekop

works well with hand and machine tools and is an excellent

wood for turnery. It also slices well into veneer and has good

gluing properties. The heartwood is only moderately durable

and is moderately resistant to impregnation with preservative

treatments.

Ekop is a general utility wood that is used for veneer,

plywood, and furniture components.

Encino (see Oak)

Gola (see Ekop)

Goncalo Alves

Most imports of goncalo alves (Astronium graveolens and

A. fraxinifolium) have been from Brazil. These species range

from southern Mexico through Central America into the

Amazon basin.

Freshly cut heartwood is russet brown, orange–brown, or

reddish brown to red with narrow to wide, irregular, medium- to very-dark brown stripes. After exposure to air, the

heartwood becomes brown, red, or dark reddish brown with

nearly black stripes. The sapwood is grayish white and

sharply demarcated from the heartwood. The texture is fine to

medium and uniform. The grain varies from straight to

interlocked and wavy.

Goncalo alves turns readily, finishes very smoothly, and

takes a high natural polish. The heartwood is highly resistant to moisture absorption; pigmented areas may present

some difficulties in gluing because of their high density. The

heartwood is very durable and resistant to both white- and

brown-rot organisms. The high density (1,010 kg/m3

(63 lb/ft3)) of the air-dried wood is accompanied by equally

high strength values, which are considerably higher in most

respects than those of any U.S. species. Despite its strength,

however, goncalo alves is imported primarily for its beauty.

In the United States, goncalo alves has the greatest value for

specialty items such as archery bows, billiard cue butts,

brushbacks, and cutlery handles, and in turnery and carving

applications.

Greenheart

Greenheart (Chlorocardium rodiei [= Ocotea rodiei]) is

essentially a Guyana tree although small stands also occur in

Suriname.

The heartwood varies from light to dark olive green or nearly

black. The texture is fine and uniform, and the grain is

straight to wavy. Greenheart is stronger and stiffer than white

oak (Quercus alba) and generally more difficult to work with

tools because of its high density; density of air-dried wood is

more than 960 kg/m3 (60 lb/ft3). The heartwood is rated as

very resistant to decay fungi and termites. It is also very

resistant to marine borers in temperate waters but much less

so in warm tropical waters.

Greenheart is used principally where strength and resistance

to wear are required. Uses include ship and dock building,

lock gates, wharves, piers, jetties, vats, piling, planking,

industrial flooring, bridges, and some specialty items

(fishing rods and billiard cue butts).

Guatambu (see Pau Marfim)

Guayacan (see Ipe)

Hura

Hura (Hura crepitans) grows throughout the West Indies

from Central America to northern Brazil and Bolivia.

It is a large tree, commonly reaching a height of 30 to 43 m

(90 to 130 ft), with clear boles of 12 to 23 m (40 to 75 ft).

The diameter often reaches 1 to 1.5 m (3 to 5 ft) and occasionally to 3 m (9 ft).

The pale yellowish-brown or pale olive-gray heartwood is

indistinct from the yellowish-white sapwood. The texture is

fine to medium and the grain straight to interlocked. Hura is

a low-strength and low-density wood (density of air-dried

wood is 240 to 448 kg/m3 (15 to 28 lb/ft3

)); the wood is

moderately difficult to air dry. Warping is variable and sometimes severe. The wood usually machines easily, but green

material is somewhat difficult to work because of tension
 1–22

wood, which results in a fuzzy surface. The wood finishes

well and is easy to glue and nail. Hura is variable in resistance to attack by decay fungi, but it is highly susceptible to

blue stain and very susceptible to wood termites. However,

the wood is easy to treat with preservative.

Hura is often used in general carpentry, boxes and crates, and

lower grade furniture. Other important uses are veneer and

plywood, fiberboard, and particleboard.

Ilomba

Ilomba (Pycnanthus angolensis) is a tree of the rainforest and

ranges from Guinea and Sierra Leone through tropical West

Africa to Uganda and Angola. Common names include

pycnanthus, walele, and otie.

The wood is grayish white to pinkish brown and, in some

trees, a uniform light brown. There is generally no distinction between heartwood and sapwood. The texture is medium to coarse, and the grain is generally straight. This

species is generally similar to banak (Virola) but has a

coarser texture. Air-dry density is about 512 kg/m3

(31 lb/ft3), and the wood is about as strong as yellow-poplar

(Liriodendron tulipifera). Ilomba dries rapidly but is prone

to collapse, warp, and splits. It is easily sawn and can be

worked well with hand and machine tools. It is excellent for

veneer and has good gluing and nailing characteristics. Green

wood is subject to insect and fungal attack. Logs require

rapid extraction and conversion to avoid degrade. Both

sapwood and heartwood are permeable and can be treated

with preservatives.

In the United States, this species is used only in the form of

plywood for general utility purposes. However, ilomba is

definitely suited for furniture components, interior joinery,

and general utility purposes.

Ipe

Ipe, the common name for the lapacho group of the genus

Tabebuia, consists of about 20 species of trees and occurs in

practically every Latin America country except Chile. Other

commonly used names are guayacan and lapacho.

Sapwood is relatively wide, yellowish gray or gray–brown,

and sharply differentiated from heartwood, which is light to

dark olive brown. The texture is fine to medium. The grain

is straight to very irregular and often narrowly interlocked.

The wood is very heavy and averages about 1,025 kg/m3

(64 lb/ft3) at 12% moisture content. Thoroughly air-dried

heartwood specimens generally sink in water. Because of its

high density and hardness, ipe is moderately difficult to

machine, but glassy smooth surfaces can be produced. Ipe is

very strong; in the air-dried condition, it is comparable with

greenheart (Chlorocardium rodiei). Hardness is two to three

times that of white oak (Quercus alba) or keruing (Dipterocarpus). The wood is highly resistant to decay and insects,

including both subterranean and dry-wood termites, but

susceptible to marine borer attack. The heartwood is impermeable, but the sapwood can be readily treated with

preservatives.

Ipe is used almost exclusively for heavy-duty and durable

construction. Because of its hardness and good dimensional

stability, it is particularly well suited for heavy-duty flooring

in trucks and boxcars. It is also used for decks, railroad

crossties, turnery, tool handles, decorative veneers, and some

specialty items in textile mills.

Ipil (see Merbau)

Iroko

Iroko consists of two species (Milicia excelsa [= Chlorophora excelsa] and M. regia [= C. regia]). Milicia excelsa

grows across the entire width of tropical Africa from the Ivory

Coast southward to Angola and eastward to East Africa.

Milicia regia, however, is limited to extreme West Africa

from Gambia to Ghana; it is less resistant to drought than is

M. excelsa.

The heartwood varies from a pale yellowish brown to dark

chocolate brown with light markings occurring most conspicuously on flat-sawn surfaces; the sapwood is yellowish

white. The texture is medium to coarse, and the grain is

typically interlocked. Iroko can be worked easily with hand

or machine tools but with some tearing of interlocked grain.

Occasional deposits of calcium carbonate severely damage

cutting edges. The wood dries rapidly with little or no

degrade. The strength is similar to that of red maple

(Acer rubrum), and the weight is about 688 kg/m3

 (43 lb/ft3)

at 12% moisture content. The heartwood is very resistant to

decay fungi and resistant to termite and marine borer attack.

Because of its color and durability, iroko has been suggested

as a substitute for teak (Tectona grandis). Its durability

makes it suitable for boat building, piles, other marine work,

and railroad crossties. Other uses include joinery, flooring,

furniture, veneer, and cabinetwork.

Jacaranda (see Rosewood, Brazilian)

Jarrah

Jarrah (Eucalyptus marginata) is native to the coastal belt of

southwestern Australia and is one of the principal species for

that country’s sawmill industry.

The heartwood is a uniform pink to dark red, often turning

to deep brownish red with age and exposure to air. The

sapwood is pale and usually very narrow in old trees. The

texture is even and moderately coarse, and the grain is frequently interlocked or wavy. The wood weighs about

865 kg/m3 (54 lb/ft3) at 12% moisture content. The common

defects of jarrah include gum veins or pockets, which in

extreme instances, separate the log into concentric shells.

Jarrah is a heavy, hard timber possessing correspondingly

high strength properties. It is resistant to attack by termites

and rated as very durable with respect to decay. The wood is

difficult to work with hand and machine tools because of its

high density and irregular grain.

Jarrah is used for decking and underframing of piers, jetties,

and bridges, as well as piles and fenders for docks and
1–23

harbors. As flooring, jarrah has high resistance to wear, but it

is inclined to splinter under heavy traffic. It is also used for

railroad crossties and other heavy construction.

Jatoba (see Courbaril)

Jelutong

Jelutong (Dyera costulata) is an important species in Malaysia where it is best known for its latex production in the

manufacture of chewing gum rather than for its wood.

The wood is white or straw colored, and there is no differentiation between heartwood and sapwood. The texture is

moderately fine and even. The grain is straight, and luster is

low. The wood weighs about 465 kg/m3

 (28 lb/ft3) at 12%

moisture content. The wood is very easy to dry with little

tendency to split or warp, but staining may cause trouble. It

is easy to work in all operations, finishes well, and glues

satisfactorily. The wood is rated as nondurable but readily

permeable to preservatives.

Because of its low density and ease of working, jelutong is

well suited for sculpture and pattern making, wooden shoes,

picture frames, and drawing boards.

Jequitiba (see Albarco)

Kakaralli (see Manbarklak)

Kaneelhart

Kaneelhart or brown silverballi are names applied to the

genus Licaria. Species of this genus grow mostly in New

Guinea and Papau New Guinea and are found in association

with greenheart (Chlorocardium rodiei) on hilly terrain and

wallaba (Eperua) in forests.

The orange or brownish yellow heartwood darkens to yellowish or coffee brown on exposure to air. The wood is

sometimes tinged with red or violet. The texture is fine to

medium, and the grain is straight to slightly interlocked.

The wood has a fragrant odor, which is lost in drying.

Kaneelhart is a very strong and very heavy wood (density of

air-dried wood is 833 to 1,153 kg/m3

 (52 to 72 lb/ft3)); the

wood is difficult to work. It cuts smoothly and takes an

excellent finish but requires care in gluing. Kaneelhart has

excellent resistance to both brown- and white-rot fungi and is

also rated very high in resistance to dry-wood termites.

Uses of kaneelhart include furniture, turnery, boat building,

heavy construction, and parquet flooring.

Kapur

The genus Dryobalanops consists of nine species distributed

over parts of Malaysia and Indonesia. For the export trade,

the species are combined under the name kapur.

The heartwood is reddish brown and clearly demarcated from

the pale sapwood. The wood is fairly coarse textured but

uniform. In general, the wood resembles keruing

(Dipterocarpus), but on the whole, kapur is straighter

grained and not quite as coarse in texture. Density of the

wood averages about 720 to 800 kg/m3

 (45 to 50 lb/ft3) at

12% moisture content. Strength properties are similar to

those of keruing at comparable specific gravity. The heartwood is rated resistant to attack by decay fungi; it is reported

to be vulnerable to termites. Kapur is extremely resistant to

preservative treatment. The wood works with moderate ease

in most hand and machine operations, but blunting of cutters

may be severe because of silica content, particularly when the

dry wood is machined. A good surface can be obtained from

various machining operations, but there is a tendency toward

raised grain if dull cutters are used. Kapur takes nails and

screws satisfactorily. The wood glues well with urea formaldehyde but not with phenolic adhesives.

Kapur provides good and very durable construction wood

and is suitable for all purposes for which keruing

(Dipterocarpus) is used in the United States. In addition,

kapur is extensively used in plywood either alone or with

species of Shorea (lauan–meranti).

Karri

Karri (Eucalyptus diversicolor) is a very large tree limited to

southwestern Australia.

Karri resembles jarrah (E. marginata) in structure and general

appearance. It is usually paler in color and, on average,

slightly heavier (913 kg/m3

 (57 lb/ft3)) at 12% moisture

content. Karri is a heavy hardwood with mechanical properties of a correspondingly high order, even somewhat higher

than that of jarrah. The heartwood is rated as moderately

durable, though less so than that of jarrah. It is extremely

difficult to treat with preservatives. The wood is fairly hard

to machine and difficult to cut with hand tools. It is generally more resistant to cutting than is jarrah and has a slightly

more dulling effect on tool edges.

Karri is inferior to jarrah for underground use and waterworks. However, where flexural strength is required, such as

in bridges, floors, rafters, and beams, karri is an excellent

wood. Karri is popular in heavy construction because of its

strength and availability in large sizes and long lengths that

are free of defects.

Kauta (see Marishballi)

Kempas

Kempas (Koompassia malaccensis) is distributed throughout

the lowland forest in rather swampy areas of Malaysia and

Indonesia.

When exposed to air, the freshly cut brick-red heartwood

darkens to an orange–red or red–brown with numerous yellow–brown streaks as a result of the soft tissue (axial parenchyma) associated with the pores. The texture is rather

coarse, and the grain is typically interlocked. Kempas is a

hard, heavy wood (density of air-dried wood is 880 kg/m3

(55 lb/ft3)); the wood is difficult to work with hand and

machine tools. The wood dries well, with some tendency to

warp and check. The heartwood is resistant to attack by

decay fungi but vulnerable to termite activity. However, it

treats readily with preservative retention as high as

320 kg/m3 (20 lb/ft3).
 1–24

Kempas is ideal for heavy construction work, railroad

crossties, and flooring.

Keruing (Apitong)

Keruing or apitong (Dipterocarpus) is widely scattered

throughout the Indo-Malaysian region. Most of the more

than 70 species in this genus are marketed under the name

keruing. Other important species are marketed as apitong in

the Philippine Islands and yang in Thailand.

The heartwood varies from light to dark red–brown or brown

to dark brown, sometimes with a purple tint; the heartwood

is usually well defined from the gray or buff-colored

sapwood. Similar to kapur (Dryobalanops), the texture of

keruing is moderately coarse and the grain is straight or

shallowly interlocked. The wood is strong, hard, and heavy

(density of air-dried wood is 720 to 800 kg/m3

 (45 to

50 lb/ft3)); this wood is characterized by the presence of resin

ducts, which occur singly or in short arcs as seen on endgrain surfaces. This resinous condition and the presence of

silica can present troublesome problems. Sapwood and

heartwood are moderately resistant to preservative treatments.

However, the wood should be treated with preservatives

when it is used in contact with the ground. Durability varies

with species, but the wood is generally classified as moderately durable. Keruing generally takes to sawing and machining, particularly when green, but saws and cutters dull easily

as a result of high silica content in the wood. Resin adheres

to machinery and tools and may be troublesome. Also, resin

may cause gluing and finishing difficulties.

Keruing is used for general construction work, framework for

boats, flooring, pallets, chemical processing equipment,

veneer and plywood, railroad crossties (if treated), truck

floors, and boardwalks.

Khaya (see Mahogany, African)

Kokrodua (see Afrormosia)

Korina (see Limba)

Krabak (see Mersawa)

Kwila (see Merbau)

Lapacho (see Ipe)

Lapuna (see Ceiba)

Lauan (see Meranti Groups)

Lemonwood (see Degame)

Lignumvitae

For many years, the only species of lignumvitae used on a

large scale was Guaiacum officinale, which is native to the

West Indies, northern Venezuela, northern Colombia, and

Panama. With the near exhaustion of G. officinale, harvesters turned to G. sanctum, which is now the principal commercial species. Guaiacum sanctum occupies the same range

as G. officinale but is more extensive and includes the

Pacific side of Central America as well as southern Mexico.

Lignumvitae is one of the heaviest and hardest woods on the

market. The wood is characterized by its unique green color

and oily or waxy feel. The wood has a fine uniform texture

and closely interlocked grain. Its resin content may constitute up to one-fourth of the air-dried weight of the heartwood.

Lignumvitae wood is used chiefly for bearing or bushing

blocks for ship propeller shafts. The great strength and tenacity of lignumvitae, combined with self-lubricating properties

resulting from the high resin content, make it especially

adaptable for underwater use. It is also used for such articles

as mallets, pulley sheaves, caster wheels, stencil and chisel

blocks, and turned products.

Limba

Limba (Terminalia superba), also referred to as afara, is

widely distributed from Sierra Leone to Angola and Zaire in

the rainforest and savanna forest. Limba is also favored as a

plantation species in West Africa.

The heartwood varies from gray–white to creamy or yellow

brown and may contain dark streaks that are nearly black,

producing an attractive figure that is valued for decorative

veneer. The light color of the wood is considered an important asset for the manufacture of blond furniture. The wood is

generally straight grained and of uniform but coarse texture.

The wood is easy to dry and shrinkage is reported to be

rather low. Limba is not resistant to decay, insects, or termites. It is easy to work with all types of tools and is made

into veneer without difficulty.

Principal uses include plywood, furniture, interior joinery,

and sliced decorative veneer.

Macacauba (see Macawood)

Macawood (Trebol)

Macawood and trebol are common names applied to species

in the genus Platymiscium. Other common names include

cristobal and macacauba. This genus is distributed across

continental tropical America from southern Mexico to the

Brazilian Amazon region and Trinidad.

The bright red to reddish or purplish brown heartwood is

more or less striped. Darker specimens look waxy, and the

sapwood is sharply demarcated from the heartwood. The

texture is medium to fine, and the grain is straight to curly

or striped. The wood is not very difficult to work, and it

finishes smoothly and takes on a high polish. Generally,

macawood air dries slowly with a slight tendency to warp

and check. Strength is quite high, and density of air-dried

wood ranges from 880 to 1,170 kg/m3

 (55 to 73 lb/ft3). The

heartwood is reported to be highly resistant to attack by

decay fungi, insects, and dry-wood termites. Although the

sapwood absorbs preservatives well, the heartwood is resistant to treatment.

Macawood is a fine furniture and cabinet wood. It is also

used in decorative veneers, musical instruments, turnery,

joinery, and specialty items such as violin bows and

billiard cues.
1–25

Machinmango (see Manbarklak)

Mahogany

The name mahogany is presently applied to several distinct

kinds of commercial wood. The original mahogany wood,

produced by Swietenia mahagoni, came from the American

West Indies. This was the premier wood for fine furniture

cabinet work and shipbuilding in Europe as early as the

1600s. Because the good reputation associated with the name

mahogany is based on this wood, American mahogany is

sometimes referred to as true mahogany. A related African

wood, of the genus Khaya, has long been marketed as

“African mahogany” and is used for much the same purposes

as American mahogany because of its similar properties and

overall appearance. A third kind of wood called mahogany,

and the one most commonly encountered in the market, is

“Philippine mahogany.” This name is applied to a group of

Asian woods belonging to the genus Shorea. In this chapter,

information on the “Philippine mahoganies” is given under

lauan and meranti groups.

Mahogany, African—The bulk of “African mahogany”

shipped from west–central Africa is Khaya ivorensis, the

most widely distributed and plentiful species of the genus

found in the coastal belt of the so-called high forest. The

closely allied species K. anthotheca has a more restricted

range and is found farther inland in regions of lower rainfall

but well within the area now being used for the export trade.

The heartwood varies from pale pink to dark reddish brown.

The grain is frequently interlocked, and the texture is medium to coarse, comparable with that of American mahogany

(Swietenia macrophylla). The wood is easy to dry, but

machining properties are rather variable. Nailing and gluing

properties are good, and an excellent finish is readily obtained. The wood is easy to slice and peel. In decay resistance, African mahogany is generally rated as moderately

durable, which is below the durability rating for American

mahogany.

Principal uses for African mahogany include furniture and

cabinetwork, interior woodwork, boat construction, and

veneer.

Mahogany, American—True, American, or Honduras

mahogany (Swietenia macrophylla) ranges from southern

Mexico through Central America into South America as far

south as Bolivia. Plantations have been established within

its natural range and elsewhere throughout the tropics.

The heartwood varies from pale pink or salmon colored to

dark reddish brown. The grain is generally straighter than

that of African mahogany (Khaya ivorensis); however, a wide

variety of grain patterns are obtained from American mahogany. The texture is rather fine to coarse. American mahogany

is easily air or kiln dried without appreciable warp or checks,

and it has excellent dimensional stability. It is rated as

durable in resistance to decay fungi and moderately resistant

to dry-wood termites. Both heartwood and sapwood are

resistant to treatment with preservatives. The wood is very

easy to work with hand and machine tools, and it slices and

rotary cuts into fine veneer without difficulty. It also is easy

to finish and takes an excellent polish. The air-dried strength

of American mahogany is similar to that of American elm

(Ulmus americana). Density of air-dried wood varies from

480 to 833 kg/m3 (30 to 52 lb/ft3

).

The principal uses for mahogany are fine furniture and

cabinets, interior woodwork, pattern woodwork, boat construction, fancy veneers, musical instruments, precision

instruments, paneling, turnery, carving, and many other uses

that call for an attractive and dimensionally stable wood.

Mahogany, Philippine (see Meranti Groups)

Manbarklak

Manbarklak is a common name applied to species in the

genus Eschweilera. Other names include kakaralli machinmango, and mata–mata. About 80 species of this genus are

distributed from eastern Brazil through the Amazon basin, to

the Guianas, Trinidad, and Costa Rica.

The heartwood of most species is light, grayish, reddish

brown, or brownish buff. The texture is fine and uniform, and

the grain is typically straight. Manbarklak is a very hard and

heavy wood (density of air-dried wood ranges from 768 to

1,185 kg/m3

 (48 to 74 lb/ft3)) that is rated as fairly difficult to

dry. Most species are difficult to work because of the high

density and high silica content. Most species are highly

resistant to attack by decay fungi. Also, most species have

gained wide recognition for their high degree of resistance to

marine borer attack. Resistance to dry-wood termite attack is

variable depending on species.

Manbarklak is an ideal wood for marine and other heavy

construction uses. It is also used for industrial flooring, mill

equipment, railroad crossties, piles, and turnery.

Manni

Manni (Symphonia globulifera) is native to the West Indies,

Mexico, and Central, North, and South America. It also

occurs in tropical West Africa. Other names include ossol

(Gabon), anani (Brazil), waika (Africa), and chewstick

(Belize), a name acquired because of its use as a primitive

toothbrush and flossing tool.

The heartwood is yellowish, grayish, or greenish brown and

is distinct from the whitish sapwood. The texture is coarse

and the grain straight to irregular. The wood is very easy to

work with both hand and machine tools, but surfaces tend to

roughen in planing and shaping. Manni air-dries rapidly with

only moderate warp and checking. Its strength is similar to

that of hickory (Carya), and the density of air-dried wood is

704 kg/m3

 (44 lb/ft3). The heartwood is durable in ground

contact but only moderately resistant to dry-wood and subterranean termites. The wood is rated as resistant to treatment with preservatives.

Manni is a general purpose wood that is used for railroad

ties, general construction, cooperage, furniture components,

flooring, and utility plywood.
 1–26

Marishballi

Marishballi is the common name applied to species of the

genus Licania. Other names include kauta and anaura. Species of Licania are widely distributed in tropical America but

most abundant in the Guianas and the lower Amazon region

of Brazil.

The heartwood is generally a yellowish to dark brown,

sometimes with a reddish tinge. The texture is fine and

close, and the grain is usually straight. Marishballi is strong

and very heavy; density of air-dried wood is 833 to

1,153 kg/m3

 (52 to 72 lb/ft3). The wood is rated as easy to

moderately difficult to air dry. Because of its high density

and silica content, marishballi is difficult to work. The use of

hardened cutters is suggested to obtain smooth surfaces.

Durability varies with species, but marishballi is generally

considered to have low to moderately low resistance to attack

by decay fungi. However, it is known for its high resistance

to attack by marine borers. Permeability also varies, but the

heartwood is generally moderately responsive to treatment.

Marishballi is ideal for underwater marine construction,

heavy construction above ground, and railroad crossties

(treated).

Mata–Mata (see Manbarklak)

Mayflower (see Roble)

Melapi (see Meranti Groups)

Meranti Groups

Meranti is a common name applied commercially to four

groups of species of Shorea from southeast Asia, most commonly Malaysia, Indonesia, and the Philippines. There are

thousands of common names for the various species of

Shorea, but the names Philippine mahogany and lauan are

often substituted for meranti. The four groups of meranti are

separated on the basis of heartwood color and weight (Table

1–3). About 70 species of Shorea belong to the light and

dark red meranti groups, 22 species to the white meranti

group, and 33 species to the yellow meranti group.

Meranti species as a whole have a coarser texture than that of

mahogany (Swietenia macrophylla) and do not have darkcolored deposits in pores. The grain is usually interlocked.

All merantis have axial resin ducts aligned in long, continuous, tangential lines as seen on the end surface of the wood.

These ducts sometimes contain white deposits that are visible to the naked eye, but the wood is not resinous like some

keruing (Dipterocarpus) species that resemble meranti. All

the meranti groups are machined easily except white meranti,

which dulls cutters as a result of high silica content in the

wood. The light red and white merantis dry easily without

degrade, but dark red and yellow merantis dry more slowly

with a tendency to warp. The strength and shrinkage properties of the meranti groups compare favorably with that of

northern red oak (Quercus rubra). The light red, white, and

yellow merantis are not durable in exposed conditions or in

ground contact, whereas dark red meranti is moderately

durable. Generally, heartwood is extremely resistant to moderately resistant to preservative treatments.

Species of meranti constitute a large percentage of the total

hardwood plywood imported into the United States. Other

uses include joinery, furniture and cabinetwork, moulding

and millwork, flooring, and general construction. Some dark

red meranti is used for decking.

Merbau

Merbau (Malaysia), ipil (Philippines), and kwila (New

Guinea) are names applied to species of the genus Intsia,

most commonly I. bijuga. Intsia is distributed throughout

the Indo–Malaysian region, Indonesia, Philippines, and

many western Pacific islands, as well as Australia.

Freshly cut yellowish to orange–brown heartwood turns

brown or dark red–brown on exposure to air. The texture is

rather coarse, and the grain is straight to interlocked or wavy.

The strength of air-dried merbau is comparable with that of

hickory (Carya), but density is somewhat lower (800 kg/m3

(50 lb/ft3) at 12% moisture content). The wood dries well

with little degrade but stains black in the presence of iron

and moisture. Merbau is rather difficult to saw because it

sticks to saw teeth and dulls cutting edges. However, the

wood dresses smoothly in most operations and finishes well.

Merbau has good durability and high resistance to termite

attack. The heartwood resists treatment, but the sapwood can

be treated with preservatives.

Table 1–3. Woods belonging to Shorea and Parashorea genera

Name Color Density of air-dried wood

Dark red meranti (also called

tanguile and dark red seraya)

Dark brown; medium to deep red, sometimes with a purplish tinge640+ kg/m3 (40+ lb/ft3)

Light red meranti (also called

red seraya)

Variable—from almost white to pale pink,

dark red, pale brown, or deep brown

400 to 640 kg/m3, averaging 512 kg/m3

(25 to 40 lb/ft3, averaging 32 lb/ft3)

White meranti (also called melapi) Whitish when freshly cut, becoming light

yellow-brown on exposure to air

480 to 870 kg/m3 (30 to 54 lb/ft3)

Yellow meranti (also called yellow

seraya)

Light yellow or yellow-brown, sometimes with

a greenish tinge; darkens on exposure to air

480 to 640 kg/m3

 (30 to 40 lb/ft3)
1–27

Merbau is used in furniture, fine joinery, turnery, cabinets,

flooring, musical instruments, and specialty items.

Mersawa

Mersawa is one of the common names applied to the genus

Anisoptera, which has about 15 species distributed from the

Philippine Islands and Malaysia to east Pakistan. Names

applied to this wood vary with the source, and three names

are generally used in the lumber trade: krabak (Thailand),

mersawa (Malaysia), and palosapis (Philippines).

Mersawa wood is light in color and has a moderately coarse

texture. Freshly sawn heartwood is pale yellow or yellowish

brown and darkens on exposure to air. Some wood may

show a pinkish cast or pink streaks, but these eventually

disappear on exposure to air. The wood weighs between 544

and 752 kg/m3

 (34 and 47 lb/ft3) at 12% moisture content

and about 945 kg/m3 (59 lb/ft3) when green. The sapwood is

susceptible to attack by powderpost beetles, and the heartwood is not resistant to termites. The heartwood is rated as

moderately resistant to fungal decay and should not be used

under conditions that favor decay. The heartwood does not

absorb preservative solutions readily. The wood machines

easily, but because of the presence of silica, the wood severely dulls the cutting edges of ordinary tools and is very

hard on saws.

The major volume of mersawa will probably be used as

plywood because conversion in this form presents considerably less difficulty than does the production of lumber.

Mora

Mora (Mora excelsa and M. gonggrijpii) is widely distributed in the Guianas and also occurs in the Orinoco Delta of

Venezuela.

The yellowish red–brown, reddish brown, or dark red heartwood with pale streaks is distinct from the yellowish to pale

brown sapwood. The texture is moderately fine to rather

coarse, and the grain is straight to interlocked. Mora is a

strong and heavy wood (density of air-dried wood is 945 to

1,040 kg/m3

 (59 to 65 lb/ft3)); this wood is moderately

difficult to work but yields smooth surfaces in sawing, planing, turning, and boring. The wood is generally rated as

moderately difficult to dry. Mora is rated as durable to very

durable in resistance to brown- and white-rot fungi. Mora

gonggrijpii is rated very resistant to dry-wood termites, but

M. excelsa is considerably less resistant. The sapwood responds readily to preservative treatments, but the heartwood

resists treatment.

Mora is used for industrial flooring, railroad crossties, shipbuilding, and heavy construction.

Oak (Tropical)

The oaks (Quercus) are abundantly represented in Mexico

and Central America with about 150 species, which are

nearly equally divided between the red and white oak groups.

More than 100 species occur in Mexico and about 25 in

Guatemala; the number diminishes southward to Colombia,

which has two species. The usual Spanish name applied to

the oaks is encino or roble, and both names are used interchangeably irrespective of species or use of the wood.

In heartwood color, texture, and grain characteristics, tropical

oaks are similar to the oaks in the United States, especially

live oak (Quercus virginiana). In most cases, tropical oaks

are heavier (density of air-dried wood is 704 to 993 kg/m3

(44 to 62 lb/ft3)) than the U.S. species. Strength data are

available for only four species, and the values fall between

those of white oak (Q. alba) and live oak (Q. virginiana) or

are equal to those of live oak. Average specific gravity for the

tropical oaks is 0.72 based on volume when green and

ovendry weight, with an observed maximum average of 0.86

for one species from Guatemala. The heartwood is rated as

very resistant to decay fungi and difficult to treat with

preservatives.

Utilization of the tropical oaks is very limited at present

because of difficulties encountered in the drying of the wood.

The major volume is used in the form of charcoal, but the

wood is used for flooring, railroad crossties, mine timbers,

tight cooperage, boat and ship construction, and decorative

veneers.

Obeche

Obeche (Triplochiton scleroxylon) trees of west–central Africa

reach a height of 50 m (150 ft) or more and a diameter of up

to 2 m (5 ft). The trunk is usually free of branches for a

considerable height so that clear lumber of considerable size

can be obtained.

The wood is creamy white to pale yellow with little or no

difference between sapwood and heartwood. The wood is

fairly soft, of uniform medium to coarse texture, and the grain

is usually interlocked but sometimes straight. Air-dry wood

weighs about 385 kg/m3

 (24 lb/ft3). Obeche dries readily

with little degrade. It is not resistant to decay, and green

sapwood is subject to blue stain. The wood is easy to work

and machine, veneers and glues well, and takes nails and

screws without splitting.

The characteristics of obeche make it especially suitable for

veneer and corestock. Other uses include furniture, components, millwork, blockboard, boxes and crates, particleboard

and fiberboard, patterns, and artificial limbs.

Ofram (see Limba)

Okoume

The natural distribution of okoume (Aucoumea klaineana) is

rather restricted; the species is found only in west–central

Africa and Guinea. However, okoume is extensively planted

throughout its natural range.

The heartwood is salmon-pink in color, and the narrow

sapwood is whitish or pale gray. The wood has a high luster

and uniform texture. The texture is slightly coarser than that

of birch (Betula). The nondurable heartwood dries readily

with little degrade. Sawn lumber is somewhat difficult to
 1–28

machine because of the silica content, but the wood glues,

nails, and peels into veneer easily. Okoume offers unusual

flexibility in finishing because the color, which is of medium

intensity, permits toning to either lighter or darker shades.

In the United States, okoume is generally used for decorative

plywood paneling, general utility plywood, and doors.

Other uses include furniture components, joinery, and light

construction.

Opepe

Opepe (Nauclea diderrichii) is widely distributed in Africa

from Sierra Leone to the Congo region and eastward to

Uganda. It is often found in pure stands.

The orange or golden yellow heartwood darkens on exposure

to air and is clearly defined from the whitish or pale yellow

sapwood. The texture is rather coarse, and the grain is usually interlocked or irregular. The density of air-dried wood

(752 kg/m3

 (47 lb/ft3)) is about the same as that of true hickory (Carya), but strength properties are somewhat lower.

Quartersawn stock dries rapidly with little checking or warp,

but flat-sawn lumber may develop considerable degrade. The

wood works moderately well with hand and machine tools.

It also glues and finishes satisfactorily. The heartwood is

rated as very resistant to decay and moderately resistant to

termite attacks. The sapwood is permeable to preservatives,

but the heartwood is moderately resistant to preservative

treatment.

Opepe is a general construction wood that is used in dock

and marine work, boat building, railroad crossties, flooring,

and furniture.

Ossol (see Manni)

Otie (see Ilomba)

Ovangkol (see Benge)

Palosapis (see Mersawa)

Para–Angelim (see Sucupira)

Pau Marfim

The range of pau marfim (Balfourodendron riedelianum) is

rather limited, extending from the State of Sao Paulo, Brazil,

into Paraguay and the provinces of Corrientes and Missiones

of northern Argentina. In Brazil, it is generally known as pau

marfim and in Argentina and Paraguay, as guatambu.

In color and general appearance, pau marfim wood is very

similar to birch (Betula) or sugar maple (Acer saccharum)

sapwood. Although growth rings are present, they do not

show as distinctly as those in birch and maple. There is no

apparent difference in color between heartwood and sapwood.

The wood is straight grained and easy to work and finish,

but it is not considered resistant to decay. In Brazil, average

specific gravity of pau marfim is about 0.73 based on volume

of green wood and ovendry weight. Average density of airdried wood is about 802 kg/m3

 (50 lb/ft3). On the basis of

specific gravity, strength values are higher than those of sugar

maple, which has an average specific gravity of 0.56.

In its areas of growth, pau marfim is used for much the same

purposes as are sugar maple and birch in the United States.

Introduced to the U.S. market in the late 1960s, pau marfim

has been very well received and is especially esteemed for

turnery.

Peroba, White (see Peroba de Campos)

Peroba de Campos

Peroba de campos (Paratecoma peroba), also referred to as

white peroba, grows in the coastal forests of eastern Brazil,

ranging from Bahia to Rio de Janeiro. It is the only species

in the genus Paratecoma.

The heartwood varies in color but is generally shades of

brown with tendencies toward olive and red. The sapwood is

a yellowish gray and is clearly defined from the heartwood.

The texture is relatively fine and approximates that of birch

(Betula). The grain is commonly interlocked, with a narrow

stripe or wavy figure. The wood machines easily; however,

particular care must be taken in planing to prevent excessive

grain tearing of quartered surfaces. There is some evidence

that the fine dust from machining operations may produce

allergic responses in certain individuals. Density of air-dried

wood averages about 738 kg/m3

 (46 lb/ft3). Peroba de campos is heavier than teak (Tectona grandis) or white oak

(Quercus alba), and it is proportionately stronger than either

of these species. The heartwood of peroba de campos is rated

as very durable with respect to decay and difficult to treat

with preservatives.

In Brazil, peroba de campos is used in the manufacture of fine

furniture, flooring, and decorative paneling. The principal use

in the United States is shipbuilding, where peroba de campos serves as substitute for white oak (Quercus alba) for all

purposes except bent members.

Peroba Rosa

Peroba rosa is the common name applied to a number of

similar species in the genus Aspidosperma. These species

occur in southeastern Brazil and parts of Argentina.

The heartwood is a distinctive rose-red to yellowish, often

variegated or streaked with purple or brown, and becomes

brownish yellow to dark brown upon exposure to air; the

heartwood is often not demarcated from the yellowish sapwood. The texture is fine and uniform, and the grain is

straight to irregular. The wood is moderately heavy; weight

of air-dried wood is 752 kg/m3

 (47 lb/ft3). Strength properties

are comparable with those of U.S. oak (Quercus). The wood

dries with little checking or splitting. It works with moderate ease, and it glues and finishes satisfactorily. The heartwood is resistant to decay fungi but susceptible to dry-wood

termite attack. Although the sapwood takes preservative

treatment moderately well, the heartwood resists treatment.
1–29

Peroba is suited for general construction work and is favored

for fine furniture and cabinetwork and decorative veneers.

Other uses include flooring, interior woodwork, sashes and

doors, and turnery.

Pilon

The two main species of pilon are Hyeronima alchorneoides

and H. laxiflora, also referred to as suradan. These species

range from southern Mexico to southern Brazil including the

Guianas, Peru, and Colombia. Pilon species are also found

throughout the West Indies.

The heartwood is a light reddish brown to chocolate brown

or sometimes dark red; the sapwood is pinkish white. The

texture is moderately coarse and the grain interlocked. The

wood air-dries rapidly with only a moderate amount of warp

and checking. It has good working properties in all operations except planing, which is rated poor as a result of the

characteristic interlocked grain. The strength of pilon is

comparable with that of true hickory (Carya), and the density

of air-dried wood ranges from 736 to 849 kg/m3

 (46 to

53 lb/ft3). Pilon is rated moderately to very durable in

ground contact and resistant to moderately resistant to subterranean and dry-wood termites. Both heartwood and sapwood are reported to be treatable with preservatives by both

open tank and pressure vacuum processes.

Pilon is especially suited for heavy construction, railway

crossties, marinework, and flooring. It is also used for furniture, cabinetwork, decorative veneers, turnery, and joinery.

Piquia

Piquia is the common name generally applied to species in

the genus Caryocar. This genus is distributed from Costa

Rica southward into northern Colombia and from the upland

forest of the Amazon valley to eastern Brazil and the

Guianas.

The yellowish to light grayish brown heartwood is hardly

distinguishable from the sapwood. The texture is medium to

rather coarse, and the grain is generally interlocked. The

wood dries at a slow rate; warping and checking may develop, but only to a minor extent. Piquia is reported to be

easy to moderately difficult to saw; cutting edges dull rapidly. The heartwood is very durable and resistant to decay

fungi and dry-wood termites but only moderately resistant to

marine borers.

Piquia is recommended for general and marine construction,

heavy flooring, railway crossties, boat parts, and furniture

components. It is especially suitable where hardness and

high wear resistance are needed.

Primavera

The natural distribution of primavera (Tabebuia donnell–

smithii [=Cybistax donnell-smithii]) is restricted to southwestern Mexico, the Pacific coast of Guatemala and El Salvador, and north-central Honduras. Primavera is regarded as

one of the primary light-colored woods, but its use has been

limited because of its rather restricted range and relative

scarcity of naturally grown trees. Recent plantations have

increased the availability of this species and have provided a

more constant source of supply. The quality of the plantation-grown wood is equal in all respects to the wood obtained from naturally grown trees.

The heartwood is whitish to straw-yellow, and in some logs,

it may be tinted with pale brown or pinkish streaks. The

texture is medium to rather coarse, and the grain is straight

to wavy, which produces a wide variety of figure patterns.

The wood also has a very high luster. Shrinkage is rather

low, and the wood shows a high degree of dimensional

stability. Despite considerable grain variation, primavera

machines remarkably well. The density of air-dried wood is

465 kg/m3 (29 lb/ft3), and the wood is comparable in strength

with water tupelo (Nyssa aquatica). Resistance to both

brown- and white-rot fungi varies. Weathering characteristics

are good.

The dimensional stability, ease of working, and pleasing

appearance make primavera a suitable choice for solid furniture, paneling, interior woodwork, and special exterior uses.

Purpleheart

Purpleheart, also referred to as amaranth, is the name applied

to species in the genus Peltogyne. The center of distribution

is in the north-central part of the Brazilian Amazon region,

but the combined range of all species is from Mexico through

Central America and southward to southern Brazil.

Freshly cut heartwood is brown. It turns a deep purple upon

exposure to air and eventually dark brown upon exposure to

light. The texture is medium to fine, and the grain is usually

straight. This strong and heavy wood (density of air-dried

wood is 800 to 1,057 kg/m3

 (50 to 66 lb/ft3)) is rated as easy

to moderately difficult to air dry. It is moderately difficult to

work with using either hand or machine tools, and it dulls

cutters rather quickly. Gummy resin exudes when the wood

is heated by dull tools. A slow feed rate and specially hardened cutters are suggested for optimal cutting. The wood

turns easily, is easy to glue, and takes finishes well. The

heartwood is rated as highly resistant to attack by decay

fungi and very resistant to dry-wood termites. It is extremely

resistant to treatment with preservatives.

The unusual and unique color of purpleheart makes this

wood desirable for turnery, marquetry, cabinets, fine furniture, parquet flooring, and many specialty items, such as

billiard cue butts and carvings. Other uses include heavy

construction, shipbuilding, and chemical vats.

Pycnanthus (see Ilomba)

Ramin

Ramin (Gonystylus bancanus) is native to southeast Asia

from the Malaysian Peninsula to Sumatra and Borneo.

Both the heartwood and sapwood are the color of pale straw,

yellow, or whitish. The grain is straight or shallowly
 1–30

interlocked. The texture is even, moderately fine, and similar

to that of American mahogany (Swietenia macrophylla). The

wood is without figure or luster. Ramin is moderately hard

and heavy, weighing about 672 kg/m3

 (42 lb/ft3) in the airdried condition. The wood is easy to work, finishes well,

and glues satisfactorily. Ramin is rated as not resistant to

decay but permeable with respect to preservative treatment.

Ramin is used for plywood, interior woodwork, furniture,

turnery, joinery, moulding, flooring, dowels, and handles of

nonstriking tools (brooms), and as a general utility wood.

Roble

Roble, a species in the roble group of Tabebuia (generally

T. rosea), ranges from southern Mexico through Central

America to Venezuela and Ecuador. The name roble comes

from the Spanish word for oak (Quercus). In addition, T.

rosea is called roble because the wood superficially resembles U.S. oak. Other names for T. rosea are mayflower and

apamate.

The sapwood becomes a pale brown upon exposure to air.

The heartwood varies from golden brown to dark brown, and

it has no distinctive odor or taste. The texture is medium

and the grain narrowly interlocked. The wood weighs about

642 kg/m3

 (40 lb/ft3) at 12% moisture content. Roble has

excellent working properties in all machine operations. It

finishes attractively in natural color and takes finishes with

good results. It weighs less than the average of U.S. white

oaks (Quercus) but is comparable with respect to bending

and compression parallel to grain. The heartwood of roble is

generally rated as moderately to very durable with respect to

decay; the darker and heavier wood is regarded as more

resistant than the lighter-colored woods.

Roble is used extensively for furniture, interior woodwork,

doors, flooring, boat building, ax handles, and general construction. The wood veneers well and produces attractive

paneling. For some applications, roble is suggested as a

substitute for American white ash (Fraxinus americana) and

oak (Quercus).

Rosewood, Brazilian

Brazilian rosewood (Dalbergia nigra), also referred to as

jacaranda, occurs in eastern Brazilian forests from the State of

Bahia to Rio de Janeiro. Since it was exploited for a long

time, Brazilian rosewood is no longer abundant.

The heartwood varies with respect to color, through shades

of brown, red, and violet, and it is irregularly and conspicuously streaked with black. It is sharply demarcated from the

white sapwood. Many kinds of rosewood are distinguished

locally on the basis of prevailing color. The texture is coarse,

and the grain is generally straight. The heartwood has an

oily or waxy appearance and feel, and its odor is fragrant

and distinctive. The wood is hard and heavy (weight of airdried wood is 752 to 897 kg/m3

 (47 to 56 lb/ft3)); thoroughly air-dried wood will barely float in water. Strength

properties of Brazilian rosewood are high and are more than

adequate for the purposes for which this wood is used.

For example, Brazilian rosewood is harder than any U.S.

native hardwood species used for furniture and veneer. The

wood machines and veneers well. It can be glued satisfactorily, provided the necessary precautions are taken to ensure

good glue bonds, with respect to oily wood. Brazilian rosewood has an excellent reputation for durability with respect

to fungal and insect attack, including termites, although the

wood is not used for purposes where durability is necessary.

Brazilian rosewood is used primarily in the form of veneer for

decorative plywood. Limited quantities are used in the solid

form for specialty items such as cutlery handles, brush backs,

billiard cue butts, and fancy turnery.

Rosewood, Indian

Indian rosewood (Dalbergia latifolia) is native to most

provinces of India except in the northwest.

The heartwood varies in color from golden brown to dark

purplish brown with denser blackish streaks at the end of

growth zones, giving rise to an attractive figure on flat-sawn

surfaces. The narrow sapwood is yellowish. The average

weight is about 849 kg/m3

 (53 lb/ft3) at 12% moisture content. The texture is uniform and moderately coarse. Indian

rosewood is quite similar in appearance to Brazilian

(Dalbergia nigra) and Honduran (Dalbergia stevensonii)

rosewood. The wood is reported to kiln-dry well though

slowly, and the color improves during drying. Indian rosewood is a heavy wood with high strength properties; after

drying, it is particularly hard for its weight. The wood is

moderately hard to work with hand tools and offers a fair

resistance in machine operations. Lumber with calcareous

deposits tends to dull tools rapidly. The wood turns well

and has high screw-holding properties. If a very smooth

surface is required for certain purposes, pores (vessels) may

need to be filled.

Indian rosewood is essentially a decorative wood for highquality furniture and cabinetwork. In the United States, it is

used primarily in the form of veneer.

Sande

Practically all commercially available sande (mostly

Brosimum utile) comes from Pacific Ecuador and Colombia.

However, the group of species ranges from the Atlantic Coast

in Costa Rica southward to Colombia and Ecuador.

The sapwood and heartwood show no distinction; the wood

is uniformly yellowish white to yellowish or light brown.

The texture is medium to moderately coarse and even, and

the grain can be widely and narrowly interlocked. The density of air-dried wood ranges from 384 to 608 kg/m3

 (24 to

38 lb/ft3), and the strength is comparable with that of U.S.

oak (Quercus). The lumber air dries rapidly with little or no

degrade. However, material containing tension wood is

subject to warp, and the tension wood may cause fuzzy grain

as well as overheating of saws as a result of pinching. The

wood is not durable with respect to stain, decay, and insect

attack, and care must be exercised to prevent degrade from

these agents. The wood stains and finishes easily and

presents no gluing problems.
1–31

Sande is used for plywood, particleboard, fiberboard, carpentry, light construction, furniture components, and moulding.

Santa Maria

Santa Maria (Calophyllum brasiliense) ranges from the West

Indies to southern Mexico and southward through Central

America into northern South America.

The heartwood is pinkish to brick red or rich reddish brown

and marked by fine and slightly darker striping on flat-sawn

surfaces. The sapwood is lighter in color and generally distinct from the heartwood. The texture is medium and fairly

uniform, and the grain is generally interlocked. The heartwood is rather similar in appearance to dark red meranti

(Shorea). The wood is moderately easy to work and good

surfaces can be obtained when attention is paid to machining

operations. The wood averages about 608 kg/m3

 (38 lb/ft3) at

12% moisture content. Santa Maria is in the density class of

sugar maple (Acer saccharum), and its strength properties are

generally similar; the hardness of sugar maple is superior to

that of Santa Maria. The heartwood is generally rated as

moderately durable to durable in contact with the ground,

but it apparently has no resistance against termites and

marine borers.

The inherent natural durability, color, and figure on the

quarter-sawn face suggest that Santa Maria could be used as

veneer for plywood in boat construction. Other uses are

flooring, furniture, cabinetwork, millwork, and decorative

plywood.

Sapele

Sapele (Entandrophragma cylindricum) is a large African tree

that occurs from Sierra Leone to Angola and eastward

through the Congo to Uganda.

The heartwood ranges in color from that of American mahogany (Swietenia macrophylla) to a dark reddish or purplish

brown. The lighter-colored and distinct sapwood may be up

to 10 cm (4 in.) wide. The texture is rather fine. The grain is

interlocked and produces narrow and uniform striping on

quarter-sawn surfaces. The wood averages about 674 kg/m3

(42 lb/ft3) at 12% moisture content, and its mechanical properties are in general higher than those of white oak (Quercus

alba). The wood works fairly easily with machine tools,

although the interlocked grain makes it difficult to plane.

Sapele finishes and glues well. The heartwood is rated as

moderately durable and is resistant to preservative treatment.

As lumber, sapele is used for furniture and cabinetwork,

joinery, and flooring. As veneer, it is used for decorative

plywood.

Selangan Batu (see Balau)

Sepetir

The name sepetir applies to species in the genus Sindora and

to Pseudosindora palustris. These species are distributed

throughout Malaysia, Indochina, and the Philippines.

The heartwood is brown with a pink or golden tinge that

darkens on exposure to air. Dark brown or black streaks

are sometimes present. The sapwood is light gray, brown,

or straw-colored. The texture is moderately fine and even,

and the grain is narrowly interlocked. The strength of sepetir

is similar to that of shellbark hickory (Carya laciniosa),

and the density of the air-dried wood is also similar (640 to

720 kg/m3

 (40 to 45 lb/ft3)). The wood dries well but rather

slowly, with a tendency to end-split. The wood is difficult to

work with hand tools and has a rather rapid dulling effect on

cutters. Gums from the wood tend to accumulate on saw

teeth, which causes additional problems. Sepetir is rated as

nondurable in ground contact under Malaysian exposure. The

heartwood is extremely resistant to preservative treatment;

however, the sapwood is only moderately resistant.

Sepetir is a general carpentry wood that is also used for

furniture and cabinetwork, joinery, flooring (especially truck

flooring), plywood, and decorative veneers.

Seraya, Red and Dark Red (see Meranti Groups)

Seraya, White

White seraya or bagtikan, as it is called in the Philippines,

is a name applied to the 14 species of Parashorea, which

grow in Sabah and the Philippines.

The heartwood is light brown or straw-colored, sometimes

with a pinkish tint. The texture is moderately coarse and the

grain interlocked. White seraya is very similar in appearance

and strength properties to light red meranti, and sometimes

the two are mixed in the market. White seraya dries easily

with little degrade, and works fairly well with hand and

machine tools. The heartwood is not durable to moderately

durable in ground contact, and it is extremely resistant to

preservative treatments.

White seraya is used for joinery, light construction,

moulding and millwork, flooring, plywood, furniture, and

cabinet work.

Seraya, Yellow (see Meranti Groups)

Silverballi, Brown (see Kaneelhart)

Spanish-Cedar

Spanish-cedar or cedro consists of a group of about seven

species in the genus Cedrela that are widely distributed

in tropical America from southern Mexico to northern

Argentina.

Spanish-cedar is one of only a few tropical species that are

ring-porous. The heartwood varies from light to dark reddish

brown, and the sapwood is pinkish to white. The texture is

rather fine and uniform to coarse and uneven. The grain is

not interlocked. The heartwood is characterized by a distinctive odor. The wood dries easily. Although Spanish-cedar is

not high in strength, most other properties are similar to

those of American mahogany (Swietenia macrophylla),

except for hardness and compression perpendicular to the
 1–32

grain, where mahogany is definitely superior. Spanish-cedar

is considered decay resistant; it works and glues well.

Spanish-cedar is used locally for all purposes that require an

easily worked, light but straight grained, and durable wood.

In the United States, the wood is favored for millwork,

cabinets, fine furniture, boat building, cigar wrappers and

boxes, humidores, and decorative and utility plywood.

Sucupira (Angelin, Para-Angelim)

Sucupira, angelin, and para-angelim apply to species in four

genera of legumes from South America. Sucupira applies to

Bowdichia nitida from northern Brazil, B. virgilioides from

Venezuela, the Guianas, and Brazil, and Diplotropis purpurea from the Guianas and southern Brazil. Angelin

(Andira inermis) is a widespread species that occurs

throughout the West Indies and from southern Mexico

through Central America to northern South America and

Brazil. Para-angelim (Hymenolobium excelsum) is generally

restricted to Brazil.

The heartwood of sucupira is chocolate-brown, red–brown, or

light brown (especially in Diplotropis purpurea). Angelin

heartwood is yellowish brown to dark reddish brown; paraangelim heartwood turns pale brown upon exposure to air.

The sapwood is generally yellowish to whitish and is

sharply demarcated from the heartwood. The texture of all

three woods is coarse and uneven, and the grain can be interlocked. The density of air-dried wood of these species ranges

from 720 to 960 kg/m3

 (45 to 60 lb/ft3), which makes them

generally heavier than true hickory (Carya). Their strength

properties are also higher than those of true hickory. The

heartwood is rated very durable to durable in resistance to

decay fungi but only moderately resistant to attack by drywood termites. Angelin is reported to be difficult to treat

with preservatives, but para-angelim and sucupira treat adequately. Angelin can be sawn and worked fairly well, except

that it is difficult to plane to a smooth surface because of

alternating hard (fibers) and soft (parenchyma) tissue. Paraangelim works well in all operations. Sucupira is difficult to

moderately difficult to work because of its high density,

irregular grain, and coarse texture.

Sucupira, angelin, and para-angelim are ideal for heavy

construction, railroad crossties, and other uses that do not

require much fabrication. Other suggested uses include

flooring, boat building, furniture, turnery, tool handles,

and decorative veneer.

Suradan (see Pilon)

Tangare (see Andiroba)

Tanguile (see Lauan–Meranti Groups)

Teak

Teak (Tectona grandis) occurs in commercial quantities in

India, Burma, Thailand, Laos, Cambodia, North and South

Vietnam, and the East Indies. Numerous plantations have

been developed within its natural range and in tropical areas

of Latin America and Africa, and many of these are now

producing teakwood.

The heartwood varies from yellow–brown to dark golden–

brown and eventually turns a rich brown upon exposure to

air. Teakwood has a coarse uneven texture (ring porous), is

usually straight grained, and has a distinctly oily feel. The

heartwood has excellent dimensional stability and a very

high degree of natural durability. Although teak is not generally used in the United States where strength is of prime

importance, its properties are generally on par with those of

U.S. oaks (Quercus). Teak is generally worked with moderate ease with hand and machine tools. However, the presence

of silica often dulls tools. Finishing and gluing are satisfactory, although pretreatment may be necessary to ensure good

bonding of finishes and glues.

Teak is one of the most valuable woods, but its use is limited by scarcity and high cost. Because teak does not cause

rust or corrosion when in contact with metal, it is extremely

useful in the shipbuilding industry, for tanks and vats, and

for fixtures that require high acid resistance. Teak is currently

used in the construction of boats, furniture, flooring, decorative objects, and decorative veneer.

Tornillo

Tornillo (Cedrelinga cateniformis), also referred to as cedrorana, grows in the Loreton Huanuco provinces of Peru and in

the humid terra firma of the Brazilian Amazon region.

Tornillo can grow up to 52.5 m (160 ft) tall, with trunk

diameters of 1.5 to 3 m (5 to 9 ft). Trees in Peru are often

smaller in diameter, with merchantable heights of 15 m

(45 ft) or more.

The heartwood is pale brown with a golden luster and

prominently marked with red vessel lines; the heartwood

gradually merges into the lighter-colored sapwood.

The texture is coarse. The density of air-dried material

collected in Brazil averages 640 kg/m3

 (40 lb/ft3); for

Peruvian stock, average density is about 480 kg/m3

(30 lb/ft3). The wood is comparable in strength with American elm (Ulmus americana). Tornillo cuts easily and can be

finished smoothly, but areas of tension wood may result in

woolly surfaces. The heartwood is fairly durable and reported

to have good resistance to weathering.

Tornillo is a general construction wood that can be used for

furniture components in lower-grade furniture.

Trebol (see Macawood)

Virola (see Banak)

Waika (see Manni)

Walele (see Ilomba)

Wallaba

Wallaba is a common name applied to the species in the

genus Eperua. Other names include wapa and apa. The

center of distribution is in the Guianas, but the species
1–33

extends into Venezuela and the Amazon region of northern

Brazil. Wallaba generally occurs in pure stands or as the

dominant tree in the forest.

The heartwood ranges from light to dark red to reddish or

purplish brown with characteristically dark, gummy streaks.

The texture is rather coarse and the grain typically straight.

Wallaba is a hard, heavy wood; density of air-dried wood is

928 kg/m3

 (58 lb/ft3). Its strength is higher than that of

shagbark hickory (Carya ovata). The wood dries very slowly

with a marked tendency to check, split, and warp. Although

the wood has high density, it is easy to work with hand and

machine tools. However, the high gum content clogs sawteeth and cutters. Once the wood has been kiln dried, gum

exudates are not a serious problem in machining. The heartwood is reported to be very durable and resistant to subterranean termites and fairly resistant to dry-wood termites.

Wallaba is well suited for heavy construction, railroad

crossties, poles, industrial flooring, and tank staves. It is

also highly favored for charcoal.

Wapa (see Wallaba)

Yang (see Keruing)

Softwoods

Cypress, Mexican

Native to Mexico and Guatemala, Mexican cypress

(Cupressus lusitanica) is now widely planted at high elevations throughout the tropical world.

The heartwood is yellowish, pale brown, or pinkish, with

occasional streaking or variegation. The texture is fine and

uniform, and the grain is usually straight. The wood is

fragrantly scented. The density of air-dried wood is

512 kg/m3 (32 lb/ft3), and the strength is comparable with

that of yellow-cedar (Chamaecyparis nootkatensis) or western

hemlock (Tsuga heterophylla). The wood is easy to work

with hand and machine tools, and it nails, stains, and polishes well. Mexican cypress air dries very rapidly with little

or no end- or surface-checking. Reports on durability are

conflicting. The heartwood is not treatable by the open tank

process and seems to have an irregular response to pressure–

vacuum systems.

Mexican cypress is used mainly for posts and poles, furniture

components, and general construction.

Parana Pine

The wood commonly called parana pine (Araucaria angustifolia) is a softwood but not a true pine. It grows in southeastern Brazil and adjacent areas of Paraguay and Argentina.

Parana pine has many desirable characteristics. It is available

in large-size clear boards with uniform texture. The small

pinhead knots (leaf traces) that appear on flat-sawn surfaces

and the light or reddish-brown heartwood provide a desirable

figure for matching in paneling and interior woodwork.

Growth rings are fairly distinct and similar to those of eastern

white pine (Pinus strobus). The grain is not interlocked, and

the wood takes paint well, glues easily, and is free from resin

ducts, pitch pockets, and pitch streaks. Density of air-dried

wood averages 545 kg/m3 (34 lb/ft3). The strength of parana

pine compares favorably with that of U.S. softwood species

of similar density and, in some cases, approaches that of

species with higher density. Parana pine is especially strong

in shear strength, hardness, and nail-holding ability, but it is

notably deficient in strength in compression across the grain.

The tendency of the kiln-dried wood to split and warp is

caused by the presence of compression wood, an abnormal

type of wood with intrinsically large shrinkage along the

grain. Boards containing compression wood should be

excluded from exacting uses.

The principal uses of parana pine include framing lumber,

interior woodwork, sashes and door stock, furniture case

goods, and veneer.

Pine, Caribbean

Caribbean pine (Pinus caribaea) occurs along the Caribbean

side of Central America from Belize to northeastern

Nicaragua. It is also native to the Bahamas and Cuba. This

low-elevation tree is widely introduced as a plantation

species throughout the world tropics.

The heartwood is golden- to red-brown and distinct from the

sapwood, which is light yellow and roughly 2 to 5 cm (1 to

2 in.) wide. This softwood species has a strong resinous

odor and a greasy feel. The weight varies considerably and

may range from 416 to 817 kg/m3

 (26 to 51 lb/ft3) at 12%

moisture content. Caribbean pine may be appreciably heavier

than slash pine (P. elliottii), but the mechanical properties of

these two species are rather similar. The lumber can be kiln

dried satisfactorily. Caribbean pine is easy to work in all

machining operations, but its high resin content may cause

resin to accumulate on the equipment. Durability and resistance to insect attack vary with resin content; in general, the

heartwood is rated as moderately durable. The sapwood is

highly permeable and is easily treated by open tank or pressure–vacuum systems. The heartwood is rated as moderately

resistant to preservative treatment, depending on resin

content.

Caribbean pine is used for the same purposes as are the

southern pines (Pinus spp.).

Pine, Ocote

Ocote pine (Pinus oocarpa) is a high-elevation species that

occurs from northwestern Mexico southward through

Guatemala into Nicaragua. The largest and most extensive

stands occur in Guatemala, Nicaragua, and Honduras.

The sapwood is a pale yellowish brown and generally up to

7 cm (3 in.) wide. The heartwood is a light reddish brown.

The grain is not interlocked. The wood has a resinous odor,

and it weighs about 656 kg/m3

 (41 lb/ft3) at 12% moisture

content. The strength properties of ocote pine are comparable

in most respects with those of longleaf pine (P. palustris).
 1–34

Decay resistance studies have shown ocote pine heartwood to

be very durable with respect to white-rot fungal attack and

moderately durable with respect to brown rot.

Ocote pine is comparable with the southern pines (Pinus) in

workability and machining characteristics. It is a general

construction wood suited for the same uses as are the

southern pines.

Pine, Radiata

Radiata pine (Pinus radiata), also known as Monterey pine,

is planted extensively in the southern hemisphere, mainly in

Chile, New Zealand, Australia, and South Africa. Plantationgrown trees may reach a height of 26 to 30 m (80 to 90 ft) in

20 years.

The heartwood from plantation-grown trees is light brown to

pinkish brown and is distinct from the paler cream-colored

sapwood. Growth rings are primarily wide and distinct.

False rings may be common. The texture is moderately even

and fine, and the grain is not interlocked. Plantation-grown

radiata pine averages about 480 kg/m3

 (30 lb/ft3) at 12%

moisture content. Its strength is comparable with that of red

pine (P. resinosa), although location and growth rate may

cause considerable variation in strength properties. The wood

air or kiln dries rapidly with little degrade. The wood machines easily although the grain tends to tear around large

knots. Radiata pine nails and glues easily, and it takes paint

and finishes well. The sapwood is prone to attack by stain

fungi and vulnerable to boring insects. However, plantationgrown stock is mostly sapwood, which treats readily with

preservatives. The heartwood is rated as durable above

ground and is moderately resistant to preservative treatment.

Radiata pine can be used for the same purposes as are the

other pines grown in the United States. These uses include

veneer, plywood, pulp, fiberboard, construction, boxes, and

millwork.

References

Alden, H.A. 1995. Hardwoods of North America. Gen.

Tech. Rep. FPL–GTR–83. Madison, WI: U.S. Department

of Agriculture, Forest Service, Forest Products Laboratory.

Alden, H.A. 1997. Softwoods of North America. Gen.

Tech. Rep. FPL–GTR–102. Madison, WI: U.S. Department

of Agriculture, Forest Service, Forest Products Laboratory.

Berni, C.A.; Bolza, E.; Christensen, F.J. 1979. South

American timbers—characteristics, properties, and uses of

190 species. Melbourne, Australia: Commonwealth

Scientific and Industrial Research Organization, Division

of Building Research.

Bolza, E.; Keating, W.G. 1972. African timbers—the

properties, uses, and characteristics of 700 species. Melbourne, Australia: Commonwealth Scientific and Industrial

Research Organization, Division of Building Research.

Building Research Establishment, Department of

Environment. 1977. A handbook of softwoods. London:

H. M. Stationery Office.

Building Research Establishment, Princes Risborough

Laboratory; Farmer, R.H. 1972. Handbook of hardwoods.

Rev., 2d ed. London: H. M. Stationery Office.

Chudnoff, Martin. 1984. Tropical timbers of the world.

Agric. Handb. 607. Washington DC: U.S. Department of

Agriculture.

Hardwood Market Report: Lumber News Letter. [Current

edition]. Memphis, TN.

Haynes, Richard W.; Adams, Darius M.; Mills, John R.

1993. The 1993 RPA timber assessment update. Gen. Tech.

Rep. RM–GTR–259. Fort Collins, Colorado: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest

and Range Experiment Station.

Howard, James L. 1997. U.S. timber production, trade,

consumption, and price statistics, 1965–1994. Gen. Tech.

Rep. FPL–GTR–98. Madison, Wisconsin: U.S. Department

of Agriculture, Forest Service, Forest Products Laboratory.

Keating, W.G.; Bolza, E. 1982. Characteristics, properties,

and uses of timbers: Vol. 1. Southeast Asia, Northern Australia, and the Pacific. Melbourne, Australia: Inkata Press.

Kukachka, B.F. 1970. Properties of imported tropical

woods. Res. Pap. FPL 125. Madison, WI: U.S. Department

of Agriculture, Forest Service, Forest Products Laboratory.

Little E.L. 1979. Checklist of United States trees (native

and naturalized). Agric. Handb. 541. Washington, DC:

U.S. Department of Agriculture.

Markwardt, L.J. 1930. Comparative strength properties of

woods grown in the United States. Tech. Bull. 158. Washington, DC: U.S. Department of Agriculture.

Panshin, A.J.; deZeeuw, C. 1980. Textbook of wood

technology. 4th ed. New York: McGraw–Hill.

Record, S.J.; Hess, R.W. 1949. Timbers of the new world.

New Haven, CT: Yale University Press.

Ulrich, Alice H. 1981. U.S. timber production, trade, consumption, and price statistics, 1950–1980. Misc. Pub. 1408.

Washington, DC: U.S. Department of Agriculture.

USDA. 1990. An analysis of the timber situation in the

United States: 1989–2040. Gen. Tech. Rep. RM–199. Fort

Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
2–1

Chapter 2

Structure of Wood

Regis B. Miller

Contents

Bark, Wood, Branches, and Cambium 2–1

Sapwood and Heartwood 2–2

Growth Rings 2–2

Wood Cells 2–3

Chemical Composition 2–3

Species Identification 2–4

References 2–4

he fibrous nature of wood strongly influences how it

is used. Wood is primarily composed of hollow,

elongate, spindle-shaped cells that are arranged

parallel to each other along the trunk of a tree. When lumber

and other products are cut from the tree, the characteristics of

these fibrous cells and their arrangement affect such properties

as strength and shrinkage as well as the grain pattern of the

wood. This chapter briefly describes some elements of wood

structure.

Bark, Wood, Branches,

and Cambium

A cross section of a tree (Fig. 2–1) shows the following welldefined features (from outside to center): bark, which may be

divided into an outer corky dead part (A), whose thickness

varies greatly with species and age of trees, and an inner thin

living part (B), which carries food from the leaves to growing

parts of the tree; wood, which in merchantable trees of most

species is clearly differentiated into sapwood (D) and heartwood (E); and pith (F), a small core of tissue located at the

center of tree stems, branches, and twigs about which initial

wood growth takes place. Sapwood contains both living and

dead tissue and carries sap from the roots to the leaves.

Heartwood is formed by a gradual change in the sapwood and

is inactive. The wood rays (G), horizontally oriented tissue

through the radial plane of the tree, vary in size from one cell

wide and a few cells high to more than 15 cells wide and

several centimeters high. The rays connect various layers

from pith to bark for storage and transfer of food. The cambium layer (C), which is inside the inner bark and forms

wood and bark cells, can be seen only with a microscope.

As the tree grows in height, branching is initiated by lateral

bud development. The lateral branches are intergrown with

the wood of the trunk as long as they are alive. After a branch

dies, the trunk continues to increase in diameter and surrounds that portion of the branch projecting from the trunk

when the branch died. If the dead branches drop from the tree,

the dead stubs become overgrown and clear wood is formed.

T
 2–2

Most growth in thickness of bark and wood is caused by cell

division in the cambium (Fig. 2–1C). No growth in diameter takes place in wood outside the cambial zone; new

growth is purely the addition and growth of new cells, not

the further development of old ones. New wood cells are

formed on the inside of the cambium and new bark cells on

the outside. Thus, new wood is laid down to the outside of

old wood and the diameter of the woody trunk increases.

In most species, the existing bark is pushed outward by the

formation of new bark, and the outer bark layers become

stretched, cracked, and ridged and are finally sloughed off.

Sapwood and Heartwood

Sapwood is located between the cambium and heartwood

(Fig. 2–1D). Sapwood contains both living and dead cells

and functions primarily in the storage of food; in the outer

layers near the cambium, sapwood handles the transport of

water or sap. The sapwood may vary in thickness and number of growth rings. Sapwood commonly ranges from 4 to

6 cm (1-1/2 to 2 in.) in radial thickness. In certain species,

such as catalpa and black locust, the sapwood contains few

growth rings and usually does not exceed 1 cm (1/2 in.) in

thickness. The maples, hickories, ashes, some southern

pines, and ponderosa pine of North America and cativo

(Prioria copaifera), ehie (Guibourtia ehie), and courbaril

(Hymenaea courbaril) of tropical origin may have sapwood

8 to 15 cm (3 to 6 in.) or more in thickness, especially in

second-growth trees. As a rule, the more vigorously growing

trees have wider sapwood. Many second-growth trees of

merchantable size consist mostly of sapwood.

In general, heartwood consists of inactive cells that do not

function in either water conduction or food storage. The

transition from sapwood to heartwood is accompanied by an

increase in extractive content. Frequently, these extractives

darken the heartwood and give species such as black walnut

and cherry their characteristic color. Lighter colored heartwood occurs in North American species such as the spruces

(except Sitka spruce), hemlocks, true firs, basswood, cottonwood, and buckeye, and in tropical species such as ceiba

(Ceiba pentandra), obeche (Triplochiton scleroxylon), and

ramin (Gonystylus bancanus). In some species, such as black

locust, western redcedar, and redwood, heartwood extractives

make the wood resistant to fungi or insect attack. All darkcolored heartwood is not resistant to decay, and some nearly

colorless heartwood is decay resistant, as in northern whitecedar. However, none of the sapwood of any species is resistant to decay. Heartwood extractives may also affect wood by

(a) reducing permeability, making the heartwood slower to

dry and more difficult to impregnate with chemical preservatives, (b) increasing stability in changing moisture conditions, and (c) increasing weight (slightly). However, as

sapwood changes to heartwood, no cells are added or taken

away, nor do any cells change shape. The basic strength of

the wood is essentially not affected by the transition from

sapwood cells to heartwood cells.

In some species, such as the ashes, hickories, and certain

oaks, the pores (vessels) become plugged to a greater or

lesser extent with ingrowths known as tyloses. Heartwood in

which the pores are tightly plugged by tyloses, as in white

oak, is suitable for tight cooperage, because the tyloses

prevent the passage of liquid through the pores. Tyloses also

make impregnation of the wood with liquid preservatives

difficult.

Growth Rings

In most species in temperate climates, the difference between

wood that is formed early in a growing season and that

formed later is sufficient to produce well-marked annual

growth rings (Fig. 2–2). The age of a tree at the stump or the

age at any cross section of the trunk may be determined by

counting these rings. However, if the growth in diameter is

interrupted, by drought or defoliation by insects for example,

more than one ring may be formed in the same season. In

such an event, the inner rings usually do not have sharply

defined boundaries and are termed false rings. Trees that have

only very small crowns or that have accidentally lost most of

their foliage may form an incomplete growth layer, sometimes called a discontinuous ring.

The inner part of the growth ring formed first in the growing

season is called earlywood and the outer part formed later in

the growing season, latewood. Actual time of formation of

these two parts of a ring may vary with environmental and

weather conditions. Earlywood is characterized by cells with

relatively large cavities and thin walls. Latewood cells have

smaller cavities and thicker walls. The transition from earlywood to latewood may be gradual or abrupt, depending on

Figure 2–1. Cross section of white oak tree trunk:

(A) outer bark (dry dead tissue), (B) inner bark (living

tissue), (C) cambium, (D) sapwood, (E) heartwood,

(F) pith, and (G) wood rays.
2–3

the kind of wood and the growing conditions at the time it

was formed.

Growth rings are most readily seen in species with sharp

contrast between latewood formed in one year and earlywood

formed in the following year, such as in the native ringporous hardwoods ash and oak, and in softwoods like southern pines. In some other species, such as water tupelo, aspen,

and sweetgum, differentiation of earlywood and latewood is

slight and the annual growth rings are difficult to recognize.

In many tropical regions, growth may be practically continuous throughout the year, and no well-defined growth rings

are formed.

When growth rings are prominent, as in most softwoods and

ring-porous hardwoods, earlywood differs markedly from latewood in physical properties. Earlywood is lighter in weight,

softer, and weaker than latewood. Because of the greater

density of latewood, the proportion of latewood is sometimes

used to judge the strength of the wood. This method is

useful with such species as the southern pines, Douglas-fir,

and the ring-porous hardwoods (ash, hickory, and oak).

Wood Cells

Wood cells—the structural elements of wood tissue—are of

various sizes and shapes and are quite firmly cemented together. Dry wood cells may be empty or partly filled with

deposits, such as gums and resins, or with tyloses. The

majority of wood cells are considerably elongated and

pointed at the ends; these cells are customarily called fibers

or tracheids. The length of wood fibers is highly variable

within a tree and among species. Hardwood fibers average

about 1 mm (1/25 in.) in length; softwood fibers range from

3 to 8 mm (1/8 to 1/3 in.) in length.

In addition to fibers, hardwoods have cells of relatively large

diameter known as vessels or pores. These cells form the

main conduits in the movement of sap. Softwoods do not

contain vessels for conducting sap longitudinally in the tree;

this function is performed by the tracheids.

Both hardwoods and softwoods have cells (usually grouped

into structures or tissues) that are oriented horizontally in the

direction from pith toward bark. These groups of cells conduct sap radially across the grain and are called rays or wood

rays (Fig. 2–1G). The rays are most easily seen on edgegrained or quartersawn surfaces, and they vary greatly in size

in different species. In oaks and sycamores, the rays are

conspicuous and add to the decorative features of the wood.

Rays also represent planes of weakness along which seasoning checks readily develop.

Another type of wood cells, known as longitudinal or axial

parenchyma cells, function mainly in the storage of food.

Chemical Composition

Dry wood is primarily composed of cellulose, lignin, hemicelluloses, and minor amounts (5% to 10%) of extraneous

materials. Cellulose, the major component, constitutes

approximately 50% of wood substance by weight. It is a

high-molecular-weight linear polymer consisting of chains of

1 to more than 4 β-linked glucose monomers. During

growth of the tree, the cellulose molecules are arranged into

ordered strands called fibrils, which in turn are organized into

the larger structural elements that make up the cell wall of

wood fibers. Most of the cell wall cellulose is crystalline.

Delignified wood fibers, which consist mostly of cellulose,

have great commercial value when formed into paper. Delignified fibers may also be chemically altered to form textiles,

films, lacquers, and explosives.

Lignin constitutes 23% to 33% of the wood substance in

softwoods and 16% to 25% in hardwoods. Although lignin

occurs in wood throughout the cell wall, it is concentrated

toward the outside of the cells and between cells. Lignin is

often called the cementing agent that binds individual cells

together. Lignin is a three-dimensional phenylpropanol

polymer, and its structure and distribution in wood are still

not fully understood. On a commercial scale, it is necessary

to remove lignin from wood to make high-grade paper or

other paper products.

Theoretically, lignin might be converted to a variety of

chemical products, but in commercial practice a large percentage of the lignin removed from wood during pulping

operations is a troublesome byproduct, which is often burned

for heat and recovery of pulping chemicals. One sizable

commercial use for lignin is in the formulation of oil-well

drilling muds. Lignin is also used in rubber compounding

and concrete mixes. Lesser amounts are processed to yield

Figure 2–2. Cross section of ponderosa pine log

showing growth rings. Light bands are earlywood,

dark bands latewood. An annual (growth) ring is

composed of an inner earlywood zone and outer

latewood zone.
 2–4

vanillin for flavoring purposes and to produce solvents.

Current research is examining the potential of using lignin in

the manufacture of wood adhesives.

The hemicelluloses are associated with cellulose and are

branched, low-molecular-weight polymers composed of

several different kinds of pentose and hexose sugar monomers. The relative amounts of these sugars vary markedly

with species. Hemicelluloses play an important role in fiberto-fiber bonding in the papermaking process. The component

sugars of hemicellulose are of potential interest for conversion

into chemical products.

Unlike the major constituents of wood, extraneous materials

are not structural components. Both organic and inorganic

extraneous materials are found in wood. The organic component takes the form of extractives, which contribute to such

wood properties as color, odor, taste, decay resistance, density, hygroscopicity, and flammability. Extractives include

tannins and other polyphenolics, coloring matter, essential

oils, fats, resins, waxes, gum starch, and simple metabolic

intermediates. This component is termed extractives because

it can be removed from wood by extraction with solvents,

such as water, alcohol, acetone, benzene, or ether. Extractives

may constitute roughly 5% to 30% of the wood substance,

depending on such factors as species, growth conditions, and

time of year when the tree is cut.

The inorganic component of extraneous material generally

constitutes 0.2% to 1.0% of the wood substance, although

greater values are occasionally reported. Calcium, potassium,

and magnesium are the more abundant elemental constituents. Trace amounts (<100 parts per million) of phosphorus,

sodium, iron, silicon, manganese, copper, zinc, and perhaps

a few other elements are usually present.

Valuable nonfibrous products produced from wood include

naval stores, pulp byproducts, vanillin, ethyl alcohol, charcoal, extractives, and products made from bark.

Species Identification

Many species of wood have unique physical, mechanical, or

chemical properties. Efficient utilization dictates that species

should be matched to end-use requirements through an understanding of their properties. This requires identification of

the species in wood form, independent of bark, foliage, and

other characteristics of the tree.

General wood identification can often be made quickly on the

basis of readily visible characteristics such as color, odor,

density, presence of pitch, or grain pattern. Where more

positive identification is required, a laboratory investigation

must be made of the microscopic anatomy of the wood.

Identifying characteristics are described in publications such

as the Textbook of Wood Technology by Panshin and de

Zeeuw and Identifying Wood: Accurate Results With Simple

Tools by R.B. Hoadley.

References

Bratt, L.C. 1965. Trends in the production of silvichemicals in the United States and abroad. Tappi Journal.

48(7): 46A–49A.

Browning, B.L. 1975. The chemistry of wood. Huntington,

NY: Robert E. Krieger Publishing Company.

Core, H.A.; Côté, W.A.; Day, A.C. 1979. Wood structure

and identification. 7th ed. Syracuse, NY: Syracuse

University Press.

Desch, H.E.; revised by Dinwoodie, J.M. 1996. Timber,

structure, properties, conversion, and use. 7th ed. London:

MacMillan Press, Ltd.

Fengel, D.; Wegener, G. 1984. Wood: Chemistry, ultrastructure, reactions. Berlin and New York: W. deGruyter.

Hamilton, J.K.; Thompson, N.C. 1959. A comparison of

the carbohydrates of hardwoods and softwoods. Tappi

Journal. 42: 752–760.

Hoadley, R.B. 1980. Identifying wood: Accurate results

with simple tools. Newtown, CT: Taunton Press.

Hoadley, R.B. 1990. Understanding wood: A craftsmen’s

guide to wood technology. Newtown, CT: Taunton Press.

Kribs, D.A. 1968. Commercial woods on the American

market. New York: Dover Publications.

Panshin, A.J.; de Zeeuw, C. 1980. Textbook of wood

technology. 4th ed. New York: McGraw–Hill.

Rowell, R.M. 1984. The chemistry of solid wood. Advances

in Chemistry Series No. 207. Washington, DC: American

Chemical Society.

Sarkanen, K.V.; Ludwig, C.H. (eds.). 1971. Lignins:

occurrence, formation, structure and reactions. New York:

Wiley–Interscience.

Sjöström, E. 1981. Wood chemistry: fundamentals and

applications. New York: Academic Press.

Stamm, A.J. 1964. Wood and cellulose science. New York:

Ronald Press Company.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
3–1

Chapter 3

Physical Properties and

Moisture Relations of Wood

William Simpson and Anton TenWolde

Contents

Appearance 3–1

Grain and Texture 3–1

Plainsawn and Quartersawn 3–2

Decorative Features 3–2

Moisture Content 3–5

Green Wood and Fiber Saturation Point 3–5

Equilibrium Moisture Content 3–5

Sorption Hysteresis 3–7

Shrinkage 3–7

Transverse and Volumetric 3–7

Longitudinal 3–8

Moisture–Shrinkage Relationship 3–8

Weight, Density, and Specific Gravity 3–11

Working Qualities 3–15

Decay Resistance 3–15

Thermal Properties 3–15

Conductivity 3–15

Heat Capacity 3–17

Thermal Diffusivity 3–17

Thermal Expansion Coefficient 3–21

Electrical Properties 3–21

Conductivity 3–21

Dielectric Constant 3–22

Dielectric Power Factor 3–22

Coefficient of Friction 3–22

Nuclear Radiation 3–23

References 3–23

he versatility of wood is demonstrated by a wide

variety of products. This variety is a result of a

spectrum of desirable physical characteristics or

properties among the many species of wood. In many cases,

more than one property of wood is important to the end

product. For example, to select a wood species for a product,

the value of appearance-type properties, such as texture, grain

pattern, or color, may be evaluated against the influence of

characteristics such as machinability, dimensional stability,

or decay resistance.

Wood exchanges moisture with air; the amount and direction

of the exchange (gain or loss) depend on the relative humidity and temperature of the air and the current amount of water

in the wood. This moisture relationship has an important

influence on wood properties and performance. This chapter

discusses the physical properties of most interest in the

design of wood products.

Some physical properties discussed and tabulated are influenced by species as well as variables like moisture content;

other properties tend to be independent of species. The thoroughness of sampling and the degree of variability influence

the confidence with which species-dependent properties are

known. In this chapter, an effort is made to indicate either

the general or specific nature of the properties tabulated.

Appearance

Grain and Texture

The terms grain and texture are commonly used rather

loosely in connection with wood. Grain is often used in

reference to annual rings, as in fine grain and coarse grain,

but it is also used to indicate the direction of fibers, as in

straight grain, spiral grain, and curly grain. Grain, as a synonym for fiber direction, is discussed in detail relative to

mechanical properties in Chapter 4. Wood finishers refer to

wood as open grained and close grained, which are terms

reflecting the relative size of the pores, which determines

whether the surface needs a filler. Earlywood and latewood

within a growth increment usually consist of different kinds

and sizes of wood cells. The difference in cells results in

difference in appearance of the growth rings, and the resulting

appearance is the texture of the wood. Coarse texture can

result from wide bands of large vessels, such as in oak.
 3–2

“Even” texture generally means uniformity in cell dimensions. Fine-textured woods have small, even-textured cells.

Woods that have larger even-sized cells are considered medium-textured woods. When the words grain or texture are

used in connection with wood, the meaning intended should

be made clear (see Glossary).

Plainsawn and Quartersawn

Lumber can be cut from a log in two distinct ways: (a) tangential to the annual rings, producing flatsawn or plainsawn

lumber in hardwoods and flatsawn or slash-grained lumber in

softwoods, and (b) radially from the pith or parallel to the

rays, producing quartersawn lumber in hardwoods and edgegrained or vertical-grained lumber in softwoods (Fig. 3–1).

Quartersawn lumber is not usually cut strictly parallel with

the rays. In plainsawn boards, the surfaces next to the edges

are often far from tangential to the rings. In commercial

practice, lumber with rings at angles of 45° to 90° to the

wide surface is called quartersawn, and lumber with rings at

angles of 0° to 45° to the wide surface is called plainsawn.

Hardwood lumber in which annual rings form angles of 30°

to 60° to the wide faces is sometimes called bastard sawn.

For many purposes, either plainsawn or quartersawn lumber

is satisfactory. Each type has certain advantages that can be

important for a particular use. Some advantages of plainsawn

and quartersawn lumber are given in Table 3–1.

Decorative Features

The decorative value of wood depends upon its color, figure,

and luster, as well as the way in which it bleaches or takes

fillers, stains, and transparent finishes. Because of the combinations of color and the multiplicity of shades found in

wood, it is impossible to give detailed color descriptions of

the various kinds of wood. Sapwood of most species is light

in color; in some species, sapwood is practically white.

White sapwood of certain species, such as maple, may be

preferred to the heartwood for specific uses. In most species,

heartwood is darker and fairly uniform in color. In some

species, such as hemlock, spruce, the true firs, basswood,

cottonwood, and beech, there is little or no difference in color

between sapwood and heartwood. Table 3–2 describes the

color and figure of several common domestic woods.

On the surface of plainsawn boards and rotary-cut veneer,

the annual growth rings frequently form elliptic and parabolic

patterns that make striking figures, especially when the rings

are irregular in width and outline on the cut surface.

Figure 3–1. Quartersawn (A) and plainsawn (B)

boards cut from a log.

Table 3–1. Some advantages of plainsawn and quartersawn lumber

Plainsawn Quartersawn

Shrinks and swells less in thickness Shrinks and swells less in width

Surface appearance less affected by round or oval knots compared to effect

of spike knots in quartersawn boards; boards with round or oval knots not

as weak as boards with spike knots

Cups, surface-checks, and splits less in seasoning and in use

Shakes and pitch pockets, when present, extend through fewer boards Raised grain caused by separation in annual rings does not become

as pronounced

Figure patterns resulting from annual rings and some other types of figure

brought out more conspicuously

Figure patterns resulting from pronounced rays, interlocked grain,

and wavy grain are brought out more conspicuously

Is less susceptible to collapse in drying Does not allow liquids to pass through readily in some species

Costs less because it is easy to obtain Holds paint better in some species

Sapwood appears in boards at edges and its width is limited by the

width of the log
3–3

Table 3–2. Color and figure of several common domestic woods

Type of figure

Species Color of dry heartwooda

Plainsawn lumber or

rotary-cut veneer

Quartersawn lumber or

quarter-sliced veneer

Hardwoods

Alder, red Pale pinkish brown Faint growth ring Scattered large flakes, sometimes

entirely absent

Ash, black Moderately dark grayish brown Conspicuous growth ring; occasional

burl

Distinct, inconspicuous growth ring

stripe; occasional burl

Ash, Oregon Grayish brown, sometimes with

reddish tinge

Conspicuous growth ring; occasional

burl

Distinct, inconspicuous growth ring

stripe; occasional burl

Ash, white Grayish brown, sometimes with

reddish tinge

Conspicuous growth ring; occasional

burl

Distinct, inconspicuous growth ring

stripe; occasional burl

Aspen Light brown Faint growth ring None

Basswood Creamy white to creamy brown,

sometimes reddish

Faint growth ring None

Beech, American White with reddish to reddish brown

tinge

Faint growth ring Numerous small flakes up to 3.2 mm

(1/8 in.) in height

Birch, paper Light brown Faint growth ring None

Birch, sweet Dark reddish brown Distinct, inconspicuous growth ring;

occasionally wavy

Occasionally wavy

Birch, yellow Reddish brown Distinct, inconspicuous growth ring;

occasionally wavy

Occasionally wavy

Butternut, light Chestnut brown with occasional

reddish tinge or streaks

Faint growth ring None

Cherry, black Light to dark reddish brown Faint growth ring; occasional burl Occasional burl

Chestnut, American Grayish brown Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

Cottonwood Grayish white to light grayish brown Faint growth ring None

Elm, American & rock Light grayish brown, usually with

reddish tinge

Distinct, inconspicuous grown ring

with fine wavy pattern

Faint growth ring stripe

Elm, slippery Dark brown with shades of red Conspicuous growth ring with fine

pattern

Distinct, inconspicuous growth ring

stripe

Hackberry Light yellowish or greenish gray Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

Hickory Reddish brown Distinct, inconspicuous growth ring Faint growth ring stripe

Honeylocust Cherry red Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

Locust, black Golden brown, sometimes with tinge

of green

Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

Magnolia Light to dark yellowish brown with

greenish or purplish tinge

Faint growth ring None

Maple: black, bigleaf,

red, silver, and sugar

Light reddish brown Faint growth ring, occasionally birdseye, curly, and wavyOccasionally curly and wavy

Oaks, all red oaks Light brown, usually with pink or red

tinge

Conspicuous growth ring Pronounced flake; distinct, inconspicuous growth ring stripe

Oaks, all white oaks Light to dark brown, rarely with

reddish tinge

Conspicuous growth ring Pronounced flake; distinct, inconspicuous growth ring stripe

Sweetgum Reddish brown Faint growth ring; occasional irregular

streaks

Distinct, inconspicuous ribbon; occasional streak

Sycamore Light to dark or reddish brown Faint growth ring Numerous pronounced flakes up to 6.4

mm (1/4 in.) in height

Tupelo, black and water Pale to moderately dark brownish

gray

Faint growth ring Distinct, not pronounced ribbon

Walnut, black Chocolate brown, occasionally with

darker, sometimes purplish streaks

Distinct, inconspicuous growth ring;

occasionally wavy, curly, burl, and

other types

Distinct, inconspicuous growth ring

stripe; occasionally wavy, curly, burl,

crotch, and other types

Yellow-poplar Light to dark yellowish brown with

greenish or purplish tinge

Faint growth ring None
 3–4

On quartersawn surfaces, these rings form stripes, which are

not especially ornamental unless they are irregular in width

and direction. The relatively large rays sometimes appear as

flecks that can form a conspicuous figure in quartersawn oak

and sycamore. With interlocked grain, which slopes in

alternate directions in successive layers from the center of the

tree outward, quartersawn surfaces show a ribbon effect, either

because of the difference in reflection of light from successive

layers when the wood has a natural luster or because cross

grain of varying degree absorbs stains unevenly. Much of this

type of figure is lost in plainsawn lumber.

In open-grained hardwoods, the appearance of both plainsawn

and quartersawn lumber can be varied greatly by the use of

fillers of different colors. In softwoods, the annual growth

layers can be made to stand out by applying a stain. The

visual effect of applying stain to softwood is an overall

darkening and a contrast reversal with earlywood of initially

lighter color absorbing more stain, thus becoming darker

than latewood. The final contrast is often greater than that

in unstained softwood and sometimes appears unnatural.

Knots, pin wormholes, bird pecks, decay in isolated

pockets, birdseye, mineral streaks, swirls in grain, and

ingrown bark are decorative in some species when the

wood is carefully selected for a particular architectural

treatment.

Table 3–2. Color and figure of several common domestic woods—con.

Type of figure

Species Color of dry heartwooda

Plainsawn lumber or

rotary-cut veneer

Quartersawn lumber or

quarter-sliced veneer

Softwoods

Baldcypress Light yellowish to reddish brown Conspicuous irregular growth ring Distinct, inconspicuous growth ring

stripe

Cedar, Atlantic White Light brown with reddish tinge Distinct, inconspicuous growth ring None

Cedar, Eastern red Brick red to deep reddish brown Occasionally streaks of white sapwood alternating with heartwoodOccasionally streaks of white sapwood

alternating with heartwood

Cedar, incense Reddish brown Faint growth ring Faint growth ring stripe

Cedar, northern White Light to dark brown Faint growth ring Faint growth ring stripe

Cedar, Port-Orford Light yellow to pale brown Faint growth ring None

Cedar, western red Reddish brown Distinct, inconspicuous growth ring Faint growth ring stripe

Cedar, yellow Yellow Faint growth ring None

Douglas-fir Orange red to red, sometimes

yellow

Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

Fir, balsam Nearly white Distinct, inconspicuous growth ring Faint growth ring stripe

Fir, white Nearly white to pale reddish brown Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

Hemlock, eastern Light reddish brown Distinct, inconspicuous growth ring Faint growth ring stripe

Hemlock, western Light reddish brown Distinct, inconspicuous growth ring Faint growth ring stripe

Larch, western Russet to reddish brown Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

Pine, eastern white Cream to light reddish brown Faint growth ring None

Pine, lodgepole Light reddish brown Distinct, inconspicuous growth ring;

faint pocked appearance

None

Pine, ponderosa Orange to reddish brown Distinct, inconspicuous growth ring Faint growth ring

Pine, red Orange to reddish brown Distinct, inconspicuous growth ring Faint growth ring

Pine, Southern: longleaf,

loblolly, shortleaf, and

slash

Orange to reddish brown Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

Pine, sugar Light creamy brown Faint growth ring None

Pine, western white Cream to light reddish brown Faint growth ring None

Redwood Cherry red to deep reddish brown Distinct, inconspicuous growth ring;

occasionally wavy and burl

Faint growth ring stripe; occasionally

wavy and burl

Spruce: black, Engelmann, red, and whiteNearly white Faint growth ring None

Spruce, Sitka Light reddish brown Distinct, inconspicuous growth ring Faint growth ring stripe

Tamarack Russet brown Conspicuous growth ring Distinct, inconspicuous growth ring

stripe

a

Sapwood of all species is light in color or virtually white unless discolored by fungus or chemical stains.
3–5

Moisture Content

Moisture content of wood is defined as the weight of water in

wood expressed as a fraction, usually a percentage, of the

weight of ovendry wood. Weight, shrinkage, strength, and

other properties depend upon the moisture content of wood.

In trees, moisture content can range from about 30% to more

than 200% of the weight of wood substance. In softwoods,

the moisture content of sapwood is usually greater than that

of heartwood. In hardwoods, the difference in moisture content between heartwood and sapwood depends on the species.

The average moisture content of heartwood and sapwood of

some domestic species is given in Table 3–3. These values

are considered typical, but there is considerable variation

within and between trees. Variability of moisture content

exists even within individual boards cut from the same tree.

Additional information on moisture in wood is given in

Chapter 12.

Green Wood and Fiber

Saturation Point

Moisture can exist in wood as liquid water (free water) or

water vapor in cell lumens and cavities and as water held

chemically (bound water) within cell walls. Green wood is

often defined as freshly sawn wood in which the cell walls are

completely saturated with water; however, green wood usually contains additional water in the lumens. The moisture

content at which both the cell lumens and cell walls are

completely saturated with water is the maximum possible

moisture content. Specific gravity is the major determinant of

maximum moisture content. Lumen volume decreases as

specific gravity increases, so maximum moisture content also

decreases as specific gravity increases because there is less

room available for free water. Maximum moisture content

 

Mmax for any specific gravity can be calculated from

 M GG max b b = − 100 1 54 1 54 ( . )/ . (3–1)

where Gb is basic specific gravity (based on ovendry weight

and green volume) and 1.54 is specific gravity of wood cell

walls. Maximum possible moisture content varies from

267% at specific gravity of 0.30 to 44% at specific gravity

0.90. Maximum possible moisture content is seldom attained in trees. However, green moisture content can be quite

high in some species naturally or through waterlogging. The

moisture content at which wood will sink in water can be

calculated by

 M GG sink b b = − 100 1( )/ (3–2)

Conceptually, the moisture content at which only the cell

walls are completely saturated (all bound water) but no water

exists in cell lumens is called the fiber saturation point.

While a useful concept, the term fiber saturation point is not

very precise. In concept, it distinguishes between the two

ways water is held in wood. In fact, it is possible for all cell

lumens to be empty and have partially dried cell walls in one

part of a piece of wood, while in another part of the same

piece, cell walls may be saturated and lumens partially or

completely filled with water. It is even probable that a cell

wall will begin to dry before all the water has left the lumen

of that same cell. The fiber saturation point of wood averages

about 30% moisture content, but in individual species and

individual pieces of wood it can vary by several percentage

points from that value. The fiber saturation point also is

often considered as that moisture content below which the

physical and mechanical properties of wood begin to change

as a function of moisture content. During drying, the outer

parts of a board can be less than fiber saturation while the

inner parts are still greater than fiber saturation.

Equilibrium Moisture Content

The moisture content of wood below the fiber saturation

point is a function of both relative humidity and temperature

of the surrounding air. Equilibrium moisture content (EMC)

is defined as that moisture content at which the wood is

neither gaining nor losing moisture; an equilibrium condition has been reached. The relationship between EMC,

relative humidity, and temperature is shown in Table 3–4.

For most practical purposes, the values in Table 3–4 may be

applied to wood of any species. Data in Table 3–4 can be

approximated by the following:

 

 

M

W

Kh

Kh

K Kh + K K K h

+ K Kh + K K K h = − +

















1 800

1

2

1

1 12

2 2

1 12

2 2

, (3–3)

where h is relative humidity (%/100), and M is moisture

content (%).

For temperature T in Celsius,

W = 349 + 1.29T + 0.0135T2

K = 0.805 + 0.000736T − 0.00000273T2

K1 = 6.27 − 0.00938T − 0.000303T2

K2 = 1.91 + 0.0407T − 0.000293T2

and for temperature in Fahrenheit,

W = 330 + 0.452T + 0.00415T2

K = 0.791 + 0.000463T − 0.000000844T2

K1 = 6.34 + 0.000775T − 0.0000935T2

K2 = 1.09 + 0.0284T − 0.0000904T2

Wood in service is exposed to both long-term (seasonal) and

short-term (daily) changes in relative humidity and temperature of the surrounding air. Thus, wood is always undergoing at least slight changes in moisture content. These

changes usually are gradual, and short-term fluctuations tend

to influence only the wood surface. Moisture content changes

can be retarded, but not prevented, by protective coatings,

such as varnish, lacquer, or paint. The objective of wood

drying is to bring the wood close to the moisture content a

finished product will have in service (Chs. 12 and 15).
 3–6

Table 3–3. Average moisture content of green wood, by species

Moisture contenta (%) Moisture contenta (%)

Species Heartwood Sapwood Species Heartwood Sapwood

Hardwoods Softwoods

Alder, red — 97 Baldcypress 121 171

Apple 81 74 Cedar, eastern red 33 —

Ash, black 95 — Cedar, incense 40 213

Ash, green — 58 Cedar, Port-Orford 50 98

Ash, white 46 44 Cedar, western red 58 249

Aspen 95 113 Cedar, yellow 32 166

Basswood, American 81 133 Douglas-fir, coast type 37 115

Beech, American 55 72 Fir, balsam 88 173

Birch, paper 89 72 Fir, grand 91 136

Birch, sweet 75 70 Fir, noble 34 115

Birch, yellow 74 72 Fir, Pacific silver 55 164

Cherry, black 58 — Fir, white 98 160

Chestnut, American 120 — Hemlock, eastern 97 119

Cottonwood 162 146 Hemlock, western 85 170

Elm, American 95 92 Larch, western 54 119

Elm, cedar 66 61 Pine, loblolly 33 110

Elm, rock 44 57 Pine, lodgepole 41 120

Hackberry 61 65 Pine, longleaf 31 106

Hickory, bitternut 80 54 Pine, ponderosa 40 148

Hickory, mockernut 70 52 Pine, red 32 134

Hickory, pignut 71 49 Pine, shortleaf 32 122

Hickory, red 69 52 Pine, sugar 98 219

Hickory, sand 68 50 Pine, western white 62 148

Hickory, water 97 62 Redwood, old growth 86 210

Magnolia 80 104 Spruce, black 52 113

Maple, silver 58 97 Spruce, Engelmann 51 173

Maple, sugar 65 72 Spruce, Sitka 41 142

Oak, California black 76 75 Tamarack 49 —

Oak, northern red 80 69

Oak, southern red 83 75

Oak, water 81 81

Oak, white 64 78

Oak, willow 82 74

Sweetgum 79 137

Sycamore, American 114 130

Tupelo, black 87 115

Tupelo, swamp 101 108

Tupelo, water 150 116

Walnut, black 90 73

Yellow-poplar 83 106

a

Based on weight when ovendry.
3–7

Sorption Hysteresis

The amount of water adsorbed from a dry condition to equilibrium with any relative humidity is always less than the

amount retained in the process of drying from a wetter condition to equilibrium with that same relative humidity. The

ratio of adsorption EMC to desorption EMC is constant at

about 0.85. Furthermore, EMC in the initial desorption

(that is, from the original green condition of the tree) is

always greater than in any subsequent desorptions. Data in

Table 3–4 were derived primarily under conditions described

as oscillating desorption (Stamm and Loughborough 1935),

which is thought to represent a condition midway between

adsorption and desorption and a suitable and practical compromise for use when the direction of sorption is not always

known. Hysteresis is shown in Figure 3–2.

Shrinkage

Wood is dimensionally stable when the moisture content is

greater than the fiber saturation point. Wood changes dimension as it gains or loses moisture below that point. It shrinks

when losing moisture from the cell walls and swells when

gaining moisture in the cell walls. This shrinking and swelling can result in warping, checking, splitting, and loosening

of tool handles, gaps in strip flooring, or performance

problems that detract from the usefulness of the wood product. Therefore, it is important that these phenomena be

understood and considered when they can affect a product in

which wood is used.

With respect to shrinkage characteristics, wood is an anisotropic material. It shrinks most in the direction of the annual

growth rings (tangentially), about half as much across the

rings (radially), and only slightly along the grain (longitudinally). The combined effects of radial and tangential

shrinkage can distort the shape of wood pieces because of the

difference in shrinkage and the curvature of annual rings.

The major types of distortion as a result of these effects are

illustrated in Figure 3–3.

Transverse and Volumetric

Data have been collected to represent the average radial,

tangential, and volumetric shrinkage of numerous domestic

species by methods described in American Society for Testing and Materials (ASTM) D143Standard Method of

Testing Small Clear Specimens of Timber (ASTM 1997).

Shrinkage values, expressed as a percentage of the green

dimension, are listed in Table 3–5. Shrinkage values

Table 3–4. Moisture content of wood in equilibrium with stated temperature and relative humidity

Temperature Moisture content (%) at various relative humidity values

(°C (°F)) 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95%

−1.1 (30) 1.4 2.6 3.7 4.6 5.5 6.3 7.1 7.9 8.7 9.5 10.4 11.3 12.4 13.5 14.9 16.5 18.5 21.0 24.3

4.4 (40) 1.4 2.6 3.7 4.6 5.5 6.3 7.1 7.9 8.7 9.5 10.4 11.3 12.3 13.5 14.9 16.5 18.5 21.0 24.3

10.0 (50) 1.4 2.6 3.6 4.6 5.5 6.3 7.1 7.9 8.7 9.5 10.3 11.2 12.3 13.4 14.8 16.4 18.4 20.9 24.3

15.6 (60) 1.3 2.5 3.6 4.6 5.4 6.2 7.0 7.8 8.6 9.4 10.2 11.1 12.1 13.3 14.6 16.2 18.2 20.7 24.1

21.1 (70) 1.3 2.5 3.5 4.5 5.4 6.2 6.9 7.7 8.5 9.2 10.1 11.0 12.0 13.1 14.4 16.0 17.9 20.5 23.9

26.7 (80) 1.3 2.4 3.5 4.4 5.3 6.1 6.8 7.6 8.3 9.1 9.9 10.8 11.7 12.9 14.2 15.7 17.7 20.2 23.6

32.2 (90) 1.2 2.3 3.4 4.3 5.1 5.9 6.7 7.4 8.1 8.9 9.7 10.5 11.5 12.6 13.9 15.4 17.3 19.8 23.3

37.8 (100) 1.2 2.3 3.3 4.2 5.0 5.8 6.5 7.2 7.9 8.7 9.5 10.3 11.2 12.3 13.6 15.1 17.0 19.5 22.9

43.3 (110) 1.1 2.2 3.2 4.0 4.9 5.6 6.3 7.0 7.7 8.4 9.2 10.0 11.0 12.0 13.2 14.7 16.6 19.1 22.4

48.9 (120) 1.1 2.1 3.0 3.9 4.7 5.4 6.1 6.8 7.5 8.2 8.9 9.7 10.6 11.7 12.9 14.4 16.2 18.6 22.0

54.4 (130) 1.0 2.0 2.9 3.7 4.5 5.2 5.9 6.6 7.2 7.9 8.7 9.4 10.3 11.3 12.5 14.0 15.8 18.2 21.5

60.0 (140) 0.9 1.9 2.8 3.6 4.3 5.0 5.7 6.3 7.0 7.7 8.4 9.1 10.0 11.0 12.1 13.6 15.3 17.7 21.0

65.6 (150) 0.9 1.8 2.6 3.4 4.1 4.8 5.5 6.1 6.7 7.4 8.1 8.8 9.7 10.6 11.8 13.1 14.9 17.2 20.4

71.1 (160) 0.8 1.6 2.4 3.2 3.9 4.6 5.2 5.8 6.4 7.1 7.8 8.5 9.3 10.3 11.4 12.7 14.4 16.7 19.9

76.7 (170) 0.7 1.5 2.3 3.0 3.7 4.3 4.9 5.6 6.2 6.8 7.4 8.2 9.0 9.9 11.0 12.3 14.0 16.2 19.3

82.2 (180) 0.7 1.4 2.1 2.8 3.5 4.1 4.7 5.3 5.9 6.5 7.1 7.8 8.6 9.5 10.5 11.8 13.5 15.7 18.7

87.8 (190) 0.6 1.3 1.9 2.6 3.2 3.8 4.4 5.0 5.5 6.1 6.8 7.5 8.2 9.1 10.1 11.4 13.0 15.1 18.1

93.3 (200) 0.5 1.1 1.7 2.4 3.0 3.5 4.1 4.6 5.2 5.8 6.4 7.1 7.8 8.7 9.7 10.9 12.5 14.6 17.5

98.9 (210) 0.5 1.0 1.6 2.1 2.7 3.2 3.8 4.3 4.9 5.4 6.0 6.7 7.4 8.3 9.2 10.4 12.0 14.0 16.9

104.4 (220) 0.4 0.9 1.4 1.9 2.4 2.9 3.4 3.9 4.5 5.0 5.6 6.3 7.0 7.8 8.8 9.9

110.0 (230) 0.3 0.8 1.2 1.6 2.1 2.6 3.1 3.6 4.2 4.7 5.3 6.0 6.7

115.6 (240) 0.3 0.6 0.9 1.3 1.7 2.1 2.6 3.1 3.5 4.1 4.6

121.1 (250) 0.2 0.4 0.7 1.0 1.3 1.7 2.1 2.5 2.9

126.7 (260) 0.2 0.3 0.5 0.7 0.9 1.1 1.4

132.2 (270) 0.1 0.1 0.2 0.3 0.4 0.4
 3–8

collected from the world literature for selected imported

species are listed in Table 3–6.

The shrinkage of wood is affected by a number of variables.

In general, greater shrinkage is associated with greater density. The size and shape of a piece of wood can affect shrinkage, and the rate of drying for some species can affect shrinkage. Transverse and volumetric shrinkage variability can be

expressed by a coefficient of variation of approximately 15%.

Longitudinal

Longitudinal shrinkage of wood (shrinkage parallel to the

grain) is generally quite small. Average values for shrinkage

from green to ovendry are between 0.1% and 0.2% for most

species of wood. However, certain types of wood exhibit

excessive longitudinal shrinkage, and these should be

avoided in uses where longitudinal stability is important.

Reaction wood, whether compression wood in softwoods

or tension wood in hardwoods, tends to shrink excessively

parallel to the grain. Wood from near the center of trees

(juvenile wood) of some species also shrinks excessively

lengthwise. Reaction wood and juvenile wood can shrink

2% from green to ovendry. Wood with cross grain exhibits

increased shrinkage along the longitudinal axis of the piece.

Reaction wood exhibiting excessive longitudinal shrinkage

can occur in the same board with normal wood. The presence

of this type of wood, as well as cross grain, can cause serious

warping, such as bow, crook, or twist, and cross breaks can

develop in the zones of high shrinkage.

Moisture–Shrinkage Relationship

The shrinkage of a small piece of wood normally begins at

about the fiber saturation point and continues in a fairly

linear manner until the wood is completely dry. However, in

the normal drying of lumber or other large pieces, the surface

of the wood dries first. When the surface gets below the fiber

saturation point, it begins to shrink. Meanwhile, the interior

can still be quite wet and not shrink. The result is that

shrinkage of lumber can begin before the average moisture

content of the entire piece is below the fiber saturation point,

and the moisture content–shrinkage curve can actually look

like the one in Figure 3–4. The exact form of the curve

depends on several variables, principally size and shape of

the piece, species of wood, and drying conditions used.

Considerable variation in shrinkage occurs for any species.

Shrinkage data for Douglas-fir boards, 22.2 by 139.7 mm

(7/8 by 5-1/2 in.) in cross section, are given in Figure 3–5.

The material was grown in one locality and dried under mild

conditions from green to near equilibrium at 18°C (65°F)

and 30% relative humidity. The figure shows that it is impossible to accurately predict the shrinkage of an individual

piece of wood; the average shrinkage of a quantity of pieces is

more predictable.

If the shrinkage–moisture content relationship is not known

for a particular product and drying condition, data in

Tables 3–5 and 3–6 can be used to estimate shrinkage from

the green condition to any moisture content using

 

 

S S M m =  −



 

 0  30

30 (3–4)

where Sm is shrinkage (%) from the green condition to moisture content M (<30%), and S0 is total shrinkage (radial,

tangential, or volumetric (%)) from Table 3–5 or 3–6. 

Figure 3–2. Moisture content–relative humidity

relationship for wood under adsorption and

various desorption conditions.

Figure 3–3. Characteristic shrinkage and distortion

of flat, square, and round pieces as affected

by direction of growth rings. Tangential shrinkage

is about twice as great as radial.
3–9

Table 3–5. Shrinkage values of domestic woods

Shrinkagea (%) from green

to ovendry moisture content

Shrinkagea (%) from green

to ovendry moisture content

Species Radial Tangential Volumetric Species Radial Tangential Volumetric

Hardwoods Oak, white—con.

Alder, red 4.4 7.3 12.6 Chestnut

Ash Live 6.6 9.5 14.7

Black 5.0 7.8 15.2 Overcup 5.3 12.7 16.0

Blue 3.9 6.5 11.7 Post 5.4 9.8 16.2

Green 4.6 7.1 12.5 Swamp, chestnut 5.2 10.8 16.4

Oregon 4.1 8.1 13.2 White 5.6 10.5 16.3

Pumpkin 3.7 6.3 12.0 Persimmon, common 7.9 11.2 19.1

White 4.9 7.8 13.3 Sassafras 4.0 6.2 10.3

Aspen Sweetgum 5.3 10.2 15.8

Bigtooth 3.3 7.9 11.8 Sycamore, American 5.0 8.4 14.1

Quaking 3.5 6.7 11.5 Tanoak 4.9 11.7 17.3

Basswood, American 6.6 9.3 15.8 Tupelo

Beech, American 5.5 11.9 17.2 Black 5.1 8.7 14.4

Birch Water 4.2 7.6 12.5

Alaska paper 6.5 9.9 16.7 Walnut, black 5.5 7.8 12.8

Gray 5.2 — 14.7 Willow, black 3.3 8.7 13.9

Paper 6.3 8.6 16.2 Yellow-poplar 4.6 8.2 12.7

River 4.7 9.2 13.5 Softwoods

Sweet 6.5 9.0 15.6 Cedar

Yellow 7.3 9.5 16.8 Yellow 2.8 6.0 9.2

Buckeye, yellow 3.6 8.1 12.5 Atlantic white 2.9 5.4 8.8

Butternut 3.4 6.4 10.6 Eastern redcedar 3.1 4.7 7.8

Cherry, black 3.7 7.1 11.5 Incense 3.3 5.2 7.7

Chestnut, American 3.4 6.7 11.6 Northern white 2.2 4.9 7.2

Cottonwood Port-Orford 4.6 6.9 10.1

Balsam poplar 3.0 7.1 10.5 Western redcedar 2.4 5.0 6.8

Black 3.6 8.6 12.4 Douglas-fir,

Eastern 3.9 9.2 13.9 Coastb 4.8 7.6 12.4

Elm Interior northb 3.8 6.9 10.7

American 4.2 9.5 14.6 Interior westb 4.8 7.5 11.8

Cedar 4.7 10.2 15.4 Fir

Rock 4.8 8.1 14.9 Balsam 2.9 6.9 11.2

Slippery 4.9 8.9 13.8 California red 4.5 7.9 11.4

Winged 5.3 11.6 17.7 Grand 3.4 7.5 11.0

Hackberry 4.8 8.9 13.8 Noble 4.3 8.3 12.4

Hickory, pecan 4.9 8.9 13.6 Pacific silver 4.4 9.2 13.0

Hickory, true Subalpine 2.6 7.4 9.4

Mockernut 7.7 11.0 17.8 White 3.3 7.0 9.8

Pignut 7.2 11.5 17.9 Hemlock

Shagbark 7.0 10.5 16.7 Eastern 3.0 6.8 9.7

Shellbark 7.6 12.6 19.2 Mountain 4.4 7.1 11.1

Holly, American 4.8 9.9 16.9 Western 4.2 7.8 12.4

Honeylocust 4.2 6.6 10.8 Larch, western 4.5 9.1 14.0

Locust, black 4.6 7.2 10.2 Pine

Madrone, Pacific 5.6 12.4 18.1 Eastern white 2.1 6.1 8.2

Magnolia Jack 3.7 6.6 10.3

Cucumbertree 5.2 8.8 13.6 Loblolly 4.8 7.4 12.3

Southern 5.4 6.6 12.3 Lodgepole 4.3 6.7 11.1

Sweetbay 4.7 8.3 12.9 Longleaf 5.1 7.5 12.2

Maple Pitch 4.0 7.1 10.9

Bigleaf 3.7 7.1 11.6 Pond 5.1 7.1 11.2

Black 4.8 9.3 14.0 Ponderosa 3.9 6.2 9.7

Red 4.0 8.2 12.6 Red 3.8 7.2 11.3

Silver 3.0 7.2 12.0 Shortleaf 4.6 7.7 12.3

Striped 3.2 8.6 12.3 Slash 5.4 7.6 12.1

Sugar 4.8 9.9 14.7 Sugar 2.9 5.6 7.9

Oak, red Virginia 4.2 7.2 11.9

Black 4.4 11.1 15.1 Western white 4.1 7.4 11.8

Laurel 4.0 9.9 19.0 Redwood

Northern red 4.0 8.6 13.7 Old growth 2.6 4.4 6.8

Pin 4.3 9.5 14.5 Young growth 2.2 4.9 7.0

Scarlet 4.4 10.8 14.7 Spruce

Southern red 4.7 11.3 16.1 Black 4.1 6.8 11.3

Water 4.4 9.8 16.1 Engelmann 3.8 7.1 11.0

Willow 5.0 9.6 18.9 Red 3.8 7.8 11.8

Oak, white 4.4 8.8 12.7 Sitka 4.3 7.5 11.5

Bur 5.3 10.8 16.4 Tamarack 3.7 7.4 13.6

a

Expressed as a percentage of the green dimension.

b

Coast type Douglas-fir is defined as Douglas-fir growing in the States of Oregon and Washington west of the summit of the Cascade Mountains.

 Interior West includes the State of California and all counties in Oregon and Washington east of but adjacent to the Cascade summit. Interior North

 includes the remainder of Oregon and Washington and the States of Idaho, Montana, and Wyoming.
 3–10

Table 3–6. Shrinkage for some woods imported into the United Statesa

Shrinkageb from 

green to ovendry

moisture content (%)

Shrinkageb from 

green to ovendry

moisture content (%)

Species Radial

TangentialVolumetricLocationc Species RadialTangentialVolumetricLocationc

Afrormosia (Pericopsis elata) 3.0 6.4 10.7 AF Lauan, white (Pentacme contorta) 4.0 7.7 11.7 AS

Albarco (Cariniana spp.) 2.8 5.4 9.0 AM Limba (Terminalia superba) 4.5 6.2 10.8 AF

Andiroba (Carapa guianensis) 3.1 7.6 10.4 AM Macawood (Platymiscium spp.) 2.7 3.5 6.5 AM

Angelin (Andira inermis) 4.6 9.8 12.5 AM Mahogany, African (Khaya spp.) 2.5 4.5 8.8 AF

Angelique (Dicorynia guianensis) 5.2 8.8 14.0 AM Mahogany, true (Swietenia macrophylla) 3.0 4.1 7.8 AM

Apitong (Dipterocarpus spp.) 5.2 10.9 16.1 AS Manbarklak (Eschweilera spp.) 5.8 10.3 15.9 AM

Avodire (Turreanthus africanus) 4.6 6.7 12.0 AF Manni (Symphonia globulifera) 5.7 9.7 15.6 AM

Azobe (Lophira alata) 8.4 11.0 17.0 AM Marishballi (Licania spp.) 7.5 11.7 17.2 AM

Balata (Manilkara bidentata) 6.3 9.4 16.9 AM Meranti, white (Shorea spp.) 3.0 6.6 7.7 AS

Balsa (Ochroma pyramidale) 3.0 7.6 10.8 AM Meranti, yellow (Shorea spp.) 3.4 8.0 10.4 AS

Banak (Virola spp.) 4.6 8.8 13.7 AM Merbau (Intsia bijuga and I. palembanica) 2.7 4.6 7.8 AS

Benge (Guibourtia arnoldiana) 5.2 8.6 13.8 AF Mersawa (Anisoptera spp.) 4.0 9.0 14.6 AS

Bubinga (Guibourtia spp.) 5.8 8.4 14.2 AF Mora (Mora spp.) 6.9 9.8 18.8 AM

Bulletwood (Manilkara bidentata) 6.3 9.4 16.9 AM Obeche (Triplochiton scleroxylon) 3.0 5.4 9.2 AF

Caribbean pine (Pinus caribaea) 6.3 7.8 12.9 AM Ocota pine (Pinus oocarpa) 4.6 7.5 12.3 AM

Cativo (Prioria copaifera) 2.4 5.3 8.9 AM Okoume (Aucoumea klaineana) 4.1 6.1 11.3 AF

Ceiba (Ceiba pentandra) 2.1 4.1 10.4 AM Opepe (Nauclea spp.) 4.5 8.4 12.6 AF

Cocobolo (Dalbergia retusa) 2.7 4.3 7.0 AM Ovangkol (Guibourta ehie) 4.5 8.2 12 AF

Courbaril (Hymenaea courbaril) 4.5 8.5 12.7 AM Para-angelium (Hymenolobium excelsum) 4.4 7.1 10.2 AM

Cuangare (Dialyanthera spp.) 4.2 9.4 12.0 AM Parana pine (Araucaria angustifolia) 4.0 7.9 11.6 AS

Degame (Calycophyllum cand

idissimum)

4.8 8.6 13.2 AM Pau Marfim (Balfourodendron

riedelianum)

4.6 8.8 13.4 AM

Determa (Ocotea rubra) 3.7 7.6 10.4 AM Peroba de campos (Paratecoma peroba) 3.8 6.6 10.5 AM

Ebony, East Indian (Diospyros spp.) 5.4 8.8 14.2 AS Peroba Rosa (Aspidosperma spp.) 3.8 6.4 11.6 AM

Ebony, African (Diospyros spp.) 9.2 10.8 20.0 AF Piquia (Caryocar spp.) 5.0 8.0 13.0 AM

Ekop (Tetraberlinia tubmaniana) 5.6 10.2 15.8 AF Pilon (Hyeronima spp.) 5.4 11.7 17.0 AM

Gmelina (Gmelina arborea) 2.4 4.9 8.8 AS Primavera (Cybistax donnell-smithii) 3.1 5.1 9.1 AM

Goncalo alves (Astronium graveolens) 4.0 7.6 10.0 AM Purpleheart (Peltogyne spp.) 3.2 6.1 9.9 AM

Greenheart (Ocotea rodiaei) 8.8 9.6 17.1 AM Ramin (Gonystylus spp.) 4.3 8.7 13.4 AS

Hura (Hura crepitans) 2.7 4.5 7.3 AM Roble (Quercus spp.) 6.4 11.7 18.5 AM

Ilomba (Pycnanthus angolensis) 4.6 8.4 12.8 AF Roble (Tabebuia spp. Roble group) 3.6 6.1 9.5 AM

Imbuia (Phoebe porosa) 2.7 6.0 9.0 AM Rosewood, Brazilian (Dalbergia nigra) 2.9 4.6 8.5 AM

Ipe (Tabebuia spp.) 6.6 8.0 13.2 AM Rosewood, Indian (Dalbergia latifolia) 2.7 5.8 8.5 AS

Iroko (Chlorophora excelsa and C. regia) 2.8 3.8 8.8 AF Rubberwood (Hevea brasiliensis) 2.3 5.1 7.4 AM

Jarrah (Eucalyptus marginata) 7.7 11.0 18.7 AS Sande (Brosimum spp. Utile group) 4.6 8.0 13.6 AM

Jelutong (Dyera costulata) 2.3 5.5 7.8 AS Sapele (Entandrophragma cylindricum) 4.6 7.4 14.0 AF

Kaneelhart (Licaria spp.) 5.4 7.9 12.5 AM Sepetir (Pseudosindora spp. and

Sindora spp.)

3.7 7.0 10.5 AS

Kapur (Dryobalanops spp.) 4.6 10.2 14.8 AS Spanish-cedar (Cedrela spp.) 4.2 6.3 10.3 AM

Karri (Eucalyptus diversicolor) 7.8 12.4 20.2 AS Sucupira (Diplotropis purpurea) 4.6 7.0 11.8 AM

Kempas (Koompassia malaccensis) 6.0 7.4 14.5 AS Teak (Tectona grandis) 2.5 5.8 7.0 AS

Keruing (Dipterocarpus spp.) 5.2 10.9 16.1 AS Wallaba (Eperua spp.) 3.6 6.9 10.0 AM

Lauan, light red and red (Shorea spp.) 4.6 8.5 14.3 AS

Lauan, dark red (Shorea spp.) 3.8 7.9 13.1 AS

a

Shrinkage values were obtained from world literature and may not represent a true species average.

b

Expressed as a percentage of the green dimension.

c

AF is Africa; AM is Tropical America; AS is Asia and Oceania.
3–11

If the moisture content at which shrinkage from the green

condition begins is known to be other than 30% for a species, the shrinkage estimate can be improved by replacing the

value of 30 in Equation (3–4) with the appropriate moisture

content value.

Tangential values for S0 should be used for estimating width

shrinkage of flatsawn material and radial values for quartersawn material. For mixed or unknown ring orientations,

tangential values are suggested. Shrinkage values for individual pieces will vary from predicted shrinkage values. As

noted previously, shrinkage variability is characterized by a

coefficient of variation of approximately 15%. This applies to

pure tangential or radial ring orientation and is probably

somewhat greater in commercial lumber, where ring orientation is seldom aligned perfectly parallel or perpendicular to

board faces. Chapter 12 contains additional discussion of

shrinkage–moisture content relationships, including a

method to estimate shrinkage for the relatively small moisture content changes of wood in service. Shrinkage assumptions for commercial lumber, which typically is not perfectly

plainsawn or quartersawn, are discussed in Chapter 6.

Weight, Density, and

Specific Gravity

Two primary factors affect the weight of wood products:

density of the basic wood structure and moisture content. A

third factor, minerals and extractable substances, has a

marked effect only on a limited number of species.

The density of wood, exclusive of water, varies greatly both

within and between species. Although the density of most

species falls between about 320 and 720 kg/m3 (20 and

45 lb/ft3), the range of density actually extends from about

160 kg/m3 (10 lb/ft3) for balsa to more than 1,040 kg/m3

(65 lb/ft3) for some other imported woods. A coefficient of

variation of about 10% is considered suitable for describing

the variability of density within common domestic species.

Wood is used in a wide range of conditions and has a wide

range of moisture content values in use. Moisture makes up

part of the weight of each product in use; therefore, the density must reflect this fact. This has resulted in the density of

wood often being determined and reported on the basis of

moisture content in use.

The calculated density of wood, including the water contained in the wood, is usually based on average species

characteristics. This value should always be considered an

approximation because of the natural variation in anatomy,

moisture content, and ratio of heartwood to sapwood that

occurs. Nevertheless, this determination of density usually

is sufficiently accurate to permit proper utilization of wood

products where weight is important. Such applications range

from the estimation of structural loads to the calculation of

approximate shipping weights.

To standardize comparisons of species or products and estimations of product weight, specific gravity is used as a

standard reference basis, rather than density. The traditional

definition of specific gravity is the ratio of the density of the

wood to the density of water at a specified reference temperature (often 4.4°C (40°F)) where the density of water is

1.0000 g/cm3

). To reduce confusion introduced by the variable of moisture content, the specific gravity of wood usually

is based on the ovendry weight and the volume at some

specified moisture content.

Commonly used bases for determining specific gravity are

ovendry weight and volume at (a) green, (b) ovendry, and

(c) 12% moisture content. Ovendry weight and green volume

are often used in databases to characterize specific gravity of

species, which is referred to as basic specific gravity. Some

specific gravity data are reported in Tables 4–3, 4–4, and

4–5 (Ch. 4) on both the 12% and green volume basis.

A coefficient of variation of about 10% describes the variability inherent in many common domestic species.

Design specifications for wood, such as contained in the

National Design Specification for Wood Construction, are

based on ovendry weight and ovendry volume.

Figure 3–4. Typical moisture content–shrinkage

curves.

7

Tangential shrinkage (%)6

5

4

3

2

1

0 2 4 6 10 8 12 14 16 18 20 22

Moisture content (%)

Figure 3–5. Variation in individual tangential shrinkage

values of several Douglas-fir boards from one locality,

dried from green condition.
 3–12

If the specific gravity of wood is known, based on ovendry

weight and volume at a specified moisture content, the

specific gravity at any other moisture content between 0 and

30% can be approximated from Figure 3–6. This figure

adjusts for average shrinkage and swelling that occurs below

30% moisture content and affects the volume of wood. The

specific gravity of wood based on ovendry weight does not

change at moisture content values above approximately 30%

(the approximate fiber saturation point) because the volume

does not change. To use Figure 3–6, locate the inclined line

corresponding to the known specific gravity (volume when

green). From this point, move left parallel to the inclined

lines until vertically above the target moisture content.

Then, read the new specific gravity corresponding to this

point at the left-hand side of the graph.

For example, to estimate the density of white ash at 12%

moisture content, consult Table 4–3a in Chapter 4. The

average green (basic) specific gravity Gb for this species is

0.55. Using Figure 3–6, the 0.55 green specific gravity curve

is found to intersect with the vertical 12% moisture content

line at a point corresponding to a specific gravity of 0.605

based on ovendry weight and volume at 12% moisture content, Gm (see dashed lines in Fig. 3–6). The density of wood

including water at this moisture content can then be obtained

from Table 3–7, which converts the specific gravity of

0.605 to a density of 675 kg/m3 (42 lb/ft3). An alternative to

usage of Figure 3–6 is direct calculation of Gm using the

following:

 G G aG mb b = − /( . ) 1 0 265 (3–5)

where Gm is specific gravity based on volume at moisture

content M, Gb is basic specific gravity (based on green volume), and a = (30 − M)/30, where M < 30.

Alternatively, the density values in Table 3–7 can be calculated by

 ρ = 1,000 Gm(1 + M/100) (kg/m3) (3–6a)

 ρ = 62.4 Gm(1 + M/100) (lb/ft3) (3–6b)

It is often useful to know the weight of lumber on a volumetric basis. We can make these estimates using Table 3–7 or

with equations only. These results assume an average

shrinkage–specific gravity relationship and provide a good

estimate. Both methods are illustrated. For weights based on

the actual shrinkage of individual species, refer to the Dry

Kiln Operator’s Manual (Simpson 1991).

Method 1—Use of Table 3–7

Determine the weight per actual unit volume (cubic meter

or 1,000 board feet) of sugar maple at 20% moisture content and at 50% moisture content. From Table 4–3a, the

specific gravity Gb (ovendry weight–green volume) is 0.56.

Because the specific gravity in Table 3–7 is based on

volume at tabulated moisture content Gm, we must convert

Gb to Gm by either Figure 3–6 or Equation (3–5):

At 20%,

 Gm = 0.56/{1 – 0.265[(30 – 20)/30]0.56} = 0.59

Determine the density from Table 3–7 at Gm = 0.59 and

20% moisture content. The result is approximately

708 kg/m3 (44.1 lb/ft3) (by interpolation).

At 50%,

Gm = Gb = 0.56

Determine the density from Table 3–7 at Gm = 0.56

and 50% moisture content. The result is 840 kg/m3

(52.4 lb/ft3).

Method 2—Use of equations only

At 20%, Gm is calculated as 0.589 as in Method 1.

Density is then calculated from Equation (3–6) as

ρ = 1,000 Gm(1+M/100)

= 1,000 (0.58 (1+20/100) = 707 kg/m3

ρ = 62.4 Gm(1+M/100)

= 62.4(0.589) (1+20/100) = 44.1 lb/ft3

At 50%,

ρ = 1,000 (0.56)(1+50/100) = 840 kg/m3

ρ = 62.4(0.56)(1+50/100) = 52.4 lb/ft3

0 6 12 18 24 30

0.82

0.18

0.22

0.26

0.30

0.34

0.38

0.42

0.78

0.74

0.70

0.66

0.46

0.62

0.58

0.50

0.54

Specific gravity (volume at current moisture content)

Moisture content (%)

2 4 8 10 14 16 20 22 26 28

 Specific gravity

(volume when green)

0.44

0.40

0.36

0.32

0.28

0.24

0.20

0.64

0.60

0.56

0.48

0.52

Figure 3–6. Relationship of specific gravity and

moisture content.
3–13

Table 3–7a. Density of wood as a function of specific gravity and moisture content (metric)

Moisture

content Density (kg/m3

) when the specific gravity Gm is

of wood

(%) 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50 0.52 0.54 0.56 0.58 0.60 0.62 0.64 0.66 0.68 0.70

0 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700

4 312 333 354 374 395 416 437 458 478 499 520 541 562 582 603 624 645 666 686 707 728

8 324 346 367 389 410 432 454 475 497 518 540 562 583 605 626 648 670 691 713 734 756

12 336 358 381 403 426 448 470 493 515 538 560 582 605 627 650 672 694 717 739 762 784

16 348 371 394 418 441 464 487 510 534 557 580 603 626 650 673 696 719 742 766 789 812

20 360 384 408 432 456 480 504 528 552 576 600 624 648 672 696 720 744 768 792 816 840

24 372 397 422 446 471 496 521 546 570 595 620 645 670 694 719 744 769 794 818 843 868

28 384 410 435 461 486 512 538 563 589 614 640 666 691 717 742 768 794 819 845 870 896

32 396 422 449 475 502 528 554 581 607 634 660 686 713 739 766 792 818 845 871 898 924

36 408 435 462 490 517 544 571 598 626 653 680 707 734 762 789 816 843 870 898 925 952

40 420 448 476 504 532 560 588 616 644 672 700 728 756 784 812 840 868 896 924 952 980

44 432 461 490 518 547 576 605 634 662 691 720 749 778 806 835 864 893 922 950 979 1,008

48 444 474 503 533 562 592 622 651 681 710 740 770 799 829 858 888 918 947 977 1,006 1,036

52 456 486 517 547 578 608 638 669 699 730 760 790 821 851 882 912 942 973 1,003 1,034 1,064

56 468 499 530 562 593 624 655 686 718 749 780 811 842 874 905 936 967 998 1,030 1,061 1,092

60 480 512 544 576 608 640 672 704 736 768 800 832 864 896 928 960 992 1,024 1,056 1,088 1,120

64 492 525 558 590 623 656 689 722 754 787 820 853 886 918 951 984 1,017 1,050 1,082 1,115 1,148

68 504 538 571 605 638 672 706 739 773 806 840 874 907 941 974 1,008 1,042 1,075 1,109 1,142 1,176

72 516 550 585 619 854 688 722 757 791 826 860 894 929 963 998 1,032 1,066 1,101 1,135 1,170 1,204

76 528 563 598 634 669 704 739 774 810 845 8B0 915 950 986 1,021 1,056 1,091 1,126 1,162 1,197

80 540 576 612 648 684 720 756 792 828 864 900 936 972 1,008 1,044 1,080 1,116 1,152 1,188

84 552 589 626 662 699 736 773 810 846 883 920 957 994 1030 1,067 1,104 1,141 1,178

88 564 602 639 677 714 752 790 827 865 902 940 978 1,015 1,053 1,090 1,128 1,166

92 576 614 653 691 730 768 806 845 883 922 960 998 1,037 1,075 1,114 1,152 1,190

96 588 627 666 706 745 784 823 862 902 941 980 1,019 1,058 1,098 1,137 1,176

100 600 640 680 720 760 800 840 880 920 960 l,000 1,040 1,080 1,120 1,160 1,200

110 630 672 714 756 798 840 832 924 966 1,008 1,050 1,092 1,134 1,176 1,218

120 660 704 748 792 836 880 924 968 1,012 1,056 1,100 1,144 1,188 1,232

130 690 736 782 828 874 920 966 1,012 1,058 1,104 1,150 1,196 1,242 1,288

140 720 768 816 864 912 960 1,008 1,056 1,104 1,152 1,200 1,248 1,296

150 750 800 850 900 950 1,000 1,050 1,100 1,150 1,200 1,250 1,300 1,350
 3–14

Table 3–7b. Density of wood as a function of specific gravity and moisture content (inch–pound)

Moisture

content Density (lb/ft3

) when the specific gravity Gm is

of wood

(%) 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50 0.52 0.54 0.56 0.58 0.60 0.62 0.64 0.66 0.68 0.70

0 18.7 20.0 21.2 22.5 23.7 25.0 26.2 27.5 28.7 30.0 31.2 32.4 33.7 34.9 36.2 37.4 38.7 39.9 41.2 42.4 43.7

4 19.5 20.8 22.1 23.4 24.7 26.0 27.2 28.6 29.8 31.2 32.4 33.7 35.0 36.6 37.6 38.9 40.2 41.5 42.8 44.1 45.4

8 20.2 21.6 22.9 24.3 25.6 27.0 28.3 29.6 31.0 32.3 33.7 35.0 36.4 37.7 39.1 40.4 41.8 43.1 44.5 45.8 47.2

12 21.0 22.4 23.8 25.2 26.6 28.0 29.4 30.8 32.2 33.5 34.9 36.3 37.7 39.1 40.5 41.9 43.3 44.7 46.1 47.5 48.9

16 21.7 23.2 24.6 26.0 27.5 29.0 30.4 31.8 33.3 34.7 36.2 37.6 39.1 40.5 42.0 43.4 44.9 46.3 47.8 49.2 50.7

20 22.5 24.0 25.5 27.0 28.4 30.0 31.4 32.9 34.4 35.9 37.4 38.9 40.4 41.9 43.4 44.9 46.4 47.9 49.4 50.9 52.4

24 23.2 24.8 26.3 27.8 29.4 31.0 32.5 34.0 35.6 37.1 38.7 40.2 41.8 43.3 44.9 46.4 48.0 49.5 51.1 52.6 54.2

28 24.0 25.6 27.2 28.8 30.4 31.9 33.5 35.1 36.7 38.3 39.9 41.5 43.1 44.7 46.3 47.9 49.5 51.1 52.7 54.3 55.9

32 24.7 26.4 28.0 29.7 31.3 32.9 34.6 36.2 37.9 39.5 41.2 42.8 44.5 46.1 47.8 49.4 51.1 52.7 54.4 56.0 57.7

36 25.5 27.2 28.9 30.6 32.2 33.9 35.6 37.3 39.0 40.7 42.4 44.1 45.8 47.5 49.2 50.9 52.6 54.3 56.0 57.7 59.4

40 26.2 28.0 29.7 31.4 33.2 34.9 36.7 38.4 40.2 41.9 43.7 45.4 47.2 48.9 50.7 52.4 54.2 55.9 57.7 59.4 61.2

44 27.0 28.8 30.6 32.3 34.1 35.9 37.7 39.5 41.3 43.1 44.9 46.7 48.5 50.3 52.1 53.9 55.7 57.5 59.3 61.1 62.9

48 27.7 29.6 31.4 33.2 35.1 36.9 38.8 40.6 42.5 44.3 46.2 48.0 49.9 51.7 53.6 55.4 57.3 59.1 61.0 62.8 64.6

52 28.5 30.4 32.2 34.1 36.0 37.9 39.8 41.7 43.6 45.5 47.4 49.3 51.2 53.1 55.0 56.9 58.8 60.7 62.6 64.5 66.4

56 29.2 31.2 33.1 35.0 37.0 38.9 40.9 42.8 44.8 46.7 48.7 50.6 52.6 54.5 56.5 58.4 60.4 62.3 64.2 66.2 68.1

60 30.0 31.9 33.9 35.9 37.9 39.9 41.9 43.9 45.9 47.9 49.9 51.9 53.9 55.9 57.9 59.9 61.9 63.9 65.9 67.9 69.9

64 30.7 32.7 34.8 36.8 38.9 40.9 43.0 45.0 47.1 49.1 51.2 53.2 55.3 57.3 59.4 61.4 63.4 65.5 67.5 69.6 71.6

68 31.4 33.5 35.6 37.7 39.8 41.9 44.0 46.1 48.2 50.3 52.4 54.5 56.6 58.7 60.8 62.9 65.0 67.1 69.2 71.3 73.4

72 32.2 34.3 36.5 38.6 40.8 42.9 45.1 47.2 49.4 51.5 53.7 55.8 58.0 60.1 62.3 64.4 66.5 68.7 70.8 73.0 75.1

76 32.9 35.1 37.3 39.5 41.7 43.9 46.1 48.3 50.5 52.7 54.9 57.1 59.3 61.5 63.7 65.9 68.1 70.3 72.5

80 33.7 35.9 38.2 40.4 42.7 44.9 47.2 49.4 51.7 53.9 56.2 58.4 60.7 62.9 65.1 67.4 69.6 71.9 74.1

84 34.4 36.7 39.0 41.3 43.6 45.9 48.2 50.5 52.8 55.1 57.4 59.7 62.0 64.3 66.6 68.9 71.2 73.5

88 35.2 37.5 39.9 42.2 44.6 46.9 49.3 51.6 54.0 56.3 58.7 61.0 63.3 65.7 68.0 70.4 72.7

92 35.9 38.3 40.7 43.1 45.5 47.9 50.3 52.7 55.1 57.5 59.9 62.3 64.7 67.1 69.5 71.9 74.3

96 36.7 39.1 41.6 44.0 46.5 48.9 51.4 53.8 56.3 58.7 61.2 63.6 66.0 68.5 70.9 73.4

100 37.4 39.9 42.4 44.9 47.4 49.9 52.4 54.9 57.4 59.9 62.4 64.9 67.4 69.9 72.4 74.9

110 39.3 41.9 44.6 47.2 49.8 52.4 55.0 57.7 60.3 62.9 65.5 68.1 70.8 73.4 76.0

120 41.2 43.9 46.7 49.4 52.2 54.9 57.7 60.4 63.1 65.9 68.6 71.4 74.1 76.9

130 43.1 45.9 48.8 51.7 54.5 57.4 60.3 63.1 66.0 68.9 71.8 74.6 77.5 80.4

140 44.9 47.9 50.9 53.9 56.9 59.9 62.9 65.9 68.9 71.9 74.9 77.9 80.9

150 46.8 49.9 53.0 56.2 59.3 62.4 65.5 68.6 71.8 74.9 78.0 81.1 84.2
3–15

Working Qualities

The ease of working wood with hand tools generally varies

directly with the specific gravity of the wood. The lower

the specific gravity, the easier it is to cut the wood with a

sharp tool. Tables 4–3 and 4–5 (Ch. 4) list the specific

gravity values for various native and imported species. These

specific gravity values can be used as a general guide to the

ease of working with hand tools.

A wood species that is easy to cut does not necessarily

develop a smooth surface when it is machined. Consequently, tests have been made with many U.S. hardwoods to

evaluate them for machining properties. Results of these

evaluations are given in Table 3–8.

Machining evaluations are not available for many imported

woods. However, three major factors other than density can

affect production of smooth surfaces during wood machining:

interlocked and variable grain, hard mineral deposits, and

reaction wood, particularly tension wood in hardwoods.

Interlocked grain is characteristic of a few domestic species

and many tropical species, and it presents difficulty in planing quartersawn boards unless attention is paid to feed rate,

cutting angles, and sharpness of knives. Hard deposits in the

cells, such as calcium carbonate and silica, can have a pronounced dulling effect on all cutting edges. This dulling

effect becomes more pronounced as the wood is dried to the

usual in-service requirements. Tension wood can cause

fibrous and fuzzy surfaces. It can be very troublesome in

species of lower density. Reaction wood can also be responsible for the pinching effect on saws as a result of stress relief.

The pinching can result in burning and dulling of the saw

teeth. Table 3–9 lists some imported species that have irregular grain, hard deposits, or tension wood.

Decay Resistance

Wood kept constantly dry does not decay. In addition, if

wood is kept continuously submerged in water, even for long

periods of time, it does not decay significantly by the common decay fungi regardless of the wood species or the presence of sapwood. Bacteria and certain soft-rot fungi can attack

submerged wood, but the resulting deterioration is very

slow. A large proportion of wood in use is kept so dry at all

times that it lasts indefinitely.

Moisture and temperature, which vary greatly with local

conditions, are the principal factors that affect rate of decay.

Wood deteriorates more rapidly in warm, humid areas than

in cool or dry areas. High altitudes, as a rule, are less favorable to decay than are low altitudes because the average

temperatures at higher altitudes are lower and the growing

season for fungi, which cause decay, is shorter. The heartwood of common native species of wood has varying degrees

of natural decay resistance. Untreated sapwood of substantially all species has low resistance to decay and usually has

a short service life under decay-producing conditions. The

decay resistance of heartwood is greatly affected by

differences in the preservative qualities of the wood extractives, the attacking fungus, and the conditions of exposure.

Considerable difference in service life can be obtained from

pieces of wood cut from the same species, even from the

same tree, and used under apparently similar conditions.

There are further complications because, in a few species,

such as the spruces and the true firs (not Douglas-fir), heartwood and sapwood are so similar in color that they cannot

be easily distinguished.

Marketable sizes of some species, such as the southern and

eastern pines and baldcypress, are becoming primarily second

growth and contain a high percentage of sapwood. Consequently, substantial quantities of heartwood lumber of these

species are not available.

Precise ratings of decay resistance of heartwood of different

species are not possible because of differences within species

and the variety of service conditions to which wood is exposed. However, broad groupings of many native species,

based on service records, laboratory tests, and general experience, are helpful in choosing heartwood for use under conditions favorable to decay. Table 3–10 lists such groupings for

some domestic and imported woods, according to their

average heartwood decay resistance. The extent of variations

in decay resistance of individual trees or wood samples of a

species is much greater for most of the more resistant species

than for the slightly or nonresistant species.

Where decay hazards exist, heartwood of species in the resistant or very resistant category generally gives satisfactory

service, but heartwood of species in the other two categories

will usually require some form of preservative treatment. For

mild decay conditions, a simple preservative treatment—

such as a short soak in preservative after all cutting and

boring operations are complete—will be adequate for wood

low in decay resistance. For more severe decay hazards,

pressure treatment is often required. Even the very decayresistant species may require preservative treatment for important structural uses or other uses where failure would

endanger life or require expensive repairs. Preservative treatments and methods for wood are discussed in Chapter 14.

Thermal Properties

Four important thermal properties of wood are thermal conductivity, heat capacity, thermal diffusivity, and coefficient of

thermal expansion.

Conductivity

Thermal conductivity is a measure of the rate of heat flow

through one unit thickness of a material subjected to a temperature gradient. The thermal conductivity of common

structural woods is much less than the conductivity of metals

with which wood often is mated in construction. It is about

two to four times that of common insulating material. For

example, the conductivity of structural softwood lumber at

12% moisture content is in the range of 0.1 to 1.4 W/(m⋅K)

(0.7 to 1.0 Btu⋅in/(h⋅ft2⋅

o

F)) compared with 216 (1,500) for

aluminum, 45 (310) for steel, 0.9 (6) for concrete, 1 (7) for

glass, 0.7 (5) for plaster, and 0.036 (0.25) for mineral wool.
 3–16

Table 3–8. Some machining and related properties of selected domestic hardwoods

Kind of wooda

Planing:

perfect

pieces

(%)

Shaping:

good to

excellent

pieces

(%)

Turning:

fair to

excellent

pieces

(%)

Boring:

good to

excellent

pieces

 (%)

Mortising:

 fair to

excellent

pieces

(%)

Sanding:

good to

excellent

pieces

(%)

Steam

bending:

unbroken

pieces

 (%)

Nail splitting:

pieces free

from complete

splits

(%)

Screw splitting:

pieces free

from complete

splits

(%)

Alder, red 61 20 88 64 52 — — — —

Ash 75 55 79 94 58 75 67 65 71

Aspen 26 7 65 78 60 — — — —

Basswood 64 10 68 76 51 17 2 79 68

Beech 83 24 90 99 92 49 75 42 58

Birch 63 57 80 97 97 34 72 32 48

Birch, paper 47 22 — — — — — — —

Cherry, black 80 80 88 100 100 — — — —

Chestnut 74 28 87 91 70 64 56 66 60

Cottonwoodb

21 3 70 70 52 19 44 82 78

Elm, softb

33 13 65 94 75 66 74 80 74

Hackberry 74 10 77 99 72 — 94 63 63

Hickory 76 20 84 100 98 80 76 35 63

Magnolia 65 27 79 71 32 37 85 73 76

Maple, bigleaf 52 56 80 100 80 — — — —

Maple, hard 54 72 82 99 95 38 57 27 52

Maple, soft 41 25 76 80 34 37 59 58 61

Oak, red 91 28 84 99 95 81 86 66 78

Oak, white 87 35 85 95 99 83 91 69 74

Pecan 88 40 89 100 98 — 78 47 69

Sweetgumb

51 28 86 92 58 23 67 69 69

Sycamoreb

22 12 85 98 96 21 29 79 74

Tanoak 80 39 81 100 100 — — — —

Tupelo, waterb

55 52 79 62 33 34 46 64 63

Tupelo, blackb

48 32 75 82 24 21 42 65 63

Walnut, black 62 34 91 100 98 — 78 50 59

Willow 52 5 58 71 24 24 73 89 62

Yellow-poplar 70 13 81 87 63 19 58 77 67

a

Commercial lumber nomenclature.

b

Interlocked grain present.
3–17

The thermal conductivity of wood is affected by a number of

basic factors: density, moisture content, extractive content,

grain direction, structural irregularities such as checks and

knots, fibril angle, and temperature. Thermal conductivity

increases as density, moisture content, temperature, or extractive content of the wood increases. Thermal conductivity is

nearly the same in the radial and tangential directions with

respect to the growth rings. Conductivity along the grain has

been reported as 1.5 to 2.8 times greater than conductivity

across the grain, with an average of about 1.8, but reported

values vary widely.

For moisture content levels below 25%, approximate thermal

conductivity k across the grain can be calculated with a linear

equation of the form

 k = G(B + CM) + A (3–7)

where G is specific gravity based on ovendry weight and

volume at a given moisture content M (%) and A, B, and C

are constants. For specific gravity >0.3, temperatures around

24°C (75°F), and moisture content values <25%,

A = 0.01864, B = 0.1941, and C = 0.004064 (with k in

W/(m·K)) (or A = 0.129, B = 1.34, and C = 0.028 with k in

Btu·in/(h·ft2

·F)). Equation (3–7) was derived from measurements made by several researchers on a variety of species.

Table 3–11 provides average approximate conductivity

values for selected wood species, based on Equation (3–7).

However, actual conductivity may vary as much as 20%

from the tabulated values.

Although thermal conductivity measurements have been

made at moisture content values >25%, measurements have

been few in number and generally lacking in accuracy.

Therefore, we do not provide values for moisture content

values >25%.

The effect of temperature on thermal conductivity is relatively

minor: conductivity increases about 2% to 3% per 10°C

(1% to 2% per 10°F).

Heat Capacity

Heat capacity is defined as the amount of energy needed to

increase one unit of mass (kg or lb) one unit in temperature

(K or °F). The heat capacity of wood depends on the temperature and moisture content of the wood but is practically

independent of density or species. Heat capacity of dry wood

cp0 (kJ/kg·K, Btu/lb·°F) is approximately related to temperature t (K, °F ) by

cp0 = 0.1031 + 0.003867t (metric) (3–8a)

cp0 = 0.2605 + 0.0005132t (inch–pound) (3–8b)

The heat capacity of wood that contains water is greater than

that of dry wood. Below fiber saturation, it is the sum of the

heat capacity of the dry wood and that of water (cpw) and an

additional adjustment factor Ac that accounts for the additional energy in the wood–water bond:

cp = (cp0 + 0.01Mcpw)/(1 + 0.01M) + Ac (3–9)

where M is moisture content (%). The heat capacity of water

is about 4.19 kJ/kg·K (1 Btu/lb·°F). The adjustment factor

can be derived from

 Ac = M(b1 + b2t + b3M) (3–10)

with b1 = −0.06191, b2 = 2.36 × 10−4, and b3 = −1.33 × 10−4

with temperature in kelvins (b1 = −4.23 × 10−4,

b2 = 3.12 × 10−5, and b3 = −3.17 × 10−5 with temperature in

°F). These formulas are valid for wood below fiber saturation

at temperatures between 7°C (45°F) and 147°C (297°F).

Representative values for heat capacity can be found in

Table 3–12. The moisture above fiber saturation contributes

to specific heat according to the simple rule of mixtures.

Thermal Diffusivity

Thermal diffusivity is a measure of how quickly a material

can absorb heat from its surroundings; it is the ratio of thermal conductivity to the product of density and heat capacity.

Diffusivity is defined as the ratio of conductivity to the product of heat capacity and density; therefore, conclusions regarding its variation with temperature and density are often

based on calculating the effect of these variables on heat

capacity and conductivity. Because of the low thermal

conductivity and moderate density and heat capacity of

wood, the thermal diffusivity of wood is much lower than

that of other structural materials, such as metal, brick, and

stone. A typical value for wood is 0.161 × 10−6

 m2/s

(0.00025 in2/s) compared with 12.9 × 10−6 m2/s (0.02 in2/s)

for steel and 0.645 × 10−6 m2/s (0.001 in2/s) for mineral

wool. For this reason, wood does not feel extremely hot or

cold to the touch as do some other materials.

Table 3–9. Some characteristics of imported woods

that may affect machining

Irregular and

interlocked grain

Hard mineral

deposits (silica

or calcium carbonate)

Reaction wood

(tension wood)

Avodire Angelique Andiroba

Courbaril Iroko Banak

Ekop Kapur Cativo

Goncalo alves Keruing (Apitong) Ceiba

Ipe Manbarklak Hura

Iroko Marishballi Mahogany, African

Jarrah Mersawa Mahogany, American

Kapur Okoume Sande

Karri Rosewood, Indian Spanish-cedar

Keruing (Apitong) Teak

Kokrodua

Lauan/meranti

Lignumvitae

Limba

Mahogany, African

Merasawa

Obeche

Okoume

Rosewood, Indian

Santa Maria

Sapele
 3–18

Table 3–10. Grouping of some domestic and imported woods according to average heartwood

decay resistance

Resistant or very resistant Moderately resistant Slightly or nonresistant

Domestic

Baldcypress, old growth Baldcypress, young growth Alder, red

Catalpa Douglas-fir Ashes

Cedar Larch, western Aspens

Atlantic white Pine, longleaf, old growth Beech

Eastern redcedar Pine, slash, old growth Birches

Incense Redwood, young growth Buckeye

Northern white Tamarack Butternut

Port-Orford Cottonwood

Western redcedar Elms

Yellow Pine, eastern white, old growth Basswood

Cherry, black Firs, true

Chestnut Hackberry

Cypress, Arizona Hemlocks

Junipers Hickories

Locust, Magnolia

Blacka Maples

Honeylocust Pines (other than those listed)b

Mesquite Spruces

Mulberry, reda Sweetgum

Oaks, whiteb Sycamore

Osage orangea Tanoak

Redwood, old growth Willows

Sassafras Yellow-poplar

Walnut, black

Yew, Pacifica

Imported

Aftotmosia (Kokrodua) Andiroba Balsa

Angeliquea Avodire Banak

Apamate (Roble) Benge Cativo

Azobea Bubinga Ceiba

Balataa Ehie Hura

Balaub Ekop Jelutong

Courbaril Keruingb Limba

Determa Mahogany, African Meranti, light redb

Goncalo alvesa Meranti, dark redb Meranti, yellowb

Greenhearta Mersawab Meranti, whiteb

Ipe (lapacho)a Sapele Obeche

Iroko Teak , young growth Okoume

Jarraha Tornillo Parana pine

Kapur Ramin

Karri Sande

Kempas Sepitir

Lignumvitaea Seraya, white

Mahogany, American

Manni

Purplehearta

Spanish-cedar

Sucupira

Teak, old growtha

Wallaba

a

Exceptionally high decay resistance.

b

More than one species included, some of which may vary in resistance from that indicated.
3–19

Table 3–11. Thermal conductivity of selected hardwoods and softwoodsa

Conductivity

(W/m·K (Btu·in/h·ft2·°F))

Resistivity

(K·m/W (h·ft2·°F/Btu·in))

Species Specific gravity Ovendry 12% MC Ovendry 12% MC

Hardwoods

Ash

Black 0.53 0.12 (0.84) 0.15 (1.0) 8.2 (1.2) 6.8 (0.98)

White 0.63 0.14 (0.98) 0.17 (1.2) 7.1 (1.0) 5.8 (0.84)

Aspen

Big tooth 0.41 0.10 (0.68) 0.12 (0.82) 10 (1.5) 8.5 (1.2)

Quaking 0.40 0.10 (0.67) 0.12 (0.80) 10 (1.5) 8.6 (1.2)

Basswood, American 0.38 0.092 (0.64) 0.11 (0.77) 11 (1.6) 9.0 (1.3)

Beech, American 0.68 0.15 (1.0) 0.18 (1.3) 6.6 (0.96) 5.4 (0.78)

Birch

Sweet 0.71 0.16 (1.1) 0.19 (1.3) 6.4 (0.92) 5.2 (0.76)

Yellow 0.66 0.15 (1.0) 0.18 (1.2) 6.8 (0.98) 5.6 (0.81)

Cherry, black 0.53 0.12 (0.84) 0.15 (1.0) 8.2 (1.2) 6.8 (0.98)

Chestnut, American 0.45 0.11 (0.73) 0.13 (0.89) 9.4 (1.4) 7.8 (1.1)

Cottonwood

Black 0.35 0.087 (0.60) 0.10 (0.72) 12 (1.7) 9.6 (1.4)

Eastern 0.43 0.10 (0.71) 0.12 (0.85) 9.8 (1.4) 8.1 (1.2)

Elm

American 0.54 0.12 (0.86) 0.15 (1.0) 8.1 (1.2) 6.7 (0.96)

Rock 0.67 0.15 (1.0) 0.18 (1.3) 6.7 (0.97) 5.5 (0.80)

Slippery 0.56 0.13 (0.88) 0.15 (1.1) 7.9 (1.1) 6.5 (0.93)

Hackberry 0.57 0.13 (0.90) 0.16 (1.1) 7.7 (1.1) 6.4 (0.92)

Hickory, pecan 0.69 0.15 (1.1) 0.19 (1.3) 6.6 (0.95) 5.4 (0.77)

Hickory, true

Mockernut 0.78 0.17 (1.2) 0.21 (1.4) 5.9 (0.85) 4.8 (0.69)

Shagbark 0.77 0.17 (1.2) 0.21 (1.4) 5.9 (0.86) 4.9 (0.70)

Magnolia, southern 0.52 0.12 (0.83) 0.14 (1.0) 8.4 (1.2) 6.9 (1.0)

Maple

Black 0.60 0.14 (0.94) 0.16 (1.1) 7.4 (1.1) 6.1 (0.88)

Red 0.56 0.13 (0.88) 0.15 (1.1) 7.9 (1.1) 6.5 (0.93)

Silver 0.50 0.12 (0.80) 0.14 (0.97) 8.6 (1.2) 7.1 (1.0)

Sugar 0.66 0.15 (1.0) 0.18 (1.2) 6.8 (0.98) 5.6 (0.81)

Oak, red

Black 0.66 0.15 (1.0) 0.18 (1.2) 6.8 (0.98) 5.6 (0.81)

Northern red 0.65 0.14 (1.0) 0.18 (1.2) 6.9 (1.0) 5.7 (0.82)

Southern red 0.62 0.14 (0.96) 0.17 (1.2) 7.2 (1.0) 5.9 (0.85)

Oak, white

Bur 0.66 0.15 (1.0) 0.18 (1.2) 6.8 (0.98) 5.6 (0.81)

White 0.72 0.16 (1.1) 0.19 (1.3) 6.3 (0.91) 5.2 (0.75)

Sweetgum 0.55 0.13 (0.87 0.15 (1.1) 8.0 (1.2) 6.6 (0.95)

Sycamore, American 0.54 0.12 (0.86) 0.15 (1.0) 8.1 (1.2) 6.7 (0.96)

Tupelo

Black 0.54 0.12 (0.86) 0.15 (1.0) 8.1 (1.2) 6.7 (0.96)

Water 0.53 0.12 (0.84) 0.15 (1.0) 8.2 (1.2) 6.8 (0.98)

Yellow-poplar 0.46 0.11 (0.75) 0.13 (0.90) 9.3 (1.3) 7.7 (1.1)
 3–20

Table 3–11. Thermal conductivity of selected hardwoods and softwoodsa—con.

Conductivity

(W/m·K (Btu·in/h·ft2·°F))

Resistivity

(W/m·K (h·ft2·°F/Btu·in))

Species Specific gravity Ovendry 12% MC Ovendry 12% MC

Softwoods

Baldcypress 0.47 0.11 (0.76) 0.13 (0.92) 9.1 (1.3) 7.5 (1.1)

Cedar

Atlantic white 0.34 0.085 (0.59) 0.10 (0.70) 12 (1.7) 9.9 (1.4)

Eastern red 0.48 0.11 (0.77) 0.14 (0.94) 8.9 (1.3) 7.4 (1.1)

Northern white 0.31 0.079 (0.55) 0.094 (0.65) 13 (1.8) 11 (1.5)

Port-Orford 0.43 0.10 (0.71) 0.12 (0.85) 9.8 (1.4) 8.1 (1.2)

Western red 0.33 0.083 (0.57) 0.10 (0.68) 12 (1.7) 10 (1.5)

Yellow 0.46 0.11 (0.75) 0.13 (0.90) 9.3 (1.3) 7.7 (1.1)

Douglas-fir

Coast 0.51 0.12 (0.82) 0.14 (0.99) 8.5 (1.2) 7.0 (1.0)

Interior north 0.50 0.12 (0.80) 0.14 (0.97) 8.6 (1.2) 7.1 (1.0)

Interior west 0.52 0.12 (0.83) 0.14 (1.0) 8.4 (1.2) 6.9 1.0)

Fir

Balsam 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)

White 0.41 0.10 (0.68) 0.12 (0.82) 10 (1.5) 8.5 (1.2)

Hemlock

Eastern 0.42 0.10 (0.69) 0.12 (0.84) 10 (1.4) 8.3 (1.2)

Western 0.48 0.11 (0.77) 0.14 (0.94) 8.9 (1.3) 7.4 (1.1)

Larch, western 0.56 0.13 (0.88) 0.15 (1.1) 7.9 (1.1) 6.5 (0.93)

Pine

Eastern white 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)

Jack 0.45 0.11 (0.73) 0.13 (0.89) 9.4 (1.4) 7.8 (1.1)

Loblolly 0.54 0.12 (0.86) 0.15 (1.0) 8.1 (1.2) 6.7 (0.96)

Lodgepole 0.43 0.10 (0.71) 0.12 (0.85) 9.8 (1.4) 8.1 (1.2)

Longleaf 0.62 0.14 (0.96) 0.17 (1.2) 7.2 (1.0) 5.9 (0.85)

Pitch 0.53 0.12 (0.84) 0.15 (1.0) 8.2 (1.2) 6.8 (0.98)

Ponderosa 0.42 0.10 (0.69) 0.12 (0.84) 10 (1.4) 8.3 (1.2)

Red 0.46 0.11 (0.75) 0.13 (0.90) 9.3 (1.3) 7.7 (1.1)

Shortleaf 0.54 0.12 (0.86) 0.15 (1.0) 8.1 (1.2) 6.7 (0.96)

Slash 0.61 0.14 (0.95) 0.17 (1.2) 7.3 (1.1) 6.0 (0.86)

Sugar 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)

Western white 0.40 0.10 (0.67) 0.12 (0.80) 10 (1.5) 8.6 (1.2)

Redwood

Old growth 0.41 0.10 (0.68) 0.12 (0.82) 10 (1.5) 8.5 (1.2)

Young growth 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)

Spruce

Black 0.43 0.10 (0.71) 0.12 (0.85) 9.8 (1.4) 8.1 (1.2)

Engelmann 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)

Red 0.42 0.10 (0.69) 0.12 (0.84) 10 (1.4) 8.3 (1.2)

Sitka 0.42 0.10 (0.69) 0.12 (0.84) 10 (1.4) 8.3 (1.2)

White 0.37 0.090 (0.63) 0.11 (0.75) 11 (1.6) 9.2 (1.3)

a

Values in this table are approximate and should be used with caution; actual conductivities may vary by as much as 20%.

 The specific gravities also do not represent species averages.
3–21

Thermal Expansion Coefficient

The coefficient of thermal expansion is a measure of the

change of dimension caused by temperature change. The

thermal expansion coefficients of completely dry wood are

positive in all directions; that is, wood expands on heating

and contracts on cooling. Limited research has been carried

out to explore the influence of wood property variability on

thermal expansion. The thermal expansion coefficient of

ovendry wood parallel to the grain appears to be independent

of specific gravity and species. In tests of both hardwoods

and softwoods, the parallel-to-grain values have ranged from

about 0.000031 to 0.0000045 per K (0.0000017 to

0.0000025 per °F).

The thermal expansion coefficients across the grain (radial

and tangential) are proportional to wood specific gravity.

These coefficients range from about 5 to more than 10 times

greater than the parallel-to-grain coefficients and are of more

practical interest. The radial and tangential thermal expansion coefficients for ovendry wood, αr and αt, can be approximated by the following equations, over an ovendry

specific gravity range of about 0.1 to 0.8:

αr = (32.4G + 9.9)10−6 per K (3–11a)

αr = (18G + 5.5)10−6 per °F (3–11b)

αt = (32.4G + 18.4)10−6 per K (3–12a)

αt = (18G + 10.2)10−6 per °F (3–12b)

Thermal expansion coefficients can be considered independent of temperature over the temperature range of −51.1°C to

54.4°C (−60°F to 130°F).

Wood that contains moisture reacts differently to varying

temperature than does dry wood. When moist wood is

heated, it tends to expand because of normal thermal expansion and to shrink because of loss in moisture content. Unless the wood is very dry initially (perhaps 3% or 4% moisture content or less), shrinkage caused by moisture loss on

heating will be greater than thermal expansion, so the net

dimensional change on heating will be negative. Wood at

intermediate moisture levels (about 8% to 20%) will expand

when first heated, then gradually shrink to a volume smaller

than the initial volume as the wood gradually loses water

while in the heated condition.

Even in the longitudinal (grain) direction, where dimensional

change caused by moisture change is very small, such

changes will still predominate over corresponding dimensional changes as a result of thermal expansion unless the

wood is very dry initially. For wood at usual moisture

levels, net dimensional changes will generally be negative

after prolonged heating.

Electrical Properties

The most important electrical properties of wood are conductivity, dielectric constant, and dielectric power factor. The

conductivity of a material determines the electric current that

will flow when the material is placed under a given voltage

gradient. The dielectric constant of a nonconducting material

determines the amount of potential electric energy, in the

form of induced polarization, that is stored in a given volume

of the material when that material is placed in an electric

field. The power factor of a nonconducting material determines the fraction of stored energy that is dissipated as heat

when the material experiences a complete polarize–depolarize

cycle.

Examples of industrial wood processes and applications in

which electrical properties of wood are important include

crossarms and poles for high voltage powerlines, utility

worker’s tools, and the heat-curing of adhesives in wood

products by high frequency electric fields. Moisture meters

for wood utilize the relationship between electrical properties

and moisture content to estimate the moisture content.

Conductivity

The electrical conductivity of wood varies slightly with

applied voltage and approximately doubles for each temperature increase of 10°C (18°F). The electrical conductivity of

wood (or its reciprocal, resistivity) varies greatly with moisture content, especially below the fiber saturation point. As

the moisture content of wood increases from near zero to fiber

saturation, electrical conductivity increases (resistivity decreases) by 1010 to 1013 times. Resistivity is about 1014 to

1016 Ω·m for ovendry wood and 103 to 104 Ω·m for wood at

fiber saturation. As the moisture content increases from fiber

saturation to complete saturation of the wood structure, the

Table 3–12. Heat capacity of solid wood at selected temperatures and moisture contents

Temperature Specific heat (kJ/kg·K (Btu/lb·°F))

(K) (°C (°F)) Ovendry 5% MC 12% MC 20% MC

280 7 (45) 1.2 (0.28) 1.3 (0.32) 1.5 (0.37) 1.7 (0.41)

290 17 (75) 1.2 (0.29) 1.4 (0.33) 1.6 (0.38) 1.8 (0.43)

300 27 (80) 1.3 (0.30) 1.4 (0.34) 1.7 (0.40) 1.9 (0.45)

320 47 (116) 1.3 (0.32) 1.5 (0.37) 1.8 (0.43) 2.0 (0.49)

340 67 (152) 1.4 (0.34) 1.6 (0.39) 1.9 (0.46) 2.2 (0.52)

360 87 (188) 1.5 (0.36) 1.7 (0.41) 2.0 (0.49) 2.3 (0.56)
 3–22

further increase in conductivity is smaller and erratic, generally amounting to less than a hundredfold.

Figure 3–7 illustrates the change in resistance along the grain

with moisture content, based on tests of many domestic

species. Variability between test specimens is illustrated by

the shaded area. Ninety percent of the experimental data

points fall within this area. The resistance values were obtained using a standard moisture meter electrode at 27°C

(80°F). Conductivity is greater along the grain than across

the grain and slightly greater in the radial direction than in

the tangential direction. Relative conductivity values in the

longitudinal, radial, and tangential directions are related by

the approximate ratio of 1.0:0.55:0.50.

When wood contains abnormal quantities of water-soluble

salts or other electrolytic substances, such as preservative or

fire-retardant treatment, or is in prolonged contact with

seawater, electrical conductivity can be substantially increased. The increase is small when the moisture content of

the wood is less than about 8% but quickly increases as the

moisture content exceeds 10% to 12%.

Dielectric Constant

The dielectric constant is the ratio of the dielectric permittivity of the material to that of free space; it is essentially a

measure of the potential energy per unit volume stored in the

material in the form of electric polarization when the material

is in a given electric field. As measured by practical tests, the

dielectric constant of a material is the ratio of the capacitance

of a capacitor using the material as the dielectric to the

capacitance of the same capacitor using free space as the

dielectric.

The dielectric constant of ovendry wood ranges from about

2 to 5 at room temperature and decreases slowly but steadily

with increasing frequency of the applied electric field. It

increases as either temperature or moisture content increases,

with a moderate positive interaction between temperature and

moisture. There is an intense negative interaction between

moisture and frequency. At 20 Hz, the dielectric constant

may range from about 4 for dry wood to near 1,000,000 for

wet wood; at 1 kHz, from about 4 when dry to about 5,000

when wet; and at 1 MHz, from about 3 when dry to about

100 when wet. The dielectric constant is larger for polarization parallel to the grain than across the grain.

Dielectric Power Factor

When a nonconductor is placed in an electric field, it absorbs

and stores potential energy. The amount of energy stored per

unit volume depends upon the dielectric constant and the

magnitude of the applied field. An ideal dielectric releases all

this energy to the external electric circuit when the field is

removed, but practical dielectrics dissipate some of the energy as heat. The power factor is a measure of that portion of

the stored energy converted to heat. Power factor values

always fall between zero and unity. When the power factor

does not exceed about 0.1, the fraction of the stored energy

that is lost in one charge–discharge cycle is approximately

equal to 2π times the power factor of the dielectric; for larger

power factors, this fraction is approximated simply by the

power factor itself.

The power factor of wood is large compared with that of inert

plastic insulating materials, but some materials, for example

some formulations of rubber, have equally large power factors. The power factor of wood varies from about 0.01 for

dry, low density woods to as large as 0.95 for dense woods

at high moisture levels. The power factor is usually, but not

always, greater for electric fields along the grain than across

the grain.

The power factor of wood is affected by several factors, including frequency, moisture content, and temperature. These

factors interact in complex ways to cause the power factor to

have maximum and minimum values at various combinations of these factors.

Coefficient of Friction

The coefficient of friction depends on the moisture content of

the wood and the roughness of the surface. It varies little

with species except for those species, such as lignumvitae,

that contain abundant oily or waxy extractives.

On most materials, the coefficients of friction for wood increase continuously as the moisture content of the wood

increases from ovendry to fiber saturation, then remain about

constant as the moisture content increases further until considerable free water is present. When the surface is flooded

with water, the coefficient of friction decreases.

6

6 8 10 12 14 16 18 20 22 24 26

-2

0

2

4

Moisture content (%)

Logarithm of electrical resistance (MΩ)

Figure 3–7. Change in electrical resistance of wood with

varying moisture content levels for many U.S. species;

90% of test values are represented by the shaded area.
3–23

Static coefficients of friction are generally greater than sliding

coefficients, and the latter depend somewhat on the speed of

sliding. Sliding coefficients of friction vary only slightly

with speed when the wood moisture content is less than

about 20%; at high moisture content, the coefficient of friction decreases substantially as the speed increases.

Coefficients of sliding friction for smooth, dry wood against

hard, smooth surfaces commonly range from 0.3 to 0.5; at

intermediate moisture content, 0.5 to 0.7; and near fiber

saturation, 0.7 to 0.9.

Nuclear Radiation

Radiation passing through matter is reduced in intensity

according to the relationship

 

II x = − 0 exp( μ ) (3–13)

where I is the reduced intensity of the beam at depth x in the

material, I0 is the incident intensity of a beam of radiation,

and μ, the linear absorption coefficient of the material, is the

fraction of energy removed from the beam per unit depth

traversed. When density is a factor of interest in energy

absorption, the linear absorption coefficient is divided by the

density of the material to derive the mass absorption coefficient. The absorption coefficient of a material varies with the

type and energy of radiation.

The linear absorption coefficient of wood for γ radiation is

known to vary directly with moisture content and density

and inversely with the γ ray energy. As an example, the

irradiation of ovendry yellow-poplar with 0.047-MeV γ rays

yields linear absorption coefficients ranging from about 0.065

to about 0.11 cm-1 over the ovendry specific gravity range of

about 0.33 to 0.62. An increase in the linear absorption

coefficient of about 0.01 cm-1 occurs with an increase in

moisture content from ovendry to fiber saturation. Absorption of γ rays in wood is of practical interest, in part for

measuring the density of wood.

The interaction of wood with β radiation is similar in

character to that with γ radiation, except that the absorption

coefficients are larger. The linear absorption coefficient of

wood with a specific gravity of 0.5 for a 0.5-MeV β ray

is about 3.0 cm−1. The result of the larger coefficient is that

even very thin wood products are virtually opaque to β rays.

The interaction of neutrons with wood is of interest because

wood and the water it contains are compounds of hydrogen,

and hydrogen has a relatively large probability of interaction

with neutrons. Higher energy neutrons lose energy much

more quickly through interaction with hydrogen than with

other elements found in wood. Lower energy neutrons that

result from this interaction are thus a measure of the hydrogen density of the specimen. Measurement of the lower

energy level neutrons can be related to the moisture content

of the wood.

When neutrons interact with wood, an additional result is

the production of radioactive isotopes of the elements present

in the wood. The radioisotopes produced can be identified by

the type, energy, and half-life of their emissions, and the

specific activity of each indicates the amount of isotope

present. This procedure, called neutron activation analysis,

provides a sensitive nondestructive method of analysis for

trace elements.

In the previous discussions, moderate radiation levels that

leave the wood physically unchanged have been assumed.

Very large doses of γ rays or neutrons can cause substantial

degradation of wood. The effect of large radiation doses on

the mechanical properties of wood is discussed in Chapter 4.

References

ASHRAE. 1981. American Society of Heating, Refrigeration, and Air-Conditioning Engineers handbook, 1981

fundamentals. Atlanta, GA: American Society of Heating,

Refrigeration, and Air-Conditioning Engineers.

ASTM. 1997. Standard methods for testing small clear

specimens of timber. ASTM D143. West Conshohocken,

PA: American Society for Testing and Materials.

Beall, F.C. 1968. Specific heat of wood—further research

required to obtain meaningful data. Res. Note FPL–RN–

0184. Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

James, W.L. 1975. Electric moisture meters for wood. Gen.

Tech. Rep. FPL–GTR–6. Madison WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Kleuters, W. 1964. Determining local density of wood by

beta ray method. Forest Products Journal. 14(9): 414.

Kollman, F.F.P.; Côté, W.A., Jr. 1968. Principles of

wood science and technology I—solid wood. New York,

Springer–Verlag New York, Inc.

Kubler, H.; Liang, L.; Chang, L.S. 1973. Thermal expansion of moist wood. Wood and Fiber. 5(3): 257–267.

Kukachka, B.F. 1970. Properties of imported tropical

woods. Res. Pap. FPL–RP–125. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Lin, R.T. 1967. Review of dielectric properties of wood and

cellulose. Forest Products Journal. 17(7): 61.

McKenzie, W.M.; Karpovich, H. 1968. Frictional behavior

of wood. Munich: Wood Science and Technology. 2(2):

138.

Murase, Y. 1980. Frictional properties of wood at high

sliding speed. Journal of the Japanese Wood Research

Society. 26(2): 61–65.

Panshin, A.J.; deZeeuw, C. 1980. Textbook of wood

technology. New York: McGraw–Hill. Vol. 1, 4th ed.
 3–24

Simpson, W.T., ed. 1991. Dry kiln operator’s manual.

Agric. Handb. 188. Washington, DC: U.S. Department of

Agriculture, Forest Service.

Simpson, W.T. 1993. Specific gravity, moisture content,

and density relationships for wood. U.S. Department of

Agriculture Gen. Tech. Rep. FPL–GTR–76. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Skaar, C. 1988. Wood–water relations. New York:

Springer–Verlag. New York, Inc.

Stamm, A.J.; Loughborough, W.K. 1935. Thermodynamics of the swelling of wood. Journal of Physical

Chemistry. 39(1): 121.

Steinhagen, H.P. 1977. Thermal conductive properties of

wood, green or dry, from −40° to +100°C: a literature review. Gen. Tech. Rep. FPL–GTR–9. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

TenWolde, A., McNatt, J.D., Krahn, L. 1988. Thermal

properties of wood panel products for use in buildings.

ORNL/Sub/87–21697/1. Oak Ridge, TN: Oak Ridge

National Laboratory.

Weatherwax, R.C.; Stamm, A.J. 1947. The coefficients of

thermal expansion of wood and wood products. Transactions

of American Society of Mechanical Engineers. 69(44):

421–432.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
4–1

Chapter 4

Mechanical Properties of Wood

David W. Green, Jerrold E. Winandy, and David E. Kretschmann

Contents

Orthotropic Nature of Wood 4–1

Elastic Properties 4–2

Modulus of Elasticity 4–2

Poisson’s Ratio 4–2

Modulus of Rigidity 4–3

Strength Properties 4–3

Common Properties 4–3

Less Common Properties 4–24

Vibration Properties 4–25

Speed of Sound 4–25

Internal Friction 4–26

Mechanical Properties of Clear Straight-Grained Wood 4–26

Natural Characteristics Affecting Mechanical Properties 4–27

Specific Gravity 4–27

Knots 4–27

Slope of Grain 4–28

Annual Ring Orientation 4–30

Reaction Wood 4–31

Juvenile Wood 4–32

Compression Failures 4–33

Pitch Pockets 4–33

Bird Peck 4–33

Extractives 4–33

Properties of Timber From Dead Trees 4–33

Effects of Manufacturing and Service Environments 4–34

Moisture Content 4–34

Temperature 4–35

Time Under Load 4–37

Aging 4–41

Exposure to Chemicals 4–41

Chemical Treatment 4–41

Nuclear Radiation 4–43

Mold and Stain Fungi 4–43

Decay 4–43

Insect Damage 4–43

References 4–44

he mechanical properties presented in this chapter

were obtained from tests of small pieces of wood

termed “clear” and “straight grained” because they

did not contain characteristics such as knots, cross grain,

checks, and splits. These test pieces did have anatomical

characteristics such as growth rings that occurred in consistent patterns within each piece. Clear wood specimens are

usually considered “homogeneous” in wood mechanics.

Many of the mechanical properties of wood tabulated in this

chapter were derived from extensive sampling and analysis

procedures. These properties are represented as the average

mechanical properties of the species. Some properties, such

as tension parallel to the grain, and all properties for some

imported species are based on a more limited number of

specimens that were not subjected to the same sampling and

analysis procedures. The appropriateness of these latter properties to represent the average properties of a species is uncertain; nevertheless, the properties represent the best information available.

Variability, or variation in properties, is common to all

materials. Because wood is a natural material and the tree is

subject to many constantly changing influences (such as

moisture, soil conditions, and growing space), wood properties vary considerably, even in clear material. This chapter

provides information, where possible, on the nature and

magnitude of variability in properties.

This chapter also includes a discussion of the effect of growth

features, such as knots and slope of grain, on clear wood

properties. The effects of manufacturing and service environments on mechanical properties are discussed, and their

effects on clear wood and material containing growth features

are compared. Chapter 6 discusses how these research results

have been implemented in engineering standards.

Orthotropic Nature of Wood

Wood may be described as an orthotropic material; that is, it

has unique and independent mechanical properties in the

directions of three mutually perpendicular axes: longitudinal,

radial, and tangential. The longitudinal axis L is parallel to

the fiber (grain); the radial axis R is normal to the growth

rings (perpendicular to the grain in the radial direction); and
 4–2

the tangential axis T is perpendicular to the grain but tangent

to the growth rings. These axes are shown in Figure 4–1.

Elastic Properties

Twelve constants (nine are independent) are needed to describe the elastic behavior of wood: three moduli of elasticity

E, three moduli of rigidity G, and six Poisson’s ratios μ.

The moduli of elasticity and Poisson’s ratios are related by

expressions of the form

 

 

μ μ ij

i

ji

E Ej

= ≠= , i j i, j L,R,T (4–1)

General relations between stress and strain for a homogeneous orthotropic material can be found in texts on anisotropic

elasticity.

Modulus of Elasticity

Elasticity implies that deformations produced by low stress

are completely recoverable after loads are removed. When

loaded to higher stress levels, plastic deformation or failure

occurs. The three moduli of elasticity, which are denoted by

EL, ER, and ET, respectively, are the elastic moduli along the

longitudinal, radial, and tangential axes of wood. These

moduli are usually obtained from compression tests; however, data for ER and ET are not extensive. Average values of

ER and ET for samples from a few species are presented in

Table 4–1 as ratios with EL; the Poisson’s ratios are shown

in Table 4–2. The elastic ratios, as well as the elastic constants themselves, vary within and between species and with

moisture content and specific gravity.

The modulus of elasticity determined from bending, EL,

rather than from an axial test, may be the only modulus of

elasticity available for a species. Average EL values obtained

from bending tests are given in Tables 4–3 to 4–5. Representative coefficients of variation of EL determined with bending

tests for clear wood are reported in Table 4–6. As tabulated,

EL includes an effect of shear deflection; EL from bending can

be increased by 10% to remove this effect approximately.

This adjusted bending EL can be used to determine ER and ET

based on the ratios in Table 4–1.

Poisson’s Ratio

When a member is loaded axially, the deformation perpendicular to the direction of the load is proportional to the

deformation parallel to the direction of the load. The ratio of

the transverse to axial strain is called Poisson’s ratio. The

Poisson’s ratios are denoted by μLR, μRL, μLT, μTL, μRT, and

μTR. The first letter of the subscript refers to direction of

applied stress and the second letter to direction of lateral

deformation. For example, μLR is the Poisson’s ratio for

deformation along the radial axis caused by stress along the

longitudinal axis. Average values of Poisson’s ratios for

samples of a few species are given in Table 4–2. Values for

μRL and μTL are less precisely determined than are those for

the other Poisson’s ratios. Poisson’s ratios vary within and

between species and are affected by moisture content and

specific gravity.

Radial

Tangential

Longitudinal

Fiber direction

Figure 4–1. Three principal axes of wood with

respect to grain direction and growth rings.

Table 4–1. Elastic ratios for various species at

approximately 12% moisture contenta

Species ET/EL ER/EL GLR/EL GLT/EL GRT/EL

Hardwoods

Ash, white 0.080 0.125 0.109 0.077 —

Balsa 0.015 0.046 0.054 0.037 0.005

Basswood 0.027 0.066 0.056 0.046 —

Birch, yellow 0.050 0.078 0.074 0.068 0.017

Cherry, black 0.086 0.197 0.147 0.097 —

Cottonwood, eastern 0.047 0.083 0.076 0.052 —

Mahogany, African 0.050 0.111 0.088 0.059 0.021

Mahogany, Honduras 0.064 0.107 0.066 0.086 0.028

Maple, sugar 0.065 0.132 0.111 0.063 —

Maple, red 0.067 0.140 0.133 0.074 —

Oak, red 0.082 0.154 0.089 0.081 —

Oak, white 0.072 0.163 0.086 — —

Sweet gum 0.050 0.115 0.089 0.061 0.021

Walnut, black 0.056 0.106 0.085 0.062 0.021

Yellow-poplar 0.043 0.092 0.075 0.069 0.011

Softwoods

Baldcypress 0.039 0.084 0.063 0.054 0.007

Cedar, northern white 0.081 0.183 0.210 0.187 0.015

Cedar, western red 0.055 0.081 0.087 0.086 0.005

Douglas-fir 0.050 0.068 0.064 0.078 0.007

Fir, subalpine 0.039 0.102 0.070 0.058 0.006

Hemlock, western 0.031 0.058 0.038 0.032 0.003

Larch, western 0.065 0.079 0.063 0.069 0.007

Pine

Loblolly 0.078 0.113 0.082 0.081 0.013

Lodgepole 0.068 0.102 0.049 0.046 0.005

Longleaf 0.055 0.102 0.071 0.060 0.012

Pond 0.041 0.071 0.050 0.045 0.009

Ponderosa 0.083 0.122 0.138 0.115 0.017

Red 0.044 0.088 0.096 0.081 0.011

Slash 0.045 0.074 0.055 0.053 0.010

Sugar 0.087 0.131 0.124 0.113 0.019

Western white 0.038 0.078 0.052 0.048 0.005

Redwood 0.089 0.087 0.066 0.077 0.011

Spruce, Sitka 0.043 0.078 0.064 0.061 0.003

Spruce, Engelmann 0.059 0.128 0.124 0.120 0.010

a

EL may be approximated by increasing modulus of elasticity values

 in Table 4–3 by 10%.
4–3

Modulus of Rigidity

The modulus of rigidity, also called shear modulus, indicates the resistance to deflection of a member caused by shear

stresses. The three moduli of rigidity denoted by GLR, GLT,

and GRT are the elastic constants in the LR, LT, and RT

planes, respectively. For example, GLR is the modulus of

rigidity based on shear strain in the LR plane and shear

stresses in the LT and RT planes. Average values of shear

moduli for samples of a few species expressed as ratios with

EL are given in Table 4–1. As with moduli of elasticity, the

moduli of rigidity vary within and between species and with

moisture content and specific gravity.

Strength Properties

Common Properties

Mechanical properties most commonly measured and represented as “strength properties” for design include modulus of

rupture in bending, maximum stress in compression parallel

to grain, compressive stress perpendicular to grain, and shear

strength parallel to grain. Additional measurements are often

made to evaluate work to maximum load in bending, impact

bending strength, tensile strength perpendicular to grain, and

hardness. These properties, grouped according to the broad

forest tree categories of hardwood and softwood (not correlated with hardness or softness), are given in Tables 4–3 to

4–5 for many of the commercially important species. Average

coefficients of variation for these properties from a limited

sampling of specimens are reported in Table 4–6.

Modulus of rupture—Reflects the maximum loadcarrying capacity of a member in bending and is proportional to maximum moment borne by the specimen.

Modulus of rupture is an accepted criterion of strength, although it is not a true stress because the formula by which

it is computed is valid only to the elastic limit.

Work to maximum load in bending—Ability to absorb

shock with some permanent deformation and more or less

injury to a specimen. Work to maximum load is a measure of the combined strength and toughness of wood under

bending stresses.

Compressive strength parallel to grain—Maximum

stress sustained by a compression parallel-to-grain specimen having a ratio of length to least dimension of less

than 11.

Compressive stress perpendicular to grain—Reported

as stress at proportional limit. There is no clearly defined

ultimate stress for this property.

Shear strength parallel to grain—Ability to resist internal slipping of one part upon another along the grain.

Values presented are average strength in radial and tangential shear planes.

Impact bending—In the impact bending test, a hammer

of given weight is dropped upon a beam from successively

increased heights until rupture occurs or the beam deflects

152 mm (6 in.) or more. The height of the maximum

drop, or the drop that causes failure, is a comparative value

that represents the ability of wood to absorb shocks that

cause stresses beyond the proportional limit.

Tensile strength perpendicular to grain—Resistance of

wood to forces acting across the grain that tend to split a

member. Values presented are the average of radial and

tangential observations.

Hardness—Generally defined as resistance to indentation

using a modified Janka hardness test, measured by the load

required to embed a 11.28-mm (0.444-in.) ball to one-half

its diameter. Values presented are the average of radial and

tangential penetrations.

Tensile strength parallel to grain—Maximum tensile

stress sustained in direction parallel to grain. Relatively

few data are available on the tensile strength of various

species of clear wood parallel to grain. Table 4–7 lists average tensile strength values for a limited number of

specimens of a few species. In the absence of sufficient tension test data, modulus of rupture values are sometimes

substituted for tensile strength of small, clear, straightgrained pieces of wood. The modulus of rupture is considered to be a low or conservative estimate of tensile strength

for clear specimens (this is not true for lumber).

Table 4–2. Poisson’s ratios for various species at

approximately 12% moisture content

Species μLR μLT μRT μTR μRL μTL

Hardwoods

Ash, white 0.371 0.440 0.684 0.360 0.059 0.051

Aspen, quaking 0.489 0.374 — 0.496 0.054 0.022

Balsa 0.229 0.488 0.665 0.231 0.018 0.009

Basswood 0.364 0.406 0.912 0.346 0.034 0.022

Birch, yellow 0.426 0.451 0.697 0.426 0.043 0.024

Cherry, black 0.392 0.428 0.695 0.282 0.086 0.048

Cottonwood, eastern 0.344 0.420 0.875 0.292 0.043 0.018

Mahogany, African 0.297 0.641 0.604 0.264 0.033 0.032

Mahogany, Honduras 0.314 0.533 0.600 0.326 0.033 0.034

Maple, sugar 0.424 0.476 0.774 0.349 0.065 0.037

Maple, red 0.434 0.509 0.762 0.354 0.063 0.044

Oak, red 0.350 0.448 0.560 0.292 0.064 0.033

Oak, white 0.369 0.428 0.618 0.300 0.074 0.036

Sweet gum 0.325 0.403 0.682 0.309 0.044 0.023

Walnut, black 0.495 0.632 0.718 0.378 0.052 0.035

Yellow-poplar 0.318 0.392 0.703 0.329 0.030 0.019

Softwoods

Baldcypress 0.338 0.326 0.411 0.356 — —

Cedar, northern white 0.337 0.340 0.458 0.345 — —

Cedar, western red 0.378 0.296 0.484 0.403 — —

Douglas-fir 0.292 0.449 0.390 0.374 0.036 0.029

Fir, subalpine 0.341 0.332 0.437 0.336 — —

Hemlock, western 0.485 0.423 0.442 0.382 — —

Larch, western 0.355 0.276 0.389 0.352 — —

Pine

Loblolly 0.328 0.292 0.382 0.362 — —

Lodgepole 0.316 0.347 0.469 0.381 — —

Longleaf 0.332 0.365 0.384 0.342 — —

Pond 0.280 0.364 0.389 0.320 — —

Ponderosa 0.337 0.400 0.426 0.359 — —

Red 0.347 0.315 0.408 0.308 — —

Slash 0.392 0.444 0.447 0.387 — —

Sugar 0.356 0.349 0.428 0.358 — —

Western white 0.329 0.344 0.410 0.334 — —

Redwood 0.360 0.346 0.373 0.400 — —

Spruce, Sitka 0.372 0.467 0.435 0.245 0.040 0.025

Spruce, Engelmann 0.422 0.462 0.530 0.255 0.083 0.058
 4–4

Table 4–3a. Strength properties of some commercially important woods grown in the United States (metric)a

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(kPa)

elasticityc

(MPa)

load

(kJ/m3)

bending

(mm)

to grain

(kPa)

to grain

(kPa)

grain

(kPa)

to grain

(kPa)

ness

(N)

Hardwoods

Alder, red Green 0.37 45,000 8,100 55 560 20,400 1,700 5,300 2,700 2,000

12% 0.41 68,000 9,500 58 510 40,100 3,000 7,400 2,900 2,600

Ash

Black Green 0.45 41,000 7,200 83 840 15,900 2,400 5,900 3,400 2,300

12% 0.49 87,000 11,000 103 890 41,200 5,200 10,800 4,800 3,800

Blue Green 0.53 66,000 8,500 101 — 24,800 5,600 10,600 — —

12% 0.58 95,000 9,700 99 — 48,100 9,800 14,000 — —

Green Green 0.53 66,000 9,700 81 890 29,000 5,000 8,700 4,100 3,900

12% 0.56 97,000 11,400 92 810 48,800 9,000 13,200 4,800 5,300

Oregon Green 0.50 52,000 7,800 84 990 24,200 3,700 8,200 4,100 3,500

12% 0.55 88,000 9,400 99 840 41,600 8,600 12,300 5,000 5,200

White Green 0.55 66,000 9,900 108 970 27,500 4,600 9,300 4,100 4,300

12% 0.60 103,000 12,000 115 1,090 51,100 8,000 13,200 6,500 5,900

Aspen

Bigtooth Green 0.36 37,000 7,700 39 — 17,200 1,400 5,000 — —

12% 0.39 63,000 9,900 53 — 36,500 3,100 7,400 — —

Quaking Green 0.35 35,000 5,900 44 560 14,800 1,200 4,600 1,600 1,300

12% 0.38 58,000 8,100 52 530 29,300 2,600 5,900 1,800 1,600

Basswood, American Green 0.32 34,000 7,200 37 410 15,300 1,200 4,100 1,900 1,100

12% 0.37 60,000 10,100 50 410 32,600 2,600 6,800 2,400 1,800

Beech, American Green 0.56 59,000 9,500 82 1,090 24,500 3,700 8,900 5,000 3,800

12% 0.64 103,000 11,900 104 1,040 50,300 7,000 13,900 7,000 5,800

Birch

Paper Green 0.48 44,000 8,100 112 1,240 16,300 1,900 5,800 2,600 2,500

12% 0.55 85,000 11,000 110 860 39,200 4,100 8,300 — 4,000

Sweet Green 0.60 65,000 11,400 108 1,220 25,800 3,200 8,500 3,000 4,300

12% 0.65 117,000 15,000 124 1,190 58,900 7,400 15,400 6,600 6,500

Yellow Green 0.55 57,000 10,300 111 1,220 23,300 3,000 7,700 3,000 3,600

12% 0.62 114,000 13,900 143 1,400 56,300 6,700 13,000 6,300 5,600

Butternut Green 0.36 37,000 6,700 57 610 16,700 1,500 5,200 3,000 1,700

12% 0.38 56,000 8,100 57 610 36,200 3,200 8,100 3,000 2,200

Cherry, black Green 0.47 55,000 9,000 88 840 24,400 2,500 7,800 3,900 2,900

12% 0.50 85,000 10,300 79 740 49,000 4,800 11,700 3,900 4,200

Chestnut, American Green 0.40 39,000 6,400 48 610 17,000 2,100 5,500 3,000 1,900

12% 0.43 59,000 8,500 45 480 36,700 4,300 7,400 3,200 2,400

Cottonwood

Balsam poplar Green 0.31 27,000 5,200 29 — 11,700 1,000 3,400 — —

12% 0.34 47,000 7,600 34 — 27,700 2,100 5,400 — —

Black Green 0.31 34,000 7,400 34 510 15,200 1,100 4,200 1,900 1,100

12% 0.35 59,000 8,800 46 560 31,000 2,100 7,200 2,300 1,600

Eastern Green 0.37 37,000 7,000 50 530 15,700 1,400 4,700 2,800 1,500

12% 0.40 59,000 9,400 51 510 33,900 2,600 6,400 4,000 1,900

Elm

American Green 0.46 50,000 7,700 81 970 20,100 2,500 6,900 4,100 2,800

12% 0.50 81,000 9,200 90 990 38,100 4,800 10,400 4,600 3,700

Rock Green 0.57 66,000 8,200 137 1,370 26,100 4,200 8,800 — —

12% 0.63 102,000 10,600 132 1,420 48,600 8,500 13,200 — —

Slippery Green 0.48 55,000 8,500 106 1,190 22,900 2,900 7,700 4,400 2,900

12% 0.53 90,000 10,300 117 1,140 43,900 5,700 11,200 3,700 3,800

Hackberry Green 0.49 45,000 6,600 100 1,220 18,300 2,800 7,400 4,300 3,100

12% 0.53 76,000 8,200 88 1,090 37,500 6,100 11,000 4,000 3,900
4–5

Table 4–3a. Strength properties of some commercially important woods grown in the United States (metric)a—con.

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(kPa)

elasticityc

(MPa)

load

(kJ/m3)

bending

(mm)

to grain

(kPa)

to grain

(kPa)

grain

(kPa)

to grain

(kPa)

ness

(N)

Hickory, pecan

Bitternut Green 0.60 71,000 9,700 138 1,680 31,500 5,500 8,500 — —

12% 0.66 118,000 12,300 125 1,680 62,300 11,600 — — —

Nutmeg Green 0.56 63,000 8,900 157 1,370 27,400 5,200 7,100 — —

12% 0.60 114,000 11,700 173 — 47,600 10,800 — — —

Pecan Green 0.60 68,000 9,400 101 1,350 27,500 5,400 10,200 4,700 5,800

12% 0.66 94,000 11,900 95 1,120 54,100 11,900 14,300 — 8,100

Water Green 0.61 74,000 10,800 130 1,420 32,100 6,100 9,900 — —

12% 0.62 123,000 13,900 133 1,350 59,300 10,700 — — —

Hickory, true

Mockernut Green 0.64 77,000 10,800 180 2,240 30,900 5,600 8,800 — —

12% 0.72 132,000 15,300 156 1,960 61,600 11,900 12,000 — —

Pignut Green 0.66 81,000 11,400 219 2,260 33,200 6,300 9,400 — —

12% 0.75 139,000 15,600 210 1,880 63,400 13,700 14,800 — —

Shagbark Green 0.64 76,000 10,800 163 1,880 31,600 5,800 10,500 — —

12% 0.72 139,000 14,900 178 1,700 63,500 12,100 16,800 — —

Shellbark Green 0.62 72,000 9,200 206 2,640 27,000 5,600 8,200 — —

12% 0.69 125,000 13,000 163 2,240 55,200 12,400 14,500 — —

Honeylocust Green 0.60 70,000 8,900 87 1,190 30,500 7,900 11,400 6,400 6,200

12% — 101,000 11,200 92 1,190 51,700 12,700 15,500 6,200 7,000

Locust, black Green 0.66 95,000 12,800 106 1,120 46,900 8,000 12,100 5,300 7,000

12% 0.69 134,000 14,100 127 1,450 70,200 12,600 17,100 4,400 7,600

Magnolia

Cucumber tree Green 0.44 51,000 10,800 69 760 21,600 2,300 6,800 3,000 2,300

12% 0.48 85,000 12,500 84 890 43,500 3,900 9,200 4,600 3,100

Southern Green 0.46 47,000 7,700 106 1,370 18,600 3,200 7,200 4,200 3,300

12% 0.50 77,000 9,700 88 740 37,600 5,900 10,500 5,100 4,500

Maple

Bigleaf Green 0.44 51,000 7,600 60 580 22,300 3,100 7,700 4,100 2,800

12% 0.48 74,000 10,000 54 710 41,000 5,200 11,900 3,700 3,800

Black Green 0.52 54,000 9,200 88 1,220 22,500 4,100 7,800 5,000 3,700

12% 0.57 92,000 11,200 86 1,020 46,100 7,000 12,500 4,600 5,200

Red Green 0.49 53,000 9,600 79 810 22,600 2,800 7,900 — 3,100

12% 0.54 92,000 11,300 86 810 45,100 6,900 12,800 — 4,200

Silver Green 0.44 40,000 6,500 76 740 17,200 2,600 7,200 3,900 2,600

12% 0.47 61,000 7,900 57 640 36,000 5,100 10,200 3,400 3,100

Sugar Green 0.56 65,000 10,700 92 1,020 27,700 4,400 10,100 — 4,300

12% 0.63 109,000 12,600 114 990 54,000 10,100 16,100 — 6,400

Oak, red

Black Green 0.56 57,000 8,100 84 1,020 23,900 4,900 8,400 — 4,700

12% 0.61 96,000 11,300 94 1,040 45,000 6,400 13,200 — 5,400

Cherrybark Green 0.61 74,000 12,300 101 1,370 31,900 5,200 9,100 5,500 5,500

12% 0.68 125,000 15,700 126 1,240 60,300 8,600 13,800 5,800 6,600

Laurel Green 0.56 54,000 9,600 77 990 21,900 3,900 8,100 5,300 4,400

12% 0.63 87,000 11,700 81 990 48,100 7,300 12,600 5,400 5,400

Northern red Green 0.56 57,000 9,300 91 1,120 23,700 4,200 8,300 5,200 4,400

12% 0.63 99,000 12,500 100 1,090 46,600 7,000 12,300 5,500 5,700

Pin Green 0.58 57,000 9,100 97 1,220 25,400 5,000 8,900 5,500 4,800

12% 0.63 97,000 11,900 102 1,140 47,000 7,000 14,300 7,200 6,700

Scarlet Green 0.60 72,000 10,200 103 1,370 28,200 5,700 9,700 4,800 5,300

12% 0.67 120,000 13,200 141 1,350 57,400 7,700 13,000 6,000 6,200

Southern red Green 0.52 48,000 7,900 55 740 20,900 3,800 6,400 3,300 3,800

12% 0.59 75,000 10,300 65 660 42,000 6,000 9,600 3,500 4,700

Water Green 0.56 61,000 10,700 77 990 25,800 4,300 8,500 5,700 4,500

12% 0.63 106,000 13,900 148 1,120 46,700 7,000 13,900 6,300 5,300
 4–6

Table 4–3a. Strength properties of some commercially important woods grown in the United States (metric)a—con.

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(kPa)

elasticityc

(MPa)

load

(kJ/m3)

bending

(mm)

to grain

(kPa)

to grain

(kPa)

grain

(kPa)

to grain

(kPa)

ness

(N)

Oak, red—con.

Willow Green 0.56 51,000 8,900 61 890 20,700 4,200 8,100 5,200 4,400

12% 0.69 100,000 13,100 101 1,070 48,500 7,800 11,400 — 6,500

Oak, white

Bur Green 0.58 50,000 6,100 74 1,120 22,700 4,700 9,300 5,500 4,900

12% 0.64 71,000 7,100 68 740 41,800 8,300 12,500 4,700 6,100

Chestnut Green 0.57 55,000 9,400 65 890 24,300 3,700 8,300 4,800 4,000

12% 0.66 92,000 11,000 76 1,020 47,100 5,800 10,300 — 5,000

Live Green 0.80 82,000 10,900 85 — 37,400 14,100 15,200 — —

12% 0.88 127,000 13,700 130 — 61,400 19,600 18,300 — —

Overcup Green 0.57 55,000 7,900 87 1,120 23,200 3,700 9,100 5,000 4,300

12% 0.63 87,000 9,800 108 970 42,700 5,600 13,800 6,500 5,300

Post Green 0.60 56,000 7,500 76 1,120 24,000 5,900 8,800 5,400 5,000

12% 0.67 91,000 10,400 91 1,170 45,300 9,900 12,700 5,400 6,000

Swamp chestnut Green 0.60 59,000 9,300 88 1,140 24,400 3,900 8,700 4,600 4,900

12% 0.67 96,000 12,200 83 1,040 50,100 7,700 13,700 4,800 5,500

Swamp white Green 0.64 68,000 11,000 100 1,270 30,100 5,200 9,000 5,900 5,200

12% 0.72 122,000 14,100 132 1,240 59,300 8,200 13,800 5,700 7,200

White Green 0.60 57,000 8,600 80 1,070 24,500 4,600 8,600 5,300 4,700

12% 0.68 105,000 12,300 102 940 51,300 7,400 13,800 5,500 6,000

Sassafras Green 0.42 41,000 6,300 49 — 18,800 2,600 6,600 — —

12% 0.46 62,000 7,700 60 — 32,800 5,900 8,500 — —

Sweetgum Green 0.46 49,000 8,300 70 910 21,000 2,600 6,800 3,700 2,700

12% 0.52 86,000 11,300 82 810 43,600 4,300 11,000 5,200 3,800

Sycamore, American Green 0.46 45,000 7,300 52 660 20,100 2,500 6,900 4,300 2,700

12% 0.49 69,000 9,800 59 660 37,100 4,800 10,100 5,000 3,400

Tanoak Green 0.58 72,000 10,700 92 — 32,100 — — — —

12% — — — — — — — — — —

Tupelo

Black Green 0.46 48,000 7,100 55 760 21,000 3,300 7,600 3,900 2,800

12% 0.50 66,000 8,300 43 560 38,100 6,400 9,200 3,400 3,600

Water Green 0.46 50,000 7,200 57 760 23,200 3,300 8,200 4,100 3,200

12% 0.50 66,000 8,700 48 580 40,800 6,000 11,000 4,800 3,900

Walnut, black Green 0.51 66,000 9,800 101 940 29,600 3,400 8,400 3,900 4,000

12% 0.55 101,000 11,600 74 860 52,300 7,000 9,400 4,800 4,500

Willow, black Green 0.36 33,000 5,400 76 — 14,100 1,200 4,700 — —

12% 0.39 54,000 7,000 61 — 28,300 3,000 8,600 — —

Yellow-poplar Green 0.40 41,000 8,400 52 660 18,300 1,900 5,400 3,500 2,000

12% 0.42 70,000 10,900 61 610 38,200 3,400 8,200 3,700 2,400

Softwoods

Baldcypress Green 0.42 46,000 8,100 46 640 24,700 2,800 5,600 2,100 1,700

12% 0.46 73,000 9,900 57 610 43,900 5,000 6,900 1,900 2,300

Cedar

Atlantic white Green 0.31 32,000 5,200 41 460 16,500 1,700 4,800 1,200 1,300

12% 0.32 47,000 6,400 28 330 32,400 2,800 5,500 1,500 1,600

Eastern redcedar Green 0.44 48,000 4,500 103 890 24,600 4,800 7,000 2,300 2,900

12% 0.47 61,000 6,100 57 560 41,500 6,300 — — 4,000

Incense Green 0.35 43,000 5,800 44 430 21,700 2,600 5,700 1,900 1,700

12% 0.37 55,000 7,200 37 430 35,900 4,100 6,100 1,900 2,100

Northern white Green 0.29 29,000 4,400 39 380 13,700 1,600 4,300 1,700 1,000

12% 0.31 45,000 5,500 33 300 27,300 2,100 5,900 1,700 1,400
4–7

Table 4–3a. Strength properties of some commercially important woods grown in the United States (metric)a—con.

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(kPa)

elasticityc

(MPa)

load

(kJ/m3)

bending

(mm)

to grain

(kPa)

to grain

(kPa)

grain

(kPa)

to grain

(kPa)

ness

(N)

Cedar—con.

Port-Orford Green 0.39 45,000 9,000 51 530 21,600 2,100 5,800 1,200 1,700

12% 0.43 88,000 11,700 63 710 43,100 5,000 9,400 2,800 2,800

Western redcedar Green 0.31 35,900 6,500 34 430 19,100 1,700 5,300 1,600 1,200

12% 0.32 51,700 7,700 40 430 31,400 3,200 6,800 1,500 1,600

Yellow Green 0.42 44,000 7,900 63 690 21,000 2,400 5,800 2,300 2,000

12% 0.44 77,000 9,800 72 740 43,500 4,300 7,800 2,500 2,600

Douglas-fird

Coast Green 0.45 53,000 10,800 52 660 26,100 2,600 6,200 2,100 2,200

12% 0.48 85,000 13,400 68 790 49,900 5,500 7,800 2,300 3,200

Interior West Green 0.46 53,000 10,400 50 660 26,700 2,900 6,500 2,000 2,300

12% 0.50 87,000 12,600 73 810 51,200 5,200 8,900 2,400 2,900

Interior North Green 0.45 51,000 9,700 56 560 23,900 2,500 6,600 2,300 1,900

12% 0.48 90,000 12,300 72 660 47,600 5,300 9,700 2,700 2,700

Interior South Green 0.43 47,000 8,000 55 380 21,400 2,300 6,600 1,700 1,600

12% 0.46 82,000 10,300 62 510 43,000 5,100 10,400 2,300 2,300

Fir

Balsam Green 0.33 38,000 8,600 32 410 18,100 1,300 4,600 1,200 1,300

12% 0.35 63,000 10,000 35 510 36,400 2,800 6,500 1,200 1,800

California red Green 0.36 40,000 8,100 44 530 19,000 2,300 5,300 2,600 1,600

12% 0.38 72,400 10,300 61 610 37,600 4,200 7,200 2,700 2,200

Grand Green 0.35 40,000 8,600 39 560 20,300 1,900 5,100 1,700 1,600

12% 0.37 61,400 10,800 52 710 36,500 3,400 6,200 1,700 2,200

Noble Green 0.37 43,000 9,500 41 480 20,800 1,900 5,500 1,600 1,300

12% 0.39 74,000 11,900 61 580 42,100 3,600 7,200 1,500 1,800

Pacific silver Green 0.40 44,000 9,800 41 530 21,600 1,500 5,200 1,700 1,400

12% 0.43 75,800 12,100 64 610 44,200 3,100 8,400 — 1,900

Subalpine Green 0.31 34,000 7,200 — — 15,900 1,300 4,800 — 1,200

12% 0.32 59,000 8,900 — — 33,500 2,700 7,400 — 1,600

White Green 0.37 41,000 8,000 39 560 20,000 1,900 5,200 2,100 1,500

12% 0.39 68,000 10,300 50 510 40,000 3,700 7,600 2,100 2,100

Hemlock

Eastern Green 0.38 44,000 7,400 46 530 21,200 2,500 5,900 1,600 1,800

12% 0.40 61,000 8,300 47 530 37,300 4,500 7,300 — 2,200

Mountain Green 0.42 43,000 7,200 76 810 19,900 2,600 6,400 2,300 2,100

12% 0.45 79,000 9,200 72 810 44,400 5,900 10,600 — 3,000

Western Green 0.42 46,000 9,000 48 560 23,200 1,900 5,900 2,000 1,800

12% 0.45 78,000 11,300 57 580 49,000 3,800 8,600 2,300 2,400

Larch, western Green 0.48 53,000 10,100 71 740 25,900 2,800 6,000 2,300 2,300

12% 0.52 90,000 12,900 87 890 52,500 6,400 9,400 3,000 3,700

Pine

Eastern white Green 0.34 34,000 6,800 36 430 16,800 1,500 4,700 1,700 1,300

12% 0.35 59,000 8,500 47 460 33,100 3,000 6,200 2,100 1,700

Jack Green 0.40 41,000 7,400 50 660 20,300 2,100 5,200 2,500 1,800

12% 0.43 68,000 9,300 57 690 39,000 4,000 8,100 2,900 2,500

Loblolly Green 0.47 50,000 9,700 57 760 24,200 2,700 5,900 1,800 2,000

12% 0.51 88,000 12,300 72 760 49,200 5,400 9,600 3,200 3,100

Lodgepole Green 0.38 38,000 7,400 39 510 18,000 1,700 4,700 1,500 1,500

12% 0.41 65,000 9,200 47 510 37,000 4,200 6,100 2,000 2,100

Longleaf Green 0.54 59,000 11,000 61 890 29,800 3,300 7,200 2,300 2,600

12% 0.59 100,000 13,700 81 860 58,400 6,600 10,400 3,200 3,900

Pitch Green 0.47 47,000 8,300 63 — 20,300 2,500 5,900 — —

12% 0.52 74,000 9,900 63 — 41,000 5,600 9,400 — —
 4–8

Table 4–3a. Strength properties of some commercially important woods grown in the United States (metric)a—con.

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(kPa)

elasticityc

(MPa)

load

(kJ/m3)

bending

(mm)

to grain

(kPa)

to grain

(kPa)

grain

(kPa)

to grain

(kPa)

ness

(N)

Pine—con.

Pond Green 0.51 51,000 8,800 52 — 25,200 3,000 6,500 — —

12% 0.56 80,000 12,100 59 — 52,000 6,300 9,500 — —

Ponderosa Green 0.38 35,000 6,900 36 530 16,900 1,900 4,800 2,100 1,400

12% 0.40 65,000 8,900 49 480 36,700 4,000 7,800 2,900 2,000

Red Green 0.41 40,000 8,800 42 660 18,800 1,800 4,800 2,100 1,500

12% 0.46 76,000 11,200 68 660 41,900 4,100 8,400 3,200 2,500

Sand Green 0.46 52,000 7,000 66 — 23,700 3,100 7,900 — —

12% 0.48 80,000 9,700 66 — 47,700 5,800 — — —

Shortleaf Green 0.47 51,000 9,600 57 760 24,300 2,400 6,300 2,200 2,000

12% 0.51 90,000 12,100 76 840 50,100 5,700 9,600 3,200 3,100

Slash Green 0.54 60,000 10,500 66 — 26,300 3,700 6,600 — —

12% 0.59 112,000 13,700 91 — 56,100 7,000 11,600 — —

Spruce Green 0.41 41,000 6,900 — — 19,600 1,900 6,200 — 2,000

12% 0.44 72,000 8,500 — — 39,000 5,000 10,300 — 2,900

Sugar Green 0.34 34,000 7,100 37 430 17,000 1,400 5,000 1,900 1,200

12% 0.36 57,000 8,200 38 460 30,800 3,400 7,800 2,400 1,700

Virginia Green 0.45 50,000 8,400 75 860 23,600 2,700 6,100 2,800 2,400

12% 0.48 90,000 10,500 94 810 46,300 6,300 9,300 2,600 3,300

Western white Green 0.36 32,000 8,200 34 480 16,800 1,300 4,700 1,800 1,200

12% 0.38 67,000 10,100 61 580 34,700 3,200 7,200 — 1,900

Redwood

Old-growth Green 0.38 52,000 8,100 51 530 29,000 2,900 5,500 1,800 1,800

12% 0.40 69,000 9,200 48 480 42,400 4,800 6,500 1,700 2,100

Young-growth Green 0.34 41,000 6,600 39 410 21,400 1,900 6,100 2,100 1,600

12% 0.35 54,000 7,600 36 380 36,000 3,600 7,600 1,700 1,900

Spruce

Black Green 0.38 42,000 9,500 51 610 19,600 1,700 5,100 700 1,600

12% 0.46 74,000 11,100 72 580 41,100 3,800 8,500 — 2,300

Engelmann Green 0.33 32,000 7,100 35 410 15,000 1,400 4,400 1,700 1,150

12% 0.35 64,000 8,900 44 460 30,900 2,800 8,300 2,400 1,750

Red Green 0.37 41,000 9,200 48 460 18,800 1,800 5,200 1,500 1,600

12% 0.40 74,000 11,100 58 640 38,200 3,800 8,900 2,400 2,200

Sitka Green 0.33 34,000 7,900 43 610 16,200 1,400 4,400 1,700 1,600

12% 0.36 65,000 9,900 65 640 35,700 3,000 6,700 2,600 2,300

White Green 0.37 39,000 7,400 41 560 17,700 1,700 4,800 1,500 1,400

12% 0.40 68,000 9,200 53 510 37,700 3,200 7,400 2,500 2,100

Tamarack Green 0.49 50,000 8,500 50 710 24,000 2,700 5,900 1,800 1,700

12% 0.53 80,000 11,300 49 580 49,400 5,500 8,800 2,800 2,600

a

Results of tests on small clear specimens in the green and air-dried conditions, converted to metric units directly from

 Table 4–3b. Definition of properties: impact bending is height of drop that causes complete failure, using

 0.71-kg (50-lb) hammer; compression parallel to grain is also called maximum crushing strength; compression

 perpendicular to grain is fiber stress at proportional limit; shear is maximum shearing strength; tension is maximum

 tensile strength; and side hardness is hardness measured when load is perpendicular to grain.

b

Specific gravity is based on weight when ovendry and volume when green or at 12% moisture content.

c

Modulus of elasticity measured from a simply supported, center-loaded beam, on a span depth ratio of 14/1. To correct

 for shear deflection, the modulus can be increased by 10%.

d

Coast Douglas-fir is defined as Douglas-fir growing in Oregon and Washington State west of the Cascade Mountains

 summit. Interior West includes California and all counties in Oregon and Washington east of, but adjacent to, the

 Cascade summit; Interior North, the remainder of Oregon and Washington plus Idaho, Montana, and Wyoming; and

 Interior South, Utah, Colorado, Arizona, and New Mexico.
4–9

Table 4–3b. Strength propertiesof some commercially important woods grown in the United States (inch–pound)a

Static bending ComModulus

 of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(lbf/in2

)

elasticityc

(×106 lbf/in2)

load

 (in-lbf/in3

)

bending

(in.)

to grain

(lbf/in2)

to grain

(lbf/in2)

grain

(lbf/in2)

to grain

(lbf/in2)

ness

(lbf)

Hardwoods

Alder, red Green 0.37 6,500 1.17 8.0 22 2,960 250 770 390 440

12% 0.41 9,800 1.38 8.4 20 5,820 440 1,080 420 590

Ash

Black Green 0.45 6,000 1.04 12.1 33 2,300 350 860 490 520

12% 0.49 12,600 1.60 14.9 35 5,970 760 1,570 700 850

Blue Green 0.53 9,600 1.24 14.7 — 4,180 810 1,540 — —

12% 0.58 13,800 1.40 14.4 — 6,980 1,420 2,030 — —

Green Green 0.53 9,500 1.40 11.8 35 4,200 730 1,260 590 870

12% 0.56 14,100 1.66 13.4 32 7,080 1,310 1,910 700 1,200

Oregon Green 0.50 7,600 1.13 12.2 39 3,510 530 1,190 590 790

12% 0.55 12,700 1.36 14.4 33 6,040 1,250 1,790 720 1,160

White Green 0.55 9,500 1.44 15.7 38 3,990 670 1,350 590 960

12% 0.60 15,000 1.74 16.6 43 7,410 1,160 1,910 940 1,320

Aspen

Bigtooth Green 0.36 5,400 1.12 5.7 — 2,500 210 730 — —

12% 0.39 9,100 1.43 7.7 — 5,300 450 1,080 — —

Quaking Green 0.35 5,100 0.86 6.4 22 2,140 180 660 230 300

12% 0.38 8,400 1.18 7.6 21 4,250 370 850 260 350

Basswood, American Green 0.32 5,000 1.04 5.3 16 2,220 170 600 280 250

12% 0.37 8,700 1.46 7.2 16 4,730 370 990 350 410

Beech, American Green 0.56 8,600 1.38 11.9 43 3,550 540 1,290 720 850

12% 0.64 14,900 1.72 15.1 41 7,300 1,010 2,0101,010 1,300

Birch

Paper Green 0.48 6,400 1.17 16.2 49 2,360 270 840 380 560

12% 0.55 12,300 1.59 16.0 34 5,690 600 1,210 — 910

Sweet Green 0.60 9,400 1.65 15.7 48 3,740 470 1,240 430 970

12% 0.65 16,900 2.17 18.0 47 8,540 1,080 2,240 950 1,470

Yellow Green 0.55 8,300 1.50 16.1 48 3,380 430 1,110 430 780

12% 0.62 16,600 2.01 20.8 55 8,170 970 1,880 920 1,260

Butternut Green 0.36 5,400 0.97 8.2 24 2,420 220 760 430 390

12% 0.38 8,100 1.18 8.2 24 5,110 460 1,170 440 490

Cherry, black Green 0.47 8,000 1.31 12.8 33 3,540 360 1,130 570 660

12% 0.50 12,300 1.49 11.4 29 7,110 690 1,700 560 950

Chestnut, American Green 0.40 5,600 0.93 7.0 24 2,470 310 800 440 420

12% 0.43 8,600 1.23 6.5 19 5,320 620 1,080 460 540

Cottonwood

Balsam, poplar Green 0.31 3,900 0.75 4.2 — 1,690 140 500 — —

12% 0.34 6,800 1.10 5.0 — 4,020 300 790 — —

Black Green 0.31 4,900 1.08 5.0 20 2,200 160 610 270 250

12% 0.35 8,500 1.27 6.7 22 4,500 300 1,040 330 350

Eastern Green 0.37 5,300 1.01 7.3 21 2,280 200 680 410 340

12% 0.40 8,500 1.37 7.4 20 4,910 380 930 580 430

Elm

American Green 0.46 7,200 1.11 11.8 38 2,910 360 1,000 590 620

12% 0.50 11,800 1.34 13.0 39 5,520 690 1,510 660 830

Rock Green 0.57 9,500 1.19 19.8 54 3,780 610 1,270 — 940

12% 0.63 14,800 1.54 19.2 56 7,050 1,230 1,920 — 1,320

Slippery Green 0.48 8,000 1.23 15.4 47 3,320 420 1,110 640 660

12% 0.53 13,000 1.49 16.9 45 6,360 820 1,630 530 860

Hackberry Green 0.49 6,500 0.95 14.5 48 2,650 400 1,070 630 700

12% 0.53 11,000 1.19 12.8 43 5,440 890 1,590 580 880
 4–10

Table 4–3b. Strength propertiesof some commercially important woods grown in the United States (inch–pound)a—con.

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(lbf/in2

)

elasticityc

(×106 lbf/in2)

load

 (in-lbf/in3

)

bending

(in.)

to grain

(lbf/in2)

to grain

(lbf/in2)

grain

(lbf/in2)

to grain

(lbf/in2)

ness

(lbf)

Hickory, pecan

Bitternut Green 0.60 10,300 1.40 20.0 66 4,570 800 1,240 — —

12% 0.66 17,100 1.79 18.2 66 9,040 1,680 — — —

Nutmeg Green 0.56 9,100 1.29 22.8 54 3,980 760 1,030 — —

12% 0.60 16,600 1.70 25.1 — 6,910 1,570 — — —

Pecan Green 0.60 9,800 1.37 14.6 53 3,990 780 1,480 680 1,310

12% 0.66 13,700 1.73 13.8 44 7,850 1,720 2,080 — 1,820

Water Green 0.61 10,700 1.56 18.8 56 4,660 880 1,440 — —

12% 0.62 17,800 2.02 19.3 53 8,600 1,550 — — —

Hickory, true

Mockernut Green 0.64 11,100 1.57 26.1 88 4,480 810 1,280 — —

12% 0.72 19,200 2.22 22.6 77 8,940 1,730 1,740 — —

Pignut Green 0.66 11,700 1.65 31.7 89 4,810 920 1,370 — —

12% 0.75 20,100 2.26 30.4 74 9,190 1,980 2,150 — —

Shagbark Green 0.64 11,000 1.57 23.7 74 4,580 840 1,520 — —

12% 0.72 20,200 2.16 25.8 67 9,210 1,760 2,430 — —

Shellbark Green 0.62 10,500 1.34 29.9 104 3,920 810 1,190 — —

12% 0.69 18,100 1.89 23.6 88 8,000 1,800 2,110 — —

Honeylocust Green 0.60 10,200 1.29 12.6 47 4,420 1,150 1,660 930 1,390

12% — 14,700 1.63 13.3 47 7,500 1,840 2,250 900 1,580

Locust, black Green 0.66 13,800 1.85 15.4 44 6,800 1,160 1,760 770 1,570

12% 0.69 19,400 2.05 18.4 57 10,180 1,830 2,480 640 1,700

Magnolia

Cucumbertree Green 0.44 7,400 1.56 10.0 30 3,140 330 990 440 520

12% 0.48 12,300 1.82 12.2 35 6,310 570 1,340 660 700

Southern Green 0.46 6,800 1.11 15.4 54 2,700 460 1,040 610 740

12% 0.50 11,200 1.40 12.8 29 5,460 860 1,530 740 1,020

Maple

Bigleaf Green 0.44 7,400 1.10 8.7 23 3,240 450 1,110 600 620

12% 0.48 10,700 1.45 7.8 28 5,950 750 1,730 540 850

Black Green 0.52 7,900 1.33 12.8 48 3,270 600 1,130 720 840

12% 0.57 13,300 1.62 12.5 40 6,680 1,020 1,820 670 1,180

Red Green 0.49 7,700 1.39 11.4 32 3,280 400 1,150 — 700

12% 0.54 13,400 1.64 12.5 32 6,540 1,000 1,850 — 950

Silver Green 0.44 5,800 0.94 11.0 29 2,490 370 1,050 560 590

12% 0.47 8,900 1.14 8.3 25 5,220 740 1,480 500 700

Sugar Green 0.56 9,400 1.55 13.3 40 4,020 640 1,460 — 970

12% 0.63 15,800 1.83 16.5 39 7,830 1,470 2,330 — 1,450

Oak, red

Black Green 0.56 8,200 1.18 12.2 40 3,470 710 1,220 — 1,060

12% 0.61 13,900 1.64 13.7 41 6,520 930 1,910 — 1,210

Cherrybark Green 0.61 10,800 1.79 14.7 54 4,620 760 1,320 800 1,240

12% 0.68 18,100 2.28 18.3 49 8,740 1,250 2,000 840 1,480

Laurel Green 0.56 7900 1.39 11.2 39 3,170 570 1,180 770 1,000

12% 0.63 12,600 1.69 11.8 39 6,980 1,060 1,830 790 1,210

Northern red Green 0.56 8300 1.35 13.2 44 3,440 610 1,210 750 1,000

12% 0.63 14,300 1.82 14.5 43 6,760 1,010 1,780 800 1,290

Pin Green 0.58 8300 1.32 14.0 48 3,680 720 1,290 800 1,070

12% 0.63 14000 1.73 14.8 45 6,820 1,020 2,080 1,050 1,510

Scarlet Green 0.60 10,400 1.48 15.0 54 4,090 830 1,410 700 1,200

12% 0.67 17400 1.91 20.5 53 8,330 1,120 1,890 870 1,400

Southern red Green 0.52 6,900 1.14 8.0 29 3,030 550 930 480 860

12% 0.59 10,900 1.49 9.4 26 6,090 870 1,390 510 1,060
4–11

Table 4–3b. Strength propertiesof some commercially important woods grown in the United States (inch–pound)a—con.

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(lbf/in2

)

elasticityc

(×106 lbf/in2)

load

 (in-lbf/in3

)

bending

(in.)

to grain

(lbf/in2)

to grain

(lbf/in2)

grain

(lbf/in2)

to grain

(lbf/in2)

ness

(lbf)

Oak, red—con.

Water Green 0.56 8,900 1.55 11.1 39 3,740 620 1,240 820 1,010

12% 0.63 15,400 2.02 21.5 44 6,770 1,020 2,020 920 1,190

Willow Green 0.56 7400 1.29 8.8 35 3,000 610 1,180 760 980

12% 0.69 14,500 1.90 14.6 42 7,040 1,130 1,650 — 1,460

Oak, white

Bur Green 0.58 7,200 0.88 10.7 44 3,290 680 1,350 800 1,110

12% 0.64 10,300 1.03 9.8 29 6,060 1,200 1,820 680 1,370

Chestnut Green 0.57 8,000 1.37 9.4 35 3,520 530 1,210 690 890

12% 0.66 13,300 1.59 11.0 40 6,830 840 1,490 — 1,130

Live Green 0.80 11,900 1.58 12.3 — 5,430 2,040 2,210 — —

12% 0.88 18,400 1.98 18.9 — 8,900 2,840 2,660 — —

Overcup Green 0.57 8,000 1.15 12.6 44 3,370 540 1,320 730 960

12% 0.63 12,600 1.42 15.7 38 6,200 810 2,000 940 1,190

Post Green 0.60 8,100 1.09 11.0 44 3,480 860 1,280 790 1,130

12% 0.67 13,200 1.51 13.2 46 6,600 1,430 1,840 780 1,360

Swamp chestnut Green 0.60 8,500 1.35 12.8 45 3,540 570 1,260 670 1,110

12% 0.67 13,900 1.77 12.0 41 7,270 1,110 1,990 690 1,240

Swamp white Green 0.64 9,900 1.59 14.5 50 4,360 760 1,300 860 1,160

12% 0.72 17,700 2.05 19.2 49 8,600 1,190 2,000 830 1,620

White Green 0.60 8,300 1.25 11.6 42 3,560 670 1,250 770 1,060

12% 0.68 15,200 1.78 14.8 37 7,440 1,070 2,000 800 1,360

Sassafras Green 0.42 6,000 0.91 7.1 — 2,730 370 950 — —

12% 0.46 9,000 1.12 8.7 — 4,760 850 1,240 — —

Sweetgum Green 0.46 7,100 1.20 10.1 36 3,040 370 990 540 600

12% 0.52 12,500 1.64 11.9 32 6,320 620 1,600 760 850

Sycamore, American Green 0.46 6,500 1.06 7.5 26 2,920 360 1,000 630 610

12% 0.49 10,000 1.42 8.5 26 5,380 700 1,470 720 770

Tanoak Green 0.58 10,500 1.55 13.4 — 4,650 — — — —

12% — — — — — — — — — —

Tupelo

Black Green 0.46 7,000 1.03 8.0 30 3,040 480 1,100 570 640

12% 0.50 9,600 1.20 6.2 22 5,520 930 1,340 500 810

Water Green 0.46 7,300 1.05 8.3 30 3,370 480 1,190 600 710

12% 0.50 9,600 1.26 6.9 23 5,920 870 1,590 700 880

Walnut, Black Green 0.51 9,500 1.42 14.6 37 4,300 490 1,220 570 900

12% 0.55 14,600 1.68 10.7 34 7,580 1,010 1,370 690 1,010

Willow, Black Green 0.36 4,800 0.79 11.0 — 2,040 180 680 — —

12% 0.39 7,800 1.01 8.8 — 4,100 430 1,250 — —

Yellow-poplar Green 0.40 6,000 1.22 7.5 26 2,660 270 790 510 440

12% 0.42 10,100 1.58 8.8 24 5,540 500 1,190 540 540

Softwoods

Baldcypress Green 0.42 6,600 1.18 6.6 25 3,580 400 810 300 390

12% 0.46 10,600 1.44 8.2 24 6,360 730 1,000 270 510

Cedar

Atlantic white Green 0.31 4,700 0.75 5.9 18 2,390 240 690 180 290

12% 0.32 6,800 0.93 4.1 13 4,700 410 800 220 350

Eastern redcedar Green 0.44 7,000 0.65 15.0 35 3,570 700 1,010 330 650

12% 0.47 8,800 0.88 8.3 22 6,020 920 — — —

Incense Green 0.35 6,200 0.84 6.4 17 3,150 370 830 280 390

12% 0.37 8,000 1.04 5.4 17 5,200 590 880 270 470

Northern White Green 0.29 4,200 0.64 5.7 15 1,990 230 620 240 230

12% 0.31 6,500 0.80 4.8 12 3,960 310 850 240 320
 4–12

Table 4–3b. Strength propertiesof some commercially important woods grown in the United States (inch–pound)a—con.

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(lbf/in2

)

elasticityc

(×106 lbf/in2)

load

 (in-lbf/in3

)

bending

(in.)

to grain

(lbf/in2)

to grain

(lbf/in2)

grain

(lbf/in2)

to grain

(lbf/in2)

ness

(lbf)

Cedar—con.

Port-Orford Green 0.39 6,600 1.30 7.4 21 3,140 300 840 180 380

12% 0.43 12,700 1.70 9.1 28 6,250 720 1,370 400 630

Western redcedar Green 0.31 5,200 0.94 5.0 17 2,770 240 770 230 260

12% 0.32 7,500 1.11 5.8 17 4,560 460 990 220 350

Yellow Green 0.42 6,400 1.14 9.2 27 3,050 350 840 330 440

12% 0.44 11,100 1.42 10.4 29 6,310 620 1,130 360 580

Douglas-fird

Coast Green 0.45 7,700 1.56 7.6 26 3,780 380 900 300 500

12% 0.48 12,400 1.95 9.9 31 7,230 800 1,130 340 710

Interior West Green 0.46 7,700 1.51 7.2 26 3,870 420 940 290 510

12% 0.50 12,600 1.83 10.6 32 7,430 760 1,290 350 660

Interior North Green 0.45 7,400 1.41 8.1 22 3,470 360 950 340 420

12% 0.48 13,100 1.79 10.5 26 6,900 770 1,400 390 600

Interior South Green 0.43 6,800 1.16 8.0 15 3,110 340 950 250 360

12% 0.46 11,900 1.49 9.0 20 6,230 740 1,510 330 510

Fir

Balsam Green 0.33 5,500 1.25 4.7 16 2,630 190 662 180 290

12% 0.35 9,200 1.45 5.1 20 5,280 404 944 180 400

California red Green 0.36 5,800 1.17 6.4 21 2,760 330 770 380 360

12% 0.38 10,500 1.50 8.9 24 5,460 610 1,040 390 500

Grand Green 0.35 5,800 1.25 5.6 22 2,940 270 740 240 360

12% 0.37 8,900 1.57 7.5 28 5,290 500 900 240 490

Noble Green 0.37 6,200 1.38 6.0 19 3,010 270 800 230 290

12% 0.39 10,700 1.72 8.8 23 6,100 520 1,050 220 410

Pacific silver Green 0.40 6,400 1.42 6.0 21 3,140 220 750 240 310

12% 0.43 11,000 1.76 9.3 24 6,410 450 1,220 — 430

Subalpine Green 0.31 4,900 1.05 — — 2,300 190 700 — 260

12% 0.32 8,600 1.29 — — 4,860 390 1,070 — 350

White Green 0.37 5,900 1.16 5.6 22 2,900 280 760 300 340

12% 0.39 9,800 1.50 7.2 20 5,800 530 1,100 300 480

Hemlock

Eastern Green 0.38 6,400 1.07 6.7 21 3,080 360 850 230 400

12% 0.40 8,900 1.20 6.8 21 5,410 650 1,060 — 500

Mountain Green 0.42 6,300 1.04 11.0 32 2,880 370 930 330 470

12% 0.45 11,500 1.33 10.4 32 6,440 860 1,540 — 680

Western Green 0.42 6,600 1.31 6.9 22 3,360 280 860 290 410

12% 0.45 11,300 1.63 8.3 23 7,200 550 1,290 340 540

Larch, western Green 0.48 7,700 1.46 10.3 29 3,760 400 870 330 510

12% 0.52 13,000 1.87 12.6 35 7,620 930 1,360 430 830

Pine

Eastern white Green 0.34 4,900 0.99 5.2 17 2,440 220 680 250 290

12% 0.35 8,600 1.24 6.8 18 4,800 440 900 310 380

Jack Green 0.40 6,000 1.07 7.2 26 2,950 300 750 360 400

12% 0.43 9,900 1.35 8.3 27 5,660 580 1,170 420 570

Loblolly Green 0.47 7,300 1.40 8.2 30 3,510 390 860 260 450

12% 0.51 12,800 1.79 10.4 30 7,130 790 1,390 470 690

Lodgepole Green 0.38 5,500 1.08 5.6 20 2,610 250 680 220 330

12% 0.41 9,400 1.34 6.8 20 5,370 610 880 290 480

Longleaf Green 0.554 8,500 1.59 8.9 35 4,320 480 1,040 330 590

12% 0.59 14,500 1.98 11.8 34 8,470 960 1,510 470 870

Pitch Green 0.47 6,800 1.20 9.2 — 2,950 360 860 — —

12% 0.52 10,800 1.43 9.2 — 5,940 820 1,360 — —
4–13

Table 4–3b. Strength propertiesof some commercially important woods grown in the United States (inch–pound)a—con.

Static bending ComModulus

of

Modulus

of

Work to

maximum Impact

Compression

parallel

pression

perpendicular

Shear

parallel

to

Tension

perpendicularSide

hardCommon species

names

Moisture

content

Specific

gravityb

rupture

(lbf/in2

)

elasticityc

(×106 lbf/in2)

load

 (in-lbf/in3

)

bending

(in.)

to grain

(lbf/in2)

to grain

(lbf/in2)

grain

(lbf/in2)

to grain

(lbf/in2)

ness

(lbf)

Pine—con.

Pond Green 0.51 7,400 1.28 7.5 — 3,660 440 940 — —

12% 0.56 11,600 1.75 8.6 — 7,540 910 1,380 — —

Ponderosa Green 0.38 5,100 1.00 5.2 21 2,450 280 700 310 320

12% 0.40 9,400 1.29 7.1 19 5,320 580 1,130 420 460

Red Green 0.41 5,800 1.28 6.1 26 2,730 260 690 300 340

12% 0.46 11,000 1.63 9.9 26 6,070 600 1,210 460 560

Sand Green 0.46 7,500 1.02 9.6 — 3,440 450 1,140 — —

12% 0.48 11,600 1.41 9.6 — 6,920 836 — — —

Shortleaf Green 0.47 7,400 1.39 8.2 30 3,530 350 910 320 440

12% 0.51 13,100 1.75 11.0 33 7,270 820 1,390 470 690

Slash Green 0.54 8,700 1.53 9.6 — 3,820 530 960 — —

12% 0.59 16,300 1.98 13.2 — 8,140 1020 1,680 — —

Spruce Green 0.41 6,000 1.00 — — 2,840 280 900 — 450

12% 0.44 10,400 1.23 — — 5,650 730 1,490 — 660

Sugar Green 0.34 4,900 1.03 5.4 17 2,460 210 720 270 270

12% 0.36 8,200 1.19 5.5 18 4,460 500 1,130 350 380

Virginia Green 0.45 7,300 1.22 10.9 34 3,420 390 890 400 540

12% 0.48 13,000 1.52 13.7 32 6,710 910 1,350 380 740

Western white Green 0.35 4,700 1.19 5.0 19 2,430 190 680 260 260

12% 0.38 9,700 1.46 8.8 23 5,040 470 1,040 — 420

Redwood

Old-growth Green 0.38 7,500 1.18 7.4 21 4,200 420 800 260 410

12% 0.40 10,000 1.34 6.9 19 6,150 700 940 240 480

Young-growth Green 0.34 5,900 0.96 5.7 16 3,110 270 890 300 350

12% 0.35 7,900 1.10 5.2 15 5,220 520 1,110 250 420

Spruce

Black Green 0.38 6,100 1.38 7.4 24 2,840 240 739 100 370

12% 0.42 10,800 1.61 10.5 23 5,960 550 1,230 — 520

Engelmann Green 0.33 4,700 1.03 5.1 16 2,180 200 640 240 260

12% 0.35 9,300 1.30 6.4 18 4,480 410 1,200 350 390

Red Green 0.37 6,000 1.33 6.9 18 2,720 260 750 220 350

12% 0.40 10,800 1.61 8.4 25 5,540 550 1,290 350 490

Sitka Green 0.37 5,700 1.23 6.3 24 2,670 280 760 250 350

12% 0.40 10,200 1.57 9.4 25 5,610 580 1,150 370 510

White Green 0.33 5,000 1.14 6.0 22 2,350 210 640 220 320

12% 0.36 9,400 1.43 7.7 20 5,180 430 970 360 480

Tamarack Green 0.49 7,200 1.24 7.2 28 3,480 390 860 260 380

12% 0.53 11,600 1.64 7.1 23 7,160 800 1,280 400 590

a

Results of tests on small clear specimens in the green and air-dried conditions. Definition of properties: impact bending is

 height of drop that causes complete failure, using 0.71-kg (50-lb) hammer; compression parallel to grain is also called maxi-

 mum crushing strength; compression perpendicular to grain is fiber stress at proportional limit; shear is maximum shearing

 strength; tension is maximum tensile strength; and side hardness is hardness measured when load is perpendicular to grain.

b

Specific gravity is based on weight when ovendry and volume when green or at 12% moisture content.

c

Modulus of elasticity measured from a simply supported, center-loaded beam, on a span depth ratio of 14/1. To correct for

 shear deflection, the modulus can be increased by 10%.

d

Coast Douglas-fir is defined as Douglas-fir growing in Oregon and Washington State west of the Cascade Mountains summit.

 Interior West includes California and all counties in Oregon and Washington east of, but adjacent to, the Cascade summit;

 Interior North, the remainder of Oregon and Washington plus Idaho, Montana, and Wyoming; and Interior South, Utah,

 Colorado, Arizona, and New Mexico.
 4–14

Table 4–4a. Mechanical properties of some commercially important woods grown in Canada and imported into

the United States (metric)a

Static bending Compression Compression Shear

Common species

names

Moisture

content

Specific

gravity

Modulus of

rupture (kPa)

Modulus of

elasticity (MPa)

parallel to

grain (kPa)

perpendicular

 to grain (kPa)

parallel to

grain (kPa)

Hardwoods

Aspen

Quaking Green 0.37 38,000 9,000 16,200 1,400 5,000

12% 68,000 11,200 36,300 3,500 6,800

Big-toothed Green 0.39 36,000 7,400 16,500 1,400 5,400

12% 66,000 8,700 32,800 3,200 7,600

Cottonwood

Black Green 0.30 28,000 6,700 12,800 700 3,900

12% 49,000 8,800 27,700 1,800 5,900

Eastern Green 0.35 32,000 6,000 13,600 1,400 5,300

12% 52,000 7,800 26,500 3,200 8,000

Balsam, poplar Green 0.37 34,000 7,900 14,600 1,200 4,600

12% 70,000 11,500 34,600 2,900 6,100

Softwoods

Cedar

Northern white Green 0.30 27,000 3,600 13,000 1,400 4,600

12% 42,000 4,300 24,800 2,700 6,900

Western redcedar Green 0.31 36,000 7,200 19,200 1,900 4,800

12% 54,000 8,200 29,600 3,400 5,600

Yellow Green 0.42 46,000 9,200 22,300 2,400 6,100

12% 80,000 11,000 45,800 4,800 9,200

Douglas-fir Green 0.45 52,000 11,100 24,900 3,200 6,300

12% 88,000 13,600 50,000 6,000 9,500

Fir

Subalpine Green 0.33 36,000 8,700 17,200 1,800 4,700

12% 56,000 10,200 36,400 3,700 6,800

Pacific silver Green 0.36 38,000 9,300 19,100 1,600 4,900

12% 69,000 11,300 40,900 3,600 7,500

Balsam Green 0.34 36,000 7,800 16,800 1,600 4,700

12% 59,000 9,600 34,300 3,200 6,300

Hemlock

Eastern Green 0.40 47,000 8,800 23,600 2,800 6,300

12% 67,000 9,700 41,200 4,300 8,700

Western Green 0.41 48,000 10,200 24,700 2,600 5,200

12% 81,000 12,300 46,700 4,600 6,500

Larch, western Green 0.55 60,000 11,400 30,500 3,600 6,300

12% 107,000 14,300 61,000 7,300 9,200

Pine

Eastern white Green 0.36 35,000 8,100 17,900 1,600 4,400

12% 66,000 9,400 36,000 3,400 6,100

Jack Green 0.42 43,000 8,100 20,300 2,300 5,600

12% 78,000 10,200 40,500 5,700 8,200

Lodgepole Green 0.40 39,000 8,800 19,700 1,900 5,000

12% 76,000 10,900 43,200 3,600 8,500

Ponderosa Green 0.44 39,000 7,800 19,600 2,400 5,000

12% 73,000 9,500 42,300 5,200 7,000

Red Green 0.39 34,000 7,400 16,300 1,900 4,900

12% 70,000 9,500 37,900 5,200 7,500

Western white Green 0.36 33,000 8,200 17,400 1,600 4,500

12% 64,100 10,100 36,100 3,200 6,300

Spruce

Black Green 0.41 41,000 9,100 19,000 2,100 5,500

12% 79,000 10,500 41,600 4,300 8,600

Engelmann Green 0.38 39,000 8,600 19,400 1,900 4,800

12% 70,000 10,700 42,400 3,700 7,600

Red Green 0.38 41,000 9,100 19,400 1,900 5,600

12% 71,000 11,000 38,500 3,800 9,200

Sitka Green 0.35 37,000 9,400 17,600 2,000 4,300

12% 70,000 11,200 37,800 4,100 6,800

White Green 0.35 35,000 7,900 17,000 1,600 4,600

12% 63,000 10,000 37,000 3,400 6,800

Tamarack Green 0.48 47,000 8,600 21,600 2,800 6,300

12% 76,000 9,400 44,900 6,200 9,000

a

Results of tests on small, clear, straight-grained specimens. Property values based on ASTM Standard D2555–88. Information on additional

 properties can be obtained from Department of Forestry, Canada, Publication No. 1104. For each species, values in the first line are from

 tests of green material; those in the second line are adjusted from the green condition to 12% moisture content using dry to green clear wood

 property ratios as reported in ASTM D2555–88. Specific gravity is based on weight when ovendry and volume when green.
4–15

Table 4–4b. Mechanical properties of some commercially important woods grown in Canada and imported into the

United States (inch–pound)a

Static bending Compression Compression Shear

Common species

names

Moisture

content

Specific

gravity

Modulus of

rupture (lbf/in2)

Modulus of elasticity (×106 lbf/in2

)

parallel to

grain (lbf/in2)

perpendicular

 to grain (lbf/in2)

parallel to

grain (lbf/in2)

Hardwoods

Aspen

Quaking Green 0.37 5,500 1.31 2,350 200 720

12% 9,800 1.63 5,260 510 980

Bigtooth Green 0.39 5,300 1.08 2,390 210 790

12% 9,500 1.26 4,760 470 1,100

Cottonwood

Balsam, poplar Green 0.37 5,000 1.15 2,110 180 670

12% 10,100 1.67 5,020 420 890

Black Green 0.30 4,100 0.97 1,860 100 560

12% 7,100 1.28 4,020 260 860

Eastern Green 0.35 4,700 0.87 1,970 210 770

12% 7,500 1.13 3,840 470 1,160

Softwoods

Cedar

Northern white Green 0.30 3,900 0.52 1,890 200 660

12% 6,100 0.63 3,590 390 1,000

Western redcedar Green 0.31 5,300 1.05 2,780 280 700

12% 7,800 1.19 4,290 500 810

Yellow Green 0.42 6,600 1.34 3,240 350 880

12% 11,600 1.59 6,640 690 1,340

Douglas-fir Green 0.45 7,500 1.61 3,610 460 920

12% 12,800 1.97 7,260 870 1,380

Fir

Balsam Green 0.34 5,300 1.13 2,440 240 680

12% 8,500 1.40 4,980 460 910

Pacific silver Green 0.36 5,500 1.35 2,770 230 710

12% 10,000 1.64 5,930 520 1,190

Subalpine Green 0.33 5,200 1.26 2,500 260 680

12% 8,200 1.48 5,280 540 980

Hemlock

Eastern Green 0.40 6,800 1.27 3,430 400 910

12% 9,700 1.41 5,970 630 1,260

Western Green 0.41 7,000 1.48 3,580 370 750

12% 11,800 1.79 6,770 660 940

Larch, western Green 0.55 8,700 1.65 4,420 520 920

12% 15,500 2.08 8,840 1,060 1,340

Pine

Eastern white Green 0.36 5,100 1.18 2,590 240 640

12% 9,500 1.36 5,230 490 880

Jack Green 0.42 6,300 1.17 2,950 340 820

12% 11,300 1.48 5,870 830 1,190

Lodgepole Green 0.40 5,600 1.27 2,860 280 720

12% 11,000 1.58 6,260 530 1,240

Ponderosa Green 0.44 5,700 1.13 2,840 350 720

12% 10,600 1.38 6,130 760 1,020

Red Green 0.39 5,000 1.07 2,370 280 710

12% 10,100 1.38 5,500 720 1,090

Western white Green 0.36 4,800 1.19 2,520 240 650

12% 9,300 1.46 5,240 470 920

Spruce

Black Green 0.41 5,900 1.32 2,760 300 800

12% 11,400 1.52 6,040 620 1,250

Engelmann Green 0.38 5,700 1.25 2,810 270 700

12% 10,100 1.55 6,150 540 1,100

Red Green 0.38 5,900 1.32 2,810 270 810

12% 10,300 1.60 5,590 550 1,330

Sitka Green 0.35 5,400 1.37 2,560 290 630

12% 10,100 1.63 5,480 590 980

White Green 0.35 5,100 1.15 2,470 240 670

12% 9,100 1.45 5,360 500 980

Tamarack Green 0.48 6,800 1.24 3,130 410 920

12% 11,000 1.36 6,510 900 1,300

a

Results of tests on small, clear, straight-grained specimens. Property values based on ASTM Standard D2555–88. Information on additional

 properties can be obtained from Department of Forestry, Canada, Publication No. 1104. For each species, values in the first line are from

 tests of green material; those in the second line are adjusted from the green condition to 12% moisture content using dry to green clear wood

 property ratios as reported in ASTM D2555–88. Specific gravity is based on weight when ovendry and volume when green.
 4–16

Table 4–5a. Mechanical propertiesof some woods imported into the United States other than Canadian

imports (metric)a

Static bending ComCommon and botanical Moisture Specific

Modulus

of

rupture

Modulus

of

elasticity

Work to

maximum

load

pression

parallel

to grain

Shear

parallel

to grain

Side

hardness Sample

names of species content gravity (kPa) (MPa) (kJ/m3

) (kPa) (kPa) (N) originb

Afrormosia (Pericopsis elata) Green 0.61 102,000 12,200 135 51,600 11,500 7,100 AF

12% 126,900 13,400 127 68,500 14,400 6,900

Albarco (Cariniana spp.) Green 0.48 — — — — — — AM

12% 100,000 10,300 95 47,000 15,900 4,500

Andiroba (Carapa guianensis) Green 0.54 71,000 11,700 68 33,000 8,400 3,900 AM

12% — 106,900 13,800 97 56,000 10,400 5,000

Angelin (Andira inermis) Green 0.65 — — — — — — AF

12% 124,100 17,200 — 63,400 12,700 7,800

Angelique (Dicorynia Green 0.6 78,600 12,700 83 38,500 9,200 4,900 AM

 guianensis) 12% — 120,000 15,100 105 60,500 11,400 5,700

Avodire (Turraeanthus Green 0.48 — — — — — — AF

 africanus) 12% 87,600 10,300 65 49,300 14,000 4,800

Azobe (Lophira alata) Green 0.87 116,500 14,900 83 65,600 14,100 12,900 AF

12% 168,900 17,000 — 86,900 20,400 14,900

Balsa (Ochroma pyramidale) Green 0.16 — — — — — — AM

12% 21,600 3,400 14 14,900 2,100 —

Banak (Virola spp.) Green 0.42 38,600 11,300 28 16,500 5,000 1,400 AM

12% — 75,200 14,100 69 35,400 6,800 2,300

Benge (Guibourtia arnoldiana) Green 0.65 — — — — — — AF

12% 147,500 14,100 — 78,600 14,400 7,800

Bubinga (Guibourtia spp.) Green 0.71 — — — — — — AF

12% 155,800 17,100 — 72,400 21,400 12,000

Bulletwood (Manilkara Green 0.85 119,300 18,600 94 59,900 13,100 9,900 AM

 bidentata) 12% 188,200 23,800 197 80,300 17,200 14,200

Cativo (Prioria copaifera) Green 0.4 40,700 6,500 37 17,000 5,900 2,000 AM

12% — 59,300 7,700 50 29,600 7,300 2,800

Ceiba (Ceiba pentandra) Green 0.25 15,200 2,800 8 7,300 2,400 1,000 AM

12% 29,600 3,700 19 16,400 3,800 1,100

Courbaril (Hymenaea Green 0.71 88,900 12,700 101 40,000 12,200 8,800 AM

 courbaril) 12% — 133,800 14,900 121 65,600 17,000 10,500

Cuangare (Dialyanthera spp.) Green 0.31 27,600 7,000 — 14,300 4,100 1,000 AM

12% 50,300 10,500 — 32,800 5,700 1,700

Cypress, Mexican (Cupressus Green 0.93 42,700 6,300 — 19,900 6,600 1,500 AF

 lustianica) 12% 71,000 7,000 — 37,100 10,900 2,000

Degame (Calycophyllum Green 0.67 98,600 13,300 128 42,700 11,400 7,300 AM

 candidissimum) 12% 153,800 15,700 186 66,700 14,600 8,600

Determa (Ocotea rubra) Green 0.52 53,800 10,100 33 25,900 5,900 2,300 AM

12% 72,400 12,500 44 40,000 6,800 2,900

Ekop (Tetraberlinia Green 0.6 — — — — — — AF

 tubmaniana) 12% 115,100 15,200 — 62,100 — —

Goncalo alves (Astronium Green 0.84 83,400 13,400 46 45,400 12,100 8,500 AM

 graveolens) 12% — 114,500 15,400 72 71,200 13,500 9,600

Greenheart (Chlorocardium Green 0.8 133,100 17,000 72 64,700 13,300 8,400 AM

 rodiei) 12% 171,700 22,400 175 86,300 18,100 10,500

Hura (Hura crepitans) Green 0.38 43,400 7,200 41 19,200 5,700 2,000 AM

12% 60,000 8,100 46 33,100 7,400 2,400
4–17

Table 4–5a. Mechanical propertiesof some woods imported into the United States other than Canadian

imports (metric)a

—con.

Static bending ComCommon and botanical Moisture Specific

Modulus

of

rupture

Modulus

of

elasticity

Work to

maximum

load

pression

parallel

to grain

Shear

parallel

to grain

Side

hardness Sample

names of species content gravity (kPa) (MPa) (kJ/m3

) (kPa) (kPa) (N) originb

llomba (Pycnanthus Geen 0.4 37,900 7,900 — 20,000 5,800 2,100 AF

 angolensis) 12% 68,300 11,000 — 38,300 8,900 2,700

Ipe (Tabebuia spp., Green 0.92 155,800 20,100 190 71,400 14,600 13,600 AM

 lapacho group) 12% 175,100 21,600 152 89,700 14,200 16,400

Iroko (Chlorophora spp.) Green 0.54 70,300 8,900 72 33,900 9,000 4,800 AF

12% 85,500 10,100 62 52,300 12,400 5,600

Jarrah (Eucalyptus marginata) Green 0.67 68,300 10,200 — 35,800 9,100 5,700 AS

12% — 111,700 13,000 — 61,200 14,700 8,500

Jelutong (Dyera costulata) Green 0.36 38,600 8,000 39 21,000 5,200 1,500 AS

15% 50,300 8,100 44 27,000 5,800 1,700

Kaneelhart (Licaria spp.) Green 0.96 153,800 26,300 94 92,300 11,600 9,800 AM

12% 206,200 28,000 121 120,000 13,600 12,900

Kapur (Dryobalanops spp.) Green 0.64 88,300 11,000 108 42,900 8,100 4,400 AS

12% 126,200 13,000 130 69,600 13,700 5,500

Karri (Eucalyptus diversicolor) Green 0.82 77,200 13,400 80 37,600 10,400 6,000 AS

12% 139,000 17,900 175 74,500 16,700 9,100

Kempas (Koompassia Green 0.71 100,000 16,600 84 54,700 10,100 6,600 AS

 malaccensis) 12% 122,000 18,500 106 65,600 12,300 7,600

Keruing (Dipterocarpus spp.) Green 0.69 82,000 11,800 96 39,200 8,100 4,700 AS

12% 137,200 14,300 162 72,400 14,300 5,600

Lignumvitae (Guaiacum spp.) Green 1.05 — — — — — — AM

12% — — — — 78,600 — 20,000

Limba (Terminalia superba) Green 0.38 41,400 5,300 53 19,200 600 1,800 AF

12% 60,700 7,000 61 32,600 9,700 2,200

Macawood (Platymiscium spp.) Green 0.94 153,800 20,800 — 72,700 12,700 14,800 AM

12% 190,300 22,100 — 111,000 17,500 14000

Mahogany, African Green 0.42 51,000 7,900 49 25,700 6,400 2,800 AF

 (Khaya spp.) 12% 73,800 9,700 57 44,500 10,300 3,700

Mahogany, true Green 0.45 62,100 9,200 63 29,900 8,500 3,300 AM

(Swietenia macrophylla) 12% — 79,300 10,300 52 46,700 8,500 3,600

Manbarklak (Eschweilera spp.) Green 0.87 117,900 18,600 120 50,600 11,200 10,100 AM

12% 182,700 21,600 230 77,300 14,300 15,500

Manni (Symphonia globulifera) Green 0.58 77,200 13,500 77 35,600 7,900 4,200 AM

12% 116,500 17,000 114 60,800 9,800 5,000

Marishballi (Lincania spp.) Green 0.88 117,900 20,200 92 52,300 11,200 10,000 AM

12% 191,000 23,000 98 92,300 12,100 15,900

Merbau (Intsia spp.) Green 0.64 88,900 13,900 88 46,700 10,800 6,100 AS

15% — 115,800 15,400 102 58,200 12,500 6,700

Mersawa (Anisoptera spp.) Green 0.52 55,200 12,200 — 27,300 5,100 3,900 AS

12% 95,100 15,700 — 50,800 6,100 5,700

Mora (Mora spp.) Green 0.78 86,900 16,100 93 44,100 9,700 6,400 AM

12% 152,400 20,400 128 81,600 13,100 10,200

Oak (Quercus spp.) Green 0.76 — — — — — — AM

12% 158,600 20,800 114 — — 11,100

Obeche (Triplochiton Green 0.3 35,200 5,000 43 17,700 4,600 1,900 AF

 scleroxylon) 12% 51,000 5,900 48 27,100 6,800 1,900
 4–18

Table 4–5a. Mechanical propertiesof some woods imported into the United States other than Canadian

imports (metric)a

—con.

Static bending ComCommon and botanical Moisture Specific

Modulus

of

rupture

Modulus

of

elasticity

Work to

 maximum

load

pression

parallel

to grain

Shear

parallel

to grain

Side

hardness Sample

names of species content gravity (kPa) (MPa) (kJ/m3

) (kPa) (kPa) (N) originb

Okoume (Aucoumea Green 0.33 — — — — — — AF

 klaineana) 12% 51,000 7,900 — 27,400 6,700 1,700

Opepe (Nauclea diderrichii) Green 0.63 93,800 11,900 84 51,600 13,100 6,800 AF

12% 120,000 13,400 99 71,700 17,100 7,300

Ovangkol (Guibourtia ehie) Green 0.67 — — — — — — AF

12% 116,500 17,700 — 57,200 — —

Para-angelim (Hymenolobium Green 0.63 100,700 13,400 88 51,400 11,000 7,700 AM

 excelsum) 12% 121,300 14,100 110 62,000 13,900 7,700

Parana-pine (Araucaria Green 0.46 49,600 9,300 67 27,600 6,700 2,500 AM

 augustifolia) 12% — 93,100 11,100 84 52,800 11,900 3,500

Pau marfim (Balfourodendron Green 0.73 99,300 11,400 — 41,900 — — AM

 riedelianum) 15% 130,300 — — 56,500 — —

Peroba de campos Green 0.62 — — — — — — AM

 (Paratecoma peroba) 12% 106,200 12,200 70 61,200 14,700 7,100

Peroba rosa (Aspidosperma Green 0.66 75,200 8,900 72 38,200 13,000 7,000 AM

 spp., peroba group) 12% 83,400 10,500 63 54,600 17,200 7,700

Pilon (Hyeronima spp.) Green 0.65 73,800 13,000 57 34,200 8,300 5,400 AM

12% 125,500 15,700 83 66,300 11,900 7,600

Pine, Caribbean (Pinus Green 0.68 77,200 13,000 74 33,800 8,100 4,400 AM

caribaea) 12% — 115,100 15,400 119 58,900 14,400 5,500

Pine, ocote (Pinus oocarpa) Green 0.55 55,200 12,000 48 25,400 7,200 2,600 AM

12% — 102,700 15,500 75 53,000 11,900 4,000

Pine, radiata (Pinus radiata) Green 0.42 42,100 8,100 — 19,200 5,200 2,100 AS

12% — 80,700 10,200 — 41,900 11,000 3,300

Piquia (Caryocar spp.) Green 0.72 85,500 12,500 58 43,400 11,300 7,700 AM

12% 117,200 14,900 109 58,000 13,700 7,700

Primavera (Tabebuia Green 0.4 49,600 6,800 50 24,200 7,100 3,100 AM

donnell–smithii) 12% 65,500 7,200 44 38,600 9,600 2,900

Purpleheart (Peltogyne spp.) Green 0.67 9,400 13,800 102 48,400 11,300 8,100 AM

12% 132,400 15,700 121 71,200 15,300 8,300

Ramin (Gonystylus bancanus) Green 0.52 67,600 10,800 62 37,200 6,800 2,800 AS

12% — 127,600 15,000 117 69,500 10,500 5,800

Robe (Tabebuia spp., Green 0.52 74,500 10,000 81 33,900 8,600 4,000 AM

 roble group) 12% 95,100 11,000 86 50,600 10,000 4,300

Rosewood, Brazilian Green 0.8 97,200 12,700 91 38,000 16,300 10,900 AM

 (Dalbergia nigra) 12% — 131,000 13,000 — 66,200 14,500 12,100

Rosewood, Indian (Dalbergia Green 0.75 63,400 8,200 80 31,200 9,700 6,900 AS

 latifolia) 12% 116,500 12,300 90 63,600 14,400 14,100

Sande (Brosimum spp., Green 0.49 58,600 13,400 — 31,000 7,200 2,700 AM

 utile group) 12% 98,600 16,500 — 56,700 8,900 4,000

Santa Maria (Calophyllum Green 0.52 72,400 11,000 88 31,400 8,700 4,000 AM

 brasiliense) 12% — 100,700 12,600 111 47,600 14,300 5,100

Sapele (Entandrophragma Green 0.55 70,300 10,300 72 34,500 8,600 4,500 AF

 cylindricum) 12% — 105,500 12,500 108 56,300 15,600 6,700

Sepetir (Pseudosindora Green 0.56 77,200 10,800 92 37,600 9,000 4,200 AS

 palustris) 12% 118,600 13,600 92 61,200 14,000 6,300
4–19

Table 4–5a. Mechanical propertiesof some woods imported into the United States other than Canadian

imports (metric)a

—con.

Static bending ComCommon and botanical Moisture Specific

Modulus

of

rupture

Modulus

of

elasticity

Work to

maximum

load

pression

parallel

to grain

Shear

parallel

 to grain

Side

hardness Sample

names of species content gravity (kPa) (MPa) (kJ/m3

) (kPa) (kPa) (N) originb

Shorea (Shorea spp., Green 0.68 80,700 14,500 — 37,100 9,900 6,000 AS

 baulau group) 12% 129,600 18,000 — 70,200 15,100 7,900

Shorea, lauan–meranti group

Dark red meranti Green 0.46 64,800 10,300 59 32,500 7,700 3,100 AS

12% 87,600 12,200 95 50,700 10,000 3,500

Light red meranti Green 0.34 45,500 7,200 43 23,000 4,900 2,000 AS

12% 65,500 8,500 59 40,800 6,700 2,000

White meranti Green 0.55 67,600 9,000 57 37,900 9,100 4,400 AS

15% 85,500 10,300 79 43,800 10,600 5,100

Yellow meranti Green 0.46 55,200 9,000 56 26,800 7,100 3,300 AS

12% 78,600 10,700 70 40,700 10,500 3,400

Spanish-cedar (Cedrela spp.) Green 0.41 51,700 9,000 49 23,200 6,800 2,400 AM

12% — 79,300 9,900 65 42,800 7,600 2,700

Sucupira (Bowdichia spp.) Green 0.74 118,600 15,700 — 67,100 — — AM

15% 133,800 — — 76,500 — —

Sucupira (Diplotropis purpurea) Green 0.78 120,000 18,500 90 55,300 12,400 8,800 AM

12% 142,000 19,800 102 83,700 13,500 9,500

Teak (Tectona grandis) Green 0.55 80,000 9,400 92 41,100 8,900 4,100 AS

12% 100,700 10,700 83 58,000 13,000 4,400

Tornillo (Cedrelinga Green 0.45 57,900 — — 28,300 8,100 3,900 AM

 cateniformis) 12% — — — — — — —

Wallaba (Eperua spp.) Green 0.78 98,600 16,100 — 55,400 — 6,900 AM

12% — 131,700 15,700 — 74,200 — 9,100

a

Results of tests on small, clear, straight-grained specimens. Property values were taken from world literature

 (not obtained from experiments conducted at the Forest Products Laboratory). Other species may be reported

 in the world literature, as well as additional data on many of these species. Some property values have been

 adjusted to 12% moisture content.

b

AF is Africa; AM, America; AS, Asia.
 4–20

Table 4–5b. Mechanical properties of some woods imported into the United States other than Canadian imports

(inch–pound)a

Static bending ComCommon and botanical Moisture Specific

Modulus

of

rupture

Modulus

of

elasticity

Work to

maximum

load

pression

parallel

to grain

Shear

parallel

to grain

Side

hardness Sample

names of species content gravity (lbf/in2

) (×106 lbf/in2) (in-lbf/in3) (lbf/in2) (lbf/in2) (lbf) originb

Afrormosia (Pericopsis elata) Green 0.61 14,800 1.77 19.5 7,490 1,670 1,600 AF

12% 18,400 1.94 18.4 9,940 2,090 1,560

Albarco (Cariniana spp.) Green 0.48 — — — — — — AM

12% 14,500 1.5 13.8 6,820 2,310 1,020

Andiroba (Carapa guianensis) Green 0.54 10,300 1.69 9.8 4,780 1,220 880 AM

12% — 15,500 2 14 8,120 1,510 1,130

Angelin (Andira inermis) Green 0.65 — — — — — — AF

12% 18,000 2.49 — 9,200 1,840 1,750

Angelique (Dicorynia Green 0.6 11,400 1.84 12 5,590 1,340 1,100 AM

 guianensis) 12% — 17,400 2.19 15.2 8,770 1,660 1,290

Avodire (Turraeanthus Green 0.48 — — — — — — AF

 africanus) 12% 12,700 1.49 9.4 7,150 2,030 1,080

Azobe (Lophira alata) Green 0.87 16,900 2.16 12 9,520 2,040 2,890 AF

12% 24,500 2.47 — 12,600 2,960 3,350

Balsa (Ochroma pyramidale) Green 0.16 — — — — — — AM

12% 3,140 0.49 2.1 2,160 300 —

Banak (Virola spp.) Green 0.42 5,600 1.64 4.1 2,390 720 320 AM

12% — 10,900 2.04 10 5,140 980 510

Benge (Guibourtia arnoldiana) Green 0.65 — — — — — — AF

12% 21,400 2.04 — 11,400 2,090 1,750

Bubinga (Guibourtia spp.) Green 0.71 — — — — — — AF

12% 22,600 2.48 — 10,500 3,110 2,690

Bulletwood (Manilkara Green 0.85 17,300 2.7 13.6 8,690 1,900 2,230 AM

 bidentata) 12% 27,300 3.45 28.5 11,640 2,500 3,190

Cativo (Prioria copaifera) Green 0.4 5,900 0.94 5.4 2,460 860 440 AM

12% — 8,600 1.11 7.2 4,290 1,060 630

Ceiba (Ceiba pentandra) Green 0.25 2,200 0.41 1.2 1,060 350 220 AM

12% 4,300 0.54 2.8 2,380 550 240

Courbaril (Hymenaea Green 0.71 12,900 1.84 14.6 5,800 1,770 1,970 AM

 courbaril) 12% — 19,400 2.16 17.6 9,510 2,470 2,350

Cuangare (Dialyanthera spp.) Green 0.31 4,000 1.01 — 2,080 590 230 AM

12% 7,300 1.52 — 4,760 830 380

Cypress, Mexican (Cupressus Green 0.93 6,200 0.92 — 2,880 950 340 AF

 lustianica) 12% 10,300 1.02 — 5,380 1,580 460

Degame (Calycophyllum Green 0.67 14,300 1.93 18.6 6,200 1,660 1,630 AM

 candidissimum) 12% 22,300 2.27 27 9,670 2,120 1,940

Determa (Ocotea rubra) Green 0.52 7,800 1.46 4.8 3,760 860 520 AM

12% 10,500 1.82 6.4 5,800 980 660

Ekop (Tetraberlinia Green 0.6 — — — — — — AF

 tubmaniana) 12% 16,700 2.21 — 9,010 — —

Goncalo alves (Astronium Green 0.84 12,100 1.94 6.7 6,580 1,760 1,910 AM

 graveolens) 12% — 16,600 2.23 10.4 10,320 1,960 2,160

Greenheart (Chlorocardium rodiei) Green 0.8 19,300 2.47 10.5 9,380 1,930 1,880 AM

12% 24,900 3.25 25.3 12,510 2,620 2,350

Hura (Hura crepitans) Green 0.38 6,300 1.04 5.9 2,790 830 440 AM

12% 8,700 1.17 6.7 4,800 1,080 550
4–21

Table 4–5b. Mechanical properties of some woods imported into the United States other than Canadian imports

(inch–pound)a

—con.

Static bending ComCommon and botanical Moisture Specific

Modulus

of

rupture

Modulus

of

elasticity

Work to

maximum

load

pression

parallel

to grain

Shear

parallel

to grain

Side

hardness Sample

names of species content gravity (lbf/in2

) (×106 lbf/in2) (in-lbf/in3) (lbf/in2) (lbf/in2) (lbf) originb

llomba (Pycnanthus Geen 0.4 5,500 1.14 — 2,900 840 470 AF

 angolensis) 12% 9,900 1.59 — 5,550 1,290 610

Ipe (Tabebuia spp., Green 0.92 22,600 2.92 27.6 10,350 2,120 3,060 AM

 lapacho group) 12% 25,400 3.14 22 13,010 2,060 3,680

Iroko (Chlorophora spp.) Green 0.54 10,200 1.29 10.5 4,910 1,310 1,080 AF

12% 12,400 1.46 9 7,590 1,800 1,260

Jarrah (Eucalyptus marginata) Green 0.67 9,900 1.48 — 5,190 1,320 1,290 AS

12% — 16,200 1.88 — 8,870 2,130 1,910

Jelutong (Dyera costulata) Green 0.36 5,600 1.16 5.6 3,050 760 330 AS

15% 7,300 1.18 6.4 3,920 840 390

Kaneelhart (Licaria spp.) Green 0.96 22,300 3.82 13.6 13,390 1,680 2,210 AM

12% 29,900 4.06 17.5 17,400 1,970 2,900

Kapur (Dryobalanops spp.) Green 0.64 12,800 1.6 15.7 6,220 1,170 980 AS

12% 18,300 1.88 18.8 10,090 1,990 1,230

Karri (Eucalyptus diversicolor) Green 0.82 11,200 1.94 11.6 5,450 1,510 1,360 AS

12% 20,160 2.6 25.4 10,800 2,420 2,040

Kempas (Koompassia Green 0.71 14,500 2.41 12.2 7,930 1,460 1,480 AS

 malaccensis) 12% 17,700 2.69 15.3 9,520 1,790 1,710

Keruing (Dipterocarpus spp.) Green 0.69 11,900 1.71 13.9 5,680 1,170 1,060 AS

12% 19,900 2.07 23.5 10,500 2,070 1,270

Lignumvitae (Guaiacum spp.) Green 1.05 — — — — — — AM

12% — — — — 11,400 — 4,500

Limba (Terminalia superba) Green 0.38 6,000 0.77 7.7 2,780 88 400 AF

12% 8,800 1.01 8.9 4,730 1,410 490

Macawood (Platymiscium spp.) Green 0.94 22,300 3.02 — 10,540 1,840 3,320 AM

12% 27,600 3.2 — 16,100 2,540 3,150

Mahogany, African (Khaya spp.) Green 0.42 7,400 1.15 7.1 3,730 931 640 AF

12% 10,700 1.4 8.3 6,460 1,500 830

Mahogany, true Green 0.45 9,000 1.34 9.1 4,340 1,240 740 AM

(Swietenia macrophylla) 12% — 11,500 1.5 7.5 6,780 1,230 800

Manbarklak (Eschweilera spp.) Green 0.87 17,100 2.7 17.4 7,340 1,630 2,280 AM

12% 26,500 3.14 33.3 11,210 2,070 3,480

Manni (Symphonia globulifera) Green 0.58 11,200 1.96 11.2 5,160 1,140 940 AM

12% 16,900 2.46 16.5 8,820 1,420 1,120

Marishballi (Lincania spp.) Green 0.88 17,100 2.93 13.4 7,580 1,620 2,250 AM

12% 27,700 3.34 14.2 13,390 1,750 3,570

Merbau (Intsia spp.) Green 0.64 12,900 2.02 12.8 6,770 1,560 1,380 AS

15% — 16,800 2.23 14.8 8,440 1,810 1,500

Mersawa (Anisoptera spp.) Green 0.52 8,000 1.77 — 3,960 740 880 AS

12% 13,800 2.28 — 7,370 890 1,290

Mora (Mora spp.) Green 0.78 12,600 2.33 13.5 6,400 1,400 1,450 AM

12% 22,100 2.96 18.5 11,840 1,900 2,300

Oak (Quercus spp.) Green 0.76 — — — — — — AM

12% 23,000 3.02 16.5 — — 2,500

Obeche (Triplochiton Green 0.3 5,100 0.72 6.2 2,570 660 420 AF

 scleroxylon) 12% 7,400 0.86 6.9 3,930 990 430
 4–22

Table 4–5b. Mechanical properties of some woods imported into the United States other than Canadian imports

(inch–pound)a

—con.

Static bending ComCommon and botanical Moisture Specific

Modulus

of

rupture

Modulus

of

elasticity

Work to

maximum

load

pression

para to

grain llel

Shear

parallel

to grain

Side

hardness Sample

names of species content gravity (lbf/in2

) (×106 lbf/in2) (in-lbf/in3) (lbf/in2) (lbf/in2) (lbf) originb

Okoume (Aucoumea Green 0.33 — — — — — — AF

 klaineana) 12% 7,400 1.14 — 3,970 970 380

Opepe (Nauclea diderrichii) Green 0.63 13,600 1.73 12.2 7,480 1,900 1,520 AF

12% 17,400 1.94 14.4 10,400 2,480 1,630

Ovangkol (Guibourtia ehie) Green 0.67 — — — — — — AF

12% 16,900 2.56 — 8,300 — —

Para-angelim (Hymenolobium Green 0.63 14,600 1.95 12.8 7,460 1,600 1,720 AM

 excelsum) 12% 17,600 2.05 15.9 8,990 2,010 1,720

Parana-pine (Araucaria Green 0.46 7,200 1.35 9.7 4,010 970 560 AM

 augustifolia) 12% — 13,500 1.61 12.2 7,660 1,730 780

Pau marfim (Balfourodendron Green 0.73 14,400 1.66 — 6,070 — — AM

 riedelianum) 15% 18,900 — — 8,190 — —

Peroba de campos Green 0.62 — — — — — — AM

(Paratecoma peroba) 12% 15,400 1.77 10.1 8,880 2,130 1,600

Peroba rosa (Aspidosperma Green 0.66 10,900 1.29 10.5 5,540 1,880 1,580 AM

 spp., peroba group) 12% 12,100 1.53 9.2 7,920 2,490 1,730

Pilon (Hyeronima spp.) Green 0.65 10,700 1.88 8.3 4,960 1,200 1,220 AM

12% 18,200 2.27 12.1 9,620 1,720 1,700

Pine, Caribbean (Pinus caribaea) Green 0.68 11,200 1.88 10.7 4,900 1,170 980 AM

12% — 16,700 2.24 17.3 8,540 2,090 1,240

Pine, ocote (Pinus oocarpa) Green 0.55 8,000 1.74 6.9 3,690 1,040 580 AM

12% — 14,900 2.25 10.9 7,680 1,720 910

Pine, radiata (Pinus radiata) Green 0.42 6,100 1.18 — 2,790 750 480 AS

12% — 11,700 1.48 — 6,080 1,600 750

Piquia (Caryocar spp.) Green 0.72 12,400 1.82 8.4 6,290 1,640 1,720 AM

12% 17,000 2.16 15.8 8,410 1,990 1,720

Primavera (Tabebuia Green 0.4 7,200 0.99 7.2 3,510 1,030 700 AM

 donnell–smithii) 12% 9,500 1.04 6.4 5,600 1,390 660

Purpleheart (Peltogyne spp.) Green 0.67 1,370 2 14.8 7,020 1,640 1,810 AM

12% 19,200 2.27 17.6 10,320 2,220 1,860

Ramin (Gonystylus bancanus) Green 0.52 9,800 1.57 9 5,390 990 640 AS

12% — 18,500 2.17 17 10,080 1,520 1,300

Robe (Tabebuia spp., Green 0.52 10,800 1.45 11.7 4,910 1,250 910 AM

 roble group) 12% 13,800 1.6 12.5 7,340 1,450 960

Rosewood, Brazilian Green 0.8 14,100 1.84 13.2 5,510 2,360 2,440 AM

 (Dalbergia nigra) 12% — 19,000 1.88 — 9,600 2,110 2,720

Rosewood, Indian (Dalbergia Green 0.75 9,200 1.19 11.6 4,530 1,400 1,560 AS

 latifolia) 12% 16,900 1.78 13.1 9,220 2,090 3,170

Sande (Brosimum spp., Green 0.49 8,500 1.94 — 4,490 1,040 600 AM

 utile group) 12% 14,300 2.39 — 8,220 1,290 900

Santa Maria (Calophyllum Green 0.52 10,500 1.59 12.7 4,560 1,260 890 AM

 brasiliense) 12% — 14,600 1.83 16.1 6,910 2,080 1,150

Sapele (Entandrophragma Green 0.55 10,200 1.49 10.5 5,010 1,250 1,020 AF

 cylindricum) 12% — 15,300 1.82 15.7 8,160 2,260 1,510

Sepetir (Pseudosindora palustris) Green 0.56 11,200 1.57 13.3 5,460 1,310 950 AS

12% 17,200 1.97 13.3 8,880 2,030 1,410
4–23

Table 4–5b. Mechanical properties of some woods imported into the United States other than Canadian imports

(inch–pound)a

—con.

Static bending ComCommon and botanical Moisture Specific

Modulus

of

 rupture

Modulus

of

elasticity

Work to

maximum

load

pression

parallel

to grain

Shear

parallel

to grain

Side

hardness Sample

names of species content gravity (lbf/in2

) (×106 lbf/in2) (in-lbf/in3) (lbf/in2) (lbf/in2) (lbf) originb

Shorea (Shorea spp., Green 0.68 11,700 2.1 — 5,380 1,440 1,350 AS

 bullau group) 12% 18,800 2.61 — 10,180 2,190 1,780

Shorea, lauan–meranti group

Dark red meranti Green 0.46 9,400 1.5 8.6 4,720 1,110 700 AS

12% 12,700 1.77 13.8 7,360 1,450 780

Light red meranti Green 0.34 6,600 1.04 6.2 3,330 710 440 AS

12% 9,500 1.23 8.6 5,920 970 460

White meranti Green 0.55 9,800 1.3 8.3 5,490 1,320 1,000 AS

15% 12,400 1.49 11.4 6,350 1,540 1,140

Yellow meranti Green 0.46 8,000 1.3 8.1 3,880 1,030 750 AS

12% 11,400 1.55 10.1 5,900 1,520 770

Spanish-cedar (Cedrela spp.) Green 0.41 7,500 1.31 7.1 3,370 990 550 AM

12% — 11,500 1.44 9.4 6,210 1,100 600

Sucupira (Bowdichia spp.) Green 0.74 17,200 2.27 — 9,730 — — AM

15% 19,400 — — 11,100 — —

Sucupira (Diplotropis purpurea) Green 0.78 17,400 2.68 13 8,020 1,800 1,980 AM

12% 20,600 2.87 14.8 12,140 1,960 2,140

Teak (Tectona grandis) Green 0.55 11,600 1.37 13.4 5,960 1,290 930 AS

12% 14,600 1.55 12 8,410 1,890 1,000

Tornillo (Cedrelinga Green 0.45 8,400 — — 4,100 1,170 870 AM

 cateniformis) 12% — — — — — — —

Wallaba (Eperua spp.) Green 0.78 14,300 2.33 — 8,040 — 1,540 AM

12% — 19,100 2.28 — 10,760 — 2,040

a

Results of tests on small, clear, straight-grained specimens. Property values were taken from world literature

 (not obtained from experiments conducted at the Forest Products Laboratory). Other species may be reported

 in the world literature, as well as additional data on many of these species. Some property values have been

 adjusted to 12% moisture content.

b

AF is Africa; AM, America; AS, Asia.

Table 4–6. Average coefficients of variation for some mechanical properties

of clear wood

Coefficient of variationa

Property (%)

Static bending

Modulus of rupture 16

Modulus of elasticity 22

Work to maximum load 34

Impact bending 25

Compression parallel to grain 18

Compression perpendicular to grain 28

Shear parallel to grain, maximum shearing strength 14

Tension parallel to grain 25

Side hardness 20

Toughness 34

Specific gravity 10

a

Values based on results of tests of green wood from approximately 50 species.

 Values for wood adjusted to 12% moisture content may be assumed to be

 approximately of the same magnitude.
 4–24

Less Common Properties

Strength properties less commonly measured in clear wood

include torsion, toughness, rolling shear, and fracture toughness. Other properties involving time under load include

creep, creep rupture or duration of load, and fatigue strength.

Torsion strength—Resistance to twisting about a longitudinal axis. For solid wood members, torsional shear

strength may be taken as shear strength parallel to grain.

Two-thirds of the value for torsional shear strength may be

used as an estimate of the torsional shear stress at the proportional limit.

Toughness—Energy required to cause rapid complete

failure in a centrally loaded bending specimen. Tables 4–8

and 4–9 give average toughness values for samples of a few

hardwood and softwood species. Average coefficients of

variation for toughness as determined from approximately

50 species are shown in Table 4–6.

Creep and duration of load—Time-dependent deformation of wood under load. If the load is sufficiently high and

the duration of load is long, failure (creep–rupture) will

eventually occur. The time required to reach rupture is

commonly called duration of load. Duration of load is an

important factor in setting design values for wood. Creep

and duration of load are described in later sections of this

chapter.

Fatigue—Resistance to failure under specific combinations

of cyclic loading conditions: frequency and number of

cycles, maximum stress, ratio of maximum to minimum

stress, and other less-important factors. The main factors

affecting fatigue in wood are discussed later in this chapter.

The discussion also includes interpretation of fatigue data

and information on fatigue as a function of the service

environment.

Rolling shear strength—Shear strength of wood where

shearing force is in a longitudinal plane and is acting perpendicular to the grain. Few test values of rolling shear in

solid wood have been reported. In limited tests, rolling

shear strength averaged 18% to 28% of parallel-to-grain

shear values. Rolling shear strength is about the same in

the longitudinal–radial and longitudinal–tangential planes.

Fracture toughness—Ability of wood to withstand flaws

that initiate failure. Measurement of fracture toughness

helps identify the length of critical flaws that initiate failure

in materials.

To date there is no standard test method for determining

fracture toughness in wood. Three types of stress fields, and

associated stress intensity factors, can be defined at a crack

tip: opening mode (I), forward shear mode (II), and transverse

shear mode (III) (Fig. 4–2a). A crack may lie in one of these

Table 4–7. Average parallel-to-grain tensile strength of

some wood speciesa

 Tensile strength

Species (kPa (lb/in2))

Hardwoods

Beech, American 86,200 (12,500)

Elm, cedar 120,700 (17,500)

Maple, sugar 108,200 (15,700)

Oak

 Overcup 77,900 (11,300)

 Pin 112,400 (16,300)

Poplar, balsam 51,000 (7,400)

Sweetgum 93,800 (13,600)

Willow, black 73,100 (10,600)

Yellow-poplar 109,600 (15,900)

Softwoods

Baldcypress 58,600 (8,500)

Cedar

 Port-Orford 78,600 (11,400)

 Western redcedar 45,500 (6,600)

Douglas-fir, interior north 107,600 (15,600)

Fir

 California red 77,900 (11,300)

 Pacific silver 95,100 (13,800)

Hemlock, western 89,600 (13,000)

Larch, western 111,700 (16,200)

Pine

 Eastern white 73,100 (10,600)

 Loblolly 80,000 (11,600)

 Ponderosa 57,900 (8,400)

 Virginia 94,500 (13,700)

Redwood

 Virgin 64,800 (9,400)

 Young growth 62,700 (9,100)

Spruce

 Engelmann 84,800 (12,300)

 Sitka 59,300 (8,600)

a

Results of tests on small, clear, straight-grained specimens tested

 green. For hardwood species, strength of specimens tested at

 12% moisture content averages about 32% higher; for softwoods,

 about 13% higher.

Table 4–8. Average toughness values for a few hardwood

speciesa

Toughness

Moisture Specific Radial Tangential

Species content gravity (J (in-lbf)) (J (in-lbf))

Birch, yellow 12% 0.65 8,100 (500) 10,100 (620)

Hickory (mocker- Green 0.64 11,400 (700) 11,700 (720)

 nut, pignut, sand) 12% 0.71 10,100 (620) 10,700 (660)

Maple, sugar 14% 0.64 6,000 (370) 5,900 (360)

Oak, red

Pin 12% 0.64 7,000 (430) 7,000 (430)

Scarlet 11% 0.66 8,300 (510) 7,200 (440)

Oak, white

Overcup Green 0.56 11,900 (730) 11,100 (680)

13% 0.62 5,500 (340) 5,000 (310)

Sweetgum Green 0.48 5,500 (340) 5,400 (330)

13% 0.51 4,200 (260) 4,200 (260)

Willow, black Green 0.38 5,000 (310) 5,900 (360)

11% 0.4 3,400 (210) 3,700 (230)

Yellow-poplar Green 0.43 5,200 (320) 4,900 (300)

12% 0.45 3,600 (220) 3,400 (210)
4–25

three planes and may propagate in one of two directions in

each plane. This gives rise to six crack-propagation systems

(RL, TL, LR, TR, LT, and RT) (Fig. 4–2b). Of these crackpropagation systems, four systems are of practical importance: RL, TL, TR, and RT. Each of these four systems allow

for propagation of a crack along the lower strength path

parallel to the grain. The RL and TL orientations in wood

(where R or T is perpendicular to the crack plane and L is the

direction in which the crack propagates) will predominate as

a result of the low strength and stiffness of wood perpendicular to the grain. It is therefore one of these two orientations

that is most often tested. Values for Mode I fracture

toughness range from 220 to 550 

kPa m (200 to

500 lbf in in / . 2 ) and for Mode II range from 1,650 to

2,400 kPa m (1,500 to 2,200 lbf in in / . 2 ). Table 4–10

summarizes selected mode I and mode II test results at 10%

to 12% moisture content available in the literature. The

limited information available on moisture content effects on

fracture toughness suggests that fracture toughness is either

insensitive to moisture content or increases as the material

dries, reaching a maximum between 6% and 15% moisture

content; fracture toughness then decreases with further drying.

Vibration Properties

The vibration properties of primary interest in structural

materials are speed of sound and internal friction (damping

capacity).

Speed of Sound

The speed of sound in a structural material is a function of

the modulus of elasticity and density. In wood, the speed of

sound also varies with grain direction because the transverse

modulus of elasticity is much less than the longitudinal

value (as little as 1/20); the speed of sound across the grain

is about one-fifth to one-third of the longitudinal value.

For example, a piece of wood with a longitudinal modulus

of elasticity of 12.4 GPa (1.8 × 106 lbf/in2) and density of

Table 4–9. Average toughness values for a few softwood

speciesa

Toughness

Moisture Specific Radial Tangential

Species content gravity (J (in-lbf)) (J (in-lbf))

Cedar

Western red 9% 0.33 1,500 (90) 2,100 (130)

Yellow 10% 0.48 3,400 (210) 3,700 (230)

Douglas-fir

 Coast Green

12%

0.44

0.47

3,400

3,300

(210)

(200)

5,900

5,900

(360)

(360)

Interior west Green

13%

0.48

0.51

3,300

3,400

(200)

(210)

4,900

5,500

(300)

(340)

Interior north Green

14%

0.43

0.46

2,800

2,600

(170)

(160)

3,900

4,100

(240)

(250)

Interior south Green

14%

0.38

0.4

2,100

2,000

(130)

(120)

2,900

2,900

(180)

(180)

Fir

 California red Green

12%

0.36

0.39

2,100

2,000

(130)

(120)

2,900

2,800

(180)

(170)

Noble Green 0.36 — — 3,900 (240)

12% 0.39 — — 3,600 (220)

Pacific silver Green 0.37 2,400 (150) 3,700 (230)

13% 0.4 2,800 (170) 4,200 (260)

White Green 0.36 2,300 (140) 3,600 (220)

13% 0.38 2,100 (130) 3,300 (200)

Hemlock

Mountain Green 0.41 4,100 (250) 4,600 (280)

14% 0.44 2,300 (140) 2,800 (170)

Western Green 0.38 2,400 (150) 2,800 (170)

12% 0.41 2,300 (140) 3,400 (210)

Larch, western Green 0.51 4,400 (270) 6,500 (400)

12% 0.55 3,400 (210) 5,500 (340)

Pine

Eastern white Green 0.33 2,000 (120) 2,600 (160)

12% 0.34 1,800 (110) 2,000 (120)

Jack Green 0.41 3,300 (200) 6,200 (380)

12% 0.42 2,300 (140) 3,900 (240)

Loblolly Green 0.48 5,000 (310) 6,200 (380)

12% 0.51 2,600 (160) 4,200 (260)

Lodgepole Green 0.38 2,600 (160) 3,400 (210)

Ponderosa Green 0.38 3,100 (190) 4,400 (270)

11% 0.43 2,400 (150) 3,100 (190)

Red Green 0.4 3,400 (210) 5,700 (350)

12% 0.43 2,600 (160) 4,700 (290)

Shortleaf Green 0.47 4,700 (290) 6,500 (400)

13% 0.5 2,400 (150) 3,700 (230)

Slash Green 0.55 5,700 (350) 7,300 (450)

12% 0.59 3,400 (210) 5,200 (320)

Virginia Green 0.45 5,500 (340) 7,600 (470)

12% 0.49 2,800 (170) 4,100 (250)

Redwood

Old-growth Green 0.39 1,800 (110) 3,300 (200)

11% 0.39 1,500 (90) 2,300 (140)

Young-growth Green 0.33 1,800 (110) 2,300 (140)

12% 0.34 1,500 (90) 1,800 (110)

Spruce, Green 0.34 2,400 (150) 3,100 (190)

 Engelmann 12% 0.35 1,800 (110) 2,900 (180)

a

Results of tests on small, clear, straight-grained specimens.

Figure 4–2. Possible crack propagation systems for

wood.
 4–26

480 kg/m3 (30 lb/ft3) would have a speed of sound in the

longitudinal direction of about 3,800 m/s (12,500 ft/s).

In the transverse direction, modulus of elasticity would be

about 690 MPa (100 × 103 lbf/in2) and the speed of sound

approximately 890 m/s (2,900 ft/s).

The speed of sound decreases with increasing temperature or

moisture content in proportion to the influence of these

variables on modulus of elasticity and density. The speed of

sound decreases slightly with increasing frequency and amplitude of vibration, although for most common applications

this effect is too small to be significant. There is no recognized independent effect of species on the speed of sound.

Variability in the speed of sound in wood is directly related

to the variability of modulus of elasticity and density.

Internal Friction

When solid material is strained, some mechanical energy is

dissipated as heat. Internal friction is the term used to denote

the mechanism that causes this energy dissipation. The

internal friction mechanism in wood is a complex function of

temperature and moisture content. In general, there is a value

of moisture content at which internal friction is minimum.

On either side of this minimum, internal friction increases as

moisture content varies down to zero or up to the fiber saturation point. The moisture content at which minimum internal friction occurs varies with temperature. At room temperature (23oC (73oF)), the minimum occurs at about 6%

moisture content; at −20oC (−4oF), it occurs at about 14%

moisture content, and at 70oC (158oF), at about 4%. At

90oC (194oF), the minimum is not well defined and occurs

near zero moisture content.

Similarly, there are temperatures at which internal friction is

minimum, and the temperatures of minimum internal friction

vary with moisture content. The temperatures of minimum

internal friction are higher as the moisture content is decreased. For temperatures above 0oC (32oF) and moisture

content greater than about 10%, internal friction increases

strongly as temperature increases, with a strong positive

interaction with moisture content. For very dry wood, there

is a general tendency for internal friction to decrease as the

temperature increases.

The value of internal friction, expressed by logarithmic

decrement, ranges from about 0.1 for hot, moist wood to less

than 0.02 for hot, dry wood. Cool wood, regardless of moisture content, would have an intermediate value.

Mechanical Properties of

Clear Straight-Grained Wood

The mechanical properties listed in Table 4–1 through

Table 4–9 are based on a variety of sampling methods.

Generally, the most extensive sampling is represented in

Tables 4–3 and 4–4. The values in Table 4–3 are averages

derived for a number of species grown in the United States.

The tabulated value is an estimate of the average clear wood

property of the species. Many values were obtained from test

specimens taken at a height of 2.4 to 5 m (8 to 16 ft) above

the stump of the tree. Values reported in Table 4–4 represent

estimates of the average clear wood properties of species

grown in Canada and commonly imported into the United

States.

Methods of data collection and analysis changed over the

years during which the data in Tables 4–3 and 4–4 were

collected. In addition, the character of some forests has

changed with time. Because not all the species were reevaluated to reflect these changes, the appropriateness of the data

should be reviewed when used for critical applications such

as stress grades of lumber.

Values reported in Table 4–5 were collected from the world

literature; thus, the appropriateness of these properties to

represent a species is not known. The properties reported in

Tables 4–1, 4–2, 4–5, 4–7, 4–8, 4–9 and 4–10 may not

necessarily represent average species characteristics because of

inadequate sampling; however, they do suggest the relative

influence of species and other specimen parameters on the

mechanical behavior recorded.

Variability in properties can be important in both production

and consumption of wood products. The fact that a piece

may be stronger, harder, or stiffer than the average is often of

less concern to the user than if the piece is weaker; however,

this may not be true if lightweight material is selected for a

specific purpose or if harder or tougher material is difficult to

work. Some indication of the spread of property values is

therefore desirable. Average coefficients of variation for many

mechanical properties are presented in Table 4–6.

Table 4–10. Summary of selected fracture toughness

results

Fracture toughness ( kPa m ( lbf/in in. 2 ))

Mode I Mode II

Species TL RL TL RL

Douglas-fir 320

(290)

360

(330)

2,230

(2,030)

Western hemlock 375

(340)

2,240

(2,040)

Pine

Western white 250

(225)

260

(240)

Scots 440

(400)

500

(455)

2,050

(1,860)

Southern 375

(340)

2,070

(1,880)

Ponderosa 290

(265)

Red spruce 420

(380)

2,190

(1,990)

1,665

(1,510)

Northern red oak 410

(370)

Sugar maple 480

(430)

Yellow-poplar 517

(470)
4–27

The mechanical properties reported in the tables are significantly affected by specimen moisture content at time of test.

Some tables include properties that were evaluated at differing moisture levels; these moisture levels are reported. As

indicated in the tables, many of the dry test data were adjusted to a common moisture content base of 12%.

Specific gravity is reported in many tables because this

property is used as an index of clear wood mechanical properties. The specific gravity values given in Tables 4–3 and 4–4

represent the estimated average clear wood specific gravity of

the species. In the other tables, the specific gravity values

represent only the specimens tested. The variability of specific gravity, represented by the coefficient of variation derived from tests on 50 species, is included in Table 4–6.

Mechanical and physical properties as measured and reported

often reflect not only the characteristics of the wood but also

the influence of the shape and size of the test specimen and

the test mode. The test methods used to establish properties

in Tables 4–3, 4–4, 4–7, 4–8 and 4–9 are based on standard

procedures (ASTM D143). The test methods for properties

presented in other tables are referenced in the selected bibliography at the end of this chapter.

Common names of species listed in the tables conform to

standard nomenclature of the U.S. Department of Agriculture,

Forest Service. Other names may be used locally for a species. Also, one common name may be applied to groups of

species for marketing.

Natural Characteristics

Affecting Mechanical Properties

Clear straight-grained wood is used for determining fundamental mechanical properties; however, because of natural

growth characteristics of trees, wood products vary in specific

gravity, may contain cross grain, or may have knots and

localized slope of grain. Natural defects such as pitch pockets

may occur as a result of biological or climatic elements

influencing the living tree. These wood characteristics must

be taken into account in assessing actual properties or estimating the actual performance of wood products.

Specific Gravity

The substance of which wood is composed is actually heavier than water; its specific gravity is about 1.5 regardless of

wood species. In spite of this, the dry wood of most species

floats in water, and it is thus evident that part of the volume

of a piece of wood is occupied by cell cavities and pores.

Variations in the size of these openings and in the thickness

of the cell walls cause some species to have more wood

substance per unit volume than other species and therefore

higher specific gravity. Thus, specific gravity is an excellent

index of the amount of wood substance contained in a piece

of wood; it is a good index of mechanical properties as long

as the wood is clear, straight grained, and free from defects.

However, specific gravity values also reflect the presence of

gums, resins, and extractives, which contribute little to

mechanical properties.

Approximate relationships between various mechanical

properties and specific gravity for clear straight-grained wood

of hardwoods and softwoods are given in Table 4–11 as

power functions. Those relationships are based on average

values for the 43 softwood and 66 hardwood species presented in Table 4–3. The average data vary around the relationships, so that the relationships do not accurately predict

individual average species values or an individual specimen

value. In fact, mechanical properties within a species tend to

be linearly, rather than curvilinearly, related to specific gravity; where data are available for individual species, linear

analysis is suggested.

Knots

A knot is that portion of a branch that has become incorporated in the bole of a tree. The influence of a knot on the

mechanical properties of a wood member is due to the interruption of continuity and change in the direction of wood

fibers associated with the knot. The influence of knots depends on their size, location, shape, and soundness; attendant local slope of grain; and type of stress to which the

wood member is subjected.

The shape (form) of a knot on a sawn surface depends upon

the direction of the exposing cut. A nearly round knot is

produced when lumber is sawn from a log and a branch is

sawn through at right angles to its length (as in a flatsawn

board). An oval knot is produced if the saw cut is diagonal

to the branch length (as in a bastard-sawn board) and a

“spiked” knot when the cut is lengthwise to the branch (as

in a quartersawn board).

Knots are further classified as intergrown or encased

(Fig. 4–3). As long as a limb remains alive, there is continuous growth at the junction of the limb and the bole of the

tree, and the resulting knot is called intergrown. After the

branch has died, additional growth on the trunk encloses the

dead limb, resulting in an encased knot; bole fibers are not

continuous with the fibers of the encased knot. Encased knots

and knotholes tend to be accompanied by less cross-grain

than are intergrown knots and are therefore generally less

problematic with regard to most mechanical properties.

Most mechanical properties are lower in sections containing

knots than in clear straight-grained wood because (a) the clear

wood is displaced by the knot, (b) the fibers around the knot

are distorted, resulting in cross grain, (c) the discontinuity of

wood fiber leads to stress concentrations, and (d) checking

often occurs around the knots during drying. Hardness and

strength in compression perpendicular to the grain are exceptions, where knots may be objectionable only in that they

cause nonuniform wear or nonuniform stress distributions at

contact surfaces.

Knots have a much greater effect on strength in axial tension

than in axial short-column compression, and the effects on

bending are somewhat less than those in axial tension.
 4–28

For this reason, in a simply supported beam, a knot on the

lower side (subjected to tensile stresses) has a greater effect

on the load the beam will support than does a knot on the

upper side (subjected to compressive stresses).

In long columns, knots are important because they affect

stiffness. In short or intermediate columns, the reduction in

strength caused by knots is approximately proportional to

their size; however, large knots have a somewhat greater

relative effect than do small knots.

Knots in round timbers, such as poles and piles, have less

effect on strength than do knots in sawn timbers. Although

the grain is irregular around knots in both forms of timber,

the angle of the grain to the surface is smaller in naturally

round timber than in sawn timber. Furthermore, in round

This page revised June 2002

timbers there is no discontinuity in wood fibers, which

results from sawing through both local and general slope of

grain.

The effects of knots in structural lumber are discussed in

Chapter 6.

Slope of Grain

In some wood product applications, the directions of important stresses may not coincide with the natural axes of fiber

orientation in the wood. This may occur by choice in

design, from the way the wood was removed from the log, or

because of grain irregularities that occurred while the tree was

growing.

Table 4–11a. Functions relating mechanical properties to specific gravity of clear, straight-grained wood (metric)

Specific gravity–strength relationship

Green wood Wood at 12% moisture content

Propertya Softwoods Hardwoods Softwoods Hardwoods

Static bending

MOR (kPa) 109,600 G1.01 118,700 G1.16 170,700 G1.01 171,300 G1.13

MOE (MPa) 16,100 G0.76 13,900 G0.72 20,500 G0.84 16,500 G0.7

WML (kJ/m3) 147 G1.21 229 G1.52 179 G1.34 219 G1.54

Impact bending (N) 353 G1.35 422 G1.39 346 G1.39 423 G1.65

Compression parallel (kPa) 49,700 G0.94 49,000 G1.11 93,700 G0.97 76,000 G0.89

Compression perpendicular (kPa) 8,800 G1.53 18,500 G2.48 16,500 G1.57 21,600 G2.09

Shear parallel (kPa) 11,000 G0.73 17,800 G1.24 16,600 G0.85 21,900 G1.13

Tension perpendicular (kPa) 3,800 G0.78 10,500 G1.37 6,000 G1.11 10,100 G1.3

Side hardness (N) 6,230 G1.41 16,550 G2.31 85,900 G1.5 15,300 G2.09

a

Compression parallel to grain is maximum crushing strength; compression perpendicular to grain is fiber stress at

 proportional limit. MOR is modulus of rupture; MOE, modulus of elasticity; and WML, work to maximum load. For green

 wood, use specific gravity based on ovendry weight and green volume; for dry wood, use specific gravity based on

 ovendry weight and volume at 12% moisture content.

Table 4–11b. Functions relating mechanical properties to specific gravity of clear, straight-grained wood (inch–pound)

Specific gravity–strength relationship

Green wood Wood at 12% moisture content

Propertya Softwoods Hardwoods Softwoods Hardwoods

Static bending

MOR (lb/in2) 15,890 G1.01 17,210 G1.16 24,760 G1.01 24,850 G1.13

MOE (×106 lb/in2) 2.33 G0.76 2.02 G0.72 2.97 G.0.84 2.39 G0.7

WML (in-lbf/in3) 21.33 G1.21 33.2 G1.52 25.9 G1.34 31.8 G1.54

Impact bending (lbf) 79.28 G1.35 94.9 G1.39 77.7 G1.39 95.1 G1.65

Compression parallel (lb/in2) 7,210 G0.94 7,110 G1.11 13,590 G0.97 11,030 G0.89

Compression perpendicular (lb/in2) 1,270 G1.53 2,680 G2.48 2,390 G1.57 3,130 G2.09

Shear parallel (lb/in2) 1,590 G0.73 2,580 G1.24 2,410 G.0.85 3,170 G1.13

Tension perpendicular (lb/in2) 550 G0.78 1,520 G1.37 870 G1.11 1,460 G1.3

Side hardness (lbf) 1,400 G1.41 3,720 G2.31 1,930 G1.5 3,440 G2.09

a

Compression parallel to grain is maximum crushing strength; compression perpendicular to grain is fiber stress at

 proportional limit. MOR is modulus of rupture; MOE, modulus of elasticity; and WML, work to maximum load. For green

 wood, use specific gravity based on ovendry weight and green volume; for dry wood, use specific gravity based on

 ovendry weight and volume at 12% moisture content.
4–29

Elastic properties in directions other than along the natural

axes can be obtained from elastic theory. Strength properties

in directions ranging from parallel to perpendicular to the

fibers can be approximated using a Hankinson-type formula

(Bodig and Jayne 1982):

 

 

N PQ

P Q n n = sin cos θ θ + (4–2)

where N is strength at angle θ from fiber direction,

Q strength perpendicular to grain, P strength parallel to

grain, and n an empirically determined constant.

This formula has been used for modulus of elasticity as well

as strength properties. Values of n and associated ratios of

Q/P tabulated from available literature are as follows:

Property n Q/P

Tensile strength 1.5–2 0.04–0.07

Compression strength 2–2.5 0.03–0.40

Bending strength 1.5–2 0.04–0.10

Modulus of elasticity 2 0.04–0.12

Toughness 1.5–2 0.06–0.10

The Hankinson-type formula can be graphically depicted as a

function of Q/P and n. Figure 4–4 shows the strength in any

direction expressed as a fraction of the strength parallel to

fiber direction, plotted against angle to the fiber direction θ.

The plot is for a range of values of Q/P and n.

The term slope of grain relates the fiber direction to the edges

of a piece. Slope of grain is usually expressed by the ratio

between 25 mm (1 in.) of the grain from the edge or long

axis of the piece and the distance in millimeters (inches)

within which this deviation occurs (tan θ). The effect of grain

slope on some properties of wood, as determined from tests,

is shown in Table 4–12. The values for modulus of rupture

fall very close to the curve in Figure 4–4 for Q/P = 0.1 and

n = 1.5. Similarly, the impact bending values fall close to

the curve for Q/P = 0.05 and n =1.5, and the compression

values for the curve for Q/P = 0.1, n = 2.5.

The term cross grain indicates the condition measured by

slope of grain. Two important forms of cross grain are spiral

and diagonal (Fig. 4–5). Other types are wavy, dipped,

interlocked, and curly.

Spiral grain is caused by winding or spiral growth of wood

fibers about the bole of the tree instead of vertical growth. In

sawn products, spiral grain can be defined as fibers lying in

the tangential plane of the growth rings, rather than parallel

to the longitudinal axis of the product (see Fig. 4–5 for a

simple case). Spiral grain in sawn products often goes undetected by ordinary visual inspection. The best test for spiral

grain is to split a sample section from the piece in the radial

direction. A visual method of determining the presence of

spiral grain is to note the alignment of pores, rays, and resin

ducts on a flatsawn face. Drying checks on a flatsawn surface

follow the fibers and indicate the slope of the fiber. Relative

Figure 4–3. Types of knots. A, encased knot;

B, intergrown.

1.0

Fraction of property parallel to the fiber direction N/P

0.8

0.6

0.4

0.2

0 10 20 30 40 50 60 70

Q/P =

0.20

0.10

0.05

Angle to fiber direction (deg)

Figure 4–4. Effect of grain angle on mechanical property

of clear wood according to Hankinson-type formula.

Q/P is ratio of mechanical property across the grain (Q)

to that parallel to the grain (P); n is an empirically

determined constant.
 4–30

change in electrical capacitance is an effective technique for

measuring slope of grain.

Diagonal grain is cross grain caused by growth rings that are

not parallel to one or both surfaces of the sawn piece. Diagonal grain is produced by sawing a log with pronounced taper

parallel to the axis (pith) of the tree. Diagonal grain also

occurs in lumber sawn from crooked logs or logs with butt

swell.

Cross grain can be quite localized as a result of the disturbance of a growth pattern by a branch. This condition,

termed local slope of grain, may be present even though the

branch (knot) may have been removed by sawing. The degree

of local cross grain may often be difficult to determine. Any

form of cross grain can have a deleterious effect on mechanical

properties or machining characteristics.

Spiral and diagonal grain can combine to produce a more

complex cross grain. To determine net cross grain, regardless

of origin, fiber slopes on the contiguous surface of a piece

must be measured and combined. The combined slope of

grain is determined by taking the square root of the sum of

the squares of the two slopes. For example, assume that the

spiral grain slope on the flat-grained surface of Figure 4–5D

is 1 in 12 and the diagonal-grain slope is 1 in 18. The combined slope is

 (/ ) (/ ) / 1 18 1 12 1 10 2 2 + =

or a slope of 1 in 10.

A regular reversal of right and left spiraling of grain in a tree

stem produces the condition known as interlocked grain.

Interlocked grain occurs in some hardwood species (Ch. 3,

Table 3–9) and markedly increases resistance to splitting in

the radial plane. Interlocked grain decreases both the static

bending strength and stiffness of clear wood specimens. The

data from tests of domestic hardwoods shown in Table 4–3

do not include pieces that exhibited interlocked grain. Some

mechanical property values in Table 4–5 are based on specimens with interlocked grain because that is a characteristic of

some species. The presence of interlocked grain alters the

relationship between bending strength and compressive

strength of lumber cut from tropical hardwoods.

Annual Ring Orientation

Stresses perpendicular to the fiber (grain) direction may be

at any angle from 0° (T ) to 90o (R) to the growth rings

(Fig. 4–6). Perpendicular-to-grain properties depend somewhat upon orientation of annual rings with respect to the

direction of stress. The compression perpendicular-to-grain

values in Table 4–3 were derived from tests in which the

load was applied parallel to the growth rings (T direction);

shear parallel-to-grain and tension perpendicular-to-grain

values are averages of equal numbers of specimens with 0o

and 90o growth ring orientations. In some species, there is

no difference in 0o and 90 o orientation properties. Other

species exhibit slightly higher shear parallel or tension perpendicular-to-grain properties for the 0o

 orientation than for

Table 4–12. Strength of wood members with various

grain slopes compared with strength of a straightgrained membera

Maximum slope

of grain in

member

Modulus

of rupture

(%)

Impact

bending

(%)

Compression

parallel to grain

(%)

Straight-grained 100 100 100

1 in 25 96 95 100

1 in 20 93 90 100

1 in 15 89 81 100

1 in 10 81 62 99

1 in 5 55 36 93

a

Impact bending is height of drop causing complete

 failure (0.71-kg (50-lb) hammer); compression parallel

 to grain is maximum crushing strength.

Figure 4–5. Relationship of fiber orientation (O-O) to

axes, as shown by schematic of wood specimens

containing straight grain and cross grain. Specimens A

through D have radial and tangential surfaces;

E through H do not. Specimens A and E contain no

cross grain; B, D, F, and H have spiral grain;

C, D, G, and H have diagonal grain.
4–31

the 90o orientation; the converse is true for about an equal

number of species.

The effects of intermediate annual ring orientations have been

studied in a limited way. Modulus of elasticity, compressive

perpendicular-to-grain stress at the proportional limit, and

tensile strength perpendicular to the grain tend to be about

the same at 45o and 0o, but for some species these values are

40% to 60% lower at the 45o orientation. For those species

with lower properties at 45o ring orientation, properties tend

to be about equal at 0o and 90o orientations. For species with

about equal properties at 0o and 45o orientations, properties

tend to be higher at the 90o orientation.

Reaction Wood

Abnormal woody tissue is frequently associated with leaning

boles and crooked limbs of both conifers and hardwoods. It

is generally believed that such wood is formed as a natural

response of the tree to return its limbs or bole to a more

normal position, hence the term reaction wood. In softwoods, the abnormal tissue is called compression wood; it

is common to all softwood species and is found on the lower

side of the limb or inclined bole. In hardwoods, the abnormal tissue is known as tension wood; it is located on the

upper side of the inclined member, although in some instances it is distributed irregularly around the cross section.

Reaction wood is more prevalent in some species than in

others.

Many of the anatomical, chemical, physical, and mechanical

properties of reaction wood differ distinctly from those of

normal wood. Perhaps most evident is the increase in density compared with that of normal wood. The specific gravity

of compression wood is commonly 30% to 40% greater than

that of normal wood; the specific gravity of tension wood

commonly ranges between 5% and 10% greater than that of

normal wood, but it may be as much as 30% greater.

Compression wood is usually somewhat darker than normal

wood because of the greater proportion of latewood, and it

frequently has a relatively lifeless appearance, especially in

woods in which the transition from earlywood to latewood is

abrupt. Because compression wood is more opaque than

normal wood, intermediate stages of compression wood can

be detected by transmitting light through thin cross sections;

however, borderline forms of compression wood that merge

with normal wood can commonly be detected only by microscopic examination.

Tension wood is more difficult to detect than is compression

wood. However, eccentric growth as seen on the transverse

section suggests its presence. Also, because it is difficult to

cleanly cut the tough tension wood fibers, the surfaces of

sawn boards are “woolly,” especially when the boards are

sawn in the green condition (Fig. 4–7). In some species,

tension wood may be evident on a smooth surface as areas of

contrasting colors. Examples of this are the silvery appearance of tension wood in sugar maple and the darker color of

tension wood in mahogany.

Reaction wood, particularly compression wood in the green

condition, may be stronger than normal wood. However,

compared with normal wood with similar specific gravity,

reaction wood is definitely weaker. Possible exceptions to

this are compression parallel-to-grain properties of compression wood and impact bending properties of tension wood.

Figure 4–6. Direction of load in relation to direction of

annual growth rings: 90o

 or perpendicular (R), 45°, 0°

or parallel (T).

Figure 4–7. Projecting tension wood fibers on sawn

surface of mahogany board.
 4–32

Because of the abnormal properties of reaction wood, it may

be desirable to eliminate this wood from raw material. In

logs, compression wood is characterized by eccentric growth

about the pith and the large proportion of latewood at the

point of greatest eccentricity (Fig. 4–8A). Fortunately, pronounced compression wood in lumber can generally be

detected by ordinary visual examination.

Compression and tension wood undergo extensive longitudinal shrinkage when subjected to moisture loss below the

fiber saturation point. Longitudinal shrinkage in compression

wood may be up to 10 times that in normal wood and in

tension wood, perhaps up to 5 times that in normal wood.

When reaction wood and normal wood are present in the

same board, unequal longitudinal shrinkage causes internal

stresses that result in warping. In extreme cases, unequal

longitudinal shrinkage results in axial tension failure over a

portion of the cross section of the lumber (Fig. 4–8B). Warp

sometimes occurs in rough lumber but more often in planed,

ripped, or resawn lumber (Fig. 4–8C).

Juvenile Wood

Juvenile wood is the wood produced near the pith of the tree;

for softwoods, it is usually defined as the material 5 to

20 rings from the pith depending on species. Juvenile wood

has considerably different physical and anatomical properties

than that of mature wood (Fig. 4–9). In clear wood, the

properties that have been found to influence mechanical

behavior include fibril angle, cell length, and specific gravity,

the latter a composite of percentage of latewood, cell wall

thickness, and lumen diameter. Juvenile wood has a high

fibril angle (angle between longitudinal axis of wood cell

and cellulose fibrils), which causes longitudinal shrinkage

that may be more than 10 times that of mature wood. Compression wood and spiral grain are also more prevalent in

juvenile wood than in mature wood and contribute to longitudinal shrinkage. In structural lumber, the ratio of modulus

of rupture, ultimate tensile stress, and modulus of elasticity

for juvenile to mature wood ranges from 0.5 to 0.9, 0.5 to

0.95, and 0.45 to 0.75, respectively. Changes in shear

strength resulting from increases in juvenile wood content

can be adequately predicted by monitoring changes in density alone for all annual ring orientations. The same is true

for perpendicular-to-grain compressive strength when the load

is applied in the tangential direction. Compressive strength

perpendicular-to-grain for loads applied in the radial direction, however, is more sensitive to changes in juvenile wood

content and may be up to eight times less than that suggested by changes in density alone. The juvenile wood to

mature wood ratio is lower for higher grades of lumber than

for lower grades, which indicates that juvenile wood has

greater influence in reducing the mechanical properties of

high-grade structural lumber. Only a limited amount of

research has been done on juvenile wood in hardwood

species.

Figure 4–8. Effects of compression wood. A, eccentric

growth about pith in cross section containing compression wood—dark area in lower third of cross section is

compression wood; B, axial tension break caused by

excessive longitudinal shrinkage of compression wood;

C, warp caused by excessive longitudinal shrinkage.

Fibril angleLongitudinal shrinkageMoisture contentSpiral grain

Specific gravityCell lengthStrengthCell wall thicknessTransverse shrinkagePercentage latewood

Juvenile

wood

Mature wood

Juvenile

wood

Mature wood

Pith 5-20 rings Bark

Figure 4–9. Properties of juvenile wood.
4–33

Compression Failures

Excessive compressive stresses along the grain that produce

minute compression failures can be caused by excessive

bending of standing trees from wind or snow; felling of trees

across boulders, logs, or irregularities in the ground; or

rough handling of logs or lumber. Compression failures

should not be confused with compression wood. In some

instances, compression failures are visible on the surface of

a board as minute lines or zones formed by crumpling or

buckling of cells (Fig. 4–10A), although the failures usually

appear as white lines or may even be invisible to the naked

eye. The presence of compression failures may be indicated

by fiber breakage on end grain (Fig. 4–10B). Since compression failures are often difficult to detect with the unaided eye,

special efforts, including optimum lighting, may be required

for detection. The most difficult cases are detected only by

microscopic examination.

Products containing visible compression failures have low

strength properties, especially in tensile strength and shock

resistance. The tensile strength of wood containing compression failures may be as low as one-third the strength of

matched clear wood. Even slight compression failures, visible only under a microscope, may seriously reduce strength

and cause brittle fracture. Because of the low strength associated with compression failures, many safety codes require

certain structural members, such as ladder rails and scaffold

planks, to be entirely free of such failures.

Pitch Pockets

A pitch pocket is a well-defined opening that contains free

resin. The pocket extends parallel to the annual rings; it is

almost flat on the pith side and curved on the bark side.

Pitch pockets are confined to such species as the pines,

spruces, Douglas-fir, tamarack, and western larch.

The effect of pitch pockets on strength depends upon their

number, size, and location in the piece. A large number of

pitch pockets indicates a lack of bond between annual growth

layers, and a piece with pitch pockets should be inspected for

shake or separation along the grain.

Bird Peck

Maple, hickory, white ash, and a number of other species are

often damaged by small holes made by woodpeckers.

These bird pecks often occur in horizontal rows, sometimes

encircling the tree, and a brown or black discoloration known

as a mineral streak originates from each hole. Holes for tapping maple trees are also a source of mineral streaks. The

streaks are caused by oxidation and other chemical changes

in the wood. Bird pecks and mineral streaks are not generally

important in regard to strength of structural lumber, although

they do impair the appearance of the wood.

Extractives

Many wood species contain removable extraneous materials

or extractives that do not degrade the cellulose–lignin structure of the wood. These extractives are especially abundant in

species such as larch, redwood, western redcedar, and black

locust.

A small decrease in modulus of rupture and strength in

compression parallel to grain has been measured for some

species after the extractives have been removed. The extent to

which extractives influence strength is apparently a function

of the amount of extractives, the moisture content of the

piece, and the mechanical property under consideration.

Properties of Timber From Dead Trees

Timber from trees killed by insects, blight, wind, or fire may

be as good for any structural purpose as that from live trees,

provided further insect attack, staining, decay, or drying

degrade has not occurred. In a living tree, the heartwood is

entirely dead and only a comparatively few sapwood cells are

alive. Therefore, most wood is dead when cut, regardless of

Figure 4–10. Compression failures. A, compression

failure shown by irregular lines across grain; B, fiber

breakage in end-grain surfaces of spruce lumber caused

by compression failures below dark line.
 4–34

whether the tree itself is living or not. However, if a tree

stands on the stump too long after its death, the sapwood is

likely to decay or to be attacked severely by wood-boring

insects, and eventually the heartwood will be similarly

affected. Such deterioration also occurs in logs that have been

cut from live trees and improperly cared for afterwards. Because of variations in climatic and other factors that affect

deterioration, the time that dead timber may stand or lie in

the forest without serious deterioration varies.

Tests on wood from trees that had stood as long as 15 years

after being killed by fire demonstrated that this wood was as

sound and strong as wood from live trees. Also, the heartwood of logs of some more durable species has been found to

be thoroughly sound after lying in the forest for many years.

On the other hand, in nonresistant species, decay may cause

great loss of strength within a very brief time, both in trees

standing dead on the stump and in logs cut from live trees

and allowed to lie on the ground. The important consideration is not whether the trees from which wood products are

cut are alive or dead, but whether the products themselves are

free from decay or other degrading factors that would render

them unsuitable for use.

Effects of Manufacturing and

Service Environments

Moisture Content

Many mechanical properties are affected by changes in moisture content below the fiber saturation point. Most properties

reported in Tables 4–3, 4–4, and 4–5 increase with decrease

in moisture content. The relationship that describes these

changes in clear wood property at about 21oC (70oF)is

 

 

P P P

P

M

M

= 











−

−













12

12

g

12

p 12

 (4–3)

where P is the property at moisture content M (%), P12 the

same property at 12% MC, Pg the same property for green

wood, and Mp moisture content at the intersection of a

horizontal line representing the strength of green wood and

an inclined line representing the logarithm of the strength–

moisture content relationship for dry wood. This assumed

linear relationship results in an Mp value that is slightly less

than the fiber saturation point. Table 4–13 gives values of Mp

for a few species; for other species, Mp = 25 may be assumed.

Average property values of P12 and Pg are given for many

species in Tables 4–3 to 4–5. The formula for moisture

content adjustment is not recommended for work to maximum load, impact bending, and tension perpendicular to

grain. These properties are known to be erratic in their

response to moisture content change.

The formula can be used to estimate a property at any moisture content below Mp from the species data given. For

example, suppose you want to find the modulus of rupture of

white ash at 8% moisture content. Using information from

Tables 4–3a and 4–13,

 

P8

4 12

103 000 103 000

66 000 = 119 500 

  , = ,

, ,

/

kPa

Care should be exercised when adjusting properties below

12% moisture. Although most properties will continue to

increase while wood is dried to very low moisture content

levels, for most species some properties may reach a

maximum value and then decrease with further drying

(Fig. 4–11). For clear Southern Pine, the moisture content

at which a maximum property has been observed is given

in Table 4–14.

This increase in mechanical properties with drying assumes

small, clear specimens in a drying process in which no

deterioration of the product (degrade) occurs. For 51-mm-

(2-in.-) thick lumber containing knots, the increase in property with decreasing moisture content is dependent upon

lumber quality. Clear, straight-grained lumber may show

increases in properties with decreasing moisture content that

approximate those of small, clear specimens. However, as the

frequency and size of knots increase, the reduction in strength

resulting from the knots begins to negate the increase in

property in the clear wood portion of the lumber. Very low

quality lumber, which has many large knots, may be insensitive to changes in moisture content. Figures 4–12 and 4–13

illustrate the effect of moisture content on the properties of

lumber as a function of initial lumber strength (Green and

others 1989). Application of these results in adjusting allowable properties of lumber is discussed in Chapter 6.

Additional information on influences of moisture content

on dimensional stability is included in Chapter 12.

Table 4–13. Intersection moisture content values for

selected speciesa

Mp

Species (%)

Ash, white 24

Birch, yellow 27

Chestnut, American 24

Douglas-fir 24

Hemlock, western 28

Larch, western 28

Pine, loblolly 21

Pine, longleaf 21

Pine, red 24

Redwood 21

Spruce, red 27

Spruce, Sitka 27

Tamarack 24

a

Intersection moisture content is point at which

 mechanical properties begin to change when wood

 is dried from the green condition.
4–35

Temperature

Reversible Effects

In general, the mechanical properties of wood decrease when

heated and increase when cooled. At a constant moisture

content and below approximately 150oC (302oF), mechanical

properties are approximately linearly related to temperature.

The change in properties that occurs when wood is quickly

heated or cooled and then tested at that condition is termed

an immediate effect. At temperatures below 100oC (212oF),

the immediate effect is essentially reversible; that is, the

property will return to the value at the original temperature

if the temperature change is rapid.

Figure 4–14 illustrates the immediate effect of temperature on

modulus of elasticity parallel to grain, modulus of rupture,

and compression parallel to grain, 20o

C (68oF), based on a

composite of results for clear, defect-free wood. This figure

represents an interpretation of data from several investigators.

The width of the bands illustrates variability between and

within reported trends.

Table 4–15 lists changes in clear wood properties at −50o

C

(−58oF) and 50oC (122oF) relative to those at 20oC (68oF) for

a number of moisture conditions. The large changes at

−50oC (−58oF) for green wood (at fiber saturation point or

wetter) reflect the presence of ice in the wood cell cavities.

The strength of dry lumber, at about 12% moisture content,

may change little as temperature increases from −29oC

(−20oF) to 38oC (100oF). For green lumber, strength generally decreases with increasing temperature. However, for

temperatures between about 7oC (45oF) and 38oC (100oF),

the changes may not differ significantly from those at room

temperature. Table 4–16 provides equations that have been

Property (MPa)

Property (x103 lbf/in2)

150 22.0

120

90

60

30

0 5 10 15 20 25 30

Moisture content (%)

16.5

11.0

5.5

A

B

C

D

E 0

Figure 4–11. Effect of moisture content on wood

strength properties. A, tension parallel to grain;

B, bending; C, compression parallel to grain;

D, compression perpendicular to grain; and

E, tension perpendicular to grain.

Table 4–14. Moisture content for maximum property

value in drying clear Southern Pine from green to

4% moisture content

Property

Moisture content

at which peak

property occurs

(%)

Ultimate tensile stress

parallel to grain 12.6

Ultimate tensile stress

perpendicular to grain 10.2

MOE tension perpendicular to grain 4.3

MOE compression parallel to grain 4.3

Modulus of rigidity, GRT 10.0

120

80

40

0

Ultimate tensile stress (MPa)

16

Ultimate tensile stress (x103 lbf/in2)

12

8

4

0

8 12 16 20 24

Moisture content (%)

Figure 4–12. Effect of moisture content on tensile

strength of lumber parallel to grain.

12

8

4

0

90

60

30

0

8 12 16 20 24

Ultimate compressive strength (x103 lbf/in2)

Ultimate compressive strength (MPa)

Moisture content (%)

Figure 4–13. Effect of moisture content on

compressive strength of lumber parallel to grain.
 4–36

used to adjust some lumber properties for the reversible

effects of temperature.

Irreversible Effects

In addition to the reversible effect of temperature on wood,

there is an irreversible effect at elevated temperature. This

permanent effect is one of degradation of wood substance,

which results in loss of weight and strength. The loss depends on factors that include moisture content, heating medium, temperature, exposure period, and to some extent,

species and size of piece involved.

The permanent decrease of modulus of rupture caused by

heating in steam and water is shown as a function of temperature and heating time in Figure 4–15, based on tests of clear

pieces of Douglas-fir and Sitka spruce. In the same studies,

heating in water affected work to maximum load more than

modulus of rupture (Fig. 4–16). The effect of heating dry

wood (0% moisture content) on modulus of rupture and

modulus of elasticity is shown in Figures 4–17 and 4–18,

respectively, as derived from tests on four softwoods and two

hardwoods.

200

150

100

50

0

Relative modulus of elasticity (%)

-200 -100 0 100 200 300

12% moisture content

0% moisture content

(a)

Relative modulus of rupture (%)

250

200

150

100

50

0

-200 -150 -100 -50 0 50 100 150

18% moisture content

0%

moisture content 12% moisture content

(b)

300

250

200

150

100

50

0

-200 -100 0 100 200 300

12% moisture content

0% moisture content

Temperature (°C)

Relative compressive strength (%)

(c)

Figure 4–14. Immediate effect of temperature at two

moisture content levels relative to value at 20°C (68°F)

for clear, defect-free wood: (a) modulus of elasticity

parallel to grain, (b) modulus of rupture in bending,

(c) compressive strength parallel to grain. The plot is a

composite of results from several studies. Variability

in reported trends is illustrated by width of bands.

Table 4–15. Approximate middle-trend effects of

temperature on mechanical properties of clear wood

at various moisture conditions

Relative change in

mechanical property

from 20°C (68°F) at

Moisture

conditiona

−50°C

(−58°F)

+50°C

(+122°F)

Property (%) (%) (%)

MOE parallel to grain 0 +11 −6

12 +17 −7

>FSP +50 —

MOE perpendicular to grain 6 — −20

12 — −35

≥20 — −38

Shear modulus >FSP — −25

Bending strength ≤4 +18 −10

11–15 +35 −20

18–20 +60 −25

>FSP +110 −25

Tensile strength parallel to grain 0–12 — −4

Compressive strength parallel 0 +20 −10

 to grain 12–45 +50 −25

Shear strength parallel to grain >FSP — −25

Tensile strength perpendicular 4–6 — −10

 to grain 11–16 — −20

≥18 — −30

Compressive strength perpendicular to grain at proportional

limit

0–6

≥10

—

—

−20

−35

a

FSP indicates moisture content greater than fiber saturation point.
4–37

Figure 4–19 illustrates the permanent loss in bending

strength of Spruce–Pine–Fir standard 38- by 89-mm

(nominal 2- by 4-in.) lumber heated at 66o

C (150oF) and

about 12% moisture content. During this same period,

modulus of elasticity barely changed. Most in-service

exposures at 66°C (150°F) would be expected to result in

much lower moisture content levels. Additional results for

other lumber products and exposure conditions will be reported as Forest Products Laboratory studies progress.

The permanent property losses discussed here are based on

tests conducted after the specimens were cooled to room

temperature and conditioned to a range of 7% to 12% moisture content. If specimens are tested hot, the percentage of

strength reduction resulting from permanent effects is based

on values already reduced by the immediate effects. Repeated

exposure to elevated temperature has a cumulative effect on

wood properties. For example, at a given temperature the

property loss will be about the same after six 1-month exposure as it would be after a single 6-month exposure.

The shape and size of wood pieces are important in analyzing

the influence of temperature. If exposure is for only a short

time, so that the inner parts of a large piece do not reach the

temperature of the surrounding medium, the immediate effect

on strength of the inner parts will be less than that for the

outer parts. However, the type of loading must be considered. If the member is to be stressed in bending, the outer

fibers of a piece will be subjected to the greatest stress and

will ordinarily govern the ultimate strength of the piece;

hence, under this loading condition, the fact that the inner

part is at a lower temperature may be of little significance.

For extended noncyclic exposures, it can be assumed that the

entire piece reaches the temperature of the heating medium

and will therefore be subject to permanent strength losses

throughout the volume of the piece, regardless of size and

mode of stress application. However, in ordinary construction wood often will not reach the daily temperature extremes

of the air around it; thus, long-term effects should be based

on the accumulated temperature experience of critical

structural parts.

Time Under Load

Rate of Loading

Mechanical property values, as given in Tables 4–3, 4–4,

and 4–5, are usually referred to as static strength values.

Static strength tests are typically conducted at a rate of loading or rate of deformation to attain maximum load in about

5 min. Higher values of strength are obtained for wood

loaded at a more rapid rate and lower values are obtained at

slower rates. For example, the load required to produce

failure in a wood member in 1 s is approximately 10%

higher than that obtained in a standard static strength test.

Over several orders of magnitude of rate of loading, strength

is approximately an exponential function of rate. See

Chapter 6 for application to treated woods.

Figure 4–20 illustrates how strength decreases with time to

maximum load. The variability in the trend shown is based

on results from several studies pertaining to bending, compression, and shear.

Creep and Relaxation

When initially loaded, a wood member deforms elastically.

If the load is maintained, additional time-dependent deformation occurs. This is called creep. Creep occurs at even very

low stresses, and it will continue over a period of years. For

sufficiently high stresses, failure eventually occurs. This

failure phenomenon, called duration of load (or creep

rupture), is discussed in the next section.

At typical design levels and use environments, after several

years the additional deformation caused by creep may

approximately equal the initial, instantaneous elastic

deformation. For illustration, a creep curve based on creep as

a function of initial deflection (relative creep) at several stress

levels is shown in Figure 4–21; creep is greater under higher

stresses than under lower ones.

Table 4–16. Percentage change in bending properties of lumber with change in temperaturea

Lumber Moisture ((P–P70) / P70)100 = A + BT + CT 2 Temperature range

Property gradeb content A B CTmin Tmax

MOE All Green 22.0350 −0.4578 0 0 32

Green 13.1215 −0.1793 0 32 150

12% 7.8553 −0.1108 0 −15 150

MOR SS Green 34.13 −0.937 0.0043 −20 46

Green 0 0 0 46 100

12% 0 0 0 −20 100

No. 2 Green 56.89 −1.562 0.0072 −20 46

or less Green 0 0 0 46 100

Dry 0 0 0 −20 100

a

For equation, P is property at temperature T in °F; P70, property at 21°C (70°F). b

SS is Select Structural.
 4–38

Ordinary climatic variations in temperature and humidity

will cause creep to increase. An increase of about 28oC (50oF)

in temperature can cause a two- to threefold increase in creep.

Green wood may creep four to six times the initial deformation as it dries under load.

Unloading a member results in immediate and complete

recovery of the original elastic deformation and after time, a

recovery of approximately one-half the creep at deformation as

well. Fluctuations in temperature and humidity increase the

magnitude of the recovered deformation.

Relative creep at low stress levels is similar in bending,

tension, or compression parallel to grain, although it may be

somewhat less in tension than in bending or compression

under varying moisture conditions. Relative creep across the

grain is qualitatively similar to, but likely to be greater than,

creep parallel to the grain. The creep behavior of all species

studied is approximately the same.

If instead of controlling load or stress, a constant deformation

is imposed and maintained on a wood member, the initial

stress relaxes at a decreasing rate to about 60% to 70% of its

original value within a few months. This reduction of stress

with time is commonly called relaxation.

120°C (250°F)

100

 Modulus of rupture (percentage of value at 26.7°C (80° F))

93°C (200°F)

150°C (300°F)

175°C (350°F)

Heating period (h)

0 8 16 24 32

90

80

70

60

50

40

Figure 4–15. Permanent effect of heating in water

(solid line) and steam (dashed line) on modulus of rupture of clear, defect-free wood. All data based on tests

of Douglas-fir and Sitka spruce at room temperature.

Modulus of rupture

Work

66°C (150°F)

93°C (200°F)

Property (percentage of untreated controls)100

90

80

70

60

50

0 50 100 150 200 250 300

Heating period (days)

Figure 4–16. Permanent effect of heating in water on

work to maximum load and modulus of rupture of clear,

defect-free wood. All data based on tests of Douglas-fir

and Sitka spruce at room temperature.

100

Modulus of rupture (percentage of untreated controls) 70

90

80

60

50

40

0 50 100 150 200 250 300

Time of exposure (days)

155°C (310°F)

115°C (240°F)

135°C (275°F)

175°C (350°F)

Figure 4–17. Permanent effect of oven heating at four

temperatures on modulus of rupture, based on clear

pieces of four softwood and two hardwood species.

All tests conducted at room temperature.

115°C (240°F)

135°C (275°F)

155°C (310°F)

175°C (350°F)

104

102

100

98

96

94

92

90

88

0 50 100 150 200 250 300

Time of exposure (days)

Modulus of elasticity (percentage of untreated controls)

Figure 4–18. Permanent effect of oven heating at four

temperatures on modulus of elasticity, based on clear

pieces of four softwood and two hardwood species.

All tests conducted at room temperature.
4–39

In limited bending tests carried out between approximately

18oC (64oF) and 49oC (120oF) over 2 to 3 months, the curve

of stress as a function of time that expresses relaxation is

approximately the mirror image of the creep curve

(deformation as a function of time). These tests were carried

out at initial stresses up to about 50% of the bending

strength of the wood. As with creep, relaxation is markedly

affected by fluctuations in temperature and humidity.

Duration of Load

The duration of load, or the time during which a load acts on

a wood member either continuously or intermittently, is an

important factor in determining the load that the member can

safely carry. The duration of load may be affected by changes

in temperature and relative humidity.

The constant stress that a wood member can sustain is approximately an exponential function of time to failure, as

illustrated in Figure 4–22. This relationship is a composite

of results of studies on small, clear wood specimens, conducted at constant temperature and relative humidity.

1.0

0.9

0.8

0.7

0.6

MOR after exposure/MOR of controls

0.5

0 12 24 36 48 60 72

Exposure time (months)

2100f-1.8E

1650f-1.5E

Figure 4–19. Permanent effect of heating at 66°C (150°F)

on modulus of rupture for two grades of machine-stressrated Spruce–Pine–Fir lumber at 12% moisture content.

All tests conducted at room temperature.

140

120

100

80

60

40

20

0

10-2 102 104 106 108 100

Ultimate stress (percentage of static strength)

Time to ultimate stress (s)

≈12% moisture content

Figure 4–20. Relationship of ultimate stress at shorttime loading to that at 5-min loading, based on composite of results from rate-of-load studies on bending,

compression, and shear parallel to grain. Variability

in reported trends is indicated by width of band.

2

1

0

Creep deflection (multiple of initial deflection)

 MPa x103 lbf/in2

 3.4 0.5

 6.9 1.0

13.8 2.0

27.6 4.0

100 200 300 400 500

Time under load (days)

Stress

Figure 4–21. Influence of four levels of stress on creep

(Kingston 1962).

6% and 12% moisture content

Time to failure (h)

Constant stress (percentage of static strength)

10-6 10-4 10-2 100 102 104 106

120

100

80

60

40

20

0

Figure 4–22. Relationship between stress due to constant

load and time to failure for small clear wood specimens,

based on 28 s at 100% stress. The figure is a composite

of trends from several studies; most studies involved

bending but some involved compression parallel to grain

and bending perpendicular to grain. Variability in

reported trends is indicated by width of band.
 4–40

For a member that continuously carries a load for a long

period, the load required to produce failure is much less than

that determined from the strength properties in Tables 4–3 to

4–5. Based on Figure 4–22, a wood member under the

continuous action of bending stress for 10 years may carry

only 60% (or perhaps less) of the load required to produce

failure in the same specimen loaded in a standard bending

strength test of only a few minutes duration. Conversely, if

the duration of load is very short, the load-carrying capacity

may be higher than that determined from strength properties

given in the tables.

Time under intermittent loading has a cumulative effect. In

tests where a constant load was periodically placed on a

beam and then removed, the cumulative time the load was

actually applied to the beam before failure was essentially

equal to the time to failure for a similar beam under the same

load applied continuously.

The time to failure under continuous or intermittent loading

is looked upon as a creep–rupture process; a member has to

undergo substantial deformation before failure. Deformation at

failure is approximately the same for duration of load tests as

for standard strength tests.

Changes in climatic conditions increase the rate of creep and

shorten the duration during which a member can support a

given load. This effect can be substantial for very small wood

specimens under large cyclic changes in temperature and

relative humidity. Fortunately, changes in temperature and

relative humidity are moderate for wood in the typical service

environment.

Fatigue

In engineering, the term fatigue is defined as the progressive

damage that occurs in a material subjected to cyclic loading.

This loading may be repeated (stresses of the same sign; that

is, always compression or always tension) or reversed

(stresses of alternating compression and tension). When

sufficiently high and repetitious, cyclic loading stresses can

result in fatigue failure.

Fatigue life is a term used to define the number of cycles that

are sustained before failure. Fatigue strength, the maximum

stress attained in the stress cycle used to determine fatigue

life, is approximately exponentially related to fatigue life;

that is, fatigue strength decreases approximately linearly as

the logarithm of number of cycles increases. Fatigue strength

and fatigue life also depend on several other factors: frequency

of cycling; repetition or reversal of loading; range factor (ratio

of minimum to maximum stress per cycle); and other factors

such as temperature, moisture content, and specimen size.

Negative range factors imply repeated reversing loads,

whereas positive range factors imply nonreversing loads.

Results from several fatigue studies on wood are given in

Table 4–17. Most of these results are for repeated loading

with a range ratio of 0.1, meaning that the minimum stress

per cycle is 10% of the maximum stress. The maximum

stress per cycle, expressed as a percentage of estimated static

strength, is associated with the fatigue life given in millions

of cycles. The first three lines of data, which list the same

cyclic frequency (30 Hz), demonstrate the effect of range ratio

on fatigue strength (maximum fatigue stress that can be

maintained for a given fatigue life); fatigue bending strength

decreases as range ratio decreases. Third-point bending results show the effect of small knots or slope of grain on

fatigue strength at a range ratio of 0.1 and frequency of

8.33 Hz. Fatigue strength is lower for wood containing small

knots or a 1-in-12 slope of grain than for clear straightgrained wood and even lower for wood containing a combination of small knots and a 1-in-12 slope of grain. Fatigue

strength is the same for a scarf joint in tension as for tension

parallel to the grain, but a little lower for a finger joint in

tension. Fatigue strength is slightly lower in shear than in

tension parallel to the grain. Other comparisons do not have

much meaning because range ratios or cyclic frequency differ;

however, fatigue strength is high in compression parallel to

the grain compared with other properties. Little is known

about other factors that may affect fatigue strength in wood.

Creep, temperature rise, and loss of moisture content occur in

tests of wood for fatigue strength. At stresses that cause

failure in about 106 cycles at 40 Hz, a temperature rise of

Table 4–17. Summary of reported results on cyclic

fatiguea

Range

Cyclic

frequency

Maximum

stress per

cycleb

Approximate

fatigue

life

Property ratio (Hz) (%) (×106 cycles)

Bending, clear,

 straight grain

Cantilever 0.45 30 45 30

Cantilever 0 30 40 30

Cantilever −1.0 30 30 30

Center-point −1.0 40 30 4

Rotational −1.0 — 28 30

Third-point 0.1 8-1/3 60 2

Bending, third-point

Small knots 0.1 8-1/3 50 2

Clear, 1:12 slope

 of grain

0.1 8-1/3 50 2

Small knots, 1:12

 slope of grain

0.1 8-1/3 40 2

Tension parallel

 to grain

Clear, straight grain 0.1 15 50 30

Clear, straight grain 0 40 60 3.5

Scarf joint 0.1 15 50 30

Finger joint 0.1 15 40 30

Compression parallel

 to grain

Clear, straight grain 0.1 40 75 3.5

Shear parallel to grain

Glue-laminated 0.1 15 45 30

a

Initial moisture content about 12% to 15%.

b

Percentage of estimated static strength.
4–41

15oC (27oF) has been reported for parallel-to-grain compression fatigue (range ratio slightly greater than zero), parallelto-grain tension fatigue (range ratio = 0), and reversed bending fatigue (range ratio = −1). The rate of temperature rise is

high initially but then diminishes to moderate; a moderate

rate of temperature rise remains more or less constant during

a large percentage of fatigue life. During the latter stages of

fatigue life, the rate of temperature rise increases until failure

occurs. Smaller rises in temperature would be expected for

slower cyclic loading or lower stresses. Decreases in moisture content are probably related to temperature rise.

Aging

In relatively dry and moderate temperature conditions where

wood is protected from deteriorating influences such as decay, the mechanical properties of wood show little change

with time. Test results for very old timbers suggest that

significant losses in clear wood strength occur only after

several centuries of normal aging conditions. The soundness

of centuries-old wood in some standing trees (redwood, for

example) also attests to the durability of wood.

Exposure to Chemicals

The effect of chemical solutions on mechanical properties

depends on the specific type of chemical. Nonswelling liquids, such as petroleum oils and creosote, have no appreciable effect on properties. Properties are lowered in the presence

of water, alcohol, or other wood-swelling organic liquids

even though these liquids do not chemically degrade the

wood substance. The loss in properties depends largely on

the amount of swelling, and this loss is regained upon removal of the swelling liquid. Anhydrous ammonia markedly

reduces the strength and stiffness of wood, but these properties are regained to a great extent when the ammonia is

removed. Heartwood generally is less affected than sapwood

because it is more impermeable. Accordingly, wood treatments that retard liquid penetration usually enhance natural

resistance to chemicals.

Chemical solutions that decompose wood substance (by

hydrolysis or oxidation) have a permanent effect on strength.

The following generalizations summarize the effect of

chemicals:

• Some species are quite resistant to attack by dilute

mineral and organic acids.

• Oxidizing acids such as nitric acid degrade wood more

than do nonoxidizing acids.

• Alkaline solutions are more destructive than are acidic

solutions.

• Hardwoods are more susceptible to attack by both acids

and alkalis than are softwoods.

• Heartwood is less susceptible to attack by both acids and

alkalis than is sapwood.

Because both species and application are extremely important, reference to industrial sources with a specific history of

use is recommended where possible. For example, large

cypress tanks have survived long continuous use where

exposure conditions involved mixed acids at the boiling

point. Wood is also used extensively in cooling towers

because of its superior resistance to mild acids and solutions

of acidic salts.

Chemical Treatment

Wood is often treated with chemicals to enhance its fire

performance or decay resistance in service. Each set of

treatment chemicals and processes has a unique effect on the

mechanical properties of the treated wood.

Fire-retardant treatments and treatment methods distinctly

reduce the mechanical properties of wood. Some fireretardant-treated products have experienced significant inservice degradation on exposure to elevated temperatures

when used as plywood roof sheathing or roof-truss lumber.

New performance requirements within standards set by the

American Standards for Testing and Materials (ASTM) and

American Wood Preservers’ Association (AWPA) preclude

commercialization of inadequately performing fire-retardanttreated products.

Although preservative treatments and treatment methods

generally reduce the mechanical properties of wood, any

initial loss in strength from treatment must be balanced

against the progressive loss of strength from decay when

untreated wood is placed in wet conditions. The effects of

preservative treatments on mechanical properties are directly

related to wood quality, size, and various pretreatment,

treatment, and post-treatment processing factors. The key

factors include preservative chemistry or chemical type,

preservative retention, initial kiln-drying temperature, posttreatment drying temperature, and pretreatment incising (if

required). North American design guidelines address the

effects of incising on mechanical properties of refractory wood

species and the short-term duration-of-load adjustments for

all treated lumber. These guidelines are described in

Chapter 6.

Oil-Type Preservatives

Oil-type preservatives cause no appreciable strength loss

because they do not chemically react with wood cell wall

components. However, treatment with oil-type preservatives

can adversely affect strength if extreme in-retort seasoning

parameters are used (for example, Boultonizing, steaming, or

vapor drying conditions) or if excessive temperatures or

pressures are used during the treating process. To preclude

strength loss, the user should follow specific treatment processing requirements as described in the treatment standards.

Waterborne Preservatives

Waterborne preservative treatments can reduce the mechanical

properties of wood. Treatment standards include specific

processing requirements intended to prevent or limit strength

reductions resulting from the chemicals and the waterborne

preservative treatment process. The effects of waterborne

preservative treatment on mechanical properties are related to
 4–42

species, mechanical properties, preservative chemistry or

type, preservative retention, post-treatment drying temperature, size and grade of material, product type, initial kilndrying temperature, incising, and both temperature and

moisture in service.

Species—The magnitude of the effect of various waterborne preservatives on mechanical properties does not

appear to vary greatly between different species.

Mechanical property—Waterborne preservatives affect

each mechanical property differently. If treated according to

AWPA standards, the effects are as follows: modulus of

elasticity (MOE), compressive strength parallel to grain,

and compressive stress perpendicular to grain are unaffected

or slightly increased; modulus of rupture (MOR) and tensile strength parallel to grain are reduced from 0% to 20%,

depending on chemical retention and severity of redrying

temperature; and energy-related properties (for example,

work to maximum load and impact strength) are reduced

from 10% to 50%.

Preservative chemistry or type—Waterborne preservative

chemical systems differ in regard to their effect on strength,

but the magnitude of these differences is slight compared

with the effects of treatment processing factors. Chemistryrelated differences seem to be related to the reactivity of the

waterborne preservative and the temperature during the

fixation/precipitation reaction with wood.

Retention—Waterborne preservative retention levels of

≤16 kg/m3 (≤1.0 lb/ft3) have no effect on MOE or compressive strength parallel to grain and a slight negative effect

(−5% to −10%) on tensile or bending strength. However,

energy-related properties are often reduced from 15% to

30%. At a retention level of 40 kg/m3 (2.5 lb/ft3),

MOR and energy-related properties are further reduced.

Post-treatment drying temperature—Air drying after

treatment causes no significant reduction in the static

strength of wood treated with waterborne preservative at a

retention level of 16 kg/m3 (1.0 lb/ft3). However, energyrelated properties are reduced. The post-treatment redrying

temperature used for material treated with waterborne preservative has been found to be critical when temperatures

exceed 75 oC (167 oF). Redrying limitations in treatment

standards have precluded the need for an across-the-board

design adjustment factor for waterborne-preservative-treated

lumber in engineering design standards. The limitation on

post-treatment kiln-drying temperature is set at 74oC

(165oF).

Size of material—Generally, larger material, specifically

thicker, appears to undergo less reduction in strength than

does smaller material. Recalling that preservative treatments usually penetrate the treated material to a depth of

only 6 to 51 mm (0.25 to 2.0 in.), depending on species

and other factors, the difference in size effect appears to be

a function of the product’s surface-to-volume ratio, which

affects the relative ratio of treatment-induced weight gain

to original wood weight.

Grade of material—The effect of waterborne preservative

treatment is a quality-dependent phenomenon. Higher

grades of wood are more affected than lower grades. When

viewed over a range of quality levels, higher quality lumber is reduced in strength to a proportionately greater

extent than is lower quality lumber.

Product type—The magnitude of the treatment effect on

strength for laminated veneer lumber conforms closely to

effects noted for higher grades of solid-sawn lumber. The

effects of waterborne preservative treatment on plywood

seem comparable to that on lumber. Fiber-based composite

products may be reduced in strength to a greater extent

than is lumber. This additional effect on fiber-based composites may be more a function of internal bond damage

caused by waterborne-treatment-induced swelling rather

than actual chemical hydrolysis.

Initial kiln-drying temperature—Although initial kiln

drying of some lumber species at 100oC to 116oC (212oF

to 240oF) for short durations has little effect on structural

properties, such drying results in more hydrolytic degradation of the cell wall than does drying at lower temperature

kiln schedules. Subsequent preservative treatment and

redrying of material initially dried at high temperatures

causes additional hydrolytic degradation. When the material is subsequently treated, initial kiln drying at 113o

C

(235oF) has been shown to result in greater reductions over

the entire bending and tensile strength distributions than

does initial kiln drying at 91oC (196oF). Because Southern

Pine lumber, the most widely treated product, is most often initially kiln dried at dry-bulb temperatures near or

above 113oC (235oF), treatment standards have imposed a

maximum redrying temperature limit of 74oC (165oF) to

preclude the cumulative effect of thermal processing.

Incising—Incising, a pretreatment mechanical process in

which small slits (incisions) are punched in the surface of

the wood product, is used to improve preservative penetration and distribution in difficult-to-treat species. Incising

may reduce strength; however, because the increase in

treatability provides a substantial increase in biological

performance, this strength loss must be balanced against

the progressive loss in strength of untreated wood from the

incidence of decay. Most incising patterns induce some

strength loss, and the magnitude of this effect is related to

the size of material being incised and the incision depth

and density (that is, number of incisions per unit area).

In less than 50 mm (2 in.) thick, dry lumber, incising and

preservative treatment induces losses in MOE of 5% to

15% and in static strength properties of 20% to 30%. Incising and treating timbers or tie stock at an incision density of ≤1,500 incisions/m2 (≤140 incisions/ft2

) and to a

depth of 19 mm (0.75 in.) reduces strength by 5% to 10%.
4–43

In-service temperature—Both fire-retardant and preservative treatments accelerate the thermal degradation of

bending strength of lumber when exposed to temperatures

above 54 ̊C (130 ̊F).

In-service moisture content—Current design values apply

to material dried to ≤19% maximum (15% average) moisture content or to green material. No differences in strength

have been found between treated and untreated material

when tested green or at moisture contents above 12%.

When very dry treated lumber of high grade was tested at

10% moisture content, its bending strength was reduced

compared with that of matched dry untreated lumber.

Duration of load—When subjected to impact loads,

wood treated with chromated copper arsenate (CCA) does

not exhibit the same increase in strength as that exhibited

by untreated wood. However, when loaded over a long

period, treated and untreated wood behave similarly.

Polymerization

Wood is also sometimes impregnated with monomers, such

as methyl methacrylate, which are subsequently polymerized.

Many of the mechanical properties of the resultant wood–

plastic composite are higher than those of the original wood,

generally as a result of filling the void spaces in the wood

structure with plastic. The polymerization process and both

the chemical nature and quantity of monomers influence

composite properties.

Nuclear Radiation

Wood is occasionally subjected to nuclear radiation. Examples are wooden structures closely associated with nuclear

reactors, the polymerization of wood with plastic using

nuclear radiation, and nondestructive estimation of wood

density and moisture content. Very large doses of gamma

rays or neutrons can cause substantial degradation of wood.

In general, irradiation with gamma rays in doses up to about

1 megarad has little effect on the strength properties of wood.

As dosage exceeds 1 megarad, tensile strength parallel to

grain and toughness decrease. At a dosage of 300 megarads,

tensile strength is reduced about 90%. Gamma rays also

affect compressive strength parallel to grain at a dosage above

1 megarad, but higher dosage has a greater effect on tensile

strength than on compressive strength; only approximately

one-third of compressive strength is lost when the total dose

is 300 megarads. Effects of gamma rays on bending and shear

strength are intermediate between the effects on tensile and

compressive strength.

Mold and Stain Fungi

Mold and stain fungi do not seriously affect most mechanical

properties of wood because such fungi feed on substances

within the cell cavity or attached to the cell wall rather than

on the structural wall itself. The duration of infection and the

species of fungi involved are important factors in determining

the extent of degradation.

Although low levels of biological stain cause little loss in

strength, heavy staining may reduce specific gravity by 1%

to 2%, surface hardness by 2% to 10%, bending and crushing

strength by 1% to 5%, and toughness or shock resistance by

15% to 30%. Although molds and stains usually do not

have a major effect on strength, conditions that favor these

organisms also promote the development of wood-destroying

(decay) fungi and soft-rot fungi (Ch. 13). Pieces with mold

and stain should be examined closely for decay if they are

used for structural purposes.

Decay

Unlike mold and stain fungi, wood-destroying (decay) fungi

seriously reduce strength by metabolizing the cellulose

fraction of wood that gives wood its strength.

Early stages of decay are virtually impossible to detect. For

example, brown-rot fungi may reduce mechanical properties

in excess of 10% before a measurable weight loss is observed

and before decay is visible. When weight loss reaches 5% to

10%, mechanical properties are reduced from 20% to 80%.

Decay has the greatest effect on toughness, impact bending,

and work to maximum load in bending, the least effect on

shear and hardness, and an intermediate effect on other properties. Thus, when strength is important, adequate measures

should be taken to (a) prevent decay before it occurs,

(b) control incipient decay by remedial measures (Ch. 13), or

(c) replace any wood member in which decay is evident or

believed to exist in a critical section. Decay can be prevented

from starting or progressing if wood is kept dry (below 20%

moisture content).

No method is known for estimating the amount of reduction

in strength from the appearance of decayed wood. Therefore,

when strength is an important consideration, the safe procedure is to discard every piece that contains even a small

amount of decay. An exception may be pieces in which decay

occurs in a knot but does not extend into the surrounding

wood.

Insect Damage

Insect damage may occur in standing trees, logs, and undried

(unseasoned) or dried (seasoned) lumber. Although damage

is difficult to control in the standing tree, insect damage can

be eliminated to a great extent by proper control methods.

Insect holes are generally classified as pinholes, grub holes,

and powderpost holes. Because of their irregular burrows,

powderpost larvae may destroy most of a piece’s interior

while only small holes appear on the surface, and the

strength of the piece may be reduced virtually to zero. No

method is known for estimating the reduction in strength

from the appearance of insect-damaged wood. When strength

is an important consideration, the safe procedure is to eliminate pieces containing insect holes.
 4–44

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Bendtsen, B.A. 1976. Rolling shear characteristics of nine

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Bendtsen, B.A.; Freese, F.; Ethington, R.L. 1970. Methods for sampling clear, straight-grained wood from the forest.

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Bodig, J.; Goodman, J.R. 1973. Prediction of elastic

parameters for wood. Wood Science. 5(4): 249–264.

Bodig, J.; Jayne, B.A. 1982. Mechanics of wood and wood

composites. New York: Van Nostrand Reinhold Company.

Boller, K.H. 1954. Wood at low temperatures. Modern

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Coffey, D.J. 1962. Effects of knots and holes on the fatigue

strength of quarter-scale timber bridge stringers. Madison,

WI: University of Wisconsin, Department of Civil

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Gerhards, C.C. 1968. Effects of type of testing equipment

and specimen size on toughness of wood. Res. Pap. FPL–

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Gerhards, C.C. 1977. Effect of duration and rate of loading

on strength of wood and wood based materials. Res. Pap.

FPL–RP–283. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

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Gerhards, C.C. 1982. Effect of moisture content and temperature on the mechanical properties of wood: an analysis of

immediate effects. Wood and Fiber. 14(1): 4–36.

Green, D.W.; Evans, J.W. 1994. Effect of ambient temperatures on the flexural properties of lumber. In: PTEC 94

Timber shaping the future: Proceedings, Pacific timber engineering conference; 1994 July 11–15; Gold Coast, Australia.

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Hearmon, R.F.S. 1948. The elasticity of wood and plywood. Special Rep. 7. London, England: Department of

Scientific and Industrial Research, Forest Products Research.

Hearmon, R.F.S. 1961. An introduction to applied anisotropic elasticity. London, England: Oxford University Press.

Kingston, R.S.T. 1962. Creep, relaxation, and failure of

wood. Research Applied in Industry. 15(4).

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wood science and technology. New York: Springer Verlag.

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OR: Oregon State University, School of Forestry, Forestry

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Little, E.L., Jr. 1979. Checklist of United States trees

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5–1

Chapter 5

Commercial Lumber

Kent A. McDonald and David E. Kretschmann

Contents

Hardwood Lumber 5–1

Factory Lumber 5–2

Dimension and Component Parts 5–2

Finished Market Products 5–6

Lumber Species 5–7

Softwood Lumber 5–7

Lumber Grades 5–7

Lumber Manufacture 5–10

Softwood Lumber Species 5–12

Softwood Lumber Grading 5–12

Purchase of Lumber 5–12

Retail Yard Inventory 5–16

Important Purchase Considerations 5–17

Commonly Used Lumber Abbreviations 5–18

Reference 5–20

n a broad sense, commercial lumber is any lumber

that is bought or sold in the normal channels of

commerce. Commercial lumber may be found in a

variety of forms, species, and types, and in various commercial establishments, both wholesale and retail. Most commercial lumber is graded by standardized rules that make

purchasing more or less uniform throughout the country.

When sawn, a log yields lumber of varying quality. To

enable users to buy the quality that best suits their purposes,

lumber is graded into use categories, each having an appropriate range in quality.

Generally, the grade of a piece of lumber is based on the

number, character, and location of features that may lower the

strength, durability, or utility value of the lumber. Among

the more common visual features are knots, checks, pitch

pockets, shake, and stain, some of which are a natural part of

the tree. Some grades are free or practically free from these

features. Other grades, which constitute the great bulk of

lumber, contain fairly numerous knots and other features.

With proper grading, lumber containing these features is

entirely satisfactory for many uses.

The grading operation for most lumber takes place at the

sawmill. Establishment of grading procedures is largely the

responsibility of manufacturers’ associations. Because of the

wide variety of wood species, industrial practices, and customer needs, different lumber grading practices coexist. The

grading practices of most interest are considered in the sections that follow, under the major categories of hardwood

lumber and softwood lumber.

Hardwood Lumber

The principal use of hardwood lumber is for remanufacture

into furniture, cabinetwork, and pallets, or direct use as

flooring, paneling, moulding, and millwork. Hardwood

lumber is graded and marketed in three main categories:

Factory lumber, dimension parts, and finished market products. Several hardwood species are graded under the American Softwood Lumber Standard and sold as structural lumber

(Ch. 6). Also, specially graded hardwood lumber can be used

for structural glued-laminated lumber.
 5–2

Prior to 1898, hardwoods were graded by individual mills

for local markets. In 1898, manufacturers and users formed

the National Hardwood Lumber Association to standardize

grading for hardwood lumber. Between 1898 and 1932,

grading was based on the number and size of visual features.

In 1932, the basis for grading was changed to standard clearcutting sizes.

Both Factory lumber and dimension parts are intended to

serve the industrial customer. The important difference is that

for Factory lumber, the grades reflect the proportion of a piece

that can be cut into useful smaller pieces, whereas the grades

for dimension parts are based on use of the entire piece.

Finished market products are graded for their unique end-use

with little or no remanufacture. Examples of finished products include moulding, stair treads, and hardwood flooring.

Factory Lumber

Grades

The rules adopted by the National Hardwood Lumber Association are considered standard in grading hardwood lumber

intended for cutting into smaller pieces to make furniture or

other fabricated products. In these rules, the grade of a piece

of hardwood lumber is determined by the proportion of a

piece that can be cut into a certain number of smaller pieces

of material, commonly called cuttings, which are generally

clear on one side, have the reverse face sound, and are not

smaller than a specified size.

The best grade in the Factory lumber category is termed

FAS. The second grade is F1F. The third grade is Selects,

which is followed by No. 1 Common, No. 2A Common,

No. 2B Common, Sound Wormy, No. 3A Common, and

No. 3B Common. Except for F1F and Selects, the poorer

side of a piece is inspected for grade assignment. Standard

hardwood lumber grades are described in Table 5–1. This

table illustrates, for example, that FAS includes pieces that

will allow at least 83-1/3% of their surface measure to be cut

into clear face material. Except for Sound Wormy, the minimum acceptable length, width, surface measure, and percentage of piece that must work into a cutting decrease with

decreasing grade. Figure 5–1 is an example of grading for

cuttings.

This brief summary of grades for Factory lumber should not

be regarded as a complete set of grading rules because many

details, exceptions, and special rules for certain species are

not included. The complete official rules of the National

Hardwood Lumber Association (NHLA) should be followed

as the only full description of existing grades (see Table 5–2

for addresses of NHLA and other U.S. hardwood grading

associations). Table 5–3 lists names of commercial domestic

hardwood species that are graded by NHLA rules.

Standard Dimensions

Standard lengths of hardwood lumber are in 300-mm (1-ft)

increments from 1.2 to 4.8 m (4 to 16 ft). Standard thickness

values for hardwood lumber, rough and surfaced on two sides

(S2S), are given in Table 5–4. The thickness of S1S lumber

is subject to contract agreement. Abbreviations commonly

used in contracts and other documents for the purchase and

sale of lumber are listed at the end of this chapter.

Hardwood lumber is usually manufactured to random width.

The hardwood lumber grades do not specify standard widths;

however, the grades do specify minimum width for each

grade as follows:

Grade

Minimum width

 (mm (in.))

FAS 150 (6)

F1F 150 (6)

Selects 100 (4)

No. 1, 2A, 2B, 3A, 3B Common 80 (3)

If the width is specified by purchase agreement, S1E or S2E

lumber is 10 mm (3/8 in.) scant of nominal size in lumber

less than 200 mm (8 in.) wide and 13 mm (1/2 in.) scant in

lumber ≥200 mm (≥8 in.) wide.

Dimension and Component Parts

The term “dimension parts” for hardwoods signifies stock

that is processed in specific thickness, width, and length, or

multiples thereof and ranges from semi-machined to completely machined component products. This stock is sometimes referred to as “hardwood dimension stock” or

“hardwood lumber for dimension parts.” This stock should

not be confused with “dimension lumber,” a term used in

the structural lumber market to mean lumber standard

38 mm to less than 114 mm thick (nominal 2 in. to less

than 5 in. thick).

Dimension component parts are normally kiln dried and

generally graded under the rules of the Wood Components

Manufacturers Association (WCMA). These rules encompass

three classes of material, each of which is classified into

various grades:

Hardwood

dimension parts

(flat stock)

Solid kilndried squares

(rough)

Solid kiln-dried

 squares

(surfaced)

Clear two faces Clear Clear

Clear one face Select Select

Paint Sound Paint

Core Second

Sound

Each class may be further defined as semifabricated (rough or

surfaced) or completely fabricated, including edge-glued

panels. The rough wood component parts are blank-sawn

and ripped to size. Surfaced semifabricated parts have been

through one or more manufacturing stages. Completely

fabricated parts have been completely processed for their

end use.
5–3

Table 5–1. Standard hardwood lumber gradesa,b

Allowable

Allowable

surface

measure

Minimum

amount of

piece in

clearface Allowable cuttings

Grade and allowable lengths

width

(in.)

of pieces

(ft2)

cuttings

(%)

Maximum

no. Minimum size

FASc 6+

4 to 9

10 to 14

15+

83-1/3

1

2

3

4 in. by 5 ft, or

3 in. by 7 ft

F1Fc 6+

4 to 7

6 and 7

8 to 11

8 to 11

12 to 15

12 to 15

16+

83-1/3

91-2/3

83-1/3

91-2/3

83-1/2

91-2/3

83-1/3

1

2

2

3

3

4

4

4 in. by 5 ft, or

3 in. by 7 ft

Selects

 6 to 16 ft (will admit 30% of 6 to 11 ft) 4+

2 and 3

4+

91-2/3

 —d 1 4 in. by 5 ft, or

3 in. by 7 ft

No. 1 Common

 4 to 16 ft (will admit 10% of 4 to 7 ft,

 1/2 of which may be 4 and 5 ft)

3+

1

2

3 and 4

3 and 4

5 to 7

5 to 7

8 to 10

11 to 13

14+

100

75

66-2/3

75

66-2/3

75

66-2/3

66-2/3

66-2/3

0

1

1

2

2

3

3

4

5

4 in. by 2 ft, or

3 in. by 3 ft

No. 2 Common

 4 to 16 ft (will admit 30% of 4 to 7 ft,

 1/3 of which may be 4 and 5 ft)

3+

1

2 and 3

2 and 3

4 and 5

4 and 5

6 and 7

6 and 7

8 and 9

10 and 11

12 and 13

14+

66-2/3

50

66-2/3

50

66-2/3

50

66-2/3

50

50

50

50

1

1

2

2

3

3

4

4

5

6

7

3 in. by 2 ft

Sound Wormye

No. 3A Common

 4 to 16 ft (will admit 50% of 4 to 7 ft,

 1/2 of which may be 4 and 5 ft)

3+ 1+ 33-1/3f —g 3 in. by 2 ft

Sound Wormye

No. 3B Common

 4 to 16 ft (will admit 50% of 4 to 7 ft,

 1/2 of which may be 4 and 5 ft)

3+ 1+ 25h —g 1-1/2 in. by 2 ft

a

Current grading rules are written only in the inch–pound system of measurement.

b

Inspection made on poorer side of piece, except in Selects grade.

c

FAS is a grade that designates Firsts and Seconds. F1F is a grade that designates FAS one face.

d

Same as F1F, with reverse side of board not below No. 1 Common or reverse side of sound cuttings.

e

Same requirements as those for No. 1 Common and better except that wormholes and limited sound knots

 and other imperfections are allowed in cuttings.

f

Also admits pieces that grade not below No. 2 Common on the good face and reverse side of sound cuttings.

g

Unlimited.

h

Cuttings must be sound; clear face not required.
 5–4

Figure 5–1. Example of hardwood grading for cuttings using No. 1 Common lumber grade. Current grading

rules are written only in the inch–pound system of measurement.

Table 5–2. Hardwood grading associations in United Statesa

Name and address Species covered by grading rules (products)

National Hardwood Lumber Association

P.O. Box 34518

Memphis, TN 38184–0518

All hardwood species (furniture cuttings, construction lumber,

siding, panels)

Wood Components Manufacturers Association

1000 Johnson Ferry Rd., Suite A-130

Marietta, GA 30068

All hardwood species (hardwood furniture dimension, squares,

laminated stock, interior trim, stair treads and risers)

Maple Flooring Manufacturers Association

60 Revere Dr., Suite 500

Northbrook, IL 60062

Maple, beech, birch (flooring)

National Oak Flooring Manufacturers Association

P.O. Box 3009

Memphis, TN 38173–0009

www.nofma.org

Oak, ash, pecan, hickory, pecan, beech, birch, hard maple

(flooring, including prefinished)

a

Grading associations that include hardwood species in structural grades are listed in Table 5–5.
5–5

Table 5–3. Nomenclature of commercial hardwood lumber

Commercial

name for

lumber Common tree name Botanical name

Commercial

name for

lumber Common tree name Botanical name

Alder, Red Red alder Alnus rubra Maple, Oregon Big leaf maple Acer macrophyllum

Ash, Black Black ash Fraxinus nigra Maple, Soft Red maple Acer rubrum

Ash, Oregon Oregon ash Fraxinus latifolia Silver maple Acer saccharinum

Ash, White Blue ash Fraxinus quadrangulata Oak, Red Black oak Quercus velutina

Green ash Fraxinus pennsylvanica Blackjack oak Quercus marilandica

White ash Fraxinus americana California black oak Quercus kelloggi

Aspen (popple) Bigtooth aspen Populus grandidentata Cherrybark oak Quercus falcata var.

 pagodaefolia

Quaking aspen Populus tremuloides Laurel oak Quercus laurifolia

Basswood American basswood Tilia americana Northern pin oak Quercus ellipsoidalis

White basswood Tilia heterophylla Northern red oak Quercus rubra

Beech American beech Fagus grandifolia Nuttall oak Quercus nuttallii

Birch Gray birch Betula populifolia Pin oak Quercus palustris

Paper birch Betula papyrifera Scarlet oak Quercus coccinea

River birch Betula nigra Shumard oak Quercus shumardii

Sweet birch Betula lenta Southern red oak Quercus falcata

Yellow birch Betula alleghaniensis Turkey oak Quercus laevis

Box Elder Boxelder Acer negundo Willow oak Quercus phellos

Buckeye Ohio buckeye Aesculus glabra Oak, White Arizona white oak Quercus arizonica

Yellow buckeye Aesculus octandra Blue oak Quercus douglasii

Butternut Butternut Juglans cinerea Bur oak Quercus macrocarpa

Cherry Black cherry Prunus serotina Valley oak Quercus lobata

Chestnut American chestnut Castanea dentata Chestnut oak Quercus prinus

Cottonwood Balsam poplar Populus balsamifera Chinkapin oak Quercus muehlenbergii

Eastern cottonwood Populus deltoides Emory oak Quercus emoryi

Black cottonwood Populus trichocarpa Gambel oak Quercus gambelii

Cucumber Cucumbertree Magnolia acuminata Mexican blue oak Quercus oblongifolia

Dogwood Flowering dogwood Cornus florida Live oak Quercus virginiana

Pacific dogwood Cornus nuttallii Oregon white oak Quercus garryana

Elm, Rock Cedar elm Ulmus crassifolia Overcup oak Quercus lyrata

Rock elm Ulmus thomasii Post oak Quercus stellata

September elm Ulmus serotina Swamp chestnut oak Quercus michauxii

Winged elm Ulmus alata Swamp white oak Quercus bicolor

Elm, Soft American elm Ulmus americana White oak Quercus alba

Slippery elm Ulmus rubra Oregon Myrtle California-laurel Umbellularia californica

Gum Sweetgum Liquidambar styraciflua Osage Orange Osage-orange Maclura pomifera

Hackberry Hackberry Celtis occidentalis Pecan Bitternut hickory Carya cordiformis

Sugarberry Celtis laevigata Nutmeg hickory Carya myristiciformis

Hickory Mockernut hickory Carya tomentosa Water hickory Carya aquatica

Pignut hickory Carya glabra Pecan Carya illinoensis

Shagbark hickory Carya ovata Persimmon Common persimmon Diospyros virginiana

Shellbark hickory Carya lacinosa Poplar Yellow-poplar Liriodendron tulipifera

Holly American holly Ilex opaca Sassafras Sassafras Sassafras albidum

Ironwood Eastern hophornbeam Ostrya virginiana Sycamore Sycamore Platanus occidentalis

Locust Black locust Robinia pseudoacacia Tanoak Tanoak Lithocarpus densiflorus

Honeylocust Gleditsia triacanthos Tupelo Black tupelo, blackgum Nyssa sylvatica

Madrone Pacific madrone Arbutus menziesii Ogeechee tupelo Nyssa ogeche

Magnolia Southern magnolia Magnolia grandiflora Water tupelo Nyssa aquatica

Sweetbay Magnolia virginiana Walnut Black walnut Juglans nigra

Maple, Hard Black maple Acer nigrum Willow Black willow Salix nigra

Sugar maple Acer saccharum Peachleaf willow Salix amygdaloides
 5–6

Finished Market Products

Some hardwood lumber products are graded in relatively

finished form, with little or no further processing anticipated.

Flooring is probably the finished market product with the

highest volume. Other examples are lath, siding, ties,

planks, carstock, construction boards, timbers, trim, moulding, stair treads, and risers. Grading rules promulgated for

flooring anticipate final consumer use and are summarized in

this section. Details on grades of other finished products are

found in appropriate association grading rules.

Hardwood flooring generally is graded under the rules of the

Maple Flooring Manufacturers Association (MFMA) or the

National Oak Flooring Manufacturers Association

(NOFMA). Tongued-and-grooved, end-matched hardwood

flooring is commonly furnished. Square-edge, square-endstrip flooring is also available as well as parquet flooring

suitable for laying with mastic.

The grading rules of the Maple Flooring Manufacturers

Association cover flooring that is manufactured from hard

maple, beech, and birch. Each species is graded into four

categories:

• First grade—one face practically free of all imperfections;

variations in natural color of wood allowed

• Second grade—tight, sound knots (except on edges or

ends) and other slight imperfections allowed; must be

possible to lay flooring without waste

• Third grade—may contain all visual features common to

hard maple, beech, and birch; will not admit voids on

edges or ends, or holes over 9.5-mm (3/8-in.) in

diameter; must permit proper laying of floor and provide a

serviceable floor; few restrictions on imperfections; must

be possible to lay flooring properly

• Fourth grade—may contain all visual features, but must

be possible to lay a serviceable floor, with some cutting

Combination grades of “Second and Better” and “Third and

Better” are sometimes specified. There are also special grades

based on color and species.

The standard thickness of MFMA hard maple, beech, and

birch flooring is 19.8 mm (25/32 in.). Face widths are 38,

51, 57, and 83 mm (1-1/2, 2, 2-1/4, and 3-1/4 in.). Standard

lengths are 610 mm (2 ft) and longer in First- and Secondgrade flooring and 381 mm (1-1/4 ft) and longer in Thirdgrade flooring.

The Official Flooring Grading Rules of NOFMA cover oak

(unfinished and prefinished), beech, birch, hard maple, ash,

and hickory/pecan. Flooring grades are determined by the

appearance of the face surface.

Oak is separated as red oak and white oak and by grain

direction: plain sawn (all cuts), quartersawn (50% quartered

character), rift sawn (75% rift character), and quarter/rift sawn

(a combination). Oak flooring has four main grade separations—Clear, Select, No. 1 Common, and No. 2 Common.

Clear is mostly heartwood and accepts a 10-mm (3/8-in.)

strip of bright sapwood or an equivalent amount not more

than 25 mm (1 in.) wide along the edge and a minimum

number of character marks and discoloration, allowing for all

natural heartwood color variations. Select allows all color

variations of natural heartwood and sapwood along with

characters such as small knots, pinworm holes, and brown

streaks. No. 1 Common contains prominent variations in

coloration, which include heavy streaks, sticker stains, open

checks, knots, and small knot holes that fill. No. 2 Common

contains sound natural variation of the forest product and

manufacturing imperfections to provide a serviceable floor.

Average lengths for unfinished oak grades are as follows:

Grade Standard packaging Shorter packaging

Clear 1.14 m (3-3/4 ft) 1.07 m (3-1/2 ft)

Select 0.99 m (3-1/4 ft) 0.91 m (3 ft)

No. 1 Common 0.84 m (2-3/4 ft) 0.76 m (2-/1/2 ft)

No. 2 Common 0.69 m (2-1/4 ft) 0.61 m (2 ft)

Table 5–4. Standard thickness values

for rough and surfaced (S2S) hardwood lumber

Rough Surfaced

(mm (in.)) (mm (in.))

9.5 (3/8) 4.8 (3/16)

12.7 (1/2) 7.9 (5/16)

15.9 (5/8) 9.4 (7/16)

19.0 (3/4) 14.3 (9/16)

25.4 (1) 20.6 (13/16)

31.8 (1-1/4) 27.0 (1-1/16)

38.1 (1-1/2) 33.3 (1-5/16)

44.4 (1-3/4) 38.1 (1-1/2)

50.8 (2) 44.4 (1-3/4)

63.5 (2-1/2) 57.2 (2-1/4)

76.2 (3) 69.8 (2-3/4)

88.9 (3-1/2) 82.6 (3-1/4)

101.6 (4) 95.2 (3-3/4)

114.3 (4-1/2) —a —a

127.0 (5) —a —a

139.7 (5-1/2) —a —a

152.4 (6) —a —a

a

Finished size not specified in rules.

 Thickness subject to special contract.
5–7

Standard packaging refers to nominal 2.4-m (8-ft) pallets or

nested bundles. Shorter packaging refers to nominal 2.13-m

(7-ft) and shorter pallets or nested bundles.

Standard and special NOFMA grades for species other than

oak are as follows:

Species Grade

Standard grades

Beech, birch,

and hard maple

First, Second, Third, Second & Better, Third

& Better

Hickory and pecan First, Second, Third, Second & Better, Third

& Better

Ash Clear, Select, No. 1 Common,

No. 2 Common

Special grades

Beech and birch First Grade Red

Hard maple First Grade White

Hickory and pecan First Grade White, First Grade Red, Second

Grade Red

Standard thickness values for NOFMA tongue and groove

flooring are 19, 12, 9.5 (3/4, 1/2, 3/8 in.), with 19.8, and

26.2 mm (25/32 and 33/32 in.) for maple flooring. Standard

face widths are 38, 51, 57, and 83 mm (1-1/2, 2, 2-1/4, and

3-1/4 in.). Strips are random length from minimum 0.23 m

to maximum 2.59 m (9 to 102 in.).

Lumber Species

The names used by the trade to describe commercial lumber

in the United States are not always the same as the names of

trees adopted as official by the USDA Forest Service.

Table 5–3 shows the common trade name, the USDA Forest

Service tree name, and the botanical name. United States

agencies and associations that prepare rules for and supervise

grading of hardwoods are given in Table 5–2.

Softwood Lumber

For many years, softwood lumber has demonstrated the

versatility of wood by serving as a primary raw material for

construction and manufacture. In this role, softwood lumber

has been produced in a wide variety of products from many

different species. The first industry-sponsored grading rules

(product descriptions) for softwoods, which were established

before 1900, were comparatively simple because sawmills

marketed their lumber locally and grades had only local

significance. As new timber sources were developed and

lumber was transported to distant points, each producing

region continued to establish its own grading rules; thus,

lumber from various regions differed in size, grade name, and

allowable grade characteristics. When different species were

graded under different rules and competed in the same consuming areas, confusion and dissatisfaction were inevitable.

To minimize unnecessary differences in the grading rules of

softwood lumber and to improve and simplify these rules, a

number of conferences were organized by the U.S. Department of Commerce from 1919 to 1925. These meetings were

attended by representatives of lumber manufacturers, distributors, wholesalers, retailers, engineers, architects, and contractors. The result was a relative standardization of sizes,

definitions, and procedures for deriving allowable design

properties, formulated as a voluntary American Lumber

Standard. This standard has been modified several times,

including addition of hardwood species to the standard

beginning in 1970. The current edition is the American

Softwood Lumber Standard PS–20. Lumber cannot be

graded as American Standard lumber unless the grade rules

have been approved by the American Lumber Standard

Committee (ALSC), Inc., Board of Review.

Softwood lumber is classified for market use by form of

manufacture, species, and grade. For many products, the

American Softwood Lumber Standard and the grading rules

certified through it serve as a basic reference. For specific

information on other products, reference must be made to

grade rules, industry marketing aids, and trade journals.

Lumber Grades

Softwood lumber grades can be classified into three major

categories of use: (a) yard lumber, (b) structural lumber, and

(c) Factory and Shop lumber. Yard lumber and structural

lumber relate principally to lumber expected to function as

graded and sized after primary processing (sawing and planing). Factory and Shop refer to lumber that will undergo a

number of further manufacturing steps and reach the consumer

in a significantly different form.

Yard Lumber

The grading requirements of yard lumber are specifically

related to the construction uses intended, and little or no

further grading occurs once the piece leaves the sawmill.

Yard lumber can be placed into two basic classifications,

Select and Common. Select and Common lumber, as

categorized here, encompass those lumber products in which

appearance is of primary importance; structural integrity,

while sometimes important, is a secondary feature.

Select Lumber—Select lumber is generally non-stressgraded, but it forms a separate category because of the distinct importance of appearance in the grading process. Select

lumber is intended for natural and paint finishes. This category of lumber includes lumber that has been machined to a

pattern and S4S lumber. Secondary manufacture of these

items is usually restricted to on-site fitting such as cutting to

length and mitering. The Select category includes trim,

siding, flooring, ceiling, paneling, casing, base, stepping,

and finish boards.

Most Select lumber grades are generally described by letters

and combinations of letters (B&BTR, C&BTR, D) or

names (Superior, Prime) depending upon the species and the

grading rules under which the lumber is graded. (See list of
 5–8

commonly used lumber abbreviations at the end of this

chapter.) The specifications FG (flat grain), VG (vertical

grain), and MG (mixed grain) are offered as a purchase option

for some Select lumber products.

In cedar and redwood, there is a pronounced difference in

color between heartwood and sapwood. Heartwood also has

high natural resistance to decay, so some grades are denoted

as “heart.” Because Select lumber grades emphasize the

quality of one face, the reverse side may be lower in quality.

Select lumber grades are not uniform across species and

products, so certified grade rules for the species must be used

for detailed reference.

Common Lumber—Common lumber is normally a nonstress-graded product. The grades of Common lumber are

suitable for construction and utility purposes. Common

lumber is generally separated into three to five different

grades depending upon the species and grading rules

involved. Grades may be described by number (No. 1,

No. 2, No. 1 Common, No. 2 Common) or descriptive

term (Select Merchantable, Construction, Standard).

Because there are differences in the inherent properties of

various species and their corresponding names, the grades

for different species are not always interchangeable. The topgrade boards (No. 1, No. 1 Common, Select Merchantable)

are usually graded for serviceability, but appearance is also

considered. These grades are used for such purposes as

siding, cornice, shelving, and paneling. Features such as

knots and knotholes are permitted to be larger and more

frequent as the grade level becomes lower. Intermediate-grade

boards are often used for such purposes as subfloors, roof and

wall sheathing, and rough concrete work. The lower grade

boards are selected for adequate strength, not appearance.

They are used for roof and wall sheathing, subfloor, and

rough concrete form work (Fig. 5–2).

Grading provisions for other non-stress-graded products

vary by species, product, and applicable grading rules. For

detailed descriptions, consult the appropriate grade rule

for these products (see Table 5–5 for softwood grading

organizations).

Structural Lumber—Almost all softwood lumber standard

38 to 89 mm thick (nominal 2 to 4 in. thick, actual 1-1/2 to

3-1/2 in. thick) is produced as dimension lumber. Dimension lumber is stress graded and assigned allowable properties under the National Grading Rule, a part of the American

Softwood Lumber Standard. For dimension lumber, a single

set of grade names and descriptions is used throughout the

United States, although the allowable properties vary with

species. Timbers (lumber standard 114 mm (nominal 5 in.)

or more in least dimension) are also structurally graded under

ALSC procedures. Unlike grade descriptions for dimension

lumber, grade descriptions for structural timbers are not

standardized across species. For most species, timber grades

are classified according to intended use. Beams and stringers

are members standard 114 mm (nominal 5 in.) or more in

thickness with a width more than 51 mm (2 in.) greater than

the thickness. Beams and stringers are primarily used to

resist bending stresses, and the grade description for the

middle third of the length of the beam is more stringent than

that for the outer two-thirds. Posts and timbers are members

standard 114 by 114 mm (nominal 5 by 5 in.) and larger,

where the width is not more than 51 mm (2 in.) greater than

the thickness. Post and timbers are primarily used to resist

axial stresses. Structural timbers of Southern Pine are graded

without regard to anticipated use, as with dimension lumber.

Other stress-graded products include decking and some

boards. Stress-graded lumber may be graded visually or

mechanically. Stress grades and the National Grading Rule

are discussed in Chapter 6.

Structural Laminations—Structural laminating grades

describe the characteristics used to segregate lumber to be

used in structural glued-laminated (glulam) timbers.

Generally, allowable properties are not assigned separately to

laminating grades; rather, the rules for laminating grades are

based on the expected effect of that grade of lamination on the

combined glulam timber.

Figure 5–2. Typical examples of softwood boards

in the lower grades.
5–9

There are two kinds of graded material: visually graded and

E-rated. Visually graded material is graded according to one

of three sets of grading rules: (1) the first set is based on the

grading rules certified as meeting the requirements of the

American Softwood Lumber Standard with additional requirements for laminating; (2) the second set involves laminating grades typically used for visually graded western

species and includes three basic categories (L1, L2, L3); and

(3) the third set includes special requirements for tension

members and outer tension laminations on bending members. The visual grades have provisions for dense, closegrain, medium-grain, or coarsegrain lumber.

The E-rated grades are categorized by a combination of visual

grading criteria and lumber stiffness. These grades are expressed in terms of the size of maximum edge characteristic

permitted (as a fraction of the width) along with a specified

long-span modulus of elasticity (for example, 1/6–2.2E).

Table 5–5. Organizations promulgating softwood grades

Name and address Species covered by grading rules

Cedar Shingle & Shake Bureau

515 116th Avenue NE, Suite 275

Bellevue, WA 98004–5294

Western redcedar (shingles and shakes)

National Hardwood Lumber Association

P.O. Box 34518

Memphis, TN 38184–0518

Baldcypress, eastern redcedar

National Lumber Grades Authoritya

406 First Capital Place

960 Quamside Drive

New Westminister, BC, Canada V3M6G2

Northern white cedar, western red cedar, yellow cedar, alpine fir,

amabilis fir, balsam fir, Douglas-fir, grand fir, eastern hemlock,

western hemlock, western larch, eastern white pine, jack pine,

lodgepole pine, ponderosa pine, red pine, western white pine,

black spruce, sitka spruce, red spruce, Engelmann spruce,

white spruce, tamarack, aspen, black cottonwood, balsam

poplar, red alder, white birch

Northeastern Lumber Manufacturers Association, Inc.

272 Tuttle Road, P.O. Box 87A

Cumberland Center, ME 04021

Balsam fir, eastern white pine, red pine, eastern hemlock, black

spruce, white spruce, red spruce, pitch pine, tamarack, jack

pine, northern white cedar, aspen, red maple, mixed maple,

beech, birch, hickory, mixed oaks, red oak, northern red oak,

white oak, yellow poplar

Northern Softwood Lumber Bureaua

272 Tuttle Road, P.O. Box 87A

Cumberland Center, ME 04021

Eastern white pine, jack pine, red pine, pitch pine, eastern

spruce (red, white, and black), balsam fir, eastern hemlock,

tamarack, eastern cottonwood, aspen (bigtooth and quaking),

yellow poplar

Redwood Inspection Service

405 Enfrente Drive, Suite 200

Novato, CA 94949

Redwood

Southern Cypress Manufacturers Association

400 Penn Center Boulevard Suite 530

Pittsburgh, PA 15235

Baldcypress

Southern Pine Inspection Bureaua

4709 Scenic Highway

Pensacola, FL 32504

Longleaf pine, slash pine, shortleaf pine, loblolly pine,

Virginia pine, pond pine, pitch pine

West Coast Lumber Inspection Bureaua

Box 23145

6980 SW. Varns Road

Portland, OR 97223

Douglas-fir, western hemlock, western redcedar, incense-cedar,

Port-Orford-cedar, yellow-cedar, western true firs, mountain

hemlock, Sitka spruce, western larch

Western Wood Products Associationa

Yeon Building, 522 SW Fifth Avenue

Portland, OR 97204–2122

Ponderosa pine, western white pine, Douglas-fir, sugar pine,

western true firs, western larch, Engelmann spruce, incensecedar, western hemlock, lodgepole pine, western redcedar,

mountain hemlock, red alder, aspen, alpine fir, Idaho white pine

a

Publishes grading rules certified by the Board of Review of the American Lumber Standard Committee

 as conforming to the American Softwood Lumber Standard PS–20.
 5–10

Factory and Shop Lumber

A wide variety of species, grades, and sizes of softwood

lumber is supplied to industrial accounts for cutting to

specific smaller sizes, which become integral parts of other

products. In the secondary manufacturing process, grade

descriptions, sizes, and often the entire appearance of the

wood piece are changed. Thus, for Factory and Shop lumber,

the role of the grading process is to reflect as accurately as

possible the yield to be obtained in the subsequent cutting

operation. Typical of lumber for secondary manufacture are

the factory grades, industrial clears, box lumber, moulding

stock, and ladder stock. The variety of species available for

these purposes has led to a variety of grade names and grade

definitions. The following sections briefly outline some of

the more common classifications. For details, reference must

be made to industry sources, such as certified grading rules.

Availability and grade designation often vary by region and

species.

Factory (Shop) Grades—Traditionally, softwood lumber

used for cuttings has been called Factory or Shop. This

lumber forms the basic raw material for many secondary

manufacturing operations. Some grading rules refer to these

grades as Factory, while others refer to them as Shop. All

impose a somewhat similar nomenclature in the grade structure. Shop lumber is graded on the basis of characteristics

that affect its use for general cut-up purposes or on the basis

of size of cutting, such as for sash and doors. Factory Select

and Select Shop are typical high grades, followed by No. 1

Shop, No. 2 Shop, and No. 3 Shop.

Grade characteristics of boards are influenced by the width,

length, and thickness of the basic piece and are based on the

amount of high-quality material that can be removed by

cutting. Typically, Factory Select and Select Shop lumber

would be required to contain 70% of cuttings of specified

size, clear on both sides. No. 1 Shop would be required to

have 50% cuttings and No. 2 Shop, 33-1/3%. Because of

different characteristics assigned to grades with similar nomenclature, the grades of Factory and Shop lumber must be

referenced to the appropriate certified grading rules.

Industrial Clears—These grades are used for trim, cabinet

stock, garage door stock, and other product components

where excellent appearance, mechanical and physical properties, and finishing characteristics are important. The principal

grades are B&BTR, C, and D Industrial. Grading is primarily based on the best face, although the influence of edge

characteristics is important and varies depending upon piece

width and thickness. In redwood, the Industrial Clear All

Heart grade includes an “all heart” requirement for decay

resistance in the manufacture of cooling towers, tanks, pipe,

and similar products.

Moulding, Ladder, Pole, Tank, and Pencil Stock—

Within producing regions, grading rules delineate the requirements for a variety of lumber classes oriented to specific

consumer products. Custom and the characteristics of the

wood supply have led to different grade descriptions and

terminology. For example, in West Coast species, the ladder

industry can choose from one “ladder and pole stock” grade

plus two ladder rail grades and one ladder rail stock grade. In

Southern Pine, ladder stock is available as Select and Industrial. Moulding stock, tank stock, pole stock, stave stock,

stadium seat stock, box lumber, and pencil stock are other

typical classes oriented to the final product. Some product

classes have only one grade level; a few offer two or three

levels. Special features of these grades may include a restriction on sapwood related to desired decay resistance, specific

requirements for slope of grain and growth ring orientation

for high-stress use such as ladders, and particular cutting

requirements as in pencil stock. All references to these grades

should be made directly to current certified grading rules.

Lumber Manufacture

Size

Lumber length is recorded in actual dimensions, whereas

width and thickness are traditionally recorded in “nominal”

dimensions—actual dimensions are somewhat less.

Softwood lumber is manufactured in length multiples of

300 mm (1 ft) as specified in various grading rules. In practice, 600-mm (2-ft) multiples (in even numbers) are common

for most construction lumber. Width of softwood lumber

varies, commonly from standard 38 to 387 mm (nominal

2 to 16 in.). The thickness of lumber can be generally

categorized as follows:

• Boards—lumber less than standard 38 mm (nominal

2 in.) in thickness

• Dimension—lumber from standard 38 mm (nominal 2 in.)

to, but not including, 114 mm (5 in.) in thickness

• Timbers—lumber standard 114 mm (nominal 5 in.) or

more in thickness in least dimension

To standardize and clarify nominal to actual sizes, the

American Softwood Lumber Standard PS–20 specifies the

actual thickness and width for lumber that falls under the

standard. The standard sizes for yard and structural lumber

are given in Table 5–6. Timbers are usually surfaced while

“green” (unseasoned); therefore, only green sizes are given.

Because dimension lumber and boards may be surfaced green

or dry at the prerogative of the manufacturer, both green and

dry standard sizes are given. The sizes are such that a piece

of green lumber, surfaced to the standard green size, will

shrink to approximately the standard dry size as it dries to

about 15% moisture content. The definition of dry is lumber

that has been seasoned or dried to a maximum moisture

content of 19%. Lumber may also be designated as kiln dried

(KD), meaning the lumber has been seasoned in a chamber to

a predetermined moisture content by applying heat.
5–11

Factory and Shop lumber for remanufacture is offered in

specified sizes to fit end-product requirements. Factory

(Shop) grades for general cuttings are offered in thickness

from standard 19 to 89 mm (nominal 1 to 4 in.). Thicknesses of door cuttings start at 35 mm (nominal 1-3/8 in.).

Cuttings are of various lengths and widths. Laminating stock

is sometimes offered oversize, compared with standard dimension sizes, to permit resurfacing prior to laminating.

Industrial Clears can be offered rough or surfaced in a variety

of sizes, starting from standard 38 mm (nominal 2 in.) and

thinner and as narrow as standard 64 mm (nominal 3 in.).

Sizes for special product grades such as moulding stock and

ladder stock are specified in appropriate grading rules or

handled by purchase agreements.

Surfacing

Lumber can be produced either rough or surfaced (dressed).

Rough lumber has surface imperfections caused by the primary sawing operations. It may be greater than target size by

variable amounts in both thickness and width, depending

upon the type of sawmill equipment. Rough lumber serves

as a raw material for further manufacture and also for some

decorative purposes. A roughsawn surface is common in post

and timber products. Because of surface roughness, grading of

rough lumber is generally more difficult.

Surfaced lumber has been surfaced by a machine on one side

(S1S), two sides (S2S), one edge (S1E), two edges (S2E), or

combinations of sides and edges (S1S1E, S2S1E, S1S2,

S4S). Lumber is surfaced to attain smoothness and uniformity of size.

Imperfections or blemishes defined in the grading rules and

caused by machining are classified as “manufacturing imperfections.” For example, chipped and torn grain are surface

irregularities in which surface fibers have been torn out by the

surfacing operation. Chipped grain is a “barely perceptible”

characteristic, while torn grain is classified by depth. Raised

grain, skip, machine burn and gouge, chip marks, and wavy

surfacing are other manufacturing imperfections. Manufacturing imperfections are defined in the American Softwood

Table 5–6. American Standard Lumber sizes for yard and structural lumber for construction

Thickness Face width

Minimum dressed Minimum dressed

Nominal Dry Green Nominal Dry Green

Item (in.) (mm (in.)) (mm (in.)) (in.) (mm (in.)) (mm (in.))

Boards 1 19 (3/4) 20 (25/32) 2 38 (1-1/2) 40 (1-9/16)

1-1/4 25 (1) 26 (1-1/32) 3 64 (2-1/2) 65 (2-9/16)

1-1/2 32 (1-1/4) 33 (1-9/32) 4 89 (3-1/2) 90 (3-9/16)

5 114 (4-1/2) 117 (4-5/8)

6 140 (5-1/2) 143 (5-5/8)

7 165 (6-1/2) 168 (6-5/8)

8 184 (7-1/4) 190 (7-1/2)

9 210 (8-1/4) 216 (8-1/2)

10 235 (9-1/4) 241 (9-1/2)

11 260 (10-1/4) 267 (10-1/2)

12 286 (11-1/4) 292 (11-1/2)

14 337 (13-1/4) 343 (13-1/2)

16 387 (15-1/4) 394 (15-1/2)

Dimension 2 38 (1-1/2) 40 (1-9/16) 2 38 (1-1/2) 40 (1-9/16)

2-1/2 51 (2) 52 (2-1/16) 3 64 (2-1/2) 65 (2-9/16)

3 64 (2-1/2) 65 (2-9/16) 4 89 (3-1/2) 90 (3-9/16)

3-1/2 76 (3) 78 (3-1/16) 5 114 (4-1/2) 117 (4-5/8)

4 89 (3-1/2) 90 (3-9/16) 6 140 (5-1/2) 143 (5-5/8)

4-1/2 102 (4) 103 (4-1/16) 8 184 (7-1/4) 190 (7-1/2)

10 235 (9-1/4) 241 (9-1/2)

12 286 (11-1/4) 292 (11-1/2)

14 337 (13-1/4) 343 (13-1/2)

16 387 (15-1/4) 394 (15-1/2)

Timbers ≥5 13 mm

 off

(1/2 in.

 off)

13 mm

 off

(1/2 in.

 off)

≥5 13 mm

 off

(1/2 in.

 off)

13 mm

 off

(1/2 in.

 off)
 5–12

Lumber Standard and further detailed in the grading rules.

Classifications of manufacturing imperfections (combinations

of imperfections allowed) are established in the rules as

Standard A, Standard B, and so on. For example, Standard

A admits very light torn grain, occasional slight chip marks,

and very slight knife marks. These classifications are used as

part of the grade rule description of some lumber products to

specify the allowable surface quality.

Patterns

Lumber that has been matched, shiplapped, or otherwise

patterned, in addition to being surfaced, is often classified

as “worked lumber.” Figure 5–3 shows typical patterns.

Softwood Lumber Species

The names of lumber species adopted by the trade as standard may vary from the names of trees adopted as official by

the USDA Forest Service. Table 5–7 shows the American

Softwood Lumber Standard commercial names for lumber,

the USDA Forest Service tree names, and the botanical

names. Some softwood species are marketed primarily in

combinations. Designations such as Southern Pine and

Hem–Fir represent typical combinations. Grading rule agencies (Table 5–5) should be contacted for questions regarding

combination names and species not listed in Table 5–7.

Species groups are discussed further in Chapter 6.

Softwood Lumber Grading

Most lumber is graded under the supervision of inspection

bureaus and grading agencies. These organizations supervise

lumber mill grading and provide re-inspection services to

resolve disputes concerning lumber shipments. Some of

these agencies also write grading rules that reflect the species

and products in the geographic regions they represent. These

grading rules follow the American Softwood Lumber Standard (PS–20). This is important because it provides for

recognized uniform grading procedures. Names and addresses

of rules-writing organizations in the United States and the

species with which they are concerned are listed in

Table 5–5. Canadian softwood lumber imported into the

United States and graded by inspection agencies in Canada

also follows the PS–20 standard. Names and addresses of

accredited Canadian grading agencies may be obtained from

the American Lumber Standard Committee, P.O. Box 210,

Germantown, Maryland 20874.

Purchase of Lumber

After primary manufacture, most lumber products are marketed through wholesalers to remanufacturing plants or retail

outlets. Because of the extremely wide variety of lumber

products, wholesaling is very specialized—some organizations deal with only a limited number of species or products.

Where the primary manufacturer can readily identify the

customers, direct sales may be made. Primary manufacturers

often sell directly to large retail-chain contractors, manufacturers of mobile and modular housing, and truss fabricators.

Flooring (standard match)

Ceiling (edge beading)

Decking

Heavy decking

Drop siding (shiplapped)

Bevel siding

Dressed and matched (center matched)

Shiplap

Figure 5–3. Typical patterns of worked lumber.
5–13

Table 5–7. Nomenclature of commercial softwood lumber

Commercial species or species

group names under American

Softwood Lumber Standard

Tree name used

in this handbook Botanical name

Cedar

Alaska yellow-cedar Chamaecyparis nootkatensis

Eastern Red eastern redcedar Juniperus virginiana

Incense incense-cedar Libocedrus decurrens

Northern White northern white-cedar Thuja occidentalis

Port Orford Port-Orford-cedar Chamaecyparis lawsoniana

Southern White Atlantic white-cedar Chamaecyparis thyoides

Western Red western redcedar Thuja plicata

Cypress

Baldcypress baldcypress Taxodium distichum

Pond cypress pond cypress Taxodium distichum var. nutans

Fir

Alpine subalpine fir (alpine fir) Abies lasiocarpa

Balsam balsam fir Abies balsamea

California Red California red fir Abies magnifica

Douglas Fir Douglas-fir Pseudotsuga menziesii

Fraser Fraser fir Abies fraseri

Grand grand fir Abies grandis

Noble Fir noble fir Abies procera

Pacific Grand Pacific silver fir Abies amabilis

White white fir Abies concolor

Hemlock

Carolina Carolina hemlock Tsuga caroliniana

Eastern eastern hemlock Tsuga canadensis

Mountain mountain hemlock Tsuga mertensiana

Western western hemlock Tsuga heterophylla

Juniper

Western alligator juniper Juniperus deppeana

Rocky Mountain juniper Juniperus scopulorum

Utah juniper Juniperus osteosperma

western juniper Juniperus occidentalis

Larch

Western western larch Larix occidentalis

Pine

Bishop bishop pine Pinus muricata

Coulter Coulter pine Pinus coulteri

Digger Digger pine Pinus sabibiana

Knobcone knobcone pine Pinus attenuata

Idaho White western white pine Pinus monticola

Jack jack pine Pinus banksiana

Jeffrey Jeffrey pine Pinus jeffreyi

Limber limber pine Pinus flexilis

Lodgepole lodgepole pine Pinus contorta

Longleaf longleaf pine Pinus palustris

slash pine Pinus elliottii

Northern White eastern white pine Pinus strobus

Norway red pine Pinus resinosa

Pitch pitch pine Pinus rigida

Ponderosa ponderosa pine Pinus ponderosa

Southern Pine Major loblolly pine Pinus taeda

longleaf pine Pinus palustris

shortleaf pine Pinus echinata

slash pine Pinus elliottii

Southern Pine Minor pond pine Pinus serotina

sand pine Pinus clausa

spruce pine Pinus glabra

Virginia pine Pinus virginiana

Southern Pine Mixed loblolly pine Pinus taeda

longleaf pine Pinus palustris

pond pine Pinus serotina

shortleaf pine Pinus echinata

slash pine Pinus elliottii

Virginia pine Pinus virginiana

Radiata/Monterey Pine Monterey pine Pinus radiata
 5–14

Table 5–7. Nomenclature of commercial softwood lumber—con.

Commercial species or species

group names under American

Softwood Lumber Standard

Tree name used in this

handbook Botanical name

Pine—con.

Sugar sugar pine Pinus lambertiana

Whitebark whitebark pine Pinus albicaulis

Redwood

Redwood redwood Sequoia sempervirens

Spruce

Blue blue spruce Picea pungens

Eastern black spruce Picea mariana

red spruce Picea rubens

white spruce Picea glauca

Engelmann Engelmann spruce Picea engelmannii

Sitka Sitka spruce Picea sitchensis

Tamarack

Tamarack tamarack Larix larcinia

Yew

Pacific Pacific yew Taxus brevifolia

Coast Species Douglas-fir Pseudotsuga menziesii

western larch Larix occidentalis

Eastern Softwoods black spruce Picea mariana

red spruce Picea rubens

white spruce Picea glauca

balsam fir Abies balsamea

eastern white pine Pinus strobus

jack pine Pinus banksiana

pitch pine Pinus rigida

red pine Pinus resinosa

eastern hemlock Tsuga canadensis

tamarack Larix occidentalis

Hem–Fir western hemlock Tsuga heterophylla

California red fir Abies magnifica

grand fir Abies grandis

noble fir Abies procera

Pacific silver fir Abies amabilis

white fir Abies concolor

Hem–Fir (North) western hemlock Tsuga heterophylla

Pacific silver fir Abies amabilis

Northern Pine jack pine Pinus banksiana

pitch pine Pinus rigida

red pine Pinus resinosa

North Species northern white cedar Thuja occidentalis

western redcedar Thuja plicanta

yellow-cedar Chamaecyparis nootkatensis

eastern hemlock Tsuga canadensis

western hemlock Tsuga heterophylla

Douglas-fir Pseudotsuga menziesii

balsam fir Abies balsamea

grand fir Abies grandis

Pacific silver fir Abies amabilis

subalpine (alpine) fir Abies lasiocarpa

western larch Larix occidentalis

tamarack Larix laricina

eastern white pine Pinus strobus

jack pine Pinus banksiana

lodgepole pine Pinus contorta

ponderosa pine Pinus ponderosa

red pine Pinus resinosa

western white pine Pinus monticola

whitebark pine Pinus albicaulis

black spruce Picea mariana

Engelmann spruce Picea engelmannii

red spruce Picea rubens

Sitka spruce Picea sitchensis
5–15

Table 5–7. Nomenclature of commercial softwood lumber—con.

Commercial species or species

group names under American

Softwood Lumber Standard

Tree name used

in this handbook Botanical name

North Species—con. white spruce Picea glauca

bigtooth aspen Populus grandidentata

quaking aspen Populus tremuloides

black cottonwood Populus trichocarpa

balsam poplar Populus balsamifera

Southern Pine loblolly pine Pinus taeda

longleaf pine Pinus palustris

shortleaf pine Pinus echinata

slash pine Pinus elliottii

Spruce–Pine–Fir black spruce Picea mariana

Engelmann spruce Picea engelmannii

red spruce Picea rubens

balsam fir Abies balsamea

subalpine (alpine) fir Abies lasiocarpa

jack pine Pinus banksiana

lodgepole pine Pinus contorta

Spruce–Pine–Fir (South) black spruce Picea mariana

Engelmann spruce Picea engelmannii

red spruce Picea rubens

Sitka spruce Picea sitchensis

white spruce Picea glauca

balsam fir Abies balsamea

jack pine Pinus banksiana

lodgepole pine Pinus contorta

red pine Pinus resinosa

Western Cedars incense cedar Libocedrus decurrens

western redcedar Thuja plicata

Port-Orford-cedar Chamaecyparis lawsoniana

yellow-cedar Chamaecyparis nootkatensis

Western Cedar (North) western redcedar Thuja plicata

yellow-cedar Chamaecyparis nootkatensis

Western Woods Douglas-fir Pseudotsuga menziesii

California red fir Abies magnifica

grand fir Abies grandis

noble fir Abies procera

Pacific silver fir Abies amabilis

subalpine fir Abies lasiocarpa

white fir Abies concolor

Hemlock mountain Tsuga mertensiana

western hemlock Tsuga heterophylla

western larch Larix occidentalis

Engelmann spruce Picea engelmannii

Sitka spruce Picea sitchensis

lodgepole pine Pinus contorta

ponderosa pine Pinus ponderosa

sugar pine Pinus lambertiana

western white pine Pinus monticola

White Woods California red fir Abies magnifica

grand fir Abies grandis

noble fir Abies procera

Pacific silver fir Abies amabilis

subalpine fir Abies lasiocarpa

white fir Abies concolor

mountain hemlock Tsuga mertensiana

western hemlock Tsuga heterophylla

Engelmann spruce Picea engelmannii

Sitka spruce Picea sitchensis

lodgepole pine Pinus contorta

ponderosa pine Pinus ponderosa

sugar pine Pinus lambertiana

western white pine Pinus monticola
 5–16

Some primary manufacturers and wholesalers set up distribution yards in lumber-consuming areas to distribute both

hardwood and softwood products more effectively. Retail

yards draw inventory from distribution yards and, in woodproducing areas, from local lumber producers. The wide

range of grades and species covered in the grade rules may

not be readily available in most retail outlets.

Transportation is a vital factor in lumber distribution. Often,

the lumber shipped by water is green because weight is not a

major factor in this type of shipping. On the other hand,

lumber reaching the East Coast from the Pacific Coast by rail

is usually kiln-dried because rail shipping rates are based on

weight. A shorter rail haul places southern and northeastern

species in a favorable economic position in regard to shipping costs in this market.

Changing transportation costs have influenced shifts in market distribution of species and products. Trucks have become

a major factor in lumber transport for regional remanufacture

plants, for retail supply from distribution yards, and for much

construction lumber distribution.

The increased production capacity of foreign hardwood and

softwood manufacturing and the availability of water transport has brought foreign lumber products to the U.S. market,

particularly in coastal areas.

Retail Yard Inventory

The small retail yards throughout the United States carry

softwoods for construction purposes and often carry small

stocks of one or two hardwoods in grades suitable for finishing or cabinetwork. Special orders must be made for other

hardwoods. Trim items such as moulding in either softwood

or hardwood are available cut to standard size and pattern.

Millwork plants usually make ready-for-installation cabinets,

and retail yards carry or catalog many common styles and

sizes. Hardwood flooring is available to the buyer only in

standard patterns. Most retail yards carry stress grades of

lumber.

The assortment of species in general construction items

carried by retail yards depends to a great extent upon geographic location, and both transportation costs and tradition

are important factors. Retail yards within, or close to, a

major lumber-producing region commonly emphasize local

timber. For example, a local retail yard on the Pacific

Northwest Coast may stock only green Douglas Fir and

cedar in dimension grades, dry pine and hemlock in boards

and moulding, and assorted special items such as redwood

posts, cedar shingles and shakes, and rough cedar siding.

The only hardwoods may be walnut and “Philippine mahogany” (the common market name encompassing many

species, including tanguile, red meranti, and white lauan).

Retail yards located farther from a major softwood supply,

such as in the Midwest, may draw from several growing

areas and may stock spruce and Southern Pine, for example.

Because they are located in a major hardwood production

area, these yards may stock, or have available to them, a

different and wider variety of hardwoods.

Geography has less influence where consumer demands are

more specific. For example, where long construction lumber

(6 to 8 m (20 to 26 ft)) is required, West Coast species are

often marketed because the height of the trees in several

species makes long lengths a practical market item. Ease of

preservative treatability makes treated Southern Pine construction lumber available in a wide geographic area.

Structural Lumber for Construction

Dimension lumber is the principal stress-graded lumber

available in a retail yard. It is primarily framing lumber for

joists, rafters, and studs. Strength, stiffness, and uniformity

of size are essential requirements. Dimension lumber is

stocked in almost all yards, frequently in only one or two of

the general purpose construction woods such as pine, fir,

hemlock, or spruce. Standard 38- by 89-mm (nominal 2- by

4-in.) and wider dimension lumber is found in Select Structural, No. 1, No. 2, and No. 3 grades. Standard 38- by

89-mm (nominal 2- by 4-in.) dimension lumber may also be

available as Construction, Standard, Utility, and STUD

grades. STUD grade is also available in wider widths.

Dimension lumber is often found in standard 38-, 89-, 140-,

184-, 235-, and 286-mm (nominal 2-, 4-, 6-, 8-, 10-, and

12-in.) widths and 2.4- to 5.4-m (8- to 18-ft) lengths in

multiples of 0.6 m (2 ft). Dimension lumber formed by

structural end-jointing procedures may be available. Dimension lumber thicker than standard 38 mm (nominal 2 in.)

and longer than 5.4 m (18 ft) is not commonly available in

many retail yards.

Other stress-graded products generally available are posts and

timbers; some beams and stringers may also be in stock.

Typical grades in these products are Select Structural, No. 1,

and No. 2.

Yard Lumber for Construction

Boards are the most common non-stress-graded general

purpose construction lumber in the retail yard. Boards are

stocked in one or more species, usually in standard 19 mm

(nominal 1 in.) thickness. Common widths are standard 38,

64, 89, 140, 184, 235, and 286 mm (nominal 2, 3, 4, 6, 8,

10, and 12 in.). Grades generally available in retail yards are

No. 1 Common, No. 2 Common, and No. 3 Common

(Construction, Standard, No. 1, No. 2, etc.). Boards are sold

square edged, dressed (surfaced) and matched (tongued and

grooved), or with a shiplapped joint. Boards formed by endjointing of shorter sections may constitute an appreciable

portion of the inventory.

Select Lumber

Completion of a construction project usually depends on the

availability of lumber items in finished or semi-finished

form. The following items often may be stocked in only a

few species, finishes, or sizes depending on the lumber yard.
5–17

Finish—Finish boards usually are available in a local yard

in one or two species, principally in grade C&BTR. Cedar

and redwood have different grade designations: grades such

as Clear Heart, A, or B are used in cedar; Clear All Heart,

Clear, and B grade are typical in redwood. Finish boards are

usually standard 19 mm (nominal 1 in.) thick, surfaced on

two sides to 19 mm (3/4 in.); 38- to 286-mm (2- to 12-in.)

widths are usually stocked, in even increments.

Siding—Siding is specifically intended to cover exterior

walls. Beveled siding is ordinarily stocked only in white

pine, ponderosa pine, western redcedar, cypress, or redwood.

Drop siding, also known as rustic or barn siding, is usually

stocked in the same species as is beveled siding. Siding may

be stocked as B&BTR or C&BTR except in cedar, where

Clear, A, and B grades may be available, and redwood,

where Clear All Heart, Clear, and B grades may be found.

Vertical grain (VG) is sometimes part of the grade designation. Drop siding is also sometimes stocked in sound knotted C and D grades of Southern Pine, Douglas Fir, and

hemlock. Drop siding may be surfaced and matched, or

shiplapped. Knotty grades of cedar (Select Tight Knot

(STK)) and redwood (Rustic) are commonly available.

Flooring—Flooring is made chiefly from hardwoods, such

as oak and maple, and the harder softwood species, such as

Douglas-fir, western larch, and Southern Pine. Often, at least

one softwood and one hardwood are stocked. Flooring is

usually 19 mm (3/4 in.) thick. Thicker flooring is available

for heavy-duty floors. Thinner flooring is available, especially for re-covering old floors. Vertical- and flat-grained

(also called quartersawn and plainsawn) flooring is manufactured from both softwoods and hardwoods. Vertical-grained

flooring shrinks and swells less than flat-grained flooring, is

more uniform in texture, and wears more uniformly, and the

edge joints have less tendency to open.

Softwood flooring is usually available in B&BTR, C Select,

or D Select grades. In maple, the chief grades are Clear,

No. 1, and No. 2. The grades in quartersawn oak are Clear

and Select, and in plainsawn, Clear, Select, and No. 1

Common. Quartersawn hardwood flooring has the same

advantages as does vertical-grained softwood flooring. In

addition, the silver or flaked grain of quartersawn flooring is

frequently preferred to the figure of plainsawn flooring.

Casing and Base—Casing and base are standard items in

the more important softwoods and are stocked in most yards

in at least one species. The chief grade, B&BTR, is designed to meet the requirements of interior trim for dwellings. Many casing and base patterns are surfaced to 17.5 by

57 mm (11/16 by 2-1/4 in.); other sizes include 14.3 mm

(9/16 in.) by 76 mm (3 in.), by 83 mm (3-1/4 in.), and by

89 mm (3-1/2 in.). Hardwoods for the same purposes, such

as oak and birch, may be carried in stock in the retail yard or

obtained on special order.

Shingles and Shakes—Commonly available shingles are

sawn from western redcedar and northern white-cedar. For

western redcedar, the shingle grades are No. 1, No. 2, and

No. 3; for northern white-cedar, Extra, Clear, 2nd Clear,

Clearwall, and Utility.

Shingles that contain only heartwood are more resistant to

decay than are shingles that contain sapwood. Edge-grained

shingles are less likely to warp and split than flat-grained

shingles, thick-butted shingles less likely than thin-butted

shingles, and narrow shingles less likely than wide shingles.

The standard thickness values of thin-butted shingles are

described as 4/2, 5/2-1/4, and 5/2 (four shingles to 51 mm

(2 in.) of butt thickness, five shingles to 57 mm (2-1/4 in.)

of butt thickness, and five shingles to 51 mm (2 in.) of butt

thickness). Lengths may be 406, 457, or 610 mm (16, 18, or

24 in.). Random widths and specified (“dimension” shingle)

widths are available in western redcedar, redwood, and

cypress.

Shingles are usually packed four bundles to a square. A

square of shingles will cover roughly 9 m2

 (100 ft2) of roof

area when the shingles are applied at standard weather

exposures.

Shakes are hand split or hand split and resawn from western

redcedar. Shakes are of a single grade and must be 100%

clear. In the case of hand split and resawn material, shakes

are graded from the split face. Hand-split shakes are graded

from the best face. Shakes must be 100% heartwood. The

standard thickness of shakes ranges from 9.5 to 32 mm (3/8

to 1-1/4 in.). Lengths are 457 and 610 mm (18 and 24 in.),

with a special “Starter–Finish Course” length of 381 mm

(15 in.).

Important Purchase Considerations

Some points to consider when ordering lumber or timbers

are the following:

1. Quantity—Lineal measure, board measure, surface measure, number of pieces of definite size and length. Consider

that the board measure depends on the thickness and

width nomenclature used and that the interpretation of

these must be clearly delineated. In other words, such

features as nominal or actual dimensions and pattern size

must be considered.

2. Size—Thickness in millimeters or inches—nominal or

actual if surfaced on faces; width in millimeters or

inches—nominal or actual if surfaced on edges; length in

meters or feet—may be nominal average length, limiting

length, or a single uniform length. Often a trade designation, “random” length, is used to denote a nonspecified

assortment of lengths. Such an assortment should contain

critical lengths as well as a range. The limits allowed in

making the assortment random can be established at the

time of purchase.

3. Grade—As indicated in grading rules of lumber manufacturing associations. In softwoods that are in compliance

with the American Softwood Lumber Standard, each

piece of lumber may be grade stamped with its official

grade species identification, a name or number identifying
 5–18

the producing mill, the dryness at the time of surfacing,

and a symbol identifying the inspection agency supervising the grading inspection. The grade designation

stamped on a piece indicates the quality at the time the

piece was graded. Subsequent exposure to unfavorable

storage conditions, improper drying, or careless handling

may cause the material to fall below its original grade.

Working or recutting a graded product to a pattern may

change or invalidate the original grade. The purchase

specification should be clear in regard to regrading or acceptance of worked lumber. In softwood lumber, grades

for dry lumber generally are determined after kiln drying

and surfacing. However, this practice is not general for

hardwood Factory lumber, where the grade is generally

based on quality and size prior to kiln drying. To be certain the product grade is correct, refer to the grading rule

by number and paragraph.

4. Species or species group of wood—Such as Douglas Fir,

Southern Pine, Hem–Fir. Some species have been

grouped for marketing convenience; others are sold under

a variety of names. Be sure the species or species group

is correctly and clearly described on the purchase

specification.

5. Product—Such as flooring, siding, timbers, boards.

Nomenclature varies by species, region, and grading

association. To be certain the nomenclature is correct for

the product, refer to the grading rule by number and

paragraph.

6. Condition of seasoning—Such as air dry, kiln dry. Softwood lumber less than 114 mm (nominal 5 in.) in thickness dried to 19% moisture content or less is defined as

dry by the American Softwood Lumber Standard. Kilndried lumber is lumber that has been seasoned in a chamber to a predetermined moisture content by applying heat.

Green lumber is lumber less than 114 mm (nominal

5 in.) in thickness, which has a moisture content in excess of 19%. If the moisture requirement is critical, the

level of moisture content and the method by which it will

be achieved must be specified.

7. Surfacing and working—Rough (unplaned), surfaced

(dressed, planed), or patterned stock. Specify condition.

If surfaced, indicate code (S4S, S1S1E). If patterned, list

pattern number with reference to appropriate grade rules.

8. Grading rules—Official grading agency name and name of

official rules under which product is graded, product identification, paragraph and page number of rules, and date of

rules or official rule edition may be specified by the

buyer.

9. Manufacturer—Name of manufacturer or trade name of

specific product or both. Most lumber products are sold

without reference to a specific manufacturer. If proprietary

names or quality features of a manufacturer are required,

this must be stipulated clearly on the purchase agreement.

10. Reinspection—Procedures for resolution of purchase

disputes. The American Softwood Lumber Standard provides for procedures to be followed in resolution of

manufacturer–wholesaler–consumer conflicts over quality

or quantity of ALS lumber grades. The dispute may be

resolved by reinspecting the shipment. Time limits, liability, costs, and complaint procedures are outlined in

the grade rules of both softwood and hardwood agencies

under which the disputed shipment was graded and

purchased.

Commonly Used Lumber

Abbreviations

The following standard lumber abbreviations are commonly

used in contracts and other documents for purchase and sale

of lumber.

AAR Association of American Railroads

AD air dried

ADF after deducting freight

AF alpine fir

ALS American Lumber Standard

AST antistain treated; at ship tackle (western softwoods)

AV or avg average

AW&L all widths and lengths

B1S see EB1S, CB1S, and E&CB1S

B2S see EB2S, CB2S, and E&CB2S

B&B, B&BTR B and Better

B&S beams and stringers

BD board

BD FT board feet

BDL bundle

BEV bevel or beveled

BH boxed heart

B/L, BL bill of lading

BM board measure

BSND bright sapwood, no defect

BTR better

CB center beaded

CB1S center bead on one side

CB2S center bead on two sides

CC cubical content

cft or cu. ft. cubic foot or feet

CF cost and freight

CIF cost, insurance, and freight

CIFE cost, insurance, freight, and exchange

CG2E center groove on two edges

C/L carload

CLG ceiling

CLR clear
5–19

CM center matched

Com Common

CONST construction

CS caulking seam

CSG casing

CV center V

CV1S center V on one side

CV2S center V on two sides

DB Clg double-beaded ceiling (E&CB1S)

DB Part double-beaded partition (E&CB2S)

DET double end-trimmed

DF Douglas-fir

DF–L Douglas-fir plus larch

DIM dimension

DKG decking

D/S, DS, D/Sdg drop siding

D1S, D2S see S1S and S2S

D&M dressed and matched

D&CM dressed and center matched

D&SM dressed and standard matched

D2S&CM dressed two sides and center matched

D2S&SM dressed two sides and standard matched

E edge

EB1S edge bead one side

EB2S, SB2S edge bead on two sides

EE eased edges

EG edge (vertical or rift) grain

EM end matched

EV1S, SV1S edge V one side

EV2S, SV2S edge V two sides

E&CB1S edge and center bead one side

E&CB2S,

DB2S, BC&2S

edge and center bead two sides

E&CV1S,

DV1S,V&CV1S

edge and center V one side

E&CV2S,

DV2S,

V&CV2S

edge and center V two sides

ES Engelmann spruce

Fb, Ft, Fc, Fv, Fcx allowable stress (MPa (lb/in2)) in bending; tension,

compression and shear parallel to grain;

and in compression perpendicular to grain,

respectively

FA facial area

Fac factory

FAS free alongside (vessel)

FAS Firsts and Seconds

FAS1F Firsts and Seconds one face

FBM, Ft. BM feet board measure

FG flat or slash grain

FJ finger joint; end-jointed lumber using finger-joint

configuration

FLG, Flg flooring

FOB free on board (named point)

FOHC free of heart center

FOK free of knots

FRT, Frt freight

FT, ft foot, feet

FT. SM feet surface measure

G girth

GM grade marked

G/R grooved roofing

HB, H.B. hollow back

HEM hemlock

H-F mixed hemlock and fir (Hem–Fir)

Hrt heart

H&M hit and miss

H or M hit or miss

IC incense cedar

IN, in. inch, inches

Ind industrial

IWP Idaho white pine

J&P joists and planks

JTD jointed

KD kiln dried

KDAT kiln-dried after treatment

L western larch

LBR, Lbr lumber

LCL less than carload

LGR longer

LGTH length

Lft, Lf lineal foot, feet

LIN, Lin lineal

LL longleaf

LNG, Lng lining

LP lodgepole pine

M thousand

MBM, MBF,

M.BM

thousand (feet) board measure

MC, M.C. moisture content

MERCH, Merch merchantable

MFMA Maple Flooring Manufacturers Association

MG medium grain or mixed grain

MH mountain hemlock

MLDG, Mldg moulding

Mft thousand feet

M-S mixed species

MSR machine stress rated

N nosed

NBM net board measure

NOFMA National Oak Flooring Manufacturers Association

No. number
 5–20

N1E or N2E nosed one or two edges

Ord order

PAD partially air-dried

PAR, Par paragraph

PART, Part partition

PAT, Pat pattern

Pcs. pieces

PE plain end

PET precision end-trimmed

PP ponderosa pine

P&T posts and timbers

P1S, P2S see S1S and S2S

RDM random

REG, Reg regular

Rfg. roofing

RGH, Rgh rough

R/L, RL random lengths

R/W, RW random widths

RES resawn

SB1S single bead one side

SDG, Sdg siding

S-DRY surfaced dry; lumber ≤ 19% moisture content per

ALS for softwood

SE square edge

SEL, Sel Select or Select grade

SE&S square edge and sound

SG slash or flat grain

S-GRN surfaced green; lumber unseasoned, >19%

moisture content per ALS for softwood

SGSSND sapwood, gum spots and streaks, no defect

SIT. SPR Sitka spruce

S/L, SL, S/Lap shiplap

SM surface measure

Specs specifications

SP sugar pine

SQ square

SQRS squares

SRB stress-rated board

STD, Std standard

Std. lgths. standard lengths

STD. M standard matched

SS Sitka spruce

SSE sound square edge

SSND sap stain, no defect (stained)

STK Select tight knot

STK stock

STPG stepping

STR, STRUCT structural

SYP Southern Pine

S&E side and edge (surfaced on)

S1E surfaced one edge

S2E surfaced two edges

S1S surfaced one side

S2S surfaced two sides

S4S surfaced four sides

S1S&CM surfaced one side and center matched

S2S&CM surfaced two sides and center matched

S4S&CS surfaced four sides and caulking seam

S1S1E surfaced one side, one edge

S1S2E surfaced one side, two edges

S2S1E surfaced two sides, one edge

S2S&SL surfaced two sides and shiplapped

S2S&SM surfaced two sides and standard matched

TBR timber

T&G tongued and grooved

TSO treating service only (nonconforming to standard)

UTIL utility

VG vertical (edge) grain

V1S see EV1S, CV1S, and E&CV1S

V2S see EV2S, CV2S, and E&CV2S

WC western cedar

WCH West Coast hemlock

WCW West Coast woods

WDR, wdr wider

WF white fir

WHAD worm holes (defect)

WHND worm holes (no defect)

WT weight

WTH width

WRC western redcedar

WW white woods (Engelmann spruce, any true firs,

any hemlocks, any pines)

Reference

USDC. [Current edition]. American softwood lumber

standard. Prod. Stand. PS–20–94. Washington, DC: U.S.

Department of Commerce.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
6–1

Chapter 6

Lumber Stress Grades and

Design Properties

David E. Kretschmann and David W. Green

Contents

Responsibilities and Standards for Stress Grading 6–2

American Lumber Standard Committee 6–2

National Grading Rule 6–3

Standards 6–3

Visually Graded Structural Lumber 6–3

Visual Sorting Criteria 6–3

Procedures for Deriving Design Properties 6–5

Machine-Graded Structural Lumber 6–7

Machine Sorting Criteria 6–7

Procedures for Deriving Design Properties 6–8

Quality Control 6–10

Adjustment of Properties for Design Use 6–11

Shrinkage 6–11

Size Factor 6–11

Moisture Adjustments 6–12

Duration of Load 6–12

Treatment Effects 6–13

Temperature Effects 6–14

References 6–14

umber sawn from a log, regardless of species and

size, is quite variable in mechanical properties.

Pieces may differ in strength by several hundred

percent. For simplicity and economy in use, pieces of lumber

of similar mechanical properties are placed in categories

called stress grades, which are characterized by (a) one or

more sorting criteria, (b) a set of properties for engineering

design, and (c) a unique grade name.

This chapter briefly discusses the U.S. Department of Commerce American Softwood Lumber Standard PS20 (1994)

sorting criteria for two stress-grading methods, and the philosophy of how properties for engineering design are derived.

The derived properties are then used in one of two design

formats: (a) the load and resistance factor design (LRFD),

which is based on a reference strength at the 5th percentile

5-min bending stress (AF&PA 1996), or (b) the allowable

stress design (ASD), which is based on a design stress at the

lower 5th percentile 10-year bending stress. The properties

depend on the particular sorting criteria and on additional

factors that are independent of the sorting criteria. Design

properties are lower than the average properties of clear,

straight-grained wood tabulated in Chapter 4.

From one to six design properties are associated with a stress

grade: bending modulus of elasticity for an edgewise loading

orientation and stress in tension and compression parallel to

the grain, stress in compression perpendicular to the grain,

stress in shear parallel to the grain, and extreme fiber stress

in bending. As is true of the properties of any structural

material, the allowable engineering design properties must be

either inferred or measured nondestructively. In wood, the

properties are inferred through visual grading criteria, nondestructive measurement such as flatwise bending stiffness or

density, or a combination of these properties. These nondestructive tests provide both a sorting criterion and a means

of calculating appropriate mechanical properties.

The philosophies contained in this chapter are used by a

number of organizations to develop visual and machine stress

grades. References are made to exact procedures and the

resulting design stresses, but these are not presented in

detail.
 6–2

Responsibilities and

Standards for Stress Grading

An orderly, voluntary, but circuitous system of responsibilities has evolved in the United States for the development,

manufacture, and merchandising of most stress-graded lumber. The system is shown schematically in Figure 6–1.

Stress-grading principles are developed from research findings

and engineering concepts, often within committees and

subcommittees of the American Society for Testing and

Materials.

American Lumber

Standard Committee

Voluntary product standards are developed under procedures

published by the U.S. Department of Commerce. The Department of Commerce National Institute of Standards and

Technology (NIST), working with rules-writing agencies,

lumber inspection agencies, lumber producers, distributors

and wholesalers, retailers, end users, and members of Federal

agencies, work through the American Lumber Standard

Committee (ALSC) to maintain a voluntary consensus

softwood standard, called the American Softwood Lumber

Standard (PS 20–94). The PS 20–94 Standard prescribes the

ways in which stress-grading principles can be used to

formulate grading rules designated as conforming to the

American Lumber Standard. Under the auspices of the ALSC

is the National Grading Rule, which specifies grading characteristics for different grade specifications.

Organizations that write and publish grading rule books

containing stress-grade descriptions are called rules-writing

agencies. Grading rules that specify American Softwood

Lumber Standard PS 20–94 must be certified by the ALSC

Board of Review for conformance with this standard.

Organizations that write grading rules, as well as independent agencies, can be accredited by the ALSC Board of

Review to provide grading and grade-marking supervision

and reinspection services to individual lumber manufacturers.

Accredited rules-writing and independent agencies are listed

in Table 6–1. The continued accreditation of these organizations is under the scrutiny of the ALSC Board of Review.

Most commercial softwood species manufactured in the

United States are stress graded under American Lumber

Standard practice. Distinctive grade marks for each species or

species grouping are provided by accredited agencies. The

principles of stress grading are also applied to several hardwood species under provisions of the American Softwood

Lumber Standard. Lumber found in the marketplace may be

stress graded under grading rules developed in accordance

Review and adoption

Formulation and publication of

stress-grading rules

Rules-writing agencies

Product standards

American Lumber Standard Committee

 and its Board of Review

National Grading Rule Committee

National Institute of Standards and Technology

Formulation of stress grading principles

University staff members

Government researchers

Industry R&D staff

Consumer representatives

Grading agency accreditation

American Lumber Standard Committee

Grade mark supervision and reinspection

Rules-writing agencies

Independent inspection agencies

Manufacture and marketing of American

standard stress-graded lumber

Sawmills

(1)

(2)

(3)

(4)

(5)

(6)

Figure 6–1. Voluntary system of responsibilities for

stress grading under the American Softwood Lumber

Standard.

Table 6–1. Sawn lumber grading agenciesa

Rules-writing agencies

Northeastern Lumber Manufacturers Association

(NELMA)

Northern Softwood Lumber Bureau (NSLB)

Redwood Inspection Service (RIS)

Southern Pine Inspection Bureau (SPIB)

West Coast Lumber Inspection Bureau (WCLIB)

Western Wood Products Association (WWPA)

National Lumber Grades Authority (NLGA)

Independent agencies

California Lumber Inspection Service

Pacific Lumber Inspection Bureau, Inc.

Renewable Resource Associates, Inc.

Timber Products Inspection

Alberta Forest Products Association

Canadian Lumbermen’s Association

Canadian Mill Services Association

Canadian Softwood Inspection Agency, Inc.

Cariboo Lumber Manufacturers Association

Central Forest Products Association

Coniferous Lumber Inspection Bureau

Council of Forest Industries of British Columbia

Interior Lumber Manufacturers Association

MacDonald Inspection

Maritime Lumber Bureau

Newfoundland Lumber Producers Association

Northern Forest Products Association

Ontario Lumber Manufacturers Association

Pacific Lumber Inspection Bureau

Quebec Lumber Manufacturers Association

a

For updated information, contact American Lumber

 Standard Committee, P.O. Box 210, Germantown,

 MD 20874.
6–3

with methods approved by the ALSC or by some other

stress-grading rule, or it may not be stress graded. Only

those stress grades that meet the requirements of the voluntary American Softwood Lumber Standard system are discussed in this chapter.

National Grading Rule

Stress grading under the auspices of the ALSC is applied to

many sizes and several patterns of lumber that meet the

American Softwood Lumber Standard provision. However,

most stress-graded lumber is dimension lumber (standard 38

to 89 mm (nominal 2 to 4 in.) thick) and is governed by

uniform specifications under the National Grading Rule. The

National Grading Rule provides guidelines for writing grading rules for lumber in this thickness range and specifies

grading characteristics for different grade specifications.

American Softwood Lumber Standard dimension lumber in

this thickness range is required to conform to the National

Grading Rule, except for special products such as scaffold

planks. Grade rules for other sizes, such as nominal 5-in.

(standard 114-mm) or larger structural timbers may vary

between rules-writing agencies or species.

The National Grading Rule establishes the lumber classifications and grade names for visually stress-graded dimension

lumber (Table 6–2) and also provides for the grading of

dimension lumber by a combination of machine and visual

methods. Visual requirements for this type of lumber are

developed by the respective rules-writing agencies for

particular species grades.

Standards

Table 6–2 also shows associated minimum bending strength

ratios to provide a comparative index of quality. The

strength ratio is the hypothetical ratio of the strength of a

piece of lumber with visible strength-reducing growth characteristics to its strength if those characteristics were absent.

Formulas for calculating strength ratios are given in American Society of Testing and Materials (ASTM) standard

D245. The corresponding visual description of the dimension lumber grades can be found in the grading rule books of

the rules-writing agencies listed in Table 6–1. Design properties will vary by species. The design properties for each

species and grade are published in the appropriate rule books

and in the National Design Specification for Wood

Construction (AF&PA 1997).

Grouping of Species

Most species are grouped together and the lumber from them

treated as equivalent. Species are usually grouped when they

have about the same mechanical properties, when the wood

of two or more species is very similar in appearance, or for

marketing convenience. For visual stress grades, ASTM

D2555 contains procedures for calculating clear wood properties for groups of species to be used with ASTM D245.

ASTM D1990 contains procedures for calculating design

properties for groups of species tested as full-sized members.

The properties assigned to a group by such procedures will

often be different from those of any species that make up the

group. The group will have a unique identity, with nomenclature approved by the Board of Review of the ALSC. The

identities, properties, and characteristics of individual species

of the group are found in the grade rules for any particular

species or species grouping. In the case of machine stress

grading, the inspection agency that supervises the grading

certifies by testing that the design properties in that grade

are appropriate for the species or species grouping and the

grading process.

Foreign species

Currently, the importation of structural lumber is governed

by two ALSC guidelines that describe the application of the

American Lumber Standard and ASTM D1990 procedures

to foreign species. The approval process is outlined in

Table 6–3.

Visually Graded

Structural Lumber

Visual Sorting Criteria

Visual grading is the original method for stress grading. It is

based on the premise that mechanical properties of lumber

differ from mechanical properties of clear wood because many

growth characteristics affect properties and these characteristics can be seen and judged by eye. Growth characteristics are

used to sort lumber into stress grades. The typical visual

sorting criteria discussed here are knots, slope of grain,

Table 6–2. Visual grades described in National

Grading Rule

Lumber classificationa Grade name

Bending

strength

ratio (%)

Light framingb Construction 34

Standard 19

Utility 9

Structural light framingb Select Structural 67

1 55

2 45

3 26

Studc Stud 26

Structural joists and planksd Select Structural 65

1 55

2 45

3 26

a

Contact rules-writing agencies for additional information.

 bStandard 38 to 89 mm (nominal 2 to 4 in.) thick and wide.

 Widths narrower than 89 mm (4 in.) may have different

 strength ratio than shown.

c

Standard 38 to 89 mm (nominal 2 to 4 in.) thick,

≥38 mm (≥4 in.) wide. d

Standard 38 to 89 mm (nominal 2 to 4 in.) thick,

≥140 mm (≥6 in.) wide.
 6–4

checks and splits, shake, density, decay, heartwood and

sapwood, pitch pockets, and wane.

Knots

Knots cause localized cross grain with steep slopes. A very

damaging aspect of knots in sawn lumber is that the continuity of the grain around the knot is interrupted by the sawing

process.

In general, knots have a greater effect on strength in tension

than compression; in bending, the effect depends on whether

a knot is in the tension or compression side of a beam (knots

along the centerline have little or no effect). Intergrown (or

live) knots resist (or transmit) some kinds of stress, but

encased knots (unless very tight) or knotholes resist (or

transmit) little or no stress. On the other hand, distortion of

grain is greater around an intergrown knot than around an

encased (or dead) knot of equivalent size. As a result, overall

strength effects are roughly equalized, and often no distinction is made in stress grading between intergrown knots,

dead knots, and knotholes.

The zone of distorted grain (cross grain) around a knot has

less “parallel to piece” stiffness than does straight-grained

wood; thus, localized areas of low stiffness are often associated with knots. However, such zones generally constitute

only a minor part of the total volume of a piece of lumber.

Because overall stiffness of a piece reflects the character of

all parts, stiffness is not greatly influenced by knots.

The presence of a knot has a greater effect on most strength

properties than on stiffness. The effect on strength depends

approximately on the proportion of the cross section of the

piece of lumber occupied by the knot, knot location, and

distribution of stress in the piece. Limits on knot sizes are

therefore made in relation to the width of the face and location on the face in which the knot appears. Compression

members are stressed about equally throughout, and no

limitation related to location of knots is imposed. In tension,

knots along the edge of a member cause an eccentricity that

induces bending stresses, and they should therefore be more

restricted than knots away from the edge. In simply supported structural members subjected to bending, stresses are

greater in the middle of the length and at the top and bottom

edges than at midheight. These facts are recognized in some

grades by differing limitations on the sizes of knots in

different locations.

Knots in glued-laminated structural members are not continuous as in sawn structural lumber, and different methods

are used for evaluating their effect on strength (Ch. 11).

Slope of Grain

Slope of grain (cross grain) reduces the mechanical properties

of lumber because the fibers are not parallel to the edges.

Severely cross-grained pieces are also undesirable because

they tend to warp with changes in moisture content. Stresses

caused by shrinkage during drying are greater in structural

lumber than in small, clear straight-grained specimens and

are increased in zones of sloping or distorted grain. To provide a margin of safety, the reduction in design properties

resulting from cross grain in visually graded structural lumber is considerably greater than that observed in small, clear

specimens that contain similar cross grain.

Checks and Splits

Checks are separations of the wood that normally occur

across or through the annual rings, usually as a result of

seasoning. Splits are a separation of the wood through the

piece to the opposite surface or to an adjoining surface caused

by tearing apart of the wood cells. As opposed to shakes,

checks and splits are rated by only the area of actual opening.

An end-split is considered equal to an end-check that extends

through the full thickness of the piece. The effects of checks

and splits on strength and the principles of their limitation

are the same as those for shake.

Shake

Shake is a separation or a weakness of fiber bond, between or

through the annual rings, that is presumed to extend lengthwise without limit. Because shake reduces resistance to shear

Table 6–3. Approval process for acceptance of design values for foreign species

1 Rules-writing agency seeks approval to include species in grade-rule book.

2 Agency develops sampling and testing plan, following American Lumber Standard Committee (ALSC) foreign

importation guidelines, which must then be approved by ALSC Board of Review.

3 Lumber is sampled and tested in accordance with approved sampling and testing plan.

4 Agency analyzes data by ALSC Board of Review and ASTM D1990 procedures and other appropriate criteria

(if needed).

5 Agency submits proposed design values to ALSC Board of Review.

6 Submission is reviewed by ALSC Board of Review and USDA Forest Service, Forest Products Laboratory.

7 Submission is available for comment by other agencies and interested parties.

8 ALSC Board of Review approves (or disapproves) design values, with modification (if needed) based on all

available information.

9 Agency publishes new design values for species.
6–5

in members subjected to bending, grading rules therefore

restrict shake most closely in those parts of a bending member where shear stresses are highest. In members with limited

cross grain, which are subjected only to tension or compression, shake does not affect strength greatly. Shake may be

limited in a grade because of appearance and because it

permits entrance of moisture, which results in decay.

Density

Strength is related to the mass per unit volume (density) of

clear wood. Properties assigned to lumber are sometimes

modified by using the rate of growth and percentage of latewood as measures of density. Typically, selection for density

requires that the rings per unit length and the percentage of

latewood be within a specified range. It is possible to eliminate some very low-strength pieces from a grade by excluding those that are exceptionally low in density.

Decay

Decay in most forms should be prohibited or severely restricted in stress grades because the extent of decay is difficult

to determine and its effect on strength is often greater than

visual observation would indicate. Decay of the pocket type

(for example, Fomes pini) can be permitted to some extent in

stress grades, as can decay that occurs in knots but does not

extend into the surrounding wood.

Heartwood and Sapwood

Heartwood does not need to be taken into account in stress

grading because heartwood and sapwood have been assumed

to have equal mechanical properties. However, heartwood is

sometimes specified in a visual grade because the heartwood

of some species is more resistant to decay than is the sapwood; heartwood may be required if untreated wood will be

exposed to a decay hazard. On the other hand, sapwood takes

preservative treatment more readily than heartwood and it is

preferable for lumber that will be treated with preservatives.

Pitch Pockets

Pitch pockets ordinarily have so little effect on structural

lumber that they can be disregarded in stress grading if they

are small and limited in number. The presence of a large

number of pitch pockets, however, may indicate shake or

weakness of bond between annual rings.

Wane

Wane refers to bark or lack of wood on the edge or corner of

a piece of lumber, regardless of cause (except eased edges).

Requirements of appearance, fabrication, or ample bearing or

nailing surfaces generally impose stricter limitations on wane

than does strength. Wane is therefore limited in structural

lumber on those bases.

Procedures for Deriving

Design Properties

The mechanical properties of visually graded lumber may be

established by (a) tests of a representative sample of full-size

members (ASTM D1990 in-grade testing procedure) or

(b) appropriate modification of test results conducted on

small clear specimens (ASTM D245 procedure for small

clear wood). Design properties for the major commercial

softwood dimension lumber species given in current design

specification and codes in the United States have been derived from full-size member test results. However, design

properties for most hardwood dimension and structural timbers (larger than standard 89-mm- (nominal 4-in.-, actual

3-1/2-in.-) thick “timbers”) of all species are still derived

using results of tests on small clear samples.

Procedure for Small Clear Wood

The derivation of mechanical properties of visually graded

lumber was historically based on clear wood properties with

appropriate modifications for the lumber characteristics allowed by visual sorting criteria. Sorting criteria that influence mechanical properties are handled with “strength ratios”

for the strength properties and with “quality factors” for the

modulus of elasticity.

From piece to piece, there is variation in both the clear wood

properties and the occurrence of growth characteristics.

The influence of this variability on lumber properties is

handled differently for strength properties than for modulus of

elasticity.

Strength Properties—Each strength property of a piece of

lumber is derived from the product of the clear wood strength

for the species and the limiting strength ratio. The strength

ratio is the hypothetical ratio of the strength of a piece of

lumber with visible strength-reducing growth characteristics

to its strength if those characteristics were absent. The true

strength ratio of a piece of lumber is never known and must

be estimated. Therefore, the strength ratio assigned to a

growth characteristic serves as a predictor of lumber strength.

Strength ratio is expressed as a percentage, ranging from

0 to 100.

Estimated strength ratios for cross grain and density have

been obtained empirically; strength ratios for other growth

characteristics have been derived theoretically. For example,

to account for the weakening effect of knots, the assumption

is made that the knot is effectively a hole through the piece,

reducing the cross section, as shown in Figure 6–2. For a

beam containing an edge knot, the bending strength ratio can

be idealized as the ratio of the bending moment that can be

resisted by a beam with a reduced cross section to that of a

beam with a full cross section:

 SR / = −1 ( )2

k h

where SR is strength ratio, k knot size, and h width of face

containing the knot. This is the basic expression for the effect

of a knot at the edge of the vertical face of a beam that is

deflected vertically. Figure 6–3 shows how strength ratio

changes with knot size according to the formula.
 6–6

Strength ratios for all knots, shakes, checks, and splits are

derived using similar concepts. Strength ratio formulas are

given in ASTM D245. The same reference contains guidelines for measuring various growth characteristics.

An individual piece of lumber will often have several characteristics that can affect any particular strength property. Only

the characteristic that gives the lowest strength ratio is used

to derive the estimated strength of the piece. In theory, a

visual stress grade contains lumber ranging from pieces with

the minimum strength ratio permitted in the grade up to

pieces with the strength ratio just below the next higher

grade. In practice, there are often pieces in a grade with

strength ratios of a higher grade. This is a result of grade

reduction for appearance factors such as wane that do not

affect strength.

The range of strength ratios in a grade and the natural variation in clear wood strength give rise to variation in strength

between pieces in the grade. To account for this variation and

to ensure safety in design, it is intended that the actual

strength of at least 95% of the pieces in a grade exceed the

design properties (before reduction for duration of load and

safety) assigned to that grade. In visual grading, according to

ASTM D245, this is handled by using a near-minimum

clear wood strength as a base value and multiplying it by the

minimum strength ratio permitted in the grade to obtain the

grade strength property. The near-minimum value is called

the 5% exclusion limit. ASTM D2555 provides clear wood

strength data and gives a method for estimating the 5%

exclusion limit.

For example, suppose a 5% exclusion limit for the clear

wood bending strength of a species in the green condition

is 48 MPa (7,000 lb/in2

). Suppose also that among the

characteristics allowed in a grade of lumber, one characteristic

(a knot, for example) provides the lowest strength ratio in

bending—assumed in this example as 40%. Using the numbers, the bending strength for the grade is estimated by

multiplying the strength ratio (0.40) by 48 MPa

(7,000 lb/in2), equaling 19 MPa (2,800 lb/in2) (Fig. 6–4).

The bending strength in the green condition of 95% of the

pieces in this species in a grade that has a strength ratio of

40% is expected to be ≥19 MPa (≥2,800 lb/in2). Similar

procedures are followed for other strength properties, using

the appropriate clear wood property value and strength ratio.

Additional multiplying factors are then applied to produce

properties for design, as summarized later in this chapter.

Modulus of Elasticity—Modulus of elasticity E is a measure of the ability of a beam to resist deflection or of a column

to resist buckling. The assigned E is an estimate of the

average modulus, adjusted for shear deflection, of the lumber

grade when tested in static bending. The average modulus of

elasticity for clear wood of the species, as recorded in ASTM

D2555, is used as a base. The clear wood average is multiplied by empirically derived “quality factors” to represent the

reduction in modulus of elasticity that occurs by lumber

grade for pieces tested in an edgewise orientation. This

procedure is outlined in ASTM D245.

For example, assume a clear wood average modulus of elasticity of 12.4 GPa (1.8 × 106

 lb/in2)for the example shown

earlier. The limiting bending strength ratio was 40%.

ASTM D245 assigns a quality multiplying factor of 0.80

for lumber with this bending strength ratio. The modulus

of elasticity for that grade would be the product of the clear

wood modulus and the quality factor; that is,

12.4 × 0.8 = 9.9 GPa (1.8 × 0.8 = 1.44 × 106 lb/in2).

Actual modulus of elasticity of individual pieces of a grade

varies from the average assumed for design (Fig. 6–5). Small

individual lots of lumber can be expected to deviate from the

distribution shown by this histogram. The additional multiplying factors used to derive final design values of modulus

of elasticity are discussed later in this chapter.

In-Grade Procedure

To establish the mechanical properties of specified grades of

lumber from tests of full-size specimens, a representative

sample of the lumber population is obtained following procedures in ASTM D2915 and D1990. The specimens are

tested using appropriate procedures given in ASTM D198

k

h

A B

Figure 6–2. Effect of edge knot: A, edge knot in lumber

and B, assumed loss of cross section (cross-hatched

area).

100

80

60

40

20

0

Strength ratio (%)

0.2 0.4 0.6 0.8 1.0

k/h

Figure 6–3. Relation between bending strength ratio and

size of edge knot expressed as fraction of face width.

k is knot size; h, width of face containing the knot.
6–7

or D4761. Because the range of quality with any one specific

grade may be large, it is necessary to assess the grade quality

index (GQI) of the sampled material in relation to the

assumed GQI. In the North American In-Grade Program,

GQI was the strength ratio calculated according to formulas

in ASTM D245. The sample GQI and the assumed GQI are

compared to see if adjustment to the test data is necessary.

An average value for the edgewise modulus of elasticity or a

near-minimum estimate of strength properties is obtained

using ASTM D1990 procedures. The grade GQI is also used

as a scaling perimeter that allows for modeling of strength

and modulus of elasticity with respect to grade. These properties are further modified for design use by consideration of

service moisture content, duration of load, and safety.

Machine-Graded

Structural Lumber

Machine-graded lumber is lumber evaluated by a machine

using a nondestructive test followed by visual grading to

evaluate certain characteristics that the machine cannot or

may not properly evaluate. Machine-stress-rated (MSR),

machine-evaluated-lumber (MEL), and E-rated lumber are

three types of machine-graded lumber. Machine-graded lumber allows for better sorting of material for specific applications in engineered structures. The basic components of a

machine-grading system are as follows:

1. sorting and prediction of strength through machinemeasured nondestructive determination of properties

coupled with visual assessment of growth characteristics,

2. assignment of design properties based on strength

prediction, and

3. quality control to ensure that assigned properties are

being obtained. The quality control procedures ensure

a. proper operation of the machine used to make the

nondestructive measurements,

b. appropriateness of the predictive parameter–bending

strength relationship, and

c. appropriateness of properties assigned for tension

and compression.

The MSR and MEL systems differ in grade names, quality

control, and coefficient of variation (COV) for E values.

Grade names for MSR lumber are a combination of the

design bending stress and average modulus of elasticity,

whereas grade names for MEL lumber start with an M designation. For quality control, MSR requires pieces to be tested

daily for at least one strength property and bending modulus

of elasticity in an edgewise orientation, whereas MEL requires daily tension quality control and edgewise bending

strength and stiffness testing. Finally, MSR grades are

assigned a COV = 11% on E, whereas MEL grades are

assigned a COV ≤ 15% on E. Grade names for a wide range

of machine-graded lumber commonly available across North

America are given in Table 6–4. Not all grades are available

in all sizes or species.

Machine Sorting Criteria

The most common method of sorting machine-graded lumber is modulus of elasticity E. When used as a sorting criterion for mechanical properties of lumber, E can be measured

in a variety of ways. Usually, the apparent E, or deflection

related to stiffness, is actually measured. Because lumber is

heterogeneous, the apparent E depends on span, orientation

(edge- or flatwise in bending), load speed of test (static or

dynamic), and method of loading (tension, bending, concentrated, or uniform). Any of the apparent E values can be used,

as long as the grading machine is properly calibrated, to

Expected bending strength (x103 lb/in2)

50

8

Expected bending strength (MPa)

6

4

2

40

30

20

10

0 20 40 60 80 100

Strength ratio (%)

0

Clear wood 5% exclusion limit

Figure 6–4. Example of relation between strength

and strength ratio.

20

16

12

8

4

0

4.13 6.89 9.65 12.41 15.17 17.93

(0.6) (1.0) (1.4) (1.8) (2.2) (2.6)

Modulus of elasticity in edgewise bending

 (GPa (x106 lb/in2))

Frequency (%)

Figure 6–5. Histogram of modulus of elasticity

observed in a single visual grade, from pieces

selected over a broad geographical range.
 6–8

assign the graded piece to a “not to exceed” grade category.

Most grading machines in the United States are designed to

detect the lowest flatwise bending E that occurs in any

approximately 1.2-m (4-ft) span and the average flatwise E for

the entire length of the piece.

Another method of sorting machine-graded lumber is using

density measurements to estimate knot sizes and frequency.

X-ray sources in conjunction with a series of detectors are

used to determine density information. Density information

is then used to assign the graded piece to a “not to exceed”

grade category.

In the United States and Canada, MSR and MEL lumber are

also subjected to a visual override because the size of edge

knots in combination with E is a better predictor of strength

than is E alone. Maximum edge knots are limited to a

specified proportion of the cross section, depending on

grade level. Other visual restrictions, which are primarily

appearance rather than strength criteria, are placed on checks,

shake, skips (portions of board “skipped” by the planer),

splits, wane, and warp.

Procedures for Deriving

Design Properties

Allowable Stress for Bending

A stress grade derived for machine-graded lumber relates

design strength to a nondestructive parameter. For this example, it will be considered to be E. Because E is an imperfect predictor of strength, lumber sorted solely by average E

falls into one of four categories, one of which is sorted correctly and three incorrectly (Fig. 6–6).

Consider, for example, the most simple case (sometimes

referred to as “go” or “no go”) where lumber is sorted into

two groups: one with sufficient strength and stiffness for a

specific application, the other without. In Figure 6–6a, a

regression line relating E and strength is used as the

prediction model. The “accept–reject” groups identified by

the regression sort can be classified into four categories:

• Category 1—Material that has been accepted correctly,

that is, pieces have sufficient strength and stiffness as defined

• Category 2—Material that has been accepted incorrectly,

that is, pieces do not have sufficient strength

Table 6–4. Common grades for machine-graded lumbera

Fb E Ft Fc||

Grade name (MPa (lb/in2)) (GPa (×106 lb/in2

)) (MPa (lb/in2

)) (MPa (lb/in2))

MSR

1350f–1.3E 9.3 (1,350) 9.0 (1.3) 5.2 (750) 11.0 (1,600)

1450f–1.3E 10.0 (1,450) 9.0 (1.3) 5.5 (800) 11.2 (1,625)

1650f–1.5E 11.4 (1,650) 10.3 (1.5) 7.0 (1,020) 11.7 (1,700)

1800f–1.6E 12.4 (1,800) 11.0 (1.6) 8.1 (1,175) 12.1 (1,750)

1950f–1.7E 13.4 (1,950) 11.7 (1.7) 9.5 (1,375) 12.4 (1,800)

2100f–1.8E 14.5 (2,100) 12.4 (1.8) 10.9 (1,575) 12.9 (1,875)

2250f–1.9E 15.5 (2,250) 13.1 (1.9) 12.1 (1,750) 13.3 (1,925)

2400f–2.0E 16.5 (2,400) 13.8 (2.0) 13.3 (1,925) 13.6 (1,975)

2550f–2.1E 17.6 (2,550) 14.5 (2.1) 14.1 (2,050) 14.0 (2,025)

2700F–

2.2E

18.6 (2,700) 15.2 (2.2) 14.8 (2,150) 14.4 (2,100)

2850f–2.3E 19.7 (2,850) 15.9 (2.3) 15.9 (2,300) 14.8 (2,150)

MEL

M–10 9.7 (1,400) 8.3 (1.2) 5.5 (800) 11.0 (1,600)

M–11 10.7 (1,550) 10.3 (1.5) 5.9 (850) 11.5 (1,675)

M–14 12.4 (1,800) 11.7 (1.7) 6.9 (1,000) 12.1 (1,750)

M–19 13.8 (2,000) 11.0 (1.6) 9.0 (1,300) 12.6 (1,825)

M–21 15.9 (2,300) 13.1 (1.9) 9.7 (1,400) 13.4 (1,950)

M–23 16.5 (2,400) 12.4 (1.8) 13.1 (1,900) 13.6 (1,975)

M–24 18.6 (2,700) 13.1 (1.9) 12.4 (1,800) 14.5 (2,100)

a

Forest Products Society 1997. Other grades are available and permitted.

Fb is allowable 10-year load duration bending stress parallel to grain.

E is modulus of elasticity.

Ft is allowable 10-year load duration tensile stress parallel to grain.

Fc|| is allowable 10-year load duration compressive stress parallel to grain.
6–9

• Category 3—Material that has been rejected correctly

because it does not have sufficient strength

• Category 4—Material that has been rejected correctly

because it does not have sufficient stiffness

Thus, the sort shown in Figure 6–6a has worked correctly for

categories 1, 3, and 4 but incorrectly for category 2. Pieces in

category 2 present a problem. These pieces are accepted as

having sufficient strength but in reality they do not, and they

are mixed with the accepted pieces of category 1. The number of problem pieces that fall in category 2 depends on the

variability in the prediction model.

To minimize the material that falls into category 2, adjustments are made to the property assignment claims made

about the sorted material. An appropriate model is one that

minimizes the material in category 2 or at least reduces it to

a lower risk level. Additional grading criteria (edge-knot

limitations, for example) are also added to improve the

efficiency of the sorting system relative to the resource and

the claimed properties.

Commonly, a lower confidence line is used as the prediction

model (Fig. 6–6b). The number of pieces that fall into category 2 is now low compared with the regression line model.

Furthermore, the probability of a piece (and thus the number

of pieces) falling into category 2 is controlled by the confidence line selected.

In actual MSR systems, the lumber is sorted (graded) into E

classes. In the United States and Canada, the number of

grades has increased as specific market needs have developed

for MSR lumber. Today, individual grading agencies list as

many as 13 E classifications and more than 20 different

grades. The grades are designated by the recommended

extreme fiber stress in bending Fb and edgewise modulus of

elasticity E. For example, “2100F–1.8E” designates an

MSR grade with a design stress Fb = 14 MPa (2,100 lb/in2)

and E = 12.4 GPa (1.8 × 106 lb/in2).

In theory, any F–E combination can be marketed that can be

supported by test data. In practice, a mill will usually produce only a few of the possible existing F–E classifications

depending on the potential of the timber being harvested,

mill production capabilities, and product or market demand.

When a mill has determined the grades it would like to

produce (based on their lumber resource and marketing issues), grade boundary machine settings are used to separate

the lumber into F–E classifications. A qualification sample

of lumber is tested by a grading agency for strength and

stiffness, to verify that the proper machine settings are being

used. After initial qualification, additional quality control

tests are performed during production.

Figure 6–7 illustrates how Fb–E classifications have been

developed historically for species groups. Data for a particular

species group are collected, the relationship of E and MOR is

evaluated, and a lower confidence line is established for the

species, as illustrated in Figure 6–6b. Using the lower

confidence line of this relationship, an MOR value corresponding to the “minimum E” assigned to the grade is

determined. The “minimum E” assigned to the grade represents the 5th percentile of the E distribution. The 5th percentile value is expected to be exceeded by 95% of the pieces in

a grade or class. In this example, for a grade with an assigned

E of 13.8 GPa (2.0 × 106

 lb/in2), the “minimum E” is

11.3 GPa (1.64 × 106 lb/in2). The corresponding MOR value

from the lower confidence line prediction model, approximately a 5th percentile MOR value, is 34.8 MPa

(5.04 × 103 lb/in2). This value is then adjusted by a factor

(2.1) for assumed 10-year duration of load and safety to

obtain Fb. This factor applied to an estimated 5th percentile

Acceptable

strength level

Grouping of data

Regression line

Reject Accept

E sort

4

2

3

1

(a)

Strength

Regression line

E sort

Lower confidence line

Acceptable

strength level

(b)

Strength

Figure 6–6. Schematic E sort: (a) using a regression

line as the predictor showing four categories:

1—accepted correctly; 2—accepted incorrectly;

3—rejected correctly; and 4—rejected correctly;

(b) using a lower confidence line as the predictor and

showing the relatively low proportion of material in

the accepted incorrectly category (lower right).
 6–10

MOR value of 34.8 MPa (5.04 × 103 lb/in2) yields an Fb of

16.5 MPa (2.40 × 103 lb/in2) for the 2.0E grade; in other

words, a 2400f –2.0E MSR grade.

Design Stresses for Other Properties

Properties in tension and compression are commonly developed from relationships with bending rather than estimated

directly by the nondestructive parameter E. In Canada and

the United States, the relationships between the 5th percentile 10-year bending stress and those in tension and compression are based upon limited lumber testing for the three

properties but supported by years of successful experience in

construction with visual stress grades of lumber. For tension,

it is assumed that the ratio of design bending stress Fb to

design tensile stress Fc is between 0.5 and 0.8, depending on

the grade, whereas the relationship between Fb and fiber

stress in design compressive stress Fc is assumed to be

Fc = [0.338 (2.1Fb) + 2060.7]/1.9

Strength in shear parallel to the grain and in compression

perpendicular to the grain is poorly related to modulus of

elasticity. Therefore, in machine stress grading these

properties are assumed to be grade-independent and are

assigned the same values as those for visual lumber grades,

except when predicted from specific gravity on a mill-by-mill

basis. It is permissible to assign higher allowable stress for

shear parallel to grain and compression perpendicular to grain

to specific grades based on additional specific gravity

research.

Quality Control

Quality control procedures are necessary to ensure that

stresses assigned by a machine-grading system reflect the

actual properties of the lumber graded. These procedures

must check for correct machine operation. Verification of the

relationships between bending and other properties may also

be required by the rules-writing agency, particularly for fiber

stress in tension Ft.

Daily or even more frequent calibration of machine operation

may be necessary. Depending upon machine principle, calibration may involve operating the machine on a calibration

bar of known stiffness, comparing grading machine E values

to those obtained on the same pieces of lumber by calibrated

laboratory test equipment, determining if machine-predicted

density matches a calibration sample density, or in some

instances, using two or more procedures. Machine operation

should be certified for all sizes of lumber being produced.

Machine settings may need to be adjusted to produce the

same grade material from different widths.

Quality control procedures of the MSR prediction model

(E–bending strength relationship) have been adopted in

Canada and the United States. Daily, or more frequently,

lumber production is representatively sampled and proofloaded, usually in bending, with supplementary testing in

tension. The pieces are proof-loaded to at least twice the

design stress (Fb or Ft) for the assigned Fb –E classification.

In bending, the pieces are loaded on a random edge with the

maximum-edge defect within the maximum moment area

(middle one-third span in third-point loading) or as near to

that point as possible. In tension, the pieces are tested with

a 2.4-m (8-ft) gauge length.

If the number of pieces in the sample failing the proof-test

load indicates a high probability that the population from

which the pieces came does not meet the minimum grade

criteria, a second sampling and proof test are conducted

immediately. If the second sample confirms the results of the

first sample, the MSR grading system is declared “out of

control” and the operation is shut down to isolate and correct

the problem. The lumber that was incorrectly labeled is then

correctly labeled.

Cumulative machine calibration records are useful for detecting trends or gradual change in machine operation that might

coincide with use and wear of machine parts. The proof-test

results are also accumulated. Standard statistical quality

control procedures (such as control charts) are used to monitor the production process so that it can be modified as

needed in response to change in the timber resource, and to

make the output fit the assumed model.

Too many failures in one, or even consecutive, samples do

not necessarily indicate that the system is out of control.

If the prediction line is based on 95% confidence, it can be

expected by chance alone that 1 sample in 20 will not meet

the proof-load requirements. One or more out-of-control

samples may also represent a temporary aberration in

48.26 (7)

Modulus of rupture (MPa (x103 lb/in2))

41.37 (6)

34.47 (5)

27.58 (4)

20.68 (3)

13.79 (2)

34.75 (5,040) Prediction model

Modulus of elasticity (x106 lb/in2)

Minimum E

(Estimator value)

Grade E

Modulus of elasticity (GPa)

11 12 13 14 15 16

1.6 1.8 2.0 2.2 2.4

(lower confidence line)

Figure 6–7. Typical assignment of Fb–E values for MSR

lumber in United States (solid lines are minimum E for

the Fb–E classification and bending strengths

predicted by minimum E values).
6–11

material properties (E–strength relationship). In any event,

this situation would call for inspection of the cumulative

quality control records for trends to determine if machine

adjustment might be needed. A “clean” record (a period

when the system does not go out of control) rectifies the

evaluation of a system thought to be out of control.

Adjustment of Properties

for Design Use

The mechanical properties associated with lumber quality are

adjusted to give design unit stresses and a modulus of elasticity suitable for engineering uses. First, a lower confidence

level is determined for the material, and this value is then

adjusted for shrinkage, size, duration of load, and in ASD, an

additional factor of safety. These adjustment factors are discussed in the following text (specific adjustments are given

in ASTM designations D245 and D1990).

Shrinkage

As described in Chapter 3, lumber shrinks and swells with

changes in moisture content. The amount of dimensional

change depends on a number of factors, such as species and

ring angle. The American Softwood Lumber Standard,

PS 20, lists specific shrinkage factors from green to 15%

moisture content that were used historically to set green

lumber dimensions for most species (2.35% for thickness and

2.80% for width). The standard does not provide a means of

adjusting lumber dimensions to any other moisture content.

The standard also does not provide specific shrinkage factors

for species such as redwood and the cedars, which shrink less

than most species. Using the PS 20 recommendations and an

assumed green moisture content Mg, we derive equations that

can be used with most species to calculate the shrinkage of

lumber as a function of percentage of moisture content M.

The equation is applicable to lumber of all annual ring orientations. For dimension lumber, the dimensions at different

moisture contents can be estimated with the following equation:

 

d d a bM

a bM 2 1

2

1

1 100

1 100 = − −− −

( )/

( )/

where d1 is dimension (mm, in.) at moisture content M1,

d2 dimension (mm, in.) at moisture content M2, M1 moisture

content (%) at d1, M2 moisture content (%) at d2, and

a and b are variables from Table 6–5.

Size Factor

In general, a size effect causes small members to have a

greater unit strength than that of large members. There are

two procedures for calculating size-adjustment factors, small

clear and In-grade.

Small Clear Procedure

ASTM D245 provides only a formula for adjusting bending

strength. The bending strength for lumber is adjusted to a

new depth Fn other than 2 in. (51 mm) using the formula

 

 

F d

d n F o

n

= o





 





1

9

where do is original depth (51 mm, 2 in.), dn new depth, and

Fo original bending strength.

This formula is based on an assumed center load and a span-todepth ratio of 14. A depth effect formula for two equal concentrated loads applied symmetrical to the midspan points is given

in Chapter 8.

In–Grade Test Procedures

ASTM D1990 provides a formula for adjusting bending, tension,

and compression parallel to grain. No size adjustments are made

to modulus of elasticity or for thickness effects in bending,

tension, and compression. The size adjustments to dimension

lumber are based on volume using the formula

 

P P W

W

L

L

w l

1 2

1

2

1

2

= 























where P1 is property value (MPa, lb/in2) at volume 1,

P2 property value (MPa, lb/in2) at volume 2, W1 width

(mm, in.) at P1, W2 width (mm, in.) at P2, L1 length (mm, in.) at

P1, and L2 length (mm, in.) at P2. Exponents are defined in

Table 6–6.

Table 6–5. Coefficients for equations to determine

dimensional changes with moisture content change

in dimension lumber

Width Thickness

Species a b a bMg

a

Redwood,

western redcedar, and

northern

white cedar

3.454 0.157 2.816 0.128 22

Other species 6.031 0.215 5.062 0.181 28

a

Mg is assumed green moisture content.

Table 6–6. Exponents for adjustment of dimension

lumber mechanical properties with change in sizea

Exponent MOR UTS UCS

w 0.29 0.29 0.13

l 0.14 0.14 0

a

MOR is modulus of rupture;

 UTS, ultimate tensile stress; and

 UCS, ultimate compressive stress.
 6–12

Moisture Adjustments

For lumber ≤102 mm (≤4 in.) thick that has been dried,

strength properties have been shown to be related quadratically to moisture content. Two relationships for modulus of

rupture at any moisture content are shown in Figure 6–8.

Both models start with the modulus of elasticity of green

lumber. The curves with solid dots represent a precise quadratic model fit to experimental results. In typical practice,

adjustments are made to correspond to average moisture

contents of 15% and 12% with expected maximum moisture

contents of 19% and 15%, respectively, using simplified

expressions represented by the open dot curves. Below about

8% moisture content, some properties may decrease with

decreasing moisture content values, and care should be exercised in these situations. Equations applicable to adjusting

properties to other moisture levels between green and 10%

moisture content are as follows:

For MOR, ultimate tensile stress (UTS), and ultimate

compressive stress (UCS), the following ASTM D1990

equations apply:

For MOR ≤ 16.7 MPa (2,415 lb/in2

)

UTS ≤ 21.7 MPa (3,150 lb/in2)

UCS ≤ 9.7 MPa (1,400 lb/in2)

 

P P 1 2 =

Thus, there is no adjustment for stresses below these levels.

For MOR > 16.6 MPa (2,415 lb/in2)

UTS > 21.7 MPa (3,150 lb/in2)

UCS > 9.7 MPa (1,400 lb/in2)

 

P P P B

B M 2 1

1 1 M M

2 1

= + 1 2

−

−





 



( ) −

where M1 is moisture content 1 (%), M2 is moisture content

2 (%), and B1, B2 are constants from Table 6–7.

For E, the following equation applies:

 

E E M

M 1 2

2

1

1 857 0 0237

1 857 0 0237 = −−





 



 . (. )

. (. )

where E1 is property (MPa, lb/in2) at moisture content 1 and

E2 is property (MPa, lb/in2) at moisture content 2.

For lumber thicker than 102 mm (4 in.), often no adjustment

for moisture content is made because properties are assigned

on the basis of wood in the green condition. This lumber is

usually put in place without drying, and it is assumed that

drying degrade offsets the increase in strength normally

associated with loss in moisture.

Duration of Load

Design may be based on either design stresses and a duration

of load factor or on ultimate limit state design stresses and a

time effects factor. Both the duration of load and time effects

factor describe the same phenomenon. In allowable stress

design, design stresses are based on an assumed 10-year

loading period (called normal loading). If duration of loading, either continuously or cumulatively, is expected to

exceed 10 years, design stresses are reduced 10%. If the

expected duration of loading is for shorter periods, published

design stresses can be increased using Figure 6–9. Ultimate

limit-state design stresses are based on a 5-min loading

period. If the duration of loading is expected to exceed

5 min, limit-state design stresses are reduced by applying the

time effects factor. Intermittent loading causes cumulative

effects on strength and should be treated as continuous load

of equivalent duration. The effects of cyclic loads of short

duration must also be considered in design (see discussion of

fatigue in Ch. 4). These duration of load modifications are

not applicable to modulus of elasticity.

Modulus of rupture (MPa)

6

5

3

2

1

0 0

7 9 11 14 16 18 20 23 25

Moisture content (%)

40

30

20

10

4

Modulus of rupture (x103 lb/in2)

Figure 6–8. Modulus of rupture as a function of

moisture content for dimension lumber. Open dots

represent the ASTM D1990 model, and solid dots

represent the more precise quadratic surface model

on which the ASTM D1990 model was based.

Table 6–7. Coefficients for moisture adjustment of

dimension lumber mechanical properties with change

in moisture contenta

Property (MPa (lb/in2))

Coefficients MOR UTS UCS

B1 16.6 (2,415) 21.7 (3,150) 9.6 (1,400)

B2 0.276 (40) 0.552 (80) 0.234 (34)

a

MOR is modulus of rupture; UTS, ultimate tensile stress;

 and UCS, ultimate compressive stress.
6–13

In many design circumstances there are several loads on the

structure, some acting simultaneously and each with a different duration. When loads of different time duration are applied, the load duration factor corresponding to the shortest

time duration is used. Each increment of time during which

the total load is constant should be treated separately, and

the most severe condition governs the design. Either the

design stress or the total design load (but not both) can be

adjusted using Figure 6–9.

For example, suppose a structure is expected to support a

load of 4.8 kPa (100 lb/ft2

) on and off for a cumulative duration of 1 year. Also, it is expected to support its own dead

load of 0.96 kPa (20 lb/ft2) for the anticipated 50-year life of

the structure. The adjustments to be made to arrive at an

equivalent 10-year design load are listed in Table 6–8.

The more severe design load is 5.36 kPa (112 lb/ft2), and

this load and the design stress for lumber would be used to

select members of suitable size. In this case, it was convenient to adjust the loads on the structure, although the same

result can be obtained by adjusting the design stress.

Treatment Effects

Treatments have been shown to affect the final strength of

wood (Ch. 4 for detailed discussion). There is a 5% reduction in E and a 15% reduction in strength properties of

incised and treated dimension lumber for both dry- and wetuse conditions in the United States. In Canada, a 10% reduction in E and a 30% reduction in all strength properties from

incising is applied to dry-use conditions whereas 5% and

15% reductions are used for wet-use conditions. The wet-use

factors are applied in addition to the traditional wet-use

service factor. Reductions in energy-related properties are

about 1.5 to 2 times those reported for static strength properties. There is no difference in long-term duration of load

behavior between treated and untreated material (Fig. 6–10).

Current design standards prohibit increases in design stresses

beyond the 1.6 factor for short-term duration of load when

considering impact-type loading for material treated with

waterborne preservative.

2.0 0.50

Ratio of allowable stress to that for normal loading

Ratio of load adjusted to 10-year duration to actual load

0.56

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.53

0.59

0.62

0.67

0.71

0.77

0.83

0.91

1.00

1.11

1 second

1 minute

1 hour

1 day

1 month

1 year

10 years

50 years

Duration of load

Figure 6–9. Relation of strength to duration of load.

2.0

Load duration factor 

Cd

1.8

1.6

1.4

1.2

1.0

0.8

0 2 4 6 8 10

Impact

10 minutes

1 day

10 years

7 days

2 months

1 year

Untreated

Treated

log load duration (s)

▲

▲

▲

50 years

▲

▲

▲ ▲

▲

▲

Figure 6–10. Load duration factor for material treated

with waterborne preservative.

Table 6–8. Example of duration of load adjustments

Time

(year)

Total load

(kPa (lb/ft2

))

Load

adjustmenta

Equivalent 10-year

design load

(kPa (lb/ft2

))

1 4.8 (100) + 0.96 (20) = 5.7 (120) 0.93 5.36 (112)

50 0.96 (20) 1.04 1.0 (21)

a

Figure 6–9.
 6–14

Temperature Effects

As wood is cooled below normal temperatures, its properties

increase. When heated, its properties decrease. The magnitude of the change depends upon moisture content. Up to

65°C (150°F), the effect of temperature is assumed by design

codes to be reversible. For structural members that will be

exposed to temperatures up to 65°C (150°F), design values

are multiplied by the factors given in Table 6–9 (AF&PA

1997). Prolonged exposure to heat can lead to a permanent

loss in strength (see Ch. 4).

References

AF&PA. 1997. Washington, DC: American Forest & Paper

Association.

National design specification for wood construction.

Design values for wood construction—a supplement to the

national design specification for wood construction.

AF&PA. 1996. Load and resistance factor design manual for

engineered wood construction. Washington, DC: American

Forest & Paper Association.

ASTM. 1998. West Conshohocken, PA: American Society

for Testing and Materials.

ASTM D198–97. Standard methods of static tests of timbers in structural sizes.

ASTM D245–93. Standard methods for establishing structural grades for visually graded lumber.

ASTM D1990–97. Standard methods for establishing allowable properties for visually-graded dimension lumber

from In-grade tests of full-size specimens.

ASTM D2555–96. Standard methods for establishing clear

wood strength values.

ASTM D2915–94. Standard method for evaluating properties for stress grades of structural lumber.

ASTM D4761–96. Standard methods for mechanical properties of lumber and wood-base structural materials.

Forest Products Society. 1997. Machine-graded lumber.

Madison, WI: Forest Products Society. Wood Design

Focus. 8(2): 1–24.

Galligan, W.L.; Green, D.W.; Gromala, D.S.; Haskell,

J.H. 1980. Evaluation of lumber properties in the United

States and their application to structural research. Forest

Products Journal. 30(10): 45–51.

Gerhards, C.C. 1977. Effect of duration and rate of loading

on strength of wood and wood based materials. Res. Pap.

FPL–RP–283. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Green, D.W. 1989. Moisture content and the shrinkage of

lumber. Res. Pap. FPL–RP–489. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Green, D.W.; Evans, J.W. 1987. Mechanical properties

of visually graded dimension lumber. Vol. 1–Vol. 7.

Springfield VA: National Technical Information Service.

PB–88–159–371.

Green, D.W.; Kretschmann, D.E. 1992. Properties and

grading of Southern Pine timbers. Forest Products Journal.

47(9): 78–85.

Green, D.W.; Shelley, B.E. 1992. Guidelines for assigning

allowable properties to visually grade foreign species based

on test data from full sized specimens. Germantown, MD:

American Lumber Standards Committee.

Green, D.W.; Shelley, B.E. 1993. Guidelines for assigning

allowable properties to mechanically graded foreign species.

Germantown, MD: American Lumber Standards Committee.

Green, D.W.; Shelley, B.E.; and Vokey, H.P. 1989.

In-grade testing of structural lumber. In: Proceedings of

workshop sponsored by In-grade Testing Committee and

Forest Products Society. Proceedings 47363. Madison, WI:

Forest Products Society.

Kretschmann, D.E.; Green D.W. 1996. Modeling moisture content–mechanical property relationships for clear

Southern Pine. Wood and Fiber Science. 28(3): 320–337.

U.S. Department of Commerce. 1994. American softwood

lumber standard. Prod. Stand. PS20–94. Washington, DC:

U.S. Department of Commerce.

Winandy, J.E. 1995. The influence of time–to–failure on

the strength of CCA-treated lumber. Forest Products Journal.

45(2): 82–85.

Table 6–9. Property adjustment factors for in-service temperature exposures

Factor

Design values

In-service

moisture content

T ≤ 37 ̊C

(T ≤ 100 ̊F)

37 ̊C < T ≤ 52 ̊C

 (100 ̊F < T ≤ 125 ̊F)

52 ̊C < T ≤ 65 ̊C

(125 ̊F < T ≤ 150 ̊F)

Ft, E Wet or dry 1.0 0.9 0.9

Fb, Fv, Fc, Fc⊥ Dry 1.0 0.8 0.7

Wet 1.0 0.7 0.5
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
7–1

Chapter 7

Fastenings

Lawrence A. Soltis

Contents

Nails 7–2

Withdrawal Resistance 7–2

Lateral Resistance 7–5

Spikes 7–8

Staples 7–8

Drift Bolts 7–9

Wood Screws 7–9

Withdrawal Resistance 7–9

Lateral Resistance 7–10

Lag Screws 7–11

Withdrawal Resistance 7–11

Lateral Resistance 7–12

Bolts 7–14

Bearing Stress of Wood Under Bolts 7–14

Loads at an Angle to the Grain 7–14

Steel Side Plates 7–15

Bolt Quality 7–15

Effect of Member Thickness 7–15

Two-Member, Multiple-Member Joints 7–15

Spacing, Edge, and End Distance 7–16

Effect of Bolt Holes 7–16

Pre-1991 Allowable Loads 7–17

Post-1991 Yield Model 7–18

Connector Joints 7–18

Parallel-to-Grain Loading 7–18

Perpendicular-to-Grain Loading 7–18

Design Loads 7–20

Modifications 7–21

Net Section 7–23

End Distance and Spacing 7–23

Placement of Multiple Connectors 7–23

Cross Bolts 7–24

Multiple-Fastener Joints 7–24

Metal Plate Connectors 7–25

Fastener Head Embedment 7–26

References 7–27

he strength and stability of any structure depend

heavily on the fastenings that hold its parts

together. One prime advantage of wood as a

structural material is the ease with which wood structural

parts can be joined together with a wide variety of fastenings—nails, spikes, screws, bolts, lag screws, drift pins,

staples, and metal connectors of various types. For utmost

rigidity, strength, and service, each type of fastening requires

joint designs adapted to the strength properties of wood

along and across the grain and to dimensional changes that

may occur with changes in moisture content.

Maximum lateral resistance and safe design load values for

small-diameter (nails, spikes, and wood screws) and largediameter dowel-type fasteners (bolts, lag screws, and drift

pins) were based on an empirical method prior to 1991.

Research conducted during the 1980s resulted in lateral

resistance values that are currently based on a yield model

theory. This theoretical method was adapted for the 1991

edition of the National Design Specification for Wood

Construction (NDS). Because literature and design procedures exist that are related to both the empirical and theoretical methods, we refer to the empirical method as pre-1991

and the theoretical method as post-1991 throughout this

chapter. Withdrawal resistance methods have not changed,

so the pre- and post-1991 refer only to lateral resistance.

The information in this chapter represents primarily Forest

Products Laboratory research results. A more comprehensive

discussion of fastenings is given in the American Society of

Civil Engineers Manuals and Reports on Engineering

Practice No. 84, Mechanical Connections in Wood Structures. The research results of this chapter are often modified

for structural safety, based on judgment or experience, and

thus information presented in design documents may differ

from information presented in this chapter. Additionally,

research by others serves as a basis for some current design

criteria. Allowable stress design criteria are presented in the

National Design Specification for Wood Construction published by the American Forest and Paper Association; limit

states design criteria are presented in the Standard for Load

and Resistance Factor Design (LRFD) for Engineered Wood

Construction published by the American Society of

Civil Engineers.
 7–2

Nails

Nails are the most common mechanical fastenings used in

wood construction. There are many types, sizes, and forms of

nails (Fig. 7–1). The load equations presented in this chapter

apply for bright, smooth, common steel wire nails driven

into wood when there is no visible splitting. For nails other

than common wire nails, the loads can be adjusted by factors

given later in the chapter.

Nails in use resist withdrawal loads, lateral loads, or a combination of the two. Both withdrawal and lateral resistance

are affected by the wood, the nail, and the condition of use.

In general, however, any variation in these factors has a more

pronounced effect on withdrawal resistance than on lateral

resistance. The serviceability of joints with nails laterally

loaded does not depend greatly on withdrawal resistance

unless large joint distortion is tolerable.

The diameters of various penny or gauge sizes of bright

common nails are given in Table 7–1. The penny size designation should be used cautiously. International nail producers sometimes do not adhere to the dimensions of

Table 7–1. Thus penny sizes, although still widely used, are

obsolete. Specifying nail sizes by length and diameter dimensions is recommended. Bright box nails are generally of

the same length but slightly smaller diameter (Table 7–2),

while cement-coated nails such as coolers, sinkers, and

coated box nails are slightly shorter (3.2 mm (1/8 in.)) and

of smaller diameter than common nails of the same penny

size. Helically and annularly threaded nails generally have

smaller diameters than common nails for the same penny size

(Table 7–3).

Withdrawal Resistance

The resistance of a nail shank to direct withdrawal from a

piece of wood depends on the density of the wood, the

diameter of the nail, and the depth of penetration. The surface

condition of the nail at the time of driving also influences the

initial withdrawal resistance.

Figure 7–1. Various types of nails: (left to right) bright

smooth wire nail, cement coated, zinc-coated, annularly

threaded, helically threaded, helically threaded and

barbed, and barbed.

Table 7–1. Sizes of bright common wire nails

Size Gauge

Length

(mm (in.))

Diameter

(mm (in.))

6d 11-1/2 50.8 (2) 2.87 (0.113)

 8d 10-1/4 63.5 (2-1/2) 3.33 (0.131)

10d 9 76.2 (3) 3.76 (0.148)

 12d 9 82.6 (3-1/4) 3.76 (0.148)

 16d 8 88.9 (3-1/2) 4.11 (0.162)

 20d 6 101.6 (4) 4.88 (0.192)

 30d 5 114.3 (4-1/2) 5.26 (0.207)

 40d 4 127.0 (5) 5.72 (0.225)

 50d 3 139.7 (5-1/2) 6.20 (0.244)

 60d 2 152.4 (6) 6.65 (0.262)

Table 7–2. Sizes of smooth box nails

Size Gauge

Length

(mm (in.))

Diameter

(mm (in.))

3d 14-1/2 31.8 (1-1/4) 1.93 (0.076)

4d 14 38.1 (1-1/2) 2.03 (0.080)

5d 14 44.5 (1-3/4) 2.03 (0.080)

6d 12-1/2 50.8 (2) 2.49 (0.098)

7d 12-1/2 57.2 (2-1/4) 2.49 (0.098)

8d 11-1/2 63.5 (2-1/2) 2.87 (0.113)

10d 10-1/2 76.2 (3) 3.25 (0.128)

16d 10 88.9 (3-1/2) 3.43 (0.135)

20d 9 101.6 (4) 3.76 (0.148)

Table 7–3. Sizes of helically and annularly

threaded nails

Size Length

 (mm (in.))

Diameter

(mm (in.))

6d 50.8 (2) 3.05 (0.120)

8d 63.5 (2-1/2) 3.05 (0.120)

10d 76.2 (3) 3.43 (0.135)

12d 82.6 (3-1/4) 3.43 (0.135)

16d 88.9 (3-1/2) 3.76 (0.148)

20d 101.6 (4) 4.50 (0.177)

30d 114.3 (4-1/2) 4.50 (0.177)

40d 127.0 (5) 4.50 (0.177)

50d 139.7 (5-1/2) 4.50 (0.177)

60d 152.4 (6) 4.50 (0.177)

70d 177.8 (7) 5.26 (0.207)

80d 203.2 (8) 5.26 (0.207)

90d 228.6 (9) 5.26 (0.207)
7–3

For bright common wire nails driven into the side grain of

seasoned wood or unseasoned wood that remains wet, the

results of many tests have shown that the maximum withdrawal load is given by the empirical equation

 

p G DL = 54 12 5 2 . / (metric) (7–1a)

 p G DL = 7 850 5 2 , / (inch–pound) (7–1b)

where p is maximum load (N, lb), L depth (mm, in.) of

penetration of the nail in the member holding the nail point,

G specific gravity of the wood based on ovendry weight and

volume at 12% moisture content (see Ch. 4, Tables 4–2 to

4–5), and D diameter of the nail (mm, in.). (The NDS and

LRFD use ovendry weight and volume as a basis.)

The loads expressed by Equation (7–1) represent average

data. Certain wood species give test values that are somewhat greater or less than the equation values. A typical load–

displacement curve for nail withdrawal (Fig. 7–2) shows

that maximum load occurs at relatively small values of

displacement.

Although the equation for nail-withdrawal resistance indicates that the dense, heavy woods offer greater resistance to

nail withdrawal than do the lower density ones, lighter

species should not be disqualified for uses requiring high

resistance to withdrawal. As a rule, the less dense species do

not split as readily as the denser ones, thus offering an opportunity for increasing the diameter, length, and number of the

nails to compensate for the wood’s lower resistance to nail

withdrawal.

The withdrawal resistance of nail shanks is greatly affected by

such factors as type of nail point, type of shank, time the nail

remains in the wood, surface coatings, and moisture content

changes in the wood.

Effect of Seasoning

With practically all species, nails driven into green wood

and pulled before any seasoning takes place offer about the

same withdrawal resistance as nails driven into seasoned

wood and pulled soon after driving. However, if common

smooth-shank nails are driven into green wood that is allowed to season, or into seasoned wood that is subjected to

cycles of wetting and drying before the nails are pulled, they

lose a major part of their initial withdrawal resistance. The

withdrawal resistance for nails driven into wood that is

subjected to changes in moisture content may be as low as

25% of the values for nails tested soon after driving. On the

other hand, if the wood fibers deteriorate or the nail corrodes

under some conditions of moisture variation and time, withdrawal resistance is erratic; resistance may be regained or

even increased over the immediate withdrawal resistance.

However, such sustained performance should not be relied on

in the design of a nailed joint.

In seasoned wood that is not subjected to appreciable moisture content changes, the withdrawal resistance of nails may

also diminish due to relaxation of the wood fibers with time.

Under all these conditions of use, the withdrawal resistance

of nails differs among species and shows variation within

individual species.

Effect of Nail Form

The surface condition of nails is frequently modified during

the manufacturing process to improve withdrawal resistance.

Such modification is usually done by surface coating, surface

roughening, or mechanical deformation of the shank. Other

factors that affect the surface condition of the nail are the oil

film remaining on the shank after manufacture or corrosion

resulting from storage under adverse conditions; but these

factors are so variable that their influence on withdrawal

resistance cannot be adequately evaluated.

Surface Modifications—A common surface treatment for

nails is the so-called cement coating. Cement coatings,

contrary to what the name implies, do not include cement as

an ingredient; they generally are a composition of resin

applied to the nail to increase the resistance to withdrawal

by increasing the friction between the nail and the wood. If

properly applied, they increase the resistance of nails to

withdrawal immediately after the nails are driven into the

softer woods. However, in the denser woods (such as hard

maple, birch, or oak), cement-coated nails have practically no

advantage over plain nails, because most of the coating is

removed in driving. Some of the coating may also be removed in the side member before the nail penetrates the

main member.

Good-quality cement coatings are uniform, not sticky to the

touch, and cannot be rubbed off easily. Different techniques of

applying the cement coating and variations in its ingredients

may cause large differences in the relative resistance to withdrawal of different lots of cement-coated nails. Some nails

may show only a slight initial advantage over plain nails. In

the softer woods, the increase in withdrawal resistance of

700

Withdrawal load (N)

Withdrawal load (lb)

6d smooth box nail

 2.49-mm (0.098-in.)

 diameter

31.8 mm (1-1/4 in.)

 penetration depth

Douglas-fir

12% moisture content

0.54 specific gravity

600

500

400

300

200

100

0.3

0 0.01 0.02 0.03 0.04 0.05

160

120

80

40

0

0.6 0.9 1.2

Displacement (mm)

Displacement (in.)

0

Figure 7–2. Typical load–displacement curve for

direct withdrawal of a nail.
 7–4

cement-coated nails is not permanent but drops off significantly after a month or so. Cement-coated nails are used

primarily in construction of boxes, crates, and other

containers usually built for rough handling and relatively

short service.

Nails that have galvanized coatings, such as zinc, are intended primarily for uses where corrosion and staining resistance are important factors in permanence and appearance. If

the zinc coating is evenly applied, withdrawal resistance may

be increased, but extreme irregularities of the coating may

actually reduce it. The advantage that uniformly coated

galvanized nails may have over nongalvanized nails in resistance to initial withdrawal is usually reduced by repeated

cycles of wetting and drying.

Nails have also been made with plastic coatings. The usefulness and characteristics of these coatings are influenced by the

quality and type of coating, the effectiveness of the bond

between the coating and base fastener, and the effectiveness of

the bond between the coating and wood fibers. Some plastic

coatings appear to resist corrosion or improve resistance to

withdrawal, while others offer little improvement.

Fasteners with properly applied nylon coating tend to retain

their initial resistance to withdrawal compared with other

coatings, which exhibit a marked decrease in withdrawal

resistance within the first month after driving.

A chemically etched nail has somewhat greater withdrawal

resistance than some coated nails, as the minutely pitted

surface is an integral part of the nail shank. Under impact

loading, however, the withdrawal resistance of etched nails is

little different from that of plain or cement-coated nails under

various moisture conditions.

Sand-blasted nails perform in much the same manner as

chemically etched nails.

Shape Modifications—Nail shanks may be varied from a

smooth, circular form to give an increase in surface area

without an increase in nail weight. Special nails with barbed,

helically or annularly threaded, and other irregular shanks

(Fig. 7–1) are commercially available.

The form and magnitude of the deformations along the shank

influence the performance of the nails in various wood species. In wood remaining at a uniform moisture content, the

withdrawal resistance of these nails is generally somewhat

greater than that of common wire nails of the same diameter.

For instance, annular-shank nails have about 40% greater

resistance to withdrawal than common nails. However, under

conditions involving changes in moisture content of the

wood, some special nail forms provide considerably greater

withdrawal resistance than the common wire nail—about four

times greater for annularly and helically threaded nails of the

same diameter. This is especially true of nails driven into

green wood that subsequently dries. In general, annularly

threaded nails sustain larger withdrawal loads, and helically

threaded nails sustain greater impact withdrawal work values

than do the other nail forms.

Nails with deformed shanks are sometimes hardened by heat

treatments for use where driving conditions are difficult or to

obtain improved performance, such as in pallet assembly.

Hardened nails are brittle and care should be exercised to

avoid injuries from fragments of nails broken during driving.

Nail Point—A smooth, round shank nail with a long, sharp

point will usually have a greater withdrawal resistance,

particularly in the softer woods, than the common wire nail

(which usually has a diamond point). However, sharp points

accentuate splitting in certain species, which may reduce

withdrawal resistance. A blunt or flat point without taper

reduces splitting, but its destruction of the wood fibers when

driven reduces withdrawal resistance to less than that of the

common wire nail. A nail tapered at the end and terminating

in a blunt point will cause less splitting. In heavier woods,

such a tapered, blunt-pointed nail will provide about the

same withdrawal resistance, but in less dense woods, its

resistance to withdrawal is less than that of the common nail.

Nail Head—Nail head classifications include flat, oval,

countersunk, deep-countersunk, and brad. Nails with all

types of heads, except the deep-countersunk, brad, and some

of the thin flathead nails, are sufficiently strong to withstand

the force required to pull them from most woods in direct

withdrawal. The deep-countersunk and brad nails are usually

driven below the wood surface and are not intended to carry

large withdrawal loads. In general, the thickness and diameter of the heads of the common wire nails increase as the size

of the nail increases.

The development of some pneumatically operated portable

nailers has introduced nails with specially configured heads,

such as T-nails and nails with a segment of the head cut off.

Corrosion and Staining

In the presence of moisture, metals used for nails may corrode when in contact with wood treated with certain preservative or fire-retardant salts (Chs. 14 and 17). Use of certain

metals or metal alloys will reduce the amount of corrosion.

Nails of copper, silicon bronze, and 304 and 316 stainless

steel have performed well in wood treated with ammoniacal

copper arsenate and chromated copper arsenate. The choice of

metals for use with fire-retardant-treated woods depends upon

the particular fire-retardant chemical.

Staining caused by the reaction of certain wood extractives

(Ch. 3) and steel in the presence of moisture is a problem if

appearance is important, such as with naturally finished

siding. Use of stainless steel, aluminum, or hot-dipped

galvanized nails can alleviate staining.

In general, the withdrawal resistance of copper and other

alloy nails is comparable with that of common steel wire

nails when pulled soon after driving.

Driving

The resistance of nails to withdrawal is generally greatest

when they are driven perpendicular to the grain of the wood.

When the nail is driven parallel to the wood fibers (that is,
7–5

into the end of the piece) withdrawal resistance in the softer

woods drops to 75% or even 50% of the resistance obtained

when the nail is driven perpendicular to the grain. The difference between side- and end-grain withdrawal loads is less for

dense woods than for softer woods. With most species, the

ratio between the end- and side-grain withdrawal loads of

nails pulled after a time interval, or after moisture content

changes have occurred, is usually somewhat greater than that

of nails pulled immediately after driving.

Toe nailing, a common method of joining wood framework,

involves slant driving a nail or group of nails through the

end or edge of an attached member and into a main member.

Toe nailing requires greater skill in assembly than does

ordinary end nailing but provides joints of greater strength

and stability. Tests show that the maximum strength of

toenailed joints under lateral and uplift loads is obtained by

(a) using the largest nail that will not cause excessive splitting, (b) allowing an end distance (distance from the end of

the attached member to the point of initial nail entry) of

approximately one-third the length of the nail, (c) driving the

nail at a slope of 30° with the attached member, and

(d) burying the full shank of the nail but avoiding excessive

mutilation of the wood from hammer blows.

The results of withdrawal tests with multiple nail joints in

which the piece attached is pulled directly away from the

main member show that slant driving is usually superior to

straight driving when nails are driven into drywood and

pulled immediately, and decidedly superior when nails are

driven into green or partially dry wood that is allowed to

season for a month or more. However, the loss in depth of

penetration due to slant driving may, in some types of

joints, offset the advantages of slant nailing. Cross slant

driving of groups of nails through the side grain is usually

somewhat more effective than parallel slant driving through

the end grain.

Nails driven into lead holes with a diameter slightly smaller

(approximately 90%) than the nail shank have somewhat

greater withdrawal resistance than nails driven without lead

holes. Lead holes also prevent or reduce splitting of the

wood, particularly for dense species.

Clinching

The withdrawal resistance of smooth-shank, clinched nails is

considerably greater than that of unclinched nails. The point

of a clinched nail is bent over where the nail protrudes

through the side member. The ratio between the loads for

clinched and unclinched nails varies enormously, depending

upon the moisture content of the wood when the nail is

driven and withdrawn, the species of wood, the size of nail,

and the direction of clinch with respect to the grain of the

wood.

In dry or green wood, a clinched nail provides 45% to 170%

more withdrawal resistance than an unclinched nail when

withdrawn soon after driving. In green wood that seasons

after a nail is driven, a clinched nail gives 250% to 460%

greater withdrawal resistance than an unclinched nail.

However, this improved strength of a clinched-nail joint does

not justify the use of green lumber, because the joints may

loosen as the lumber seasons. Furthermore, laboratory tests

were made with single nails, and the effects of drying, such

as warping, twisting, and splitting, may reduce the efficiency

of a joint that has more than one nail. Clinching of nails is

generally confined to such construction as boxes and crates

and other container applications.

Nails clinched across the grain have approximately 20%

more resistance to withdrawal than nails clinched along the

grain.

Fastening of Plywood

The nailing characteristics of plywood are not greatly different from those of solid wood except for plywood’s greater

resistance to splitting when nails are driven near an edge.

The nail withdrawal resistance of plywood is 15% to 30%

less than that of solid wood of the same thickness. The

reason is that fiber distortion is less uniform in plywood than

in solid wood. For plywood less than 12.5 mm (1/2-in.)

thick, the greater splitting resistance tends to offset the lower

withdrawal resistance compared with solid wood. The withdrawal resistance per unit length of penetration decreases as

the number of plies per unit length increases. The direction

of the grain of the face ply has little influence on the withdrawal resistance from the face near the end or edge of a piece

of plywood. The direction of the grain of the face ply may

influence the pull-through resistance of staples or nails with

severely modified heads, such as T-heads. Fastener design

information for plywood is available from APA–The

Engineered Wood Association.

Allowable Loads

The preceding discussion dealt with maximum withdrawal

loads obtained in short-time test conditions. For design,

these loads must be reduced to account for variability, duration-of-load effects, and safety. A value of one-sixth the average maximum load has usually been accepted as the allowable load for long-time loading conditions. For normal

duration of load, this value may be increased by 10%. Normal duration of load is defined as a load of 10-year duration.

Lateral Resistance

Pre-1991

Test loads at joint slips of 0.38 mm (0.015 in.)

(approximate proportional limit load) for bright common

wire nails in lateral resistance driven into the side grain

(perpendicular to the wood fibers) of seasoned wood are

expressed by the empirical equation

 p KD = 3 2/ (7–2)

where p is lateral load per nail, K a coefficient, and D diameter of the nail. Values of coefficient K are listed in Table 7–4

for ranges of specific gravity of hardwoods and softwoods.

The loads given by the equation apply only where the side

member and the member holding the nail point are of
 7–6

approximately the same density. The thickness of the side

member should be about one-half the depth of penetration of

the nail in the member holding the point.

The ultimate lateral nail loads for softwoods may approach

3.5 times the loads expressed by the equation, and for hardwoods they may be 7 times as great. The joint slip at

maximum load, however, is more than 20 times 0.38 mm

(0.015 in.). This is demonstrated by the typical load–slip

curve shown in Figure 7–3. To maintain a sufficient ratio

between ultimate load and the load at 0.38 mm (0.015 in.),

the nail should penetrate into the member holding the point

by not less than 10 times the nail diameter for dense woods

(specific gravity greater than 0.61) and 14 times the diameter

for low density woods (specific gravity less than 0.42). For

species having densities between these two ranges, the

penetration may be found by straight line interpolation.

Post-1991

The yield model theory selects the worst case of yield modes

based on different possibilities of wood bearing and nail

bending. It does not account for nail head effects. A description of the various combinations is given in Figure 7–4.

Mode I is a wood bearing failure in either the main or side

member; mode II is a rotation of the fastener in the joint

without bending; modes III and IV are a combination of

wood bearing failure and one or more plastic hinge yield

formations in the fastener. Modes Im and II have not been

observed in nail and spike connections. The yield model

theory is applicable to all types of dowel fasteners (nails,

screws, bolts, lag screws) , and thus the wood bearing capacity is described by a material property called the dowel

bearing strength.

The yield mode equations (Table 7–5) are entered with the

dowel bearing strength and dimensions of the wood members

and the bending yield strength and diameter of the fastener.

The dowel bearing strength of the wood is experimentally

determined by compressing a dowel into a wood member.

The strength basis is the load representing a 5% diameter

offset on the load–deformation curve (Fig. 7–3). Dowel

bearing strength Fe (Pa, lb/in2) is empirically related to

specific gravity G by

 

F G e = 114 5 1 84 . . (metric) (7–3a)

 

F G e = 16 600 1 84 , . (inch–pound) (7–3b)

where specific gravity is based on ovendry weight and

volume.

Spacing

End distance, edge distance, and spacing of nails should be

such as to prevent unusual splitting. As a general rule, nails

should be driven no closer to the edge of the side member

than one-half its thickness and no closer to the end than the

thickness of the piece. Smaller nails can be driven closer to

the edges or ends than larger ones because they are less likely

to split the wood.

Grain Direction Effects

The lateral load for side-grain nailing applies whether the

load is in a direction parallel to the grain of the pieces joined

or at right angles to it. When nails are driven into the end

grain (parallel with the wood fibers), limited data on softwood species indicate that their maximum resistance to

lateral displacement is about two-thirds that for nails driven

into the side grain. Although the average proportional limit

loads appear to be about the same for end- and side-grain

nailing, the individual results are more erratic for end-grain

nailing, and the minimum loads approach only 75% of

corresponding values for side-grain nailing.

Table 7–4. Coefficients for computing test loads for

fasteners in seasoned wooda

 (pre-1991)

Specific

gravity

Lateral load coefficient K (metric (inch–pound))

rangeb Nailsc Screws Lag screws

Hardwoods

0.33–0.47 50.04 (1,440) 23.17 (3,360) 26.34 (3,820)

0.48–0.56 69.50 (2,000) 31.99 (4,640) 29.51 (4,280)

0.57–0.74 94.52 (2,720) 44.13 (6,400) 34.13 (4,950)

Softwoods

0.29–0.42 50.04 (1,440) 23.17 (3,360) 23.30 (3,380)

0.43–0.47 62.55 (1,800) 29.79 (4,320) 26.34 (3,820)

0.48–0.52 76.45 (2,200) 36.40 (5,280) 29.51 (4,280)

a

Wood with a moisture content of 15%.

b

Specific gravity based on ovendry weight and volume

 at 12% moisture content.

c

Coefficients based on load at joint slip of 0.38 mm

 (0.015 in.)

3 6 9

0 0.12 0.24 0.36

8d common nail

1.80

1.35

0.90

0.45

Load (kN)

Load (lb)

400

320

240

160

80

0

0

Slip in joint (mm)

Slip in joint (in.)

Yield

strength

0.05 x

fastener

diameter

Figure 7–3. Typical relation between lateral

load and slip in the joint and 5% offset definition.
7–7

Moisture Content Effects

Nails driven into the side grain of unseasoned wood give

maximum lateral resistance loads approximately equal to

those obtained in seasoned wood, but the lateral resistance

loads at 0.38 mm (0.015 in.) joint slip are somewhat less.

To prevent excessive deformation, lateral loads obtained for

seasoned wood should be reduced by 25% for unseasoned

wood that will remain wet or be loaded before seasoning

takes place.

When nails are driven into green wood, their lateral proportional limit loads after the wood has seasoned are also less

than when they are driven into seasoned wood and loaded.

The erratic behavior of a nailed joint that has undergone one

or more moisture content changes makes it difficult to establish a lateral load for a nailed joint under these conditions.

Structural joints should be inspected at intervals, and if it is

apparent that the joint has loosened during drying, the joint

should be reinforced with additional nails.

Deformed-Shank Nails

Deformed-shank nails carry somewhat higher maximum

lateral loads than do the same pennyweight common wire

nails, but both perform similarly at small distortions in the

joint. It should be noted that the same pennyweight deformed-shank nail has a different diameter than that of the

common wire nail. These nails often have higher bending

yield strength than common wire nails, resulting in higher

lateral strength in modes III and IV.

Lateral Load–Slip Models

A considerable amount of work has been done to describe, by

mathematical models, the lateral load–slip curve of nails.

These models have become important because of their need

as input parameters for advanced methods of structural

analysis.

One theoretical model, which considers the nail to be a beam

supported on an elastic foundation (the wood), describes the

initial slope of the curve:

 

δ= + − −

+

















PLL J J

K K

2 1 2

1 2

2

1 2

( ) ( )

( ) (7–4)

where P is the lateral load and δ is the joint slip. The factors

L1, L2, J1, J2, K1, and K2 (Table 7–6) are combinations of

hyperbolic and trigonometric functions of the quantities λ1a

and λ2b in which a and b are the depth of penetration of the

nail in members 1 and 2, respectively. For smooth round

nails,

 

λ

π = 2 0

3

4 k

ED

(7–5)

where k0 is elastic bearing constant, D nail diameter, and E

modulus of elasticity of the nail. For seasoned wood, the

elastic bearing constant k0 (N/mm3, lb/in3) has been shown to

be related to average species specific gravity G if no lead hole

is used by

 

k G 0 = 582 (metric) (7–6a)

 

k G 0 = 2 144 000 , , (inch–pound (7–6b)

If a prebored lead hole equal to 90% of the nail diameter is

used,

 

k G 0 = 869 (metric) (7–7a)

 

k G 0 = 3 200 000 , , (inch–pound) (7–7b)

Other empirically derived models attempt to describe the

entire load–slip curve. One such expression is

 

PA B = + log10 ( ) 1 δ (7–8)

where the parameters A and B are empirically fitted.

Mode Im Mode Is Mode II

(Not applicable)

(b)

Mode Im Mode Is Mode II

(a)

Mode IIIm Mode IIIs Mode IV

(Not applicable)

Mode IIIm Mode IIIs Mode IV

Figure 7–4. Various combinations of wood-bearing and fastener-bending yields for (a) two-member connections

and (b) three-member connections.
 7–8

Spikes

Common wire spikes are manufactured in the same manner

as common wire nails. They have either a chisel point or a

diamond point and are made in lengths of 76 to 305 mm

(3 to 12 in.). For corresponding lengths in the range of 76 to

152 (3 to 6 in.), they have larger diameters (Table 7–7) than

common wire nails, and beyond the 60d size they are usually

designated by diameter.

The withdrawal and lateral resistance equations and limitations given for common wire nails are also applicable to

spikes, except that in calculating the withdrawal load for

spikes, the depth of penetration is taken as the length of the

spike in the member receiving the point, minus two-thirds

the length of the point.

Staples

Different types of staples have been developed with various

modifications in points, shank treatment and coatings,

gauge, crown width, and length. These fasteners are available

in clips or magazines for use in pneumatically operated

portable staplers. Most factors that affect the withdrawal and

lateral loads of nails similarly affect the loads on staples. The

withdrawal resistance, for example, varies almost directly

with the circumference and depth of penetration when the

type of point and shank are similar to nails. Thus, Equation

(7–1) has been used to predict the withdrawal load for one

leg of a staple, but no verification tests have been done.

The load in lateral resistance varies approximately as the 3/2

power of the diameter when other factors, such as quality of

metal, type of shank, and depth of penetration, are similar to

nails. The diameter of each leg of a two-legged staple must

therefore be about two-thirds the diameter of a nail to provide

a comparable load. Equation (7–2) has been used to predict

the lateral resistance of staples. However, yield model

theory equations have not yet been experimentally verified

for staples.

Table 7–5. The 5% offset lateral yield strength (Z)

for nails and screws for a two-member joint

Mode Z value for nails Z value for screws

Is 

Dt Fs es Dt Fs es

IIIm

 

k DpF

+ R

1

1 2

em

e

 —

IIIs

 

k Dt F

R

2

2

s em

+ e 

k Dt F

R

3

2

s em

+ e

IV

 

D

F F

R

2 2

3 1

em yb

e ( ) + 

D

F F

R

2 1 75

3 1

.

( )

em yb

+ e

Definitions

D nail, spike, or screw diameter, mm (in.) (for

annularly threaded nails, D is thread-root diameter;

for screws, D is either the shank diameter or the root

diameter if the threaded portion of the screw is in the

shear plane)

Fem dowel bearing stress of main member

(member holding point), kPa (lb/in2)

Fes dowel bearing stress of side member, kPa (lb/in2)

Fyb bending yield stress of nail, spike, or screw, kPa

 (lb/in2)

p penetration of nail or spike in main member, mm (in.)

ts thickness of side member, mm (in.)

Z offset lateral yield strength

Re = Fem/Fes

 

k R

F RD

 Fp

1

2

2

1 21

2 12

3

 () ( )=− + + +

+

e

yb e

em

 

k R

R

F RD

 Ft

2

2

2

1 2 1 2 2

3

( ) ( )

=− +

+

+

+ e

e

yb e

em s

 

k R

R

F RD

 Ft

3

2

2

1 2 1 2

2

( ) ( )

=− +

+

+

+ e

e

yb e

em s

Table 7–6. Expressions for factors in Equation (7–4)

Factor Expressiona

 

L

k

a a a a

a a

L

k

b b b b

b b

J

k

a + a

a a

J

k

b +

1

1

1

1 1 11

2

1

2

1

2

2

2

2 2 22

2

2

2

2

1

1

2

1

2

1

2

1

2

1

2

1

2

2

2

2

2

2

 sinh cosh sin cos

sinh sin

sinh cosh sin cos

sinh sin

 sinh sin

sinh sin

 sinh

 

λλ λ λ λ

λ λ

λλ λ λ λ

λ λ

λλ λ

λ λ

λ λ

−

−

−

−

−

sin

sinh sin

 sinh cosh sin cos

sinh sin

 sinh cosh sin cos

sinh sin

2

2

2

2

2

2

1

1

3

1

1 1 11

2

1

2

1

2

2

3

2

2 2 22

2

2

2

2

λ

λ λ

λλ λ λ λ

λ λ

λλ λ λ λ

λ λ

b

b b

K

k

a a + a a

a a

K

k

b b + b b

b b

−

−

−

_____________________________________________

a

k1 = k01d and k2 = k02d, where k1 and k2 are the

 foundation moduli of members 1 and 2, respectively.
7–9

In addition to the immediate performance capability of staples and nails as determined by test, factors such as corrosion, sustained performance under service conditions, and

durability in various uses should be considered in evaluating

the relative usefulness of a stapled connection.

Drift Bolts

A drift bolt (or drift pin) is a long pin of iron or steel, with

or without head or point. It is driven into a bored hole

through one timber and into an adjacent one, to prevent the

separation of the timbers connected and to transmit lateral

load. The hole in the second member is drilled sufficiently

deep to prevent the pin from hitting the bottom.

The ultimate withdrawal load of a round drift bolt or pin

from the side grain of seasoned wood is given by

 

p G DL = 45 51 2 . (metric) (7–9a)

 p G DL = 6 600 2 , (inch–pound) (7–9b)

where p is the ultimate withdrawal load (N, lb), G specific

gravity based on the ovendry weight and volume at 12%

moisture content of the wood, D diameter of the drift bolt

(mm, in.), and L length of penetration of the bolt (mm, in.).

(The NDS and LRFD use ovendry weight and volume as a

basis.)

This equation provides an average relationship for all species, and the withdrawal load for some species may be above

or below the equation values. It also presumes that the bolts

are driven into prebored holes having a diameter 3.2 mm

(1/8 in.) less than the bolt diameter.

Data are not available on lateral resistance of drift bolts. The

yield model should provide lateral strength prediction, but

the model has not been experimentally verified for drift bolts.

Designers have used bolt data and design methods based on

experience. This suggests that the load for a drift bolt driven

into the side grain of wood should not exceed, and ordinarily

should be taken as less than, that for a bolt of the same

diameter. Bolt design values are based on the thickness of

the main member in a joint. Thus the depth of penetration

of the drift bolt must be greater than or equal to the mainmember thickness on which the bolt design value is based.

However, the drift bolt should not fully penetrate its joint.

Wood Screws

The common types of wood screws have flat, oval, or round

heads. The flathead screw is most commonly used if a flush

surface is desired. Ovalhead and roundhead screws are used

for appearance, and roundhead screws are used when countersinking is objectionable. The principal parts of a screw are

the head, shank, thread, and core (Fig. 7–5). The root diameter for most sizes of screws averages about two-thirds the

shank diameter. Wood screws are usually made of steel,

brass, other metals, or alloys, and may have specific finishes

such as nickel, blued, chromium, or cadmium. They are

classified according to material, type, finish, shape of head,

and diameter or gauge of the shank.

Current trends in fastenings for wood also include tapping

screws. Tapping screws have threads the full length of the

shank and may have some advantage for certain specific uses.

Withdrawal Resistance

Experimental Loads

The resistance of wood screw shanks to withdrawal from the

side grain of seasoned wood varies directly with the square of

the specific gravity of the wood. Within limits, the withdrawal load varies directly with the depth of penetration of

the threaded portion and the diameter of the screw, provided

the screw does not fail in tension. The screw will fail in

tension when its strength is exceeded by the withdrawal

strength from the wood. The limiting length to cause a

tension failure decreases as the density of the wood increases

since the withdrawal strength of the wood increases with

density. The longer lengths of standard screws are therefore

superfluous in dense hardwoods.

Table 7–7. Sizes of common wire spikes

Length Diameter

Size (mm (in.)) (mm (in.))

10d 76.2 (3) 4.88 (0.192)

12d 82.6 (3-1/4) 4.88 (0.192)

16d 88.9 (3-1/2) 5.26 (0.207)

20d 101.6 (4) 5.72 (0.225)

30d 114.3 (4-1/2) 6.20 (0.244)

40d 127.0 (5) 6.68 (0.263)

50d 139.7 (5-1/2) 7.19 (0.283)

60d 152.4 (6) 7.19 (0.283)

5/16 in. 177.8 (7) 7.92 (0.312)

3/8 in. 215.9 (8-1/2) 9.53 (0.375)

Core or

root

diameter

Gage or

diameter

of shank 2/3 length

Length

A B C

Figure 7–5. Common types of wood screws:

A, flathead; B, roundhead; and C, ovalhead.
 7–10

The withdrawal resistance of type A tapping screws, commonly called sheet metal screws, is in general about 10%

greater than that for wood screws of comparable diameter and

length of threaded portion. The ratio between the withdrawal

resistance of tapping screws and wood screws varies from

1.16 in denser woods, such as oak, to 1.05 in lighter woods,

such as redwood.

Ultimate test values for withdrawal loads of wood screws

inserted into the side grain of seasoned wood may be

expressed as

 

p G DL = 108 25 2 . (metric) (7–10a)

 

p G DL = 15 700 2 , (inch–pound) (7–10b)

where p is maximum withdrawal load (N, lb), G specific

gravity based on ovendry weight and volume at 12% moisture content, D shank diameter of the screw (mm, in.), and L

length of penetration of the threaded part of the screw (mm,

in.). (The NDS and LRFD use ovendry weight and volume

as a basis.) These values are based on reaching ultimate load

in 5- to 10-min.

This equation is applicable when screw lead holes have a

diameter of about 70% of the root diameter of the threads in

softwoods, and about 90% in hardwoods.

The equation values are applicable to the screw sizes listed

in Table 7–8. (Shank diameters are related to screw gauges.)

For lengths and gauges outside these limits, the actual

values are likely to be less than the equation values.

The withdrawal loads of screws inserted in the end grain of

wood are somewhat erratic, but when splitting is avoided,

they should average 75% of the load sustained by screws

inserted in the side grain.

Lubricating the surface of a screw with soap or similar lubricant is recommended to facilitate insertion, especially in

dense woods, and it will have little effect on ultimate withdrawal resistance.

Fastening of Particleboard

Tapping screws are commonly used in particleboard where

withdrawal strength is important. Care must be taken when

tightening screws in particleboard to avoid stripping the

threads. The maximum amount of torque that can be applied

to a screw before the threads in the particleboard are stripped

is given by

 

T X = + 3 16 0 0096 . . (metric) (7–11a)

 

T X = + 27 98 1 36 . . (inch–pound) (7–11b)

where T is torque (N–m, in–lb) and X is density of the

particleboard (kg/m3

, lb/ft3). Equation (7–11) is for 8-gauge

screws with a depth of penetration of 15.9 mm (5/8 in.). The

maximum torque is fairly constant for lead holes of 0 to 90%

of the root diameter of the screw.

Ultimate withdrawal loads P (N, lb) of screws from particleboard can be predicted by

 

P = KD L D G 12 54 2 3 / / ( ) − (7–12)

where D is shank diameter of the screw (mm, in.), L depth of

embedment of the threaded portion of the screw (mm, in.),

and G specific gravity of the board based on ovendry weight

and volume at current moisture content. For metric measurements, K = 41.1 for withdrawal from the face of the board

and K = 31.8 for withdrawal from the edge; for inch–pound

measurements, K = 2,655 for withdrawal from the face and

K = 2,055 for withdrawal from the edge. Equation (7–12)

applies when the setting torque is between 60% to 90% of T

(Eq. ( 7–11)).

Withdrawal resistance of screws from particleboard is not

significantly different for lead holes of 50% to 90% of the root

diameter. A higher setting torque will produce a somewhat

higher withdrawal load, but there is only a slight difference

(3%) in values between 60% to 90% setting torques

(Eq. (7–11)). A modest tightening of screws in many cases

provides an effective compromise between optimizing withdrawal resistance and stripping threads.

Equation (7–12) can also predict the withdrawal of screws

from fiberboard with K = 57.3 (metric) or 3,700 (inch–

pound) for the face and K = 44.3 (metric) or 2,860 (inch–

pound) for the edge of the board.

Lateral Resistance

Pre-1991

The proportional limit loads obtained in tests of lateral

resistance for wood screws in the side grain of seasoned wood

are given by the empirical equation

 p KD = 2 (7–13)

where p is lateral load, D diameter of the screw shank, and

K a coefficient depending on the inherent characteristics of the

wood species. Values of screw shank diameters for various

screw gauges are listed in Table 7–9.

Table 7–8. Screw sizes

appropriate for Equation (7–10)

Screw length

 (mm (in.)) Gauge limits

12.7 (1/2) 1 to 6

19.0 (3/4) 2 to 11

25.4 (1) 3 to 12

38.1 (1-1/2) 5 to 14

50.8 (2) 7 to 16

63.5 (2-1/2) 9 to 18

76.2 (3) 12 to 20
7–11

Values of K are based on ranges of specific gravity of hardwoods and softwoods and are given in Table 7–4. They

apply to wood at about 15% moisture content. Loads computed by substituting these constants in the equation are

expected to have a slip of 0.18 to 0.25 mm (0.007 to

0.010 in.), depending somewhat on the species and density

of the wood.

Equation (7–13) applies when the depth of penetration of the

screw into the block receiving the point is not less than

seven times the shank diameter and when the side member

and the main member are approximately of the same density.

The thickness of the side member should be about one-half

the depth of penetration of the screw in the member holding

the point. The end distance should be no less than the side

member thickness, and the edge distances no less than onehalf the side member thickness.

This depth of penetration (seven times shank diameter) gives

an ultimate load of about four times the load obtained by the

equation. For a depth of penetration of less than seven times

the shank diameter, the ultimate load is reduced about in

proportion to the reduction in penetration, and the load at the

proportional limit is reduced somewhat less rapidly. When

the depth of penetration of the screw in the holding block is

four times the shank diameter, the maximum load will be

less than three times the load expressed by the equation, and

the proportional limit load will be approximately equal to

that given by the equation. When the screw holds metal to

wood, the load can be increased by about 25%.

For these lateral loads, the part of the lead hole receiving the

shank should be the same diameter as the shank or slightly

smaller; that part receiving the threaded portion should be

the same diameter as the root of the thread in dense species

or slightly smaller than the root in low-density species.

Screws should always be turned in. They should never be

started or driven with a hammer because this practice tears

the wood fibers and injures the screw threads, seriously

reducing the load carrying capacity of the screw.

Post-1991

Screw lateral strength is determined by the yield model

theory (Table 7–5). Modes I, III, and IV failures may occur

(Fig. 7–4). The dowel bearing strength values are based on

the same specific gravity equation used to establish values for

nails (Eq. (7–3)). Further discussion of screw lateral strength

is found in ASCE Manual No. 84, Mechanical Connections

in Wood Structures.

Lag Screws

Lag screws are commonly used because of their convenience,

particularly where it would be difficult to fasten a bolt or

where a nut on the surface would be objectionable. Commonly available lag screws range from about 5.1 to 25.4 mm

(0.2 to 1 in.) in diameter and from 25.4 to 406 mm (1 to

16 in.) in length. The length of the threaded part varies with

the length of the screw and ranges from 19.0 mm (3/4 in.)

with the 25.4- and 31.8-mm (1- and 1-1/4-in.) screws to half

the length for all lengths greater than 254 mm (10 in.). Lag

screws have a hexagonal-shaped head and are tightened by a

wrench (as opposed to wood screws, which have a slotted

head and are tightened by a screw driver). The following

equations for withdrawal and lateral loads are based on lag

screws having a base metal average tensile yield strength of

about 310.3 MPa (45,000 lb/in2

) and an average ultimate

tensile strength of 530.9 MPa (77,000 lb/in2).

Withdrawal Resistance

The results of withdrawal tests have shown that the maximum direct withdrawal load of lag screws from the side grain

of seasoned wood may be computed as

 p GDL = 125 4 32 34 . / / (metric) (7–14a)

 p GDL = 8 100 32 34 , / / (inch–pound) (7–14b)

where p is maximum withdrawal load (N, lb), D shank

diameter (mm, in.), G specific gravity of the wood based on

ovendry weight and volume at 12% moisture content, and L

length (mm, in.) of penetration of the threaded part. (The

NDS and LRFD use ovendry weight and volume as a basis.)

Equation (7–14) was developed independently of Equation

(7–10) but gives approximately the same results.

Lag screws, like wood screws, require prebored holes of the

proper size (Fig. 7–6). The lead hole for the shank should be

the same diameter as the shank. The diameter of the lead

hole for the threaded part varies with the density of the wood:

For low-density softwoods, such as the cedars and white

pines, 40% to 70% of the shank diameter; for Douglas-fir and

Southern Pine, 60% to 75%; and for dense hardwoods, such

as oaks, 65% to 85%. The smaller percentage in each range

applies to lag screws of the smaller diameters and the larger

Table 7–9. Screw shank diameters

for various screw gauges

Screw number Diameter

or gauge (mm (in.))

4 2.84 (0.112)

5 3.18 (0.125)

6 3.51 (0.138)

7 3.84 (0.151)

8 4.17 (0.164)

9 4.50 (0.177)

10 4.83 (0.190)

11 5.16 (0.203)

12 5.49 (0.216)

14 6.15 (0.242)

16 6.81 (0.268)

18 7.47 (0.294)

20 8.13 (0.320)

24 9.45 (0.372)
 7–12

percentage to lag screws of larger diameters. Soap or similar

lubricants should be used on the screw to facilitate turning,

and lead holes slightly larger than those recommended for

maximum efficiency should be used with long screws.

In determining the withdrawal resistance, the allowable

tensile strength of the lag screw at the net (root) section

should not be exceeded. Penetration of the threaded part to a

distance about seven times the shank diameter in the denser

species (specific gravity greater than 0.61) and 10 to 12 times

the shank diameter in the less dense species (specific gravity

less than 0.42) will develop approximately the ultimate

tensile strength of the lag screw. Penetrations at intermediate

densities may be found by straight-line interpolation.

The resistance to withdrawal of a lag screw from the endgrain surface of a piece of wood is about three-fourths as great

as its resistance to withdrawal from the side-grain surface of

the same piece.

Lateral Resistance

Pre-1991

The experimentally determined lateral loads for lag screws

inserted in the side grain and loaded parallel to the grain of a

piece of seasoned wood can be computed as

 p KD = 2 (7–15)

where p is proportional limit lateral load (N, lb) parallel to

the grain, K a coefficient depending on the species specific

gravity, and D shank diameter of the lag screw (mm, in.).

Values of K for a number of specific gravity ranges can be

found in Table 7–4. These coefficients are based on average

results for several ranges of specific gravity for hardwoods and

softwoods. The loads given by this equation apply when the

thickness of the side member is 3.5 times the shank diameter

of the lag screw, and the depth of penetration in the main

member is seven times the diameter in the harder woods and

11 times the diameter in the softer woods. For other thicknesses, the computed loads should be multiplied by the

factors listed in Table 7–10.

The thickness of a solid wood side member should be about

one-half the depth of penetration in the main member.

When the lag screw is inserted in the side grain of wood and

the load is applied perpendicular to the grain, the load given

by the lateral resistance equation should be multiplied by the

factors listed in Table 7–11.

For other angles of loading, the loads may be computed from

the parallel and perpendicular values by the use of the

Scholten nomograph for determining the bearing strength of

wood at various angles to the grain (Fig. 7–7).

Figure 7–6. A, Clean-cut, deep penetration of thread

made by lag screw turned into a lead hole of proper

size, and B, rough, shallow penetration of thread

made by lag screw turned into oversized lead hole.

Table 7–10. Multiplication factors for

loads computed from Equation (7–15)

Ratio of thickness of

side member to shank

diameter of lag screw Factor

2 0.62

2.5 0.77

3 0.93

3.5 1.00

4 1.07

4.5 1.13

5 1.18

5.5 1.21

6 1.22

6.5 1.22

Table 7–11. Multiplication factors for

loads applied perpendicular to grain

computed from Equation (7–15) with

lag screw in side grain of wood

 Shank diameter

 of lag screw

 (mm (in.)) Factor

4.8 (3/16) 1.00

6.4 (1/4) 0.97

7.9 (5/16) 0.85

9.5 (3/8) 0.76

11.1 (7/16) 0.70

12.7 (1/2) 0.65

15.9 (5/8) 0.60

19.0 (3/4) 0.55

22.2 (7/8) 0.52

25.4 (1) 0.50
7–13

The nomograph provides values as given by the Hankinson

equation,

 

N PQ

P Q = sin cos + 2 2 θ θ (7–16)

where P is load or stress parallel to the grain, Q load or

stress perpendicular to the grain, and N load or stress at an

inclination θ with the direction of the grain.

Example: P, the load parallel to grain, is 6,000 lb, and Q,

the load perpendicular to the grain, is 2,000 lb. The load at

an angle of 40° to grain, N, is found as follows: Connect

with a straight line 6,000 lb (a) on line OX of the nomograph

with the intersection (b) on line OY of a vertical line through

2,000 lb. The point where line ab intersects the line representing the given angle 40° is directly above the load,

3,300 lb.

Values for lateral resistance as computed by the preceding

methods are based on complete penetration of the unthreaded

shank into the side member but not into the main member.

When the shank penetrates the main member, the permitted

increases in loads are given in Table 7–12.

When lag screws are used with metal plates, the lateral loads

parallel to the grain may be increased 25%, provided the

plate thickness is sufficient so that the bearing capacity of the

steel is not exceeded. No increase should be made when the

applied load is perpendicular to the grain.

Lag screws should not be used in end grain, because splitting may develop under lateral load. If lag screws are so

used, however, the loads should be taken as two-thirds those

for lateral resistance when lag screws are inserted into side

grain and the loads act perpendicular to the grain.

The spacings, end and edge distances, and net section for lag

screw joints should be the same as those for joints with bolts

(discussed later) of a diameter equal to the shank diameter of

the lag screw.

Lag screws should always be inserted by turning with a

wrench, not by driving with a hammer. Soap, beeswax, or

other lubricants applied to the screw, particularly with the

denser wood species, will facilitate insertion and prevent

damage to the threads but will not affect performance of the

lag screw.

Post-1991

Lag screw lateral strength is determined by the yield model

theory table similar to the procedure for bolts. Modes I, III,

and IV yield may occur (Fig. 7–4). The dowel bearing

a

b

0 1 2 4 3 5 7 8 9 10

Allowable load or stress for P, Q, and N in units, tens, hundreds, or thousands

6

90°

75°

60°

45°

30°

15°

0°

 Load or stress parallel to grain

 Load or stress perpendicular to grain

 Load of stress at inclination θ

 with direction of grain

Y

X

P

Q

N

Figure 7–7. Scholten nomograph for determining the bearing stress of wood at various

angles to the grain. The dashed line ab refers to the example given in the text.

Table 7–12. Permitted increases

in loads when lag screw unthreaded

shank penetrates foundation member

 Ratio of penetration of

 shank into foundation

member to shank diameter

Increase

in load

(%)

1 8

2 17

3 26

4 33

5 36

6 38

7 39
 7–14

strength values are based on the same parallel- and perpendicular-to-grain specific gravity equations used to establish

values for bolts.

Bolts

Bearing Stress of Wood Under Bolts

The bearing stress under a bolt is computed by dividing the

load on a bolt by the product LD, where L is the length of a

bolt in the main member and D is the bolt diameter. Basic

parallel-to-grain and perpendicular-to-grain bearing stresses

have been obtained from tests of three-member wood joints

where each side member is half the thickness of the main

member. The side members were loaded parallel to grain for

both parallel- and perpendicular-to-grain tests. Prior to 1991,

bearing stress was based on test results at the proportional

limit; since 1991, bearing stress is based on test results at a

yield limit state, which is defined as the 5% diameter offset

on the load–deformation curve (similar to Fig. 7–3).

The bearing stress at proportional limit load is largest when

the bolt does not bend, that is, for joints with small L/D

values. The curves of Figures 7–8 and 7–9 show the reduction in proportional limit bolt-bearing stress as L/D increases. The bearing stress at maximum load does not decrease as L/D increases, but remains fairly constant, which

means that the ratio of maximum load to proportional limit

load increases as L/D increases. To maintain a fairly constant

ratio between maximum load and design load for bolts, the

relations between bearing stress and L/D ratio have been

adjusted as indicated in Figures 7–8 and 7–9.

The proportional limit bolt-bearing stress parallel to grain for

small L/D ratios is approximately 50% of the small clear

crushing strength for softwoods and approximately 60% for

hardwoods. For bearing stress perpendicular to the grain, the

ratio between bearing stress at proportional limit load and

the small clear proportional limit stress in compression

perpendicular to grain depends upon bolt diameter

(Fig. 7–10) for small L/D ratios.

Species compressive strength also affects the L/D ratio relationship, as indicated in Figure 7–9. Relatively higher bolt

proportional-limit stress perpendicular to grain is obtained

with wood low in strength (proportional limit stress of

3,930 kPa (570 lb/in2

) than with material of high strength

(proportional limit stress of 7,860 kPa (1,140 lb/in2)). This

effect also occurs for bolt-bearing stress parallel to grain, but

not to the same extent as for perpendicular-to-grain loading.

The proportional limit bolt load for a three-member joint

with side members half the thickness of the main member

may be estimated by the following procedures.

For parallel-to-grain loading, (a) multiply the species small

clear compressive parallel strength (Tables 4–3, 4–4, or 4–5)

by 0.50 for softwoods or 0.60 for hardwoods, (b) multiply

this product by the appropriate factor from Figure 7–8 for the

L/D ratio of the bolt, and (c) multiply this product by LD.

For perpendicular-to-grain loading, (a) multiply the species

compression perpendicular-to-grain proportional limit stress

(Tables 4–3, 4–4, or 4–5) by the appropriate factor from

Figure 7–10, (b) multiply this product by the appropriate

factor from Figure 7–9, and (c) multiply this product by LD.

Loads at an Angle to the Grain

For loads applied at an angle intermediate between those

parallel to the grain and perpendicular to the grain, the boltbearing stress may be obtained from the nomograph in

Figure 7–7. Ratio of long- to short-bolt bearing stress (%)

100

80

60

40

20

0 2 4 6 8 10 12

A

B

L/D ratio

Figure 7–8. Variation in bolt-bearing stress at the proportional limit parallel to grain with L/D ratio. Curve A,

relation obtained from experimental evaluation; curve B,

modified relation used for establishing design loads. Ratio of long- to short-bolt bearing stress (%)

100

80

60

40

20

0 2 4 6 8 10 12

L/D ratio

A-1

A-2

B-1

B-2

Figure 7–9. Variation in bolt-bearing stress at the

proportional limit perpendicular to grain with L/D ratio.

Relations obtained from experimental evaluation for

materials with average compression perpendicular

stress of 7,860 kPa (1,140 lb/in2

) (curve A–1) and

3,930 kPa (570 lb/in2

) (curve A–2). Curves B–1 and B–2,

modified relations used for establishing design loads.
7–15

Steel Side Plates

When steel side plates are used, the bolt-bearing stress parallel to grain at joint proportional limit is approximately 25%

greater than that for wood side plates. The joint deformation

at proportional limit is much smaller with steel side plates.

If loads at equivalent joint deformation are compared, the

load for joints with steel side plates is approximately 75%

greater than that for wood side plates. Pre-1991 design criteria included increases in connection strength with steel side

plates; post-1991 design criteria include steel side plate

behavior in the yield model equations.

For perpendicular-to-grain loading, the same loads are obtained for wood and steel side plates.

Bolt Quality

Both the properties of the wood and the quality of the bolt

are factors in determining the strength of a bolted joint. The

percentages given in Figures 7–8 and 7–9 for calculating

bearing stress apply to steel machine bolts with a yield stress

of 310 MPa (45,000 lb/in2). Figure 7–11 indicates the increase in bearing stress parallel to grain for bolts with a yield

stress of 862 MPa (125,00 lb/in2).

Effect of Member Thickness

The proportional limit load is affected by the ratio of the

side member thickness to the main member thickness

(Fig. 7–12).

Pre-1991 design values for bolts are based on joints with the

side member half the thickness of the main member. The

usual practice in design of bolted joints is to take no increase

in design load when the side members are greater than half

the thickness of the main member. When the side members

are less than half the thickness of the main member, a design

load for a main member that is twice the thickness of the side

member is used. Post-1991 design values include member

thickness directly in the yield model equations.

Two-Member, Multiple-Member Joints

In pre-1991 design, the proportional limit load was taken as

half the load for a three-member joint with a main member

the same thickness as the thinnest member for two-member

joints.

For four or more members in a joint, the proportional limit

load was taken as the sum of the loads for the individual

shear planes by treating each shear plane as an equivalent

two-member joint.

 Ratio of bolt bearing stress to compressionperpendicular to grain proportional limit stress 2.6

Bolt diameter (in.)

Bolt diameter (mm)

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0

0 0.5 1.0 2.0 2.5

16 32 48 64

1.5

Figure 7–10. Bearing stress perpendicular to the grain

as affected by bolt diameter.

Ratio of long- to short-bolt bearing stress (%)

100

80

60

40

20

0 2 468 10 12

L/D ratio

A

B

Figure 7–11. Variation in the proportional limit boltbearing stress parallel to grain with L/D ratio. Curve A,

bolts with yield stress of 861.84 MPa (125,000 lb/in2

);

curve B, bolts with yield stress of 310.26 MPa

(45,000 lb/in2

).

 Ratio to joint with side memberhalf the thickness of main member1.6

1.2

0.8

0.4

0 0.25 0.50 0.75 1.00 1.25 1.50

Side member thickness/main member thickness

L/D = 2.67

L/D = 5.33

L/D = 4.00

Figure 7–12. Proportional limit load related to side

member thickness for three-member joints. Center

member thickness was 50.8 mm (2 in.).
 7–16

Post-1991 design for joints with four or more members also

results in values per shear plane. Connection strength for any

number of members is conservatively found by multiplying

the value for the weakest shear plane by the number of

shear planes.

Spacing, Edge, and End Distance

The center-to-center distance along the grain should be at

least four times the bolt diameter for parallel-to-grain loading. The minimum center-to-center spacing of bolts in the

across-the-grain direction for loads acting through metal side

plates and parallel to the grain need only be sufficient to

permit the tightening of the nuts. For wood side plates, the

spacing is controlled by the rules applying to loads acting

parallel to grain if the design load approaches the boltbearing capacity of the side plates. When the design load is

less than the bolt-bearing capacity of the side plates, the

spacing may be reduced below that required to develop their

maximum capacity.

When a joint is in tension, the bolt nearest the end of a

timber should be at a distance from the end of at least seven

times the bolt diameter for softwoods and five times for

hardwoods. When the joint is in compression, the end margin may be four times the bolt diameter for both softwoods

and hardwoods. Any decrease in these spacings and margins

will decrease the load in about the same ratio.

For bolts bearing parallel to the grain, the distance from the

edge of a timber to the center of a bolt should be at least 1.5

times the bolt diameter. This margin, however, will usually

be controlled by (a) the common practice of having an edge

margin equal to one-half the distance between bolt rows and

(b) the area requirements at the critical section. (The critical

section is that section of the member taken at right angles to

the direction of load, which gives the maximum stress in the

member based on the net area remaining after reductions are

made for bolt holes at that section.) For parallel-to-grain

loading in softwoods, the net area remaining at the critical

section should be at least 80% of the total area in bearing

under all the bolts in the particular joint under consideration;

in hardwoods it should be 100%.

For bolts bearing perpendicular to the grain, the margin

between the edge toward which the bolt pressure is acting

and the center of the bolt or bolts nearest this edge should be

at least four times the bolt diameter. The margin at the

opposite edge is relatively unimportant.

Effect of Bolt Holes

The bearing strength of wood under bolts is affected considerably by the size and type of bolt holes into which the

bolts are inserted. A bolt hole that is too large causes

nonuniform bearing of the bolt; if the bolt hole is too small,

the wood will split when the bolt is driven. Normally, bolts

should fit so that they can be inserted by tapping lightly

with a wood mallet. In general, the smoother the hole, the

higher the bearing values will be (Fig. 7–13). Deformations

accompanying the load are also less with a smoother bolthole surface (Fig. 7–14).

Rough holes are caused by using dull bits and improper rates

of feed and drill speed. A twist drill operated at a peripheral

speed of approximately 38 m/min (1,500 in/min) produces

uniformly smooth holes at moderate feed rates. The rate of

feed depends upon the diameter of the drill and the speed of

Figure 7–13. Effect of rate of feed and drill speed on the

surface condition of bolt holes drilled in Sitka spruce.

A, hole was bored with a twist drill rotating at a

peripheral speed of 7.62 m/min (300 in/min); feed rate

was 1.52 m/min (60 in/min). B, hole was bored with the

same drill at a peripheral speed of 31.75 m/min

(1,250 in/min); feed rate was 50.8 mm/min (2 in/min).

4.5

Load (kN)

Load (x103 lb)

20

16

12

8

4

0

3.0

1.5

0

1.5 3.0 4.5 6.0 7.5

0 0.010 0.020 0.030

Slow feed

Fast feed

Deformation (in.)

Deformation (mm)

Figure 7–14. Typical load–deformation curves

showing the effect of surface condition of bolt holes,

resulting from a slow feed rate and a fast feed rate,

on the deformation in a joint when subjected to

loading under bolts. The surface conditions of the bolt

holes were similar to those illustrated in Figure 7–13.
7–17

rotation but should enable the drill to cut rather than tear the

wood. The drill should produce shavings, not chips.

Proportional limit loads for joints with bolt holes the same

diameter as the bolt will be slightly higher than for joints

with a 1.6-mm (1/16-in.) oversized hole. However, if drying

takes place after assembly of the joint, the proportional limit

load for snug-fitting bolts will be considerably less due to

the effects of shrinkage.

Pre-1991 Allowable Loads

The following procedures are used to calculate allowable bolt

loads for joints with wood side members, each half the

thickness of the main member.

Parallel to Grain—The starting point for parallel-to-grain

bolt values is the maximum green crushing strength for the

species or group of species. Procedures outlined in ASTM

D2555 are used to establish a 5% exclusion value. The

exclusion value is divided by a factor of 1.9 to adjust to a

10-year normal duration of load and provide a factor of safety.

This value is multiplied by 1.20 to adjust to a seasoned

strength. The resulting value is called the basic bolt-bearing

stress parallel to grain.

The basic bolt-bearing stress is then adjusted for the effects of

L/D ratio. Table 7–13 gives the percentage of basic stress for

three classes of species. The particular class for the species is

determined from the basic bolt-bearing stress as indicated in

Table 7–14. The adjusted bearing stress is further multiplied

Table 7–13. Percentage of basic bolt-bearing stress used for calculating allowable bolt loads

Ratio L/D adjustment factor by classa

of bolt

length to Parallel to grain Perpendicular to grain

diameter

(L/D)1 2 3 1 2 3 4

1 100.0 100.0 100.0 100.0 100.0 100.0 100.0

2 100.0 100.0 100.0 100.0 100.0 100.0 100.0

3 100.0 100.0 99.0 100.0 100.0 100.0 100.0

4 99.5 97.4 92.5 100.0 100.0 100.0 100.0

5 95.4 88.3 80.0 100.0 100.0 100.0 100.0

6 85.6 75.8 67.2 100.0 100.0 100.0 96.3

7 73.4 65.0 57.6 100.0 100.0 97.3 86.9

8 64.2 56.9 50.4 100.0 96.1 88.1 75.0

9 57.1 50.6 44.8 94.6 86.3 76.7 64.6

10 51.4 45.5 40.3 85.0 76.2 67.2 55.4

11 46.7 41.4 36.6 76.1 67.6 59.3 48.4

12 42.8 37.9 33.6 68.6 61.0 52.0 42.5

13 39.5 35.0 31.0 62.2 55.3 45.9 37.5

a

Class determined from basic bolt-bearing stress according to Table 7–14.

Table 7–14. L/D adjustment class associated with basic bolt-bearing stress

Basic bolt-bearing stress for species group (MPa (lb/in2

))

Loading direction Softwoods Hardwoods

L/D adjustment

(Table 7–13)

Parallel <7.93 (<1,150) <7.33 (<1,063) 1

7.93–10.37 (1,150–1,504) 7.33–9.58 (1,063–1,389) 2

>10.37 (>1,504) >9.58 (>1,389) 3

Perpendicular <1.31 (<190) <1.44 (<209) 1

1.31–2.00 (190–290) 1.44–2.20 (209–319) 2

2.00–2.59 (291–375) 2.21–2.84 (320–412) 3

>2.59 (>375) >2.84 (>412) 4
 7–18

by a factor of 0.80 to adjust to wood side plates. The allowable bolt load in pounds is then determined by multiplying

by the projected bolt area, LD.

Perpendicular to Grain—The starting point for perpendicular-to-grain bolt values is the average green proportional

limit stress in compression perpendicular to grain. Procedures in ASTM D2555 are used to establish compression

perpendicular values for groups of species. The average proportional limit stress is divided by 1.5 for ring position

(growth rings neither parallel nor perpendicular to load during test) and a factor of safety. This value is then multiplied

by 1.20 to adjust to a seasoned strength and by 1.10 to

adjust to a normal duration of load. The resulting value is

called the basic bolt-bearing stress perpendicular to grain.

The basic bolt-bearing stress is then adjusted for the effects of

bolt diameter (Table 7–15) and L/D ratio (Table 7–13).

The allowable bolt load is then determined by multiplying

the adjusted basic bolt-bearing stress by the projected bolt

area, LD.

Post-1991 Yield Model

The empirical design approach used prior to 1991 was based

on a tabular value for a single bolt in a wood-to-wood, threemember connection where the side members are each a

minimum of one-half the thickness of the main member. The

single-bolt value must then be modified for any variation

from these reference conditions. The theoretical approach,

after 1991, is more general and is not limited to these

reference conditions.

The theoretical approach is based on work done in Europe

(Johansen 1949) and is referred to as the European Yield

Model (EYM). The EYM describes a number of possible

yield modes that can occur in a dowel-type connection

(Fig. 7–4). The yield strength of these different modes is

determined from a static analysis that assumes the wood and

the bolt are both perfectly plastic. The yield mode that results in the lowest yield load for a given geometry is the

theoretical connection yield load.

Equations corresponding to the yield modes for a threemember joint are given in Table 7–16. (Equations for twomember allowable values are given in the AF&PA National

Design Specification for Wood Construction) The nominal

single-bolt value is dependent on the joint geometry

(thickness of main and side members), bolt diameter and

bending yield strength, dowel bearing strength, and direction

of load to the grain. The equations are equally valid for wood

or steel side members, which is taken into account by thickness and dowel bearing strength parameters. The equations

are also valid for various load-to-grain directions, which are

taken into account by the Kθ and Fe parameter.

The dowel bearing strength is a material property not generally familiar to structural designers. The dowel bearing

strength of the wood members is determined from tests that

relate species specific gravity and dowel diameter to bearing

strength. Empirical equations for these relationships are as

follows:

Parallel to grain

 

F G e = 77 2. (metric) (7–17a)

 

F G e = 11 200 , (inch–pound) (7–17b)

Perpendicular to grain

 

F GD-0.5

e = 212 0 1 45 . . (metric) (7–18a)

 

F GD-0.5

e = 6 100 1 45 , . (inch–pound) (7–18b)

where Fe is dowel bearing strength (MPa, lb/in2), G specific

gravity based on ovendry weight and volume, and D bolt

diameter (mm, in.).

Connector Joints

Several types of connectors have been devised that increase

joint bearing and shear areas by utilizing rings or plates

around bolts holding joint members together. The primary

load-carrying portions of these joints are the connectors; the

bolts usually serve to prevent transverse separation of the

members but do contribute some load-carrying capacity.

The strength of the connector joint depends on the type and

size of the connector, the species of wood, the thickness and

width of the member, the distance of the connector from the

end of the member, the spacing of the connectors, the direction of application of the load with respect to the direction of

the grain of the wood, and other factors. Loads for wood

joints with steel connectors—split ring (Fig. 7–15) and shear

plate (Fig. 7–16)—are discussed in this section. These

connectors require closely fitting machined grooves in the

wood members.

Parallel-to-Grain Loading

Tests have demonstrated that the density of the wood is a

controlling factor in the strength of connector joints. For

split-ring connectors, both maximum load and proportional

limit load parallel to grain vary linearly with specific gravity

(Figs. 7–17 and 7–18). For shear plates, the maximum load

and proportional limit load vary linearly with specific gravity

for the less dense species (Figs. 7–19 and 7–20). In the

higher density species, the shear strength of the bolts becomes the controlling factor. These relations were obtained

for seasoned members, approximately 12% moisture content.

Perpendicular-to-Grain Loading

Loads for perpendicular-to-grain loading have been established using three-member joints with the side members

loaded parallel to grain. Specific gravity is a good indicator

of perpendicular-to-grain strength of timber connector joints.

For split-ring connectors, the proportional limit loads perpendicular to grain are 58% of the parallel-to-grain proportional limit loads. The joint deformation at proportional

limit is 30% to 50% more than for parallel-to-grain loading.
7–19

Table 7–15. Factors for adjusting basic boltbearing stress perpendicular to grain for bolt

diameter when calculating allowable bolt loads

 Bolt diameter Adjustment

 (mm (in.)) factor

6.35 (1/4) 2.50

9.53 (3/8) 1.95

12.70 (1/2) 1.68

15.88 (5/8) 1.52

19.05 (3/4) 1.41

22.23 (7/8) 1.33

25.40 (1) 1.27

31.75 (1-1/4) 1.19

38.10 (1-1/2) 1.14

44.45 (1-3/4) 1.10

50.80 (2) 1.07

63.50 (2-1/2) 1.03

>76.20 (>3 or over) 1.00

Table 7–16. The 5% offset yield lateral strength

(Z) for three-member bolted joints

Mode

Z value for threemember bolted joint

Mode Im

 

Dt F

K

m em

θ

Mode Is

 

2Dt F

K

s es

θ

Mode IIIs

 

2

2

4 kD F

R )K

ts em

( + e θ

Mode IV

 

2 2

3 1

2 D

K

F F

θ R

em yb

e ( ) +

Definitions

D nominal bolt diameter, mm (in.)

Fem dowel bearing strength of main (center)

 member, kPa (lb/in2)

Fes dowel bearing strength of side members,

 kPa (lb/in2)

Fyb bending yield strength of bolt, kPa (lb/in2)

Kθ 1 + θ/360

tm thickness of main (center) member, mm (in.)

ts thickness of side member, mm (in.)

Z nominal single bolt design value

θ angle of load to grain (degrees)

Re = Fem/Fes

 

k e

e

yb e

4

2

2

1 2 1 2 2

3

=− +

+

+ ( ) R ( ) +

R

F RD

F t em s

Figure 7–15. Joint with split-ring connector showing

connector, precut groove, bolt, washer, and nut.

Figure 7–16. Joints with shear-plate connectors

with (A) wood side plates and (B) steel side plates.
 7–20

For shear-plate connectors, the proportional limit and

maximum loads vary linearly with specific gravity

(Figs. 7–21 and 7–22). The wood strength controls the joint

strength for all species.

Design Loads

Design loads for parallel-to-grain loading have been established by dividing ultimate test loads by an average factor of

4. This gives values that do not exceed five-eighths of the

proportional limit loads. The reduction accounts for variability in material, a reduction to long-time loading, and a factor

of safety. Design loads for normal duration of load are

10% higher.

For perpendicular-to-grain loading, ultimate load is given

less consideration and greater dependence placed on load at

proportional limit. For split rings, the proportional limit

load is reduced by approximately half. For shear plates, the

design loads are approximately five-eighths of the proportional limit test loads. These reductions again account for

material variability, a reduction to long-time loading, and a

factor of safety.

Design loads are presented in Figures 7–17 to 7–22. In

practice, four wood species groups have been established,

based primarily on specific gravity, and design loads assigned for each group. Species groupings for connectors are

presented in Table 7–17. The corresponding design loads

(for long-continued load) are given in Table 7–18. The

National Design Specification for Wood Construction

gives design values for normal-duration load for these and

additional species.

130

Load (kN)

Maximum load

Proportional limit load

104

78

52

26

30

25

20

15

10

5

0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Specific gravity

Load (x103 lb)

Design load

Figure 7–17. Relation between load bearing parallel

to grain and specific gravity (ovendry weight,

volume at test) for two 63.5-mm (2-1/2-in.) split

rings with a single 12.7-mm (1/2-in.) bolt in air-dry

material. Center member was thickness 101.6 mm

(4 in.) and side member thickness was 50.8 mm (2 in.). Load (kN)

Maximum load

Proportional limit load

30

20

10

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Specific gravity

Load (x103 lb)

0

60

50

40

250

200

150

100

50 Design load

Figure 7–18. Relation between load bearing parallel

to grain and specific gravity (ovendry weight,

volume at test) for two 101.6-mm (4-in.) split rings

and a single 19.1-mm- (3/4-in.-) diameter bolt in

air-dry material. Center member thickness was

127.0 mm (5 in.) and side member thickness

was 63.5 mm (2-1/2 in.).

Load (kN)

20

15

5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Specific gravity

Load (x103 lb)

0

35

30

25

150

120

90

60

30

10

Maximum load

Proportional limit load

Design load

Bolt diameter (mm(in.))

19.0 (3/4)

15.9 (5/8)

Figure 7–19. Relation between load bearing parallel

to grain and specific gravity (ovendry weight,

volume at test) for two 66.7-mm (2-5/8-in.) shear

plates in air-dry material with steel side plates.

Center member thickness was 76.2 mm (3 in.). Load (kN)

Maximum load

Proportional limit load

Design load

30

20

10

0.1 0.2 0.3 0.4 0.5 0.6 0.7

Specific gravity

Load (x103 lb)

0

60

50

40

0

250

200

150

100

50

Bolt diameter (mm(in.))

19.0 (3/4)

15.9 (5/8)

Figure 7–20. Relation between load bearing parallel

to grain and specific gravity (ovendry weight, volume

at test) for two 101.6-mm (4-in.) shear plates in

air-dry material with steel side plates. Center

member thickness was 88.9 mm (3-1/2 in.).
7–21

Modifications

Some factors that affect the loads of connectors were taken

into account in deriving the tabular values. Other varied and

extreme conditions require modification of the values.

Steel Side Plates

Steel side plates are often used with shear-plate connectors.

The loads parallel to grain have been found to be approximately 10% higher than those with wood side plates. The

perpendicular-to-grain loads are unchanged.

Exposure and Moisture Condition of Wood

The loads listed in Table 7–18 apply to seasoned members

used where they will remain dry. If the wood will be more or

less continuously damp or wet in use, two-thirds of the

tabulated values should be used. The amount by which the

loads should be reduced to adapt them to other conditions of

use depends upon the extent to which the exposure favors

decay, the required life of the structure or part, the frequency

and thoroughness of inspection, the original cost and the cost

of replacements, the proportion of sapwood and durability of

the heartwood of the species (if untreated), and the character

and efficiency of any treatment. These factors should be

evaluated for each individual design. Industry recommendations for the use of connectors when the condition of the

lumber is other than continuously wet or continuously dry

are given in the National Design Specification for Wood

Construction.

Ordinarily, before fabrication of connector joints, members

should be seasoned to a moisture content corresponding as

nearly as practical to that which they will attain in service.

This is particularly desirable for lumber for roof trusses and

other structural units used in dry locations and in which

shrinkage is an important factor. Urgent construction needs

sometimes result in the erection of structures and structural

units employing green or inadequately seasoned lumber with

connectors. Because such lumber subsequently dries out in

most buildings, causing shrinkage and opening the joints,

adequate maintenance measures must be adopted. The

maintenance for connector joints in green lumber should

include inspection of the structural units and tightening of

all bolts as needed during the time the units are coming

to moisture equilibrium, which is normally during the

first year.

Load (kN)

6

4

2

0.1 0.2 0.3 0.4 0.5 0.6 0.7

Specific gravity

Load (x103 lb)

0

12

10

8

0

50

40

30

20

10

Maximum load

Proportional limit load

Design load

Bolt diameter (mm(in.))

19.0 (3/4)

15.9 (5/8)

19.0 or 15.9

(3/4 or 5/8)

Figure 7–21. Relation between load bearing

perpendicular to grain and specific gravity

(ovendry weight, volume at test) for two 66.7-mm

(2-5/8-in.) shear plates in air-dry material with

steel side plates. Center member thickness

was 76.2 mm (3 in.). Load (kN)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Specific gravity

Load (x103 lb)

90

72

54

36

18

8

4

0

20

16

12 Maximum load

Proportional limit load

Design load

Bolt diameter (mm(in.))

19.0 (3/4)

15.9 (5/8)

19.0 or 15.9

(3/4 or 5/8)

Figure 7–22. Relation between load bearing perpendicular to grain and specific gravity (ovendry

weight, volume at test) for two 101.6-mm (4-in.)

shear plates in air-dry material with steel side plates.

Center member thickness was 88.9 mm (3-1/2 in.).

Table 7–17. Species groupings for connector loadsa

Connector Species or species group

Group 1 Aspen Basswood Cottonwood

Western

 redcedar

Balsam fir White fir

Eastern hemlock Eastern white pine Ponderosa pine

Sugar pine Western white pine Engelmann

 spruce

 Group 2 Chestnut Yellow-poplar Baldcypress

Yellow-cedar Port-Orford-cedar Western

 hemlock

Red pine Redwood Red spruce

Sitka spruce White spruce

 Group 3 Elm, American Elm, slippery Maple, soft

Sweetgum Sycamore Tupelo

Douglas-fir Larch, western Southern Pine

 Group 4 Ash, white Beech Birch

Elm, rock Hickory Maple, hard

Oak

a

Group 1 woods provide the weakest connector joints;

 group 4 woods, the strongest.
 7–22

Grade and Quality of Lumber

The lumber for which the loads for connectors are applicable

should conform to the general requirements in regard to

quality of structural lumber given in the grading rule books

of lumber manufacturers’ associations for various commercial

species.

The loads for connectors were obtained from tests of joints

whose members were clear and free from checks, shakes, and

splits. Cross grain at the joint should not be steeper than

1 in 10, and knots in the connector area should be accounted

for as explained under Net Section.

Loads at Angle with Grain

The loads for the split-ring and shear-plate connectors for

angles of 0° to 90° between direction of load and grain may

be obtained by the Hankinson equation (Eq. (7–16)) or by

the nomograph in Figure 7–7.

Thickness of Member

The relationship between the loads for the different thicknesses of lumber is based on test results for connector joints.

The least thickness of member given in Table 7–18 for the

various sizes of connectors is the minimum to obtain optimum load. The loads listed for each type and size of connector are the maximum loads to be used for all thicker lumber.

The loads for wood members of thicknesses less than those

listed can be obtained by the percentage reductions indicated

in Figure 7–23. Thicknesses below those indicated by the

curves should not be used.

When one member contains a connector in only one face,

loads for thicknesses less than those listed in Table 7–18 can

be obtained by the percentage reductions indicated in Figure

7–23 using an assumed thickness equal to twice the actual

member thickness.

Table 7–18. Design loads for one connector in a jointa

Load (N (lb))

Minimum thickness of

wood member (mm (in.)) Group 1 woods Group 2 woods Group 3 woods Group 4 woods

Connector

With one

connector

only

With two

connectors

in opposite

faces, one

boltb

Minimum

width all

members

(mm (in.))

At 0°

angle

to

grain

At 90°

angle

to

grain

At 0°

angle

to

grain

At 90°

angle

to

grain

At 0°

angle

to

grain

At 90°

angle

to

grain

At 0°

angle

to

grain

At 90°

angle

to

grain

Split ring

63.5-mm (2-1/2-in.)

diameter, 19.0 mm

(3/4 in.) wide, with

12.7-mm (1/2-in.)

bolt

25 (1) 51 (2) 89 (3-1/2) 7,940

(1,785)

4,693

(1,055)

9,274

(2,085)

5,471

(1,230)

11,032

(2,480)

6,561

(1,475)

12,789

(2,875)

7,673

(1,725)

101.6-mm (4-in.)

diameter, 25.4 mm

(1 in.) wide, with

19.0-mm (3/4-in.)

bolt

38 (1-1/2) 76 (3) 140 (5-1/2) 15,324

(3,445)

8,874

(1,995)

17,726

(3,985)

10,275

(2,310)

21,262

(4,780)

12,344

(2,775)

24,821

(5,580)

14,390

(3,235)

Shear plate

66.7-mm (2-5/8-in.)

diameter, 10.7 mm

(0.42 in.) wide, with

19.0-mm (3/4-in.)

bolt

38 (1-1/2) 67 (2-5/8) 89 (3-1/2) 8,407

(1,890)

4,871

(1,095)

9,742

(2,190)

5,649

(1,270)

11,699

(2,630)

6,784

(1,525)

11,854

(2,665)

7,918

(1,780)

101.6-mm (4-in.)

diameter,16.2 mm

(0.64 in.) wide, with

19.0-mm or 22.2-mm

(3/4- or 7/8-in.) bolt

44 (1-3/4) 92 (3-518) 140 (5-1/2) 12,677

(2,850)

7,362

(1,655)

14,701

(3,305)

8,518

(1,915)

17,637

(3,965)

10,231

(2,300)

20,573

(4,625)

11,943

(2,685)

a

The loads apply to seasoned timbers in dry, inside locations for a long-continued load. It is also assumed that the joints are properly designed

 with respect to such features as centering of connectors, adequate end distance, and suitable spacing. Group 1 woods provide the weakest

 connector joints, group 4 woods the strongest. Species groupings are given in Table 7–17.

b

A three-member assembly with two connectors takes double the loads indicated.
7–23

Width of Member

The width of member listed for each type and size of connector is the minimum that should be used. When the connectors are bearing parallel to the grain, no increase in load

occurs with an increase in width. When they are bearing

perpendicular to the grain, the load increases about 10% for

each 25-mm (1-in.) increase in width of member over the

minimum widths required for each type and size of connector, up to twice the diameter of the connectors. When the

connector is placed off center and the load is applied continuously in one direction only, the proper load can be determined by considering the width of member as equal to twice

the edge distance (the distance between the center of the

connector and the edge of the member toward which the load

is acting). The distance between the center of the connector

and the opposite edge should not, however, be less than

half the permissible minimum width of the member.

Net Section

The net section is the area remaining at the critical section

after subtracting the projected area of the connectors and bolt

from the full cross-sectional area of the member. For sawn

timbers, the stress in the net area (whether in tension or

compression) should not exceed the stress for clear wood in

compression parallel to the grain. In using this stress, it is

assumed that knots do not occur within a length of half the

diameter of the connector from the net section. If knots are

present in the longitudinal projection of the net section

within a length from the critical section of one-half the

diameter of the connector, the area of the knots should be

subtracted from the area of the critical section.

In laminated timbers, knots may occur in the inner laminations at the connector location without being apparent from

the outside of the member. It is impractical to assure that

there are no knots at or near the connector. In laminated

construction, therefore, the stress at the net section is limited

to the compressive stress for the member, accounting for the

effect of knots.

End Distance and Spacing

The load values in Table 7–18 apply when the distance of

the connector from the end of the member (end distance e)

and the spacing s between connectors in multiple joints are

not factors affecting the strength of the joint (Fig. 7–24A).

When the end distance or spacing for connectors bearing

parallel to the grain is less than that required to develop the

full load, the proper reduced load may be obtained by multiplying the loads in Table 7–18 by the appropriate strength

ratio given in Table 7–19. For example, the load for a

102-mm (4-in.) split-ring connector bearing parallel to the

grain, when placed 178 mm or more (7 in. or more) from the

end of a Douglas-fir tension member that is 38 mm

(1-1/2 in.) thick is 21.3 kN (4,780 lb). When the end distance is only 133 mm (5-1/4 in.), the strength ratio obtained

by direct interpolation between 178 and 89 mm (7 and

3-1/2 in.) in Table 7–19 is 0.81, and the load equals

0.81 times 21.3 (4,780) or 17.2 kN (3,870 lb).

Placement of Multiple Connectors

Preliminary investigations of the placement of connectors in

a multiple-connector joint, together with the observed behavior of single-connector joints tested with variables that simulate those in a multiple-connector joint, are the basis for

some suggested design practices.

When two or more connectors in the same face of a member

are in a line at right angles to the grain of the member and

Percentage of optimum load at 0° or 90° to grain

Thickness of wood member with connector in each face (mm)

Thickness of wood member with connector in each face (in.)

0 26 52 78 104 130

0 1 2 3 4 5

100

80

60

100

80

60

Split ring

Shear plate

101.6-mm (4-in.)

diameter,

19-mm (3/4-in.)

bolt

66.7-mm (2-5/8-in.)

diameter,

19-mm (3/4-in.)

bolt 101.6-mm (4-in.) diameter,

19- or 22.2-mm (7/8- or 3/4-in.) bolt

63.5-mm (2-1/2-in.)

diameter,

12.9-mm (1/2-in.)

bolt

Figure 7–23. Effect of thickness of wood member on the optimum load

capacity of a timber connector.
 7–24

are bearing parallel to the grain (Fig. 7–24C), the clear distance c between the connectors should not be less than

12.7 mm (1/2 in.). When two or more connectors are acting

perpendicular to the grain and are spaced on a line at right

angles to the length of the member (Fig. 7–24B), the rules

for the width of member and edge distances used with one

connector are applicable to the edge distances for multiple

connectors. The clear distance c between the connectors

should be equal to the clear distance from the edge of the

member toward which the load is acting to the connector

nearest this edge.

In a joint with two or more connectors spaced on a line

parallel to the grain and with the load acting perpendicular to

the grain (Fig. 7–24D), the available data indicate that the

load for multiple connectors is not equal to the sum of the

loads for individual connectors. Somewhat more favorable

results can be obtained if the connectors are staggered so that

they do not act along the same line with respect to the grain

of the transverse member. Industry recommendations for

various angle-to-grain loadings and spacings are given in the

National Design Specification for Wood Construction.

Cross Bolts

Cross bolts or stitch bolts placed at or near the end of members joined with connectors or at points between connectors

will provide additional safety. They may also be used to

reinforce members that have, through change in moisture

content in service, developed splits to an undesirable degree.

Multiple-Fastener Joints

 When fasteners are used in rows parallel to the direction of

loading, total joint load is unequally distributed among

fasteners in the row. Simplified methods of analysis have

been developed to predict the load distribution among the

fasteners in a row. These analyses indicate that the load

distribution is a function of (a) the extensional stiffness EA of

the joint members, where E is modulus of elasticity and A is

gross cross-sectional area, (b) the fastener spacing, (c) the

number of fasteners, and (d) the single-fastener loaddeformation characteristics.

Theoretically, the two end fasteners carry a majority of the

load. For example, in a row of six bolts, the two end bolts

will carry more than 50% of the total joint load. Adding

bolts to a row tends to reduce the load on the less heavily

loaded interior bolts. The most even distribution of bolt

loads occurs in a joint where the extensional stiffness of the

main member is equal to that of both splice plates. Increasing the fastener spacing tends to put more of the joint load

on the end fasteners. Load distribution tends to be worse for

stiffer fasteners.

The actual load distribution in field-fabricated joints is difficult to predict. Small misalignment of fasteners, variations in

spacing between side and main members, and variations in

single-fastener load–deformation characteristics can cause the

load distribution to be different than predicted by the

theoretical analyses.

For design purposes, modification factors for application

to a row of bolts, lag screws, or timber connectors have

been developed based on the theoretical analyses. Tables

are given in the National Design Specification for

Wood Construction.

A design equation was developed to replace the double entry

required in the National Design Specification for Wood

Construction tables. This equation was obtained by algebraic simplification of the Lantos analysis that these tables

are based on

 

 

C m m

n R m m m

R

m

n

EA

n n

EA

g = −

[ ] + + −+

















+

−





 



 ( )

( )( )

1

1 11

1

1

2

2 (7–19)

where Cg is modification factor, n number of fasteners in a

row, REA the lesser of(EsAs)/ (EmAm) or (EmAm)/ (EsAs), Em

c

e

c

a

a

e

e

c

c

a

a

e s

A B

C D

Figure 7–24. Types of multiple-connector joints:

A, joint strength depends on end distance e and

connector spacing s; B, joint strength depends on e,

clear c, and edge a distances; C, joint strength depends

on end e and clear c distances; D, joint strength

depends on end e, clear c, and edge a distances.
7–25

modulus of elasticity of main member, Es modulus of elasticity of side members, Am gross cross-sectional area of main

member, As sum of gross cross-sectional areas of side members, m = u u − −2 1, u = 1 + γ(s/2)(1/EmAm + 1/ EsAs),

s center-to-center spacing between adjacent fasteners in a row,

and γ load/slip modulus for a single fastener connection.

For 102-mm (4-in.) split-ring or shear-plate connectors,

γ = 87,560 kN/m (500,000 lb/in)

For 64-mm (2-1/2-in.) split ring or 67-mm (2-5/8-in.) split

ring or shear plate connectors,

γ = 70,050 kN/m (400,000 lb/in)

For bolts or lag screws in wood-to-wood connections,

γ = 246.25 D1.5 (metric)

 = 180,000 D1.5 (inch–pound)

For bolts or lag screws in wood-to-metal connections,

γ = 369.37 D1.5 (metric)

 = 270,000 D1.5 (inch–pound)

where D is diameter of bolt or lag screw.

Metal Plate Connectors

Metal plate connectors, commonly called truss plates, have

become a popular means of joining, especially in trussed

rafters and joists. These connectors transmit loads by means

of teeth, plugs, or nails, which vary from manufacturer to

manufacturer. Examples of such plates are shown in

Figure 7–25. Plates are usually made of light-gauge galvanized steel and have an area and shape necessary to transmit

the forces on the joint. Installation of plates usually requires

a hydraulic press or other heavy equipment, although some

plates can be installed by hand.

Basic strength values for plate connectors are determined

from load–slip curves from tension tests of two butted wood

members joined with two plates. Some typical curves are

shown in Figure 7–26. Design values are expressed as load

per tooth, nail, plug, or unit area of plate. The smallest value

as determined by two different means is the design load for

normal duration of load: (1) the average load of at least five

specimens at 0.38-mm (0.015-in.) slip from plate to wood

member or 0.76-mm (0.030-in.) slip from member to member is divided by 1.6; (2) the average ultimate load of at least

five specimens is divided by 3.0.

The strength of a metal plate joint may also be controlled by

the tensile or shear strength of the plate.

Table 7–19. Strength ratio for connectors for various longitudinal spacings and end distancesa

Connector Spacing End distanceb

 (mm (in.))

diameter

(mm (in.))

Spacingc

(mm (in.))

strength

ratio

Tension

member

Compression

member

End distance

strength ratio

Split-ring

63.5 (2-1/2) 171.4+ (6-3/4+) 100 139.7+ (5-1/2+) 101.6+ (4+) 100

63.5 (2-1/2) 85.7 (3-3/8) 50 69.8 (2-3/4) 63.5 (2-1/2) 62

101.6 (4) 228.6+ (9+) 100 177.8+ (7+) 139.7+ (5-1/2+) 100

101.6 (4) 123.8 (4-7/8) 50 88.9 (3-1/2) 82.6 (3-1/4) 62

Shear-plate

66.7 (2-5/8) 171.4+ (6-3/4+) 100 139.7+(5-1/2+) 101.6+ (4+) 100

66.7 (2-5/8) 85.7 (3-3/8) 50 69.8 (2-3/4) 63.5 (2-1/2) 62

101.6 (4) 228.6+ (9+) 100 177.8+ (7+) 139.7+ (5-1/2+) 100

101.6 (4) 114.3 (4-1/2) 50 88.9 (3-1/2) 82.6 (3-1/4) 62

a

Strength ratio for spacings and end distances intermediate to those listed may be obtained by interpolation

 and multiplied by the loads in Table 7–18 to obtain design load. The strength ratio applies only to those

 connector units affected by the respective spacings or end distances. The spacings and end distances

 should not be less than the minimum shown.

b

End distance is distance from center of connector to end of member (Fig. 7–24A).

c

Spacing is distance from center to center of connectors (Fig. 7–24A).
 7–26

Fastener Head Embedment

The bearing strength of wood under fastener heads is important in such applications as the anchorage of building framework to foundation structures. When pressure tends to pull

the framing member away from the foundation, the fastening

loads could cause tensile failure of the fastenings, withdrawal

of the fastenings from the framing member, or embedment of

the fastener heads in the member. The fastener head could

even be pulled completely through.

The maximum load for fastener head embedment is related to

the fastener head perimeter, while loads at low embedments

(1.27 mm (0.05 in.)) are related to the fastener head bearing

area. These relations for several species at 10% moisture

content are shown in Figures 7–27 and 7–28.

Figure 7–25. Some typical metal plate connectors.

40

30

20

10

0

9.6

8.0

6.4

4.8

3.2

1.6

0

0

0.5 1.0 1.5 2.0 2.5 3.0 3.5

Slip, member to member (in.)

Slip, member to member (mm)

0.02 0.04 0.06 0.08 0.10 0.12 0.14

Load 

P (kN)

Load 

P (x103 lb)

P

P

Plug type plate

Toothed type plate

Figure 7–26. Typical load–slip curves for two

types of metal plate connectors loaded in tension.
7–27

References

AF&PA. 1997. National design specification for wood

construction. Washington, DC: American Forest & Paper

Association.

ASCE. 1995. Standard for load and resistance factor design

(LRFD) for engineered wood construction. Washington, DC:

American Society of Civil Engineers.

ASCE. 1996. Mechanical connections in wood structures.

Washington, DC: American Society of Civil Engineers.

ASTM. (current edition). Philadelphia, PA: American

Society for Testing and Materials.

ASTM F1667. Specification for driven fasteners: nails,

spiker, staples.

ASTM D2555–96. Standard methods for establishing clear

wood strength values.

ASTM F547. Standard terminology of nails for use with

wood and wood-base materials.

ASTM D5652–95. Standard test methods for bolted connections in wood and wood-base products.

ASTM D1761–88. Standard test methods for mechanical

fasteners in wood.

Anderson, L.O. 1959. Nailing better wood boxes and

crates. Agric. Handb. 160. Washington, DC: U.S. Department of Agriculture.

Anderson, L.O. 1970. Wood-frame house construction.

Agric. Handb. 73 (rev.). Washington, DC: U.S. Department

of Agriculture.

Cramer, C.O. 1968. Load distribution in multiple-bolt

tension joints. Proc. Pap. 5939. Journal of Structural

Division, American Society of Civil Engineers. 94(ST5):

11011117.

Doyle, D.V.; Scholten, J.A. 1963. Performance of bolted

joints in Douglas-fir. Res. Pap. FPL 2. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Eckelman, C.A. 1975. Screw holding performance in

hardwoods and particleboard. Forest Products Journal.

25(6): 30–35.

Fairchild, I.J. 1926. Holding power of wood screws.

Technol. Pap. 319. Washington, DC: U.S. National Bureau

of Standards.

Forest Products Laboratory. 1962. General observations

on the nailing of wood. FPL Tech. Note 243. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Forest Products Laboratory. 1964. Nailing dense hardwoods. Res. Note FPL–037. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products

Laboratory.

Forest Products Laboratory. 1965. Nail withdrawal

resistance of American woods. Res. Note FPL–RN–033.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Goodell, H.R.; Philipps, R.S. 1944. Bolt-bearing strength

of wood and modified wood: effect of different methods of

drilling bolt holes in wood and plywood. FPL Rep. 1523.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

0 30 60 90 120 150

0 1234 5 6

Fastener perimeter (in.)

Fastener perimeter (mm)

60

45

30

15

Maximum embedment load (kN)

Maximum embedment load (x103 lb)

14

12

10

8

6

4

2

0

Red Oak

Southern Pine

Western hemlock

White fir

Douglas-fir

Figure 7–27. Relation between maximum

embedment load and fastener perimeter for

several species of wood.

0 5 10 15 20

8

7

6

5

4

3

2

1

0

0 23

Fastener head bearing area (cm2)

Fastener head bearing area (in2)

35

30

25

20

15

10

5

Load at 1.27-mm embedment (kN)

Load at 0.05-in. embedment (x103 lb)

Red Oak

Southern Pine

Douglas-fir

Western hemlock

White fir

1

Figure 7–28. Relation between load at 1.27-mm

(0.05-in.) embedment and fastener bearing area

for several species.
 7–28

Johansen, K.W. 1949. Theory of timber connections.

Zurich, Switzerland: Publications of International Association for Bridge and Structural Engineering. 9: 249–262.

Jordan, C.A. 1963. Response of timber joints with metal

fasteners to lateral impact loads. FPL Rep. 2263. Madison,

WI: U.S. Department Agriculture, Forest Service, Forest

Products Laboratory.

Kuenzi, E.W. 1951. Theoretical design of a nailed or bolted

joint under lateral load. FPL Rep. 1951. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Kurtenacker, R.S. 1965. Performance of container fasteners

subjected to static and dynamic withdrawal. Res. Pap. FPL

29. Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Lantos, G. 1969. Load distribution in a row of fasteners

subjected to lateral load. Madison, WI: Wood Science.

1(3): 129–136.

Markwardt, L.J. 1952. How surface condition of nails

affects their holding power in wood. FPL Rep. D1927.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Markwardt, L.J.; Gahagan, J.M. 1930. Effect of nail

points on resistance to withdrawal. FPL Rep. 1226.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Markwardt, L.J.; Gahagan, J.M. 1952. Slant driving of

nails. Does it pay? Packing and Shipping. 56(10):

7–9,23,25.

McLain, T.E. 1975. Curvilinear load-slip relations in

laterally-loaded nailed joints. Fort Collins, CO: Department

of Forestry and Wood Science, Colorado State University.

Thesis.

NPA. 1968. Screw holding of particleboard. Tech. Bull. 3.

Washington, DC: National Particleboard Association.

Newlin, J.A.; Gahagan, J.M. 1938. Lag screw joints: their

behavior and design. Tech. Bull. 597. Washington, DC:

U.S. Department of Agriculture.

Perkins, N.S.; Landsem, P.; Trayer, G.W. 1933. Modern

connectors for timber construction. Washington, DC: U.S.

Department of Commerce, National Committee on Wood

Utilization, and U.S. Department of Agriculture, Forest

Service.

Scholten, J.A. 1944. Timber-connector joints, their strength

and design. Tech. Bull. 865. Washington, DC: U.S.

Department of Agriculture.

Scholten, J.A. 1946. Strength of bolted timber joints. FPL

Rep. R1202. Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory.

Scholten, J.A. 1950. Nail-holding properties of southern

hardwoods. Southern Lumberman. 181(2273): 208–210.

Scholten, J.A.; Molander, E. G. 1950. Strength of nailed

joints in frame walls. Agricultural Engineering. 31(11):

551–555.

Soltis, L.A.; Wilkinson, T.L. 1987. Bolted connection

design. Gen. Tech. Rep. FPL–GTR–54. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Stern, E.G. 1940. A study of lumber and plywood joints

with metal split-ring connectors. Bull. 53. State College,

PA: Pennsylvania Engineering Experiment Station.

Stern, E.G. 1950. Nails in end-grain lumber. Timber News

and Machine Woodworker. 58(2138): 490–492.

Trayer, G.W. 1932. Bearing strength of wood under bolts.

Tech. Bull. 332. Washington, DC: U.S. Department of

Agriculture.

Truss Plate Institute. [n.d.] Design specification for metal

plate connected wood trusses. TPI–78. Madison, WI: Truss

Plate Institute.

Wilkinson, T.L. 1971. Bearing strength of wood under

embedment loading of fasteners. Res. Pap. FPL 163. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory.

Wilkinson, T.L. 1971. Theoretical lateral resistance of

nailed joints. Proceedings of American Society of Civil

Engineering. Journal of Structural Division. ST5(97):

(Pap. 8121): 1381–1398.

Wilkinson, T.L. 1978. Strength of bolted wood joints with

various ratios of member thicknesses. Res. Pap. FPL 314.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Wilkinson, T.L. 1980. Assessment of modification factors

for a row of bolts or timber connectors. Res. Pap. FPL 376.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Wilkinson, T.L. 1991. Dowel bearing strength. Res. Paper

FPL–RP–505. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Wilkinson, T.L. 1991. Bolted connection allowable loads

based on the European yield model. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Wilkinson, T.L.; Laatsch, T.R. 1970. Lateral and withdrawal resistance of tapping screws in three densities of

wood. Forest Products Journal. 20(7): 34–41.

Zahn, J.J. 1991. Design equation for multiple-fastener wood

connections. New York, NY: Journal of Structural Engineering, American Society of Civil Engineers. Vol. 117(11):

3477–3485. Nov.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
8–1

Chapter 8

Structural Analysis Equations

Lawrence A. Soltis

Contents

Deformation Equations 8–1

Axial Load 8–1

Bending 8–1

Combined Bending and Axial Load 8–3

Torsion 8–4

Stress Equations 8–4

Axial Load 8–4

Bending 8–4

Combined Bending and Axial Load 8–7

Torsion 8–8

Stability Equations 8–8

Axial Compression 8–8

Bending 8–9

Interaction of Buckling Modes 8–10

References 8–11

quations for deformation and stress, which are the

basis for tension members and beam and column

design, are discussed in this chapter. The first two

sections cover tapered members, straight members, and

special considerations such as notches, slits, and size effect.

A third section presents stability criteria for members subject

to buckling and for members subject to special conditions.

The equations are based on mechanics principles and are not

given in the design code format found in Allowable Stress

Design or Load and Resistance Factor Design specifications.

Deformation Equations

Equations for deformation of wood members are presented as

functions of applied loads, moduli of elasticity and rigidity,

and member dimensions. They may be solved to determine

minimum required cross-sectional dimensions to meet deformation limitations imposed in design. Average moduli of

elasticity and rigidity are given in Chapter 4. Consideration

must be given to variability in material properties and uncertainties in applied loads to control reliability of the design.

Axial Load

The deformation of an axially loaded member is not usually

an important design consideration. More important considerations will be presented in later sections dealing with

combined loads or stability. Axial load produces a change of

length given by

 δ = PL

AE (8–1)

where δ is change of length, L length, A cross-sectional area,

E modulus of elasticity (EL when grain runs parallel to member axis), and P axial force parallel to grain.

Bending

Straight Beam Deflection

The deflection of straight beams that are elastically stressed

and have a constant cross section throughout their length is

given by
 8–2

 

δ= + ′

k WL

EI

k WL

GA

b s

3

 (8–2)

where δ is deflection, W total beam load acting perpendicular

to beam neutral axis, L beam span, kb and ks constants dependent upon beam loading, support conditions, and location of point whose deflection is to be calculated, I beam

moment of inertia, A′ modified beam area, E beam modulus

of elasticity (for beams having grain direction parallel to their

axis, E = EL), and G beam shear modulus (for beams with

flat-grained vertical faces, G = GLT, and for beams with edgegrained vertical faces, G = GLR). Elastic property values are

given in Tables 4–1 and 4–2 (Ch. 4).

The first term on the right side of Equation (8–2) gives the

bending deflection and the second term the shear deflection.

Values of kb and ks for several cases of loading and support are

given in Table 8–1.

The moment of inertia I of the beams is given by

 

I bh =

3

12 for beam of rectangular cross section

(8–3)

 

= πd4

64

 for beam of circular cross section

where b is beam width, h beam depth, and d beam diameter.

The modified area A′ is given by

 

A = bh ′ 5

6 for beam of rectangular cross section

(8–4)

 

= d 9

40

2 π for beam of circular cross section

If the beam has initial deformations such as bow (lateral

bend) or twist, these deformations will be increased by the

bending loads. It may be necessary to provide lateral or

torsional restraints to hold such members in line. (See

Interaction of Buckling Modes section.)

Tapered Beam Deflection

Figures 8–1 and 8–2 are useful in the design of tapered

beams. The ordinates are based on design criteria such as

span, loading, difference in beam height (hc − h0) as required

by roof slope or architectural effect, and maximum allowable

deflection, together with material properties. From this, the

value of the abscissa can be determined and the smallest

beam depth h0 can be calculated for comparison with that

given by the design criteria. Conversely, the deflection of a

beam can be calculated if the value of the abscissa is known.

Tapered beams deflect as a result of shear deflection in addition to bending deflections (Figs. 8–1 and 8–2), and this

shear deflection ∆s can be closely approximated by

 

∆s = 3

20 0

WL

Gbh for uniformly distributed load

 (8–5)

 

 

= 3

10 0

PL

Gbh for midspan-concentrated load

The final beam design should consider the total deflection as

the sum of the shear and bending deflection, and it may be

necessary to iterate to arrive at final beam dimensions. Equations (8–5) are applicable to either single-tapered or doubletapered beams. As with straight beams, lateral or torsional

restraint may be necessary.

Effect of Notches and Holes

The deflection of beams is increased if reductions in crosssection dimensions occur, such as by holes or notches. The

deflection of such beams can be determined by considering

them of variable cross section along their length and appropriately solving the general differential equations of the elastic curves, EI(d 2 

y/dx 2) = M, to obtain deflection expressions

or by the application of Castigliano’s theorem. (These procedures are given in most texts on strength of materials.)

Table 8–1. Values of kb and ks for several beam loadings

Loading Beam ends Deflection at kb ks

Uniformly distributed Both simply supported Midspan 5/384 1/8

Both clamped Midspan 1/384 1/8

Concentrated at midspan Both simply supported Midspan 1/48 1/4

Both clamped Midspan 1/192 1/4

Concentrated at outer

 quarter span points

Both simply supported Midspan 11/768 1/8

Both simply supported Load point 1/96 1/8

Uniformly distributed Cantilever, one free, one clamped Free end 1/8 1/2

Concentrated at free end Cantilever, one free, one clamped Free end 1/3 1
8–3

Effect of Time: Creep Deflections

In addition to the elastic deflections previously discussed,

wood beams usually sag in time; that is, the deflection

increases beyond what it was immediately after the load was

first applied. (See the discussion of creep in Time Under

Load in Ch. 4.)

Green timbers, in particular, will sag if allowed to dry under

load, although partially dried material will also sag to some

extent. In thoroughly dried beams, small changes in deflection occur with changes in moisture content but with little

permanent increase in deflection. If deflection under longtime

load with initially green timber is to be limited, it has been

customary to design for an initial deflection of about half the

value permitted for longtime deflection. If deflection under

longtime load with initially dry timber is to be limited, it

has been customary to design for an initial deflection of about

two-thirds the value permitted for longtime deflection.

Water Ponding

Ponding of water on roofs already deflected by other loads

can cause large increases in deflection. The total deflection ∆

due to design load plus ponded water can be closely estimated by

 

∆ ∆ = −

0

1 S Scr

 (8–6)

where ∆0 is deflection due to design load alone, S beam

spacing, and Scr critical beam spacing (Eq. (8–31)).

Combined Bending and Axial Load

Concentric Load

Addition of a concentric axial load to a beam under loads

acting perpendicular to the beam neutral axis causes increase

in bending deflection for added axial compression and

decrease in bending deflection for added axial tension.

∆

Bb (hc–h0)

3 E

WL3

γ

0 1 2 3 4 5

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

W = Total load on beam

 (uniformly distributed)

h0

γ =

∆B = Maximum bending deflection

E = Elastic modulus of beam

b = Beam width

h Single taper 0

L/2

L

Single taper

Double taper

hc

hc

h0

L/2

hc–h0

Figure 8–1. Graph for determining tapered beam size

based on deflection under uniformly distributed load.

∆

Bb (hc–h0)

3 E

PL3

γ

0

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

h0

Single taper

Double taper

hc

h0

Single taper

L

L/ 2

hc

L/ 2

∆B = Maximum bending deflection

E = Elastic modulus of beam

b = Beam width

1 2 3 4 5

P

L

P

P = Concentrated midspan load

Double taper

hc–h0

h0

h0 =

γ =

γ

hc–h0

Figure 8–2. Graph for determining tapered beam size

on deflection under concentrated midspan load.
 8–4

The deflection under combined loading at midspan for

pin-ended members can be estimated closely by

 

∆ ∆ = ±

0

1 P Pcr

(8–7)

where the plus sign is chosen if the axial load is tension and

the minus sign if the axial load is compression, ∆ is midspan deflection under combined loading, 

∆0 beam midspan

deflection without axial load, P axial load, and Pcr a constant

equal to the buckling load of the beam under axial compressive load only (see Axial Compression in Stability Equations section.) based on flexural rigidity about the neutral

axis perpendicular to the direction of bending loads. This

constant appears regardless of whether P is tension or compression. If P is compression, it must be less than Pcr to

avoid collapse. When the axial load is tension, it is conservative to ignore the P/Pcr term. (If the beam is not supported

against lateral deflection, its buckling load should be checked

using Eq. (8–35).)

Eccentric Load

If an axial load is eccentrically applied to a pin-ended member, it will induce bending deflections and change in length

given by Equation (8–1). Equation (8–7) can be applied to

find the bending deflection by writing the equation in the

form

 

δ ε ε

b

cr

+ =

± 0

0

1 P P (8–8)

where δb is the induced bending deflection at midspan and

 

ε0 the eccentricity of P from the centroid of the cross section.

Torsion

The angle of twist of wood members about the longitudinal

axis can be computed by

 θ = TL

GK (8–9)

where θ is angle of twist in radians, T applied torque, L

member length, G shear modulus (use G G LR LT , or approximate G by EL/16 if measured G is not available), and K

a cross-section shape factor. For a circular cross section,

K is the polar moment of inertia:

 

K D = π 4

32 (8–10)

where D is diameter. For a rectangular cross section,

 

K hb =

3

φ (8–11)

where h is larger cross-section dimension, b is smaller crosssection dimension, and φ is given in Figure 8–3.

Stress Equations

The equations presented here are limited by the assumption

that stress and strain are directly proportional (Hooke’s law)

and by the fact that local stresses in the vicinity of points of

support or points of load application are correct only to the

extent of being statically equivalent to the true stress distribution (St. Venant’s principle). Local stress concentrations

must be separately accounted for if they are to be limited in

design.

Axial Load

Tensile Stress

Concentric axial load (along the line joining the centroids of

the cross sections) produces a uniform stress:

 f P

A t = (8–12)

where ft is tensile stress, P axial load, and A cross-sectional

area.

Short-Block Compressive Stress

Equation (8–12) can also be used in compression if the

member is short enough to fail by simple crushing without

deflecting laterally. Such fiber crushing produces a local

“wrinkle” caused by microstructural instability. The member

as a whole remains structurally stable and able to bear load.

Bending

The strength of beams is determined by flexural stresses

caused by bending moment, shear stresses caused by shear

load, and compression across the grain at the end bearings

and load points.

8

7

6

5

4

3

φ

0 0.2 0.4 0.6 0.8 1.0

b/h

b

h

Figure 8–3. Coefficient φ for determining torsional

rigidity of rectangular member (Eq. (8 –11)).
8–5

Straight Beam Stresses

The stress due to bending moment for a simply supported

pin-ended beam is a maximum at the top and bottom edges.

The concave edge is compressed, and the convex edge is

under tension. The maximum stress is given by

 f M

Z b = (8–13)

where fb is bending stress, M bending moment, and Z beam

section modulus (for a rectangular cross section, Z = bh2/6;

for a circular cross section, Z = πD3/32).

This equation is also used beyond the limits of Hooke’s law

with M as the ultimate moment at failure. The resulting

pseudo-stress is called the “modulus of rupture,” values of

which are tabulated in Chapter 4. The modulus of rupture

has been found to decrease with increasing size of member.

(See Size Effect section.)

The shear stress due to bending is a maximum at the centroidal axis of the beam, where the bending stress happens to

be zero. (This statement is not true if the beam is tapered—

see following section.) In wood beams this shear stress may

produce a failure crack near mid-depth running along the axis

of the member. Unless the beam is sufficiently short and

deep, it will fail in bending before shear failure can develop;

but wood beams are relatively weak in shear, and shear

strength can sometimes govern a design. The maximum

shear stress is

 

f k V

A s = (8–14)

where f s is shear stress, V vertical shear force on cross section, A cross-sectional area, and k = 3/2 for a rectangular

cross section or k = 4/3 for a circular cross section.

Tapered Beam Stresses

For beams of constant width that taper in depth at a slope

less than 25°, the bending stress can be obtained from Equation (8–13) with an error of less than 5%. The shear stress,

however, differs markedly from that found in uniform beams.

It can be determined from the basic theory presented by Maki

and Kuenzi (1965). The shear stress at the tapered edge can

reach a maximum value as great as that at the neutral axis at

a reaction.

Consider the example shown in Figure 8–4, in which concentrated loads farther to the right have produced a support

reaction V at the left end. In this case the maximum stresses

occur at the cross section that is double the depth of the

beam at the reaction. For other loadings, the location of the

cross section with maximum shear stress at the tapered edge

will be different.

For the beam depicted in Figure 8–4, the bending stress is

also a maximum at the same cross section where the shear

stress is maximum at the tapered edge. This stress situation

also causes a stress in the direction perpendicular to the

neutral axis that is maximum at the tapered edge. The effect

of combined stresses at a point can be approximately accounted for by an interaction equation based on the Henky–

von Mises theory of energy due to the change of shape. This

theory applied by Norris (1950) to wood results in

 

f

F

f

F

f

F

x

x

xy

xy

y

y

2

2

2

2

2

2 ++= 1 (8–15)

where fx is bending stress, fy stress perpendicular to the

neutral axis, and fxy shear stress. Values of Fx, Fy, and Fxy are

corresponding stresses chosen at design values or maximum

values in accordance with allowable or maximum values

being determined for the tapered beam. Maximum stresses in

Values of h0/h

1.0 7/8 3/4 2/3 1/2 1/4

V 7/16α

3/4α

8/9α

α

α

α = 3/4α 3V

2bh0

h0

M = Vx

h = h0 + x tan θ

yl θ y

Particular tapered beam where

y

x1

x

 Figure 8–4. Shear stress distribution for a tapered beam.
 8–6

the beam depicted in Figure 8–4 are given by

 

f M

bh

f f

f f

x

xy x

y x

=

=

=

3

2 0

2

2

tan

tan

θ

θ

 (8–16)

Substitution of these equations into the interaction Equation

(8–15) will result in an expression for the moment capacity

M of the beam. If the taper is on the beam tension edge, the

values of fx and fy are tensile stresses.

Example: Determine the moment capacity (newton-meters)

of a tapered beam of width b = 100 mm, depth

h0 = 200 mm, and taper tan θ = 1/10. Substituting these

dimensions into Equation (8–16) (with stresses in pascals)

results in

 

f M

f M

f M

x

xy

y

=

=

=

375

37 5

3 75

.

.

Substituting these into Equation (8–15) and solving for M

results in

 

M

F FF x xy y

=

+ + [ ]

1

3 75 10 10 1 42 22 2 1 2

. /

where appropriate allowable or maximum values of the F

stresses (pascals) are chosen.

Size Effect

The modulus of rupture (maximum bending stress) of wood

beams depends on beam size and method of loading, and the

strength of clear, straight-grained beams decreases as size

increases. These effects were found to be describable by

statistical strength theory involving “weakest link” hypotheses and can be summarized as follows: For two beams under

two equal concentrated loads applied symmetrical to the

midspan points, the ratio of the modulus of rupture of beam

1 to the modulus of rupture of beam 2 is given by

 

 

R

R

h L ma L

h L ma L

m

1

2

22 2 2

11 1 1

1

1

1 = ++





 



 ( )

( )

/

 (8–17)

where subscripts 1 and 2 refer to beam 1 and beam 2, R is

modulus of rupture, h beam depth, L beam span, a distance

between loads placed a/2 each side of midspan, and m a

constant. For clear, straight-grained Douglas-fir beams,

m = 18. If Equation (8–17) is used for beam 2 size (Ch. 4)

loaded at midspan, then h2 = 5.08 mm (2 in.),

L2 = 71.112 mm (28 in.), and a2 = 0 and Equation (8–17)

becomes

 

R

R h L ma L

m

1

2 11 1 1

1

361 29

1 = +





 



 .

( )

/

(metric) (8–18a)

 

R

R h L ma L

m

1

2 11 1 1

1

56

1 = +





 



 ( )

/

(inch–pound) (8–18b)

Example: Determine modulus of rupture for a beam 10 in.

deep, spanning 18 ft, and loaded at one-third span points

compared with a beam 2 in. deep, spanning 28 in., and

loaded at midspan that had a modulus of rupture of

10,000 lb/in2. Assume m = 18. Substituting the dimensions

into Equation (8–18) produces

 

R1

1 18

10 000 56

2 160 1 6

7 330

= +





 





=

, ,( )

,

/

lb/in2

Application of the statistical strength theory to beams under

uniformly distributed load resulted in the following relationship between modulus of rupture of beams under uniformly

distributed load and modulus of rupture of beams under

concentrated loads:

 

R

R

a L hL

h L

u

c

c c cc

u u

=

( ) +















1 18

3 876

1 18

.

/

 (8–19)

where subscripts u and c refer to beams under uniformly

distributed and concentrated loads, respectively, and other

terms are as previously defined.

Shear strength for non-split, non-checked, solid-sawn, and

glulam beams also decreases as beam size increases. A relationship between beam shear τ and ASTM shear block

strength τASTM, including a stress concentration factor for the

re-entrant corner of the shear block, Cf, and the shear area A,

is

 

τ

τ = 1 9

1 5

.

/

C

A

f ASTM (metric) (8–20a)

 

τ

τ = 1 3

1 5

.

/

C

A

f ASTM (inch–pound) (8–20b)

where τ is beam shear (MPa, lb/in2), Cf stress concentration

factor, τASTM ASTM shear block strength (MPa, lb/in2), and

A shear area (cm2, in2).

This relationship was determined by empirical fit to test

data. The shear block re-entrant corner concentration factor is

approximately 2; the shear area is defined as beam width

multiplied by the length of beam subjected to shear force.

Effect of Notches, Slits, and Holes

In beams having notches, slits, or holes with sharp interior

corners, large stress concentrations exist at the corners. The

local stresses include shear parallel to grain and tension
8–7

perpendicular to grain. As a result, even moderately low

loads can cause a crack to initiate at the sharp corner and

propagate along the grain. An estimate of the crack-initiation

load can be obtained by the fracture mechanics analysis of

Murphy (1979) for a beam with a slit, but it is generally

more economical to avoid sharp notches entirely in wood

beams, especially large wood beams, since there is a size

effect: sharp notches cause greater reductions in strength for

larger beams. A conservative criterion for crack initiation for

a beam with a slit is

 

h A M

bh

B V

bh

6 3

2

1 2





 



 + 



 





















= (8–21)

where h is beam depth, b beam width, M bending moment,

and V vertical shear force, and coefficients A and B are presented in Figure 8–5 as functions of a/h, where a is slit

depth. The value of A depends on whether the slit is on the

tension edge or the compression edge. Therefore, use either

At or Ac as appropriate. The values of A and B are dependent

upon species; however, the values given in Figure 8–5 are

conservative for most softwood species.

Effects of Time: Creep Rupture,

Fatigue, and Aging

See Chapter 4 for a discussion of fatigue and aging. Creep

rupture is accounted for by duration-of-load adjustment in the

setting of allowable stresses, as discussed in Chapters 4

and 6.

Water Ponding

Ponding of water on roofs can cause increases in bending

stresses that can be computed by the same amplification

factor (Eq. (8–6)) used with deflection. (See Water Ponding

in the Deformation Equations section.)

Combined Bending and Axial Load

Concentric Load

Equation (8–7) gives the effect on deflection of adding an end

load to a simply supported pin-ended beam already bent by

transverse loads. The bending stress in the member is modified by the same factor as the deflection:

 

f f

P P b

b

cr

= ±

0

1 (8–22)

where the plus sign is chosen if the axial load is tension and

the minus sign is chosen if the axial load is compression, fb

is net bending stress from combined bending and axial load,

fb0 bending stress without axial load, P axial load, and Pcr

the buckling load of the beam under axial compressive load

only (see Axial Compression in the Stability Equations

section), based on flexural rigidity about the neutral axis

perpendicular to the direction of the bending loads. This Pcr

is not necessarily the minimum buckling load of the member. If P is compressive, the possibility of buckling under

combined loading must be checked. (See Interaction of

Buckling Modes.)

The total stress under combined bending and axial load is

obtained by superposition of the stresses given by

Equations (8–12) and (8–22).

Example: Suppose transverse loads produce a bending stress

fb0 tensile on the convex edge and compressive on the concave edge of the beam. Then the addition of a tensile axial

force P at the centroids of the end sections will produce a

maximum tensile stress on the convex edge of

 

f f

P P

P

A t b

cr

max = +

+ 0

1

and a maximum compressive stress on the concave edge of

 

f f

P P

P

A c

b

cr

max = + − 0

1

where a negative result would indicate that the stress was in

fact tensile.

Eccentric Load

If the axial load is eccentrically applied, then the bending

stress fb0 should be augmented by ±Pε0/Z, where ε0 is

eccentricity of the axial load.

Example: In the preceding example, let the axial load be

eccentric toward the concave edge of the beam. Then the

maximum stresses become

 

f f PZ

P P

P

A t

b

cr

max = −

+

+ 0 0

1

ε

 

f f PZ

P P

P

A c

b

cr

max = −

+ − 0

1

ε 0

2.0 0.007

B

At

Ac

1.5

1.0

0.5

0

a h

0.1 0.2 0.3 0.4 0.5 0.6

a/h

A or 

B (x10-4 (kPa mm )-1)

0.006

0.005

0.004

0.003

0.002

0.001

0

A or 

B ((lb/in2 in. )-1)

Figure 8–5. Coefficients A and B for crackinitiation criterion (Eq. (8–21)).
 8–8

Torsion

For a circular cross section, the shear stress induced by

torsion is

 

f T

D s = 16

3 π

 (8–23)

where T is applied torque and D diameter. For a rectangular

cross section,

 

f T

hb s = β 2 (8–24)

where T is applied torque, h larger cross-section dimension,

and b smaller cross-section dimension, and β is presented in

Figure 8–6.

Stability Equations

Axial Compression

For slender members under axial compression, stability is

the principal design criterion. The following equations are for

concentrically loaded members. For eccentrically loaded

columns, see Interaction of Buckling Modes section.

Long Columns

A column long enough to buckle before the compressive

stress P/A exceeds the proportional limit stress is called a

“long column.” The critical stress at buckling is calculated

by Euler’s formula:

 

f E

L r

L

cr 2 ( ) = π2

 (8–25)

where EL is elastic modulus parallel to the axis of the member, L unbraced length, and r least radius of gyration (for a

rectangular cross section with b as its least dimension,

 

r b = / 12 , and for a circular cross section, r = d/4).

Equation (8–25) is based on a pinned-end condition but may

be used conservatively for square ends as well.

Short Columns

Columns that buckle at a compressive stress P/A beyond the

proportional limit stress are called “short columns.” Usually

the short column range is explored empirically, and appropriate design equations are proposed. Material of this nature

is presented in USDA Technical Bulletin 167 (Newlin and

Gahagan 1930). The final equation is a fourth-power parabolic function that can be written as

 

f F L

r

F

EL

cr c

c = − 































1 4

27 4

4

π

 (8–26)

where Fc is compressive strength and remaining terms are

defined as in Equation (8–25). Figure 8–7 is a graphical

representation of Equations (8–25) and (8–26).

Short columns can be analyzed by fitting a nonlinear function

to compressive stress–strain data and using it in place of

Hooke’s law. One such nonlinear function proposed by

Ylinen (1956) is

 

ε= − − − 



 





















F

E

c f

F

c f

L F e cc c

( )log 1 1 (8–27)

where ε is compressive strain, f compressive stress, c a

constant between 0 and 1, and EL and Fc are as previously

defined. Using the slope of Equation (8–27) in place of EL in

Euler’s formula (Eq. (8–25)) leads to Ylinen’s buckling

equation

 

f F f

c

F f

c

F f

c cr

c e c e ce = + −  +



 



 − 2 2

2

 (8–28)

5

4

3

2

0 0.2 0.4 0.8 0.6 1.0

b/h

h

b

β Figure 8–6. Coefficient β for computing maximum shear

stress in torsion of rectangular member (Eq. (8 –24)).

1.0

0.8

0.667

0.6

0.4

0.2

0 2 4 6 8 10 12 14

3.85

FPL fourth-power formula

Euler's formula fcr/Fc

Fc

EL

L

r

Figure 8–7. Graph for determining critical buckling

stress of wood columns.
8–9

where Fc is compressive strength and fe buckling stress given

by Euler’s formula (Eq. (8–25)). Equation (8–28) can be

made to agree closely with Figure 8–7 by choosing

c = 0.957.

Comparing the fourth-power parabolic function

Equation (8–26) to experimental data indicates the function

is nonconservative for intermediate L/r range columns. Using

Ylinen’s buckling equation with c = 0.8 results in a better

approximation of the solid-sawn and glued-laminated data.

Built-Up and Spaced Columns

Built-up columns of nearly square cross section with the

lumber nailed or bolted together will not support loads as

great as if the lumber were glued together. The reason is that

shear distortions can occur in the mechanical joints.

If built-up columns are adequately connected and the axial

load is near the geometric center of the cross section, Equation (8–28) is reduced with a factor that depends on the type

of mechanical connection. The built-up column capacity is

 

 

f K F f

c

F f

c

F f

c cr

c e c e ce = + −  +



 



 −





















f 2 2

2

 (8–29)

where Fc, fe, and c are as defined for Equation (8–28). Kf is

the built-up stability factor, which accounts for the efficiency

of the connection; for bolts, Kf = 0.75, and for nails,

Kf = 0.6, provided bolt and nail spacing requirements meet

design specification approval.

If the built-up column is of several spaced pieces, the spacer

blocks should be placed close enough together, lengthwise in

the column, so that the unsupported portion of the spaced

member will not buckle at the same or lower stress than that

of the complete member. “Spaced columns” are designed

with previously presented column equations, considering

each compression member as an unsupported simple column;

the sum of column loads for all the members is taken as the

column load for the spaced column.

Columns With Flanges

Columns with thin, outstanding flanges can fail by elastic

instability of the outstanding flange, causing wrinkling of the

flange and twisting of the column at stresses less than those

for general column instability as given by Equations (8–25)

and (8–26). For outstanding flanges of cross sections such as

I, H, +, and L, the flange instability stress can be estimated

by

 

f E t

b2 cr = 0 044

2

. (8–30)

where E is column modulus of elasticity, t thickness of the

outstanding flange, and b width of the outstanding flange. If

the joints between the column members are glued and reinforced with glued fillets, the instability stress increases to as

much as 1.6 times that given by Equation (8–30).

Bending

Beams are subject to two kinds of instability: lateral–

torsional buckling and progressive deflection under water

ponding, both of which are determined by member stiffness.

Water Ponding

Roof beams that are insufficiently stiff or spaced too far apart

for their given stiffness can fail by progressive deflection

under the weight of water from steady rain or another continuous source. The critical beam spacing Scr is given by

 

S m EI

L cr = πρ

4

4 (8–31)

where E is beam modulus of elasticity, I beam moment of

inertia, ρ density of water (1,000 kg/m3, 0.0361 lb/in3),

L beam length, and m = 1 for simple support or m = 16/3 for

fixed-end condition. To prevent ponding, the beam spacing

must be less than Scr.

Lateral–Torsional Buckling

Since beams are compressed on the concave edge when bent

under load, they can buckle by a combination of lateral

deflection and twist. Because most wood beams are rectangular in cross section, the equations presented here are for

rectangular members only. Beams of I, H, or other built-up

cross section exhibit a more complex resistance to twisting

and are more stable than the following equations would

predict.

Long Beams—Long slender beams that are restrained

against axial rotation at their points of support but are otherwise free to twist and to deflect laterally will buckle when the

maximum bending stress fb equals or exceeds the following

critical value:

 

f EL

b cr = π

α

2

2 (8–32)

where α is the slenderness factor given by

 

 

α π = 2 4

EI

GK

L h

b

y e (8–33)

where EI y is lateral flexural rigidity equal to E hb L

3 12,

h is beam depth, b beam width, GK torsional rigidity defined in Equation (8–9), and 

Le effective length determined by

type of loading and support as given in Table 8–2. Equation

(8–32) is valid for bending stresses below the proportional

limit.

Short Beams—Short beams can buckle at stresses beyond

the proportional limit. In view of the similarity of

Equation (8–32) to Euler’s formula (Eq. (8–25)) for column

buckling, it is recommended that short-beam buckling be

analyzed by using the column buckling criterion in

Figure 8–7 applied with α in place of L/r on the abscissa
 8–10

and f b cr / F b in place of fcr /Fc on the ordinate. Here F b is

beam modulus of rupture.

Effect of Deck Support—The most common form of support against lateral deflection is a deck continuously attached

to the top edge of the beam. If this deck is rigid against shear

in the plane of the deck and is attached to the compression

edge of the beam, the beam cannot buckle. In regions where

the deck is attached to the tension edge of the beam, as where

a beam is continuous over a support, the deck cannot be

counted on to prevent buckling and restraint against axial

rotation should be provided at the support point.

If the deck is not very rigid against in-plane shear, as for

example standard 38-mm (nominal 2-in.) wood decking,

Equation (8–32) and Figure 8–7 can still be used to check

stability except that now the effective length is modified by

dividing by θ, as given in Figure 8–8. The abscissa of this

figure is a deck shear stiffness parameter τ given by

 

τ =

SG L

EI y

D

2

 (8–34)

where EI y is lateral flexural rigidity as in Equation (8–33),

S beam spacing, GD in-plane shear rigidity of deck (ratio of

shear force per unit length of edge to shear strain), and

L actual beam length. This figure applies only to simply

supported beams. Cantilevers with the deck on top have their

tension edge supported and do not derive much support from

the deck.

Interaction of Buckling Modes

When two or more loads are acting and each of them has a

critical value associated with a mode of buckling, the combination can produce buckling even though each load is less

than its own critical value.

The general case of a beam of unbraced length le includes a

primary (edgewise) moment M1, a lateral (flatwise) moment

M2, and axial load P. The axial load creates a secondary

moment on both edgewise and flatwise moments due to the

deflection under combined loading given by Equation (8–7).

In addition, the edgewise moment has an effect like the

secondary moment effect on the flatwise moment.

The following equation contains two moment modification

factors, one on the edgewise bending stress and one on the

flatwise bending stress that includes the interaction of biaxial

bending. The equation also contains a squared term for axial

load to better predict experimental data:

 

 

f

F

f edf

F

f edf

F

c

c

b c

c1

b c

c2





 



 +

+ −

′

+

+ −

′ ≤

2

1 11 1

1

2 22 2

2

6 1 234 0 234

6 1 234 0 234

1 0

( / ) (. . )

( / ) (. . ) .

c

b

c

b

θ

θ

θ

θ

 (8–35)

where f is actual stress in compression, edgewise bending, or

flatwise bending (subscripts c, b1, or b2, respectively), F

buckling strength in compression or bending (a single prime

denotes the strength is reduced for slenderness), e/d ratio of

eccentricity of the axial compression to member depth ratio

for edgewise or flatwise bending (subscripts 1 or 2, respectively), and θc moment magnification factors for edgewise

and flatwise bending, given by

Table 8–2. Effective length for checking lateral–

torsional stability of beamsa

Support Load

Effective

length Le

Simple support Equal end moments L

Concentrated force at

center

 

0.742

1 2

L

− h L

Uniformly distributed force

 

0.887

1 2

L

− h L

Cantilever Concentrated force at end

 

0.783

1 2

L

− h L

Uniformly distributed force

 

0.489

1 2

L

− h L

a

These values are conservative for beams with a

 width-to-depth ratio of less than 0.4. The load is

 assumed to act at the top edge of the beam.

10

8

6

4

2

0 100 200 300 400 500 600 700 800

θ

τ

1

Case 3

Case 2

Case 1

3

2

Case

Figure 8–8. Increase in buckling stress resulting from

attached deck; simply supported beams. To apply

this graph, divide the effective length by θ.
8–11

 

θc c

cr

S

S 1

1

= −1 ′′+ 









 f

Fc

(8–36)

 

θc c c 2

2

1 11

1

1 6 = − ′′ +

+

′′





 



 f

F

f edf

c F

b

b

( ) (8–37)

 

F′′ = E

l d c

e

1

1 1

2

0 822 .

( ) (8–38)

 

F′′ = E

l d c

e

2

2 2

2

0 822 .

( ) (8–39)

 

F′′ = E

l

d

d b

e

1

2

1

1 44 . (8–40)

where le is effective length of member and S and Scr a r e 

previously defined ponding beam spacing.

References

ASTM. [current edition]. Standard methods for testing clear

specimens of timber. ASTM D143–94. West Conshohocken, PA: American Society for Testing and Materials.

Bohannan, B. 1966. Effect of size on bending strength of

wood members. Res. Pap. FPL–RP–56. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Gerhardt, T.D.; Liu, J.Y. 1983. Orthotropic beams under

normal and shear loading. Journal of Engineering Mechanics,

ASCE. 109(2): 394–410.

Kuenzi, E.W.; Bohannan, B. 1964. Increases in deflection

and stress caused by ponding of water on roofs. Forest Products Journal. 14(9): 421–424.

Liu, J.Y. 1980. Shear strength of wood beams: A Weibull

analysis. Journal of Structural Division, ASCE. 106(ST10):

2035– 2052.

Liu, J.Y. 1981. Shear strength of tapered wood beams.

Journal of Structural Division, ASCE. 107(ST5): 719–731.

Liu, J.Y. 1982. A Weibull analysis of wood member bending strength. Transactions, American Society of Mechanical

Engineers. Journal of Mechanical Design. 104: 572–579.

Liu, J.Y. 1984. Evaluation of the tensor polynomial

strength theory for wood. Journal of Composite Materials.

18(3): 216–226. (May).

Liu, J.Y.; Cheng, S. 1979. Analysis of orthotropic beams.

Res. Pap. FPL–RP–343. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Maki, A C.; Kuenzi, E.W. 1965. Deflection and stresses of

tapered wood beams. Res. Pap. FPL–RP–34. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Malhorta, S.K.; Sukumar, A.P. 1989. A simplied procedure for built-up wood compression members. St. Johns,

New Foundland: Annual conference, Canadian Society for

Civil Engineering: 1–18 (June).

Murphy, J.F. 1979. Using fracture mechanics to predict

failure of notched wood beams. In: Proceedings of first international conference on wood fracture; 1978, Aug. 14–16;

Banff, AB. Vancouver, BC: Forintek Canada Corporation:

159: 161–173.

Newlin, J.A.; Gahagan, J.M. 1930. Tests of large timber

columns and presentation of the Forest Products Laboratory

column formula. Tech. Bull. 167. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Newlin, J.A.; Trayer, G.W. 1924. Deflection of beams

with special reference to shear deformations. Rep. 180.

Washington, DC: U.S. National Advisory Committee on

Aeronautics.

Norris, C.B. 1950. Strength of orthotropic materials subjected to combined stresses. Rep. 1816. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Rammer, D.R.; Soltis, L.A. 1994. Experimental shear

strength of glued-laminated beams. Res. Rep. FPL–RP–527.

Madison, WI, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Rammer, D.R.; Soltis, L.A.; Lebow, P.K. 1996. Experimental shear strength of unchecked solid sawn Douglas-fir.

Res. Pap. FPL–RP–553. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Soltis, L.A., Rammer, D.R. 1997. Bending to shear ratio

approach to beam design. Forest Products Journal. 47(1):

104–108.

Trayer, G.W. 1930. The torsion of members having sections common in aircraft construction. Rep. 334.

Washington, DC: U.S. National Advisory Committee on

Aeronautics.

Trayer, G.W.; March, H.W. 1931. Elastic instability of

members having sections common in aircraft construction.

Rep. 382. Washington, DC: U.S. National Advisory

Committee on Aeronautics.

Ylinen, A. 1956. A method of determining the buckling

stress and the required cross-sectional area for centrally

loaded straight columns in elastic and inelastic range.

Publication of the International Association for Bridge and

Structural Engineering. Zurich. Vol. 16.

Zahn, J.J. 1973. Lateral stability of wood beam-and-deck

systems. Journal of the Structural Division, ASCE.

99(ST7): 1391–1408.

Zahn, J.J. 1986. Design of wood members under combined

loads. Journal of Structural Engineering, ASCE. 112(ST9):

2109–2126.

Zahn, J.J. 1988. Combined-load stability criterion for wood

beam-columns. Journal of Structural Engineering, ASCE.

114(ST11): 2612–2628.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
9–1

Chapter 9

Adhesive Bonding of

Wood Materials

Charles B. Vick

Contents

Adhesion to Wood 9–1

Surface Properties of Wood Adherends 9–2

Extractives on Surfaces 9–3

Knife- and Abrasive-Planed Surfaces 9–3

Veneer Surfaces 9–4

Surfaces of Wood and Nonwood Composite Products 9–5

Physical Properties of Wood Adherends 9–6

Density and Porosity 9–6

Moisture Content and Dimensional Changes 9–7

Adhesives 9–9

Composition 9–9

Health and Safety 9–10

Strength and Durability 9–10

Adhesive Selection 9–12

Bonding Process 9–15

Moisture Content Control 9–15

Surface Preparation 9–16

Adhesive Spreading 9–16

Assembly and Pressing 9–16

Post-Cure Conditioning 9–18

Bonded Joints 9–18

Edge-Grain Joints 9–18

End-Grain Joints 9–18

End-to-Edge-Grain Joints 9–19

Construction Joints 9–19

Testing and Performance 9–20

Analytic Chemical and Mechanical Testing

of Polymers 9–20

Mechanical Testing of Bonded Assemblies 9–20

Short- and Long-Term Performance 9–21

Product Quality Assurance 9–22

References 9–23

dhesive bonding of wood components has played

an essential role in the development and growth of

the forest products industry and has been a key

factor in the efficient utilization of our timber resource. The

largest use of adhesives is in the construction industry. By

far, the largest amounts of adhesives are used to manufacture

building materials, such as plywood, structural flakeboards,

particleboards, fiberboards, structural framing and timbers,

architectural doors, windows and frames, factory-laminated

wood products, and glass fiber insulation. Adhesives are

used in smaller amounts to assemble building materials in

residential and industrial construction, particularly in panelized floor and wall systems. Significant amounts are also

used in nonstructural applications, such as floor coverings,

countertops, ceiling and wall tile, trim, and accessories.

Adhesives can effectively transfer and distribute stresses,

thereby increasing the strength and stiffness of the composite.

Effective transfer of stress from one member to another depends on the strength of the links in an imaginary chain of an

adhesive-bonded joint. Thus, performance of the bonded

joint depends on how well we understand and control the

complexity of factors that constitute the individual links—

wood, adhesive, and the interphasing regions between—

which ultimately determine the strength of the chain.

Adhesion to Wood

The American Society for Testing and Materials (ASTM)

defines an adhesive as a substance capable of holding

materials together by surface attachment. An adherend is a

substrate held to another substrate by an adhesive. Adhesion

is the state in which two surfaces are held together by interfacial forces, which may be valence forces, interlocking action,

or both. Valence forces are forces of attraction produced by

the interactions of atoms, ions, and molecules that exist

within and at the surfaces of both adhesive and adherend.

Interlocking action, also called mechanical bonding, means

surfaces are held together by an adhesive that has penetrated

the porous surface while it is liquid, then anchored itself

during solidification. The extent to which valence forces and

interlocking action develop between adhesive polymers and

wood adherends is uncertain, but both are generally acknowledged as essential for the most effective bonding. Bonding to

porous surfaces, such as wood, paper, and textiles, was
 9–2

thought to be primarily mechanical, but now there is

evidence supporting bonding by primary valence forces. In

contrast, bonding to hard metal surfaces was believed to

involve only valence forces, but this is no longer the accepted view. Metal surfaces roughened by chemical etching

or made microscopically porous with a layer of oxide are

capable of mechanical interlocking with an adhesive to produce exceptionally strong and durable bonds.

Mechanical interlocking is probably the primary mechanism

by which adhesives adhere to porous structures, such as

wood. Effective mechanical interlocking takes place when

adhesives penetrate beyond the surface debris and damaged

fibers into sound wood two to six cells deep. Deeper penetration into the fine microstructure increases the surface area of

contact between adhesive and wood for more effective mechanical interlocking. The most durable structural bonds to

wood are believed to develop not only when an adhesive

penetrates deeply into cell cavities, but also when an adhesive diffuses into cell walls to make molecular-level contact

with the hemicellulosics and cellulosics of wood. If an adhesive penetrates deeply enough into sound wood and becomes

rigid enough upon curing, the strength of the bond can be

expected to exceed the strength of the wood.

Physical forces of attraction composed of three intermolecular

attraction forces are believed to be important to the formation

of bonds between adhesive polymers and molecular structures

of wood. Generally called van der Waal’s forces, these include dipole–dipole forces, which are positively and negatively charged polar molecules that have strong attractions for

other polar molecules; London forces, which include the

weaker forces of attraction that nonpolar molecules have for

each other; and hydrogen bonding, a special type of dipole–

dipole force that accounts for strong attractions between

positively charged hydrogen atoms of one polar molecule and

the electronegative atom of another molecule. Hydrogen

bonding forces are important in the interfacial attraction of

polar adhesive polymers for the hemicellulosics and cellulosics, which are rich with polar hydroxyl groups. These

physical forces of attraction, sometimes referred to as specific

adhesion, are particularly important in wetting of water

carriers and adsorption of adhesive polymers onto the molecular structures of wood.

Covalent chemical bonds form when atoms of nonmetals

interact by sharing electrons to form molecules. The simplest

example of a purely covalent bond is the sharing of electrons

by two hydrogen atoms to form hydrogen. These covalent

bonds are the strongest of chemical bonds; they are more

than 11 times the strength of the hydrogen bond. Even

though covalent chemical bonds between adhesive polymer

and the molecular structure of wood seem a possibility, there

is no clear evidence that such bonds constitute an important

mechanism in adhesive bonding to wood.

For two wood adherends to be held together with maximum

strength, a liquid adhesive must wet and spread freely to

make intimate contact with both surfaces. Molecules of the

adhesive must diffuse over and into each surface to make

contact with the molecular structure of wood so that

intermolecular forces of attraction between adhesive and wood

can become effective. As will be discussed later, wood adherends, as well as other materials, differ widely in their attractive energies, bulk properties, surface roughness, and surface

chemistry. Wood surfaces may appear to be smooth and flat,

but on microscopic examination, they become peaks, valleys, and crevices, littered with loose fibers and other debris.

Such surface conditions cause gas pockets and blockages that

prevent complete wetting by the adhesive and introduce

stress concentrations when the adhesive has cured. Thus, the

liquid adhesive must have high wettability, coupled with a

viscosity that will produce good capillary flow to penetrate

sound wood structure, while displacing and absorbing air,

water, and contaminants at the surface. Pressure is normally

used to enhance wetting by forcing liquid adhesive to flow

over the surfaces, displace air blockages, and penetrate to

sound wood.

Wetting of a surface occurs when the contact angle (the angle

between the edge of a drop of adhesive and the surface of

wood) approaches zero. The contact angle approaches zero

when the surface has high attractive energy, the adhesive has

an affinity for the adherend, and the surface tension of the

adhesive is low. If a drop of adhesive spreads to a thin film

approaching zero contact angle, the adhesive has spread well

and made intimate contact with the surface. The differences in

wettabilities of various wood surfaces are illustrated by a

simple water drop test in Figure 9–1.

The process of adhesion is essentially completed after transition of the adhesive from liquid to solid form. After the

viscosity of a liquid adhesive has increased and the adhesive

has solidified to the point where the film effectively resists

shear and tensile forces tending to separate the surfaces, the

surfaces are effectively bonded. An adhesive film changes

from liquid to solid form by one of three mechanisms, although two may be involved in some curing mechanisms.

This transition can be a physical change as in thermoplastic

adhesives or it can be a chemical change as in thermosetting

adhesives. In thermoplastics, the physical change to solid

form may occur by either (a) loss of solvent from the adhesive through evaporation and diffusion into the wood, or

(b) cooling of molten adhesive on a cooler surface. In thermosets, the solid form occurs through chemical polymerization into cross-linked structures that resist softening on

heating. Most thermosetting wood adhesives contain water

as a carrier; therefore, water also must be evaporated and

absorbed by the wood so that the adhesive can cure

completely.

Surface Properties of

Wood Adherends

Because adhesives bond by surface attachment, the physical

and chemical conditions of the adherend’s surface is

extremely important to satisfactory joint performance.

Wood surfaces should be smooth, flat, and free of machine

marks and other surface irregularities, including planer skips

and crushed, torn, and chipped grain. The surface should be

free of burnishes, exudates, oils, dirt, and other debris.
9–3

Overdrying and overheating deteriorates the physical condition of the wood surfaces by forcing extractives to diffuse to

the surface, by reorienting surface molecules, and by irreversibly closing the larger micropores of cell walls. Wood

surfaces can be chemically inactivated with respect to adhesion by airborne chemical contaminants, hydrophobic and

chemically active extractives from the wood, oxidation and

pyrolysis of wood bonding sites from overdrying, and impregnation with preservatives, fire retardants, and other

chemicals. Unfortunately, some of these surface conditions

are difficult to detect. Physical deterioration and chemical

contamination interfere with essential wetting, flow, and

penetration of adhesive but can also interfere with the cure

and resulting cohesive strength of the adhesive.

Extractives on Surfaces

Extensive research indicates that extractives on wood surfaces

are the principal physical and chemical contributors to surface

inactivation, hence to poor wettability by adhesives. This is

particularly true for resinous species, such as the southern

pines and Douglas-fir. When subjected to high temperatures

during processing, extractives diffuse to the surface where

they concentrate and physically block adhesive contact with

wood. Furthermore, resinous and oily exudates are hydrophobic; that is, they repel water. Most wood adhesives

contain water as a carrier; therefore, they do not properly wet,

flow, and penetrate extractive-covered surfaces. The acidity of

extractives of some Southeast Asian hardwoods and oak

species can interfere with the chemical cure of adhesives. The

acid may accelerate the cure of an alkaline phenolic adhesive,

causing the adhesive to gel prematurely and reducing its

ability to wet, flow, and penetrate. In contrast, normal

polymerization of an acidic adhesive, such as ureaformaldehyde, can be retarded by an alkaline wood surface,

which would compromise the integrity of the adhesive film

and bond.

A simple water test can reveal much about the state of inactivation of a wood surface and how difficult it may be to wet

and bond with adhesive. As a first test, place a small drop of

water on the surface and observe how it spreads and absorbs.

If the drop remains a bead and does not begin to spread

within 30 s, the surface is resistant to adhesive wetting

(Fig. 9–1). Another water drop test can be used to estimate

the degree of surface inactivation of veneer. Place a drop of

water in an area on the earlywood of a flat-grain surface that

does not have checks or splits in the area of the drop. Good

wettability is indicated if the drop is absorbed within

20 min. If the drop has spread out but some water still remains on the surface after 40 min, then bonding problems are

likely to occur. If after 40 min the water drop still retains

much of its original shape with little spreading, then bonding problems from surface inactivation is a certainty.

Knife- and Abrasive-Planed Surfaces

Wood should be surfaced or resurfaced within 24 h before

bonding to remove extractives and other physical and chemical contaminants that interfere with bonding. Surfacing also

removes any unevenness that may have occurred from

changes in moisture content. Parallel and flat surfaces allow

the adhesive to flow freely and form a uniformly thin layer of

adhesive that is essential to the best performance of waterbased wood adhesives.

Figure 9–1. A simple water drop test shows differences in the wettability of a yellow birch veneer surface.

Three drops were applied to the surface at the same time, then photographed after 30 s. The drop on the left

retains a large contact angle on the aged, unsanded surface; the drop in the center has a smaller contact angle

and improved wettability after the surface is renewed by two passes with 320-grit sandpaper; the drop on the right

shows a small contact angle and good wettability after four passes with the sandpaper.
 9–4

Experience and testing have proven that a smooth, knife-cut

surface is best for bonding. Surfaces made by saws usually

are rougher than those made by planers and jointers. However, surfaces sawn with special blades on properly set

straight-line ripsaws are satisfactory for both structural and

nonstructural joints. Precision sawing of wood joints rather

than two-step sawing and jointing is commonplace in furniture manufacture for purposes of reducing costs for labor,

equipment, and material. Unless the saws and feed works are

well maintained, however, joints made with sawed surfaces

will be weaker and less uniform in strength than those made

with sharp planer or jointer knives. Dull cutting edges of

planer or jointer knives crush and burnish the wood surface.

The crushed and burnished surface inhibits adhesive wetting

and penetration. If the adhesive does not completely penetrate

crushed cells to restore their original strength, a weak joint

results. Another simple water test can be used to detect a

surface that has been damaged during machining. Wipe a

very wet rag over a portion of the surface. After waiting for a

minute, remove any remaining water by blotting with a

paper towel. Then compare the roughness of the wet and dry

surfaces. If the wetted area is much rougher than the dry area,

then the surface has been damaged in machining. This damage will significantly reduce the strength of adhesive-bonded

joints.

Abrasive planing with grit sizes from 24 to 80 causes surface

and subsurface crushing of wood cells. Figure 9–2 shows

cross sections of bondlines between undamaged, knife-planed

Douglas-fir lumber compared with surfaces damaged by

abrasive planing. Such damaged surfaces are inherently weak

and result in poor bond strength. Similar damage can be

caused by dull planer knives or saws. There is some evidence that sanding with grits finer than 100 may improve an

abrasive-planed surface. However, abrasive-planing is not

recommended for structural joints that will be subjected to

high swelling and shrinkage stresses from water soaking and

drying. If abrasive-planing is to be used before bonding, then

belts must be kept clean and sharp, and sanding dust must

be removed completely from the sanded surface.

Veneer Surfaces

The wood properties of veneer are essentially no different

from those of lumber; however, manufacturing processes,

including cutting, drying, and laminating into plywood, can

drastically change physical and chemical surface properties of

veneer. Special knowledge and attention to these characteristics are required to ensure good wetting, flow, and penetration of adhesive.

Rotary cutting produces continuous sheets of flat-grain veneer

by rotating a log by its ends against a knife. As the knife

peels veneer from the log, the knife forces the veneer away

from the log at a sharp angle, thereby breaking or checking

the veneer on the knife side. The checked side is commonly

called the loose side, and the opposite side without checking

is called the tight side. When rotary-cut veneer is used for

faces in plywood, the loose side should be bonded with the

tight side presented to view. Otherwise, open checks in the

faces produce imperfections in any finish that may be applied.

Adhesive overpenetration into lathe checks usually is not a

problem if the adhesive spread rate is adjusted correctly.

Sliced veneer is produced in long strips by moving a squared

log, called a flitch, against a knife. As in rotary cutting, the

veneer is forced by the knife away from the flitch at a sharp

angle, causing fine checking of the veneer on the knife side.

This checked surface will show imperfections in a finished

surface, so the loose side should be bonded and the tight side

finished. For book-matched face veneers, where grain patterns

of adjacent veneers are near mirror images, half the veneers

will be loosely cut and must be finished, so the veneer must

be cut as tightly as possible. Generally, hardwood face veneers are sliced to reveal the most attractive grain patterns.

Sawn veneer is produced in long narrow strips from flitches

that have been selected and sawn for attractive grain patterns.

The two sides of sawn veneer are free from knife checks, so

either surface may be bonded or exposed to view with satisfactory results.

Figure 9–2. (A) Cross section of a bonded joint between

two undamaged Douglas-fir surfaces that were planed

with a sharp knife (120X). The wood cells are open, and

their walls are distinct. The dark area at the center of

micrograph is the adhesive bondline. (B) Cross section

of a bonded joint between two damaged Douglas-fir

surfaces abrasively planed with 36-grit sandpaper.

The cells in and adjacent to the bondline are crushed,

and their walls are indistinct.
9–5

Veneer is dried promptly after cutting, using continuous,

high temperature dryers that are heated either with steam or

hot gases from wood-residue or gas-fired burners. Drying

temperatures range from 170°C to 230°C (330°F to 446°F)

for short periods. Drying veneer to very low moisture content

levels at very high temperatures and drying at moderate

temperatures for prolonged periods inactivates surfaces,

causing poor wetting of veneer, hence poor bonding of the

plywood. Residues deposited on veneer surfaces from incomplete combustion of gases and fuel oils can cause serious

adhesion problems in plywood production.

Veneer selected for its attractive appearance, or for use in

sanded grades of plywood, should be uniform in thickness,

smooth, flat, free from deep checks, knots, holes, and decay,

and have face grain suitable for the intended face grade. For

plywood of the lower grades, defect requirements are not as

restricted. For example, loosely cut veneer with frequent deep

checks and large defects is suitable for structural plywood,

but more adhesive is required than for tightly cut veneer.

Higher spread rates compensate for overpenetration of adhesive into loosely cut veneer. When rotary-cut veneer is

bonded into plywood, the tight side is usually bonded to the

loose side, except that in one bondline, the loose side must

be bonded to the loose side. This orientation permits the face

veneer to be presented with its tight side facing outward for

sanding and appearance.

Surfaces of Wood and Nonwood

Composite Products

The surfaces of wood products such as plywood, structural

flakeboard, particleboard, fiberboard, and hardboard generally

have poor wettability relative to that of freshly cut, polar

wood surfaces. Surfaces of these materials may have a glazed

appearance indicating they have been inactivated by pressing

at high temperatures. During hot pressing, resinous extractives migrate to the surface, adhesives on the outer surfaces of

particles and fibers cure, and caul release agents remain on

product surfaces—all of which inactivate or block surfaces

from being wetted by water-based wood adhesives. Furthermore, the strength of bonds to the surfaces of these products

is limited by the strength with which surface flakes, particles,

and fibers are bound to the inner flakes, particles, and fibers

of the product. A much lower bond strength can be expected

to the surfaces of products of particulate structure than to

products of natural wood structure. Adhesion to composite

panel products having poor wettability (Fig. 9–1) can be

improved by lightly sanding with 320-grit sandpaper. However, too much sanding can change a flat surface to an uneven

surface and perhaps produce too much loose-fiber debris that

would interfere with adhesion.

Metal foils and plastic films are commonly laminated to

wood panels usually by product manufacturers. Although

high cohesive strength is not required of adhesives to support

these materials in an indoor environment, adhesives still

must be reasonably compatible with both the wood and

nonwood surfaces. If a bond of greater structural integrity is

required to bond wood to heavier, rigid metals and plastics,

then only epoxy, polyurethane, and other isocyanate-based

adhesives may be sufficiently compatible with metals and

plastics. Even then, cleaning or special preparation of the

nonwood surfaces may be required to remove contaminants

and chemically activate the surfaces. Composite materials are

becoming more common as manufacturers learn to bond

dissimilar materials to gain extraordinary composite properties or cost advantages not available from a single component. Composite materials in which nonpolar thermoplastics

are successfully bonded to polar wood materials with the aid

of coupling agents are becoming commonplace.

Metals are stronger and stiffer than wood and if bonded well

enough to effectively transfer stresses between metal and

wood, the mechanical properties of wood can be enhanced by

the metal so that the resultant composite performs as a single

material. Metal has a much higher energy surface than does

wood. On exposure to air, oxides of the metal quickly form,

and with moisture, gases, and debris adsorbed from the air,

the surfaces quickly develop a low energy, weak boundary

layer. To restore the high energy surfaces, a series of cleaning

procedures are required to prepare the surfaces for structural

bonding. Steps in surface preparation include cleaning with

liquid or vapor organic solvents, abrading by sandblasting,

alkaline washing, chemical etching, and priming with adhesive solutions or coupling agents.

Plastics are organic polymers that may be either thermoplastic (soften on heating) or thermosetting (cross-linked and

resist softening on heating). Thermoplastics generally are not

as strong and stiff as wood, but thermoset materials approximate and even exceed the mechanical properties of

wood. When plastics contain fibrous reinforcing materials,

such as fiberglass, strength and stiffness of the composite

materials greatly exceed some of the mechanical properties of

wood. In so doing, reinforced plastics that are effectively

bonded to wood offer stronger and more cost-effective structural composites. The surfaces of plastics generally are low

energy, nonpolar, and hydrophobic. Traditional aqueousbased wood adhesives are polar and hydrophilic, so they do

not bond well to plastics. Epoxies, polyurethanes, and isocyanate-based adhesives are capable of bonding many plastics

to wood. Adhesion to plastic surfaces occurs primarily by

physical intermolecular attraction forces and, in some cases,

hydrogen bonding. Abrading and chemical etching of plastic

surfaces provide some mechanical interlocking, thereby

increasing adhesion. Coupling agents are particularly useful

for chemically bridging dissimilar materials. They have

molecules that are of either unlike or like functionalities that

are capable of reacting with both the adhesive and the surface

of the adherend. Treatment of plastic surfaces with an inert

gas, including oxygen plasma activated by radio-frequency

energy, cleans and activates surfaces for enhanced adhesion.

Grafting of monomers onto cleaned plastic surfaces by means

of plasma polymerization creates a polar surface that is more

compatible with adhesives.

Chemical treatment of wood with preservatives, fire retardants, and dimensional stabilizers interferes with adhesion to

the treated wood. Types of chemical treatment and adhesives,
 9–6

conditions of joint assembly and adhesive cure, and prebonding chemical surface treatments have varied, interacting,

and even strong effects on the strength and durability of

bonds. Certain combinations of these factors can lead to

excellent bonds, despite the interference from chemical

treatments.

Lumber treated with chromated copper arsenate (CCA) preservatives dominates the treated wood market; however, very

little of the CCA-treated wood is used in adhesively bonded

lumber products. Commercial adhesives do not adhere to

CCA-treated wood well enough to consistently meet rigorous industrial standards for resistance to delamination in

accelerated exterior service tests. Analytical studies have

shown that cellular surfaces of CCA-treated wood are thoroughly covered with microscopic-size deposits of mixtures of

chromium, copper, and arsenic oxides that are physicochemically fixed to cell walls. The presence of these insoluble

metallic deposits is so pervasive that intermolecular forces of

attraction that normally act between polar wood and adhesive

are physically blocked (Fig. 9–3). A new hydroxymethylated

resorcinol (HMR) coupling agent greatly improves adhesion

to CCA-treated wood when HMR is applied as a dilute

aqueous primer on lumber surfaces before bonding. The

HMR physicochemically couples phenol-resorcinol, epoxy,

emulsion polymer–isocyanate, polymeric methylene

diphenyl disocyanate, and melamine-urea adhesives to treated

wood so that bonds can meet rigorous industrial standards

for strength and durability.

Wood preservatives other than CCA, even nonacidic waterborne preservatives including emulsion types, interfere with

adhesion of hot-pressed phenolic plywood adhesives, particularly as levels of chemical retention in the wood increase.

Generally, preservatives containing boron, copper, and zinc

interfere with the cure of phenolic resins, although assembly

conditions can be optimized to improve bonding. Certain

alkyl ammonium and fluoride-based salt preservatives have

demonstrated limited interference with adhesion.

The most common fire-retarding chemicals used for wood are

inorganic salts based on phosphorous, nitrogen, and boron.

These acid salts release acid at elevated temperatures to

decrease flammable volatiles and increase char in wood,

thereby effectively reducing flame spread. A few salts release

acid at temperatures lower than fire conditions, and in the

presence of elevated temperature and moisture service conditions, increasing acidity leads to destructive hydrolysis of the

wood. The acidity of the fire-retardant-treated wood, particularly at the elevated temperature and moisture conditions of

hot-press curing, also inhibits the cure and bond formation of

alkaline phenolic adhesive. By priming treated-wood surfaces

with certain alkaline aqueous solutions before bonding and

selecting resins of appropriate molecular-size distribution,

strong and durable bonds can be made to certain fireretardant-treated woods.

Acetylation is a chemical modification of wood that drastically reduces moisture-related dimensional changes and rate

of biodeterioration. Acetic anhydride is reacted with the

hydroxyl groups of hemicelluloses and lignin of wood. For

every acetyl group reacted, one hydroxyl group is blocked

from hydrogen bonding with a water molecule, and the result

is lower affinity of acetylated wood for water. Reduced wettability from fewer available hydroxyl groups means poorer

adhesion of aqueous-based wood adhesives. Adhesion is

reduced to varying degrees among thermoplastic and thermosetting adhesives in proportion to their compatibility with

the amount of nonpolar, hydrophobic acetate groups formed

in the acetylated wood. Only room-temperature-curing resorcinolic adhesives and an acid-catalyzed phenolic hot-press

adhesive have been found to develop durable bonds to acetylated wood. All other wood adhesives develop poorer bonds

to acetylated wood than to untreated wood.

Physical Properties of

Wood Adherends

Density and Porosity

The bondability of wood is not only affected by the surface

properties of wood adherends but also by wood’s physical

properties, particularly density, porosity, moisture content,

and dimensional movement.

Wood substance without void volume has a density approximating 1.5 g/cm3

 (93.6 lb/ft3), regardless of the wood

species. But density varies greatly between wood species,

and even within a species, because species vary in void

volume and thickness of cell walls. High density woods have

thick walls and small lumen volumes, whereas low density

woods have thin walls with large lumen volumes. The

strength of wood is directly related to its density because

thick-walled cells are capable of withstanding much greater

stress than are thin-walled cells. Wood cells are an integral

Figure 9–3. Surface of cell lumen of CCA-treated

Southern Pine covered with chemically fixed

deposits of insoluble mixture of chromium, copper,

and arsenic oxides.
9–7

part of the wood–adhesive interphasing region; therefore, the

adhesive bond must be at least as strong as the wood if the

strength capability of the wood adherend is to be fully

utilized.

The strength of adhesive bonds to wood increases with wood

density up to a range of 0.7 to 0.8 g/cm3

 (43.7 to 49.9 lb/ft3)

(moisture content 12%). Above this level, joint strength

decreases. Although strength increases with wood density,

wood failure decreases gradually up to a density range

of 0.7 to 0.8 g/cm3 (43.7 to 49.9 lb/ft3), then decreases more

rapidly above 0.8 g/cm3 (49.9 lb/ft3). As wood density increases, high strength joints with high wood failure are more

difficult to achieve consistently. (Wood failure means rupture

of wood fibers during strength tests of adhesive bonds to

wood. It is usually expressed as a percentage of the total

bonded area of the joint.)

High density woods are difficult to bond for several reasons.

Because of thicker cell walls and less lumen volume, adhesives do not penetrate easily, so important mechanical interlocking of adhesives is limited to one or two cells deep.

Much greater pressure is required to compress stronger,

stiffer, high density wood to bring contact between wood

surface and adhesive. Higher concentrations of extractives

that may interfere with the cure of adhesives are common in

high density species, particularly domestic oaks and imported tropical hardwoods. The severe stresses produced by

high density species as they change dimensions with changes

in moisture content also contribute heavily to bonding

difficulties.

Density is perhaps a crude indicator, but as previously noted,

it is useful for estimating the bondability of a great variety of

wood species. Table 9–1 categorizes commonly used domestic and imported species according to their relative ease of

bonding. The categories for domestic woods are based on the

average strength of side-grain joints of lumber as determined

in laboratory tests and industrial experience. The laboratory

tests included animal, casein, starch, urea-formaldehyde, and

resorcinol-formaldehyde adhesives. The categories for imported woods are based on information found in the literature

on bond strength, species properties, extractives content, and

industrial experience. In most cases, the amount of data

available for categorizing imported woods is not equivalent

to that for domestic woods. However, a species that bonds

poorly with one adhesive may develop much better bonds

with another adhesive. A similar type of adhesive but with

somewhat different working, penetration, curing, and even

strength properties can often dramatically improve bondability of a given species. Adhesive suppliers will quite

often adjust adhesive formulations to solve specific

adhesion problems.

The void volume of wood, which can range from 46% to

80% of total volume, strongly affects the depth and direction

that an adhesive flows. To attain the highest joint strength,

the adhesive must penetrate and mechanically interlock

several cells deep into sound, undamaged cell structure. In

wood, porosity varies according to the grain direction. It is

most porous on end-grain surfaces, being many times greater

than on radial or tangential surfaces. Adhesives penetrate

deeply into open fibers and vessels along the grain, so deeply

that overpenetration occurs when pressure is applied to endgrain surfaces. This is a primary reason why it is so difficult

to form strong, load-bearing bondlines in butt joints. Across

the grain, porosity is limited because of fewer pathways in

which adhesive can flow, so overpenetration under pressure

generally is not a problem with a properly formulated

adhesive.

The porosity of hardwoods and softwoods, both as species

groups and as species within a group, varies greatly, which

dramatically affects the amount and direction of adhesive

flow. Highly porous softwoods, such as the southern pines,

have fiber lumens that are interconnected by open pits. Pits

are the small openings between fibers that permit lateral

transfer of fluids in living trees. They form a complex capillary system that also allows adhesives to penetrate deeply,

even in tangential and radial directions. The relatively large

vessels in hardwoods have no end walls, so adhesive can

penetrate indefinitely along the end grain. The remaining

fibers have relatively few pits for lateral transfer of adhesive,

except that hardwoods, such as the red oaks, have radially

oriented rays that can allow excessive flow and overpenetration. Although adhesives for hardwoods and softwoods

generally differ by chemical type according to product markets, adhesives must be specifically formulated for hardwoods

or softwoods, including specific species within the groups, or

have adjustable working properties for specific manufacturing

situations.

Moisture Content and

Dimensional Changes

Water occurs naturally in living trees—as free water in cell

lumens and as adsorbed water within cell walls. Total water

content of wood can range well above 200% (based on ovendry weight), but when the free water is removed from cell

lumens by drying, approximately 30% remains bound within

cell walls. Water has strong molecular attraction to wood,

primarily through hydrogen bonding with hydroxyl groups

of wood cellulosics. Therefore, cell walls remain saturated

with moisture (called the fiber saturation point) until the

moisture content of the surrounding air falls below that of

saturated cell walls. Actual moisture content at fiber saturation (roughly 30%) varies, depending on species, tree, temperature, and pressure. This is the critical point at which

wood begins to shrink. If wood has dried below the fiber

saturation point, then regains moisture, the wood will swell.

These dimensional changes differ with the three principal

directions, or grain directions in wood, that is, longitudinal,

radial, and tangential, with intermediate changes varying

with the angle between the principal directions. Longitudinal

dimensional change along the grain is least and amounts to

less than 1% in drying from fiber saturation point to ovendry. Dimensional change is greatest across the grain, but the
 9–8

Table 9–1. Categories of selected wood species according to ease of bonding

U.S. hardwoods U.S. softwoods Imported woods

Bond easilya

Alder Fir Balsa Hura

Aspen White Cativo Purpleheart

Basswood Grand Courbaril Roble

Cottonwood Noble Determab

Chestnut, American Pacific

Magnolia Pine

Willow, black Eastern white

 Western white

Redcedar, western

Redwood

Spruce, Sitka

Bond wellc

Butternut Douglas-fir Afromosia Meranti (lauan)

Elm Larch, westernd Andiroba Light red

 American Pine Angelique White

 Rock Sugar Avodire Yellow

Hackberry Ponderosa Banak Obeche

Maple, soft Redcedar, eastern Iroko Okoume

Sweetgum Jarrah Opepe

Sycamore Limba Peroba rosa

Tupelo Mahogany Sapele

Walnut, black African Spanish-cedar

Yellow-poplar American Sucupira

Wallaba

Bond satisfactorilye

Ash, white Yellow-cedar Angelin Meranti (lauan), dark red

Beech, American Port-Orford-cedar Azobe Pau marfim

Birch Pines, southern Benge Parana-pine

 Sweet Bubinga Pine

 Yellow Karri Caribbean

Cherry Radiata

Hickory Ramin

 Pecan

 True

Madrone

Maple, hard

Oak

 Redb

 Whiteb

Bond with difficultyf

Osage-orange Balata Keruing

Persimmon Balau Lapacho

Greenheart Lignumvitae

Kaneelhart Rosewood

Kapur Teak

a

Bond very easily with adhesives of a wide range of properties and under a wide range of bonding conditions.

b

Difficult to bond with phenol-formaldehyde adhesive.

c

Bond well with a fairly wide range of adhesives under a moderately wide range of bonding conditions.

d

Wood from butt logs with high extractive content is difficult to bond.

e

Bond satisfactorily with good-quality adhesives under well-controlled bonding conditions.

f

Satisfactory results require careful selection of adhesives and very close control of bonding conditions;

 may require special surface treatment.
9–9

amounts differ with the direction; dimensional change varies

with and within species. As a rule of thumb, tangential

dimensional change is about twice that of the radial direction; but again, there are variations by species. (See Ch. 3

for a detailed discussion of wood moisture relations.)

Dimensional changes that accompany changes in moisture

content have broad-ranging and significant consequences on

performance of bonded joints. As wood in bonded assemblies

swells and shrinks, stresses develop that can be great enough

to rupture adhesive bond and wood. Ruptures may develop

when adjacent pieces of wood in a bonded joint differ in grain

direction and shrinkage coefficients, for example, radial grain

bonded to tangential grain, or in the worst case, longitudinal

grain bonded to either tangential or radial grain. Even if

moisture content levels in adjacent pieces are equal, but

changing, stresses could be severe. Moreover, if moisture

content in one piece is at equilibrium with surrounding air,

that is, stable, but the other piece with differing grain direction is shrinking as it approaches equilibrium moisture

content (EMC), then resultant stresses would be compounded and almost sure to rupture either the adhesive bond

or the wood, whichever is weaker. Some wood adhesives are

elastic enough to yield to stresses so that fracture does not

occur. Structural wood adhesives have greater moduli of

elasticity than wood and can effectively transfer stresses from

one adherend to the other without failure. However, if

stresses are great enough from extraordinary moisture content

changes within adjacent pieces of wood of differing shrinkage

coefficients, then fracture in either wood or a poor bond is

almost inevitable. Severe stresses on bondlines can be

minimized by bonding pieces of wood with compatible grain

directions of low shrinkage coefficients at a uniform moisture

content equivalent to that which the bonded assembly will

encounter in service.

The amount of moisture in wood combined with water in

adhesive will greatly influence the wetting, flow, penetration,

and even cure of aqueous wood adhesives. In general, these

adhesives bond satisfactorily across moisture content levels

ranging from 6% to 14% and even below and above this

range when adhesives are formulated for specialized processing. The optimum moisture content range for bonding a

specific product with a specific adhesive is determined from

practical experience and product performance. Aqueous adhesives tend to dry out when applied to wood below 6% moisture content. Wood absorbs water from the adhesive so

quickly that adhesive flow and penetration into the wood is

drastically inhibited, even under high pressure. Wood may

become so dry below 3% moisture content that it temporarily resists wetting by the adhesive because insufficient water

remains bound to the wood to establish intermolecular attraction forces with water in the adhesive.

When wood contains excess amounts of moisture, then less

water and adhesive can be absorbed by the wood. This leads

to excessive adhesive mobility, followed by squeeze-out

when pressure is applied. Control of moisture content is

particularly critical to bonding in hot presses because

excess moisture increases adhesive mobility, followed by

overpenetration of the adhesive. Furthermore, high vapor

pressure builds internally as water boils, and on release of

platen pressure, sudden release of internal pressure actually

separates laminates along the bondlines, called blows. Even

if blows do not occur, excess moisture within thermosetting

adhesives can prevent complete cross-linking with accompanying weakened adhesive film and bond. Appropriate moisture content levels of wood for bonding by hot-press methods

are well known, as are target moisture content levels for

satisfactory service of wood products throughout the United

States. However, control of moisture content in bonding

wood materials is not easily achieved. This is discussed in

the Moisture Content Control section.

Adhesives

Composition

Organic polymers of either natural or synthetic origin are the

major chemical ingredients in all formulations of wood

adhesives. According to ASTM, a polymer is a compound

formed by the reaction of simple molecules having functional

groups that permit their combination to proceed to higher

molecular weights under suitable conditions. Polysaccharides

and proteins are high molecular weight natural polymers

derived from plants and animals. Animal, blood, hide,

casein, starch, soybean, dextrin, and cellulosic adhesives are

all derived from the natural polymers found in these indicated

sources. They have been used as adhesives for centuries and

are still in use today, although they have been replaced

mostly by adhesives made with synthetic polymers. The first

wood adhesives based on synthetic polymers were produced

commercially during the 1930s. This marked the beginning

of fundamental changes in composition of adhesives from

natural to synthesized polymers. These adhesives could not

only be stronger, more rigid, and more durable than wood,

but also have much greater resistance to water than adhesives

from natural polymers.

Synthetic polymers are chemically designed and formulated

into adhesives to perform a great variety of bonding functions. Whether the base polymer is thermoplastic or thermosetting has a major influence on how an adhesive will perform in service. Thermoplastics are long-chain polymers

that soften and flow on heating, then harden again by cooling. They generally have less resistance to heat, moisture,

and long-term static loading than do thermosetting polymers. Common wood adhesives that are based on thermoplastic polymers include polyvinyl acetate emulsions, elastomerics, contacts, and hot-melts. Thermosetting polymers

make excellent structural adhesives because they undergo

irreversible chemical change, and on reheating, they do not

soften and flow again. They form cross-linked polymers that

have high strength, have resistance to moisture and other

chemicals, and are rigid enough to support high, long-term

static loads without deforming. Phenolic, resorcinolic,

melamine, isocyanate, urea, and epoxy are examples of types

of wood adhesives that are based on thermosetting polymers.
 9–10

A formulation of wood adhesive consists of a mixture of

several chemically active and inert materials that vary in

proportion with the basic adhesive polymer, which enhances

performance, whether it be working characteristics, strength

properties, shelf life, or durability. Solvents disperse or

dissolve adhesive polymers, act as carriers of polymer and

additives, aid wetting, and control flow and penetration of

the adhesive. Water is used as the carrier for most wood

adhesives, primarily because water readily absorbs into

wood, is inexpensive, and is free of toxicity problems. Adhesive polymers can be brought into intimate, even molecular,

contact with wood by water as the carrier. Organic solvents

are used with elastomeric and contact adhesives, although

water-based adhesive systems have lower toxicity and flammability. Fillers of both organic and inorganic origins contribute to rheological control of the fluid system, particularly

in reducing the spreading and penetrating of the adhesive into

wood. Reinforcing fibers, mostly inert and of organic origins,

can enhance an adhesive film’s mechanical properties, especially toughness, impact resistance, and shrinkage. Extenders

are filler-like organic materials that may have sufficient

chemical activity to improve adhesion to a small degree, but

they are used primarily to control flow and other working

characteristics, without excess sacrifice of adhesion capability, as is the case with most fillers.

Certain chemicals and polymeric systems plasticize adhesive

polymers, and others are used to enhance tackiness. Plasticizers, such as dibutyl phthalate, are used to soften brittle

vinyl acetate homopolymer in polyvinyl acetate emulsion

adhesives, which facilitates diffusion of adhesive and formation of a flexible adhesive film from the emulsion at and

below room temperature. Phenolic polymers are used as

tackifiers and adhesion promoters in neoprene and nitrile

rubber contact adhesives. Reactive polymeric fortifiers, such

as melamine-formaldehyde, can be substituted in limited

proportions in urea-formaldehyde adhesives to improve

resistance to moisture and heat. Phenol-formaldehyde may be

substituted for resorcinol-formaldehyde to reduce adhesive

costs, without sacrificing adhesive strength and durability.

Catalysts are chemicals used to accelerate the rate of chemical

reaction of polymeric components. Acids, bases, salts, peroxides, and sulfur compounds are a few examples of catalysts.

Catalysts do not become a part of the reacted compound;

they simply increase the rate of reaction. Hardeners are added

to base polymers as reactive components, and they do become a part of the reacted compound. Examples are an amine

hardener added to epoxy and formaldehyde added to resorcinol—all produce cross-linking reactions to solidify the adhesive. Other chemicals, such as antioxidants, acid scavengers,

preservatives, wetting agents, defoamers, even colorants, may

be added to control or eliminate some of the less desirable

characteristics of certain adhesive formulations.

Health and Safety

Wood adhesives contain chemicals that are toxic to people if

they are exposed to sufficient concentrations for prolonged

periods. Generally, it is accepted that wood adhesives in a

cured state do not present toxicity problems. A notable

exception is urea-formaldehyde adhesive, which can release

low concentrations of formaldehyde from bonded wood products under certain service conditions. Formaldehyde is a

toxic gas that can react with proteins of the body to cause

irritation and, in some cases, inflammation of membranes of

eyes, nose, and throat. It is a suspected carcinogen, based on

laboratory experiments with rats. Considerable research has

led to new adhesive formulations with significantly reduced

levels of formaldehyde emissions in both manufacturing

operations and bonded wood products. Phenol-formaldehyde

adhesives, which are used to manufacture plywood, flakeboard, and fiberglass insulation, also contain formaldehyde.

However, formaldehyde is efficiently consumed in the curing

reaction, and the highly durable phenol-formaldehyde, resorcinol-formaldehyde, and phenol-resorcinol-formaldehyde

polymers do not chemically break down in service to release

toxic gas.

Diisocyanates are highly reactive chemicals that polymerize

rapidly on contact with strong alkali, mineral acids, and

water. Polymeric methylene diphenyl diisocyanate (PMDI)

adhesives develop strong and durable bonds to wood, so

they are now widely used to manufacture composite wood

products. They are potentially hazardous if mishandled, but

the low vapor pressure of PMDI adhesives coupled with

adequate ventilation to remove airborne PMDI on dust particles, permits manufacturing plants to operate safely. Properly

cured PMDI adhesives are not considered hazardous in

bonded wood products.

Construction and contact adhesives contain organic solvents

that have low flash points. If these adhesives are used in

unventilated areas where concentrations build to dangerously

high levels, explosions can occur with an ignition source.

Some adhesive producers now offer less flammable formulations based on chlorinated solvents. Organic solvents in

these adhesives are toxic, but by following the manufacturer’s handling and use instructions, coupled with adequate

ventilation, harmful effects can be avoided.

Health and safety regulations require that toxic and hazardous

chemicals be identified and visibly labeled to warn of their

dangers. Material safety data sheets (MSDS) or instructions

are provided with adhesive products to advise of proper

handling procedures, protective gear and clothing, and procedures for dealing with spills and fire, as well as to offer guidance for first-aid and professional treatment of injuries. The

statements made in this section concerning safety of adhesives and effects on the health of the user are general and not

meant to be all inclusive. The user should consult the

MSDS and follow the manufacturer’s instructions and precautions before using any adhesive.

Strength and Durability

The ability of an adhesive to transfer load from one member

of an assembly to another and to maintain integrity of the

assembly under the expected conditions of service will

govern the choice of adhesive for a given application.
9–11

In building construction, adhesives that contribute strength

and stiffness during the life of the structure are considered

structural. They generally are stronger and stiffer than the

wood members. Structural bonds are critical because bond

failure could result in serious damage to the structure, even

loss of life. Examples of structural applications include

glued-laminated beams, prefabricated I-joists, and stressedskin panels. Adhesives that are strongest, most rigid, and

most resistant to deterioration in service, unfortunately, are

those least tolerant of wide variations in wood surface condition, wood moisture content, and assembly conditions including pressures, temperatures, and curing conditions.

Examples of rigid structural adhesives include phenolic,

resorcinol, melamine, urea, and casein (Table 9–2).

Adhesives are further categorized in Table 9–2 as to how

well they transfer load relative to wood as the service environment becomes more severe. Structural adhesives that

maintain their strength and rigidity under the most severe

cyclic water-saturation and drying are considered fully exterior adhesives. Rigid adhesives that lose their ability to

transfer load faster than does wood as service conditions

worsen, particularly with regard to moisture, are considered

interior adhesives. Between exterior and interior adhesives

are the intermediate adhesives that maintain strength and

rigidity in short-term water soaking but deteriorate faster than

wood during long-term exposure to water and heat. Adhesives that are the weakest, least rigid, and least resistant to

severe service conditions are those most tolerant of wide

variations in wood surface, assembly, and curing conditions.

Semistructural adhesives impart strength and stiffness to an

adhesive-bonded assembly, and in some instances, they may

be as strong and rigid as wood. However, semistructural

adhesives generally do not withstand long-term static loading without deformation. They are capable of short-term

exposure to water but not long-term saturation, hence their

limited exterior classification. Examples are cross-linking

polyvinyl acetate and polyurethane adhesives. Another

example of the semistructural adhesive application is the

nailed–glued assembly where failure of the bond would not

cause serious loss of structural integrity because the load

would be carried by mechanical fasteners.

Table 9–2. Wood adhesives categorized according to their expected structural performance

at varying levels of environmental exposure a,b

Structural integrity Service environment Adhesive type

Structural Fully exterior Phenol-formaldehyde

(withstands long-term Resorcinol-formaldehyde

water soaking and drying) Phenol-resorcinol-formaldehyde

Emulsion polymer/isocyanate

Melamine-formaldehyde

Limited exterior Melamine-urea-formaldehyde

(withstands short-term Isocyanate

water soaking) Epoxy

Interior Urea-formaldehyde

(withstands short-term Casein

high humidity)

Semistructural Limited exterior Cross-linked polyvinyl acetate

Polyurethane

Nonstructural Interior Polyvinyl acetate

Animal

Soybean

Elastomeric construction

Elastomeric contact

Hot-melt

Starch

a

Assignment of an adhesive type to only one structural/service environment category does not

 exclude certain adhesive formulations from falling into the next higher or lower category.

b

Priming wood surfaces with hydroxymethylated resorcinol coupling agent improves resistance to

 delamination of epoxy, isocyanate, emulsion polymer/isocyanate, melamine and urea, phenolic, and

 resorcinolic adhesives in exterior service environment, particularly bonds to CCA-treated lumber.
 9–12

Nonstructural adhesives typically support the dead weight of

the material being bonded and can equal the strength and

rigidity of wood in the dry condition. However, on exposure

to water or high humidity, nonstructural adhesives quickly

lose their load transfer ability. Examples are adhesives used

for bonding wall tiles and fixtures.

Elastomeric construction adhesives are categorized as nonstructural. However, they are used normally for field assembly of panelized floor and wall systems in the light-frame

construction industry. Nails are used in the assembly so that

if failure did occur in the adhesive bond, the structural load

would be carried by nails. The adhesive enables the nailed

assembly to act as a composite with increased stiffness. With

nails providing structural safety in this application, elastomeric adhesives could be included in the semistructural

category.

Some adhesives listed in Table 9–2 could be included easily

in more than one category because they can be formulated for

a broad range of applications. Isocyanate and polyurethane

adhesives are examples. Polymeric methylene diphenyl

diisocyanates of low molecular weight develop highly durable bonds in structural flakeboards, although flakeboard

products deteriorate from swelling and shrinkage stresses.

One-part polyurethane adhesives have highly durable adhesive films, but as molecular weight increases, adhesion to

porous wood generally decreases and bonds become increasingly susceptible to deterioration from swelling and shrinkage stresses. Polyurethane adhesives liberate carbon dioxide

on reaction with water. As a result, they foam, and in thick

bondlines, polyurethane bonds become more deformable

under static loading. Two-part polyurethanes can be formulated for rigidity, depending on the degree of structural

loading required.

Adhesive Selection

Adhesive selection begins by considering the types of wood

adhesives, along with their strength and durability, preparation and use characteristics, and typical applications, as

shown in abbreviated form in Table 9–3. Their relative

strength and durability are categorized into levels of structural integrity (Table 9–2) and were discussed previously.

Adhesive selection for a wood product manufacturer may

begin as a cooperative effort between the manufacturer and an

adhesive supplier. Together, they completely review the

product, its intended service environment, and all production

processes and equipment before choosing an appropriate

adhesive. Whatever the approach to adhesive selection might

be, the following general discussion should be helpful.

A broad array of adhesive types, with significant variations

within each type, are available for bonding wood materials,

even for bonding wood to nonwood materials. The selection

process begins with determining which adhesives are compatible with the physical and chemical properties of the

adherends, particularly their surface properties. The polar,

aqueous wood adhesive must be capable of wetting the usually polar wood surface, within its normal variations in

hydrophilicity. As the adhesive wets, it must have flow

properties that enable it to spread over surfaces of variable

roughness and to penetrate wood structures that differ in

porosity, with respect to grain orientation at the bondline.

The adhesive must make molecular contact with the lignocellulosics of wood and penetrate deeply enough to mechanically interlock with the wood’s cell structure. Metals and

plastics cannot be penetrated, so these materials generally

cannot be bonded with aqueous wood adhesives. However,

nonaqueous, 100% solids adhesives, including epoxy, isocyanate, and polyurethane, are capable of sound bonds to nonwood and wood materials.

The structural integrity expected of the adhesive bond under

anticipated service loads in the presence of expected environmental exposure conditions should be one of the foremost

considerations. To intelligently select an adhesive for a given

bonded assembly, it is necessary to have an approximation of

the nature, direction, level, and duration of loading that the

assembly and bondlines must withstand. Furthermore, it is

essential to know the range and duration of temperature and

moisture content levels to which bondlines will be subjected. For example, prolonged exposure to high moisture

content levels will significantly reduce the load-carrying

ability of any adhesive in a wood joint. Failure to give full

consideration to these factors could risk structural failure of

the bonded assembly, even severe personal injury.

There may be need for tradeoffs between bonding requirements of adhesives and their resistance to stress, duration of

load, and service environment. Adhesives that are the strongest, most rigid, and durable are generally those least tolerant

of bonding conditions, including wood moisture content,

surface roughness, cleanliness, inactivation, grain orientation,

bondline thickness, and pressure and temperature of cure.

Adhesives that are the weakest, least rigid, and least resistant

to service conditions are those most tolerant of bonding

conditions. Many adhesives are positioned between these

extremes of bonding requirements and performance

(Tables 9–2 and 9–3).

When a group of adhesives with suitable performance capabilities for a particular bonded assembly has been determined, the user also must choose within that group an adhesive that can be mixed, applied, and cured with available

equipment or consider the cost of purchasing equipment to

meet specific working properties of another adhesive. Important working properties must be considered when making

cost decisions. The working life of an adhesive is the time

between mixing and the end of its useful life when it becomes too viscous to properly wet and flow over a surface.

If an adhesive requires mixing with a hardener or catalyst,

then mixing and application equipment appropriate for the

working life must be considered. Given the consistency of an

adhesive, specific types of application equipment are required. Depending on the size of the spreading operation, the

equipment can range from brush to roll-spreader to extruder

to spray to meter-mixed extrusion. Wood adhesives, including phenolic, melamine, urea, and isocyanate adhesives,
9–13

Table 9–3. Working and strength properties of adhesives, with typical uses

Type Form and color Preparation and application Strength properties Typical uses

Natural origin

Animal, protein Solid and liquid; brown to

white bondline

Solid form added to water,

soaked, and melted; adhesive kept

warm during application; liquid

form applied directly; both

pressed at room temperature;

bonding process must be adjusted

for small changes in temperature

High dry strength; low

resistance to water and

damp atmosphere

Assembly of furniture and

stringed instruments;

repairs of antique furniture

Blood, protein Solid and partially dried

whole blood; dark red to

black bondline

Mixed with cold water, lime,

caustic soda, and other chemicals; applied at room temperature;

pressed either at room temperature or 120o

C (250oF) and higher

High dry strength; moderate

resistance to water and

damp atmosphere and to

microorganisms

Interior-type softwood

plywood, some times in

combination with soybean

adhesive; mostly replaced

by phenolic adhesive

Casein, protein Powder with added

chemicals; white to tan

bondline

Mixed with water; applied and

pressed at room temperature

High dry strength; moderate

resistance to water, damp

atmospheres, and intermediate temperatures; not

suitable for exterior uses

Interior doors; discontinued

use in laminated timbers

Soybean, protein Powder with added

chemicals; white to tan,

similar color in bondline

Mixed with cold water, lime,

caustic soda, and other chemicals; applied and pressed at room

temperatures, but more frequently

hot pressed when blended with

blood adhesive

Moderate to low dry

strength; moderate to low

resistance to water and

damp atmospheres; moderate resistance to intermediate temperatures

Softwood plywood for

interior use, now replaced

by phenolic adhesive. New

fast-setting resorcinolsoybean adhesives for

fingerjointing of lumber

being developed

Lignocellulosic

residues and

extracts

Powder or liquid; may be

blended with phenolic

adhesive; dark brown

bondline

Blended with extender and filler by

user; adhesive cured in hot-press

130oC to 150oC (266oF to 300 oF)

similar to phenolic adhesive

Good dry strength; moderate

to good wet strength; durability improved by blending

with phenolic adhesive

Partial replacement for

phenolic adhesive in

composite and plywood

panel products

Synthetic origin

Cross-linkable

polyvinyl acetate

emulsion

Liquid, similar to polyvinyl

acetate emulsions but

includes copolymers

capable of cross-linking

with a separate catalyst;

white to tan with colorless

bondline

Liquid emulsion mixed with

catalyst; cure at room temperature or at elevated temperature in

hot press and radio-frequency

press

High dry strength; improved

resistance to moisture and

elevated temperatures,

particularly long-term

performance in moist

environment

Interior and exterior doors;

moulding and architectural

woodwork; cellulosic

overlays

Elastomeric

contact

Viscous liquid, typically

neoprene or styrenebutadine elastomers in

organic solvent or water

emulsion; tan to yellow

Liquid applied directly to both

surfaces, partially dried after

spreading and before pressing;

roller-pressing at room temperature produces instant bonding

Strength develops immediately upon pressing, increases slowly over a period

of weeks; dry strengths

much lower than those of

conventional wood adhesives; low resistance to

water and damp atmospheres; adhesive film readily

yields under static load

On-the-job bonding of

decorative tops to kitchen

counters; factory lamination

of wood, paper, metal, and

plastic sheet materials

Elastomeric

mastic

(construction

adhesive)

Putty like consistency,

synthetic or natural

elastomers in organic

solvent or latex emulsions; tan, yellow, gray

Mastic extruded in bead to framing members by caulking gun or

like pressure equipment; nailing

required to hold materials in place

during setting and service

Strength develops slowly

over several weeks; dry

strength lower than conventional wood adhesives;

resistant to water and moist

atmospheres; tolerant of out

door assembly conditions;

gap-filling; nailing required to

ensure structural integrity

Lumber to plywood in floor

and wall systems; laminating gypsum board and rigid

foam insulating; assembly

of panel system in manufactured homes

Emulsion polymer/isocyanateLiquid emulsion and

separate isocyanate

hardener; white with

hardener; colorless

bondline

Emulsion and hardener mixed by

user; reactive on mixing with

controllable pot-life and curing

time; cured at room and elevated

temperatures; radio-frequency

curable; high pressure required

High dry and wet strength;

very resistant to water and

damp atmosphere; very

resistant to prolonged and

repeated wetting and drying;

adheres to metals and

plastics

Laminated beams for

interior and exterior use;

lamination of plywood to

steel metals and plastics;

doors and architectural

materials
 9–14

Table 9–3. Working and strength properties of adhesives, with typical uses—con.

Type Form and color Preparation and application Strength properties Typical uses

Epoxy Liquid resin and hardener

supplied as two parts;

completely reactive

leaving no free solvent;

clear to amber; colorless

bondline

Resin and hardener mixed by

user; reactive with limited pot-life;

cured at room or elevated temperatures; only low pressure

required for bond development

High dry and wet strength to

wood, metal, glass, and

plastic; formulations for

wood resist water and damp

atmospheres; delaminate

with repeated wetting and

drying; gap-filling

Laminating veneer and

lumber in cold-molded

wood boat hulls; assembly

of wood components in

aircraft; lamination of

architectural railings and

posts; repair of laminated

wood beams and architectural building components;

laminating sports equipment; general purpose

home and shop

Hot melt Solid blocks, pellets,

ribbons, rods, or films;

solvent-free; white to tan;

near colorless bondline

Solid form melted for spreading;

bond formed on solidification;

requires special application

equipment for controlling melt and

flow

Develops strength quickly on

cooling; lower strength than

conventional wood adhesives; moderate resistance

to moisture; gap-filling with

minimal penetration

Edge-banding of panels;

plastic lamination; patching;

film and paper overlays;

furniture assembly; general

purpose home and shop

Isocyanate Liquid containing isomers

and oligomers of

methylene diphenyl

diisocyanate; light brown

liquid and clear bondline

Adhesive applied directly by

spray; reactive with water; requires high temperature and high

pressure for best bond development in flake boards

High dry and wet strength;

very resistant to water and

damp atmosphere; adheres

to metals and plastics

Flakeboards; strand-wood

products

Melamine and

melamine-urea

Powder with blended

catalyst; may be blended

up to 40% with urea; white

to tan; colorless bondline

Mixed with water; cured in hot

press at 120°C to 150°C (250°F to

300°F); particularly suited for fast

curing in high-frequency presses

High dry and wet strength;

very resistant to water and

damp atmospheres

Melamine-urea primary

adhesive for durable bonds

in hardwood plywood; endjointing and edge-gluing of

lumber; and scarf joining

softwood plywood

Phenolic Liquid, powder, and dry

film; dark red bondline

Liquid blended with extenders and

fillers by user; film inserted

directly between laminates;

powder applied directly to flakes

in composites; all formulations

cured in hot press at 120°C to

150°C (250°F to 300°F) up to

200°C (392°F) in flakeboards

High dry and wet strength;

very resistant to water and

damp atmospheres; more

resistant than wood to high

temperatures and chemical

aging

Primary adhesive for

exterior softwood plywood,

flakeboard, and hardboard

Polyvinyl

acetate

emulsion

Liquid ready to use; often

polymerized with other

polymers; white to tan to

yellow; colorless bondline

Liquid applied directly; pressed at

room temperatures and in highfrequency press

High dry strength; low

resistance to moisture and

elevated temperatures; joints

yield under continued stress

Furniture; flush doors;

plastic laminates; panelized

floor and wall systems in

manufactured housing;

general purpose in home

and shop

Polyurethane Low viscosity liquid to

high viscosity mastic;

supplied as one part; twopart systems completely

reactive; color varies

from clear to brown;

colorless bondline

Adhesive applied directly to one

surface, preferably to watermisted surface; reactive with

moisture on surface and in air;

cures at room temperature; high

pressure required, but mastic

required only pressure from

nailing

High dry and wet strength;

resistant to water and damp

atmosphere; limited resistance to prolonged and

repeated wetting and drying;

gap-filling

General purpose home and

shop; construction adhesive

for panelized floor and wall

systems; laminating

plywood to metal and

plastic sheet materials;

specialty laminates; installation of gypsum board

Resorcinol and

phenolresorcinol

Liquid resin and powdered

hardener supplied as two

parts; phenol may be

copolymerized with

resorcinol; dark red

bondline

Liquid mixed with powdered or

liquid hardener; resorcinol adhesives cure at room temperatures;

phenol-resorcinols cure at temperatures from 21°C to 66°C

(70°F to 150°F)

High dry and wet strength;

very resistant to moisture

and damp atmospheres;

more resistant than wood to

high temperature and

chemical aging.

Primary adhesives for

laminated timbers and

assembly joints that must

withstand severe service

conditions.

Urea Powder and liquid forms;

may be blended with

melamine or other more

durable resins; white to

tan resin with colorless

bondline

Powder mixed with water, hardener, filler, and extender by user;

some formulations cure at room

temperatures, others require hot

pressing at 120°C (250°F);

curable with high-frequency

heating

High dry and wet strength;

moderately durable under

damp atmospheres; moderate to low resistance to

temperatures in excess of

50°C (122°F)

Hardwood plywood; furniture; fiberboard; particleboard; underlayment; flush

doors; furniture cores
9–15

must be cured at high temperatures and require expensive,

heated presses. Some of these can be cured within minutes in

expensive high frequency heated presses. Cold presses or

clamps are satisfactory for room-temperature-curing adhesives, although the long curing time in production can be a

constraint. Even after hot or cold pressing, adhesive bonds

must remain undisturbed until most of the curing has

occurred.

There are other important considerations, particularly in

furniture and interior millwork, where appearance is allimportant. Adhesive color, ability to absorb stains and

finishes, and freedom from bleeding and staining are critical

factors. The urea-formaldehyde and polyvinyl acetate adhesives used in the furniture industry are formulated to give a

tan or colorless joint with good acceptance of stain.

Ease and simplicity of use can also be important factors.

One-part adhesives, like liquid animal, polyvinyl acetate,

hot-melt, and phenol-formaldehyde film, are the simplest to

use because there is no chance for error in weighing and

mixing components. Water-dispersed and film adhesives are

easy to clean up, whereas films are the least messy. Two-,

three-, or multiple-part adhesives require careful measuring

and mixing of components. They often require special solvents for cleanup after bonding. Frequently, adhesives are

toxic to the skin or give off toxic fumes. Formaldehyde

hardener for resorcinol, phenol, melamine, and urea adhesives

is an irritant to many people. Amine hardeners in some

epoxy adhesives are strong skin sensitizers.

The cost of an adhesive and related application equipment

must be balanced against comparable cost factors for substituted adhesives. In recent years, the cost of organic solvents

and the cost of recovering volatiles to prevent air pollution

have increased. Substituted water-based systems can be

cheaper due to low cost of the solvent; however, grain raising

of the wood and slower drying must be considered because of

their effects on performance and overall cost.

Bonding Process

The bonding process involves a great number of factors that

determine how successfully an adhesive bond will ultimately

perform in service. The better these factors are understood

and controlled, the fewer bonding problems will be encountered, along with their attendant expense. It is not necessary

to be an adhesive expert to manufacture acceptable bonds,

although more knowledge is always helpful. However, it is

essential that the user follow the instructions of the adhesive

supplier during the entire bonding process. The supplier has

extensive technical knowledge of an adhesive’s composition,

working characteristics, and performance properties, which is

reinforced by the experience of customers.

Moisture Content Control

After adhesive selection, the next most important factor

contributing to trouble-free service of adhesive bonds is

control of wood moisture content before and during the

bonding process. Moisture content strongly affects the final

strength and durability of joints, development of surface

checks in the wood, and dimensional stability of the bonded

assembly. Large changes in the moisture content compared

with that at the time of bonding will cause shrinking or

swelling stresses that can seriously weaken both wood and

joints and can cause warping, twisting, and surface irregularities. Wood should not be bonded at high moisture content,

particularly high density hardwoods that have large coefficients of shrinkage, unless the in-service moisture content is

also expected to be high. The wood should be dry enough so

that even if moisture is added during bonding, the moisture

content is at about the level expected for the assembly

in service.

Determining the proper moisture content for bonding depends primarily on the amount of moisture that is contained

in the wood and adhesive and whether or not the adhesive

curing process involves heating. For example, if boards are

bonded at room temperature, the final moisture content is

controlled mainly by the moisture content of the wood. In a

lumber laminate, the number of bondlines are so few that a

waterborne adhesive adds only 1% to 2% to the total moisture content of the laminate. However, if several pieces of

veneer are bonded at room temperature, the moisture added

by the adhesive in many bondlines can significantly increase

the moisture content of the wood well above the target inservice level. Thus, thickness of the laminates, number of

laminates, density of the wood, water content of the adhesive, quantity of adhesive spread, and hot or cold pressing

all have a cumulative effect on the moisture content of the

wood. During hot pressing, a moderate amount of water

evaporates from the laminate as it is removed from the press.

However, to minimize plastic flow of the hot and moist

wood and prevent steam blisters or blows, the total moisture

content of the assembly should not exceed 10% during hot

pressing. A lumber moisture content of 6% to 7%, assuming

1% to 2% will be added by aqueous adhesives, is satisfactory

for cold pressing of furniture and interior millwork. Lumber

being laminated for exterior use should contain 10% to

12% moisture before bonding. A moisture content of 3% to

5% in veneer at the time of hot pressing is satisfactory for

hardwood plywood intended for furniture and interior millwork and for softwood plywood intended for construction

and industrial uses.

Lumber that has been kiln dried to the approximate average

moisture content intended for bonding may still be at different moisture content levels between boards and within individual boards. Large differences in the moisture content

between adjacent boards bonded together result in considerable stress on the common joint as the boards equalize

toward a common moisture content. Best results are achieved

when differences are not greater than about 5% for lower

density species and 2% for high density species.

The moisture content of wood in bonded products should be

targeted to the EMC that the product will experience in
 9–16

service. These conditions vary in the United States; regional

average EMC values of wood in building interiors are shown

in Figure 9–4. The average moisture content for most of the

United States is 8%. The average increases to 11% along the

Atlantic and Gulf coastal regions; in the arid southwest, the

EMC is relatively low at 6%. The moisture content of wood

exposed to outdoor air generally is higher and more variable

and averages near 12% and ranges from 7% to 14% in most

of the United States. During winter in the northern states,

heating of indoor air that is normally dry lowers wood EMC

to 4% to 5%. Furniture manufactured in the southeast at

11% EMC, then sold or moved to northern states where

EMC drops to 4%, usually will experience some splitting,

delamination of joints, or other noticeable appearance defects.

Manufacturers of bonded wood products must be aware of

these regional and seasonal variations, then condition the

wood and bond it at moisture content levels that are consistent with regional service conditions.

Surface Preparation

The physical and chemical condition of wood and nonwood

surfaces was described in a previous section where emphasis

was placed on understanding the relationships between surface condition and adhesive bond performance. Wood surfaces

are best prepared for maximum adhesive wetting, flow, and

penetration by removing all materials that might interfere

with bond formation to sound wood. Ideally, wood should

be knife-planed within 24 h of adhesive spreading. However,

other surfacing methods have been used successfully for

certain types of bonded joints, including sawing for furniture

and millwork, knife-cutting for veneer, and abrasive-planing

for panels. All must produce smooth, flat, parallel surfaces,

free from machining irregularities, such as burnishes, skips,

and crushed, torn, and chipped grain. Properly planed flat

surfaces help ensure that a layer of adhesive of uniform thickness can be uniformly spread over the adherend.

Adhesive Spreading

Regardless of method, the purpose in spreading adhesive is

to distribute an adequate amount of adhesive of uniform

thickness over the bonding area, so that under pressure, the

adhesive will flow into a uniformly thin layer. Assuming

that the spreader is capable of applying adhesive uniformly

and that surfaces are smooth, flat, and parallel, then adhesive

will flow ideally if uniform pressure is applied. The amount

of adhesive needed will depend on the wood species, moisture content, type of adhesive, temperature and humidity of

the air, assembly time, and whether adhesive will be applied

to one or both surfaces. Adhesives can be spread by hand

with brush, roller, or bead-extruder, but in manufacturing,

adhesives are applied by machines, such as roll-spreader,

extruder, curtain-coater, or spray. Instead of applying a uniform film, extruders apply continuous, uniformly spaced

beads of discreet diameter and flow rate. When pressure is

applied to both adherends, the adhesive is squeezed into a

uniformly thin layer. An extruder of this type is used to

apply adhesive to veneer in the manufacture of laminated

veneer lumber (LVL) (Fig. 9–5). A pressurized extruder is

used in the field to apply a single bead of elastomeric construction adhesive to joists for a plywood floor system

(Fig. 9–6).

Assembly and Pressing

Control of consistency after the adhesive has been spread and

until pressure is applied is a balancing act of a variety of

factors. The relationships between adhesive consistency and

bonding pressure as they affect formation of strong bonds are

illustrated in Figure 9–7. Adhesive consistency strongly

affects adhesive wetting, flow, and penetration, particularly

the transfer of adhesive to an unspread wood surface, when

pressure is applied to the assembly. Adhesive consistency

depends upon type of adhesive, type of solvent, and proportion of solvent in the mixture, age of adhesive mixture,

amount of adhesive spread, species of wood, moisture content of wood, temperature of wood, temperature and humidity

of surrounding air, and the critically important evaporation

and absorption of solvent during the assembly time. Assembly time is the time between spreading adhesive on wood

surfaces and applying pressure to the assembly. When the

adhesive-spread surfaces remain open before assembly (open

assembly), then consistency is most affected by evaporative

capacity of the surrounding air and absorbency of the wood’s

surface. When the assembly is closed and before applying

pressure (closed assembly), consistency is most influenced

by absorbency factors and least affected by evaporation. Coldsetting waterborne wood adhesives lose water by absorption

and evaporation so that consistency steadily increases until

they eventually set. Thermosetting waterborne adhesives also

dry out, but despite water loss, they flow to some extent in

the presence of heat, then harden with additional heating.

Pressure serves several useful purposes: it forces entrapped air

from the joint; it brings adhesive into molecular contact with

the wood surfaces; it forces adhesive to penetrate into the

wood structure for more effective mechanical interlocking;

6% average

moisture content

8% average moisture content

11% average

moisture content

Figure 9–4. Average equilibrium moisture content for

wood in building interiors in regions of the United

States.
9–17

it squeezes the adhesive into a thin continuous film; and it

holds the assembly in position while the adhesive cures. But

if pressure is too high, the adhesive can overpenetrate porous

woods and cause starved joints that are inferior in bond

strength (Fig. 9–7). The strongest joints result when the

consistency of the adhesive permits the use of moderately

high pressures that are consistent with the recommended

pressures for the density of the wood.

Low pressures near 700 kPa (100 lb/in2

) are suitable for low

density wood because the surfaces easily conform to each

other, thus ensuring intimate contact between adhesive and

wood. High pressures up to 1,700 kPa (247 lb/in2) are required for the highest density woods that are difficult to

compress. Flat, well-planed surfaces of small area can be

bonded satisfactorily at lower pressures; however, because

high pressure tends to squeeze adhesive into the wood or out

of the joint, adhesives of greater consistency are required for

denser woods (Fig. 9–7). Greater consistency can be achieved

with longer assembly time, which allows increased absorption of liquid solvent by the wood and evaporation into the

air. Care is required, regardless of wood density, to ensure

that the assembly time is not excessive, lest the adhesive dry

out or even precure before pressure is applied. Predried or

precured adhesive will result in inadequate transfer of adhesive to an opposite unspread surface, and the bondline will

be thick and weak (Fig. 9–7).

Lumber joints should be kept under pressure until they have

enough strength to withstand handling stresses that tend to

separate the pieces of wood. When cold-pressing lumber

under normal bonding conditions, this stage can be reached

in as little as 15 min or as long as 24 h, depending on the

temperature of the room and the wood, the curing characteristics of the adhesive, and the thickness, density, and absorptive characteristics of the wood. When hot pressing, the time

under pressure varies with temperature of platens, thickness

and species of wood, and adhesive formulation. In actual

practice, hot-pressing times vary from 2 to 15 min and up

to 30 min for very thick laminates. The time under pressure

can be reduced to less than 3 min with high frequency

heating. High frequency concentrates energy in the conductive bondline to rapidly cure the adhesive. It is commonly

used for bonding lumber, forming end- and edge-grain

joints, patching, scarfing, fingerjointing plywood, and in

Figure 9–5. An extruder applies continuous and

uniformly sized and spaced beads of adhesive to veneer

for laminating into LVL.

Figure 9–6. A pressurized extruder applies a single

bead of elastomeric construction adhesive to floor joists

for assembly of a plywood floor system.

Figure 9–7. An illustration of the relationships

between adhesive consistency and bonding pressure

as they affect bond formation by a thermosetting

adhesive.
 9–18

manufacturing various panel products. Careful control of

power and press time is essential to prevent formation of

steam that could lead to steam blows and even arcing.

It has been observed that bondlines of structural adhesives

that withstand the highest of stresses from mechanical loading and dimensional changes generally have bondline thicknesses within the range of 0.076 to 0.152 mm (0.003 to

0.006 in.). Below this range, the bondlines are too thin to

effectively transfer stresses from one adherend to the other,

particularly stresses from moisture-induced dimensional

changes. Above this range, bond strength becomes progressively weaker as bondline thickness increases. Structural

wood adhesives are brittle, so they fracture more in thicker

bondlines than in thinner ones. These adhesives also contain

solvents, and because solvent is lost while curing, the

thicker adhesive film shrinks and fractures more than the

thinner and may contain more voids from entrapped solvent

gases. Thick bondlines result from inadequate pressure,

either from low applied pressure or from rough, uneven,

poorly mated surfaces. When uneven surfaces are joined,

pressure will not be uniform along the bondline. As a result,

the adhesive will be squeezed out from the areas of very high

pressure, and the areas of little to no pressure will have very

thick bondlines. Both starved and thick bondlines produce

weak joints.

Post-Cure Conditioning

In the process of bonding edge-grain joints, the wood in the

joint absorbs moisture from the adhesive, then swells. If the

bonded assembly is surfaced before this excess moisture is

evaporated or absorbed uniformly, more wood is removed

along the swollen joint than elsewhere. Later, when the

added moisture evaporates, the wood in the joint shrinks

beneath the surface. These sunken bondlines become very

conspicuous under a high-gloss finish. This is a particularly

important consideration when using adhesives that contain

relatively large amounts of water. Redistribution of moisture

added by the adhesive can be accomplished by conditioning

the bonded assembly for 24 h at 70°C (158°F), 4 days at

50°C (122°F), or at least 7 days at room temperature before

surfacing. In each case, the relative humidity must be adjusted to prevent drying the wood below the target moisture

content.

After bonding, plywood-type constructions should be conditioned to the average moisture content expected in service.

The best conditioning is accomplished by controlling humidity on time schedules. If bonded products cured at room

temperature are exposed to excessively low moisture content,

warping, checking, and opening of joints will increase significantly. Softwood plywood is very dry after hot pressing,

so panels may be sprayed with water and tightly stacked to

allow moisture to diffuse uniformly. This practice restores

some of the panel thickness lost by compression during hot

pressing and apparently minimizes warping in service.

Bonded Joints

Edge-Grain Joints

Face-grain joints (wide surface of a board) are commonly seen

in structural laminated lumber products, where adhesive

bonds are stronger than the wood. Edge-grain joints (narrow

surface of a board) (Fig. 9–8) can be almost as strong as the

wood in shear parallel to the grain, tension across the grain,

and cleavage. The tongue-and-groove joint (Fig. 9–8) and

other shaped edge-grain joints have a theoretical strength

advantage because of greater surface area than the straight,

edge-grain joints, but they do not produce higher strength.

The theoretical advantage is lost, wholly or partly, because

the shaped sides of the two mating surfaces cannot be machined precisely enough to produce the perfect fit that will

distribute pressure uniformly over the entire joint area. Because of poor contact, the effective bonding area and strength

can actually be less in a shaped joint than on a flat surface.

The advantage of the tongue-and-groove and other shaped

joints is that the parts can be more quickly aligned in clamps

or presses. A shallow-cut tongue-and-groove is just as useful

in this respect as a deeper cut, and less wood is wasted.

End-Grain Joints

It is practically impossible to make end-grain butt joints

(Fig. 9–9) sufficiently strong to meet the requirements of

ordinary service with conventional bonding techniques. Even

with special techniques, not more than about 25% of the

tensile strength of the wood parallel-to-grain can be obtained

in a butt joint. To approximate the tensile strength of clear

solid wood, a scarf joint or fingerjoint must closely approach

the parallel-to-grain direction of the edge-grain joint

(Fig. 9–8). The surface area of this edge-grain joint should be

at least 10 times greater than the cross-sectional area of the

piece, because wood is approximately 10 times stronger in

tension than in shear. In plywood scarfs and fingerjoints, a

slope of 1 in 8 is typical for structural products. For nonstructural, low-strength joints, these requirements need

not be met.

Figure 9–8. Edge-grain joints: A, plain;

B, tongue-and-groove.
9–19

Fingerjoints can be cut with the profile showing either on the

wide face (vertical joint) or on the edge (horizontal joint)

(Fig. 9–9). There is greater area for designing shapes of

fingers in the vertical joint, but a longer cutting head with

more knives is needed. When the adhesive is cured by high

frequency heating, the cure is more rapid with the vertical

than with the horizontal joint. A nonstructural fingerjoint,

with fingers much shorter than in the two structural fingerjoints, is shown in Figure 9–9.

A scarf joint is shown in Figure 9–9. Slopes of 1 in 12 or

flatter produce the highest strength. This is also true in

fingerjoints, but the tip thickness must be small and no

greater than 0.8 mm (0.031 in.). A thickness of 0.4 to

0.8 mm (0.016 to 0.031 in.) is about the practical minimum

for machined tips. Sharper tips can be created with dies,

which are forced into the end grain of the board.

A well-manufactured end joint of either scarf, finger, or lap

type can have up to 90% of the tensile strength of clear wood

and exhibit behavior much like that of clear wood. However,

test results indicate that the cycles-to-failure for a wellmanufactured end joint are somewhat lower compared with

the results of similar tests for clear wood.

End-to-Edge-Grain Joints

Plain end-to-edge-grain joints (Fig. 9–10) are difficult to

design to carry appreciable loading. Furthermore, internal

stresses develop in the members in service from unequal

dimensional changes with moisture content changes.

Such stresses can be great enough to cause failure. As a

result, it is necessary to design these joints with interlocking

surfaces, for example, dowels, mortise and tenons, rabbets

(Figs. 9–10), so that edge grain of the interlocking piece is

bonded to the edge grain of the adjoining piece. The joint

area is enlarged as well. All end-to-edge-grain joints should

be protected from appreciable changes in moisture content in

service.

Construction Joints

Elastomeric construction adhesives are commonly used in

the light-frame construction industry for field assembly of

panelized floor and wall systems. Structural panels are

bonded to floor joists and wall studs with mastic adhesives

that have the unique capability of bridging gaps up to

6.5 mm (0.25 in.) between rough and poorly fitting surfaces

(Fig. 9 –11). Without any premixing, the adhesive is extruded in a bead along framing members with a hand-held

caulking gun or a pressurized dispenser similar to that shown

in Figure 9–6. Nails or screws provide the only pressure for

bonding, and they hold materials in position while the

adhesive sets. Elastomerics are also uniquely tolerant of the

Figure 9–9. End-grain joints: A, butt; B, plain

scarf; C, vertical structural fingerjoint;

D, horizontal structural fingerjoint;

E, nonstructural fingerjoint.

Figure 9–10. End-to-edge-grain joints: A, plain; B, miter;

C, dowel; D, mortise and tenon; E, dado tongue and

rabbet; F, slip or lock corner; G, dovetail; H, blocked;

I, tongue-and-groove.
 9–20

temperature and moisture content variations at field construction sites. Although they do not deliver the strength and

durability of conventional structural adhesives, elastomerics

are strong and flexible enough to give long-term performance

under most conditions of installation and service.

Construction adhesives enable a nailed floor system to act to

some degree as a composite assembly with increased stiffness. Greater stiffness permits joists to be longer and spaced

more widely, with one layer of plywood subflooring replacing two. Floors are less bouncy with fewer squeaks and nail

pops. However, structural design of the composite assembly

is based only on the increased stiffness of nailed panel and

framing materials. Structural credit for strength is not

allowed for the adhesive in the engineering design.

Testing and Performance

An adhesive is expected to hold materials together and

transfer design loads from one adherend to the other within a

given service environment for the life of the structure. The

purpose of testing performance is to ensure that adhesive

bonds will not deteriorate before they can meet these expectations. A variety of methods are available to test bonding

performance, particularly for bonded assemblies. Generally,

these testing methods attempt to predict how bonded joints

are likely to perform in a specific loading mode (shear, tensile, creep) in an assembly at specific temperature and moisture conditions for a specific time.

Most performance tests are short term. They are based on

chemical, mechanical, and rheological laboratory tests of

adhesive polymers and their adhesives and bonds. Intermediate-term tests of products that are conducted in pilot operations and field experiments are integrated with short-term

laboratory tests in an effort to extrapolate these data into

long-term performance. Long-term tests of bonded assemblies

under actual environmental exposures are conducted, but

these supporting data may not be available for 10 to

30 years. Therefore, heavy reliance must be placed on

short-term tests to predict long-term performance. As the

relationships between chemical structure and mechanical

performance, particularly long-term performance, are better

understood, the greater the reliance will be on short-term

testing.

Analytic Chemical and

Mechanical Testing of Polymers

The molecular structures of adhesive polymers are chemically

characterized spectroscopically by nuclear magnetic resonance, either in the liquid or solid state. Molecular-size

distributions of polymers are determined by gel permeation

chromatography. Rates of chemical reaction are studied by

differential scanning calorimetry. The rheological properties

of curing and cured adhesives are characterized by dynamic

mechanical analysis and torsional-braid analysis. Sophisticated fracture mechanics techniques are used to measure

toughness of adhesive bonds as they fail in a cleavage mode.

High magnification microscopes, including scanning electron

microscope, transmission electron microscope, and atomic

force microscope, enable scientists to visually analyze surfaces of adhesives and adherends before, during, and after

fracture. Much can be learned from measurements of chemical, mechanical, and rheological properties of polymers and

adhesives as they exist apart from adherends. Until such data

can be correlated with performance, there is no substitute for

testing performance in bonded assemblies prepared with

specific adhesives and materials, and tested under specific

loading modes, environmental conditions, and duration of

loading. When adhesives are formulated through a blend of

scientific analysis and art of formulation, they are tested for

strength and durability in the laboratory and field, usually by

industry- and government-accepted standard methods of test

and product specifications.

Mechanical Testing of

Bonded Assemblies

Responses of adhesive-bonded assemblies to mechanical

loading are defined in terms of several commonly used

modes of applying stress to joints. In all test modes, specific

materials, conditions of materials and test, and testing procedures are completely specified to ensure repeatability to

enable valid comparisons of data. Most test methods, specifications, and practices for adhesives and bonded assemblies

are consensus standards published each year in the Annual

Book of ASTM Standards by the American Society for Testing and Materials (ASTM). Several trade associations have

their own specifications and performance standards that apply

to their specific wood products. The Federal government also

has specifications that are used by the General Services

Administration to purchase products.

Four basic stressing modes—shear, tensile, cleavage, and

peel—are commonly used to test bonded wood assemblies

with variations of these to determine strength levels during

impact, flexure, fatigue, and creep under long-term stress.

Figure 9–11. Gap-filling construction adhesive in

field-assembled plywood floor system.
9–21

The following describes the basic stress modes in adhesivebonded joints:

• Shear, resulting from forces applied parallel to the

bondline

• Tensile, resulting from forces applied perpendicular to the

bondline

• Cleavage, resulting from separation along a bondline by a

wedge or other crack-opening type of force

• Peel, resulting from forces applied to a bondline that tend

to progressively separate a flexible member from a rigid

member or another flexible member

As the names imply, impact, fatigue, and creep are tests that

have more to do with the rate at which basic modes and

variations are applied. Impact loads are sudden, much faster

relative to the controlled slow rates of shear or tensile stressing. Fatigue is the loss in strength from repeated loading and

reflects deterioration of bonds from mechanical rather than

environmental stresses, although the latter may be imposed

during fatigue testing. Creep loads are statically applied but

are of prolonged duration that can last from a few days to

years, usually at extreme conditions of environmental exposure. The flexure test applies a bending force to a simple

beam at midspan, perpendicular to the bondline. In a laminated beam, the test directs a large proportion of the shear

forces to bondlines between the laminates.

The common measures used to estimate potential performance of bonded wood joints are strength, wood failure, and

delamination. Best performance produces a bond strength

that is greater than that of the wood, wood failure that is

more than 75% over the bonded area, and delamination of the

joint that is less than 5% for softwoods and 8% for hardwoods, under severe service conditions. These performance

values reflect how wood adherend, adhesive bond, and environmental exposure have interacted in response to loading.

Bond strength is tested most commonly in shear parallel to

the grain. Because most wood adhesives exceed the shear

strength of wood in this direction, the maximum potential

strength of the adhesive may not be realized, particularly for

moderate to lower density species. Bonds in structural assemblies are expected to exceed the strength of the wood, so

in traditional design of joints, adhesive strength has been

ignored. Adhesives not as strong as wood simply have not

been used in design because methods for determining allowable mechanical properties of adhesives for engineering design had not been developed. One such method now exists

as a consensus standard—ASTM D5574–97 (ASTM 1997).

Exceeding the strength of wood is an essential performance

criterion; therefore, the amount of wood that fails in a joint is

estimated as a percentage of the area of the bonded joint.

This is an important indicator of bond strength, often more

important than the measured shear strength of the bond. The

higher the wood failure and the deeper the fracture into the

grain of the wood, the stronger and more durable the bond,

particularly with durable types of adhesives. If wood failure is

shallow with only wood fibers remaining attached to the

adhesive film, then bond strength and probably durability is

lacking in the bond. Thus, a consistently high level of wood

failure, above 75% in some standards and above 85% in

others, means that shear strength associated with these average wood failures are good estimates of the load-carrying

capability of the joint. High levels of wood failure and shear

strength in a wet and hot environment might indicate that

the adhesive bond is as strong as the wood. If cycles of

alternate drying were included with cycles of wet and hot

conditions, then high wood failure would indicate even more

durable bonds. High wood failure in shear tests of watersaturated bonds is also a strong indicator of bond durability,

particularly with durable types of adhesives. Wood failure is

considered a valid measure of bond strength only to solid

wood, not to reconstituted products made of bonded wood

particles.

High shear strength and wood failure in themselves are not

sufficient indicators of the durability of a structural bond.

Delamination is an indicator of how well the bonded joint

withstands severe swelling and shrinking stresses in the

presence of high moisture and heat. Delamination is the

separation between laminates because of adhesive failure,

either in the adhesive or at the interface between adhesive and

adherend. If strength of adhesion is not as strong as the wood

in resisting forces tending to separate laminates, then delamination occurs. If adhesion does resist delaminating

forces, then the wood will fail adjacent to the bondline, but

not within the adhesive. The stressing modes induced by

stresses from moisture-related dimensional changes are combinations of tensile and shear forces with cleavage acting at

joint edges. Delamination of adhesives in structural laminated wood products exposed to the cyclic delamination test

in ASTM D2559–97 (ASTM 1997) cannot exceed 5% in

softwoods and 8% in hardwoods.

Short- and Long-Term Performance

In the short term, the mechanical properties of wood, adhesives, and bonded products vary with the specific environmental exposure. In most cases, all properties decrease as the

temperature and moisture levels increase. Strength and stiffness may return to their original levels if the yield points of

the materials have not been exceeded while under load. The

properties of rigid thermosetting adhesives like resorcinolformaldehyde, phenol-formaldehyde, melamine-formaldehyde,

and urea-formaldehyde change less than do wood properties

under equivalent temperature and moisture changes. Therefore, evaluating short-term performance of products made

with these adhesives is simply a matter of testing bonds at

room temperature in dry and wet conditions. Thermoplastic

adhesives like casein, polyvinyl acetate, and elastomerics,

whose properties change more rapidly than those of wood

with changes in moisture and heat, are tested dry, dry after

water soaking, and after prolonged exposure to high humidity environments. In addition, some specifications require

testing of bonded structural and nonstructural products at

elevated temperatures such as occur in roofs or enclosed

shipping containers. A short-term dead-load test at elevated

temperatures may also be required. Specifications for
 9–22

adhesives for structural products like laminated beams and

plywood require conformance to high minimum strength and

wood failure values after several different water exposure tests.

Adhesive bonds in laminated beams must also withstand

severe cyclic moisture content and temperature changes, with

only low levels of delamination allowable.

In the long term, wood, adhesives, and bonded products

deteriorate at a rate determined by the levels of temperature,

moisture, stress and, in some instances, by concentrations of

certain chemicals and presence of microorganisms. Long-term

performance is equated with the ability of a product to resist

loss of a measured mechanical property over the time of

exposure. A durable product is one that shows no greater

loss of properties during its life in service than wood of the

same species and quality.

Many adhesives in bonded products have decades of documented performance in many environments. Thus, it is

possible to predict with a high degree of certainty the longterm performance of similar products. Well-designed and

well-made joints with any of the commonly used woodworking adhesives will retain their strength indefinitely if the

moisture content of the wood does not exceed approximately

15% and if the temperature remains within the range of human comfort. However, some adhesives deteriorate when

exposed either intermittently or continuously to temperatures

greater than 38°C (100°F) for long periods. Low temperatures seem to have no significant effect on strength of

bonded joints.

Products made with phenol-formaldehyde, resorcinolformaldehyde, and phenol-resorcinol-formaldehyde adhesives

have proven to be more durable than wood when exposed to

warm and humid environments, water, alternate wetting and

drying, and even temperatures sufficiently high to char wood.

These adhesives are entirely adequate for use in products that

are exposed indefinitely to the weather (Fig. 9–12).

Products well-made with melamine-formaldehyde,

melamine-urea-formaldehyde, and urea-formaldehyde resin

adhesives have proven to be less durable than wood.

Melamine-formaldehyde is only slightly less durable than

phenol-formaldehyde or resorcinol-formaldehyde, but it is

still considered acceptable for structural products. Although

considered less durable, melamine-urea-formaldehyde is also

accepted in structural products at a melamine-to-urea ratio of

60:40. Urea-formaldehyde resin is susceptible to deterioration

by heat and moisture (Fig. 9–12).

Products bonded with polyvinyl acetate and protein-based

adhesives will not withstand prolonged exposure to water or

repeated high–low moisture content cycling in bonds of high

density woods. However, if they are properly formulated,

these adhesives are durable in a normal interior environment.

Some isocyanate, epoxy, polyurethane, and cross-linked

polyvinyl acetate adhesives are durable enough to use on

lower density species even under exterior conditions, but

exterior exposure must be limited for most of these. Some

elastomer-based adhesives may be durable enough for

limited exposure to moisture with lower density species in

nonstructural applications or in structural applications when

used in conjunction with approved nailing schedules. Polyurethane adhesives that chemically cure and still remain flexible are among the most durable construction adhesives.

New adhesives do not have a history of long-term performance in service environments, so accelerated laboratory exposures that include cycles of heat, moisture, and stress are

used to estimate long-term performance. However, laboratory

exposures cannot duplicate the actual conditions of a service

environment. Estimates of long-term performance can be

obtained by exposing specimens outdoors for up to 30 years.

Outdoor exposures may be intensified by facing specimens

south at an angle perpendicular to the noonday sun and by

establishing exposure sites in regions with the most extreme

of service environments, for example, southern coastal and

arid southwestern regions. Only four long-term laboratory

aging methods have been standardized, and none specifies

minimum performance levels. Therefore, performance of any

new adhesive or bonded product must be compared with the

performance of established adhesives or products tested in the

same laboratory exposure.

Product Quality Assurance

After the short- and long-term performance of a product has

been established, then maintenance of the manufacturing

process to ensure that the product will be made and perform

at that level is the major concern of a quality-assurance program that consists of three parts:

1. Establishing limits on bonding process factors

that will ensure acceptable joints and product.

2. Monitoring the production processes and quality

of bond in joints and product.

3. Detecting unacceptable joints and product, determining

the cause, and correcting the problem.

Urea

Melamine-urea

Melamine

Phenol Phenol-resorcinol

Wood Resorcinol

Percentage of original strength

120

100

80

60

40

20

0 2 4 6 8

Aging time (years)

Figure 9–12. Relative rates of deterioration of bond

strength of small specimens exposed directly to

weather.
9–23

The structural panel, laminated-beam, particleboard, millwork, and other industrial trade associations have established

quality-assurance programs that effectively monitor the joint

and product performance at the time of manufacture for compliance with voluntary product standards. Usually, product

performance is evaluated immediately after manufacture by

subjecting specimens from the product to a series of swell–

shrink cycles. The treatments are more rigorous for products

intended for exterior exposure. For example, exterior softwood plywood is subjected to two boil–dry cycles, while

interior plywood is subjected to a single soak–dry cycle at

room temperature. After exposure, the specimens are examined for delamination or evaluated for percentage wood failure. The test results are compared with the minimum requirement in the trade association’s standards. Lengthy

experience and correlations between exterior performance and

accelerated laboratory tests have shown that products with at

least the minimum values will probably perform satisfactorily in service. If the product meets the requirement, it is

certified by the association as meeting the standard for

satisfactory performance.

References

AITC. 1992. Inspection manual for structural glued laminated timber, AITC 200–92. Englewood, CO: American

Institute of Timber Construction.

AITC. 1992. American national standard for wood products–

structural glued laminated timber ANSI/AITC A190.1–

1992. New York, NY: American National Standards

Institute, Inc.

APA. 1983. U.S. product standard PS1–83 for construction

and industrial plywood with typical APA trademarks. Washington, DC: U.S. Department of Commerce, National

Bureau of Standards.

APA. 1988. Performance standards and policies for structural-use panels, APA PRP–108. Tacoma, WA: American

Plywood Association.

ASTM. 1997. Annual book of ASTM standards, Vol. 15.06

Adhesives. West Conshohocken, PA: American Society for

Testing and Materials.

ASTM D2559. Standard specification for adhesives for

structural laminated wood products for use under exterior

(wet use) exposure conditions.

ASTM D5574. Standard methods for establishing allowable mechanical properties of wood bonding adhesives for

design of structural joints.

Blomquist, R.F.; Christiansen, A.W.; Gillespie, R.H.;

Myers, G.E. eds. 1984. Adhesive bonding of wood and

other structural materials. Clark C. Heritage memorial series

on wood, Vol. 3. Educational modules for material science

and engineering (EMMSE). University Park, PA:

Pennsylvania State University.

Blomquist, R.F.; Vick, C.B. 1977. Adhesives for building

construction. In: Skeist, I., ed. Handbook of adhesives, 2d

edition. New York, NY: Van Nostrand Reinhold Company.

Bryant, B.S. 1977. Wood adhesion. In: Skeist, I., ed.

Handbook of adhesives, 2d edition. New York, NY: Van

Nostrand Reinhold Company.

Caster, R.W. 1980. Correlation between exterior exposure

and automatic boil test results. In: John, W.E.; Gillespie,

R.H., eds. Proceedings of a symposium, Wood adhesives—

research, application, needs. 1980 September 23–25; Madison, WI: Madison, WI: U.S. Department of Agriculture,

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Christiansen, A.W. 1990. How overdrying wood reduces

its bonding to phenol-formaldehyde adhesives: a critical

review of the literature. Part I. Physical responses. Wood and

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Christiansen, A.W. 1991. How overdrying wood reduces

its bonding to phenol-formaldehyde adhesives: a critical

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and Fiber Science. 23(1): 69–84.

Collett, B.M. 1972. A review of surface and interfacial adhesion in wood science and related fields. Wood Science and

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Gillespie, R.H. 1965. Accelerated aging of adhesives in

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Gillespie, R.H. 1981. Wood composites. In: Oliver, J.F.,

ed. Adhesion in cellulose and wood-based composites. New

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Gollob, L.; Wellons, J.D. 1990. Wood adhesion. In:

Skeist, I., ed. Handbook of adhesives, 3d ed. New York,

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elastomeric adhesives. Forest Products Journal. 26(3):

28–34.
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Jarvi, R.A. 1967. Exterior glues for plywood. Forest

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processing of tropical hardwoods. 1977 October; Merida,

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10–1

Wood-based Composites

and Panel Products

John A. Youngquist

Chapter 10

Contents

Scope 10–2

Types of Conventional Composite Materials 10–3

Adhesive Considerations 10–3

Additives 10–4

General Manufacturing Issues 10–4

Standards for Wood–Based Panels 10–4

Product Standards 10–5

Performance Standards 10–5

Plywood 10–6

General Description 10–6

Types of Plywood 10–7

Processing Considerations 10–7

Specifications 10–8

Grades and Classification 10–9

Specialty Panels 10–13

Particle and Fiber Composites 10–13

General Processing Considerations 10–13

Oriented Strandboard 10–13

Particleboard 10–14

Fiberboard 10–17

Specialty Composites 10–23

Wood–Nonwood Composites 10–24

Inorganic–Bonded Composites 10–24

Wood Fiber–Thermoplastic Composites 10–26

References 10–30

ecause wood properties vary among species,

between trees of the same species, and between

pieces from the same tree, solid wood cannot match

reconstituted wood in the range of properties that can be

controlled in processing. When processing variables are

properly selected, the end result can sometimes surpass

nature’s best effort. With solid wood, changes in properties

are studied at the cellular level. With reconstituted wood

materials, changes in properties are studied at the fiber,

particle, flake, or veneer level. Properties of such materials

can be changed by combining, reorganizing, or stratifying

these elements.

The basic element for composite wood products may be the

fiber, as it is in paper, but it can also be larger wood particles

composed of many fibers and varying in size and geometry.

These characteristics, along with control of their variations,

provide the chief means by which materials can be fabricated

with predetermined properties.

In any discussion of the strength properties of wood-based

panels and other adhesive-bonded wood composites, the first

consideration is the constituents from which these products

are made (O’Halloran and Youngquist 1984; Youngquist

1987, 1988). The basic wood elements that can be used in

the production of wood-based panels are shown in

Figure 10–1. The elements can be made in a great variety

of sizes and shapes and can be used alone or in combination.

The choice is almost unlimited.

Currently, the term composite is being used to describe any

wood material adhesive-bonded together. This product mix

ranges from fiberboard to laminated beams and components.

Table 10–1 shows a logical basis for classifying wood composites proposed by Maloney (1986). For the purposes of

this chapter, these classifications were slightly modified from

those in the original version to reflect the latest product

developments. Composites are used for a number of structural and nonstructural applications in product lines ranging

from panels for interior covering purposes to panels for exterior uses and in furniture and support structures in many

different types of buildings.
 10–2

Figure 10–2 provides a useful way to further classify woodbased composite materials. This figure presents an overview

of the most common types of products discussed in this

chapter as well as a quick reference to how these composite

materials compare to solid wood from the standpoint of

density and general processing considerations. The raw

material classifications of fibers, particles, and veneers are

shown on the left y axis. Specific gravity and density are

shown on the top and bottom horizontal axes (x axes). The

right y axis, wet and dry processes, describes in general

terms the processing method used to produce a particular

product. Note that both roundwood and chips can serve as

sources of fiber for wet-process hardboard. Roundwood or

wood in the form of a waste product from a lumber or planing operation can be used for dry-processed products. For

medium-density fiberboard (MDF), resin is usually applied

to the fiber after the fiber is released from the pressurized

refiner. The fiber is then dried, formed into a mat, and

pressed into the final product. For other dry-processed products, the material is fiberized and dried and then adhesive is

added in a separate operation prior to hot pressing into the

final composite product. Figure 10–3 shows examples of

some composite materials that are represented in schematic

form in Figure 10–2.

Scope

Although there is a broad range of wood composites and

many applications for such products, for the purposes of this

chapter, wood composites are grouped into three general

categories: plywood, particle and fiber composites, and

wood–nonwood composites. Books have been written about

each of these categories, and the constraints of this chapter

necessitate that the discussion be general and brief. References are provided for more detailed information. Information

on adhesive-bonded-laminated (glulam, timbers, and structural composite lumber, including laminated veneer lumber)

and adhesive-bonded members for lumber and panel products

Figure 10–1. Basic wood elements, from largest to smallest (Marra 1979).

Table 10–1. Classification of wood-based

compositesa

Veneer-based material

Plywood

Laminated veneer lumber (LVL)

Parallel-laminated veneer (PLV)

Laminates

Laminated beams

Overlayed materials

Wood–nonwood compositesb

Composite material

Cellulosic fiberboard

Hardboard

Particleboard

Waferboard

Flakeboard

Oriented strandboard (OSB)

COM-PLYc

Edge-adhesive-bonded material

Lumber panels

Components

I-beams

T-beam panels

Stress-skin panels

Wood–nonwood composites

Wood fiber–plastic composites

Inorganic-bonded composites

Wood fiber–agricultural fiber composites

a

Maloney 1986.

b

Panels or shaped materials combined with nonwood

 materials such as metal, plastic, and fiberglass.

c

Registered trademark of APA–The Engineered

 Wood Association.
10–3

is presented in Chapter 11 of this handbook. Many composite materials, like fiberboard, MDF, and particleboard, can be

made from wood alone or in combination with agricultural

fibers (Youngquist and others 1993a, 1994; Rowell and

others 1997).

The first category, plywood, is covered in some detail because the process for manufacturing this kind of material is

quite different from that used for other composite materials

and because there are many different classes and grades of

plywood in the marketplace. The second category, composite materials, includes oriented strandboard (OSB),

particleboard, and fiberboard. These types of composites

undergo similar processing steps, which are discussed in

general terms for all the products in the Particle and Fiber

Composites section. The first and second categories of composite materials are further generally classified as conventional composite materials. The third category, wood–

nonwood composites, includes products made from combining wood fibers with agricultural fibers, with thermoplastics,

and with inorganic materials.

Types of Conventional

Composite Materials

Conventional wood composite materials fall into five main

categories based on the physical configuration of the wood

used to make the products: plywood, oriented strandboard,

particleboard, hardboard, and cellulosic fiberboard. Within

limits, the performance of a conventional type of composite

can be tailored to the end-use application of the product.

Varying the physical configuration of the wood and adjusting

the density of the composites are just two ways to accomplish this. Other ways include varying the resin type and

amount and incorporating additives to increase water or fire

resistance or to resist specific environmental conditions.

Adhesive Considerations

The conventional wood-based composite products discussed

in this chapter are typically made with a thermosetting or

heat-curing resin or adhesive that holds the lignocellulosic

Hardboard—Dry

Hardboard—Wet

Paper

Insulation board

Plywood

 Oriented

strandboard

Waferboard

MDF—Dry

MDF—Wet

Particleboard

Solid wood Specific gravity Raw material

Wet Dry

Process

Particles

Veneer Fibers

Density (kg/m3)

Figure 10–2. Classification of wood composite boards by particle size, density, and process

type (Suchsland and Woodson 1986).

Figure 10–3. Examples of various composite products.

From left to right: plywood, OSB, particleboard, MDF,

and hardboard.
 10–4

(wood) fiber together. The physical and mechanical properties of wood-based veneer, fiber, and particle panel materials

are determined by standard American Society for Testing and

Materials (ASTM) test methods. Commonly used resin–

binder systems include phenol-formaldehyde, ureaformaldehyde, melamine-formaldehyde, and isocyanate.

Phenol-formaldehyde (PF) resins are typically used in the

manufacture of products requiring some degree of exterior

exposure durability, for example, OSB, softwood plywood,

and siding. These resins require longer press times and

higher press temperatures than do urea-formaldehyde resins,

which results in higher energy consumption and lower line

speeds (productivity). Products using PF resins (often referred to as phenolics) may have lowered dimensional stability because of lower moisture contents in the finished products. The inherently dark color of PF resins may render them

unsuitable for decorative product applications such as paneling and furniture.

Urea-formaldehyde (UF) resins are typically used in the

manufacture of products where dimensional uniformity and

surface smoothness are of primary concern, for example,

particleboard and MDF. Products manufactured with UF

resins are designed for interior applications. They can be

formulated to cure anywhere from room temperature to 150°C

(300°F); press times and temperatures can be moderated

accordingly. Urea-formaldehyde resins (often referred to as

urea resins) are more economical than PF resins and are the

most widely used adhesive for composite wood products.

The inherently light color of UF resins make them quite

suitable for the manufacture of decorative products.

Melamine-formaldehyde (MF) resins are used primarily for

decorative laminates, paper treating, and paper coating. They

are typically more expensive than PF resins. MF resins may

be blended with UF resins for certain applications (melamine

urea).

Isocyanate as diphenylmethane di-isocyanate (MDI) is

commonly used in the manufacture of composite wood products; MDI is used primarily in the manufacture of OSB.

Facilities that use MDI are required to take special precautionary protective measures.

These adhesives have been chosen based upon their suitability for the particular product under consideration. Factors

taken into account include the materials to be bonded together, moisture content at time of bonding, mechanical

property and durability requirements of the resultant composite products, and of course, resin system costs.

Some natural options may someday replace or supplement

these synthetic resins. Tannins, which are natural phenols,

can be modified and reacted with formaldehyde to produce a

satisfactory resin. Resins have also been developed by acidifying spent sulfite liquor, which is generated when wood is

pulped for paper. In the manufacture of wet-process fiberboard, lignin, which is inherent in lignocellulosic material,

is frequently used as the resin (Suchsland and Woodson

1986).

Except for two major uncertainties, UF and PF systems are

expected to continue to be the dominant wood adhesives for

lignocellulosic composites. The two uncertainties are the

possibility of much more stringent regulation of formaldehyde-containing products and the possibility of limitations

to or interruptions in the supply of petrochemicals. One

result of these uncertainties is that considerable research has

been conducted in developing new adhesive systems from

renewable resources.

Additives

A number of additives are used in the production of conventional composite products. One of the most notable additives

is wax, which is used to provide finished products with

resistance to aqueous penetration. In particle- and fiberboard

products, wax emulsion provides excellent water resistance

and dimensional stability when the board is wetted. Even

small amounts (0.5% to 1%) act to retard the rate of liquid

water pickup. These improved water penetration properties

are important for ensuring the success of subsequent secondary gluing operations and for providing protection upon

accidental wetting to the product during and after construction. The water repellency provided by the wax has practically no effect upon dimensional changes or water adsorption

of composites exposed to equilibrium conditions. Other

additives used for specialty products include preservatives,

fire retardants, and impregnating resins.

General Manufacturing Issues

Successful manufacture of any composite wood product

requires control over raw materials. Ideally, raw materials are

uniform, consistent, and predictable. Wood does not offer

these qualities but instead varies widely between species. For

the purpose of producing a composite product, uniformity,

consistency, and predictability are accomplished by reducing

separated portions of the wood into small, relatively uniform

and consistent particles, flakes, or fibers where effects of

differences will average out. Size reduction is sometimes

augmented by chemical treatments designed to weaken the

bonds between the components. The degree of size reduction

and the shape of individual lignocellulosic components will

depend on the application. Different composites tolerate or

demand different sizes and shapes. Generally speaking, all the

conventional composite products discussed in this chapter

are made to conform to product or performance standards

(English and others 1997).

Standards for Wood–Based

Panels

The general types of standards for panel products are product

standards and performance standards. Table 10–2 lists

standards for common conventional composite products. The

term adhesive, as used in the following descriptions of product and performance standards, is synonymous with glue.
10–5

Product Standards

Product standards may be further classified as manufacturing

method standards and laboratory test standards. Probably the

best example of a manufacturing method standard is Voluntary Product Standard PS 1–95 for construction and industrial plywood (NIST 1995). This standard specifies such

matters as what wood species and grades of veneer may be

used, what repairs are permissible, and how repairs must be

made. For panels produced according to prescriptive manufacturing requirements, a comparison of wood failure to

adhesive failure in small test specimens of plywood is the

performance test specified.

A good example of a laboratory test product standard is the

American National Standard for mat-formed particleboard,

ANSI A208.1 (NPA 1993). The American National Standards Institute (ANSI) product standards for both particleboard and MDF are sponsored by the Composite Panel

Association (CPA) in Gaithersburg, Maryland. The CPA is

the association resulting from the 1997 consolidation of the

U.S.-based National Particleboard Association and the

Canadian Particleboard Association. This standard states

that in laboratory tests, specimens show certain minimally

acceptable physical and mechanical properties, identified by

numeric values. The test values give some indication of

product quality, but the tests on small specimens were not

specifically developed to correlate with performance of whole

panels in specific end-uses.

Performance Standards

Performance standards are written for panels in specific

end-uses. These standards focus on panel performance in

laboratory tests developed to indicate panel performance for

particular end-uses. Federal legislation (Abourezk 1977)

encourages the development of performance standards in

preference to commodity-type standards. The Voluntary

Standards and Accreditation Act of 1977 states that “a performance standard does not limit the manufacturer’s freedom

to choose any method of design or any form of construction

that achieves the desired level of performance” (Abourezk

1977)

The APA–The Engineered Wood Association (formerly

American Plywood Association) was the leading proponent

of performance-type standards for panel products, and their

early work formed the basis for the performance standards in

existence today (O’Halloran 1979, 1980; APA 1981).

Wood-based panels manufactured in conformance with performance standards (APA–The Engineered Wood Association 1995a, TECO 1991) are approved by the three major

model codes by virtue of approval by the Council of American Building Officials through the issuance of a national

evaluation report. These wood-based panels can be used for

construction applications such as sheathing for roofs, subflooring, and walls.

Similarly, wood-based panels may be used in light-frame

construction for many single-layer floor applications.

Plywood, OSB, and COM-PLY, a proprietary product, are

all span-rated for particular end uses.

Under PS 1–95 (NIST 1995), plywood panels intended for

structural uses may be certified or rated using either prescriptive or performance-based criteria. Standard PS 2–92 (NIST

1992) is strictly performance based because it applies to all

structural-use wood-based panels, including plywood, waferboard, and OSB; OSB is a second generation panel, with

aligned fibers, that evolved from the original product called

waferboard. The PS 2–92 standard is not a replacement for

PS 1–95, which contains necessary veneer-grade and

Table 10–2. Standards for frequently used panel products

Product category Applicable standard Name of standard Source

Plywood PS 1–95 Voluntary product standard PS 1–95

Construction and industrial plywood

NIST 1995

PS 2–92 Voluntary product standard PS 2–92

Performance standard for wood-based

structural-use panels

NIST 1992

Oriented strandboard PS 2–92 Voluntary product standard PS 2–92

Performance standard for wood-based

structural-use panels

NIST 1992

Particleboard ANSI A208.1–1993 Particleboard NPA 1993

Hardboard ANSI/AHA A135.4–1995 Basic hardboard AHA 1995a

ANSI/AHA A135.5–1995 Prefinished hardboard paneling AHA 1995b

ANSI/AHA A135.6–1990 Hardboard siding AHA 1990

Insulation board ASTM C208–94 Standard specification for cellulosic fiber

insulating board

ASTM current

edition

ANSI/AHA A194.1–1985 Cellulosic fiberboard AHA 1985

Medium-density fiberboard ANSI A208.2–1994 Medium-density fiberboard (MDF) NPA 1994
 10–6

adhesive-bond requirements as well as prescriptive lay-up

provisions and includes many plywood grades not covered

under PS 2–92.

A significant portion of the market for construction and

industrial plywood is in residential construction. This situation has resulted in the development of performance standards

for sheathing and single-layer subflooring or underlayment for

residential construction. Plywood panels conforming to these

performance standards for sheathing are marked with grade

stamps such as those shown in Figure 10–4a,b. Structural

flakeboards are usually marketed as conforming to a product

standard for sheathing or single-layer subflooring or underlayment and are graded as a performance-rated product (PRP–

108) similar to the grading for construction plywood. Voluntary Product Standard PS 2–92 is the performance standard

for wood-based structural-use panels, which include such

products as plywood, OSB, and waferboard. Panels conforming to these performance standards for sheathing are marked

with grade stamps such as those shown in Figure 10–4c,d.

As seen in Figure 10–4a,b, the grade stamps must show (1)

conformance to plywood product standards, (2) nominal

panel thickness, (3) grades of face and back veneers or grade

name based on panel use, (4) performance-rated panel standard, (5) recognition as a quality assurance agency by the

National Evaluation Service (NES), which is affiliated with

the Council of American Building Officials, (6) exposure

durability classification, (7) span rating, which refers to

maximum allowable roof support spacing and maximum

floor joist spacing, and (8) panel sizing for spacing.

Plywood

General Description

Plywood is a flat panel built up of sheets of veneer called

plies, united under pressure by a bonding agent to create a

panel with an adhesive bond between plies. Plywood can be

made from either softwoods or hardwoods. It is always constructed with an odd number of layers with the grain direction of adjacent layers oriented perpendicular to one another.

Since layers can consist of a single ply or of two or more

plies laminated such that their grain is parallel, a panel can

contain an odd or even number of plies but always an odd

number of layers. The outside plies are called faces or face

and back plies; the inner plies are called cores or centers; and

the plies with grain perpendicular to that of the face and back

are called crossbands. The core may be veneer, lumber, or

particleboard, with the total panel thickness typically not

less than 1.6 mm (1/16 in.) or more than 76 mm (3 in.).

The plies may vary in number, thickness, species, and grade

of wood. To distinguish the number of plies (individual

sheets of veneer in a panel) from the number of layers

(number of times the grain orientation changes), panels are

sometimes described as three-ply, three-layer or four-ply,

three-layer. The outer layers (face and back) and all oddnumbered layers (centers) generally have their grain direction

oriented parallel to the length or long dimension of the

panel. The grain of even-numbered layers (cores) is perpendicular to the length of the panel.

The alternation of grain direction in adjacent plies provides

plywood panels with dimensional stability across their

width. It also results in fairly similar axial strength and

stiffness properties in perpendicular directions within the

panel plane. The laminated construction distributes defects,

markedly reduces splitting when the plywood is penetrated

by fasteners (compared with splitting of solid wood), and

improves resistance to checking.

❶

❷

❸

❹

❽

(a)

❶

❷

❹ ❺

❽

(c)

(b)

(d)

❶

❷

❸

❹ ❽

❺

❶

❷

❹

❺

❼

➏

➏

➏

❼

➏

❼

❼

Product Standard that governs specifics of production for

construction and industrial plywood

Nominal panel thickness subject to acceptable tolerances

Panel grade designation indicating minimum veneer grade

used for panel face and back, or grade name based on

panel use

Performance-rated panel standard indicating structural-use

panel test procedure recognized by National Evaluation

Service (NES)

NES report number from Council of American Building

Officials (CABO)

Exposure durability classification: Exposure 1 indicates

interior panel bonded with exterior glue suitable for uses

not permanently exposed to weather

Span rating indicating maximum spacing of roof and floor

supports for ordinary residential construction applications;

32/16 rating identifies a panel rated for use on roof supports

spaced up to 813 mm (32 in.) o.c., or floor supports spaced

up to 406 mm (16 in.) o.c.

Sized for spacing denotes panels that have been sized to

allow for spacing of panel edges during installation to reduce

the possibility of buckling

❶

❷

❸

❹

❽

❺

➏

❼

Figure 10–4. Typical grade stamps for plywood and OSB.
10–7

Compared with solid wood, the chief advantages of plywood

are that the properties along the length of the panel are more

nearly equal to properties along the width, there is greater

resistance to splitting, and the form permits many applications where large sheets are desirable. The use of plywood

may result in improved utilization of wood. Plywood can

cover large areas with a minimum amount of wood fiber

because plywood that is thinner than sawn lumber can be

used in some applications. The properties of plywood depend on the quality of the different layers of veneer, order of

layer placement, adhesive used, and control of bonding

conditions. The grade of the panel depends upon the quality

of the veneers used, particularly of the face and back. The

type of panel refers to the durability of the adhesive-to-wood

bond and depends upon the adhesive-bonded joint, particularly its water resistance, and upon veneer grades used. Generally, face veneers with figured grain that are used in panels

where appearance is important have numerous short, or

otherwise deformed, wood fibers. These may significantly

reduce strength and stiffness of the panels. On the other hand,

face veneers and other plies may contain certain sizes and

distributions of knots, splits, or growth characteristics that

have no undesirable effects on strength properties for specific

uses, such as sheathing for walls, roofs, or floors.

The plywood industry continues to develop new products.

Hence, the reader should always refer directly to current

specifications on plywood and its use for specific details.

Types of Plywood

Broadly speaking, two classes of plywood are available,

covered by separate standards: (a) construction and industrial,

and (b) hardwood and decorative. Construction and industrial

plywood has traditionally been made from softwoods such as

Douglas-fir, Southern Pine, white fir, larch, western hemlock, and redwood. However, the current standard lists a

large number of hardwoods as qualifying for use. At the same

time, the standard for hardwood and decorative plywood

covers certain decorative softwood species for nonconstruction use.

Most construction and industrial plywood used in the United

States is produced domestically, and U.S. manufacturers

export some material. Generally speaking, the bulk of construction and industrial plywood is used where strength,

stiffness, and construction convenience are more important

than appearance. However, some grades of construction and

industrial plywood are made with faces selected primarily for

appearance and are used either with clear natural finishes or

pigmented finishes.

Hardwood and decorative plywood is made of many different

species, both in the United States and overseas. Well over

half of all such panels used in the United States are imported.

Hardwood plywood is normally used in such applications as

decorative wall panels and for furniture and cabinet panels

where appearance is more important than strength. Most of

the production is intended for interior or protected uses,

although a very small proportion is made with adhesives

suitable for exterior service, such as in marine applications.

A significant portion of all hardwood plywood is available

completely finished.

The adhesives used in the manufacture of the two classes of

plywood are quite different, but each type is selected to

provide the necessary performance required by the appropriate

specifications.

Construction and industrial plywood covered by Product

Standard PS 1 is classified by exposure capability (type) and

grade. The two exposure capabilities are exterior and interior.

Exterior plywood is bonded with exterior adhesive, and

veneers used in manufacture cannot be less than “C” grade as

defined in PS 1. Interior-type plywood may be bonded with

interior, intermediate, or exterior (waterproof) adhesive. “D”

grade veneer is allowed as inner and back plies of certain

interior-type plywoods. Adhesive bond performance requirements are specified in PS 1.

The four types of hardwood and decorative plywood in decreasing order of resistance to water are Technical (Exterior),

Type I (Exterior), Type II (Interior), and Type III (Interior);

adhesive bond requirements for these are specified in

ANSI/HPVA–1–1994 (HPVA 1994).

Processing Considerations

After trees are felled and bucked to length, the logs are graded

and sorted to make the most appropriate and efficient use of

the wood fiber. For softwood plywood, in the past, logs

graded as “peelers” were sent to veneer mills or plywood

plants and “sawlogs” were shipped to lumber mills. Because

of the dwindling availability of the clear, large-diameter

peeler logs on which the plywood industry was founded, this

practice has changed. Today, the higher grades of softwood

peeler logs are sent to sawmills, and with few exceptions,

plywood is made from low-grade sawlogs or peeler logs.

This change came about because of the increasing demand for

clear sawn lumber, and it has been made possible by innovations in veneer and plywood manufacturing and testing

practices that ensure that panels are suitable for their intended

use (McKay 1997).

Logs delivered to a veneer mill are sorted by grade and

species, then debarked and crosscut into peeler blocks. Peeler

blocks are often heated or conditioned by steaming or immersion in hot water prior to peeling, which makes them

easier to peel, reduces veneer breakage, and results in

smoother, higher quality veneer. The heated blocks are then

conveyed to a veneer lathe. To maximize veneer yield, each

block is gripped on the ends at the block’s geometric center.

While rotating at high speed, the block is fed against a

stationary knife parallel to its length. Veneer is peeled from

the block in a continuous, uniformly thin sheet, much like

unwinding a roll of paper towels, but at a speed of up to

4.1 m/s (13.3 linear ft/s).

Depending on its intended use, veneer may range in thickness from 1.6 to 4.8 mm (1/16 to 3/16 in.) for softwood
 10–8

plywood and much thinner for hardwood and decorative

plywood. After being peeled to a diameter from 127 to

51 mm (5 to 2 in.), the peeler core is ejected from the lathe.

Peeler cores may be sawn into standard 38- by 89-mm

(nominal 2- by 4-in.) lumber, used for fence posts, and landscape timbers, or chipped for use as pulp chips or fuel.

The continuous sheet of veneer is then transported by conveyor to a clipping station where it is clipped into usable

widths and defects are removed. The wet veneer is then dried

to an average moisture content that is compatible with the

adhesive system being used to bond the panels. Since it is

critical that veneer moisture content be low at the time adhesive is applied, each sheet is metered as it exits the dryer.

Pieces that are too wet or dry are rerouted to be redried or

reconditioned, respectively. Properly dried veneer is then

sorted into one of as many as 15 to 20 different grades according to the size and number of knots and other natural and

processing defects. Each grade has a specific use; some veneer

requires special processing before it is assembled into plywood. After grading and/or processing, the veneer is taken to

the lay-up area.

Adhesive is applied to veneers in the lay-up area by spray,

curtain coating, roller coating, extrusion, and recently, foaming. Veneer is laid up into plywood by hand, machine, or a

combination of both. Hand lay-up is the oldest method, and

it is still the only practical way of making plywood for some

applications. With this method, the face, back, and center

veneers are hand-placed by workers called sheet turners. After

being coated on both sides with adhesive, the alternating

core plies are placed by hand or machine. The lay-up process

is almost completely automated in newer plywood plants,

although the narrow strips used for cores may still be placed

manually. Before veneers are laid up, narrow strips are sometimes joined into full-width sheets with hot-melt adhesivecoated fiberglass thread so that they can be handled by machine. Also, veneers may be upgraded by punching out knots

and other defects and replacing them with wood plugs or

synthetic patches.

Once assembled, panels are conveyed from the lay-up area

to the pressing area. Panels are first subjected to cold prepressing to flatten the veneers and transfer the adhesive to

uncoated sheets; panels are then hot pressed. After hot pressing, panels are solid-piled or hot-stacked to ensure complete

curing of the adhesive, then sawn to size. Panels are then

graded with regard to the product standard under which they

were manufactured. Knotholes and splits on the faces and

backs of some panels may be repaired with wood plugs or

with synthetic patches (by filling the holes and splits with

what is essentially liquid plastic that quickly hardens).

Those panels that do not meet the specification are downgraded or rejected. Panels needing further processing are sent

to the finishing area where, depending on their intended use,

they may be sanded to thickness, profiled with tongue and

groove edges, surface textured, scarf- or finger-jointed, oiled

and edge-sealed, or given other treatments. The panels are

then ready for shipping (McKay 1997).

Specifications

The two general classes of plywood—(a) construction and

industrial plywood and (b) hardwood and decorative plywood—are covered by separate standards. Construction and

industrial plywood are covered by Product Standard PS 1–95

(NIST 1995), and hardwood and decorative plywood by

American National Standard ANSI/HPVA–1–1994 (HPVA

1994). Each standard recognizes different exposure durability

classifications, which are primarily based on moisture resistance of the adhesive and the grade of veneer used.

Model building codes in the United States stipulate that

plywood used for structural applications like subflooring and

sheathing must meet the requirements of certain U.S.

Department of Commerce standards. Voluntary Product

Standard PS 1–95 for construction and industrial plywood

(NIST 1995) and Performance Standard PS 2–92 for woodbased structural-use panels (NIST 1992) spell out the ground

rules for manufacturing plywood and establishing plywood or

OSB properties, respectively. These standards have evolved

over time from earlier documents (O’Halloran 1979, 1980;

APA 1981) and represent a consensus opinion of the makers,

sellers, and users of plywood products as well as other concerned parties. In addition, model building codes require that

plywood manufacturers be inspected and their products certified for conformance to PS 1–95, PS 2–92, APA PRP–108,

or TECO PRP–133 by qualified independent third-party

agencies on a periodic unannounced basis.

With PS 1–95, as long as a plywood panel is manufactured

using the veneer grades, adhesive, and construction established in the standard’s prescriptive requirements, the panel

is by definition acceptable. When plywood is assembled so

that the proportion of wood with the grain perpendicular to

the panel’s face grain is greater than 33% or more than 70%

of the panel’s thickness, the plywood automatically meets

the span rating. In panels with four or more plies, the combined thickness of the inner layers must equal 45% or more

of the panel’s thickness. Generally speaking, for panels of the

same thickness and made with the face and back veneer of the

same species, stiffness and strength increase as the thickness

of the face and back veneers increases. All other things being

equal, the stiffness and strength of plywood also increase as

panel thickness increases.

All hardwood plywood represented as conforming to American National Standard ANSI/HPVA–1–1994 (HPVA 1994)

is identified by one of two methods: by marking each panel

with the Hardwood Plywood & Veneer Association (HPVA)

plywood grade stamp (Fig. 10–5) or by including a written

statement with this information with the order or shipment.

The HPVA grade stamp shows (1) HPVA trademark, (2)

standard that governs manufacture, (3) HPVA mill number,

(4) plywood adhesive bond type, (5) flame spread index

class, (6) description of lay-up, (7) formaldehyde emission

characteristics, (8) face species, and (9) veneer grade of face.
10–9

The span-rating system for plywood was established to

simplify plywood specification without resorting to specific

structural engineering design. This system indicates performance without the need to refer to species group or panel

thickness. It gives the allowable span when the face grain is

placed across supports with a minimum of three supports.

If design calculations are desired, a design guide is provided

by the APA–The Engineered Wood Association in Plywood

Design Specification (PDS) and APA Technical Note

N375B (APA–The Engineered Wood Association 1995a,b).

The design guide contains tables of grade stamp references,

section properties, and allowable stresses for plywood used

in construction of buildings and similar structures.

Grades and Classification

Plywood is classified by both exposure durability class and

grade. Exposure durability class refers to the ability of a

panel to resist the damaging effects of exposure to the weather

or moisture. Panel grades are either names that describe the

intended use of the panel, such as underlayment or concrete

form, or letters that identify the grades of the face and back

veneers, such as A–B.

Veneers for plywood are visually graded according to the

size, number, and location of natural and processing defects

that affect their strength and appearance. Knots, decay, splits,

insect holes, surface roughness, number of surface repairs, and

other defects are considered. More surface repairs, such as

elliptical (boat-shaped) wood patches and bigger knots are

allowed in the lower veneer grades. Veneers are graded as N,

A, B, C, C-Plugged, and D. N-grade or natural finish veneers are virtually blemish-free, and they contain only a few

minor surface repairs. A and B veneers have solid surfaces

with neatly made repairs and small, tight knots. Knotholes

up to 25 mm (1 in.) in diameter are allowed in C veneers,

whereas D veneers may have knotholes as large as 51 mm

(2 in.) across. Because their appearance is usually of secondary importance, panels meant for sheathing and other structural uses are made mostly from C and D veneers. The N, A,

and B veneers are reserved for panels where appearance is the

primary consideration in such uses as exterior trim and

soffits, interior paneling, doors, and cabinets.

Construction Plywood Exposure Durability Class

The exposure durability classifications for construction and

industrial plywood specified in PS–1 are as follows: exterior,

exposure 1, intermediate adhesive, exposure 2, and interior.

Exterior plywood is bonded with exterior (waterproof) adhesive and is composed of C-grade or better veneers throughout. Exposure 1 plywood is bonded with exterior adhesives,

but it may include D-grade veneers. Exposure 2 plywood is

made with adhesive of intermediate resistance to moisture.

Interior-type plywood may be bonded with interior, intermediate, or exterior (waterproof) adhesive. D-grade veneer is

allowed on inner and back plies of certain interior-type

grades.

The exposure durability classifications for hardwood and

decorative plywood specified in ANSI/HPVA HP–1–1994

are as follow, in decreasing order of moisture resistance:

technical (exterior), type I (exterior), type II (interior), and

type III (interior). Hardwood and decorative plywood are not

typically used in applications where structural performance is

a prominent concern. Therefore, most of the remaining

discussion of plywood performance will concern construction

and industrial plywood.

Plywood Grades

There are many plywood grade names (Tables 10–3 and

10–4). In addition to the 30 or so generic names listed in

PS 1–95, each agency that inspects plywood mills and

certifies their products has coined its own trademarked grade

names. For example, panels intended for use as single-layer

❾

❶

❷

❸ ❹

❽

❺

➏

❼

Explanation of numbering

HPVA trademark

Standard governing manufacture

HPVA mill number

Plywood bondline type

Flame spread index class as determined by testing in

accordance with ASTM E84, standard test method for

surface burning characteristics of building materials

Lay-up description references structural attributes of wall

panels as described in HPMA design guide HP-SG-86,

Structural design Guide for Hardwood Plywood Wall Panels

as published by the Hardwood Plywood & Veneer

Association

Formaldehyde emission characteristics to determine

compliance with U.S. Department of Housing and Urban

Development requirements for building product use in

manufactured homes by testing in accordance with

ASTM E1333, Standard Test Method for Determining

Formaldehyde Levels From Wood Products Under Defined

Test Conditions Using a Large Chamber

Face species (face species designation is not required for

wall panels when the surface is a decorative simulation

such as that of a wood grain of another species or of a

pattern)

Veneer grade of face (grade of veneer of back is shown

following grade of face for industrial panels)

❾

❷

❸

❹

➏

❶

❽

❺

❼

Figure 10–5. Grade stamp for hardwood plywood

conforming to ANSI/HPVA–1–1994.
 10–10

flooring (combined subfloor and underlayment) made by

TECO-certified manufacturers are called Floorspan, while

those made by mills certified by the APA–The Engineered

Wood Association are named Sturd-I-Floor. Although the

trade names may be different, the minimum stiffness and

strength properties of the panels are not. With the exception

of custom-order panels, plywood is strictly a commodity

product; panels of the same grade and thickness conforming

to either PS 1–95 or PS 2–92 are interchangeable among

manufacturers.

Span Rating and General Property Values

The more than 70 species of wood used for making softwood

plywood (including some hardwoods) are classified into five

groups according to their stiffness and strength (Table 10–5).

The strongest woods are in Group 1; the weakest, in

Group 5. Today, almost all plywood intended for structural

use is marked with a two-number span rating (for example,

32/16) instead of a species group number (Fig. 10–4).

As with softwood lumber allowable design values, plywood

span ratings were developed by breaking thousands of fullsize panels of varying construction and thickness. The lefthand number of the rating represents the maximum

Table 10–3. Grade names for interior plywood gradesa

Panel grade designation

Minimum

face

Veneer

back

Quality

inner plies Surface

N–N N N C S2Sb

N–A N A C S2S

N–B N B C S2S

N–D N D D S2S

A–A A A D S2S

A–B A B D S2S

A–D A D D S2S

B–B B B D S2S

B–D B D D S2S

Underlayment C plugged D C & D Touch sanded

C–D plugged C plugged D D Touch sanded

Structural I C–D Unsanded

Structural I C–D plugged, underlayment Touch sanded

C–D C D D Unsanded

C–D with exterior adhesive C D D Unsanded

a

NIST 1995.

b

Sanded on two sides.

Table 10–4. Grade names for exterior plywood gradesa

Panel grade designation

Minimum

face

Veneer

back

Quality inner

plies Surface

Marine, A–A, A–B. B–B, HDO, MDO See regular grades

Special exterior, A–A, A–B, B–B, HDO, MDO See regular grades

A–A A A C S2Sb

A–B A B C S2S

A–C A C C S2S

B–B (concrete form)

B–B B B C S2S

B–C B C C S2S

C–C plugged C plugged C C Touch sanded

C–C C C C Unsanded

A–A high-density overlay A A C plugged —

B–B high-density overlay B B C plugged —

B–B high-density concrete form overlay B B C plugged —

B–B medium-density overlay B B C —

Special overlays C C C —

a

NIST 1995.

b

Sanded on two sides.
10–11

recommended on-center (OC) spacing for framing when the

panel is used as roof sheathing; the right-hand number is the

maximum recommended OC spacing for framing when the

panel is used as subflooring. Panels intended for single-layer

flooring (combined subfloor and underlayment) have only

one span-rating number; for example, 24 OC. In all cases,

the panels are meant to be installed with their length perpendicular to framing and across three or more supports. Again,

panels of the same grade and span rating can be substituted

for one another regardless of who made or certified them.

Table 10–6 provides approximate properties of sheathinggrade plywood. Plywood may be used under loading

conditions that require the addition of stiffeners to prevent it

from buckling. It may also be used in the form of cylinders

or curved plates, which are beyond the scope of this handbook but are discussed in U.S. Department of Defense

Bulletin ANC–18.

It is obvious from its construction that a strip of plywood

cannot be as strong in tension, compression, or bending as

a strip of solid wood of the same size. Those layers having

Table 10–5. Softwood plywood species groups by stiffness and strengtha

 Group 1 Group 2 Group 3 Group 4 Group 5

Apitong Cedar, Port Orford Alder, red Aspen Basswood

Beech, American Cypress Birch, paper Bigtooth Poplar

Birch Douglas-firb Cedar, yellow Quaking Balsam

 Sweet Fir Fir, subalpine Cativo

 Yellow Balsam Hemlock, eastern Cedar

Douglas-firc California red Maple, bigleaf Incense

Kapur Grand Pine Western

Keruing Noble Jack Red

Larch, western Pacific silver Lodgepole Cottonwood

Maple, sugar White Ponderosa Eastern

Pine Hemlock, western Spruce Black

 Caribbean Lauan Redwood (Western Poplar)

 Ocote Almon Spruce Pine, eastern

Pine, Southern Bagtikan Engelman White, sugar

 Loblolly Mayapis White

 Longleaf Red lauan

 Shortleaf Tangile

 Slash White lauan

Tanoak Maple, black

Mengkulang

Meranti, red

Mersawa

Pine

 Pond

 Red

 Virginia

 Western white

Spruce

 Black

 Red

 Sitka

Sweetgum

Tamarack

Yellow poplar

a

From NIST 1995. Strongest species in Group 1; weakest in Group 5.

b

Trees grown in Nevada, Utah, Colorado, Arizona, and New Mexico.

c

Trees grown in Washington, Oregon, California, Idaho, Montana, Wyoming, and Canadian provinces

 of Alberta and British Columbia.
 10–12

their grain direction oriented at 90° to the direction of stress

can contribute only a fraction of the strength contributed by

the corresponding areas of a solid strip because they are

stressed perpendicular to the grain. Strength properties in the

length and width directions tend to be equalized in plywood

because adjacent layers are oriented at an angle of 90° to each

other.

Characteristics

Although plywood is an engineered wood product, it is also

used as a component in other engineered wood products and

systems in applications such as prefabricated I-joists, box

beams, stressed-skin panels, and panelized roofs. Plywood

has high strength-to-weight and strength-to-thickness ratios,

and its stiffness and strength are more equal in width and

length than are stiffness and strength of solid wood. Plywood

also has excellent dimensional stability along its length and

across its width. Minimal edge-swelling makes plywood

perhaps the best choice for adhesive-bonded tongue-andgroove joints, even where some wetting is expected. Because

the alternating grain direction of its layers significantly reduces splitting, plywood is an excellent choice for uses that

call for fasteners to be placed very near the edges of a panel.

In uses where internal knotholes and voids may pose a

problem, such as in small pieces, plywood can be ordered

with a solid core and face veneers.

Other Considerations

Plywood of thin, cross-laminated layers is very resistant to

splitting. Therefore, nails and screws can be placed close

together and close to the edges of panels. Of course, highly

efficient, rigid joints can be obtained by bonding plywood to

itself or to heavier wood members, such as those needed in

prefabricated wood I-joists, box beams, and stressed-skin

panels. Adhesive-bonded joints should not be designed to

transmit load in tension primarily normal to the plane of the

plywood sheet because of the rather low tensile strength of

wood perpendicular to grain. Adhesive-bonded joints should

be arranged to transmit loads through shear. It must be

recognized that shear strength across the grain of wood (often

called rolling shear strength because of the tendency to roll

the wood fibers) is only 20% to 30% of that parallel to the

grain. Thus, sufficient area must be provided between plywood and flange members of box beams and between plywood and stringers of stressed-skin panels to avoid perpendicular-to-grain shearing failure in the face veneer, in the

crossband veneer next to the face veneer, or in the wood

member. Various details of design are given in Chapter 11.

Table 10–6. General property values for sheathing-grade plywooda

Property Value

ASTM test methodb

(where applicable)

Linear hygroscopic expansion

 (30%–90% RH) 0.15%

Linear thermal expansion 6.1 × 10-6 cm/cm/°C (3.4 × 10-6 in/in/°F)

Flexure

Modulus of rupture 20.7–48.3 MPa (3,000–7,000 lb/in2

) D3043

Modulus of elasticity 6.89–13.1 GPa (1–1.9 × 106

 lb/in2)

Tensile strength l0.3–27.6 MPa (1,500–4,000 lb/in2

) D3500

Compressive strength 20.7–34.5 MPa (3,000–5,000 lb/in2

) D3501

Shear through thickness

 (edgewise shear)

Shear strength 4.1–7.6 MPa (600–1,100 lb/in2

) D2719

Shear modulus 0.47–0.761 GPa (68–110 × 103

 lb/in2) D3044

Shear in plane of plies (rolling shear) D2718

Shear strength 1.7–2.1 MPa (250–300 lb/in2

)

Shear modulus 0.14–0.21 GPa (20–30 × 103

 lb/in2)

a

All mechanical properties are based on gross section properties of plywood panels, with stress applied parallel to

 grain direction of face plies where applicable. Note: Data are not to be used in developing allowable design values.

 Information on engineering design methods for plywood courtesy of APA–The Engineered Wood Association,

 Tacoma, WA.

b

Standard methods of testing strength and elastic properties of structural panels are given in ASTM standards

 (see References).
10–13

Specialty Panels

Some plywood panels are designed for special uses, including marine decorative underlayment and concrete form and

special exterior applications. The treating of plywood with

preservatives and fire retardants is done by manufacturers

outside of the plywood industry. Plywood is easily pressuretreated with waterborne preservatives and fire retardants, and

treated plywood is readily available for use where such protection is needed.

Particle and Fiber Composites

Many wood-based composite materials have become popular.

These composites are usually available in panel form and are

widely used in housing and furniture. Conventional composites are typically made with a heat-curing adhesive that holds

the wood fiber components together. The physical and mechanical properties of wood-based fiber and particle panel

materials are determined by standard ASTM test methods.

General Processing Considerations

All the products in the family of particle and fiber composite

materials are processed in similar ways. Raw material for

OSB, waferboard, and fiberboard is obtained by flaking or

chipping roundwood. For fiberboard, chips are reduced to

wood fiber using refiners that usually use steam to soften the

wood. The comminuted wood is then dried, adhesive is

applied, and a mat of wood particles, fibers, or strands is

formed; the mat is then pressed in a platen-type press under

heat and pressure until the adhesive is cured. The bonded

product is allowed to cool and is further processed into

specified width, length, and surface qualities.

Oriented Strandboard

Oriented strandboard is an engineered structural-use panel

manufactured from thin wood strands bonded together with

waterproof resin under heat and pressure, and it is used extensively for roof, wall, and floor sheathing in residential and

commercial construction. Orientation of wood strands with a

typical aspect ratio (that is, strand length divided by width)

of at least 3 can produce a panel product with greater bending

strength and stiffness in the oriented or aligned direction.

Raw Materials

The raw material for the original waferboard product, which

was made from square wafers, was aspen. As this industry

expanded and OSB became the predominant product manufactured, other species such as Southern Pine, white birch,

red maple, sweetgum, and yellow-poplar were found to be

suitable raw materials as well. Small amounts of some other

hardwoods can also be used for OSB.

Manufacturing Process

In the general manufacturing process for OSB, debarked logs

are often heated in soaking ponds, then sliced into thin wood

elements. The strands are dried, blended with resin and wax,

and formed into thick, loosely consolidated mats that are

pressed under heat and pressure into large panels.

Figure 10–6 shows an OSB manufacturing process. Oriented

strandboard is made from long, narrow strands, with the

strands of each layer aligned parallel to one another but

perpendicular to strands in adjacent layers, like the crosslaminated veneers of plywood. It is this perpendicular orientation of different layers of aligned strands that gives OSB its

unique characteristics and allows it to be engineered to suit

different uses.

Stranding Process

Typically, logs are debarked and then sent to a soaking pond

or directly to the stranding process. Long log disk or ring

stranders are commonly used to produce wood strands typically measuring 114 to 152 mm (4.5 to 6 in.) long,

12.7 mm (0.5 in.) wide, and 0.6 to 0.7 mm (0.023 to

0.027 in.) thick.

Drying Process

Green strands are stored in wet bins and then dried in a

traditional triple-pass dryer, a single-pass dryer, a combination triple-pass/single-pass dryer, or a three-section conveyor

dryer. A relatively recent development is a continuous chain

dryer, in which the strands are laid on a chain mat that is

mated with an upper chain mat and the strands are held in

place as they move through the dryer. The introduction of

new drying techniques allows the use of longer strands,

reduces surface inactivation of strands, and lowers dryer

outfeed temperatures. Dried strands are screened and sent to

dry bins.

Adhesive Application or Blending

The blending of strands with adhesive and wax is a highly

controlled operation, with separate rotating blenders used for

face and core strands. Typically, different resin formulations

are used for face and core layers. Face resins may be liquid or

powdered phenolics, whereas core resins may be phenolics or

isocyanates. Several different resin application systems are

used; spinning disk resin applicators are frequently used.

Mat Formation

Mat formers take on a number of configurations, ranging from

electrostatic equipment to mechanical devices containing

spinning disks to align strands along the panel’s length and

star-type cross-orienters to position strands across the panel’s

width. All formers use the long and narrow characteristic of

the strand to place it between the spinning disks or troughs

before it is ejected onto a moving screen or conveyor belt

below the forming heads. Oriented layers of strands within

the mat—face, core, face, for example—are dropped sequentially, each by a different forming head. Modern mat formers

either use wire screens laid over a moving conveyor belt to

carry the mat into the press or screenless systems in which

the mat lies directly on the conveyor belt.
 10–14

Hot Pressing

In hot pressing, the loose layered mat of oriented strands is

compressed under heat and pressure to cure the resin. As

many as sixteen 3.7- by 7.3-m (12- by 24-ft) panels may be

formed simultaneously in a multiple-opening press. A more

recent development is the continuous press for OSB. The

press compacts and consolidates the oriented and layered mat

of strands and heats it to 177°C to 204°C (350°F to 400°F)

to cure the resin in 3 to 5 min.

Design Capacities and Panel Certification

Design capacities of performance-rated products, which include OSB and waferboard, can be determined by using

procedures outlined in Technical Note N375B (APA–The

Engineered Wood Association 1995a). In this reference,

allowable design strength and stiffness properties, as well as

nominal thickness and section properties, are specified based

on the span rating of the panel. Additional adjustment factors

based on panel grade and construction are also provided.

Table 10–7 provides general property values for sheathinggrade OSB.

Under PS 2–92, a manufacturer is required to enter into an

agreement with an accredited testing agency to demonstrate

that its panels conform with the requirements of the chosen

standard. The manufacturer must also maintain an in-plant

quality control program in which panel properties are regularly checked, backed by an independent third-partyadministered quality assurance program. The third-party

agency must visit the mill on a regular unannounced basis.

The agency must confirm that the in-plant quality control

program is being maintained and that panels meet the minimum requirements of the standard. Today, OSB manufactured to standard PS 2–92 is quality-certified by the following organizations: APA–The Engineered Wood Association,

Professional Services and Industries, Inc., Pittsburgh Testing

Laboratories, and PFS/TECO Corporations. Examples of

grade stamps for performance-rated panels are shown in

Figure 10–4c,d.

Particleboard

The wood particleboard industry grew out of a need to dispose of large quantities of sawdust, planer shavings, and to a

lesser extent, the use of mill residues and other relatively

homogeneous waste materials produced by other wood industries. Simply put, particleboard is produced by mechanically reducing the material into small particles, applying

adhesive to the particles, and consolidating a loose mat of

Figure 10–6. Schematic of OSB manufacturing process. (Courtesy of Structural Board Association,

Willowdale, Ontario, Canada.)
10–15

the particles with heat and pressure into a panel product

(Fig. 10–7). All particleboard is currently made using a dry

process, where air or mechanical formers are used to distribute the particles prior to pressing.

Particleboard is typically made in three layers. The faces of

the board consists of fine wood particles, and the core is

made of the coarser material. Producing a panel this way

improves utilization of the material and the smooth face

presents a better surface for laminating, overlaying, painting,

or veneering. Particleboard is also readily made from a variety of agricultural residues. Low-density insulating or soundabsorbing particleboard can be made from kenaf core or jute

stick. Low-, medium-, and high-density panels can be produced with cereal straw, which has begun to be used in

North America. Rice husks are commercially manufactured

into medium- and high-density products in the Middle East.

All other things being equal, reducing lignocellulosic

materials to particles requires less energy than reducing the

same material into fibers. However, particleboard is generally

not as strong as fiberboard because the fibrous nature of

lignocellulosics is not exploited as well. Particleboard is

used for furniture cores, where it is typically overlaid with

other materials for decorative purposes. Particleboard can be

used in flooring systems, in manufactured houses, for stair

treads, and as underlayment. Thin panels can be used as a

paneling substrate. Since most applications are interior,

Figure 10–7. Particles, which are sometimes produced

by hammermilling, are used to produce composites

such as particleboard.

particleboard is usually bonded with a UF resin, although

PF and MF resins are sometimes used for applications

requiring more moisture resistance. The various steps

involved in particleboard manufacturing are described in

the following text.

Table 10–7. General property values for sheathing-grade OSBa

Property Value

ASTM test methodb

(where applicable)

Linear hygroscopic expansion

 (30%–90% RH) 0.15%

Linear thermal expansion 6.1 × 10-6 cm/cm/°C (3.4 × 10-6 in/in/°F)

Flexure

Modulus of rupture 20.7–27.6 MPa (3,000–4,000 lb/in2

) D3043

Modulus of elasticity 4.83–8.27 GPa (700–1,200 × 103

 lb/in2)

Tensile strength 6.9–l0.3 MPa (1,000–1,500 lb/in2

) D3500

Compressive strength 10.3–17.2 MPa (1,500–2,500 lb/in2

) D3501

Shear through thickness

 (edgewise shear)

Shear strength 6.9–10.3 MPa (1,000–1,500 lb/in2

) D2719

Shear modulus 1.24–2.00 GPa (180–290 × 103

 lb/in2) D3044

Shear in plane of plies (rolling shear) D2718

Shear strength 1.38–2.1 MPa (200–300 lb/in2

)

Shear modulus 0.14–0.34 GPa (20–50 × 103

 lb/in2)

a

All mechanical properties are based on gross section properties of OSB panels, with stress applied parallel to panel

 major axis where applicable. Note: Data are not to be used in developing allowable design values. Information

 courtesy of APA–The Engineered Wood Association, Tacoma, WA.

b

Standard methods of testing strength and elastic properties of structural panels are given in ASTM standards

(see References).
 10–16

Particle Preparation

Standard particleboard plants based on particulate material

use combinations of hogs, chippers, hammermills, ring

flakers, ring mills, and attrition mills. To obtain particleboards with good strength, smooth surfaces, and equal swelling, manufacturers ideally use a homogeneous material with

a high degree of slenderness (long, thin particles), no oversize particles, no splinters, and no dust. Depending on the

manufacturing process, the specifications for the ideal particle

size are different. For a graduated board, wider tolerances are

acceptable. For a three-layer board, the core particles should

be longer and surface particles shorter, thinner, and smaller.

For a five-layer or multi-layer board, the furnish for the intermediate layer between surface and core should have long

and thin particles for building a good carrier for the fine

surface and to give the boards high bending strength and

stiffness.

Particle Classification and Conveying

Very small particles increase furnish surface area and thus

increase resin requirements. Oversized particles can adversely

affect the quality of the final product because of internal flaws

in the particles. While some particles are classified through

the use of air streams, screen classification methods are the

most common. In screen classification, the particles are fed

over a vibrating flat screen or a series of screens. The screens

may be wire cloth, plates with holes or slots, or plates set on

edge.

The two basic methods of conveying particles are by mechanical means and by air. The choice of conveying method

depends upon the size of the particles. In air conveying, care

should be taken that the material does not pass through

many fans, which reduces the size of the particles. In some

types of flakes, damp conditions are maintained to reduce

break-up of particles during conveying.

Particle Drying

The furnish drying operation is a critical step in the processing of composite products. The raw materials for these products do not usually arrive at the plant at a low enough moisture content for immediate use. Furnish that arrives at the

plant can range from 10% to 200% moisture content. For use

with liquid resins, for example, the furnish must be reduced

to about 2% to 7% moisture content.

The moisture content of particles is critical during hotpressing operations. Thus, it is essential to carefully select

proper dryers and control equipment. The moisture content

of the material depends on whether resin is to be added dry

or in the form of a solution or emulsion. The moisture content of materials leaving the dryers is usually in the range of

4% to 8%. The main methods used to dry particles are

rotary, disk, and suspension drying.

A triple-pass rotary dryer consists of a large horizontal rotating drum that is heated by either steam or direct heat. Operating temperatures depend on the moisture content of the

incoming furnish. The drum is set at a slight angle, and

material is fed into the high end and discharged at the low

end. A series of flights forces the furnish to flow from one end

to the other three times before being discharged. The rotary

movement of the drum moves the material from input to

output.

Addition of Resins and Wax

Frequently used resins for particleboard include ureaformaldehyde and, to a much lesser extent, phenolformaldehyde, melamine-formaldehyde, and isocyanates. The

type and amount of resin used for particleboard depend on the

type of product desired. Based on the weight of dry resin

solids and ovendry weight of the particles, the resin content

can range between 4% and 10%, but usually ranges between

6% and 9% for UF resins. The resin content of the outer face

layers is usually slightly higher than that of the core layer.

Urea-formaldehyde resin is usually introduced in water solutions containing about 50% to 65% solids. Besides resin,

paraffin or microcrystalline wax emulsion is added to improve short-term moisture resistance. The amount of wax

ranges from 0.3% to 1% based on the ovendry weight of the

particles.

Mat Formation

After the particles have been prepared, they must be laid into

an even and consistent mat to be pressed into a panel. This

is typically accomplished in a batch mode or by continuous

formation. The batch system employs a caul or tray on

which a deckle frame is placed. The mat is formed by the

back-and-forth movement of the tray or hopper feeder. The

mat is usually cold pressed to reduce mat thickness prior to

hot pressing. The production of three-layer boards requires

three or more forming stations. The two outer layers consist

of particles that differ in geometry from those in the core. The

resin content of the outer layers is usually higher (about 8%

to 15%) than that of the core (about 4% to 8%).

In continuous mat-forming systems, the particles are distributed in one or several layers on traveling cauls or on a moving belt. Mat thickness is controlled volumetrically. The

two outer face layers usually consist of particles that differ in

geometry from those in the core. Continuous-formed mats are

often pre-pressed, with either a single-opening platen or a

continuous press. Pre-pressing reduces mat height and helps

to consolidate the mat for pressing.

Hot Pressing

After pre-pressing, the mats are hot-pressed into panels.

Presses can be divided into platen and continuous types.

Further development in the industry has made possible the

construction of presses for producing increasingly larger panel

sizes in both single- and multi-opening presses. Both of

these types of presses can be as wide as 3.7 m (12 ft). Multiopening presses can be as long as 10 m (33 ft) and singleopening presses, up to 30.5 m (100 ft) long. Hot-press temperatures for UF resins usually range from 140°C to 165°C

(284°F to 325°F). Pressure depends on a number of factors,

but it is usually in the range of 1.37 to 3.43 MPa (199 to

498 lb/in2

) for medium-density boards. Upon entering the
10–17

hot press, mats usually have a moisture content of 8% to

12%, but this is reduced to about 5% to 9% during pressing.

Alternatively, some particleboards are made by the extrusion

process. In this system, formation and pressing occur in one

operation. The particles are forced into a long, heated die

(made of two sets of platens) by means of reciprocating pistons. The board is extruded between the platens. The particles are oriented in a plane perpendicular to the plane of the

board, resulting in properties that differ from those obtained

with flat pressing.

Finishing

After pressing, the board is trimmed to obtain the desired

length and width and to square the edges. Trim losses usually amount to 0.5% to 8%, depending on the size of the

board, the process employed, and the control exercised.

Trimmers usually consist of saws with tungsten carbide tips.

After trimming, the boards are sanded or planed prior to

packaging and shipping. Particleboards may also be veneered

or overlaid with other materials to provide a decorative

surface, or they may be finished with lacquer or paint.

Treatments with fire-resistant chemicals are also available.

Properties

Tables 10–8 and 10–9 show requirements for grades of particleboard and particleboard flooring products, as specified by

the American National Standard for Particleboard A208.1

(NPA 1993). This standard is typically updated at least

every 5 years. Today, approximately 85% of interior-type

particleboard is used as core stock for a wide variety of furniture and cabinet applications. Floor underlayment and

manufactured home decking represent particleboard construction products and approximately 10% of the market. Lowdensity panels produced in thicknesses >27 mm

(>1-1/16 in.) are used for solid-core doors.

Particleboard Grade Marks and Product

Certification

Particleboard that has been grade marked ensures that the

product has been periodically tested for compliance with

voluntary industry product performance standards. These

inspection or certification programs also generally require

that the quality control system of a production plant meets

strict criteria. Particleboard panels conforming to these product performance standards are marked with grade stamps such

as those shown in Figure 10–8.

Fiberboard

The term fiberboard includes hardboard, medium-density

fiberboard (MDF), and insulation board. Several things

differentiate fiberboard from particleboard, most notably the

physical configuration of the comminuted material

(Fig. 10–9). Because wood is fibrous by nature, fiberboard

exploits the inherent strength of wood to a greater extent than

does particleboard.

To make fibers for composites, bonds between the wood

fibers must be broken. In its simplest form, this is

Table 10–8. Particleboard grade requirementsa,b,c

Linear Formaldehyde

Internal expansion maximum

MOR MOE bond Hardness max avg Screw-holding (N) emission

Graded (MPa) (MPa) (MPa) (N) (%) Face Edge (ppm)

H–1 16.5 2,400 0.90 2,225 NS 1,800 1,325 0.30

H–2 20.5 2,400 0.90 4,450 NS 1,900 1,550 0.30

H–3 23.5 2,750 1.00 6,675 NS 2,000 1,550 0.30

M–1 11.0 1,725 0.40 2,225 0.35 NS NS 0.30

M–S 12.5 1,900 0.40 2,225 0.35 900 800 0.30

M–2 14.5 2,225 0.45 2,225 0.35 1,000 900 0.30

M–3 16.5 2,750 0.55 2,225 0.35 1,100 1,000 0.30

LD–1 3.0 550 0.10 NS 0.35 400 NS 0.30

LD–2 5.0 1,025 0.15 NS 0.35 550 NS 0.30

a

From NPA (1993). Particleboard made with phenol-formaldehyde-based resins does not emit signifi-

 cant quantities of formaldehyde. Therefore, such products and other particleboard products made

 with resin without formaldehyde are not subject to formaldehyde emission conformance testing.

b

Panels designated as “exterior adhesive” must maintain 50% MOR after ASTM D1037 accelerated

 aging.

c

MOR = modulus of rupture; MOE = modulus of elasticity. NS = not specified. 1 MPa = 145 lb/in2;

 1 N = 0.22 lb.

d

H = density > 800 kg/m3 (> 50 lb/ft3), M = density 640 to 800 kg/m3 (40 to 50 lb/ft3). LD = density

 < 640 kg/m3

 (< 40 lb/ft3). Grade M–S refers to medium density; “special” grade added to standard

 after grades M–1, M–2, and M–3. Grade M–S falls between M–1 and M–2 in physical properties.
 10–18

accomplished by attrition milling. Attrition milling is an

age-old concept whereby material is fed between two disks,

one rotating and the other stationary. As the material is

forced through the preset gap between the disks, it is sheared,

cut, and abraded into fibers and fiber bundles. Grain has been

ground in this way for centuries.

Attrition milling, or refining as it is commonly called, can

be augmented by water soaking, steam cooking, or chemical

treatments. Steaming the lignocellulosic weakens the lignin

bonds between the cellulosic fibers. As a result, the fibers are

more readily separated and usually are less damaged than

fibers processed by dry processing methods. Chemical treatments, usually alkali, are also used to weaken the lignin

bonds. All of these treatments help increase fiber quality and

reduce energy requirements, but they may reduce yield as

well. Refiners are available with single- or double-rotating

disks, as well as steam-pressurized and unpressurized configurations. For MDF, steam-pressurized refining is typical.

Fiberboard is normally classified by density and can be made

by either dry or wet processes (Fig. 10–2). Dry processes are

applicable to boards with high density (hardboard) and medium density (MDF). Wet processes are applicable to both

high-density hardboard and low-density insulation board.

The following subsections briefly describe the manufacturing

of high- and medium-density dry-process fiberboard, wetprocess hardboard, and wet-process low-density insulation

board. Suchsland and Woodson (1986) and Maloney (1993)

provide more detailed information.

Table 10–9. Particleboard flooring product grade requirementsa

Formaldehyde

MOR MOE

Internal

bond Hardness

Linear expansion

max avg

maximum

emission

Gradeb (MPa) (MPa) (MPa) (N) (%) (ppm)

 PBU 11.0 1,725 0.40 2,225 0.35 0.20

 D–2 16.5 2,750 0.55 2,225 0.30 0.20

 D–3 19.5 3,100 0.55 2,225 0.30 0.20

a

From NPA (1993). Particleboard made with phenol-formaldehyde-based resins does not emit significant

 quantities of formaldehyde. Therefore, such products and other particleboard products made with resin without

 formaldehyde are not subject to formaldehyde emission conformance testing. Grades listed here shall also

 comply with appropriate requirements listed in section 3. Panels designated as “exterior adhesive” must

 maintain 50% MOR after ASTM D1037 accelerated aging (3.3.3).

b

PBU = underlayment; D = manufactured home decking.

Figure 10–8. Examples of grade stamps for particleboard.
10–19

Dry-Process Fiberboard

Dry-process fiberboard is made in a similar fashion to particleboard. Resin (UF, PF) and other additives may be applied

to the fibers by spraying in short-retention blenders or introduced as the wet fibers are fed from the refiner into a blowline dryer. Alternatively, some fiberboard plants add the resin

in the refiner. The adhesive-coated fibers are then air-laid into

a mat for subsequent pressing, much the same as mat

formation for particleboard.

Pressing procedures for dry-process fiberboard differ somewhat from particleboard procedures. After the fiber mat is

formed (Fig. 10–10), it is typically pre-pressed in a band

press. The densified mat is then trimmed by disk cutters and

transferred to caul plates for the hardboard pressing operation;

for MDF, the trimmed mat is transferred directly to the press

(Fig. 10–11). All dry-formed boards are pressed in multiopening presses at approximately 140°C to 165°C (284°F to

329°F) for UF-bonded products and 190°C (410°F) for PFbonded products. Continuous pressing using large, highpressure band presses is also gaining in popularity. Board

density is a basic property and an indicator of board quality.

Since density is greatly influenced by moisture content, this

is constantly monitored by moisture sensors using infrared

light. An example of an MDF formaldehyde emissions

certification tag is shown in Figure 10–12.

Wet-Process Hardboard

Wet-process hardboards differ from dry-process fiberboards in

several significant ways. First, water is used as the distribution medium for forming the fibers into a mat. As such, this

technology is really an extension of paper manufacturing

Figure 10–9. Fibers can be made from many

lignocellulosics and form the raw materials for

many composites, most notably fiberboard. Fibers

are typically produced by the refining process.

Figure 10–10. Laboratory-produced air-laid mat before

pressing. Approximate dimensions are 686 by 686 by

152 mm (27 by 27 by 6 in.) thick. Resin was applied

to fibers before mat production. This mat will be made

into a high-density fiberboard approximately 3 mm

(0.12 in.) thick.

Figure 10–11. Air-laid mat about to enter a

laboratory press.

Figure 10–12. Example of MDF formaldehyde

emissions certification tag.
 10–20

technology. Secondly, some wet-process boards are made

without additional binders. If the lignocellulosic contains

sufficient lignin and if lignin is retained during the refining

operation, lignin can serve as the binder. Under heat and

pressure, lignin will flow and act as a thermosetting adhesive, enhancing the naturally occurring hydrogen bonds.

Refining is an important step for developing strength in wetprocess hardboards. The refining operation must also yield a

fiber of high “freeness;” that is, it must be easy to remove

water from the fibrous mat. The mat is typically formed on a

Fourdrinier wire, like papermaking, or on cylinder formers.

The wet process employs a continuously traveling mesh

screen, onto which the soupy pulp flows rapidly and

smoothly. Water is drawn off through the screen and then

through a series of press rolls, which use a wringing action

to remove additional water.

Wet-process hardboards are pressed in multi-opening presses

heated by steam. The press cycle consists of three phases and

lasts 6 to 15 min. The first phase is conducted at high pressure, and it removes most of the water while bringing the

board to the desired thickness. The primary purpose of the

second phase is to remove water vapor. The final phase is

relatively short and results in the final cure. A maximum

pressure of about 5 MPa (725 lb/in2

) is used. Heat is essential during pressing to induce fiber-to-fiber bond. A high

temperature of up to 210°C (410°F) is used to increase production by causing faster evaporation of the water. Lack of

sufficient moisture removal during pressing adversely affects

strength and may result in “springback” or blistering.

Post-Treatment of Wet- and

Dry-Process Hardboard

Several treatments are used to increase the dimensional

stability and mechanical performance of hardboard. Heat

treatment, tempering, and humidification may be done singularly or in conjunction with one another.

Heat treatment—exposure of pressed fiberboard to dry heat—

improves dimensional stability and mechanical properties,

reduces water adsorption, and improves interfiber bonding.

Tempering is the heat treatment of pressed boards, preceded

by the addition of oil. Tempering improves board surface

hardness and is sometimes done on various types of wetformed hardboards. It also improves resistance to abrasion,

scratching, scarring, and water. The most common oils used

include linseed oil, tung oil, and tall oil.

Humidification is the addition of water to bring the board

moisture content into equilibrium with the air. Initially, a

pressed board has almost no moisture content. When the

board is exposed to air, it expands linearly by taking on 3%

to 7% moisture. Continuous or progressive humidifiers are

commonly used for this purpose. Air of high humidity is

forced through the stacks where it provides water vapor to the

boards. The entire process is controlled by a dry-bulb-wetbulb controller. Another method involves spraying water on

the back side of the board.

Insulation Board

Insulation boards are low-density, wet-laid panel products

used for insulation, sound deadening, carpet underlayment,

and similar applications. In the manufacture of insulation

board, the need for refining and screening is a function of the

raw material available, the equipment used, and the desired

end-product. Insulation boards typically do not use a binder,

and they rely on hydrogen bonds to hold the board components together. Sizing agents are usually added to the furnish

(about 1%) to provide the finished board with a modest

degree of water resistance and dimensional stability. Sizing

agents include rosin, starch, paraffin, cumarone, resin,

asphalt, and asphalt emulsions.

Like the manufacture of wet-process hardboard, insulation

board manufacture is a modification of papermaking. A thick

fibrous sheet is made from a low-consistency pulp suspension in a process known as wet felting. Felting can be accomplished through use of a deckle box, Fourdrinier screen,

or cylinder screen. A deckle box is a bottomless frame that is

placed over a screen. A measured amount of stock is put in

the box to form one sheet; vacuum is then applied to remove

most of the water. The use of Fourdrinier screen for felting is

similar to that for papermaking, except that line speeds are

reduced to 1.5 to 15 m/min (5 to 49 ft/min).

Insulation board is usually cold-pressed to remove most of

the free water after the mat is formed. The wet mats are then

dried to the final moisture content. Dryers may be a continuous tunnel or a multi-deck arrangement. The board is generally dried in stages at temperatures ranging from 120°C to

190°C (248°F to 374°F). Typically, about 2 to 4 h are

required to reduce moisture content to about 1% to 3%.

After drying, some boards are treated for various applications.

Boards may be given tongue-and-groove or shiplap edges or

can be grooved to produce a plank effect. Other boards are

laminated by means of asphalt to produce roof insulation.

Properties and Applications

Medium-Density Fiberboard—Minimum property requirements, as specified by the American National Standard

for MDF, A208.2 (NPA 1994) are given in Table 10–10.

This standard is typically updated every 5 years or less. The

furniture industry is by far the dominant MDF market. Medium-density fiberboard is frequently used in place of solid

wood, plywood, and particleboard in many furniture applications. It is also used for interior door skins, mouldings, and

interior trim components (Youngquist and others 1997).

Hardboard—Table 10–11 provides basic hardboard physical properties (ANSI/AHA A135.4–1995 (AHA 1995a)) for

selected products. The uses for hardboard can generally be

grouped as construction, furniture and furnishings, cabinet

and store work, appliances, and automotive and rolling

stock. Typical hardboard products are prefinished paneling

(ANSI/AHA A135.5–1995 (AHA 1995b)), house siding

(ANSI/AHA A135.6–1990 (AHA 1990)), floor underlayment, and concrete form board. Table 10–12 shows physical
10–21

Table 10–10. Medium-density fiberboard (MDF) property requirementsa

Nominal Internal Formaldehyde

thickness MOR MOE bond Screw-holding (N) emissionc

Product classb (mm) (MPa) (MPa) (MPa) Face Edge (ppm)

Interior MDF

HD 34.5 3,450 0.75 1,555 1,335 0.30

MD ≤21 24.0 2,400 0.60 1,445 1,110 0.30

>21 24.0 2,400 0.55 1,335 1,000 0.30

LD 14.0 1,400 0.30 780 670 0.30

Exterior MDF

MD–Exterior

 adhesive

≤21

>21

34.5

31.0

3,450

3,100

0.90

0.70

1,445

1,335

1,110

1,000

0.30

0.30

a

From NPA (1994). Metric property values shall be primary in determining product performance

 requirements.

b

MD–Exterior adhesive panels shall maintain at least 50% of listed MOR after ASTM D1037–1991,

 accelerated aging (3.3.4). HD = density > 800 kg/m3

 (> 50 lb/ft3), MD = density 640 to 800 kg/m3

 (40 to 50 lb/ft3), LD = density < 640 kg/m3 (< 40 lb/ft3). c

Maximum emission when tested in accordance with ASTM E1333–1990, Standard test method

 for determining formaldehyde levels from wood products under defined test conditions using

 a larger chamber (ASTM).

Table 10–11. Hardboard physical property requirementsa

Water resistance

(max avg/panel)

Tensile strength

(min avg/panel) (MPa)

Product class

Normal

thickness

(mm)

Water

absorption

based on

weight (%)

Thickness

swelling

(%)

MOR

(min avg/

panel)

(MPa)

Parallel

to

 surface

Perpendicular

to

surface

Tempered 2.1 30 25 41.4 20.7 0.90

2.5 25 20 41.4 20.7 0.90

3.2 25 20 41.4 20.7 0.90

4.8 25 20 41.4 20.7 0.90

6.4 20 15 41.4 20.7 0.90

7.9 15 10 41.4 20.7 0.90

9.5 10 9 41.4 20.7 0.90

Standard 2.1 40 30 31.0 15.2 0.62

2.5 35 25 31.0 15.2 0.62

3.2 35 25 31.0 15.2 0.62

4.8 35 25 31.0 15.2 0.62

6.4 25 20 31.0 15.2 0.62

7.9 20 15 31.0 15.2 0.62

9.5 15 10 31.0 15.2 0.62

Service-tempered 3.2 35 30 31.0 3.8 0.52

4.8 30 30 31.0 3.8 0.52

6.4 30 25 31.0 3.8 0.52

9.5 20 15 31.0 3.8 0.52

a

AHA 1995a.
 10–22

properties of hardboard siding. Hardboard siding products

come in a great variety of finishes and textures (smooth or

embossed) and in different sizes. For application purposes,

the AHA siding classifies into three basic types:

Lap siding—boards applied horizontally, with each board

overlapping the board below it

Square edge panels—siding intended for vertical application

in full sheets

Shiplap edge panel siding—siding intended for vertical

application, with the long edges incorporating shiplap joints

The type of panel dictates the application method. The AHA

administers a quality conformance program for hardboard for

both panel and lap siding. Participation in this program is

voluntary and is open to all (not restricted to AHA members). Under this program, hardboard siding products are

tested by an independent laboratory in accordance with product standard ANSI/AHA A135.6. Figure 10–13a provides an

example of a grade stamp for a siding product meeting this

standard.

Insulation Board—Physical and mechanical properties of

insulation board are published in the ASTM C208 standard

specification for cellulosic fiber insulation board. Physical

Table 10–12. Physical and mechanical properties of hardboard sidinga

Propertyb Requirement

Water absorption (based on weight) 12% (max avg/panel)

Thickness swelling 8% (max avg/panel)

Weatherability of substrate (max residual swell) 20%

Weatherability of primed substrate No checking, erosion, flaking, or objectionable fiber raising; adhesion, less than

3.2 mm (0.125 in.) of coating picked up

Linear expansion 30% to 90% RH (max) Thickness range

 (cm)

Maximum linear

expansion (%)

0.220–0.324 0.36

0.325–0.375 0.38

0.376–0.450 0.40

>0.451 0.40

Nail-head pull-through 667 N (150 lb) (min avg/panel)

Lateral nail resistance 667 N (150 lb) (min avg/panel)

Modulus of rupture 12.4 MPa (1,800 lb/in2

) for 9.5, 11, and

12.7 mm (3/8, 7/16, and 1/2 in.) thick

(min avg/panel)

20.7 MPa (3,000 lb/in2

) for 6.4 mm (1/4 in.)

thick (min avg/panel)

Hardness 2002 N (450 lb) (min avg/panel)

Impact 229 mm (9 in.) (min avg/panel)

Moisture contentc 4% to 9% included, and not more than 3%

variance between any two boards in any

one shipment or order

a

From Youngquist and others 1992.

b

Refer to ANSI/AHA A135.6 I–1990 for test method for determining information on properties.

c

Since hardboard is a wood-based material, its moisture content varies with environmental

 humidity conditions. When the environmental humidity conditions in the area of intended use are

 a critical factor, the purchaser should specify a moisture content range more restrictive than

 4% to 9% so that fluctuation in the moisture content of the siding will be kept to a minimum.

(a) (b)

Figure 10–13. Examples of grade stamps: (a) grade

stamp for siding conforming to ANSI/AHA A135.6

standard, and (b) grade mark stamp for cellulosic

fiberboard products conforming to ANSI/AHA A194.1

standard.
10–23

properties are also included in the ANSI standard for

cellulosic fiberboard, ANSI/AHA A194.1 (AHA 1985).

Insulation board products can be divided into three categories

(Suchsland and Woodson 1986): exterior, interior, and

industrial.

Exterior products

• Sheathing—board used in exterior construction because of

its insulation and noise control qualities, bracing strength,

and low price

• Roof decking—three-in-one component that provides roof

deck, insulation, and a finished interior ceiling surface; insulation board sheets are laminated together with waterproof adhesive Roof insulation—insulation board designed

for use on flat roof decks

• Aluminum siding backer board—fabricated insulation

board for improving insulation of aluminum-sided houses

Interior products

• Building board—general purpose product for interior

construction

• Ceiling tile—insulation board embossed and decorated for

interior use; valued for acoustical qualities; also decorative, nonacoustical tiles

• Sound-deadening board—special product designed to

control noise levels in buildings

Industrial products

• Mobile home board

• Expansion joint strips

• Boards for automotive and furniture industries

The AHA administers a quality conformance program for

cellulosic fiberboard products including sound-deadening

board, roof insulation boards, structural and nonstructural

sheathings, backer board, and roof decking in various thicknesses. These products are tested by an independent laboratory in accordance with product standard ANSI/AHA

A194.1. An example of the grade mark stamp for these

products is shown in Figure 10–13b.

Finishing Techniques

Several techniques are used to finish fiberboard: trimming,

sanding, surface treatment, punching, and embossing.

Trimming—Trimming consists of reducing products into

standard sizes and shapes. Generally, double-saw trimmers

are used to saw the boards. Trimmers consist of overheadmounted saws or multiple saw drives. Trimmed boards are

stacked in piles for future processing.

Sanding—If thickness tolerance is critical, hardboard is

sanded prior to finishing. S1S (smooth on one side) boards

require this process. Sanding reduces thickness variation and

improves surface paintability. Single-head, wide-belt sanders

are used with 24- to 36-grit abrasive.

Surface treatment—Surface treatments improve the appearance and performance of boards. Boards are cleaned by

spraying with water and then dried at about 240°C (464°F)

for 30 seconds. Board surfaces are then modified with paper

overlay, paint, or stain or are printed directly on the panel.

Punching—Punching changes boards into the perforated

sheets used as peg board. Most punching machines punch

three rows of holes simultaneously while the board advances.

Embossing—Embossing consists of pressing the unconsolidated mat of fibers with a textured form. This process results

in a slightly contoured board surface that can enhance the

resemblance of the board to that of sawn or weathered wood,

brick, and other materials.

Specialty Composites

Special-purpose composites are produced to obtain desirable

properties like water resistance, mechanical strength, acidity

control, and decay and insect resistance. Overlays and veneers can also be added to enhance both structural properties

and appearance (Fig. 10–14).

Moisture-Resistant Composites

Sizing agents, wax, and asphalt can be used to make composites resistant to moisture. Sizing agents cover the surface

of fibers, reduce surface energy, and render the fibers relatively

hydrophobic. Sizing agents can be applied in two ways. In

the first method, water is used as a medium to ensure thorough mixing of sizing and fiber. The sizing is forced to

precipitate from the water and is fixed to the fiber surface. In

the second method, the sizing is applied directly to the

fibers. Rosin is a common sizing agent that is obtained from

living pine trees, from pine stumps, and as a by-product of

kraft pulping of pines. Rosin sizing is added in amounts of

less than 3% solids based on dry fiber weight.

Waxes are high molecular weight hydrocarbons derived from

crude oil. Wax sizing is used in dry-process fiberboard production; for wet processes, wax is added in solid form or as

Figure 10–14. Medium-density fiberboard with veneer

overlay. Edges can be shaped and finished as required

by end product.
 10–24

an emulsion. Wax sizing tends to lower strength properties

to a greater extent than does rosin.

Asphalt is also used to increase water resistance, especially

in low-density wet-process insulation board. Asphalt is a

black–brown solid or semi-solid material that liquefies when

heated. The predominant component of asphalt is bitumen.

Asphalt is precipitated onto fiber by the addition of alum.

Flame-Retardant Composites

Two general application methods are available for improving

the fire performance of composites with fire-retardant chemicals. One method consists of pressure impregnating the wood

with waterborne or organic solventborne chemicals. The

second method consists of applying fire-retardant chemical

coatings to the wood surface. The impregnation method is

usually more effective and longer lasting; however, this

technique sometimes causes damage to the wood–adhesive

bonds in the composite and results in the degradation of

some physical and mechanical properties of the composite.

For wood in existing constructions, surface application of

fire-retardant paints or other finishes offers a practical method

to reduce flame spread.

Preservative-Treated Composites

Wood is highly susceptible to attack by fungi and insects;

thus, treatment is essential for maximum durability in adverse conditions.

Composites can be protected from the attack of decay fungi

and harmful insects by applying selected chemicals as wood

preservatives. The degree of protection obtained depends on

the kind of preservative used and the ability to achieve proper

penetration and retention of the chemicals. Wood preservative chemicals can be applied using pressure or nonpressure

processes. As in the application of fire-retardant chemicals,

the application of wood preservatives can sometimes cause

damage to wood–adhesive bonds, thus reducing physical and

mechanical properties of the composite. Common preservative treatments include chromated copper arsenate (CCA) and

boron compounds.

Wood–Nonwood Composites

Interest has burgeoned in combining wood and other raw

materials, such as plastics, gypsum, and concrete, into composite products with unique properties and cost benefits

(Youngquist and others 1993a, 1993b, 1994; Rowell and

others 1997). The primary impetus for developing such

products has come from one or more of the following research

and development goals:

• Reduce material costs by combining a lower cost material

(acting as a filler or extender) with an expensive material

• Develop products that can utilize recycled materials and be

recyclable in themselves

• Produce composite products that exhibit specific properties that are superior to those of the component materials

alone (for example, increased strength-to-weight ratio, improved abrasion resistance)

Composites made from wood and other materials create

enormous opportunities to match product performance to

end-use requirements (Youngquist 1995).

Inorganic–Bonded Composites

Inorganic-bonded wood composites have a long and varied

history that started with commercial production in Austria in

1914. A plethora of building materials can be made using

inorganic binders and lignocellulosics, and they run the

normal gamut of panel products, siding, roofing tiles, and

precast building members (Fig. 10–15).

Inorganic-bonded wood composites are molded products or

boards that contain between 10% and 70% by weight wood

particles or fibers and conversely 90% to 30% inorganic

binder. Acceptable properties of an inorganic-bonded wood

composite can be obtained only when the wood particles are

fully encased with the binder to make a coherent material.

This differs considerably from the technique used to manufacture thermosetting-resin-bonded boards where flakes or particles are “spot welded” by a binder applied as a finely distributed spray or powder. Because of this difference and

because hardened inorganic binders have a higher density

than that of most thermosetting resins, the required amount

of inorganic binder per unit volume of composite material is

much higher than that of resin-bonded wood composites.

The properties of inorganic-bonded wood composites are

significantly influenced by the amount and nature of the

inorganic binder and the woody material as well as the density of the composites.

Inorganic binders fall into three main categories: gypsum,

magnesia cement, and Portland cement. Gypsum and magnesia cement are sensitive to moisture, and their use is

Figure 10–15. Laboratory-produced low-density,

cement-bonded composite panel. Full-scale panels

such as these are used in construction.
10–25

generally restricted to interior applications. Composites

bonded with Portland cement are more durable than those

bonded with gypsum or magnesia cement and are used in

both interior and exterior applications. Inorganic-bonded

composites are made by blending proportionate amounts of

lignocellulosic fiber with inorganic materials in the presence

of water and allowing the inorganic material to cure or “set

up” to make a rigid composite. All inorganic-bonded composites are very resistant to deterioration, particularly by

insects, vermin, and fire.

A unique feature of inorganic-bonded composites is that their

manufacture is adaptable to either end of the cost and technology spectrum. This is facilitated by the fact that no heat

is required to cure the inorganic material. For example, in

the Philippines, Portland cement-bonded composites are

mostly fabricated using manual labor and are used in lowcost housing. In Japan, the fabrication of these composites is

automated, and they are used in very expensive modular

housing.

The versatility of manufacture makes inorganic-bonded composites ideally suited to a variety of lignocellulosic materials. With a very small capital investment and the most

rudimentary of tools, satisfactory inorganic-bonded lignocellulosic composite building materials can be produced on a

small scale using mostly unskilled labor. If the market for

such composites increases, technology can be introduced to

increase manufacturing throughput. The labor force can be

trained concurrently with the gradual introduction of more

sophisticated technology.

Gypsum-Bonded Composites

Gypsum can be derived by mining from natural sources or

obtained as a byproduct of flue gas neutralization. Flue gas

gypsum, now being produced in very large quantities in the

United States because of Clean Air Act regulations, is the

result of introducing lime into the combustion process to

reduce sulfur dioxide emissions. In 1995, more than 100

power plants throughout the United States were producing

gypsum. Flue gas gypsum can be used in lieu of mined

gypsum.

Gypsum panels are frequently used to finish interior wall and

ceiling surfaces. In the United States, these products are

generically called “dry wall” because they replace wet plaster

systems. To increase the bending strength and stiffness,

gypsum panels are frequently wrapped in paper, which provides a tension surface. An alternative to wrapping gypsum

with fiber is to place the fiber within the panel, as several

U.S. and European firms are doing with recycled paper fiber.

There is no technical reason that other lignocellulosics

cannot be used in this way. Gypsum is widely available and

does not have the highly alkaline environment of cement.

Gypsum panels are normally made from a slurry of gypsum,

water, and lignocellulosic fiber. In large-scale production, the

slurry is extruded onto a belt, which carries the slurry

through a drying oven to evaporate water and facilitate cure of

the gypsum. The panel is then cut to length and trimmed if

necessary.

Magnesia-Cement-Bonded Composites

Fewer boards bonded with magnesia cement have been produced than cement- or gypsum-bonded panels, mainly because of price. However, magnesia cement does offer some

manufacturing advantages over Portland cement. First, the

various sugars in lignocellulosics apparently do not have as

much effect on the curing and bonding of the binder. Second,

magnesia cement is reported to be more tolerant of high

water content during production. This opens up possibilities

to use lignocellulosics not amenable to Portland cement

composites, without leaching or other modification, and to

use alternative manufacturing processes and products.

Although composites bonded with magnesia cement are

considered water-sensitive, they are much less so than

gypsum-bonded composites.

One successful application of magnesia cement is a lowdensity panel made for interior ceiling and wall applications.

In the production of this panel product, wood wool

(excelsior) is laid out in a low-density mat. The mat is then

sprayed with an aqueous solution of magnesia cement,

pressed, and cut into panels.

In Finland, magnesia-cement-bonded particleboard is manufactured using a converted conventional particleboard plant.

Magnesia oxide is applied to the lignocellulosic particles in

a batch blender along with other chemicals and water.

Depending on application and other factors, boards may

be cold- or hot-pressed.

Other processes have been suggested for manufacturing magnesia-cement-bonded composites. One application may be to

spray a slurry of magnesia cement, water, and lignocellulosic

fiber onto existing structures as fireproofing. Extrusion into a

pipe-type profile or other profiles is also possible.

Portland-Cement-Bonded Composites

The most apparent and widely used inorganic-bonded composites are those bonded with Portland cement. Portland

cement, when combined with water, immediately reacts in a

process called hydration to eventually solidify into a solid

stone-like mass. Successfully marketed Portland-cementbonded composites consist of both low-density products

made with excelsior and high-density products made with

particles and fibers. General mechanical property values for a

low density cement–wood excelsior product are given in

Table 10–13.

The low-density products may be used as interior ceiling and

wall panels in commercial buildings. In addition to the

advantages described for low-density magnesia-bonded composites, low-density composites bonded with Portland

cement offer sound control and can be quite decorative. In

some parts of the world, these panels function as complete

wall and roof decking systems. The exterior of the panels is

stuccoed, and the interior is plastered. High-density panels

can be used as flooring, roof sheathing, fire doors, loadbearing walls, and cement forms. Fairly complex molded

shapes can be molded or extruded, such as decorative roofing

tiles or non-pressure pipes.
 10–26

Problems and Solutions

Although the entire sphere of inorganic-bonded lignocellulosic composites is attractive, and cement-bonded composites are especially so, the use of cement involves limitations

and tradeoffs. Marked embrittlement of the lignocellulosic

component is known to occur and is caused by the alkaline

environment provided by the cement matrix. In addition,

hemicellulose, starch, sugar, tannins, and lignin, all to a

varying degree, affect the cure rate and ultimate strength of

these composites. To make strong and durable composites,

measures must be taken to ensure long-term stability of the

lignocellulosic in the cement matrix. To overcome these

problems, various schemes have been developed. The most

common is leaching, whereby the lignocellulosic is soaked

in water for 1 or 2 days to extract some of the detrimental

components. However, in some parts of the world, the water

containing the leachate is difficult to dispose of. Low water–

cement ratios are helpful, as is the use of curing accelerators

like calcium carbonate. Conversely, low alkali cements have

been developed, but they are not readily available throughout

the world. Two other strategies are natural pozzolans and

carbon dioxide treatment.

Natural Pozzolans—Pozzolans are defined as siliceous or

siliceous and aluminous materials that can react chemically

with calcium hydroxide (lime) at normal temperatures in the

presence of water to form cement compounds (ASTM 1988).

Some common pozzolanic materials include volcanic ash, fly

ash, rice husk ash, and condensed silica fume. All these

materials can react with lime at normal temperatures to make

a natural water-resistant cement.

In general, when pozzolans are blended with Portland cement, they increase the strength of the cement but slow the

cure time. More important, pozzolans decrease the alkalinity

of Portland cement, which indicates that adding lignocellulosic-based material (rice husk ash) to cement-bonded lignocellulosic composites may be advantageous.

Carbon Dioxide Treatment—In the manufacture of a cement-bonded lignocellulosic composite, the cement hydration process normally requires from 8 to 24 h to develop

sufficient board strength and cohesiveness to permit the

release of consolidation pressure. By exposing the cement to

carbon dioxide, the initial hardening stage can be reduced to

less than 5 min. This phenomenon results from the chemical

reaction of carbon dioxide with calcium hydroxide to form

calcium carbonate and water.

Reduction of initial cure time of the cement-bonded lignocellulosic composite is not the only advantage of using carbon

dioxide injection. Certain species of wood have varying

amounts of sugars and tannins that interfere with the hydration or setting of Portland cement. Research has shown that

the use of carbon dioxide injection reduces the likelihood of

these compounds to inhibit the hydration process, thus

allowing the use of a wider range of species in these composites. In addition, research has demonstrated that composites

treated with carbon dioxide can be twice as stiff and strong as

untreated composites (Geimer and others 1992). Finally,

carbon-dioxide-treated composites do not experience efflorescence (migration of calcium hydroxide to surface of material),

so the appearance of the surface of the final product is not

changed over time.

Wood Fiber–Thermoplastic

Composites

As described elsewhere in this chapter, the use of lignocellulosic materials with thermosetting polymeric materials, like

phenol- or urea-formaldehyde, in the production of composites has a long history. The use of lignocellulosics with

thermoplastics, however, is a more recent innovation.

Broadly defined, a thermoplastic softens when heated and

hardens when cooled. Thermoplastics selected for use

with lignocellulosics must melt or soften at or below the

degradation point of the lignocellulosic component, normally

200°C to 220°C (392°F to 428°F). These thermoplastics

Table 10–13. General properties of low-density cement–wood composites fabricated using an

excelsior-type particlea,b

Property From To

Bending strength 1.7 MPa (250 lb/in2) 5.5 MPa (800 lb/in2)

Modulus of elasticity 621 MPa (0.9 × 105

 lb/in2) 1,241 MPa (1.8 × 105 lb/in2)

Tensile strength 0.69 MPa (100 lb/in2

) 4.1 MPa (600 lb/in2)

Compression strength 0.69 MPa (100 lb/in2

) 5.5 MPa (800 lb/in2)

Shearc 0.69 MPa (100 lb/in2

) 1.4 MPa (200 lb/in2)

E/Gd 40 100

a

Data represent compilation of raw data from variety of sources for range of board properties. Variables

 include cement–wood mix, particle configuration, board density, and the forming and curing methods.

b

Specific gravity range, 0.5 to 1.0.

c

Shear strength data are limited to a small sample of excelsior boards having a specific gravity of 0.5 to 0.65.

d

E/G is ratio of bending modulus of elasticity to modulus of rigidity or shear modulus. For wood, this ratio is

 often assumed to be around 16.
10–27

include polypropylene, polystyrene, vinyls, and low- and

high-density polyethylenes.

Wood flour is a readily available resource that can be used as

a filler in thermoplastic composites. Wood flour is processed

commercially, often from post-industrial materials such as

planer shavings, chips, and sawdust. Several grades are

available depending upon wood species and particle size.

Wood fibers, although more difficult to process compared

with wood flour, can lead to superior composite properties

and act more as a reinforcement than as a filler. A wide variety of wood fibers are available from both virgin and recycled

resources.

Other materials can be added to affect processing and product

performance of wood–thermoplastic composites. These additives can improve bonding between the thermoplastic and

wood component (for example, coupling agents), product

performance (impact modifiers, UV stabilizers, flame retardants), and processability (lubricants).

Several considerations must be kept in mind when processing wood with thermoplastics. Moisture can disrupt many

thermoplastic processes, resulting in poor surface quality,

voids, and unacceptable parts. Materials must either be

predried or vented equipment must be used to remove moisture. The low degradation temperature of wood must also be

considered. As a general rule, melt temperatures should be

kept below 200°C (392°F), except for short periods. Higher

temperatures can result in the release of volatiles, discoloration, odor, and embrittlement of the wood component.

There are two main strategies for processing thermoplastics

in lignocellulosic composites (Youngquist and others

1993b). In the first, the lignocellulosic component serves as

a reinforcing agent or filler in a continuous thermoplastic

matrix. In the second, the thermoplastic serves as a binder to

the majority lignocellulosic component. The presence or

absence of a continuous thermoplastic matrix may also determine the processability of the composite material. In

general, if the matrix is continuous, conventional thermoplastic processing equipment may be used to process

composites; however, if the matrix is not continuous, other

processes may be required. For the purpose of discussion, we

present these two scenarios for composites with high and low

thermoplastic content.

Composites With High Thermoplastic Content

In composites with high thermoplastic content, the thermoplastic component is in a continuous matrix and the lignocellulosic component serves as a reinforcement or filler

(Fig. 10–16). In the great majority of reinforced thermoplastic composites available commercially, inorganic materials

(for example, glass, clays, and minerals) are used as reinforcements or fillers. Lignocellulosic materials offer some

advantages over inorganic materials; they are lighter, much

less abrasive, and renewable. As a reinforcement, lignocellulosics can stiffen and strengthen the thermoplastic and can

improve thermal stability of the product compared with that

of unfilled material.

Thermoplastics in pellet form have bulk density in the range

of 500 to 600 kg/m3

 (31 to 37 lb/ft3). Lignocellulosics typically have an uncompacted bulk density of 25 to 250 kg/m3

(1.6 to 16 lb/ft3). Wood fibers are at the low end of the lignocellulosic bulk density continuum and wood flours at the

high end. Although processing of wood flour in thermoplastics is relatively easy, the low bulk density and difficulty of

dispersing fibrous materials make thermoplastics more difficult to compound. More intensive mixing and the use of

special feeding equipment may be necessary to handle longer

fibers.

The manufacture of thermoplastic composites is usually a

two-step process. The raw materials are first mixed together,

and the composite blend is then formed into a product. The

combination of these steps is called in-line processing, and

the result is a single processing step that converts raw

materials to end products. In-line processing can be very

difficult because of control demands and processing trade-offs.

As a result, it is often easier and more economical to separate

the processing steps.

Compounding is the feeding and dispersing of the lignocellulosic component in a molten thermoplastic to produce a

homogeneous material. Various additives are added and

moisture is removed during compounding. Compounding

may be accomplished using either batch mixers (for example,

internal and thermokinetic mixers) or continuous mixers (for

example, extruders and kneaders). Batch systems allow

closer control of residence time, shear, and temperature than

do continuous systems. Batch systems are also more

appropriate for operations consisting of short runs and frequent change of materials. On the other hand, continuous

systems are less operator-dependent than are batch systems

and have less batch-to-batch differences(Anon. 1997).

The compounded material can be immediately pressed or

shaped into an end product while still in its molten state or

pelletized into small, regular pellets for future reheating and

forming. The most common types of product-forming

methods for wood–thermoplastic composites involve forcing

Figure 10–16. The use of lignocelulosics as reinforcing

fillers allows thermoplastics to be molded into a wide

variety of shapes and forms.
 10–28

molten material through a die (sheet or profile extrusion) into

a cold mold (injection molding) or pressing in calenders

(calendering) or between mold halves (thermoforming and

compression molding).

Properties of wood–plastic composites can vary greatly

depending upon such variables as type, form, and weight

fractions of constituents, types of additives, and processing

history. Table 10–14 shows some of the properties for

several unfilled polypropylene and wood–polypropylene

composites.

Composites with high thermoplastic content are not without

tradeoffs. Impact resistance of such composites decreases

compared with that of unfilled thermoplastics, and these

composites are also more sensitive to moisture than unfilled

material or composites filled with inorganic material. From a

practical standpoint, however, the thermoplastic component

usually makes the temperature sensitivity of the composite

more significant than any change in properties brought about

by moisture absorption.

Composites With Low Thermoplastic Content

Composites with low thermoplastic content can be made in a

variety of ways. In the simplest form, the thermoplastic

component acts much the same way as a thermosetting resin;

that is, as a binder to the lignocellulosic component. An

alternative is to use the thermoplastic in the form of a textile

fiber. The thermoplastic textile fiber enables a variety of

lignocellulosics to be incorporated into a low-density, nonwoven, textile-like mat. The mat may be a product in itself,

or it may be consolidated into a high-density product.

Experimentally, low-thermoplastic-content composites have

been made that are very similar to conventional lignocellulosic composites in many performance characteristics

(Youngquist and others 1993b). In their simplest form,

lignocellulosic particles or fibers can be dry-blended with

thermoplastic granules, flakes, or fibers and pressed into

panel products.

Because the thermoplastic component remains molten when

hot, different pressing strategies must be used than when

thermosetting binders are used. Two options have been

developed to accommodate these types of composites. In the

first, the material is placed in the hot press at ambient temperature. The press then closes and consolidates the material,

and heat is transferred through conduction to melt the thermoplastic component, which flows around the lignocellulosic component. The press is then cooled, “freezing” the

thermoplastic so that the composite can be removed from the

press. Alternatively, the material can be first heated in an

oven or hot press. The hot material is then transferred to a

cool press where it is quickly consolidated and cooled to

make a rigid panel. Some commercial nonstructural lignocellulosic–thermoplastic composites are made in this way.

Nonwoven Textile-Type Composites

In contrast to high-thermoplastic-content and conventional

low-thermoplastic-content composites, nonwoven textiletype composites typically require long fibrous materials for

their manufacture. These fibers might be treated jute or kenaf,

but more typically they are synthetic thermoplastic materials.

Nonwoven processes allow and tolerate a wider range of

lignocellulosic materials and synthetic fibers, depending on

product applications. After fibers are dry-blended, they are

air-laid into a continuous, loosely consolidated mat. The

mat is then passed through a secondary operation in which

the fibers are mechanically entangled or otherwise bonded

together. This low-density mat may be a product in itself, or

the mat may be shaped and densified in a thermoforming step

(Youngquist and others 1993b).

If left as low density and used without significant modification by post-processing, the mats have a bulk density of

Table 10–14. Mechanical properties of wood–polypropylene compositesa,b

Tensile Flexural Izod impact energy

Compositec

Density

(g/cm3

(lb/ft3))

Strength

(MPa

(lb/in2))

Modulus

(GPa

(lb/in2))

Elongation

(%)

Strength

(MPa

(lb/in2))

Modulus

(GPa

(lb/in2))

Notched

(J/m

(ft-lbf/in))

Unnotched

(J/m

(ft-lbf/in))

Heat

deflection

temperature

(

°

C (°F))

Polypropylene 0.9

(56.2)

28.5

(4,130)

1.53

(221,000)

5.9 38.3

(5,550)

1.19

(173,000)

20.9

(0.39)

656

(12.3)

57

(135)

PP + 40%

wood flour

1.05

(65.5)

25.4

(3,680)

3.87

(561,000)

1.9 44.2

(6,410)

3.03

(439,000)

22.2

(0.42)

73

(1.4)

89

(192)

PP + 40%

hardwood fiber

1.03

(64.3)

28.2

(4,090)

4.20

(609,000)

2.0 47.9

(6,950)

3.25

(471,000)

26.2

(0.49)

91

(1.7)

100

(212)

PP + 40%

hardwood fiber

+ 3% coupling

agent

1.03

(64.3)

52.3

(7,580)

4.23

(613,000)

3.2 72.4

(10,500)

3.22

(467,000)

21.6

(0.41)

162

(3.0)

105

(221)

a

Unpublished data.

b

Properties measured according to ASTM standards for plastics.

c

PP is polypropylene; percentages based on weight.
10–29

50 to 250 kg/m3 (3 to 16 lb/ft3). These products are particularly well known in the consumer products industry, where

nonwoven technology is used to make a variety of absorbent

personal care products, wipes, and other disposable items.

The products are made from high-quality pulps in conjunction with additives to increase absorptive properties. A much

wider variety of lignocellulosics can be used for other applications, as described in the following text.

One interesting application for low-density nonwoven mats

is for mulch around newly planted seedlings. The mats

provide the benefits of natural mulch; in addition, controlledrelease fertilizers, repellents, insecticides, and herbicides can

be added to the mats. The addition of such chemicals could

be based on silvicultural prescriptions to ensure seedling

survival and early development on planting sites where

severe nutritional deficiencies, animal damage, insect attack,

and weeds are anticipated.

Low-density nonwoven mats can also be used to replace dirt

or sod for grass seeding around new home sites or along

highway embankments. Grass seed can be incorporated

directly into the mat. These mats promote seed germination

and good moisture retention. Low-density mats can also be

used for filters. The density can be varied, depending on the

material being filtered and the volume of material that passes

through the mat per unit of time.

High-density fiber mats can be defined as composites that are

made using the nonwoven mat process and then formed into

rigid shapes by heat and pressure. To ensure good bonding,

the lignocellulosic can be precoated with a thermosetting

resin such as phenol–formaldehyde, or it can be blended with

synthetic fibers, thermoplastic granules, or any combination

of these materials. High-density fiber mats can typically be

pressed into products having a specific gravity of 0.60 to

1.40. Table 10–15 presents mechanical and physical property

Table 10–15. Properties of nonwoven web composite panels with specific gravity of 1.0a

Formulationb

Property 90H/10PE 90H/10PP 80H/10PE/PR

Static bending MOR, MPa (lb/in2

) 23.3 (3,380) 25.5 (3,700) 49.3 (7,150)

Cantilever bending MOR, MPa (lb/in2) 21.1 (3,060) 27.1 (3,930) 45.6 (6,610)

Static bending MOE, GPa (×103 lb/in2) 2.82 (409) 2.99 (434) 3.57 (518)

Dynamic MOE, GPa (×103 lb/in2) 4.75 (689) 5.27 (764) 5.52 (800)

Tensile strength, MPa (lb/in2) 13.5 (1,960) 12.5 (1,810) 27.7 (4,020)

Tensile MOE, GPa (×103 lb/in2) 3.87 (561) 420 (609) 5.07 (735)

Internal bond, MPa (lb/in2) 0.14 (20) 0.28 (41) 0.81 (120)

Impact energy, J (ft·lbf) 26.7 (19.7) 21.5 (15.9) 34.3 (25.3)

Water-soak, 24 h

 Thickness swell, % 60.8 40.3 21.8

 Water absorption, % 85.0 54.7 45.1

Water boil, 2 h

 Thickness swell, % 260.1 77.5 28.2

 Water absorption, % 301.6 99.5 55.7

Linear expansionc

 Ovendry to

30% RH, % 0.13 0.00 0.55

65% RH, % 0.38 0.25 0.76

90% RH, % 0.81 0.78 0.93

 Equilibrium MC at

30% RH, % 3.4 3.4 3.4

65% RH, % 6.4 6.2 6.3

90% RH, % 15.6 14.9 14.1

a

From Youngquist and others 1992.

b

Values connected by solid line are not statistically different at 0.05 significance level.

 90H/10PE, 90% hemlock and 10% polyester; 90H/10PP, 90% hemlock and 10% poly-

 propylene; 80H/10PE/10PR, 80% hemlock, 10% polyester, and 10% phenolic resin.

c

RH = relative humidity.
 10–30

data for nonwoven web composite panels with a specific

gravity of 1.0 for three different formulations of wood, synthetic fibers, and phenolic resin. After thermoforming, the

products possess good temperature resistance. Because longer

fibers are used, these products exhibit better mechanical

properties than those obtained with high-thermoplasticcontent composites; however, the high lignocellulosic

content leads to increased moisture sensitivity.

References

Abourezk, J. 1977. Statements on introduced bills and joint

resolutions. Congressional Record–U.S. Senate Mar. 1

S3156-S3179.

AHA. 1985. Cellulosic fiberboard, ANSI/AHA A194.1–

1985. Palatine, IL: American Hardboard Association.

AHA. 1990. Hardboard siding, ANSI/AHA A135.6–1990.

Palatine, IL: American Hardboard Association.

AHA. 1995a. Basic hardboard, ANSI/AHA A135.4–1995.

Palatine, IL: American Hardboard Association.

AHA. 1995b. Prefinished hardboard paneling, ANSI/AHA

A135.5–1995. Palatine, IL: American Hardboard Association.

Anon. 1997. Machinery and equipment. Plastics Compounding: 1996/97 Redbook. Advanstar Communications,

Inc. 19: 58–70.

APA. 1981. Performance standards and policies for APA

structural use panels. Tacoma, WA: American Plywood

Association.

APA–The Engineered Wood Association. 1991. Performance standards and policies for structural use panels. APA

PRP–108. Tacoma, WA: APA–The Engineered Wood

Association.

APA–The Engineered Wood Association. 1995a. Design

capacities of APA performance-rated structural-use panels.

Technical Note N375 B. Tacoma, WA: APA–The

Engineered Wood Association.

APA–The Engineered Wood Association. 1995b. Plywood design specification. Tacoma, WA: APA–The Engineered Wood Association.

ASTM. 1988. Concrete and mineral aggregates. 1988.

Annual Book of ASTM Standards, Sec. 4, Vol. 4.02, 4.03.

Philadelphia, PA: American Society for Testing and

Materials.

ASTM. (Current edition). Annual Book of ASTM Standards. Philadelphia, PA: American Society for Testing and

Materials.

ASTM C208–94. Standard specification for cellulosic fiber

insulating board.

ASTM D1037–94. Standard test methods for evaluating

the properties of wood-based fiber and particle panel materials.

ASTM D2718–90. Standard test method for structural

panels in planar shear (rolling shear).

ASTM D2719–89. Standard test methods for structural

panels in shear through-the-thickness.

ASTM D3043–87. Standard methods of testing structural

panels in flexure.

ASTM D3044–76. Standard test method for shear modulus of plywood.

ASTM D3500–90. Standard test methods for structural

panels in tension.

ASTM D3501–76. Standard methods of testing plywood

in compression.

ASTM E1333–90. Standard test method for determining

formaldehyde levels from wood products under defined test

conditions using a large chamber.

English, B.; Chow, P.; Bajwa, D.S. 1997. Processing into

composites. In: Rowell, Roger M.; Young, Raymond A.;

Rowell, Judith K., eds. Paper and composites from agrobased resources. Boca Raton, FL: CRC Lewis Publishers:

269–299. Chapter 8.

Geimer, R.L.; Souza, M.R.; Moslemi, A.A.; Simatupang,

M.H. 1992. Carbon dioxide application for rapid production

of cement particleboard. In: Proceedings, inorganic bonded

wood and fiber composite materials conference; 1992

September 27–30; Spokane, WA.

HPVA. 1994. American national standard for hardwood and

decorative plywood, ANSI/HPVA–1–1994. Reston, VA:

Hardwood Plywood & Veneer Association.

Maloney, T.M. 1986. Terminology and products definitions—A suggested approach to uniformity worldwide.

In: Proceedings, 18th international union of forest research

organization world congress; 1986 September; Ljubljana,

Yugoslavia. IUFRO World Congress Organizing

Committee.

Maloney, T.M. 1993. Modern particleboard and dry-process

fiberboard manufacturing. San Francisco, CA: Miller

Freeman Publications.

Marra, G. 1979. Overview of wood as material. Journal of

Educational Modules for Materials Science and Engineering.

1(4): 699–710.

McKay, M. 1997. Plywood. In: Smulski, S., ed.. Engineered wood products—A guide for specifiers, designers and

users. Madison, WI: PFS Research Foundation.

NIST. 1992. Voluntary product standard PS 2–92. Performance standard for wood-base structural-use panels. National

Institute of Standards and Technology. Gaithersburg, MD:

United States Department of Commerce.

NIST. 1995. Voluntary product standard PS 1–95 Construction and industrial plywood. National Institute of Standards

and Technology. Gaithersburg, MD: United States Department of Commerce.
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NPA. 1993. Particleboard, ANSI A208.1–1993. Gaithersburg, MD: National Particleboard Association.

NPA. 1994. Medium density fiberboard (MDF), ANSI

A208.2–1994. Gaithersburg, MD: National Particleboard

Association.

O’Halloran, M.R. 1979. Development of performance

specifications for structural panels in residential markets.

Forest Products Journal. 29(12): 21–26.

O’Halloran, M.R. 1980. The performance approach to

acceptance of building products. In: Proceedings, 14th

Washington State University international symposium on

particleboard. Pullman, WA: 77–84.

O’Halloran, M.R.; Youngquist, J.A. 1984. An overview

of structural panels and structural composite products. In:

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research. State-of-the-art and research needs. Proceedings,

American Society of Civil Engineers; 1983 October 5–6;

Milwaukee, WI. New York, NY: American Society of

Civil Engineers: 133–147.

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Raton, FL: CRC Lewis Publishers.

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policies for structural-use panels. Madison, WI: TECO.

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structures. ANC–18 Bull. (Issued by Subcommittee on Air

Force–Navy–Civil Aircraft Design Criteria. Aircraft Comm.)

2d ed. Washington, DC: Munitions Board.

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properties and uses—A review. In: Proceedings, Technical

consultation on wood-based panel. Expert Consultation,

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1987 September 28–October 1; Rome, Italy: 116–124.

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panel and building components of the future. In: Proceedings, IUFRO Division 5, Forest Products subject group

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Youngquist, J,A. 1995. Unlikely partners? The

marriage of wood and nonwood materials. Forest Products

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Youngquist, J.A.; Krzysik, A.M.; Muehl, J.H.; Carll, C.

1992. Mechanical and physical properties of air-formed

wood-fiber/polymer–fiber composites. Forest Products

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particleboard/composite materials symposium; 1993 March

30–April 1; Pullman, WA. Pullman, WA: Washington

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FPL–GTR–80. Madison, WI: U.S. Department of

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Forest Products Laboratory. 463 p.
11–1

Glued Structural Members

Russell C. Moody, Roland Hernandez, and Jen Y. Liu

Chapter 11

Contents

Structural Composite Lumber 11–1

Types 11–2

Advantages and Uses 11–2

Standards and Specifications 11–3

Glulam 11–3

Advantages 11–3

History 11–4

Types of Glulam Combinations 11–4

Standards and Specifications 11–6

Manufacture 11–6

Development of Design Values 11–9

Designs for Glued-Laminated Timber 11–10

Glued Members With Lumber and Panels 11–12

Box Beams and I-Beams 11–12

Prefabricated Wood I-Joists 11–13

Stressed-Skin Panels 11–14

Structural Sandwich Construction 11–16

Fabrication 11–16

Structural Design 11–17

Dimensional Stability, Durability, and Bowing 11–20

Thermal Insulation 11–20

Fire Resistance 11–21

References 11–21

lued structural members are manufactured in a

variety of configurations. Structural composite

lumber (SCL) products consist of small pieces of

wood glued together into sizes common for solid-sawn

lumber. Glued-laminated timber (glulam) is an engineered

stress-rated product that consists of two or more layers of

lumber in which the grain of all layers is oriented parallel to

the length of the lumber. Glued structural members also

include lumber that is glued to panel products, such as box

beams and I-beams, and structural sandwich construction.

Structural Composite Lumber

Structural composite lumber was developed in response to

the increasing demand for high quality lumber at a time

when it was becoming difficult to obtain this type of lumber

from the forest resource. Structural composite lumber products are characterized by smaller pieces of wood glued together into sizes common for solid-sawn lumber.

One type of SCL product is manufactured by laminating

veneer with all plies parallel to the length. This product is

called laminated veneer lumber (LVL) and consists of specially graded veneer. Another type of SCL product consists

of strands of wood or strips of veneer glued together under

high pressures and temperatures. Depending upon the component material, this product is called laminated strand

lumber (LSL), parallel strand lumber (PSL), or oriented

strand lumber (OSL) (Fig. 11–1). These types of SCL products can be manufactured from raw materials, such as aspen

or other underutilized species, that are not commonly used

for structural applications. Different widths of lumber can be

ripped from SCL for various uses.

Structural composite lumber is a growing segment of the

engineered wood products industry. It is used as a replacement for lumber in various applications and in the manufacture of other engineered wood products, such as prefabricated

wood I-joists, which take advantage of engineering design

values that can be greater than those commonly assigned to

sawn lumber.

G
 11–2

Types

Laminated Veneer Lumber

Work in the 1940s on LVL targeted the production of high

strength parts for aircraft structures using Sitka spruce veneer.

Research on LVL in the 1970s was aimed at defining the

effects of processing variables for veneer up to 12.7 mm

(1/2 in.) thick. In the 1990s, production of LVL uses veneers

3.2 to 2.5 mm (1/8 to 1/10 in.) thick, which are hot pressed

with phenol-formaldehyde adhesive into lengths from 2.4 to

18.3 m (8 to 60 ft) or more.

The veneer for the manufacture of LVL must be carefully

selected for the product to achieve the desired engineering

properties. The visual grading criteria of PS 1–95 (NIST

1995) are sometimes used but are generally not adequate

without additional grading. Veneers are often sorted using

ultrasonic testing to ensure that the finished product will

have the desired engineering properties.

End joints between individual veneers may be staggered

along the product to minimize their effect on strength. These

end joints may be butt joints, or the veneer ends may overlap for some distance to provide load transfer. Some producers provide structural end joints in the veneers using either

scarf or fingerjoints. Laminated veneer lumber may also be

made in 2.4-m (8-ft) lengths, having no end joints in the

veneer; longer pieces are then formed by end jointing these

pieces to create the desired length.

Sheets of LVL are commonly produced in 0.6- to 1.2-m

(2- to 4-ft) widths in a thickness of 38 mm (1.5 in.). Continuous presses can be used to form a potentially endless

sheet, which is cut to the desired length. Various widths of

lumber can be manufactured at the plant or the retail facility.

Parallel Strand Lumber

Parallel strand lumber (PSL) is defined as a composite of

wood strand elements with wood fibers primarily oriented

along the length of the member. The least dimension of the

strands must not exceed 6.4 mm (0.25 in.), and the average

length of the strands must be a minimum of 150 times the

least dimension. In 1997, one commercial product in the

United States was classified as PSL.

Parallel strand lumber is manufactured using veneer about

3 mm (1/8 in.) thick, which is then clipped into strands

about 19 mm (3/4 in.) wide. These strands are commonly at

least 0.6 m (24 in.) long. The manufacturing process was

designed to use the material from roundup of the log in the

veneer cutting operation as well as other less than full-width

veneer. Thus, the process can utilize waste material from a

plywood or LVL operation. Species commonly used for PSL

include Douglas-fir, southern pines, western hemlock, and

yellow-poplar, but there are no restrictions on using other

species.

The strands are coated with a waterproof structural adhesive,

commonly phenol-resorcinol formaldehyde, and oriented in a

press using special equipment to ensure proper orientation

and distribution. The pressing operation results in densification of the material, and the adhesive is cured using microwave technology. Billets larger than those of LVL are commonly produced; a typical size is 0.28 by 0.48 m (11 by

19 in.). This product can then be sawn into smaller pieces, if

desired. As with LVL, a continuous press is used so that the

length of the product is limited by handling restrictions.

Laminated Strand Lumber and

Oriented Strand Lumber

Laminated strand lumber (LSL) and oriented strand lumber

(OSL) products are an extension of the technology used to

produce oriented strandboard (OSB) structural panels. One

type of LSL uses strands that are about 0.3 m (12 in.) long,

which is somewhat longer than the strands commonly used

for OSB. Waterproof adhesives are used in the manufacture of

LSL. One type of product uses an isocyanate type of adhesive

that is sprayed on the strands and cured by steam injection.

This product needs a greater degree of alignment of the

strands than does OSB and higher pressures, which result in

increased densification.

Advantages and Uses

In contrast with sawn lumber, the strength-reducing characteristics of SCL are dispersed within the veneer or strands

and have much less of an effect on strength properties. Thus,

relatively high design values can be assigned to strength

properties for both LVL and PSL. Whereas both LSL and

OSL have somewhat lower design values, they have the

advantage of being produced from a raw material that need

not be in a log size large enough for peeling into veneer. All

SCL products are made with structural adhesives and are

dependent upon a minimum level of strength in these bonds.

All SCL products are made from veneers or strands that are

dried to a moisture content that is slightly less than that for

most service conditions. Thus, little change in moisture

content will occur in many protected service conditions.

Figure 11–1. Examples of three types of SCL (top to

bottom): laminated veneer lumber (LVL), parallel strand

lumber (PSL), and oriented strand lumber (OSL).
11–3

When used indoors, this results in a product that is less

likely to warp or shrink in service. However, the porous

nature of both LVL and PSL means that these products can

quickly absorb water unless they are provided with some

protection.

All types of SCL products can be substituted for sawn lumber products in many applications. Laminated veneer lumber

is used extensively for scaffold planks and in the flanges of

prefabricated I-joists, which takes advantage of the relatively

high design properties. Both LVL and PSL beams are used

as headers and major load-carrying elements in construction.

The LSL and OSL products are used for band joists in floor

construction and as substitutes for studs and rafters in wall

and roof construction. Various types of SCL are also used in

a number of nonstructural applications, such as the manufacture of windows and doors.

Standards and Specifications

The ASTM D5456 (ASTM 1997a) standard provides methods to develop design properties for SCL products as well as

requirements for quality assurance during production. Each

manufacturer of SCL products is responsible for developing

the required information on properties and ensuring that the

minimum levels of quality are maintained during production.

An independent inspection agency is required to monitor the

quality assurance program.

Unlike lumber, no standard grades or design stresses have

been established for SCL. Each manufacturer may have

unique design properties and procedures. Thus, the designer

should consult information provided by the manufacturer.

Glulam

Structural glued-laminated timber (glulam) is one of the

oldest glued engineered wood products. Glulam is an engineered, stress-rated product that consists of two or more

layers of lumber that are glued together with the grain of all

layers, which are referred to as laminations, parallel to the

length. Glulam is defined as a material that is made from

suitably selected and prepared pieces of wood either in a

straight or curved form, with the grain of all pieces essentially parallel to the longitudinal axis of the member. The

maximum lamination thickness permitted is 50 mm (2 in.),

and the laminations are typically made of standard 25- or

50-mm- (nominal 1- or 2-in.-) thick lumber. North American

standards require that glulam be manufactured in an approved

manufacturing plant. Because the lumber is joined end to

end, edge to edge, and face to face, the size of glulam is

limited only by the capabilities of the manufacturing plant

and the transportation system.

Douglas Fir–Larch, Southern Pine, Hem–Fir, and Spruce–

Pine–Fir (SPF) are commonly used for glulam in the United

States. Nearly any species can be used for glulam timber,

provided its mechanical and physical properties are suitable

and it can be properly glued. Industry standards cover many

softwoods and hardwoods, and procedures are in place for

including other species.

Advantages

Compared with sawn timbers as well as other structural

materials, glulam has several distinct advantages in size

capability, architectural effects, seasoning, variation of cross

sections, grades, and effect on the environment.

Size Capabilities—Glulam offers the advantage of the

manufacture of structural timbers that are much larger than

the trees from which the component lumber was sawn.

In the past, the United States had access to large trees that

could produce relatively large sawn timbers. However, the

present trend is to harvest smaller diameter trees on much

shorter rotations, and nearly all new sawmills are built to

accommodate relatively small logs. By combining the lumber in glulam, the production of large structural elements is

possible. Straight members up to 30 m (100 ft) long are not

uncommon and some span up to 43 m (140 ft). Sections

deeper than 2 m (7 ft) have been used. Thus, glulam offers

the potential to produce large timbers from small trees.

Architectural Effects—By curving the lumber during the

manufacturing process, a variety of architectural effects can be

obtained that are impossible or very difficult with other

materials. The degree of curvature is controlled by the thickness of the laminations. Thus, glulam with moderate curvature is generally manufactured with standard 19-mm-

(nominal 1-in.-) thick lumber. Low curvatures are possible

with standard 38-mm (nominal 2-in.) lumber, whereas

13 mm (1/2 in.) or thinner material may be required for very

sharp curves. As noted later in this chapter, the radius of

curvature is limited to between 100 and 125 times the

lamination thickness.

Seasoning Advantages—The lumber used in the manufacture of glulam must be seasoned or dried prior to use, so the

effects of checking and other drying defects are minimized. In

addition, design can be on the basis of seasoned wood,

which permits greater design values than can be assigned to

unseasoned timber.

Varying Cross Sections—Structural elements can be designed with varying cross sections along their length as

determined by strength and stiffness requirements. The

beams in Figure 11–2 show how the central section of the

beam can be made deeper to account for increased structural

requirements in this region of the beam. Similarly, arches

often have varying cross sections as determined by design

requirements.

Varying Grades—One major advantage of glulam is that a

large quantity of lower grade lumber can be used within the

less highly stressed laminations of the beams. Grades are

often varied within the beams so that the highest grades are

used in the highly stressed laminations near the top and

bottom and the lower grade for the inner half or more of the

beams. Species can also be varied to match the structural

requirements of the laminations.
 11–4

Environmentally Friendly—Much is being written and

discussed regarding the relative environmental effects of

various materials. Several analyses have shown that the

renewability of wood, its relatively low requirement for

energy during manufacture, its carbon storage capabilities,

and its recyclability offer potential long-term environmental

advantages over other materials. Although aesthetics and

economic considerations usually are the major factors influencing material selection, these environmental advantages

may increasingly influence material selection.

The advantages of glulam are tempered by certain factors

that are not encountered in the production of sawn timber.

In instances where solid timbers are available in the required

size, the extra processing in making glulam timber usually

increases its cost above that of sawn timbers. The manufacture of glulam requires special equipment, adhesives, plant

facilities, and manufacturing skills, which are not needed to

produce sawn timbers. All steps in the manufacturing process

require care to ensure the high quality of the finished product.

One factor that must be considered early in the design of

large straight or curved timbers is handling and shipping.

History

Glulam was first used in Europe in the construction of an

auditorium in Basel, Switzerland, in 1893, which is often

cited as the first known significant use of this product. It was

patented as the “Hertzer System” and used adhesives that, by

today’s standards, are not waterproof. Thus, applications

were limited to dry-use conditions. Improvements in

adhesives during and following World War I stimulated

additional interest in Europe in regard to using glulam in

aircraft and building frames.

In the United States, one of the first examples of glulam

arches designed and built using engineering principles is in a

building erected in 1934 at the USDA Forest Service, Forest

Products Laboratory, Madison, Wisconsin (Fig. 11–3). The

founder of a company that produced many of these initial

buildings in the United States was a German immigrant who

transferred the technology to his manufacturing facility in

Peshtigo, Wisconsin. Applications included gymnasiums,

churches, halls, factories, and barns. Several other companies

based on the same technology were soon established.

World War II stimulated additional interest and the development of synthetic resin adhesives that were waterproof.

This permitted the use of glulam timber in bridges and other

exterior applications that required preservative treatment. By

the early 1950s, there were at least a dozen manufacturers of

glulam timber in the United States, who joined together to

form the American Institute of Timber Construction (AITC).

In 1963, this association produced the first national manufacturing standard. The AITC continues to prepare, update, and

distribute industry standards for manufacture and design of

glulam. By the mid-1990s, about 30 manufacturing plants

across the United States and Canada were qualified to produce glulam, according to the requirements of the AITC

standard.

From the mid-1930s through the 1980s, nearly all glulam

production was used domestically. During the 1990s, the

export market was developed and significant quantities of

material were shipped to Pacific Rim countries, mainly

Japan.

Types of Glulam Combinations

Bending Members

The configuring of various grades of lumber to form a glulam

cross section is commonly referred to as a glulam combination. Glulam combinations subjected to flexural loads, called

bending combinations, were developed to provide the most

efficient and economical section for resisting bending stress

caused by loads applied perpendicular to the wide faces of the

laminations. This type of glulam is commonly referred to as

a horizontally laminated member. Lower grades of laminating lumber are commonly used for the center portion of the

combination, or core, where bending stress is low, while a

higher grade of material is placed on the outside faces where

bending stress is relatively high. To optimize the bending

stiffness of this type of glulam member, equal amounts of

high quality laminations on the outside faces should be

included to produce a “balanced” combination. To optimize

bending strength, the combination can be “unbalanced” with

more high quality laminations placed on the tension side of

the member compared with the quality used on the compression side. For high quality lumber placed on the tension

side of the glulam combination, stringent requirements are

(a)

(c)

(b)

(d)

Figure 11–2. Glulam timbers may be (a) single tapered,

(b) double tapered, (c) tapered at both ends, or

(d) tapered at one end.
11–5

placed on knot size, slope of grain, and lumber stiffness.

For compression-side laminations, however, knot size and

slope-of-grain requirements are less stringent and only lumber stiffness is given high priority. In the case where the

glulam member is used over continuous supports, the combination would need to be designed as a balanced member for

strength and stiffness because of the exposure of both the top

and bottom of the beam to tensile stresses. The knot and

slope-of-grain requirements for this type of combination are

generally applied equally to both the top and bottom

laminations.

Axial Members

Glulam axial combinations were developed to provide the

most efficient and economical section for resisting axial forces

and flexural loads applied parallel to the wide faces of the

laminations. Members having loads applied parallel to the

wide faces of the laminations are commonly referred to as

vertically laminated members. Unlike the practice for bending combinations, the same grade of lamination is used

throughout the axial combination. Axial combinations may

also be loaded perpendicular to the wide face of the laminations, but the nonselective placement of material often results

in a less efficient and less economical member than does the

bending combination. As with bending combinations, knot

and slope-of-grain requirements apply based on the intended

use of the axial member as a tension or compression

member.

Curved Members

Efficient use of lumber in cross sections of curved glulam

combinations is similar to that in cross sections of straight,

horizontally-laminated combinations. Tension and compression stresses are analyzed as tangential stresses in the curved

portion of the member. A unique behavior in these curved

members is the formation of radial stresses perpendicular to

the wide faces of the laminations. As the radius of curvature

of the glulam member decreases, the radial stresses formed in

the curved portion of the beam increase. Because of the relatively low strength of lumber in tension perpendicular-to-thegrain compared with tension parallel-to-the-grain, these radial

stresses become a critical factor in designing curved glulam

combinations. Curved members are commonly manufactured

with standard 19- and 38-mm- (nominal 1- and 2-in.-) thick

lumber. Naturally, the curvature that is obtainable with the

Figure 11–3. Erected in 1934 at the Forest Products Laboratory in Madison, Wisconsin, this building is one of the

first constructed with glued-laminated timbers arched, designed, and built using engineering principles.
 11–6

standard 19-mm- (nominal 1-in.-) thick lumber will be

sharper than that for the standard 38-mm- (nominal 2-in.-)

thick lumber. Recommended practice specifies that the ratio

of lamination thickness t to the radius of curvature R should

not exceed 1/100 for hardwoods and Southern Pine and

1/125 for other softwoods (AF&PA 1997). For example, a

curved Southern Pine beam (t/R ≤ 1/100) manufactured with

standard 38-mm- (nominal 2-in.-) thick lumber (t = 1.5 in.)

should have a radius of curvature greater than or equal to

3.81 m (150 in.)

Tapered Straight Members

Glulam beams are often tapered to meet architectural requirements, provide pitched roofs, facilitate drainage, and

lower wall height requirements at the end supports. The

taper is achieved by sawing the member across one or more

laminations at the desired slope. It is recommended that the

taper cut be made only on the compression side of the glulam member, because violating the continuity of the tensionside laminations would decrease the overall strength of the

member. Common forms of straight, tapered glulam combinations include (a) single tapered, a member having a continuous slope from end to end on the compression side;

(b) double tapered, a member having two separate slopes

sawn on the compression side; (c) tapered at both ends, a

member with slopes sawn on the ends, but the middle portion remains straight; and (d) tapered at one end, similar to

(c) with only one end having a slope. These four examples

are illustrated in Figure 11–2.

Standards and Specifications

Manufacture

The ANSI/AITC A190.1 standard of the American National

Standards Institute (ANSI 1992) contains requirements for

the production, testing, and certification of structural glulam

timber in the United States. Additional details and commentary on the requirements specified in ANSI A190.1 are provided in AITC 200 (AITC 1993a), which is part of ANSI

A190.1 by reference. A standard for glulam poles, ANSI

O5.2 (ANSI 1996), addresses special requirements for utility

uses. Requirements for the manufacture of structural glulam

in Canada are given in CAN/CSA O122 (CSA 1989).

Derivation of Design Values

ASTM D3737 (ASTM 1997b) covers the procedures to

establish design values for structural glulam timber. Properties considered include bending, tension, compression parallel to grain, modulus of elasticity, horizontal shear, radial

tension, and compression perpendicular to grain.

Design Values and Procedures

Manufacturers of glulam timber have standardized the target

design values in bending for beams. For softwoods, these

design values are given in AITC 117, “Standard Specifications for Structural Glued-Laminated Timber of Softwood

Species” (AITC 1993b). This specification contains design

values and recommended modification of stresses for the

design of glulam timber members in the United States. A

comparable specification for hardwoods is AITC 119,

“Standard Specifications for Structural Glued-Laminated

Timber of Hardwood Species” (AITC 1996). The National

Design Specification for Wood Construction (NDS) summarizes the design information in AITC 117 and 119 and defines the practice to be followed in structural design of glulam timbers (AF&PA 1997). For additional design

information, see the Timber Construction Manual (AITC

1994). APA—The Engineered Wood Association has also

developed design values for glulam under National Evaluation Report 486, which is recognized by all the model building codes.

In Canada, CAN/CSA O86, the code for engineering design

in wood, provides design criteria for structural glulam

timbers (CSA 1994).

Manufacture

The manufacture of glulam timber must follow recognized

national standards to justify the specified engineering design

values. When glulam is properly manufactured, both the

quality of the wood and the adhesive bonds should demonstrate a balance in structural performance.

The ANSI A190.1 standard (ANSI 1992) has a two-phase

approach to all phases of manufacturing. First is the qualification phase in which all equipment and personnel critical to

the production of a quality product are thoroughly examined

by a third-party agency and the strength of samples of glued

joints is determined. In the second phase, after successful

qualification, daily quality assurance procedures and criteria

are established, which are targeted to keep each of the critical

phases of the process under control. An employee is assigned

responsibility for supervising the daily testing and inspection. The third-party agency makes unannounced visits to

the plants to monitor the manufacturing process and the

finished product and to examine the daily records of the

quality assurance testing.

The manufacturing process can be divided into four major

parts: (a) drying and grading the lumber, (b) end jointing the

lumber, (c) face bonding, and (d) finishing and fabrication.

In instances where the glulam will be used in high moisture

content conditions, it is also necessary to pressure treat the

member with preservative. A final critical step in ensuring

the quality of glulam is protection of the glulam timber

during transit and storage.

Lumber Drying and Grading

To minimize dimensional changes following manufacture

and to take advantage of the increased structural properties

assigned to lumber compared with large sawn timbers, it is

critical that the lumber be properly dried. This generally

means kiln drying. For most applications, the maximum

moisture content permitted in the ANSI standard is 16%

(ANSI 1992). Also, the maximum range in moisture content

is 5% among laminations to minimize differential changes in

dimension following manufacture. Many plants use lumber at
11–7

or slightly below 12% moisture content for two reasons. One

reason is that the material is more easily end jointed at 12%

moisture content than at higher levels. The other reason is

that 12% is an overall average equilibrium moisture content

for many interior applications in the United States (see Ch.

12, Tables 12–1 and 12–2). Exceptions are some areas in the

southwest United States. Matching the moisture content of

the glulam timber at the time of manufacture to that which it

will attain in application minimizes shrinkage and swelling,

which are the causes of checking.

The moisture content of lumber can be determined by sampling from the lumber supply and using a moisture meter.

Alternatively, most manufacturers use a continuous in-line

moisture meter to check the moisture content of each piece of

lumber as it enters the manufacturing process. Pieces with

greater than a given moisture level are removed and redried.

Grading standards published by the regional lumber grading

associations describe the characteristics that are permitted in

various grades of lumber. Manufacturing standards for glulam

timber describe the combination of lumber grades necessary

for specific design values (AITC 117) (AITC 1993b). Two

types of lumber grading are used for laminating: visual

grading and E-rating.

The rules for visually graded lumber are based entirely upon

the characteristics that are readily apparent. The lumber grade

description consists of limiting characteristics for knot sizes,

slope of grain, wane, and several other characteristics. An

example of the knot size limitation for visually graded

western species is as follows:

Laminating grade Maximum knot size

 L1 1/4 of width

L2 1/3 of width

L3 1/2 of width

E-rated lumber is graded by a combination of lumber stiffness

determination and visual characteristics. Each piece of lumber

is evaluated for stiffness by one of several acceptable procedures, and those pieces that qualify for a specific grade are

then visually inspected to ensure that they meet the requirement for maximum allowable edge knot size. The grades are

expressed in terms of their modulus of elasticity followed by

their limiting edge knot size. Thus, a 2.0E–1/6 grade has

a modulus of elasticity of 13.8 GPa (2 × 106

 lb/in2) and a

maximum edge knot size of 1/6 the width.

Manufacturers generally purchase graded lumber and verify

the grades through visual inspection of each piece and, if

E-rated, testing of a sample. To qualify the material for some

of the higher design stresses for glulam timber, manufacturers

must also conduct additional grading for material to be used

in the tension zone of certain beams. High quality material is

required for the outer 5% of the beam on the tension size, and

the grading criteria for these “tension laminations” are given

in AITC 117 (AITC 1993b). Special criteria are applied to

provide material of high tensile strength. Another option is

to purchase special lumber that is manufactured under a

quality assurance system to provide the required tensile

strength. Another option practiced by at least one manufacturer has been to use LVL to provide the required tensile

strength.

End Jointing

To manufacture glulam timber in lengths beyond those

commonly available for lumber, laminations must be made

by end jointing lumber to the proper length. The most

common end joint, a fingerjoint, is about 28 mm (1.1 in.)

long (Fig. 11–4). Other configurations are also acceptable,

provided they meet specific strength and durability requirements. The advantages of fingerjoints are that they require

only a short length of lumber to manufacture (thus reducing

waste) and continuous production equipment is readily

available. Well-made joints are critical to ensure adequate

performance of glulam timber. Careful control at each stage of

the process—determining lumber quality, cutting the joint,

applying the adhesive, mating, applying end pressure, and

curing—is necessary to produce consistent high strength

joints.

Just prior to manufacture, the ends of the lumber are inspected to ensure that there are no knots or other features that

would impair joint strength. Then, joints are cut on both

ends of the lumber with special knives. Adhesive is applied.

The joints in adjacent pieces of lumber are mated, and the

adhesive is cured under end pressure. Most manufacturing

equipment features a continuous radio-frequency curing system that provides heat to partially set the adhesive in a

matter of a few seconds. Fingerjoints obtain most of their

strength during this process, and residual heat permits the

joint to reach its full strength within a few hours.

Figure 11–4. Typical fingerjoint used in the

manufacture of glulam.
 11–8

Fingerjoints have the potential to reach at least 75% of the

strength of clear wood in many species if properly manufactured. These joints are adequate for most applications because most lumber grades used in the manufacture of glulam

timber permit natural characteristics that result in strength

reductions of at least 25% less than that of clear wood.

The ANSI standard requires that manufacturers qualify their

production joints to meet the required strength level of the

highest grade glulam timber they wish to produce. This

requires that the results of tensile tests of end-jointed lumber

meet certain strength criteria and that durability meets certain

criteria. When these criteria are met, daily quality control

testing in tension is required to ensure that the strength level

is being maintained. Durability tests are also required.

A continuing challenge in the glulam production process is

to eliminate the occurrence of an occasional low-strength end

joint. Visual inspection and other nondestructive techniques

have been shown to be only partially effective in detecting

low-strength joints. An approach used by many manufacturers to ensure end joint quality is the use of a proof loading

system for critical end joints. This equipment applies a

specified bending or tension load to check the joint strength

for critical laminations on the tension side of beams. By

applying loads that are related to the strength desired, lowstrength joints can be detected and eliminated. The qualification procedures for this equipment must prove that the applied loads do not cause damage to laminations that are

accepted.

Face Bonding

The assembly of laminations into full-depth members is

another critical stage in manufacture. To obtain clear, parallel, and gluable surfaces, laminations must be planed to strict

tolerances. The best procedure is to plane the two wide faces

of the laminations just prior to the gluing process. This

ensures that the final assembly will be rectangular and that

the pressure will be applied evenly. Adhesives that have been

prequalified are then spread, usually with a glue extruder.

Phenol resorcinol is the most commonly used adhesive for

face gluing, but other adhesives that have been adequately

evaluated and proven to meet performance and durability

requirements may also be used.

The laminations are then assembled into the required layup;

after the adhesive is given the proper open assembly time,

pressure is applied. The most common method for applying

pressure is with clamping beds; the pressure is applied with

either a mechanical or hydraulic system (Fig. 11–5). This

results in a batch-type process, and the adhesive is allowed

to cure at room temperature from 6 to 24 h. Some newer

automated clamping systems include continuous hydraulic

presses and radio-frequency curing to shorten the face gluing

process from hours to minutes. Upon completion of the face

bonding process, the adhesive is expected to have attained

90% or more of its bond strength. During the next few days,

curing continues, but at a much slower rate.

The face bonding process is monitored by controls in the

lumber planing, adhesive mixing, and adhesive spreading

and clamping processes. Performance is evaluated by conducting shear tests on samples cut off as end trim from the

finished glulam timber. The target shear strength of small

specimens is prescribed in ANSI A190.1 (ANSI 1992) and

equals about 90% of the average shear strength for the

species. Thus, the adhesive bonds are expected to develop

nearly the full strength of the wood soon after manufacture.

Finishing and Fabrication

After the glulam timber is removed from the clamping system, the wide faces are planed to remove the adhesive that

has squeezed out between adjacent laminations and to

smooth out any slight irregularities between the edges of

adjacent laminations. As a result, the finished glulam timber

is slightly narrower than nominal dimension lumber. The

remaining two faces of the member can be lightly planed or

sanded using portable equipment.

The appearance requirements of the beam dictate the additional finishing necessary at this point. Historically, three

classifications of finishing have been included in the industry

standard, AITC 110: Industrial, Architectural, and Premium

(AITC 1984). Industrial appearance is generally applicable

when appearance is not a primary concern, such as industrial

plants and warehouses. Architectural appearance is suitable

for most applications where appearance is an important requirement. Premium appearance is the highest classification.

The primary difference among these classifications is the

Figure 11–5. After being placed in the clamping bed,

the laminations of these arches are forced together

with an air-driven screw clamp.
11–9

amount of knot holes and occasional planer skips that are

permitted. A recently introduced classification, called Framing, consists of hit-and-miss planing and permits a significant amount of adhesive to remain on the surface. This finishing is intended for uses that require one member to have

the same width as the lumber used in manufacture for framing

into walls. These members are often covered in the finished

structure.

The next step in the manufacturing process is fabrication,

where the final cuts are made, holes are drilled, connectors

are added, and a finish or sealer is applied, if specified. For

various members, different degrees of prefabrication are done

at this point. Trusses may be partially or fully assembled.

Moment splices can be fully fabricated, then disconnected for

transportation and erection. End sealers, surface sealers,

primer coats, and wrapping with waterproof paper or plastic

all help to stabilize the moisture content of the glulam timber between the time it is manufactured and installed. The

extent of protection necessary depends upon the end use and

must be specified.

Preservative Treatment

In instances where the moisture content of the finished glulam timber will approach or exceed 20% (in most exterior

and some interior uses), the glulam timber should be preservative treated following AITC (1990) and AWPA

(1997b). Three main types of preservatives are available:

creosote, oilborne, and waterborne. Creosote and oilborne

preservatives are applied to the finished glulam timbers.

Some light oil solvent treatments can be applied to the

lumber prior to gluing, but the suitability must be verified

with the manufacturer. Waterborne preservatives are best

applied to the lumber prior to the laminating and manufacturing process because they can lead to excessive checking if

applied to large finished glulam timbers.

Creosote Solutions—Treatment with creosote solutions is

suitable for the most severe outdoor exposure. It results in a

dark, oily surface appearance that is difficult to alter. This,

coupled with a distinct odor, restricts creosote solutions to

structures, such as bridges, that do not come in direct contact

with humans. Creosote solutions are an extremely effective

preservative as proven by their continued use for railway

structures. Another advantage is that the creosote treatment

renders the timbers much less susceptible to moisture content changes than are untreated timbers. Creosote solutions

are often used as a preservative treatment on bridge stringers.

Oilborne Treatments—Pentachlorophenol and copper

napthanate are the most common oilborne preservatives. The

solvents are classified in AWPA Standard P9 as Type A,

Type C, and Type D (AWPA 1997a). Type A results in an

oily finish and should not be used when a plain table surface

is needed. Type B or C can be stained or painted. More

details are given in AITC (1990) and AWPA (1997a).

Waterborne Treatments—Waterborne preservative treatments conform to AWPA P5 (AWPA 1997b) and use watersoluble preservative chemicals that become fixed in the

wood. The effectiveness of this treatment depends upon the

depth to which the chemicals penetrate into the lumber.

Different processes are quite effective for some species but not

for others. In addition, the treated lumber is generally more

difficult to bond effectively and requires special manufacturing

procedures. Thus, it is recommended that the manufacturer

be contacted to determine the capabilities of waterbornepreservative-treated products.

The major advantage of a waterborne treatment is that the

surface of the timber appears little changed by the treatment.

Different chemicals can leave a green, gray, or brown color;

all result in a surface that is easily finished with stains or

paints. To avoid the potential of corrosive interactions with

the chemical treatments, special care must be given when

selecting the connection hardware. In addition, waterbornepreservative-treated glulam timber is much more subject to

moisture content cycling than is creosote-treated or oilbornepreservative-treated glulam timber.

A major consideration in selecting a preservative treatment is

the local regulations dealing with the use and disposal of

waste from preservative-treated timber. Recommended retention levels for applications of various preservatives are given

in AITC 109 (AITC 1990) along with appropriate quality

assurance procedures.

Development of Design Values

The basic approach to determine the engineered design

values of glulam members is through the use of stress index

values and stress modification factors.

Stress Index Values

Stress index values are related to the properties clear of wood

that is free of defects and other strength-reducing characteristics. Stress index values for several commonly used species

and E-rated grades of lumber are given in ASTM D3737

(ASTM 1997b). Procedures are also given for developing

these values for visual grades of other species.

Stress Modification Factors

Stress modification factors are related to strength-reducing

characteristics and are multiplied by the stress index values

to obtain allowable design properties. Detailed information

on determination of these factors for bending, tension, compression, and modulus of elasticity are given in ASTM

D3737 (1997b).

Other Considerations

Effect of End Joints on Strength—Both fingerjoints and

scarf joints can be manufactured with adequate strength for

use in structural glulam. Adequacy is determined by physical

testing procedures and requirements in ANSI A190.1 (ANSI

1992).

Joints should be well scattered in portions of structural

glulam that is highly stressed in tension. Required spacings

of end joints are given in ANSI A190.1. End joints of two

qualities can be used in a glulam member, depending upon

strength requirements at various depths of the cross section.
 11–10

However, laminators usually use the same joint throughout

the members for ease in manufacture.

The highest strength values are obtained with well-made

plain scarf joints; the lowest values are obtained with butt

joints. This is because scarf joints with flat slopes have

essentially side-grain surfaces that can be well bonded to

develop high strength, and butt joints have end-grain surfaces

that cannot be bonded effectively. Structural fingerjoints

(either vertical or horizontal) are a compromise between scarf

and butt joints; the strength of structural fingerjoints varies

with joint design.

No statement can be made regarding the specific joint

strength factor of fingerjoints, because fingerjoint strength

depends on the type and configuration of the joint and the

manufacturing process. However, the joint factor of commonly used fingerjoints in high-quality lumber used for

laminating can be about 75%. High-strength fingerjoints can

be made when the design is such that the fingers have relatively flat slopes and sharp tips. Tips are essentially a series

of butt joints that reduce the effectiveness of fingerjoints as

well as creating sources of stress concentration.

Generally, butt joints cannot transmit tensile stress and can

transmit compressive stress only after considerable deformation or if a metal bearing plate is tightly fitted between the

abutting ends. In normal assembly operations, such fitting

would not be done. Therefore, it is necessary to assume that

butt joints are ineffective in transmitting both tensile and

compressive stresses. Because of this ineffectiveness and

because butt joints cause concentration of both shear stress

and longitudinal stress, butt joints are not permitted for use

in structural glued-laminated timbers.

Effect of Edge Joints on Strength—It is sometimes necessary to place laminations edge-to-edge to provide glulam

members of sufficient width. Because of difficulties in fabrication, structural edge joint bonding may not be readily available, and the designer should investigate the availability of

such bonding prior to specifying.

For tension, compression, and horizontally laminated bending members, the strength of edge joints is of little importance to the overall strength of the member. Therefore, from

the standpoint of strength, it is unnecessary that edge joints

be glued if they are not in the same location in adjacent

laminations. However, for maximum strength, edge joints

should be glued where torsional loading is involved. Other

considerations, such as the appearance of face laminations or

the possibility that water will enter the unglued joints and

promote decay, should also dictate if edge joints are glued.

If edge joints in vertically laminated beams are not glued,

shear strength could be reduced. The amount of reduction can

be determined by engineering analysis. Using standard laminating procedures with edge joints staggered in adjacent

laminations by at least one lamination thickness, shear

strength of vertically laminated beams with unglued edge

joints is approximately half that of beams with adhesivebonded edge joints.

Effect of Shake, Checks, and Splits on Shear Strength—

In general, checks and splits have little effect on the shear

strength of glulam. Shake occurs infrequently and should be

excluded from material for laminations. Most laminated

timbers are made from laminations that are thin enough to

season readily without developing significant checks and

splits.

Designs for Glued-Laminated Timber

Most basic engineering equations used for sawn lumber also

apply to glulam beams and columns. The design of glulam

in this chapter is only applicable to glulam combinations

that conform to AITC 117 (AITC 1993b) for softwood species and AITC 119 (AITC 1996) for hardwood species and

are manufactured in accordance with ANSI/AITC A190.1

(ANSI 1992). The AITC 117 standard is made up of two

parts: (a) manufacturing, which provides details for the many

configurations of glulam made from visually graded and

E-rated softwood lumber; and (b) design, which provides

tabular design values of strength and stiffness for these glulam combinations. The AITC 119 standard provides similar

information for glulam made from hardwood species of lumber. These standards are based on laterally-braced straight

members with an average moisture content of 12%. For

bending members, the design values are based on an assumed reference size of 305 mm deep, 130 mm wide, and

6.4 m long (12 in. deep, 5.125 in. wide, and 21 ft long).

Tabular Design Values

Tabular design values given in AITC 117 and AITC 119

include the following:

Fb allowable bending design value,

Ft allowable tension design value parallel to grain,

Fv allowable shear design value parallel to grain,

Fc-perp allowable compression design value perpendicular

 to grain,

Fc allowable compression design value parallel

to grain,

E allowable modulus of elasticity, and

Frt allowable radial tension design value

perpendicular to grain.

Because glulam members can have different properties when

loaded perpendicular or parallel to the wide faces of the laminations, a common naming convention is used to specify the

design values that correspond to a particular type of orientation. For glulam members loaded perpendicular to the wide

faces of the laminations, design values are commonly denoted with a subscript x. For glulam members loaded parallel to the wide faces of the laminations, design values are

commonly denoted with a subscript y. Some examples

include Fbx and Ex for design bending stress and design

modulus of elasticity, respectively.
11–11

End-Use Adjustment Factors

When glulam members are exposed to conditions other than

the described reference condition, the published allowable

design values require adjustment. The following text describes each of the adjustment factors that account for the enduse condition of glulam members.

Volume—The volume factor Cv accounts for an observed

reduction in strength when length, width, and depth of structural glulam members increase. This strength reduction is

due to the higher probability of occurrence of strengthreducing characteristics, such as knots and slope of grain, in

higher volume beams. This volume factor adjustment is

given in the National Design Specification for Wood

Construction (AF&PA 1997) in the form

 

 

C

dwL v = 

































 305 130 6 4 0 10 0 10 0 10 . ..

. (metric) (11–1a)

 

 

C

dwL v = 



 



 



 



 



 



 12 5 125 21

0 10 0 10 0 10 . ..

. (inch– pound) (11–1b)

for Douglas-fir and other species, and

 

 

C

dwL v = 

































 305 130 6 4 0 05 0 05 0 05 . ..

. (metric) (11–2a)

 

 

C

dwL v = 

































 12 5 125 21 0 05 0 05 0 05 . ..

. (inch–pound) (11–2b)

for southern pines, where d is depth (mm, in.), w width

(mm, in.), and L length (m, ft). (Eqs. (11–1a) and (11–2a) in

metric, Eqs. (11–1b) and (11–2b) in inch–pound system.)

Moisture Content—The moisture content factor CM

accounts for the reduction in strength as moisture content

increases. A moisture content adjustment is listed in both

ASTM D3737 (ASTM 1997b) and AITC 117–Design

(AITC 1993b).

CM = 1.0 for moisture content ≤16%

For moisture content >16%, as in ground contact and many

other exterior conditions, use the following CM values:

Fb Ft Fv Fc-perp Fc E

CM 0.8 0.8 0.875 0.53 0.73 0.833

Loading—An adjustment for the type of loading on the

member is also necessary because the volume factors are

derived assuming a uniform load. This method of loading

factor CL is recommended in the National Design

Specification for Wood Construction (AF&PA 1997).

CL = 1.00 for uniform loading on a simple span

= 1.08 for center point loading on a simple span

= 0.92 for constant stress over the full length

For other loading conditions, values of CL can be estimated

using the proportion of the beam length subjected to 80% or

more of the maximum stress L0 and

 

C

L L

0

= 



 



 0 45

0 1

. .

 (11–3)

Tension Lamination—Past research has shown that special

provisions are required for the tension lamination of a glulam

beam to achieve the specified design bending strength levels.

Properties listed in AITC 117 and 119 are applicable to

beams with these special tension laminations. If a special

tension lamination is not included in the beam combination,

strength reduction factors must be applied. Tension lamination factors CT, which can be found in ASTM D3737

(ASTM 1997b), have the following values:

CT = 1.00 for special tension laminations per AITC 117

= 0.85 without tension laminations and for depth

≤380 mm (≤15 in.)

= 0.75 without tension laminations and for depth

>380 mm (>15 in.).

Curvature—The curvature factor accounts for the increased

stresses in the curved portion of curved glulam beams. This

factor does not apply to design values in the straight portion

of a member, regardless of the curvature elsewhere. The

curvature factor Cc, which can be found in the National

Design Specification (AF&PA 1997), has the following

relation:

 

C t

R c = − 









 1 2000

2

 (11–4)

where t is thickness of lamination and R is radius of curvature on inside face of lamination. The value t/R ≤ 1/100

for hardwoods and southern pines; t/R ≤ 1/125 for other

softwoods.

Flat Use—The flat use factor is applied to bending design

values when members are loaded parallel to wide faces of

laminations and are less than 305 mm (12 in.) in depth. Flat

use factors Cfu, which can be found in the National Design

Specification (AF&PA 1997), have the following values:
 11–12

Lateral Stability—The lateral stability factor is applied to

bending design values to account for the amount of lateral

support applied to bending members. Deep bending members that are unsupported along the top surface are subject to

lateral torsional buckling and would have lower bending

design values. Members that are fully supported would have

no adjustments (CL = 1.0).

Glued Members With

Lumber and Panels

Highly efficient structural components can be produced by

combining lumber with panel products through gluing.

These components, including box beams, I-beams,

“stressed-skin” panels, and folded plate roofs, are discussed

in detail in technical publications of the APA—The Engineered Wood Association (APA 1980). One type of member,

prefabricated wood I-joists, is discussed in detail. Details on

structural design are given in the following portion of this

chapter for beams with webs of structural panel products and

stressed-skin panels wherein the parts are glued together with

a rigid, durable adhesive.

These highly efficient designs, although adequate structurally, can suffer from lack of resistance to fire and decay unless

treatment or protection is provided. The rather thin portions

of the cross section (the panel materials) are more vulnerable

to fire damage than are the larger, solid cross sections.

Box Beams and I-Beams

Box beams and I-beams with lumber or laminated flanges

and structural panel webs can be designed to provide the

desired stiffness, bending, moment resistance, and shear

resistance. The flanges resist bending moment, and the webs

provide primary shear resistance. Proper design requires that

the webs must not buckle under design loads. If lateral stability is a problem, the box beam design should be chosen

because it is stiffer in lateral bending and torsion than is the

I-beam. In contrast, the I-beam should be chosen if buckling

of the web is of concern because its single web, double the

thickness of that of a box beam, will offer greater buckling

resistance.

Design details for beam cross sections (including definitions

of terms in the following equations) are presented in

Figure 11–6. Both flanges in these beams are the same

thickness because a construction symmetrical about the

neutral plane provides the greatest moment of inertia for the

amount of material used. The following equations were

derived by basic principles of engineering mechanics.

These methods can be extended to derive designs for

unsymmetrical constructions, if necessary.

Beam Deflections

Beam deflections can be computed using Equation (8–2) in

Chapter 8. The following equations for bending stiffness (EI)x

and shear stiffness GA′ apply to the box and I-beam shown in

Figure 11–6. The bending stiffness is given by

 

( ) [( ) ] EI E d c b E Wd x = −+

1

12

2 33 3

w (11–5)

where E is flange modulus of elasticity and Ew is web modulus of elasticity. For plywood, values of Ew for the appropriate structural panel construction and grain direction can be

computed from Equations (11–1), (11–2), and (11–3).

An approximate expression for the shear stiffness is

 GA WcG ′ = 2 (11–6)

where G is shear modulus for the structural panel for appropriate direction and A′ is the effective area of the web. An

improvement in shear stiffness can be made by properly

orienting the web, depending upon its directional properties.

Equation (11–6) is conservative because it ignores the shear

stiffness of the flange. This contribution can be included by

use of APA design methods that are based on Orosz (1970).

(For further information on APA design methods, contact

APA—The Engineered Wood Association in Tacoma,

Washington.)

Flange Stresses

Flange compressive and tensile stresses at outer beam fibers

are given by

Member dimension parallel

to wide faces of laminations Cfu

273 or 267 mm (10-3/4 or 10-1/2 in.) 1.01

222 or 216 mm (8-3/4 or 8-1/2 in.) 1.04

171 mm (6-3/4 in.) 1.07

130 or 127 mm (5-1/8 or 5 in.) 1.10

79 or 76 mm (3-1/8 or 3 in.) 1.16

64 mm (2-1/2 in.) 1.19

Figure 11–6. Beams with structural panel webs.
11–13

 

f M

d c b

d

E Wd

E

x =

− +

6

3 3 2 2

( w )

 (11–7)

where M is bending moment.

Web Shear Stress

Web shear stress at the beam neutral plane is given by

 

f V

W

E d c b E Wd

E d c b E Wd xy = − +− +

















3

4

2

2

22 2

33 3

( )

( )

w

w

 (11–8)

where V is shear load. The shear stress must not exceed

allowable values. To avoid web buckling, either the web

should be increased in thickness or the clear length of the

web should be broken by stiffeners glued to the web.

Web edgewise bending stresses at the inside of the flanges

can be computed by

 

f M

E

E

d c b

c

d

c

W

xw

w

=

− +

6

2 3 3

3

( )

 (11–9)

Although it is not likely, the web can buckle as a result of

bending stresses. Should buckling as a result of edgewise

bending appear possible, the interaction of shear and edgewise bending buckling can be examined using the principles

of Timoshenko (1961).

Lateral Buckling

Possible lateral buckling of the entire beam should be

checked by calculating the critical bending stress (Ch. 8,

Lateral–Torsional Buckling section). The slenderness factor

p, required to calculate this stress, includes terms for lateral

flexural rigidity EIy and torsional rigidity GK that are defined

as follows:

For box beams,

 

EI E d c b

E b W bd

y = −

+ +−

1

12

2

3

3 3

( )

w [( ) ]

 (11–10)

 

 

GK d cd c bW W

d c b WW = G +−+−++

















( )( )( )

( )( )

22 2

2 2 4 (11–11)

For I-beams,

 

 

EI E b W W d c

E Wd

y = +− −

+

1

12

2 2

2

3 3

3

{

}

[( ) ( ) ]( )

( ) fw

 (11–12)

 

 

GK d c b d W G = −+





 



 1

3

1

4

2 3 3 ( ) () (11–13)

where Efw is flexural elastic modulus of the web.

In Equations (11–11) and (11–13), the shear modulus G can

be assumed without great error to be about 1/16 of the flange

modulus of elasticity EL. The resultant torsional stiffness GK

will be slightly low if beam webs have plywood grain at 45°

to the neutral axis. The lateral buckling of I-beams will also

be slightly conservative because bending rigidity of the

flange has been neglected in writing the equations given here.

If buckling of the I-beam seems possible at design loads, the

more accurate analysis of Forest Products Laboratory Report

1318B (Lewis and others 1943) should be used before

redesigning.

Stiffeners and Load Blocks

Determination of the number and sizes of stiffeners and load

blocks needed in a particular construction does not lend itself

to a rational procedure, but certain general rules can be given

that will help the designer of a structure obtain a satisfactory

structural member. Stiffeners serve a dual purpose in a structural member of this type. One function is to limit the size of

the unsupported panel in the web, and the other is to restrain

the flanges from moving toward each other as the beam is

stressed.

Stiffeners should be glued to the webs and in contact with

both flanges. A rational way of determining how thick the

stiffener should be is not available, but tests of box beams

made at the Forest Products Laboratory indicate that a thickness of at least six times the thickness of the web is sufficient. Because stiffeners must also resist the tendency of the

flanges to move toward each other, the stiffeners should be as

wide as (extend to the edge of) the flanges.

For plywood webs containing plies with the grain of the

wood oriented both parallel and perpendicular to the axis of

the member, the spacing of the stiffeners is relatively unimportant for the web shear stresses that are allowed. Maximum

allowable stresses are less than those that will produce buckling. A clear distance between stiffeners equal to or less than

two times the clear distance between flanges is adequate.

Load blocks are special stiffeners placed along the member at

points of concentrated load. Load blocks should be designed

so that stresses caused by a load that bears against the sidegrain material in the flanges do not exceed the allowable

design for the flange material in compression perpendicular

to grain.

Prefabricated Wood I-Joists

In recent years, the development of improved adhesives and

manufacturing techniques has led to the development of the

prefabricated I-joist industry. This product is a unique type

of I-beam that is replacing wider lumber sizes in floor and

roof applications for both residential and commercial buildings (Fig. 11–7).

Significant savings in materials are possible with prefabricated I-joists that use either plywood or oriented strandboard

(OSB) for the web material and small dimension lumber or

structural composite lumber (SCL) for the flanges. The high

quality lumber needed for these flanges has been difficult to

obtain using visual grading methods, and both mechanically
 11–14

graded lumber and SCL are being used by several manufacturers. The details of fastening the flanges to the webs vary

between manufacturers; all must be glued with a waterproof

adhesive. Prefabricated I-joists are becoming popular with

builders because of their light weight, dimensional stability

and ease of construction. Their accurate and consistent dimensions, as well as uniform depth, allow the rapid creation

of a level floor. Utility lines pass easily through openings in

the webs.

The ASTM standard D5055 (ASTM 1997d) gives procedures for establishing, monitoring, and reevaluating structural capacities of prefabricated I-joists. Each manufacturer of

prefabricated I-joists is responsible for developing the required property information and ensuring that the minimum

levels of quality are maintained during production. An independent inspection agency is required to monitor the quality

assurance program.

Standard grades, sizes, and span tables have not been established for all prefabricated I-joists. The production of each

manufacturer may have unique design properties and procedures. Thus, the designer must consult information provided

by the manufacturer. Many engineering equations presented

in the previous section also apply to prefabricated I-joists.

During the 1980s, the prefabricated wood I-joists industry

was one of the fastest growing segments of the wood products industry. Prefabricated I-joists are manufactured by about

15 companies in the United States and Canada and are often

distributed through building material suppliers. Each manufacturer has developed its building code acceptance and provides catalogs with span tables and design information.

Recently, a performance standard for prefabricted I-joists

has been promulgated for products used in residential floor

construction (APA 1997).

Stressed-Skin Panels

Constructions consisting of structural panel “skins” glued to

wood stringers are often called stressed-skin panels. These

panels offer efficient structural constructions for floor, wall,

and roof components. They can be designed to provide

desired stiffness, bending moment resistance, and shear

resistance. The skins resist bending moment, and the wood

stringers provide shear resistance.

The details of design for a panel cross section are given in

Figure 11–8. The following equations were derived by basic

principles of engineering mechanics. A more rigorous design

procedure that includes the effects of shear lag is available in

Kuenzi and Zahn (1975).

Panel deflections can be computed using Equation (8–2) in

Chapter 8. The bending stiffness EI and shear stiffness GA'

are given by the following equations for the stressed-skin

panel shown in Figure 11–8.

 

EI b

E t E t Et s b

EtEt t t t t

E t Et s b t t E t Et s b t t

b E t E t Et s

b

=

( ) + +

















× +++ {

+ ++ + }

+ ++

11 2 2

11 2 2 1 2

11 1 2 2 2

1 1

3

2 2

3 3

2

2 2

12

c

c c

c cc c

c

(/)

[( ) ( )]

( / )( ) ( / )( )

f f





 





(11–14)

where E1 and E2 are modulus of elasticity values for skins

1 and 2, Ef1 and Ef2 flexural modulus of elasticity values for

skins 1 and 2, E stringer modulus of elasticity, and s total

width of all stringers in a panel.

An approximate expression for shear stiffness is

 

GA Gst ′ = c (11–15)

where G is stringer shear modulus.

Skin Stresses

Skin tensile and compressive stresses are given by

 

f ME y

EI

f ME y

EI

x

x

1

1 1

2

2 2

=

=

 (11–16)

where EI is given by Equation (11–14), M is bending

moment, and

Figure 11–7. Prefabricated I-joists with laminated veneer

lumber flanges and structural panel webs. (A) One experimental product has a hardboard web. The other two

commercial products have (B) oriented strandboard and

(C) plywood webs.
11–15

 

y

E t t t t t Et s

b

t t

E t E t Et s

b

y

E t t t t t Et s

b

t t

E t E t Et s

b

1

22 1 2 1

11 2 2

2

11 1 2 2

11 2 2

2

2

=

+++ + +

+ + 



 





=

+++ + +

+ + 



 





[( ) ( )] ( )

[( ) ( )] ( )

c cc c

c

c cc c

c

Either the skins should be thick enough or the stringers

spaced closely enough so that buckling does not occur in the

compression skin. Buckling stress can be analyzed by the

principles in Ding and Hou (1995). The design stress for the

structural panel in tension and compression strength should

not be exceeded.

Stringer Bending Stress

The stringer bending stress is the larger value given by

 

f ME y t

EI

f ME y t

EI

x

x

2

s

s

1

1 1

2

2

2

2

= −

= −

( )

( ) (11–17)

and these should not exceed appropriate values for the

species.

The stringer shear stress is given by

 

f V EQ

sEI sxy = ( ) (11–18)

where EQ = (E1t1b + Es y1/2) y1. This also should not exceed

appropriate values for the species.

Glue Shear Stress

Glue shear stress in the joint between the skins and stringers

is given by

 

f V EQ

sEI gl = ( ) (11–19)

where EQ = E1t1by1. This stress should not exceed values for

the glue and species. It should also not exceed the wood

stress fTR (“rolling” shear) for solid wood because, for plywood, the thin plies allow the glue shear stresses to be

transmitted to adjacent plies and could cause rolling shear

failure in the wood.

Buckling

Buckling of the stressed-skin panel of unsupported length

under end load applied in a direction parallel to the length of

the stringers can be computed by

 

P EI

L cr = π2

2 (11–20)

where L is unsupported panel length and EI is bending

stiffness given by Equation (11–14).

Compressive stress in the skins is given by

 

f PE

EA

f PE

EA

x

x

c

c

1

1

2

2

=

=

 (11–21)

and in the stringers by

 

f PE

EA s cx = (11–22)

Figure 11–8. Stressed-skin panel cross section.
 11–16

where EA = E1t1b + E2t2b + Etcs. These compressive stresses

should not exceed stress values for the structural panel or

stringer material. For plywood, compressive stress should

also be less than the critical buckling stress.

Structural Sandwich

Construction

Structural sandwich construction is a layered construction

formed by bonding two thin facings to a thick core

(Fig. 11–9). The thin facings are usually made of a strong

and dense material because they resist nearly all the applied

edgewise loads and flatwise bending moments. The core,

which is made of a weak and low density material, separates

and stabilizes the thin facings and provides most of the shear

rigidity of the sandwich construction. By proper choice of

materials for facings and core, constructions with high ratios

of stiffness to weight can be achieved. As a crude guide to the

material proportions, an efficient sandwich is obtained when

the weight of the core is roughly equal to the total weight of

the facings. Sandwich construction is also economical because the relatively expensive facing materials are used in

much smaller quantities than are the usually inexpensive core

materials. The materials are positioned so that each is used

to its best advantage.

Specific nonstructural advantages can be incorporated in a

sandwich construction by proper selection of facing and core

materials. An impermeable facing can act as a moisture

barrier for a wall or roof panel in a house; an abrasionresistant facing can be used for the top facing of a floor panel;

and decorative effects can be obtained by using panels with

plastic facings for walls, doors, tables, and other furnishings.

Core material can be chosen to provide thermal insulation,

fire resistance, and decay resistance. Because of the light

weight of structural sandwich construction, sound transmission problems must also be considered in choosing sandwich

component parts.

Methods of joining sandwich panels to each other and other

structures must be planned so that the joints function properly and allow for possible dimensional change as a result of

temperature and moisture variations. Both structural and

nonstructural advantages need to be analyzed in light of the

strength and service requirements for the sandwich construction. Moisture-resistant facings, cores, and adhesives should

be used if the construction is to be exposed to adverse moisture conditions. Similarly, heat-resistant or decay-resistant

facings, cores, and adhesives should be used if exposure to

elevated temperatures or decay organisms is expected.

Fabrication

Facing Materials

One advantage of sandwich construction is the great latitude

it provides in choice of facings and the opportunity to use

thin sheet materials because of the nearly continuous support

by the core. The stiffness, stability, and to a large extent, the

strength of the sandwich are determined by the characteristics

of the facings. Facing materials include plywood, single

veneers, or plywood overlaid with a resin-treated paper,

oriented strandboard, hardboard, particleboard, glass–fiberreinforced polymers or laminates, veneer bonded to metal,

and metals, such as aluminum, enameled steel, stainless

steel, magnesium, and titanium.

Core Materials

Many lightweight materials, such as balsa wood, rubber

foam, resin-impregnated paper, reinforced plastics, perforated

chipboard, expanded plastics, foamed glass, lightweight

concrete and clay products, and formed sheets of cloth, metal,

or paper have been used as a core for sandwich construction.

New materials and new combinations of old materials are

constantly being proposed and used. Cores of formed sheet

materials are often called honeycomb cores. By varying the

sheet material, sheet thickness, cell size, and cell shape,

cores of a wide range in density can be produced. Various

core configurations are shown in Figures 11–10 and 11–11.

The core cell configurations shown in Figure 11–10 can be

formed to moderate amounts of single curvature, but cores

shown in Figure 11–11 as configurations A, B, and C can

be formed to severe single curvature and mild compound

curvature (spherical).

Four types of readily formable cores are shown as configurations D, E, F, and G in Figure 11–11. The type D and F

cores form to a cylindrical shape, the type D and E cores to a

spherical shape, and the type D and G cores to various compound curvatures.

Figure 11–9. Cutaway section of sandwich construction

with plywood facings and a paper honeycomb core.
11–17

If the sandwich panels are likely to be subjected to damp or

wet conditions, a core of paper honeycomb should contain a

synthetic resin. When wet, paper with 15% phenolic resin

provides good strength, decay resistance, and desirable handling characteristics during fabrication. Resin amounts in

excess of about 15% do not seem to produce a gain in

strength commensurate with the increased quantity of resin

required. Smaller amounts of resin may be combined with

fungicides to offer primary protection against decay.

Manufacturing Operations

The principal operation in the manufacture of sandwich

panels is bonding the facings to the core. Special presses are

needed for sandwich panel manufacture to avoid crushing

lightweight cores, because the pressures required are usually

lower than can be obtained in the range of good pressure

control on presses ordinarily used for structural panels or

plastic products. Because pressure requirements are low,

simple and perhaps less costly presses could be used. Continuous roller presses or hydraulic pressure equipment may

also be suitable. In the pressing of sandwich panels, special

problems can occur, but the manufacturing process is basically not complicated.

Adhesives must be selected and applied to provide the necessary joint strength and permanence. The facing materials,

especially if metallic, may need special surface treatment

before the adhesive is applied.

In certain sandwich panels, loading rails or edgings are

placed between the facings at the time of assembly. Special

fittings or equipment, such as heating coils, plumbing, or

electrical wiring conduit, can easily be installed in the panel

before its components are fitted together.

Some of the most persistent difficulties in the use of sandwich panels are caused by the necessity of introducing edges,

inserts, and connectors. In some cases, the problem involves

tying together thin facing materials without causing severe

stress concentrations. In other cases, such as furniture manufacture, the problem is “show through” of core or inserts

through decorative facings. These difficulties are minimized

by a choice of materials in which the rate and degree of differential dimensional movement between core and insert are at a

minimum.

Structural Design

The structural design of sandwich construction can be compared with the design of an I-beam. The facings and core of

the sandwich are analogous to the flanges and web of the

I-beam, respectively. The two thin and stiff facings, separated

by a thick and light core, carry the bending loads. The functions of the core are to support the facings against lateral

wrinkling caused by in-plane compressive loads and to carry,

through the bonding adhesive, shear loads. When the

strength requirements for the facings and core in a particular

design are met, the construction should also be checked for

possible buckling, as for a column or panel in compression,

and for possible wrinkling of the facings.

Figure 11–10. Honeycomb core cell configurations.

Figure 11–11. Cell configurations for formable paper

honeycomb cores.
 11–18

The contribution of the core material to the stiffness of the

sandwich construction can generally be neglected because of

the core’s low modulus of elasticity; when that is the case,

the shear stress can be assumed constant over the depth of the

core. The facing moduli of elasticity are usually more than

100 times as great as the core modulus of elasticity. The core

material may also have a small shear modulus. This small

shear modulus causes increased deflections of sandwich

construction subjected to bending and decreased buckling

loads of columns and edge-loaded panels, compared with

constructions in which the core shear modulus is high. The

effect of this low shear modulus is greater for short beams and

columns and small panels than it is for long beams and

columns and large panels.

Without considering the contribution of core material, the

bending stiffness of sandwich beams having facings of equal

or unequal thickness is given by

 

 

D htt Et E t

t t = Et Et ++

+ +

2

12 12 21

1 2

2 1 1

3

2 2

1 3

12

( )

( ) ( ) (11–23)

where D is the stiffness per unit width of sandwich construction (product of modulus of elasticity and moment of inertia

of the cross section), E1 and E2 moduli of elasticity of facings

1 and 2, t1 and t2 facing thickness, and h distance between

facing centroids.

The shear stiffness per unit width is given by

 

U h

t = G

2

c

c (11–24)

where Gc is the core shear modulus associated with distortion of the plane perpendicular to the facings and parallel to

the sandwich length and tc is the thickness of the core.

The bending stiffness D and shear stiffness U are used to

compute deflections and buckling loads of sandwich beams.

The general expression for the deflection of flat sandwich

beams is given by

 

d y

dx

M

D U

dS

dx

x x

2

2

1

=− + 



 



 (11–25)

where y is deflection, x distance along the beam, Mx bending

moment per unit width at point x, and Sx shear force per unit

width at point x.

Integration of Equation (11–25) leads to the following

general expression for deflection of a sandwich beam:

 

y

k Pa

D

k Pa

U

= + b s

3

 (11–26)

where P is total load per unit width of beam, a is span, and

kb and ks are constants dependent upon the loading condition.

The first term in the right side of Equation (11–26) gives the

bending deflection and the second term the shear deflection.

Values of kb and ks for several loadings are given in

Table 11–1.

For sandwich panels supported on all edges, the theory of

plates must be applied to obtain analytical solutions. A

comprehensive treatment of sandwich plates under various

loading and boundary conditions can be found in the books

by Allen (1969), Whitney (1987), and Vinson and Sierakowski (1986). Many extensive studies of sandwich construction performed at the Forest Products Laboratory are referenced in those books. In addition, some high-order analyses

of sandwich construction that consider general material properties for component parts in specified applications can be

found in the references at the end of this chapter.

The buckling load per unit width of a sandwich panel with

no edge members and loaded as a simply supported column

is given by

 

N N

+N U = E

1 E

 (11–27)

where critical load

 

N n D

a E = π2 2

2 (11–28)

in which n is the number of half-waves into which the column buckles and a is the panel length. The minimum value

of NE is obtained for n = 1 and is called the Euler load.

Table 11–1. Values of kb and ks for several beam loadings

Loading Beam ends Deflection at kb ks

Uniformly distributed Both simply supported Midspan 5/384 1/8

Both clamped Midspan 1/384 1/8

Concentrated at midspan Both simply supported Midspan 1/48 1/4

Both clamped Midspan 1/192 1/4

Concentrated at outer

 quarter points

Both simply supported

Both simply supported

Midspan

Load point

11/76

1/96

1/8

1/8

Uniformly distributed Cantilever, 1 free, 1 clamped Free end 1/8 1/2

Concentrated at free end Cantilever, 1 free, 1 clamped Free end 1/3 1
11–19

At this load, the buckling form is often called “general

buckling,” as illustrated in Figure 11–12A.

The buckling load N is often expressed in the equivalent

form

 

1 11

NN U

= +

E

 (11–29)

When U is finite, N < NE; when U is infinite, N = NE; and

when NE is infinite (that is, n → ∞ in Eq. (11–28)), N = U,

which is often called the “shear instability” limit. The

appearance of this buckling failure resembles a crimp

(Fig. 11–12B). Shear instability or crimping failure is always possible for edge-loaded sandwich construction and is a

limit for general instability and not a localized failure.

For a sandwich panel under edge load and with edge members, the edge members will carry a load proportional to their

transformed area (area multiplied by ratio of edge member

modulus of elasticity to facing modulus of elasticity). Edge

members will also increase the overall panel buckling load

because of restraints at edges. Estimates of the effects of edge

members can be obtained from Zahn and Cheng (1964).

Buckling criteria for flat rectangular sandwich panels under

edgewise shear, bending, and combined loads and those for

sandwich walls of cylinders under torsion, axial compression

or bending, and external pressure have all been investigated

by various researchers at the Forest Products Laboratory.

Details can be found in Military Handbook 23A by the U.S.

Department of Defense (1968) and some publications listed

in the References.

Buckling of sandwich components has been emphasized

because it causes complete failure, usually producing severe

shear crimping at the edges of the buckles. Another important factor is the necessity that the facing stress be no more

than its allowable value at the design load. The facing stress

is obtained by dividing the load by the facing area under

load. For an edgewise compressive load per unit width N,

the facing stress is given by

 

f N

t t =

1 2 +

 (11–30)

In a strip of sandwich construction subjected to bending

moments, the mean facing stresses are given by

 

f M

t h

i i

i

= = 1 2, (11–31)

where fi is mean compressive or tensile stress per unit width

in facing i and M is bending moment per unit width of

sandwich. If the strip is subjected to shear loads, the shear

stress in the core is given by

 

f S

h cs = (11–32)

where S is the applied shear load per unit width of sandwich.

Localized failure of sandwich construction must be avoided.

Such failure is shown as dimpling and wrinkling of the

facings in Figure 11–12C and D, respectively. The stress at

which dimpling of the facing into a honeycomb core begins

is given by the empirical equation

 

f E t

s d

f = 









 2

2

 (11–33)

where fd is facing stress at dimpling, E facing modulus of

elasticity at stress fd, tf facing thickness, and s cell size of

honeycomb core (diameter of inscribed circle).

Increase in dimpling stress can be attained by decreasing the

cell size. Wrinkling of the sandwich facings can occur because they are thin and supported by a lightweight core that

functions as their elastic foundation. Wrinkling can also

occur because of a poor facing-to-core bond, resulting in

separation of facing from the core (Fig. 11–12D). Increase in

bond strength should produce wrinkling by core crushing.

Thus, a convenient rule of thumb is to require that the sandwich flatwise tensile strength (bond strength) is no less than

flatwise compressive core strength. Approximate wrinkling

stress for a fairly flat facing (precluding bond failure) is given

by

 

f EE G w cc = 3

4

1 3 ( ) / (11–34)

Core

crushing

Facing

Core

Facing

Honeycomb

core

Separation

from

core

A. General buckling B. Shear crimping

C. Dimpling of facings D. Wrinkling of facings

Figure 11–12. Modes of failure of sandwich

construction under edgewise loads.
 11–20

where fw is facing wrinkling stress, E facing modulus of

elasticity, Ec core modulus of elasticity in a direction perpendicular to facing, and Gc core shear modulus.

Wrinkling and other forms of local instability are described

in detail in Military Handbook 23A (U.S. Department of

Defense 1968) and in a book by Allen (1969). Localized

failure is not accurately predictable, and designs should be

checked by ASTM tests of laboratory specimens.

Because sandwich constructions are composed of several

materials, it is often of interest to attempt to design a construction of minimum weight for a particular component.

One introduction to the problem of optimum design is presented by Kuenzi (1970). For a sandwich with similar facings having a required bending stiffness D, the dimensions

for the minimum weight design are given by

 

h Dw

Ew = 



 



 2

1 3

c

/

 (11–35)

 

t

w

w = h c

4

where h is distance between facing centroids, t facing thickness, E facing modulus of elasticity, w facing density, and wc

core density.

The resulting construction will have very thin facings on a

very thick core and will be proportioned so that the total core

weight is two-thirds the total sandwich weight minus the

bond weight. However, such a construction may be impracticable because the required facings may be too thin.

Many detailed design procedures necessary for rapid design of

sandwich components for aircraft are summarized in Military

Handbook 23A (U.S. Department of Defense 1968). The

principles contained therein and in some publications listed

in the References are broad and can be applied to sandwich

components of all structures.

Dimensional Stability,

Durability, and Bowing

In a sandwich panel, any dimensional movement of one

facing with respect to the other as a result of changes in

moisture content and temperature causes bowing of an unrestrained panel. Thus, although the use of dissimilar facings

is often desirable from an economic or decorative standpoint,

the dimensional instability of the facings during panel

manufacture or exposure may rule out possible benefits. If

dimensional change of both facings is equal, the length and

width of the panel will increase or decrease but bowing will

not result.

The problem of dimensional stability is chiefly related to the

facings because the core is not stiff enough either to cause

bowing of the panel or to cause the panel to remain flat.

However, the magnitude of the bowing effect depends on the

thickness of the core.

It is possible to calculate mathematically the bowing of a

sandwich construction if the percentage of expansion of each

facing is known. The maximum deflection is given approximately by

 

∆ = ka

h

2

800

where k is the percentage of expansion of one facing compared

with the opposite facing, a the length of the panel, and h the

distance between facing centroids.

In conventional construction, vapor barriers are often installed to block migration of vapor to the cold side of a wall.

Various methods have been tried or suggested for reducing

vapor movement through sandwich panels, which causes a

moisture differential with resultant bowing of the panels.

These methods include bonding metal foil within the sandwich construction, blending aluminum flakes with the resin

bonding adhesives, and using plastic vapor barriers between

veneers, overlay papers, special finishes, or metal or plastic

facings. Because added cost is likely, some methods should

not be used unless their need has been demonstrated.

A large test unit simulating the use of sandwich panels in

houses was constructed at the Forest Products Laboratory.

The panels consisted of a variety of facing materials, including plywood, aluminum, particleboard, hardboard, paperboard, and cement asbestos, with cores of paper honeycomb,

polyurethane, or extruded polystyrene. These panels were

evaluated for bowing and general performance after various

lengths of service between 1947 and 1978. The experimental

assembly shown in Figure 11–13 represents the type of

construction used in the test unit. The major conclusions

were that (a) bowing was least for aluminum-faced panels,

(b) bowing was greater for plywood-faced panels with

polyurethane or polystyrene cores than for plywood-faced

panels with paper cores, and (c) with proper combinations

of facings, core, and adhesives, satisfactory sandwich panels

can be ensured by careful fabrication techniques.

Thermal Insulation

Satisfactory thermal insulation can best be obtained with

sandwich panels by using cores having low thermal conductivity, although the use of reflective layers on the facings is of

some value. Paper honeycomb cores have thermal conductivity values (k values), ranging from 0.04 to 0.09 W/m·K

(0.30 to 0.65 Btu·in/h·ft2·°F), depending on the particular

core construction. The k value does not vary linearly with

core thickness for a true honeycomb core because of direct

radiation through the core cell opening from one facing to the

other. Honeycomb with open cells can also have greater

conductivity if the cells are large enough (greater than about

9 mm (3/8 in.)) to allow convection currents to develop.

An improvement in the insulation value can be realized by

filling the honeycomb core with insulation or a foamedin-place resin.
11–21

Fire Resistance

In tests at the Forest Products Laboratory, the fire resistance

of wood-faced sandwich panels was appreciably greater than

that of hollow panels faced with the same thickness of

plywood. Fire resistance was greatly increased when coatings

that intumesce on exposure to heat were applied to the core

material. The spread of fire through the honeycomb core

depended to a large extent on the alignment of the flutes in

the core. In panels with flutes perpendicular to the facings,

only slight spread of flame occurred. In cores in which flutes

were parallel to the length of the panel, the spread of flame

occurred in the vertical direction along open channels.

Resistance to flame spread could be improved by placing a

barrier sheet at the top of the panel or at intervals in the panel

height, or if strength requirements permit, by simply turning

the length of the core blocks at 90° angles in the vertical

direction.

References

General

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Structural Composite Lumber

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Conshohocken, PA: American Society for Testing and

Materials.

Bohlen, J.C. 1972. Laminated veneer lumber—development

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Jung, J. 1982. Properties of parallel-laminated veneer from

stress-wave-tested veneers. Forest Products Journal.

32(7): 30–35.

Kunesh, R.H. 1978. MICRO=LAM: Structural laminated

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Laufenberg, T. 1983. Parallel laminated veneer: processing

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33(9):21–28.

Moody, R.C. 1972. Tensile strength of lumber laminated

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NIST. 1995. Voluntary product standard PS 1–95. Construction and industrial plywood. Gaithersburg, MD: U.S.

Department of Commerce, National Institute of Standards

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Press–Lam Team. 1972. Feasibility of producing a highyield laminated structural product. Res. Pap. FPL–RP–175.

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Glulam

AF&PA. 1997. National design specification for wood

construction. Washington, DC: American Forest & Paper

Association.

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erection. AITC 111. Englewood, CO: American Institute

of Timber Construction.

AITC. 1984. Standard appearance grades for structural gluedlaminated timber. AITC 110. Englewood, CO: American

Institute of Timber Construction.

Figure 11–13. Cutaway to show details of sandwich

construction in an experimental structure.
 11–22

AITC. 1990. Standard for preservative treatment of structural

glued-laminated timber. AITC 109. Englewood, CO:

American Institute of Timber Construction.

AITC. 1993a. Inspection manual. AITC 200. Englewood,

CO: American Institute of Timber Construction.

AITC. 1993b. Standard specifications for structural gluedlaminated timber of softwood species. AITC 117. Englewood, CO: American Institute of Timber Construction.

AITC. 1994. Timber construction manual. American Institute of Timber Construction. 4th ed. New York: John Wiley

& Sons.

AITC. 1996. Standard specifications for structural gluedlaminated timber of hardwood species. AITC 119. Englewood, CO: American Institute of Timber Construction.

ANSI. 1992. Structural glued laminated timber.

ANSI/AITC A190.1. New York: American National

Standards Institute.

ANSI. 1996. Structural glued laminated timber for utility

structures. ANSI O5.2. New York: American National

Standards Institute.

ASCE. 1975. Wood structures, a design guide and commentary. New York: American Society of Civil Engineers.

ASCE. 1982. Evaluation, maintenance and upgrading of

wood structures. New York: American Society of Civil

Engineers.

ASTM. 1997b. Standard practice for establishing stresses for

structural glued-laminated timber (glulam). ASTM D3737.

Philadelphia, PA: American Society for Testing and

Materials.

ASTM. 1997c. Standard practice for establishing structural

grades and related allowable properties for visually graded

lumber. ASTM D245. Philadelphia, PA: American Society

for Testing and Materials.

AWPA. 1997a. Standards for solvents and formulations for

organic preservative system. P9. Woodstock, MD: American

Wood Preservers’ Association.

AWPA. 1997b. Standards for waterborne preservatives. P5.

Woodstock, MD: American Wood Preservers’ Association.

CSA. 1989. Structural glued-laminated timbers. CAN/CSA

O122. Rexdale, ON: Canadian Standards Association.

CSA. 1994. Engineering design of wood (limit state design).

CAN/CSA O86. Rexdale, ON: Canadian Standards

Association.

Freas, A.D.; Selbo, M.L. 1954. Fabrication and design of

glued laminated wood structural members. U.S. Department

of Agriculture Tech. Bull. 1069. Available from: Englewood, CO: American Institute of Timber Construction.

Jokerst, R.W. 1981. Finger-jointed wood products. Res.

Pap. FPL–RP–382. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Moody, R.C. 1977. Improved utilization of lumber in glued

laminated beams. Res. Pap. FPL–RP–292. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Peterson, J.; Madson, G.; Moody, R.C. 1981. Tensile

strength of one-, two-, and three-ply glulam members of 2 by

6 Douglas-fir. Forest Products Journal. 31(1): 42–48.

Selbo, M.L.; Knauss, A.C.; Worth, H.E. 1965. After two

decades of service, glulam timbers show good performance.

Forest Products Journal. 15(11): 466–472.

Wolfe, R.W.; Moody, R.C. 1979. Bending strength of

vertically glued laminated beams with one to five plies. Res.

Pap. FPL–RP–333. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Glued Members With Lumber and Panels

APA. 1980. Plywood Design Specification. Tacoma, WA:

APA—The Engineered Wood Association.

Supp. 1. Design and fabrication of plywood curved panels

Supp. 2. Design and fabrication of plywood-lumber beams

Supp. 3. Design and fabrication of plywood stressed-skin

panels

Supp. 4. Design and fabrication of plywood sandwich

panels

APA. 1997. Performance standard for I-joists used in residential floor construction. PRI–400. Tacoma, WA: APA—The

Engineered Wood Association.

ASTM. 1997d. Standard specification for establishing and

monitoring structural capacities of prefabricated wood Ijoists. ASTM D5055. West Conshohocken, PA: American

Society for Testing and Materials.

ASTM. 1997e. Standard methods for testing veneer, plywood, and other glued veneer constructions. ASTM D805.

West Conshohocken, PA: American Society for Testing and

Materials.

Ding, Y.; Hou, J. 1995. General buckling analysis of sandwich constructions. Computers & Structures. 55(3):

485–493.

Forest Products Laboratory. 1943. Design of plywood

webs for box beams. FPL Rep. 1318. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Kuenzi, E.W.; Zahn, J.J. 1975. Stressed-skin panel deflection and stresses. Res. Pap. FPL–RP–251. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Lewis, W.C.; Heebink, T.B.; Cottingham, W.S.;

Dawley, E.R. 1943. Buckling in shear webs of box and Ibeams and their effect upon design criteria. FPL Rep. 1318B.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.
11–23

Lewis, W.C.; Heebink, T.B.; Cottingham, W.S. 1944.

Effects of certain defects and stress concentrating factors on

the strength of tension flanges of box beams. FPL Rep.

1513. Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Lewis, W.C.; Heebink, T.B.; Cottingham, W. S. 1945.

Effect of increased moisture on the shear strength at glue lines

of box beams and on the glue–shear and glue–tension

strengths of small specimens. FPL Rep. 1551. Madison,

WI: U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

McNatt, J.D. 1980. Hardboard-webbed beams: Research and

application. Forest Products Journal. 30(10): 57–64.

Orosz, I. 1970. Simplified method for calculating shear

deflections of beams. Res. Note FPL–RN–0210. Madison,

WI: U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Superfesky, M.J.; Ramaker, T.J. 1976. Hardboard-webbed

I-beams subjected to short-term loading. Res. Pap. FPL–

RP–264. Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory.

Superfesky, M.J.; Ramaker, T.J. 1978. Hardboard-webbed

I-beams: Effects of long-term loading and loading environment. Res. Pap. FPL–RP–306. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products

Laboratory.

Timoshenko, S. 1961. Theory of elastic stability. 2d ed.

New York: McGraw–Hill.

Structural Sandwich Construction

Allen, H.G. 1969. Analysis and design of structural sandwich panels. Oxford, England: Pergamon.

ASTM. 1997f. Annual book of ASTM standards. ASTM

Section 15, Vol. 03. Philadelphia, PA: American Society for

Testing and Materials.

C271–88. Density of core materials for structural sandwich

constructions

C273–88. Shear properties in flatwise plane of flat

sandwich constructions or sandwich core

C297–88. Tensile strength of flat sandwich constructions

in flatwise plane

C363–88. Delamination strength of honeycomb type core

material

C364–88. Compressive strength, edgewise, of flat

sandwich constructions

C365–88. Compressive strength, flatwise, of sandwich

cores

C366–88. Thickness of sandwich cores, measurement of

C393–88. Flexural properties of flat sandwich

constructions

C394–88. Shear fatigue of sandwich core materials

C480–88. Flexure-creep of sandwich constructions

C481–88. Laboratory aging of sandwich constructions

Cheng, S. 1961. Torsion of sandwich plates of trapezoidal

cross section. Journal of Applied Mechanics, American

Society of Mechanical Engineers Transactions. 28(3):

363–366.

Hall, R.B. 1996. Performance limits for stiffness-critical

graphitic foam structures. Pt. II. Comparisons of foams,

foam-core and honeycomb-core sandwiches in bending/shear.

Journal of Composite Materials. 30(17): 1938–1956.

Holmes, C.A. 1978. Room corner-wall fire tests of some

structural sandwich panels and components. Journal

of Fire and Flammability. 9: 467–488.

Holmes, C.A.; Eickner, H.W.; Brenden, J.J. [and

others]. 1980. Fire development and wall endurance in

sandwich and wood-frame structures. Res. Pap. FPL–RP–

364. Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Karlsson, K.F.; Astrom, B.T. 1997. Manufacturing and

applications of structural sandwich components. Composites,

Part A: Applied Science and Manufacturing. 28(2): 88–97.

Kimel, W.R. 1956. Elastic buckling of a simply supported

rectangular sandwich panel subjected to combined edgewise

bending and compression- results for panels with facings of

either equal or unequal thickness and with orthotropic cores.

FPL Rep. 1857-A. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Krajcinovic, D. 1972. Sandwich beam analysis. Journal of

Applied Mechanics, American Society of Mechanical

Engineers Transactions. 39(3): 773–778.

Kuenzi, E.W. 1970. Minimum weight structural sandwich.

Res. Note FPL–086. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Kuenzi, E.W.; Ericksen, W.S.; Zahn, J.J. 1962. Shear

stability of flat panels of sandwich construction. FPL Rep.

1560. (Rev.) Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory.

Kuenzi, E.W.; Bohannan, B.; Stevens, G.H. 1965. Buckling coefficients for sandwich cylinders of finite length under

uniform external later pressure. Res. Note FPL–RN–0104.

Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Noor, A.K.; Burton, W.S.; Bert, C.W. 1996. Computational models for sandwich panels and shells. Applied

Mechanics Reviews. 49(3): 155–199.

Palms, J.; Sherwood, G.E. 1979. Structural sandwich

performance after 31 years of service. Res. Pap. FPL–RP–

342. Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.
 11–24

Plantema, F.J. 1966. Sandwich construction. New York,

NY: John Wiley.

Reddy, J.N.; Miravete, A. 1995. Practical analysis of composite laminates. Boca Raton, FL: CRC Press, Inc.

Seidl, R.J. 1952. Paper honeycomb cores for structural

sandwich panels. FPL Rep. R1918. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Sherwood, G.E. 1970. Longtime performance of sandwich

panels in Forest Products Laboratory experimental unit. Res.

Pap. FPL–RP–144. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

U.S. Department of Defense. 1968. Structural sandwich

composites. Military Handbook 23A. Washington, DC:

Superintendent of Documents.

Vinson, J.R.; Sierakowski, R.L. 1986. The behavior of

structures composed of composite materials. Martinus

Nijhoff.

Whitney, J.M. 1987. Structural analysis of laminated

anisotropic plates. Lancaster, PA: Technomic Publishing

Co., Inc.

Zahn, J.J.; Cheng, S. 1964. Edgewise compressive

buckling of flat sandwich panels: Loaded ends simply

supported and sides supported by beams. Res. Note

FPL–RN–019. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

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539–548.
From

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Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
12–1

Drying and Control of Moisture

Content and Dimensional Changes

William T. Simpson

Chapter 12

Contents

Determination of Moisture Content 12–1

Oven-Drying Method 12–2

Electrical Method 12–2

Recommended Moisture Content 12–3

Timbers 12–3

Lumber 12–3

Glued Wood Products 12–3

Drying of Wood 12–5

Air Drying 12–6

Accelerated Air Drying and Pre-Drying 12–6

Kiln Drying 12–6

Drying Mechanism 12–6

Drying Stresses 12–7

Dry Kilns 12–7

Kiln Schedules 12–8

Drying Defects 12–9

Moisture Content of Dried Lumber 12–10

Moisture Control During Transit and Storage 12–14

Plywood and Structural Items 12–14

Finish and Factory Lumber 12–15

Dimensional Changes in Wood 12–15

Estimation Using Dimensional Change Coefficient 12–15

Calculation Based on Green Dimensions 12–17

Design Factors Affecting Dimensional Change 12–18

Framing Lumber in House Construction 12–18

Heavy Timber Construction 12–18

Interior Finish 12–18

Flooring 12–18

Wood Care and Installation During Construction 12–18

Lumber and Trusses 12–18

Exterior Trim and Millwork 12–19

Finished Flooring 12–19

Interior Finish 12–19

Plastering 12–19

References 12–20

n the living tree, wood contains large quantities of

water. As green wood dries, most of the water is

removed. The moisture remaining in the wood

tends to come to equilibrium with the relative humidity of

the surrounding air. Correct drying, handling, and storage of

wood will minimize moisture content changes that might

occur after drying when the wood is in service and such

changes are undesirable. If moisture content is controlled

within reasonable limits by such methods, major problems

from dimensional changes can usually be avoided.

The discussion in this chapter is concerned with moisture

content determination, recommended moisture content values, drying methods, methods of calculating dimensional

changes, design factors affecting such changes in structures,

and moisture content control during transit, storage, and

construction. Data on green moisture content, fiber saturation

point, shrinkage, and equilibrium moisture content are given

with information on other physical properties in Chapter 3.

Wood in service is virtually always undergoing at least

slight changes in moisture content. Changes in response to

daily humidity changes are small and usually of no consequence. Changes that occur as a result of seasonal variation,

although gradual, tend to be of more concern. Protective

coatings can retard dimensional changes in wood but do not

prevent them. In general, no significant dimensional changes

will occur if wood is fabricated or installed at a moisture

content corresponding to the average atmospheric conditions

to which it will be exposed. When incompletely dried material is used in construction, some minor dimensional

changes can be tolerated if the proper design is used.

Determination of

Moisture Content

The amount of moisture in wood is ordinarily expressed as a

percentage of the weight of the wood when ovendry. Four

methods of determining moisture content are covered in

ASTM D4442. Two of these—the oven-drying and the

electrical methods—are described in this chapter.
 12–2

The oven-drying method has been the most universally

accepted method for determining moisture content, but it is

slow and necessitates cutting the wood. In addition, the

oven-drying method may give values slightly greater than

true moisture content with woods containing volatile extractives. The electrical method is rapid, does not require cutting

the wood, and can be used on wood in place in a structure.

However, considerable care must be taken to use and interpret the results correctly. Use of the electrical method is

generally limited to moisture content values less than 30%.

Oven-Drying Method

In the oven-drying method, specimens are taken from representative boards or pieces of a quantity of lumber. With

lumber, the specimens should be obtained at least 500 mm

(20 in.) from the end of the pieces. They should be free from

knots and other irregularities, such as bark and pitch pockets.

Specimens from lumber should be full cross sections and

25 mm (1 in.) long. Specimens from larger items may be

representative sectors of such sections or subdivided increment borer or auger chip samples. Convenient amounts of

chips and particles can be selected at random from larger

batches, with care taken to ensure that the sample is representative of the batch. Veneer samples should be selected from

four or five locations in a sheet to ensure that the sample

average will accurately indicate the average of the sheet.

Each specimen should be weighed immediately, before any

drying or reabsorption of moisture has taken place. If the

specimen cannot be weighed immediately, it should be

placed in a plastic bag or tightly wrapped in metal foil to

protect it from moisture change until it can be weighed. After

weighing, the specimen is placed in an oven heated to 101°C

to 105°C (214°F to 221°F) and kept there until no appreciable weight change occurs in 4-h weighing intervals. A lumber section 25 mm (1 in.) along the grain will reach a constant weight in 12 to 48 h. Smaller specimens will take less

time. The constant or ovendry weight and the weight of the

specimen when cut are used to determine the percentage of

moisture content using the formula

 Moisture content (%)

 

 

= − × Weight when cut Ovendry weight

Ovendry weight

100 (12–1)

Electrical Method

The electrical method of determining the moisture content of

wood uses the relationships between moisture content and

measurable electrical properties of wood, such as conductivity (or its inverse, resistivity), dielectric constant, or powerloss factor. These properties vary in a definite and predictable

way with changing moisture content, but correlations are not

perfect. Therefore, moisture determinations using electrical

methods are always subject to some uncertainty.

Electric moisture meters are available commercially and are

based on each of these properties and identified by the

property measured. Conductance-type (or resistance) meters

measure moisture content in terms of the direct current conductance of the specimen. Dielectric-type meters are of two

types. Those based principally on dielectric constant are

called capacitance or capacitive admittance meters; those

based on loss factor are called power-loss meters.

The principal advantages of the electrical method compared

with the oven-drying method are speed and convenience.

Only a few seconds are required for the determination, and

the piece of wood being tested is not cut or damaged, except

for driving electrode needle points into the wood when using

conductance-type meters. Thus, the electrical method is

adaptable to rapid sorting of lumber on the basis of moisture

content, measuring the moisture content of wood installed in

a building, or establishing the moisture content of a quantity

of lumber or other wood items, when used in accordance

with ASTM D4442.

For conductance meters, needle electrodes of various lengths

are driven into the wood. There are two general types of

electrodes: insulated and uninsulated. Uninsulated electrodes

will sense the highest moisture content along their length

(highest conductance). Moisture gradients between the surface

and the interior can lead to confusion. If the wood is wetter

near the center than the surface, which is typical for drying

wood, the reading will correspond to the depth of the tip of

the insulated electrodes. If a meter reading increases as the

electrodes are being driven in, then the moisture gradient is

typical. In this case, the pins should be driven in about onefifth to one-fourth the thickness of the wood to reflect the

average moisture content of the entire piece. Dried or partially dried wood sometimes regains moisture in the surface

fibers, and the surface moisture content is greater than the

interior. In this case, the meter with the uninsulated pins

will read the higher moisture content surface, possibly causing a significant deviation from the average moisture content.

To guard against this problem, electrodes with insulated

shanks have been developed. They measure moisture content

of only the wood at the tips of the electrodes.

Dielectric-type meters are fitted with surface contact electrodes designed for the type of specimen material being

tested. The electric field from these electrodes penetrates well

into the specimen, but with a strength that decreases rapidly

with depth of penetration. For this reason, the readings of

dielectric meters are influenced predominantly by the surface

layers of the specimen, and the material near midthickness

may not be adequately represented in the meter reading if

there is a moisture content gradient.

To obtain accurate moisture content values, each instrument

should be used in accordance with its manufacturer’s instructions. The electrodes should be appropriate for the material

being tested and properly oriented according to meter manufacturer’s instructions. The readings should be carefully taken

as soon as possible after inserting the electrode. A species

correction supplied with the instrument should be applied

when appropriate. Temperature corrections should then be

made if the temperature of the wood differs considerably from

the temperature of calibration used by the manufacturer.
12–3

Approximate corrections for conductance-type (resistance)

meters are made by adding or subtracting about 0.5% for

each 5.6°C (10°F) the wood temperature differs from the

calibration temperature. The correction factors are added to

the readings for temperatures less than the calibration temperature and subtracted from the readings for temperatures

greater than the calibration temperature. Temperature corrections for dielectric meters are rather complex and are best

made from published charts (James 1988).

Although some meters have scales that go up to 120%, the

range of moisture content that can be measured reliably is 4%

to about 30% for commercial dielectric meters and about 6%

to 30% for resistance meters. The precision of the individual

meter readings decreases near the limits of these ranges.

Readings greater than 30% must be considered only qualitative. When the meter is properly used on a quantity of lumber dried to a reasonably constant moisture content below

fiber saturation, the average moisture content from the

corrected meter readings should be within 1% of the true

average.

Recommended Moisture

Content

Wood should be installed at moisture content levels as close

as possible to the average moisture content it will experience

in service. This minimizes the seasonal variation in moisture

content and dimension after installation, avoiding problems

such as floor buckling or cracks in furniture. The in-service

moisture content of exterior wood (siding, wood trim)

primarily depends on the outdoor relative humidity and

exposure to rain or sun. The in-service moisture content of

interior wood primarily depends on indoor relative humidity,

which in turn is a complex function of moisture sources,

ventilation rate, dehumidification (for example, air

conditioning), and outdoor humidity conditions.

The recommended values for interior wood presented in this

chapter are based on measurements in well-ventilated buildings without unusual moisture sources and without air conditioning. In air-conditioned buildings, moisture conditions

depend to a great extent on the proper sizing of the airconditioning equipment. Wood installed in basements or

over a crawl space may experience a moisture content greater

than the range provided, and wood in insulated walls or roofs

and attics may experience a moisture content greater or less

than the range. Nevertheless, the recommended values for

installation provide a useful guideline.

Timbers

Ideally, solid timbers should be dried to the average moisture content they will reach in service. Although this optimum is possible with lumber less than 76 mm (3 in.) thick,

it is seldom practical to obtain fully dried timbers, thick

joists, and planks. When thick solid members are used,

some shrinkage of the assembly should be expected. In the

case of built-up assemblies, such as roof trusses, it may be

necessary to tighten bolts or other fastenings occasionally to

maintain full bearing of the connectors as the members

shrink.

Lumber

The recommended moisture content of wood should be

matched as closely as is practical to the equilibrium moisture

content (EMC) conditions in service. Table 12–1 shows the

EMC conditions in outdoor exposure in various U.S. cities

for each month. The EMC data are based on the average

relative humidity and temperature data (30 or more years)

available from the National Climatic Data Center of the

National Oceanic and Atmospheric Administration. The

relative humidity data were the average of the morning and

afternoon values, and in most cases would be representative

of the EMC attained by the wood. However, in some locations, early morning relative humidity may occasionally

reach 100%. Under these conditions, condensation may occur

and the surface fibers of wood will exceed the EMC. The

moisture content requirements are more exacting for finished

lumber and wood products used inside heated and airconditioned buildings than those for lumber used outdoors or

in unheated buildings. For general areas of the United States,

the recommended moisture content values for wood used

inside heated buildings are shown in Figure 12–1. Values

and tolerances for both interior and exterior uses of wood in

various forms are given in Table 12–2. If the average moisture content is within 1% of that recommended and all pieces

fall within the individual limits, the entire lot is probably

satisfactory.

General commercial practice is to kiln dry wood for some

products, such as flooring and furniture, to a slightly lower

moisture content than service conditions demand, anticipating a moderate increase in moisture content during processing and construction. This practice is intended to ensure

uniform distribution of moisture among the individual

pieces. Common grades of softwood lumber and softwood

dimension lumber are not normally dried to the moisture

content values indicated in Table 12–2. Dry lumber, as

defined in the American Softwood Lumber Standard, has a

maximum moisture content of 19%. Some industry grading

rules provide for an even lower maximum. For example, to

be grade marked KD 15, the maximum moisture content

permitted is generally 15%.

Glued Wood Products

When veneers are bonded with cold-setting adhesives to

make plywood, they absorb comparatively large quantities of

moisture. To keep the final moisture content low and to

minimize redrying of the plywood, the initial moisture

content of the veneer should be as low as practical. However,

very dry veneer is brittle and difficult to handle without

damage, so the minimum practical moisture content is about

4%. Freshly glued plywood intended for interior service

should be dried to the moisture content values given in

Table 12–2.
 12–4

Table 12–1. Equilibrium moisture content of wood, exposed to outdoor atmosphere, in several U.S. locations

in 1997

Equilibrium moisture contenta (%)

State City Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

AK Juneau 16.5 16.0 15.1 13.9 13.6 13.9 15.1 16.5 18.1 18.0 17.7 18.1

AL Mobile 13.8 13.1 13.3 13.3 13.4 13.3 14.2 14.4 13.9 13.0 13.7 14.0

AZ Flagstaff 11.8 11.4 10.8 9.3 8.8 7.5 9.7 11.1 10.3 10.1 10.8 11.8

AZ Phoenix 9.4 8.4 7.9 6.1 5.1 4.6 6.2 6.9 6.9 7.0 8.2 9.5

AR Little Rock 13.8 13.2 12.8 13.1 13.7 13.1 13.3 13.5 13.9 13.1 13.5 13.9

CA Fresno 16.4 14.1 12.6 10.6 9.1 8.2 7.8 8.4 9.2 10.3 13.4 16.6

CA Los Angeles 12.2 13.0 13.8 13.8 14.4 14.8 15.0 15.1 14.5 13.8 12.4 12.1

CO Denver 10.7 10.5 10.2 9.6 10.2 9.6 9.4 9.6 9.5 9.5 11.0 11.0

DC Washington 11.8 11.5 11.3 11.1 11.6 11.7 11.7 12.3 12.6 12.5 12.2 12.2

FL Miami 13.5 13.1 12.8 12.3 12.7 14.0 13.7 14.1 14.5 13.5 13.9 13.4

GA Atlanta 13.3 12.3 12.0 11.8 12.5 13.0 13.8 14.2 13.9 13.0 12.9 13.2

HI Honolulu 13.3 12.8 11.9 11.3 10.8 10.6 10.6 10.7 10.8 11.3 12.1 12.9

ID Boise 15.2 13.5 11.1 10.0 9.7 9.0 7.3 7.3 8.4 10.0 13.3 15.2

IL Chicago 14.2 13.7 13.4 12.5 12.2 12.4 12.8 13.3 13.3 12.9 14.0 14.9

IN Indianapolis 15.1 14.6 13.8 12.8 13.0 12.8 13.9 14.5 14.2 13.7 14.8 15.7

IA Des Moines 14.0 13.9 13.3 12.6 12.4 12.6 13.1 13.4 13.7 12.7 13.9 14.9

KS Wichita 13.8 13.4 12.4 12.4 13.2 12.5 11.5 11.8 12.6 12.4 13.2 13.9

KY Louisville 13.7 13.3 12.6 12.0 12.8 13.0 13.3 13.7 14.1 13.3 13.5 13.9

LA New Orleans 14.9 14.3 14.0 14.2 14.1 14.6 15.2 15.3 14.8 14.0 14.2 15.0

ME Portland 13.1 12.7 12.7 12.1 12.6 13.0 13.0 13.4 13.9 13.8 14.0 13.5

MA Boston 11.8 11.6 11.9 11.7 12.2 12.1 11.9 12.5 13.1 12.8 12.6 12.2

MI Detroit 14.7 14.1 13.5 12.6 12.3 12.3 12.6 13.3 13.7 13.5 14.4 15.1

MN Minneapolis–St.Paul 13.7 13.6 13.3 12.0 11.9 12.3 12.5 13.2 13.8 13.3 14.3 14.6

MS Jackson 15.1 14.4 13.7 13.8 14.1 13.9 14.6 14.6 14.6 14.1 14.3 14.9

MO St. Louis 14.5 14.1 13.2 12.4 12.8 12.6 12.9 13.3 13.7 13.1 14.0 14.9

MT Missoula 16.7 15.1 12.8 11.4 11.6 11.7 10.1 9.8 11.3 12.9 16.2 17.6

NE Omaha 14.0 13.8 13.0 12.1 12.6 12.9 13.3 13.8 14.0 13.0 13.9 14.8

NV Las Vegas 8.5 7.7 7.0 5.5 5.0 4.0 4.5 5.2 5.3 5.9 7.2 8.4

NV Reno 12.3 10.7 9.7 8.8 8.8 8.2 7.7 7.9 8.4 9.4 10.9 12.3

NM Albuquerque 10.4 9.3 8.0 6.9 6.8 6.4 8.0 8.9 8.7 8.6 9.6 10.7

N Y New York 12.2 11.9 11.5 11.0 11.5 11.8 11.8 12.4 12.6 12.3 12.5 12.3

NC Raleigh 12.8 12.1 12.2 11.7 13.1 13.4 13.8 14.5 14.5 13.7 12.9 12.8

ND Fargo 14.2 14.6 15.2 12.9 11.9 12.9 13.2 13.2 13.7 13.5 15.2 15.2

OH Cleveland 14.6 14.2 13.7 12.6 12.7 12.7 12.8 13.7 13.8 13.3 13.8 14.6

OK Oklahoma City 13.2 12.9 12.2 12.1 13.4 13.1 11.7 11.8 12.9 12.3 12.8 13.2

OR Pendleton 15.8 14.0 11.6 10.6 9.9 9.1 7.4 7.7 8.8 11.0 14.6 16.5

OR Portland 16.5 15.3 14.2 13.5 13.1 12.4 11.7 11.9 12.6 15.0 16.8 17.4

PA Philadelphia 12.6 11.9 11.7 11.2 11.8 11.9 12.1 12.4 13.0 13.0 12.7 12.7

SC Charleston 13.3 12.6 12.5 12.4 12.8 13.5 14.1 14.6 14.5 13.7 13.2 13.2

SD Sioux Falls 14.2 14.6 14.2 12.9 12.6 12.8 12.6 13.3 13.6 13.0 14.6 15.3

TN Memphis 13.8 13.1 12.4 12.2 12.7 12.8 13.0 13.1 13.2 12.5 12.9 13.6

TX Dallas–Ft.Worth 13.6 13.1 12.9 13.2 13.9 13.0 11.6 11.7 12.9 12.8 13.1 13.5

TX El Paso 9.6 8.2 7.0 5.8 6.1 6.3 8.3 9.1 9.3 8.8 9.0 9.8

UT Salt Lake City 14.6 13.2 11.1 10.0 9.4 8.2 7.1 7.4 8.5 10.3 12.8 14.9

VA Richmond 13.2 12.5 12.0 11.3 12.1 12.4 13.0 13.7 13.8 13.5 12.8 13.0

WA Seattle–Tacoma 15.6 14.6 15.4 13.7 13.0 12.7 12.2 12.5 13.5 15.3 16.3 16.5

WI Madison 14.5 14.3 14.1 12.8 12.5 12.8 13.4 14.4 14.9 14.1 15.2 15.7

WV Charleston 13.7 13.0 12.1 11.4 12.5 13.3 14.1 14.3 14.0 13.6 13.0 13.5

W Y Cheyenne 10.2 10.4 10.7 10.4 10.8 10.5 9.9 9.9 9.7 9.7 10.6 10.6

a

EMC values were determined from the average of 30 or more years of relative humidity and temperature data

 available from the National Climatic Data Center of the National Oceanic and Atmospheric Administration.
12–5

Hot-pressed plywood and other board products, such as

particleboard and hardboard, usually do not have the same

moisture content as lumber. The high temperatures used in

hot presses cause these products to assume a lower moisture

content for a given relative humidity. Because this lower

equilibrium moisture content varies widely, depending on

the specific type of hot-pressed product, it is recommended

that such products be conditioned at 30% to 40% relative

humidity for interior use and 65% for exterior use.

Lumber used in the manufacture of large laminated members

should be dried to a moisture content slightly less than the

moisture content expected in service so that moisture absorbed from the adhesive will not cause the moisture content

of the product to exceed the service value. The range of

moisture content between laminations assembled into a

single member should not exceed 5 percentage points.

Although laminated members are often massive and respond

rather slowly to changes in environmental conditions, it is

desirable to follow the recommendations in Table 12–2 for

moisture content at time of installation.

Drying of Wood

Drying is required for wood to be used in most products.

Dried lumber has many advantages over green lumber for

producers and consumers. Removal of excess water reduces

weight, thus shipping and handling costs. Proper drying

confines shrinking and swelling of wood in use to manageable amounts under all but extreme conditions of relative

humidity or flooding. As wood dries, most of its strength

properties increase, as well as its electrical and thermal insulating properties. Properly dried lumber can be cut to precise

dimensions and machined more easily and efficiently; wood

parts can be more securely fitted and fastened together with

nails, screws, bolts, and adhesives; warping, splitting,

checking, and other harmful effects of uncontrolled drying are

largely eliminated; and paint, varnish, and other finishes are

more effectively applied and maintained. Wood must be

relatively dry before it can be glued or treated with decaypreventing and fire-retardant chemicals.

The key to successful and efficient drying is control of the

drying process. Timely application of optimum or at least

adequate temperature, relative humidity, and air circulation

conditions is critical. Uncontrolled drying leads to drying

defects that can adversely affect the serviceability and economics of the product. The usual strategy is to dry as fast as

the particular species, thickness, and end-product requirements allow without damaging the wood. Slower drying can

be uneconomical as well as introduce the risk of stain.

Softwood lumber intended for framing in construction is

usually targeted for drying to an average moisture content of

15%, not to exceed 19%. Softwood lumber for many other

uses is dried to a low moisture content, 10% to 12% for

many appearance grades to as low as 7% to 9% for furniture,

cabinets, and millwork. Hardwood lumber for framing in

construction, although not in common use, should also be

dried to an average moisture content of 15%, not to exceed

19%. Hardwood lumber for furniture, cabinets, and millwork

is usually dried to 6% to 8% moisture content.

6% average

moisture content

8% average moisture content

11% average

moisture content

Figure 12–1. Recommended average moisture

content for interior use of wood products in

various areas of the United States.

Table 12–2. Recommended moisture content values for various wood items at time of installation

Recommended moisture content (%) in various climatological regions

Most areas of the

United States Dry southwestern areaa Damp, warm coastal areaa

Use of wood Averageb

Individual

pieces Averageb

Individual

pieces Averageb

Individual

pieces

Interior: woodwork, flooring, furniture,

 wood trim

8 6–10 6 4–9 11 8–13

Exterior: siding, wood trim,

 sheathing, laminated timbers

12 9–14 9 7–12 12 9–14

a

Major areas are indicated in Figure 12–1.

b

To obtain a realistic average, test at least 10% of each item. If the quantity of a given item is small, make several

 tests. For example, in an ordinary dwelling having about 60 floor joists, at least 10 tests should be made on joists

 selected at random.
 12–6

Lumber drying is usually accomplished by some combination of air drying, accelerated air drying or pre-drying, and

kiln drying. Wood species, lumber thickness, economics,

and end use are often the main factors in determining the

details of the drying process.

Air Drying

The main purpose of air drying lumber is to evaporate as

much of the water as possible before end use or transfer to a

dry kiln. Air drying usually extends until wood moisture

content is as low as 20% to 25%, at which time the lumber

is transferred to a dry kiln if final drying to a lower moisture

content is required. Sometimes, depending on a mill’s

scheduling, air drying may be cut short at a higher moisture

content before the wood is sent to the dry kiln. Air drying

saves energy costs and reduces required dry kiln capacity.

Limitations of air drying are generally associated with uncontrolled drying. The drying rate is very slow during the cold

winter months. At other times, hot, dry winds may increase

degrade and volume losses as a result of severe surface checking and end splitting. Warm, humid periods with little air

movement may encourage the growth of fungal stains, as

well as aggravate chemical stains. Another limitation of air

drying is the high cost of carrying a large inventory of high

value lumber for extended periods. Air drying time to 20%

to 25% moisture content varies widely, depending on species, thickness, location, and the time of year the lumber is

stacked. Some examples of extremes for 25-mm- (1-in.-)

thick lumber are 15 to 30 days for some of the low density

species, such as pine, spruce, red alder, and soft maple,

stacked in favorable locations and favorable times of the year,

to 200 to 300 days for slow drying species, such as sinker

hemlock and pine, oak, and birch, in northern locations and

stacked at unfavorable times of the year. Details of important

air drying considerations, such as lumber stacking and air

drying yard layout, are covered in Air Drying of Lumber:

A Guide to Industry Practices (Rietz and Page 1971).

Accelerated Air Drying

and Pre-Drying

The limitations of air drying have led to increased use of

technology that reduces drying time and introduces some

control into drying from green to 20% to 25% moisture

content. Accelerated air drying involves the use of fans to

force air through lumber piles in a shed. This protects the

lumber from the elements and improves air circulation compared with air drying. Small amounts of heat are sometimes

used to reduce relative humidity and slightly increase temperature. Pre-dryers take this acceleration and control a step

further by providing control of both temperature and relative

humidity and providing forced air circulation in a completely

enclosed compartment. Typical conditions in a pre-dryer are

27°C to 38°C (80°F to 100°F) and 65% to 85% relative

humidity.

Kiln Drying

In kiln drying, higher temperatures and faster air circulation

are used to increase drying rate considerably. Specific kiln

schedules have been developed to control temperature and

relative humidity in accordance with the moisture content

and stress situation within the wood, thus minimizing

shrinkage-caused defects.

Drying Mechanism

Water in wood normally moves from high to low zones of

moisture content, which means that the surface of the wood

must be drier than the interior if moisture is to be removed.

Drying can be broken down into two phases: movement of

water from the interior to the surface of the wood and evaporation of water from the surface. The surface fibers of most

species reach moisture equilibrium with the surrounding air

soon after drying begins. This is the beginning of the

development of a typical moisture gradient (Fig. 12–2), that

is, the difference in moisture content between the inner and

outer portions of a board. If air circulation is too slow, a

longer time is required for the surfaces of the wood to reach

moisture equilibrium. This is one reason why air circulation

is so important in kiln drying. If air circulation is too slow,

drying is also slower than necessary and mold could develop

on the surface of lumber. If drying is too fast, electrical

energy in running the fans is wasted, and in certain species,

Figure 12–2. Typical moisture gradient in lumber

during drying at time increasing from t1 to t3.
12–7

surface checking and other drying defects can develop if

relative humidity and air velocity are not coordinated.

Water moves through the interior of wood as a liquid or

vapor through various air passageways in the cellular structure of the wood, as well as through the wood cell walls.

Moisture moves in these passageways in all directions, both

across and with the grain. In general, lighter species dry

faster than heavier species because the structure of lighter

wood contains more openings per unit volume and moisture

moves through air faster than through wood cell walls. Water

moves by two main mechanisms: capillary action (liquid)

and diffusion of bound water (vapor). Capillary action causes

free water to flow through cell cavities and the small passageways that connect adjacent cell cavities. Diffusion of

bound water moves moisture from areas of high concentration

to areas of low concentration. Diffusion in the longitudinal

direction is about 10 to 15 times faster than radial or tangential diffusion, and radial diffusion is somewhat faster than

tangential diffusion. This explains why flatsawn lumber

generally dries faster than quartersawn lumber. Although

longitudinal diffusion is much faster than diffusion across the

grain, it generally is not of practical importance in lumber

that is many times longer than it is thick.

Because chemical extractives in heartwood plug up passageways, moisture generally moves more freely in sapwood than

in heartwood; thus, sapwood generally dries faster than

heartwood. However, the heartwood of many species is lower

in moisture content than is the sapwood and can reach final

moisture content as fast.

The rate at which moisture moves in wood depends on the

relative humidity of the surrounding air, the steepness of the

moisture gradient, and the temperature of the wood. The

lower the relative humidity, the greater the capillary flow.

Low relative humidity also stimulates diffusion by lowering

the moisture content at the surface, thereby steepening the

moisture gradient and increasing the diffusion rate. The

greater the temperature of the wood, the faster moisture will

move from the wetter interior to the drier surface. If relative

humidity is too low in the early stages of drying, excessive

shrinkage may occur, resulting in surface and end checking.

If the temperature is too high, collapse, honeycomb, or

strength reduction can occur.

Drying Stresses

Drying stresses are the main cause of nonstain-related drying

defects. Understanding these stresses provides a means for

minimizing and recognizing the damage they can cause.

The cause of drying stresses in the differential shrinkage

between the outer part of a board (the shell) and the interior

part (the core) can also cause drying defects. Early in drying,

the fibers in the shell dry first and begin to shrink. However,

the core has not yet begun to dry and shrink; consequently,

the core prevents the shell from shrinking. Thus, the shell

goes into tension and the core into compression (Fig. 12–3).

If the shell dries too rapidly, it is stressed beyond the elastic

limit and dries in a permanently stretched (set) condition

without attaining full shrinkage. Sometimes surface cracks,

or checks, occur during this initial stage of drying, and they

can be a serious defect for many uses. As drying progresses,

the core begins to dry and attempts to shrink. However, the

shell is set in a permanently expanded condition and prevents normal shrinkage of the core. This causes the stresses

to reverse; the core goes into tension and the shell into

compression. The change in the shell and core stresses and

in the moisture content level during drying is shown in

Figure 12–4. These internal tension stresses may be severe

enough to cause internal cracks (honeycomb).

Differential shrinkage caused by differences in radial, tangential, and longitudinal shrinkage is a major cause of warp.

The distortions shown in Figure 3–3 in Chapter 3 are due to

differential shrinkage. When juvenile or reaction wood is

present on one edge or face of a board and normal wood is

present on the opposite side, the difference in their longitudinal shrinkage can also cause warp.

Dry Kilns

Most dry kilns are thermally insulated compartments designed for a batch process in which the kiln is completely

loaded with lumber in one operation and the lumber remains

stationary during the entire drying cycle. Temperature and

relative humidity are kept as uniform as possible throughout

the kiln and can be controlled over a wide range. Temperature and relative humidity are changed as the wood dries

based on a schedule that takes into account the moisture

content and/or the drying rate of the lumber. All dry kilns

Figure 12–3. End view of board showing development

of drying stresses (a) early and (b) later in drying.
 12–8

use some type of forced-air circulation, with air moving

through the lumber perpendicular to the length of the lumber

and parallel to the spacers (stickers) that separate each layer of

lumber in a stack.

Three general types of kilns are in common use. One is the

track-loaded type (Fig. 12–5), where lumber is stacked on

kiln trucks that are rolled in and out of the kiln on tracks.

The majority of softwood lumber in the United States is

dried in this kiln type. Another major type is the packageloaded kiln (Fig 12–6), where individual stacks of lumber are

fork-lifted into place in the kiln. This type of kiln is commonly used for drying hardwood lumber. These kilns are

most commonly heated with steam, although softwood

lumber kilns are sometimes directly heated. A third common

type of kiln, usually package loaded, is the dehumidification

kiln. Instead of venting humid air to remove water, as the

other two types of kilns do, water is removed by condensation on cold dehumidifier coils (Fig. 12–7).

Kiln Schedules

A kiln schedule is a carefully developed compromise between

the need to dry lumber as fast as possible for economic

efficiency and the need to avoid severe drying conditions that

will lead to drying defects. A kiln schedule is a series of

temperatures and relative humidities that are applied at various stages of drying. In most schedules, the temperature is

gradually increased and the relative humidity decreased. The

schedule for Southern Pine structural lumber is an exception

to this general rule. This is lumber usually dried at a constant temperature and relative humidity. Temperatures are

chosen to strike this compromise of a satisfactory drying rate

and avoidance of objectionable drying defects. The stresses

that develop during drying are the limiting factor in determining the kiln schedule. The schedule must be developed

so that the drying stresses do not exceed the strength of the

wood at any given temperature and moisture content. Otherwise, the wood will crack either on the surface or internally

or be crushed by forces that collapse the wood cells. Wood

generally becomes stronger as the moisture content decreases,

and to a lesser extent, it becomes weaker as temperature

increases. The net result is that as wood dries it becomes

stronger because of the decreasing moisture content and can

tolerate higher drying temperatures and lower relative humidities without cracking. This is a fortunate circumstance

because as wood dries, its drying rate decreases at any given

temperature, and the ability to increase drying temperature

helps maintain a reasonably fast drying rate. Thus, rapid

drying is achieved in kilns by the use of temperatures as high

as possible and relative humidities as low as possible.

Drying schedules vary by species, thickness, grade, and end

use of lumber. There are two general types of kiln schedules:

moisture content schedules and time-based schedules. Most

hardwood lumber is dried by moisture content schedules.

This means that the temperature and relative humidity conditions are changed according to various moisture content 

Figure 12–4. Moisture–stress relationship during

six stages of kiln drying 50-mm- (2-in.-) thick

red oak.

Figure 12–5. Lineshaft, double-track, compartment kiln

with alternately opposing fans. Vents are over fan shaft

between fans. Vent on high pressure side of fans

becomes fresh air inlet when direction of circulation

is reversed.
12–9

levels attained by the lumber during drying. A typical hardwood schedule might begin at 49°C (120°F) and 80% relative humidity when the lumber is green. By the time the

lumber has reached 15% moisture content, the temperature is

as high as 82°C (180°F). A typical hardwood drying schedule is shown in Table 12–3. Some method of monitoring

moisture content during drying is required for schedules

based on moisture content. One common method is the use

of short kiln samples that are periodically weighed, usually

manually but potentially remotely with load cells. Alternatively, electrodes are imbedded in sample boards to sense the

change in electrical conductivity with moisture content. This

system is limited to moisture content values less than 30%.

Softwood kiln schedules generally differ from hardwood

schedules in that changes in kiln temperature and relative

humidity are made at predetermined times rather than moisture content levels. Examples of time-based schedules, both

conventional temperature (<100°C (<212°F )) and high

temperature (>110°C (>230°F )), are given in Table 12–3.

Drying Defects

Most drying defects or problems that develop in wood products during drying can be classified as fracture or distortion,

warp, or discoloration. Defects in any one of these categories

are caused by an interaction of wood properties with processing factors. Wood shrinkage is mainly responsible for wood

ruptures and distortion of shape. Cell structure and chemical

extractives in wood contribute to defects associated with

uneven moisture content, undesirable color, and undesirable

surface texture. Drying temperature is the most important

processing factor because it can be responsible for defects in

each category.

Fracture or Distortion

Surface checks occur early in drying when the shell of a board

is stressed in tension enough to fracture the wood. These

checks occur most often on the face of flatsawn boards and are

illustrated in Figure 12–8. End checks (Fig. 12–9) are similar to surface checks but appear on the ends of boards. End

checks occur because the rapid longitudinal movement of

moisture causes the board end to dry very quickly and

Figure 12–6. Package-loaded kiln with fans connected directly to motors.
 12–10

develop high stresses, therefore fracturing. End coatings,

either on the log or freshly sawn lumber, are an effective

preventative measure. Collapse is a distortion, flattening, or

crushing of wood cells. In severe cases (Fig. 12–10), collapse

usually shows up as grooves or corrugations, a washboarding

effect. Less severe collapse shows up as excessive thickness

shrinkage and may not be a serious problem. Honeycomb

(Fig. 12–11) is an internal crack that occurs in the later

stages of kiln drying when the core of a board is in tension.

It is caused when the core is still at a relatively high moisture content and drying temperatures are too high for too

long during this critical drying period. Nondestructive testing methods, using speed of sound, have been found to be

effective in detecting the presence of these cracks in dried

lumber. Knots may loosen during drying because of the

unequal shrinkage between the knot and the surrounding

wood (Fig. 12–12).

Warp

Warp in lumber is any deviation of the face or edge of a

board from flatness or any edge that is not at right angles to

the adjacent face or edge. Warp can be traced to two causes:

(a) differences between radial, tangential, and longitudinal

shrinkage in the piece as it dries or (b) growth stresses. Warp

is aggravated by irregular or distorted grain and the presence

of abnormal types of wood, such as juvenile and reaction

wood. The six major types of warp are bow, crook, twist,

oval, diamond, and cup (Fig. 12–13).

Discoloration

The use of dried wood products can be impaired by discoloration, particularly when the end use requires a clear, natural

finish. Unwanted discoloration can develop in the tree,

during storage of logs and green lumber, or during drying.

There are two general types of discoloration: chemical and

fungal.

Chemical discoloration is the result of oxidative and enzymatic reactions with chemical constituents in wood. Discolorations range from pinkish, bluish, and yellowish hues

through gray and reddish brown to dark brown shades.

Brown stain in pines and darkening in many hardwoods is a

common problem when drying temperatures are too high

(Fig. 12–14). A deep grayish-brown chemical discoloration

can occur in many hardwood species if initial drying is too

slow (Fig. 12–15).

Fungal stains, often referred to as blue or sap stain, are

caused by fungi that grow in the sapwood (Fig. 12–16).

Blue-stain fungi do not cause decay of the sapwood, and

fungi generally do not grow in heartwood. Blue stain can

develop if initial drying is too slow.

Another common type of stain develops under stickers

(Fig. 12–17). This stain results from contact of the sticker

with the board. Sticker stains (sometimes called shadow) are

imprints of the sticker that are darker or lighter than the

wood between the stickers and can be caused by either

chemical or fungal action, or both.

Moisture Content of Dried Lumber

Although widely used, the trade terms “shipping dry,” “air

dry,” and “kiln dry” may not have identical meanings as to

moisture content in the different producing regions. Despite

the wide variations in the use of these terms, they are sometimes used to describe dried lumber. The following statements, which are not exact definitions, outline these

categories.

Shipping Dry

Shipping dry means lumber that has been partially dried to

prevent stain or mold during brief periods of transit; ideally

the outer 3.2 mm (1/8 in.) is dried to 25% or less moisture

content.

Fig. 12–7. A typical dehumidification kiln (top) and

dehumidification drying system (bottom).
12–11

Air Dry

Air dry means lumber that has been dried by exposure to the

air outdoors or in a shed or by forced circulation of air that

has not been heated above 49°C (120°F ). Commercial airdry stock generally has an average moisture content low

enough for rapid kiln drying or rough construction use.

Moisture content is generally in the range of 20% to 25% for

dense hardwoods and 15% to 20% for softwoods and lowdensity hardwoods. Extended exposure can bring standard

19- and 38-mm (nominal 1- and 2-in.) lumber within one or

two percentage points of the average exterior equilibrium

moisture content of the region. For much of the United

States, the minimum moisture content of thoroughly airdried lumber is 12% to 15%.

Table 12–3. Typical dry kiln schedules for lumber

Moisture content-based schedule for 25-mm (1-in.) (4/4) black walnut,

dried to 7% moisture content

Temperature (°C(°F)) Relative Equilibrium

Moisture

content (%) Dry-bulb Wet-bulb

humidity 

(%)

moisture content

(%)

Above 50 49.0 (120) 45.0 (113) 80 14.4

50 to 40 49.0 (120) 43.5 (110) 72 12.1

40 to 35 49.0 (120) 40.5 (105) 60 9.6

35 to 30 49.0 (120) 35.0 (95) 40 6.5

30 to 25 54.5 (130) 32.0 (90) 22 4.0

25 to 20 60.0 (140) 32.0 (90) 15 2.9

20 to 15 65.5 (150) 37.5 (100) 18 3.2

15 to 7 82.2 (180) 54.5 (130) 26 3.5

Equalize 82.2 (180) 58.3 (137) 30 3.8

Condition 82.2 (180) 76.7 (170) 79 11.1

Time-based schedule for 25- to 50-mm (1- to 2-in.) (4/4 to 8/4) Douglas Fir,

upper grades, dried to 12% moisture content

Temperature (°C(°F)) Relative Equilibrium

Time (h) Dry-bulb Wet-bulb

humidity

(%)

moisture content

(%)

 0 to 12 76.5 (170) 73.5 (164) 86 14.1

12 to 24 76.5 (170) 71.0 (160) 78 11.4

24 to 48 79.5 (175) 71.0 (160) 69 9.1

48 to 72 82.2 (180) 71.0 (160) 62 7.7

72 to 96

or until dry

82.2 (180) 60.0 (140) 36 4.5

High temperature schedule for 50- by 100-mm to 50- by 250-mm (2- by 4-in. to

2- by 10-in.) Southern Pine, dried to 15% moisture content

Temperature (°C(°F)) Relative Equilibrium

Time (h) Dry-bulb Wet-bulb

humidity

(%)

moisture content

(%)

0 until dry 116 (240) 82.2 (180) 29 2.5
 12–12

Figure 12–11. Board machined into millwork shows

honeycomb (top). Surface of planed red oak board

shows no honeycomb (bottom).

Figure 12–12. Loose knot in Southern Pine.

Kiln Dry

Kiln dry means lumber that has been dried in a kiln or by

some special drying method to an average moisture content

specified or understood to be suitable for a certain use. The

average moisture content should have upper and lower tolerance limits, and all values should fall within these limits.

Kiln-dried softwood dimension lumber generally has an

average moisture content of 19% or less; the average moisture content for many other softwood uses is 10% to 20%.

Hardwood and softwood lumber for furniture, cabinetry, and

millwork usually has a final moisture content of 6% to 8%

and can be specified to be free of drying stresses. The importance of suitable moisture content values is recognized, and

provisions covering them are now incorporated in some

softwood standards as grading rules. Moisture content values

in the general grading rules may or may not be suitable for a

specific use; if not, a special moisture content specification

should be made.

Figure 12–8. Surface checking on Douglas Fir

dimension lumber.

Figure 12–9. End checking in oak lumber.

Figure 12–10. Severe collapse in western redcedar.
12–13

Figure 12–15. Gray sapwood stain in southern red oak

that was dried green with humid, low temperature

conditions and poor air circulation.

Figure 12–16. Sap stain in Southern Pine. Color

ranges from bluish gray to black.

Figure 12–13. Various types of warp that can develop

in boards during drying.

Figure 12–14. Brown sapwood stain in Southern Pine

lumber.
 12–14

Moisture Control During

Transit and Storage

Lumber and other wood items may change in moisture

content and dimension while awaiting shipment, during

fabrication, in transit, and in storage.

When standard 19-mm (nominal 1-in.) dry softwood lumber

is shipped in tightly closed boxcars, shipping containers, or

trucks or in packages with complete and intact wrappers,

average moisture content changes for a package can generally

be held to 0.2% or less per month. In holds or between

decks of ships, dry material usually adsorbs about 1.5%

moisture during normal shipping periods. If green material is

included in the cargo, the moisture regain of the dry lumber

may be doubled. On the top deck, if unprotected from the

elements, the moisture regain can be as much as 7%.

When standard 19-mm (nominal 1-in.) softwood lumber,

kiln dried to 8% or less, is piled solid under a good pile roof

in a yard in humid weather, average moisture content of a

pile can increase at the rate of about 2% per month during the

first 45 days. An absorption rate of about 1% per month can

then be sustained throughout a humid season. Comparable

initial and sustaining absorption rates are about 1% per

month in open (roofed) sheds and 0.3% per month in closed

sheds. Stock that was piled for a year in an open shed in a

western location increased 2.7% on the inside of solid piles

and 3.5% on the outside of the piles. All stock that has been

manufactured in any way should be protected from precipitation and spray, because water that gets into a solid pile tends

to be absorbed by the wood instead of evaporating. The

extent to which additional control of the storage environment

is required depends upon the use to which the wood will be

put and the corresponding moisture content recommendations. The moisture content of all stock should be determined when it is received. If moisture content is not as

specified or required, stickered storage in an appropriate

condition could ultimately bring the stock within the desired

moisture content range. If a large degree of moisture change

is required, the stock must be redried.

Plywood and Structural Items

Green or partially dried lumber and timbers should be open

piled on stickers and protected from sunshine and precipitation by a tight roof. Framing lumber and plywood with 20%

or less moisture content can be solid piled in a shed that

provides good protection against sunshine and direct or

wind-driven precipitation. However, a better practice for

stock with greater than 12% moisture content is the use of

stickered piling to bring moisture content more in line with

the moisture content in use. Dry lumber can be piled solid in

the open for relatively short periods, but at least a minimum

pile cover of waterproofed paper should be used whenever

possible. Because it is difficult to keep rain out completely,

storing solid-piled lumber in the open for long periods is not

recommended. If framing lumber must be stored in the open

for a long time, it should be piled on stickers over good

supports and the piles should be roofed. Solid-piled material

that has become wet again should also be re-piled on

stickers.

Figure 12–17. Sticker stain in sapwood of sugar

maple after planing.

Table 12–4. Amount by which temperature of storage area must be increased above outside

temperature to maintain equilibrium moisture content

Outside relative Temperature differential (°C (°F)) for desired equilibrium moisture content

humidity

(%) 6% 7% 8% 9% 10% 11% 12%

90 18.3 (33) 16.1 (29) 12.8 (23) 10.0 (18) 8.3 (15) 6.1 (11) 5.0 (9)

80 16.7 (30) 13.9 (25) 10.5 (19) 7.8 (14) 6.1 (11) 4.4 (8) 3.3 (6)

70 13.9 (25) 11.1 (20) 8.3 (15) 5.6 (10) 3.9 (7) 2.2 (4) 1.7 (3)

60 11.1 (20) 8.3 (15) 5.0 (9) 3.3 (6) 1.7 (3) — —

50 8.3 (15) 5.6 (10) 2.8 (5) 0.6 (1) — — —
12–15

Finish and Factory Lumber

Such kiln-dried items as exterior finish, siding, and exterior

millwork should be stored in a closed but unheated shed.

They should be placed on supports raised above the floor, at

least 150 mm (6 in.) high if the floor is paved or 300 mm

(12 in.) if not paved. Interior trim, flooring, cabinet work,

and lumber for processing into furniture should be stored in a

room or closed shed where relative humidity is controlled.

Kiln-dried and machined hardwood dimension or softwood

cut stock should also be stored under controlled humidity

conditions.

Dried and machined hardwood dimension or softwood

lumber intended for remanufacture should also be stored

under controlled humidity conditions. Under uncontrolled

conditions, the ends of such stock may attain a greater moisture content than the balance of the length. Then, when the

stock is straight-line ripped or jointed before edge gluing,

subsequent shrinkage will cause splitting or open glue joints

at the ends of panels. The simplest way to reduce relative

humidity in storage areas of all sizes is to heat the space to a

temperature slightly greater than that of the outside air.

Dehumidifiers can be used in small, well-enclosed spaces.

If the heating method is used, and there is no source of moisture except that contained in the air, the equilibrium moisture content can be maintained by increasing the temperature

of the storage area greater than the outside temperature by the

amounts shown in Table 12–4. When a dehumidifier is

used, the average temperature in the storage space should be

known or controlled. Table 3–4 in Chapter 3 should be used

to select the proper relative humidity to give the desired

average moisture content. Wood in a factory awaiting or

following manufacture can become too dry if the area is

heated to 21°C (70°F) or greater when the outdoor temperature is low. This often occurs in the northern United States

during the winter. Under such circumstances, exposed ends

and surfaces of boards or cut pieces will tend to dry to the

low equilibrium moisture content condition, causing shrinkage and warp. In addition, an equilibrium moisture content

of 4% or more below the moisture content of the core of

freshly crosscut boards can cause end checking. Simple

remedies are to cover piles of partially manufactured items

with plastic film and lower the shop temperature during

nonwork hours. Increased control can be obtained in critical

shop and storage areas by humidification. In warm weather,

cooling can increase relative humidity and dehumidification

may be necessary.

Dimensional Changes in Wood

Dry wood undergoes small changes in dimension with normal changes in relative humidity. More humid air will cause

slight swelling, and drier air will cause slight shrinkage.

These changes are considerably smaller than those involved

with shrinkage from the green condition. Equation (12–2)

can be used to approximate dimensional changes caused by

shrinking and swelling by using the total shrinkage coefficient from green to ovendry. However, the equation assumes

that the shrinkage–moisture content relationship is linear.

Figure 3–4 (Ch. 3) shows that this is not the case, so some

error is introduced. The error is in the direction of underestimating dimensional change, by about 5% of the true

change. Many changes of moisture content in use are over the

small moisture content range of 6% to 14%, where the

shrinkage–moisture content relationship is linear (Ch. 3,

Fig. 3–4). Therefore, a set of shrinkage coefficients based on

the linear portion of the shrinkage–moisture content curve

has been developed (Table 12–5). Approximate changes in

dimension can be estimated by a simple formula that involves a dimensional change coefficient, from Table 12–5,

when moisture content remains within the range of normal

use. (Dimensional changes are further discussed in Chs. 3

and 6.)

Estimation Using Dimensional

Change Coefficient

The change in dimension within the moisture content limits

of 6% to 14% can be estimated satisfactorily by using a

dimensional change coefficient based on the dimension at

10% moisture content:

 

∆D DC M M = − I FI [ ] T ( ) (12–2)

where ∆D is change in dimension, DI dimension in units of

length at start of change, CT dimensional change coefficient

tangential direction (for radial direction, use CR), MF moisture content (%) at end of change, and MI moisture content

(%) at start of change.

Values for CT and CR, derived from total shrinkage values,

are given in Table 12–5. When MF < MI, the quantity

(MF − MI) will be negative, indicating a decrease in

dimension; when greater, it will be positive, indicating an

increase in dimension.

As an example, assuming the width of a flat-grained white fir

board is 232 mm (9.15 in.) at 8% moisture content, its

change in width at 11% moisture content is estimated as

∆D = 232[0.00245(11 − 8)]

= 232(0.00735)

= 1.705 mm

∆D = 9.15[0.00245(11 − 8)]

= 9.15[0.00735]

= 0.06725 or 0.067 in.

Then, dimension at end of change

DI + ∆D = 232 + 1.7 (= 9.15 + 0.067)

 = 233.7 mm (= 9.217 in.)

The thickness of the same board at 11% moisture content can

be estimated by using the coefficient CR = 0.00112.
 12–16

Table 12–5. Coefficients for dimensional change as a result of shrinking or swelling within moisture content limits

of 6% to 14% (CT = dimensional change coefficient for tangential direction; CR = radial direction)

Dimensional change

coefficienta

Dimensional change

coefficienta

Species CR CT Species CR CT

Hardwoods

Alder, red 0.00151 0.00256 Honeylocust 0.00144 0.00230

Apple 0.00205 0.00376 Locust, black 0.00158 0.00252

Ash, black 0.00172 0.00274 Madrone, Pacific 0.00194 0.00451

Ash, Oregon 0.00141 0.00285 Magnolia, cucumbertree 0.00180 0.00312

Ash, pumpkin 0.00126 0.00219 Magnolia, southern 0.00187 0.00230

Ash, white 0.00169 0.00274 Magnolia, sweetbay 0.00162 0.00293

Ash, green 0.00169 0.00274 Maple, bigleaf 0.00126 0.00248

Aspen, quaking 0.00119 0.00234 Maple, red 0.00137 0.00289

Basswood, American 0.00230 0.00330 Maple, silver 0.00102 0.00252

Beech, American 0.00190 0.00431 Maple, black 0.00165 0.00353

Birch, paper 0.00219 0.00304 Maple, sugar 0.00165 0.00353

Birch, river 0.00162 0.00327 Oak, black 0.00123 0.00230

Birch, yellow 0.00256 0.00338 Red Oak, commercial 0.00158 0.00369

Birch, sweet 0.00256 0.00338 Red oak, California 0.00123 0.00230

Buckeye, yellow 0.00123 0.00285 Red oak: water, laurel, willow 0.00151 0.00350

Butternut 0.00116 0.00223 White Oak, commercial 0.00180 0.00365

Catalpa, northern 0.00085 0.00169 White oak, live 0.00230 0.00338

Cherry, black 0.00126 0.00248 White oak, Oregon white 0.00144 0.00327

Chestnut, American 0.00116 0.00234 White oak, overcup 0.00183 0.00462

Cottonwood, black 0.00123 0.00304 Persimmon, common 0.00278 0.00403

Cottonwood, eastern 0.00133 0.00327 Sassafras 0.00137 0.00216

Elm, American 0.00144 0.00338 Sweet gum 0.00183 0.00365

Elm, rock 0.00165 0.00285 Sycamore, American 0.00172 0.00296

Elm, slippery 0.00169 0.00315 Tanoak 0.00169 0.00423

Elm, winged 0.00183 0.00419 Tupelo, black 0.00176 0.00308

Elm, cedar 0.00183 0.00419 Tupelo, water 0.00144 0.00267

Hackberry 0.00165 0.00315 Walnut, black 0.00190 0.00274

Hickory, pecan 0.00169 0.00315 Willow, black 0.00112 0.00308

Hickory, true 0.00259 0.00411 Willow, Pacific 0.00099 0.00319

Holly, American 0.00165 0.00353 Yellow-poplar 0.00158 0.00289

Softwoods

Baldcypress 0.00130 0.00216 Pine, eastern white 0.00071 0.00212

Cedar, yellow 0.00095 0.00208 Pine, jack 0.00126 0.00230

Cedar, Atlantic white 0.00099 0.00187 Pine, loblolly 0.00165 0.00259

Cedar, eastern red 0.00106 0.00162 Pine, pond 0.00165 0.00259

Cedar, Incense 0.00112 0.00180 Pine, lodgepole 0.00148 0.00234

Cedar, Northern whiteb 0.00101 0.00229 Pine, Jeffrey 0.00148 0.00234

Cedar, Port-Orford 0.00158 0.00241 Pine, longleaf 0.00176 0.00263

Cedar, western redb 0.00111 0.00234 Pine, ponderosa 0.00133 0.00216

Douglas-fir, Coast-type 0.00165 0.00267 Pine, red 0.00130 0.00252

Douglas-fir, Interior north 0.00130 0.00241 Pine, shortleaf 0.00158 0.00271

Douglas-fir, Interior west 0.00165 0.00263 Pine, slash 0.00187 0.00267

Fir, balsam 0.00099 0.00241 Pine, sugar 0.00099 0.00194

Fir, California red 0.00155 0.00278 Pine, Virginia 0.00144 0.00252

Fir, noble 0.00148 0.00293 Pine, western white 0.00141 0.00259
12–17

Because commercial lumber is often not perfectly flatsawn or

quartersawn, this procedure will probably overestimate width

shrinkage and underestimate thickness shrinkage. Note also

that if both a size change and the percentage of moisture

content are known, Equation (12–2) can be used to calculate

the original moisture content.

Calculation Based on

Green Dimensions

Approximate dimensional changes associated with moisture

content changes greater than 6% to 14% , or when one

moisture value is outside of those limits, can be calculated

by

 

∆D DM M

S M = −

( ) − +

IF I

T I

( )

30 100 30 / (12–3)

where ST is tangential shrinkage (%) from green to ovendry

(Ch. 3, Tables 3–5 and 3–6) (use radial shrinkage SR when

appropriate).

Neither MI nor MF should exceed 30%, the assumed moisture

content value when shrinkage starts for most species.

Table 12–5. Coefficients for dimensional change as a result of shrinkage or swelling within moisture content

limits of 6% to 14% (CT = dimensional change coefficient for tangential direction; CR = radial direction)—con.

Dimensional change

coefficienta

Dimensional change

coefficienta

Species CR CT Species CR CT

Softwoods—con.

Fir, Pacific silver 0.00151 0.00327 Redwood, old-growthb 0.00120 0.00205

Fir, subalpine 0.00088 0.00259 Redwood, second-growthb 0.00101 0.00229

Fir, grand 0.00112 0.00245 Spruce, black 0.00141 0.00237

Fir, white 0.00112 0.00245 Spruce, Engelmann 0.00130 0.00248

Hemlock, eastern 0.00102 0.00237 Spruce, red 0.00130 0.00274

Hemlock, western 0.00144 0.00274 Spruce, white 0.00130 0.00274

Larch, western 0.00155 0.00323 Spruce, Sitka 0.00148 0.00263

Tamarack 0.00126 0.00259

Imported Woods

Andiroba, crabwood 0.00137 0.00274 Light red “Philippine mahogany” 0.00126 0.00241

Angelique 0.00180 0.00312 Limba 0.00151 0.00187

Apitong, keruingb

(all Dipterocarpus spp.)

0.00243 0.00527 Mahoganyb

Meranti

0.00172

0.00126

0.00238

0.00289

Avodire 0.00126 0.00226 Obeche 0.00106 0.00183

Balsa 0.00102 0.00267 Okoume 0.00194 0.00212

Banak 0.00158 0.00312 Parana, pine 0.00137 0.00278

Cativo 0.00078 0.00183 Paumarfim 0.00158 0.00312

Cuangare 0.00183 0.00342 Primavera 0.00106 0.00180

Greenheartb 0.00390 0.00430 Ramin 0.00133 0.00308

Irokob 0.00153 0.00205 Santa Maria 0.00187 0.00278

Khaya 0.00141 0.00201 Spanish-cedar 0.00141 0.00219

Kokroduab 0.00148 0.00297 Teakb 0.00101 0.00186

Lauans: dark red

“Philippine mahogany”

0.00133 0.00267

a

Per 1% change in moisture content, based on dimension at 10% moisture content and a straight-line

 relationship between moisture content at which shrinkage starts and total shrinkage. (Shrinkage

 assumed to start at 30% for all species except those indicated by footnote b.)

b

Shrinkage assumed to start at 22% moisture content.
 12–18

Design Factors Affecting

Dimensional Change

Framing Lumber in

House Construction

Ideally, house framing lumber should be dried to the moisture content it will reach in use, thus minimizing future

dimensional changes as a result of frame shrinkage. This

ideal condition is difficult to achieve, but some drying and

shrinkage of the frame may take place without being visible

or causing serious defects after the house is completed. If, at

the time the wall and ceiling finish is applied, the moisture

content of the framing lumber is not more than about 5%

above that which it will reach in service, there will be little

or no evidence of defects caused by shrinkage of the frame. In

heated houses in cold climates, joists over heated basements,

studs, and ceiling joists may reach a moisture content as low

as 6% to 7% (Table 12–2). In mild climates, the minimum

moisture content will be greater.

The most common signs of excessive shrinkage are cracks in

plastered walls, truss rise, open joints, and nail pops in drywall construction; distortion of door openings; uneven floors;

and loosening of joints and fastenings. The extent of vertical

shrinkage after the house is completed is proportional to the

depth of wood used as supports in a horizontal position,

such as girders, floor joists, and plates. After all, shrinkage

occurs primarily in the width of members, not the length.

Thorough consideration should be given to the type of framing best suited to the whole building structure. Methods

should be chosen that will minimize or balance the use of

wood across the grain in vertical supports. These involve

variations in floor, wall, and ceiling framing. The factors

involved and details of construction are covered extensively

in Wood-Frame House Construction (Sherwood and Stroh

1991).

Heavy Timber Construction

In heavy timber construction, a certain amount of shrinkage

is to be expected. A column that bears directly on a wood

girder can result in a structure settling as a result of the

perpendicular-to-grain shrinkage of the girder. If not provided

for in the design, shrinkage may cause weakening of the

joints or uneven floors or both. One means of eliminating

part of the shrinkage in mill buildings and similar structures

is to use metal post caps; the metal in the post cap separates

the upper column from the lower column. The same thing is

accomplished by bolting wood corbels to the side of the

lower column to support the girders.

When joist hangers are installed, the top of the joist should

be above the top of the girder; otherwise, when the joist

shrinks in the stirrup, the floor over the girder will be higher

than that bearing upon the joist. Heavy planking used for

flooring should be near 12% moisture content to minimize

openings between boards as they approach moisture

equilibrium. When standard 38- or 64-mm (nominal 2- or

3-in.) joists are nailed together to provide a laminated floor

of greater depth for heavy design loads, the joist material

should be somewhat less than 12% moisture content if the

building is to be heated.

Interior Finish

The normal seasonal changes in the moisture content of

interior finish are not enough to cause serious dimensional

change if the woodwork is carefully designed. Large members, such as ornamental beams, cornices, newel posts, stair

stringers, and handrails, should be built up from comparatively small pieces. Wide door and window trim and base

should be hollow-backed. Backband trim, if mitered at the

corners, should be glued and splined before erection; otherwise butt joints should be used for the wide faces. Large,

solid pieces, such as wood paneling, should be designed and

installed so that the panels are free to move across the grain.

Narrow widths are preferable.

Flooring

Flooring is usually dried to the moisture content expected in

service so that shrinking and swelling are minimized and

buckling or large gaps between boards do not occur. For

basement, large hall, or gymnasium floors, however, enough

space should be left around the edges to allow for some

expansion.

Wood Care and Installation

During Construction

Lumber and Trusses

Although it should be, lumber is often not protected from the

weather at construction sites. Lumber is commonly placed

on the ground in open areas near the building site as bulked

and strapped packages. Supports under such packages are

useful to prevent wetting from mud and ground water and

should elevate the packages at least 150 mm (6 in.) off the

ground. The packages should also be covered with plastic

tarpaulins for protection from rain.

Lumber that is green or nearly green should be piled in

stickers under a roof for additional drying before it is built

into the structure. The same procedure is required for lumber

that has been treated with a waterborne preservative but not

fully redried. Prefabricated building parts, such as roof

trusses, sometimes lie unprotected on the ground at the

building site. In warm, rainy weather, moisture regain can

result in fungal staining. Wetting of the lumber also results

in swelling, and subsequent shrinkage of the framing may

contribute to structural distortions. Extended storage of

lumber at moisture contents greater than 20% without drying

can allow decay to develop.

If framing lumber has a greater moisture content when installed than that recommended in Table 12–2, shrinkage can
12–19

be expected. Framing lumber, even thoroughly air-dried

stock, will generally have a moisture content greater than

that recommended when it is delivered to the building site. If

carelessly handled in storage at the site, the lumber can take

up more moisture. Builders can schedule their work so an

appreciable amount of drying can take place during the early

stages of construction. This minimizes the effects of additional drying and shrinkage after completion. When the

house has been framed, sheathed, and roofed, the framing is

so exposed that in time it can dry to a lower moisture content than would ordinarily be expected in yard-dried lumber.

The application of the wall and ceiling finish is delayed

while wiring and plumbing are installed. If this delay is

about 30 days in warm, dry weather, framing lumber should

lose enough moisture so that any additional drying in place

will be relatively unimportant. In cool, damp weather, or if

wet lumber is used, the period of exposure should be extended. Checking moisture content of door and window

headers and floor and ceiling joists at this time with an

electric moisture meter is good practice. When these members approach an average of 12% moisture content, interior

finish and trim can normally be installed. Closing the house

and using the heating system will hasten the rate of drying.

Before wall finish is applied, the frame should be examined

and defects that may have developed during drying, such as

warped or distorted studs, shrinkage of lintels over openings,

or loosened joints, should be corrected.

Exterior Trim and Millwork

Exterior trim, such as cornice and rake mouldings, fascia

boards, and soffit material, is normally installed before the

shingles are laid. Trim, siding, and window and door frames

should be protected on the site by storing in the house or

garage until time of installation. Although items such as

window frames and sashes are usually treated with some type

of water-repellent preservative to resist absorption of water,

they should be stored in a protected area if they cannot be

installed soon after delivery. Wood siding is often received

in packaged form and can ordinarily remain in the package

until installation.

Finished Flooring

Cracks develop in flooring if it absorbs moisture either before

or after it is laid, then shrinks when the building is heated.

Such cracks can be greatly reduced by observing the following practices:

• Specify flooring manufactured according to association

rules and sold by dealers that protect it properly during

storage and delivery.

• Do not allow flooring to be delivered before masonry

and plastering are completed and fully dry, unless a dry

storage space is available.

• Install the heating plant before flooring is delivered.

• Break open flooring bundles and expose all sides of

flooring to the atmosphere inside the structure.

• Close up the house at night and increase the temperature

about 8°C (15°F) greater than the outdoor temperature

for about 3 days before laying the floor.

• If the house is not occupied immediately after the floor is

laid, keep the house closed at night or during damp

weather and supply some heat if necessary.

Better and smoother sanding and finishing can be done when

the house is warm and the wood has been kept dry.

Interior Finish

In a building under construction, average relative humidity

will be greater than that in an occupied house because of the

moisture that evaporates from wet concrete, brickwork, plaster, and even the structural wood members. The average

temperature will be lower because workers prefer a lower

temperature than is common in an occupied house. Under

such conditions, the finish tends to have greater moisture

content during construction than it will have during

occupancy.

Before the interior finish is delivered, the outside doors and

windows should be hung in place so that they can be kept

closed at night. In this way, conditions of the interior can be

held as close as possible to the higher temperature and lower

humidity that ordinarily prevail during the day. Such protection may be sufficient during dry warm weather, but during

damp or cool weather, it is highly desirable that some heat

be maintained in the house, particularly at night. Whenever

possible, the heating plant should be placed in the house

before the interior trim is installed, to be available for supplying the necessary heat. Portable heaters can also be used.

The temperature during the night should be maintained

about 8°C (15°F) greater than the outside temperature but

should not be allowed to drop below about 21°C (70°F)

during the summer or 17°C (62°F) when the outside temperature is below freezing.

After buildings have thoroughly dried, less heat is needed,

but unoccupied houses, new or old, should not be allowed to

stand without some heat during the winter. A temperature of

about 8°C (15°F) greater than the outside temperature and

above freezing at all times will keep the woodwork, finish,

and other parts of the house from being affected by dampness

or frost.

Plastering

During a plastering operation in a moderate-sized, six-room

house, approximately 450 kg (1,000 lb) of water are used, all

of which must be dissipated before the house is ready for the

interior finish. Adequate ventilation to remove the evaporated

moisture will keep it from being absorbed by the framework.

In houses plastered in cold weather, the excess moisture can

also cause paint to blister on exterior finish and siding.
 12–20

During warm, dry weather, with the windows wide open, the

moisture will be gone within a week after the final coat of

plaster is applied. During damp, cold weather, the heating

system or portable heaters are used to prevent freezing of

plaster and to hasten its drying. Adequate ventilation should

be provided at all times of the year because a large volume of

air is required to carry away the amount of water involved.

Even in the coldest weather, the windows on the side of the

house away from the prevailing winds should be opened 50

to 75 mm (2 to 3 in.), preferably from the top.

References

ASTM. [current edition]. Direct moisture content measurement of wood and wood-based materials. ASTM D4442–92.

West Conshohocken, PA: American Society for Testing and

Materials.

Forest Products Laboratory. 1961. Wood floors for dwellings. Agric. Handb. 204. Washington, DC: U.S. Department of Agriculture.

Forest Products Laboratory. 1972. Methods of controlling

humidity in woodworking plants. Res. Note FPL–RN–

0218. Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

James, W.L. 1988. Electric moisture meters for wood. Gen.

Tech. Rep. FPL–GTR–6. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

McMillen, J.M.; Wengert, E.M. 1978. Drying eastern

hardwood lumber. Agric. Handb. 528. Washington, DC:

U.S. Department of Agriculture.

Rietz, R.C. 1978. Storage of lumber. Agric. Handb. 531.

Washington, DC: U.S. Department of Agriculture.

Rietz, R.C.; Page, R.H. 1971. Air drying of lumber: A

guide to industry practices. Agric. Handb. 402. Washington,

DC: U.S. Department of Agriculture.

Sherwood, G.E.; Stroh, R.C. 1991. Wood-Frame House

Construction. USDA Agric. Handb. 73. Washington, DC:

U.S. Department of Agriculture.

Simpson, W.T. 1989. Drying wood: a review. Drying

Technology. An International Journal, Pt. 1. 2(2): 235–265,

Pt. 2, 2(3): 353–368.

Simpson, W.T., ed. 1991. Dry kiln operator’s manual.

Agric. Handb. 188. Washington, DC: U.S. Department of

Agriculture.

USDC. 1970. American softwood lumber standard. NBS

Voluntary Prod. Stand. PS 20–70; Washington, DC: U.S.

Department of Commerce.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
13–1

Biodeterioration of Wood

Terry L. Highley

Chapter 13

Contents

Fungus Damage and Control 13–1

Molds and Fungus Stains 13–2

Chemical Stains 13–3

Decay 13–3

Prevention of Mold, Stain, and Decay 13–6

Remedial Treatment of Internally Decayed Wood 13–8

Bacteria 13–8

Insect Damage and Control 13–8

Beetles 13–8

Termites 13–11

Carpenter Ants 13–13

Carpenter Bees 13–13

Marine Borer Damage and Control 13–13

Shipworms 13–13

Pholads 13–14

Limnoria and Sphaeroma 13–14

Natural Resistance to Marine Borers 13–14

Protection of Permanent Structures 13–14

Protection of Boats 13–15

References 13–15

nder proper conditions, wood will give centuries of

service. However, if conditions exist that permit the

development of wood-degrading organisms, protection must be provided during processing, merchandising,

and use.

The principal organisms that can degrade wood are fungi,

insects, bacteria, and marine borers.

Molds, most sapwood stains, and decay are caused by fungi,

which are microscopic, thread-like microorganisms that must

have organic material to live. For some of them, wood offers

the required food supply. The growth of fungi depends on

suitably mild temperatures, moisture, and air (oxygen).

Chemical stains, although they are not caused by organisms,

are mentioned in this chapter because they resemble stains

caused by fungi.

Insects also may damage wood, and in many situations must

be considered in protective measures. Termites are the major

insect enemy of wood, but on a national scale, they are a less

serious threat than fungi.

Bacteria in wood ordinarily are of little consequence, but

some may make the wood excessively absorptive. In addition, some may cause strength losses over long periods of

exposure, particularly in forest soils.

Marine borers are a fourth general type of wood-degrading

organism. They can attack susceptible wood rapidly in salt

water harbors where they are the principal cause of damage to

piles and other wood marine structures.

Wood degradation by organisms has been studied extensively, and many preventive measures are well known and

widely practiced. By taking ordinary precautions with the

finished product, the user can contribute substantially to

ensuring a long service life.

Fungus Damage and Control

Fungus damage to wood may be traced to three general

causes: (a) lack of suitable protective measures when storing
 13–2

logs or bolts; (b) improper seasoning, storing, or handling of

the raw material produced from the log; and (c) failure to take

ordinary simple precautions in using the final product. The

incidence and development of molds, decay, and stains

caused by fungi depend heavily on temperature and moisture

conditions (Fig. 13–1).

Molds and Fungus Stains

Molds and fungus stains are confined to a great extent to

sapwood and are of various colors. The principal fungus

stains are usually referred to as sap stain or blue stain. The

distinction between molding and staining is made primarily

on the basis of the depth of discoloration. With some molds

and the lesser fungus stains, there is no clear-cut differentiation. Typical sap stain or blue stain penetrates into the

sapwood and cannot be removed by surfacing. Also, the

discoloration as seen on a cross section of the wood often

appears as pie-shaped wedges oriented radially, corresponding to the direction of the wood rays (Fig. 13–2). The discoloration may completely cover the sapwood or may occur

as specks, spots, streaks, or patches of various intensities of

color. The so-called blue stains, which vary from bluish to

bluish black and gray to brown, are the most common,

although various shades of yellow, orange, purple, and red

are sometimes encountered. The exact color of the stain

depends on the infecting organisms and the species and

moisture condition of the wood. The fungal brown stain

mentioned here should not be confused with chemical brown

stain.

Mold discolorations usually become noticeable as fuzzy or

powdery surface growths, with colors ranging from light

shades to black. Among the brighter colors, green and yellowish hues are common. On softwoods, though the fungus

may penetrate deeply, the discoloring surface growth often

can easily be brushed or surfaced off. However, on large-pored

hardwoods (for example, oaks), the wood beneath the surface

growth is commonly stained too deeply to be surfaced off.

The staining tends to occur in spots of varying concentration

and size, depending on the kind and pattern of the superficial

growth.

Under favorable moisture and temperature conditions, staining and molding fungi may become established and develop

rapidly in the sapwood of logs shortly after they are cut. In

addition, lumber and such products as veneer, furniture

stock, and millwork may become infected at any stage of

manufacture or use if they become sufficiently moist. Freshly

cut or unseasoned stock that is piled during warm, humid

weather may be noticeably discolored within 5 or 6 days.

Recommended moisture control measures are given in

Chapter 12.

Figure 13–1. Climate index for decay hazard. Higher numbers indicate greater decay hazard.
13–3

Ordinarily, stain and mold fungi affect the strength of the

wood only slightly; their greatest effect is usually confined to

strength properties that determine shock resistance or toughness (Ch. 4). They increase the absorbency of wood, and this

can cause over-absorption of glue, paint, or wood preservative during subsequent processing. Increased porosity also

makes wood more wettable, which can lead to colonization

by typical wood-decay fungi.

Stain- and mold-infected stock is practically unimpaired for

many uses in which appearance is not a limiting factor, and a

small amount of stain may be permitted by standard grading

rules. Stock with stain and mold may not be entirely satisfactory for siding, trim, and other exterior millwork because

of its greater water absorbency. Also, incipient decay may be

present, though inconspicuous, in the discolored areas. Both

of these factors increase the possibility of decay in wood that

is rain-wetted unless the wood has been treated with a

suitable preservative.

Chemical Stains

Nonmicrobial or chemical stains are difficult to control and

represent substantial loss in wood quality. These stains

include a variety of discolorations in wood that are often

promoted by slow drying of lumber and warm to hot temperatures. Such conditions allow naturally occurring chemicals in wood to react with air (enzymatic oxidation) to form a

new chemical that is typically dark in color. Common

chemical stains include (a) interior sapwood graying, prevalent in oak, hackberry, ash, and maple; (b) brown stain in

softwoods; and (c) pinking and browning in the interior of

light-colored woods such as maple. Another common

discoloration is caused by the interaction of iron with tannins

in wood. Iron stain is more prevalent in hardwoods (for

example, oak and many tropical hardwoods) and in some

softwoods such as Douglas-fir. Control is achieved by

eliminating the source of iron.

Decay

Decay-producing fungi may, under conditions that favor their

growth, attack either heartwood or sapwood in most wood

species (Fig. 13–3). The result is a condition designated as

decay, rot, dote, or doze. Fresh surface growths of decay

Figure 13–2. Typical radial penetration of log by stain.

The pattern is a result of more rapid penetration by the

fungus radially (through the ray) than tangentially.

Spores Spores germinating

Infected cells

Hypha

Bore

hole

Pit

Section of post showing decay

Decay

zone

Fruit

body

Figure 13–3. The decay cycle (top to bottom).

Thousands of spores produced in a fruiting body are

distributed by wind or insects. On contacting moist,

susceptible wood, they germinate to create new

infections in the wood cells. In time, serious decay

develops that may be accompanied by formation of

new fruiting bodies.
 13–4

fungi may appear as fan-shaped patches (Fig. 13–4), strands,

or root-like structures, usually white or brown. Sometimes

fruiting bodies are produced that take the form of mushrooms, brackets, or crusts. The fungus, in the form of microscopic, threadlike strands, permeates the wood and uses parts

of it as food. Some fungi live largely on the cellulose; others

use the lignin as well as the cellulose.

Certain decay fungi colonize the heartwood (causing heart

rot) and rarely the sapwood of living trees, whereas others

confine their activities to logs or manufactured products, such

as sawn lumber, structural timbers, poles, and ties. Most

fungi that attack trees cease their activities after the trees have

been cut, as do the fungi causing brown pocket (peck) in

baldcypress or white pocket in Douglas-fir and other conifers.

Relatively few fungi continue their destruction after the trees

have been cut and worked into products and then only if

conditions remain favorable for their growth. Although

heartwood is more susceptible to decay than is sapwood in

living trees, for many species the sapwood of wood products

is more susceptible to decay than is the heartwood.

Most decay can progress rapidly at temperatures that favor

growth of plant life in general. For the most part, decay is

relatively slow at temperatures below 10°C (50°F) and above

35°C (95°F). Decay essentially ceases when the temperature

drops as low as 2°C (35°F) or rises as high as 38°C (100°F).

Serious decay occurs only when the moisture content of the

wood is above the fiber saturation point (average 30%). Only

when previously dried wood is contacted by water, such as

provided by rain, condensation, or contact with wet ground,

will the fiber saturation point be reached. By itself, the water

vapor in humid air will not wet wood sufficiently to support

significant decay, but it will permit development of some

mold fungi. Fully air-dried wood usually will have a moisture content not exceeding 20% and should provide a reasonable margin of safety against fungus damage. Thus, wood

will not decay if it is kept air dry, and decay already present

from prior infection will not progress.

Wood can be too wet for decay as well as too dry. If the

wood is water-soaked, the supply of air to the interior of a

Figure 13–4. Mycelial fans on a wood door.
13–5

piece may not be adequate to support development of typical

decay fungi. For this reason, foundation piles buried beneath

the water table and logs stored in a pond or under a suitable

system of water sprays are not subject to decay by typical

wood-decay fungi.

The early or incipient stages of decay are often accompanied

by a discoloration of the wood, which is more evident on

freshly exposed surfaces of unseasoned wood than on dry

wood. Abnormal mottling of the wood color, with either

unnatural brown or bleached areas, is often evidence of decay

infection. Many fungi that cause heart rot in the standing tree

produce incipient decay that differs only slightly from the

normal color of the wood or gives a somewhat water-soaked

appearance to the wood.

Typical or late stages of decay are easily recognized, because

the wood has undergone definite changes in color and properties, the character of the changes depending on the organism

and the substances it removes.

Two kinds of major decay fungi are recognized: brown rot

and white rot. With brown-rot fungi, only the cellulose is

extensively removed, the wood takes on a browner color, and

it can crack across the grain, shrink, collapse, and be crushed

into powder (Fig. 13–5). With white-rot fungi, both lignin

and cellulose usually are removed, the wood may lose color

and appear “whiter” than normal, it does not crack across the

grain, and until severely degraded, it retains its outward

dimensions, does not shrink or collapse, and often feels

spongy. Brown-rot fungi commonly colonize softwoods, and

white-rot fungi commonly occur on hardwoods, but both

brown- and white-rot fungi occasionally colonize both types

of wood.

Brown, crumbly rot, in the dry condition, is sometimes

called dry rot, but the term is incorrect because wood must

be damp to decay, although it may become dry later.

A few fungi, however, have water-conducting strands; such

fungi are capable of carrying water (usually from the soil) into

buildings or lumber piles, where they moisten and rot wood

that would otherwise be dry. They are sometimes referred to

technically as dry-rot fungi or water-conducting fungi. The

latter term better describes the true situation because these

fungi, like the others, must have water.

A third and generally less important kind of decay is known

as soft rot. Soft rot is caused by fungi related to the molds

rather than those responsible for brown and white rot. Soft

rot typically is relatively shallow; the affected wood is

greatly degraded and often soft when wet, but immediately

beneath the zone of rot, the wood may be firm (Fig. 13–6).

Because soft rot usually is rather shallow, it is most likely to

damage relatively thin pieces of wood such as slats in cooling towers. It is favored by wet situations but is also prevalent on surfaces that have been alternately wet and dry over a

substantial period. Heavily fissured surfaces, familiar to many

as weathered wood, generally have been quite degraded by

soft-rot fungi.

Decay Resistance of Wood

Chapter 3 discusses the natural resistance of wood to fungi

and ranks a grouping of species according to decay resistance.

In decay-resistant domestic species, only the heartwood has

significant resistance because the natural preservative chemicals in wood that retard the growth of fungi are essentially

restricted to the heartwood. Natural resistance of species to

fungi is important only where conditions conducive to decay

exist or may develop. If wood is subjected to severe decay

conditions, pressure-treated wood, rather than resistant

heartwood, is generally recommended.

Effect of Decay on Strength of Wood

Decay initially affects toughness, or the ability of wood to

withstand impacts. This is generally followed by reductions

in strength values related to static bending. Eventually, all

strength properties are seriously reduced.

Figure 13–5. Brown rot in Southern Pine railroad tie.

Note the darker color and the cubical checking in the

wood.

Figure 13–6. Soft-rotted preservative-treated pine utility

pole. Note the shallow depth of decay.
 13–6

Strength losses during early stages of decay can be considerable, depending to a great extent upon the fungi involved

and, to a lesser extent, upon the type of wood undergoing

decay. In laboratory tests, losses in toughness ranged from

6% to >50% by the time a 1% weight loss had occurred in

the wood as a result of fungal attack. By the time weight

losses resulting from decay have reached 10%, most strength

losses may be expected to exceed 50%. At such weight

losses, decay is detectable only microscopically. It may be

assumed that wood with visually discernible decay has been

greatly reduced in all strength values.

Prevention of Mold, Stain, and Decay

Logs, Poles, Piles, and Ties

The wood species, geographic region, and time of the year

determine what precautions must be taken to avoid serious

damage from fungi in logs, poles, piles, ties, and similar

thick products during seasoning or storage. In dry climates,

rapid surface seasoning of poles and piles will retard development of mold, stain, and decay. The bark is peeled from

the pole and the peeled product is decked on high skids or

piled on high, well-drained ground in the open to dry. In

humid regions, such as the Gulf States, these products often

do not air-dry fast enough to avoid losses from fungi.

Preseasoning treatments with approved preservative solutions

can be helpful in these circumstances.

For logs, rapid conversion into lumber or storage in water or

under a water spray (Fig. 13–7) is the surest way to avoid

fungal damage. Preservative sprays promptly applied to the

wood will protect most timber species during storage for 2 to

3 months, except in severe decay hazard climates, such as in

Mississippi (Fig. 13–1). For longer storage, an end coating

is needed to prevent seasoning checks, through which

infection can enter the log.

Lumber

Growth of decay fungi can be prevented in lumber and other

wood products by rapidly drying them to a moisture content

of 20% or less and keeping them dry. Standard air-drying

practices will usually dry the wood fast enough to protect it,

particularly if the protection afforded by drying is supplemented by dip or spray treatment of the stock with an EPAapproved fungicidal solution. Successful control by this

method depends not only upon immediate and adequate

treatment but also upon proper handling of the lumber after

treatment. However, kiln drying is the most reliable method

of rapidly reducing moisture content.

Figure 13–7. Spraying logs with water protects them against fungal stain and decay.
13–7

Air-drying yards should be kept as sanitary and as open as

possible to air circulation (Fig. 13–8). Recommended practices include locating yards and sheds on well-drained

ground; removing debris (which serves as a source of

infection) and weeds (which reduce air circulation); and

employing piling methods that permit rapid drying of the

lumber and protect against wetting. Storage sheds should be

constructed and maintained to prevent significant wetting of

the stock. Ample roof overhang on open sheds is desirable.

In areas where termites or water-conducting fungi may be

troublesome, stock to be held for long periods should be

set on foundations high enough so that the wood can be

inspected from beneath.

The user’s best assurance of receiving lumber free from decay

other than light stain is to buy stock marked by a lumber

association in a grade that eliminates or limits such qualityreducing features. Surface treatment for protection at the

drying yard is only temporarily effective. Except for temporary structures, lumber to be used under conditions conducive to decay should be all heartwood of a naturally durable

species or should be adequately treated with a wood preservative (Ch. 14).

Buildings

The lasting qualities of properly constructed wood buildings

are apparent in all parts of the country. Serious decay problems are almost always a sign of faulty design or construction, lack of reasonable care in the handling of the wood, or

improper maintenance of the structure.

Construction principles that ensure long service and avoid

decay in buildings include (a) building with dry lumber, free

of incipient decay and not exceeding the amounts of mold

and blue stain permitted by standard grading rules; (b) using

construction details and building designs that will keep

exterior wood dry and accelerate runoff; (c) using wood

treated with a preservative or heartwood of a decay-resistant

species for parts exposed to aboveground decay hazards; and

(d) using pressure-treated wood for the high hazard situation

associated with ground contact.

A building site that is dry or for which drainage is provided

will reduce the possibility of decay. Stumps, wood debris,

stakes, or wood concrete forms are frequently subject to decay

if left under or near a building.

Unseasoned or infected wood should not be enclosed until it

is thoroughly dried. Unseasoned wood includes green lumber. Wood can become infected because of improper handling

at the sawmill or retail yard or after delivery on the job.

Untreated wood parts of substructures should not be permitted to contact the soil. A minimum of 200 mm (8 in.) clearance between soil and framing and 150 mm (6 in.) between

soil and siding is recommended. Where frequent hard rains

occur, a foundation height above grade of 300 to 460 mm

(12 to 18 in.) is advocated. An exception may be made for

certain temporary constructions. If contact with soil is unavoidable, the wood should be pressure treated (Ch. 14).

Sill plates and other wood resting on a concrete slab foundation generally should be pressure treated and protected by

installing a moisture-resistant membrane such as polyethylene beneath the slab. Girder and joist openings in masonry

walls should be big enough to ensure an air space around the

ends of these wood members. If the members are below the

outside soil level, moisture proofing of the outer face of the

wall is essential.

In buildings without basements but with crawl spaces, wetting of the wood by condensation during cold weather or by

air-conditioning may result in serious decay damage. However, serious condensation leading to decay may be prevented

by laying a barrier such as polyethylene on the soil. To

facilitate inspection of the crawl space, a minimum 460-mm

(18-in.) clearance should be left under wood joists.

Wood should also be protected from rain during construction. Protection from rainwater or condensation in walls and

roofs will prevent the development of decay. A fairly wide

roof overhang (0.6 m (2 ft)) with gutters and downspouts that

are kept free of debris is desirable. Roofs must be kept tight,

and cross ventilation in attics is recommended in cold

climates. The use of sound, dry lumber is important in all

parts of buildings.

Where service conditions in a building are such that the

wood cannot be kept dry, the use of preservative-treated

wood (Ch. 14) or heartwood of a durable species is advised.

Examples include porches, exterior steps, and platforms and

such places as textile mills, pulp and paper mills, and cold

storage plants.

In making repairs necessitated by decay, every effort should

be made to correct the moisture condition that led to the

damage. If the condition cannot be corrected, all infected

parts should be replaced with preservative-treated wood or

with all-heartwood lumber of a naturally decay-resistant

wood species. If the sources of moisture that caused the decay

are entirely eliminated, it is necessary only to replace the

weakened wood with dry lumber.

Other Structures and Products

In general, the principles underlying the prevention of mold,

stain, or decay damage to veneer, plywood containers, boats,

and other wood products and structures are similar to those

Figure 13–8. A sanitary, well-drained air-drying yard.
 13–8

described for buildings—dry the wood rapidly and keep it

dry or treat it with approved protective and preservative

solutions. Interior grades of plywood should not be used

where the plywood will be exposed to moisture; the adhesives, as well as the wood, may be damaged by fungi and

bacteria as well as degraded by moisture. With exterior-type

panels, joint construction should be carefully designed to

prevent the entrance of rainwater.

In treated bridge or wharf timbers, checking may occur and

may expose untreated wood to fungal attack. Annual in-place

treatment of these checks will provide protection from decay.

Similarly, pile tops may be protected by treatment with a

wood preservative followed by application of a suitable

capping compound.

Wood boats present certain problems that are not encountered in other uses of wood. The parts especially subject to

decay are the stem, knighthead, transom, and frameheads,

which can be reached by rainwater from above or condensation from below. Frayed surfaces are more likely to decay

than are exposed surfaces, and in salt water service, hull

members just below the weather deck are more vulnerable

than those below the waterline. Recommendations for avoiding decay include (a) using only heartwood of durable species, free of infection, and preferably below 20% moisture

content; (b) providing and maintaining ventilation in the

hull and all compartments; (c) keeping water out as much as

is practicable, especially fresh water; and (d) where it is

necessary to use sapwood or nondurable heartwood, impregnating the wood with an approved preservative and treating

the fully cut, shaped, and bored wood before installation by

soaking it for a short time in preservative solution. Where

such mild soaking treatment is used, the wood most subject

to decay should also be flooded with an approved preservative at intervals of 2 or 3 years. During this treatment, the

wood should be dry so that joints are relatively loose.

Remedial Treatment of

Internally Decayed Wood

Four fumigants, 32% sodium N-methyldithiocarbamate in

water, methylisocyanate, Basamid (tetrahydro-3, 5-dimethyl2-H-1,3,5, thiodazine-6-thione), and chloropicrin

(trichloronitromethane), are registered for use to arrest internal decay in wood. All these fumigants produce volatile

toxic gases when applied to wood and move several meters

from the point of application. These chemicals are restricteduse preservatives, and applicators must be trained and pass a

test on pesticide handling and safety before using the chemicals. Fumigant treating poses risks, and thus the chemicals

cannot be used safely in some situations.

Water diffusible boron- and fluoride-based rods, pastes, or

solutions can be applied to wood by flooding or as external

coatings (for example, bandage wraps containing borate or

fluoride paste applied to the groundline of poles).

Bacteria

Most wood that has been wet for a considerable length of

time probably will contain bacteria. The sour smell of logs

that have been held under water for several months, or of

lumber cut from them, manifests bacterial action. Usually,

bacteria have little effect on wood properties, except over

long periods, but some may make the wood excessively

absorptive. This can result in excessive pickup of moisture,

adhesive, paint, or preservative during treatment or use. This

effect has been a problem in the sapwood of millwork cut

from pine logs that have been stored in ponds. There also is

evidence that bacteria developing in pine veneer bolts held

under water or sprayed with water may cause noticeable

changes in the physical character of the veneer, including

some strength loss. Additionally, a mixture of different

bacteria, as well as fungi, was found capable of accelerating

decay of treated cooling tower slats and mine timbers.

Insect Damage and Control

The more common types of damage caused by woodattacking insects are shown in Table 13–1 and Figure 13–9.

Methods of controlling and preventing insect attack of wood

are described in the following paragraphs.

Beetles

Bark beetles may damage the surface of the components of

logs and other rustic structures from which the bark has not

been removed. These beetles are reddish brown to black and

vary in length from approximately 1.5 to 6.5 mm (1/16 to

1/4 in.) They bore through the outer bark to the soft inner

part, where they make tunnels in which they lay their eggs.

In making tunnels, bark beetles push out fine brownish-white

sawdust-like particles. If many beetles are present, their

extensive tunneling will loosen the bark and permit it to fall

off in large patches, making the structure unsightly.

To avoid bark beetle damage, logs may be debarked rapidly,

sprayed with an approved insecticidal solution, stored in

water or under a water spray, or cut during the dormant

season (October or November, for instance). If cut during this

period, logs should immediately be piled off the ground and

arranged for good air movement, to promote rapid drying of

the inner bark. This should occur before the beetles begin to

fly in the spring. Drying the bark will almost always prevent

damage by insects that prefer freshly cut wood.

Ambrosia beetles, roundheaded and flatheaded borers, and

some powder-post beetles that get into freshly cut timber can

cause considerable damage to wood in rustic structures and

some manufactured products. Certain beetles may complete

development and emerge several years after the wood is dry,

often raising a question as to the origin of the infestation.
13–9

 

Table 13–1. Types of damage caused by wood-attacking insects

Type of Damage

damage Description Causal agent Begins Ends

Pin holes 0.25 to 6.4 mm (1/100 to 1/4 in.) in diameter, usually

circular

Tunnels open:

Holes 0.5 to 3 mm (1/50 to 1/8 in.) in diameter,

usually centered in dark streak or ring in surrounding wood

Ambrosia beetles In living trees and

unseasoned logs and

lumber

During seasoning

Holes variable sizes; surrounding wood rarely

dark stained; tunnels lined with wood-colored

substance

Timber worms In living trees and

unseasoned logs and

lumber

Before seasoning

Tunnels packed with usually fine sawdust:

Exit holes 0.8 to 1.6 mm (1/32 to 1/16 in.) in diameter; in sapwood of large-pored hardwoods;

loose floury sawdust in tunnels

Lyctid powder-post

beetles

During or after

seasoning

Reinfestation continues

until sapwood destroyed

Exit holes 1.6 to 3 mm (1/16 to 1/8 in.) in diameter;

primarily in sapwood, rarely in heartwood; tunnels

loosely packed with fine sawdust and

elongate pellets

Anobiid powder-post

beetles

Usually after wood in

use (in buildings)

Reinfestation continues;

progress of damage very

slow

Exit holes 2.5 to 7 mm (3/32 to 9/32 in.) in diameter; primarily sapwood of hard woods, minor in

softwoods; sawdust in tunnels fine to coarse and

tightly packed

Bostrichid powderpost beetlesBefore seasoning or if

wood is rewetted

During seasoning or

redrying

Exit holes 1.6 to 2 mm (1/16 to 1/12 in.) in diameter; in slightly damp or decayed wood; very fine

sawdust or pellets tightly packed in tunnels

Wood-boring weevils In slightly damp wood

in use

Reinfestation continues

while wood is damp

Grub holes 3 to 13 mm (1/8 to 1/2 in.) in diameter, circular or

oval

Exit holes 3 to 13 mm (1/8 to 1/2 in.) in diameter;

circular; mostly in sapwood; tunnels with coarse to

fibrous sawdust or it may be absent

Roundheaded borers

(beetles)

In living trees and

unseasoned logs and

lumber

When adults emerge from

seasoned wood or when

wood is dried

Exit holes 3 to 13 mm (1/8 to 1/2 in.) in diameter;

mostly oval; in sapwood and heartwood; sawdust

tightly packed in tunnels

Flatheaded borers

(beetles)

In living trees and

unseasoned logs and

lumber

When adults emerge from

seasoned wood or when

wood is dried

Exit holes ~6 mm (~1/4 in.) in diameter; circular; in

sapwood of softwoods, primarily pine; tunnels

packed with very fine sawdust

Old house borers

(a roundheaded borer)

During or after

seasoning

Reinfestation continues in

seasoned wood in use

Exit holes perfectly circular, 4 to 6 mm (1/6 to 1/4 in.)

in diameter; primarily in softwoods; tunnels tightly

packed with coarse sawdust, often in decay softened

wood

Woodwasps In dying trees or fresh

logs

When adults emerge from

seasoned wood, usually in

use, or when kiln dried

Nest entry hole and tunnel perfectly circular ~13 mm

(~1/2 in.) in diameter; in soft softwoods in structures

Carpenter bees In structural timbers,

siding

Nesting reoccurs annually

in spring at same and

nearby locations

Network of

galleries

Systems of interconnected tunnels and chambers Social insects with

colonies

Walls look polished; spaces completely clean of

debris

Carpenter ants Usually in damp partly

decayed, or softtextured wood in use

Colony persists unless

prolonged drying of wood

occurs

Walls usually speckled with mud spots; some

chambers may be filled with “clay”

Subterranean termites In wood structures Colony persists

Chambers contain pellets; areas may be walled-off

by dark membrane

Dry-wood termites

(occasionally damp

wood termites)

In wood structures Colony persists

Pitch pocket Openings between growth rings containing pitch Various insects In living trees In tree

Black check Small packets in outer layer of wood Grubs of various

insects

In living trees In tree

Pith fleck Narrow, brownish streaks Fly maggots or adult

weevils

In living trees In tree

Gum spot Small patches or streaks of gum-like substances Grubs of various

insects

In living trees In tree

Ring

distortion

Double growth rings or incomplete annual layers of

growth

Larvae of defoliating

insects or flatheaded

cambium borers

In living trees In tree

Stained area more than 25.4 mm (1 in.) long introduced by insects in trees or recently felled logsStaining fungi With insect wounds With seasoning
 13–10

Proper cutting practices, rapid debarking, storing under

water, and spraying the material with an approved chemical

solution, as recommended for bark beetles, will control these

insects. Damage by ambrosia beetles can be prevented in

freshly sawn lumber by dipping the product in a chemical

solution. The addition of one of the sap-stain preventives

approved for controlling molds, stains, and decay will keep

the lumber bright. Powder-post beetles attack both hardwoods and softwoods and both freshly cut and seasoned

lumber and timber. Powder-post damage is indicated by

holes made in the surface of the wood by the winged adults

as they emerge and by the fine powder that may fall from the

wood. The powder-post beetles that cause most of the damage to dry hardwood lumber belong to the genus Lyctus.

They attack the sapwood of ash, hickory, oak, and other

large-pored hardwoods as it begins to season. Eggs are laid

in pores of the wood, and the larvae burrow through the

wood, making tunnels from 1.5 to 2 mm (1/16 to 1/12 in.)

in diameter, which they leave packed with a fine powder.

Species of anobiid beetles colonize coniferous materials.

Susceptible hardwood lumber used for manufacturing purposes should be protected from powder-post beetle attack as

soon as it is sawn and when it arrives at the plant. An approved insecticide applied in water emulsion to the green

lumber will provide protection. Such treatment may be

effective even after the lumber is kiln dried, until it is

surfaced.

Good plant sanitation is extremely important in alleviating

the problem of infestation. Proper sanitation measures can

often eliminate the necessity for other preventative steps.

Damage to manufactured items frequently is traceable to

infestation that occurred before the products were placed on

the market, particularly if a finish is not applied to the surface

of the items until they are sold. Once wood is infested, the

larvae will continue to develop, even though the surface is

subsequently painted, oiled, waxed, or varnished.

When selecting hardwood lumber for building or manufacturing purposes, any evidence of powder-post infestation should

not be overlooked, because the beetles may continue to be

active long after the wood is put to use. For standard 19-mm

(nominal 1-in.) lumber, sterilization of green wood with

steam at 54°C (130°F) or sterilization of wood with a lower

moisture content at 82°C (180°F) under controlled conditions of relative humidity for about 2 h is effective for checking infestation or preventing attack. Thicker material requires

a longer time. A 3-min soaking in a petroleum oil solution

containing an insecticide is also effective for checking infestation or preventing attack on lumber up to standard 19 mm

(nominal 1 in.) thick. Small dimension stock also can be

protected by brushing or spraying with approved chemicals.

For infested furniture or finished woodwork in a building, the

same insecticides may be used, but they should be dissolved

in a refined petroleum oil, like mineral spirits. Because the

Lyctus beetles lay their eggs in the open pores of wood,

infestation can be prevented by covering the entire surface of

each piece of wood with a suitable finish.

Powder-post beetles in the family Anobiidae, depending on

the species, infest hardwoods and softwoods. Their life cycle

takes 2 to 3 years and they require a wood moisture content

around 15% or greater for viable infestation. Therefore, in

most modern buildings, the wood moisture content is generally too low for anobiids. When ventilation is inadequate or

in more humid regions of the United States, wood components of a building can reach the favorable moisture conditions for anobiids. This is especially a problem in airconditioned buildings where water condenses on cooled

exterior surfaces. Susceptibility to anobiid infestation can be

alleviated by lowering the moisture content of wood through

improved ventilation and the judicious use of insulation and

vapor barriers. Insecticides registered for use against these

beetles are generally restricted for exterior applications to

avoid potential safety hazards indoors. Wood being reused or

recycled from older structures often has lyctid or anobiid

larvae in it. Such wood should be fumigated or kiln dried

before use in another structure.

Figure 13–9. Types of insect damage most likely to

occur in a building. Upper left—Termite attack; feeding

galleries (often parallel to the grain) contain excrement

and soil. Upper right—Powder-post beetle attack; exit

holes usually filled with wood flour and not associated

with discolored wood. Lower left—Carpenter ant attack;

nesting galleries usually cut across grain and are free

of residue. Lower right—Beetle attack; feeding galleries

(made in the wood while green) free of residue and

surrounding wood darkly stained.
13–11

Beetles in the family Bostrichidae and weevils in the family

Curculionidae are associated with wood moisture contents

favorable for wood-infesting fungi because they may benefit

nutritionally from the fungi. Thus, protection against these

insects consists of the same procedures as for protection

against wood-decay fungi.

A roundheaded beetle, commonly known as the old house

borer, causes damage to seasoned coniferous building materials. The larvae reduce the sapwood to a powdery or granular

consistency and make a ticking sound while at work. When

mature, the beetles make an oval hole approximately

6.5 mm (1/4 in.) in diameter in the surface of the wood and

emerge. Anobiid powder-post beetles, which make holes 1.6

to 3.2 mm (1/16 to 1/8 in.) in diameter, also cause damage

to pine joists. Infested wood should be drenched with a

solution of one of the currently recommended insecticides in

a highly penetrating solvent. Beetles nesting in wood behind

plastered or paneled walls can be eliminated through fumigation of the building by a licensed operator.

Termites

Termites superficially resemble ants in size, general appearance, and habit of living in colonies. About 56 species are

known in the United States. From the standpoint of their

methods of attack on wood, termites can be grouped into two

main classes: (a) ground-inhabiting or subterranean termites

and (b) wood-inhabiting or nonsubterranean termites.

Subterranean Termites

Subterranean termites are responsible for most of the termite

damage done to wood structures in the United States. This

damage can be prevented. Subterranean termites are more

prevalent in the southern than in the northern states, where

low temperatures do not favor their development

(Fig. 13–10). The hazard of infestation is greatest (a) beneath

buildings without basements that were erected on a concrete

slab foundation or were built over a crawl space that is

poorly drained and ventilated and (b) in any substructure

wood component close to the ground or an earth fill (for

example, an earth-filled porch).

The subterranean termites develop their colonies and maintain their headquarters in the ground. They build their tunnels through earth and around obstructions to reach the wood

they need for food. They also must have a constant source of

moisture, whether from the wood on which they are feeding

or the soil where they nest. The worker members of the

colony cause destruction of wood. At certain seasons of the

year, usually spring, male and female winged forms swarm

from the colony, fly a short time, lose their wings, mate, and

if successful in locating a suitable home, start new colonies.

The appearance of “flying ants” or their shed wings is an

indication that a termite colony may be near and causing

serious damage. Not all “flying ants” are termites; therefore,

suspicious insects should be identified before investing in

eradication (Fig. 13–11).

Subterranean termites normally do not establish themselves

in buildings by being carried there in lumber; they primarily

enter from ground nests after the building has been constructed. An introduced species, the Formosan termite, is

adept at initiating aboveground infestations and nests in

structures where wood remains wet for prolonged periods,

such as from roof leaks. Telltale signs of subterranean termite

presence are the earthen tubes or runways built by these

insects over the surfaces of the foundation or other exposed

areas to reach the wood above. Another sign is the swarming

of winged adults early in the spring or fall. In the wood

itself, the termites make galleries that generally follow the

grain, leaving a shell of sound wood to conceal their activities. Because the galleries seldom show on the wood surfaces, probing with a pick or knife is advisable if the presence

of termites is suspected.

The best protection for wood in areas where subterranean

termites are prevalent is to prevent the termites from gaining

hidden access to a building. The foundations should be of

concrete, pressure-treated wood, or other material through

which the termites cannot penetrate. With brick, stone, or

concrete block, cement mortar should be used because

Figure 13–10. A, the northern limit of recorded

damage done by subterranean termites in the

United States; B, the northern limit of damage

done by dry-wood termites.

Figure 13–11. A, winged termite; B, winged ant

(both greatly enlarged). The wasp waist of the ant

and the long wings of the termite are distinguishing

characteristics.
 13–12

termites can work through some other kinds of mortar. Also,

it is a good precaution to cap the foundation with 100 mm

(4 in.) of reinforced concrete. Posts supporting floor girders

should, if they bear directly on the ground, be of concrete. If

there is a basement, it should be floored with concrete. Untreated posts in such a basement should rest on concrete piers

extending a few inches above the basement floor. However,

pressure-treated posts can rest directly on the basement floor.

With the crawl-space type of foundation, wood floor joists

should be kept at least 460 mm (18 in.) and girders 300 mm

(12 in.) from the earth and good ventilation should be provided beneath the floor. A rule of thumb is to have a minimum of 1 unit area of ventilation for every 150 units of

crawlspace (for example, 1 ft2

 of ventilated area for 150 ft2 of

crawlspace).

Moisture condensation on the floor joists and subflooring,

which may cause conditions favorable to decay and contribute to infestation by termites, can be avoided by covering the

soil below with a moisture barrier, maintaining adequate

ventilation, and assuming proper drainage of rainwater away

from all sides of a structure. All concrete forms, stakes,

stumps, and wastewood should be removed from the building site because they are possible sources of infestation.

Generally, the precautions effective against subterranean

termites are also helpful against decay.

The principal method of protecting buildings in high termite

areas is to thoroughly treat the soil adjacent to the foundation

walls and piers beneath the building with a soil insecticide.

When concrete slab floors are laid directly on the ground, all

soil under the slab should be treated with an approved insecticide before the concrete is poured. Furthermore, insulation

containing cellulose that is used as a filler in expansion

joints should be impregnated with an approved chemical

toxic to termites. Sealing the top 13 mm (1/2 in.) of the

expansion joint with roofing-grade coal-tar pitch also provides effective protection from ground-nesting termites. New

modifications in soil treatment and an insecticidal bait control method are currently under investigation and appear

promising. Current references (available from national pest

control operator associations) should be consulted to take

advantage of the new developments in termite control.

To control termites already in a building, contact between

the termite colony in the soil and the woodwork must be

broken. This can be done by blocking the runways from soil

to wood, treating the soil, repairing leaks that keep wood

within the structure wet (for example, plumbing leaks), or

some combination of these techniques. Possible reinfestations can be guarded against by frequent inspections for signs

of termites.

Nonsubterranean Termites

In the United States, nonsubterranean termites have been

found only in a narrow strip of territory extending from

central California around the southern edge of the continental

United States to Virginia (Fig. 13–10) and in the West

Indies and Hawaii. Their principal damage is confined to an

area in southern California, to parts of southern Florida,

notably Key West, and to the islands of Hawaii. They also

are a localized problem in Arizona and New Mexico.

The nonsubterranean termites, especially the dry-wood type,

do not multiply as rapidly as the subterranean termites and

have somewhat different colony life and habits. The total

amount of destruction they cause in the United States is

much less than that caused by the subterranean termites. The

ability of dry-wood termites to live in dry wood without

outside moisture or contact with the ground, however, makes

them a definite menace in the regions where they occur.

Their depredations are not rapid, but they can thoroughly

riddle timbers with their tunnelings if allowed to work undisturbed for many years. Nonsubterranean termites are often

moved from structure to structure in infested items such as

furniture.

In constructing a building in localities where the dry-wood

type of nonsubterranean termite is prevalent, it is good practice to inspect the lumber carefully to see that it was not

infested before arrival at the building site. If the building is

constructed during the swarming season, the lumber should

be watched during the course of construction, because infestation by colonizing pairs can easily take place. Because paint

is a good protection against the entrance of dry-wood termites, exposed wood (except that which is preservative

treated) should be kept covered with a paint film. Fine screen

should be placed over any openings to the interior unpainted

parts of the building. As in the case of ground-nesting termites, dead trees, old stumps, posts, or wood debris of any

kind that could serve as sources of infestation should be

removed from the premises.

If a building is infested with dry-wood termites, badly damaged wood should be replaced. If the wood is only slightly

damaged or is difficult to replace, further termite activity can

be arrested by injecting a small amount of an approved pesticidal dust or liquid formulation into each nest. Current

recommendations for such formulations can be found from

state pest control associations. Buildings heavily infested

with nonsubterranean termites can be successfully fumigated.

This method is quicker than the use of poisonous liquids

and dusts and does not require finding all of the colonies.

However, it does not prevent the termites from returning

because no poisonous residue is left in the tunnels. Fumigation is very dangerous and should be conducted only by

licensed professional fumigators. Infested pieces of furniture,

picture frames, and other small pieces can be individually

fumigated, heated, or placed in a freezer for a short time. In

localities where dry-wood termites do serious damage to

posts and poles, the best protection for these and similar

forms of outdoor timbers is full-length pressure treatment

with a preservative.

Naturally Termite-Resistant Woods

Only a limited number of woods grown in the United States

offer any marked degree of natural resistance to termite attack.

The close-grained heartwood of California redwood has some

resistance, especially when used above ground. Very resinous
13–13

heartwood of Southern Pine is practically immune to attack,

but it is not available in large quantities and is seldom used.

Carpenter Ants

Carpenter ants are black or brown. They usually occur in

stumps, trees, or logs but sometimes damage poles, structural timbers, or buildings. One form is easily recognized by

its giant size relative to other ants. Carpenter ants use wood

for shelter rather than for food, usually preferring wood that is

naturally soft or has been made soft by decay. They may

enter a building directly by crawling or may be carried there

in fuelwood. If left undisturbed, they can, in a few years,

enlarge their tunnels to the point where replacement or extensive repairs are necessary. The parts of dwellings they frequent most often are porch columns, porch roofs, window

sills, and sometimes the wood plates in foundation walls.

They often nest in hollow-core doors. The logs of rustic

cabins are also attacked.

Precautions that prevent attack by decay and termites are

usually effective against carpenter ants. Decaying or infested

wood, such as logs, stumps, or retaining walls, should be

removed from the premises, and crevices present in the

foundation or woodwork of the building should be sealed.

Particularly, leaks in porch roofs should be repaired because

the decay that may result makes the wood more desirable to

the ants.

When carpenter ants are found in a structure, any badly

damaged timbers should be replaced. Because the carpenter

ant needs high humidity in its immature stages, alterations

in the construction may also be required to eliminate moisture from rain or condensation. In wood not sufficiently

damaged to require replacement, the ants can be killed by

injection of approved insecticide into the nest galleries.

Carpenter ant nests are relatively easy to find because they

keep their internal nest sites very clean and free of debris. As

particles of wood are removed to create galleries or as pieces

of insects that have been fed upon accumulate, the debris is

removed from the nest and then accumulates below the nest

opening.

Carpenter Bees

Carpenter bees resemble large bumblebees, but the top of

their abdomen is hairless, causing their abdomens to shine,

unlike bumblebees. The females make large (13-mm-

(1/2-in.-) diameter) tunnels into unfinished soft wood for

nests. They partition the hole into cells; each cell is provided with pollen and nectar for a single egg. Because carpenter bees reuse nesting sites for many years, a nesting

tunnel into a structural timber may be extended several feet

and have multiple branches. In thin wood, such as siding,

the holes may extend the full thickness of the wood. They

nest in stained wood and wood with thin paint films or light

preservative salt treatments as well as in bare wood. A favorite nesting site is in unfinished exterior wood not directly

exposed to sunlight (for example, the undersides of porch

roofs, and grape arbors).

Control is aimed at discouraging the use of nesting sites in

and near buildings. The tunnel may be injected with an

insecticide labeled for bee control and plugged with caulk.

Treating the surface around the entry hole will discourage

reuse of the tunnel during the spring nesting period. A good

paint film or pressure preservative treatment protects exterior

wood surfaces from nesting damage. Bare interior wood

surfaces, such as in garages, can be protected by screens and

tight-fitting doors.

Marine Borer Damage

and Control

Damage by marine-boring organisms to wood structures in

salt or brackish waters is practically a worldwide problem.

Evidence of attack is sometimes found in rivers even above

the region of brackishness. The rapidity of attack depends

upon local conditions and the kinds of borers present. Along

the Pacific, Gulf, and South Atlantic Coasts of the United

States, attack is rapid, and untreated pilings may be completely destroyed in a year or less. Along the coast of the

New England States, the rate of attack is slower because of

cold water temperatures but is still sufficiently rapid to require protection of wood where long life is desired. The

principal marine borers from the standpoint of wood damage

in the United States are described in this section. Control

measures discussed in this section are those in use at the

time this handbook was revised. Regulations should be

reviewed at the time control treatments are being considered

so that approved practices will be followed.

Shipworms

Shipworms are the most destructive of the marine borers.

They are mollusks of various species that superficially are

worm-like in form. The group includes several species of

Teredo and several species of Bankia, which are especially

damaging. These mollusks are readily distinguishable on

close observation but are all very similar in several respects.

In the early stages of their life, they are minute, freeswimming organisms. Upon finding suitable lodgment on

wood, they quickly develop into a new form and bury themselves in the wood. A pair of boring shells on the head

grows rapidly in size as the boring progresses, while the tail

part or siphon remains at the original entrance. Thus, the

animal grows in length and diameter within the wood but

remains a prisoner in its burrow, which it lines with a shelllike deposit. It lives on the wood borings and the organic

matter extracted from the sea water that is continuously being

pumped through its system. The entrance holes never grow

large, and the interior of wood may be completely honeycombed and ruined while the surface shows only slight

perforations. When present in great numbers, shipworms

grow only a few centimeters before the wood is so completely occupied that growth is stopped. However, when not

crowded, they can grow to lengths of 0.3 to 1.2 m (1 to 4 ft)

depending on the species.
 13–14

Pholads

Another group of wood-boring mollusks is the pholads,

which clearly resemble clams and therefore are not included

with the shipworms. They are entirely encased in their double shells. The Martesia are the best-known species, but

another well-known group is the Xylophaga. Like the shipworms, the Martesia enter the wood when they are very

small, leaving a small entrance hole, and grow larger as they

burrow into the wood. They generally do not exceed 64 mm

(2-1/2 in.) long and 25 mm (1 in.) in diameter but are capable of doing considerable damage. Their activities in the

United States appear to be confined to the Gulf Coast,

San Diego, and Hawaii.

Limnoria and Sphaeroma

Another distinct group of marine borers are crustaceans,

which are related to lobsters and shrimp. The principal

borers in this group are species of Limnoria and Sphaeroma.

Their attack differs from that of the shipworms and the

Martesia in that the bore hole is quite shallow; the result is

that the wood gradually is thinned from the surface inward

through erosion by the combined action of the borers and

water erosion. Also, the Limnoria and Sphaeroma do not

become imprisoned in the wood but may move freely from

place to place.

Limnoria are small, 3 to 4 mm (1/8 to 1/6 in.) long, and

bore small burrows in the surface of wood. Although they

can change their location, they usually continue to bore in

one place. When great numbers of Limnoria are present, their

burrows are separated by very thin walls of wood that are

easily eroded by the motion of the water or damaged by

objects floating upon it. This erosion causes the Limnoria to

burrow continually deeper; otherwise, the burrows would

probably not become greater than 51 mm (2 in.) long or

13 mm (1/2 in.) deep. Because erosion is greatest between

tide levels, piles heavily attacked by Limnoria characteristically wear within this zone to an hourglass shape. In heavily

infested harbors, untreated piling can be destroyed by

Limnoria within a year.

Sphaeroma are somewhat larger, sometimes reaching a

length of 13 mm (1/2 in.) and a width of 6 mm (1/4 in.). In

general appearance and size, they resemble the common sow

bug or pill bug that inhabits damp places. Sphaeroma are

widely distributed but are not as plentiful as Limnoria and

cause much less damage. Nevertheless, piles in some structures have been ruined by them. Occasionally, they have

been found working in fresh water. In types of damage,

Sphaeroma action resembles that of Limnoria. It has been

reported that Sphaeroma attack salt-treated wood in Florida.

The average life of well-creosoted structures is many times

the average life obtained from untreated structures. However,

even thorough creosote treatment will not always stop

Martesia, Sphaeroma, and especially Limnoria; shallow or

erratic creosote penetration affords only slight protection. The

spots with poor protection are attacked first, and from there,

the borers spread inward and destroy the untreated interior of

the pile.

When wood is to be used in salt water, avoidance of cutting

or injuring the surface after treatment is even more important

than when wood is to be used on land. No cutting or injury

of any kind for any purpose should be permitted in the underwater part of the pile. Where piles are cut to grade above

the waterline, the exposed surfaces should be protected from

decay. This may be accomplished by in-place application

of a wood preservative followed by a suitable capping

compound.

Natural Resistance to Marine Borers

No wood is immune to marine-borer attack, and no commercially important wood of the United States has sufficient

marine-borer resistance to justify its use untreated in any

important structure in areas where borers are active. The

heartwood of several foreign species, such as greenheart,

jarrah, azobe, and manbarklak, has shown resistance to marine-borer attack. Service records on these woods, however,

do not always show uniform results and are affected by local

conditions.

Protection of Permanent Structures

The best practical protection for piles in sea water with

shipworms and moderate Limnoria hazard is heavy treatment

with coal-tar creosote or creosote coal-tar solution. Where

severe Limnoria hazard exists, dual treatment (copperarsenate-containing waterborne preservatives followed by

coal-tar creosote) is recommended. The treatment must be

thorough, the penetration as deep as possible, and the retention high to give satisfactory results in heavily infested

waters. It is best to treat such piles by the full-cell process to

refusal; that is, to force in all the preservative the piles can

hold without using treatments that cause serious damage to

the wood. For highest retentions, it is necessary to air- or

kiln-dry the piling before treatment. Details of treatments are

discussed in Chapter 14.

The life of treated piles is influenced by the thoroughness of

the treatment, the care and diligence used in avoiding damage to the treated shell during handling and installation, and

the severity of borer attack. Differences in exposure conditions, such as water temperature, salinity, dissolved oxygen,

water depth, and currents, tend to cause wide variations in

the severity of borer attack even within limited areas. Service

records show average-life figures of 22 to 48 years on welltreated Douglas-fir piles in San Francisco Bay waters. In

South Atlantic and Gulf of Mexico waters, creosoted piles are

estimated to last 10 to 12 years and frequently much longer.

On the North Atlantic Coast, where exposure conditions are

less severe, piles can last even longer than the 22- to 48-year

life recorded in the San Francisco Bay.

Metal armor and concrete or plastic jacketing have been used

with varying degrees of success for the protection of marine

piles. The metal armor may be in the form of sheets, wire, or
13–15

nails. Sheathing of piles with copper or muntz metal has

been only partially successful, owing to difficulty in maintaining a continuous armor. Theft, damage in driving, damage by storm or driftwood, and corrosion of sheathing have

sooner or later let in the borers, and in only a few cases has

long pile life been reported. Attempts during World War II

to electroplate wood piles with copper were not successful.

Concrete casings are now in greater use than is metal armor,

and they appear to provide better protection when highquality materials are used and carefully applied. Unfortunately, they are readily damaged by ship impact. For this

reason, concrete casings are less practical for fender piles

than for foundation piles that are protected from mechanical

damage.

Jacketing piles by wrapping them with heavy polyvinyl

plastic is one recent form of supplementary protection. If

properly applied, the jacketing will kill any borers that may

have already become established by creating stagnant water,

thereby decreasing oxygen levels in the water that is in

contact with the piles. Like other materials, the plastic jacket

is subject to mechanical damage.

Protection of Boats

Wood barges have been constructed with planking or sheathing pressure-treated with creosote to protect the hull from

marine borers, and the results have been favorable. Although

coal-tar creosote is an effective preservative for protecting

wood against marine borers in areas of moderate borer hazard,

it has disadvantages in many types of boats. Creosote adds

considerably to the weight of the boat hull, and its odor is

objectionable to boat crews. In addition, antifouling paints

are difficult to apply over creosoted wood.

Some copper bottom paints protect boat hulls against marine-borer attack, but the protection continues only while the

coating remains unbroken. Because it is difficult to maintain

an unbroken coating of antifouling paint, the U.S. Navy has

found it desirable to impregnate the hull planking of some

wood boats with certain copper-containing preservatives.

Such preservatives, when applied with high retentions (24 to

32 kg/m3

 (1.5 to 2.0 lb/ft3)), have some effectiveness against

marine borers and should help to protect the hull of a boat

during intervals between renewals of the antifouling coating.

These copper preservatives do not provide protection equivalent to that furnished by coal-tar creosote; their effectiveness

in protecting boats is therefore best assured if the boats are

dry docked at regular and frequent intervals and the antifouling coating maintained. However, the leach-resistant wood

preservatives containing copper arsenates have shown superior performance (at a retention of 40 kg/m3

 (2.5 lb/ft3)) to

creosote in tests conducted in areas of severe borer hazard.

Plywood as well as plank hulls can be protected against

marine borers by preservative treatment. The plywood hull

presents a surface that can be covered successfully with a

protective membrane of reinforced plastic laminate. Such

coverings should not be attempted on wood that has been

treated with a preservative carried in oil, because the bond

will be unsatisfactory.

References

Beal, R.H. 1967. Formosan invader. Pest Control.

35(2): 13–17.

Beal, R.H.; Maulderi, J.K.; Jones, S.C. 1983. Subterranean termites, their prevention and control in buildings.

Home & Garden Bull. 64 (rev.). Washington, DC: U.S.

Department of Agriculture.

Cassens, D.L.; Eslyn, W.E. 1981. Fungicides to prevent

sapstain and mold on hardwood lumber. Forest Products

Journal. 31: 39–42.

Ebeling, W. 1975. Wood destroying insects and fungi. In:

Urban entomology. Berkeley, CA: University of California,

Division of Agriculture Science: 128–216.

Esenther, G.R.; Beal, R.H. 1979. Termite control: decayed

wood bait. Sociobiology. 4(2): 215–222.

Eslyn, W.E.; Clark, J.W. 1976. Appraising deterioration

in submerged piling. Materials und Organismen. Supplement 3: 43–52.

Eslyn, W.E.; Clark, J.W. 1979. Wood bridges—decay

inspection and control. Agric. Handb. 557. Washington,

DC: U.S. Department of Agriculture.

Forest Products Society. 1997. Prevention of discolorations

in hardwood and softwood logs and lumber. FPS Proceedings 7283. Madison, WI: Forest Products Society.

Greaves, H. 1969. Wood-inhabiting bacteria: general

considerations. Commonwealth Scientific and Industrial

Research Organization, Forest Products Newsletter 359.

Hartley, C.; May, C. ; 1943. Decay of wood in boats. U.S.

Department of Agriculture, Forest Path. Spec. Release 8;

U.S. Department of Agriculture, Forest Service.

Highley, T.L.; Eslyn, W.E. 1982. Using fumigants to

control interior decay in waterfront timbers. Forest Products

Journal. 32: 32–34.

Highley, T.L.; Scheffer, T.C. 1978. Controlling decay in

above-water parts of waterfront structures. Forest Products

Journal. 28: 40–43.

Hunt, G.M.; Garratt, G.A. 1967. Wood preservation, 3d

ed. The American forestry series. New York: McGraw–Hill

Book Company.

Jones, E.B.G.; Eltringham, S.K., eds. 1971. Marine

borers, fungi and fouling organisms of wood. In: Proceedings

of Organization for Economic Cooperation and Development;

1968 March 27–April 3; Paris, France. OECD.

Krishna, K.; Weesner, F.M., eds. 1969. Biology of termites. New York: Academic Press. Vol. I.

Krishna, K.; Weesner, F.M., eds. 1970. Biology of termites. New York: Academic Press. Vol. II.

Lee, K.E.; Wood, T.G. 1971. Termites and soils. New

York: Academic Press.
 13–16

Moore, H.B. 1979. Wood-inhabiting insects in houses:

their identification, biology, prevention, and control. Prepared as part of interagency agreement IAA–25–75 between

the U.S. Department of Agriculture, Forest Service, and the

Department of Housing and Urban Development. Washington, DC: U.S. Department of Agriculture, Forest Service,

and the Department of Housing and Urban Development.

Morrell, J.J. 1996. Wood pole maintenance manual.

Corvallis, OR: Forest Research Laboratory, Oregon State

University.

Morrell, J.J.; Corden, M.E. 1982. Controlling wood

deterioration with fumigants: a review. Forest Products

Journal. 36(10): 26–34.

NPCA. 1976. Carpenter ants. Tech. Release ESPC 052101.

Dunn Loring, VA: National Pest Control Association.

NPCA. 1963. Carpenter bees. Tech. Release 3–63. Dunn

Loring, VA: National Pest Control Association.

NPCA. 1964. The horntails. Tech. Release 14–64. Dunn

Loring, VA: National Pest Control Association.

Rietz, R.C. 1978. Storage of lumber. Agric. Handb. 531.

Washington, DC: U.S. Department of Agriculture.

Roff, J.W.; Cserjesi, A.J.; Swan, G.W. 1980. Prevention

of sap stain and mold in packaged lumber. FORINTEK

Canada Corp. Tech. Rep. 14 Ottawa, ON: FORINTEK.

Scheffer, T.C. 1972. A climate index for estimating potential decay in wood structures above ground. Forest Products

Journal. 21(10): 25–31.

Scheffer, T.C.; Eslyn, W.E. 1976. Winter treatments

protect birch roundwood during storage. Forest Products

Journal. 26: 27–31.

Scheffer, T.C.; Verrall, A.F. 1973. Principles of protecting

wood buildings from decay. Res. Pap. FPL 190. Madison,

WI: U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Schmidt, E. 1990. Remedial decay treatment with fused

borate rods: Recent developments and opportunities. In:

Proceedings, First international conference on wood protection with diffusible preservatives: 1989 November; Nashville, TN. Madison, WI: Forest Products Society: 91–92.

Sherwood, G.E.; TenWolde, A. 1982. Moisture movement and control in light frame structures. Forest Products

Journal. 32: 69–73.

Weesner, F.M. 1965. The termites of the United States, a

handbook. Elizabeth, NJ: National Pest Control Association.

Wilcox, W.W. 1978. Review of literature on the effect of

early stages of decay on wood strength. Wood and Fiber.

9: 252–257.

Williams, L.H. 1973. Anobiid beetles should be controlled.

Pest Control. 41(6): 18,20,22,38,40,42,44.

Zabel, R.A.; Morrell, J.J. 1992. Wood microbiology:

Decay and its prevention. San Diego, CA: Academic Press.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
14–1

Wood Preservation

Rebecca E. Ibach

Chapter 14

Contents

Wood Preservatives 14–2

Oilborne Preservatives 14–2

Waterborne Preservatives 14–9

Preservative Effectiveness 14–12

Effect of Species on Penetration 14–12

Preparation of Timber for Treatment 14–17

Peeling 14–17

Drying 14–17

Conditioning of Green Products 14–18

Incising 14–18

Cutting and Framing 14–18

Application of Preservatives 14–19

Pressure Processes 14–19

Nonpressure Processes 14–21

Effect on Mechanical Properties 14–24

Handling and Seasoning of Timber After Treatment 14–24

Quality Assurance for Treated Wood 14–25

Treating Conditions and Specifications 14–25

Inspection 14–25

Purchase of Treated Wood 14–25

References 14–26

hen left untreated in many outdoor applications,

wood becomes subject to degradation by a variety of

natural causes. Although some trees possess naturally occurring resistance to decay (Ch. 3, Decay Resistance),

many are in short supply or are not grown in ready proximity to markets. Because most commonly used wood species,

such as Southern Pine, ponderosa pine, and Douglas-fir,

possess little decay resistance, extra protection is needed

when they are exposed to adverse environments. Wood can

be protected from the attack of decay fungi, harmful insects,

or marine borers by applying chemical preservatives. The

degree of protection achieved depends on the preservative

used and the proper penetration and retention of the chemicals. Some preservatives are more effective than others, and

some are more adaptable to certain use requirements. Not

only are different methods of treating wood available, but

treatability varies among wood species—particularly their

heartwood, which generally resists preservative treatment

more than does sapwood. To obtain long-term effectiveness,

adequate penetration and retention are needed for each wood

species, chemical preservative, and treatment method.

Wood preservatives that are applied at recommended retention levels and achieve satisfactory penetration can greatly

increase the life of wood structures. Thus, the annual replacement cost of treated wood in service is much less than

that of wood without treatment. In considering preservative

treatment processes and wood species, the combination must

provide the required protection for the conditions of exposure

and life of the structure. All these factors are considered by

the consensus technical committees in setting reference levels

required by the American Wood-Preservers’ Association

(AWPA), the American Society for Testing and Materials

(ASTM), and the Federal Specification Standards. Details are

discussed later in this chapter.

Note that mention of a chemical in this chapter does not

constitute a recommendation; only those chemicals registered

by the U.S. Environmental Protection Agency (EPA) may be

recommended. Registration of preservatives is under constant

review by EPA and the U.S. Department of Agriculture. Use

only preservatives that bear an EPA registration number and

carry directions for home and farm use. Preservatives, such as

creosote and pentachlorophenol, should not be applied to the

interior of dwellings that are occupied by humans.
 14–2

Because all preservatives are under constant review by EPA,

a responsible State or Federal agency should be consulted as

to the current status of any preservative.

Wood Preservatives

The EPA regulates pesticides, and wood preservatives are

one type of pesticide. Preservatives that are not restricted by

EPA are available to the general consumer for nonpressure

treatments, and the sale of others is restricted to certified

pesticide applicators. These preservatives can be used only in

certain applications and are referred to as “restricted use.”

Restricted use refers to the chemical preservative and not to

the treated wood product. The general consumer may buy

and use wood products treated with restricted-use pesticides;

EPA does not consider treated wood a toxic substance nor is

it regulated as a pesticide.

Consumer Information Sheets (EPA-approved) are available

from retailers of treated-wood products. The sheets provide

information about the preservative and the use and disposal

of treated-wood products. Consumer information sheets are

available for three major groups of wood preservatives

(Table 14–1):

• Creosote pressure-treated wood

• Pentachlorophenol pressure-treated wood

• Inorganic arsenical pressure-treated wood

Wood preservatives can be divided into two general classes:

(1) oilborne preservatives, such as creosote and petroleum

solutions of pentachlorophenol and (2) waterborne preservatives that are applied as water solutions. Many different

chemicals are in each of these classes, and each has differing

effectiveness in various exposure conditions. The three exposure categories for preservatives are (1) ground contact (high

decay hazard that needs a heavy-duty preservative),

(2) aboveground contact (low decay hazard that does not

usually require pressure treatment), and (3) marine exposure

(high decay hazard that needs a heavy-duty preservative or

possibly dual treatment). In this chapter, both oilborne and

waterborne preservative chemicals are described as to their

potential and uses. See Table 14–2 for a summary of preservatives and their retention levels for various wood products. Some active ingredients can be used in both oilborne

and waterborne preservatives.

Oilborne Preservatives

Wood does not swell from treatment with preservative oils,

but it may shrink if it loses moisture during the treating

process. Creosote and solutions with heavy, less volatile

petroleum oils often help protect wood from weathering, but

may adversely influence its cleanliness, odor, color, paintability, and fire performance. Volatile oils or solvents with

oilborne preservatives, if removed after treatment, leave the

wood cleaner than do the heavy oils but may not provide as

much protection. Wood treated with some preservative oils

can be glued satisfactorily, although special processing or

cleaning may be required to remove surplus oils from surfaces before spreading the adhesive.

Coal-Tar Creosote

Coal-tar creosote (creosote) is a black or brownish oil made

by distilling coal tar that is obtained after high temperature

carbonization of coal. Advantages of creosote are (a) high

toxicity to wood-destroying organisms; (b) relative insolubility in water and low volatility, which impart to it a great

degree of permanence under the most varied use conditions;

(c) ease of application; (d) ease with which its depth of penetration can be determined; (e) relative low cost (when purchased in wholesale quantities); and (f) lengthy record of

satisfactory use.

The character of the tar used, the method of distillation, and

the temperature range in which the creosote fraction is collected all influence the composition of the creosote. Therefore, the composition of the various coal-tar creosotes available may vary considerably. However, small differences in

composition do not prevent creosotes from giving good

service. Satisfactory results in preventing decay may generally be expected from any coal-tar creosote that complies

with the requirements of standard specifications.

Several standards prepared by different organizations are

available for creosote oils of different kinds. Although the oil

obtained under most of these standards will probably be

effective in preventing decay, the requirements of some organizations are more exacting than others. The American

Society for Testing and Materials Standard D390 for coal-tar

creosote has been approved for use by U.S. Department of

Defense agencies. This standard covers new coal-tar creosote

and creosote in use for the preservative treatment of piles,

poles, and timber for marine, land, and fresh water use.

Under normal conditions, requirements of this standard can

be met without difficulty by most creosote producers. The

requirements of this specification are similar to those of the

AWPA standard P1/P13 for creosote, which is equally

acceptable to the user.

Although coal-tar creosote (AWPA P1/P13) or creosote

solutions (AWPA P2) are well-suited for general outdoor

service in structural timbers, this creosote has properties that

are undesirable for some purposes. The color of creosote and

the fact that creosote-treated wood usually cannot be painted

satisfactorily make this preservative unsuitable where appearance and paintability are important. Creosote is commonly

used for heavy timbers, poles, piles, and railroad ties.

The odor of creosote-treated wood is unpleasant to some

people. Also, creosote vapors are harmful to growing plants,

and foodstuffs that are sensitive to odors should not be stored

where creosote odors are present. Workers sometimes object

to creosote-treated wood because it soils their clothes, and

creosote vapor photosensitizes exposed skin. With normal

precautions to avoid direct skin contact with creosote, there

appears to be no danger to the health of workers handling or

working near the treated wood. The EPA or the treater

should be contacted for specific information on this subject.
14–3

Table 14–1. EPA-approved consumer information sheets for three major groups of preservative pressure-treated wood

Preservative

treatment Inorganic arsenicals Pentachlorophenol Creosote

Consumer

information

This wood has been preserved by

pressure-treatment with an EPAregistered pesticide containing inorganic

arsenic to protect it from insect attack

and decay. Wood treated with inorganic

arsenic should be used only where such

protection is important.

Inorganic arsenic penetrates deeply into

and remains in the pressure-treated

wood for a long time. Exposure to

inorganic arsenic may present certain

hazards. Therefore, the following precautions should be taken both when

handling the treated wood and in determining where to use or dispose of the

treated wood.

This wood has been preserved by pressure-treatment with an EPA-registered

pesticide containing pentachlorophenol to

protect it from insect attack and decay.

Wood treated with pentachlorophenol

should be used only where such protection is important.

Pentachlorophenol penetrates deeply into

and remains in the pressure-treated wood

for a long time. Exposure to pentachlorophenol may present certain hazards.

Therefore, the following precautions

should be taken both when handling the

treated wood and in determining where to

use and dispose of the treated wood.

This wood has been preserved by pressure treatment with an EPA-registered

pesticide containing creosote to protect it

from insect attack and decay. Wood

treated with creosote should be used only

where such protection is important.

Creosote penetrates deeply into and

remains in the pressure-treated wood for

a long time. Exposure to creosote may

present certain hazards. Therefore, the

following precautions should be taken both

when handling the treated wood and in

determining where to use the treated

wood.

Handling

precautions

Dispose of treated wood by ordinary

trash collection or burial. Treated wood

should not be burned in open fires or in

stoves, fireplaces, or residential boilers

because toxic chemicals may be produced as part of the smoke and ashes.

Treated wood from commercial or

industrial use (e.g., construction sites)

may be burned only in commercial or

industrial incinerators or boilers in

accordance with state and Federal

regulations.

Avoid frequent or prolonged inhalation of

sawdust from treated wood. When

sawing and machining treated wood,

wear a dust mask. Whenever possible,

these operations should be performed

outdoors to avoid indoor accumulations

of airborne sawdust from treated wood.

When power-sawing and machining,

wear goggles to protect eyes from flying

particles.

After working with the wood, and before

eating, drinking, and using tobacco

products, wash exposed areas thoroughly.

If preservatives or sawdust accumulate

on clothes, launder before reuse. Wash

work clothes separately from other

household clothing.

Dispose of treated wood by ordinary trash

collection or burial. Treated wood should

not be burned in open fires or in stoves,

fireplaces, or residential boilers because

toxic chemicals may be produced as part

of the smoke and ashes. Treated wood

from commercial or industrial use (e.g.,

construction sites) may be burned only in

commercial or industrial incinerators or

boilers rated at 20 million BTU/hour or

greater heat input or its equivalent in

accordance with state and Federal regulations.

Avoid frequent or prolonged inhalation of

sawdust from treated wood. When sawing

and machining treated wood, wear a dust

mask. Whenever possible, these operations should be performed outdoors to

avoid indoor accumulations of airborne

sawdust from treated wood.

Avoid frequent or prolonged skin contact

with pentachlorophenol-treated wood.

When handling the treated wood, wear

long-sleeved shirts and long pants and

use gloves impervious to the chemicals

(for example, gloves that are vinylcoated).

When power-sawing and machining,

wear goggles to protect eyes from flying

particles.

After working with the wood, and before

eating, drinking, and using tobacco products, wash exposed areas thoroughly.

If oily preservatives or sawdust accumulate on clothes, launder before reuse.

Wash work clothes separately from other

household clothing.

Dispose of treated wood by ordinary trash

collection or burial. Treated wood should

not be burned in open fires or in stoves,

fireplaces, or residential boilers, because

toxic chemicals may be produced as part

of the smoke and ashes. Treated wood

from commercial or industrial use (e.g.,

construction sites) may be burned only in

commercial or industrial incinerators or

boilers in accordance with state and

Federal regulations.

Avoid frequent or prolonged inhalations of

sawdust from treated wood. When sawing

and machining treated wood, wear a dust

mask. Whenever possible these operations should be performed outdoors to

avoid indoor accumulations of airborne

sawdust from treated wood.

Avoid frequent or prolonged skin contact

with creosote-treated wood; when handling the treated wood, wear long-sleeved

shirts and long pants and use gloves

impervious to the chemicals (for example, gloves that are vinyl-coated).

When power-sawing and machining,

wear goggles to protect eyes from flying

particles.

After working with the wood and before

eating, drinking, and using tobacco products, wash exposed areas thoroughly.

If oily preservative or sawdust accumulate on clothes, launder before reuse.

Wash work clothes separately from other

household clothing.
 14–4

Table 14–1. EPA-approved consumer information sheets for three major groups of preservative pressure-treated wood—con.

Preservative

treatment Inorganic arsenicals Pentachlorophenol Creosote

Use site

precautions

Wood pressure-treated with waterborne arsenical preservatives may

be used inside residences as long as

all sawdust and construction debris

are cleaned up and disposed of after

construction.

Do not use treated wood under circumstances where the preservative

may become a component of food or

animal feed. Examples of such sites

would be structures or containers for

storing silage or food.

Do not use treated wood for cutting

boards or countertops.

Only treated wood that is visibly

clean and free of surface residue

should be used for patios, decks, and

walkways.

Do not use treated wood for construction of those portions of beehives

that may come into contact with the

honey.

Treated wood should not be used

where it may come into direct or indirect contact with public drinking water, except for uses involving incidental contact such as docks and

bridges.

Logs treated with pentachlorophenol

should not be used for log homes. Wood

treated with pentachlorophenol should not

be used where it will be in frequent or

prolonged contact with bare skin (for

example, chairs and other outdoor furniture), unless an effective sealer has been

applied.

Pentachlorophenol-treated wood should

not be used in residential, industrial, or

commercial interiors except for laminated

beams or building components that are in

ground contact and are subject to decay or

insect infestation and where two coats of

an appropriate sealer are applied. Sealers

may be applied at the installation site.

Urethane, shellac, latex epoxy enamel,

and varnish are acceptable sealers for

pentachlorophenol-treated wood.

Wood treated with pentachlorophenol

should not be used in the interiors of farm

buildings where there may be direct

contact with domestic animals or livestock that may crib (bite) or lick the wood.

In interiors of farm buildings where

domestic animals or livestock are unlikely to crib (bite) or lick the wood,

pentachlorophenol-treated wood may be

used for building components which are in

ground contact and are subject to decay or

insect infestation and where two coats of

an appropriate sealer are applied. Sealers

may be applied at the installation site.

Do not use pentachlorophenol-treated

wood for farrowing or brooding facilities.

Do not use treated wood under circumstances where the preservative may

become a component of food or animal

feed. Examples of such sites would be

structures or containers for storing silage

or food.

Do not use treated wood for cutting boards

or countertops.

Only treated wood that is visibly clean and

free of surface residue should be used for

patios, decks, and walkways.

Do not use treated wood for construction

of those portions of beehives that may

come into contact with the honey.

Pentachlorophenol-treated wood should

not be used where it may come into direct

or indirect contact with public drinking

water, except for uses involving incidental

contact such as docks and bridges.

Do not use pentachlorophenol-treated

wood where it may come into direct or

indirect contact with drinking water for

domestic animals or livestock, except for

uses involving incidental contact such as

docks and bridges.

Wood treated with creosote should not be

used where it will be in frequent or prolonged contact with bare skin (for example, chairs and other outdoor furniture)

unless an effective sealer has been

applied.

Creosote-treated wood should not be used

in residential interiors. Creosote-treated

wood in interiors of industrial buildings

should be used only for industrial building

components that are in ground contact and

are subject to decay or insect infestation

and for wood-block flooring. For such

uses, two coats of an appropriate sealer

must be applied. Sealers may be applied

at the installation site.

Wood treated with creosote should not be

used in the interiors of farm buildings

where there may be direct contact with

domestic animals or livestock that may

crib (bite) or lick the wood.

In interiors of farm buildings where

domestic animals or livestock are unlikely to crib (bite) or lick the wood,

creosote-treated wood may be used for

building components that are in ground

contact and are subject to decay or insect

infestation if two coats of an effective

sealer are applied. Sealers may be

applied at the installation site. Coal-tar

pitch and coal-tar pitch emulsion are

effective sealers for creosote-treated

wood-block flooring. Urethane, epoxy, and

shellac are acceptable sealers for all

creosote-treated wood.

Do not use creosote-treated wood for

farrowing or brooding facilities.

Do not use treated wood under circumstances where the preservative may

become a component of food or animal

feed. Examples of such use would be

structures or containers for storing silage

or food.

Do not use treated wood for cutting boards

or countertops.

Only treated wood that is visibly clean and

free of surface residues should be used

for patios, decks, and walkways.

Do not use treated wood for construction

of those portions of beehives that may

come into contact with the honey.

Creosote-treated wood should not be used

where it may come into direct or indirect

contact with public drinking water, except

for uses involving incidental contact such

as docks and bridges.

Do not use creosote-treated wood where

it may come into direct or indirect contact

with drinking water for domestic animals

or livestock, except for uses involving

incidental contact such as docks and

bridges.
14–5

Table 14–2. Creosote, oilborne, and waterborne preservatives and retention levels for various wood productsa

Creosote and oilborne preservative retention (kg/m3 (lb/ft3))

Form of product and

service condition Creosote

Creosote

solutions

Creosotepetroleum

Pentachloro-

 phenol, P9,

 Type A

Pentachloro-

 phenol, P9,

 Type E

 Copper

naphthenate

Oxine

copper

 AWPA

standard

A. Ties (crossties and

switch ties)

96–128

(6–8)

112–128

(7–8)

112–128

(7–8)

5.6–6.4

(0.35–0.4)

NR NR NR C2/C6

B. Lumber, timber, plywood; bridge and mine

ties

(1) Salt waterb 400 (25) 400 (25) NR NR NR NR NR C2/C9

(2) Soil and fresh water 160 (10) 160 (10) 160 (10) 8 (0.50) NR 0.96 (0.06) NR C2/C9

(3) Above ground 128 (8) 128 (8) 128 (8) 6.41 (0.40) 6.4 (0.40) 0.64 (0.04) 0.32 (0.02) C2/C9

C. Piles

(1) Salt waterb C3/C14/C18

Borer hazard,

moderate

320 (20) 320 (20) NR NR NR NR NR

Borer hazard, severe NR NR NR NR NR NR NR

Dual treatment 320 (20) 320 (20) NR NR NR NR NR

(2) Soil, fresh water, or

foundation

96–272

(6–17)

96–272

(6–17)

96–272

(6–17)

4.8–13.6

(0.30–0.85)

NR 1.60 (0.10) NR C3/C14/C24

D. Poles (length >5 m

 (>16 ft))

(1) Utility 120–256

(7.5–16)

120–256

(7.5–16)

120–256

(7.5–16)

4.8–12.8

(0.30–0.80)

NR 1.2–2.4

(0.075–0.15)

NR C4

(2) Building, round and

sawn

144–216

(9–13.5)

NR NR 7.2–10.9

(0.45–0.68)

NR NR NR C4/C23/C24

(3) Agricultural, round

and sawn

120–256

(7.5–16)

120–256

(7.5–16)

NR,

round

(sawn,

192 (12))

6.1–9.6

(0.38–0.60)

NR NR, round

(sawn,

1.2 (0.075))

NR C4/C16

E. Posts (length <5 m

 (<16 ft))

(1) Agricultural, round

and sawn, fence

128–160

(8–10)

128–160

(8–10)

128–160

(8–10)

6.4–8.0

(0.40–0.50)

NR sawn, 0.96

(0.060)

round, 0.88

(0.055)

C2/C5/C16

(2) Commercial–

residential construction, round and sawn

128–192

(8–12)

128–192

(8–12)

128–192

(8–12)

8–9.6

(0.50–0.60)

NR NR NR C2/C5/C15/

C23

(3) Highway construction

Fence, guide, sign,

and sight

128–160

(8–10)

128–160

(8–10)

128–160

(8–10)

6.4–8.1

(0.40–0.50)

NR sawn four

sides, 0.96

(0.06)

NR C2/C5/C14

Guardrail and spacer

blocks

160–192

(10–12)

160–192

(10–12)

160–192

(10–12)

8–9.6

(0.50–0.60)

NR sawn four

sides, 1.2

(0.075)

NR C2/C5/C14

F. Glued-laminated

timbers/laminates

(1) Soil and fresh water 160 (10) 160 (10) 160 (10) 9.6 (0.60) NR 9.6 (0.60) NR C28

(2) Above ground 128 (8) 128 (8) 128 (8) 4.8 (0.30) NR 6.4 (0.40) 3.2 (0.20) C28
 14–6

Table 14–2. Creosote, oilborne, and waterborne preservatives and retention levels for various wood productsa—con.

Waterborne preservative retention (kg/m3 (lb/ft3))

Form of product and

service condition ACC

ACZA

or ACA

CCA

Types I, II, or III

ACQ

Type B

ACQ

Type D

CDDC

as Cu CC

 CBA

Type A

 AWPA

standard

A. Ties (crossties and

switch ties)

NR NR NR NR NR NR NR NR C2/C6

B.Lumber, timber,

plywood; bridge and

mine ties

(1) Salt waterb NR 40 (2.50) 40 (2.50) NR NR NR 40 (2.50) NR C2/C9

(2) Soil and fresh water 6.4 (0.40) 6.4 (0.40) 6.4 (0.40) 6.4

(0.40)

6.4

(0.40)

3.2 (0.20) 6.4 (0.40) NR C2/C9

(3) Above groundc 4.0 (0.25) 4.0 (0.25) 4.0 (0.25) 4.0

(0.25)

4.0

(0.25)

1.6 (0.10) 4.0 (0.25) 3.27

(0.20)

C2/C9

C. Piles

(1) Salt waterb C3/C14/

C18

Borer hazard,

moderate

NR 24 (1.5) 24.1 (1.5) NR NR NR NR NR

Borer hazard, severe NR 40 (2.50) 40 (2.50) NR NR NR NR NR

Dual treatment NR 16 (1.00) 16 (1.00) NR NR NR NR NR

 (2) Soil, fresh water or

foundation

NR 12–16

(0.80–1.0)

12–16

(0.80–1.0)

NR NR NR NR NR C3/C14/

C24

D. Poles (length >5 m

(>16 ft))

 (1) Utility NR 9.6 (0.60) 9.6 (0.60) 9.6

(0.60)

NR NR NR NR C4

(2) Building, round and

sawn timber

NR 9.6–12.8

(0.60–0.80)

9.6–12.8

(0.60–0.80)

9.6

(0.60)

9.6

(0.60)

3.2 (0.2) NR NR C4/C23/

C24

(3) Agricultural, round

and sawn

NR 9.6 (0.60) 9.6 (0.60) 9.6

(0.60)

NR NR NR NR C4/C16

E. Posts (length < 5 m

(<16 ft))

(1) Agricultural, round

and sawn, fence

NR 6.4 (0.40) 6.4 (0.40) 6.4

(0.40)

NR NR NR NR C2/C5/

C16

(2) Commercial–

residential construction, round and

sawn

8 (0.50),

(NR, sawn

structural

members)

6.4–9.6

(0.40–0.60)

6.4–9.6

(0.40–0.60)

6.4–9.6

(0.40–

0.60)

6.4–9.6

(0.40–

0.6)

3.2 (0.20) 6.4 (0.4),

(NR, sawn

structural

members)

NR C2/C5/

C15/

C23

(3) Highway construction

Fence, guide, sign,

and sight

8–9.9

(0.50–0.62)

6.4 (0.40) 6.4 (0.40) 6.4

(0.40)

NR NR NR NR C2/C5/

C14

Guardrail and spacer

blocks

NR 8 (0.50) 8 (0.50) 8 (0.50) NR NR NR NR C2/C5/

C14

F. Glued- laminated

timbers/laminates

 (1) Soil and fresh water 8 (0.50)d 6.4 (0.40)d 6.4 (0.40)d NR NR NR NR NR C28

 (2) Above ground 3.2 (0.20) 4 (0.25) 4 (0.25) NR NR NR NR NR C28

a

Retention levels are those included in Federal Specification TT–W–571 and Commodity Standards of the American Wood Preservers’

 Association. Refer to the current issues of these specifications for up-to-date recommendations and other details. In many cases, the retention is

 different depending on species and assay zone. Retentions for lumber, timber, plywood, piles, poles, and fence posts are determined by assay of

 borings of a number and location as specified in Federal Specification TT–W–571 or in the Standards of the American Wood Preservers’ Association

 referenced in last column. Unless noted, all waterborne preservative retention levels are specified on an oxide basis. NR is not recommended.

b

Dual treatments are recommended when marine borer activity is known to be high (see AWPA C2, C3, C14, and C18 for details).

c

For use when laminations are treated prior to bonding.
14–7

In 1986, creosote became a restricted-use pesticide and is

available only to certified pesticide applicators. For use and

handling of creosote-treated wood, refer to the EPA-approved

Consumer Information Sheet (Table 14–1).

Freshly creosoted timber can be ignited and burns readily,

producing a dense smoke. However, after the timber has

seasoned for some months, the more volatile parts of the oil

disappear from near the surface and the creosoted wood usually is little, if any, easier to ignite than untreated wood.

Until this volatile oil has evaporated, ordinary precautions

should be taken to prevent fires. Creosote adds fuel value,

but it does not sustain ignition.

Coal-Tar Creosotes for Nonpressure Treatments

Special coal-tar creosotes are available for nonpressure treatments, although these creosotes can only be purchased by

licensed pesticide applicators. Special coal-tar creosotes differ

somewhat from regular commercial coal-tar creosote in

(a) being crystal-free to flow freely at ordinary temperatures

and (b) having low-boiling distillation fractions removed to

reduce evaporation in thermal (hot and cold) treatments in

open tanks. Consensus standards do not exist for coal-tar

creosote applied by brush, spray, or open-tank treatments.

Other Creosotes

Creosotes distilled from tars other than coal tar are used to

some extent for wood preservation, although they are not

included in current Federal or AWPA specifications. These

include wood-tar creosote, oil-tar creosote, and water–gas-tar

creosote. These creosotes protect wood from decay and insect

attack but are generally less effective than coal-tar creosote.

Creosote Solution

For many years, either coal tar or petroleum oil has been

mixed with coal-tar creosote, in various proportions, to

lower preservative costs. These creosote solutions have a

satisfactory record of performance, particularly for railroad ties

and posts where surface appearance of the treated wood is of

minor importance.

The ASTM D391 “Creosote–Coal-Tar Solution” standard

covers creosote–coal-tar solution for use in the preservative

treatment of wood. This standard has been approved for use

by agencies of the U.S. Department of Defense. This specification contains four grades of creosote solutions:

• A (land and fresh water), contains no less than 80%

coal-tar distillate (creosote) by volume

• B (land and fresh water), contains no less than 70%

coal-tar distillate (creosote) by volume

• C (land and fresh water), contains no less than 60%

coal-tar distillate (creosote) by volume

• Marine

The AWPA standard P2 similarly describes the requirements

for creosote solutions. The AWPA standard P3 (for creosote–

petroleum oil solution) stipulates that creosote–petroleum oil

solution shall consist solely of specified proportions of 50%

coal-tar creosote by volume (which meets AWPA standard

P1/P13) and 50% petroleum oil by volume (which meets

AWPA standard P4). However, because no analytical standards exist to verify the compliance of P3 solutions after they

have been mixed, the consumer assumes the risk of using

these solutions.

Compared with straight creosote, creosote solutions tend to

reduce weathering and checking of the treated wood. These

solutions have a greater tendency to accumulate on the surface of the treated wood (bleed) and penetrate the wood with

greater difficulty because they are generally more viscous than

is straight creosote. High temperatures and pressures during

treatment, when they can be safely used, will often improve

penetration of high viscosity solutions.

Even though petroleum oil and coal tar are less toxic to

wood-destroying organisms and mixtures of the two are also

less toxic in laboratory tests than is straight creosote, a

reduction in toxicity does not necessarily imply less preservative protection. Creosote–petroleum and creosote–coaltar solutions help reduce checking and weathering of the

treated wood. Posts and ties treated with standard formulations of these solutions have frequently shown better service

than those similarly treated with straight coal-tar creosote.

Pentachlorophenol Solutions

Water-repellent solutions containing chlorinated phenols,

principally pentachlorophenol (penta), in solvents of the

mineral spirits type, were first used in commercial dip treatments of wood by the millwork industry about 1931. Commercial pressure treatment with pentachlorophenol in heavy

petroleum oils on poles started about 1941, and considerable

quantities of various products soon were pressure treated.

The standard AWPA P8 defines the properties of pentachlorophenol preservative. Pentachlorophenol solutions for

wood preservation shall contain not less than 95% chlorinated phenols, as determined by titration of hydroxyl and

calculated as pentachlorophenol. The performance of pentachlorophenol and the properties of the treated wood are

influenced by the properties of the solvent used.

The AWPA P9 standard defines solvents and formulations

for organic preservative systems. A commercial process using

pentachlorophenol dissolved in liquid petroleum gas (LPG)

was introduced in 1961, but later research showed that field

performance of penta/LPG systems was inferior to penta/P9

systems. Thus, penta/LPG systems are no longer used.

The heavy petroleum solvent included in AWPA P9 Type A

is preferable for maximum protection, particularly when

wood treated with pentachlorophenol is used in contact with

the ground. The heavy oils remain in the wood for a long

time and do not usually provide a clean or paintable surface.

Pentachlorophenol in AWPA P9, Type E solvent (dispersion in water), is only approved for aboveground use in

lumber, timber, bridge ties, mine ties, and plywood for

southern pines, coastal Douglas-fir, and redwood

(Table 14–2; AWPA C2 and C9).
 14–8

Because of the toxicity of pentachlorophenol, care is necessary when handling and using it to avoid excessive personal

contact with the solution or vapor. Do not use indoors or

where human, plant, or animal contact is likely. Pentachlorophenol became a restricted-use pesticide in November

1986 and is only available to certified applicators. For use

and handling precautions, refer to the EPA-approved

Consumer Information Sheet (Table 14–1).

The results of pole service and field tests on wood treated

with 5% pentachlorophenol in a heavy petroleum oil are

similar to those with coal-tar creosote. This similarity has

been recognized in the preservative retention requirements of

treatment specifications. Pentachlorophenol is effective

against many organisms, such as decay fungi, molds, stains,

and insects. Because pentachlorophenol is ineffective against

marine borers, it is not recommended for the treatment of

marine piles or timbers used in coastal waters.

Copper Naphthenate

Copper naphthenate is an organometalic compound that is a

dark-green liquid and imparts this color to the wood. Weathering turns the color of the treated wood to light brown after

several months of exposure. The wood may vary from light

brown to chocolate-brown if heat is used in the treating

process. The AWPA P8 standard defines the properties of

copper naphthenate, and AWPA P9 covers the solvents and

formulations for organic preservative systems.

Copper naphthenate is effective against wood-destroying

fungi and insects. It has been used commercially since the

1940s for many wood products (Table 14–2). It is a reaction

product of copper salts and naphthenic acids that are usually

obtained as byproducts in petroleum refining. Copper

naphthenate is not a restricted-use pesticide but should be

handled as an industrial pesticide. It may be used for superficial treatment, such as by brushing with solutions with a

copper content of 1% to 2% (approximately 10% to 20%

copper naphthenate).

Chlorothalonil

Chlorothalonil (CTL) [tetrachloroisophthalonitrile] is an

organic biocide that is used to a limited extent for mold

control in CCA-treated wood (AWPA P8). It is effective

against wood decay fungi and wood-destroying insects. The

CTL has limited solubility in organic solvents and very low

solubility in water, but it exhibits good stability and leach

resistance in wood. This preservative is being evaluated for

both aboveground and ground contact applications. The

solvent used in the formulation of the preservative is AWPA

P9 Type A.

Chlorothalonil/Chlorpyrifos

Chlorothalonil/chlorpyrifos (CTL/CPF) is a preservative

system composed of two active ingredients (AWPA P8).

The ratio of the two components depends upon the retention

specified. CTL is an effective fungicide, and CPF is very

effective against insect attack. The solvent used for formulation of this preservative is specified in AWPA P9.

Oxine Copper (copper-8-quinolinolate)

Oxine copper (copper-8-quinolinolate) is an organometalic

compound, and the formulation consists of at least 10%

copper-8-quinolinolate, 10% nickel-2-ethylhexanoate, and

80% inert ingredients (AWPA P8). It is accepted as a standalone preservative for aboveground use for sapstain and mold

control and is also used for pressure treating (Table 14–2). A

water-soluble form can be made with dodecylbenzene sulfonic

acid, but the solution is corrosive to metals.

Oxine copper solutions are greenish brown, odorless, toxic

to both wood decay fungi and insects, and have a low toxicity to humans and animals. Because of its low toxicity to

humans and animals, oxine copper is the only EPAregistered preservative permitted by the U.S. Food and Drug

Administration for treatment of wood used in direct contact

with food. Some examples of its uses in wood are commercial refrigeration units, fruit and vegetable baskets and boxes,

and water tanks. Oxine copper solutions have also been used

on nonwood materials, such as webbing, cordage, cloth,

leather, and plastics.

Zinc Naphthenate

Zinc naphthenate is similar to copper naphthenate but is less

effective in preventing decay from wood-destroying fungi and

mildew. It is light colored and does not impart the characteristic greenish color of copper naphthenate, but it does impart

an odor. Waterborne and solventborne formulations are

available. Zinc naphthenate is not used for pressure treating

and is not intended as a stand-alone preservative.

Bis(tri-n-butyltin) Oxide

Bis(tri-n-butyltin) oxide, commonly called TBTO, is a

colorless to slightly yellow organotin compound that is

soluble in many organic solvents but insoluble in water. It is

not used for pressure treating or as a stand-alone preservative

for in-ground use. TBTO concentrate contains at least 95%

bis(tri-n-butyltin) oxide by weight and from 38.2% to 40.1%

tin (AWPA P8). This preservative has lower mammalian

toxicity, causes less skin irritation, and has better paintability than does pentachlorophenol, but it is not effective

against decay when used in ground contact. Therefore,

TBTO is recommended only for aboveground use, such as

millwork. It has been used as a marine antifoulant, but this

use has been almost eliminated because of the environmental

impact of tin on shellfish.

3-Iodo-2-Propynyl Butyl Carbamate

3-Iodo-2-propynyl butyl carbamate (IPBC) is a preservative

that is intended for nonstructural, aboveground use only (for

example, millwork). It is not used for pressure treating applications such as decks. The IPBC preservative is included as

the primary fungicide in several water-repellent-preservative

formulations under the trade name Polyphase and marketed

by retail stores. However, it is not an effective insecticide.

Waterborne and solventborne formulations are available.

Some formulations yield an odorless, treated product that can

be painted if dried after treatment. IPBC is also being used in
14–9

combination with didecyldimethylammonium chloride in a

sapstain–mold formulation (NP–1). IPBC contains 97%

3-iodo-2-propynyl butyl carbamate, with a minimum of

43.4% iodine (AWPA P8).

Alkyl Ammonium Compound

Alkyl ammonium compound (AAC) or didecyldimethylammonium chloride (DDAC) is a compound that is effective

against wood decay fungi and insects. It is soluble in both

organic solvents and water and is stable in wood as a result

of chemical fixation reactions. It is currently being used as a

component of ammoniacal copper quat (ACQ) (see section on

Waterborne Preservatives) for aboveground and ground contact and is a component of NP–1 for sapstain and mold

control.

Propiconazole

Propiconazole is an organic triazole biocide that is effective

against wood decay fungi but not against insects (AWPA

P8). It is soluble in some organic solvents, but it has low

solubility in water and is stable and leach resistant in wood.

It is currently being used commercially for aboveground and

sapstain control application in Europe and Canada. Solvents

used in the formulation of the preservative are specified in

either AWPA P9 Type C or Type F.

4,5-Dichloro-2-N-Octyl-4-Isothiazolin-3-One

4,5-dichloro-2-N-octyl-4-isothiazolin-3-one is a biocide that

is effective against wood decay fungi and insects. It is soluble

in organic solvents, but not in water, and is stable and leach

resistant in wood. This biocide is not currently being used

as a wood preservative. The solvent used in the formulation

of the preservative is specified in AWPA P9 Type C.

Tebuconazole

Tebuconazole (TEB) is an organic triazole biocide that is

effective against wood decay fungi, but its efficacy against

insects has not yet been evaluated. It is soluble in organic

solvents but not in water, and it is stable and leach resistant

in wood. Currently, TEB has no commercial application.

The solvents used in the formulation of this preservative are

specified in either AWPA P9 Type C or Type F.

Chlorpyrifos

Chlorpyrifos (CPF) is a preservative recently put into standard (AWPA P8). It is very effective against insect attack but

not fungal attack. If fungal attack is a concern, then CPF

should be combined with an appropriate fungicide, such as

chlorothalonil/chlorpyrifos or IPBC/chlorpyrifos.

Water-Repellent and Nonpressure Treatments

Effective water-repellent preservatives will retard the ingress

of water when wood is exposed above ground. Therefore,

these preservatives help reduce dimensional changes in the

wood as a result of moisture changes when the wood is

exposed to rainwater or dampness for short periods. As with

any wood preservative, the effectiveness in protecting wood

against decay and insects depends upon the retention and

penetration obtained in application. These preservatives are

most often applied using nonpressure treatments like brushing, soaking, or dipping.

Preservative systems containing water-repellent components

are sold under various trade names, principally for the dip or

equivalent treatment of window sash and other millwork.

Many are sold to consumers for household and farm use.

Federal specification TT–W–572 stipulates that such preservatives (a) be dissolved in volatile solvents, such as

mineral spirits, (b) do not cause appreciable swelling of the

wood, and (c) produce a treated wood product that meets a

performance test on water repellency.

The preservative chemicals in Federal specification

TT–W–572 may be one of the following:

• Not less than 5% pentachlorophenol

• Not less than 1% copper in the form of copper naphthenate

• Not less than 2% copper in the form of copper naphthenate

for tropical conditions

• Not less than 0.045% copper in the form of oxine copper

for uses when foodstuffs will be in contact with the treated

wood

The National Wood Window and Door Association

(NWWDA) standard for water-repellent preservative nonpressure treatment for millwork, IS 4–94, permits other preservatives, provided the wood preservative is registered for use by

the EPA under the latest revision of the Federal Insecticide,

Fungicide, and Rodenticide Act (FIFRA) and that all waterrepellent preservative formulations are tested for effectiveness

against decay according to the soil block test (NWWDA

TM1).

The AWPA Standard N1 for nonpressure treatment of millwork components also states that any water-repellent preservative formulation must be registered for use by the EPA

under the latest revision of FIFRA. The preservative must

also meet the Guidelines for Evaluating New Wood Preservatives for Consideration by the AWPA for nonpressure

treatment.

Water-repellent preservatives containing oxine copper are

used in nonpressure treatment of wood containers, pallets,

and other products for use in contact with foods. When

combined with volatile solvents, oxine copper is used to

pressure-treat lumber intended for use in decking of trucks

and cars or related uses involving harvesting, storage, and

transportation of foods (AWPA P8).

Waterborne Preservatives

Waterborne preservatives are often used when cleanliness and

paintability of the treated wood are required. Several formulations involving combinations of copper, chromium, and

arsenic have shown high resistance to leaching and very good

performance in service. Waterborne preservatives are included
 14–10

in specifications for items such as lumber, timber, posts,

building foundations, poles, and piling.

Test results based on sea water exposure have shown that

dual treatment (waterborne copper-containing salt preservatives followed by creosote) is possibly the most effective

method of protecting wood against all types of marine borers.

The AWPA standards have recognized this process as well

as the treatment of marine piles with high retention levels of

ammoniacal copper arsenate (ACA), ammoniacal copper zinc

arsenate (ACZA), or chromated copper arsenate (CCA). The

recommended treatment and retention in kilograms per cubic

meter (pounds per cubic foot) for round timber piles exposed

to severe marine borer hazard are given in Table 14–3.

Poorly treated or untreated heartwood faces of wood species

containing “high sapwood” that do not require heartwood

penetration (for example, southern pines, ponderosa pine, and

red pine) have been found to perform inadequately in marine

exposure. In marine applications, only sapwood faces should

be allowed for waterborne-preservative-treated pine in direct

sea water exposure.

Waterborne preservatives leave the wood surface comparatively clean, paintable, and free from objectionable odor.

CCA and acid copper chromate (ACC) must be used at low

treating temperatures (38oC to 66oC (100oF to 150oF)) because they are unstable at higher temperatures. This restriction may involve some difficulty when higher temperatures

are needed to obtain good treating results in woods such as

Douglas-fir. Because water is added to the wood in the

treatment process, the wood must be dried after treatment to

the moisture content required for the end use intended.

Inorganic arsenicals are a restricted-use pesticide. For use and

handling precautions of pressure-treated wood containing

inorganic arsenicals, refer to the EPA-approved Consumer

Information Sheet (Table 14–1).

Standard wood preservatives used in water solution include

ACC, ACZA, and CCA (Types A and C). Other preservatives in AWPA P5 include alkyl ammonium compound

(AAC) and inorganic boron. Waterborne wood preservatives,

without arsenic or chromium, include ammoniacal copper

quat (ACQ) (Types B and D), copper bis(dimethyldithiocarbamate) (CDDC), ammoniacal copper citrate (CC), and

copper azole–Type A (CBA–A), for aboveground use only.

Acid Copper Chromate

Acid copper chromate (ACC) contains 31.8% copper oxide

and 68.2% chromium trioxide (AWPA P5). The solid,

paste, liquid concentrate, or treating solution can be made of

copper sulfate, potassium dichromate, or sodium dichromate.

Tests on stakes and posts exposed to decay and termite

attack indicate that wood well-impregnated with ACC gives

acceptable service, but it is more prone to leaching than are

most other waterborne preservatives. Use of ACC is generally limited to cooling towers that cannot allow arsenic

leachate in cooling water.

Ammoniacal Copper Zinc Arsenate

Ammoniacal copper zinc arsenate (ACZA) is used in the

United States but not in Canada. It is commonly used on the

West Coast for the treatment of Douglas-fir. The penetration

Table 14–3. Preservative treatment and retention necessary to protect round timber piles from

severe marine borer attack

Retention (kg/m3 (lb/ft3))

Treatment

Southern Pine,

red pine

Coastal

Douglas-fir

AWPA

standard

Limnoria tripunctata only

Ammoniacal copper arsenate 40 (2.50), (24 (1.5))a 40 (2.50) C3, C18

Ammoniacal copper zinc arsenate 40 (2.50), (24 (1.5))a 40 (2.50) C3, C18

Chromated copper arsenate 40 (2.50) (24 (1.5))a Not recommended C3, C18

Creosote 320 (20), (256 (16))a 320 (20) C3, C18

Limnoria tripunctata and Pholads

(dual treatment)

First treatment

Ammoniacal copper arsenate 16 (1.0) 16 (1.0) C3, C18

Ammoniacal copper zinc arsenate 16 (1.0) 16 (1.0) C3, C18

Chromated copper arsenate 16 (1.0) 16 (1.0) C3, C18

Second treatment

Creosote 320 (20.0) 320 (20.0) C3, C18

Creosote solution 320 (20.0) Not recommended C3, C18

a

Lower retention levels are for marine piling used in areas from New Jersey northward on the

 East Coast and north of San Francisco on the West Coast in the United States.
14–11

of Douglas-fir heartwood is improved with ACZA because of

the chemical composition and stability of treating at elevated

temperatures. Wood treated with ACZA performs and has

characteristics similar to those of wood treated with CCA

(Table 14–2).

ACZA should contain approximately 50% copper oxide,

25% zinc oxide, and 25% arsenic pentoxide dissolved in a

solution of ammonia in water (AWPA P5). The weight of

ammonia is at least 1.38 times the weight of copper oxide.

To aid in solution, ammonium bicarbonate is added (at least

equal to 0.92 times the weight of copper oxide).

A similar formulation, ammoniacal copper arsenate (ACA),

is used in Canada. This preservative is used most commonly

to treat refractory species, such as Douglas-fir. Service records

on structures treated with ACA show that this preservative

provides protection against decay and termites. High retention levels of preservative will provide extended service life

to wood exposed to the marine environment, provided

pholad-type borers are not present. ACZA replaced ACA in

the United States because ACZA has less arsenic and is less

expensive than ACA.

Chromated Copper Arsenate

Three types of chromated copper arsenate (CCA)—Types A,

B, C—are covered in AWPA P5, but Type C is by far the

most commonly used formulation. The compositions of the

three types are given in Table 14–4. Standard P5 permits

substitution of potassium or sodium dichromate for chromium trioxide; copper sulfate, basic copper carbonate, or

copper hydroxide for copper oxide; and arsenic acid, sodium

arsenate, or pyroarsenate for arsenic pentoxide.

1. CCA Type A (Greensalt)—Currently, CCA Type A is

only being used by a few treaters in California. CCA Type A

is high in chromium. Service data on treated poles, posts,

and stakes installed in the United States since 1938 have

shown that CCA Type A provides excellent protection

against decay fungi and termites.

2. CCA Type B (K–33) —Commercial use of this preservative in the United States started in 1964, but it is no longer

used in significant quantities. CCA Type B is high in

arsenic and has been commercially used in Sweden since

1950. It was included in stake tests in the United States in

1949 and has been providing excellent protection.

3. CCA Type C (Wolman)—Currently, Type C is by far the

most common formulation of CCA being used because it has

the best leach resistance and field efficacy of the three CCA

formulations. CCA Type C composition was selected by

AWPA technical committees to encourage a single standard

for CCA preservatives. Commercial preservatives of similar

composition have been tested and used in England since

1954, then in Australia, New Zealand, Malaysia, and in

various countries of Africa and Central Europe; they are

performing very well.

High retention levels (40 kg/m3

 (2.5 lb/ft3)) of the three types

of CCA preservative will provide good resistance to Limnoria and Teredo marine borer attack. In general, Douglas-fir

heartwood is very resistant to treatment with CCA.

Ammoniacal Copper Quat

There are basically two types of ammoniacal copper quat

(ACQ) preservatives (AWPA P5):

• Type B (ACQ–B) [ammoniacal]

• Type D (ACQ–D) [amine-based]

The compositions of these two types are given in

Table 14–5. ACQ is used for many of the same applications

as are ACZA and CCA, but it is not recommended for use in

salt water. ACQ–B, the ammoniacal formulation, is better

able to penetrate difficult to treat species such as Douglas-fir;

ACQ–D provides a more uniform surface appearance. Wood

products treated with ACQ Type B and D are included in the

AWPA Commodity Standards (Table 14–2).

Copper bis(dimethyldithiocarbamate)

Copper bis(dimethyldithiocarbamate) (CDDC) is a reaction

product formed in wood as a result of the dual treatment of

two separate treating solutions. The first treating solution

contains a maximum of 5% bivalent copper–ethanolamine

(2-aminoethanol), and the second treating solution contains

a minimum of 2.5% sodium dimethyldithiocarbamate

Table 14–4. Composition of the three types of

chromated copper arsenatea

Chromated copper arsenate

(parts by weight)

Component Type A Type B Type C

Chromium trioxide 65.5 35.3 47.5

Copper oxide 18.1 19.6 18.5

Arsenic pentoxide 16.4 45.1 34.0

a

As covered in AWPA P5.

Table 14–5. Composition of two types of

ammoniacal copper quata

Ammoniacal cooper quat

(parts by weight)

Component Type B Type D

Copper oxide 66.7 66.7

Quat as DDACb 33.3 33.3

Formulation ammoniacal amine

a

As covered in AWPA P5.

b

DDAC is didecyldimethylammonium chloride.
 14–12

(AWPA P5). CDDC-treated wood products are included in

the AWPA Commodity Standards (Table 14–2) for uses

such as residential construction. Like CCA and ACQ–D,

CDDC is not recommended for treatment of refractory species

such as Douglas-fir.

Ammoniacal Copper Citrate

Ammoniacal copper citrate (CC) has 62.3% copper as copper

oxide and 35.8% citric acid dissolved in a solution of ammonia in water (AWPA P5). CC-treated wood products are

included in the AWPA Commodity Standards (Table 14–2).

Like other ammonia-based preservatives, CC can be used to

treat refractory species such as Douglas-fir.

Copper Azole–Type A

Copper azole–Type A (CBA–A) has 49% copper as Cu, 49%

boron as boric acid, and 2% azole as tebuconazole dissolved

in a solution of ethanolamine in water (AWPA P5). Wood

products treated with CBA–A are included in the AWPA

Commodity Standards for aboveground use only

(Table 14–2).

Inorganic Boron (Borax/Boric Acid)

Borate preservatives are readily soluble in water, are highly

leachable, and should only be used above ground where the

wood is protected from wetting. When used above ground

and protected from wetting, this preservative is very effective

against decay, termites, beetles, and carpenter ants. Borates

are odorless and can be sprayed, brushed, or injected. They

will diffuse into wood that is wet; therefore, these preservatives are often used as a remedial treatment. Borates are

widely used for log homes, natural wood finishes, and hardwood pallets.

The solid or treating solution for borate preservatives

(borates) should be greater than 98% pure, on an anhydrous

basis (AWPA P5). Acceptable borate compounds are sodium

octaborate, sodium tetraborate, sodium pentaborate, and

boric acid. These compounds are derived from the mineral

sodium borate, which is the same material used in laundry

additives.

Preservative Effectiveness

Preservative effectiveness is influenced not only by the protective value of the preservative chemical, but also by the

method of application and extent of penetration and retention

of the preservative in the treated wood. Even with an effective

preservative, good protection cannot be expected with poor

penetration or substandard retention levels. The species of

wood, proportion of heartwood and sapwood, heartwood

penetrability, and moisture content are among the important

variables that influence the results of treatment. For various

wood products, the preservatives and retention levels listed

in Federal Specification TT–W–571 and the AWPA Commodity Standards are given in Table 14–2.

Few service tests include a variety of preservatives under

comparable conditions of exposure. Furthermore, service

tests may not show a good comparison between different

preservatives as a result of the difficulty in controlling the

previously mentioned variables. Such comparative data under

similar exposure conditions, with various preservatives and

retention levels, are included in the USDA Forest Service,

Forest Products Laboratory, stake test study on Southern

Pine sapwood (Gutzmer and Crawford 1995). A summary of

these test results is included in Table 14–6.

In the same manner, a comparison of preservative treatments

in marine exposure (Key West, Florida) of small wood

panels is included in Johnson and Gutzmer (1990). These

preservatives and treatments include creosotes with and

without supplements, waterborne preservatives, waterborne

preservative and creosote dual treatments, chemical modifications of wood, and various chemically modified polymers. In

this study, untreated panels were badly damaged by marine

borers after 6 to 18 months of exposure while some treated

panels have remained free of attack after 19 years in the sea.

Effect of Species on Penetration

The effectiveness of preservative treatment is influenced by

the penetration and distribution of the preservative in the

wood. For maximum protection, it is desirable to select

species for which good penetration is best assured.

The heartwood of some species is difficult to treat. There

may be variations in the resistance to preservative penetration

of different wood species. Table 14–7 gives the relative

resistance of the heartwood to treatment of various softwood

and hardwood species (MacLean 1952).

In general, the sapwood of most softwood species is not

difficult to treat under pressure. Examples of species with

sapwood that is easily penetrated when it is well dried and

pressure treated are the pines, coastal Douglas-fir, western

larch, Sitka spruce, western hemlock, western redcedar,

northern white-cedar, and white fir (A. concolor). Examples

of species with sapwood and heartwood somewhat resistant

to penetration are the red and white spruces and Rocky

Mountain Douglas-fir. Cedar poles are commonly incised to

obtain satisfactory preservative penetration. With round

members, such as poles, posts, and piles, the penetration of

the sapwood is important in achieving a protective outer

zone around the heartwood.

The heartwood of most species resists penetration of preservatives, but well-dried white fir, western hemlock, northern red oak, the ashes, and tupelo are examples of species

with heartwood that is reasonably easy to penetrate. The

southern pines, ponderosa pine, redwood, Sitka spruce,

coastal Douglas-fir, beech, maples, and birches are examples

of species with heartwood that is moderately resistant to

penetration.
14–13

Table 14–6. Results of Forest Products Laboratory studies on 5- by 10- by 46-cm (2- by 4- by 18-in.)

Southern Pine sapwood stakes, pressure-treated with commonly used wood preservatives,

installed at Harrison Experimental Forest, Mississippi

Preservative

Average retention

(kg/m3 (lb/ft3

))a

Average life (year) or condition

at last inspection

Control (untreated stakes) 1.8 to 3.6 years

Acid copper chromate 2.08 (0.13) 11.6 years

 2.24 (0.14) 6.1 years

 4.01 (0.25) 70% failed after 24 years

 4.17 (0.26) 60% failed after 46 years

 4.65 (0.29) 4.6 years

 5.93 (0.37) 50% failed after 46 years

 8.01 (0.50) 40% failed after 24 years

12.18 (0.76) 20% failed after 24 years

Ammoniacal copper borate 2.72 (0.17) 65% failed after 16 years

 3.52 (0.22) 30% failed after 16 years

 5.29 (0.33) 10% failed after 16 years

 7.21 (0.45) 5% failed after 16 years

.41 (0.65) 5% failed after 16 years

21.31 (1.33) No failures after 16 years

Ammoniacal copper arsenate 2.56 (0.16) 60% failed after 16 years

 3.52 (0.22) 10% failed after 16 years

 3.84 (0.24) 67% failed after 47 years

 4.01 (0.25) 20% failed after 24 years

 7.37 (0.46) 10% failed after 24 years

 8.17 (0.51) 10% failed after 47 years

15.54 (0.97) No failures after 47 years

20.02 (1.25) No failures after 47 years

Chromated copper arsenate 2.40 (0.15) 70% failed after 46 years

Type I 3.52 (0.22) 30% failed after 24 years

 4.65 (0.29) 30% failed after 46 years

 7.05 (0.44) 10% failed after 24 years

 7.05 (0.44) 10% failed after 46 years

Type II 3.68 (0.23) 30% failed after 24 years

 4.17 (0.26) 10% failed after 42 years

 5.93 (0.37) No failures after 42 years

 8.33 (0.52) No failures after 42 years

12.66 (0.79) No failures after 42 years

16.66 (1.04) No failures after 42 years

Type III 2.24 (0.14) No failures after 12-1/2 years

 3.20 (0.20) No failures after 20 years

 4.01 (0.25) No failures after 14 years

 4.33 (0.27) No failures after 12-1/2 years

 6.41 (0.40) No failures after 20 years

 6.41 (0.40) No failures after 14 years

 6.41 (0.40) No failures after 12-1/2 years

 9.61 (0.60) No failures after 20 years

 9.93 (0.62) No failures after 12-1/2 years

12.34 (0.77) No failures after 14 years

12.66 (0.79) No failures after 12-1/2 years

Chromated zinc arsenate 1.76 (0.11) 22.1 years

 3.52 (0.22) 33.0 years

 4.65 (0.29) 89% failed after 51-1/2 years

 3.20 (0.20) 10% failed after 40 years

 6.41 (0.40) No failures after 40 years

 8.49 (0.53) No failures after 40 years

 6.09 (0.38) 40% failed after 51-1/2 years

 8.33 (0.52) 10% failed after 51-1/2 years

11.21 (0.70) No failures after 51-1/2 years
 14–14

Table 14–6. Results of Forest Products Laboratory studies on 5- by 10- by 46-cm (2- by 4- by 18-in.)

Southern Pine sapwood stakes, pressure-treated with commonly used wood preservatives, installed

at Harrison Experimental Forest, Mississippi—con.

Preservative

Average retention

(kg/m3 (lb/ft3

))a

Average life (year) or condition

at last inspection

Chromated zinc chloride 4.81 (0.30) 14.2 years

 7.53 (0.47) 20.2 years

 7.37 (0.46) 13.7 years

10.09 (0.63) 20.1 years

 9.93 (0.62) 14.9 years

14.74 (0.92) 23.4 years

15.38 (0.96 90% failed after 24 years

28.52 (1.78) 32.7 years

90% failed after 38 years

58.79 (3.67) No failures after 38 years

Oxine copper 0.16 (0.01) 5.3 years

 (Copper-8-quinolinoate) 0.32 (0.02) 4.2 years

 Stoddard solvent 0.96 (0.06) 5.6 years

 1.92 (0.12) 7.8 years

Oxine copper 0.22 (0.014) 80% failed after 28 years

 (Copper-8-quinolinolate) 0.48 (0.03) 70% failed after 28 years

 AWPA P9 heavy petroleum 0.95 (0.059) 20% failed after 28 years

 1.99 (0.124) No failures after 28 years

Copper naphthenate

0.11% copper in No. 2 fuel oil 0.19 (0.012) 15.9 years

0.29% copper in No. 2 fuel oil 0.46 (0.029) 21.8 years

0.57% copper in No. 2 fuel oil 0.98 (0.061) 27.2 years

0.86% copper in No. 2 fuel oil 1.31 (0.082) 29.6 years

Creosote, coal-tar 52.87 (3.3) 24.9 years

 65.68 (4.1) 14.2 years

 67.28 (4.2) 17.8 years

 73.69 (4.6) 21.3 years

124.96 (7.8) 70% failed after 49-1/2 years

128.24 (8.0) 80% failed after 51-1/2 years

132.97 (8.3) 40% failed after 42 years

160.2 (10.0) 90% failed after 51 years

189.04 (11.8) 30% failed after 51-1/2 years

211.46 (13.2) 20% failed after 49-1/2 years

232.29 (14.5) No failures after 51 years

264.33 (16.5) No failures after 51-1/2 years

Low residue, straight run 128.16 (8.0) 17.8 years

Medium residue, straight run 128.16 (8.0) 18.8 years

High residue, straight run 124.96 (7.8) 20.3 years

Medium residue, low in tar acids 129.76 (8.1) 19.4 years

Low in naphthalene 131.36 (8.2) 21.3 years

Low in tar acids and naphthalene 128.16 (8.0) 18.9 years

Low residue, low in tar

 acids and naphthalene 128.16 (8.0) 19.2 years

High residue, low in tar acids

 and naphthalene 131.36 (8.2) 20.0 years

English vertical retort 84.91 (5.3) 80% failed after 44 years

128.16 (8.0) 18.9 years

161.80 (10.1) 80% failed after 44 years

240.30 (15.0) No failures after 44 years

English coke oven 75.29 (4.7) 16.3 years

126.56 (7.9) 13.6 years

161.80 (10.1) 70% failed after 44 years

237.10 (14.8) 70% failed after 44 years
14–15

Table 14–6. Results of Forest Products Laboratory studies on 5- by 10- by 46-cm (2- by 4- by 18-in.)

Southern Pine sapwood stakes, pressure-treated with commonly used wood preservatives, installed

at Harrison Experimental Forest, Mississippi—con.

Preservative

Average retention

(kg/m3 (lb/ft3

))a

Average life (year) or condition

at last inspection

Fluor chrome arsenate phenol 1.92 (0.12) 10.2 years

 type A 3.04 (0.19) 18.0 years

 3.52 (0.22) 18.3 years

 4.97 (0.31) 18.5 years

 6.09 (0.38) 24.1 years

Pentachlorophenol (various solvents)

Liquefied petroleum gas 2.24 (0.14) 90% failed after 30-1/2 years

 3.04 (0.19) 15.9 years

 5.45 (0.34) No failures after 30-1/2 years

 5.45 (0.34) 70% failed after 28 years

 7.85 (0.49) No failures after 28 years

 9.29 (0.58) No failures after 30-1/2 years

10.41 (0.65) No failures after 28 years

Stoddard solvent 2.24 (0.14) 13.7 years

 (mineral spirits) 2.88 (0.18) 15.9 years

 3.20 (0.20) 9.5 years

 3.20 (0.20) 13.7 years

 6.09 (0.38) 40% failed after 30-1/2 years

 6.41 (0.40) 15.5 years

10.73 (0.67) No failures after 30-1/2 years

Heavy gas oil 3.20 (0.20) 67% failed after 44-1/2 years

 (Mid-United States) 6.41 (0.40) 60% failed after 44-1/2 years

 9.61 (0.60) 10% failed after 44-1/2 years

No. 4 aromatic oil 3.36 (0.21) 21.0 years

 (West Coast) 6.57 (0.41) 50% failed after 42 years

AWPA P9 (heavy petroleum) 1.76 (0.11) 80% failed after 30-1/2 years

 3.04 (0.19) No failures after 30-1/2 years

 4.65 (0.29) No failures after 30-1/2 years

 8.49 (0.53) No failures after 28 years

10.73 (0.67) No failures after 30-1/2 years

Tributyltin oxide

Stoddard solvent 0.24 (0.015) 6.3 years

 0.40 (0.025) 4.5 years

 0.48 (0.030) 7.2 years

 0.72 (0.045) 7.4 years

 0.75 (0.047) 7.0 years

AWPA P9 (heavy petroleum) 0.38 (0.024) 20.8 years

 0.77 (0.048) 24.0 years

Petroleum solvent controls 64.08 (4.0) 7.6 years

 65.68 (4.1) 4.4 years

 75.29 (4.7) 12.9 years

123.35 (7.7) 14.6 years

126.56 (7.9) 90% failed after 44-1/2 years

128.16 (8.0) 19.7 years

128.16 (8.0) 23.3 years

128.16 (8.0) 14.6 years

129.76 (8.1) 3.4 years

136.17 (8.5) 90% failed after 28 years

157.00 (9.8) 6.3 years

192.24 (12.0) 17.1 years

193.84 (12.1) 20% failed after 44-1/2 years

310.79 (19.4) 9.1 years

a

Retention values are based on preservative oxides or copper metal.
 14–16

Table 14–7. Penetration of the heartwood of various softwood and hardwood speciesa

Ease of treatment Softwoods Hardwoods

Least difficult Bristlecone pine (Pinus aristata) American basswood (Tilia americana)

Pinyon (P. edulis) Beech (white heartwood) (Fagus grandifolia)

Pondersosa pine (P. pondersosa) Black tupelo (blackgum) (Nyssa sylvatica)

Redwood (Sequoia sempervirens) Green ash (Fraxinus pennsylvanica var. lanceolata)

Pin cherry (Prunus pensylvanica)

River birch (Betula nigra)

Red oaks (Quercus spp.)

Slippery elm (Ulmus fulva)

Sweet birch (Betula lenia)

Water tupelo (Nyssa aquatica)

White ash (Fraxinus americana)

Moderately difficult Baldcypress (Taxodium distichum) Black willow (Salix nigra)

California red fir (Abies magnifica) Chestnut oak (Quercus montana)

Douglas-fir (coast) (Pseudotsuga taxifolia)) Cottonwood (Populus sp.)

Eastern white pine (Pinus strobus) Bigtooth aspen (P. grandidentata)

Jack pine (P. banksiana) Mockernut hickory (Carya tomentosa)

Loblolly pine (P. taeda) Silver maple (Acer saccharinum)

Longleaf pine (P. palustris) Sugar maple (A. saccharum)

Red pine (P. resinosa) Yellow birch (Betula lutea)

Shortleaf pine (P. echinata)

Sugar pine (P. lambertiana)

Western hemlock (Tsuga heterophylla)

Difficult Eastern hemlock (Tsuga canadensis) American sycamore (Platanus occidentalis)

Engelmann spruce (Picea engelmanni) Hackberry (Celtis occidentalis)

Grand fir (Abies grandis) Rock elm (Ulmus thomoasi)

Lodgepole pine (Pinus contorta var. latifolia) Yellow-poplar (Liriodendron tulipifera)

Noble fir (Abies procera)

Sitka spruce (Picea sitchensis)

Western larch (Larix occidentalis)

White fir (Abies concolor)

White spruce (Picea glauca)

Very difficult Alpine fir (Abies lasiocarpa) American beech (red heartwood) (Fagus grandifolia)

Corkbark fir (A. lasiocarpa var. arizonica) American chestnut (Castanea dentata)

Douglas-fir (Rocky Mountain) (Pseudotsuga

taxifolia)

Black locust (Robinia pseudoacacia)

Northern white-cedar (Thuja occidentalis) Blackjack oak (Quercus marilandica)

Tamarack (Larix laricina) Sweetgum (redgum) (Liquidambar styraciflua)

Western redcedar (Thuja plicata) White oaks (Quercus spp.)

a

As covered in MacLean (1952).
14–17

Preparation of Timber

for Treatment

For satisfactory treatment and good performance, the timber

must be sound and suitably prepared. Except in specialized

treating methods involving unpeeled or green material, the

wood should be well peeled and either seasoned or conditioned in the cylinder before treatment. It is also highly

desirable that all machining be completed before treatment.

Machining may include incising to improve the preservative

penetration in woods that are resistant to treatment, as well

as the operations of cutting or boring of holes.

Peeling

Peeling round or slabbed products is necessary to enable the

wood to dry quickly enough to avoid decay and insect damage and to permit the preservative to penetrate satisfactorily.

Even strips of the thin inner bark may prevent penetration.

Patches of bark left on during treatment usually fall off in

time and expose untreated wood, thus permitting decay to

reach the interior of the member.

Careful peeling is especially important for wood that is to be

treated by a nonpressure method. In the more thorough

processes, some penetration may take place both longitudinally and tangentially in the wood; consequently, small

strips of bark are tolerated in some specifications. Processes

in which a preservative is forced or permitted to diffuse

through green wood lengthwise do not require peeling of

the timber. Machines of various types have been developed

for peeling round timbers, such as poles, piles, and posts

(Fig. 14–1).

Drying

Drying of wood before treatment is necessary to prevent

decay and stain and to obtain preservative penetration. However, for treatment with waterborne preservatives by certain

diffusion methods, high moisture content levels may be

permitted. For treatment by other methods, however, drying

before treatment is essential. Drying before treatment opens

up the checks before the preservative is applied, thus increasing penetration, and reduces the risk of checks opening after

treatment and exposing unpenetrated wood. Good penetration

of heated organic-based preservatives may be possible in

wood with a moisture content as high as 40% to 60%, but

severe checking while drying after treatment can expose

untreated wood.

For large timbers and railroad ties, air drying is a widely

used method of conditioning. Despite the increased time,

labor, and storage space required, air drying is generally the

most inexpensive and effective method, even for pressure

treatment. However, wet, warm climatic conditions make it

difficult to air dry wood adequately without objectionable

infection by stain, mold, and decay fungi. Such infected

wood is often highly permeable; in rainy weather, infected

wood can absorb a large quantity of water, which prevents

satisfactory treatment.

Figure 14–1. Machine peeling of poles. The outer bark has been removed by hand, and the inner bark

is being peeled by machine. Frequently, all the bark is removed by machine.
 14–18

How long the timber must be air dried before treatment

depends on the climate, location, and condition of the seasoning yard, methods of piling, season of the year, timber

size, and species. The most satisfactory seasoning practice

for any specific case will depend on the individual drying

conditions and the preservative treatment to be used. Therefore, treating specifications are not always specific as to

moisture content requirements.

To prevent decay and other forms of fungal infection during

air drying, the wood should be cut and dried when conditions are less favorable for fungus development (Ch. 13). If

this is impossible, chances for infection can be minimized by

prompt conditioning of the green material, careful piling and

roofing during air drying, and pretreating the green wood

with preservatives to protect it during air drying.

Lumber of all species, including Southern Pine poles, is

often kiln dried before treatment, particularly in the southern

United States where proper air seasoning is difficult. Kiln

drying has the important added advantage of quickly reducing moisture content, thereby reducing transportation charges

on poles.

Conditioning of Green Products

Plants that treat wood by pressure processes can condition

green material by means other than air and kiln drying.

Thus, they avoid a long delay and possible deterioration of

the timber before treatment.

When green wood is to be treated under pressure, one of

several methods for conditioning may be selected. The

steaming-and-vacuum process is used mainly for southern

pines, and the Boulton or boiling-under-vacuum process is

used for Douglas-fir and sometimes hardwoods.

In the steaming process, the green wood is steamed in the

treating cylinder for several hours, usually at a maximum of

118oC (245oF). When steaming is completed, a vacuum is

immediately applied. During the steaming period, the outer

part of the wood is heated to a temperature approaching that

of the steam; the subsequent vacuum lowers the boiling

point so that part of the water is evaporated or forced out of

the wood by the steam produced when the vacuum is

applied. The steaming and vacuum periods used depend

upon the wood size, species, and moisture content. Steaming

and vacuum usually reduce the moisture content of green

wood slightly, and the heating assists greatly in getting the

preservative to penetrate. A sufficiently long steaming period

will also sterilize the wood.

In the Boulton or boiling-under-vacuum method of partial

seasoning, the wood is heated in the oil preservative under

vacuum, usually at about 82oC to 104oC (180oF to 220oF).

This temperature range, lower than that of the steaming

process, is a considerable advantage in treating woods that

are especially susceptible to injury from high temperatures.

The Boulton method removes much less moisture from

heartwood than from sapwood.

Incising

Wood that is resistant to penetration by preservatives may be

incised before treatment to permit deeper and more uniform

penetration. To incise, lumber and timbers are passed

through rollers equipped with teeth that sink into the wood

to a predetermined depth, usually 13 to 19 mm (1/2 to

3/4 in.). The teeth are spaced to give the desired distribution

of preservative with the minimum number of incisions. A

machine of different design is required for deeply incising

the butts of poles, usually to a depth of 64 mm (2.5 in.)

(Fig. 14–2).

The effectiveness of incising depends on the fact that preservatives usually penetrate into wood much farther in the

longitudinal direction than in a direction perpendicular to the

faces of the timber. The incisions open cell lumens along the

grain, which greatly enhances penetration. Incising is especially effective in improving penetration in the heartwood

areas of sawn surfaces.

Incising is practiced primarily on Douglas-fir, western hemlock, and western larch ties and timbers for pressure treatment and on cedar and Douglas-fir poles. Incising can result

in significant reductions in strength (Ch. 4).

Cutting and Framing

All cutting and boring of holes should be done prior to

preservative treatment. Cutting into the wood in any way

after treatment will frequently expose the untreated interior of

the timber and permit ready access to decay fungi or insects.

Figure 14–2. Deep incising permits better penetration

of preservative.
14–19

In some cases, wood structures can be designed so that all

cutting and framing is done before treatment. Railroad companies have followed this practice and have found it not only

practical but economical. Many wood-preserving plants are

equipped to carry on such operations as the adzing and boring of crossties; gaining, roofing, and boring of poles; and

framing of material for bridges and specialized structures,

such as water tanks and barges.

Treatment of the wood with preservative oils results in little

or no dimensional change. With waterborne preservatives,

however, some change in the size and shape of the wood may

occur even though the wood is redried to the moisture content it had before treatment. If precision fitting is necessary,

the wood is cut and framed before treatment to its approximate final dimensions to allow for slight surfacing, trimming, and reaming of bolt holes. Grooves and bolt holes for

timber connectors are cut before treatment and can be reamed

out if necessary after treatment.

Application of Preservatives

Wood-preserving methods are of two general types: (a) pressure processes, in which the wood is impregnated in closed

vessels under pressures considerably above atmospheric, and

(b) nonpressure processes, which vary widely in the procedures and equipment used.

Pressure Processes

In commercial practice, wood is most often treated by immersing it in a preservative in a high pressure apparatus and

applying pressure to drive the preservative into the wood.

Pressure processes differ in details, but the general principle

is the same. The wood, on cars or trams, is run into a long

steel cylinder (Fig. 14–3), which is then closed and filled

with preservative. Pressure forces the preservative into the

wood until the desired amount has been absorbed. Considerable preservative is absorbed, with relatively deep penetration. Three pressure processes are commonly used: full-cell,

modified full-cell, and empty-cell.

Full-Cell

The full-cell (Bethel) process is used when the retention of a

maximum quantity of preservative is desired. It is a standard

procedure for timbers to be treated full-cell with creosote

when protection against marine borers is required. Waterborne preservatives are generally applied by the full-cell

process, and control over preservative retention is obtained

by regulating the concentration of the treating solution.

Steps in the full-cell process are essentially the following:

1. The charge of wood is sealed in the treating cylinder, and

a preliminary vacuum is applied for a half-hour or more to

remove the air from the cylinder and as much as possible

from the wood.

2. The preservative, at ambient or elevated temperature

depending on the system, is admitted to the cylinder

without breaking the vacuum.

3. After the cylinder is filled, pressure is applied until the

wood will take no more preservative or until the required

retention of preservative is obtained.

4. When the pressure period is completed, the preservative is

withdrawn from the cylinder.

5. A short final vacuum may be applied to free the charge

from dripping preservative.

When the wood is steamed before treatment, the preservative

is admitted at the end of the vacuum period that follows

steaming. When the timber has received preliminary conditioning by the Boulton or boiling-under-vacuum process, the

cylinder can be filled and the pressure applied as soon as the

conditioning period is completed.

Modified Full-Cell

The modified full-cell process is basically the same as the

full-cell process except for the amount of initial vacuum and

the occasional use of an extended final vacuum. The modified

full-cell process uses lower levels of initial vacuum; the

actual amount is determined by the wood species, material

size, and final retention desired.

Empty-Cell

The objective of the empty-cell process is to obtain deep

penetration with a relatively low net retention of preservative.

For treatment with oil preservatives, the empty-cell process

should always be used if it will provide the desired retention.

Two empty-cell processes, the Rueping and the Lowry, are

commonly employed; both use the expansive force of compressed air to drive out part of the preservative absorbed

during the pressure period.

The Rueping empty-cell process, often called the empty-cell

process with initial air, has been widely used for many years

in Europe and the United States. The following general

procedure is employed:

1. Air under pressure is forced into the treating cylinder,

which contains the charge of wood. The air penetrates

some species easily, requiring but a few minutes application of pressure. In treating the more resistant species,

common practice is to maintain air pressure from 1/2 to

1 h before admitting the preservative, but the necessity for

lengthy air-pressure periods does not seem fully established. The air pressures employed generally range between 172 to 689 kPa (25 to 100 lb/in2

), depending on

the net retention of preservative desired and the resistance

of the wood.

2. After the period of preliminary air pressure, preservative is

forced into the cylinder. As the preservative is pumped in,

the air escapes from the treating cylinder into an equalizing or Rueping tank, at a rate that keeps the pressure constant within the cylinder. When the treating cylinder is

filled with preservative, the treating pressure is increased

above that of the initial air and is maintained until the

wood will absorb no more preservative, or until enough

has been absorbed to leave the required retention of preservative in the wood after the treatment.
 14–20

3. At the end of the pressure period, the preservative is

drained from the cylinder, and surplus preservative is removed from the wood with a final vacuum. The amount of

preservative recovered can be from 20% to 60% of the

gross amount injected.

The Lowry is often called the empty-cell process without

initial air pressure. Preservative is admitted to the cylinder

without either an initial air pressure or a vacuum, and the air

originally in the wood at atmospheric pressure is imprisoned

during the filling period. After the cylinder is filled with the

preservative, pressure is applied, and the remainder of the

treatment is the same as described for the Rueping treatment.

The Lowry process has the advantage that equipment for the

full-cell process can be used without other accessories that

the Rueping process usually requires, such as an air compressor, an extra cylinder or Rueping tank for the preservative, or a suitable pump to force the preservative into the

cylinder against the air pressure. However, both processes

have advantages and are widely and successfully used.

With poles and other products where bleeding of preservative

oil is objectionable, the empty-cell process is followed by

either heating in the preservative (expansion bath) at a

maximum of 104oC (220oF) or a final steaming for a specified

time limit at a maximum of 116oC (240oF) prior to the final

vacuum.

Figure 14–3. Interior view of treating cylinder at wood-preserving plant, with a load about to come in.
14–21

Treating Pressures and

Preservative Temperatures

The pressures used in treatments vary from about 345 to

1,723 kPa (50 to 250 lb/in2), depending on the species and

the ease with which the wood takes the treatment; most

commonly, pressures range from about 862 to 1,207 kPa

(125 to 175 lb/in2). Many woods are sensitive to high treating pressures, especially when hot. For example, AWPA

standards permit a maximum pressure of 1,034 kPa

(150 lb/in2) in the treatment of Douglas-fir, 862 kPa

(125 lb/in2) for redwood, and 1,723 kPa (250 lb/in2) for oak.

In commercial practice, even lower pressures are frequently

used on such woods.

The AWPA C1 standard requires that the temperature of

creosote and creosote solutions, as well as that of the oilborne preservatives, during the pressure period shall not be

greater than 93oC (200oF) for Western redcedar and 99oC

(210oF) for all other species. With a number of waterborne

preservatives, especially those containing chromium salts,

maximum temperatures are limited to avoid premature precipitation of the preservative. The AWPA specifications

require that the temperature of the preservative during the

entire pressure period not exceed the maximum of 49oC

(120oF) for ACC and CCA and 60oC (150oF) for ACA, CC,

ACQ Type B, ACQ Type D, ACZA, CBA–A, and CDDC.

The limit for inorganic boron is 93oC (200oF).

Penetration and Retention

Penetration and retention requirements are equally important

in determining the quality of preservative treatment. Penetration levels vary widely, even in pressure-treated material. In

most species, heartwood is more difficult to penetrate than

sapwood. In addition, species differ greatly in the degree to

which their heartwood may be penetrated. Incising tends to

improve penetration of preservative in many refractory species, but those highly resistant to penetration will not have

deep or uniform penetration even when incised. Penetration

in unincised heart faces of these species may occasionally be

as deep as 6 mm (1/4 in.) but is often not more than 1.6 mm

(1/16 in.).

Experience has shown that even slight penetration has some

value, although deeper penetration is highly desirable to

avoid exposing untreated wood when checks occur, particularly for important members that are costly to replace. The

heartwood of coastal Douglas-fir, southern pines, and various

hardwoods, although resistant, will frequently show transverse penetrations of 6 to 12 mm (1/4 to 1/2 in.) and sometimes considerably more.

Complete penetration of the sapwood should be the ideal in

all pressure treatments. It can often be accomplished in

small-size timbers of various commercial woods, and with

skillful treatment, it may often be obtained in piles, ties, and

structural timbers. Practically, however, the operator cannot

always ensure complete penetration of sapwood in every

piece when treating large pieces of round material with thick

sapwood, for example, poles and piles. Therefore, specifications permit some tolerance. For instance, AWPA C4 for

Southern Pine poles requires that 63 mm (2-1/2 in.) or 85%

of the sapwood thickness be penetrated for 96 kg/m3

 (6 lb/ft3)

retention of creosote. This applies only to the smaller class

of poles. The requirements vary, depending on the species,

size, class, and specified retention levels.

At one time, all preservative retention levels were specified

in terms of the weight of preservative per cubic foot

(0.028 m3) of wood treated, based on total weight of preservative retained and the total volume of wood treated in a

charge. This is commonly called gauge retention. However,

specifications for most products now stipulate a minimum

retention of preservative as determined from chemical analysis of borings from specified zones of the treated wood,

known as a “assay-retention” or results-type specification.

The preservatives and retention levels listed in Federal

Specification TT–W–571 and the AWPA Commodity

Standards are shown in Table 14–2. The retention levels are

often a range. The current issues of these specifications

should be referenced for up-to-date recommendations and

other details. In many cases, the retention level is different

depending on species and assay zone. Higher preservative

retention levels are justified in products to be installed under

severe climatic or exposure conditions. Heavy-duty transmission poles and items with a high replacement cost, such as

structural timbers and house foundations, are required to be

treated to higher retention levels. Correspondingly, deeper

penetration or heartwood limitations are also necessary for

the same reasons.

It may be necessary to increase retention levels to ensure

satisfactory penetration, particularly when the sapwood is

either unusually thick or is somewhat resistant to treatment.

To reduce bleeding of the preservative, however, it may be

desirable to use preservative-oil retention levels less than the

stipulated minimum. Treatment to refusal is usually specified for woods that are resistant to treatment and will not

absorb sufficient preservative to meet the minimum retention

requirements. However, such a requirement does not ensure

adequate penetration of preservative, should be avoided, and

must not be considered as a substitute for results-type specification in treatment.

Nonpressure Processes

The numerous nonpressure processes differ widely in the

penetration and retention levels of preservative attained, and

consequently in the degree of protection they provide to the

treated wood. When similar retention and penetration levels

are achieved, wood treated by a nonpressure method should

have a service life comparable to that of wood treated by

pressure. Nevertheless, results of nonpressure treatments,

particularly those involving surface applications, are not

generally as satisfactory as those of pressure treatment. The

superficial processes do serve a useful purpose when more

thorough treatments are impractical or exposure conditions

are such that little preservative protection is required.

Nonpressure methods, in general, consist of (a) surface

application of preservatives by brushing or brief dipping,
 14–22

(b) soaking in preservative oils or steeping in solutions of

waterborne preservatives, (c) diffusion processes with waterborne preservatives, (d) vacuum treatment, and (e) a variety

of miscellaneous processes.

Surface Applications

The simplest treatment is to apply the preservative to the

wood with a brush or by dipping. Preservatives that are

thoroughly liquid when cold should be selected, unless it is

possible to heat the preservative. The preservative should be

flooded over the wood rather than merely painted. Every

check and depression in the wood should be thoroughly

filled with the preservative, because any untreated wood left

exposed provides ready access for fungi. Rough lumber may

require as much as 40 L of oil per 100 m2

 (10 gallons of oil

per 1,000 ft2) of surface, but surfaced lumber requires considerably less. The transverse penetration obtained will usually

be less than 2.5 mm (1/10 in.), although in easily penetrated

species, end-grain (longitudinal) penetration is considerably

greater. The additional life obtained by such treatments over

that of untreated wood will be affected greatly by the conditions of service. For wood in contact with the ground,

service life may be from 1 to 5 years.

Compared with brushing, dipping for a few seconds to several minutes in a preservative gives greater assurance that all

surfaces and checks are thoroughly coated with the preservative; it usually results in slightly greater penetration. It is a

common practice to treat window sash, frames, and other

millwork, either before or after assembly, by dipping the

item in a water-repellent preservative. Such treatment is

covered by NWWDA IS 4–94, which also provides for

equivalent treatment by the vacuum process. AWPA also has

a new nonpressure standard, N1, that includes preservative

treatments by nonpressure processes for all millwork

products.

In some cases, preservative oil penetrates the end surfaces of

ponderosa pine sapwood as much as 25 to 76 mm (1 to

3 in.). However, end penetration in such woods as the heartwood of Southern Pines and Douglas-fir is much less.

Transverse penetration of the preservative applied by brief

dipping is very shallow, usually only less than a millimeter

(a few hundredths of an inch). The exposed end surfaces at

joints are the most vulnerable to decay in millwork products;

therefore, good end penetration is especially advantageous.

Dip applications provide very limited protection to wood

used in contact with the ground or under very moist conditions, and they provide very limited protection against attack

by termites. However, they do have value for exterior woodwork and millwork that is painted, not in contact with the

ground, and exposed to moisture only for brief periods.

Cold Soaking and Steeping

Cold soaking well-seasoned wood for several hours or days

in low viscosity preservative oils or steeping green or

seasoned wood for several days in waterborne preservatives

has provided varying success on fence posts, lumber, and

timbers.

Pine posts treated by cold soaking for 24 to 48 h or longer in

a solution containing 5% of pentachlorophenol in No. 2 fuel

oil have shown an average life of 16 to 20 years or longer.

The sapwood in these posts was well penetrated, and

preservative solution retention levels ranged from 32 to

96 kg/m3 (2 to 6 lb/ft3

). Most species do not treat as satisfactorily as do the pines by cold soaking, and test posts of such

woods as birch, aspen, and sweetgum treated by this method

have failed in much shorter times.

Preservative penetration and retention levels obtained by cold

soaking lumber for several hours are considerably better than

those obtained by brief dipping of similar species. However,

preservative retention levels seldom equal those obtained in

pressure treatment except in cases such as sapwood of pines

that has become highly absorptive through mold and stain

infection.

Steeping with waterborne preservatives has very limited use

in the United States but it has been used for many years in

Europe. In treating seasoned wood, both the water and the

preservative salt in the solution soak into the wood. With

green wood, the preservative enters the water-saturated wood

by diffusion. Preservative retention and penetration levels

vary over a wide range, and the process is not generally

recommended when more reliable treatments are practical.

Diffusion Processes

In addition to the steeping process, diffusion processes are

used with green or wet wood. These processes employ

waterborne preservatives that will diffuse out of the water of

the treating solution or paste into the water of the wood.

The double-diffusion process developed by the Forest Products Laboratory has shown very good results in fence post

tests and standard 38- by 89-mm (nominal 2- by 4-in.) stake

tests, particularly for full-length immersion treatments. This

process consists of steeping green or partially seasoned wood

first in one chemical solution, then in another (Fig. 14–4).

The two chemicals diffuse into the wood, then react to precipitate an effective preservative with high resistance to leaching. The process has had commercial application in cooling

towers and fence posts where preservative protection is

needed to avoid early replacement of the wood. 

Figure 14–4. Double-diffusion steps for applying

preservatives.
14–23

Other diffusion processes involve applying preservatives to

the butt or around the groundline of posts or poles. In treatments of standing poles, the preservative can be injected into

the pole at groundline with a special tool, applied on the

pole surface as a paste or bandage (Fig. 14–5), or poured into

holes bored in the pole at the groundline. These treatments

have recognized value for application to untreated standing

poles and treated poles where preservative retention levels are

determined to be inadequate.

Vacuum Process

The vacuum process, or “VAC–VAC” as referred to in

Europe, has been used to treat millwork with water-repellent

preservatives and construction lumber with waterborne and

water-repellent preservatives.

In treating millwork, the objective is to use a limited quantity of water-repellent preservative and obtain retention and

penetration levels similar to those obtained by dipping for

3 min. The vacuum process treatment is included in

NWWDA IS–94 for “Water-Repellent Preservative Nonpressure Treatment for Millwork.” In this treatment, a quick, low

initial vacuum is followed by filling the cylinder under

vacuum, releasing the vacuum and soaking, followed by a

final vacuum. The treatment is better than the 3-min dip

treatment because of better penetration and retention, and the

surface of the wood is quickly dried, thus expediting glazing,

priming, and painting. The vacuum treatment is also reported to be less likely than dip treatment to leave objectionably high retention levels in bacteria-infected wood

referred to as “sinker stock.”

Lumber intended for buildings has been treated by the vacuum process, either with a waterborne preservative or a

water-repellent pentachlorophenol solution, with preservative

retention levels usually less than those required for pressure

treatment. The process differs from that used in treating

millwork in employing a higher initial vacuum and a longer

immersion or soaking period.

Figure 14–5. Methods of applying groundline treatment to utility poles. Preservative

is injected into the pole at the groundline with a special tool or applied on the pole

surface as a paste or bandage.
 14–24

In a study by the Forest Products Laboratory, an initial

vacuum of −93 kPa (27.5 inHg) was applied for 30 min,

followed by a soaking for 8 h, and a final or recovery vacuum

of −93 kPa (27.5 inHg) for 2 h. Results of the study showed

good penetration of preservative in the sapwood of dry lumber of easily penetrated species such as the pines. However,

in heartwood and unseasoned sapwood of pine and heartwood

of seasoned and unseasoned coastal Douglas-fir, penetration

was much less than that obtained by pressure treatment.

Preservative retention was less controllable in vacuum than

in empty-cell pressure treatment. Good control over retention

levels is possible in vacuum treatment with a waterborne

preservative by adjusting concentration of the treating

solution.

Miscellaneous Nonpressure Processes

Several other nonpressure methods of various types have

been used to a limited extent. Many of these involve the

application of waterborne preservatives to living trees. The

Boucherie process for the treatment of green, unpeeled poles

has been used for many years in Europe. This process involves attaching liquid-tight caps to the butt ends of the

poles. Then, through a pipeline or hose leading to the cap,

a waterborne preservative is forced under hydrostatic pressure

into the pole.

A tire-tube process is a simple adaptation of the Boucherie

process used for treating green, unpeeled fence posts. In this

treatment, a section of used inner tube is fastened tight

around the butt end of the post to make a bag that holds a

solution of waterborne preservative. There are limitations for

application of this process in the United States because of the

loss of preservative to the soil around the treatment site.

Effect on Mechanical Properties

Coal-tar creosote, creosote solutions, and pentachlorophenol

dissolved in petroleum oils are practically inert to wood and

have no chemical influence that would affect its strength.

Chemicals commonly used in waterborne salt preservatives,

including chromium, copper, arsenic, and ammonia, are

reactive with wood. Thus, these chemicals are potentially

damaging to mechanical properties and may also promote

corrosion of mechanical fasteners.

Significant reductions in mechanical properties may be observed if the treating and subsequent drying processes are not

controlled within acceptable limits. Factors that influence the

effect of the treating process on strength include (a) species of

wood, (b) size and moisture content of the timbers treated,

(c) type and temperature of heating medium, (d) length of the

heating period in conditioning the wood for treatment and

time the wood is in the hot preservative, (e) post-treatment

drying temperatures, and (f) amount of pressure used. Most

important of those factors are the severity and duration of the

in-retort heating or post-treatment redrying conditions used.

The effect of wood preservatives on the mechanical properties

of wood is covered in Chapter 4.

Handling and Seasoning of

Timber After Treatment

Treated timber should be handled with sufficient care to

avoid breaking through the treated areas. The use of pikes,

cant hooks, picks, tongs, or other pointed tools that dig

deeply into the wood should be prohibited. Handling heavy

loads of lumber or sawn timber in rope or cable slings can

crush the corners or edges of the outside pieces. Breakage or

deep abrasions can also result from throwing or dropping the

lumber. If damage results, the exposed places should be

retreated, if possible.

Wood treated with preservative oils should generally be

installed as soon as practicable after treatment to minimize

lateral movement of the preservative, but sometimes cleanliness of the surface can be improved by exposing the treated

wood to the weather for a limited time before installation.

Waterborne preservatives or pentachlorophenol in a volatile

solvent are best suited to uses where cleanliness or

paintability is of great importance.

Lengthy, unsheltered exterior storage of treated wood before

installation should be avoided because such storage encourages deep and detrimental checking and can also result in

significant loss of some preservatives. Treated wood that

must be stored before use should be covered for protection

from the sun and weather.

Although cutting wood after treatment is highly undesirable,

it cannot always be avoided. When cutting is necessary, the

damage can be partly overcome in timber for land or freshwater use by a thorough application of copper naphthenate

(2% copper) to the cut surface. This provides a protective

coating of preservative on the surface that may slowly migrate into the end grain of the wood. A special device is

available for pressure treating bolt holes that are bored after

treatment. For wood treated with waterborne preservatives, a

2% (as copper) solution of copper naphthenate should be

used. Thoroughly brushing cut surfaces with two coats of hot

creosote (applicator license required) is also helpful, although

brush coating of cut surfaces provides little protection against

marine borers.

For treating the end surfaces of piles where they are cut off

after driving, at least two generous coats of creosote should

be applied. A coat of asphalt or similar material may be

thoroughly applied over the creosote, followed by some

protective sheet material, such as metal, roofing felt, or

saturated fabric, fitted over the pile head and brought down

the sides far enough to protect against damage to the treatment and against the entrance of storm water. AWPA M4

contains instructions for the care of pressure-treated wood

after treatment.

With waterborne preservatives, seasoning after treatment is

important for wood that will be used in buildings or other

places where shrinkage after placement in the structure would

be undesirable. Injecting waterborne preservatives puts large

amounts of water into the wood, and considerable shrinkage
14–25

is to be expected as subsequent seasoning takes place. For

best results, the wood should be dried to approximately the

moisture content it will ultimately reach in service. During

drying, the wood should be carefully piled and, whenever

possible, restrained by sufficient weight on the top of the pile

to prevent warping.

With some waterborne preservatives, seasoning after treatment is recommended. During this seasoning period, volatile

chemicals can escape and chemical reactions are completed

within the wood. Thus, the resistance of the preservative to

leaching by water is increased. This physical or chemical

process whereby a wood preservative system is rendered

leach resistant in both water and soil application is called

“fixation.” In this process, the active ingredient or ingredients maintain fungal or insecticidal efficacy.

The Western Wood Preservers’ Institute and the Canadian

Institute of Treated Wood (1996) have developed a publication to address best management practices (BMPs) for the

use of treated wood in aquatic environments. Their purpose

is to protect the quality of the water and diversity of the

various life forms found in the lakes, streams, estuaries, bays,

and wetlands of North America. The document is continually

updated as better methods for risk assessment and research

are developed.

Quality Assurance for

Treated Wood

Treating Conditions and Specifications

Specifications on the treatment of various wood products by

pressure processes have been developed by AWPA. These

specifications limit pressures, temperatures, and time of

conditioning and treatment to avoid conditions that will

cause serious injury to the wood. The specifications also

contain minimum requirements for preservative penetration

and retention levels and recommendations for handling wood

after treatment to provide a quality product.

Specifications are broad in some respects, allowing the purchaser some latitude in specifying the details of individual

requirements. However, the purchaser should exercise great

care so as not to hinder the treating plant operator from doing

a good treating job and not to require treating conditions so

severe that they will damage the wood. Federal Specification

TT–W–571 lists treatment practices for use on U.S. Government orders for treated wood products; other purchasers

have specifications similar to those of AWPA.

The AWPA is working on the development of a Use Category System (UCS), which is a new way to organize the

Commodity Standards. The system utilizes seven different

exposure categories for treated-wood products, with each

exposure category representing a different degree of biodeterioration hazard and/or product expectation. Product users will

be able to specify treated-wood products based on the

biodeterioration risk to which the product will be exposed.

The UCS is expected to appear in the 1998 AWPA Book of

Standards for information only and with standardization

parallel to the current C-Standards in 1999.

Inspection

There are two important factors to consider depending upon

the intended end use of preservative-treated wood: (a) the

grade or appearance of the lumber and (b) the quality of the

preservative treatment in the lumber. The U.S. Department

of Commerce American Lumber Standard Committee

(ALSC), an accrediting agency for treatment quality assurance, has an ink stamp or end tag for each grade stamp

(Fig. 14–6) and quality mark (Fig. 14–7). These marks

indicate that the producer of the treated-wood product subscribes to an independent inspection agency. However, there

are non-ALSC end tags or ink stamps that are similar to

ALSC tags. Only end tags or ink stamps with the logo of an

accredited ALSC–QA agency are acceptable. (A current list is

available from ALSC.)

Quality control overview by ALSC is preferable to simple

treating plant certificates or other claims of conformance made

by the producer without inspection by an independent

agency. These third-party agencies verify for customers that

the wood was properly treated in accordance with AWPA

standards. Thus, the purchaser may either accept the stamps

as their quality assurance or have an independent inspector

inspect and analyze the treated products to ensure compliance

with the specifications. The latter is recommended for

treated-wood products used for critical structures. Railroad

companies and other corporations that purchase large quantities of treated timber usually maintain their own inspection

services.

Purchase of Treated Wood

To obtain a treated-wood product of high quality, the

purchaser should use the appropriate specifications.

Specifications and standards of importance here are Federal

Specification TT–W–571, “Wood Preservation—Treating

Practices;” Federal Specification TT–W–572, "Fungicide:

Pentachlorophenol;" and the AWPA Book of Standards. The

inspection of material for conformity to the minimum requirements listed in these specifications should be in accordance with the American Wood Preservers’ M2, “Standard

for Inspection of Treated Timber Products.”
 14–26

References

AWPA. Annual proceedings. (Reports of Preservations and

Treatment Committees contain information on new wood

preservatives considered in the development of standards.)

Granbury, TX: American Wood Preservers’ Association.

AWPA. 1995. Answers to often-asked question about treated

wood. Vienna, VA: American Wood Preservers’ Institute.

AWPA. 1997. Book of Standards. (Includes standards on

preservatives, treatments, methods of analysis, and inspection.) Granbury, TX: American Wood Preservers’

Association.

ASTM. 1992. Standard specification for coal-tar creosote for

the preservative treatment of piles, poles, and timbers for

marine, land, and freshwater use. ASTM D390. Philadelphia, PA: American Society for Testing and Materials.

ASTM. 1994. Standard specification for creosote-coal tar

solution. ASTM D391. Philadelphia, PA: American Society

for Testing and Materials.

Baechler, R.H.; Roth, H.G. 1964. The double-diffusion

method of treating wood: a review of studies. Forest

Products Journal. 14(4): 171–178.

Baechler, R.H.; Blew, J.O.; Roth, H.G. 1962. Studies on

the assay of pressure-treated lumber. Proceedings of American

Wood Preservers’ Association. 58: 21–34.

Baechler, R.H.; Gjovik, L.R.; Roth, H.G. 1969. Assay

zones for specifying preservative-treated Douglas-fir and

Southern Pine timbers. Proceedings of American Wood

Preservers’ Association. 65: 114–123.

Baechler, R.H.; Gjovik, L.R.; Roth, H.G. 1970. Marine

tests on combination-treated round and sawed specimens.

Proceedings of American Wood Preservers’ Association.

66: 249–257.

Blew, J.O.; Davidson, H.L. 1971. Preservative retentions

and penetration in the treatment of white fir. Proceedings of

American Wood Preservers’ Association. 67: 204–221.

Boone, R.S.; Gjovik, L.R.; Davidson, H.L. 1976. Treatment of sawn hardwood stock with double-diffusion and

modified double-diffusion methods. Res. Pap. FPL–RP–265.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Cassens, D.L.; Johnson, B.R.; Feist, W.C.; De Groot,

R.C. 1995. Selection and use of preservative-treated wood.

Publication N. 7299. Madison, WI: Forest Products

Society.

Eaton, R.A.; Hale, M.D.C. 1993. Wood: decay, pests and

protection. New York, NY: Chapman & Hall.

Gaby, L.I.; Gjovik, L.R. 1984. Treating and drying composite lumber with waterborne preservatives: Part I. Short

specimen testing. Forest Products Journal. 34(2): 23–26.

Gjovik, L.R.; Baechler, R.H. 1970. Treated wood foundations for buildings. Forest Products Journal. 20(5): 45–48.

No. 1

12 S-DRY D

FIR

(a) (c)

(b) (d) (e)

ABC

a Trademark indicates agency quality supervision.

b Mill Identification—firm name, brand, or assigned

 mill number

c Grade Designation—grade name, number, or

 abbreviation

d Species Identification—indicates species

 individually or in combination

e Condition of Seasoning at time of surfacing

 S-DRY

 MC 15

 S-GRN

—

—

—

19% max. moisture content

15% max. moisture content

over 19% moisture content

(unseasoned)

Figure 14–6. Typical lumber grade stamp as approved

by ALSC and its interpretation for Douglas Fir lumber.

ABC

XXX

GROUND CONTACT

19 -19

.40

AWPA STDS

PRESERVATIVE

KDAT

X-XX

(a)

(g)

(c)

(f)

(e)

(b)

(d)

(h)

(i)

Identifying symbol, logo, or name of the accredited agency.

Applicable American Wood Preservers' Association (AWPA)

commodity standard.

Year of treatment, if required by AWPA standard.

Preservative used, which may be abbreviated.

Preservative retention.

Exposure category (e.g. Above Ground, Ground Contact,

etc.).

Plant name and location, plant name and number, or

plant number.

If applicable, moisture content after treatment.

If applicable, length, and/or class.

a

b

c

d

e

f

g

h

i

Figure 14–7. Typical quality mark for preservativetreated lumber to conform to the ALSC accreditation

program.
14–27

Gjovik, L.R.; Baechler, R.H. 1977. Selection, production,

procurement and use of preservative treated wood. Gen.

Tech. Rep. FPL–15. Supplementing Federal Specification

TT–W–571. Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory.

Gjovik, L.R.; Davidson, H.L. 1975. Service records on

treated and untreated posts. Res. Note FPL–068. Madison,

WI: U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Gjovik, L.R.; Roth, H.G.; Davidson, H.L. 1972. Treatment of Alaskan species by double-diffusion and modified

double-diffusion methods. Res. Pap. FPL–182. Madison,

WI: U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Gjovik, L.R.; Johnson, D.B.; Kozak, V.; [and others].

1980. Biologic and economic assessment of pentachlorophenol, inorganic arsenicals, and creosote. Vol. I: Wood preservatives. Tech. Bull 1658–1. Washington, DC: U.S.

Department of Agriculture, in cooperation with State

Agricultural Experimental Stations, Cooperative Extension

Service, other state agencies and the Environmental

Protection Agency.

Gutzmer, D.I.; Crawford, D.M. 1995. Comparison of

wood preservative in stake tests. 1995 Progress Report. Res.

Note FPL–RN–02. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Hunt, G.M.; Garratt, G.A. 1967. Wood preservation. 3d

ed. The American Forestry Series. New York, NY:

McGraw–Hill.

Johnson, B.R.; Gutzmer, D.I. 1990. Comparison of preservative treatments in marine exposure of small wood panels. Res. Note. FPL–RN–0258. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products

Laboratory.

Lebow, S. 1996. Leaching of wood preservative components

and their mobility in the environment—summary of pertinent literature. Gen. Tech. Rep. FPL–GTR–93. Madison,

WI: U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Mac Lean, J.D. 1952. Preservation of wood by pressure

methods. Agric. Handb. 40. Washington, DC: U. S.

Department of Agriculture, Forest Service.

Micklewright, J.T.; Gjovik, L.R. 1981. Wood preserving

statistics: update. Proceedings of American Wood

Preservers’ Association. 77: 143–147.

NFPA. 1982. The all-weather wood foundation. NFPA

Tech. Rep. 7. Washington, DC: National Forest Products

Association.

NFPA. 1982. All-weather wood foundation system, design

fabrication installation manual. NFPA report; Washington

DC: National Forest Products Association.

NWWDA. 1994. Industry standard for water-repellent preservative non-pressure treatment for millwork. IS–4–94. Des

Plaines, IL: National Wood Window and Door Association.

Naval Facilities Engineering Command. 1990. Wood

Protection. NAVFAC MO–312, Philadelphia, PA: Naval

Facilities Engineering Command. Wood Protection. May.

Naval Facilities Engineering Command. 1992. Wood

Protection Training Manual. NAVFAC MO–312.4, Philadelphia, PA: Naval Facilities Engineering Command. Wood

Protection. March.

Nicholas, D.D.; Schultz, T.P. 1994 Biocides that have

potential as wood preservatives—an overview. In: Wood

preservatives in the ‘90s and beyond. Proceedings, conference sponsored by the Forest Products Society; 1994

September 26–28; Savannah, GA.

USFSS. 1968. Wood preservation treating practices. Federal

Specification TT–W–571. Washington, DC: U.S. Federal

Supply Service.

USFSS. 1969. Fungicide: Pentachlorophenol. Federal

Specification TT–W–572. Washington, DC: U.S. Federal

Supply Service.

Western Wood Preservers Institute and Canadian

Institute of Treated Wood. 1996. Best management practices for the use of treated wood in aquatic environments.

Vancouver, WA: Western Wood Preservers Institute and

Canadian Institute of Treated Wood. (USA Version).

July rev.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
15–1

Finishing of Wood

R. Sam Williams

Chapter 15

Contents

Factors Affecting Finish Performance 15–1

Wood Properties 15–1

Wood Extractives 15–2

Wood Product Characteristics 15–4

Weathering 15–6

Control of Water or Moisture in Wood 15–9

Moisture Content 15–9

Water Repellents 15–10

Finish Moisture-Excluding Effectiveness 15–10

Effect of Finish on Liquid Water and Water Vapor Absorption 15–11

Types of Exterior Wood Finishes 15–14

Weathered Wood as Natural Finish 15–16

Penetrating Wood Finishes 15–16

Film-Forming Finishes 15–18

Compliance of VOC Finishes With Pollution Regulations 15–19

Application of Wood Finishes 15–19

Type of Finish 15–19

Porches, Decks, and Fences 15–21

Treated Wood 15–22

Marine Uses 15–22

Refinishing 15–22

Back-Priming 15–23

Factory Finishing 15–24

Finish Failure or Discoloration 15–24

Moisture Blisters 15–25

Mill Glaze 15–25

Intercoat Peeling 15–26

Cross-Grain Cracking 15–26

Chalking 15–26

Mildew 15–27

Discoloration From Water-Soluble Extractives 15–28

Blue Stain 15–29

Iron Stain 15–29

Brown Stain Over Knots 15–29

Finishing of Interior Wood 15–30

Types of Finish and Wood Fillers 15–30

Finishes for Floors 15–32

Finishes for Items Used for Food 15–32

Types of Finish 15–32

Eating Utensils 15–32

Butcher Blocks and Cutting Boards 15–33

Wood Cleaners and Brighteners 15–33

Paint Strippers 15–33

Mechanical Methods 15–34

Chemical Methods 15–34

Avoidance of Problems 15–35

Disposal of Old Paint 15–35

Lead-Based Paint 15–35

References 15–36

he primary function of any wood finish (paint,

varnish, and stain, for example) is to protect the

wood surface, help maintain a certain appearance,

and provide a cleanable surface. Although wood can be used

both outdoors and indoors without finishing, unfinished

wood surfaces exposed to the weather change color, are

roughened by photodegradation and surface checking, and

erode slowly. Unfinished wood surfaces exposed indoors may

also change color; moreover, unfinished wood is more difficult to clean than is finished wood.

Wood and wood-based products in a variety of species, grain

patterns, textures, and colors can be finished effectively by

many different methods. Selection of a finish will depend on

the appearance and degree of protection desired and on the

substrates used. Because different finishes give varying degrees of protection, the type of finish, its quality and quantity, and the method used to apply the finish must be considered when finishing or refinishing wood and wood

products.

Factors Affecting Finish

Performance

Satisfactory performance of wood finishes is achieved when

the many factors that affect these finishes are given full

consideration. These factors include the effect of the wood

substrate, properties of the finishing material, details of

application, and severity of exposure. Some important considerations are reviewed in this chapter. Sources of more

detailed information are provided in a list of references at

the end of this chapter.

Wood Properties

Wood surfaces that have the least tendency to shrink and

swell are best for painting. For this reason, vertical- or

edge-grain surfaces are far better than flat-grain surfaces

(Fig. 15–1), especially when the wood is used outside where

wide ranges of relative humidity and periodic wetting can

produce wide ranges of swelling and shrinking. In addition,

because the swelling of wood is directly proportional to

specific gravity, species with low specific gravity are preferred

to those with high specific gravity. Vertical-grain heartwood

T
 15–2

of western redcedar and redwood are the species usually

recommended for use as exterior siding and trim when painting is desired. These species are classified in Group I, woods

with the best paint-holding characteristics (Table 15–1).

Although vertical-grain surfaces of most species are considered excellent for painting, most species are generally available only as flat-grain lumber.

Very few wood species are graded according to vertical- or

flat-grain specifications. Without a grade for marketing the

lumber, there is no incentive for a mill to either cut to

maximize the yield of vertical-grain lumber or to select

vertical-grain lumber from the mill run. Exceptions are redwood and western redcedar, which are marketed in a range of

grades, including vertical grain. The premium grade is allheartwood and vertical-grain. This grade is usually sold as

resawn bevel siding and it demands a high price; it is

worthwhile for a mill to cut to maximize the yield of this

grade. Most often, cutting is only practical with fairly largediameter logs. For those species that are primarily available

in small-diameter logs, the yield of vertical-grain lumber is

small. It is not practical to cut the log to maximize the

vertical grain because such cutting would substantially

decrease overall yield from the log.

Species normally cut as flat-grain lumber that are high in

specific gravity and swelling, or have defects such as knots or

pitch, are classified in Groups II through V, depending upon

their general paint-holding characteristics. Many species in

Groups II through IV are commonly painted, particularly the

pines, Douglas-fir, and spruce; however, these species generally require more careful surface preparation than do the

vertical-grain (also called edge-grain) surfaces of Group I.

Exterior paint will be more durable on vertical-grain boards

than on flat-grain boards for any species with marked differences in specific gravity between earlywood and latewood,

even if the species are rated in Group I (Fig. 15–2). Flatgrain lumber will hold paint reasonably well if it is used in

areas protected from rain and sun, particularly if the wood is

rough sawn or scuff sanded.

Other wood properties that affect wood finishing are defects

such as knots and colored materials (extractives) in the

wood. These colored materials include a wide range of

chemicals with different solubilities in water, organic solvents, and paint polymers. Their effects on wood finishing

are covered in detail later in this chapter. See Chapters 1 to 3

for more detailed information on wood properties.

Wood Extractives

Water-soluble colored extractives occur naturally in the

heartwood of such species as western redcedar, cypress, and

redwood. These substances give the heartwood of some

species their attractive color, water repellency, and natural

decay resistance. However, discoloration of paint may occur

when the extractives are dissolved and leached from the wood

by water. The water carries the extractives to the painted

surface, then evaporates, leaving the extractives as a yellow

to reddish brown stain on the paint. The water that gets

behind the paint and causes moisture blisters also causes

migration of extractives.

Wood also contains resins and oils that are insoluble in

water. The type and amount of these compounds in lumber

depend on the wood species. For example, many pines

contain pitch and the knots of almost all wood species contain sufficient oils and resins to cause discoloration of lightcolored paint. Since these oils and resins are organic in

nature, they are similar chemically to oil-based and/or alkyd

paints; therefore, they cannot be blocked by typical oilborne

stain-blocking primers as can the water-soluble extractives.

Latex-based formulations are also ineffective. Knots can be

sealed prior to priming with shellac or similar finishes specifically formulated to block oils and resins. Because shellac

is sensitive to moisture, it is essential to use it only over the

knots and to seal it into the knots with a good paint system.

In many species, bleeding of oils and resins from knots is a

difficult problem. At present, there is no easy fix other than

the extra step of sealing knots before priming.

Figure 15–1. Lumber grain affects finish performance:

(a) edge-grain (vertical-grain or quartersawn) board;

(b) edge-grain board containing pith; (c) flat-grain

(slash-grain or plainsawn) board. Arrows show radial

(R), tangential (T), and longitudinal (L) orientation of

wood grain.
15–3

Table 15–1. Characteristics of selected woods for painting

Paint-holding

characteristic Weathering

(I, best; ConspicuV, worst)c Resistance ousness of

Specific Shrinkage (%)b Oil- to cupping checking

gravitya Flat Vertical based Latex (1, most; (1, least; Color of

Wood species green/dry grain grain paint paint 4, least) 2, most) heartwood

Softwoods

Baldcypress 0.42/0.46 6.2 3.8 I I 1 1 Light brown

Cedars

 Incense 0.35/0.37 5.2 3.3 I I — — Brown

 Northern white 0.29/0.31 4.9 2.2 I I — — Light brown

 Port-Orford 0.39/0.43 6.9 4.6 I I — 1 Cream

 Western red 0.31/0.32 5 2.4 I I 1 1 Brown

 Yellow 0.42/0.44 6 2.8 I I 1 1 Yellow

Douglas-fird 0.45/0.48e 7.6 4.8 IV II 2 2 Pale red

Larch, western 0.48/0.52 9.1 4.5 IV II 2 2 Brown

Pine

 Eastern white 0.34/0.35 6.1 2.1 II II 2 2 Cream

 Ponderosa 0.38/0.42 6.2 3.9 III II 2 2 Cream

 Southernd 0.47/0.51f 8 5 IV III 2 2 Light brown

 Sugar 0.34/0.36 5.6 2.9 II II 2 2 Cream

 Western white 0.36/0.38 7.4 4.1 II II 2 2 Cream

Redwood, old growth 0.38/0.40 4.4 2.6 I I 1 1 Dark brown

Spruce, Engelmann 0.33/0.35 7.1 3.8 III II 2 2 White

Tamarack 0.49/0.53 7.4 3.7 IV — 2 2 Brown

White fir 0.37/0.39 7.0 3.3 III — 2 2 White

Western hemlock 0.42/0.45 7.8 4.2 III II 2 2 Pale brown

Hardwoods

Alder 0.37/0.41 7.3 4.4 III — — — Pale brown

Ash, white 0.55/0.60 8 5 V or III — 4 2 Light brown

Aspen, bigtooth 0.36/0.39 7 3.5 III II 2 1 Pale brown

Basswood 0.32/0.37 9.3 6.6 III — 2 2 Cream

Beech 0.56/0.64 11.9 5.5 IV — 4 2 Pale brown

Birch, yellow 0.55/0.62 9.5 7.3 IV — 4 2 Light brown

Butternut 0.36/0.38 6.4 3.4 V or III — — — Light brown

Cherry 0.47/0.50 7.1 3.7 IV — — — Brown

Chestnut 0.40/0.43 6.7 3.4 V or III — 3 2 Light brown

Cottonwood, eastern 0.37/0.40 9.2 3.9 III II 4 2 White

Elm, American 0.46/0.50 9.5 4.2 V or III — 4 2 Brown

Hickory, shagbark 0.64/0.72 11 7 V or IV — 4 2 Light brown

Lauan plywood —g 8 4 IV — 2 2 Brown

Magnolia, southern 0.46/0.50 6.6 5.4 III — 2 — Pale brown

Maple, sugar 0.56/0.63 9.9 4.8 IV — 4 2 Light brown

Oak

 White 0.60/0.68 8.8 4.4 V or IV — 4 2 Brown

 Northern red 0.56/0.63 8.6 4.0 V or IV — 4 2 Brown

Sweetgum 0.46/0.52 10.2 5.3 IV III 4 2 Brown

Sycamore 0.46/0.49 8.4 5 IV — — — Pale brown

Walnut 0.51/0.55 7.8 5.5 V or III — 3 2 Dark brown

Yellow-poplar 0.40/0.42 8.2 4.6 III II 2 1 Pale brown

a

Specific gravity based on weight ovendry and volume at green or 12% moisture content.

b

Value obtained by drying from green to ovendry.

c

Woods ranked in Group V have large pores that require wood filler for durable painting. When pores are properly filled

 before painting, Group II applies. Vertical-grain lumber was used for cedars and redwood. Other species were primarily

 flat-grain. Decrease in paintability is caused by a combination of species characteristics, grain orientation, and greater

 dimensional change of flat-grain lumber. Flat-grain lumber causes at least 1 unit decrease in paintability.

d

Lumber and plywood.

e

Coastal Douglas-fir.

f

Loblolly, shortleaf, specific gravity of 0.54/0.59 for longleaf and slash.

g

Specific gravity of different species varies from 0.33 to 0.55.
 15–4

Wood Product Characteristics

Five general categories of wood products are commonly used

in exterior construction: (a) lumber, (b) plywood, (c) fingerjointed wood, (d) reconstituted wood products (such as

hardboard, oriented strandboard (OSB), and particleboard),

and (e) preservative–fire-retardant-treated wood. Each product

has unique characteristics that affect the application and

performance of finishes.

Lumber

Although several alternative materials are being used for

siding (such as vinyl, aluminum, OSB, and hardboard),

lumber is still the preferred choice for siding in many areas of

the country and for a variety of architectural designs. Many

older homes have wood siding. The ability of lumber to

retain and hold a finish is affected by species, grain orientation, and surface texture.

The specific gravity of wood varies tremendously among

wood species (Table 15–1). The specific gravity of wood is

important because denser woods generally shrink and swell

more than less dense woods. In lumber, this dimensional

change occurs as the wood gains or loses moisture. Excessive dimensional change in wood constantly stresses a paint

film and may cause early paint failure. If two species have the

same specific gravity but shrink and swell differently, their

paintability will be greatly affected by dimensional changes.

For example, redwood and western white pine have about the

same specific gravity (0.38), but their shrinkage values for

flat- and vertical-grain wood are different (4.4% and 2.6% for

redwood and 7.4% and 4.1% for western white pine, respectively) (Table 15–1). Redwood has a paintability rating of I

and western white pine, a rating of II. The greater dimensional instability of the flat-grain western white pine results

in lower paintability compared with that of the vertical-grain

redwood.

The shrinkage values given in Table 15–1 were obtained

from drying wood from its green state to ovendry. The swelling rates would be about the same. The paintability values

for western redcedar and redwood were obtained from verticalgrain lumber; other species were primarily flat-grain. Note

that the shrinkage values for vertical-grain lumber are about

half that of flat-grain lumber. The paintability rating for flatgrain lumber is probably at least one unit lower than that for

vertical-grain lumber. The values given in Table 15–1 for

oil-based paints were obtained from research conducted in the

1930s and 1940s using lumber from large-diameter logs.

It is not known how the properties of lumber from smalldiameter logs and new paint formulations would affect these

ratings. Therefore, the ratings given in Table 15–1 should

be used to rank paintability rather than obtain absolute

paintability values.

Some species have wide bands of earlywood and latewood

(Fig. 15–3). These distinct bands often lead to early paint

failure. Wide, prominent bands of latewood are characteristic

of the southern pines and Douglas-fir, and paint will not hold

well on these species. In contrast, redwood and cedar do not

have wide latewood bands, and these species are preferred

for painting.

Grain orientation also affects paint-holding characteristics

and is determined by the way lumber is cut from a log

(Fig. 15–1). Most standard grades of lumber contain a high

percentage of flat-grain lumber. Lumber used for board and

Figure 15–2. Paint applied over edge-grain boards

(top and bottom) performs better than that applied to

flat-grain boards (middle).

Figure 15–3. Earlywood and latewood bands in

Southern Pine.
15–5

batten, drop, or shiplap siding is frequently flat-grain. Bevel

siding is commonly produced in several grades. The highest

grade of redwood and western redcedar bevel siding is vertical-grain all-heartwood. Other grades of redwood and western

redcedar may be flat, vertical, or mixed grain and may not be

required to be all-heartwood.

The texture (roughness or smoothness) of the wood surface

has an important effect on the selection, application, and

service life of finishes. Until recently, a general rule of thumb

for matching substrates to finishes was to paint smooth wood

and stain rough-sawn wood. This easy rule of thumb no

longer applies. Although it is true that penetrating finishes

such as semitransparent stains give much better service life

on rough-sawn wood compared with smooth wood, many

film-forming finishes such as opaque stains and paints also

give much better service life on rough-sawn wood. The paint

adheres better, the film buildup is better, and the service life

is longer on a roughened than a smooth (planed) surface,

particularly when flat-grain lumber or siding is used.

Surface texture is discussed in more detail in later sections

of this chapter.

Plywood

As with lumber, species, grain orientation, and surface texture are important variables that affect the finishing of plywood. In addition, plywood contains small checks (face

checks) that are caused by the lathe when the veneer is cut

during plywood manufacture. Cycles of wetting and drying

with subsequent swelling and shrinking tend to worsen facechecking of plywood veneer. Face checking sometimes extends through paint coatings to detract from the appearance

and durability of the paint. Face checks can lead to early

paint failure, particularly with oil or alkyd paint systems

(Fig. 15–4). Latex primer and top coat paint systems generally perform better than oil or alkyd systems. For use as

exterior siding, plywood is often overlaid with resin-treated

paper (medium-density overlay (MDO)); MDO eliminates

cracks caused by lathe checking and provides plywood with

excellent paintability (equal to or better than that of Group I

vertical-grain lumber).

Plywood for exterior use nearly always has a flat-grain surface, and if it is used for exterior wood siding, the surface is

rough sawn. Smooth-sanded plywood is not recommended

for siding, although it is often used for soffits. The flat-grain

pattern in nearly all plywood can contribute to early paint

failure. Therefore, if plywood is to be painted, take special

care to prepare the surface and use high quality latex paint.

Rough-sawn plywood holds paint much better than does

smooth plywood. Smooth plywood should be scuff-sanded

with 50-grit sandpaper prior to priming, and both smooth

and rough plywood should be edge-treated with a waterrepellent preservative. Penetrating stains are often more

appropriate for rough-sawn than smooth-sawn exterior

plywood surfaces.

Fingerjointed Lumber

In recent years, many mills have been producing lumber that

consists of many small pieces of wood that are glued together

and have fingerjoints to improve strength (Chs. 9 and 11).

This process is done to eliminate knots and other defects

from the lumber. The lumber is commonly used for fascia

boards, interior and exterior trim, windows and doors, and

siding. Although fingerjointed lumber contains no knots or

other defects, the wood pieces are generally not sorted in

regard to heartwood or sapwood or to grain orientation prior

to gluing. However, with some suppliers, care is taken to

decrease variability in fingerjointed lumber. For example,

fingerjointed redwood siding is available in Clear All Heart

vertical grain and Clear flat grain. Fingerjointed lumber is

usually sold as a particular species, although this is not

always the case. Because a particular board may contain

pieces from many trees and in many grain orientations, the

finishing requirements are determined by the worst piece of

wood in a single board. It is quite common for paint failure

to occur in a “patchwork” manner according to the paintability of the particular piece of wood in the board (Fig. 15–5).

The finishing of fingerjointed lumber requires special care to

ensure that the finish will adhere to the whole board. Roughsawn lumber should hold paint better than will planed lumber. Planed wood should be scuff-sanded with 50-grit sandpaper prior to priming.

Figure 15–4. Early paint failure on plywood caused by

penetration of moisture into surface face-checks.

Figure 15–5. Differences in stain from extractives on

fingerjointed yellow pine (probably ponderosa pine)

painted with acrylic solid-color stain.
 15–6

Particleboard and Similar

Reconstituted Wood Products

Reconstituted wood products are those made by forming

small pieces of wood into large sheets, usually 1.2 by 2.4 m

(4 by 8 ft) or as required for a specialized use such as clapboard siding. These products may be classified as fiberboard

or particleboard, depending upon the nature of the basic

wood component (see Ch. 10).

Although wood characteristics such as grain orientation,

specific gravity of earlywood and latewood, warping, and

splitting are not considerations with reconstituted wood

products, other characteristics must be addressed when finishing these products. The surface of fiberboard accepts and

holds paint very well, and it can be improved with the addition of a resin-treated paper overlay. Film-forming finishes

such as paints and solid-color stains will provide the most

protection to reconstituted wood products. Some reconstituted wood products may be factory primed with paint, and

factory-applied top-coats are becoming more common. The

edges of these products are sensitive to moisture, and extra

care should be used to assure that edges get a good coat of

paint. Better yet, edges can be sealed with a paintable waterrepellent preservative. Reconstituted wood products should

not be finished with semitransparent stain or other penetrating finishes.

Fiberboard is produced from wood that is pulped by mechanical means. Hardboard is a relatively heavy type of

fiberboard. The tempered or treated form of hardboard is

designed for outdoor exposure and is used for exterior siding.

Hardboard is often sold in 1.2- by 2.4-m (4- by 8-ft) sheets

and in 152- to 203-mm (6- to 8-in.) widths as a substitute

for solid-wood beveled siding.

Particleboard is manufactured from whole wood in the form

of splinters, chips, flakes, strands, or shavings. Flakeboard is

a type of particleboard made from relatively large flakes or

shavings. Oriented strandboard (OSB) is a refinement of

flakeboard in that the flakes have a large length-to-width

aspect ratio and are laid down in layers, with the flakes in

each layer oriented 90 ̊ to each other as are veneers in plywood (Ch. 10). Particleboard that is to be used outdoors

must be overlaid with either wood veneer or resin-treated

paper; exterior particleboard can be finished in the same way

as are other paper over-laid products. As with fiberboard,

special care must taken to assure a good paint film on the

edges of particleboard.

Treated Wood

Wood used in severe outdoor exposures requires special

treatment for proper protection and best service. The most

common hazard in such exposures is decay (rot) and insect

attack, particularly by termites. Marine exposure also requires wood to be protected with special treatment. Many

building codes require fire-retardant treatment of wood for

some uses.

When wood is used in situations with high decay and termite hazards, it is usually treated with a wood preservative.

The three main types of preservatives are (a) preservative oils

(such as coal–tar creosote), (b) organic solvent solution (such

as pentachlorophenol), and (c) waterborne salts (such as

chromated copper arsenate (CCA)) (Ch. 14). These preservatives can be applied in several ways, but pressure treatment

generally provides the greatest protection against decay.

Wood preservatives may also improve the wood’s resistance

to weathering, particularly if the preservative contains chromium salts. Chromium-containing preservatives protect

wood against ultraviolet degradation, an important factor in

the weathering process.

Wood treated with waterborne preservatives, such as CCA,

can be painted or stained if the wood is clean and dry. Wood

treated with a water-repellent preservative, by vacuumpressure or dipping, is paintable. Wood treated with coal–tar

creosote or other dark oily preservatives is not paintable;

even if the paint adheres to the treated wood, the dark oils

tend to discolor the paint, especially light-colored paint.

Fire-retardant treatment of wood does not generally interfere

with adhesion of paint coatings, unless the treated wood has

extremely high moisture content because of its increased

hygroscopicity. Fire-retardant-treated wood is generally

painted according to the manufacturer’s recommendations

rather than left unfinished because the treatment and subsequent drying often darken and discolor the wood. It is critical

that wood to be used outside be treated with only those fireretardant treatments that are specifically recommended for

outdoor exposure.

Weathering

Weathering is the general term used to describe the degradation of materials exposed outdoors. This degradation occurs

on the surface of all organic materials, including wood and

finishes used on wood such as paints and stains. The process

occurs through photo-oxidation of the surface catalyzed by

ultraviolet (UV) radiation in sunlight, and it is augmented

by other processes such as washing by rain, changes in

temperature, changes in moisture content, and abrasion by

windblown particles. The weathering process can take many

forms depending on the exposed material; in general, the

process begins with a color change, followed by slow erosion

(loss of material) from the surface. The surface initially develops slight checking; with some materials, deep cracks

may ultimately develop. Weathering is dependent on the

chemical makeup of the affected material. Because the surface

of a material may be composed of many different chemicals,

not all materials on the surface may erode at the same rate.

Effect on Wood

The surface of wood consists of four types of organic materials: cellulose, hemicellulose, lignin, and extractives. Each of

these materials is affected by the weathering process in a

different way. The extractives (that is, the material in the

wood that gives each species its distinctive color) undergo

changes upon exposure to sunlight and lighten or darken in

color. With some wood species, this color change can take

place within minutes of exposure. Changes in the color of the
15–7

surface are accompanied by other changes that affect the wettability and surface chemistry of the wood. The mechanism

of these early changes is not very well understood, but these

changes can have a drastic effect on the surface chemistry of

wood and thus the interaction of the wood with other chemicals, such as paint and other finishes.

From 20% to 30% of the wood surface is composed of lignin, a polymeric substance that is the adhesive that holds

wood celluloses together. Because lignin is affected by photodegradation more than are celluloses, lignin degrades and

cellulose fibers remain loosely attached to the wood surface.

Further weathering causes fibers to be lost from the surface

(a process called erosion); but this process is so slow that on

the average only about 6 mm (1/4 in.) of wood is lost in a

century (Fig. 15–6). This erosion rate is slower for most

hardwoods and faster for certain softwoods. Other factors like

growth rate, degree of exposure, grain orientation, temperature, and wetting and drying cycles are important in determining the rate of erosion. Table 15–2 shows erosion rates

for several wood species that were measured over a 16-year

period.

Water and the swelling and shrinking stresses set up by

fluctuations in moisture content accelerate erosion. Cyclic

wetting and drying roughen the surface, raise the grain, cause

differential swelling of earlywood and latewood bands, and

result in many small, parallel checks and cracks. Larger and

deeper cracks may also develop. Fewer checks develop in

woods with moderate to low specific gravity than in those

with high specific gravity, and vertical-grain boards have

fewer checks than do flat-grain boards. Flat-grain lumber

frequently warps as well.

Figure 15–6. Artist’s rendition of weathering process of round and square timbers. As cutaway shows, interior

wood below surface is relatively unchanged.
 15–8

The time required for wood to become fully weathered depends on the severity of the exposure. Once weathered, and

in the absence of decay, stain, and mildew, wood remains

nearly unaltered in appearance (Fig. 15–7). As a result of

weathering, boards tend to warp (particularly cup) and fasteners are loosened. The tendency to cup varies with the specific

gravity, width, and thickness of the board. The greater the

specific gravity and the greater the width in proportion to

thickness, the greater the tendency to cup. For best resistance

to cup, the width of a board should not exceed eight times

its thickness. Warping also is more pronounced in flat-grain

boards than in vertical-grain boards.

Biological attack of a wood surface by microorganisms is

recognized as a contributing factor to color change or graying

of wood. This biological attack, commonly called mildew,

does not cause erosion of the surface, but it may cause initial

graying or an unsightly dark gray and blotchy appearance.

These color changes are caused by dark-colored fungal spores

and mycelia on the wood surface. In advanced stages of

weathering, when the surface has been enriched by cellulose,

it may develop a silvery-gray sheen. This formation of a

bright, light gray, silvery sheen on weathered wood occurs

most frequently where micro-organism growth is inhibited

by a hot, arid climate or a salty atmosphere in coastal regions. The microorganisms primarily responsible for gray

discoloration of wood are commonly found on weathered

wood (see subsection on mildew under Finish Failure or

Discoloration).

Effect on Paint Adhesion

Although the erosion of the wood surface through weathering

is a slow process, the chemical changes that occur within a

few weeks of outdoor exposure can drastically decrease the

adhesion of paints subsequently applied to the weathered

surface. It is fairly obvious that a badly weathered, powdery

wood surface cannot hold paint very well. This fact is not so

obvious for wood that has weathered for only 2 to 3 weeks.

The wood appears sound and much the same as when it was

installed. The extent of damage to the wood surface after such

a short exposure has yet to be determined. However,

Table 15–2. Erosion of earlywood and latewood on smooth planed surfaces of various wood species

after outdoor exposurea

Erosion (μm) after various exposure timesc

Avg 4 years 8 years 10 years 12 years 14 years 16 years

Wood species SGb LW EW LW EW LW EW LW EW LW EW LW EW

Western redcedar

 plywood

— 170 580 290 920 455 1,095 615 1,165 805 1,355 910 1,475

Redwood plywood — 125 440 295 670 475 800 575 965 695 1,070 845 1,250

Douglas-fir plywood— 110 270 190 390 255 500 345 555 425 770 515 905

Douglas-fir 0.46 105 270 210 720 285 905 380 980 520 1,300 500 1,405

Southern Pine 0.45 135 320 275 605 315 710 335 710 445 1,180 525 1,355

Western redcedar 0.31 200 500 595 1,090 765 1,325 970 1,565 1,160 1,800 1,380 1,945

Redwood 0.36 165 405 315 650 440 835 555 965 670 1,180 835 1,385

Loblolly pine 0.66 80 205 160 345 220 490 — — — — — —

Western redcedar 0.35 115 495 240 1,010 370 1,225 — — — — — —

Southern Pine 0.57 95 330 180 640 195 670 — — — — — —

Yellow-poplar 0.47 — 220 — 530 — 640 — — — — — —

Douglas-fir 0.48 75 255 175 605 225 590 — — — — — —

Red oak 0.57 180 245 340 555 440 750 — — — — — —

Ponderosa pine 0.35 130 270 315 445 430 570 Decay Decay Decay Decay — —

Lodgepole pine 0.38 105 255 265 465 320 580 475 745 560 810 — —

Engelmann spruce 0.36 125 320 310 545 390 650 505 795 590 950 — —

Western hemlock 0.34 145 320 310 575 415 680 515 1,255 600 1,470 — —

Red alder 0.39 — 295 — 545 — 620 — 920 — 955 — —

a

Data from three studies are shown. Specimens were exposed vertically facing south. Radial surfaces

 were exposed with the grain vertical.

b

SG is specific gravity.

c

All erosion values are averages of nine observations (three measurements of three specimens).

 EW denotes earlywood; LW, latewood.
15–9

long-term outdoor exposure of panels that had been preweathered for 1, 2, 4, 8, or 16 weeks before being painted

showed a direct relationship between preweathering time and

the time when the paint started to peel. For panels that had

been preweathered for 16 weeks, the paint peeled within

3 years; for panels preweathered for only 1 week, the paint

peeled after 13 years. Panels that were not preweathered

showed no sign of peeling after 13 years. The paint system

was a commercial oil–alkyd primer with two acrylic latex

top-coats over planed all-heartwood vertical-grain western

redcedar.

Several other wood species were tested in addition to western

redcedar. In general, there was a direct relationship between

wood specific gravity and amount of time the wood could be

exposed without a deleterious effect on paint performance.

More dense wood species such as Douglas-fir and the southern pines showed no preweathering effect until they had been

preweathered for 3 to 4 weeks. For species with low specific

gravity, it is essential to finish the wood as soon as possible

after installation, or better yet, to preprime it before installation. The wood could be back-primed at the same time (see

section on back-priming).

The best remedy for restoring a weathered wood surface is to

sand it with 50- to 80-grit sandpaper. Sanding can easily be

done by hand using a sheet rock sander. This tool consists

of a sanding pad attached to a pole with a swivel connection.

Large areas of siding can be quickly scuff-sanded to remove

the weathered surface. Even if wood has not been weathered,

scuff sanding provides a much better surface for painting,

increases the service life of the paint, and improves the paint

bond.

Effect on Wood Finishes

Finishes used on wood also undergo surface photodegradation because the primary ingredient that holds a paint film

together or seals the wood surface is an organic polymer and

thus is susceptible to photo-oxidative degradation. The UV

radiation in sunlight breaks down the polymer in paint,

causing a slow erosion similar to that which occurs on

wood. The pigments in paint are not usually affected by UV

radiation. Therefore, as film-forming finishes such as paints

or solid-color stains weather, they do so by the slow breakdown of the polymer, which loosens the pigments. The

surface becomes chalky because of the loose pigments. Eventually, these pigments and the degraded polymer erode from

the surface. The rate of weathering primarily depends on the

resistance of the polymer to UV radiation. Paints and stains

based on acrylic polymers are more UV-resistant than those

based on oil and oil–alkyds. Weathering is strictly a surface

phenomenon on the finish, and as with wood, a painted

surface can be attacked by mildew.

Control of Water or

Moisture in Wood

Moisture Content

The moisture content of wood is the amount of water contained in the wood (see Ch. 3). Moisture content includes

both water absorbed into the wood cell wall and free water

within the hollow center of the cell, and it is expressed as a

weight percentage. The amount of water that wood can absorb (that is, that can be bound in the cell wall) depends on

the wood species; most species can absorb about 30% water.

This limit to the amount of water that can be bound in the

wood cell wall is called the fiber saturation point. Wood can

reach the fiber saturation point by absorbing either liquid

water or water vapor.

The amount of water vapor that can be absorbed primarily

depends on the relative humidity (RH) of the surrounding

air. If wood is stored at zero RH, the moisture content will

eventually reach 0%. If wood is stored at 100% RH, it will

eventually reach fiber saturation (about 30% water). Of

course, if kept at a constant RH between these two extremes,

the wood will reach a moisture content between 0 and 30%.

The moisture content is controlled by the RH, and when the

moisture content is in balance with the RH, the wood is at

its equilibrium moisture content. This rarely happens because as the RH changes so does the moisture content of the

wood, and atmospheric RH is almost always changing. It

varies through daily and seasonal cycles, thus driving the

moisture content of wood through daily and seasonal cycles.

See Chapter 3 for a more detailed discussion of moisture

content and equilibrium moisture content.

Equilibrium moisture content cannot be changed through the

application of finishes. The only way that finishes can affect

absorption of water or water vapor is to affect the rate at

which absorption occurs. Finishes can decrease daily and

seasonal moisture absorption and desorption, but they do not

Figure 15–7. Weathered surfaces of softwood after

15 years of exposure in Madison, Wisconsin.
 15–10

change the equilibrium moisture content. See the section on

moisture-excluding effectiveness of finishes for discussion of

this topic.

Wood exposed outdoors cycles around a moisture content of

about 12% in most areas of the United States. In the Southeast, average moisture content can be slightly higher and in

the Southwest, the average can be lower (9%) (Ch. 12,

Table 12–1). Daily and annual moisture content will vary

from these average values. In general, for wood exposed

outdoors, moisture content decreases during the summer and

increases during the winter. (For wood in interior use in

northern climates, moisture content increases during the

summer and decreases during the winter.) Even in very

humid areas, the RH is rarely high enough for long enough

to bring the moisture content of wood above 20%. Wood

that is warmed by the sun experiences a virtual RH far below

the ambient RH. Wood will dry faster and become drier than

expected given the ambient RH. This is why checking often

occurs on decking boards; the surface is much drier than the

rest of the board. Shrinkage of the top portion of the board

commensurate with this dryness goes beyond the elastic

limit of the wood at the surface and checks form parallel to

the grain.

As mentioned, fiber saturation is the greatest amount of water

that can be absorbed by wood via water vapor absorption.

This absorption is rather slow compared with the moisture

changes that can occur through absorption of liquid water.

Liquid water can quickly cause the wood to reach fiber saturation, and it is the only way to bring the moisture content

of wood above fiber saturation. Liquid water must be present.

Liquid water can reach wood through windblown rain, leaks,

condensation, dew, melting ice and snow, and other ways.

As wood continues to absorb water above its fiber saturation

point, the water is stored in the hollow center of the wood

cell; when all the air in the hollow center has been replaced

by water, the wood is waterlogged and moisture content can

be as high as 200%. The sources and ways by which wood

can get wet sometimes seem endless. The result is always

the same—poor performance, both of the wood and of

the finish.

Wood decay (rot) cannot occur unless the moisture content of

the wood is near fiber saturation. This requires water. Water

also causes peeling of paint. Even if other factors are involved, water accelerates paint degradation. Fortunately, the

moisture content of lumber can be controlled. But all too

often, this critical factor is neglected during the construction

and finishing processes. It is best to paint wood when its

average moisture content is about that expected to prevail

during its service life. Painting at this time can prevent a

drastic change in wood dimension, which occurs as wood

equilibrates to ambient conditions. The moisture content and

thus the dimensions of the piece will still fluctuate somewhat, depending on the cyclic changes in atmospheric RH,

but the dimensional change will not be excessive. Therefore,

film-forming finishes (such as paints) will not be stressed

unnecessarily, and service life should be better.

The recommended moisture content for wood used in exterior applications varies somewhat depending on climatic

conditions. These conditions include, but are not limited to,

coastal exposure, rainfall, elevation, and wind. However,

problems associated with changes in moisture content should

be minimized if the moisture content is between 9% and

14%. Most lumber is kiln dried to less than 20% moisture

content before shipment. Material that has been kept dry

during shipment and storage at the construction site should

be close to the desired moisture content.

Lumber is often marketed for construction purposes in the

kiln-dried condition, but it is sometimes exposed to moisture later during shipping, storage, and/or at the construction

site. Wood that is obviously wet and sometimes discolored

may not give optimum performance. If wet wood is used, it

will dry in service, but shrinkage and accompanying warping, twisting, and checking can occur. If the moisture content

of the wood exceeds 20% when the wood is painted, the risk

of blistering and peeling is increased. Moreover, dark water-soluble extractives in woods like redwood and western

redcedar may discolor the paint shortly after it is applied.

Plywood, particleboard, hardboard, and other wood composites undergo a significant change in moisture content during

manufacture. Frequently, the moisture content of these materials is not known and may vary depending on the manufacturing process. To improve the service life of the finish,

wood composites should be conditioned prior to finishing,

as are other wood products.

Water Repellents

The control of water and/or water vapor requires different

types of finishes. Water repellent is a generic name for a wide

variety of sealers and wood treatments that change the surface

properties of wood so that the wood sheds liquid water.

Water repellents have almost no effect on the transmission of

water vapor; that is, they have little effect on the change in

wood moisture content caused by changes in RH. Water

repellents work exceptionally well to retard the absorption of

water into the end grain of wood, the most absorptive of the

wood surfaces. Although water repellents do not stop all

water absorption, they are an excellent treatment for wood

used outdoors because they inhibit the absorption of liquid

water during rain, yet allow the wood to dry after rain.

Water-repellent formulations usually include a mildewcide or

a wood preservative and are then referred to as water-repellent

preservatives. These finishes are discussed in greater detail in

later sections of this chapter.

Finish Moisture-Excluding

Effectiveness

The moisture-excluding effectiveness of a finish is a measure

of its resistance to the transmission of water vapor to the

finished wood. It is basically a measure of the permeability of

a coating to water vapor. It is not a measure of water repellency. Moisture-excluding effectiveness is determined by

comparing the moisture pickup of a coated specimen with
15–11

that of a matched uncoated control. A coating that blocks all

moisture would be 100% effective; however, no coating is

entirely moisture proof. There is as yet no way of completely

keeping moisture out of wood that is exposed to prolonged

periods of high RH. As wood is exposed to varying RH

conditions, it absorbs or desorbs moisture depending on the

RH. A coating that is effective at excluding moisture merely

slows absorption or desorption of moisture; it cannot change

the equilibrium moisture content (Ch. 3).

To achieve a high degree of moisture-excluding effectiveness,

it is necessary to form a moisture barrier on the wood surface.

In addition to repelling liquid water, this film will slow the

diffusion of water vapor into or out of the wood. Waterrepellent treatments differ from moisture-excluding coatings

in that they do not slow the absorption–desorption of water

vapor. They repel liquid water only. For example, a waterrepellent treatment, which may have no moisture-excluding

effectiveness against water vapor, might have more than 60%

water repellency when tested using standard immersion tests.

The high degree of protection provided by water repellents

and water-repellent preservatives to short periods of wetting

by liquid water is the major reason they are recommended for

exterior finishing.

The protection afforded by coatings in excluding moisture

from wood depends on a great number of variables. Among

them are coating film thickness, defects and voids in the

film, type of pigment, chemical composition of the oil or

polymer, volume ratio of pigment to vehicle (pigment volume concentration), vapor-pressure gradient across the film,

and length of exposure. Values in Table 15–3 indicate the

range in protection against moisture in vapor form for some

conventional finish systems when exposed to continuous

high humidity. The degree of protection provided also

depends on the kind of exposure.

Porous paints, such as latex paints and low-luster (flat) or

breather-type oil-based paints formulated at a pigment volume concentration usually above 40%, afford little protection

against moisture. These paints permit rapid entry of water

vapor and water from dew and rain unless applied over a

nonporous primer or pretreated with a paintable waterrepellent preservative. In addition to being porous, latex

finishes contain surfactants that can encourage absorption of

water into the coating and wood, particularly just after the

coating has been applied. It is thought that these surfactants

wash out of the coating after a short time, but detailed information on this is not available.

The moisture-excluding effectiveness of coatings changes

only slightly with age. As long as the original appearance

and integrity of the coatings are retained, most effectiveness

remains. Paint that is slowly fading or chalking will remain

effective at excluding moisture; the paint is still effective if

there is a glossy film underneath the chalk (which can be

removed by rubbing). Deep chalking, checking, or cracking

indicates serious impairment of moisture-excluding

effectiveness.

The numerical values for percentage of effectiveness in

Table 15–3 should be considered relative rather than absolute

because the percentage of effectiveness varies substantially

with exposure to moisture conditions. The values for effective coatings (≥60%) are reliable in the sense that they can be

reproduced closely on repeating the test; values for ineffective

coatings (<20%) must be regarded as rough approximations

only. These percentages are based on average amounts of

moisture absorbed per unit surface area by newly coated and

uncoated wood panels. In addition, the values were determined from specimens coated on all sides. Since wood used

in normal construction is seldom coated on all sides, the

actual absorption–desorption will differ from the values listed

in Table 15–3.

Effect of Finish on Liquid Water

and Water Vapor Absorption

The various dimensions of wood and wood-based building

materials are constantly changing because of changes in

moisture content, which in turn are caused by fluctuations in

atmospheric RH as well as the periodic presence of free moisture such as rain or dew. Water repellents provide protection

against liquid water but are ineffective against water vapor

(humidity). Film-forming finishes such as paint and varnish

shed liquid water and retard the absorption of water vapor,

provided the films are thick enough. Because film-forming

wood finishes like paint will last longer on stable wood, it is

desirable to stabilize the wood by finishing it with a waterrepellent preservative as the first step in the finish system. As

mentioned previously, there is no way to completely eliminate the changing moisture content of wood in response to

changing RH. The coating simply slows down the rate at

which the wood changes moisture content.

Film-forming finishes slow both the absorption of water

vapor and drying of wood (Fig. 15–8). Aluminum flake paint

is a laboratory formulation designed to block water vapor

movement into wood. It is about 80% effective at blocking

water vapor absorption compared with water vapor absorption in an unpainted control. Almost all common wood

finishes, both oil and latex, are less effective than aluminum

flake paint at blocking water vapor absorption. However, oilbased formulations are more effective than latex formulations.

The coating slows the rate of drying. In cyclic high and low

RH, the moisture content of the wood increases with time

(Fig. 15–9).

The moisture-excluding effectiveness described in the previous section was obtained from specimens consisting of single

pieces of wood that were painted on all sides. In normal

construction, wood is seldom coated on all sides. In addition

to absorbing water vapor, paint coatings usually crack at the

joint between two pieces of wood, particularly if they have

different grain orientations (and thus different dimensional

stability). Water enters the wood through these cracks and is

trapped by the coating, thus causing an increase in moisture

content much higher than that shown in Figure 15–9.
 15–12

Table 15–3. Moisture-excluding effectiveness of various finishes on ponderosa pinea

No.

Moisture-excluding

effectiveness (%) No.

Moisture-excluding

effectiveness (%)

Finish

of

coats

1

day

7

days

14

days Finish

of

coats

1

day

7

days

14

days

Linseed oil sealer (50%) 1 7 0 0 Alkyd house primer paint 1 85 46 24

2 15 1 0 (tall maleic alkyd resin) 2 93 70 49

3 18 2 0 3 95 78 60

Linseed oil 1 12 0 0 Enamel paint, satin 1 93 69 50

2 22 0 0 (soya/tung/alkyd; 2 96 83 70

3 33 2 0 interior/exterior) 3 97 86 80

Tung oil 1 34 0 0 4 98 92 85

2 46 2 0 5 98 93 88

3 52 6 2 6 98 94 89

Paste furniture wax 1 6 0 0 Floor and deck enamel 1 80 31 18

2 11 0 0 (phenolic alkyd) 2 89 53 35

3 17 0 0 3 92 63 46

Water repellent 1 12 0 0 Shellac 1 65 10 3

2 46 2 0 2 84 43 20

3 78 27 11 3 91 64 42

Latex flat wall paint 1 5 0 0 4 93 75 58

(vinyl acrylic resin) 2 11 0 0 5 94 81 67

3 22 0 0 6 95 85 73

Latex primer wall paint 1 78 37 20 Nitrocellulose lacquer 1 40 4 1

(butadiene–styrene resin) 2 86 47 27 2 70 22 8

3 88 55 33 3 79 37 19

Alkyd flat wall paint 1 9 1 0 Floor seal 1 31 1 0

(soya alkyd) 2 21 2 0 (phenolic resin/tung oil) 2 80 37 18

3 37 5 0 3 88 56 35

Acrylic latex house 1 43 6 1 Spar varnish 1 48 6 0

primer paint 2 66 14 2 (soya alkyd) 2 80 36 15

3 72 20 4 3 87 53 30

Acrylic latex flat 1 52 12 5 Urethane varnish 1 55 10 2

house paint 2 77 28 11 (oil-modified) 2 83 43 23

3 84 39 16 3 90 64 44

Solid-color latex stain 1 5 0 0 4 91 68 51

(acrylic resin) 2 38 4 0 5 93 72 57

3 50 6 0 6 93 76 62

Solid-color oil-based stain 1 45 7 1 Aluminum flake pigmented 1 90 61 41

(linseed oil) 2 84 48 26 urethane varnish 2 97 87 77

3 90 64 42 (oil-modified) 3 98 91 84

FPL natural finish (linseed- 1 62 14 3 4 98 93 87

oil-based semitransparent 2 70 21 6 5 98 94 89

stain) 3 76 30 11 6 99 95 90

Semitransparent oil-based 1 7 0 0 Polyurethane finish, clear 1 48 6 0

stain (commercial) 2 13 0 0 (two components) 2 90 66 46

3 21 1 0 3 94 81 66

Marine enamel, gloss (soya

alkyd)

1

2

79

91

38

66

18

46

Polyurethane paint, gloss (two

components)

1

2

91

94

66

79

44

62

3 93 74 57 3 96 86 74

Paraffin wax, brushed 1 97 82 69

Paraffin wax, dipped 1 100 97 95

a

Sapwood was initially finished and conditioned to 26°C (80°F) and 30% RH, then exposed to the same temperature and

90% RH.
15–13

The paint film inhibits drying, as shown. This retardation of

drying can have a drastic effect on the durability of painted

wood fully exposed to the weather. The moisture content of

the wood can approach the range where decay fungi can

become active. This type of wood paint failure usually occurs

on painted fences and porch railings that are fully exposed to

the weather (Fig. 15–10). Applying a water-repellent preservative or priming the end grain of wood used in these

applications inhibits the absorption of water at the end grain

and thus works in concert with the coating to keep the

wood dry.

For a coating to be effective in minimizing moisture content

changes in the wood, it must be applied to all surfaces,

particularly the end grain. The end grain of wood absorbs

moisture much faster than does the face grain, and finishes

generally fail in the end grain first (Fig. 15–11). Coatings

with good moisture-excluding effectiveness that are applied

to only one side of the wood will cause unequal sorption of

moisture, increasing the likelihood that the wood will cup

(warp). When finishing siding, it is important to allow the

back side of the wood to dry, particularly if it is finished

with paint with high moisture-excluding effectiveness. Applying a water-repellent preservative or primer to the end

grain and back of siding (see section on back-priming) prior

to installing the siding improves resistance to water yet

allows the siding to dry. Cupping can be minimized by

using vertical-grain lumber and by minimizing the

aspect ratio.

In those houses where moisture moves from the living quarters to the outside wall because of the lack of a vapor barrier

Figure 15–8. Change in moisture content of ponderosa

pine sapwood finished with three coats of aluminum

pigmented alkyd paint and exposed to 90% and 30% RH

at 26 ̊C (80 ̊F), compared with moisture content of

unfinished wood.

Figure 15–9. Change in moisture content of ponderosa

pine sapwood finished with three coats of aluminum

pigmented alkyd paint and exposed to alternating cycles

of 90% and 30% RH at 26 ̊C (80 ̊F), compared with

moisture content of unfinished wood.

Figure 15–10. Decay in wood railing fully exposed

to weather.

Figure 15–11. Paint failure at ends of boards.
 15–14

(or a poor vapor barrier), the application of moistureexcluding finishes to the outside will not prevent paint

peeling. In fact, finishes with higher moisture-excluding

effectiveness are more prone to fail by peeling because they

trap moisture.

Types of Exterior

Wood Finishes

The types of exterior finishes for wood are separated into two

groups, those that penetrate wood and those that form a film.

As a general rule, penetrating finishes tend to give a more

“natural” look to the wood. That is, they allow some of the

character of the wood to show through the finish. Also, in

general, the more natural a finish, the less durable it is.

Natural finishes may be penetrating finishes such as semitransparent stains or film-forming finishes such as varnish.

The penetrating natural finishes generally give better performance and are easier to refinish. This section also addresses weathered wood as a “finish.”

The properties, treatment, and maintenance of exterior finishes are summarized in Table 15–4. The suitability and

expected life of the most commonly used exterior finishes on

several wood and wood-based products are summarized in

Table 15–5. The information in these tables should be considered as a general guideline only. Many factors affect the

performance and lifetime of wood finishes.

Table 15–4. Initial application and maintenance of exterior wood finishesa

Initial application Maintenance

Finish Process Cost Appearance of wood Process Cost Service lifeb

Water-repellent

preservative

Brushing Low Grain visible; wood

brown to black, fades

slightly with age

Brush to remove

surface dirt;

remove mildew

Low 1–3 years

Waterborne

preservativec

Pressure

(factory applied)

Medium Grain visible; wood

greenish or brownish,

fades with age

Brush to remove

surface dirt;

remove mildew

Nil, unless

stained or

painted

None, unless

stained, or

painted

Organic solvent

preservatived

Pressure, steeping,

dipping, and

brushing

Low to

medium

Grain visible; color as

desired

Brush and

reapply

Medium 2–3 years

or when

preferred

Water repellente One or two brush

coats of clear

material or, preferably, dip application

Low Grain and natural

color visible, becoming darker and

rougher textured with

age

Clean and

reapply

Low to

medium

1–3 years

or when

preferred

Semitransparent

stain

One or two brush

coats

Low to

medium

Grain visible; color as

desired

Clean and

reapply

Low to

medium

3–6 years

or when

preferred

Clear varnish Three coats

(minimum)

High Grain and natural

color unchanged if

adequately maintained

Clean, sand, and

stain bleached

areas; apply two

more coats

High 2 years or at

breakdown

Paint and solidcolor stainBrushing: water

repellent, prime,

and two top-coats

Medium

to high

Grain and natural

color obscured

Clean and apply

top coat, or

re-move and

repeat initial

treatment if

damaged

Medium 7–10 years

for paint;f

3–7 years for

solid-color

stain

a

Compilation of data from observations of many researchers.

b

For vertical exposure.

c

Although wood treated with waterborne preservative may be left unfinished, it is best to finish it with water-

 repellent preservative or semitransparent stain. See maintenance of water repellent and semitransparent stain.

d

Pentachlorophenol, bis(tri-n-butyltin oxide), copper naphthenate, copper-8-quinolinolate, and similar materials.

e

With or without added preservatives. Addition of preservative helps control mildew growth.

f

If top-quality acrylic latex top-coats are used.
15–15

Table 15–5. Suitability and expected service life of finishes for exterior wood surfacesa

Paint and solid-color stain

Water-repellent

preservative and oil Semitransparent stain

Expected lifed

(years)

Type of exterior wood surface

SuitabilityExpected

lifeb

 (years) Suitability

Expected

lifec (years) Suitability Paint

Solid-color

stain

Siding

Cedar and redwood

Smooth (vertical grain) High 1–2 Moderate 2–4 High 4–6 3–5

Rough-sawn High 2–3 High 5–8 Moderate 5–7 4–6

Pine, fir, spruce

Smooth (flat grain) High 1–2 Low 2–3 Moderate 3–5 3–4

Rough (flat grain) High 2–3 High 4–7 Moderate 4–6 4–5

Shingles

Sawn High 2–3 High 4–8 Moderate 3–5 3–4

Split High 1–2 High 4–8 — 3–5 3–4

Plywood (Douglas-fir and

Southern Pine)

Sanded Low 1–2 Moderate 2–4 Moderate 2–4 2–3

Textured (smooth-sawn) Low 1–2 Moderate 2–4 Moderate 3–4 2–3

Textured (rough-sawn) Low 2–3 High 4–8 Moderate 4–6 3–5

MDO plywood, cedar and

redwoode

— — — — Excellent 6–8 5–7

Sanded Low 1–2 Moderate 2–4 Moderate 2–4 2–3

Textured (smooth-sawn) Low 1–2 Moderate 2–4 Moderate 3–4 2–3

Textured (rough-sawn) Low 2–3 High 5–8 Moderate 4–6 3–5

Hardboard, medium densityf

Smooth-sawn

Unfinished — — — — High 4–6 3–5

Preprimed — — — — High 4–6 3–5

Textured

Unfinished — — — — High 4–6 3–5

Preprimed — — — — High 4–6 3–5

Millwork (usually pine)g Highh — Moderate 2–3 High 3–6 3–4

Decking

New (smooth-sawn) High 1–2 Moderate 2–3 Low 2–3 1–2

Weathered (rough-sawn) High 2–3 High 3–6 Low 2–3 1–2

Glued-laminated members

Smooth-sawn High 1–2 Moderate 3–4 Moderate 3–4 2–3

Rough-sawn High 2–3 High 6–8 Moderate 3–5 3–4

Oriented strandboard — — Low 1–3 Moderate 2–4 2–3

a

Data were compiled from observations of many researchers. Expected life predictions are for average location in

 continental United States; expected life will vary in extreme climates or exposure (such as desert, seashore, and

 deep woods).

b

Development of mildew on surface indicates need for refinishing.

c

Smooth, unweathered surfaces are generally finished with only one coat of stain. Rough-sawn or weathered sur-

 faces, which are more adsorptive, can be finished with two coats; second coat is applied while first coat is still wet.

d

Expected life of two coats, one primer and one top-coat. Applying second top-coat (three-coat job) will

 approximately double the life. Top-quality acrylic latex paints have the best durability.

e

Medium-density overlay (MDO) is generally painted.

f

Semitransparent stains are not suitable for hardboard. Solid-color stains (acrylic latex) will perform like paints.

 Paints are preferred.

g

Windows, shutters, doors, exterior trim.

h

Exterior millwork, such as windows, should be factory treated according to Industry Standard IS4–99 of the Window

 and Door Manufacturer’s Association. Other trim should be liberally treated by brushing before painting.
 15–16

Weathered Wood as Natural Finish

The simplest finish for wood is that created by the weathering process. Without paint or treatment of any kind, wood

surfaces gradually change in color and texture, and they may

stay almost unaltered for a long time if the wood does not

decay. Generally, dark-colored woods become lighter and

light-colored woods become darker. As weathering continues, all woods become gray because of the loss of colored

components from the wood surface and the growth of mildew. As the surface erodes, it becomes uneven because of

the different erosion rates of earlywood and latewood.

(Fig. 15–6).

Although leaving wood to weather to a natural finish may

seem like an inexpensive low-maintenance alternative to

finishing, there are many problems to this approach. To

avoid decay, wood must be all heartwood from a decayresistant species such as redwood or western redcedar.

Wood should have vertical grain to decrease the potential for

splitting, grain raising, and cupping. Composite wood

products, such as plywood, must never be left unprotected to

weather. The surface veneer of plywood can be completely

destroyed within 10 years if not protected from weathering.

Figure 15–12 shows weathering of unfinished plywood; the

intact portion of the plywood (left) had been covered with a

board to give a board-and-batten appearance.

To allow a wood structure to weather to a natural finish, the

structure must be designed to keep the wood from getting

wet from wind-driven rain (for example, wide roof overhangs). In most climates in the United States, exterior wood

develops blotchy mildew growth and there is no protection

against surface erosion or decay. It is very difficult to obtain

the silvery-gray weathered patina that weathering can give.

The climate along the coastal regions of New England and in

some high mountains seems to encourage the development of

this finish. Even when the climatic conditions favor the

development of a weathered finish, it takes several years to

achieve an even silvery-gray appearance.

Penetrating Wood Finishes

Penetrating finishes constitute a broad classification of natural

wood finishes that do not form a film on the wood surface.

Penetrating finishes are classified as (a) transparent or clear

systems, (b) lightly colored systems, (c) pigmented or semitransparent systems, and (d) oils.

Transparent or Clear Finishes

Penetrating transparent or clear finishes are generally a type of

water repellent or water-repellent preservative. Waterrepellent preservatives may be used as a natural finish. They

differ from water repellents in that they contain a fungicide

such as 3-iodo-2-propynyl butyl carbamate. As with water

repellents, water-repellent preservatives contain a small

amount of wax, a resin, or a drying oil. They were traditionally formulated using a solvent such as turpentine or mineral

spirits, but they are presently available in a wide range of

other solvent systems, including waterborne formulations.

Penetrating finishes that use paraffin oil as the solvent system

are also available. These formulations penetrate wood like

solventborne formulations do and the oil helps improve

water repellency. Since penetrating finishes with paraffin oil

are usually formulated without any volatile solvents, they

meet air quality requirements. (See section on VOCcompliant finishes.) They are usually a good value because

virtually all of what comes in the can ends up in the wood.

Water-repellent preservatives maintain the original appearance of the wood, but they are not very durable. Treating

wood surfaces with a water-repellent preservative will protect

wood exposed outdoors with little initial change in appearance. A bright, golden-tan color can be achieved with most

wood species. The treatment decreases warping and cracking,

prevents water staining at edges and ends of wood siding,

and helps control mildew growth. The first application of a

water-repellent preservative may protect exposed wood surfaces for only l to 2 years, but subsequent reapplications may

last 2 to 4 years because the weathered boards absorb more

finish. When a surface starts to show blotchy discoloration

caused by extractives or mildew, it should be cleaned with a

commercial cleaner or liquid household bleach and detergent

solution, allowed to dry, and retreated.

Caution: Because of the toxicity of some fungicides

in water-repellent preservative solutions and some

semitransparent stains, care should be exercised to

avoid excessive contact with the solution or its vapor. Shrubs and plants should also be protected

from accidental contamination.

Paintable water-repellent preservatives may also be used as a

treatment for bare wood before priming and painting or in

areas where old paint has peeled and the bare wood is exposed, particularly around butt joints or in corners. This

treatment keeps rain or dew from penetrating into the wood,

especially at joints and end grain, and thus decreases shrinking and swelling of the wood. As a result, less stress is

placed on the paint film and its service life is extended

Figure 15–12. Front view of exterior grade of plywood

siding after 10 years of exposure.
15–17

(Fig. 15–13). This stability is achieved by the small amount

of wax present in water-repellent preservatives. The wax

decreases the capillary movement or wicking of water up the

back side of lap or drop siding. The fungicide inhibits decay.

A large number and variety of waterborne penetrating clear

finishes are available for use on wood. The formulations of

these finishes are generally proprietary, and it is difficult to

determine the nature of these finishes. These formulations are

usually water emulsions of synthetic polymers. The polymers do not penetrate the lateral surface of the wood very

well, but they can change the surface properties. The polymer

helps seal the surface and provides some water repellency.

The formulations may include additional additives such as

UV stabilizers, additional water repellents, mildewcides, and

colorants.

Lightly Colored Finishes

Traditional solventborne formulations of water-repellent

preservatives did not contain any coloring pigments. Therefore, the resulting finish varied little from the original color

of the wood. Many of the newer formulations are slightly

colored and have other additives such as UV stabilizers. As

with traditional formulations, the preservative also prevents

wood from darkening (graying) through mildew growth.

These lightly colored finishes may be water- or solventborne

formulations. The color may be obtained from dyes or finely

ground pigment. Although they are still classified as a

penetrating finish or sealer for wood, many of the newer

formulations form a slight film on the wood surface. This is

particularly true for the waterborne formulations. As with the

uncolored clear finishes, the durability of lightly colored

finishes is somewhat limited. Although their durability is

improved by the inclusion of UV stabilizers and finely

ground pigment, lightly colored finishes still lack sufficient

pigment to stop UV degradation of the wood.

Semitransparent Stains

Inorganic pigments can also be added to water-repellent

preservative solutions to provide special color effects, and the

mixture is then classified as a semitransparent stain. A semitransparent stain is a pigmented penetrating stain. Colors

that match the natural color of the wood and extractives are

usually preferred. The addition of pigment to the finish helps

stabilize the color and increase the durability of the finish,

but they give a less natural appearance because the pigment

partially hides the original grain and color of the wood.

Semitransparent stains are generally much more durable than

are water-repellent preservatives and provide more protection

against weathering. These stains slow weathering by retarding the alternate wetting and drying of wood, and the pigment particles on the wood surface minimize the degrading

effects of sunlight. The amount of pigment in semitransparent

stains can vary considerably, thus providing different degrees

of protection against UV degradation and masking of the

original wood surface. Higher pigment concentration yields

greater protection against weathering, but it also hides the

natural color of the wood.

Solventborne oil-based semitransparent penetrating stains

penetrate the wood surface, are porous, and do not form a

surface film like paints. As a result, they will not blister or

peel even if moisture moves through the wood. Semitransparent penetrating stains are only moderately pigmented and

do not totally hide the wood grain. Penetrating stains are

alkyd or oil based, and some may contain a fungicide as well

as a water repellent. Moderately pigmented latex-based

(waterborne) stains are also available, but they do not penetrate the wood surface as well as the oil-based stains. Some

latex-based formulations are oil modified. These formulations

give better penetration than do the unmodified formulations.

Semitransparent stains are most effective on rough lumber or

rough-sawn plywood surfaces. They may be used on smooth

surfaces but have less than half the service life compared with

that on rough surfaces. Stains are available in a variety of

colors and are especially popular in the brown or red earth

tones because these give a natural or rustic appearance to the

wood. They are an excellent finish for weathered wood.

Semitransparent stains are not effective when applied over a

solid-color stain or old paint.

Many resin and paint manufacturers have tried to achieve the

properties of solventborne semitransparent stains using

waterborne formulations. Some of these finishes achieved a

semitransparent appearance by the formation of a rather thin

coating on the wood surface. The resins used in these formulations did not penetrate the wood surface. Therefore, these

finishes were prone to fail within a few years through flaking

Figure 15–13. Effect of water-repellent preservative

treatment. A, Window sash and frame treated with

a water-repellent preservative and then painted;

B, window sash and frame not treated before painting.

Both window sash–frame sets were weathered for

5 years.
 15–18

of the thin coating from the surface. When the surfaces were

refinished, the subsequent finish increased the film thickness

and obscured the original appearance of the wood. Because

the film buildup is not sufficient to give the good performance provided by a film-forming finish, waterborne semitransparent stains generally continue to fail by flaking. Many

new formulations are modified with oil–alkyds. The oil

penetrates the surface, thus improving the performance of the

finish. Efforts are continuing to improve these formulations;

it is advisable to check with a local paint supplier for the

latest developments in this area.

Oils

Drying oils, such as linseed and tung, are sometimes used

by themselves as natural finishes. Such oils are not recommended for exterior use unless they are formulated with a

mildewcide. These oils are natural products and therefore

provide food for mildew. When drying oils are used on

highly colored woods such as redwood or the cedars, they

tend to increase problems with mildew.

Film-Forming Finishes

Clear Varnish

Clear varnish is the primary transparent film-forming material

used for a natural wood finish, and it greatly enhances the

natural beauty and figure of wood. However, varnish lacks

exterior permanence unless protected from direct exposure to

sunlight, and varnish finishes on wood exposed outdoors

without protection will generally require refinishing every

l to 2 years. Thus, varnish is not generally recommended for

exterior use on wood. Varnish coatings embrittle by exposure to sunlight and develop severe cracking and peeling.

Varnish used in areas that are protected from direct sunlight

by an overhang or used on the north side of the structure will

last considerably longer. However, even in protected areas, a

minimum of three coats of varnish is recommended, and the

wood should be treated with a paintable water-repellent

preservative before finishing. The use of pigmented stains

and sealers as undercoats will also contribute to greater life of

the clear finish. In marine exposures, up to six coats of varnish should be used for best performance.

Pigmented Varnish

Several finish manufacturers have formulated varnish with

finely ground inorganic pigments that partially block UV

radiation yet allow much of the visible light to pass through

the finish. These products give much better performance than

do traditional clear varnishes, and if a clear film is desired for

exterior use, they may be a better choice. Pigmented varnish

gives excellent performance on structures that are protected

from sunlight by wide overhangs and wooded surroundings.

The degradation of pigmented varnish initially occurs on the

film surface as crazing and checking. These surface checks can

be repaired by refinishing in a timely manner. Eventually,

however, the buildup of coats will block much of the visible

light and the wood will appear dark.

Solid-Color Stains

Solid-color stains are opaque finishes (also called hiding,

heavy-bodied, or blocking) that come in a wide range of

colors and are made with a much higher concentration of

pigment than are semitransparent penetrating stains. As a

result, solid-color stains totally obscure the natural color and

grain of the wood. Solid-color stains (both oil- and latexbased) tend to form a film much like paint, and as a result

they can also peel from the substrate. Both oil and latex

solid-color stains are similar to paints and can usually be

applied over old paint or to unfinished wood if adequately

primed. As with any film-forming finish, good service life

requires 4- to 5-mil dry film thickness.

Paint

Paints are highly pigmented film-forming coatings that give

the most protection to wood. Paints are used for esthetic

purposes, to protect the wood surface from weathering, and to

conceal certain defects. They also provide a cleanable surface.

Of all the finishes, paints provide the most protection for

wood against surface erosion and offer the widest selection of

colors. Paints are the only way to achieve a bright white

finish. A nonporous paint film retards penetration of moisture

and decreases discoloration by wood extractives as well as

checking and warping of the wood. Paint is not a preservative. It will not prevent decay if conditions are favorable for

fungal growth.

Paints do not penetrate the surface of the wood except to fill

cut cells and vessels. They do not penetrate the cell wall of

the wood as do some penetrating finishes. The wood grain is

completely obscured as the surface film is formed. Paints

perform best on vertical-grain lumber of species with low

specific gravity. As with other film-forming finishes, paints

can blister or peel if the wood is wetted or if inside water

vapor moves through the house wall to the wood.

Latex paints are generally easier to use because water is used

in cleanup. They are also porous and thus allow some moisture movement. In comparison, oil-based paints require

organic solvents for cleanup, and some oil-based paints are

resistant to moisture movement. Latex paints mainly formulated with acrylic resins are extremely resistant to weathering

and maintain their gloss better than do oil-based paints.

Such latex paints remain flexible throughout their service

life. Oil-based paints tend to lose gloss within a year or two

and are prone to embrittle over time.

The cost of finishes varies widely depending on the type of

finish and quality (Table 15–4). Within a particular type of

finish (for example, oil-based paint, all-acrylic latex paint,

oil-based solid-color stain), cost usually correlates with

quality. Better quality paints usually contain higher amounts

of solids by weight. Paints with a lower percentage of solids

may cost less by the unit but be more expensive per unit of

solids, and more or heavier coats will have to be applied to

achieve equal coverage. Comparing solids content and price

can be the first criterion for selecting the better value because

only the solids are left on the surface after the solvent
15–19

evaporates. For example, if one paint is 50% solids and costs

$20 and a second paint is 40% solids and costs $18, all

other things being equal the $20 paint is a better value (25%

more solids for about 11% more money). Another criterion is

the amount and type of pigment because these determine the

hiding power of the finish. Paint that contains primarily

titanium dioxide pigment will have better hiding power than

that with calcium carbonate filler. A paint with poor hiding

power may require the application of more coats. Finally, the

type and amount of binder affect the quality of the paint. For

latex paints, all acrylic binders are more weather-resistant

than are vinyl and vinyl–acrylic binders.

Fire-Retardant Coatings

Many commercial fire-retardant coating products are available

to provide varying degrees of protection of wood against fire.

These paint coatings generally have low surface flammability

characteristics and “intumesce” to form an expanded lowdensity film upon exposure to fire, thus insulating the wood

surface from heat and retarding pyrolysis reactions. The

paints have added ingredients to restrict the flaming of any

released combustible vapors. Chemicals may also be present

in these paints to promote decomposition of the wood surface

to charcoal and water rather than the formation of volatile

flammable products. Most fire-retardant coatings are intended

for interior use, but some are available for exterior application. Wood shakes and shingles are often impregnated with a

fire retardant.

Compliance of VOC Finishes

With Pollution Regulations

Volatile organic compounds (VOCs) are those organic materials in finishes that evaporate as the finish dries and/or cures.

These materials are regarded as air pollutants, and the

amount that can be released for a given amount of solids (for

example, binder, pigments) in the paints is now regulated in

many areas. Regulations that restrict the amount of VOCs in

paints have been enacted in many states, including California, New York, Texas, Massachusetts, New Jersey, and

Arizona, and legislation is pending in many others.

The result of such legislation is that all major paint companies have had to either change their paint formulation or

market additional low-VOC formulations. Some smaller

companies have been unaffected by VOC regulations because

they market their products in limited geographic areas outside those affected by existing State and local legislation.

This situation is slated to change soon. Under the 1990 New

Clean Air Act, the U.S. Environmental Protection Agency

(EPA) has been charged to enact a regulation that affects all of

the United States. This regulation will take effect in 1999

and will regulate the amount of VOC in all types of architectural finishes, including paints, solid-color stains, and penetrating finishes, such as semitransparent stains and waterrepellent preservatives.

Existing and pending regulations are a serious concern

throughout the U.S. paint industry, particularly with regard

to a national rule that will affect areas of the country that have

not previously had to comply with VOC regulations. Many

traditional wood finishes may no longer be acceptable, including oil-based semi-transparent stains, oil- and alkydbased primers and top coats, solventborne water-repellents,

and solventborne water-repellent preservatives. Many current

wood finishes, including some latex-based materials, may be

reformulated. These changes affect the properties of the finish,

application, interaction with the wood (for example, adhesion, penetration, moisture-excluding effectiveness), and

possibly durability.

Many penetrating finishes, such as semitransparent stains,

have low solids content (pigment, oils, polymers) levels and

are being reformulated to meet low-VOC regulations. To

meet the VOC requirements, these reformulated finishes may

contain higher solids content, reactive diluents, new types of

solvents and/or cosolvents, or other nontraditional substituents. These low-VOC formulations are prone to form films

rather than penetrate the wood surface. There is little information about the way these new penetrating finishes interact

with the substrate to protect the wood or about the degradation mechanisms of these finishes when exposed to various

outdoor conditions. Because such formulations may not

interact with the wood in the same way as do traditional

finishes, the effect of moisture may be different.

Application of Wood Finishes

Type of Finish

Water-Repellent Preservatives

The most effective method of applying a water repellent or

water-repellent preservative is to dip the entire board into the

solution. However, other application methods can be used if

they are followed by back brushing. It is advantageous to

treat the back side of the siding, particularly with highly

colored wood species. (See section on back-priming.) When

wood is treated in place, liberal amounts of the solution

should be applied to all lap and butt joints, edges and ends

of boards, and edges of panels with end grain. Other areas

especially vulnerable to moisture, such as the bottoms of

doors and window frames, should also be treated. Coverage

is about 6.1 m2/L (250 ft2/gal) on a smooth surface or

3.7 m2/L (150 ft2/gal) on a rough surface. Smooth wood will

usually accept only a single coat; a second coat will not

penetrate the wood. Water-repellent preservative treatment

generally lasts longer on rough surfaces than on smooth

surfaces because more finish penetrates the wood. As a natural finish, the life expectancy of a water-repellent preservative

is only 1 to 2 years, depending upon the wood and exposure.

However, reapplication is easy, particularly on decks and

fences. Multiple coats brush-applied to the point of refusal

(failure to penetrate) will enhance durability and performance

of the wood.

Water-repellent-preservative-treated wood that is painted will

not need retreatment unless the protective paint layer has

peeled or weathered away. The water-repellent preservative

should be applied only to the areas where the paint has

peeled. The water-repellent preservative should be allowed
 15–20

to dry for 3 days, and the peeled area should be reprimed

before it is repainted.

Semitransparent Penetrating Stains

Semitransparent penetrating stains may be brushed, sprayed,

or rolled on, but they must be back-brushed. Brushing works

the finish into the wood and evens out the application so that

there is less chance for lap marks. Semitransparent penetrating stains are generally thin and runny, so application can be

messy. Lap marks may form if stains are improperly applied,

but such marks can be prevented by staining only a small

number of boards or one panel at a time (Fig. 15–14). This

method prevents the front edge of the stained area from drying out before a logical stopping place is reached. Working

in the shade is desirable because the drying rate is slower.

Coverage is usually about 4.9 to 9.8 m2

/L (200 to

400 ft2/gal) on a smooth wood surface and from 2.4 to

4.9 m2/L (100 to 200 ft2/gal) on a rough or weathered

surface. Stains perform much better on rough-sawn wood.

To give penetrating oil-based semitransparent stains a long

life on rough-sawn or weathered lumber, use two coats and

apply the second coat before the first is dry (wet on wet

application). Apply the first coat to a panel or area in a manner to prevent lap marks. Then, work on another area so that

the first coat can soak into the wood for 20 to 60 min. Apply

the second coat before the first coat has dried. If the first coat

dries completely, it may seal the wood surface so that the

second coat cannot penetrate the wood. About an hour after

applying the second coat, use a cloth, sponge, or dry brush

lightly wetted with stain to wipe off excess stain that has not

penetrated into the wood. Otherwise, areas of stain that did

not penetrate may form an unsightly shiny surface film.

Avoid intermixing different brands or batches of stain. Stir

the stain occasionally and thoroughly during application to

prevent settling and color change.

A two-coat system of semitransparent penetrating stain may

last as long as 10 years on rough wood in certain exposures

as a result of the large amount of stain absorbed. By comparison, the life expectancy of one coat of stain on new

smooth wood is only 2 to 4 years; successive recoats last

longer (Table 15–5).

Caution: Sponges or cloths that are wet with oilbased stain are particularly susceptible to spontaneous combustion. To prevent fires, immerse such

materials in water and seal in a water-filled air-tight

metal container immediately after use.

Waterborne Semitransparent Stains

Waterborne semitransparent stains do not penetrate the wood

surface as well as oilborne semitransparent stains, but they

are easy to apply and less likely to form lap marks. These

stains form a thin film, and a second coat will improve their

durability. Apply the second coat any time after the first

has dried.

Solid-Color Stains

Solid-color stains may be applied to a smooth wood surface

by brush, spray, or roller; if the finish is applied by spray or

roller, it is necessary to “back-brush” immediately after

application. Solid-color stains act much like paint. One coat

of solid-color stain is not considered adequate for siding.

Some manufacturers recommend using the first coat as a

primer, but a primer paint might be better, particularly if

there is a possibility for extractives bleed. Two coats of

solid-color stain applied over a quality latex or oil primer

should give service life similar to that of a good paint system. Solid-color stains are not generally recommended for

horizontal wood surfaces such as decks, roofs, and

window sills.

Unlike paint, solid-color stain is subject to lap marks during

application. Latex-based stains are particularly fast-drying

and are more likely to show lap marks than are oil-based

stains. To prevent lap marks, follow the procedures suggested in the section on application of semitransparent penetrating stains.

Paint

Wood and wood-based products should be protected from

sunlight and water while stored prior to delivery to a construction site and while stored on the construction site. The

finish should be applied as soon as possible after the wood is

installed. Surface contamination from dirt, oil, and other

foreign substances must be eliminated. The paint bond with

the wood is greatly increased if the wood is painted within

1 week, weather permitting, after installation (see Weathering—Effect of weathering on paint adhesion). To achieve

maximum paint life, do the following:

1. Treat wood siding and trim with a paintable waterrepellent preservative or water repellent. Water repellents

protect the wood against the absorption of rain and dew

and thus help to minimize swelling and shrinking. Water

repellents can be applied by brushing or dipping. Lap and

butt joints and the edges of panel products such as plywood, hardboard, and particleboard should be especially

well treated because these areas are prone to absorb

Figure 15–14. Lap marks on wood finished with

semitransparent stain.
15–21

moisture, which leads to paint failure. Allow at least three

warm, sunny days for adequate drying before painting the

treated surface. If the wood has been dip treated, allow at

least 1 week of favorable weather before painting.

2. Prime the bare wood after the water-repellent preservative

has dried (see section on back-priming). The primer coat

forms a base for all succeeding paint coats. For woods

with water-soluble extractives, such as redwood and cedar,

primers block the bleed of extractives into the top coat.

Use a primer that is labeled to “block extractives bleed,”

usually a quality alkyd-based paint. Many manufacturers

are also formulating stain-blocking acrylic-latex-based

paints. Allow a latex stain-blocking primer to dry for at

least 24 to 48 h before applying the top coat. If the primer

has not fully cured, extractives may bleed into the top

coat. Apply a primer regardless of whether the top coat is

an oil-based or latex-based paint. For species that are predominantly sapwood and free of extractives, such as pine,

using a quality primer is still necessary to give a good

base for the top coat. Apply enough primer to obscure the

wood grain. Follow the application rates recommended by

the manufacturer. Do not spread the primer too thinly. A

primer coat that is uniform and of the proper thickness

will distribute the swelling stresses that develop in wood

and thus help to prevent premature paint failure.

3. Apply two coats of a good-quality acrylic latex house

paint over the primer. Oil-based, alkyd-based, and vinyl–

acrylic paints can also be used. If it is not practical to

apply two top-coats to the entire house, consider two topcoats for fully exposed areas on the south and west sides

as a minimum for good protection. Areas fully exposed to

sunshine and rain are the first to deteriorate and therefore

should receive two top-coats. On those wood surfaces best

suited for painting, one coat of a good house paint over a

properly applied primer (a conventional two-coat paint

system) should last 4 to 5 years, but two top-coats can

last 10 years (Table 15–5).

Primer will cover about 6.1 to 7.4 m2

/L (250 to

300 ft2/gal) on smooth bare wood; for repainting, coverage

will be about 9.8 m2/L (400 ft2/gal). However, coverage

can vary with different paints, surface characteristics, and

application procedures. Research has indicated that the optimal thickness for the total dry paint coat (primer and two

top-coats) is 0.10 to 0.13 mm (4 to 5 mils) (or about the

thickness of a sheet of newspaper). The quality of paint is

usually, but not always, related to price. Brush application is always superior to roller or spray application, especially for the first coat.

4. To avoid peeling between paint coats, apply the first topcoat within 2 weeks after the primer and the second coat

within 2 weeks of the first. As certain paints weather, they

can form a soaplike substance on their surface that may

prevent proper adhesion of new paint coats. If more than

2 weeks elapse before applying another paint coat, scrub

the old surface with water using a bristle brush or sponge.

If necessary, use a mild detergent to remove all dirt and

deteriorated paint. Then rinse the cleaned wood with water

and allow all surfaces to dry before painting.

5. To avoid temperature blistering, do not apply oil-based

paint on a cool surface that will be heated by the sun

within a few hours. Temperature blistering is most common with thick coats of dark-colored paint applied in cool

weather. The blisters usually show up in the last coat of

paint and occur within a few hours or up to 1 or 2 days

after painting. They do not contain water.

6. Apply latex-based waterborne paints when the temperature

is at least 10°C (50°F); oil-based paint may be applied

when the temperature is at least 4°C (40°F). For proper

curing of latex paint films, the temperature should not

drop below 10°C (50°F) for at least 24 h after paint application. Low temperatures will result in poor coalescence of

the paint film and early paint failure. Some new latex formulations are being developed for application at lower

temperatures. Refer to application instructions on the label

of the paint can.

7. To avoid wrinkling, fading, or loss of gloss of oil-based

paints and streaking of latex paints, do not apply the paint

during autumn days or cool spring evenings when heavy

dews form during the night. Serious water absorption

problems and major finish failure can occur with some

paints when applied under these conditions.

Porches, Decks, and Fences

Exposed flooring on porches is usually painted. Since

porches often get wet from windblown rain, it is particularly

important to pretreat the wood surface with a water-repellent

preservative prior to painting. Use primers and paints specially formulated for porches. These paints are formulated to

resist abrasion and wear.

Many fully exposed decks are more effectively finished with

only a water-repellent preservative or a penetrating-type

semitransparent pigmented stain. Decks finished with these

finishes will need more frequent refinishing than do painted

surfaces, but refinishing is easy because there is no need for

the laborious surface preparation required for painted surfaces

that have peeled. It is essential to limit the application of

semitransparent stain to what the surface can absorb. Roller

and spray application may put too much stain on the horizontal surfaces of decks. The best application method for

such smooth surfaces is by brush. Unless specially formulated for use on decks, solid-color stains should not be used

on any horizontal surface because they lack abrasion

resistance, and because they form a film, they tend to fail by

flaking.

Like decks, fences are fully exposed to the weather and at

least some parts (such as posts) are in contact with the soil.

As a result, wood decay and termite attack are potential

problems. Often in the design of fences, little consideration is

given to protecting exposed end-grain of various fence components or to avoiding trapped moisture. If a film-forming

finish is to be used on a fence, it is extremely
 15–22

important to seal the end grain and protect exposed end-grain

wherever possible. Use lumber pressure-treated with preservatives or naturally durable wood species for all posts and other

fence components that are in ground contact.

In regard to the service life of naturally durable wood species

compared with wood pressure-treated with preservatives,

there are no absolute “rules.” In ground contact uses, pressure-treated wood species often outperform naturally durable

species in warm wet climates, but less difference in service

life often occurs in dry climates. The service life of naturally

durable and preservative-treated woods is quite comparable in

aboveground exposures, such as decking boards, railing, and

fence boards. In selecting wood for porches, decks, and

fences, whether preservative treated or a naturally durable

species, consideration must be given to the exposure conditions, design of the structure, and properties of the wood,

including its variability.

In aboveground uses, the weathering of wood can be as much

a factor in long-term service life as is decay resistance.

Whether naturally durable wood species or preservativetreated wood is used in full exposures to weather, it is necessary to protect the wood with a finish. Periodic treatment

with a penetrating sealer, such as a water-repellent preservative, will decrease checking and splitting, and pigmented

finishes will retard weathering.

Treated Wood

Treated wood is often used to construct porches, decks, and

fences, particularly wood treated with chromated copper

arsenate (CCA). Woods that have been pressure treated for

decay sometimes have special finishing requirements. Wood

pressure treated with waterborne chemicals, such as copper,

chromium, and arsenic salts (CCA), that react with the wood

or form an insoluble residue presents no major problem in

finishing if the wood is properly redried and thoroughly

cleaned after treating. The finishing characteristics are more

controlled by species and grain orientation than by preservative treatment. Wood treated with solvent- or oilborne preservative chemicals, such as creosote or pentachlorophenol,

is not considered paintable.

None of the common pressure preservative treatments

(creosote, pentachlorophenol, water-repellent preservatives,

and waterborne preservatives) will significantly change the

weathering characteristics of woods. All preservative-treated

wood will weather when exposed above ground and may

develop severe checking and cracking. Finishing generally

retards this weathering. However, there is one exception:

waterborne treatments containing chromium decrease the

degrading effects of weathering.

Creosote and pentachlorophenol are generally used only for

industrial and commercial applications where applying a

finish is not considered practical. Creosote is oily and therefore does not accept a finish very well. Pentachlorophenol is

often formulated in heavy oil. In general, preservatives formulated in oil will not accept a finish. In some cases, oil-based

semitransparent penetrating stains can be used on these

products, but only after the preservative-treated wood has

weathered for 1 to 2 years, depending on exposure.

The only preservative-treated woods that should be painted

or stained immediately after treatment and without further

exposure are the waterborne preservative treatments (such as

CCA-treated wood). Since wood treated with these preservatives is often used for residential structures, it needs to be

finished not only for esthetic reasons, but also to protect it

from weathering. Many manufacturers of chemicals for treating wood with waterborne preservatives include a waterrepellent treatment to give the treated wood better resistance

to weathering, particularly checking and splitting. Even if the

wood was treated with water repellent by the manufacturer, it

should be maintained with a finish to extend its service life.

Wood used in aboveground applications that has been properly treated with preservative is usually replaced because of

weathering, not decay.

Marine Uses

The marine environment is particularly harsh on wood. As

discussed, the natural surface deterioration process occurs

slowly. Marine environments speed up the natural weathering process to some extent, and wood for marine uses is

often finished with paint or varnish for protection. Certain

antifouling paints are also used to protect piers and ship

hulls against marine organisms.

For best protection, wood exposed to marine environments

above water and above ground should be treated with a

paintable water-repellent preservative, painted with a suitable

paint primer, and top coated (at least two coats) with quality

exterior marine products.

Note: Any wood in contact with water or the

ground should be pressure treated to specifications

recommended for in-ground or marine use. Such

treated woods are not always paintable. As indicated previously, CCA-treated woods are paintable

when dry and clean.

Wood trim on boats is often varnished. When applied to

boats, varnish is subjected to greater exposure to sunlight

and water than when used on structures; therefore, it needs

regular and frequent care and refinishing. Varnishes should be

specially formulated for harsh exposure; three to six coats

should be applied for best performance. The durability of the

varnish can be extended by finishing the wood with a semitransparent stain prior to varnishing, but this obscures many

natural characteristics of the wood. Keeping the appearance of

varnished wood trim bright and new is labor intensive but

often well worth the effort.

Refinishing

Exterior wood surfaces need to be refinished only when the

old finish has worn thin and no longer protects the wood. In

repainting, one coat may be adequate if the old paint surface

is in good condition. Dirty paint can often be renewed and
15–23

cleaned by washing with detergent. Too-frequent repainting

with an oil-based system produces an excessively thick film

that is likely to crack abnormally across the grain of the

wood. Complete removal of the paint and repainting are the

only cure for cross-grain cracking (see subsection on crossgrain cracking under Finish Failure or Discoloration). Latex

paints seldom develop cross-grain cracking because they are

more flexible than are oil-based paints. Since latex paints

have replaced oil-based paints for most exterior application

on residential structures, cross-grain cracking is rather rare

unless the latex paint has been applied over many coats of

oil-based paint. However, even with latex paints, excessive

paint buildup should be avoided. Additional top-coats

should be applied only when the primer begins to show.

Water-Repellent Preservatives

Water-repellent preservatives used as natural finishes can be

renewed by simply brushing the old surface with a dry stiffbristle brush to remove dirt and applying a new coat of

finish. To determine if a water-repellent preservative has lost

its effectiveness, splash a small quantity of water against the

wood surface. If the water beads up and runs off the surface,

the treatment is still effective. If the water soaks in, the wood

needs to be refinished. Refinishing is also required when the

wood surface shows signs of graying. Gray discoloration can

be removed by washing the wood with a commercial mildew

cleaner or liquid household bleach (see subsection on mildew

under Finish Failure or Discoloration).

Semitransparent Penetrating Stains

Surfaces finished with semitransparent penetrating stains are

relatively easy to refinish; heavy scraping and sanding are

generally not required. Simply use a dry stiff-bristle brush to

remove all surface dirt, dust, and loose wood fibers, and then

apply a new coat of stain. The second coat of penetrating

stain often lasts longer than the first because it penetrates into

small surface checks that open as the wood weathers.

In refinishing surfaces originally finished with semitransparent stains, it is extremely important that the wood accept the

stain. That is, the stain must penetrate the wood. Since the

weathering rate of a stain varies with exposure, the stain may

not penetrate well in some areas. For example, an area under

the eaves, even on the south side of a structure, may be

relatively unweathered. When applying stain to such an area,

feather the new stain into the old. If the stain does not penetrate the wood within an hour, remove the excess. If the

excess stain is not removed it will form shiny spots, which

will flake from the surface as it weathers. The north side of a

structure may not need to be restained nearly as often as the

south side (northern hemisphere).

Note: Steel wool and wire brushes should not be

used to clean surfaces to be finished with semitransparent stain or water-repellent preservatives because

small iron deposits may be left behind. These small

iron deposits can react with certain water-soluble

extractives in woods like western redcedar, redwood, Douglas-fir, and the oaks, to yield dark

blue–black stains on the surface (see subsection on

iron stain under Finish Failure or Discoloration).

Paint and Solid-Color Stains

In refinishing painted (or solid-color stained) surfaces, proper

surface preparation is essential if the new coat is to have a

long service life. First, scrape away all loose paint. Sand

areas of exposed wood with 50- to 80-grit sandpaper to

remove the weathered surface and to feather the abrupt paint

edge. Then scrub any remaining old paint with a brush or

sponge and water. Rinse the scrubbed surface with clean

water, then wipe the surface with your hand or cloth (see

subsection on chalking under Finish Failure or Discoloration). If the surface is still dirty or chalky, scrub it again

using a detergent. Use a commercial cleaner or a dilute

household bleach solution to remove mildew (see subsection

on mildew under Finish Failure or Discoloration). Rinse the

cleaned surface thoroughly with fresh water and allow it to

dry before repainting. Treat bare wood with a water-repellent

preservative and allow it to dry for at least 3 days before

priming. Top coats can then be applied.

Note: Special precautions are necessary if the old

paint contains lead. See section on lead-based paint.

It is particularly important to clean areas that are protected

from sun and rain, such as porches, soffits, and side walls

protected by overhangs. These areas tend to collect dirt and

water-soluble materials that interfere with the adhesion of

new paint. It is probably adequate to repaint these protected

areas every other time the house is painted.

Latex paint or solid-color stain can be applied over freshly

primed surfaces and on weathered paint surfaces if the old

paint is clean and sound (chalk-free). Before repainting surfaces with latex paint, conduct a simple test. After cleaning

the surface, repaint a small, inconspicuous area with latex

paint and allow it to dry at least overnight. Then, to test for

adhesion, firmly press one end of an adhesive bandage onto

the repainted surface. Remove the bandage with a snapping

action. If the tape is free of paint, the fresh latex paint is wellbonded and the old surface does not need priming or additional cleaning. If the fresh latex paint adheres to the tape, the

old surface is too chalky and needs more cleaning or priming

with an oil-based primer. If both the fresh latex paint and the

old paint coat adhere to the tape, the old paint is not wellbonded to the wood and must be removed before repainting.

Back-Priming

Back-priming simply means the application of a primer or

water-repellent preservative to the back side of wood (usually

wood siding) before the wood is installed. Back-priming

retards absorption of water, thus improving dimensional

stability and extending the service life of the paint. It

improves the appearance of the wood by decreasing extractives staining, particularly run-down extractives bleed. Treating the back side of siding with a water-repellent preservative

is probably more effective than back-priming for improving

dimensional stability and retarding extractives bleed.

Water-repellent preservatives are particularly effective if used
 15–24

as a pretreatment before back-priming. However, backpriming with a stain-blocking primer alone has some benefit.

By slowing the absorption of water, the primer or waterrepellent preservative improves dimensional stability of

siding. Siding is less likely to cup, an important consideration for flat-grain wood. By decreasing shrinking and swelling, less stress is placed on the finish, thereby extending its

service life. At the same time that the siding is back-primed,

the end grain should be sealed with primer. This process has

an even greater effect in stopping water absorption. Most

paint failure near the end grain of siding can be eliminated by

including end-grain priming along with the back-priming.

When boards are cut during installation, the cut ends should

be spot-primed.

Run-down extractives bleed occurs because water from windblown rain, leaks, and/or condensation of moisture wets the

back of siding and absorbs extractives from the wood. If

water from one course of siding runs down the front face of

the course below it, the water may deposit the extractives on

this surface, causing unsightly streaks (see subsection on

extractives bleed under Finish Failure or Discoloration).

Back-priming stops extractives bleed by forming a barrier

between the water and the extractives. The primer should be

stain-blocking, just as the primer used for the front (outside)

surface of the siding. When finish is applied to siding in the

factory, the back surface of the siding is routinely finished at

the same time as the front surface.

Factory Finishing

Many siding, trim, and decking products are now available

prefinished. Although it has been standard industry practice

to preprime hardboard siding, factory finishing of solid wood

products has rapidly grown during the last several years. The

industry is currently growing at about 60% per year, and this

growth is anticipated to continue into the early part of the

next century. Coating suppliers for this industry predict that

more than half of all wood siding materials will be factory

finished by that time. In addition to siding, other wood

products like interior trim and paneling are being prefinished.

Much of this factory finishing has been made possible by the

development of rapid-cure finish systems and the availability

of efficient equipment to apply the finish.

Prefinishing wood at the factory rather than after installation

results in overall cost savings as well as several other advantages. Weather and climate conditions during construction

do not affect prefinished wood. This is a crucial consideration

in northern climates where acceptable exterior finishing is

impossible during the winter. In factory finishing, coverage

can be controlled to give a consistent 100 to 127 μm (4 to

5 mil) dry film. The controlled conditions enable many

factory finishers to guarantee their products against cracking,

peeling, and blistering for 15 years. Another advantage of

factory finishing is that siding is finished on all sides, including the end grain. When prefinished siding is installed,

the end grain is sealed after any cross-cuts are made. This

end-grain sealing is seldom done during installation of unfinished siding. The end-grain seal greatly increases resistance

of siding to end-grain absorption of water, thus decreasing

extractives bleed and other problems related to moisture.

Finish Failure or Discoloration

Paint is probably the most common exterior finish in use on

wood today. It appears somewhere on practically every residential structure and on most commercial buildings. Even

brick and aluminum-sided structures usually have some

painted wood trim. When properly applied to the appropriate

type of wood substrate, paint should have a service life of at

least 10 years. If it does not, the selection of the paint, application, type of substrate, type of structure, and construction

practices were not done properly or were not compatible.

Modern paint formulations based on acrylic polymers are

extremely resistant to degradation by ultraviolet (UV) radiation. These paints degrade by a slow erosion process, which

eventually exposes the primer. The erosion process depends

on the exposure to the weather. Areas that deteriorate rapidly

are those exposed to the greatest amount of sunshine and

rain, usually on the west and south sides of a building (in

the northern hemisphere). The normal deterioration process

begins with soiling or a slight accumulation of dirt and then

leads to gradual change and erosion of the coating. When the

primer begins to show, that side of the structure should be

repainted. It may not be necessary to paint all sides of the

structure, since the erosion rate varies depending on exposure. This is particularly true for structures finished with

white paint.

Note: The most common cause of premature paint failure

on wood is moisture.

Early paint failure may develop under certain conditions of

service. Excessive moisture, flat grain, high coating porosity,

and application of a new paint coat without proper preparation of the old surface can all contribute to early paint failure.

Paint on the outside walls of residential structures is subject

to wetting from rain, dew, and frost. Equally serious is

“unseen” moisture that moves from inside the structure to

the outside. This is particularly true for buildings in cold

northern climates that do not have effective air and vapor

barriers. Many moisture-related problems can be prevented

by furring out the siding 9 to 19 mm (3/8 to 3/4 in.) prior to

installation. For siding placed directly on insulation board or

a wind barrier, placing wedges between the siding courses

can reduce problems with moisture.

The next most common cause of paint failure is a poor bond

between the substrate and the coating. Even in the absence of

moisture, paint can peel if it does not bond well to the

wood. If moisture is also present, paint failure is accelerated.

The wide bands of latewood on flat-grain surfaces hold paint

very poorly. If possible, flat-grain boards should be exposed

“bark-side” out to minimize raising and separation of grain,

and the boards should either be rough-sawn or scuff-sanded

with 50-grit sandpaper prior to priming. Wood must be

protected from the weather prior to installation and painted as

soon as possible afterwards. Exposure to the weather for as
15–25

little as 2 weeks will reduce the paint-holding properties of

smooth wood. Scuff sanding prior to painting is necessary if

the wood is exposed to the weather for more than 2 weeks.

In fact, scuff sanding is always a good idea on planed lumber.

Moisture Blisters

Moisture blisters are bubble-like swellings of the paint film

on the wood surface. As the name implies, these blisters

usually contain moisture when they are formed. Moisture

blisters may occur where outside moisture, such as rain,

enters through joints and other end-grain areas of boards and

siding. Moisture may also enter as a result of poor construction and maintenance practices. The blisters appear after

spring rains and throughout the summer. Paint failure is

most severe on the sides of buildings that face the prevailing

winds and rain. Blisters may occur in both heated and

unheated buildings.

Moisture blisters may also result from the movement of

water from the inside of a structure to the outside. Plumbing

leaks, humidifiers, overflow (sinks, bathtubs), and shower

spray are sources of inside water, and improperly sealed walls

can contribute to the problem. Such blisters are not seasonal

and occur when the faulty condition develops.

Moisture blisters form between the wood substrate and the

first coat of paint. After the blisters appear, they may dry out

and collapse. Small blisters may disappear completely and

fairly large ones may leave rough spots; in severe cases, the

paint peels (Fig. 15–15). Thin coatings of new oil-based

paint are the most likely to blister. Old, thick coats are

usually too rigid to swell and form blisters; cracking and

peeling usually result. Elimination of the moisture problem

is the only practical way to prevent moisture blisters in

paint. In addition, elimination of moisture problems can help

prevent more serious problems such as decay (rot), warp, and

splitting of the wood substrate.

To prevent moisture-related paint problems, follow good

construction and painting practices. First, do whatever is

possible to keep the wood dry. Provide an adequate roof

overhang and properly maintain shingles, gutters, and downspouts. Window and door casings should slope away from

the house, allowing water to drain away rapidly. Vent

clothes dryers, showers, and cooking areas to the outside,

not to the crawl space or attic. Avoid the use of humidifiers.

If the house contains a crawl space, cover the soil with a

vapor-retarding material to prevent migration of water vapor

into the living quarters. In northern climates, use a vapor

retarder on the interior side of all exterior walls and an air

barrier to prevent condensation in the wall. In buildings in

southern climates that are air conditioned a substantial part of

the year, place the vapor retarder directly under the sheathing.

Mill Glaze

Since the mid-1980s, a condition known as “mill glaze”

(also called planer’s glaze) has occasionally occurred on

smooth flat-grain western redcedar siding as well as other

species. There is controversy over the exact cause of this

condition, but it seems to occur as a result of planing and/or

drying of the lumber. The condition seems to be caused by

dull planer blades and is exacerbated on flat-grain surfaces,

which are more difficult to plane. The problem is most

severe on flat-grain boards because of the orientation of latewood to earlywood. Dull blades tend to burnish the surface

and crush the less dense earlywood bands that lie directly

beneath the more dense latewood bands at the surface. Later,

when these boards are exposed to weather, particularly cyclic

moisture conditions, the crushed earlywood absorbs moisture

and rebounds, which causes the surface latewood bands to

raise. In vertical-grain wood, the earlywood–latewood bands

are perpendicular to the surface and the lumber is easier to

plane, even with dull tooling.

During the planing or milling process, overheating may

bring more water-soluble extractives to the surface, creating a

hard, varnish-like glaze. Excess water-soluble extractives can

also form (bleed) on the surface during kiln drying. As these

extractives age, particularly in direct sunlight, they become

insoluble and are difficult to remove. If extractives bleed to

the surface prior to final planing or sanding of the lumber,

this final surface preparation usually removes them.

Sanding may remove some extractives buildup, but it is not

likely to remove all the crushed wood. Subsequent wetting

may still cause the surface to deform. One or more wetting

and drying cycles are necessary to remove these planerinduced stresses in the wood, but the wood should not be

exposed to sunlight for more than 2 weeks before application

of a film-forming finish because exposure decreases the

adhesion of the coating (see Weathering, Effects on Paint

Adhesion).

Figure 15–15. Paint can peel from wood when

excessive moisture moves through house wall. Some

cross-grain cracking is also evident on this older home.
 15–26

Mill glaze can cause failure of the finish. Failure is most

common on flat-grain siding finished with one or two thin

coats of oil-based solid-color stain (also called opaque or fullbodied stain). These low-solids coatings provide only 25 to

50 μm (1 to 2 mil) of dry-film thickness, whereas a brushapplied three-coat paint system (primer and two top-coats)

provides 100 to 127 μm (4 to 5 mil) of dry-film thickness.

Thin coatings of solid-color stain do not build up enough

film to withstand the stresses caused by raised grain, particularly if the coating–wood bond is weakened by extractives

buildup on the wood surface.

When using flat-grain bevel siding, the simplest and best

solution to the problem of mill glaze and finish failure is to

install the siding rough-side out. The rough side is the side

of choice for application of penetrating semi-transparent

stains, and although solid-color stains form films, they also

will provide much better service life when applied to the

rough-sawn side. In addition to the lack of mill glaze, the

rough side gives two additional advantages. The film

buildup on the rough side will be greater and the film will

have greater mechanical adhesion or “bite.” The best film

buildup is obtained by brush application. If the finish is

applied by roller or spray, it is advisable to back-brush

immediately after application to even out the finish and to

work it into the wood surface, thus avoiding bridging, gaps,

and lap marks.

If the flat-grain siding must be installed smooth-side out,

remove the planing stresses by wetting the surface, then

allow 2 to 3 days for the surface to dry before applying the

finish. Scratch-sanding the surface with 50- to 80-grit sandpaper also improves paint adhesion. Use either a top quality

three-coat paint system or apply a stain-blocking primer prior

to applying solid-color stain. In selecting finishes for highly

colored wood such as western redcedar or redwood, choose a

primer that is impervious to bleed of water-soluble extractives. Although many waterborne primers are being marketed

for use on western redcedar and redwood, many paint manufacturers still recommend an oil-based, stain-blocking primer

followed by two coats of high quality, acrylic latex top coat.

Solid-color stains, particularly the latex formulations, do not

block water-soluble extractives very well, especially when

only one coat is applied.

Mill glaze has not been common in recent years because

paint companies are recommending the use of a primer prior

to the application of a solid-color stain, and painting contractors are generally following these recommendations.

Intercoat Peeling

Intercoat peeling is the separation of the new paint film from

the old paint coat, which indicates a weak bond between the

two (Fig. 15–16). Intercoat peeling usually results from

inadequate cleaning of weathered paint and usually occurs

within 1 year of repainting. This type of paint peeling can be

prevented by following good painting practices. Intercoat

peeling can also result from allowing too much time between

applying the primer coat and top coat in a new paint job. If

more than 2 weeks elapse between applying an oil-based

primer and a top coat, soap-like materials may form on the

surface and interfere with bonding of the next coat of paint.

When the period between applications exceeds 2 weeks,

scrub the surface before applying the second coat. Do not

apply a primer coat in the fall and wait until spring to finish

with the top coat.

Cross-Grain Cracking

Cross-grain cracking occurs when oil-based or alkyd paint

coatings become too thick (Fig. 15–17). This problem often

occurs on older homes that have been painted many times.

Paint usually cracks parallel to the wood grain; cross-grain

cracks run across the grain. Once cross-grain cracking has

occurred, the only solution is to completely remove the old

paint and apply a new finishing system to the bare wood. To

prevent cross-grain cracking, follow the paint manufacturer’s

recommendations for spreading rates. Do not repaint unweathered, protected areas such as porch ceilings and roof

overhangs as often as the rest of the house. If possible, repaint these areas only as they weather and require new paint.

Chalking

Chalking results from weathering of the paint’s surface,

which releases pigment and degraded resin particles. These

particles form a fine powder on the paint surface. Most paints

chalk to some extent. This phenomenon is desirable because

it allows the paint surface to self-clean, and it is the most

desirable mechanism for removing degraded paint. However,

chalking is objectionable when the paint pigment washes

down a surface with a different color or when it causes premature paint failure through excessive erosion.

The paint formulation determines how fast the paint chalks;

discoloration from chalking can be decreased by selecting a

paint with a slow chalking rate. Therefore, if chalking is

likely to be a problem, select a paint that the manufacturer

has indicated will chalk slowly. Latex paints, particularly

those based on acrylic polymers, chalk very slowly.

Figure 15–16. Intercoat peeling of paint, usually

caused by poor preparation of old paint surface.
15–27

When repainting surfaces that have chalked excessively,

proper preparation of the old surface is essential to prevent

premature paint peeling. Scrub the old surface thoroughly

with a detergent solution to remove all old deposits and dirt.

Rinse thoroughly with clean water before repainting. To

check for excessive chalking, lightly rub the paint surface

with a dark (for light-colored paint) or white (for dark-colored

paint) cloth. The amount of pigment removed by the cloth is

a good indication of the chalking. If the surface is still chalky

after cleaning, it may need to be primed prior to repainting.

Otherwise, the new paint coat may peel. Discoloration or

chalk that has run down a lower surface may be removed by

vigorous scrubbing with a good detergent. This discoloration will gradually weather away if chalking on the painted

surface above the discolored surface is corrected.

Mildew

Mildew is probably the most common cause of house paint

discoloration and gray discoloration of unfinished wood

(Fig. 15–18). Mildew is a form of microscopic stain fungi.

The most common fungal species are black, but some are

red, green, or other colors. Mildew grows most extensively

in warm, humid climates, but it is also found in cold northern climates. Mildew may be found anywhere on a building,

although it is most common on walls behind trees or shrubs

where air movement is restricted. Mildew may also be associated with the dew pattern of the house. Dew will form on

those parts of the house that are not heated and tend to cool

rapidly, such as eaves and ceilings of carports and porches.

The dew then provides a source of moisture for mildew

fungi.

Mildew fungi can be distinguished from dirt by examination

under a high-power magnifying glass. In the growing stage,

when the surface is damp or wet, the fungus is characterized

by its threadlike growth. In the dormant stage, when the

surface is dry, the fungus has numerous egg-shaped spores;

by contrast, granular particles of dirt appear irregular in size

and shape. A simple test for the presence of mildew on wood

or paint is to apply a drop or two of liquid household bleach

solution (5% sodium hypochlorite) to the discolored surface.

The dark color of mildew will usually bleach out in

1 or 2 min. A surface discoloration that does not bleach is

probably dirt. It is important to use fresh bleach solution

because bleach deteriorates upon aging and loses its potency.

In warm, damp climates where mildew occurs frequently, use

a paint containing zinc oxide and a mildewcide for both the

primer and top coats. Before repainting mildew-infected

wood or painted wood, the mildew must be killed or it will

grow through the new paint coat. To kill mildew on wood

or on paint, and to clean an area for general appearance or for

repainting, use a bristle brush or sponge to scrub the painted

surface with a commercial cleaner formulated for mildew

removal. Mildew can also be removed using a dilute solution of household bleach with detergent:

• 1 part household detergent

• 10 parts (5%) sodium hypochlorite (household bleach)

• 30 parts warm water

Figure 15–17. Cross-grain cracking from excessive

buildup of paint.

Figure 15–18. Mildew is most common in shaded,

moist, or protected areas.
 15–28

Warning: Do not mix bleach with ammonia or

with any detergents or cleansers that contain ammonia. Mixed together, bleach and ammonia form a

lethal combination, similar to mustard gas. Many

household cleaners contain ammonia, so be extremely careful in selecting the type of cleaner to

mix with bleach. Avoid splashing the cleaning solution on yourself or on shrubbery or grass.

Rinse the cleaned surface thoroughly with fresh water. Before

the cleaned surface can become contaminated, repaint it with

a paint containing a mildewcide. When finishing new wood

or refinishing areas that have peeled, pretreatment of wood

surfaces with a water-repellent preservative prior to priming

can also help deter mildew growth, even after the wood has

been painted. Oil-based paints are somewhat more prone to

mildew than are latex paints because the oils may be a food

source for mildew.

Discoloration From

Water-Soluble Extractives

In some wood species, the heartwood contains water-soluble

extractives. (Sapwood does not contain extractives.) These

extractives can occur in both hardwoods and softwoods.

Western redcedar and redwood are two common softwood

species that contain large quantities of extractives. The extractives give these species their attractive color, good stability, and natural decay resistance, but they can also discolor

paint. Extractive staining problems can occur occasionally

with such woods as Douglas-fir and southern yellow pine.

When extractives discolor paint, moisture is usually the

culprit. The extractives are dissolved and leached from the

wood by water. The water then moves to the paint surface,

evaporates, and leaves the extractives behind as a reddish

brown stain (Fig. 15–19). Diffused discoloration from wood

extractives is caused by water from rain and dew that penetrates a porous or thin paint coat. It may also be caused by

rain and dew that penetrates joints in the siding or by water

from faulty roof drainage and gutters.

Diffused discoloration is best prevented by following good

painting practices. Apply a water-repellent preservative or

water repellent to the bare wood before priming. Use an oilbased, stain-resistant primer or a latex primer especially

formulated for use over woods likely to discolor from extractives. Do not use porous paints such as flat alkyds and latex

directly over these extractive-rich woods. If the wood is

already painted, clean the surface, apply an oil-based or latex

stain-resistant primer and then the top coat. Be sure to allow

sufficient time for the primer to cure so that it blocks the

extractives stain. Before priming and repainting, apply a

water-repellent preservative or water repellent to any wood

exposed by peeled paint.

Water-soluble extractives can also cause a run-down or

streaked type of discoloration. This discoloration results

when the back of siding is wetted, the extractives are dissolved, and the colored water then runs down the face of the

adjacent painted board below the lap joint.

Water that produces a run-down discoloration can result from

the movement of water vapor within the house to the exterior

walls and condensation during cold weather. Major sources

of water vapor are humidifiers, unvented clothes dryers,

showers, and moisture from cooking and dishwashing. Rundown discoloration may also be caused by draining of water

into exterior walls from roof leaks, faulty gutters, ice dams,

and wind-driven rain blown beneath the siding.

Run-down discoloration can be prevented by decreasing

condensation or the accumulation of moisture in the wall.

The same precautions to avoid moisture buildup in walls as

described in the section on moisture blisters will also prevent extractives bleed. Water from rain and snow can be

Figure 15–19. Water-soluble extractive discoloration

can result from water wetting the back of the siding and

then running down the front (top). Water causing

discoloration also leads to paint failure (bottom).
15–29

prevented from entering the walls by proper maintenance of

the gutters and roof. The formation of ice dams can be prevented by installing adequate insulation in the attic and by

providing adequate ventilation. If discoloration is to be

stopped, moisture problems must be eliminated.

Extractives discoloration will usually weather away in a few

months once the cause of the extractives bleed is eliminated.

However, discoloration in protected areas can become darker

and more difficult to remove with time. In these cases, wash

the discolored areas with a mild detergent soon after the

problem develops. Paint cleaners are effective on darker

stains.

Highly colored woods such as redwood and the cedars benefit

from back-priming or treatment with a water-repellent preservative. Although such methods will not completely

eliminate extractives staining, they will help reduce staining,

particularly from wind-driven rain blown underneath siding

(see subsection on back-priming in Application of Wood

Finishes).

Blue Stain

Blue stain is caused by microscopic fungi that commonly

infect only the sapwood of trees. In some species, these fungi

are prone to develop a blue–black discoloration of the wood.

Blue stain does not weaken wood structurally, but conditions that favor blue stain are also ideal for wood decay and

paint failure.

Wood in service may contain blue stain, and no detrimental

effects will result as long as the moisture content is kept

below 20%. (Wood in properly designed and wellmaintained structures usually has a moisture content of 8%

to 13%.) However, if the wood is exposed to moisture from

sources such as rain, condensation, or leaky plumbing, the

moisture content will increase and the blue-stain fungi may

develop and become visible.

A commercial mildew cleaner or a 5% sodium hypochlorite

solution (ordinary liquid household bleach) with detergent

may remove some blue discoloration, but it is not a permanent cure. The bleach removes the stain from the surface

only. To prevent blue stain, the lumber must be cut and

dried as soon as possible after harvesting the logs. The

lumber must then be kept dry until used and while it is in

service. With some wood species that are prone to develop

blue stain, the logs are often treated with a fungicide while in

storage before the lumber is cut.

Iron Stain

Iron stains on wood can occur through rusting of fasteners or

by the reaction of iron with tannins in the wood. When

standard steel nails are used on exterior siding and then

painted, a reddish brown discoloration may occur through

the paint in the immediate vicinity of the nailhead. This

reddish brown discoloration is rust, and it can be prevented

by using corrosion-resistant nails, which include highquality galvanized, stainless steel, and aluminum nails. Poor

quality galvanized nails can corrode easily and, like steel

nails, can cause unsightly staining of the wood and paint.

The galvanizing on nailheads should not “chip loose” as

the nails are driven into the wood.

Unsightly rust stains may also occur when standard steel

nails are used in association with finishing systems such as

solid-color or opaque stains, semitransparent penetrating

stains, and water-repellent preservatives. Rust stains can also

result from screens and other steel objects or fasteners, which

corrode and/or release iron compounds.

A chemical reaction of iron with tannins in wood results in

an unsightly blue–black discoloration of wood. In this case,

discoloration results from the reaction of iron with certain

wood extractives. Steel nails are the most common source of

iron for such discoloration, but problems have also been

associated with traces of iron left from cleaning the wood

surface with steel wool or wire brushes. The discoloration

can sometimes become sealed beneath a new finishing system. When this happens, the problem is extremely difficult

to fix. The coating must be stripped before the iron stain can

be removed.

Oxalic acid will remove the blue–black discoloration from

iron. Apply a saturated solution containing about 0.5 kg

(1 lb) of oxalic acid per 4 L (1 gal) of hot water to the stained

surface. Many commercial brighteners contain oxalic acid,

and these are usually effective for removing iron stains. A

saturated solution of sodium bifluoride (NaHF2) works as

well but it may be more difficult to obtain than oxalic acid.

After removing the stain, wash the surface thoroughly with

warm fresh water to remove the oxalic acid. If all sources of

iron are not removed or the wood is not protected from

corrosion, the discoloration will recur.

Caution: Use extreme care when using oxalic acid,

which is toxic.

If iron stain is a serious problem on a painted surface, the

nails can be countersunk and caulked, and the area spot

primed and top coated. This is a costly and time-consuming

process that is only possible with opaque finishes. Little can

be done to give a permanent fix to iron stains on natural

finishes other than removing the fasteners, cleaning the affected areas with oxalic acid solution, and replacing the

fasteners. It is best to use corrosion-resistant fasteners such as

stainless steel rather than risk iron stain, particularly when

using natural finishes on wood containing high amounts of

tannin, such as western redcedar, redwood, and oak.

Brown Stain Over Knots

The knots in many softwood species, particularly pine,

contain an abundance of resins and other highly colored

compounds. These compounds can sometimes cause paint to

peel or turn brown. The resins that compose pitch can be

“set” or hardened by the high temperatures used in kiln

drying construction lumber if the proper kiln schedule is

used. Some of the other compounds are not affected by

kiln drying.
 15–30

The elimination of staining of paint by colored resins and

water-soluble extractives in knots is often difficult because

the resins are soluble in oil-based primers and diffuse through

them. Latex-based formulations are also not very effective in

this regard. It is generally necessary to treat the knot with a

specially formulated knot sealer or shellac. Do not use ordinary shellac or varnish to seal knots because such finishes are

not formulated for this use; they can cause early paint failure

in outdoor exposure. After sealing the knots, apply primer,

followed by two top-coats.

Finishing of Interior Wood

Interior finishing differs from exterior finishing primarily in

that interior woodwork usually requires much less protection

against moisture but more exacting standards of appearance

and cleanability. A much wider range of finishes and finish

methods are possible indoors because weathering does not

occur. Good finishes used indoors should last much longer

than paint or other coatings on exterior surfaces. The finishing of veneered panels and plywood may still require extra

care because of the tendency of these wood composites to

surface check.

Much of the variation in finishing methods for wood used

indoors is caused by the wide latitude in the uses of wood—

from wood floors to cutting boards. There is a wide range of

finishing methods for just furniture. Factory finishing of

furniture is often proprietary and may involve more than a

dozen steps. Methods for furniture finishing will not be

included in this publication; however, most public libraries

contain books on furniture finishing. In addition, product

literature often contains recommendations for application

methods. This section will include general information on

wood properties, some products for use in interior finishing,

and brief subsections on finishing of wood floors and

kitchen utensils.

Color change of wood can sometimes cause concern when

using wood in interiors, particularly if the wood is finished

to enhance its natural appearance. This color change is a

natural aging of the newly cut wood, and nothing can be

done to prevent it, except, of course, to keep the wood in the

dark. The color change is caused by visible light, not the

UV radiation associated with weathering. It is best to keep

all paintings and other wall coverings off paneling until most

of the color change has occurred. Most of this change occurs

within 2 to 3 months, depending on the light intensity. If a

picture is removed from paneling and there is a color difference caused by shadowing by the picture, it can be corrected

by leaving the wood exposed to light. The color will even

out within several months.

To avoid knots, the use of fingerjointed lumber has become

common for interior trim. As with exterior wood, the quality

of the lumber is determined by the poorest board. Pieces of

wood for fingerjointed lumber often come from many different

trees that have different amounts of extractives and resins.

These extractives and resins can discolor the finish, particularly in humid environments such as bathrooms and

kitchens. When finishing fingerjointed lumber, it is prudent

to use a high-quality stain-blocking primer to minimize

discoloration.

Types of Finish and Wood Fillers

Opaque Finishes

The procedures used to paint interior wood surfaces are

similar to those used for exterior surfaces. However, interior

woodwork, especially wood trim, requires smoother surfaces,

better color, and a more lasting sheen. Therefore, enamels or

semigloss enamels are preferable to flat paints. Imperfections

such as planer marks, hammer marks, and raised grain are

accentuated by high-gloss finishes. Raised grain is especially

troublesome on flat-grain surfaces of the denser softwoods

because the hard bands of latewood are sometimes crushed

into the soft earlywood in planing, and later expand when the

wood moisture content changes. To obtain the smoothest

wood surface, it is helpful to sponge it with water, allow to

dry thoroughly, and sand before finishing. Remove surface

dust with a tack cloth. In new buildings, allow woodwork

adequate time to come to equilibrium moisture content in

the completed building before finishing the woodwork.

To effectively paint hardwoods with large pores, such as oak

and ash, the pores must be filled with wood filler (see subsection on wood fillers). The pores are first filled and sanded,

then interior primer/sealer, undercoat, and top coat are applied. Knots, particularly in the pines, should be sealed with

shellac or a special knot-sealer before priming to retard discoloration of light-colored finishes by colored resins in the

heartwood of these species. One or two coats of undercoat are

next applied, which should completely hide the wood and

also provide a surface that can be easily sanded smooth. For

best results, the surface should be sanded just before applying

the coats of finish. After the final coat has been applied, the

finish may be left as is, with its natural gloss, or rubbed to a

soft sheen.

Transparent Finishes

Transparent finishes are often used on hardwoods and some

softwood trim and paneling. Most finish processes consist of

some combination of the fundamental operations of sanding,

staining, filling, sealing, surface coating, and sometimes

waxing. Before finishing, planer marks and other blemishes

on the wood surface that would be accentuated by the finish

must be removed.

Stains

Some softwoods and hardwoods are often finished without

staining, especially if the wood has an attractive color. When

stain is used, however, it often accentuates color differences

in the wood surface because of unequal absorption into different parts of the grain pattern. With hardwoods, such emphasis of the grain is usually desirable; the best stains for this

purpose are dyes dissolved in either water or solvent. The

water-soluble stains give the most pleasing results, but they

raise the grain of the wood and require extra sanding after

they dry.
15–31

The most commonly used stains are those that do not raise

grain and are dissolved in solvents that dry quickly. These

stains often approach the water-soluble stains in clearness and

uniformity of color. Stains on softwoods color the earlywood

more strongly than the latewood, reversing the natural gradation in color unless the wood has been initially sealed. To

give more nearly uniform color, softwoods may be coated

with penetrating clear sealer before applying any type of

stain. This sealer is often called a “wash coat.”

If stain absorbs into wood unevenly causing a blotchy appearance, the tree was probably infected with bacteria and/or

blue-stain fungi prior to being cut for lumber. Once the log is

cut into lumber, the infection occurs across grain boundaries

and makes infected areas more porous than normal wood.

When such areas are stained, they absorb excessive amounts

of stain very quickly, giving the wood an uneven blotchy

appearance. Although this problem is not very common,

should it occur it can be difficult to fix. Blue stain on lumber

can easily be seen; the infected pieces can either be discarded

or sealed before staining. However, bacteria-infected areas

cannot be detected prior to staining. If the wood is to be used

for furniture or fine woodwork, it might be a good idea to

check the lumber, before planing, by applying a stain. Pieces

on which the stain appears blotchy should not be used.

Sealing the lumber with varnish diluted 50/50 with mineral

spirits prior to staining may help; commercial sealers are

also available. Bacteria or blue-stain infection may occur in

the sapwood of any species, but it seems to be more problematic with the hardwoods because these species tend to be

used for furniture, cabinets, and fine woodwork.

Fillers

In hardwoods with large pores, the pores must be filled,

usually after staining and before varnish or lacquer is applied,

if a smooth coating is desired. The filler may be transparent

and not affect the color of the finish, or it may be colored to

either match or contrast with the surrounding wood. For

finishing purposes, hardwoods may be classified as shown in

Table 15–6. Hardwoods with small pores may be finished

with paints, enamels, and varnishes in exactly the same

manner as softwoods. A filler may be a paste or liquid,

natural or colored. Apply the filler by brushing it first across

and then with the grain. Remove surplus filler immediately

after the glossy wet appearance disappears. First, wipe across

the grain of the wood to pack the filler into the pores; then,

wipe with a few light strokes along the grain. Allow the

filler to dry thoroughly and lightly sand it before finishing

the wood.

Sealers

Sealers are thinned varnish, shellac, or lacquer that are used

to prevent absorption of surface coatings and to prevent the

bleeding of some stains and fillers into surface coatings,

especially lacquer coatings. Lacquer and shellac sealers have

the advantage of drying very quickly.

Surface Coats

Transparent surface coatings over the sealer may be gloss

varnish, semigloss varnish, shellac, nitrocellulose lacquer, or

wax. Wax provides protection without forming a thick coating and without greatly enhancing the natural luster of the

wood. Other coatings are more resinous, especially lacquer

and varnish; they accentuate the natural luster of some hardwoods and seem to give the surface more “depth.” Shellac

applied by the laborious process of French polishing probably achieves this impression of depth most fully, but the

coating is expensive and easily marred by water. Rubbing

varnishes made with resins of high refractive index for light

(ability to bend light rays) are nearly as effective as shellac.

Lacquers have the advantages of drying rapidly and forming a

hard surface, but more applications of lacquer than varnish are

required to build up a lustrous coating. If sufficient film

buildup is not obtained and the surface is cleaned often, such

as the surface of kitchen cabinets, these thin films can fail.

Varnish and lacquer usually dry to a high gloss. To decrease

the gloss, surfaces may be rubbed with pumice stone and

water or polishing oil. Waterproof sandpaper and water may

be used instead of pumice stone. The final sheen varies with

the fineness of the powdered pumice stone; coarse powders

make a dull surface and fine powders produce a bright sheen.

For very smooth surfaces with high polish, the final rubbing

is done with rottenstone and oil. Varnish and lacquer made

to produce a semigloss or satin finish are also available.

Flat oil finishes commonly called Danish oils are also very

popular. This type of finish penetrates the wood and does not

form a noticeable film on the surface. Two or more coats of

oil are usually applied; the oil may be followed by a paste

wax. Such finishes are easily applied and maintained but

they are more subject to soiling than is a film-forming type

of finish. Simple boiled linseed oil or tung oil are also used

extensively as wood finishes.

Table 15–6. Classification of hardwoods by size of

poresa

Large pores Small pores

Ash Aspen

Butternut Basswood

Chestnut Beech

Elm Cherry

Hackberry Cottonwood

Hickory Gum

Lauan Magnolia

Mahogany Maple

Mahogany, African Red alder

Oak Sycamore

Sugarberry Yellow-poplar

Walnut

a

Birch has pores large enough to take wood filler effectively, but small enough to be finished satisfactorily

without filling.
 15–32

Finishes for Floors

Wood possesses a variety of properties that make it a highly

desirable flooring material for homes, factories, and public

buildings. A variety of wood flooring products are available,

both unfinished and prefinished, in many wood species, grain

characteristics, flooring types, and flooring patterns.

The natural color and grain of wood floors accentuate many

architectural styles. Floor finishes enhance the natural beauty

of wood, protect it from excessive wear and abrasion, and

make the floor easier to clean. The finishing process consists

of four steps: sanding the surface, applying a filler (for opengrain woods), staining to achieve a desired color effect, and

finishing. Detailed procedures and specified materials depend

to a great extent on the species of wood used and finish

preference.

Careful sanding to provide a smooth surface is essential for a

good finish because any irregularities or roughness in the

surface will be accentuated by the finish. Development of a

top-quality surface requires sanding in several steps with

progressively finer sandpaper, usually with a machine unless

the area is small. When sanding is complete, all dust must

be removed with a vacuum cleaner and then a tack cloth.

Steel wool should not be used on floors unprotected by

finish because minute steel particles left in the wood later

cause iron stains. A filler is required for wood with large

pores, such as oak and walnut, if a smooth, glossy varnish

finish is desired (Table 15–6).

Stains are sometimes used to obtain a more nearly uniform

color when individual boards vary too much in their natural

color. However, stains may also be used to accent the grain

pattern. The stain should be an oil-based or non-grain-raising

type. Stains penetrate wood only slightly; therefore, the

finish should be carefully maintained to prevent wearing

through to the wood surface; the clear top-coats must be

replaced as they wear. It is difficult to renew the stain at

worn spots in a way that will match the color of the

surrounding area.

Finishes commonly used for wood floors are classified as

sealers or varnishes. Sealers, which are usually thinned

varnishes, are widely used for residential flooring. They

penetrate the wood just enough to avoid formation of a surface coating of appreciable thickness. Wax is usually applied

over the sealer; however, if greater gloss is desired, the sealed

floor makes an excellent base for varnish. The thin surface

coat of sealer and wax needs more frequent attention than do

varnished surfaces. However, rewaxing or resealing and

waxing of high traffic areas is a relatively simple maintenance

procedure, as long as the stained surface of the wood hasn’t

been worn.

Varnish may be based on phenolic, alkyd, epoxy, or polyurethane resins. Varnish forms a distinct coating over the wood

and gives a lustrous finish. The kind of service expected

usually determines the type of varnish. Varnishes especially

designed for homes, schools, gymnasiums, or other public

buildings are available. Information on types of floor finishes

can be obtained from flooring associations or individual

flooring manufacturers.

The durability of floor finishes can be improved by keeping

them waxed. Paste waxes generally provide the best appearance and durability. Two coats are recommended, and if a

liquid wax is used, additional coats may be necessary to get

an adequate film for good performance.

Finishes for Items Used

for Food

The durability and beauty of wood make it an attractive

material for bowls, butcher blocks, and other items used to

serve or prepare food. A finish also helps keep the wood dry,

which makes it less prone to harbor bacteria and less likely

to crack. When wood soaks up water, it swells; when it dries

out, it shrinks. If the wood dries out rapidly, its surface dries

faster than the inside, resulting in cracks and checks.

Finishes that repel water will decrease the effects of brief

periods of moisture (washing), making the wood easier to

clean.

Finishes that form a film on wood, such as varnish or lacquer, may be used but they may eventually chip, crack, and

peel. Penetrating finishes, either drying or nondrying, are

often a better choice for some products.

Types of Finish

Sealers and Drying Oils

Sealers and drying oils penetrate the wood surface, then

solidify to form a barrier to liquid water. Many commercial

sealers are similar to thinned varnish. These finishes can

include a wide range of formulations including polyurethane,

alkyds, and modified oils. Unmodified oils such as tung,

linseed, and walnut oil can also be used as sealers if they are

thinned to penetrate the wood.

Nondrying Oils

Nondrying oils simply penetrate the wood. They include

both vegetable and mineral oils. Vegetable oils (such as

olive, corn, peanut, and safflower) are edible and are sometimes used to finish wood utensils. Mineral (or paraffin) oil

is a nondrying oil from petroleum. Since it is not a natural

product, it is not prone to mildew or to harbor bacteria.

Paraffin Wax

Paraffin wax is similar to paraffin oil but is solid at room

temperature. Paraffin wax is one of the simplest ways to

finish wood utensils, especially countertops, butcher blocks,

and cutting boards.

Eating Utensils

Wood salad bowls, spoons, and forks used for food service

need a finish that is resistant to abrasion, water, acids, and

stains and a surface that is easy to clean when soiled.
15–33

Appropriate finishes are varnishes and lacquers, penetrating

wood sealers and drying oils, and nondrying vegetable oils.

Many varnishes and lacquers are available, and some of these

are specifically formulated for use on wood utensils, bowls,

and/or cutting boards. These film-forming finishes resist

staining and provide a surface that is easy to keep clean;

however, they may eventually chip, peel, alligator, or crack.

These film-forming finishes should perform well if care is

taken to minimize their exposure to water. Utensils finished

with such finishes should never be placed in a dishwasher.

Penetrating wood sealers and drying oils may also be used

for eating utensils. Some of these may be formulated for use

on utensils. Wood sealers and oils absorb into the pores of

the wood and fill the cavities of the wood cells. This decreases the absorption of water and makes the surface easy to

clean and more resistant to scratching compared with unfinished wood. Penetrating wood sealers are easy to apply and

dry quickly. Worn places in the finish may be easily

refinished. Some of these finishes, particularly drying oils,

should be allowed to dry thoroughly for several weeks

before use.

Nondrying vegetable oils are edible and are sometimes used

to finish wood utensils. They penetrate the wood surface,

improve its resistance to water, and can be refurbished easily.

However, such finishes can become rancid and can sometimes impart undesirable odors and/or flavors to food.

Of these finish types, the impermeable varnishes and lacquers

may be the best option for bowls and eating utensils; this

kind of finish is easiest to keep clean and most resistant to

absorption of stains.

Note: Whatever finish is chosen for wood utensils

used to store, handle, or eat food, it is important to

be sure that the finish is safe and not toxic

(poisonous). Also be sure that the finish you select

is recommended for use with food or is described as

food grade. For information on the safety and toxicity of any finish, check the label, contact the

manufacturer and/or the Food and Drug Administration, or check with your local extension home economics expert or county agent.

Butcher Blocks and Cutting Boards

One of the simplest treatments for wood butcher blocks and

cutting boards is the application of melted paraffin wax (the

type used for home canning). The wax is melted in a doubleboiler over hot water and liberally brushed on the wood

surface. Excess wax, which has solidified on the surface, can

be melted with an iron to absorb it into the wood, or it may

be scraped off. Refinishing is simple and easy. Other penetrating finishes (sealers, drying and nondrying oils) may also

be used for butcher blocks and cutting boards. As mentioned

in the subsection on eating utensils, vegetable oils may

become rancid. If a nondrying oil is desired, mineral oil may

be used. Film-forming finishes are not recommended for

butcher blocks or cutting boards.

Wood Cleaners and

Brighteners

The popularity of wood decks and the desire to keep them

looking bright and new has led to a proliferation of commercial cleaners and brighteners. The removal of mildew from

wood was discussed in an earlier section of this chapter (see

Finish Failure or Discoloration). Mildew growth on unpainted and painted wood continues to be the primary cause

of discoloration. Although it can be removed with a dilute

solution of household bleach and detergent, many commercial products are available that can both remove mildew and

brighten the wood surface.

The active ingredient in many of these products is sodium

percarbonate (disodium peroxypercarbonate). This chemical

is an oxidizing agent as is bleach, and it is an effective mildew cleaner. It also helps brighten the wood surface. Some

cleaners and brighteners are reported to restore color to wood.

It is not possible to add color to wood by cleaning it. Removing the discoloration reveals the original color. Brightening the wood may make it appear as if it has more color.

Once all the colored components of the wood surface have

been removed through the weathering process, the surface

will be a silvery gray. If color is desired after weathering

occurs, it must be added to the wood by staining.

In addition to sodium percarbonate, other oxidizing products

may contain hydrogen peroxide by itself or in combination

with sodium hydroxide. If sodium hydroxide is used without

a brightener, it will darken the wood. Commercial products

are also formulated with sodium hypochlorite and/or calcium

hypochlorite (household bleach is a solution of sodium

hypochlorite). These products usually contain a surfactant or

detergent to enhance the cleansing action of the oxidizing

agent. Other types of brighteners contain oxalic acid. This

chemical removes stains caused by extractives bleed and iron

stains and also brightens the wood, but it is not very effective for removing mildew.

Paint Strippers

Removing paint and other film-forming finishes from wood

is a time-consuming and often difficult process. It is generally not done unless absolutely necessary to refinish the

wood. Removing the finish is necessary if the old finish has

extensive cross-grain cracking caused by buildup of many

layers of paint, particularly oil-based paint. If cracking and

peeling are extensive, it is usually best to remove all the

paint from the affected area. Total removal of paint is also

necessary if the paint has failed by intercoat peeling. It may

be necessary to remove paint containing lead; however, if the

paint is still sound and it is not illegal to leave it on the

structure, it is best to repaint the surface without removing

the old paint (see Lead-Based Paint).

This discussion of paint strippers is limited to film-forming

finishes on wood used in structures. Removing paint from

furniture can be done using the same methods as described

here. Companies that specialize in stripping furniture usually
 15–34

immerse the furniture in a vat of paint stripper and then clean

and brighten the wood. This procedure removes the paint

very efficiently.

Some of the same methods can be used for the removal of

interior and exterior paint. Because of the dust caused by

mechanical methods or the fumes given off by chemical

strippers, it is extremely important to use effective safety

equipment, particularly when working indoors. A good

respirator is essential, even if the paint does not contain lead

(see Lead-Based Paint).

Note: The dust masks sold in hardware stores do not

block chemical fumes and are not very effective

against dust.

Two general types of stripping methods are discussed here:

mechanical and chemical. The processes are discussed in

general terms primarily in regard to their effect on wood;

some attention is given to their ease of use and safety requirements. Consult product literature for additional information on appropriate uses and safety precautions.

Mechanical Methods

Finishes can be removed by scraping, sanding, wet or dry

sandblasting, spraying with pressurized water (power washing), and using electrically heated pads, hot air guns, and

blow torches. Scraping is effective only in removing loosely

bonded paint or paint that has already partially peeled from

the wood. It is generally used when paint needs to be removed only from small areas of the structure, and it is generally combined with sanding to feather the edge of the paint

still bonded to the wood (see Lead-Based Paint).

When the paint is peeling and partially debonded on large

areas of a structure, the finish is usually removed by power

washing or wet sandblasting. These methods work well for

paint that is loosely bonded to the wood. If the paint is well

bonded, complete removal can be difficult without severely

damaging the wood surface. The pressure necessary to debond paint from the wood can easily cause deep erosion of

the wood. The less dense earlywood erodes more than the

dense latewood, leaving behind a surface consisting of latewood, which is more difficult to repaint. Power washing is

less damaging to the wood than is wet or dry sandblasting,

particularly if low pressure is used. If high pressure is necessary to remove the paint, it is probably bonded well enough

that it does not need to be removed for normal refinishing. If

more aggressive mechanical methods are required, wet sandblasting can remove even well-bonded paint, but it causes

more damage to the wood than does water blasting. Dry

sandblasting is not very suitable for removing paint from

wood because it can quickly erode the wood surface along

with the paint, and it tends to glaze the surface.

A number of power sanders and similar devices are available

for complete paint removal. Many of these devices are suitable for removing paint that contains lead; they have attachments for containing the dust. Equipment that has a series of

blades similar to a power hand-planer is less likely to “gum

up” with paint than equipment that merely sands the surface.

Some of this equipment is advertised in the Old House

Journal and the Journal of Light Construction. Please

consult the manufacturers’ technical data sheets for detailed

information to determine the suitability of their equipment

for your needs and to meet government regulations on leadcontaining paint.

Paint can be removed by heating then scraping it from the

wood, but this method must not be used for paint that contains lead. Paint can be softened by using electrically heated

pads, hot air guns, or blow torches. Heated pads and hot air

guns are slow methods, but they cause little damage to the

wood. Sanding is still necessary, but the wood should be

sound after the paint is removed. Blow torches have been

used to remove paint and, if carefully used, do not damage

the wood. Blow torches are extremely hazardous; the flames

can easily ignite flammable materials beneath the siding

through gaps in the siding. These materials may smolder,

undetected, for hours before bursting into flame and causing

loss of the structure.

Note: Removing paint with a blow torch is not

recommended.

Chemical Methods

If all the paint needs to be removed, then mechanical methods should be used in concert with other methods, such as

chemical paint strippers. For all chemical paint strippers, the

process involves applying paint stripper, waiting, scraping

off the softened paint, washing the wood (and possibly neutralizing the stripper), and sanding the surface to remove the

wood damaged by the stripper and/or the raised grain caused

by washing. Chemical paint strippers, although tedious to

use, are sometimes the most reasonable choice. A range of

paint strippers are available. Some are extremely strong

chemicals that quickly remove paint but are dangerous to

use. Others remove the paint slowly but are safer. With the

exception of alkali paint stripper (discussed below), there

appears to be an inverse correlation between how safe a

product is and how fast it removes the paint.

Solvent-Based Strippers

Fast-working paint strippers usually contain methylene

chloride, a possible carcinogen that can burn eyes and skin.

Eye and skin protection and a supplied-air respirator are

essential when using this paint stripper. Paint strippers

having methylene chloride can remove paint in as little as

10 min. Because of concerns with methylene chloride, some

paint strippers are being formulated using other strong solvents; the same safety precautions should be used with these

formulations as with those containing methylene chloride.

To remain effective in removing paint, a paint stripper must

remain liquid or semiliquid; slow-acting paint stripers are

often covered to keep them active. Solvent-type strippers

contain a wax that floats to the surface to slow the evaporation of the solvent. Covering the paint stripper with plastic

wrap also helps to contain the solvent.
15–35

Alkali-Based Strippers

As an alternative to strong solvents, some paint strippers

contain strong bases (alkali). Like solvent-based paint strippers, alkali-based strippers require eye and skin protection.

Follow the manufacturer’s recommendations about whether a

respirator is necessary as well. Although alkali-based paint

strippers soften the paint rather slowly, they are strong

chemicals and can severely damage the wood substrate.

Because they degrade the paint slowly, these strippers are

often left on the painted wood a full day or overnight. They

are usually covered with a cloth, which helps in peeling the

weakened paint from the surface.

These cloth-covered types of products have the advantage of

containing the paint stripper and paint extremely well, an

important consideration when removing paint containing

lead. They have the disadvantage of severely degrading the

wood substrate. Strong alkali actually pulps the wood surface. Once the paint is removed, it is essential to neutralize

the surface with acid. Oxalic acid is frequently used for this

process. Unfortunately, it is extremely difficult to balance the

acid and base concentrations. If excess alkali is left in the

wood, it will continue to degrade it and to degrade the subsequent paint coating. Excess oxalic acid can also damage

the wood. The neutralization procedure leaves behind reaction products of the acid and base (water and a salt). Often,

the salt is hygroscopic (absorbs moisture from the air) and

causes the wood to get wet. Wet wood does not hold paint

very well.

Note: Alkali-based strippers require extra care to

ensure that the wood is neutralized and that residual

salts are washed from the wood. The surface must

be sanded before repainting.

Since the surface must be sanded before repainting, paint

performance might be improved by letting the wood weather

for an extended period (possibly as long as a year) before

repainting to let rain leach unwanted chemicals from the

wood. In addition, rinse the siding periodically using a hose,

particularly areas that rain does not reach, such as siding

under eaves and porches. Once all the residue has been

removed, the surface can be sanded (50-grit sandpaper)

and painted.

Although alkali paint strippers can cause burns on unprotected skin, the fumes are not nearly as toxic as those in

solvent-type strippers. Alkali paint strippers are an excellent

choice for indoor use such as door and window trim and

fireplace mantles. Indoors, the weakened wood surface may

not be as much of a concern because less stress is placed on

the wood–paint interface; the wood is not exposed to

weather extremes.

“Safe” Paint Strippers

Several paint strippers are being marketed under the “safe”

caveat. These strippers work much slower than those having

strong chemical solvents. The active ingredient in such paint

strippers is usually proprietary. In regard to safety, follow the

manufacturer’s recommendations.

Avoidance of Problems

Failure of the finish on wood that has been stripped can be

avoided by using methods that do not damage the wood

surface. The best way to remove paint may involve a combination of methods. For example, use power washing to

remove as much paint as possible. Then, use a solvent-based

chemical paint stripper on paint that could not be removed

by power washing. Avoid using excessive amounts of

chemical stripper. Applying too much stripper or leaving it

on the painted wood for too long can damage the wood. It is

better to use less stripper and reapply it, if necessary, than to

try to remove all the paint with one application, leaving the

stripper on the paint for an extended period.

The problem of paint removal is complicated by the wide

range of paint types and wood species. Companies that make

paint strippers may optimize the formulations without considering their effects on the wood. Removing the paint from

the wood is only half the task. Getting a paintable surface is

the other half. Companies that formulate paint strippers must

consider this other half. Those who use paint strippers need

to understand the added burden of surface preparation.

Disposal of Old Paint

No matter what method you use to remove paint, be careful

in disposing of the old paint, particularly paint that contains

lead. Lead is considered hazardous waste, and there are regulations that restrict the handling and disposal of this material. Be sure to follow all regulations, both national and

local, during the removal, storage, and disposal of paint,

especially paint containing lead (see Lead-Based Paint).

Lead-Based Paint

The information in this section is taken from material prepared by the National Association of Home Builders

(NAHB) and is contained in Rehabilitation of Wood-Frame

Houses (USDA 1998). Lead-based paint was widely used in

residential applications in the United States until the early

1940s, and its use was continued to some extent, particularly

for the exterior of dwellings, until 1976. In 1971, Congress

passed the Lead-Based Paint Poisoning Prevention Act, and

in 1976, the Consumer Product Safety Commission (CPSC)

issued a ruling under this Act that limited the lead content

of paint used in residential dwellings, toys, and furniture

to 0.06%.

Lead-based paint is still manufactured today for applications

not covered by the CPSC ruling, such as paint for metal

products, particularly those made of steel. Occasionally, such

lead-based paint (for example, surplus paint from a shipyard)

inadvertently gets into retail stores and the hands of consumers. A study conducted for the Environmental Protection

Agency in 1986 indicated that about 42 million U.S. homes

still contain interior and/or exterior lead-based paint. As

rehabilitation of these homes increases, how to abate the

toxicity of lead-based paint has become the subject of increased public and official concern.
 15–36

Studies have shown that ingestion of even minute amounts

of lead can have serious effects on health, including hypertension, fetal injury, and damage to the brain, kidneys, and red

blood cells. Low levels of ingestion can also cause partial

loss of hearing, impairment of mental development and IQ,

growth retardation, inhibited metabolism of vitamin D, and

disturbances in blood formation. The American Academy of

Pediatrics regards lead as one of the foremost toxicological

dangers to children.

Lead-based paint applied to the exterior of homes disintegrates into chalk and powder as a result of the effects of moisture and ultraviolet radiation. This extremely fine lead dust

can accumulate in the soil near the house and can ultimately

enter the house. Poor quality lead-based paint used on interior surfaces can also produce dust. Lead dust can be generated when coatings on surfaces are broken through aging or

as a result of rehabilitation. The dust cannot be completely

removed by conventional house-cleaning methods.

Methods used to abate the toxicity of lead-based paint or to

remove the paint can themselves generate lead dust. This is

particularly true when unacceptable methods and work practices are used. Poorly performed abatement can be worse than

no abatement. The micron-sized lead dust particles can

remain airborne for substantial periods and cannot be fully

removed by standard cleaning methods from the surfaces on

which they have settled. When working on old painted

surfaces, the worker should assume that one or more of the

paint coats contain lead. Proper precautions should be taken

accordingly.

Paint coats may be checked for lead content. A portable x-ray

fluorescence (XRF) analyzer is commonly used to determine

the level of lead in paint. Because this device has the potential for giving very inaccurate results if used by an inexperienced person, the analysis should be done by a qualified

professional. Chemical spot testing, using a solution of 6%

to 8% sodium sulfide in water, is sometimes used to screen

painted surfaces for the presence of lead. Be certain to check

all paint coats, because the older ones are more likely to be

lead based. Test kits for detecting lead-based paint are available in most paint and hardware stores.

Removal of lead-based paints can present some serious health

problems. The U.S. Department of Health and Urban Development (HUD) has taken a leading role in developing guidelines for the removal of lead-based paints. At this time, HUD

has approved three approaches to abating the toxicity of

lead-based paint:

1. Covering the painted surface with wallboard, a fiberglass

cloth barrier, or permanently attached wallpaper

2. Removing the paint

3. Replacing the entire surface to which lead-based paint has

been applied

Certain practices are prohibited in residential structures

owned and operated by HUD: machine sanding without an

attached high-efficiency particulate air (HEPA) vacuum

filtration apparatus, use of propane torches, contained water

blasting, washing, and repainting.

Removal of lead-based paint by scraping or application of

heat does not solve the problem of lead-particulate dust.

Scraping should be accompanied by misting. Dry scraping is

prohibited by Maryland abatement regulations. Sanding

without a HEPA-filtered vacuum should not be used as a

finishing method after scraping or any other method of toxicity abatement. The HEPA sanders are recommended for

limited surface areas only; they are most appropriate for flat

surfaces such as door jambs and stair risers. Open abrasive

blasting is also prohibited by some regulations.

High levels of airborne lead can be produced by heat guns,

and the use of a respirator is essential. Some lead is likely to

be volatilized at the operating temperatures of most heat

guns. Lead fumes are released at about 371°C (700°F). Heat

guns capable of reaching or exceeding this temperature

should not be operated in that range.

Chemical methods for removing lead-based paint may require

multiple applications, depending on the number of paint

coats. Caustic and solvent-based chemicals should not be

allowed to dry on the lead-painted surface. If drying occurs,

paint removal will not be satisfactory and the potential for

creating lead dust will be increased.

Chemical substances used for paint removal are usually

hazardous and should be used with great care. Some solvent-based chemical strippers are flammable and require

ventilation. They may contain methylene chloride, which is

a central nervous system depressant that at high concentrations can cause kidney and liver damage and is a possible

carcinogen. Supplied-air respirators should be used when

working with strippers containing this substance. If the

solvent-based strippers do not contain methylene chloride,

organic vapor filters must be added to respirators. Caustic

chemical strippers also have a very high pH (alkaline content), which can cause severe skin and eye injuries.

Caution: Remodeling or refinishing projects that

require disturbing, removing, or demolishing portions of the structure that are coated with lead-based

paint pose serious problems. The consumer should

seek information, advice, and perhaps professional

assistance for addressing these problems. Contact

HUD for the latest information on the removal of

lead-based paints. Debris coated with lead-based

paint is regarded as hazardous waste.

References

APA. 1979. Stains and paints on plywood. Pamphlet

B407B. Tacoma, WA: American Plywood Association.

Black, J.M.; Mraz, E.A. 1974. Inorganic surface treatments

for weather-resistant natural finishes. Res. Pap. FPL–232.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.
15–37

Cassens, D.L.; Feist, W.C. 1980. Wood finishing: Finishing exterior plywood, hardboard and particle board. North

Central Region Extension Pub. 132. West Lafayette, IN:

Purdue University, Cooperative Extension Service.

Cassens, D.L.; Feist, W.C. 1980. Wood finishing: paint

failure problems and their cure. North Central Region Extension Publ. 133. West Lafayette, IN: Purdue University,

Cooperative Extension Service.

Cassens, D.L.; Feist, W.C. 1980. Wood finishing: discoloration of house paint—causes and cures. North Central

Region Extension Publ. 134. West Lafayette, IN: Purdue

University, Cooperative Extension Service.

Cassens, D.L.; Feist, W.C. 1980. Wood finishing: selection and application of exterior finishes for wood. North

Central Region Extension Publ. 135. West Lafayette, IN:

Purdue University, Cooperative Extension Service.

Cassens, D.L.; Feist, W.C. 1980. Wood finishing: finishing and maintaining wood floors. North Central Region

Extension Publ. 136. West Lafayette, IN: Purdue University,

Cooperative Extension Service.

Feist, W.C. 1979. Protection of wood surfaces with chromium trioxide. Res. Pap. FPL–339. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Feist, W.C. 1982. Weathering of wood in structural uses.

In: Meyer, R.W.; Kellogg, R.M., eds. Structural use of

wood in adverse environments. New York: Van Nostrand

Reinhold Company: 156–178.

Feist, W.C. 1982. Weathering characteristics of finished

wood-based panel products. Journal of Coating Technology.

54(686): 43–50.

Feist, W.C. 1990. Outdoor wood weathering and protection.

In: Rowell, R., ed. Archaeological wood, properties, chemistry, and preservation. Advanced in Chemistry Series No.

225. Washington, DC: American Chemical Society.

263–298. Chapter 11.

Feist, W.C. 1996. Finishing exterior wood. Federation

Series on Coatings Technology. Blue Bell, PA: Federation

of Societies for Coatings Technology.

Feist, W.C.; Hon, D.N.–S. 1984. Chemistry of weathering

and protection. In: Rowell, R.M., ed. The chemistry of solid

wood. Advances in Chemistry Series No. 207. Washington

DC: American Chemical Society: 401–451. Chapter 11.

Feist, W.C.; Mraz, E.A. 1980. Performance of mildewcides

in a semitransparent stain wood finish. Forest Products

Journal. 30(5): 43–46.

Feist, W.C.; Ross, A.S. 1995. Performance and durability of

finishes on previously coated CCA-treated wood. Forest

Products Journal. 45(9): 29–36.

Gorman, T.M.; Feist, W.C. 1989. Chronicle of 65 years of

wood finishing research of the Forest Products Laboratory.

Gen. Tech. Rep. FPL–GTR–60. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Kalnins, M.A.; Feist, W.C. 1993. Increase in wettability

of wood with weathering. Forest Products Journal.

43(2): 55–57.

McDonald, K.A.; Falk, R.H.; Williams, R.S.; Winandy,

J.E. 1996. Wood decks: materials, construction, and

finishing. Madison, WI: Forest Products Society.

Niemiec, S.S.; Brown, T.D. 1988. Care and maintenance of

wood shingle and shake roofs. Corvallis, OR: Oregon State

University Extension Service. EC 1271, September.

Richter, K.; Feist, W.C.; Knaebe, M.T. 1995. The effect

of surface roughness on the performance of finishes. Part 1.

Roughness characterization and stain performance. Forest

Products Journal. 45(7/8): 91–97.

Ross, A.S.; Feist, W.C. 1993. The effects of CCA-treated

wood on the performance of surface finishes. American Paint

and Coatings Journal. 78(9): 41–54.

Ross, A.S.; Bussjaeger, R.C.; Feist, W.C. 1992. Professional finishing of CCA pressure-treated wood. American

painting Contractor. 69(7): 107–114.

Sell, J.; Feist, W.C. 1986. Role of density in the erosion

of wood during weathering. Forest Products Journal.

36(3): 57–60.

Tichy, R.J. 1997. Interior wood finishing: industrial use

guide. Madison, WI: Forest Products Society.

USDA. 1998. Rehabilitation of wood-frame houses. Agric.

Handb. 804. Washington, DC: U.S. Department of Agriculture, Forest Service.

WDMA. 1999. Industry standard for water-repellent preservative treatment for millwork. IS4–99. Des Plaines, IL:

Window and Door Manufacturer’s Association.

Williams, R.S. 1986. Effects of acid rain on painted wood

surfaces: importance of the substrate. In: Baboian, R., ed.

Materials degradation caused by acid rain. ACS Symposium

Series 318. Washington DC: American Chemical Society:

310–331.

Williams, R.S. 1990. Effects of acidic deposition on painted

wood. In: Effects of acidic deposition on materials. State of

Science and State of Technology, Report 19. National Acid

Precipitation Assessment Program: 19/165–19/202. Vol. 3.

Williams, R.S.; Feist, W.C. 1993. Durability of paint or

solid-color stain applied to preweathered wood. Forest

Products Journal. 43(1): 8–14.

Williams, R.S.; Feist, W.C. 1994. Effect of preweathering,

surface roughness, and wood species on the performance of

paint and stains. Journal of Coatings Technology.

66(828): 109–121.

Williams, R.S.; Winandy, J.E.; Feist, W.C. 1987. Adhesion of paint to weathered wood. Forest Products Journal.

37(11/12): 29–31.

Williams, R.S.; Winandy, J.E.; Feist, W.C. 1987. Paint

adhesion to weathered wood. Journal of Coatings

Technology. 59(749): 43–49.

Williams, R.S.; Knaebe, M.T.; Feist, W.C. 1996.

Finishes for exterior wood. Madison, WI: Forest Products

Society.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
16–1

Use of Wood in Buildings

and Bridges

Russell C. Moody and Anton TenWolde

Chapte r 16

Contents

Light-Frame Buildings 16–1

Foundations 16–2

Floors 16–2

Exterior Walls 16–3

Ceiling and Roof 16–4

Wood Decks 16–4

Post-Frame and Pole Buildings 16–4

Log Buildings 16–6

Heavy Timber Buildings 16–6

Timber Frame 16–6

Mill Type 16–7

Glulam Beam 16–8

Arch Structure 16–8

Dome 16–8

Timber Bridges 16–9

Log Stringer 16–9

Sawn Lumber 16–9

Glulam 16–10

Structural Composite Lumber 16–10

Considerations for Wood Buildings 16–10

Structural 16–10

Thermal Insulation and Air Infiltration Control 16–11

Moisture Control 16–12

Sound Control 16–13

References 16–14

n North America, most housing and commercial

structures built prior to the 20th century used

wood as the major structural material. The abundant wood resource formed the basic structure for most

houses, commercial buildings, bridges, and utility poles.

Today, houses and many light commercial and industrial

buildings are made using modern wood structural materials.

Recently, there has been increased interest in using wood for

various types of transportation structures, including bridges.

In this chapter, the features of various types of building

systems are described. Emphasis is placed on how these

systems have adapted to the use of modern materials and

techniques. For example, where floor, wall, and roof sheathing for light-frame construction were once commonly made

from wood boards, sheathing is now commonly made from

structural panel products, such as plywood and structural

flakeboard. Compared with boards, these panel products are

quicker to install and provide improved structural resistance

to wind and earthquake loadings. Furthermore, prefabricated

floor and wall panels along with prefabricated roof and floor

trusses or I-joists are replacing piece-by-piece on-site

construction with dimension lumber. A structure can be

enclosed within a short time on site using factory-made

panelized systems.

Glulam and other panelized wood systems are being used

increasingly for both highway and railroad bridges. A brief

description of the uses of wood in these types of structures is

included.

Light-Frame Buildings

Historically, two general types of light-frame construction

have been used—balloon and platform framing. Balloon

framing, which was used in the early part of the 20th century,

consists of full-height wall framing members for two-story

construction. Additional information on balloon framing is

available from older construction manuals. In the latter part

of the 20th century, platform framing has dominated the

housing market and is widely used in commercial and light

industrial applications. Platform framing features the construction of each floor on top of the one beneath. Platform

framing construction differs from that of 50 years ago in the

use of new and innovative materials, panel products for floor
 16–2

and roof sheathing, and prefabricated components and modules as opposed to “stick built” or on-site construction. A

detailed description of the platform-type of construction is

given in Wood Frame House Construction (Sherwood and

Stroh 1989); additional information is given in the Wood

Frame Construction Manual for One- and Two-Family

Dwellings, 1995 SBC High Wind Edition (AF&PA 1995).

Foundations

Light-frame buildings with basements are typically supported

on cast-in-place concrete walls or concrete block walls supported by footings. This type of construction with a basement is common in northern climates. Another practice is to

have concrete block foundations extend a short distance

above ground to support a floor system over a “crawl space.”

In southern and western climates, some buildings have no

foundation; the walls are supported by a concrete slab, thus

having no basement or crawl space.

Treated wood is also used for basement foundation walls.

Basically, such foundations consist of wood-frame wall

sections with studs and plywood sheathing supported on

treated wood plates, all of which are preservatively treated to

a specified level of protection. To distribute the load, the

plates are laid on a layer of crushed stone or gravel. Walls,

which must be designed to resist the lateral loads of the

backfill, are built using the same techniques as conventional

walls. The exterior surface of the foundation wall below grade

is draped with a continuous moisture barrier to prevent direct

water contact with the wall panels. The backfill must be

designed to permit easy drainage and provide drainage from

the lowest level of the foundation.

Because a foundation wall needs to be permanent, the preservative treatment of the plywood and framing as well as the

fasteners used for connections are very important. A special

foundation (FDN) treatment has been established for the

plywood and framing, with strict requirements for depth of

chemical penetration and amount of chemical retention.

Corrosion-resistant fasteners (for example, stainless steel) are

recommended for all preservatively treated wood. Additional

information and materials and construction procedures are

given in Permanent Wood Foundation Basic Requirements

(AF&PA 1987).

Floors

For houses with basements, the central supporting structure

may consist of wood posts on suitable footings that carry a

built-up girder, which is frequently composed of planks the

same width as the joists (standard 38 by 184 mm to 38 by

286 mm (nominal 2 by 8 in. to 2 by 12 in.)), face-nailed

together, and set on edge. Because planks are seldom sufficiently long enough to span the full length of the beam, butt

joints are required in the layers. The joints are staggered in

the individual layers near the column supports. The girder

may also be a glulam beam or steel I-beam, often supported

on adjustable steel pipe columns. Similar details may be

applied to a house over a crawl space. The floor framing in

residential structures typically consists of wood joists on

400- or 600-mm (16- or 24-in.) centers supported by the

foundation walls and the center girder (Fig. 16–1).

Double joists

under partitions

Solid bridging

under load bearing

partitions only

Anchored sill

Lap joists

over girder

10 cm minimum (4 in.)

or butt and scab

Stringer joist

Header joist

Structural panel

subfloor

Figure 16–1. Typical floor details for platform construction with joists spliced on center beam.
16–3

Joist size depends on the anticipated loading, spacing between joists, distance between supports (span), species, and

grade of lumber. Commonly used joists are standard 38- by

184-mm or 38- by 235-mm (nominal 2- by 8-in. or 2- by

10-in.) lumber, prefabricated wood I-joists, or parallel chord

trusses. Lumber joists typically span from 3.6 to 4.8 m (12

to 16 ft). Span tables are available from the American Forest

& Paper Association (AF&PA 1993). Span capabilities of

the prefabricated wood I-joists or parallel chord trusses are

recommended by the manufacturer.

Floor openings for stairways, fireplaces, and chimneys may

interrupt one or more joists. Preferably, such openings are

parallel to the length of the joists to reduce the number of

joists that will be interrupted. At the interruption, a support

(header) is placed between the uninterrupted joists and attached to them. A single header is usually adequate for openings up to about 1.2 m (4 ft) in width, but double headers

are required for wider openings. Special care must be taken to

provide adequate support at headers (using joist hangers, for

example).

Cutting of framing members to install items such as plumbing lines and heating ducts should be minimized. Cut members may require a reinforcing scab, or a supplementary

member may be needed. Areas of highly concentrated loads,

such as under bathtubs, require doubling of joists or other

measures to provide adequate support. One advantage of

framing floors with parallel-chord trusses or prefabricated Ijoists is that their longer span capabilities may eliminate the

need for interior supports. An additional advantage is that the

web areas of these components are designed for easy passing

of plumbing, electrical, and heating ducts.

Floor sheathing, or subflooring, is used over the floor framing to provide a working platform and a base for the finish

flooring. Older homes have board sheathing but newer homes

generally use panel products. Common sheathing materials

include plywood and structural flakeboard, which are available in a number of types to meet various sheathing requirements. Exterior-type panels with water-resistant adhesive are

desirable in locations where moisture may be a problem,

such as floors near plumbing fixtures or situations where the

subfloor may be exposed to the weather for some time during

construction.

Plywood should be installed with the grain direction of the

face plies at right angles to the joists. Structural flakeboard

also has a preferred direction of installation. Nailing patterns

are either prescribed by code or recommended by the manufacturer. About 3 mm (1/8 in.) of space should be left between the edges and ends of abutting panels to provide for

dimensional changes associated with moisture content.

Literature from APA–The Engineered Wood Association

includes information on the selection and installation of the

types of structural panels suitable for subfloors (APA 1996).

Exterior Walls

Exterior walls of light-frame structures are generally load

bearing; they support upper floors and the roof. An exception

is the gable ends of a one- or two-story building. Basically,

wall framing consists of vertical studs and horizontal members, including top and bottom plates and headers (or lintels)

over window and door openings. The studs are generally

standard 38- by 89 mm, 38- by 114-mm, or 38- by 140-mm

(nominal 2- by 4-in., 2- by 5-in., or 2- by 6-in.) members

spaced between 300 and 600 mm (12 and 24 in.) on center.

Selection of the stud size depends on the load the wall will

carry, the need for support of wall-covering materials, and the

need for insulation thickness in the walls. Headers over

openings up to 1.2 m (4 ft) are often 38 by 140 mm (2 by

6 in.), nailed together face to face with spacers to bring the

headers flush with the faces of the studs. Special headers that

match the wall thickness are also available in the form of

either prefabricated I-joists or structural composite lumber.

Wall framing is erected over the platform formed by the firstfloor joists and subfloor. In most cases, an entire wall is

framed in a horizontal position on the subfloor, then tilted

into place. If a wall is too long to make this procedure practical, sections of the wall can be formed horizontally and

tilted up, then joined to adjacent sections.

Corner studs are usually prefabricated in such a configuration as to provide a nailing edge for the interior finish

(Fig. 16–2). Studs are sometimes doubled at the points of

intersection with an interior partition to provide backup

support for the interior wall finish. Alternatively, a horizontal

block is placed midheight between exterior studs to support

the partition wall. In such a case, backup clips on the partition stud are needed to accommodate the interior finish.

Upper plates are usually doubled, especially when rafters or

floor joists will bear on the top plate between studs. The

second top plate is added in such a way that it overlaps the

first plate at corners and interior wall intersections. This

provides a tie and additional rigidity to the walls. In areas

subject to high winds or earthquakes, ties should be provided between the wall, floor framing, and sill plate that

should be anchored to the foundation. If a second story is

added to the structure, the edge floor joist is nailed to the top

wall plate, and subfloor and wall framing are added in the

same way as the first floor.

Sheathing for exterior walls is commonly some type of panel

product. Here again, plywood or structural flakeboard may be

used. Fiberboard that has been treated to impart some degree

of water resistance is another option. Several types of fiberboard are available. Regular-density board sometimes requires additional bracing to provide necessary resistance to

lateral loads. Intermediate-density board is used where structural support is needed. Numerous foam-type panels can also

be used to impart greater thermal resistance to the walls.

In cases where the sheathing cannot provide the required

racking resistance, diagonal bracing must be used. Many

foam sheathings cannot provide adequate racking resistance,
 16–4

so either diagonal braces must be placed at the corners or

structural panels must be applied over the first 1.2 m (4 ft) of

the wall from the corner. When light-weight insulating foam

sheathings are used, bracing is commonly provided by standard 19- by 89-mm (nominal 1- by 4-in.) lumber or steel

strapping.

Ceiling and Roof

Roof systems are generally made of either the joists-and-rafter

systems or with trusses. Engineered trusses reduce on-site

labor and can span greater distances without intermediate

support, thus eliminating the need for interior load-carrying

partitions. This provides greater flexibility in the layout of

interior walls. Prefabricated roof trusses are used to form the

ceiling and sloped roof of more than two-thirds of current

light-frame buildings. For residential buildings, the trusses

are generally made using standard 38- by 89-mm (nominal

2- by 4-in.) lumber and metal plate connectors with teeth

that are pressed into the pieces that form the joints (TPI

1995).

Joists and rafter systems are found in most buildings constructed prior to 1950. Rafters are generally supported on the

top plate of the wall and attached to a ridge board at the roof

peak. However, because the rafters slope, they tend to push

out the tops of the walls. This is prevented by nailing the

rafters to the ceiling joists and nailing the ceiling joists to

the top wall plates (Fig. 16–3a).

A valley or hip is formed where two roof sections meet

perpendicular to each other. A valley rafter is used to support

short-length jack rafters that are nailed to the valley rafter and

the ridge board (Fig. 16–3b). In some cases, the roof does

not extend to a gable end but is sloped from some point

down to the end wall to form a “hip” roof. A hip rafter supports the jack rafters, and the other ends of the jack rafters are

attached to the top plates (Fig. 16–3c). In general, the same

materials used for wall sheathing and subflooring are used for

roof sheathing.

Wood Decks

A popular method of expanding the living area of a home is

to build a wood deck adjacent to one of the exterior walls.

Decks are made of preservatively treated lumber, which is

generally available from the local building supply dealer and,

depending upon the complexity, may be built by the “do-ityourselfer.” To ensure long life, acceptable appearance, and

structural safety, several important guidelines should be

followed. Proper material selection is the first step. Then,

proper construction techniques are necessary. Finally, proper

maintenance practices are necessary. Detailed recommendations for all these areas are included in Wood Decks: Materials, Construction, and Finishing (McDonald and others

1996).

Post-Frame and Pole Buildings

In post-frame and pole buildings, round poles or rectangular

posts serve both as the foundation and the principal vertical

framing element. This type of construction was known as

“pole buildings” but today, with the extensive use of posts,

is commonly referred to as “post-frame” construction. For

relatively low structures, light wall and roof framing are

nailed to poles or posts set at fairly frequent centers, commonly 2.4 to 3.6 m (8 to 12 ft). This type of construction

2 by 4 block

(a) Nailing areas for

inside finish

Sole plate

(b)

Metal wall board

backup clip

(c)

Subfloor

Figure 16–2. Corner details for wood stud walls that

provide support for interior sheathing: (a) traditional

three-stud corner with blocking; (b) three-stud corner

without blocking; (c) two-stud corner with wallboard

backup clips.
16–5

was originally used with round poles for agricultural buildings, but the structural principle has been extended to commercial and residential buildings (Fig. 16–4).

Round poles present some problems for connecting framing

members; these problems can be eased by slabbing the outer

face of the pole. For corner poles, two faces may be slabbed

at right angles. This permits better attachment of both light

and heavy framing by nails or timber connectors. When the

pole is left round, the outer face may be notched to provide

seats for beams.

Rectangular posts are the most commonly used and may be

solid sawn, glulam, or built-up by nail laminating. Built-up

posts are advantageous because only the base of the post

must be preservatively treated. The treated portion in the

ground may have laminations of varying lengths that are

matched with the lengths of untreated laminations in the

upper part of the post. The design of these types of posts

must consider the integrity of the splice between the treated

and untreated lumber. The wall system consists of horizontal

girts often covered by light-gauge metal that provides some

degree of racking resistance.

Hip rafter

Jack rafter

Top

plates

Ceiling

joist

Nailing block

(for ceiling

finish)

(a)

(b) (c)

Rafter

Collar beam

Ridge board

Rafter

Block

Notch or

"bird's mouth"

Top plates

End stud

Ceiling joist

Ceiling

joist

Nailer for

cornice trim

Stud

Top plates

Rafter

Valley rafter

Jack rafter

Figure 16–3. (a) A rafter-type roof with typical framing details for (b) a valley and (c) a hip corner.
 16–6

Roof trusses made with metal plate connectors are attached to

each pole, or posts, and roof purlins are installed perpendicular to the trusses at spacings from 1.2 to 3.7 m (4 to 12 ft),

with 2.4 m (8 ft) as a common spacing. For 2.4-m (8-ft)

truss spacing, these purlins are often standard 38 by 89 mm

(nominal 2 by 4 in.) spaced on 0.6-m (2-ft) centers and

attached to either the top of the trusses or between the trusses

using joists hangers. The roofing is often light-gauge metal

that provides some diaphragm stiffness to the roof and transmits a portion of the lateral loading to the walls parallel to

the direction of the load. Detailed information on the design

of post-frame buildings is given in the National Frame

Builders Association ([n.d.]) or Walker and Woeste (1992).

Log Buildings

Interest is growing in log houses—from small, simple

houses for vacation use to large, permanent residences

(Fig. 16–5). Many U.S. firms specialize in the design and

material for log houses. Log homes nearly always feature

wall systems built from natural or manufactured logs rather

than from dimension lumber. Roof and floor systems may be

also be built with logs or conventional framing. Log home

companies tend to categorize log types into two systems:

round and shaped. In the round log system, the logs are

machined to a smooth, fully rounded surface, and they are

generally all the same diameter. In the shaped system, the

logs are machined to specific shapes, generally not fully

round. The exterior surfaces of the logs are generally

rounded, but the interior surfaces may be either flat or round.

The interface between logs is machined to form an interlocking joint.

Consensus standards have been developed for log grading

and the assignment of allowable properties, and these standards are being adopted by building codes (ASTM 1996).

Builders and designers need to realize that logs can reach the

building site at moisture content levels greater than ideal.

The effects of seasoning and the consequences of associated

shrinkage and checking must be considered. Additional

information on log homes is available from The Log Home

Council, National Association of Home Builders,

Washington, DC.

Heavy Timber Buildings

Timber Frame

Timber frame houses were common in early America and are

enjoying some renewed popularity today. Most barns and

factory buildings dating prior to the middle of the 20th

century were heavy timber frame. The traditional timber

frame is made of large sawn timbers (larger than 114 by

114 mm (5 by 5 in.)) connected to one another by handfabricated joints, such as mortise and tenon. Construction

of such a frame involves rather sophisticated joinery, as

illustrated in Figure 16–6.

Roof structure

Roof structure

Top plate

Round pole or square post

Finish floor

Subfloor

Joist

Ribbon plate

Gravel or concrete

Auger drilled hole

Concrete pad

Round pole

or square post

Perimeter plate

Panel top plate

Post

Sole plate

Finish floor

Subfloor

Joist

Ribbon plate

Concrete

Auger-drilled hole

Conventional

stud wall

Figure 16–4. Pole and post-frame buildings: (left) pole or post forms both foundation and wall; (right)

pole or post forms only the foundation for conventional platform-framed structure.
16–7

In today’s timber frame home, a prefabricated, composite

sheathing panel (1.2 by 2.4 m (4 by 8 ft)) is frequently applied directly to the frame. This panel may consist of an

inside layer of 13-mm (1/2-in.) gypsum, a core layer of rigid

foam insulation, and an outside layer of exterior plywood or

structural flakeboard. Finish siding is applied over the composite panel. In some cases, a layer of standard 19-mm

(nominal l-in.) tongue-and-groove, solid-wood boards is

applied to the frame, and a rigid, foam-exterior, plywood

composite panel is then applied over the boards to form the

building exterior. Local fire regulations should be consulted

about the acceptance of various foam insulations.

Framing members are cut in large cross sections; therefore,

seasoning them before installation is difficult, if not impossible. Thus, the builder (and the owner) should recognize the

dimensional changes that may occur as the members dry in

place. The structure must be designed to accommodate these

dimensional changes as well as seasoning checks, which are

almost inevitable.

Mill Type

Mill-type construction has been widely used for warehouse

and manufacturing structures, particularly in the eastern

United States. This type of construction uses timbers of large

cross sections with columns spaced in a grid according to the

available lengths of beam and girder timbers. The size of the

timbers makes this type of construction resistant to fire. The

good insulating qualities of wood as well as the char that

develops during fire result in slow penetration of fire into the

large members. Thus, the members retain a large proportion

of their original load-carrying capacity and stiffness for a

relatively lengthy period after the onset of fire. Mill-type

construction is recognized by some building codes as a 1-h

fire-resistant construction, with some limitations.

To be recognized as mill-type construction, the structural

elements must meet specific sizes—columns cannot be less

than standard 184 mm (nominal 8 in.) in dimension and

beams and girders cannot be less than standard 140 by

235 mm (nominal 6 by 10 in.) in cross section. Other limitations must be observed as well. For example, walls must

be made of masonry, and concealed spaces must be avoided.

The structural frame has typically been constructed of solidsawn timbers, which should be stress graded. These timbers

can now be supplanted with glulam timbers, and longer

spans are permitted.

Figure 16–5. Modern log homes are available in a variety of designs.
 16–8

Glulam Beam

A panelized roof system using glulam roof framing is widely

used for single-story commercial buildings in the southwestern United States. This system is based on supporting columns located at the corners of pre-established grids. The

main glulam beams support purlins, which may be sawn

timbers, glulam, parallel chord trusses, or prefabricated wood

I-joists. These purlins, which are normally on 2.4-m (8-ft)

centers, support preframed structural panels. The basic unit of

the preframed system is a 1.2- by 2.4-m (4- by 8-ft) structural

panel nailed to standard 38- by 89-mm or 38- by 140-mm

(nominal 2- by 4-in. or 2- by 6-in.) stiffeners (subpurlins).

The stiffeners run parallel to the 2.4-m (8-ft) dimension of the

structural panel. One stiffener is located at the centerline of

the panel; the other is located at an edge, with the plywood

edge at the stiffener centerline. The stiffeners are precut to a

length equal to the long dimension of the plywood less the

thickness of the purlin, with a small allowance for the

hanger.

In some cases, the purlins are erected with the hangers in

place. The prefabricated panels are lifted and set into place in

the hangers, and the adjoining basic panels are then attached

to each other. In other cases, the basic panels are attached to

one purlin on the ground. An entire panel is lifted into place

to support the loose ends of the stiffeners. This system is

fully described in the Laminated Timber Design Guide

(AITC 1994a).

Arch Structure

Arch structures are particularly suited to applications in

which large, unobstructed areas are needed, such as churches,

recreational buildings, and aircraft hangars. Many arch forms

are possible with the variety limited only by the imagination

of the architect. Churches have used arches from the beginning of glulam manufacture in the United States. Additional

information on the use and design of arches is given in The

Timber Construction Manual (AITC 1994b).

Dome

Radial-rib domes consist of curved members extending from

the base ring (tension ring) to a compression ring at the top

of the dome along with other ring members at various

elevations between the tension and compression rings

(Fig. 16–7). The ring members may be curved or straight. If

they are curved to the same radius as the rib and have their

centers at the center of the sphere, the dome will have a

spherical surface. If the ring members are straight, the dome

will have an umbrella look. Connections between the ribs

and the ring members are critical because of the high compressive loads in the ring members. During construction,

care must be taken to stabilize the structure because the dome

has a tendency to rotate about the central vertical axis.

Other dome patterns called Varax and Triax are also used.

Their geometries are quite complex and specialized computer

Figure 16–6. Timber frame structure with typical

joint details. Figure 16–7. Member layout for a radial-rib dome.
16–9

programs are used in their design. Steel hubs used at the

joints and supports are critical. An example of a Triax dome

is shown in Figure 16–8.

Timber Bridges

Prior to the 20th century, timber was the major material used

for both highway and railroad bridges. The development of

steel and reinforced concrete provided other options, and

these have become major bridge building materials. However, the U.S. inventory does contain a significant number of

timber bridges, many of which continue to carry loads beyond their design life. A recent initiative in the United States

has focused research and technology transfer efforts on improving the design and performance of timber bridges. As a

result, hundreds of timber highway bridges were built across

the United States during the 1990s; many using innovative

designs and materials.

Bridges consist of a substructure and a superstructure. The

substructure consists of abutments, piers, or piling, and it

supports the superstructure that consists of stringers and/or a

deck. The deck is often covered with a wearing surface of

asphalt. Timber may be combined with other materials to

form the superstructure, for example, timber deck over steel

stringers. Covered bridges, although once popular, are usually not economically feasible. The various types of timber

bridge superstructures are described in the following sections.

Detailed information on modern timber bridges is given in

Timber Bridges: Design, Construction, Inspection, and

Maintenance (Ritter 1990).

Log Stringer

A simple bridge type that has been used for centuries consists of one or more logs used to span the opening. Several

logs may be laid side-by-side and fastened together. The log

stringer bridge has been used to access logging areas and is

advantageous when adequate-sized logs are available and the

bridge is only needed for a short time. Unless built with a

durable species, the life span of log stringer bridges is usually limited to less than 10 years.

Sawn Lumber

Several types of bridges can be built with sawn lumber. Even

though the span is usually limited to about 9 m (30 ft)

because of the limited size of lumber available, this span

length entails the majority of bridges in the United States.

Several timbers can be used to span the opening, and a

transverse lumber deck can be placed over them to form a

stringer and deck bridge. Lumber can be placed side-by-side

and used to span the entire opening, forming a longitudinal

deck bridge. The lumber can be fastened together with large

spikes or held together with tensioned rods to form a “stresslaminated” deck.

Figure 16–8. This 161.5-m- (530-ft-) diameter Tacoma dome (Tacoma, Washington), built in 1982–1983, is one of

the longest clear roof spans in the world. (Photo courtesy of Western Wood Structures, Inc., Tualatin, Oregon.)
 16–10

Glulam

Structural glued-laminated (glulam) timber greatly extends

the span capabilities of the same types of bridges described in

the previous paragraph. Glulam stringers placed 0.6 to 1.8 m

(2 to 6 ft) on center can support a glulam deck system and

result in spans of 12 to 30 m (40 to 100 ft) or more

(Fig. 16–9). Using glulam panels to span the opening results

in a longitudinal deck system, but this is usually limited to

about 9-m (30-ft) spans. These panels are either interconnected or supported at one or more locations with transverse

distributor beams. Glulam beams can be used to form a solid

deck and are held together with tensioned rods to form a

stress-laminated deck. Curved glulam members can be used

to produce various aesthetic effects and special types of

bridges (Fig. 16–10).

Structural Composite Lumber

Two types of structural composite lumber (SCL)—laminated

veneer and oriented strand—are beginning to be used to

build timber bridges. Most of the same type of bridges built

with either solid sawn or glulam timber can be built with

SCL (Ch. 11).

Considerations for

Wood Buildings

Many factors must be considered when designing and constructing wood buildings, including structural, insulation,

moisture, and sound control. The following sections provide

a brief description of the design considerations for these

factors. Fire safety, another important consideration, is

addressed in Chapter 17.

Structural

The structural design of any building consists of combining

the prescribed performance requirements with the anticipated

loading. One major performance requirement is that there be

an adequate margin of safety between the structures ultimate

capacity and the maximum anticipated loading. The probability that the building will ever collapse is minimized

using material property information recommended by the

material manufacturers along with code-recommended design

loads.

Another structural performance requirement relates to serviceability. These requirements are directed at ensuring that the

structure is functional, and the most notable one is that

Figure 16–9. Glulam beam bridge over the Dangerous River, near Yukatat, Alaska, consists of three 43.5-m (143-ft)

spans. Each span is supported by four 2.3-m- (91.5-in.-) deep glulam beams.
16–11

deformations are limited. It is important to limit deformations so that floors are not too “bouncy” or that doors do not

bind under certain loadings. Building codes often include

recommended limits on deformation, but the designer may

be provided some latitude in selecting the limits. The basic

reference for structural design of wood in all building systems

is the National Design Specification for Wood Construction

(AF&PA 1991).

Thermal Insulation and

Air Infiltration Control

For most U.S. climates, the exterior envelope of a building

needs to be insulated either to keep heat in the building or

prevent heat from entering. Wood frame construction is wellsuited to application of both cavity insulation and surfaceapplied insulation. The most common materials used for

cavity insulation are glass fiber, mineral fiber, cellulose

insulation, and spray-applied foams. For surface applications,

a wide variety of sheathing insulations exist, such as rigid

foam panels. Insulating sheathing placed on exterior walls

may also have sufficient structural properties to provide

required lateral bracing. Prefinished insulating paneling can

be used as an inside finish on exterior walls or one or both

sides of the interior partitions. In addition, prefinished

insulation can underlay other finishes.

Attic construction with conventional rafters and ceiling joists

or roof trusses can be insulated between framing members

with batt, blanket, or loose-fill insulation. In some warm

climates, radiant barriers and reflective insulations can provide an additional reduction in cooling loads. The “Radiant

Barrier Attic Fact Sheet” from the U.S. Department of Energy (1991) provides information on climatic areas that are

best suited for radiant barrier applications. This document

also provides comparative information on the relative

performance of these products and conventional fibrous

insulations.

Existing frame construction can be insulated pneumatically

using suitable loose-fill insulating material. When loose-fill

materials are used in wall retrofit applications, extra care

must be taken during the installation to eliminate the existence of voids within the wall cavity. All cavities should be

checked prior to installation for obstructions, such as fire

stop headers and wiring, that would prevent the cavity from

being completely filled. Care must also be taken to install

the material at the manufacturer’s recommended density to

ensure that the desired thermal performance is obtained.

Figure 16–10. Three-hinge glulam deck arch bridge at the Keystone Wye interchange off U.S. Highway 16, near

Mount Rushmore, South Dakota. The arch spans 47 m (155 ft) and supports an 8-m- (26-ft-) wide roadway.
 16–12

Accessible space can be insulated by manual placement of

batt, blanket, or loose-fill material.

In addition to being properly insulated, the exterior envelope

of all buildings should be constructed to minimize air flow

into or through the building envelope. Air flow can degrade

the thermal performance of insulation and cause excessive

moisture accumulation in the building envelope.

More information on insulation and air flow retarders can be

found in the ASHRAE Handbook of Fundamentals, chapters

22 to 24 (ASHRAE 1997).

Moisture Control

Moisture control is necessary to avoid moisture-related

problems with building energy performance, building maintenance and durability, and human comfort and health. Moisture degradation is the largest factor limiting the useful life of

a building and can be visible or invisible. Invisible degradation includes the degradation of thermal resistance of building materials and the decrease in strength and stiffness of

some materials. Visible degradation may be in the form of

(a) mold and mildew, (b) decay of wood-based materials,

(c) spalling caused by freeze–thaw cycles, (d) hydration of

plastic materials, (e) corrosion of metals, (f) damage caused

by expansion of materials from moisture (for example, buckling of wood floors), and (g) decline in visual appearance (for

example, buckling of wood siding or efflorescence of masonry

materials). In addition, high moisture levels can lead to

mold spores in indoor air and odors, seriously affecting the

occupant’s health and comfort. Detailed discussions on the

effects of moisture can be found in the ASHRAE Handbook

of Fundamentals, chapters 22 and 23, (ASHRAE 1997) and

Lstiburek and Carmody (1991).

Mold, Mildew, Dust Mites, and Human Health

Mold and mildew in buildings are offensive, and the spores

can cause respiratory problems and allergic reactions in

humans. Mold and mildew will grow on most surfaces if the

relative humidity at the surface is above a critical value and

the surface temperatures are conducive to growth. The longer

the surface remains above this critical relative humidity level,

the more likely mold will appear; the higher the humidity or

temperature, the shorter the time needed for germination. The

surface relative humidity is a complex function of material

moisture content, material properties, local temperature, and

humidity conditions. In addition, mold growth depends on

the type of surface. Mildew and mold can usually be avoided

by limiting surface relative humidity conditions >80% to

short periods. Only for nonporous surfaces that are regularly

cleaned should this criterion be relaxed. Most molds grow at

temperatures approximately above 4°C (40°F). Moisture

accumulation at temperatures below 4°C (40°F) may not

cause mold and mildew if the material is allowed to dry out

below the critical moisture content before the temperature

increases above 4°C (40°F).

Dust mites can trigger allergies and are an important cause of

asthma. They thrive at high relative humidity levels (>70%)

at room temperature, but will not survive at sustained relative humidity levels less than 50%. However, these relative

humidity levels relate to local conditions in the typical

places that mites tend to inhabit (for example, mattresses,

carpets, soft furniture).

Paint Failure and Other Appearance Problems

Moisture trapped behind paint films may cause failure of the

paint (Ch. 15). Water or condensation may also cause streaking or staining. Excessive swings in moisture content of

wood-based panels or boards may cause buckling or warp.

Excessive moisture in masonry and concrete can produce

efflorescence, a white powdery area or lines. When combined

with low temperatures, excessive moisture can cause freeze–

thaw damage and spalling (chipping).

Structural Failures

Structural failures caused by decay of wood are rare but have

occurred. Decay generally requires a wood moisture content

equal to or greater than fiber saturation (usually about 30%)

and between 10°C (50°F) and 43°C (100°F). Wood moisture

content levels above fiber saturation are only possible in

green lumber or by absorption of liquid water from condensation, leaks, ground water, or other saturated materials in

contact with the wood. To maintain a safety margin, a 20%

moisture content is sometimes used during field inspections

as the maximum allowable level. Once established, decay

fungi produce water that enables them to maintain moisture

conditions conducive to their growth. See Chapter 13 for

more information on wood decay.

Rusting or corrosion of nails, nail plates, or other metal

building products is also a potential cause of structural failure. Corrosion may occur at high relative humidity levels

near the metal surface or as a result of liquid water from

elsewhere. Wood moisture content levels >20% encourage

corrosion of steel fasteners in wood, especially if the wood is

treated with preservatives. In buildings, metal fasteners are

often the coldest surfaces, which encourages condensation and

corrosion of fasteners.

Effect on Heat Flow

Moisture in the building envelope can significantly degrade

the thermal performance of most insulation materials but

especially the thermal resistance of fibrous insulations and

open cell foams. The degradation is most pronounced when

daily temperature reversals across the insulation drive moisture back and forth through the insulation.

Moisture Control Strategies

Strategies to control moisture accumulation fall into two

general categories: (1) minimize moisture entry into the

building envelope and (2) remove moisture from the building

envelope. When basic moisture transport mechanisms and

specific moisture control practices are understood, roof, wall,

and foundation constructions for various climates can be

reviewed in a systematic fashion to determine if every potentially significant moisture transport mechanism is explicitly

controlled. It is not possible to prevent moisture migration
16–13

completely; therefore, construction should include drainage,

ventilation, and removal by capillary suction, or other

provisions to carry away unwanted water.

The major moisture transport mechanisms, in order of importance, are (a) liquid water movement, including capillary

movement; (b) water vapor transport by air movement; and

(c) water vapor diffusion. In the past, much attention has

focused on limiting movement by diffusion with vapor retarders (sometimes called vapor barriers), even though vapor

diffusion is the least important of all transport mechanisms.

Control of moisture entry should be accomplished in accordance with the importance of the transport mechanism:

(a) control of liquid entry by proper site grading and installing gutters and downspouts and appropriate flashing around

windows, doors, and chimneys; (b) control of air leakage by

installing air flow retarders or careful sealing by taping and

caulking; and (c) control of vapor diffusion by placing vapor

retarders on the “warm” side of the insulation.

Options for moisture control under heating conditions often

differ from those under cooling conditions, even though the

physical principles of moisture movement are the same.

Which moisture control options apply depends on whether

the local climate is predominantly a heating or cooling

climate. In heating climates, ventilation with outdoor air and

limiting indoor sources of moisture (wet fire wood, unvented

dryers, humidifiers) can be effective strategies. In cooling

climates, proper dehumidification can provide moisture

control. More information on the definition of heating and

cooling climates and specific moisture control strategies can

be found in the ASHRAE Handbook of Fundamentals,

chapter 23 (ASHRAE 1997).

Sound Control

An important design consideration for residential and office

buildings is the control of sound that either enters the structure from outside or is transmitted from one room to another.

Wood frame construction can achieve the levels of sound

control equal to or greater than more massive construction,

such as concrete. However, to do so requires designing for

both airborne and impact noise insulation.

Airborne noise insulation is the resistance to transmission of

airborne noises, such as traffic or speech, either through or

around an assembly such as a wall. Noises create vibrations

on the structural surfaces that they contact, and the design

challenge is to prevent this vibration from reaching and

leaving the opposite side of the structural surface. Sound

transmission class (STC) is the rating used to characterize

airborne noise insulation. A wall system with a high STC

rating is effective in preventing the transmission of sound.

Table 16–1 lists the STC ratings for several types of wall

systems; detailed information for both wall and floor are

given in FPL–GTR–43 (Rudder 1985).

Impact noise insulation is the resistance to noise generated

by footsteps or dropping objects, generally addressed at

floor–ceiling assemblies in multi-family dwellings. Impact

insulation class (IIC) is the rating used to characterize the

impact noise insulation of an assembly. Both the character of

the flooring material and the structural details of the floor

influence the IIC rating. Additional information on IIC

ratings for wood construction is given in FPL–GTR–59

(Sherwood and Moody 1989).

Table 16–1. Sound transmission class (STC) ratings for typical wood-frame walls

STC

rating Privacy afforded Wall structure

25 Normal speech easily understood 6-mm (1/4-in.) wood panels nailed on each side of standard 38- by 89-mm

(nominal 2- by 4-in.) studs.

30 Normal speech audible but not

intelligible

9.5-mm (3/8-in.) gypsum wallboard nailed to one side of standard 38- by

89-mm (nominal 2- by 4-in.) studs.

35 Loud speech audible and fairly

understandable

20-mm (5/8-in.) gypsum wallboard nailed to both sides of standard 38- by

89-mm (nominal 2- by 4-in.) studs.

40 Loud speech audible but not

intelligible

Two layers of 20-mm (5/8-in.) gypsum wallboard nailed to both sides of standard 38- by 89-mm (nominal 2- by 4-in.) studs.

45 Loud speech barely audible Two sets of standard 38- by 64-mm (nominal 2- by 3-in.) studs staggered

0.2 m (8 in.) on centers fastened by standard 38- by 89-mm (nominal 2- by

4-in.) base and head plates with two layers of 20-mm (5/8-in.) gypsum wallboard nailed on the outer edge of each set of studs.

50 Shouting barely audible Standard 38- by 89-mm (nominal 2- by 4-in.) wood studs with resilient channels

nailed horizontally to both sides with 20-mm (5/8-in.) gypsum wallboard

screwed to channels on each side.

55 Shouting not audible Double row of standard 38- by 89-mm (nominal 2- by 4-in.) studs 0.4 m

(16 in.) on centers fastened to separate plates spaced 25 mm (1 in.) apart.

Two layers of 20-mm (5/8-in.) gypsum wallboard screwed 0.3 m (12 in.) on

center to the studs. An 89-mm- (3.5-in.-) thick sound-attenuation blanket is

installed in one stud cavity.
 16–14

References

AF&PA. 1987. Permanent wood foundation basic requirements. Tech. Rep. 7. Washington, DC: American Forest &

Paper Association.

AF&PA. 1991. National design specification for wood construction. Washington, DC: American Forest & Paper

Association.

AF&PA. 1993. Span tables for joists and rafters. Washington, DC: American Forest & Paper Association.

AF&PA. 1995. Wood frame construction manual for oneand two-family dwellings, 1995 SBC high wind edition.

Washington, DC: American Forest & Paper Association.

AITC. 1994a. Laminated timber design guide. Englewood,

CO: American Institute of Timber Construction.

AITC. 1994b. Timber construction manual. American

Institute of Timber Construction. New York: John Wiley &

Sons, Inc.

APA. 1996. Residential and commercial design/construction

guide. E30P, April. Tacoma, WA: APA–The Engineered

Wood Association, Tacoma, WA.

ASHRAE. 1997. Handbook of fundamentals. Atlanta, GA:

American Society of Heating, Refrigerating and AirConditioning Engineers.

ASTM. 1996. Standard methods for establishing stress

grades for structural members used in log buildings. ASTM

D3957-80. Philadelphia, PA: American Society for Testing

and Materials.

Lstiburek, J.; Carmody, J. 1991. The moisture control

handbook—new low-rise, residential construction.

ORNL/Sub/89-SD350/1. Oak Ridge, TN: Martin Marietta

Energy Systems, Inc., Oak Ridge National Laboratory.

McDonald, K.A.; Falk, R.H.; Williams, R.S.; Winandy,

J.E. 1996. Wood decks: materials, construction, and finishing. Madison, WI: Forest Products Society.

National Frame Builders Association. [n.d.] Recommended practices for the design and construction of agricultural and commercial post-frame buildings. Lawrence, KS:

National Frame Builders Association.

Ritter, M.A. 1990. Timber bridges—design, construction,

inspection and maintenance. EM 7700-8. Washington, DC:

U.S. Department of Agriculture, Forest Service, Engineering

Staff.

Rudder, F.F. Jr. 1985. Airborne sound transmission loss

characteristics of wood-frame construction. Gen. Tech. Rep.

FPL–GTR–43. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Sherwood, G.E.; Moody, R.C. 1989. Light-frame wall

and floor systems—analysis and performance. Gen. Tech.

Rep. FPL–GTR–59. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Sherwood, G.E.; Stroh, R.C. 1989. Wood frame house

construction. Agric. Handb. 73. Washington, DC: U.S.

Government Printing Office. (also available from Armonk

Press, Armonk, NY).

TPI. 1995. National design standards for metal plate connected wood truss construction. ANSI/TPI–1995. Madison,

WI: Truss Plate Institute.

U.S. Department of Energy. 1991. Radiant barrier attic fact

sheet. Oak Ridge, TN: Oak Ridge National Laboratory.

Walker, J.N.; Woeste, F.E. 1992. Post-frame building

design. ASAE Monograph No. 11, St. Joseph, MI.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
17–1

Fire Safety

Robert H. White and Mark A. Dietenberger

Chapte r 17

Contents

Fire Safety Design and Evaluation 17–1

Types of Construction 17–2

Fire Growth Within Compartment 17–2

Flashover 17–4

Containment to Compartment of Origin 17–4

Fire Safety Engineering 17–6

Fire Performance Characteristics of Wood 17–6

Ignition 17–6

Heat Release 17–7

Flame Spread 17–8

Smoke and Toxic Gases 17–9

Charring and Fire Resistance 17–10

Flame-Retardant Treatments 17–12

Fire-Retardant-Treated Wood 17–12

Flame-Retardant Pressure Treatments 17–13

Flame-Retardant Coatings 17–13

References 17–13

ire safety is an important concern in all types of

construction. The high level of national concern

for fire safety is reflected in limitations and design

requirements in building codes. These code requirements are

discussed in the context of fire safety design and evaluation

in the initial section of this chapter. Since basic data on fire

behavior of wood products are needed to evaluate fire safety

for wood construction, the second major section of this

chapter covers fire performance characteristics of wood

products. The chapter concludes with a discussion of

flame-retardant treatments that can be used to reduce the

combustibility of wood.

Fire Safety Design

and Evaluation

Fire safety involves prevention, containment, detection, and

evacuation. Fire prevention basically means preventing the

ignition of combustible materials by controlling either the

source of heat or the combustible materials. This involves

proper design, installation or construction, and maintenance

of the building and its contents. Proper fire safety measures

depend upon the occupancy or processes taking place in the

building. Design deficiencies are often responsible for spread

of heat and smoke in a fire. Spread of a fire can be prevented

with design methods that limit fire growth and spread within

a compartment and with methods that contain fire to the

compartment of origin. Egress, or the ability to escape from a

fire, often is a critical factor in life safety. Early detection is

essential for ensuring adequate time for egress.

Statutory requirements pertaining to fire safety are specified

in the building codes or fire codes. These requirements fall

into two broad categories: material requirements and building requirements. Material requirements include such things

as combustibility, flame spread, and fire endurance. Building

requirements include area and height limitations, firestops

and draftstops, doors and other exits, automatic sprinklers,

and fire detectors.

Adherence to codes will result in improved fire safety. Code

officials should be consulted early in the design of a building

F
 17–2

because the codes offer alternatives. For example, floor areas

can be increased if automatic sprinkler systems are added.

Code officials have the option to approve alternative materials and methods of construction and to modify provisions of

the codes when equivalent fire protection and structural

integrity is documented.

Most building codes in the United States are based on model

building codes produced by the three building code organizations (Building Officials and Code Administrators International, Inc.; International Conference of Building Officials;

and the Southern Building Code Congress International,

Inc.). These three organizations are developing a single

international building code that will replace the existing

three model building codes. In addition to the building

codes and the fire codes, the National Fire Protection Association’s Life Safety Code provides guidelines for life safety

from fire in buildings and structures. As with the model

building codes, provisions of the life safety code are statutory

requirements when adopted by local or State authorities.

In the following sections, various aspects of the building

code provisions pertaining to fire safety of building materials

are discussed under the broad categories of (a) types of construction, (b) fire growth within compartment, and (c) containment to compartment of origin. These are largely

requirements for materials. Information on prevention and

building requirements not related to materials (for example,

detection) can be found in publications such as those listed at

the end of this chapter. Central aspects of the fire safety provisions of the building codes are the classification of buildings by types of construction and the use or occupancy.

Types of Construction

Based on classifications of building type and occupancy, the

codes set limits on the areas and heights of buildings. Major

building codes generally recognize five classifications of

construction based on types of materials and required fire

resistance ratings. The two classifications known as fireresistant construction (Type I) and noncombustible construction (Type II) basically restrict the construction to noncombustible materials. Wood is permitted to be used more

liberally in the other three classifications, which are ordinary

(Type III), heavy timber (Type IV), and light-frame (Type

V). Heavy timber construction has wood columns, beams,

floors, and roofs of certain minimum dimensions. Ordinary

construction has smaller wood members used for walls,

floors, and roofs including wood studs, wood joists, wood

trusses, and wood I-joists. In both heavy timber and ordinary

construction, the exterior walls must be of noncombustible

materials. In light-frame construction, the walls, floors, and

roofs may be of any dimension lumber and the exterior walls

may be of combustible materials. Type II, III, and IV constructions are further subdivided based on fire-resistance

requirements. Light-frame construction, or Type V, is subdivided into two parts, protected (1-hour) and unprotected.

In protected light-frame construction, most of the structural

elements have a 1-hour fire resistance rating. There are no

general requirements for fire resistance for buildings of unprotected light-frame construction.

Based on their performance in the American Society for

Testing and Materials (ASTM) E136 test, both untreated

and fire-retardant-treated wood are combustible materials.

However, the building codes permit substitution of fireretardant-treated wood for noncombustible materials in some

specific applications otherwise limited to noncombustible

materials.

In addition to the type of construction, the height and area

limitations also depend on the use or occupancy of a structure. Fire safety is improved by automatic sprinklers,

property line setbacks, or more fire-resistant construction.

Building codes recognize the improved fire safety resulting

from application of these factors by increasing the allowable

areas and heights beyond that designated for a particular type

of construction and occupancy. Thus, proper site planning

and building design may result in a desired building area

classification being achieved with wood construction.

Fire Growth Within Compartment

A second major set of provisions in the building codes are

those that regulate the exposed interior surface of walls and

ceilings (that is, the interior finish). Codes typically exclude

trim and incidental finish, as well as decorations and furnishings that are not affixed to the structure, from the more rigid

requirements for walls and ceilings. For regulatory purposes,

interior finish materials are classified according to their flame

spread index. Thus, flame spread is one of the most tested

fire performance properties of a material. Numerous flame

spread tests are used, but the one cited by building codes is

ASTM E84, the “25-ft tunnel” test. In this test method, the

508-mm-wide, 7.32-m-long specimen completes the top of

the tunnel furnace. Flames from a burner at one end of the

tunnel provide the fire exposure, which includes forced draft

conditions. The furnace operator records the flame front

position as a function of time and the time of maximum

flame front travel during a 10-min period. The standard

prescribes a formula to convert these data to a flame spread

index (FSI), which is a measure of the overall rate of flame

spreading in the direction of air flow. In the codes, the

classes for flame spread index are I (FSI of 0 to 25), II (FSI of

26 to 75), and III (FSI of 76 to 200). Some codes use A, B,

and C instead of I, II, and III. Generally, codes specify FSI

for interior finish based on building occupancy, location

within the building, and availability of automatic sprinkler

protection. The more restrictive classes, Classes I and II, are

generally prescribed for stairways and corridors that provide

access to exits. In general, the more flammable classification

(Class III) is permitted for the interior finish of other areas of

the building that are not considered exit ways or where the

area in question is protected by automatic sprinklers. In other

areas, there are no flammability restrictions on the interior

finish and unclassified materials (that is, more than 200 FSI)

can be used.
17–3

The FSI for most domestic wood species is between 90 and

160 (Table 17–1). Thus, unfinished lumber, 10 mm or

thicker, is generally acceptable for interior finish applications

requiring a Class III rating. Flame-retardant treatments are

usually necessary when a Class I or II flame spread index is

required for a wood product. A few domestic softwood species can meet the Class II flame spread index and only

require flame-retardant treatments to meet a Class I rating.

A few imported species have reported FSIs of less than 25.

Additional FSI for many solid-sawn and panel products are

provided in the American Forest and Paper Association’s

(AF&PA) design for code acceptance (DCA) No. 1, “Flame

Spread Performance of Wood Products” (AWC 1999).

There are many other test methods for flame spread or flammability. Most are used only for research and development or

quality control, but some are used in product specifications

and regulations of materials in a variety of applications.

Table 17–1. ASTM E84 flame spread indexes for 19-mm-thick solid lumber of various wood species

as reported in the literature

Speciesa

Flame spread

indexb

Smoke developed

indexb Sourcec

Softwoods

Yellow-cedar (Pacific Coast yellow cedar) 78 90 CWC

Baldcypress (cypress) 145–150 — UL

Douglas-fir 70–100 — UL

Fir, Pacific silver 69 58 CWC

Hemlock, western (West Coast) 60–75 — UL

Pine, eastern white (eastern white, northern white) 85, 120–215d 122, — CWC, UL

Pine, lodgepole 93 210 CWC

Pine, ponderosa 105–230d — UL

Pine, red 142 229 CWC

Pine, Southern (southern) 130–195 — UL

Pine, western white 75e — UL

Redcedar, western 70 213 HPVA

Redwood 70 — UL

Spruce, eastern (northern, white) 65 — UL, CWC

Spruce, Sitka (western, Sitka) 100, 74 —, 74 UL, CWC

Hardwoods

Birch, yellow 105–110 — UL

Cottonwood 115 — UL

Maple (maple flooring) 104 — CWC

Oak (red, white) 100 100 UL

Sweetgum (gum, red) 140–155 — UL

Walnut 130–140 — UL

Yellow-poplar (poplar) 170–185 — UL

a

In cases where the name given in the source did not conform to the official nomenclature of the

 Forest Service, the probable official nomenclature name is given and the name given by the source is

 given in parentheses.

b

Data are as reported in the literature (dash where data do not exist). Changes in the ASTM E84 test

 method have occurred over the years. However, data indicate that the changes have not significantly

 changed earlier data reported in this table. The change in the calculation procedure has usually resulted

 in slightly lower flame spread results for untreated wood. Smoke developed index is not known to exceed

 450, the limiting value often cited in the building codes.

c

CWC, Canadian Wood Council (CWC 1996); HPVA, Hardwood Plywood

 Manufacturers Association (Tests) (now Hardwood Plywood & Veneer Assoc.); UL, Underwriters

 Laboratories, Inc. (Wood-fire hazard classification. Card Data Service, Serial No. UL 527, 1971).

d

Footnote of UL: In 18 tests of ponderosa pine, three had values over 200 and the average of all tests

 is 154.

e

Footnote of UL: Due to wide variations in the different species of the pine family and local connotations

 of their popular names, exact identification of the types of pine tested was not possible. The effects of

 differing climatic and soil conditions on the burning characteristics of given species have not been

 determined.
 17–4

Since the fire exposure is on the underside of a horizontal

specimen in the ASTM E84 test, it is not suitable for materials that melt and drip or are not self-supporting. Code

provisions pertaining to floors and floor coverings may be

based on another test criterion, the critical radiant flux test

(ASTM E648, Critical Radiant Flux of Floor-Covering

Systems Using a Radiant Heat Energy Source). The critical

radiant flux apparatus is also used to test the flammability of

cellulosic insulation (ASTM E970, Critical Radiant Flux of

Exposed Attic Floor Insulation Using a Radiant Heat Energy

Source). In the critical radiant flux test, the placement of the

radiant panel is such that the radiant heat being imposed on

the surface has a gradient in intensity down the length of the

horizontal specimen. Flames spread from the ignition source

at the end of high heat flux (or intensity) to the other end

until they reach a location where the heat flux is not sufficient

for further propagation. This is reported as the critical radiant

flux. Thus, low critical radiant flux reflects materials with

high flammability. Typical requirements are for a minimum

critical radiant flux level of 2.2 or 4.5 kW/m2

 depending on

location and occupancy. Data in the literature indicate that

oak flooring has a critical radiant flux of 3.5 kW/m2

(Benjamin and Adams 1976).

There is also a smoldering combustion test for cellulosic

insulation. Cellulosic insulation is regulated by a product

safety standard of the U.S. Consumer Product Safety Commission (Interim Safety Standard for Cellulosic Insulation:

Cellulosic Insulation Labeling and Requirements, 44FR

39938, 16CFR Part 1209, 1979; also Gen. Serv. Admin.

Spec. HH–I–515d). Proper chemical treatments of cellulosic

insulation are required to reduce its tendency for smoldering

combustion and to reduce flame spread. Proper installation

around recessed light fixtures and other electrical devices is

necessary.

Other tests for flammability include those that measure heat

release. Other flammability tests and fire growth modeling

are discussed in the Fire Performance Characteristics of

Wood section.

Rated roof covering materials are designated either Class A,

B, or C according to their performance in the tests described

in ASTM E108, Fire Tests of Roof Coverings. This test

standard includes intermittent flame exposure, spread of

flame, burning brand, flying brand, and rain tests. There is a

different version of the pass/fail test for each of the three

classes. Class A test is the most severe and Class C the

least. In the case of the burning brand tests, the brand for the

Class B test is larger than that for the Class C test. Leachresistant fire-retardant-treated shingles are available that carry

a Class B or C fire rating.

Information on ratings for different products can be obtained

from industry literature, evaluation reports issued by the

model code organizations, and listings published by testing

laboratories or quality assurance agencies. Products listed by

Underwriters Laboratories, Inc., and other such organizations

are stamped with the rating information.

Flashover

With sufficient heat generation, the initial growth of a fire in

a compartment leads to the condition known as flashover.

The visual criteria for flashover are full involvement of the

compartment and flames out the door or window. The intensity over time of a fire starting in one room or compartment

of a building depends on the amount and distribution of

combustible contents in the room and the amount of

ventilation.

The standard full-scale test for pre-flashover fire growth is the

room/corner test (International Organization for Standardization (ISO) 9705, Fire Tests—Full-Scale Room Test for

Surface Products). In this test, a gas burner is placed in the

corner of the room, which has a single door for ventilation.

Three of the walls are lined with the test material, and the

ceiling may also be lined with the test material. Other

room/corner tests use a wood crib or similar item as the

ignition source. Such a room/corner test is used to regulate

foam plastic insulation, a material that is not properly evaluated in the ASTM E84 test.

Observations are made of the growth of the fire and the duration of the test until flashover occurs. Instruments record the

heat generation, temperature development within the room,

and the heat flux to the floor. Results of full-scale room/

corner tests are used to validate fire growth models and

bench-scale test results. Fire endurance tests evaluate the

relative performance of the assemblies during a post-flashover

fire.

Containment to Compartment

of Origin

The growth, intensity, and duration of the fire is the “load”

that determines whether a fire is confined to the room of

origin. Whether a given fire will be contained to the compartment depends on the fire resistance of the walls, doors,

ceilings, and floors of the compartment. Requirements for fire

resistance or fire endurance ratings of structural members and

assemblies are another major component of the building code

provisions. Fire resistance is the ability of materials or their

assemblies to prevent or retard the passage of excessive heat,

hot gases, or flames while continuing to support their structural loads. Fire-resistance ratings are usually obtained by

conducting standard fire tests. In the standard fire-resistance

test (ASTM E119), there are three failure criteria: element

collapse, passage of flames, or excessive temperature rise on

the non-fire-exposed surface (average increase of several locations exceeding 139°C or 181°C at a single location).

The self-insulating qualities of wood, particularly in the large

wood sections of heavy timber construction, are an important

factor in providing a degree of fire resistance. In Type IV or

heavy timber construction, the need for fire-resistance requirements is achieved in the codes by specifying minimum

sizes for the various members or portions of a building and

other prescriptive requirements. In this type of construction,

the wood members are not required to have specific
17–5

fire-resistance ratings. The acceptance of heavy timber

construction is based on historical experience with its performance in actual fires. Proper heavy timber construction

includes using approved fastenings, avoiding concealed

spaces under floors or roofs, and providing required fire

resistance in the interior and exterior walls.

In recent years, the availability and code acceptance of a

procedure to calculate the fire-resistance ratings for large

timber beams and columns have allowed their use in firerated buildings not classified as heavy timber construction

(Type IV). In the other types of construction, the structural

members and assemblies are required to have specified fireresistance ratings. Details on the procedure for large timbers

can be found in American Institute of Timber Construction

(AITC) Technical Note 7 and the AF&PA DCA #2 “Design

of Fire-Resistive Exposed Wood Members” (AWC 1985).

The fire resistance of glued-laminated structural members,

such as arches, beams, and columns, is approximately

equivalent to the fire resistance of solid members of similar

size. Available information indicates that laminated members

glued with phenol, resorcinol, or melamine adhesives are at

least equal in their fire resistance to a one-piece member of

the same size. Laminated members glued with casein have

only slightly less fire resistance.

Light-frame wood construction can provide a high degree of

fire containment through use of gypsum board as the interior

finish. This effective protective membrane provides the initial

fire resistance rating. Many recognized assemblies involving

wood-frame walls, floors, and roofs provide a 1- or 2-hour fire

resistance rating. Fire-rated gypsum board (Type X or C) is

used in rated assemblies. Type X and the higher grade Type

C gypsum boards have textile glass filaments and other

ingredients that help to keep the gypsum core intact during a

fire. Fire-resistance ratings of various assemblies are listed in

the model codes and other publications such as the Fire

Resistance Design Manual (Gypsum Association). Traditional constructions of regular gypsum wallboard (that is, not

fire rated) or lath and plaster over wood joists and studs have

fire-resistance ratings of 15 to 30 min.

While fire-resistance ratings are for the entire wall, floor, or

roof assembly, the fire resistance of a wall or floor can be

viewed as the sum of the resistance of the interior finish and

the resistance of the framing members. In a code-accepted

procedure, the fire rating of a light-frame assembly is calculated by adding the tabulated times for the fire-exposed

membrane to the tabulated times for the framing. For example, the fire-resistance rating of a wood stud wall with

16-mm-thick Type X gypsum board and rock wool insulation is computed by adding the 20 min listed for the stud

wall, the 40 min listed for the gypsum board, and the

15 min listed for the rock wool insulation to obtain a rating

for the assembly of 75 min. Additional information on this

component additive method (CAM) can be found in the

AF&PA DCA No. 4 “Component Additive Method (CAM)

for Calculating and Demonstrating Assembly Fire Endurance” (AWC 1991). More sophisticated mechanistic models

are being developed.

The relatively good structural behavior of a traditional wood

member in a fire test results from the fact that its strength is

generally uniform through the mass of the piece. Thus, the

unburned fraction of the member retains high strength, and

its load-carrying capacity is diminished only in proportion to

its loss of cross section. Innovative designs for structural

wood members may reduce the mass of the member and

locate the principal load-carrying components at the outer

edges where they are most vulnerable to fire, as in structural

sandwich panels. With high strength facings attached to a

low-strength core, unprotected load-bearing sandwich panels

have failed to support their load in less than 6 min when

tested in the standard test. If a sandwich panel is to be used

as a load-bearing assembly, it should be protected with

gypsum wallboard or some other thermal barrier. In any

protected assembly, the performance of the protective membrane is the critical factor in the performance of the assembly.

Unprotected light-frame wood buildings do not have the

natural fire resistance achieved with heavier wood members.

In these, as in all buildings, attention to good construction

details is important to minimize fire hazards. Quality of

workmanship is important in achieving adequate fire resistance. Inadequate nailing and less than required thickness of

the interior finish can reduce the fire resistance of an assembly. The method of fastening the interior finish to the framing members and the treatment of the joints are significant

factors in the fire resistance of an assembly. The type and

quantity of any insulation installed within the assembly may

also affect the fire resistance of an assembly. Electrical receptacle outlets, pipe chases, and other through openings that

are not adequately firestopped can affect the fire resistance. In

addition to the design of walls, ceilings, floors, and roofs for

fire resistance, stairways, doors, and firestops are of particular

importance.

Fires in buildings can spread by the movement of hot fire

gases through open channels in concealed spaces. Codes

specify where firestops and draftstops are required in concealed spaces, and they must be designed to interfere with the

passage of flames up or across a building. In addition to

going along halls, stairways, and other large spaces, heated

gases also follow the concealed spaces between floor joists

and between studs in partitions and walls of frame construction. Obstruction of these hidden channels provides an effective means of restricting fire from spreading to other parts of

the structure. Firestops are materials used to block off relatively small openings passing through building components

such as floors and walls. Draftstops are barriers in larger

concealed spaces such as those found within wood joist floor

assemblies with suspended dropped ceilings or within an

attic space with pitched chord trusses.

Doors can be critical in preventing the spread of fires. Doors

left open or doors with little fire resistance can easily defeat

the purpose of a fire-rated wall or partition. Listings of firerated doors, frames, and accessories are provided by various

fire testing agencies. When a fire-rated door is selected,

details about which type of door, mounting, hardware, and

closing mechanism need to be considered.
 17–6

Fire Safety Engineering

The field of fire safety engineering is undergoing rapid

changes because of the development of more engineering and

scientific approaches to fire safety. This development is

evidenced by the publication of The Society of Fire Protection Engineers Handbook of Fire Protection Engineering

and formation of fire safety engineering subcommittees in

ISO and ASTM. Steady advances are being made in the

fields of fire dynamics, fire hazard calculations, fire design

calculations, and fire risk analysis. Such efforts support the

worldwide trend to develop alternative building codes based

on performance criteria rather than prescriptive requirements.

Additional information on fire protection can be found in the

various publications of the National Fire Protection

Association (NFPA).

Fire Performance

Characteristics of Wood

Wood will burn when exposed to heat and air. Thermal

degradation of wood occurs in stages. The degradation process and the exact products of thermal degradation depend

upon the rate of heating as well as the temperatures. The

sequence of events for wood combustion is as follows:

• The wood, responding to heating, decomposes or pyrolyzes into volatiles and char. Char is the dominant product at internal temperatures less than 300o

C, whereas

volatiles become much more pronounced above 300oC.

• The volatiles, some of which are flammable, can be ignited if the volatile–air mixture is of the right composition

in a temperature range of about 400oC to 500oC within the

mixture. This gas-phase combustion appears as flames.

• With air ventilation, the char oxidation becomes significant around 200o

C with two peaks in intensity reported at

360oC and 520oC. This char oxidation is seen as glowing

or smoldering combustion until only ash residue remains.

This solid-phase combustion will not proceed if flaming

combustion prevents a supply of fresh air to the char

surfaces.

Several characteristics are used to quantify this burning

behavior of wood, including ignition from heat sources,

growing rate of heat release leading to room flashover, flame

spread in heated environments, smoke and toxic gases,

flashover, and charring rates in a contained room.

Ignition

Ignition of wood takes place when wood is subject to sufficient heat and in atmospheres that have sufficient oxygen.

Ignition can be of two types: piloted or unpiloted. Piloted

ignition occurs in the presence of an ignition source (such as

a spark or a flame). Unpiloted ignition is ignition that occurs

where no pilot source is available. The wood surface is

ignited by the flow of energy or heat flux from a fire or other

heated objects. This flow of energy or heat flux can have both

convective and radiative components.

Piloted ignition above a single flat surface has recently been

studied in some depth because of the advent of fire growth

research. The surface temperature of wood materials has been

measured somewhere between 300o

C to 400oC prior to piloted ignition. Surface temperature at ignition is an illusive

quantity that is experimentally difficult to obtain. Equipment

such as the Ohio State University (OSU) apparatus (ASTM

E906), the cone calorimeter (ASTM 1354), and the lateral

ignition and flame spread test (LIFT) apparatus (ASTM

1321) are used to obtain data on time to piloted ignition as a

function of heater irradiance. Table 17–2 indicates the decrease in time to ignition with the increase in imposed heat

flux for different species of wood measured with the OSU

apparatus. Similar, perhaps identical, materials have been

tested recently in cone calorimeter and LIFT apparatuses

with somewhat similar results. From such tests, values of

ignition temperature, critical ignition flux (heat flux below

which ignition would not occur), and thermophysical properties have been derived using a transient heat conduction

theory. These properties are also material dependent; they

depend heavily on density of the material and moisture

content. A range of wood products tested have ignition

surface temperatures of 300o

C to 400oC and a critical ignition

flux of between 10 and 13 kW/m2 in the cone calorimeter.

The ignition surface temperature is lower for low density

woods. Estimates of piloted ignition in various scenarios can

be obtained using the derived thermal properties and an

applicable heat conduction model.

Some, typically old, apparatuses for testing piloted ignition

measured the temperature of the air flow rather than the imposed heat flux with the time to ignition measurement.

These results were often reported as the ignition temperature

and as varying with time to ignition, which is misleading.

When the imposed heat flux is due to a radiant source, such

reported air flow ignition temperature can be as much as

100°C lower than the ignition surface temperature. For a

proper heat conduction analysis in deriving thermal properties, measurements of the radiant source flux and air flow rate

are also required. Since imposed heat flux to the surface and

the surface ignition temperature are the factors that directly

determine ignition, some data of piloted ignition are

inadequate or misleading.

Unpiloted ignition depends on special circumstances that

result in different ranges of ignition temperatures. At this

time, it is not possible to give specific ignition data that

apply to a broad range of cases. For radiant heating of cellulosic solids, unpiloted transient ignition has been reported at

600°C. With convective heating of wood, unpiloted ignition

has been reported as low as 270°C and as high as 470°C.

Unpiloted spontaneous ignition can occur when a heat source

within the wood product is located such that the heat is not

readily dissipated. This kind of ignition involves smoldering

and generally occurs over a longer period of time. Smoldering is thermal degradation that proceeds without flames or
17–7

visible glowing. Examples of such fires are (a) panels or

paper removed from the press or dryer and stacked in large

piles without adequate cooling and (b) very large piles of

chips or sawdust with internal exothermic reactions such as

biological activities. Potential mechanisms of internal heat

generation include respiration, metabolism of microorganisms, heat of pyrolysis, abiotic oxidation, and adsorptive

heat. These mechanisms, often in combination, may proceed

to smoldering or flaming ignition through a thermal runaway

effect within the pile if sufficient heat is generated and is not

dissipated. The minimum environmental temperature to

achieve ignition is called the self-accelerating decomposition

temperature and includes the effects of specimen mass and air

ventilation.

Unpiloted ignitions that involve wood exposed to low level

external heat sources over very long periods is an area of

dispute. This kind of ignition, which involves considerable

charring, does appear to occur, based on fire investigations.

However, these circumstances do not lend themselves easily

to experimentation and observation. There is some evidence

that the char produced under low heating temperatures can

have a different chemical composition, which results in a

somewhat lower ignition temperature than normally recorded. Thus, a major issue is the question of safe working

temperature for wood exposed for long periods. Temperatures

between 80°C to 100°C have been recommended as safe

surface temperatures for wood. Since thermal degradation is a

prerequisite for ignition of the char layer, conservative criteria

for determining safe working temperatures can be the temperature and duration needed for thermal degradation. Schaffer

(1980) used a residual weight criterion of 40% of the initial

weight to suggest that wood can safely be heated to 150°C

for a year or more before satisfying this conservative predictor

of heating time to reach an incipient smoldering state.

Building codes do not generally regulate building materials

on the basis of ignition or ignitability. As a result, general

fire safety design criteria have not been developed. Rather,

this subject is considered in conjunction with limits on

combustibility and flame spread.

Heat Release

Heat release rates are important because they indicate the

potential fire hazard of a material and also the combustibility

of a material. Materials that release their potential chemical

energy (and also the smoke and toxic gases) relatively

quickly are more hazardous than those that release it more

slowly. There are materials that will not pass the current

definition of noncombustible in the model codes but will

release only limited amounts of heat during the initial and

critical periods of fire exposure. There is also some criticism

of using limited flammability to partially define noncombustibility. One early attempt was to define combustibility in

terms of heat release in a potential heat method (NFPA 259),

with the low levels used to define low combustibility or

noncombustibility. This test method is being used to regulate materials under some codes. The ground-up wood sample in this method is completely consumed during the exposure to 750°C for 2 h, which makes the potential heat for

wood identical to the gross heat of combustion from the

oxygen bomb calorimeter (the higher heating value in Table

17–2). The typical gross heat of combustion averaged around

20 MJ/kg for ovendried wood, depending on the lignin and

extractive content of the wood.

A better or a supplementary measure of degrees of combustibility is a determination of the rate of heat release (RHR) or

heat release rate (HRR). This measurement efficiently

assesses the relative heat contribution of materials—thick,

Table 17–2. Flammability data for selected wood species

Ignition timeb (s) Higher

Effective heat of

combustiond (MJ/kg)

Average heat release

rateb

 (kW/m2)

Species

Densitya

(kg/m3)

18-

kW/m2

heat flux

55-

kW/m2

heat flux

heating

valuec

(MJ/kg)

18-

kW/m2

heat flux

55-

 kW/m2

heat flux

18-

kW/m2

heat flux

55-

kW/m2

heat flux

Softwoods

Pine, Southern 508 740 5 20.5 9.1 13.9 40.4 119.6

Redwood 312 741 3 21.1 10.7 14.2 39.0 85.9

Hardwoods

Basswood 312 183 5 20.0 10.9 12.2 52.8 113.0

Oak, red 660 930 13 19.8 9.0 11.7 48.7 113.3

a

Based on weight and volume of ovendried wood.

b

Ignition times, effective heat of combustion, and average rate of heat release (HRR) obtained using an ASTM

 E906 heat release apparatus modified to measured heat release using oxygen consumption method.

 Test durations were 50 to 98 min for 18-kW/m2

 heat flux and 30 to 53 min for 55-kW/m2 heat flux. Test was

 terminated prior to the usual increase in HRR to a second peak as the specimen is consumed.

c

From oxygen bomb calorimeter test.

d

Apparent effective heat of combustion based on average HRR and mass loss rate, which includes the

 moisture driven from the wood. See footnote b.
 17–8

thin, untreated, or treated—under fire exposure. The cone

calorimeter (ASTM E1354) is the most commonly used

bench-scale HRR apparatus and is based on the oxygen

consumption method. An average value of 13.1 kJ/g of

oxygen consumed was the constant found for organic solids

and is accurate with very few exceptions to within 5%. Thus,

it is sufficient to measure the mass flow rate of oxygen consumed in a combustion system to determine the net HRR.

The procedure known as ASTM E906 (the OSU apparatus)

is a well-known and widely used calorimeter based on measurements of heat content of incoming and exiting air flow

through the apparatus. Because of the errors caused by the

heat losses and the fact that the mass flow rate is controlled

in the OSU apparatus, several researchers have modified it to

the oxygen consumption method. These bench-scale apparatuses use a radiant source to provide the external heat exposure to the test specimen. The imposed heat flux is kept

constant at a specified heat flux level. The intermediate-scale

apparatus (ASTM E1623) for testing 1- by 1-m assemblies

or composites and the room full-scale test (ISO 9705) also

use the oxygen consumption technique to measure the HRR

of fires at larger scales.

The cone calorimeter is ideal for product development with

its small specimen size of 100 by 100 mm. The specimen is

continuously weighed by use of a load cell. In conjunction

with HRR measurements, the effective heat of combustion as

a function of time is calculated by the ASTM E1354

method. Basically, the effective heat of combustion is the

HRR divided by the mass loss rate as determined from the

cone calorimeter test as a function of time. A typical HRR

profile as shown in Figure 17–1 for plywood begins with a

sharp peak upon ignition, and as the surface chars, the HRR

drops to some minimum value. After the thermal wave

travels completely through the wood thickness, the back side

of a wood sample reaches pyrolysis temperature, thus giving

rise to a second, broader, and even higher HRR peak. For

fire-retardant-treated wood products, the first HRR peak may

be reduced or eliminated. Table 17–3 provides the peak and

averaged HRR at 1-, 3-, and 5-min periods for various wood

species.

Heat release rate depends upon the intensity of the imposed

heat flux. Table 17–2 provides the average effective heat of

combustion and average HRR for four wood species and two

levels of heat flux (18 and 55 kW/m2

). These results were

obtained in an OSU apparatus modified by the Forest Products Laboratory (FPL). Similar values were also obtained in

the cone calorimeter (Table 17–3). Generally, the averaged

effective heat of combustion is about 65% of the oxygen

bomb heat of combustion (higher heating value) with a small

linear increase with irradiance. The HRR itself has a large

linear increase with the heat flux. Data indicate that HRRs

decrease with increasing moisture content of the sample and

are markedly reduced by fire-retardant treatment (Fig. 17–1).

Flame Spread

The spread of flames over solids is a very important phenomenon in the growth of compartment fires. Indeed, in fires

where large fuel surfaces are involved, the increase in HRR

with time is primarily due to the increase in burning area.

Many data have been acquired with the flame spread tests

used in building codes. Table 17–1 lists the FSI and smoke

index of ASTM E84 for solid wood. Some consistencies in

the FSI behavior of the hardwood species can be related to

their density. Considerable variations are found for woodbased composites; for example, the FSI of four structural

flakeboards ranged from 71 to 189.

As a prescriptive regulation, the ASTM E84 tunnel test is a

success in the reduction of fire hazards but is impractical in

providing scientific data for fire modeling or in useful benchscale tests for product development. Other full-scale tests

(such as the ISO 9705 room/corner test) also use both an

ignition burner and the ensuing flame spread to assist flow

but can produce quite different results because of the size of

the ignition burner or the test geometry. This is the case

with foam plastic panels that melt and drip during a fire test.

In the tunnel test, with the test material on top, a material

that melts can have low flammability since the specimen

does not stay in place. With an adequate burner in the

room/corner test, the same material will exhibit very high

flammability.

A flame spreads over a solid material when part of the fuel,

ahead of the pyrolysis front, is heated to the critical condition

of ignition. The rate of flame spread is controlled by how

rapidly the fuel reaches the ignition temperature in response

to heating by the flame front and external sources. The material’s thermal conductivity, heat capacitance, thickness, and

blackbody surface reflectivity influence the material’s thermal

response, and an increase in the values of these properties

corresponds to a decrease in flame spread rate. On the other

hand, an increase in values of the flame features, such as the

imposed surface fluxes and spatial lengths, corresponds to a

increase in the flame spread rate.

200

150

100

50

HRR (kW/m2)

0 200 400 600 800

Time (s)

FRT

Untreated

Figure 17–1. Heat release curves for untreated and

FRT plywood exposed to 50-kW/m2

 radiance.
17–9

Flame spread occurs in different configurations, which are

organized by orientation of the fuel and direction of the main

flow of gases relative to that of flame spread. Downward and

lateral creeping flame spread involves a fuel orientation with

buoyantly heated air flowing opposite of the flame spread

direction. Related bench-scale test methods are ASTM E162

for downward flame spread, ASTM E648 for horizontal flame

spread to the critical flux level, and ASTM E1321 (LIFT

apparatus) for lateral flame spread on vertical specimen to the

critical flux level. The heat transfer from the flame to the

virgin fuel is primarily conductive within a spatial extent of a

few millimeters and is affected by ambient conditions such as

oxygen, pressure, buoyancy, and external irradiance. For

most wood materials, this heat transfer from the flame is less

than or equal to surface radiant heat loss in normal ambient

conditions, so that excess heat is not available to further raise

the virgin fuel temperature; flame spread is prevented as a

result. Therefore, to achieve creeping flame spread, an external heat source is required in the vicinity of the pyrolysis

front.

Upward or ceiling flame spread involves a fuel orientation

with the main air flowing in the same direction as the flame

spread (assisting flow). At present, there are no small-scale

tests for upward flame spread potential. Thus, testing of

flame spread in assisting flow exists mostly in both the

tunnel tests and the room/corner burn tests. The heat transfer

from the flame is both conductive and radiative, has a large

spatial feature, and is relatively unaffected by ambient conditions. Rapid acceleration in flame spread can develop because

of a large, increasing magnitude of flame heat transfer as a

result of increasing total HRR in assisting flows. These

complexities and the importance of the flame spread processes explain the many and often incompatible flame spread

tests and models in existence worldwide.

Smoke and Toxic Gases

One of the most important problems associated with fires is

the smoke they produce. The term smoke is frequently used

in an all-inclusive sense to mean the mixture of pyrolysis

products and air that is present near the fire site. In this

context, smoke contains gases, solid particles, and droplets

of liquid. Smoke presents potential hazards because it interacts with light to obscure vision and because it contains

noxious and toxic substances.

Generally, two approaches are used to deal with the smoke

problem: limit smoke production and control the smoke that

has been produced. The control of smoke flow is most often

a factor in the design and construction of large or tall buildings. In these buildings, combustion products may have

serious effects in areas remote from the actual fire site.

Currently, several bench-scale test methods provide comparative smoke yield information on materials and assemblies.

Each method has entirely different exposure conditions; none

is generally correlated to full-scale fire conditions or experience. Until the middle 1970s, smoke yield restrictions in

building codes were almost always based on data from

ASTM E84. The smoke measurement is based on a percentage attenuation of white light passing through the tunnel

exhaust stream and detected by a photocell. This is converted to the smoke development index (SDI), with red oak

flooring set at 100. The flame spread requirements for interior

finish generally are linked to an added requirement that the

SDI be less than 450.

In the 1970s, the apparatus known as the NBS smoke chamber was developed and approved as an ASTM standard for

research and development (ASTM E662). This test is a

static smoke test because the specimen is tested in a closed

Table 17–3. Heat release data for selected wood speciesa

Densityb Heat release rate (kW/m2)

Average effective

heat of combustionc Ignition

Species (kg/m3) Peak 60-s avg 180-s avg 300-s avg (MJ/kg) time (s)

Softwoods

Pine, red 525 209 163 143 132 12.9 24

Pine, white 359 209 150 117 103 13.6 17

Redcedar, eastern — 175 92 95 85 11.7 25

Redwood 408 227 118 105 95 13.2 17

Hardwoods

Birch 618 218 117 150 141 12.2 29

Maple, hard 626 218 128 146 137 11.7 31

Oak, red 593 214 115 140 129 11.4 28

a

Data for 50-kW/m2 heat flux in cone calorimeter. Tested in specimen holder without retaining frame.

 Specimens conditioned to 23°C, 50% relative humidity. b

Ovendry mass and volume.

c

Tests terminated when average mass loss rate dropped below 1.5 g/s m2 during 1-min period.
 17–10

chamber of fixed volume and the light attenuation is recorded

over a known optical path length. The corresponding light

transmission is reported as specific optical density as a function of time. Samples are normally tested in both flaming

(pilot flame) and nonflaming conditions using a radiant flux

of 25 kW/m2

.

The dynamic measurement of smoke in the heat release

calorimeter (ASTM E906 and E1354) has recently gained

increasing recognition and use. The E906 and E1354 tests

are dynamic in that the smoke continuously flows out the

exhaust pipe where the optical density is measured continuously. The appropriate smoke parameter is the smoke release

rate (SRR), which is the optical density multiplied by the

volume flow rate of air into the exhaust pipe and divided by

the product of exposed surface area of the specimen and the

light path length. Often the smoke extinction area, which is

the product of SRR and the specimen area, is preferred because it can be correlated linearly with HRR in many cases.

This also permits comparison with the smoke measured in

the room/corner fire test because HRR is a readily available

test result. Although SRR can be integrated with time to get

the same units as the specific optical density, they are not

equivalent because static tests involve the direct accumulation of smoke in a volume, whereas SRR involves accumulation of freshly entrained air volume flow for each unit of

smoke. Methods investigated to correlate smoke between

different tests included alternative parameters such as

particulate mass emitted per area of exposed sample.

Toxicity of combustion products is an area of concern. About

75% to 80% of fire victims are not touched by flame but die

as a result of exposure to smoke, exposure to toxic gases, or

oxygen depletion. These life-threatening conditions can

result from burning contents, such as furnishings, as well as

from the structural materials involved. The toxicity resulting

from the thermal decomposition of wood and cellulosic

substances is complex because of the wide variety of types of

wood smoke. The composition and the concentration of the

individual constituents depend on such factors as the fire

exposure, the oxygen and moisture present, the species of

wood, any treatments or finishes that may have been applied,

and other considerations. Toxicity data may be more widely

available in the future with the recent adoption of a standard

test method (ASTM E1678).

Carbon monoxide is a particularly insidious toxic gas. Small

amounts of carbon monoxide are particularly toxic because

the hemoglobin in the blood is much more likely to combine with carbon monoxide than with oxygen, even with

plenty of breathable oxygen. This poisoning is called carboxyhemoglobin. Recent research has shown that the kind of

fires that kill people by toxicity are principally those that

reach flashover in a compartment or room some distance from

the people. The vast majority of fires that attain flashover

generate dangerous levels of carbon monoxide, independent

of what is burning. The supertoxicants, such as hydrogen

cyanide and neurotoxin, have been proven to be extremely

rare, even in the laboratory. These factors impact the choice

of test furnace and the adjustment methods used in a standardized toxicity test.

Charring and Fire Resistance

As noted earlier in this chapter, wood exposed to high temperatures will decompose to provide an insulating layer of

char that retards further degradation of the wood. The loadcarrying capacity of a structural wood member depends upon

its cross-sectional dimensions. Thus, the amount of charring

of the cross section is the major factor in the fire endurance of

structural wood members.

When wood is first exposed to fire, the wood chars and

eventually flames. Ignition occurs in about 2 min under the

standard ASTM E119 fire-test exposures. Charring into the

depth of the wood then proceeds at a rate of approximately

0.8 mm/min for the next 8 min (or 1.25 min/mm). Thereafter, the char layer has an insulating effect, and the rate

decreases to 0.6 mm/min (1.6 min/mm). Considering the

initial ignition delay, the fast initial charring, and then the

slowing down to a constant rate, the average constant charring rate is about 0.6 mm/min (or 1.5 in/h) (Douglas-fir,

7% moisture content). In the standard fire-resistance test,

this linear charring rate is generally assumed for solid wood

directly exposed to fire.

There are differences among species associated with their

density, anatomy, chemical composition, and permeability.

Moisture content is a major factor affecting charring rate.

Density relates to the mass needed to be degraded and the

thermal properties, which are affected by anatomical features.

Charring in the longitudinal grain direction is reportedly

double that in the transverse direction, and chemical composition affects the relative thickness of the char layer. Permeability affects the movement of moisture being driven from

the wood or that being driven into the wood beneath the char

layer. Normally, a simple linear model for charring where t is

time (min), C is char rate (min/mm), and xc is char depth

(mm) is assumed:

 

t Cx = c (17–1)

The temperature at the base of the char layer is generally

taken to be 300°C or 550°F (288°C). With this temperature

criterion, empirical equations for charring rate have been

developed. Equations relating charring rate under ASTM

E119 fire exposure to density and moisture content are available for Douglas-Fir, Southern Pine, and White Oak. These

equations for rates transverse to the grain are

C = (0.002269 + 0.00457μ)ρ + 0.331 for Douglas Fir

 (17–2a)

C = (0.000461 + 0.00095μ)ρ + 1.016 for Southern Pine

(17–2b)

C = (0.001583 + 0.00318μ)ρ + 0.594 for White Oak

(17–2c)

where μ is moisture content (fraction of ovendry mass) and

ρ is density, dry mass volume at moisture content μ

(kg/m3

).
17–11

A nonlinear char rate model has been found useful. This

alternative model is

 

t mx = c

1.23 (17–3)

where m is char rate coefficient (min/mm1.23).

Based on data from eight species (Table 17–4), the following

equation was developed for the char rate coefficient:

 m = −0.147 + 0.000564ρ + 1.21μ + 0.532 fc (17–4)

where ρ is density, ovendry mass and volume, and fc is char

contraction factor (dimensionless).

The char contraction factor is the thickness of the residual

char layer divided by the original thickness of the wood layer

that was charred (char depth). Average values for the eight

species tested in the development of the equation are listed in

Table 17–4.

These equations and data are valid when the member is thick

enough to be a semi-infinite slab. For smaller dimensions,

the charring rate increases once the temperature has risen

above the initial temperature at the center of the member or at

the unexposed surface of the panel. As a beam or column

chars, the corners become rounded.

Charring rate is also affected by the severity of the fire exposure. Data on charring rates for fire exposures other than

ASTM E119 have been limited. Data for exposure to constant temperatures of 538°C, 815°C, and 927°C are available

in Schaffer (1967). Data for a constant heat flux are given in

Table 17–4.

The temperature at the innermost zone of the char layer is

assumed to be 300°C. Because of the low thermal conductivity of wood, the temperature 6 mm inward from the base of

the char layer is about 180°C. This steep temperature gradient means the remaining uncharred cross-sectional area of a

large wood member remains at a low temperature and can

continue to carry a load. Moisture is driven into the wood as

charring progresses. A moisture content peak is created

inward from the char base. The peak moisture content occurs

where the temperature of the wood is about 100°C, which is

at about 13 mm from the char base.

Once a quasi-steady-state charring rate has been obtained, the

temperature profile beneath the char layer can be expressed as

an exponential term or a power term. An equation based on a

power term is

 

T T T x/d = + 1 i i 300

2

( ) − ( ) − (17–5)

Table 17–4. Charring rate data for selected wood species

Wood exposed to ASTM E119 exposurea Wood exposed to a constant heat fluxb

Linear

Nonlinear Thermal

Linear charring ratee

(min/mm)

Thermal penetration depth d g ( mm)Average mass loss

rate (g/m2 s)

Species

Densityc

(kg/m3)

Char

contraction

factord

charring

ratee

(min/

mm)

charring

ratef

(min/

mm1.23)

penetration

depth g

(mm)

18 -

kW/m2

heat flux

55-

kW/m2

heat

flux

18-

kW/m2

heat

flux

55-

kW/m2

heat

flux

18-

kW/m2

heat flux

55-

kW/m2

heat

flux

Softwoods

Southern Pine 509 0.60 1.24 0.56 33 2.27 1.17 38 26.5 3.8 8.6

Western

 redcedar

310 0.83 1.22 0.56 33 — — — — — —

Redwood 343 0.86 1.28 0.58 35 1.68 0.98 36.5 24.9 2.9 6.0

Engelmann

 spruce

425 0.82 1.56 0.70 34 — — — — — —

Hardwoods

Basswood 399 0.52 1.06 0.48 32 1.32 0.76 38.2 22.1 4.5 9.3

Maple, hard 691 0.59 1.46 0.66 31 — — — — — —

Oak, red 664 0.70 1.59 0.72 32 2.56 1.38 27.7 27.0 4.1 9.6

Yellow-

 poplar

504 0.67 1.36 0.61 32 — — — — — —

a

Moisture contents of 8% to 9%.

b

Charring rate and average mass loss rate obtained using ASTM E906 heat release apparatus. Test durations were 50 to 98 min for 18-kW/m2

 heat flux and 30 to 53 min for 55-kW/m2 heat flux. Charring rate based on temperature criterion of 300°C and linear model. Mass loss rate based

 on initial and final weight of sample, which includes moisture driven from the wood. Initial average moisture content of 8% to 9%.

c

Based on weight and volume of ovendried wood.

d

Thickness of char layer at end of fire exposure divided by original thickness of charred wood layer (char depth).

e

Based on temperature criterion of 288°C and linear model. f

Based on temperature criterion of 288°C and nonlinear model of Equation (17–3). g

As defined in Equation (17–6). Not sensitive to moisture content.
 17–12

where T is temperature (°C), Ti initial temperature (°C),

x distance from the char front (mm), and d thermal penetration depth (mm).

In Table 17–4, values for the thermal penetration depth

parameter are listed for both the standard fire exposure and

the constant heat flux exposure. As with the charring rate,

these temperature profiles assume a semi-infinite slab. The

equation does not provide for the plateau in temperatures that

often occurs at 100°C in moist wood. In addition to these

empirical data, there are mechanistic models for estimating

the charring rate and temperature profiles. The temperature

profile within the remaining wood cross-section can be used

with other data to estimate the remaining load-carrying

capacity of the uncharred wood during a fire and the residual

capacity after a fire.

Flame-Retardant Treatments

To meet building code and standards specifications, lumber

and plywood are treated with flame retardants to improve

their fire performance. The two general application methods

are pressure treating and surface coating.

Fire-Retardant-Treated Wood

To meet the specifications in the building codes and various

standards, fire-retardant-treated lumber and plywood is wood

that has been pressure treated with chemicals to reduce its

flame spread characteristics. Flame-retardant treatment of

wood generally improves the fire performance by reducing the

amount of flammable volatiles released during fire exposure

or by reducing the effective heat of combustion, or both.

Both results have the effect of reducing the HRR, particularly

during the initial stages of fire, and thus consequently

reducing the rate of flame spread over the surface. The wood

may then self-extinguish when the primary heat source is

removed.

The performance requirement for fire-retardant-treated wood is

that its FSI is 25 or less when tested according to the

ASTM E84 flame spread test and that it shows no evidence

of significant progressive combustion when this 10-min test

is continued for an additional 20 min. In addition, it is

required that the flame front in the test shall not progress

more than 3.2 m beyond the centerline of the burner at any

given time during the test. Underwriters Laboratories, Inc.,

assigns the designation FR–S to products that satisfy these

requirements. In applications where the requirement is not for

fire-retardant-treated wood but only for Class I or II flame

spread, the flame-retardant treatments only need to reduce the

FSI to the required level in the ASTM E84 flame spread test

(25 for Class I, 75 for Class II). Various laboratories perform

fire-performance rating tests on these treated materials and

maintain lists of products that meet certain standards.

Fire-retardant-treated wood and plywood are often used for

interior finish and trim in rooms, auditoriums, and corridors

where codes require materials with low surface flammability.

While fire-retardant-treated wood is not considered a noncombustible material, many codes have accepted the use of

fire-retardant-treated wood and plywood in fire-resistive and

noncombustible construction for the framing of nonloadbearing walls, roof assemblies, and decking. Fire-retardanttreated wood is also used for such special purposes as wood

scaffolding and for the frame, rails, and stiles of wood fire

doors.

In addition to specifications for flame spread performance,

fire-retardant-treated wood for use in certain applications is

specified to meet other performance requirements. Wood

treated with inorganic flame-retardant salts is usually more

hygroscopic than is untreated wood, particularly at high

relative humidities. Increases in equilibrium moisture content of this treated wood will depend upon the type of chemical, level of chemical retention, and size and species of wood

involved. Applications that involve high humidity will

likely require wood with low hygroscopicity. The American

Wood Preservers’ Association (AWPA) Standards C20 and

C27 requirements for low hygroscopicity (Interior Type A

treatment) stipulate that the material shall have an equilibrium moisture content of not more than 28% when tested in

accordance with ASTM D3201 procedures at 92% relative

humidity.

Exterior flame-retardant treatments should be specified whenever the wood is exposed to exterior weathering conditions.

The AWPA Standards C20 and C27 also mandate that an

exterior type treatment is one that has shown no increase in

fire hazard classification after being subjected to the rain test

specified in ASTM D2898 as Method A.

For structural applications, information on the fire-retardanttreated wood product needs to be obtained from the treater or

chemical supplier. This includes the design modification

factors for initial strength properties of the fire-retardanttreated wood, including values for the fasteners. Flameretardant treatment generally results in reductions in the

mechanical properties of wood. Fire-retardant-treated wood is

often more brash than untreated wood.

In field applications with elevated temperatures, such as roof

sheathings, there is the potential for further losses in strength

with time. For such applications in elevated temperatures

and high humidity, appropriate design modification factors

need to be obtained from the treater or chemical supplier.

The AWPA Standards C20 and C27 mandate that fireretardant-treated wood that will be used in high-temperature

applications (Interior Type A High Temperature), such as

roof framing and roof sheathing, be strength tested in accordance with ASTM D5664 (lumber) or ASTM D5516

(plywood) or by an equivalent methodology. Some flameretardant treatments are not acceptable because of thermal

degradation of the wood that will occur with time at high

temperatures. Screw-withdrawal tests to predict residual

in-place strength of fire-retardant-treated plywood roof sheathing have been developed (Winandy and others 1998).

Corrosion of fasteners can be accelerated under conditions of

high humidity and in the presence of flame-retardant salts.
17–13

For flame-retardant treatments containing inorganic salts, the

type of metal and chemical in contact with each other greatly

affects the rate of corrosion. Thus, information on proper

fasteners also needs to be obtained from the treater or chemical supplier. Other issues that may require contacting the

treater or chemical supplier include machinability, gluing

characteristics, and paintability.

Flame-retardant treatment of wood does not prevent the wood

from decomposing and charring under fire exposure (the rate

of fire penetration through treated wood approximates the rate

through untreated wood). Fire-retardant-treated wood used in

doors and walls can slightly improve fire endurance of these

doors and walls. Most of this improvement is associated

with the reduction in surface flammability rather than any

changes in charring rates.

Flame-Retardant Pressure Treatments

In the impregnation treatments, wood is pressure impregnated with chemical solutions using pressure processes

similar to those used for chemical preservative treatments.

However, considerably heavier absorptions of chemicals are

necessary for flame-retardant protection. Standards C20 and

C27 of the AWPA recommend the treating conditions for

lumber and plywood. The penetration of the chemicals into

the wood depends on the species, wood structure, and moisture content. Since some species are difficult to treat, the

degree of impregnation needed to meet the performance requirements for fire-retardant-treated wood may not be possible. One option is to incise the wood prior to treatment to

improve the depth of penetration.

Inorganic salts are the most commonly used flame retardants

for interior wood products, and their characteristics have

been known for more than 50 years. These salts include

monoammonium and diammonium phosphate, ammonium

sulfate, zinc chloride, sodium tetraborate, and boric acid.

Guanylurea phosphate is also used. These chemicals are

combined in formulations to develop optimum fire performance yet still retain acceptable hygroscopicity, strength,

corrosivity, machinability, surface appearance, glueability,

and paintability. Cost is also a factor in these formulations.

Many commercial formulations are available. The AWPA

Standard P17 provides information on formulations of some

current proprietary waterborne treatments. The fire-retardant

salts are water soluble and are leached out in exterior applications or with repeated washings. Water-insoluble organic

flame retardants have been developed to meet the need for

leach-resistant systems. Such treatments are also an alternative when a low hygroscopic treatment is needed. These

water-insoluble systems include (a) resins polymerized after

impregnation into wood and (b) graft polymer flame retardants attached directly to cellulose. An amino resin system

based on urea, melamine, dicyandiamide, and related

compounds is of the first type.

Flame-Retardant Coatings

For some applications, the alternative method of applying

the flame-retardant chemical as a coating to the wood surface

may be acceptable. Such commercial coating products are

available to reduce the surface flammability characteristics of

wood. The two types of coatings are intumescent and

nonintumescent. The widely used intumescent coatings

“intumesce” to form an expanded low-density film upon

exposure to fire. This multicellular carbonaceous film insulates the wood surface below from the high temperatures.

Intumescent formulations include a dehydrating agent, a char

former, and a blowing agent. Potential dehydrating agents

include polyammonium phosphate. Ingredients for the char

former include starch, glucose, and dipentaerythritol. Potential blowing agents for the intumescent coatings include urea,

melamine, and chlorinate parafins. Nonintumescent coating

products include formulations of the water-soluble salts such

as diammonium phosphate, ammonium sulfate, and borax.

References

General

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Browne, F.L. 1958. Theories of the combustion of wood

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Protection Association.
 17–14

Fire Test Standards

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ASTM E84. Surface burning characteristics of building

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ASTM E108. Fire tests of roof coverings.

ASTM E119. Fire tests of building construction and

materials.

ASTM E136. Behavior of materials in a vertical tube

furnace at 750°C.

ASTM E162. Surface flammability of materials using a

radiant heat energy source.

ASTM E648. Critical radiant flux of floor-covering

systems using a radiant heat energy source.

ASTM E662. Specific optical density of smoke generated

by solid materials.

ASTM E906. Heat and visible smoke release rates from

materials and products.

ASTM E970. Critical radiant flux of exposed attic floor

insulation using a radiant heat energy source.

ASTM E1321. Determining material ignition and flame

spread properties.

ASTM E1354. Heat and visible smoke release rates for

materials and products using an oxygen consumption

calorimeter.

ASTM E1623. Determination of fire and thermal parameters of materials, products, and systems using an intermediate scale calorimeter (ICAL).

ASTM E1678. Measuring smoke toxicity for use in fire

hazard analysis.

ICBO. [Current edition]. Fire tests of door assemblies.

Uniform Building Code Standard 7-2. Whittier, CA: International Conference of Building Officials.

ISO. Fire tests—full-scale room test for surface products.

ISO 9705. International Organization for Standardization,

Geneva, Switzerland.

NFPA. [Current edition]. Potential heat of building materials. NFPA 259. Quincy, MA: National Fire Protection

Association.

Fire-Rated Products and Assemblies

American Insurance Association. [Current edition].

Fire resistance ratings. New York: American Insurance

Association.

Gypsum Association. [Current edition]. Fire resistance

design manual. Washington, DC: Gypsum Association.

Technomic Publishing Co., Inc. 1994. Handbook of fireretardant coatings and fire testing services. Lancaster, PA:

Technomic Publishing Co., Inc.

Underwriters Laboratories, Inc. [Current edition]. Building materials directory. Northbrook, IL: Underwriters

Laboratories, Inc.

Underwriters Laboratories, Inc. [Current edition]. Fire

resistance directory. Northbrook, IL: Underwriters Laboratories, Inc.

U.S. Department of Housing and Urban Development.

1980. Guideline on fire ratings of archaic materials and assemblies. Rehabilitation Guidelines. Part 8. Washington,

DC: Superintendent of Documents.

Ignition

Brenden, J.J.; Schaffer, E. 1980. Smoldering wave-front

velocity in fiberboard. Res. Pap. FPL 367. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

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Dietenberger, M.A. Ignitability analysis of siding materials

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Crystal City, VA. London: Interscience Communications

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Kubler, H. 1990. Self-heating of lignocellulosic materials.

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LeVan, S.; Schaffer, E. 1982. Predicting weight loss from

smoldering combustion in cellulosic insulation. Journal of

Thermal Insulation. 5: 229–244.

Matson, A.F.; Dufour, R.E.; Breen, J.F. 1959. Part II.

Survey of available information on ignition of wood exposed

to moderately elevated temperatures. In: Performance of type

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during smoldering combustion of cellulosic materials.

Combustion and Flame. 55: 171–179.

Schaffer, E.L. 1980. Smoldering in cellulosics under

prolonged low-level heating. Fire Technology. 16(1): 22–28.

Flame Spread

AWC. 1999. Flame spread performance of wood products

(1998). Design for code acceptance No. 1.

http://www.forestprod.org/awcpubs.html (11 Feb. 1999).

Benjamin, I.A.; Adams, C.H. 1976. The flooring radiant

panel test and proposed criteria. Fire Journal. 70(2): 63–70.

March.

Holmes, C.A.; Eickner, H.W.; Brenden, J.J.; White,

R.H. 1979. Fire performance of structural flakeboard from

forest residue. Res. Pap. FPL–RP–315. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.
17–15

Underwriters Laboratories, Inc. 1971. Wood-fire hazard

classification. Card Data Service, Serial No. UL527,

Chicago, IL: Underwriters Laboratories, Inc.

Yarbrough, D.W.; Wilkes, K.E. 1997. Thermal properties

and use of cellulosic insulation produced from recycled paper.

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108–114.

Flashover and Room/Corner Tests

Bruce, H.D. 1959. Experimental dwelling—room fires.

Rep. 1941. Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory.

Dietenberger, M.A.; Grexa, O.; White, R.H. [and others]. 1995. Room/corner test of wall linings with 100/300

kW burner. In: Proceedings, 4th international fire and materials conference; 1995 November 15–16; Crystal City, MD.

London: InterScience Communications Limited: 53–62.

Holmes, C. 1978. Room corner-wall fire tests of some structural sandwich panels and components. Journal of Fire &

Flammability. 9: 467–488.

Holmes, C.; Eickner, H.; Brenden, J.J. [and others].

1980. Fire development and wall endurance in sandwich and

wood-frame structures. Res. Pap. FPL 364. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Schaffer, E.L.; Eickner, H.W. 1965. Effect of wall linings

on fire performance within a partially ventilated corridor.

Res. Pap. FPL 49. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Tran, H.C. 1991. Wall and corner fire tests on selected

wood products. Journal of Fire Sciences. 9: 106–124.

March/April.

Heat Release and Heat of Combustion

Babrauskas, V.; Grayson, S.J. eds. 1992. Heat release in

fires. New York: Elsevier Applied Science.

Chamberlain, D.L. 1983. Heat release rates of lumber and

wood products. In: Schaffer, E.L., ed., Behavior of polymeric

materials in fire. ASTM STP 816. Philadelphia, PA:

American Society for Testing and Materials: 21–41.

Tran, H.C. 1990. Modifications to an Ohio State University apparatus and comparison with cone calorimeter results.

In: Quintiere, J.G.; Cooper, L.Y. eds. Heat and mass transfer

in fires. Proceedings, AIAA/ASME thermophysics and heat

transfer conference; 1990 June 18–20; Seattle, WA. New

York: The American Society of Mechanical Engineers:

141: 131–139.

Tran, H.C. 1992. (B) Experimental data on wood materials.

In: Babrauskas, V.; Grayson, S.J. eds. Heat release in fires.

Chapter 11 Part. B. New York: Elsevier Applied Science:

357–372.

White, R.H. 1987. Effect of lignin content and extractives

on the higher heating value of wood. Wood and Fiber

Science. 19(4): 446–452.

Smoke and Other

Combustion Products

Brenden, J.J. 1970. Determining the utility of a new optical test procedure for measuring smoke from various wood

products. Res. Pap. FPL 137. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products

Laboratory.

Brenden, J.J. 1975. How nine inorganics salts affected

smoke yield from Douglas-fir plywood. Res. Pap. FPL 249.

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Hall, J.R., Jr. 1996. Whatever happened to combustion

toxicity. Fire Technology. 32(4): 351–371.

Tran, H.C. 1990. Correlation of wood smoke produced

from NBS smoke chamber and OSU heat release apparatus.

In: Hasegawa, H.K. ed., Characterization and toxicity of

smoke. ASTM STP 1082. Philadelphia, PA: American

Society for Testing and Materials: 135–146.

Charring and Fire Resistance

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glued laminated timbers. Tech. Note 7. Englewood, CO:

American Institute of Timber Construction.

ASCE. 1982. Evaluation, maintenance and upgrading of

wood structures—a guide and commentary. New York:

American Society of Civil Engineers. 428 p.

AWC. 1985. Design of fire-resistive exposed wood members

(1985). Design for code acceptance No. 2. Pub. T18 Washington, DC: American Wood Council.

AWC. 1991. Component additive method (CAM) for calculating and demonstrating assembly fire endurance. DCA No.

4, Design for code acceptance. Pub. T20. Washington, DC:

American Forest & Paper Association.

Janssens, M. 1994. Thermo-physical properties for wood

pyrolysis models. In: Proceedings, Pacific Timber Engineering conference; 1994 July 11–15; Gold Coast, Australia.

Fortitude Valley MAC, Queensland, Australia: Timber

Research and Development Advisory Council: 607–618.

Janssens, M.L.; White, R.H. 1994. Short communication:

temperature profiles in wood members exposed to fire. Fire

and Materials. 18: 263–265.

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charring rate of wood. Res. Note FPL–145. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

Schaffer, E.L. 1967. Charring rate of selected woodstransverse to grain. Res. Pap. FPL 69. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.
 17–16

Schaffer, E.L. 1977. State of structural timber fire endurance. Wood and Fiber. 9(2): 145–170.

Schaffer, E.L. 1984. Structural fire design: Wood. Res.

Pap. FPL 450. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Tran, H.C.; White, R.H. 1992. Burning rate of solid wood

measured in a heat release calorimeter. Fire and Materials.

16: 197–206.

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resistance of timber members. In: The SFPE handbook of fire

protection engineering. 2d ed. Quincy, MA: National Fire

Protection Association.

White, R.H.; Nordheim, E.V. 1992. Charring rate of wood

for ASTM E119 exposure. Fire Technology. 28: 5–30.

White, R.H.; Tran, H.C. 1996. Charring rate of wood

exposed to a constant heat flux. In: Proceedings, Wood &

Fire Safety, third international conference. The High Tatras;

1996 May 6–9; Zvolen, Slovakia. Zvolen, Slovakia: Faculty of Wood Technology, Technical University: 175–183.

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fire-exposed light-frame wood floor assemblies. Res. Pap.

FPL 386. Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory.

Fire-Retardant-Treated Wood

Treated Wood Standards

ASTM. [Current edition]. West Conshohocken, PA:

American Society for Testing and Materials.

ASTM E69. Combustible properties of treated wood by

fire-tube apparatus.

ASTM D2898. Accelerated weathering of fire-retardant

treated wood for fire testing.

ASTM D3201. Hygroscopic properties of fire-retardant

wood and wood-base products.

ASTM D5516. Standard method for evaluating the mechanical properties of fire-retardant treated softwood plywood exposed to elevated temperatures.

ASTM D5664. Standard method for evaluating the effects

of fire-retardant treatments and elevated temperatures on

strength properties of fire-retardant treated lumber.

AWPA. [Current edition]. Gransbury, TX: American WoodPreservers’ Association.

Standard A2. Analysis of waterborne preservatives and fireretardant formulations.

Standard A3. Determining penetration of preservative and

fire retardants.

Standard A9. Analysis of treated wood and treating solutions by x-ray spectroscopy.

Standard C20. Structural lumber—Fire-retardant pressure

treatment by pressure processes.

Standard C27. Plywood—Fire-retardant treatment by

pressure processes.

Standard P17. Fire-retardant formulations.

Treated Wood Literature

Holmes, C.A. 1977. Effect of fire-retardant treatments on

performance properties of wood. In: Goldstein, I.S., ed.

Wood technology: Chemical aspects. Proceedings, ACS

symposium Series 43. Washington, DC: American

Chemical Society.

LeVan, S.L. 1984. Chemistry of fire retardancy. In: Rowell,

Roger M., ed. The chemistry of solid wood. Advances in

Chemistry Series 207. Washington, DC: American Chemical Society.

LeVan, S.L.; Holmes, C.A. 1986. Effectiveness of fireretardant treatments for shingles after 10 years of outdoor

weathering. Res. Pap. RP–FPL–474. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

LeVan, S.L.; Tran, H.C. 1990. The role of boron in flameretardant treatments. In: Hamel, Margaret, ed. 1st International conference on wood protection with diffusible preservatives: Proceedings 47355; 1990 November 28–30; Nashville,

TN. Madison, WI: Forest Products Research Society:

39–41.

LeVan, S.L.; Winandy, J.E. 1990. Effects of fire-retardant

treatments on wood strength: a review. Wood and Fiber

Science. 22(1): 113–131.

LeVan, S.L.; Ross, R.J.; Winandy, J.E. 1990. Effects of

fire retardant chemicals on the bending properties of wood at

elevated temperatures. Res. Pap. FPL–RP–498. Madison,

WI: U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory.

NAHB National Research Center. 1990. Home builders

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and replacement. Upper Marlboro, MD: National Association

of Home Builders, National Research Center.

Winandy, J.E. 1995. Effects of fire retardant treatments after

18 months of exposure at 150°F (66°C). Res. Note FPL–

RN–0264. Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory.

Winandy, J.E. 1997. Effects of fire retardant retention,

borate buffers, and redrying temperature after treatment on

thermal-induced degradation. Forest Products Journal.

47(6): 79–86.

Winandy, J.E.; LeVan, S.L.; Ross, R.J.; Hoffman,

S.P.; McIntyre, C.R. 1991. Thermal degradation of fireretardant-treated plywood—development and evaluation of a

test protocol. Res. Pap. FPL–RP–501. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory.

Winandy, J.E.; Lebow, P. K.; Nelson, W. 1998. Predicting bending strength of fire-retardant-treated plywood from

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Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
18–1

Round Timbers and Ties

Ronald W. Wolfe

Chapter 18

Contents

Standards and Specifications 18–1

Material Requirements 18–1

Availability 18–2

Poles 18–2

Piles 18–3

Construction Logs 18–3

Ties 18–3

Form 18–3

Poles and Piles 18–3

Construction Logs 18–4

Ties 18–5

Weight and Volume 18–5

Durability 18–6

Preservative Treatment 18–6

Service Life 18–6

Strength Properties 18–7

Poles 18–7

Piles 18–7

Construction Logs 18–7

Ties 18–8

References 18–8

ound timbers and ties represent some of the most

efficient uses of our forest resources. They require a

minimum of processing between harvesting the tree

and marketing the structural commodity. Poles and piles are

debarked or peeled, seasoned, and often treated with preservative prior to use as structural members. Construction logs are

usually shaped to facilitate construction. Ties, used for railroads, landscaping, and mining, are slab-cut to provide flat

surfaces. Because these products are relatively economical to

produce, compared with glulam, steel, and concrete products,

they are commonly used throughout the United States.

Standards and Specifications

Material standards and specifications listed in Table 18–1

were created through the joint efforts of producers and users

to ensure compatibility between product quality and end

use. These guidelines include recommendations for production, treatment, and engineering design. They are updated

periodically to conform to changes in material and design

technology.

Material Requirements

Round timber and tie material requirements vary with intended use. The majority of uses involve exposure to harsh

environments. Thus, in addition to availability, form, and

weight, durability is also an important consideration for the

use of round timbers and ties. Availability reflects the economic feasibility of procuring members of the required size

and grade. Form or physical appearance refers to visual characteristics, such as straightness and occurrence of knots and

spiral grain. Weight affects shipping and handling costs and

is a function of volume, moisture content, and wood density.

Durability is directly related to expected service life and is a

function of treatability and natural decay resistance. Finally,

regardless of the application, any structural member must be

strong enough to resist imposed loads with a reasonable

factor of safety. Material specifications available for most

applications of round timbers and ties contain guidelines

for evaluating these factors.

R
 18–2

Availability

Material evaluation begins with an assessment of availability. For some applications, local species of timber may be

readily available in an acceptable form and quality. However,

this is not normally the case. Pole producers and tie mills

are scattered throughout heavily forested regions. Their

products are shipped to users throughout North America.

Poles

Most structural applications of poles require timbers that are

relatively straight and free of large knots. Poles used to

support electric utility distribution and transmission lines

(Fig. 18–1) range in length from 6 to 38 m (20 to 125 ft) and

from 0.13 to 0.76 m (5 to 30 in.) in diameter, 1.8 m (6 ft)

from the butt. Poles used to support local area distribution

lines are normally <15 m (<50 ft) long and are predominately Southern Pine.

Hardwood species can be used for poles when the trees are of

suitable size and form; their use is limited, however, by their

weight, by their excessive checking, and because of the lack

of experience in preservative treatment of hardwoods. Thus,

most poles are softwoods.

The Southern Pine lumber group (principally loblolly,

longleaf, shortleaf, and slash) accounts for roughly 80% of

poles treated in the United States. Three traits of these pines

account for their extensive use: thick and easily treated sapwood, favorable strength properties and form, and availability

in popular pole sizes. In longer lengths, Southern Pine poles

are in limited supply, so Douglas-fir, and to some extent

western redcedar, Ponderosa pine, and western larch, are

used to meet requirements for 15-m (50-ft) and longer

transmission poles.

Douglas-fir is used throughout the United States for transmission poles and is used in the Pacific Coast region for

distribution and building poles. Because the heartwood of

Douglas-fir is resistant to preservative penetration and has

limited decay and termite resistance, serviceable poles need a

well-treated shell of sapwood that is free of checking. To

minimize checking after treatment, poles should be adequately seasoned or conditioned before treatment. With these

precautions, the poles should compare favorably with treated

Southern Pine poles in serviceability.

A small percentage of the poles treated in the United States

are of western redcedar, produced mostly in British Columbia. The number of poles of this species used without treatment is not known but is considered to be small. Used

primarily for utility lines in northern and western United

States, well-treated redcedar poles have a service life that

compares favorably with poles made from other species and

could be used effectively in pole-type buildings.

Lodgepole pine is also used in small quantities for treated

poles. This species is used both for utility lines and for

pole-type buildings. It has a good service record when well

treated. Special attention is necessary, however, to obtain

poles with sufficient sapwood thickness to ensure adequate

penetration of preservative, because the heartwood is not

usually penetrated and is not decay resistant. The poles must

also be well seasoned prior to treatment to avoid checking

and exposure of unpenetrated heartwood to attack by decay

fungi.

Western larch poles produced in Montana and Idaho came

into use after World War II because of their favorable size,

shape, and strength properties. Western larch requires

preservative treatment full length for use in most areas and,

as in the case of lodgepole pine poles, must be selected for

adequate sapwood thickness and must be well seasoned

prior to treatment. Other species occasionally used for poles

are listed in the American National Standards Institute

(ANSI) O5.1 standard. These minor species make up a very

small portion of pole production and are used locally.

Table 18–1. Standards and specifications for round timbers and tiesa

Engineering design stresses

Product Material requirements Preservative treatment Procedures Design values

Utility poles ANSI O5.1 TT-W-571

AWPA C1,C4,C35

 — ANSI O5.1

Construction poles ANSI O5.1 TT-W-571

AWPA C23

ASTM D3200 ASAE EP 388

Piles ASTM D25 TT-W-571

AWPA CI,C3

ASTM D2899 NDS

Construction logs (See material supplier) — ASTM D3957 (See material supplier)

Ties AREA TT-W-571

AWPA C2,C6 AREA

 — AREA

a

ANSI, American National Standards Institute; ASTM, American Society for Testing and Materials;

 ASAE, American Society of Agricultural Engineers; AREA, American Railway Engineers Association; NDS,

 National Design Specification (for Wood Construction); AWPA, American Wood-Preservers’ Association.
18–3

Glued-laminated, or glulam, poles are also available for use

where special sizes or shapes are required. The ANSI Standard O5.2 provides guidelines for specifying these poles.

Piles

Material available for timber piles is more restricted than that

for poles. Most timber piles used in the eastern half of the

United States are Southern Pine, while those used in western

United States are coast Douglas-fir. Oak, red pine, and cedar

piles are also referenced in timber pile literature but are not as

widely used as Southern Pine and Douglas-fir.

Construction Logs

Round timbers have been used in a variety of structures,

including bridges, log cabins, and pole buildings. Log

stringer bridges (Fig. 18–2) are generally designed for a

limited life on logging roads intended to provide access to

remote areas. In Alaska where logs may exceed 1 m (3 ft) in

diameter, bridge spans may exceed 9 m (30 ft). Building

poles, on the other hand, are preservative-treated logs in the

0.15- to 0.25-m- (6- to 10-in.-) diameter range. These poles

rarely exceed 9 m (30 ft) in length. Although poles sold for

this application are predominately Southern Pine, there is

potential for competition from local species in this category.

Finally, log cabin logs normally range from 0.2 to 0.25 m

(8 to 10 in.) in diameter, and the availability of logs in this

size range is not often a problem. However, because logs are

not normally preservative treated for this application, those

species that offer moderate to high natural decay resistance,

such as western redcedar, are preferred. Pole buildings, which

incorporate round timbers as vertical columns and cantilever

supports, require preservative-treated wood. Preservativetreated poles for this use may not be readily available.

Ties

The most important availability consideration for railroad

cross ties is quantity. Ties are produced from most native

species of timber that yield log lengths >2.4 m (8 ft) with

diameters >0.18 m (7 in.). The American Railway Engineering Association (AREA) lists 26 U.S. species that may be

used for ties. Thus, the tie market provides a use for many

low-grade hardwood and softwood logs.

Form

Natural growth properties of trees play an important role in

their use as structural round timbers. Three important form

considerations are cross-sectional dimensions, straightness,

and the presence of surface characteristics such as knots.

Poles and Piles

Standards for poles and piles have been written with the

assumption that trees have a round cross section with a

circumference that decreases linearly with height. Thus, the

shape of a pole or pile is often assumed to be that of the

frustum of a cone. Actual measurements of tree shape indicate

that taper is rarely linear and often varies with location along

the height of the tree. Average taper values from the ANSI

O5.1 standard are shown in Table 18–2 for the more popular

pole species. Guidelines to account for the effect of taper on

the location of the critical section above the groundline are

given in ANSI O5.1. The standard also tabulates pole dimensions for up to 15 size classes of 11 major pole species.

Taper also affects construction detailing of pole buildings.

Where siding or other exterior covering is applied, poles are

generally set with the taper to the interior side of the structures to provide a vertical exterior surface (Fig. 18–3).

Another common practice is to modify the round poles by

slabbing to provide a continuous flat face. The slabbed face

permits more secure attachment of sheathing and framing

members and facilitates the alignment and setting of intermediate wall and corner poles. The slabbing consists of a

minimum cut to provide a single continuous flat face from

the groundline to the top of intermediate wall poles and two

continuous flat faces at right angles to one another from the

groundline to the top of corner poles. However, preservative

Figure 18–1. Round timber poles form the major

structural element in these transmission structures.

(Photo courtesy of Koppers Co.)
 18–4

penetration is generally limited to the sapwood of most

species; therefore slabbing, particularly in the groundline area

of poles with thin sapwood, may result in somewhat less

protection than that of an unslabbed pole. All cutting and

sawing should be confined to that portion of the pole above

the groundline and should be performed before treatment.

The American Standards for Testing and Materials (ASTM)

D25 standard provides tables of pile sizes for either friction

piles or end-bearing piles. Friction piles rely on skin friction

rather than tip area for support, whereas end-bearing piles

resist compressive force at the tip. For this reason, a friction

pile is specified by butt circumference and may have a

smaller tip than an end-bearing pile. Conversely, end-bearing

piles are specified by tip area and butt circumference is

minimized.

Straightness of poles or piles is determined by two form

properties: sweep and crook. Sweep is a measure of bow or

gradual deviation from a straight line joining the ends of the

pole or pile. Crook is an abrupt change in direction of the

centroidal axis. Limits on these two properties are specified

in both ANSI O5.1 and ASTM D25.

Construction Logs

Logs used in construction are generally specified to meet the

same criteria for straightness and knots as poles and piles

(ASTM D25). For log stringer bridges, the log selection

criteria may vary with the experience of the person doing the

selection but straightness, spiral grain, wind shake, and

knots are limiting criteria. Although no consensus standard

Figure 18–2. Logs are used to construct logging bridges in remote forest areas.

Table 18–2. Circumference taper

Species

Centimeter

change in

circumference

per meter

Inch

change in

circumference

per foota

Western redcedar 3.7 0.38

Ponderosa pine 2.4 0.29

Jack, lodgepole, and red pine 2.5 0.30

Southern Pine 2.1 0.25

Douglas-fir, larch 1.7 0.21

Western hemlock 1.7 0.20

a

Taken from ANSI O5.1.
18–5

is available for specifying and designing log stringers, the

Design Guide for Native Log Stringer Bridges was prepared

by the USDA Forest Service.

Logs used for log cabins come in a wide variety of crosssectional shapes (Fig. 18–4). Commercial cabin logs are

usually milled so that their shape is uniform along their

length. The ASTM D3957 standard, a guide for establishing

stress grades for building logs, recommends stress grading

on the basis of the largest rectangular section that can be

inscribed totally within the log section. The standard also

provides commentary on the effects of knots and slope of

grain.

Ties

Railroad ties are commonly shaped to a fairly uniform section along their length. The AREA publishes specifications

for the sizes, which include seven size classes ranging from

0.13 by 0.13 m (5 by 5 in.) to 0.18 by 0.25 m (7 by 10 in.).

These tie classes may be ordered in any of three standard

lengths: 2.4 m (8 ft), 2.6 m (8.5 ft), or 2.7 m (9 ft).

Weight and Volume

The weight of any wood product is a function of its volume,

density, moisture content, and any retained treatment substance. An accurate estimate of volume of a round pole would

require numerous measurements of the circumference and

shape along the length, because poles commonly exhibit

neither a uniform linear taper nor a perfectly round shape.

The American Wood Preservers’ Association (AWPA)

Standard F3 therefore recommends volume estimates be

based on the assumption that the pole is shaped as the frustum of a cone (that is, a cone with the top cut perpendicular

to the axis), with adjustments dependent on species. The

volume in this case is determined as the average crosssectional area A times the length. Estimates of average crosssectional area may be obtained either by measuring the circumference at mid-length (A = Cm

2

/4π) or taking the average

of the butt and tip diameters (A = π(D + d)

2

/16) to estimate

the area of a circle. The AWPA recommends that these

estimates then be adjusted by the following correction factors

for the given species and application:

Oak piles 0.82

Southern Pine piles 0.93

Southern Pine and red pine poles 0.95

Tables for round timber volume are given in AWPA Standard F3. The volume of a round timber differs little whether

it is green or dry. Drying of round timbers causes checks to

open, but there is little reduction of the gross diameter of the

pole.

Wood density also differs with species, age, and growing

conditions. It will even vary along the height of a single tree.

Average values, tabulated by species, are normally expressed

as specific gravity (SG), which is density expressed as a ratio

of the density of water (see Ch. 4). For commercial species

grown in the United States, SG varies from 0.32 to 0.65. If

you know the green volume of a round timber and its SG, its

dry weight is a product of its SG, its volume, and the unit

weight of water (1000 kg/m3

 (62.4 lb/ft3)). Wood moisture

content can also be highly variable. A pole cut in the spring

when sap is flowing may have a moisture content exceeding

100% (the weight of the water it contains may exceed the

weight of the dry wood substance). If you know the moisture

content (MC) of the timber, multiply the dry weight by

(1 + MC/100) to get the wet weight.

Finally, in estimating the weight of a treated wood product

such as a pole, pile, or tie, you must take into account the

weight of the preservative. Recommended preservative retentions are listed in Table 14–3 in Chapter 14. By knowing

the volume, the preservative weight can be approximated

by multiplying volume by the recommended preservative

retention.

Figure 18–3. Poles provide economical foundation and

wall systems for agricultural and storage buildings.

Figure 18–4. Construction logs can be formed in a

variety of shapes for log homes. Vertical surfaces

may be varied for aesthetic purposes, while the

horizontal surfaces generally reflect structural

and thermal considerations.
 18–6

Durability

For most applications of round timbers and ties, durability is

primarily a question of decay resistance. Some species are

noted for their natural decay resistance; however, even these

may require preservative treatment, depending upon the

environmental conditions under which the material is used

and the required service life. For some applications, natural

decay resistance is sufficient. This is the case for temporary

piles, marine piles in fresh water entirely below the permanent water level, and construction logs used in building

construction. Any wood members used in ground contact

should be pressure treated, and the first two or three logs

above a concrete foundation should be brush treated with a

preservative–sealer.

Preservative Treatment

Federal Specification TT–W–571 (U.S. Federal Supply

Service (USFSS)) covers the inspection and treatment requirements for various wood products including poles, piles,

and ties. This specification refers to the AWPA Standards

C1 and C3 for pressure treatment, C2 and C6 for treatment of

ties, C8 for full-length thermal (hot and cold) treatment of

western redcedar poles, C10 for full-length thermal (hot and

cold) treatment of lodgepole pine poles, and C23 for pressure

treatment of construction poles. The AREA specifications for

cross ties and switch ties also cover preservative treatment.

Retention and types of various preservatives recommended

for various applications are given in Table 14–3.

Inspection and treatment of poles in service has been effective

in prolonging the useful life of untreated poles and those with

inadequate preservative penetration or retention. The Forest

Research Laboratory at Oregon State University has published guidelines for developing an in-service pole maintenance program.

Service Life

Service conditions for round timbers and ties vary from mild

for construction logs to severe for cross ties. Construction

logs used in log homes may last indefinitely if kept dry and

properly protected from insects. Most railroad ties, on the

other hand, are continually in ground contact and are subject

to mechanical damage.

Poles

The life of poles can vary within wide limits, depending

upon properties of the pole, preservative treatments, service

conditions, and maintenance practices. In distribution or

transmission line supports, however, service life is often

limited by obsolescence of the line rather than the physical

life of the pole.

It is common to report the average life of untreated or treated

poles based on observations over a period of years. These

average life values are useful as a rough guide to the service

life to be expected from a group of poles, but it should be

kept in mind that, within a given group, 60% of the poles

will have failed before reaching an age equal to the average

life.

Early or premature failure of treated poles can generally be

attributed to one or more of three factors: (a) poor penetration

and distribution of preservative, (b) an inadequate retention of

preservative, or (c) use of a substandard preservative. Properly treated poles can last 35 years or longer.

Western redcedar is one species with a naturally decayresistant heartwood. If used without treatment, however, the

average life is somewhat less than 20 years.

Piles

The expected life of a pile is also determined by treatment

and use. Wood that remains completely submerged in water

does not decay although bacteria may cause some degradation; therefore, decay resistance is not necessary in all piles,

but it is necessary in any part of the pile that may extend

above the permanent water level. When piles that support the

foundations of bridges or buildings are to be cut off above the

permanent water level, they should be treated to conform to

recognized specifications such as Federal Specification

TT-W-571 and AWPA Standards C1 and C3. The untreated

surfaces exposed at the cutoffs should also be given protection by thoroughly brushing the cut surface with coal-tar

creosote. A coat of pitch, asphalt, or similar material may

then be applied over the creosote and a protective sheet

material, such as metal, roofing felt, or saturated fabric,

should be fitted over the pile cut-off in accordance with

AWPA Standard M4. Correct application and maintenance

of these materials are critical in maintaining the integrity of

piles.

Piles driven into earth that is not constantly wet are subject

to about the same service conditions as apply to poles but

are generally required to last longer. Preservative retention

requirements for piles are therefore greater than for poles

(Table 14–3). Piles used in salt water are subject to destruction by marine borers even though they do not decay below

the waterline. The most effective practical protection against

marine borers has been a treatment first with a waterborne

preservative, followed by seasoning with a creosote treatment. Other preservative treatments of marine piles are covered in Federal Specification TT–W–571 and AWPA

Standard C3 (Table 14–3).

Ties

The life of ties in service depends on their ability to resist

decay and mechanical destruction. Under sufficiently light

traffic, heartwood ties of naturally durable wood, even if of

low strength, may give 10 or 15 years of average service

without preservative treatment; under heavy traffic without

adequate mechanical protection, the same ties might fail in

2 or 3 years. Advances in preservatives and treatment processes, coupled with increasing loads, are shifting the primary

cause of tie failure from decay to mechanical damage. Welltreated ties, properly designed to carry intended loads,
18–7

should last from 25 to 40 years on average. Records on life

of treated and untreated ties are occasionally published in the

annual proceedings of the American Railway Engineering

Association (AREA) and AWPA.

Strength Properties

Allowable strength properties of round timbers have been

developed and published in several standards. In most cases,

published values are based on strength of small clear test

samples. Allowable stresses are derived by adjusting small

clear values for effects of growth characteristics, conditioning,

shape, and load conditions as discussed in applicable standards. In addition, published values for some species of poles

and piles reflect results of full-sized tests.

Poles

Most poles are used as structural members in support structures for distribution and transmission lines. For this application, poles may be designed as single-member or guyed

cantilevers or as structural members of a more complex

structure. Specifications for wood poles used in single pole

structures have been published by ANSI in Standard O5.1.

Guidelines for the design of pole structures are given in the

ANSI National Electric Safety Code (NESC) (ANSI C2).

The ANSI O5.1 standard gives values for fiber stress in

bending for species commonly used as transmission or distribution poles. These values represent the near-ultimate fiber

stress for poles used as cantilever beams. For most species,

these values are based partly on full-sized pole tests and

include adjustments for moisture content and pretreatment

conditioning. The values in ANSI O5.1 are compatible with

the ultimate strength design philosophy of the NESC, but

they are not compatible with the working stress design

philosophy of the National Design Specification (NDS).

Reliability-based design techniques have been developed for

the design of distribution–transmission line systems. This

approach requires a strong database on the performance of

pole structures. Supporting information for these design

procedures is available in a series of reports published by the

Electric Power Research Institute (EPRI).

Piles

Bearing loads on piles are sustained by earth friction along

their surface (skin friction), by bearing of the tip on a solid

stratum, or by a combination of these two methods. Wood

piles, because of their tapered form, are particularly efficient

in supporting loads by skin friction. Bearing values that

depend upon friction are related to the stability of the soil

and generally do not approach the ultimate strength of the

pile. Where wood piles sustain foundation loads by bearing

of the tip on a solid stratum, loads may be limited by the

compressive strength of the wood parallel to the grain. If a

large proportion of the length of a pile extends above ground,

its bearing value may be limited by its strength as a long

column. Side loads may also be applied to piles extending

above ground. In such instances, however, bracing is often

used to reduce the unsupported column length or to resist the

side loads.

The most critical loads on piles often occur during driving.

Under hard driving conditions, piles that are too dry (<18%

moisture content at a 51-mm (2-in.) depth) have literally

exploded under the force of the driving hammers. Steel banding is recommended to increase resistance to splitting, and

driving the piles into predrilled holes reduces driving

stresses.

The reduction in strength of a wood column resulting from

crooks, eccentric loading, or any other condition that will

result in combined bending and compression is not as great

as would be predicted with the NDS interaction equations.

This does not imply that crooks and eccentricity should be

without restriction, but it should relieve anxiety as to the

influence of crooks, such as those found in piles. Design

procedures for eccentrically loaded columns are given in

Chapter 8.

There are several ways to determine bearing capacity of piles.

Engineering formulas can estimate bearing values from the

penetration under blows of known energy from the driving

hammer. Some engineers prefer to estimate bearing capacity

from experience or observation of the behavior of pile foundations under similar conditions or from the results of staticload tests.

Working stresses for piles are governed by building code

requirements and by recommendations of ASTM D2899.

This standard gives recommendations for adjusting small

clear strength values listed in ASTM D2555 for use in the

design of full-sized piles. In addition to adjustments for

properties inherent to the full-sized pile, the ASTM D2899

standard also provides recommendations for adjusting allowable stresses for the effects of pretreatment conditioning.

Design stresses for timber piles are tabulated in the NDS for

wood construction. The NDS values include adjustments for

the effects of moisture content, load duration, and preservative treatment. Recommendations are also given to adjust for

lateral support conditions and factors of safety.

Construction Logs

Design values for round timbers used as structural members

in pole or log buildings may be determined following standards published by ASTM and ASAE. The ASTM standard

refers pole designers to the same standard used to derive

design stresses for timber piles (D2899). The ASAE standard

(EP388), which governed the derivation of construction poles

for agricultural building applications, is being revised.

The future revision will be designated EP560 and will deal

only with round wood poles. Derivation of design stresses

for construction logs used in log homes is covered in ASTM

D3957, which provides a method of establishing stress

grades for structural members of any of the more common log

configurations. Manufacturers can use this standard to

develop grading specifications and derive engineering design

stresses for their construction logs.
 18–8

Ties

Railroad cross and switch ties have historically been overdesigned from the standpoint of rail loads. Tie service life

was limited largely by deterioration rather than mechanical

damage. However, because of advances in decay-inhibiting

treatment and increased axle loads, adequate structural design

is becoming more important in increasing railroad tie service

life.

Rail loads induce stresses in bending and shear as well as in

compression perpendicular to the grain in railroad ties. The

AREA manual gives recommended limits on ballast bearing

pressure and allowable stresses for cross ties. This information may be used by the designer to determine adequate tie

size and spacing to avoid premature failure due to mechanical

damage.

Specific gravity and compressive strength parallel to the

grain are also important properties to consider in evaluating

cross tie material. These properties indicate the resistance of

the wood to both pull out and lateral thrust of spikes.

References

General

ASTM. [Current edition]. Standard test methods for establishing clear wood strength values. ASTM D2555. West

Conshohocken, PA: American Society for Testing and

Materials.

AWPA. [Current edition]. Book of standards (includes

standards on pressure and thermal treatment of poles, piles,

and ties). (American Wood-Preserver’s Bureau official quality control standards.) Bethesda, MD: American WoodPreservers' Association.

Engineering Data Management and Colorado State

University. 1989–1998. International conference—Wood

poles and piles. Conference proceedings. Fort Collins, CO:

Engineering Data Management and Colorado State

University.

USFSS. [Current edition]. Poles and piles, wood. Federal

specification MM–P–371c—ties, railroad (cross and switch);

Federal Specification MM–T–371d—wood preservation:

treating practice; Federal Specification TT–W–571.

Washington, DC: U.S. Federal Supply Service.

Poles

ANSI. [Current edition]. New York, NY: American National

Standards Institute.

ANSI O5.1. Specifications and dimensions for wood

poles.

ANSI C2. National electrical safety code.

ANSI O5.2. Structural glued laminated timber for utility

structures.

ASTM. [Current edition]. West Conshohocken, PA:

American Society for Testing and Materials.

ASTM D3200. Standard specification and methods for establishing recommended design stresses for round timber

construction poles.

ANSI/ASTM D1036–58. Standard methods of static tests

of wood poles.

Carson, J.M.; Dougherty, M., eds. 1997. Post-frame

building handbook: Materials, design considerations, construction procedures. Ithaca, NY: Northeast Regional

Agricultural Engineering Service.

EPRI. 1981. Probability-based design of wood transmission

structures. (a) Vol. 1: Strength and stiffness of wood utility

poles. (b) Vol. 2: Analysis and probability-based design of

wood utility structures. (c) Vol. 3: Users manual. POLEDA–

80. Pole design and analysis. Prepared by Research Institute

of Colorado for Electric Power Research Institute. Palo Alto,

CA: Electric Power Research Institute. EL1–2040. Vols. 1–

3, Proj. 1352-1. September.

EPRI. 1985. Wood pole properties. Vol. 1: Background and

Southern Pine data. Prepared by Research Institute of Colorado for Electric Power Research Institute. Palo Alto, CA:

Electric Power Research Institute. EL–4109, Proj. 1352–2,

July.

EPRI. 1986. Wood pole properties. (a) Vol. 2: Douglas Fir

data. (b) Vol. 3: Western redcedar. Prepared by Research

Institute of Colorado for Electric Power Research Institute.

Palo Alto, CA: Electric Power Research Institute. EL–4109,

Proj. 1352–2, January.

Morrell, J.J. 1996. Wood pole maintenance manual. Corvallis, OR: College of Forestry, Forest Research Laboratory,

Oregon State University.

NRAES. 1997. Post-frame building construction. Ithaca,

NY: Northeast Regional Agricultural Engineering Service.

Thompson, W.S. 1969. Effect of steaming and kiln drying

on properties of Southern Pine poles. Part I—mechanical

properties. Forest Products Journal. 19(1): 21–28.

Wood, L.W.; Erickson, E.C.O.; Dohr, A.W. 1960.

Strength and related properties of wood poles. Philadelphia,

PA: American Society for Testing and Materials.

Wood, L.W.; Markwardt, L.J. 1965. Derivation of fiber

stresses from strength values of wood poles. Res. Pap. FPL

39. Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Piles

AREA. 1982. Timber structures. In: Manual for railway

engineering. Washington, DC: American Railway

Engineering Association. Chapter 7.
18–9

ASTM. [Current edition]. West Conshohocken, PA:

American Society for Testing and Materials.

ASTM D25. Standard specification for round timber piles.

ASTM D2899. Establishing design stresses for round

timber piles.

Armstrong, R.M. 1979. Structural properties of timber

piles. In: Behavior of deep foundations. ASTM STP670.

Philadelphia, PA: American Society for Testing and

Materials: 118–152.

AWPI. 1969. Pile foundations know-how. Washington,

DC: American Wood Preservers Institute.

NFPA. [Current edition]. National design specification for

wood construction. Washington, DC: National Forest

Products Association.

Thompson, W.S. 1969. Factors affecting the variation in

compressive strength of Southern Pine piling. Washington,

DC: American Wood-Preservers' Association.

Construction Logs

ASTM. [Current edition]. Standard methods for establishing

stress grades for structural members used in log buildings.

ASTM D3957. West Conshohocken, PA: American Society

for Testing and Materials.

Muchmore, F.W. 1977. Design guide for native log stringer

bridges. Juneau, AK: U.S. Department of Agriculture, Forest

Service, Region 10.

Rowell, R.M.; Black, J.M.; Gjovik, L.R.; Feist, W.C.

1977. Protecting log cabins from decay. Gen. Tech. Rep.

FPL–11. Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory.

Ties

AREA. 1982. Ties and wood preservation. In: Manual for

railway engineering. Washington, DC: American Railway

Engineering Association. Chapter 3.
From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
19–1

Specialty Treatments

Roger M. Rowell

Chapter 19

Contents

Plasticizing Wood 19–1

Principles of Plasticizing and Bending 19–1

Bent Wood Members 19–2

Laminated Members 19–2

Veneered Curved Members 19–3

Bending of Solid Members 19–3

Selection of Stock 19–3

Moisture Content of Bending Stock 19–3

Bending Operation and Apparatus 19–4

Fixing the Bend 19–4

Characteristics of Bent Wood 19–4

Modified Woods 19–4

Resin-Treated Wood (Impreg) 19–5

Resin-Treated Compressed Wood (Compreg) 19–5

Untreated Compressed Wood (Staypak) 19–9

Untreated Heated Wood (Staybwood) 19–10

Wood Treated With Polyethylene Glycol (PEG) 19–10

Wood–Polymer Composites 19–10

Chemical Modification 19–11

Paper-Based Plastic Laminates 19–12

Industrial Laminates 19–12

Decorative Laminates 19–12

Lignin-Filled Laminates 19–13

Paper-Face Overlays 19–13

References 19–14

any specialty treatments can be applied to wood to

either improve its performance or change its

properties. Treatments addressed in this chapter are

those that make permanent changes in the shape of a wood

product, improvements in dimensional stability, or improvements in performance through combinations with

nonwood resources.

Plasticizing Wood

Principles of Plasticizing and Bending

In simple terms, the wood cell wall is a composite made of a

rigid cellulose polymer in a matrix of lignin and the hemicelluloses. The lignin polymer in the middle lamella and S2

layer is thermoplastic; that is, it softens upon heating. The

glass transition temperature Tg of the lignin in the matrix is

approximately 170°C (338°F). Above the matrix Tg, it is

possible to cause the lignin to undergo thermoplastic flow

and, upon cooling, reset in the same or modified configuration. This is the principal behind bending of wood.

The matrix can be thermoplasticized by heat alone, but the

Tg of the unmodified matrix is so high that some fiber decomposition can occur if high temperatures are maintained for

a lengthy period. The Tg of the matrix can be decreased with

the addition of moisture or through the use of plasticizers

or softeners.

Heat and moisture make certain species of wood sufficiently

plastic for bending operations. Steaming at atmospheric or a

low gage pressure, soaking in boiling or nearly boiling

water, or microwave heating moist wood are satisfactory

methods of plasticizing wood. Wood at 20% to 25% moisture content needs to be heated without losing moisture; at a

lower moisture content, heat and moisture must be added.

As a consequence, the recommended plasticizing processes

are steaming or boiling for about 15 min/cm (38 min/in) of

thickness for wood at 20% to 25% moisture content and

steaming or boiling for about 30 min/cm (75 min/in) of

thickness for wood at lower moisture content levels.

Steaming at high pressures causes wood to become plastic,

but wood treated with high pressure steam generally does

not bend as successfully as does wood treated at atmospheric

or low pressure. Microwave heating requires much shorter

times.
 19–2

Wood can be plasticized by a variety of chemicals. Common

chemicals that plasticize wood include water, urea, dimethylol urea, low molecular weight phenol-formaldehyde resin,

dimethyl sulfoxide, and liquid ammonia. Urea and dimethylol urea have received limited commercial attention, and a

bending process using liquid ammonia has been patented.

Wood members can be readily molded or shaped after immersion in liquid ammonia or treatment under pressure with

ammonia in the gas phase. As the ammonia evaporates, the

lignin resets, the wood stiffens and retains its new shape.

Plasticization of the matrix alone can be done using chemical

modification technologies, which are covered later in this

chapter.

It is also possible to bend wood without softening or plasticizing treatments. However, the stability of the final product

may not be as permanent as from treatments in which softening and plasticizing methods are used.

Bent Wood Members

Bending can provide a variety of functional and esthetically

pleasing wood members, ranging from large curved arches to

small furniture components. The curvature of the bend, size

of the member, and intended use of the product determine the

production method.

Laminated Members

At one time in the United States, curved pieces of wood were

laminated chiefly to produce small items such as parts for

furniture and pianos. However, the principle was extended to

the manufacture of arches for roof supports in farm, industrial,

and public buildings and other types of structural members

(see Ch. 11). The laminations are bent without end pressure

against a form and adhesively bonded together. Both softwoods and hardwoods are suitable for laminated bent structural members, and thin material of any species can be bent

satisfactorily for such purposes. The choice of species and

adhesive depends primarily on the cost, required strength,

and demands of the application.

Laminated curved members are produced from dry stock in a

single bending and adhesive bond formation operation. This

process has the following advantages compared with bending

single-piece members:

• Bending thin laminations to the required radius involves

only moderate stress and deformation of the wood fibers,

eliminating the need for treatment with steam or hot water

and associated drying and conditioning of the finished

product. In addition, the moderate stresses involved in

curving laminated members result in stronger members

when compared with curved single-piece members.

• The tendency of laminated members to change shape with

changes in moisture content is less than that of singlepiece bent members.

• Ratios of thickness of member to radius of curvature that

are impossible to obtain by bending single pieces can be

attained readily by laminating.

• Curved members of any desired length can be produced.

Design criteria for glued-laminated timber are discussed in

Chapter 11. Straight-laminated members can be steamed and

bent after they are bonded together. However, this type of

procedure requires an adhesive that will not be affected by the

steaming or boiling treatment and complicates conditioning

of the finished product.

Curved Plywood

Curved plywood is produced either by bending and adhesive

bonding the plies in one operation or by bending previously

bonded flat plywood. Plywood curved by bending and

bonding simultaneously is more stable in curvature than

plywood curved by bending previously bonded material.

Plywood Bent and Adhesively

Bonded Simultaneously

In bending and bonding plywood in a single operation,

adhesive-coated pieces of veneer are assembled and pressed

over or between curved forms. Pressure and sometimes heat

are applied through steam or electrically heated forms until

the adhesive sets and holds the assembly to the desired

curvature. Some laminations are at an angle, usually 90°, to

other laminations, as in the manufacture of flat plywood. The

grain direction of the thicker laminations is normally parallel

to the axis of the bend to facilitate bending.

A high degree of compound curvature can be obtained in an

assembly comprising a considerable number of thin veneers.

First, for both the face and back of the assembly, the two

outer plies are bonded at 90° to each other in a flat press.

The remaining veneers are then adhesive-coated and

assembled at any desired angle to each other. The entire

assembly is hot-pressed to the desired curvature.

Bonding the two outer plies before molding allows a higher

degree of compound curvature without cracking the face plies

than could otherwise be obtained. Where a high degree of

compound curvature is required, the veneer should be relatively thin (under 3 mm (1/8 in.)) with a moisture content of

about 12%.

The molding of plywood with fluid pressure applied by

flexible bags of some impermeable material produces plywood parts of various degrees of compound curvature. In

“bag molding,” fluid pressure is applied through a rubber

bag by air, steam, or water. The veneer is wrapped around a

form, and the whole assembly is enclosed in a bag and subjected to pressure in an autoclave, the pressure in the bag

being “bled.” Or, the veneer may be inserted inside a metal

form and, after the ends have been attached and sealed, pressure is applied by inflating a rubber bag. The form may be

heated electrically or by steam.

The advantages of bending and bonding plywood simultaneously to form a curved shape are similar to those for curvedlaminated members. In addition, the cross plies give the

curved members properties that are characteristic of crossbanded plywood. Curved plywood shells for furniture
19–3

manufacture are examples of these bent veneer and adhesivebonded products.

Plywood Bent After Bonding

After the plies are bonded together, flat plywood is often bent

by methods that are somewhat similar to those used in

bending solid wood. To bend plywood properly to shape, it

must be plasticized by some means, usually moisture or

heat, or a combination of both. The amount of curvature that

can be introduced into a flat piece of plywood depends on

numerous variables, such as moisture content, direction of

grain, thickness and number of plies, species and quality of

veneer, and the technique applied in producing the bend.

Plywood is normally bent over a form or a bending mandrel.

Flat plywood bonded with a waterproof adhesive can be bent

to compound curvatures after bonding. However, no simple

criterion is available for predetermining whether a specific

compound curvature can be imparted to flat plywood. Soaking the plywood prior to bending and using heat during

forming are aids in manipulation. Usually, the plywood to

be postformed is first thoroughly soaked in hot water, then

dried between heated forming dies attached to a hydraulic

press. If the use of postforming for bending flat plywood to

compound curvatures is contemplated, exploratory trials to

determine the practicability and the best procedure are recommended. Remember that in postforming plywood to

compound curvatures, all the deformation must be by compression or shear because plywood cannot be stretched.

Hardwood species, such as birch, poplar, and gum, are

usually used in plywood that is to be postformed.

Veneered Curved Members

Veneered curved members are usually produced by bonding

veneer to one or both faces of a curved solid-wood base. The

bases are ordinarily sawn to the desired shape or bent from a

piece grooved with saw kerfs on the concave side at right

angles to the direction of bend. Pieces bent by making saw

kerfs on the concave side are commonly reinforced and kept

to the required curvature by bonding splines, veneer, or other

pieces to the curved base. Veneering over curved solid wood

is used mainly in furniture. The grain of the veneer is commonly laid in the same general direction as the grain of the

curved wood base. The use of crossband veneers, that is,

veneers laid with the grain at right angles to the grain of the

back and face veneer, reduces the tendency of the member

to split.

Bending of Solid Members

Wood of certain species that is steamed, microwaved, or

soaked in boiling water can be compressed as much as 25%

to 30% parallel to the grain. The same wood can be stretched

only 1% to 2%. Because of the relation between attainable

tensile and compressive deformations, if bending involves

severe deformation, then most of the deformation must be

compression. The inner or concave side must assume the

maximum amount of compression, and the outer or convex

side must experience zero strain or a slight tension. To

accomplish this, a metal strap equipped with end fittings is

customarily used. The strap makes contact with the outer or

convex side and, acting through the end fittings, places the

whole piece of wood in compression. The tensile stress that

would normally develop in the outer side of the piece of

wood during bending is borne by the metal strap. A bending

form is shown in Figure 19–1.

Selection of Stock

In general, hardwoods possess better bending quality than

softwoods, and certain hardwoods surpass others in this

quality. This is interesting from a theoretical point of view

because hardwoods contain less lignin than softwoods.

Hardwoods also contain much more hemicelluloses in the

matrix than do softwoods. The species commonly used to

produce bent members are white oak, red oak, elm, hickory,

ash, beech, birch, maple, walnut, sweetgum, and mahogany.

As stated, most softwoods have a poor bending quality and

are not often used in bending operations. However, Pacific

yew and yellow-cedar are exceptions to this rule. In addition,

Douglas-fir, southern yellow pine, northern and Atlantic

white-cedar, and redwood are used for ship and boat planking

for which purpose they are often bent to moderate curvature

after being steamed or soaked.

Bending stock should be free from serious cross grain and

distorted grain, such as may occur near knots. The slope of

cross grain should not be steeper than about 1 to 15. Decay,

knots, shake, pith, surface checks, and exceptionally light or

brashy wood should be avoided.

Moisture Content of Bending Stock

Although green wood can be bent to produce many curved

members, difficulties are encountered in drying and fixing the

bend. Another disadvantage with green stock is that hydrostatic pressure may be developed during bending. Hydrostatic pressure can cause compression failures on the concave

side if the wood is compressed by an amount greater than the

air space in the cells of the green wood. Bending stock that

has been dried to a low moisture content level requires a

lengthy steaming or soaking process to increase its moisture

content to the point where it can be made sufficiently plastic

for successful bending. For most chair and furniture parts, the

moisture content of the bending stock should be 12% to 20%

before it is steamed or microwave heated. The preferred

moisture content level varies with the severity of the curvature to which the wood is bent and the method used in

drying and fixing the bent member. For example, chair-back

slats, which have a slight curvature and are subjected to

severe drying conditions between steam-heated platens, can

be produced successfully from stock at 12% moisture content. For furniture parts that need a more severe bend where

the part must be bent over a form, 15% to 20% moisture

content is recommended.
 19–4

Bending Operation and Apparatus

After being plasticized, the stock should be quickly placed in

the bending apparatus and bent to shape. The bending apparatus consists essentially of a form (or forms) and a means of

forcing the piece of steamed wood against the form. If the

curvature to be obtained demands a difference of much more

than 3% between lengths of the outer and inner surfaces of the

pieces, then the apparatus should include a device for applying end pressure. This generally takes the form of a metal

strap or pan provided with end blocks, end bars, or clamps.

Fixing the Bend

After being bent, the piece should be cooled and dried while

held in its curved shape. One method is to dry the piece in

the bending machine between the plates of a hot-plate press.

Another method is to secure the bent piece to the form and

place both the piece and the form in a drying room. Still

another is to keep the bent piece in a minor strap with tie

rods or stays so that it can be removed from the form and

placed in a drying room. When the bent member has cooled

and dried to a moisture content suitable for its intended use,

the restraining devices can be removed and the piece will

hold its curved shape.

Characteristics of Bent Wood

After a bent piece of wood is cooled and dried, the curvature

will be maintained. An increase in moisture content may

cause the piece to lose some of its curvature. A decrease in

moisture content may cause the curve to become sharper,

although repeated changes in moisture content bring about a

gradual straightening. These changes are caused primarily by

lengthwise swelling or shrinking of the inner (concave) face,

the fibers of which were wrinkled or folded during the

bending operation.

A bent piece of wood has less strength than a similar unbent

piece. However, the reduction in strength brought about by

bending is seldom serious enough to affect the utility value

of the member.

Modified Woods

Wood can be chemically modified to improve water repellency, dimensional stability, resistance to acids or bases,

ultraviolet radiation, biodeterioration, and thermal degradation. Wood can also be chemically treated, then compressed

to improve dimensional stability and increase hardness.

Figure 19–1. Chair back being bent through an arc of 180° in a bending machine.
19–5

Sheets of paper treated with resins or polymers can be laminated and hot pressed into thick panels that have the appearance of plastic rather than paper. These sheets are used in

special applications because of their structural properties and

in items requiring hard, impervious, and decorative surfaces.

Modified woods, modified wood-based materials, and paperbased laminates are usually more expensive than wood because of the cost of the chemicals and the special processing

required to produce them. Thus, modified wood use is generally limited to special applications where the increased cost

is justified by the special properties needed.

Wood is treated with chemicals to increase hardness and

other mechanical properties, as well as its resistance to decay, fire, weathering, and moisture. The rate and extent of

swelling and shrinking of the wood when in contact with

water is reduced by application of water-resistant chemicals

to the surface of wood, impregnation of the wood with such

chemicals dissolved in water or volatile solvents, or bonding

chemicals to the cell wall polymer. Such treatments may

also reduce the rate at which wood changes dimension as a

result of humidity, even though these treatments do not affect

the final dimensional changes caused by lengthy duration

exposures. Paints, varnishes, lacquers, wood-penetrating

water repellents, and plastic and metallic films retard the rate

of moisture absorption but have little effect on total dimensional change if exposure to moisture is extensive and

prolonged.

Resin-Treated Wood (Impreg)

Permanent stabilization of the dimensions of wood is needed

for certain specialty uses. This can be accomplished by

depositing a bulking agent within the swollen structure of

the wood fibers. The most successful bulking agents that

have been commercially applied are highly water-soluble,

thermosetting, phenol-formaldehyde resin-forming systems,

with initially low molecular weights. No thermoplastic

resins have been found that effectively stabilize the

dimensions of wood.

Wood treated with a thermosetting, fiber-penetrating resin

and cured without compression is known as impreg. The

wood (preferably green veneer to facilitate resin pickup) is

soaked in the aqueous resin-forming solution or, if air dry, is

impregnated with the solution under pressure until the resin

content equals 25% to 35% of the weight of dry wood. The

treated wood is allowed to stand under nondrying conditions

for 1 to 2 days to permit uniform distribution of the solution

throughout the wood. The resin-containing wood is dried at

moderate temperatures to remove the water, then heated to

higher temperatures to cure the resin.

Uniform distribution of the resin has been effectively accomplished with thick wood specimens only in sapwood of

readily penetrated species. Although thicker material can be

treated, the process is usually applied to veneers up to about

8 mm (0.3 in.) thick, because treating time increases rapidly

with increases in thickness. Drying thick, resin-treated wood

may result in checking and honeycombing. For these

reasons, treatments should be confined to veneer and the

treated-cured veneer used to build the desired products. Any

species can be used for the veneer except the resinous pines.

The stronger the original wood, the stronger the end product.

Impreg has a number of properties differing from those of

normal wood and ordinary plywood. These properties are

given in Table 19–1, with similar generalized findings for

other modified woods. Data for the strength properties of

yellow birch impreg are given in Table 19–2. Information on

thermal expansion properties of ovendry impreg is given in

Table 19–3.

The good dimensional stability of impreg is the basis of one

use where its cost is not a deterrent. Wood dies of automobile body parts serve as the master from which the metalforming dies are made for actual manufacture of parts. Small

changes in moisture content, even with the most dimensionally stable wood, produce changes in dimension and curvature of an unmodified wood die. Such changes create major

problems in making the metal-forming dies where close final

tolerances are required. The substitution of impreg, with its

high antishrink efficiency (ASE) (Table 19–4), almost entirely eliminated the problem of dimensional change during

the entire period that the wood master dies were needed.

Despite the tendency of the resins to dull cutting tools,

pattern makers accepted the impreg readily because it machines with less splitting than unmodified wood.

Patterns made from impreg are also superior to unmodified

wood in resisting heat when used with shell-molding techniques where temperatures as high as 205°C (400°F) are

required to cure the resin in the molding sand.

Resin-Treated Compressed Wood

(Compreg)

Compreg is similar to impreg except that it is compressed

before the resin is cured within the wood. The resin-forming

chemicals (usually phenol-formaldehyde) act as plasticizers

for the wood so that it can be compressed under modest

pressure (6.9 MPa; 1,000 lb/in2) to a specific gravity of 1.35.

Some properties of compreg are similar to those of impreg,

and others vary considerably (Tables 19–1 and 19–2). Compared with impreg, the advantages of compreg are its natural

lustrous finish that can be developed on any cut surface by

sanding with fine-grit paper and buffing, its greater strength

properties, and its ability to mold (Tables 19–1 and 19–2).

However, thermal expansion coefficients of ovendry compreg

are also increased (Table 19–3).

Compreg can be molded by (a) gluing blocks of resin-treated

(but still uncured) wood with a phenolic glue so that the

gluelines and resin within the plies are only partially set;

(b) cutting to the desired length and width but two to three

times the desired thickness; and (c) compressing in a split

mold at about 150°C (300°F). Only a small flash squeeze

out at the parting line between the two halves of the mold

needs to be machined off. This technique was used for motortest propellers and airplane antenna masts during World

War II.
 19–6

Table 19–1. Properties of modified woods

Property Impreg Compreg Staypak

Specific gravity 15% to 20% greater than normal

wood

Usually 1.0 to 1.4 1.25 to 1.40

Equilibrium swelling

and shrinking

1/4 to 1/3 that of normal wood 1/4 to 1/3 that of normal wood at right angle to

direction of compression, greater in direction

of compression but very slow to attain

Same as normal wood at right angle to

compression, greater in direction of

compression but very slow to attain

Springback None Very small when properly made Moderate when properly made

Face checking Practically eliminated Practically eliminated for specific gravities

less than 1.3

About the same as in normal wood

Grain raising Greatly reduced Greatly reduced for uniform-texture woods,

considerable for contrasting grain woods

About the same as in normal wood

Surface finish Similar to normal wood Varnished-like appearance for specific gravities

greater than about 1.0. Cut surfaces can be

given this surface by sanding and buffing

Varnished-like appearance. Cut surfaces

can be given this surface by sanding and

buffing

Permeability to water

vapor

About 1/10 that of normal wood No data but presumably much less than impreg No data but presumably lower than impreg

Decay and termite

resistance

Considerably better than normal

wood

Considerably better than normal wood Normal but decay occurs somewhat more

slowly

Acid resistance Considerably better than normal

wood

Better than impreg because of impermeability Better than normal wood because of impermeability but not as good as compreg

Alkali resistance Same as normal wood Somewhat better than normal wood because

of impermeability

Somewhat better than normal wood

because of impermeability

Fire resistance Same as normal wood Same as normal wood for long exposures

somewhat better for short exposures

Same as normal wood for long exposures

somewhat better for short exposures

Heat resistance Greatly increased Greatly increased No data

Electrical conductivity 1/10 that of normal wood at 30%

RH; 1/1,000 that of normal wood

at 90% RH

Slightly more than impreg at low relative

humidity values due to entrapped water

No data

Heat conductivity Slightly increased Increased about in proportion to specific

gravity increase

No data but should increase about in

proportion to specific gravity increase

Compressive strength Increased more than proportional

to specific gravity increase

Increased considerably more than proportional

to specific gravity increase

Increased about in proportion to specific

gravity increase parallel to grain, increased

more perpendicular to grain

Tensile strength Decreased significantly Increased less than proportional to

specific gravity increase

Increased about in proportion to specific

gravity increase

Flexural strength Increased less than proportional

to specific gravity increase

Increased less than proportional to specific

gravity increase parallel to grain, increased

more perpendicular to grain

Increased proportional to specific gravity

increase parallel to grain, increased more

perpendicular to grain

Hardness Increased considerably more

than proportional to specific

gravity increase

10 to 20 times that of normal wood 10 to 18 times that of normal wood

Impact strength

Toughness About 1/2 of value for normal

wood but very susceptible to the

variables of manufacture

1/2 to 3/4 of value for normal wood but very

susceptible to the variables of manufacture

Same to somewhat greater than normal

wood

Izod About 1/5 of value for normal

wood

1/3 to 3/4 of value for normal wood Same to somewhat greater than normal

wood

Abrasion resistance

(tangential)

About 1/2 of value for normal

wood

Increased about in proportion to specific

gravity increase

Increased about in proportion to specific

gravity increase

Machinability Cuts cleaner than normal wood

but dulls tools more

Requires metalworking tools and metalworking tool speedsRequires metalworking tools and

metalworking tool speeds

Moldability Cannot be molded but can be

formed to single curvatures at

time of assembly

Can be molded by compression and

expansion molding methods

Cannot be molded

Gluabilily Same as normal wood Same as normal wood after light sanding or

in the case of thick stock, machining surfaces

plane

Same as normal wood after light sanding,

or in the case of thick stock, machining

surfaces plane
19–7

Table 19–2. Strength properties of normal and modified laminatesa of yellow birch and a laminated paper plastic

Property

Normal

 laminated

woodb

Impreg

(impregnated,

uncompressed)c

Compreg

(impregnated,

highly

compressed)c

Staypak

(unimpregnated, highly

compressed)b

Paper laminate

(impregnated,

highly

compressed)d

Thickness of laminate (mm (in.)) 23.9 (0.94) 26.2 (1.03) 16.0 (0.63) 12.2 (0.48) 3.2 (0.126)

13.0 (0.512)

Moisture content at time of test (%) 9.2 5.0 5.0 4.0 —

Specific gravity (based on weight and volume at test) 0.7 0.8 1.3 1.4 1.4

Parallel laminates

Flexure—grain parallel to span (flatwise)e

Proportional limit stress (MPa (lb/in2)) 79.3 (11,500) 109.6 (15,900) 184.1 (26,700) 138.6 (20,100) 109.6 (15,900)

Modulus of rupture (MPa (lb/in2)) 140.6 (20,400) 129.6 (18,800) 250.3 (36,300) 271.6 (39,400) 252.3 (36,600)

Modulus of elasticity (GPa (1,000 lb/in2)) 16.0 (2,320) 16.4 (2,380) 25.4 (3,690) 30.7 (4,450) 20.8 (3,010)

Flexure—grain perpendicular to span (flatwise)e

Proportional limit stress (MPa (lb/in2)) 6.9 (1,000) 9.0 (1,300) 29.0 (4,200) 22.1 (3,200) 72.4 (10,500)

Modulus of rupture (MPa (lb/in2)) 13.1 (1,900) 11.7 (1,700) 31.7 (4,600) 34.5 (5,000) 167.5 (24,300)

Modulus of elasticity (GPa (1,000 lb/in2)) 1.0 (153) 1.5 (220) 4.3 (626) 4.2 (602) 10.2 (1,480)

Compression parallel to grain (edgewise)e

Proportional limit stress (MPa (lb/in2)) 44.1 (6,400) 70.3 (10,200) 113.1 (16,400) 66.9 (9,700) 49.6 (7,200)

UItimate strength (MPa (lb/in2)) 65.5 (9,500) 106.2 (15,400) 180.0 (26,100) 131.7 (19,100) 144.1 (20,900)

Modulus of elasticity (GPa (1,000 lb/in2)) 15.8 (2,300) 17.0 (2,470) 26.1 (3,790) 32.2 (4,670) 21.5 (3,120)

Compression perpendicular to grain (edgewise)f

Proportional limit stress (MPa (lb/in2)) 4.6 (670) 6.9 (1,000) 33.1 (4,800) 17.9 (2,600) 29.0 (4,200)

Ultimate strength (MPa (lb/in2)) 14.5 (2,100) 24.8 (3,600) 96.5 (14,000) 64.8 (9,400) 125.5 (18,200)

Modulus of elasticity (GPa (1,000 lb/in2)) 1.1 (162) 1.7 (243) 3.9 (571) 4.0 (583) 11.0 (1,600)

Compression perpendicular to grain (flatwise)e

Maximum crushing strength (MPa (lb/in2)) — 29.5 (4,280) 115.1 (16,700) 91.0 (13,200) 291.0 (42,200)

Tension parallel to grain (lengthwise)

Ultimate strength (MPa (lb/in2)) 153.1 (22,200) 108.9 (15,800) 255.1 (37,000) 310.3 (45,000) 245.4 (35,600)

Modulus of elasticity (GPa (1,000 lb/in2)) 15.8 (2,300) 17.3 (2,510) 27.2 (3,950) 31.8 (4,610) 25.1 (3,640)

Tension perpendicular to grain (edgewise)

Ultimate strength (MPa (lb/in2)) 9.6 (1,400) 9.6 (1,400) 22.1 (3,200) 22.8 (3,300) 137.9 (20,000)

Modulus of elasticity (GPa (1,000 lb/in2)) 1.1 (166) 1.6 (227) 4.3 (622) 4.0 (575) 11.8 (1,710)

Shear strength parallel to grain (edgewise)f

Johnson double shear across laminations (MPa (lb/in2)) 20.5 (2,980) 23.8 (3,460) 50.8 (7,370) 43.9 (6,370) 122.7 (17,800)

Cylindrical double shear parallel to laminations

 (MPa (lb/in2))

20.8 (3,020) 24.5 (3,560) 39.2 (5,690) 21.2 (3,080) 20.7 (3,000)

Shear modulus

Tension method (GPa (1,000 lb/in2)) 1.2 (182) 1.8 (255) 3.1 (454) — —

Plate shear method (FPL test) (GPa (1,000 lb/in2)) — — — 2.6 (385) 6.3 (909)

Toughness (FPL test edgewise)f (J (in-lb)) 26.6 (235) 14.1 (125) 16.4 (145) 28.2 (250) —

Toughness (FPL test edgewise)f (J/mm of width

 (in-lb/in of width))

1.1 (250) 0.53 (120) 1.0 (230) 2.3 (515) —

Impact strength (Izod)—grain lengthwise

Flatwise (notch in face) (J/mm of notch (ft–lb/in of notch)) 0.75 (14.0) 0.12 (2.3) 0.23 (4.3) 0.68 (12.7) 0.25 (4.7)

Edgewise (notch in face) (J/mm of notch (ft-lb/in of notch)) 0.60 (11.3) 0.10 (1.9) 0.17 (3.2)g — 0.036 (0.67)
 19–8

A more satisfactory molding technique, known as expansion

molding, has been developed. The method consists of

rapidly precompressing dry but uncured single sheets of

resin-treated veneer in a cold press after preheating the sheets

at 90°C to 120°C (195°F to 250°F). The heat-plasticized

wood responds to compression before cooling. The heat is

insufficient to cure the resin, but the subsequent cooling sets

the resin temporarily. These compressed sheets are cut to the

desired size, and the assembly of plies is placed in a split

mold of the final desired dimensions. Because the wood was

precompressed, the filled mold can be closed and locked.

When the mold is heated, the wood is again plasticized and

tends to recover its uncompressed dimensions. This exerts

an internal pressure in all directions against the mold equal

to about half the original compressing pressure. On continued heating, the resin is set. After cooling, the object may be

removed from the mold in finished form. Metal inserts or

metal surfaces can be molded to compreg or its handles are

molded onto tools by this means. Compreg bands have been

molded to the outside of turned wood cylinders without

compressing the core. Compreg tubes and small airplane

propellers have been molded in this way.

Past uses of compreg were related largely to aircraft; however, it is a suitable material where bolt-bearing strength is

Table 19–2. Strength properties of normal and modified laminatesa of yellow birch and a laminated paper plastic—con.

Property

Normal

laminated

woodb

Impreg

(impregnated,

uncompressed)c

Compreg

(impregnated,

highly

compressed)c

Staypak

(unimpregnated, highly

compressed)b

Paper laminate

(impregnated,

highly

compressed)d

Hardness:

Rockwell flatwisee (M–numbers) — 22 84 — 110

Load to embed 11.3-mm (0.444-in.) steel ball to 1/2 its

 diameter (kN (lb))

7.1 (1,600) 10.7 (2,400) — — —

Hardness modulus (HM)

h

 (MPa (lb/in2)) 37.2 (5,400) 63.4 (9,200) 284.8 (41,300) 302.0 (43,800) 245.4 (35,600)

Abrasion—Navy wear-test machine (flatwise)e wear per

 1,000 revolutions (mm (in.))

0.76 (0.030) 1.45 (0.057) 0.46 (0.018) 0.38 (0.015) 0.46 (0.018)

Water absorption (24-h immersion) increase in weight (%) 43.6 13.7 2.7 4.3 2.2

Dimensional stability in thickness direction

Equilibrium swelling (%) 9.9 2.8 8.0 29 —

Recovery from compression (%) — 0 0 4 —

Crossband laminates

Flexure—face grain parallel to span (flatwise)e

Proportional limit stress (MPa (lb/in2)) 47.6 (6,900) 55.8 (8,100) 99.3 (14,400) 78.6 (11,400) 86.9 (12,600)

Modulus of rupture (MPa (lb/in2)) 90.3 (13,100) 78.6 (11,400) 157.2 (22,800) 173.0 (25,100) 215.8 (31,300)

Modulus of elasticity (GPa (1,000 lb/in2)) 9.0 (1,310) 11.5 (1,670) 17.1 (2,480) 20.0 (2,900) 15.4 (2,240)

Compression parallel to face grain (edgewise)f

Proportional limit stress (MPa (lb/in2)) 22.8 (3,300) 35.8 (5,200) 60.0 (8,700) 35.8 (5,200) 34.5 (5,000)

Ultimate strength (MPa (lb/in2)) 40.0 (5,800) 78.6 (11,400) 164.8 (23,900) 96.5 (14,000) 130.3 (18,900)

Modulus of elasticity (GPa (1,000 lb/in2)) 9.4 (1,360) 10.3 (1,500) 15.8 (2,300) 18.6 (2,700) 16.3 (2,370)

Tension parallel to face grain (lengthwise)

Ultimate strength (MPa (lb/in2)) 84.8 (12,300) 54.5 (7,900) 113.8 (16,500) 168.9 (24,500) 187.5 (27,200)

Modulus of elasticity (GPa (1,000 lb/in2)) 8.9 (1,290) 10.1 (1,460) 15.1 (2,190) 17.7 (2,570) 18.6 (2,700)

Toughness (FPL test edgewise)f (J/mm of width

 (in-lb/in of width))

0.47 (105) 0.18 (40) 0.51 (115) 1.4 (320) —

a

Laminates made from 17 plies of 1.6-mm (1/16-in.) rotary-cut yellow birch veneer.

b

Veneer conditioned at 27°C (80°F) and 65% relative humidity before assembly with phenol resin film adhesive. c

Impregnation, 25% to 30% of water-soluble phenol-formaldehyde resin based on the dry weight of untreated veneer.

d

High-strength paper (0.076-mm (0.003-in. thickness)) made from commercial unbleached black spruce pulp (Mitscherlich subtile), phenol resin

 content 36.3% based on weight of treated paper, Izod impact abrasion, flatwise compression, and shear specimens, all on 12.7-mm - (1/2-in.-) thick

 laminate.

e

Load applied to the surface of the original material (parallel to laminating pressure direction).

f

Forest Products Laboratory (FPL) test procedure: load applied to edge of laminations (perpendicular to laminating pressure direction).

g

Values as high as 0.53 J/mm (10.0 ft-lb/in.) of notch have been reported for compreg made with alcohol-soluble resins and 0.37 J/mm (7.0 ft-lb/in)

 with water-soluble resins.

h

Values based on the average slope of load–penetration plots where HM is an expression for load per unit of spherical area of penetration of the

 11.3-mm (0.444-in.) steel ball expressed in MPa (lb/in2).
19–9

Table 19–4. Comparison of wood treatments

and the degree of dimensional stability achieved

Treatment

Antishrink efficiency

(%)

Simple wax dip 2 to 5

Wood–plastic combination 10 to 15

Staypak/staybwood 30 to 40

Impreg 65 to 70

Chemical modification 65 to 75

Polyethylene glycol 80 to 85

Formaldehyde 82 to 87

Compreg 90 to 95

required, as in connector plates, because of its good specific

strength (strength per unit of weight). Layers of veneer

making up the compreg for such uses are often cross

laminated (alternate plies at right angles to each other, as

in plywood) to give nearly equal properties in all directions.

As a result of its excellent strength properties, dimensional

stability, low thermal conductivity, and ease of fabrication,

compreg is extremely useful for aluminum drawing and

forming dies, drilling jigs, and jigs for holding parts in place

while welding.

Compreg has also been used in silent gears, pulleys, waterlubricated bearings, fan blades, shuttles, bobbins, and picker

sticks for looms, nuts and bolts, instrument bases and cases,

musical instruments, electrical insulators, tool handles, and

various novelties. At present, compreg finds considerable use

in handles for knives and other cutlery. The expansionmolding techniques of forming and curing of the compreg

around the metal parts of the handle as well as attaching

previously made compreg with rivets are two methods used.

Veneer of any nonresinous species can be used for making

compreg. Most properties depend upon the specific gravity to

which the wood is compressed rather than the species used.

Up to the present, however, compreg has been made almost

exclusively from yellow birch or sugar maple.

Untreated Compressed Wood

(Staypak)

Resin-treated wood in both the uncompressed (impreg) and

compressed (compreg) forms is more brittle than the original

wood. To meet the demand for a tougher compressed product

than compreg, a compressed wood containing no resin

(staypak) was developed. It will not lose its compression

under swelling conditions as will untreated compressed

wood. In making staypak, the compressing conditions are

modified so that the lignin-cementing material between the

Table 19–3. Coefficients of linear thermal expansion per degree Celsius of wood, hydrolyzed wood, and paper

productsa

Linear expansion per °C

(values multiplied by 106

)

Materialb

Specific

gravity

of

product

Resin

contentc

(%)

Fiber or

machine

direction

Perpendicular

to fiber or

machine

direction in

plane of

laminations

Pressing

direction

Cubical

expansion

per °C

(values

multiplied

by 106

)

Yellow birch laminate 0.72 3.1 3.254 40.29 36.64 80.18

Yellow birch staypak laminate 1.30 4.7 3.406 37.88 65.34 106.63

Yellow birch impreg laminate 0.86 33.2 4.648 35.11 37.05 76.81

Yellow birch compreg laminate 1.30 24.8 4.251 39.47 59.14 102.86

1.31 34.3 4.931 39.32 54.83 99.08

Sitka spruce laminate 0.53 6.0d 3.887 37.14 27.67 68.65

Parallel-laminated paper laminate 1.40 36.5 5.73 15.14 65.10 85.97

Crossbanded paper laminate 1.40 36.5 10.89 11.0e 62.2 84.09

Molded hydrolyzed-wood plastic 1.33 25 42.69 42.69 42.69 128.07

Hydrolyzed-wood sheet laminate 1.39 18 13.49 224.68 77.41 115.58

a

These coefficients refer to bone-dry material. Generally, air-dry material has a negative thermal coefficient,

 because the shrinkage resulting from the loss in moisture is greater than the normal thermal expansion.

b

All wood laminates made from rotary-cut veneer, annual rings in plane of sheet.

c

On basis of dry weight of product.

d

Approximate.

e

Calculated value.
 19–10

cellulose fibers flows sufficiently to eliminate internal

stresses.

Staypak is not as water resistant as compreg, but it is about

twice as tough and has higher tensile and flexural strength

properties (Tables 19–1 and 19–2). The natural finish of

staypak is almost equal to that of compreg. Under weathering

conditions, however, it is definitely inferior to compreg. For

outdoor use, a good synthetic resin varnish or paint finish

should be applied to staypak.

Staypak can be used in the same way as compreg where

extremely high water resistance is not needed. It shows

promise in tool handles, forming dies, connector plates,

propellers, and picker sticks and shuttles for weaving, where

high impact strength is needed. Staypak is not impregnated;

therefore, it can be made from solid wood as well as from

veneer. The cost of staypak is less than compreg.

A material similar to staypak was produced in Germany prior

to World War II. It was a compressed solid wood with much

less dimensional stability than staypak and was known as

lignostone. Another similar German product was a laminated

compressed wood known as lignofol.

Untreated Heated Wood (Staybwood)

Heating wood under drying conditions at higher temperatures

(95°C to 320°C (200°F to 600°F)) than those normally used

in kiln drying produces a product known as staybwood that

reduces the hygroscopicity and subsequent swelling and

shrinking of the wood appreciably. However, the stabilization is always accompanied by loss of mechanical properties.

Toughness and resistance to abrasion are most seriously

affected.

Under conditions that cause a reduction of 40% in shrinking

and swelling, the toughness is reduced to less than half that

of the original wood. Extensive research to minimize this

loss was not successful. Because of the reduction in strength

properties from heating at such high temperatures, wood that

is dimensionally stabilized in this manner is not used

commercially.

Wood Treated With Polyethylene

Glycol (PEG)

The dimensional stabilization of wood with polyethylene

glycol-1000 (PEG), also known as Carbowax, is accomplished by bulking the fiber to keep the wood in a partially

swollen condition. PEG acts in the same manner as does the

previously described phenolic resin. It cannot be further

cured. The only reason for heating the wood after treatment is

to drive off water. PEG remains water soluble in the wood.

Above 60% relative humidity, it is a strong humectant and,

unless used with care and properly protected, PEG-treated

wood can become sticky at high levels of relative humidity.

Because of this, PEG-treated wood is usually finished with a

polyurethane varnish.

Treatment with PEG is facilitated by using green wood.

Here, pressure is not applied because the treatment is based

on diffusion. Treating times are such that uniform uptakes of

25% to 30% of chemical are achieved (based on dry weight of

wood). The time necessary for this uptake depends on the

thickness of the wood and may require weeks. The PEG

treatment is being effectively used for cross-sectional wood

plaques and other decorative items. Table tops of high quality furniture stay remarkably flat and dimensionally stable

when made from PEG-treated wood.

Another application of this chemical is to reduce the checking of green wood during drying. For this application, a high

degree of PEG penetration is not required. This method of

treatment has been used to reduce checking during drying of

small wood blanks or turnings.

Cracking and distortion that old, waterlogged wood undergoes when it is dried can be substantially reduced by treating

the wood with PEG. The process was used to dry 200-yearold waterlogged wooden boats raised from Lake George, New

York. The “Vasa,” a Swedish ship that sank on its initial

trial voyage in 1628, was also treated after it was raised.

There have been many applications of PEG treatment for the

restoration of waterlogged wood from archeological sites.

Wood–Polymer Composites

In the modified wood products previously discussed, most of

the chemical resides in cell walls; the lumens are essentially

empty. If wood is vacuum impregnated with certain liquid

vinyl monomers that do not swell wood and are later polymerized in situ by gamma radiation or chemical catalyst-heat

systems, the resulting polymer resides almost exclusively in

the lumens. Methyl methacrylate is a common monomer

used for a wood–polymer composites. It is converted to

polymethyl methacrylate. The hygroscopic characteristics of

the wood substance are not altered because little, if any,

polymer penetrates the cell walls. However, because of the

high polymer content (70% to 100% based on the dry weight

of wood), the normally high void volume of wood is greatly

reduced. With the elimination of this very important pathway for vapor or liquid water diffusion, the response of the

wood substance to changes in relative humidity or water is

very slow, and moisture resistance or water repellent

effectiveness (WRE) is greatly improved. Water repellent

effectiveness is measured as follows:

WRE = [(Swelling or moisture uptake of control specimen

during exposure to water for t minutes)

÷ (Swelling or moisture uptake of treated specimen

during exposure to water also for t minutes)]

× 100

Hardness is increased appreciably. Wood–polymer composite

materials offer desirable aesthetic appearance, high compression strength, and abrasion resistance and are much stronger

than untreated wood (Table 19–5), and commercial application of these products is largely based on increased strength

and hardness properties. Improvements in physical properties
19–11

of wood–polymer composites are related to polymer loading.

This, in turn, depends not only on the permeability of the

wood species but also on the particular piece of wood being

treated. Sapwood is filled to a much greater extent than

heartwood for most species. The most commonly used

monomers include styrene, methyl methacrylate, vinyl

acetate, and acrylonitrile. Industrial applications include

certain sporting equipment, musical instruments, decorative

objects, and high performance flooring.

At present, the main commercial use of wood polymer composites is hardwood flooring. Comparative tests with conventional wood flooring indicate that wood–polymer materials resisted indentation from rolling, concentrated, and

impact loads better than did white oak. This is largely attributed to improved hardness. Abrasion resistance is also

increased. A finish is usually used on these products to

increase hardness and wear resistance even more.

Wood–polymer composites are also being used for sporting

goods, musical instruments, and novelty items.

Chemical Modification

Through chemical reactions, it is possible to add an organic

chemical to the hydroxyl groups on wood cell wall components. This type of treatment bulks the cell wall with a

permanently bonded chemical. Many reactive chemicals have

been used experimentally to chemically modify wood. For

best results, chemicals used should be capable of reacting

with wood hydroxyls under neutral or mildly alkaline conditions at temperatures less than 120°C. The chemical system

should be simple and must be capable of swelling the wood

structure to facilitate penetration. The complete molecule

should react quickly with wood components to yield stable

chemical bonds while the treated wood retains the desirable

properties of untreated wood. Reaction of wood with chemicals such as anhydrides, epoxides, isocyanates, acid chlorides, carboxylic acids, lactones, alkyl chlorides, and nitriles

result in antishrink efficiency (ASE) values (Table 19–4) of

65% to 75% at chemical weight gains of 20% to 30%.

Antishrink efficiency is determined as follows:

 

S V V

V = − × 2 1

1

100

where S is volumetric swelling coefficient, V2 is wood volume after humidity conditioning or wetting with water, and

V1 is wood volume of ovendried sample before conditioning

or wetting.

Then,

 

ASE = − ×

S S

S

2 1

1

100

where ASE is reduction in swelling or antishrink efficiency

resulting from a treatment, S2 is treated volumetric swelling

coefficient, and S1 is untreated volumetric swelling coefficient.

Reaction of these chemicals with wood yields a modified

wood with increased dimensional stability and improved

resistance to termites, decay, and marine organisms.

Mechanical properties of chemically modified wood are

essentially unchanged compared with untreated wood.

The reaction of formaldehyde with wood hydroxyl groups is

an interesting variation of chemical modification. At weight

gains as low as 2%, formaldehyde-treated wood is not attacked by wood-destroying fungi. An antishrink efficiency

Table 19–5. Strength properties of wood–polymer compositesa

Strength property Unit Untreatedb Treatedb

Static bending

Modulus of elasticity MPa (103 lb/in2) 9.3 (1.356) 11.6 (1.691)

Fiber stress at proportional limit MPa (lb/in2

) 44.0 (6,387) 79.8 (11,582)

Modulus of rupture MPa (lb/in2

) 73.4 (10,649) 130.6 (18,944)

Work to proportional limit μJ/mm3 (in-lb/in3

) 11.4 (1.66) 29.1 (4.22)

Work to maximum load μJ/mm3 (in-lb/in3

) 69.4 (10.06) 122.8 (17.81)

Compression parallel to grain

Modulus of elasticity GPa (106

 lb/in2) 7.7 (1.113) 11.4 (1.650)

Fiber stress at proportional limit MPa (lb/in2

) 29.6 (4,295) 52.0 (7,543)

Maximum crushing strength MPa (lb/in2

) 44.8 (6,505) 68.0 (9,864)

Work to proportional limit μJ/mm3 (in-lb/in3

) 77.8 (11.28) 147.6 (21.41)

Toughness μJ/mm3 (in-lb/in3

) 288.2 (41.8) 431.6 (62.6)

a

Menthyl methacrylate impregnated basswood.

b

Moisture content 7.2%.
 19–12

(Table 19–4) of 47% is achieved at a weight gain of 3.1%,

55% at 4.1, 60% at 5.5, and 90% at 7. The mechanical

properties of formaldehyde-treated wood are all reduced from

those of untreated wood. A definite embrittlement is observed, toughness and abrasion resistance are greatly reduced,

crushing strength and bending strength are reduced about

20%, and impact bending strength is reduced up to 50%.

Paper-Based Plastic Laminates

Commercially, paper-based plastic laminates are of two

types: industrial and decorative. Total annual production is

equally divided between the two types. They are made by

superimposing layers of paper that have been impregnated

with a resinous binder and curing the assembly under heat

and pressure.

Industrial Laminates

Industrial laminates are produced to perform specific functions requiring materials with predetermined balances of

mechanical, electrical, and chemical properties. The most

common use of such laminates is electrical insulation. The

paper reinforcements used in the laminates are kraft pulp,

alpha pulp, cotton linters, or blends of these. Kraft paper

emphasizes mechanical strength and dielectric strength perpendicular to laminations. Alpha paper is used for its electric

and electronic properties, machineability, and dimensional

stability. Cotton linter paper combines greater strength than

alpha paper with excellent moisture resistance.

Phenolic resins are the most suitable resins for impregnating

the paper from the standpoint of high water resistance, low

swelling and shrinking, and high strength properties (except

for impact). Phenolics also cost less than do other resins that

give comparable properties. Water-soluble resins of the type

used for impreg impart the highest water resistance and

compressive strength properties to the product, but they

make the product brittle (low impact strength). Alcoholsoluble phenolic resins produce a considerably tougher product, but the resins fail to penetrate the fibers as well as watersoluble resins, thus imparting less water resistance and

dimensional stability to the product. In practice, alcoholsoluble phenolic resins are generally used.

Paper-based plastic laminates inherit their final properties

from the paper from which they are made. High strength

papers yield higher strength plastic laminates than do low

strength papers. Papers with definite directional properties

result in plastic laminates with definite directional properties

unless they are cross laminated (alternate sheets oriented with

the machine direction at 90° to each other).

Improving the paper used has helped develop paper-based

laminates suitable for structural use. Pulping under milder

conditions and operating the paper machines to give optimum orientation of the fibers in one direction, together with

the desired absorbency, contribute markedly to improvements in strength.

Strength and other properties of a paper plastic laminate are

shown in Table 19–2. The National Electric Manufacturers

Association L1–1 specification has additional information on

industrial laminates. Paper is considerably less expensive

than glass fabric or other woven fabric mats and can be

molded at considerably lower pressures; therefore, the paperbased laminates generally have an appreciable price advantage

over fabric laminates. However, some fabric laminates give

superior electrical properties and higher impact properties.

Glass fabric laminates can be molded to greater double

curvatures than can paper laminates.

During World War II, a high strength paper plastic known as

papreg was used for molding nonstructural and semistructural

airplane parts such as gunner’s seats and turrets, ammunition

boxes, wing tabs, and the surfaces of cargo aircraft flooring

and catwalks. Papreg was tried to a limited extent for the

skin surface of airplane structural parts, such as wing tips.

One major objection to its use for such parts is that it is

more brittle than aluminum and requires special fittings.

Papreg has been used to some extent for heavy-duty truck

floors and industrial processing trays for nonedible materials.

Because it can be molded at low pressures and is made from

thin paper, papreg is advantageous for use where accurate

control of panel thickness is required.

Decorative Laminates

Although made by the same process as industrial laminates,

decorative laminates are used for different purposes and bear

little outward resemblance to industrial laminate. They are

used as facings for doors and walls and tops of counters,

flooring, tables, desks, and other furniture.

These decorative laminates are usually composed of a combination of phenolic- and melamine-impregnated sheets of

paper. Phenolic-impregnated sheets are brown because of the

impregnating resins and comprise most of the built-up thickness of the laminate. Phenolic sheets are overlaid with paper

impregnated with melamine resin. One sheet of the overlay is

usually a relatively thick one of high opacity and has the

color or design printed on it. Then, one or more tissue-thin

sheets, which become transparent after the resin is cured, are

overlaid on the printed sheet to protect it in service. The thin

sheets generally contain more melamine resin than do the

printed sheets, providing stain and abrasion resistance as

well as resistance to cigarette burns, boiling water, and

common household solvents.

The resin-impregnated sheets of paper are hot pressed, cured,

then bonded to a wood-based core, usually plywood, hardboard, or particleboard. The thin transparent (when cured)

papers impregnated with melamine resin can be used alone as

a covering for decorative veneers in furniture to provide a

permanent finish. In this use, the impregnated sheet is

bonded to the wood surface in hot presses at the same time

the resin is cured. The heat and stain resistance and the

strength of this kind of film make it a superior finish.

The overall thickness of a laminate may obviously be varied

by the number of sheets of kraft-phenolic used in the core
19–13

assembly. Some years ago, a 2-mm (0.08-in.) thickness was

used with little exception because of its high impact strength

and resistance to substrate show through. Recently, a 1-mm

(0.04-in.) thickness has become popular on vertical surfaces

such as walls, cabinet doors, and vertical furniture faces. This

results in better economy, because the greater strength of the

heavier laminate is not necessary. As applications have

proliferated, a whole series of thicknesses have been offered

from about 20 to 60 mm (0.8 to 2.4 in.), even up to

150 mm (6 in.) when self-supportive types are needed. These

laminates may have decorative faces on both sides if desired,

especially in the heavier thicknesses. Replacement bowling

lanes made from high-density fiberboard core and phenolicmelamine, high-pressure laminated paper on the face and

back are commercially used.

The phenolic sheets may also contain special postformingtype phenolic resins or extensible papers that make it possible to postform the laminate. By heating to 160°C (320°F)

for a short time, the structure can readily undergo simple

bending to a radius of 10 mm (0.4 in.) and 5 to 6 mm (0.20

to 0.24 in.) with careful control. Rolled furniture edges,

decorative moldings, curved counter tops, shower enclosures,

and many other applications are served by this technique.

Finally, the core composition may be modified to yield a

fire-retardant, low smoking laminate to comply with fire

codes. These high-pressure decorative laminates are covered

by the National Electrical Manufacturers Association

Specification LD3.

Paper will absorb or give off moisture, depending upon

conditions of exposure. This moisture change causes paper to

shrink and swell, usually more across the machine direction

than along it. In the same manner, the laminated paper plastics shrink and swell, although at a much slower rate. Cross

laminating minimizes the amount of this shrinking and

swelling. In many furniture uses where laminates are bonded

to cores, the changes in dimension, as a result of moisture

fluctuating with the seasons, are different than those of the

core material. To balance the construction, a paper plastic

with similar properties may be glued to the opposite face of

the core to prevent bowing or cupping caused by the moisture variation.

Lignin-Filled Laminates

The cost of phenolic resins at one time resulted in considerable effort to find impregnating and bonding agents that were

less expensive and yet readily available. Lignin-filled laminates made with lignin recovered from the spent liquor of the

soda pulping process have been produced as a result of this

search. Lignin is precipitated from solution within the pulp

or added in a pre-precipitated form before the paper is made.

The lignin-filled sheets of paper can be laminated without

the addition of other resins, but their water resistance is

considerably enhanced when some phenolic resin is applied

to the paper in a second operation. The water resistance can

also be improved by impregnating only the surface sheet

with phenolic resin. It is also possible to introduce lignin,

together with phenolic resin, into untreated paper sheets.

The lignin-filled laminates are always dark brown or black.

They have better toughness than phenolic laminates; in most

other strength properties, they are comparable or lower.

Reduction in cost of phenolic resins has virtually eliminated

the lignin-filled laminates from American commerce. These

laminates have several potential applications, however, where

a cheaper laminate with less critical properties than phenolic

laminates can be used.

Paper-Face Overlays

Paper has found considerable use as an overlay material for

veneer or plywood. Overlays can be classified into three

different types according to their use—masking, structural,

and decorative. Masking overlays are used to cover minor

defects in plywood, such as face checks and patches, minimize grain raising, and provide a more uniform paintable

surface, thus making possible the use of lower grade veneer.

Paper for this purpose need not be of high strength, because

the overlays do not need to add strength to the product. For

adequate masking, a single surface sheet with a thickness of

0.5 to 1 mm (0.02 to 0.04 in.) is desirable. Paper impregnated with phenolic resins at 17% to 25% of the weight of

the paper gives the best all-around product. Higher resin

content makes the product too costly and tends to make the

overlay more transparent. Appreciably lower resin content

gives a product with low scratch and abrasion resistance,

especially when the panels are wet or exposed to high relative humidities.

The paper faces can be applied at the same time that the

veneer is assembled into plywood in a hot press. Thermal

stresses that might result in checking are not set up if the

machine direction of the paper overlays is at right angles to

the grain direction of the face plies of the plywood.

The masking-paper-based overlays or vulcanized fiber sheets

have been used for such applications as wood house siding

that is to be painted. These overlays mask defects in the

wood, prevent bleed through of resins and extractives in the

wood, and provide a better substrate for paint. The paperbased overlays improve the across-the-board stability from

changes in dimension as a result of changes in moisture

content.

The structural overlay, also known as the high-density overlay, contains no less than 45% thermosetting resin, generally

phenolic. It consists of one or more plies of paper similar to

that used in the industrial laminates described previously.

The resin-impregnated papers can be bonded directly to the

surface of a wood substrate during cure of the sheet, thus

requiring only a single pressing operation.

The decorative-type overlay is described in the Decorative

Laminates section.
 19–14

References

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Rep. 1579. Madison, WI: U.S. Department of Agriculture,

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Heebink, B.G. 1959. Fluid-pressure molding of plywood.

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Heebink, B.G. 1963. Importance of balanced construction in

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Heebink, B.G.; Haskell, H.H. 1962. Effect of heat and

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using catalyst-heat techniques. Forest Products Journal.

15(9): 362–364.

Meyer, J.A.; Loos, W.E. 1969. Treating Southern Pine

wood for modification of properties. Forest Products Journal.

19(12): 32–38.

National Electrical Manufacturers Association. (Current

edition). Standard specification for industrial laminated

thermosetting products. Designation L1-1 and Standard

specification for high-pressure decorative laminates. Designation LD–3. Washington, DC: NEMA.

Peck, E.C. 1957. Bending solid wood to form. Agric.

Handb. 125. Washington, DC: U.S. Department of

Agriculture.

Perry, T.D. 1951. Curves from flat plywood. Wood

Products. 56(4).

Rowell, R.M. 1975. Chemical modification of wood:

advantages and disadvantages. American Wood-Preservers

Association Proceedings. 71: 41–51.

Rowell, R.M., ed. 1984. The chemistry of solid wood.

Advances in Chemistry Series No. 207. American Chemical

Society.

Schuerch, C. 1964. Principles and potential of wood plasticization. Forest Products Journal. 14(9): 377–381.

Seborg, R.M.; Inverarity, R.B. 1962. Preservation of old,

waterlogged wood by treatment with polyethylene glycol.

Science. 136(3516): 649–650.

Seborg, R.M.; Vallier, A.E. 1954. Application of impreg

for patterns and die models. Forest Products Journal. 4(5):

305–312.

Seborg, R.M.; Millett, M.A.; Stamm, A.J. 1945. Heatstabilized compressed wood (staypak). Mechanical

Engineering. 67(1): 25–31.

Seidl, R.J. 1947. Paper and plastic overlays for veneer and

plywood. Madison, WI: Forest Products Research Society

Proceedings. 1: 23–32.

Spielman, F. 1980. Working green wood with PEG. New

York, NY: Sterling Publishing Company.

Stamm, A.J. 1959. Effect of polyethylene glycol on dimensional stability of wood. Forest Products Journal. 9(10):

375–381.

Stamm, A.J. 1964. Wood and cellulose science. New York,

NY: Ronald Press.

Stamm, A.J.; Seborg, R.M. 1951. Forest Products Laboratory resin-treated laminated, compressed wood (compreg).

FPL Rep. 1381. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory.

Stamm, A.J.; Seborg, R.M. 1962. Forest Products Laboratory resin-treated wood (impreg). FPL Rep. 1380. (rev.)

Madison, WI: U.S. Department of Agriculture, Forest

Service, Forest Products Laboratory.

Stevens, W.C.; Turner, N. 1970. Wood bending handbook. London, England: Her Majesty’s Stationery Office.

Weatherwax, R.C.; Stamm, A.J. 1945. Electrical resistivity of resin-treated wood (impreg and compreg), hydrolyzedwood sheet (hydroxylin), and laminated resin-treated paper

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From

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.

Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,

Forest Products Laboratory. 463 p.
A B C D E F G H I J K L M N O P Q R S T U V W X Y 

G–1 

Glossary

Adherend. A body that is held to another body by an adhesive. 

Adhesion. The state in which two surfaces are held together by

interfacial forces which may consist of valence forces or interlocking action or both. 

Adhesive. A substance capable of holding materials together by

surface attachment. It is a general term and includes cements, 

mucilage, and paste, as well as glue. 

Assembly Adhesive—An adhesive that can be used for bonding

parts together, such as in the manufacture of a boat, airplane, 

furniture, and the like. 

Cold-Setting Adhesive—An adhesive that sets at temperatures 

below 20°C (68°F). 

Construction Adhesive—Any adhesive used to assemble primary building materials into components during building construction—most commonly applied to elastomer-based mastic-type adhesives. 

Contact Adhesive—An adhesive that is apparently dry to the 

touch and, which will adhere to itself instantaneously upon contact; also called contact bond adhesive or dry bond 

adhesive. 

Gap-Filling Adhesive—An adhesive capable of forming and 

maintaining a bond between surfaces that are not close fitting. 

Hot-Melt Adhesive—An adhesive that is applied in a molten 

state and forms a bond on cooling to a solid state. 

Hot-Setting Adhesive—An adhesive that requires a temperature 

at or above 100°C (212°F) to set it. 

Room-Temperature-Curing Adhesive—An adhesive that sets 

in the temperature range of 20°C to 30°C (68°F to 86°F), in accordance with the limits for Standard Room Temperature specified in the Standard Methods of Conditioning Plastics and Electrical Insulating Materials for Testing (ASTM D618). 

Solvent Adhesive—An adhesive having a volatile organic liquid 

as a vehicle. (This term excludes water-based adhesives.) 

Structural Adhesive—A bonding agent used for transferring

required loads between adherends exposed to service environments typical for the structure involved. 

Air-Dried. (See Seasoning.) 

Allowable Property. The value of a property normally published 

for design use. Allowable properties are identified with grade 

descriptions and standards, reflect the orthotropic structure of

wood, and anticipate certain end uses. 

Allowable Stress. (See Allowable Property.) 

American Lumber Standard. The American Softwood Lumber 

Standard, Voluntary Product Standard PS–20 (National Institute of

Standards and Technology), establishes standard sizes and requirements for the development and coordination of lumber grades of

various species, the assignment of design values when called for, 

and the preparation of grading rules applicable to each species. It 

provides for implementation of the standard through an accreditation and certification program to assure uniform industry-wide 

marking and inspection. A purchaser must, however, make use of

grading association rules because the basic standards are not in 

themselves commercial rules. 

Anisotropic. Exhibiting different properties when measured along 

different axes. In general, fibrous materials such as wood are anisotropic. 

Assembly Joint. (See Joint.) 

Assembly Time. (See Time, Assembly.) 

Balanced Construction. A construction such that the forces induced by uniformly distributed changes in moisture content will not 

cause warping. Symmetrical construction of plywood in which the 

grain direction of each ply is perpendicular to that of adjacent plies 

is balanced construction. 

Bark Pocket. An opening between annual growth rings that contains bark. Bark pockets appear as dark streaks on radial surfaces 

and as rounded areas on tangential surfaces. 

Bastard Sawn. Lumber (primarily hardwoods) in which the annual 

rings make angles of 30° to 60° with the surface of the piece. 

Beam. A structural member supporting a load applied transversely

to it. 

Bending, Steam. The process of forming curved wood members by

steaming or boiling the wood and bending it to a form. 

Bent Wood. (See Bending, Steam.) 

Bird Peck. A small hole or patch of distorted grain resulting from

birds pecking through the growing cells in the tree. The shape of 

bird peck usually resembles a carpet tack with the point towards the 

bark; bird peck is usually accompanied by discoloration extending 

for considerable distance along the grain and to a much lesser 

extent across the grain. 

Birdseye. Small localized areas in wood with the fibers indented 

and otherwise contorted to form few to many small circular or 

elliptical figures remotely resembling birds' eyes on the tangential 

surface. Sometimes found in sugar maple and used for decorative 

purposes; rare in other hardwood species. 

Blister. An elevation of the surface of an adherend, somewhat 

resembling in shape a blister on human skin; its boundaries may be 

indefinitely outlined, and it may have burst and become flattened. 

(A blister may be caused by insufficient adhesive; inadequate 

curing time, temperature, or pressure; or trapped air, water, or 

solvent vapor.) 

Bloom. Crystals formed on the surface of treated wood by exudation and evaporation of the solvent in preservative solutions. 

Blow. In plywood and particleboard especially, the development of

steam pockets during hot pressing of the panel, resulting in an 

internal separation or rupture when pressure is released, sometimes 

with an audible report. 

Blue Stain. (See Stain.) 

Board. (See Lumber.) 

Board Foot. A unit of measurement of lumber represented by a 

board 12 in. long, 12 in. wide, and 1 in. thick or its cubic equivalent. In practice, the board foot calculation for lumber 1 in. or more 

in thickness is based on its nominal thickness and width and the 

actual length. Lumber with a nominal thickness of less than 1 in. is 

calculated as 1 in. 

Bole. The main stem of a tree of substantial diameter—roughly, 

capable of yielding sawtimber, veneer logs, or large poles. Seedlings, saplings, and small-diameter trees have stems, not boles. 
 G–2

Bolt. (1) A short section of a tree trunk. (2) In veneer production, a short log of a length suitable for peeling in a lathe.

Bond. (1) The union of materials by adhesives. (2) To unite

materials by means of an adhesive.

Bondability. Term indicating ease or difficulty in bonding a

material with adhesive.

Bond Failure. Rupture of adhesive bond.

Bondline. The layer of adhesive that attaches two adherends.

Bondline Slip. Movement within and parallel to the bondline

during shear.

Bond Strength. The unit load applied in tension, compression,

flexure, peel impact, cleavage, or shear required to break an

adhesive assembly, with failure occurring in or near the plane of

the bond.

Bow. The distortion of lumber in which there is a deviation, in a

direction perpendicular to the flat face, from a straight line from

end-to-end of the piece.

Box Beam. A built-up beam with solid wood flanges and plywood or wood-based panel product webs.

Boxed Heart. The term used when the pith falls entirely within

the four faces of a piece of wood anywhere in its length. Also

called boxed pith.

Brashness. A condition that causes some pieces of wood to be

relatively low in shock resistance for the species and, when

broken in bending, to fail abruptly without splintering at comparatively small deflections.

Breaking Radius. The limiting radius of curvature to which

wood or plywood can be bent without breaking.

Bright. Free from discoloration.

Broad-Leaved Trees. (See Hardwoods.)

Brown Rot. (See Decay.)

Brown Stain. (See Stain.)

Built-Up Timbers. An assembly made by joining layers of

lumber together with mechanical fastenings so that the grain of

all laminations is essentially parallel.

Burl. (1) A hard, woody outgrowth on a tree, more or less

rounded in form, usually resulting from the entwined growth of a

cluster of adventitious buds. Such burls are the source of the

highly figured burl veneers used for purely ornamental purposes.

(2) In lumber or veneer, a localized severe distortion of the grain

generally rounded in outline, usually resulting from overgrowth

of dead branch stubs, varying from one to several centimeters

(one-half to several inches) in diameter; frequently includes one

or more clusters of several small contiguous conical protuberances, each usually having a core or pith but no appreciable

amount of end grain (in tangential view) surrounding it.

Butt Joint. (See Joint.)

Buttress. A ridge of wood developed in the angle between a

lateral root and the butt of a tree, which may extend up the stem

to a considerable height.

Cambium. A thin layer of tissue between the bark and wood

that repeatedly subdivides to form new wood and bark cells.

Cant. A log that has been slabbed on one or more sides. Ordinarily, cants are intended for resawing at right angles to their

widest sawn face. The term is loosely used. (See Flitch.)

Casehardening. A condition of stress and set in dry lumber

characterized by compressive stress in the outer layers and

tensile stress in the center or core.

Catalyst. A substance that initiates or changes the rate of chemical reaction but is not consumed or changed by the reaction.

Cell. A general term for the anatomical units of plant tissue,

including wood fibers, vessel members, and other elements of

diverse structure and function.

Cellulose. The carbohydrate that is the principal constituent of

wood and forms the framework of the wood cells.

Check. A lengthwise separation of the wood that usually extends across the rings of annual growth and commonly results

from stresses set up in wood during seasoning.

Chemical Brown Stain. (See Stain.)

Chipboard. A paperboard used for many purposes that may or

may not have specifications for strength, color, or other characteristics. It is normally made from paper stock with a relatively

low density in the thickness of 0.1524 mm (0.006 in.) and up.

Cleavage. In an adhesively bonded joint, a separation in the

joint caused by a wedge or other crack-opening-type action.

Close Grained. (See Grain.)

Coarse Grained. (See Grain.)

Cohesion. The state in which the constituents of a mass of material are held together by chemical and physical forces.

Cold Pressing. A bonding operation in which an assembly is

subjected to pressure without the application of heat.

Cold-Press Plywood. (See Wood-Based Composite Panel.)

Collapse. The flattening of single cells or rows of cells in heartwood during the drying or pressure treatment of wood. Often

characterized by a caved-in or corrugated appearance of the

wood surface.

Compartment Kiln. (See Kiln.)

Composite Assembly. A combination of two or more materials

bonded together that perform as a single unit.

Composite Panel. (See Wood-Based Composite Panel.)

Compound Curvature. Wood bent to a compound curvature, no

element of which is a straight line.

Compreg. Wood in which the cell walls have been impregnated

with synthetic resin and compressed to give it reduced swelling

and shrinking characteristics and increased density and strength

properties.

Compression Failure. Deformation of the wood fibers resulting

from excessive compression along the grain either in direct end

compression or in bending. It may develop in standing trees due

to bending by wind or snow or to internal longitudinal stresses

developed in growth, or it may result from stresses imposed after

the tree is cut. In surfaced lumber, compression failures may

appear as fine wrinkles across the face of the piece.
G–3

Compression Wood. Abnormal wood formed on the lower side

of branches and inclined trunks of softwood trees. Compression

wood is identified by its relatively wide annual rings (usually

eccentric when viewed on cross section of branch or trunk),

relatively large amount of latewood (sometimes more than 50%

of the width of the annual rings in which it occurs), and its lack

of demarcation between earlywood and latewood in the same

annual rings. Compression wood shrinks excessively longitudinally, compared with normal wood.

Conditioning (pre and post). The exposure of a material to the

influence of a prescribed atmosphere for a stipulated period of

time or until a stipulated relation is reached between material

and atmosphere.

Conifer. (See Softwoods.)

Connector, Timber. Metal rings, plates, or grids that are embedded in the wood of adjacent members, as at the bolted points of a

truss, to increase the strength of the joint.

Consistency. That property of a liquid adhesive by virtue of

which it tends to resist deformation. (Consistency is not a fundamental property but is composed of rheological properties

such as viscosity, plasticity, and other phenomena.)

Construction Adhesive. (See Adhesive.)

Contact Angle. The angle between a substrate plane and the

free surface of a liquid droplet at the line of contact with the

substrate.

Cooperage. Containers consisting of two round heads and a

body composed of staves held together with hoops, such as

barrels and kegs.

Slack Cooperage—Cooperage used as containers for dry,

semidry, or solid products. The staves are usually not closely

fitted and are held together with beaded steel, wire, or wood

hoops.

Tight Cooperage—Cooperage used as containers for liquids,

semisolids, or heavy solids. Staves are well fitted and held

tightly with cooperage-grade steel hoops.

Copolymer. Substance obtained when two or more types of

monomers polymerize.

Corbel. A projection from the face of a wall or column supporting a weight.

Core Stock. A solid or discontinuous center ply used in

panel-type glued structures (such as furniture panels and solid

or hollowcore doors).

Coupling Agent. A molecule with different or like functional

groups that is capable of reacting with surface molecules of two

different substances, thereby chemically bridging the

substances.

Covalent Bond. A chemical bond that results when electrons are

shared by two atomic nuclei.

Creep. (1) Time dependent deformation of a wood member under

sustained wood. (2) In an adhesive, the time-dependent increase

in strain resulting from a sustained stress.

Crook. The distortion of lumber in which there is a deviation, in

a direction perpendicular to the edge, from a straight line from

end-to-end of the piece.

Crossband. To place the grain of layers of wood at right angles

in order to minimize shrinking and swelling; also, in plywood

of three or more plies, a layer of veneer whose grain direction is

at right angles to that of the face plies.

Cross Break. A separation of the wood cells across the grain.

Such breaks may be due to internal stress resulting from unequal

longitudinal shrinkage or to external forces.

Cross Grained. (See Grain.)

Cross-Link. An atom or group connecting adjacent molecules in

a complex molecular structure.

Cup. A distortion of a board in which there is a deviation flatwise from a straight line across the width of the board.

Cure. To change the properties of an adhesive by chemical

reaction (which may be condensation, polymerization, or vulcanization) and thereby develop maximum strength. Generally

accomplished by the action of heat or a catalyst, with or without

pressure.

Curing Agent. (See Hardener.)

Curing Temperature. (See Temperature, Curing.)

Curing Time. (See Time, Curing.)

Curly Grained. (See Grain.)

Curtain Coating. Applying liquid adhesive to an adherend by

passing the adherend under a thin curtain of liquid falling by

gravity or pressure.

Cut Stock. (See Lumber for Dimension.)

Cuttings. In hardwoods, portions of a board or plank having

the quality required by a specific grade or for a particular use.

Obtained from a board by crosscutting or ripping.

Decay. The decomposition of wood substance by fungi.

Advanced (Typical) Decay—The older stage of decay in

which the destruction is readily recognized because the wood

has become punky, soft and spongy, stringy, ringshaked, pitted, or crumbly. Decided discoloration or bleaching of the rotted wood is often apparent.

Brown Rot—In wood, any decay in which the attack concentrates on the cellulose and associated carbohydrates rather

than on the lignin, producing a light to dark brown friable

residue—hence loosely termed “dry rot.” An advanced stage

where the wood splits along rectangular planes, in shrinking,

is termed “cubical rot.”

Dry Rot—A term loosely applied to any dry, crumbly rot but

especially to that which, when in an advanced stage, permits

the wood to be crushed easily to a dry powder. The term is

actually a misnomer for any decay, since all fungi require considerable moisture for growth.

Incipient Decay—The early stage of decay that has not proceeded far enough to soften or otherwise perceptibly impair

the hardness of the wood. It is usually accompanied by a

slight discoloration or bleaching of the wood.

Heart Rot—Any rot characteristically confined to the heartwood. It generally originates in the living tree.

Pocket Rot—Advanced decay that appears in the form of a

hole or pocket, usually surrounded by apparently sound

wood.
 G–4

Soft Rot—A special type of decay developing under very wet

conditions (as in cooling towers and boat timbers) in the

outer wood layers, caused by cellulose-destroying microfungi

that attack the secondary cell walls and not the intercellular

layer.

White-Rot—In wood, any decay or rot attacking both the cellulose and the lignin, producing a generally whitish residue

that may be spongy or stringy rot, or occur as pocket rot.

Delamination. The separation of layers in laminated wood or

plywood because of failure of the adhesive, either within the

adhesive itself or at the interface between the adhesive and the

adherend.

Delignification. Removal of part or all of the lignin from wood

by chemical treatment.

Density. As usually applied to wood of normal cellular form,

density is the mass per unit volume of wood substance enclosed

within the boundary surfaces of a wood–plus–voids complex. It

is variously expressed as pounds per cubic foot, kilograms per

cubic meter, or grams per cubic centimeter at a specified moisture

content.

Density Rules. A procedure for segregating wood according to

density, based on percentage of latewood and number of growth

rings per inch of radius.

Dew Point. The temperature at which a vapor begins to deposit

as a liquid. Applies especially to water in the atmosphere.

Diagonal Grained. (See Grain.)

Diffuse-Porous Wood. Certain hardwoods in which the pores

tend to be uniform in size and distribution throughout each

annual ring or to decrease in size slightly and gradually toward

the outer border of the ring.

Dimension. (See Lumber for Dimension.)

Dipole–Dipole Forces. Intermolecular attraction forces between

polar molecules that result when positive and negative poles of

molecules are attracted to one another.

Dote. “Dote,” “doze,” and “rot” are synonymous with “decay”

and are any form of decay that may be evident as either a discoloration or a softening of the wood.

Double Spread. (See Spread.)

Dry-Bulb Temperature. The temperature of air as indicated by a

standard thermometer. (See Psychrometer.)

Dry Kiln. (See Kiln.)

Dry Rot. (See Decay.)

Dry Strength. The strength of an adhesive joint determined

immediately after drying under specified conditions or after a

period of conditioning in a standard laboratory atmosphere.

Dry Wall. Interior covering material, such as gypsum board,

hardboard, or plywood, which is applied in large sheets or

panels.

Durability. A general term for permanence or resistance to deterioration. Frequently used to refer to the degree of resistance of a

species of wood to attack by wood-destroying fungi under

conditions that favor such attack. In this connection, the term

“decay resistance” is more specific. As applied to bondlines, the

life expectancy of the structural qualities of the adhesive under

the anticipated service conditions of the structure.

Earlywood. The portion of the growth ring that is formed during

the early part of the growing season. It is usually less dense and

weaker mechanically than latewood.

Edge Grained. (See Grain.)

Edge Joint. (See Joint.)

Elastomer. A macromolecular material that, at room temperature,

is deformed by application of a relatively low force and is capable of recovering substantially in size and shape after removal of

the force.

Embrittlement. A loss in strength or energy absorption without a corresponding loss in stiffness. Clear, straight-grained

wood is generally considered a ductile material; chemical treatments and elevated temperatures can alter the original chemical

composition of wood, thereby embrittling the wood.

Encased Knot. (See Knot.)

End Grained. (See Grain.)

End Joint. (See Joint.)

Equilibrium Moisture Content. The moisture content at which

wood neither gains nor loses moisture when surrounded by air

at a given relative humidity and temperature.

Excelsior. (See Wood Wool.)

Extender. A substance, generally having some adhesive action,

added to an adhesive to reduce the amount of the primary binder

required per unit area.

Exterior Plywood. (See Wood-Based Composite Panel.)

Extractive. Substances in wood, not an integral part of the

cellular structure, that can be removed by solution in hot or cold

water, ether, benzene, or other solvents that do not react chemically with wood components.

Extrusion Spreading. A method of adhesive application in

which adhesive is forced through small openings in the spreader

head.

Factory and Shop Lumber. (See Lumber.)

Failure, Adherend. Rupture of an adhesive joint, such that the

separation appears to be within the adherend.

Failure, Adhesive. Rupture of an adhesive joint, such that the

plane of separation appears to be at the adhesive–adherend

interface.

Failure, Cohesive. Rupture of an adhesive joint, such that the

separation appears to be within the adhesive.

Feed Rate. The distance that the stock being processed moves

during a given interval of time or operational cycle.

Fiber, Wood. A wood cell comparatively long (≤40 to 300 mm,

≤1.5 to 12 in.), narrow, tapering, and closed at both ends.

Fiberboard. (See Wood-Based Composite Panel.)

Fiber Saturation Point. The stage in the drying or wetting of

wood at which the cell walls are saturated and the cell cavities

free from water. It applies to an individual cell or group of cells,

not to whole boards. It is usually taken as approximately 30%

moisture content, based on ovendry weight.

Fibril. A threadlike component of cell walls, invisible under a

light microscope.
G–5

Figure. The pattern produced in a wood surface by annual

growth rings, rays, knots, deviations from regular grain such as

interlocked and wavy grain, and irregular coloration.

Filler. In woodworking, any substance used to fill the holes and

irregularities in planed or sanded surfaces to decrease the porosity of the surface before applying finish coatings. As applied to

adhesives, a relatively nonadhesive substance added to an

adhesive to improve its working properties, strength, or other

qualities.

Fine Grained. (See Grain.)

Fingerjoint. (See Joint.)

Finish (Finishing). (1) Wood products such as doors, stairs, and

other fine work required to complete a building, especially the

interior. (2) Coatings of paint, varnish, lacquer, wax, or other

similar materials applied to wood surfaces to protect and enhance their durability or appearance.

Fire Endurance. A measure of the time during which a material

or assembly continues to exhibit fire resistance under specified

conditions of test and performance.

Fire Resistance. The property of a material or assembly to withstand fire or give protection from it. As applied to elements of

buildings, it is characterized by the ability to confine a fire or to

continue to perform a given structural function, or both.

Fire Retardant. (See Flame Retardant.)

Fire-Retardant-Treated Wood. As specified in building codes,

a wood product that has been treated with chemicals by a pressure process or treated during the manufacturing process for the

purpose of reducing its flame spread performance in an ASTM

E84 test conducted for 30 min to performance levels specified in

the codes.

Flake. A small flat wood particle of predetermined dimensions,

uniform thickness, with fiber direction essentially in the plane of

the flake; in overall character resembling a small piece of veneer.

Produced by special equipment for use in the manufacture of

flakeboard.

Flakeboard. (See Wood-Based Composite Panel.)

Flame Retardant. A treatment, coating, or chemicals that when

applied to wood products delays ignition and reduces the flame

spread of the product.

Flame Spread. The propagation of a flame away from the source

of ignition across the surface of a liquid or a solid, or through

the volume of a gaseous mixture.

Flat Grained. (See Grain.)

Flat Sawn. (See Grain.)

Flecks. (See Rays, Wood.)

Flitch. A portion of a log sawn on two or more faces—commonly

on opposite faces leaving two waney edges. When intended for

resawing into lumber, it is resawn parallel to its original wide

faces. Or, it may be sliced or sawn into veneer, in which case the

resulting sheets of veneer laid together in the sequence of cutting are called a flitch. The term is loosely used. (See Cant.)

Framing. Lumber used for the structural member of a building,

such as studs and joists.

Full-Cell Process. Any process for impregnating wood with

preservatives or chemicals in which a vacuum is drawn to remove air from the wood before admitting the preservative. This

favors heavy adsorption and retention of preservative in the

treated portions.

Furnish. Wood material that has been reduced for incorporation

into wood-based fiber or particle panel products.

Gelatinous Fibers. Modified fibers that are associated with

tension wood in hardwoods.

Girder. A large or principal beam used to support concentrated

loads at isolated points along its length.

Gluability. (See Bondability.)

Glue. Originally, a hard gelatin obtained from hides, tendons,

cartilage, bones, etc., of animals. Also, an adhesive prepared from

this substance by heating with water. Through general use the

term is now synonymous with the term “adhesive.”

Glue Laminating. Production of structural or nonstructural

wood members by bonding two or more layers of wood together

with adhesive.

Glueline. (See Bondline.)

Grade. The designation of the quality of a manufactured piece of

wood or of logs.

Grain. The direction, size, arrangement, appearance, or quality of

the fibers in wood or lumber. To have a specific meaning the term

must be qualified.

Close-Grained (Fine-Grained) Wood—Wood with narrow,

inconspicuous annual rings. The term is sometimes used to

designate wood having small and closely spaced pores, but in

this sense the term “fine textured” is more often used.

Coarse-Grained Wood—Wood with wide conspicuous annual rings in which there is considerable difference between

earlywood and latewood. The term is sometimes used to designate wood with large pores, such as oak, keruing, meranti,

and walnut, but in this sense, the term “open-grained” is more

often used.

Cross-Grained Wood—Wood in which the fibers deviate

from a line parallel to the sides of the piece. Cross grain may be

either diagonal or spiral grain or a combination of the two.

Curly-Grained Wood—Wood in which the fibers are distorted so that they have a curled appearance, as in “birdseye”

wood. The areas showing curly grain may vary up to several

inches in diameter.

Diagonal-Grained Wood—Wood in which the annual rings

are at an angle with the axis of a piece as a result of sawing at

an angle with the bark of the tree or log. A form of cross-grain.

Edge-Grained Lumber—Lumber that has been sawed so that

the wide surfaces extend approximately at right angles to the

annual growth rings. Lumber is considered edge grained

when the rings form an angle of 45° to 90° with the wide surface of the piece.

End-Grained Wood—The grain as seen on a cut made at a

right angle to the direction of the fibers (such as on a cross

section of a tree).

Fiddleback-Grained Wood—Figure produced by a type of

fine wavy grain found, for example, in species of maple; such

wood being traditionally used for the backs of violins.
 G–6

Flat-Grained (Flat-Sawn) Lumber—Lumber that has been

sawn parallel to the pith and approximately tangent to the

growth rings. Lumber is considered flat grained when the annual growth rings make an angle of less than 45° with the

surface of the piece.

Interlocked-Grained Wood—Grain in which the fibers put

on for several years may slope in a right-handed direction, and

then for a number of years the slope reverses to a left-handed

direction, and later changes back to a right-handed pitch, and

so on. Such wood is exceedingly difficult to split radially,

though tangentially it may split fairly easily.

Open-Grained Wood—Common classification for woods

with large pores such as oak, keruing, meranti, and walnut.

Also known as “coarse textured.”

Plainsawn Lumber—Another term for flat-grained lumber.

Quartersawn Lumber—Another term for edge-grained

lumber.

Side-Grained Wood—Another term for flat-grained lumber.

Slash-Grained Wood—Another term for flat-grained lumber.

Spiral-Grained Wood—Wood in which the fibers take a spiral course about the trunk of a tree instead of the normal vertical course. The spiral may extend in a right-handed or

left-handed direction around the tree trunk. Spiral grain is a

form of cross grain.

Straight-Grained Wood—Wood in which the fibers run parallel to the axis of a piece.

Vertical-Grained Lumber—Another term for edge-grained

lumber.

Wavy-Grained Wood—Wood in which the fibers collectively take the form of waves or undulations.

Green. Freshly sawed or undried wood. Wood that has become

completely wet after immersion in water would not be considered green but may be said to be in the “green condition.”

Growth Ring. The layer of wood growth put on a tree during a

single growing season. In the temperate zone, the annual growth

rings of many species (for example, oaks and pines) are readily

distinguished because of differences in the cells formed during

the early and late parts of the season. In some temperate zone

species (black gum and sweetgum) and many tropical species,

annual growth rings are not easily recognized.

Gum. A comprehensive term for nonvolatile viscous plant

exudates, which either dissolve or swell up in contact with

water. Many substances referred to as gums such as pine and

spruce gum are actually oleoresins.

Hardboard. (See Wood-Based Composite Panel.)

Hardener. A substance or mixture of substances that is part of an

adhesive and is used to promote curing by taking part in the

reaction.

Hardness. A property of wood that enables it to resist

indentation.

Hardwoods. Generally one of the botanical groups of trees that

have vessels or pores and broad leaves, in contrast to the

conifers or softwoods. The term has no reference to the actual

hardness of the wood.

Heart Rot. (See Decay.)

Heartwood. The wood extending from the pith to the sapwood,

the cells of which no longer participate in the life processes of

the tree. Heartwood may contain phenolic compounds, gums,

resins, and other materials that usually make it darker and more

decay resistant than sapwood.

Hemicellulose. A celluloselike material (in wood) that is easily

decomposable as by dilute acid, yielding several different simple

sugars.

Hertz. A unit of frequency equal to one cycle per second.

High Frequency Curing. (See Radiofrequency Curing.)

Hollow-Core Construction. A panel construction with faces of

plywood, hardboard, or similar material bonded to a framed-core

assembly of wood lattice, paperboard rings, or the like, which

support the facing at spaced intervals.

Honeycomb Core. A sandwich core material constructed of

thin sheet materials or ribbons formed to honeycomb-like

configurations.

Honeycombing. Checks, often not visible at the surface, that

occur in the interior of a piece of wood, usually along the wood

rays.

Horizontally Laminated Timber. (See Laminated Timbers.)

Hot-Setting Adhesive. (See Adhesive.)

Hydrogen Bond. An intermolecular attraction force that results

when the hydrogen of one molecule and a pair of unshared

electrons on an electronegative atom of another molecule are

attracted to one another.

Hydrophilic. Having a strong tendency to bind or absorb water.

Hydrophobic. Having a strong tendency to repel water.

Impreg. Wood in which the cell walls have been impregnated

with synthetic resin so as to reduce materially its swelling and

shrinking. Impreg is not compressed.

Incising. A pretreatment process in which incisions, slits, or

perforations are made in the wood surface to increase penetration

of preservative treatments. Incising is often required to enhance

durability of some difficult-to-treat species, but incising reduces

strength.

Increment Borer. An augerlike instrument with a hollow bit

and an extractor, used to extract thin radial cylinders of wood

from trees to determine age and growth rate. Also used in

wood preservation to determine the depth of penetration of a

preservative.

Insulating Board. (See Wood-Based Composite Panel.)

Intergrown Knot. (See Knot.)

Interlocked Grained. (See Grain.)

Interlocking Action. (See Mechanical Adhesion.)

Internal Stresses. Stresses that exist within an adhesive joint

even in the absence of applied external forces.

Interphase. In wood bonding, a region of finite thickness as a

gradient between the bulk adherend and bulk adhesive in which

the adhesive penetrates and alters the adherend’s properties and

in which the presence of the adherend influences the chemical

and/or physical properties of the adhesive.
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Intumesce. To expand with heat to provide a low-density film;

used in reference to certain fire-retardant coatings.

Isotropic. Exhibiting the same properties in all directions.

Joint. The junction of two pieces of wood or veneer.

Adhesive Joint—The location at which two adherends are

held together with a layer of adhesive.

Assembly Joint—Joints between variously shaped parts or

subassemblies such as in wood furniture (as opposed to joints

in plywood and laminates that are all quite similar).

Butt Joint—An end joint formed by abutting the squared

ends of two pieces.

Edge Joint—A joint made by bonding two pieces of wood

together edge to edge, commonly by gluing. The joints may be

made by gluing two squared edges as in a plain edge joint or

by using machined joints of various kinds, such as

tongued-and-grooved joints.

End Joint—A joint made by bonding two pieces of wood together end to end, commonly by finger or scarf joint.

Fingerjoint—An end joint made up of several meshing

wedges or fingers of wood bonded together with an adhesive.

Fingers are sloped and may be cut parallel to either the wide

or narrow face of the piece.

Lap Joint—A joint made by placing one member partly over

another and bonding the overlapped portions.

Scarf Joint—An end joint formed by joining with adhesive

the ends of two pieces that have been tapered or beveled to

form sloping plane surfaces, usually to a featheredge, and with

the same slope of the plane with respect to the length in both

pieces. In some cases, a step or hook may be machined into the

scarf to facilitate alignment of the two ends, in which case the

plane is discontinuous and the joint is known as a stepped or

hooked scarf joint.

Starved Joint—A glue joint that is poorly bonded because an

insufficient quantity of adhesive remained in the joint.

Sunken Joint—Depression in wood surface at a joint (usually

an edge joint) caused by surfacing material too soon after

bonding. (Inadequate time was allowed for moisture added

with the adhesive to diffuse away from the joint.)

Joint Efficiency or Factor. The strength of a joint expressed as a

percentage of the strength of clear straight-grained material.

Joist. One of a series of parallel beams used to support floor and

ceiling loads and supported in turn by larger beams, girders, or

bearing walls.

Kiln. A chamber having controlled air-flow, temperature, and

relative humidity for drying lumber. The temperature is increased

as drying progresses, and the relative humidity is decreased.

Kiln Dried. (See Seasoning.)

Knot. That portion of a branch or limb that has been surrounded

by subsequent growth of the stem. The shape of the knot as it

appears on a cut surface depends on the angle of the cut relative

to the long axis of the knot.

Encased Knot—A knot whose rings of annual growth are not

intergrown with those of the surrounding wood.

Intergrown Knot—A knot whose rings of annual growth are

completely intergrown with those of the surrounding wood.

Loose Knot—A knot that is not held firmly in place by

growth or position and that cannot be relied upon to remain

in place.

Pin Knot—A knot that is not more than 12 mm (1/2 in.) in

diameter.

Sound Knot—A knot that is solid across its face, at least as

hard as the surrounding wood, and shows no indication of

decay.

Spike Knot—A knot cut approximately parallel to its long

axis so that the exposed section is definitely elongated.

Laminate. A product made by bonding together two or more

layers (laminations) of material or materials.

Laminate, Paper-Based. A multilayered panel made by compressing sheets of resin-impregnated paper together into a coherent solid mass.

Laminated Timbers. An assembly made by bonding layers of

veneer or lumber with an adhesive so that the grain of all laminations is essentially parallel. (See Built-Up Timbers.)

Horizontally Laminated Timbers—Laminated timbers designed to resist bending loads applied perpendicular to the

wide faces of the laminations.

Vertically Laminated Timbers—Laminated timbers designed

to resist bending loads applied parallel to the wide faces of

the laminations.

Laminated Veneer Lumber (LVL). (See Wood-Based

Composite Panel.)

Lap Joint. (See Joint.)

Latewood. The portion of the growth ring that is formed after the

earlywood formation has ceased. It is usually denser and

stronger mechanically than earlywood.

Latex Paint. A paint containing pigments and a stable water

suspension of synthetic resins (produced by emulsion polymerization) that forms an opaque film through coalescence of the

resin during water evaporation and subsequent curing.

Lathe Checks. In rotary-cut and sliced veneer, the fractures or

checks that develop along the grain of the veneer as the knife

peels veneer from the log. The knife side of the veneer where

checks occur is called the loose side. The opposite and log side

of the veneer where checking usually does not occur is called

the tight side.

Layup. The process of loosely assembling the adhesive-coated

components of a unit, particularly a panel, to be pressed or

clamped.

Lbs/MSGL. Abbreviation for rate of adhesive application in

pounds of adhesive per 1,000 ft2

 of single glueline (bondline).

(See Spread.) When both faces of an adherend are spread as in

some plywood manufacturing processes, the total weight of

adhesive applied may be expressed as Lbs/MDGL (pounds per

1,000 ft2 double glueline).

Lignin. The second most abundant constituent of wood, located

principally in the secondary wall and the middle lamella, which

is the thin cementing layer between wood cells. Chemically, it is

an irregular polymer of substituted propylphenol groups, and

thus, no simple chemical formula can be written for it.
 G–8

London Dispersion Forces. Intermolecular attraction forces

between nonpolar molecules that result when instantaneous

(nonpermanent) dipoles induce matching dipoles in neighboring molecules. London forces also exist between polar

molecules.

Longitudinal. Generally, parallel to the direction of the wood

fibers.

Loose Knot. (See Knot.)

Lumber. The product of the saw and planing mill for which

manufacturing is limited to sawing, resawing, passing lengthwise through a standard planing machine, crosscutting to

length, and matching. Lumber may be made from either softwood

or hardwood (See also Lumber for Dimension.)

Board—Lumber that is less than 38 mm standard (2 in. nominal) thickness and greater than 38 mm standard (2 in nominal)

width. Boards less than 140 mm standard (6 in. nominal)

width are sometimes called strips.

Dimension—Lumber with a thickness from 38 mm standard

(2 in. nominal) up to but not including 114 mm standard (5 in.

nominal) and a width of greater than 38 mm standard (2 in.

nominal).

Dressed Size—The dimensions of lumber after being surfaced

with a planing machine. The dressed size is usually 1/2 to 3/4

in. less than the nominal or rough size. A 2- by 4-in. stud, for

example, actually measures about 1-1/2 by 3-1/2 in. (standard

38 by 89 mm).

Factory and Shop Lumber—Lumber intended to be cut up for

use in further manufacture. It is graded on the percentage of the

area that will produce a limited number of cuttings of a specified minimum size and quality.

Matched Lumber—Lumber that is edge dressed and shaped

to make a close tongued-and-grooved joint at the edges or

ends when laid edge to edge or end to end.

Nominal Size—As applied to timber or lumber, the size by

which it is known and sold in the market (often differs from the

actual size).

Patterned Lumber—Lumber that is shaped to a pattern or to a

molded form in addition to being dressed, matched, or

shiplapped, or any combination of these workings.

Rough Lumber—Lumber that has not been dressed (surfaced)

but has been sawed, edged, and trimmed.

Shiplapped Lumber—Lumber that is edge dressed to make a

lapped joint.

Shipping-Dry Lumber—Lumber that is partially dried to

prevent stain and mold in transit.

Shop Lumber—(See Factory and Shop Lumber.)

Side Lumber—A board from the outer portion of the log—

ordinarily one produced when squaring off a log for a tie or

timber.

Structural Lumber—Lumber that is intended for use where

allowable properties are required. The grading of structural

lumber is based on the strength or stiffness of the piece as related to anticipated uses.

Surfaced Lumber—Lumber that is dressed by running it

through a planer.

Timbers—Lumber that is standard 114 mm (nominal 5 in.) or

more in least dimension. Timbers may be used as beams,

stringers, posts, caps, sills, girders, or purlins.

Yard Lumber—A little-used term for lumber of all sizes and

patterns that is intended for general building purposes having

no design property requirements.

Lumber for Dimension. The National Dimension Manufacturers Association defines both hardwood and softwood dimension

components as being cut to a specific size from kiln-dried rough

lumber, bolts, cants, or logs. Dimension components include

Flat Stock (solid and laminated) for furniture, cabinet, and specialty manufactures. This term has largely superceded the terms

“hardwood dimension” and “dimension parts.” (See also

Lumber).

Lumen. In wood anatomy, the cell cavity.

Manufacturing Defects. Includes all defects or blemishes that

are produced in manufacturing, such as chipped grain, loosened

grain, raised grain, torn grain, skips in dressing, hit and miss

(series of surfaced areas with skips between them), variation in

sawing, miscut lumber, machine burn, machine gouge, mismatching, and insufficient tongue or groove.

Mastic. A material with adhesive properties, usually used in

relatively thick sections, that can be readily applied by extrusion, trowel, or spatula. (See Adhesive.)

Matched Lumber. (See Lumber.)

Mechanical Adhesion. Adhesion between surfaces in which the

adhesive holds the parts together by interlocking action.

Medium-Density Fiberboard. (See Wood-Based Composite

Panel.)

Millwork. Planed and patterned lumber for finish work in buildings, including items such as sash, doors, cornices, panelwork,

and other items of interior or exterior trim. Does not include

flooring, ceiling, or siding.

Mineral Streak. An olive to greenish-black or brown discoloration of undetermined cause in hardwoods.

Modified Wood. Wood processed by chemical treatment, compression, or other means (with or without heat) to impart properties quite different from those of the original wood.

Moisture Content. The amount of water contained in the wood,

usually expressed as a percentage of the weight of the ovendry

wood.

Molecular Weight. The sum of the atomic weights of the atoms

in a molecule.

Moulded Plywood. (See Wood-Based Composite Panel.)

Moulding. A wood strip having a curved or projecting surface,

used for decorative purposes.

Monomer. A relatively simple molecular compound that can

react at more than one site to form a polymer.

Mortise. A slot cut into a board, plank, or timber, usually edgewise, to receive the tenon of another board, plank, or timber to

form a joint.

Naval Stores. A term applied to the oils, resins, tars, and pitches

derived from oleoresin contained in, exuded by, or extracted from

trees, chiefly species of pines (genus Pinus). Historically, these

were important items in the stores of wood sailing vessels.
G–9

Nominal-Size Lumber. (See Lumber for Dimension.)

Nonpolar. (See Polar.)

Nonpressure Process. Any process of treating wood with a

preservative or fire retardant where pressure is not applied. Some

examples are surface applications by brushing or brief dipping,

soaking in preservative oils, or steeping in solutions of waterborne preservatives; diffusion processes with waterborne preservatives; and vacuum treatments.

Oil Paint. A paint containing a suspension of pigments in an

organic solvent and a drying oil, modified drying oil, or synthetic polymer that forms an opaque film through a combination

of solvent evaporation and curing of the oil or polymer.

Old Growth. Timber in or from a mature, naturally established

forest. When the trees have grown during most if not all of their

individual lives in active competition with their companions for

sunlight and moisture, this timber is usually straight and relatively free of knots.

Oleoresin. A solution of resin in an essential oil that occurs in

or exudes from many plants, especially softwoods. The oleoresin

from pine is a solution of pine resin (rosin) in turpentine.

Open Assembly Time. (See Time, Assembly.)

Open Grain. (See Grain.)

Orthotropic. Having unique and independent properties in

three mutually orthogonal (perpendicular) planes of symmetry. A

special case of anisotropy.

Ovendry Wood. Wood dried to a relatively constant weight in a

ventilated oven at 102°C to 105°C (215°F to 220°F).

Overlay. A thin layer of paper, plastic, film, metal foil, or other

material bonded to one or both faces of panel products or to

lumber to provide a protective or decorative face or a base for

painting.

Paint. Any pigmented liquid, liquifiable, or mastic composition

designed for application to a substrate in a thin layer that converts to an opaque solid film after application.

Pallet. A low wood or metal platform on which material can be

stacked to facilitate mechanical handling, moving, and storage.

Paperboard. The distinction between paper and paperboard is

not sharp, but broadly speaking, the thicker (greater than 0.3 mm

(0.012 in.)), heavier, and more rigid grades of paper are called

paperboard.

Papreg. Any of various paper products made by impregnating

sheets of specially manufactured high-strength paper with synthetic resin and laminating the sheets to form a dense, moisture-resistant product.

Parallel Strand Lumber. A structural composite lumber made

from wood strand elements with the wood fiber oriented

primarily along the length of the member.

Parenchyma. Short cells having simple pits and functioning

primarily in the metabolism and storage of plant food materials.

They remain alive longer than the tracheids, fibers, and vessel

elements, sometimes for many years. Two kinds of parenchyma

cells are recognized—those in vertical strands, known more

specifically as axial parenchyma, and those in horizontal series

in the rays, known as ray parenchyma.

Particles. The aggregate component of particleboard manufactured by mechanical means from wood. These include all small

subdivisions of wood such as chips, curls, flakes, sawdust,

shavings, slivers, strands, wafers, wood flour, and wood wool.

Peck. Pockets or areas of disintegrated wood caused by advanced stages of localized decay in the living tree. It is usually

associated with cypress and incense-cedar. There is no further

development of peck once the lumber is seasoned.

Peel. To convert a log into veneer by rotary cutting. In an adhesively bonded joint, the progressive separation of a flexible

member from either a rigid member or another flexible member.

Phloem. The tissues of the inner bark, characterized by the

presence of sieve tubes and serving for the transport of elaborate

foodstuffs.

Pile. A long, heavy timber, round or square, that is driven deep

into the ground to provide a secure foundation for structures

built on soft, wet, or submerged sites (for example, landing

stages, bridge abutments).

Pin Knot. (See Knot.)

Pitch Pocket. An opening extending parallel to the annual

growth rings and containing, or that has contained, pitch, either

solid or liquid.

Pitch Streaks. A well-defined accumulation of pitch in a more or

less regular streak in the wood of certain conifers.

Pith. The small, soft core occurring near the center of a tree trunk,

branch, twig, or log.

Pith Fleck. A narrow streak, resembling pith on the surface of a

piece; usually brownish, up to several centimeters long; results

from burrowing of larvae in the growing tissues of the tree.

Plainsawn. (See Grain.)

Planing Mill Products. Products worked to pattern, such as

flooring, ceiling, and siding.

Plank. A broad, thick board laid with its wide dimension horizontal and used as a bearing surface.

Plasticizing Wood. Softening wood by hot water, steam, or

chemical treatment to increase its moldability.

Pocket Rot. (See Decay.)

Polar. Characteristic of a molecule in which the positive and

negative electrical charges are permanently separated, as opposed to nonpolar molecules in which the charges coincide.

Water, alcohol, and wood are polar in nature; most hydrocarbon

liquids are not.

Polymer. A compound formed by the reaction of simple molecules having functional groups that permit their combination to

proceed to high molecular weights under suitable conditions.

Polymers may be formed by polymerization (addition polymer)

or polycondensation (condensation polymer). When two or

more different monomers are involved, the product is called a

copolymer.

Polymerization. A chemical reaction in which the molecules of a

monomer are linked together to form large molecules whose

molecular weight is a multiple of that of the original substance.

When two or more different monomers are involved, the process

is called copolymerization.

Pore. (See Vessel Elements.)
 G–10

Postformed Plywood. (See Wood-Based Composite Panel.)

Post Cure. (1) A treatment (normally involving heat) applied to

an adhesive assembly following the initial cure, to complete

cure, or to modify specific properties. (2) To expose an adhesive

assembly to an additional cure, following the initial cure; to

complete cure; or to modify specific properties.

Pot Life. (See Working Life.)

Precure. Condition of too much cure, set, or solvent loss of the

adhesive before pressure is applied, resulting in inadequate

flow, transfer, and bonding.

Preservative. Any substance that, for a reasonable length of time,

is effective in preventing the development and action of

wood-rotting fungi, borers of various kinds, and harmful insects

that deteriorate wood.

Pressure Process. Any process of treating wood in a closed

container whereby the preservative or fire retardant is forced into

the wood under pressures greater than one atmosphere. Pressure

is generally preceded or followed by vacuum, as in the vacuum-pressure and empty-cell processes respectively; or they may

alternate, as in the full-cell and alternating-pressure processes.

Progressive Kiln. (See Kiln.)

Psychrometer. An instrument for measuring the amount of water

vapor in the atmosphere. It has both a dry-bulb and wet-bulb

thermometer. The bulb of the wet-bulb thermometer is kept moistened and is, therefore, cooled by evaporation to a temperature

lower than that shown by the dry-bulb thermometer. Because

evaporation is greater in dry air, the difference between the two

thermometer readings will be greater when the air is dry than

when it is moist.

Quartersawn. (See Grain.)

Radial. Coincident with a radius from the axis of the tree or log

to the circumference. A radial section is a lengthwise section in a

plane that passes through the centerline of the tree trunk.

Radiofrequency (RF) Curing. Curing of bondlines by the

application of radiofrequency energy. (Sometimes called

high-frequency curing.)

Rafter. One of a series of structural members of a roof designed

to support roof loads. The rafters of a flat roof are sometimes

called roof joists.

Raised Grain. A roughened condition of the surface of dressed

lumber in which the hard latewood is raised above the softer

earlywood but not torn loose from it.

Rays, Wood. Strips of cells extending radially within a tree and

varying in height from a few cells in some species to 4 or more

inches in oak. The rays serve primarily to store food and transport it horizontally in the tree. On quartersawn oak, the rays

form a conspicuous figure, sometimes referred to as flecks.

Reaction Wood. Wood with more or less distinctive anatomical

characters, formed typically in parts of leaning or crooked stems

and in branches. In hardwoods, this consists of tension wood,

and in softwoods, compression wood.

Relative Humidity. Ratio of the amount of water vapor present

in the air to that which the air would hold at saturation at the

same temperature. It is usually considered on the basis of the

weight of the vapor but, for accuracy, should be considered on

the basis of vapor pressures.

Resilience. The property whereby a strained body gives up its

stored energy on the removal of the deforming force.

Resin. (1) Solid, semisolid, or pseudosolid resin—An organic

material that has an indefinite and often high molecular weight,

exhibits a tendency to flow when subjected to stress, usually

has a softening or melting range, and usually fractures conchoidally. (2) Liquid resin—an organic polymeric liquid that, when

converted to its final state for use, becomes a resin.

Resin Ducts. Intercellular passages that contain and transmit

resinous materials. On a cut surface, they are usually inconspicuous. They may extend vertically parallel to the axis of the

tree or at right angles to the axis and parallel to the rays.

Retention by Assay. The determination of preservative retention

in a specific zone of treated wood by extraction or analysis of

specified samples.

Rheology. The study of the deformation and flow of matter.

Ring Failure. A separation of the wood during seasoning,

occurring along the grain and parallel to the growth rings. (See

Shake.)

Ring-Porous Woods. A group of hardwoods in which the pores

are comparatively large at the beginning of each annual ring and

decrease in size more or less abruptly toward the outer portion of

the ring, thus forming a distinct inner zone of pores, known as

the earlywood, and an outer zone with smaller pores, known as

the latewood.

Ring Shake. (See Shake.)

Rip. To cut lengthwise, parallel to the grain.

Roll Spreading. Application of a film of a liquid material to a

surface by means of rollers.

Room-Temperature-Setting Adhesive. (See Adhesive.)

Rot. (See Decay.)

Rotary-Cut Veneer. (See Veneer.)

Rough Lumber. (See Lumber.)

Sandwich Construction. (See Structural Sandwich Construction.)

Sap Stain. (See Stain.)

Sapwood. The wood of pale color near the outside of the log.

Under most conditions, the sapwood is more susceptible to

decay than heartwood.

Sash. A frame structure, normally glazed (such as a window),

that is hung or fixed in a frame set in an opening.

Sawn Veneer. (See Veneer.)

Saw Kerf. (1) Grooves or notches made in cutting with a saw.

(2) That portion of a log, timber, or other piece of wood removed

by the saw in parting the material into two pieces.

Scarf Joint. (See Joint.)

Schedule, Kiln Drying. A prescribed series of dry- and wet-bulb

temperatures and air velocities used in drying a kiln charge of

lumber or other wood products.
G–11

Seasoning. Removing moisture from green wood to improve its

serviceability.

Air Dried—Dried by exposure to air in a yard or shed, without artificial heat.

Kiln Dried—Dried in a kiln with the use of artificial heat.

Second Growth. Timber that has grown after the removal,

whether by cutting, fire, wind, or other agency, of all or a large

part of the previous stand.

Semitransparent Stain. A suspension of pigments in either a

drying oil–organic solvent mixture or a water–polymer emulsion, designed to color and protect wood surfaces by penetration without forming a surface film and without hiding wood

grain.

Set. A permanent or semipermanent deformation. In reference to

adhesives, to convert an adhesive into a fixed or hardened state

by chemical or physical action, such as condensation, polymerization, oxidation, vulcanization, gelation, hydration, or evaporation of volatile constituents.

Shake. A separation along the grain, the greater part of which

occurs between the rings of annual growth. Usually considered

to have occurred in the standing tree or during felling.

Shakes. In construction, shakes are a type of shingle usually

hand cleft from a bolt and used for roofing or weatherboarding.

Shaving. A small wood particle of indefinite dimensions developed incidental to certain woodworking operations involving

rotary cutterheads usually turning in the direction of the grain.

This cutting action produces a thin chip of varying thickness,

usually feathered along at least one edge and thick at another

and generally curled.

Shear. In an adhesively bonded joint, stress, strain, or failure

resulting from applied forces that tends to cause adjacent planes

of a body to slide parallel in opposite directions.

Sheathing. The structural covering, usually of boards, building

fiberboards, or plywood, placed over exterior studding or rafters

of a structure.

Shelf Life. (See Storage Life.)

Shiplapped Lumber. (See Lumber.)

Shipping-Dry Lumber. (See Lumber.)

Shop Lumber. (See Lumber.)

Side Grained. (See Grain.)

Side Lumber. (See Lumber.)

Siding. The finish covering of the outside wall of a frame building, whether made of horizontal weatherboards, vertical boards

with battens, shingles, or other material.

Slash Grained. (See Grain.)

Sliced Veneer. (See Veneer.)

Soft Rot. (See Decay.)

Softwoods. Generally, one of the botanical groups of trees that

have no vessels and in most cases, have needlelike or scalelike

leaves, the conifers, also the wood produced by such trees. The

term has no reference to the actual hardness of the wood.

Solid Color Stains (Opaque Stains). A suspension of pigments

in either a drying oil–organic solvent mixture or a water–

polymer emulsion designed to color and protect a wood surface

by forming a film. Solid color stains are similar to paints in

application techniques and in performance.

Solids Content. The percentage of weight of the nonvolatile

matter in an adhesive.

Solvent Adhesive. (See Adhesive.)

Sound Knot. (See Knot.)

Specific Adhesion. Adhesion between surfaces that are held

together by valence forces of the same type as those that give rise

to cohesion.

Specific Gravity. As applied to wood, the ratio of the ovendry

weight of a sample to the weight of a volume of water equal to

the volume of the sample at a specified moisture content (green,

air dry, or ovendry).

Spike Knot. (See Knot.)

Spiral Grained. (See Grain.)

Spread. The quantity of adhesive per unit joint area applied to

an adherend. (See Lbs/MSGL.)

Single spread—Refers to application of adhesive to only one

adherend of a joint.

Double spread—Refers to application of adhesive to both

adherends of a joint.

Springwood. (See Earlywood.)

Squeezeout. Bead of adhesive squeezed out of a joint when

pressure is applied.

Stain. A discoloration in wood that may be caused by such

diverse agencies as micro-organisms, metal, or chemicals. The

term also applies to materials used to impart color to wood.

Blue Stain—A bluish or grayish discoloration of the sapwood caused by the growth of certain dark-colored fungi on

the surface and in the interior of the wood; made possible by

the same conditions that favor the growth of other fungi.

Brown Stain—A rich brown to deep chocolate-brown discoloration of the sapwood of some pines caused by a fungus

that acts much like the blue-stain fungi.

Chemical Brown Stain—A chemical discoloration of wood,

which sometimes occurs during the air drying or kiln drying

of several species, apparently caused by the concentration and

modification of extractives.

Sap Stain—A discoloration of the sapwood caused by the

growth of certain fungi on the surface and in the interior of the

wood; made possible by the same conditions that favor the

growth of other fungi.

Sticker Stain—A brown or blue stain that develops in seasoning lumber where it has been in contact with the stickers.

Starved Joint. (See Joint.)

Static Bending. Bending under a constant or slowly applied

load; flexure.
 G–12

Staypak. Wood that is compressed in its natural state (that is,

without resin or other chemical treatment) under controlled

conditions of moisture, temperature, and pressure that practically

eliminate springback or recovery from compression. The product

has increased density and strength characteristics.

Stickers. Strips or boards used to separate the layers of lumber in

a pile and thus improve air circulation.

Sticker Stain. (See Stain.)

Storage Life. The period of time during which a packaged adhesive can be stored under specific temperature conditions and

remain suitable for use. Sometimes called shelf life.

Straight Grained. (See Grain.)

Strength. (1) The ability of a member to sustain stress without

failure. (2) In a specific mode of test, the maximum stress sustained by a member loaded to failure.

Strength Ratio. The hypothetical ratio of the strength of a structural member to that which it would have if it contained no

strength-reducing characteristics (such as knots, slope-of-grain,

shake).

Stress-Wave Timing. A method of measuring the apparent

stiffness of a material by measuring the speed of an induced

compression stress as it propagates through the material.

Stressed-Skin Construction. A construction in which panels

are separated from one another by a central partition of spaced

strips with the whole assembly bonded so that it acts as a unit

when loaded.

Stringer. A timber or other support for cross members in floors or

ceilings. In stairs, the support on which the stair treads rest.

Structural Insulating Board. (See Wood-Based Composite

Panel.)

Structural Lumber. (See Lumber.)

Structural Sandwich Construction. A layered construction

consisting of a combination of relatively high-strength facing

materials intimately bonded to and acting integrally with a

low-density core material.

Structural Timbers. Pieces of wood of relatively large size, the

strength or stiffness of which is the controlling element in their

selection and use. Examples of structural timbers are trestle

timbers (stringers, caps, posts, sills, bracing, bridge ties, guardrails); car timbers (car framing, including upper framing, car

sills); framing for building (posts, sills, girders); ship timber

(ship timbers, ship decking); and crossarms for poles.

Stud. One of a series of slender wood structural members used as

supporting elements in walls and partitions.

Substrate. A material upon the surface of which an adhesive-containing substance is spread for any purpose, such as

bonding or coating. A broader term than adherend. (See

Adherend.)

Summerwood. (See Latewood.)

Surface Inactivation. In adhesive bonding to wood, physical

and chemical modifications of the wood surface that result in

reduced ability of an adhesive to properly wet, flow, penetrate,

and cure.

Surface Tension. The force per unit length acting in the surface

of a liquid that opposes the increase in area of the liquid

(spreading).

Surfaced Lumber. (See Lumber.)

Symmetrical Construction. Plywood panels in which the plies

on one side of a center ply or core are essentially equal in thickness, grain direction, properties, and arrangement to those on the

other side of the core.

Tack. The property of an adhesive that enables it to form a bond

of measurable strength immediately after adhesive and adherend

are brought into contact under low pressure.

Tangential. Strictly, coincident with a tangent at the circumference of a tree or log, or parallel to such a tangent. In practice,

however, it often means roughly coincident with a growth ring.

A tangential section is a longitudinal section through a tree or

limb perpendicular to a radius. Flat-grained lumber is sawed

tangentially.

Temperature, Curing. The temperature to which an adhesive or

an assembly is subjected to cure the adhesive. The temperature

attained by the adhesive in the process of curing (adhesive

curing temperature) may differ from the temperature of the atmosphere surrounding the assembly (assembly curing temperature).

Temperature, Setting. (See Temperature, Curing.)

Tenon. A projecting member left by cutting away the wood

around it for insertion into a mortise to make a joint.

Tension. In an adhesively bonded joint, a uniaxial force tending

to cause extension of the assembly, or the counteracting force

within the assembly that resists extension.

Tension Wood. Abnormal wood found in leaning trees of some

hardwood species and characterized by the presence of gelatinous fibers and excessive longitudinal shrinkage. Tension wood

fibers hold together tenaciously, so that sawed surfaces usually

have projecting fibers and planed surfaces often are torn or have

raised grain. Tension wood may cause warping.

Texture. A term often used interchangeably with grain. Sometimes used to combine the concepts of density and degree of

contrast between earlywood and latewood. In this handbook,

texture refers to the finer structure of the wood (See Grain.)

rather than the annual rings.

Thermoplastic. (1) Capable of being repeatedly softened by heat

and hardened by cooling. (2) A material that will repeatedly

soften when heated and harden when cooled.

Thermoset. A cross-linked polymeric material.

Thermosetting. Having the property of undergoing a chemical

reaction by the action of heat, catalyst, ultraviolet light, and

hardener, leading to a relatively infusible state.

Timbers, Round. Timbers used in the original round form, such

as poles, piling, posts, and mine timbers.

Timber, Standing. Timber still on the stump.

Timbers. (See Lumber.)

Time, Assembly. The time interval between the spreading of the

adhesive on the adherend and the application of pressure or heat,

or both, to the assembly. (For assemblies involving multiple

layers or parts, the assembly time begins with the spreading of

the adhesive on the first adherend.)

Open Assembly Time—The time interval between the spreading of the adhesive on the adherend and the completion of assembly of the parts for bonding.
G–13

Closed Assembly Time—The time interval between completion of assembly of the parts for bonding and the application

of pressure or heat, or both, to the assembly.

Time, Curing. The period during which an assembly is subjected to heat or pressure, or both, to cure the adhesive.

Time, Setting. (See Time, Curing.)

Toughness. A quality of wood that permits the material to

absorb a relatively large amount of energy, to withstand repeated

shocks, and to undergo considerable deformation before

breaking.

Tracheid. The elongated cells that constitute the greater part of

the structure of the softwoods (frequently referred to as fibers).

Also present in some hardwoods.

Transfer. In wood bonding, the sharing of adhesive between a

spread and an unspread surface when the two adherends are

brought into contact.

Transverse. Directions in wood at right angles to the wood

fibers. Includes radial and tangential directions. A transverse

section is a section through a tree or timber at right angles to

the pith.

Treenail. A wooden pin, peg, or spike used chiefly for fastening

planking and ceiling to a framework.

Trim. The finish materials in a building, such as moldings,

applied around openings (window trim, door trim) or at the floor

and ceiling of rooms (baseboard, cornice, and other moldings).

Truss. An assembly of members, such as beams, bars, rods, and

the like, so combined as to form a rigid framework. All members

are interconnected to form triangles.

Twist. A distortion caused by the turning or winding of the

edges of a board so that the four comers of any face are no longer

in the same plane.

Tyloses. Masses of parenchyma cells appearing somewhat like

froth in the pores of some hardwoods, notably the white oaks

and black locust. Tyloses are formed by the extension of the cell

wall of the living cells surrounding vessels of hardwood.

Ultrasonics. (See Stress-Wave Timing.)

van der Waal Forces. Physical forces of attraction between

molecules, which include permanent dipole, induced dipole,

hydrogen bond, and London dispersion forces.

Vapor Retarder. A material with a high resistance to vapor

movement, such as foil, plastic film, or specially coated paper,

that is used in combination with insulation to control

condensation.

Veneer. A thin layer or sheet of wood.

Rotary-Cut Veneer—Veneer cut in a lathe that rotates a log or

bolt, chucked in the center, against a knife.

Sawn Veneer—Veneer produced by sawing.

Sliced Veneer—Veneer that is sliced off a log, bolt, or flitch

with a knife.

Vertical Grained. (See Grain.)

Vertically Laminated Timbers. (See Laminated Timbers.)

Vessel Elements. Wood cells in hardwoods of comparatively

large diameter that have open ends and are set one above the

other to form continuous tubes called vessels. The openings of

the vessels on the surface of a piece of wood are usually referred

to as pores.

Virgin Growth. The growth of mature trees in the original

forests.

Viscoelasticity. The ability of a material to simultaneously

exhibit viscous and elastic responses to deformation.

Viscosity. The ratio of the shear stress existing between laminae

of moving fluid and the rate of shear between these laminae.

Waferboard. (See Wood-Based Composite Panel.)

Wane. Bark or lack of wood from any cause on edge or corner of a

piece except for eased edges.

Warp. Any variation from a true or plane surface. Warp includes

bow, crook, cup, and twist, or any combination thereof.

Water Repellent. A liquid that penetrates wood that materially

retards changes in moisture content and dimensions of the dried

wood without adversely altering its desirable properties.

Water-Repellent Preservative. A water repellent that contains a

preservative that, after application to wood and drying, accomplishes the dual purpose of imparting resistance to attack by

fungi or insects and also retards changes in moisture content.

Weathering. The mechanical or chemical disintegration and

discoloration of the surface of wood caused by exposure to light,

the action of dust and sand carried by winds, and the alternate

shrinking and swelling of the surface fibers with the continual

variation in moisture content brought by changes in the

weather. Weathering does not include decay.

Wet Strength. The strength of an adhesive joint determined

immediately after removal from water in which it has been immersed under specified conditions of time, temperature, and

pressure.

Wet-Bulb Temperature. The temperature indicated by the

wet-bulb thermometer of a psychrometer.

Wettability. A condition of a surface that determines how fast a

liquid will wet and spread on the surface or if it will be repelled

and not spread on the surface.

Wetting. The process in which a liquid spontaneously adheres

to and spreads on a solid surface.

White-Rot. (See Decay.)

Wood-Based Composite Panel. A generic term for a material

manufactured from wood veneer, strands, flakes, particles, or

fibers or other lignocellulosic material and a synthetic resin or

other binder.

Cold-Pressed Plywood—Refers to interior-type plywood

manufactured in a press without external applications of heat.

Composite Panel—A veneer-faced panel with a reconstituted

wood core. The flakeboard core may be random or have alignment in the direction 90° from the grain direction of the veneer

faces.

Exterior Plywood—A general term for plywood bonded with

a type of adhesive that by systematic tests and service records

has proved highly resistant to weather; micro-organisms;

cold, hot, and boiling water; steam; and dry heat.
 G–14

Extruded Particleboard—A particleboard made by ramming

bindercoated particles into a heated die, which subsequently

cures the binder and forms a rigid mass as the material is

moved through the die.

Fiberboard—A broad generic term inclusive of sheet materials of widely varying densities manufactured of refined or partially refined wood (or other vegetable) fibers. Bonding

agents and other materials may be added to increase strength,

resistance to moisture, fire, or decay, or to improve some other

property. (See Medium-Density Fiberboard.)

Flakeboard—A particle panel product composed of flakes.

Hardboard—A generic term for a panel manufactured primarily from interfelted lignocellulosic fibers (usually wood), consolidated under heat and pressure in a hot press to a density of

496 kg/m3

 (31 lb/ft3) or greater and to which other materials

may have been added during manufacture to improve certain

properties.

Interior Plywood—A general term for plywood manufactured

for indoor use or in construction subjected to only temporary

moisture. The adhesive used may be interior, intermediate, or

exterior.

Laminated Veneer Lumber (LVL)—A structural lumber

manufactured from veneers laminated into a panel with the

grain of all veneer running parallel to each other. The resulting panel is normally manufactured in 19- to 38-mm (3/4- to

1-1/2-in.) thicknesses and ripped to common lumber widths of

38 to 290 mm (1-1/2 to 11-1/2 in.) or wider.

Marine Plywood—Plywood panels manufactured with the

same glueline durability requirements as other exterior-type

panels but with more restrictive veneer quality requirements.

Mat-Formed Particleboard—A particleboard in which the

particles (being previously coated with the binding agent) are

formed into a mat having substantially the same length and

width as the finished panel. This mat is then duly pressed in a

heated flat-platen press to cure the binding agent.

Medium-Density Fiberboard—A panel product manufactured

from lignocellulosic fibers combined with a synthetic resin or

other suitable binder. The panels are manufactured to a density

of 496 kg/m3

 (31 lb/ft3) (0.50 specific gravity) to 880 kg/m3

(55 lb/ft3) (0.88 specific gravity) by the application of heat

and pressure by a process in which the interfiber bond is substantially created by the added binder. Other materials may

have been added during manufacturing to improve certain

properties.

Mende-Process Board—A particleboard made in a continuous ribbon from wood particles with thermosetting resins

used to bond the particles. Thickness ranges from 0.8 to

6.3 mm (1/32 to 1/4 in.).

Moulded Plywood—Plywood that is glued to the desired

shape either between curved forms or more commonly by fluid

pressure applied with flexible bags or blankets (bag moulding) or other means.

Multilayer Particleboard—A type of construction in which

the wood particles are made or classified into different sizes

and placed into the preprocessed panel configuration to

produce a panel with specific properties. Panels that are

destined for primarily nonstructural uses requiring smooth

faces are configured with small particles on the outside and

coarser particles on the interior (core). Panels designed for

structural application may have flakes aligned in orthogonal

directions in various layers that mimic the structure of plywood. Three- and five-layer constructions are most common.

Oriented Strandboard—A type of particle panel product

composed of strand-type flakes that are purposefully aligned

in directions that make a panel stronger, stiffer, and with improved dimensional properties in the alignment directions

than a panel with random flake orientation.

Plywood. A glued wood panel made up of relatively thin layers of veneer with the grain of adjacent layers at right angles

or of veneer in combination with a core of lumber or of reconstituted wood. The usual constructions have an odd number of

layers.

Postformed Plywood—The product formed when flat plywood is reshaped into a curved configuration by steaming or

plasticizing agents.

Structural Insulating Board—A generic term for a homogeneous panel made from lignocellulosic fibers (usually wood or

cane) characterized by an integral bond produced by interfelting of the fibers, to which other materials may have been added

during manufacture to improve certain properties, but which

has not been consolidated under heat and pressure as a separate stage in manufacture; has a density of less than 496 kg/m3

(31 lb/ft3) (specific gravity 0.50) but more than 160 kg/m3

(10 lb/ft3) (specific gravity 0.16).

Waferboard—A particle panel product made of wafer-type

flakes. Usually manufactured to possess equal properties in all

directions parallel to the plane of the panel.

Wood Failure. The rupturing of wood fibers in strength tests of

bonded joints usually expressed as the percentage of the total

area involved that shows such failure. (See Failure, Adherend.)

Wood Flour. Wood reduced to finely divided particles,

approximately the same as those of cereal flours in size, appearance, and texture, and passing a 40 to 100 mesh screen.

Wood Substance. The solid material of which wood is composed. It usually refers to the extractive-free solid substance of

which the cell walls are composed, but this is not always true.

There is not a wide variation in chemical composition or specific gravity between the wood substance of various species.

(The characteristic differences of species are largely due to differences in extractives and variations in relative amounts of cell

walls and cell cavities.)

Wood Wool. Long, curly, slender strands of wood used as an

aggregate component for some particleboards.

Workability. The degree of ease and smoothness of cut obtainable with hand or machine tools.

Working Life. The period of time during which an adhesive,

after mixing with catalyst, solvent, or other compounding ingredients, remains suitable for use. Also called pot life.

Working Properties. The properties of an adhesive that affect or

dictate the manner of application to the adherends to be bonded

and the assembly of the joint before pressure application (such

as viscosity, pot life, assembly time, setting time).

Xylem. The portion of the tree trunk, branches, and roots that

lies between the pith and the cambium (that is the wood).

Yard Lumber. (See Lumber.)
I–1

Index

Accelerated air-drying, 12-6

Acid copper chromate (ACC):

components, 14-10

effectiveness and leaching, 14-10

retention levels for various wood

products, 14-6t

Southern pine sapwood stakes

retention and life span test results,

14-13t

temperature for pressure treating,

14-21

Adherends:

bond strength properties, 9-21

density and porosity, 9-6 to 9-7

ease of bonding by species, 9-8t

extractives on surface, effect on, 9-3

knife- and abrasive-planed surfaces,

9-3 to 9-4, 9-4fig

mechanical testing of bonded

assemblies, 9-20 to 9-21

moisture content:

and dimensional change, 9-7

control, 9-15 to 9-16

U.S. averages, 9-16, 9-16fig

surface preparation, 9-16

surface properties, 9-2 to 9-3

veneer surfaces, 9-4 to 9-5

wettability, 9-3

wood and nonwood composites, 9-

5 to 9-6

Adhesives:

affected by:

physical properties, 9-6 to 9-9

surface properties, 9-2 to 9-5

wood density, 9-6 to 9-7

wood moisture content, 9-9

wood porosity, 9-7

analytic chemical and mechanical

testing of polymers, 9-20

assembly and pressing, 9-16 to 9-

18, 9-17fig

composition, 9-9 to 9-10

consistency, effect of, 9-16 to 9-17,

9-17fig

definition, 9-1

ease of bonding by species, 9-8t

form and color of types, 9-13t to 9-

14t

health and safety, 9-10

mechanical testing of bonded

assemblies, 9-20 to 9-21

post-cure conditioning, 9-18

preparation and application, 9-13t

to 9-14t

quality assurance programs, 9-22 to

9-23

short- and long-term performance, 9-

21 to 9-22, 9-22fig

selection, 9-12 to 9-15

spreading 9-16, 9-17fig

strength and durability, 9-10 to 9-

12, 9-11t, 9-13t to 9-14t

strength properties, 9-21

used with fire-retardant-treated

woods, 9-6

uses, 9-1, 9-13t to 9-14t

use on veneers, 9-4 to 9-5

use on wood and nonwood

composites, 9-5 to 9-6

use with chemically modified wood,

9-6

used with preservative-treated

wood, 9-6

working life, 9-12, 9-15

Adjustment of properties for design

use, 6-1 to 6-14

Advantages of using wood for

structures, 1-2

Afara. See Limba

Afrormosia:

characteristics, 1-17

decay resistance, 1-17

ease of bonding, 9-8t

locality of growth, 1-17

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

uses, 1-17

Air-drying advantages and

limitations, 12-6

Albarco:

characteristics, 1-17

locality of growth, 1-17

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

uses, 1-17

workability, 1-17

Alder, red:

characteristics, 1-3

characteristics for painting, 15-3t

color and figure, 3-3t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

erosion of planed surfaces, 15-8t

locality of growth, 1-3

machining and related properties, 3-

16t

moisture content, 3-6t

nomenclature, 5-5t

plywood stiffness and strength, 10-

11t

shock resistance, 1-3

shrinkage values, 3-9t

size of pores, 15-31t

strength properties, 4-4t, 4-9t

uses, 1-3

Alkyl ammonium compound:

effectiveness, 14-9

in ammoniacal copper quat, 14-11

solubility, 14-9

Almon. See Lauans

Alpha paper, 19-12

Amaranth. See Purpleheart

American Lumber Standard Committee

(ALSC):

accepting design values for foreign

species, 6-3, 6-4t

design properties, 6-3

stress grading, 6-2 to 6-3

American Society of Testing and

Materials (ASTM):

and AWPA standards, 17-12

calculating design properties, 6-3

calculating strength ratios, 6-3

calculating wood properties for

visual stress grades, 6-3

critical radiant flux of floorcovering systems using a radiant

heat energy source (ASTM E648),

17-4

related test methods, 17-9

cone calorimeter (ATSM 1354), 17-

6, 17-8

fire tests of roof covering (ASTM

E108), 17-4

fire-resistance test (ASTM E119),

17-4, 17-10, 17-11t

flame spread (ASTM E84), 17-2, 17-

4, 17-8, 17-12

flame spread index for solid sawn

lumber, 17-3t

NBS smoke chamber (ASTM E662),

17-9 to 17-10

American Softwood Lumber Standard,

5-1,5-7, 6-2

American standard lumber sizes, 5-10,

5-11t

American Wood Preservers’

Association:

fire-retardant-treated wood, 17-12,

17-13

Ammonia for plasticizing wood, 19-2

Ammoniacal copper citrate (CC):

retention levels for various wood

products, 14-6t

solution percentages, 14-12

temperature for pressure treating,

14-21

Ammoniacal copper quat (ACQ):

common types, 14-11

composition of common types, 14-

11t

retention levels for various wood

products, 14-6t

uses, 14-11

Ammoniacal copper zinc arsenate

(ACZA):

composition, 14-11

replacement for ACA, 14-11

retention levels for various wood

products, 14-6t

temperature for pressure treating,

14-21

use, 14-10

use with Douglas-fir, 14-10 to 14-

11

Anani. See Manni

Anaura. See Marishballi

Andiroba:

characteristics, 1-18

characteristics affecting machining,

3-17t

decay resistance, 3-18t
I–2

dimensional change coefficient, 12-

17t

durability, 1-18

ease of bonding, 9-8t

locality of growth, 1-17

mechanical properties, 4-16t, 4-20t

nomenclature, 1-17 to 1-18

resistance to decay and insects, 1-

18

shrinkage values, 3-10t

uses, 1-18

workability, 1-18

Angelin (See also Sucupira):

ease of bonding, 9-8t

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

Angelique:

characteristics, 1-18

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

machining properties, 1-18

mechanical properties, 4-16t, 4-20t

resistance to decay and insects, 1-

18

shrinkage values, 3-10t

uses, 1-18

Animal adhesives:

structural performance, 9-11t

working and strength properties,

and uses, 9-13t

Ants, carpenter, 13-13

Annual growth rings. See Growth

rings

Apa. See Wallaba

Apamate. See Roble

Apitong. (See also Keruing):

dimensional change coefficient, 12-

17t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-10t

Apple:

dimensional change coefficient, 12-

16t

moisture content, 3-6t

Ash:

decay resistance, 3-18t

for flooring, 5-6, 5-7

machining and related properties, 3-

16t

size of pores, 15-31t

Ash, black:

characteristics, 1-4

color and figure, 3-3t

dimensional change coefficient, 12-

16t

locality of growth, 1-4

moisture content, 3-6t

nomenclature, 5-5t

shrinkage values, 3-9t

species, 1-4

specific gravity, 1-4

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

uses, 1-4

Ash, blue:

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

Ash, green:

dimensional change coefficient, 12-

16t

moisture content, 3-6t

penetration, 14-16t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

Ash, Oregon:

color and figure, 3-6t

dimensional change coefficient, 12-

16t

nomenclature, 5-5t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

Ash, pumpkin:

dimensional change coefficient, 12-

16t

shrinkage values, 3-9t

Ash, white:

characteristics, 1-3

characteristics for painting, 15-3t

color and figure, 3-3t

connector joint strength, 7-21t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

locality of growth, 1-3

moisture content, 3-6t, 4-34t

nomenclature, 5-5t

penetration, 14-16t

Poisson ratio, 4-3t

shrinkage values, 3-9t

shock resistance, 1-3

species, 1-3

thermal conductivity, 3-19t

uses, 1-3

Aspen:

characteristics, 1-4

color and figure, 3-3t

connector joint strength, 7-21t

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-4

machining and related properties, 3-

16t

moisture content, 3-6t

nomenclature, 5-5t

shock resistance, 1-4

size of pores, 15-31t

species, 1-4

uses, 1-4

workability, 1-4

Aspen, bigtooth:

characteristics for painting, 15-3t

mechanical properties, 4-14t, 4-15t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

Aspen, quaking:

dimensional change coefficient, 12-

16t

mechanical properties, 4-14t, 4-15t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

Avodire:

characteristics, 1-18

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-18

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

shock resistance, 1-18

uses, 1-18

workability, 1-8

Axial load, deformation, 8-1, 8-1eq

Axial members, glulam combinations,

11-5

Azobe:

characteristics, 1-18

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-18

mechanical properties, 4-16t, 4-20t

resistance to decay and insects, 1-

18

marine borers, 13-14

shrinkage values, 3-10t

workability, 1-18

uses, 1-18

Bacteria causing decay, 13-8

Back priming, 15-23

Bagtikan. See Seraya, white

Balata:

characteristics, 1-18

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-18

resistance to decay and insects, 1-

18

shrinkage values, 3-10t

uses, 1-19

workability, 1-18

Balau:

characteristics, 1-19

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-19

species, 1-19

uses, 1-19

Baldcypress:

characteristics, 1-10

characteristics for painting, 15-3t

color and figure, 3-4t
I–3

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

elastic ratio, 4-2t

flame spread index, 17-3t

locality of growth, 1-10

moisture content, 3-6t

nomenclature, 5-13t

pecky cypress, 1-10

penetration, 14-16t

Poisson ratio, 4-3t

tensile strength, 4-24t

thermal conductivity, 3-20t

uses, 1-10

Balsa:

characteristics, 1-19

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

elastic ratio, 4-2t

locality of growth, 1-19

mechanical properties, 4-16t, 4-20t

Poisson ratio, 4-3t

shrinkage values, 3-10t

uses, 1-19

Banak:

characteristics, 1-19

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-19

machining properties, 1-19

mechanical properties, 4-16t, 4-20t

nomenclature, 1-19

resistance to decay and insects, 1-

19

shrinkage values, 3-10t

uses, 1-19

Bark:

growth, 2-2

inner and outer, 2-1

Basswood:

characteristics, 1-4

characteristics for painting, 15-3t

charring rate data, 17-11t

color and figure, 3-3t

connector joint strength, 7-21t

decay resistance, 3-18t

ease of bonding, 9-8t

elastic ratio, 4-2t

flammability data, 17-7t

locality of growth, 1-4

machineability, 1-4

machining and related properties, 3-

16t

moisture content, 3-6t

nomenclature, 5-5t

plywood stiffness and strength, 10-

11t

size of pores, 15-31t

strength properties, 4-4t, 4-9t

in wood–polymer composites,

19-11t

thermal conductivity, American, 3-

19t

uses, 1-4

workability, 1-4

Basswood, American:

dimensional change coefficient, 12-

16t

penetration, 14-16t

shrinkage values, 3-9t

Bastard sawn lumber, definition, 3-2

Beams:

bending deflection, 8-3 to 8-4, 8-

3eq, 8-3t, 8-4eq

bending stress, 8-5, 8-5eq, 8-9

combined bending and axial load,

effect of, 8-7

compressive stress, 8-4

deformation, 8-1 to 8-4

end loading, effect of, 8-7

lateral buckling, 8-9 to 8-10, 8-9eq,

8-10t

modulus of rupture, 8-6, 8-6eq

notches and holes, effect of, 8-3, 8-6

to 8-7

shear deflection, 8-3, 8-3eq, 8-3t

shear stress, 8-5, 8-5eq

size, effect on strength, 8-6, 8-6eq

size, effects on modulus of rupture,

8-6, 8-6eq

stability, 8-8 to 8-11

tapered beams:

bending stress, 8-5 to 8-6, 8-5eq

deflections, 8-3, 8-3eq, 8-4fig

glulam combinations, 11-6, 11-

4fig

shear stresses, 8-5 to 8-6, 8-5fig

tensile, stress, 8-4, 8-4eq

time, effect of, 8-3, 8-7

twist, 8-4, 8-4eq

waterponding, effect of, 8-3, 8-3eq,

8-7, 8-9, 8-9eq

Beech:

characteristics for painting, 15-3t

decay resistance, 3-18t

for flooring, 5-6, 5-7

machining and related properties, 3-

16t

nomenclature, 5-5t

penetration, 14-16t

size of pores, 15-31t

Beech, American:

characteristics, 1-4

color and figure, 3-3t

connector joint strength, 7-21t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-4

machineability, 1-4

moisture content, 3-6t

plywood stiffness and strength, 10-

11t

shock resistance, 1-4

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

tensile strength, 4-24t

thermal conductivity, 3-19t

uses, 1-4

Bees, carpenter, 13-13

Beetles:

ambrosia beetles, 13-8, 13-10

damage cause by, 13-9t

bark beetles, 13-8

old house borers, 13-11

damage caused by, 13-9t

powder-post beetles, 13-10

damage caused by, 13-9fig, 13-

10t

Bending:

creep, 4-37 to 4-39

strength and temperature, 4-37

Bending of glulam, 11-4 to 11-5

Bending properties, affected by

temperature, 4-37, 4-37t

Bending stiffness:

of box and I beams, 11-12

of sandwich panels, 11-18

of stressed-skin panels, 11-14

Bending strength, stress grading, 6-6

Bending stress:

derivations for machine-graded

lumber, 6-8 to 6-10, 6-9fig

stressed-skin panels, 11-15

Bending of wood:

apparatus, 19-4

chemicals used, 19-2

fixing the bend, 19-4

moisture content of stock, 19-3

principles of plasticizing and

bending, 19-1

selection of stock, 19-3

solid members, 19-3, 19-4fig

steaming, 19-1

Benge:

characteristics, 1-19

decay resistance, 3-18t

ease of bonding, 9-8t

mechanical properties, 4-16t, 4-20t

nomenclature, 1-19

sapwood, 2-2

shrinkage values, 3-10t

uses, 1-19

workability, 1-19

Bent wood members:

characteristics, 19-4

solid wood members, species used,

19-3

uses, 19-2

Birch:

connector joint strength, 7-21t

decay resistance, 3-18t

for casing and base, 5-17

for flooring, 5-6, 5-7

heat release data, 17-9t

machining and related properties, 3-

16t

nomenclature, 5-5t

Birch, gray, shrinkage values, 3-9t

Birch, paper:

characteristics, 1-4
I–4

color and figure, 3-3t

dimensional change coefficient, 12-

16t

locality of growth, 1-4

machining and related properties, 3-

16t

moisture content, 3-6t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

uses, 1-5

Birch, river:

dimensional change coefficient, 12-

16t

penetration, 14-16t

shrinkage values, 3-9t

Birch, sweet:

characteristics, 1-4

color and figure, 3-3t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-4

moisture content, 3-6t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shock resistance, 1-4

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

uses, 1-5

Birch, yellow:

characteristics, 1-4

characteristics for painting, 15-3t

color and figure, 3-3t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

flame spread index, 17-3t

laminated:

strength properties, 19-7t to

19-8t

thermal expansion coefficients,

19-9t

locality of growth, 1-4

moisture content, 3-6t, 4-34t

Poisson ratio, 4-3t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

shock resistance, 1-4

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

toughness values, 4-24t

uses, 1-5

Bird peck:

description, 4-33

effect on strength, 4-33

species involved, 4-33

Bis(tri-n-butyltin) oxide:

concentration values, 14-8

inappropriate uses, 14-8

paintability, 14-8

recommended uses, 14-8

toxicity, 14-8

Black locust. See Locust, black

Blood adhesive, working and strength

properties, and uses, 9-13t

Blue stain, description,13-2

Boats, wood:

control of decay in, 13-8

control of marine borers, 13-15

use of varnish on, 15-22

Bolts:

bearing stress of wood under:

bolt diameter, effect

perpendicular to grain, 7-15fig

intermediate angle to grain

loading, 7-14, 7-13fig

L/D ratios, 7-14

parallel to grain loading, 7-14,

7-14fig

perpendicular to grain loading,

7-14, 7-14fig

bearing stress with steel side

plates, 7-15

bolt holes, effect on, 7-16 to 7-17,

7-16fig

bolt quality, effect on joint

strength, 7-15, 7-14fig, 7-15fig

drift, 7-9

member thickness, effect of, 7-15,

7-15fig

multiple bolt joints, 7-15 to 7-16

pre-1991 allowable loads:

parallel to grain, 7-17 to 7-18,

7-17t

perpendicular to grain, 7-18,

7-17t, 7-19t

post-1991 yield model, 7-18, 7-

18eq, 7-19t

spacing, edge and end distance,

7-16

Bondability:

of metals and plastics to wood, 9-5

of wood species, 9-7, 9-8t

Bonded joints:

basic stress modes, 9-20 to 9-21

construction joints, 9-19 to 9-20,

9-20fig

edge-grain joints, 9-18, 9-18fig

end-grain joints, 9-18 to 9-19, 9-

19fig

end-to-edge grain joints, 9-19, 9-

19fig

mechanical testing of, 9-20 to 9-21

Bonding:

adhesive selection, 9-12 to 9-15

assembly and pressing, 9-16 to 9-

18, 9-17fig

effect of:

moisture content and

dimensional change, 9-7 to 9-9

wood density, 9-6 to 9-7

wood porosity, 9-7

elements of, 9-1 to 9-2

moisture content control, 9-15 to 9-

16

quality assurance programs, 9-22 to

9-23

short- and long-term performance of

adhesives, 9-21 to 9-22, 9-22fig

strength and durability of

adhesives, 9-11 to 9-12, 9-11t, 9-18

strength properties of adhesives, 9-

21

surface preparation, 9-16

with veneers, 9-4 to 9-5

wettability of wood, 9-2, 9-3fig, 9-5

wood and nonwood composites, 9-

5 to 9-6

Box beam, 11-12 to 11-13

Box elder, nomenclature, 5-5t

Box nails, 7-2, 7-2t

Bridges, 16-9 to 16-10, 16-10fig

Brown rot, 13-5

Bubinga (See also Benge):

decay resistance, 3-18t

ease of bonding, 9-8t

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

Buckeye:

characteristics, 1-5

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-5

machineability, 1-5

nomenclature, 5-5t

shock resistance, 1-5

species, 1-5

uses, 1-5

yellow, shrinkage values, 3-9t

Buckling:

interaction of buckling modes, 8-10

to 8-11, 8-10eq, 8-11eq

of beams, 8-9 to 8-10, 8-9eq, 8-10t

of columns, 8-8 to 8-9, 8-8eq, 8-8fig

of deck beams, 8-10, 8-10fig

of glued-laminated beams, 11-13

of roof beams, 8-9

of sandwich panels, 11-18 to 11-19

of stressed-skin panels, 11-15

Building codes:

classifications of construction, 17-2

fire safety:

containment to compartment of

origin, 17-4 to 17-6

fire growth within compartments,

17-2 to 17-4

types of construction, 17-2

organizations producing, 17-2

Buildings, control of decay in, 13-7

Built-up columns, 8-9

Bulletwood (See also Balata):

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

Butternut:

characteristics, 1-5

characteristics for painting, 15-3t

color and figure, table, 3-3t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-5
I–5

machineability, 1-5

nomenclature, 5-5t

shock resistance, 1-5

size of pores, 15-31t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

uses, 1-5

Buttonwood. See Sycamore

Cambium, 2-1, 2-2

Carapa. See Andiroba

Carbon monoxide, 17-10

Carpenter ants:

damage caused by, 13-10fig, 13-10t

discussed, 13-13

Carpenter bees:

damage caused by, 13-9t

discussed, 13-13

Casing and base, availability, 5-17

Casein adhesive:

structural performance, 9-11t

working and strength properties,

and uses, 9-13t

Catalpa:

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

Catalysts and adhesion, 9-10

Cativo:

characteristics, 1-19

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-19

mechanical properties, 4-16t, 4-20t

plywood stiffness and strength, 10-

11t

resistance to decay and insects, 1-

20

sapwood, 2-2

shrinkage values, 3-10t

uses, 1-20

Cedar:

availability at retail yards, 5-16

for finish boards, 5-17

Cedar, Atlantic-white:

characteristics, 1-17

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-17

nomenclature, 5-13t

shock resistance, 1-17

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

thermal conductivity, 3-20t

uses, 1-17

Cedar, eastern red:

characteristics, 1-15

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

heat release data, 17-9t

locality of growth, 1-15

moisture content, 3-6t

nomenclature, 5-13t

shock resistance, 1-15

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

thermal conductivity, 3-20t

uses, 1-15

Cedar, incense:

characteristics, 1-12

characteristics for painting, 15-3t

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-12

moisture content, 3-6t

pecky, 1-12

plywood stiffness and strength, 10-

11t

nomenclature, 5-13t

shock resistance, 1-12

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

uses, 1-12

Cedar, northern white:

characteristics, 1-16

characteristics for painting, 15-3t

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

elastic ratio, 4-2t

for shingles, 5-17

locality of growth, 1-16

mechanical properties, 4-14t, 4-15t

nomenclature, 5-13t

penetration, 14-16t

Poisson ratio, 4-3t

shock resistance, 1-17

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

thermal conductivity, 3-20t

uses, 1-17

Cedar, Port-Orford:

characteristics, 1-15

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-15

moisture content, 3-6t

nomenclature, 5-13t

plywood stiffness and strength, 10-

11t

shock resistance, 1-15

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

tensile strength, 4-24t

thermal conductivity, 3-20t

uses, 1-15

Cedar, western red:

characteristics, 1-20

characteristics for painting, 15-3t

charring rate data, 17-11t

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

flame spread index, 17-3t

for shingles and shakes, 5-17

for siding, 5-17

locality of growth, 1-15

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shock resistance, 1-15

shrinkage values, 3-9t

strength properties, 4-6t, 4-12t

tensile strength, 4-24t

thermal conductivity, 3-20t

toughness values, 4-25t

used for poles, 18-2, 18-4t, 18-6

uses, 1-15

Cedar, yellow:

characteristics, 1-17

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 12-16t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

flame spread index, 17-3t

locality of growth, 1-17

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

nomenclature, 5-13t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

shock resistance, 1-17

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

toughness values, 4-25t

uses, 1-17

Cedro. See Spanish-cedar

Cedro macho. See Andiroba

Cedro-Rana. See Tornillo

Ceiba:

characteristics, 1-20

characteristics affecting machining,

3-17t

decay resistance, 3-18t

locality of growth, 1-20

mechanical properties, 4-16t, 4-20t
I–6

resistance to decay and insects, 1-

20

shrinkage values, 3-10t

uses, 1-20

workability, 1-20

Cells of wood:

description, 2-3

fibers, 2-3

functions of various types, 2-3

length, 2-3

parenchyma, 2-3

rays, 2-3

tracheids, 2-3

vessels, 2-3

Cellulose, discussion, 2-3

Cellulose insulation, product safety

standard, 17-4

Cement-bonded composites, 10-24 to

10-26, 10-24fig, 10-26fig

Cement-coated nails, 17-3 to 17-4

Chalking, 15-26 to 15-27

Checks:

development due to weathering, 15-

7

during drying, 12-7, 12-9 to 12-10,

12-12fig

in decking boards, 15-10

in lumber stress grading, 6-4

in glued-laminated timbers, 11-10

in veneer adhesion, 9-4 to 9-5

Chemical composition of wood, 2-3 to

2-4

Chemical discolorations during

drying, 12-10, 12-13fig

Chemical stain, discussed, 3-13

Chemicals, effect on wood:

discussion, 4-41

strength properties, 4-41

swelling liquids, 4-41

Cherry:

characteristics for painting, 15-3t

ease of bonding, 9-8t

nomenclature, 5-5t

size of pores, 15-31t

Cherry, black:

characteristics, 1-5

color and figure, 3-3t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

elastic ratio, 4-2t

locality of growth, 1-5

machineability, 1-5

machining and related properties, 3-

16t

moisture content, 3-6t

Poisson ratio, 4-3t

shock resistance, 1-5

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

uses, 1-1, 1-5

Cherry, pin, penetration, 14-16t

Chestnut:

characteristics for painting, 15-3t

machining and related properties, 3-

16t

nomenclature, 5-5t

Chestnut, American:

availability, 1-5

characteristics, 1-5

color and figure, 3-3t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-5

moisture content, 3-6t, 4-34t

penetration, 14-16t

shock resistance, 1-5

shrinkage values, 3-9t

size of pores, 15-31t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

uses, 1-7

workability, 1-5

Chewstick. See Manni

Chlorothalonil:

effectiveness, 14-8

solubility, 14-8

stability, 14-8

Chlorothalonil/chlorpyrifos:

component rations, 14-8

effectiveness, 14-8

Chlorpyrifos:

effectiveness, 14-9

in combination, 14-9

Chromated copper arsenate (CCA):

common types, 14-11

component substitutions, 14-11

composition of common types, 14-

11t

effectiveness of common types, 14-

11

effect on adhesion, 9-6

finishing wood treated with, 15-22

resistance to marine borers, 14-11

retention levels for various wood

products, 14-6t

Southern pine sapwood stakes

retention and life span test results,

14-13t

temperature for pressure treating,

14-21

use with Douglas-fir, 14-11

Coal-tar creosote. See Creosote

Cocobolo, shrinkage values, 3-10t

Coefficient of friction, 3-21, 3-22

Coefficient of thermal expansion, 3-21

Coefficient of variation, 4-23t

Collapse during drying, 12-10, 12-

12fig

Columns:

built-up and spaced columns, 8-9

flanged columns, 8-9

long columns, compressive stress,

8-8, 8-8eq

short columns, compressive stress,

8-8 to 8-9, 8-8eq

Composite products:

additives, 10-4

adhesive considerations, 10-3 to

10-4

classification, 10-2, 10-2t, 10-3fig

manufacturing issues, 10-4

particle and fiber composites 10-13

to 10-24

specialty composites:

flame retardant, 10-24

preservative treated, 10-24

moisture-resistant, 10-23 to 10-

24

types, 10-3, 10-3fig

wood fiber–thermoplastic

composites:

nonwoven textile-type:

applications, 10-29 to 10-30

density, 10-29 to 10-30

manufacture, 10-28 to 10-30

properties, 10-28 to 10-30,

10-29t

production, 10-26 to 10-27

with high thermoplastic content:

advantages, 10-27

compounding, 10-27 to 10-28

density, 10-27

disadvantages, 10-28

manufacture, 10-27

properties, 10-28, 10-28t

with low thermoplastic content,

manufacture, 10-28

wood-based panels, 10-4 to 10-6

wood–nonwood composites:

advantages, 10-24

inorganic-bonded composites:

description, 10-24 to 10-25,

10-24fig

gypsum-bonded, 10-25

magnesia-cement-bonded, 10-

25

portland-cement-bonded, 10-

25 to 10-26, 10-26t

problems, 10-26

treatments, 10-26

Compreg:

advantages, 19-5

dimensional stability, 19-9t

molding, 19-5, 19-8

plasticizers, 19-5

properties, 19-5, 19-6t

species used, 19-9

thermal expansion coefficients, 19-

9t

uses, 19-8 to 19-9

Compressed wood, untreated (staypak)

appearance, 19-10

dimensional stability, 19-9t

purpose, 19-7t to 19-8t

strength properties, 19-7 to 19-8t

uses, 19-10

Compression failures:

causes, 4-33

description, 4-33, 4-33fig

effect on strength, 4-33

Compression wood:

definition, 4-31

density increase, 4-31
I–7

in juvenile wood, 4-32

shrinkage, 3-8, 4-32

Compression strength parallel to

grain:

affected by temperature, 4-36t

coefficient of variation, 4-23t

defined, 4-3

Compressive stress of stressed-skin

panels, 11-14 to 11-15

Compressive stress of columns, 8-8 to

8-9, 8-8eq

Compression stress perpendicular to

grain:

coefficient of variation, 4-23t

defined, 4-3

Condensation in crawl spaces, 13-7

Conductance meters and moisture

content, 12-2 to 12-3

Conductivity, thermal:

definition, 3-31

discussion, 3-31 to 3-32

Cone calorimeter, 17-8

Connector joints:

cross bolts, 7-24

design loads, 7-20, 7-20fig, 7-21fig

end distance and spacing, 7-23

multiple connectors, 7-23 to 7-24,

7-24fig

net section stress, 7-23

parallel to grain loading, 7-18, 7-

20fig

perpendicular to grain loading, 7-

18 to 7-20, 7-20fig

shear plate connector, 7-19fig

split-ring connector, 7-19fig

strength components, 7-18

strength ratios, 7-25t

working loads:

exposure and moisture

condition, effect of, 7-21

grade and quality of lumber, 7-22

loads at angle with grain, 7-22,

7-7fig, 7-13eq,

species grouping, 7-21t, 7-22t

steel side plates, effect of, 7-21

thickness of member, effect of, 7-22,

7-22t, 7-23fig

width of member, effect of, 7-23

Construction, design factors affecting

dimensional change, 12-18

Construction logs:

availability, 18-3

form, 18-4 to 18-5, 18-5fig

standards and specifications, 18-2t

strength properties, 18-7

uses, 18-3, 18-4fig

Copper azole - Type A (CBA-Type A):

retention levels for various wood

products, 14-6t

solution percentages, 14-12

temperature for pressure treating,

14-21

Copper bis(dimethyldithiocarbamate)

(CDDC):

retention levels for various wood

products, 14-6t

solution percentages, 14-11 to 14-

12

temperature for pressure treating,

14-21

uses, 14-12

Copper naphthenate:

color transfer and changes, 14-8

effectiveness, 14-8

retention levels for various wood

products, 14-5t

solution values, 14-8

Southern pine sapwood stakes

retention and life span test results,

14-14t

treatment for cutting pretreated

wood, 14-24

Cotton linter paper, 19-12

Cottonwood:

characteristics, 1-5

color and figure, 3-3t

connector joint strength, 7-21t

decay resistance, 3-18t

ease of bonding, 9-8t

elastic ratio, 4-2t

flame spread index, 17-3t

locality of growth, 1-5

machining and related properties, 3-

16t

moisture content, 3-6t

nomenclature, 5-5t

penetration, 14-16t

shock resistance, 1-6

size of pores, 15-31t

species, 1-5

uses, 1-6

workability, 1-6

Cottonwood, balsam poplar:

mechanical properties, 4-14t, 4-15t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

Cottonwood, black:

dimensional change coefficient, 12-

16t

mechanical properties, 4-14t, 4-15t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

Cottonwood, eastern:

dimensional change coefficient, 12-

16t

elastic ratio, 4-2t

characteristics for painting, 15-3t

mechanical properties, 4-14t, 4-15t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

Courbaril:

characteristics, 1-20

characteristics affecting machining,

3-17t

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-20

machineability, 1-20

mechanical properties, 4-16t, 4-20t

resistance to decay and insects, 1-

20

sapwood, 2-2

shrinkage values, 3-10t

uses, 1-20

Covalent chemical bonds, 9-2

Crabwood. See Andiroba

Crack propagation systems, 4-24 to 4-

25

Creep:

defined, 4-37

discussed, 4-37 to 4-39

influence of stress on, 4-39fig

Creosote, coal-tar:

advantages, 14-2

appearance, 14-2

composition variability, 14-2

EPA-approved customer

information sheet, 14-3t

effect on mechanical properties, 14-

24

for non-pressure treatments, 14-7

handling precautions, 14-3t

in pressure treatment process, 14-19

odor and vapors, 14-2

retention levels for various wood

products, 14-5t

standards, 14-2

temperature for pressure treating,

14-21

treatment for cutting pretreated

wood, 14-25

use site precautions, 14-3t

volatility, 14-7

Creosote-coal-tar solutions:

properties, 14-7

retention levels for various wood

products, 14-5t

standards by volume, 14-7

temperature for pressure treating, 4-

21

Creosote-petroleum oil solutions:

retention levels for various wood

products, 14-5t

Cristobal. See Macawood

Critical radiant flux test, 17-4

Cross grain:

effect on mechanical properties,

4-29 to 4-30

types, 4-28 to 4-30

Cuangare (See also Banak):

dimensional change coefficient, 12-

17t

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

Cucumber, nomenclature, 5-5t

Curved members, glulam combinations,

11-5 to 11-6

Cypress:

for siding, 5-17

plywood stiffness and strength,

10-11t
I–8

Cypress, Arizona, decay resistance, 3-

18t

Cypress, Mexican

characteristics, 1-33

locality of growth, 1-33

machineability, 1-33

mechanical properties, 4-16t, 4-20t

uses, 1-33

Dead trees, strength, 4-33 to 4-34

Decay:

and exposure to weather, 15-13

appearance of fungi, 13-4

brown rot, 13-5

conditions favoring, 13-4, 13-15

control in:

boats, wood, 13-8

buildings, 13-7

logs, poles, piling, or ties, 13-6

lumber, 13-6

plywood, 13-8

cycle, 13-3fig

dead trees, 4-33 to 4-34

dry rot, 13-5

dry rot fungi, 13-5

effect on mechanical properties, 4-

43

effect on strength, 4-43, 13-5, 13-6

fungal stain and molds, 13-3

heartwood, susceptibility to, 13-4

incipient, 13-5

sapwood, susceptibility to, 13-4

soft rot, 13-5

white rot, 13-5

Decay hazard climate index, 13-2fig

Decay resistance:

extractives, 2-2

heartwood, 2-2, 3-18t, 13-5

in visual stress grading, 6-5

Decks:

discussed, 16-4

finishes, suitability and expected

service life, 15-15t

finishing, 15-21

supports, 8-10, 8-10fig

use of cleaners, 15-33

Deflections of beams:

effect of time, creep, 8-3

straight beams, 8-1 to 8-2, 8-2t, 8-

2eq

tapered beams, 8-2, 8-2eq, 8-3fig

Deformation equations:

axial load, 8-1, 8-1eq

bending:

effect of notches and holes, 8-2

effect of time, creep deflection, 8-

3

straight beam deflection, 8-1 to

8-2, 8-2eq, 8-2t

tapered beam deflection, 8-2, 8-

2eq, 8-3fig

water ponding, 8-3, 8-3eq

combined bending and axial load:

concentric load, 8-3 to 8-4, 8-

4eq

eccentric load, 8-4, 8-4eq

torsion, 8-4, 8-4eq, 8-4fig

Deformed shank nails, strength of, 7-7

Degame:

characteristics, 1-20

locality of growth, 1-20

machineability, 1-20

mechanical properties, 4-16t, 4-20t

resistance to decay and insects, 1-

20

shrinkage values, 3-10t

strength, 1-20

uses, 1-20

Delamination and adhesive failure, 9-

21

Density:

as function of specific gravity and

moisture content, 3-12, 3-13t, 3-14t

effect on adhesive bonding, 9-6 to

9-7

effect on withdrawal resistance of

nails, 7-3

in sorting machine-graded lumber,

6-8

in visual stress grading, 6-5

variation, 3-11

Design factors affecting dimensional

change in structures:

flooring, 12-18

framing lumber in house

construction, 12-18

heavy timber construction, 12-18

interior finish, 12-18

Design properties:

and stress grading, 6-3

procedures for deriving, 6-5 to 6-7

Design values:

for foreign species, approval

process, 6-4t

for glulam, 11-9—11-10

Determa:

characteristics, 1-21

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-21

machineability, 1-21

mechanical properties, 4-16t, 4-20t

resistance to decay and insects, 1-

21

uses, 1-21

Diagonal grain, 4-29 to 4-30

Dielectric constant, definition, 3-21,

3-22

Dielectric meters and moisture content,

12-2 to 12-3

Dielectric power factor, 3-21, 3-22

Dimensional change and wood

paintability, 15-4

Dimensional changes in wood:

affected by design factors, 12-18

calculation based on green

dimensions, 12-17, 12-17eq

care during construction 12-18 to

12-20

estimation using coefficients, 12-15

to 12-17, 12-15eq, 12-16t, 12-17t

Dimpling of sandwich panel facings,

11-19

Discoloration:

by mildew, 15-8, 15-27

by mold and fungal stains, 13-2

by nonmicrobial or chemical stains,

13-3

from water-soluble extractives, 15-

28 to 15-29

of paint due to extractives, 15-2

use of wood cleaners, 15-33

Discontinuous rings, definition, 2-2

Dogwood, nomenclature, 5-5t

Doors, fire resistance in frame

construction, 17-5

Douglas-fir:

availability at retail yards, 5-16

characteristics, 1-10

characteristics for painting, 15-3t

charring rate equation, 17-10

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

ease of bonding, 9-8t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

flame spread index, 17-3t

for flooring, 5-17

for siding, 5-17

fracture toughness, 4-26t

kiln drying schedule, 12-11t

locality of growth, 1-10

mechanical properties, 4-14t, 4-15t

moisture content, 4-34t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

preservative pressure and

temperature, 14-21

preservative treatment to prevent

marine borer attack on piles, 14-10t

preservatives used, 14-7, 14-11, 14-

12

shrinkage, 3-8, 3-11fig

used for poles, 18-2, 18-4t

uses, 1-10

Douglas-fir, coast:

dimensional change coefficient, 12-

16t

moisture content, 3-6t

penetration, 14-16t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

toughness values, 4-25t

Douglas-fir, interior north

dimensional change coefficient, 12-

16t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

tensile strength, 4-24t

thermal conductivity, 3-20t

toughness values, 4-25t

Douglas-fir, interior west
I–9

dimensional change coefficient, 12-

16t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

toughness values, 4-25t

Douglas-fir, interior south

strength properties, 4-7t, 4-12t

toughness values, 4-25t

Draftstops, 17-5

Dried wood, moisture control during

transit and storage, 12-14 to 12-15,

12-14t

Drift bolts, 7-9

Dry kilns, 12-7 to 12-8, 12-8fig

Drying of wood:

accelerated air drying and

predrying, 12-6

advantages, 12-5

affect of properties, 12-5

air drying, 12-6

drying mechanism, 12-6 to 12-7,

12-6fig

drying defects:

discoloration, 12-10, 12-13fig,

12-14fig

fracture or distortion, 12-9 to 12-

10, 12-12fig

warp, 12-10 to 12-12, 12-13fig

drying schedules, 12-8 to 12-9, 12-

11t

drying stresses, 12-7, 12-7fig

kiln drying, 12-6

hardwood lumber targets, 12-5

softwood lumber targets, 12-5

Duration of load:

adjustment of design properties, 6-

12 to 6-13, 6-13t, 6-13fig

defined, 4-24, 4-39

effect on mechanical properties, 4-

39 to 4-40

relationship to failure, 4-39fig

Dutch elm disease, 1-6

Earlywood:

effect on paintability, 15-4

description, 2-2

erosion of planed surfaces, 15-8t

properties, 2-3

Ebony, shrinkage values, 3-10t

Edge-grained lumber:

advantages, 3-2t

method of producing, 3-2

preferred for painting, 15-1

weathering and check development,

15-7

Ehie (See also Benge):

decay resistance, 3-18t

Ekki. See Azobe

Ekop:

characteristics, 1-21

characteristics affecting machining,

3-17t

decay resistance, 3-18t

locality of growth, 1-21

machineability, 1-21

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

uses, 1-21

Elastic properties of clear wood:

discussion, 4-2

values of:

modulus of elasticity ratios, 4-2t

modulus of rigidity ratios, 4-3t

Poisson's ratio, 4-2

Elastomeric adhesives:

in light-frame construction, 9-19 to

9-20, 9-20fig

performance over time, 9-21 to 9-22,

9-22fig

structural performance, 9-11t

working and strength properties,

and uses, 9-13t

Electrical properties of wood:

conductivity, 3-21, 3-22

dielectric constant, 3-21, 3-22

power factor, 3-21, 3-22

resistance and moisture content, 3-

22fig

Elm:

characteristics, 1-6

connector joint strength, 7-21t

decay resistance, 3-18t

disease, 1-6

locality of growth, 1-6

moisture content, 3-6t

size of pores, 15-31t

species, 1-6

uses, 1-6

Elm, American:

characteristics for painting, 15-3t

color and figure, 3-3t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

moisture content, 3-6t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

Elm, cedar:

dimensional change coefficient, 12-

16t

moisture content, 3-6t

shrinkage values, 3-9t

tensile strength, 4-24t

Elm, rock:

color and figure, 3-3t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

moisture content, 3-6t

nomenclature, 5-5t

penetration 14-16t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

Elm, slippery:

color and figure, 3-3t

dimensional change coefficient, 12-

16t

penetration, 14-16t

shrinkage values, 3-9t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

Elm, soft:

machining and related properties, 3-

16t

nomenclature, 5-5t

Elm, winged:

dimensional change coefficient, 12-

16t

shrinkage values, 3-9t

Encased knots, definition, 4-27

Encino. See Oak

End joints in glued laminated timber,

11-7 to 11-8

Engineered trusses and light-frame

construction, 16-4

Epoxy:

performance over time, 9-22

structural performance, 9-11t

use with wood and nonwood

composites, 9-5

working and strength properties,

and uses, 9-14t

Erosion:

of earlywood and latewood planed

surfaces, 15-8t

of finishes, 15-9

of wood, discussed, 15-7

rates for hardwood and softwoods,

15-8t

Equilibrium moisture content:

definition, 3-5, 15-9

relative humidity as related to, 3-7

values for U.S. cities, 12-2, 12-3t

Extractives:

and mill glaze, 15-25

discoloration, water-soluble, 15-28

to 15-29

discussion, 2-2, 2-4, 4-33

effect on painting, 15-2, 15-6 to 15-

7, 15-21

effect on strength, 4-33

heartwood, 2-2

species involved, 4-33

Facing stresses, sandwich panels, 11-

19

Facing wrinkling, sandwich panels,

11-19 to 11-20

Factory-finished wood products, 15-

24

Factory lumber (See also Hardwood

lumber):

grades, 5-2

standard dimensions, 5-2

False rings, definition, 2-2

Fastener head embedment, 7-26, 7-

27fig

Fasteners:

and iron stain, 15-29

corrosion and fire-retardant treated

wood, 17-12 to 17-13

fire resistance in frame construction,

17-5

multiple-fastener joints, 7-24 to

7-25
I–10

Fatigue:

defined, 4-24, 4-40

discussed, 4-40 to 4-41

summary of fatigue studies, 4-40t

Fences, finishing, 15-13, 15-21 to 15-

22

Fiberboard:

attrition milling or refining, 10-17

to 10-18

classification, 10-18, 10-3fig

distinguished from particleboard,

10-17

dry-process fiberboard, 10-19, 10-

19fig

fibers used, 10-17, 10-19fig

finishing techniques, 10-23

hardboard:

heat treatment, 10-20

humidification, 10-20

physical and mechanical

properties of hardboard siding,

10-22t

property requirements 10-20 to

10-22, 10-21t

siding grade stamps, 10-22fig

standards, 10-5t

tempering, 10-20

insulation board:

cold-pressing, 10-20

felting, 10-20

grade stamp example, 10-22fig

types of products, 10-23

sizing agents, 10-20

standards, 10-5t

medium-density fiberboard (MDF):

property requirement, 10-20, 10-

21t

resins used, 10-4

standards, 10-5t

uses, 10-20

with veneer overlay, 10-23, 10-

23fig

wet-process fiberboard, 10-19 to

10-20

Fiber orientation, related to slope of

grain, 4-28 to 4-30, 4-30fig

Fibers:

description, 2-3

length, 2-3

shape, 2-3

Fiber saturation point:

average, 3-5

definition, 3-5

Fibrils, 2-3

Figure of wood, discussion, 3-4

Finger joints, in laminated members,

11-7 to 11-8, 11-9 to 11-10

Finger-jointed lumber:

defined, 15-5

finishing, 15-5, 15-30

Finish board, availability, 5-17

Finish failure:

chalking, 15-26

cross-grain cracking, 15-26, 15-

27fig

discoloration from water-soluble

extractives, 15-28 to 15-29

intercoat peeling, 15-26

mill glaze, 15-25 to 15-26

moisture blisters, 15-25

stain:

blue, 15-29

brown stain over knots, 15-29 to

15-30

iron, 15-23, 15-29

rust, 15-29

Finishes:

application and maintenance, 15-

14t

application of:

paint, 15-20 to 15-21

semitransparent penetrating

stain, 15-20

caution in use, 15-20

solid-color stain, 15-20

water-repellant preservative, 15-

19

cost, 15-20

drying oils, 15-32, 15-33

function, 15-1

factors affecting performance:

extractives, 15-2, 15-28 to 15-29

knots, 15-2

texture of wood, 15-5

weathering:

as a natural finish, 15-16

effect on paint adhesion, 15-8

to 15-9

effect on wood, 15-6 to 15-7

effect on wood finish, 15-9

wood moisture content, 15-9 to

15-10

backpriming, 15-23 to 15-24

wood product characteristics:

finger-jointed lumber, 15-5,

15-30

lumber, 15-4 to 15-5

plywood, 15-5

reconstituted wood products:

fiberboard, 15-6

particleboard, 15-6

treated wood:

fire-retardant treated, 15-6

preservative treated, 15-6

wood properties, 15-1 to 15-2,

15-30

moisture-excluding effectiveness of,

15-10 to 15-11

on ponderosa pine, 15-12t

nondrying oils, 15-32, 15-33

on:

butcher blocks and cutting

boards, 15-33

floors, 15-32

glulam, 11-8 to 11-9

interior wood, 15-30

items used for food, 15-32 to 15-

33

porches, decks, fences, 15-21 to

15-22

treated wood, 15-22

wood exposed to marine

environments, 15-22

paintability values, 15-2, 15-4

paraffin wax, 15-32, 15-33

refinishing, 15-22 to 15-23

suitability and expected service life

for exterior wood surfaces, 15-5t

types:

film-forming:

effect on water and vapor

absorption, 15-11

fire-retardant coatings, 15-19

paint, 15-18 to 15-19

solid-color stain, 15-18

varnish:

clear, 15-18

pigmented, 15-18

opaque, 15-30

penetrating, 15-14, 15-16

lightly colored, 15-17

semitransparent stains, 15-17

transparent clear, 15-16

oils, 15-18

stains, 15-30 to 15-31

surface coats, 15-31

transparent, 15-30

use of fillers, 15-30, 15-31, 15-32

use of sealers, 15-30, 15-31, 15-32

VOC regulation compliance, 15-19

See also Paint and Water-repellant

preservatives

Fire performance characteristics of

wood:

charring:

differences in wood species, 17-

10

discussed, 17-10 to 17-11

equations for charring rates, 17-

10, 17-11

moisture content, 17-11

flame spread:

and heat release rate, 17-9

configurations, 17-9

factors influencing, 17-8

flammability data for wood species,

17-7t

heat release rate:

discussed, 17-7 to 17-8

measuring, 17-8

ignition:

piloted, 17-6

unpiloted, 17-6, 17-7

smoke:

approaches for dealing with, 17-

9

carbon monoxide, 17-10

defined, 17-9

release rate, 17-10

tests for determining yield, 17-9

to 17-10

toxicity, 17-10

smouldering, 17-6 to 17-7

stages of degradation, 17-6

Fire resistance:

calculating, 17-5

defined, 17-4
I–11

failure criteria, 17-4

in heavy timber construction, 17-4

in light-frame construction, 17-5

in glued laminated members, 17-5

ratings, 17-4

Fire-retardant coatings, 15-19, 17-13

Fire-retardant-treated wood:

and hygroscopicity, 17-12, 17-13

and mechanical properties, 17-12

discussed, 17-12

effect on adhesion, 9-6

fastener corrosion, 17-12 to 17-13

heat release rates, 17-8, 17-12

in high temperature applications,

17-12

paintability, 15-16

performance requirements, 17-12

uses, 17-12

Fire-retardant treatments:

application methods, 17-12

chemical penetration, 17-13

inorganic salts, 17-13

Fire safety design:

cellulosic insulation, 17-4

code organizations, 17-2

code requirements, 17-1

components, 17-1

containment to compartment of

origin:

firestops and draftstops, 17-5

fire resistance, 17-4

of heavy timber construction, 17-

4 to 17-5

in light-frame construction, 17-5

of glued-laminated members, 17-

5

sandwich panels, 17-5

fire safety engineering, 17-6

flame spread index, 17-2 to 17-3

flashover, 17-4

flooring, 17-4

roof covering materials, 17-4

types of construction:

heavy timber, 17-2

light frame, 17-2

ordinary, 17-2

Fire tests:

critical radiant flux, 17-4

flame spread index:

discussed, 17-2

values for solid lumber, 17-3t

roof coverings, 17-4

room/corner test, 17-4

tunnel test, 17-8

wood ignition, 17-6

Firestops, 17-5

Fir, balsam:

color and figure, 3-4t

connector joint strength, 7-21t

dimensional change coefficient, 12-

16t

mechanical properties, 4-14t, 4-15t

nomenclature, 5-13t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

Fir, California red:

dimensional change coefficient, 12-

16t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

tensile strength, 4-24t

toughness values, 4-25t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

Fir, Grand:

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

moisture content, 3-6t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

Fir, Noble:

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

moisture content, 3-6t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

toughness values, 4-25t

strength properties, 4-7t, 4-12t

Fir, Pacific silver:

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

flame spread index, 17-3t

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

nomenclature, 5-13t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

tensile strength, 4-24t

toughness values, 4-25t

Fir, subalpine:

dimensional change coefficient, 12-

17t

elastic ratio 4-2t

mechanical properties, 4-14t, 4-15t

nomenclature, 5-13t

plywood stiffness and strength, 10-

11t

Poison ratio, 4-3t

shrinkage values, 3-9t

Firs, true (Eastern species):

characteristics, 1-10

decay resistance, 3-18t

locality of growth, 1-10

shock resistance, 1-10

strength properties, 1-10

uses, 1-10

Firs, true (Western species):

decay resistance, 3-18t

locality of growth, 1-10

species, 1-10

uses, 1-11

Fir, white:

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-21t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

moisture content, 3-6t

nomenclature, 5-5t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

toughness values, 4-25t

Flame-retardant composites, 10-24

Flame spread index (FSI):

classes for, 17-2

discussed, 17-2

values for solid lumber, 17-3t

wood usage, 17-3

Flat-sawn lumber:

advantages, 3-2t

and mill glaze, 15-25

disadvantages for finishing, 15-1,

15-7

method of producing, 3-2

Flashover, discussed, 17-4

Flooring:

care during construction, 12-19

design factors affecting dimensional

change, 12-18

recommended moisture content, 12-

5t

retail yard availability, 5-16, 5-17

Formaldehyde adhesives:

performance over time, 9-21 to 9-22,

9-22fig

safety concerns, 9-10

structural performance, 9-11t

use with composite products, 10-4

used with particleboard, 10-16

Formosan termite, 13-11

Foundations for light-frame buildings,

16-2

Fracture toughness, defined, 4-24

Friction, coefficient of, 3-22

Fungi:

appearance of, 13-4

conditions favorable to growth, 13-

1

definition, 13-1

discoloration caused by, 13-2

effect on wood, 13-3

prevention of damage from, 13-6

Fungus damage:

causes, 13-1 to 13-2

decay, 17-4

stains, 13-2
I–12

Glue, shear stress, stressed-skin

panels, 11-15

Glued structural members:

advantages, 11-2 to 11-3

box beams and I beams:

beam deflections, 11-12, 11-12eq

design, 11-12, 11-12fig

flange stresses, 11-12 to 11-13,

11-13eq

lateral buckling, 11-13, 11-13eq

stiffeners and load blocks, 11-13

web shear stress, 11-13, 11-13eq

glued-laminated timber, see Gluedlaminated timber (Glulam)

laminated strand and oriented

strand lumber, 11-2

laminated veneer lumber, 11-2, 11-

2fig

parallel strand lumber, 11-2, 11-2fig

prefabricated wood I-joists, 11-13

to 11-14, 11-14fig

standards, 11-3

stressed-skin panels:

buckling, 11-15 to 11-16, 11-

15eq

design, 11-14, 11-14eq, 11-15fig

glue shear stress, 11-15, 11-15eq

skin stresses, 11-14 to 11-15,

11-14eq

stringer bending stress, 11-15,

11-15eq

structural sandwich construction,

see Sandwich panels

uses, 11-3

Glued-laminated timber (Glulam):

advantages, 11-3 to 11-4

architectural effects, 11-3

combinations:

axial members, 11-5

bending members, 11-4 to 11-5

curved members, 11-5 to 11-6

tapered straight members, 11-6,

11-4fig

cross section variation, 11-3, 11-

4fig

design values, 11-6, 11-9, 11-10

effect of:

end joints on strength, 11-9 to

11-10

edge joints on strength, 11-10

shake, checks, and splits on

shear strength, 11-10

end-use adjustment factors:

curvature, 11-11

flat use, 11-11

lateral stability, 11-12

loading, 11-11

moisture content, 11-11

tension lamination, 11-11

volume, 11-11

environmental effects, 11-4

finishes, suitability and expected

service life, 15-15t

fire resistance, 17-5

grade variation, 11-3

history, 11-4

manufacture:

end jointing, 11-7 to 11-8, 11-

7fig

face bonding, 11-8, 11-8fig

finishing and fabrication, 11-8 to

11-9

lumber drying and grading, 11-6

to 11-7

preservative treatment, 11-9

preservative retention levels, 14-5t

to 14-6t

seasoning advantages, 11-3

standards 11-3, 11-6

used for poles, 18-3

species used, 11-3

size capabilities, 11-3

Glulam. See Glued-laminated timber

(Glulam)

Glulam beam construction, 16-8

Glulam timber bridge, 16-10, 16-10fig

Gluing properties of different wood,

classification of species, 9-8t

Gmelina, shrinkage values, 3-10t

Gola. See Ekop

Goncato alves:

characteristics, 1-21

characteristics affecting machining,

3-17t

decay resistance, 3-18t

locality of growth, 1-21

mechanical properties, 4-16t, 4-20t

resistance to fungus attack, 1-21

shrinkage values, 3-10t

species, 1-21

strength, 1-21

uses, 1-21

Grades and lumber, purchasing

consideration, 5-17 to 5-18

Grading hardwood lumber, 5-2 to 5-4

Grading, machine, 6-7 to 6-11

Grading softwood lumber, 5-7 to 5-10

Grading, visual, 6-3 to 6-7

Grain and texture of wood:

and finish performance, 15-2t

and paintability, 15-4 to 15-5

discussion, 3-1 to 3-2

Greenheart:

characteristics, 1-21

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-21

machineability, 1-21

mechanical properties, 4-16t, 4-20t

shrinkage values, 3-10t

resistance to fungi and insects, 1-21

marine borers, 13-14

uses, 1-21

Green wood:

and clinched nails, 7-5

bending properties, 19-3

creep and relaxation under load, 4-

38

definition, 3-5

relationship of mechanical

properties to specific gravity, 4-28t

treatment with polyethylene glycol

(PEG), 19-10

Growth of tree:

branching, 2-1

diameter, 2-2

fibrils, 2-3

Growth rings:

cross section showing, 2-3fig

determinations of tree age by, 2-2

discontinuous, definition, 2-2

discussion, 2-2, 2-3

effect on strength properties, 4-30

to 4-31

false, definition, 2-2

grain, 3-1

in sawn boards, 3-2, 3-4

principal axes with respect to, 4-2

shrinkage, 3-7 to 3-8, 3-8fig

Guatambu. See Pau marfim

Guayacan. See Ipe

Gum:

nomenclature, 5-5t

size of pores, 15-31t

Gurjun. See Apitong

Gypsum board, use in wood-frame

construction to provide fire resistance,

17-5

Gypsum-bonded composites, 10-25

Hackberry:

characteristics, 1-6

color and figure, 3-3t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-6

machining and related properties, 3-

16t

moisture content, 3-6t

nomenclature, 5-5t

penetration, 14-16t

shock resistance, 1-6

shrinkage values, 3-9t

size of pores, 15-31t

strength properties, 4-4t, 4-9t

thermal conductivity, 3-19t

uses, 1-6

Hardness:

coefficient of variation 4-23t

definition, 4-3

Hardwood flooring, grading rules:

Maple Flooring Manufacturers

Association, 5-6, 5-4t

National Oak Flooring

Manufacturers Association, 5-6, 5-

4t

Hardwood lumber:

drying targets, 12-5

finished market products:

flooring:

grading rules, 5-6 to 5-7

standard dimensions, 5-6 to

5-7
I–13

types, 5-6

kiln drying schedules, 12-8 to 12-

9, 12-11t

grades, 5-2, 5-3t, 5-4fig

grading associations and rules, 5-2,

5-4t

minimum widths, 5-2

standard dimensions, 5-2

standard thicknesses, 5-6t

uses, 5-1

Hardwoods:

availability, 1-2, 1-3

bending properties, l9-3

charring rates, 17-11t

classification by size of pores, 15-

31t

color and figure, domestic, 3-3t

definition, 1-2

figure, 3-4

flame spread index, 17-3t

flammability data, 17-7t

heat release data, 17-9t

imported, 1-17 to 1-33

locality of growth, 1-2

moisture content, heartwood and

sapwood, 3-6t

preservative penetration, 14-16t

relationship of mechanical

properties to specific gravity, 4-28t

species by region, 1-3t

uses, 1-2

vessels, 2-3

Heartwood:

color, 2-2, 3-2

decay resistance in different species,

2-2, 3-18t

extractives content, 2-2

for shakes, 5-17

formation, 2-1

in visual stress grading, 6-5

moisture content and drying, 12-7

Heat capacity:

defined, 3-17

discussed, 3-17

of solid wood, 3-21t

Heat release rate:

and smoke release rate, 17-10

discussed, 17-7 to 17-8

Heavy-timber construction:

fire resistance of, 17-2, 17-4 to 17-5

wood used in, 17-2

Hemicellulose, 2-4

Hemlock:

availability at retail yards, 5-16

for siding, 5-17

Hemlock, eastern:

characteristics, 1-11

color and figure, 3-4t

dimensional change coefficient, 12-

17t

connector joint strength, 7-21t

locality of growth, 1-11

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shock resistance, 1-11

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

uses, 1-11

Hemlock, mountain:

characteristics, 1-12

locality of growth, 1-12

nomenclature, 5-13t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

toughness values, 4-25t

uses, 1-12

Hemlock, western:

characteristics, 1-12

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-21t

dimensional change coefficient, 12-

17t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

flame spread index, 17-3t

fracture toughness, 4-26t

locality of growth, 1-12

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t, 4-34t

nomenclature, 5-13t

penetration, 4-16t

plywood stiffness and strength, 10-

11t

Poisson ration, 4-3t

shock resistance, 1-12

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

tensile strength, 4-24t

thermal conductivity, 3-20t

toughness values, 4-25t

used for poles, 18-4t

uses, 1-12

Hickory:

color and figure, 3-3t

decay resistance, 3-18t

machining and related properties, 3-

16t

nomenclature, 5-5t

size of pores, 15-31t

Hickory, bitternut:

moisture content, 3-6t

strength properties, 4-5t, 4-10t

Hickory, mockernut:

moisture content, 3-6t

penetration, 14-16t

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

toughness values, 4-24t

Hickory, nutmeg, strength properties,

4-5t, 4-10t

Hickory, pecan:

characteristics, 1-6

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

for flooring, 5-6, 5-7

locality of growth, 1-6

shrinkage values, 3-9t

species, 1-6

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

uses, 1-6

Hickory, pignut:

moisture content, 3-6t

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

toughness values, 4-24t

Hickory, red, moisture content, 3-6t

Hickory, sand:

moisture content, 3-6t

toughness values, 4-24t

Hickory, shagbark:

characteristics for painting, 15-3t

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

Hickory, shellbark:

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

Hickory, water:

moisture content, 3-6t

strength properties, 4-5t, 4-10t

Hickory, true:

characteristics, 1-6

connector joint strength, 7-21t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-6

shrinkage values, 3-9t

species, 1-6

strength properties, 4-5t, 4-10t

uses, 1-6

Holly, nomenclature, 5-5t

Holly, American:

dimensional change coefficient, 12-

16t

shrinkage values, 3-9t

Honeylocust:

availability, 1-6

characteristics, 1-7

color and figure, 3-3t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-6

shock resistance, 1-7

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

uses, 1-7

Hot melt adhesives:

bonding, 9-9

structural performance, 9-11t

working and strength properties,

and uses, 9-13t to 9-14t

Hot-press bonding, affect on moisture

content, 9-15

Hot pressing:

oriented strandboard, 10-14

particleboard, 10-16 to 10-17
I–14

Hura:

characteristics, 1-21

characteristics affecting machining,

3-17t

locality of growth, 1-21

decay resistance, 3-18t

ease of bonding, 9-8t

machineability, 1-21 to 1-22

mechanical properties, 4-16t, 4-20t

resistance to fungi and insects, 1-22

shrinkage values, 3-10t

uses, 1-22

Hydroxymethylated resorcinol (HMR),

9-6

I-beams, 11-12 to 11-13

I-joists, 11-13 to 11-14

Identification of wood, 2-4

Ignition of wood:

piloted, 17-6

unpiloted, 17-6, 17-7

Ilomba:

characteristics, 1-22

locality of growth, 1-22

machineability, 1-22

mechanical properties, 4-17t, 4-21t

resistance to fungi and insects, 1-22

shrinkage values, 3-10t

uses, 1-22

Imbuia, shrinkage values, 3-10t

Imported woods, commercially

important, 1-17 to 1-34

Impact bending:

coefficient of variation, 4-23t

defined, 4-3

Impreg:

bulking agents, 19-5

dimensional stability, 19-9t

process, 19-5

properties, 19-6t

species, 19-5

strength properties, 19-7t to 19-8t

Incising:

and fire-retardant treatments, 17-13

effect on strength properties, 4-42

Incense-cedar. See Cedar, Incense

Inorganic boron (borax/boric acid):

acceptable compounds, 14-12

effectiveness, 14-12

solubility, 14-12

temperature for pressure treating,

14-21

uses, 14-12

Insect damage and control:

beetles, 13-8 to 13-10

carpenter ants,13-13

bees, 13-13

effect on strength, 4-45

naturally termite-resistant wood,

13-12 to 13-13

termites, 13-11 to 13-13

types of damage, 13-9t, 13-10fig

Insulation board, cellulosic fiber:

exterior products, 10-23

industrial products, 10-23

interior products, 10-23

properties, 10-22 to 10-23

Insulation for sound control for wood

buildings, 16-13, 16-13t

Insulation in wood building, 16-11 to

16-12

Intergrown knots, 2-3, 4-27

Interlocked grain:

definition, 3-4

effect on strength, 4-30

in Sweetgum, 1-8

machining, 3-15

Interior finishes, care during

construction, 12-19

Internal friction, 4-26

Ipe:

characteristics affecting machining,

3-17t

decay resistance, 3-18t

locality of growth, 1-22

machineability, 1-22

mechanical properties, 4-17t, 4-21t

resistance to decay and insects, 1-

22

shrinkage values, 3-10t

uses, 1-22

Ipil. See Merbau

Iroko:

characteristics, 1-22

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-22

mechanical properties, 4-17t, 4-21t

resistance to fungi and insects, 1-22

shrinkage values, 3-10t

species, 1-22

workability, 1-22

uses, 1-22

Iron stain, 13-3, 15-23, 15-29, 15-32

Ironwood, nomenclature, 5-5t

Isocyanate adhesives:

performance over time, 9-22

structural performance, 9-11t

use with composite products, 10-4

use with particleboard, 10-16

working and strength properties,

and uses, 9-14t

Jacaranda. See Rosewood, Brazilian

Jarrah:

characteristics, 1-22

characteristics affecting machining,

3-17t

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-22

machineability, 1-22

mechanical properties, 4-17t, 4-21t

resistance to decay and insects, 1-

22

marine borers, 13-14

shrinkage values, 3-10t

uses, 1-22 to 1-23

Jatoba. See Courbaril

Jelutong:

characteristics, 1-23

decay resistance, 3-18t

locality of growth, 1-23

mechanical properties, 4-17t, 4-21t

shrinkage values, 3-10t

uses, 1-23

workability, 1-23

Jequitiba. See Albarco

Joints, glued, strength, 9-4

Joists and light-frame construction,

16-2 to 16-3

Joists and rafter systems in light-frame

construction, 16-4

Juniper, decay resistance, 3-18t

Juvenile wood:

effect on mechanical properties, 4-

32

effect on strength properties, 4-32

properties, 4-32, 4-32fig

shrinkage of, 3-8, 4-32

Kakaralli. See Manbarklak

Kaneelhart:

characteristics, 1-23

ease of bonding, 9-8t

locality of growth, 1-23

mechanical properties, 4-17t, 4-21t

resistance to fungi and insects, 1-23

shrinkage values, 3-10t

uses, 1-23

Kapur:

characteristics, 1-23

characteristics affecting machining,

3-17t

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-23

machineability, 1-23

mechanical properties, 4-17t, 4-21t

plywood stiffness and strength, 10-

11t

resistance to fungi and insects, 1-23

shrinkage values, 3-10t

strength properties, 1-23

uses, 1-23

Karri:

characteristics, 1-23

characteristics affecting machining,

3-17t

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-23

machineability, 1-23

mechanical properties, 4-17t, 4-21t

shrinkage values, 3-10t

uses, 1-23

Kauta. See Marishballi

Kempas:

characteristics, 1-23

characteristics affecting machining,

3-17t

decay resistance, 3-18t

locality of growth, 1-23

machineability, 1-23
I–15

mechanical properties, 4-17t, 4-21t

resistance to fungi and insects, 1-23

shrinkage values, 3-10t

uses, 1-24

Keruing:

characteristics, 1-24

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

durability, 1-24

locality of growth, 1-24

machineability, 1-24

mechanical properties, 4-17t, 4-21t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-10t

uses, 1-24

Khaya (See Mahogany, African):

dimensional change coefficient, 12-

17t

Kiln drying:

advantages,12-6

importance of air circulation, 12-6

kiln schedules, 12-8 to 12-9, 12-

11t

types of kilns, 12-7 to 12-8, 12-8fig

Knots:

changes during drying, 12-10, 12-

12fig

definition, 4-27

discoloration through paint, 15-2,

15-29 to 15-30

effect on:

in determining strength ratios, 6-

5 to 6-6, 6-6fig

mechanical properties of wood,

4-27 to 4-28, 4-34

stiffness, 6-4

strength properties, 6-4

encased, 4-27, 6-4

in lumber stress grades, 6-4

intergrown, 4-27, 6-4

knotholes, 6-4

Kokrodua (See also Afrormosia):

characteristics affecting machining,

3-17t

dimensional change coefficient, 12-

17t

Korina. See Limba

Krabak. See Mersawa

Kraft paper, 19-12

Kwila. See Merbau

Lag screws. See Screws, lag

Laminated members, curved:

advantages, 19-2

species, choice of, 19-2

uses, 19-2

Laminated members, glued. See Glued

structural members

Laminated wood, strength properties,

19-7t to 19-8t

Laminates. See Paper-based plastic

laminates

Laminating grades, 5-8 to 5-9

Lapacho (See also Ipe):

ease of bonding, 9-8t

Lap marks, 15-20

Lapuna. See Ceiba

Larch, western:

characteristics, 1-12

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

elastic ratio, 4-2t

for flooring, 5-17

locality of growth, 1-12

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t, 4-34t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shock resistance, 1-12

strength properties, 4-7t, 4-12t

tensile strength, 4-24t

thermal conductivity, 3-20t

toughness values, 4-25t

used for poles, 18-2

uses, 1-12

Lateral buckling, of beams, 8-9 to 8-10

Lateral resistance:

and the National Design

Specification for Wood

Construction, 7-1

of lag screws, 7-12 to 7-14

of nails, 7-5

of wood screws, 7-10 to 7-11

Latewood:

description, 2-2

erosion of planed surfaces, 15-8t

paintability, 15-4

properties, 2-3

Lauans:

dimensional change coefficient, 12-

17t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-10t

size of pores, 15-31t

Lemonwood. See Degame

Light-frame construction:

balloon framing, 16-1

ceiling and roof, 16-4

decks, 16-4

exterior walls, 16-3 to 16-4

fire resistance of, 17-2, 17-5

floors, 16-2 to 16-3, 16-2fig

foundations, 16-2

platform framing, 16-1 to 16-2

use of elastomeric adhesives, 9-19

to 9-20, 9-20fig

wood use in, 17-2

Lignin:

discussion, 2-3 to 2-4

weathering, 15-7

Lignumvitae:

characteristics, 1-24

characteristics affecting machining,

3-17t

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-24

mechanical properties, 4-17t, 4-21t

species, 1-24

uses, 1-24

Lignocellulosic adhesives:

in composite products, 10-4

working and strength properties,

and uses, 9-13t

Limba:

characteristics, 1-24

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-24

machineability, 1-24

mechanical properties, 4-17t, 4-21t

resistance to decay and insects, 1-

24

shrinkage values, 3-10t

uses, 1-24

Limnoria, 13-14

Locust, black:

characteristics, 1-7

color and figure, 3-3t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-7

nomenclature, 5-5t

penetration, 14-16t

sapwood, 2-2

shock resistance, 1-7

shrinkage values, 3-9t

strength properties, 4-5t

uses, 1-1, 1-7

Lodgepole pine, used for poles, 18-2,

18-4t

Log homes, 16-6, 16-7fig, 18-5

Logs, control of mold, stain, decay, 13-

6

Longitudinal shrinkage of wood, 3-8

Lumber:

commonly used abbreviations, 5-18

to 5-20

development of grading rules, 5-7

grading organization, 5-9t, 5-12

hardwood:

drying targets, 12-5

finished market products:

flooring:

grading rules, 5-6 to 5-7

standard dimensions, 5-6

to 5-7

types, 5-6
I–16

kiln drying schedules, 12-8 to

12-9, 12-11t

grades, 5-2, 5-3t, 5-4fig

grading associations and rules,

5-2, 5-4t

minimum widths, 5-2

standard dimensions, 5-2

standard thicknesses, 5-6t

uses, 5-1

purchase:

distribution yards, 5-13

primary manufacturers

customers, 5-12 to 5-13

retail yard inventory:

availability of hardwood and

softwoods, 5-16

boards and yard lumber, 5-16

casing and base, 5-17

dimension and structural

lumber stocked, 5-16

finish boards, 5-17

flooring, 5-17

shingles and shakes, 5-17

siding, 5-17

purchase consideration, 5-17

to 5-18

softwood:

American Lumber Standards, 5-7

classification by grades:

factory and shop lumber:

factory (shop) grades, 5-10

industrial clears, 5-10

ladder and pole stock, 5-10

moulding stock, 5-10

pencil stock, 5-10

tank stock, 5-10

structural lumber:

dimension lumber, 5-8

structural laminations, 5-8

to 5-9

yard lumber:

select lumber, 5-7 to 5-8

common lumber, 5-8, 5-8fig

development of grading rules, 5-

7

drying targets, 12-5

grading organizations, 5-9t, 5-

12

kiln drying schedules, 12-8 to

12-9, 12-11t

manufacture:

size, 5-10 to 5-11, 5-11t

surfacing, 5-11 to 5-12

patterns, 5-12, 5-12fig

species, 5-12

transportation, 5-16

Macacauba. See Macawood

Macawood:

characteristics, 1-24

common names, 1-24

locality of growth, 1-24

mechanical properties, 4-17t, 4-21t

resistance to fungi and insects, 1-24

shrinkage values, 3-10t

uses, 1-24

workability, 1-24

Machine-graded structural lumber:

common grades, 6-7, 6-8t

components of system, 6-7

design stresses for other properties,

6-10

machine sorting criteria, 6-7 to 6-8

procedures for deriving allowable

stress for bending, 6-8 to 6-10

quality control, 6-10 to 6-11

Machining of wood, factors affecting,

3-15

Machinmango. See Manbarklak

Madrone, Pacific:

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

nomenclature, 5-5t

shrinkage values, 3-9t

Magnesia-cement-bonded composites,

10-25

Magnolia:

characteristics, 1-7

characteristics for painting,

southern, 15-3t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-7

machining and related properties, 3-

16t

moisture content, 3-6t

nomenclature, 5-5t

shock resistance, 1-7

shrinkage values, 3-9t

size of pores, 15-31t

species, 1-7

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

uses, 1-7

Mahogany:

color and figure, 3-3t

size of pores, 15-31t

species, 1-25

Mahogany, African:

characteristics, 1-25

characteristics affecting machining,

3-17t

dimensional change coefficients,

12-17t

decay resistance, 1-25, 3-18t

ease of bonding, 9-8t

elastic ratio, 4-2t

locality of growth, 1-25

machineability, 1-25

mechanical properties, 4-17t, 4-21t

Poisson ratio, 4-3t

shrinkage values, 3-10t

size of pores, 15-31t

species, 1-25

uses, 1-25

Mahogany, American (Swietenia,

mahagoni):

characteristics, 1-25

characteristics affecting machining,

3-17t

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-25

machineability, 1-25

mechanical properties, 4-17t, 4-21t

uses, 1-25

Mahogany, Honduras:

elastic ratio, 4-2t

Poisson ratio, 4-3t

Mahogany, Phillippine, availability at

retail yards, 5-16

Manbarklak:

characteristics, 1-25

characteristics affecting machining,

3-17t

locality of growth, 1-25

mechanical properties, 4-17t, 4-21t

nomenclature, 1-25

shrinkage values, 3-10t

resistance to fungi and insects, 1-25

marine borers, 13-14

uses, 1-25

workability, 1-25

Manni:

characteristics, 1-25

decay resistance 3-18t

locality of growth, 1-25

machineability, 1-25

mechanical properties, 4-17t, 4-21t

resistance to insects, 1-25

shrinkage values, 3-10t

uses, 1-25

Maple, size of pores, 15-31t

Maple, black:

color and figure, 3-3t

dimensional change coefficients,

12-16t

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

Maple, bigleaf:

color and figure, 3-3t

dimensional change coefficients,

12-16t

machining and related properties, 3-

16t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

Maple, hard:

characteristics, 1-7

charring rate data, 17-11t

connector joint strength, 7-21t

decay resistance, 3-18t

ease of bonding, 9-8t

heat release data, 17-9t

locality of growth, 1-7

machining and related properties, 3-

16t

nomenclature, 5-5t

shock resistance, 1-7

species, 1-7

uses, 1-7
I–17

Maple, Oregon, nomenclature, 5-5t

Maple, red:

color and figure, 3-3t

dimensional change coefficients,

12-16t

elastic ratio, 4-2t

Poisson ratio, 4-3t

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

Maple, silver:

color and figure, 3-3t

dimensional change coefficients,

12-16t

moisture content, 3-6t

penetration, 14-16t

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

Maple, soft:

connector joint strength, 7-21t

ease of bonding, 9-8t

locality of growth, 1-7

machining and related properties, 3-

16t

nomenclature, 5-5t

species, 1-7

uses, 1-7

Maple, sugar:

characteristics for painting, 15-3t

color and figure, 3-3t

dimensional change coefficients,

12-16t

elastic ratio, 4-2t

fracture toughness, 4-26t

moisture content, 3-6t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shrinkage values, 3-9t

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

toughness values, 4-24t

Maple flooring:

availability, 5-17

grading, 5-6

Maple Flooring Manufacturers,

Association, grading rules, 5-6

Marishballi:

characteristics, 1-26

characteristics affecting machining,

3-17t

locality of growth, 1-26

mechanical properties, 4-17t, 4-21t

resistance to fungi and insects, 1-26

shrinkage values, 3-10t

uses, 1-26

Marine borer damage and control, 13-

13

Malayapis. See Lauans

Mata-mata. See Manbarklak

Mayflower. See Roble

Mecanical interlocking and adhesives,

9-2

Mechanical properties of wood

adjusted for design use, 6-11 to 6-

14

affected by:

adhesion to metals, 9-5

age, 4-41

changes in moisture content, 4-

34

chemicals:

exposure to, 4-41

treatment, 4-41 to 4-43

cross grain, 4-29 to 4-30

decay, 4-43

duration of load, 4-39 to 4-40

fire-retardant treatments, 17-12

insect damage, 4-43

knots, 4-27

juvenile wood, 4-32

mold and stain fungi, 4-43

rate of loading, 4-37

slope of grain, 4-29t

temperature, 4-35 to 4-37

waterborne preservatives, 4-42

relation to specific gravity, 4-27, 4-

28t

relation to stress grades, 6-1

Medium-density fiberboard:

property requirement, 10-20, 10-21t

resins used, 10-4

standards, 10-5t

uses, 10-20

with veneer overlay, 10-23, 10-

23fig

Medium-density hardboard, finishes,

suitability and expected service life,

15-15t

Medium density overlays:

finishes, suitability and expected

service life, 15-15t

to improve paintability of plywood.

15-5

Melamine adhesives:

performance over time, 9-21 to 9-22

use with composite products, 10-4

working and strength properties,

and uses, 9-14t

Meranti:

characteristics, 1-26

characteristics affecting machining,

3-17t

color, 1-26t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-26

machineability, 1-26

mechanical properties, 4-19t, 4-23t

uses, 1-26

Merbau:

characteristics, 1-26

locality of growth, 1-26

machineability, 1-26

mechanical properties, 4-17t, 4-21t

resistance to insects, 1-26

shrinkage values, 3-10t

uses, 1-27

Mersawa:

characteristics, 1-27

characteristics affecting machining,

3-17t

decay resistance, 3-18t

locality of growth, 1-27

machineability, 1-27

mechanical properties, 4-17t, 4-21t

plywood stiffness and strength, 10-

11t

resistance to fungi and insects, 1-27

shrinkage values, 3-10t

uses, 1-27

Metal bonding, 9-6

Metal plate connectors, 7-25, 7-26fig

Mildew:

discoloration of wood, 15-8, 15-27,

15-27fig

removal, 15-27 to 15-28

Mill glaze, 15-25 to 15-26

Mill work, finishes, suitability and

expected service life, 15-15t

Modified woods:

formaldehyde-treated wood:

dimensional stability, 19-9t, 12-

12

mechanical properties, 19-11 to

19-12

resistance to fungi, 19-11

chemical modification:

antishrink efficiency

calculations, 19-11

conditions for, 19-11

chemicals used, 19-11

dimensional stability, 19-9t, 19-

11

mechanical properties, 19-11 to

19-12

cost, 19-5

dimensional stability, 19-9t

purposes, 19-4 to 19-5

resin-treated compressed wood

(Compreg):

advantages, 19-5

dimensional stability, 19-9t

molding, 19-5, 19-8

plasticizers, 19-5

properties, 19-5, 19-6t

species used, 19-9

strength properties, 19-7t to 19-

8t

thermal expansion coefficients,

19-9t

uses, 19-9

resin-treated wood (Impreg):

bulking agents, 19-5

dimensional stability, 19-9t

process, 19-5

properties, 19-6t

species used, 19-5

strength properties, 19-7t to 19-

8t

untreated compressed wood

(Staypak):

appearance, 19-10

dimensional stability, 19-9t
I–18

properties, 19-9 to 19-10, 19-6t

purpose, 19-9

strength properties, 19-7t, 19-8t

uses, 19-10

untreated heated wood

(Staybwood):

loss of mechanical and strength

properties, 19-10

purpose, 19-10

wood-polymer composites:

advantages, 19-10 to 19-11

changing characteristics, 19-10

to 19-11

monomers, 19-10 to 19-11

species used, 19-11

strength properties, 19-11t

uses, 19-11

wood treated with polyethylene

glycol (PEG):

dimensional stability, 19-9t

finishing, 19-10

process, 19-10

uses, 19-10

Modulus of elasticity:

and columns with flanges, 8-9

coefficient of variation, 4-23t

discussed, 4-3

effect of temperature, 4-36, 4-36fig,

4-38fig

of machine graded lumber, 6-7 to 6-

8

of sandwich panels, 11-18

of visually graded lumber, 6-6

values, 4-2t

Modulus of rigidity:

discussion, 4-3

ratios, 4-3t

Modulus of rupture:

and moisture content, 6-12, 6-12t,

6-12fig

coefficient of variation, 4-23t

defined, 4-3

effect of temperature, 4-36fig, 4-

38fig, 4-39fig

of beams, 8-5, 8-6

temperature effect, 4-36

Moisture blisters, 15-25

Moisture content:

adsorption/desorption curve, 3-8fig

adjustment for, 6-12

and decay, 13-4

and electrical resistance 3-22t

and heat capacity, 3-21t

changes in finished ponderosa pine

sapwood, 15-13fig

definition, 3-5, 15-9

determined by:

electrical method, 12-2 to 12-3

ovendrying method, 12-2, 12-

2eq

dimensional changes, 9-7 to 9-9

effect on bonded joints, 9-9

effect of strength properties, 4-34,

4-35fig

equilibrium:

discussion, 3-5

relative humidity as related to, 3-

7t

green wood, 3-6t

heartwood, 3-6t

in wood exposed outdoors, 15-10

range in trees, 3-5

recommended for:

exterior siding, 12-5t

flooring, 12-5t

furniture, 12-5t

interior woodwork, 12-5t

laminated members, 12-5, 12-5t

lumber, 12-3, 12-4t, 12-5t

plywood, 12-3, 12-5, 12-5t

sheathing, 12-5t

timbers, 12-3

trim, 12-5t

veneer, 12-3

sapwood, 3-6t

shrinkage as related to, 3-8 to 3-9,

3-21

shrinkage curves, 3-11fig

specific gravity, 3-5, 3-12fig

wood sinkage, 3-5

Moisture content of dried lumber:

air-dry, 12-11

kiln dry, 12-12

shipping dry, 12-10

Moisture content during transit and

storage:

finish and factory lumber, 12-15

general, 12-14, 12-14t

plywood and structural items, 12-

14

Moisture-gradient, typical in lumber,

12-6, 12-6fig

Molding resin-treated compressed

wood (Compreg), 19-5, 19-8

Molds:

appearance of, 13-2

distinction from stain, 13-2

effect on wood, 13-3

Moment capacity, 8-6, 8-6eq

Mora:

characteristics, 1-27

locality of growth, 1-27

mechanical properties, 4-17t, 4-21t

resistance to fungi and insects, 1-27

shrinkage values, 3-10t

uses, 1-27

workability, 1-27

Multiple-fastener joints, 7-24 to 7-25,

7-24eq

Nails:

lateral resistance of common wire

nails:

pre-1991:

equations, 7-5

lateral load coefficients, 7-6t

load-slip curve, 7-6, 7-6fig

post-1991:

direction of driving, effect of,

7-6

load-slip curves, 7-7, 7-7eq,

7-8eq, 7-8fig

moisture content, effect of, 7-7

seasoning, effect of, 7-7

shank form, effect of, 7-7

spacing, 7-6

yield model theory, 7-6, 7-

6eq, 7-7fig, 7-8t

sizes:

box nails, 7-2t

common, 7-2fig

helically and annularly threaded,

7-2, 7-2t

penny size, 7-2

wire nails, 7-2, 7-2t

toenailed joints, strength of, 7-5

withdrawal resistance:

affected by, 7-2, 7-3

allowable loads,7-5

clinched nails, 7-5

corrosion, 7-4

density of wood, effect of, 7-3

direction of driving, 7-4 to 7-5

etched nails, 7-4

load displacement curve, 7-3, 7-

3fig

moisture content, effect of, 7-3, 7-

3eq, 7-4

nail heads, 7-4

nail points, effect of, 7-4

plywood, 7-5

prebored lead holes, effect of, 7-5

seasoning, effect of, 7-3

shank form, effect of, 7-4

surface coatings, effect of, 7-3 to

7-4

surface coating, used for 7-4

Naphthenate, copper:

color transfer and changes, 14-8

effectiveness, 14-8

retention levels for various wood

products, 14-5t

solution values, 14-8

Southern pine sapwood stakes

retention and life span test results,

14-14t

treatment for cutting pretreated

wood, 14-24

Naphthenate, zinc:

effectiveness, 14-8

inappropriate uses, 14-8

properties, 14-8

National Grading Rule, 6-2, 6-3, 6-3t

National Fire Protection Association,

17-2, 17-6, 17-7

National Hardwood Lumber

Association, 5-2, 5-4t

National Oak, Flooring Manufacturers

Association, grading rules, 5-5 to 5-7

Nomenclature, 5-5t, 5-13t

Nuclear radiation:

discussion, 3-23

effect on wood strength, 4-43

Oak:

for casing and base, 5-17

size of pores, 15-31t

used in piles, 18-5
I–19

Oak, black:

strength properties, 4-5t, 4-10t

thermal conductivity

Oak, bur:

strength properties, 4-6t, 4-11t

thermal conductivity, 3-19t

Oak, California black, moisture

content, 3-6t

Oak, cherrybark, strength properties,

4-5t, 4-10t

Oak, chestnut, strength properties, 4-

6t, 4-11t

Oak, laurel, strength properties, 4-5t,

4-10t

Oak, live, strength properties, 4-6t, 4-

11t

Oak, northern red:

characteristics for painting, 15-3t

fracture toughness, 4-26t

strength properties, 4-5t, 4-10t

Oak, overcup:

strength properties, 4-6t, 4-11t

tensile strength, 4-24t

toughness values, 4-24t

Oak, pin:

strength properties, 4-5t, 4-10t

tensile strength, 4-24t

toughness values, 4-24t

Oak, post, strength properties, 4-6t, 4-

11t

Oak, red:

availability for purchase, 5-17

characteristics, 1-7, 1-8

charring rate data, 17-11t

color and figure, 3-3t

connector joint strength, 7-21t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

flame spread index, 17-3t

flammability data, 17-7t

heat release data, 17-9t

locality of growth, 1-7

machining and related properties, 3-

16t

mechanical properties, 4-17t, 4-21t

nomenclature, 5-5t

Poisson ratio, 4-3t

penetration, 14-16t

shrinkage values, 3-9t

species, 1-7

uses, 1-1, 1-8

Oak, scarlet:

strength properties, 4-5t, 4-10t

toughness values, 4-24t

Oak, southern red:

moisture content, 3-6t

strength properties, 4-5t, 4-10t

thermal conductivity, 3-19t

Oak, swamp chestnut, strength

properties, 4-6t, 4-11t

Oak, swamp white, strength

properties, 4-6t, 4-11t

Oak, tropical:

characteristics, 1-27

locality of growth, 1-27

resistance to fungi, 1-27

specific gravity, 1-27

uses, 1-27

Oak, water:

moisture content, 3-6t

strength properties, 4-5t, 4-10t

Oak, white:

characteristics, 1-8

characteristics for painting, 14-16t

charring rate equation, 17-10

color and figure, 3-3t

connector joint strength, 7-21t

decay resistance, 1-8, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

flame spread index, 17-3t

locality of growth, 1-7

machining and related properties, 3-

16t

nomenclature, 5-5t

Poisson ratio, 4-3t

penetration, 14-16t

shrinkage values, 3-9t

species, 1-8

strength properties, 4-6t, 4-11t

uses, 1-8

Oak, willow, moisture content, 3-6t

Oak flooring, 5-6

Obeche:

characteristics, 1-27

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-27

machineability, 1-27

mechanical properties, 4-17t, 4-21t

shrinkage values, 3-10t

uses, 1-27

Ofram. See Limba

Oilborne preservatives. See

preservatives, oilborne

Oil-type preservatives, strength loss,

4-41

Okoume:

characteristics, 1-27, 1-28

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-27

machineability, 1-28

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

uses, 1-28

Old house borer, 13-11

Opaque finishes, 15-30

Opepe:

characteristics, 1-28

ease of bonding, 9-8t

locality of growth, 1-28

machineability, 1-28

mechanical properties, 4-18t, 4-21t

resistance to decay and insects, 1-

28

shrinkage values, 3-10t

uses, 1-28

Ordinary construction:

code requirements for fire

protection, 17-2

description, 17-2

Oriented strandboard:

adhesive application or blending,

10-13

adhesives used, 10-4

certification, 10-14, 10-16fig

defined, 10-13

design capacities, 10-14

drying process, 10-13

finishes, suitability and expected

service life, 15-15t

hot pressing, 10-14

manufacturing process, 10-13, 10-

14fig

mat formation, 10-13

sheathing grade, property values,

10-15t

species used, 10-13

standards, 10-5 to 10-6, 10-5t, 10-8

stranding process, 10-13

Orthotropic nature of wood, 4-1

Osage-orange:

decay resistance, 3-17t

ease of bonding, 9-8t

nomenclature, 5-5t

Ossol. See Manni

Otie. See Ilomba

Ovangkol (See also Benge):

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

Ovendry weight, specific gravity, 3-12

Oxine copper:

composition, 14-8

corrosiveness, 14-8

retention levels for various wood

products, 14-5t

Southern pine sapwood stakes

retention and life span test results,

14-13t

toxicity, 14-8

Pacific yew, nomenclature, 5-13t

Paint:

adhesion bandage test, 15-23

application and maintenance, 15-

14t, 15-20 to 15-21

characteristics of wood, 15-3t

cost, 15-18 to 15-19

cracking, 15-11, 15-26

discussed, 15-18 to 15-19

disposal, 15-34

failure caused by:

dimensional changes in wood,

15-4
I–20

earlywood/latewood band, 15-4,

15-24

face checks in plywood, 15-5

grain orientation, 15-4

moisture content of wood, 15-10

temperature at time of painting,

15-21

texture of wood, 15-5

water soluble extractives, 15-28

to 15-29

weathering, 15-8, 15-24

failure in finger-jointed lumber, 15-

5

lead-based:

dust from, 15-36

health effects, 15-36

removal of, 15-36

use of, 15-35

mildew removal, 15-27 to 15-28

moisture blisters, 15-25

on treated wood, 15-6

on preweathered panels, 15-9

peeling:

avoiding with proper painting,

15-21

caused by water, 15-10

intercoat, 15-26

moisture movement, 15-25fig

protection against moisture, 15-11,

15-13, 15-16, 15-24

preweathering before painting, 15-9

repainting, 15-22 to 15-23, 15-33

removal, 15-33 to 15-34, 15-35

service life, 15-24

strippers:

chemical:

alkali-based, 15-35

solvent-based, 15-34

mechanical, 15-34

“safe”, 15-35

VOC regulation compliance, 15-19

Palosapis. See Mersawa

Panel products:

performance standards, 10-5 to 10-

6, 10-6fig

plywood, 10-6 to 10-13

product standards, 10-5, 10-5t

wood elements, 10-2fig

Paper-based plastic laminates:

decorative laminates:

process, 19-12 to 19-13

thicknesses, 19-12 to 19-13

uses, 19-12 to 19-13

industrial laminates:

cost advantage, 19-12

papreg, 19-12

resins used, 19-12

strength, 19-12, 19-7t to 19-8t

uses, 19-12

lignin-filled laminates:

strength properties, 19-13

resins used, 10-4

shrinking and swelling, 19-13

Paper-faced overlays:

manufacture, 19-13

types:

decoratives, 19-13

masking, 19-13

structural, 19-13

uses, 19-13

Papreg, 19-12

Para-Angelim (See also Sucupira):

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

Parana pine:

characteristics, 1-33

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-33

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

uses, 1-33

Parenchynia cells, function, 2-3

Particle and fiberboard, 10-13 to 10-

24

Particleboard:

adhesives, 10-4

certification, 10-17, 10-18fig

finishing, 10-17

hot pressing, 10-16 to 10-17

mat formation, 10-16

particle classifications and

conveying, 10-16

particle drying, 10-16

production, 10-14 to 10-15, 10-

15fig, 10-16

properties and grades, 10-17, 10-

17t, 10-18t

resins and wax, 10-4, 10-16

screw withdrawal, 7-10

standards, 10-5t

uses, 10-15

Pau marfim:

characteristics, 1-28

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-28

machineability, 1-28

mechanical properties, 4-22t

resistance to decay, 1-28

shrinkage values, 3-10t

specific gravity, 1-28

strength values, 1-28

uses, 1-28

Pecan (See also Hickory, pecan):

machining and related properties, 3-

16t

nomenclature, 5-5t

Pecky cypress, 1-10

Peeling logs for veneer, 10-7 to 10-8

Pentachlorophenal solutions:

and nonpressure treatments, 14-24

solution standards, 14-7

solution performance, 14-7

Pentachlorophenol:

approved uses, 14-7

effect on mechanical properties of

wood, 14-24

effectiveness, 14-8

EPA-approved consumer

information sheet, 14-3t

handling precautions, 14-3t, 14-8

ineffective against marine borers,

14-8

paintability, 14-7

retentions for various wood

products, 14-5t

use site precautions, 14-4t

Peroba, white. See Peroba de Campos

Peroba de Campos:

characteristics, 1-28

locality of growth, 1-28

machineability, 1-28

mechanical properties, 4-18t, 4-22t

resistance to decay, 1-28

shrinkage values, 3-10t

uses, 1-28

Peroba Rosa:

characteristics, 1-28

ease of bonding, 4-18t, 4-22t

locality of growth, 1-28

mechanical properties, 4-18t, 4-22t

resistance to fungi and insects, 1-28

shrinkage values, 3-10t

uses, 1-29

Persimmon:

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

nomenclature, 5-5t

shrinkage values, 3-9t

Phenolic adhesives:

performance over time, 9-22, 9-22fig

structural performance, 9-11t

use with composite products, 10-4

working and strength properties,

and uses, 9-14t

Phenolic resins:

for laminates, 19-12 to 19-13

in sandwich construction, 11-17

Pholads, 13-14

Photodegradation. See Weathering

Piles:

knots, effect on strength, 4-27 to 4-

28

marine, protection against insects,

13-14 to 13-15

preservative retention levels, 14-5t

to 14-6t

preservative treatments, 18-6

service life, 18-6

straightness, 18-4

standards and specifications, 18-2t,

18-3, 18-7

standards for end-bearing piles, 18-

4

for friction piles, 18-4

strength properties, 18-7

timber availability, 18-3

weight and volume, 18-5

Pilon:

characteristics, 1-29

locality of growth, 1-29

mechanical properties, 4-18t, 4-22t

resistance to insects, 1-20
I–21

uses, 1-29

workability, 1-29

Pine, Caribbean:

characteristics, 1-33

ease of bonding, 9-8t

locality of growth, 1-33

machineability, 1-33

mechanical properties, 4-18t, 4-22t

plywood stiffness and strength, 10-

11t

resistance to insects, 1-33

shrinkage values, 3-10t

uses, 1-33

Pine, eastern white:

characteristics, 1-12

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

flame spread index, 17-3t

locality of growth, 1-12

mechanical properties, 4-14t, 4-15t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shock resistance, 1-12

shrinkage values, 3-9t

tensile strength, 4-24t

thermal conductivity, 3-20t

toughness values, 4-25t

uses, 1-12

workability, 1-12

Pine, jack:

characteristics, 1-13

decay resistance, 13-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-12

mechanical properties, 4-14t, 4-15t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shock resistance, 1-13

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

toughness values, 4-25t

used for poles, 18-4t

uses, 1-13

Pine, loblolly:

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

moisture content, 3-6t, 4-34t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

tensile strength, 4-24t

thermal conductivity, 3-20t

toughness values, 4-25t

Pine, lodgepole:

characteristics, 1-13

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

elastic ratio, 4-2t

flame spread index, 17-3t

locality of growth, 1-13

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shock resistance, 1-13

shrinkage values, 1-13, 3-9t

strength properties, 4-7t, 4-21t

thermal conductivity, 3-20t

toughness values, 4-25t

used for poles, 18-2, 18-4t

workability, 1-13

uses, 1-13

Pine, longleaf:

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

elastic ratio, 4-2t

moisture content, 3-6t, 4-34t

nomenclature, 5-13t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shrinkage values, 3-9t

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

Pine, ocote:

characteristics, 1-33

locality of growth, 1-33

mechanical properties, 4-18t, 4-22t

plywood stiffness and strength, 10-

11t

resistance to fungi, 1-34

shrinkage values, 3-10t

strength properties, 1-33

uses, 1-33

Pine, pitch:

characteristics, 1-13

decay resistance, 3-18t

locality of growth, 1-13

nomenclature, 5-13t

plywood stiffness and strength, 10-

11t

shock resistance, 1-13

shrinkage values, 1-13, 3-9t

strength properties, 4-7t, 4-12t

thermal conductivity, 3-20t

uses, 1-13

Pine, pond:

characteristics, 1-13

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-13

elastic ratio, 4-2t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shock resistance, 1-13

shrinkage values, 1-13, 3-9t

strength properties, 4-8t, 4-13t

uses, 1-13

Pine, ponderosa:

characteristics, 1-13

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

flame spread index, 17-3t

for siding, 5-17

fracture toughness, 4-26t

Jeffrey, 1-13

locality of growth, 1-13

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

changes in finished sapwood

samples, 15-13fig

moisture-excluding effectiveness of

finishes on, 15-12t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

sapwood, 2-2

shock resistance, 1-13

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

tensile strength, 3-20t

thermal conductivity, 3-20t

toughness values, 4-25t

used for poles, 18-2, 18-4t

uses, 1-13

Pine, radiata:

characteristics, 1-34

ease of bonding, 9-8t

locality of growth, 1-34

machineability, 1-34

mechanical properties, 4-18t, 4-22t

uses, 1-34

Pine, red:

characteristics, 1-14

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

flame spread index, 17-3t

heat release index, 17-9t

locality of growth, 1-14
I–22

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t, 4-34t

penetration, 14-16t

preservative treatments to prevent

marine borer attacks on piles, 14-

10t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shock resistance, 1-14

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

thermal conductivity, 3-20t

toughness values, 4-25t

used for poles, 18-4t, 18-5

uses, 1-14

Pine, sand, strength properties, 4-8t,

4-13t

Pine, scots, fracture toughness, 4-26t

Pine, shortleaf:

color and figure, 3-4t

dimensional change coefficient, 12-

16t

elastic ratio, 4-2t

moisture content, 3-6t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

thermal conductivity, 3-20t

toughness values, 4-25t

Pine, slash:

color and figure, 3-4t

dimensional change coefficient, 12-

16t

decay resistance, 3-18t

elastic ratio, 4-2t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

thermal conductivity, 3-20t

toughness values, 4-25t

Pine, southern:

characteristics, 1-14

characteristics for painting, 15-3t

charring rate data, 17-11t

charring rate equation, 17-10

connector joint strength, 7-21t

decay resistance, 3-18t

ease of bonding, 9-7, 9-8t

erosion of planed surfaces, 15-8t

flame spread index, 17-3t

flammability data, 17-7t

for flooring, 5-17

fracture toughness, 4-26t

grading, 5-8

kiln drying schedule, 12-8, 12-11t

moisture content and property

values, 4-35t

nomenclature, 5-13t

plywood stiffness and strength, 10-

11t

preservative retention and life span

tests, 14-13t to 14-15t

preservative treatments to prevent

marine borer attacks on piles, 14-

10t

shock resistance, 1-14

shrinkage values, 1-14, 3-9t

species, 1-14

used for piles, 18-5

used for poles, 18-2, 18-4t, 18-5

uses, 1-14

Pine, spruce:

characteristics, 1-14

decay resistance, 3-18t

locality of growth, 1-14

plywood stiffness and strength, 10-

11t

strength properties, 4-8t, 4-13t

uses, 1-14

Pine, sugar:

characteristics, 1-14

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-12t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

locality of growth, 1-14

moisture content, 3-6t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shock resistance, 1-14

shrinkage values, 1-14, 3-9t

strength properties, 4-8t, 4-13t

thermal conductivity, 3-20t

uses, 1-14

workability, 1-14, 1-15

Pine, Virginia:

characteristics, 1-15

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-15

plywood stiffness and strength, 10-

11t

shock resistance, 1-15

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

tensile strength, 4-24t

toughness values, 4-25t

uses, 1-15

Pine, western white:

characteristics, 1-15

characteristics for painting, 15-3t

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

flame spread index, 17-3t

for siding, 5-17

fracture toughness, 4-26t

heat release data, 17-9t

locality of growth, 1-15

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

paintability rating, 15-4

Poisson ratio, 4-3t

shock resistance, 1-15

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

thermal conductivity, 3-20t

uses, 1-15

workability, 1-15

Pitch pockets:

description, 4-33

effect on strength, 4-33

in lumber stress grading, 6-5

species involved, 4-33

Pith, 2-1, 2-2fig

Piquia:

characteristics, 1-29

locality of growth, 1-29

machineability, 1-29

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

resistance to fungi and insects, 1-29

uses, 1-29

Plainsawn lumber:

advantages, 3-2t

color and figure:

hardwoods, 3-3t

softwoods, 3-4t

method of producing, 3-2

shrinkage, 3-11

Plasticizing adhesive polymers, 9-10

Plasticizing wood:

bent wood members, 19-2

bending operation and apparatus,

19-4

characteristics of bent wood, 19-4

chemicals used, 19-2

fixing the bend, 19-4

laminated members, 19-2 to 19-3

moisture content of bending stock,

19-3

principles of plasticizing and

bending, 19-1

resin-treated compressed wood, 19-

5

selection of stock, 19-3

steaming, 19-1

veneered curved members, 19-3

Plastering, care during construction,

12-19 to 12-20

Plastic bonding, 9-5

Plastic-coated nails, 7-4

Port-Orford Cedar, See Cedar, PortOrford

Plywood:

adhesives, 10-4, 10-8

advantages over solid wood, 10-7

assembly, 10-8

classification by:

exposure durability, 10-9

grades, 10-9 to 10-10, 10-10t

span rating, 10-10 to 10-11
I–23

strength and stiffness, 10-10 to

10-12, 10-11t

cores, 10-6

description, 10-6 to 10-7

dimensional stability, 10-12

and grain direction, 10-6

edge swelling, 10-12

erosion of planed surfaced, 15-8t

finishes, suitability and expected

service life, 15-15t

finishing, 15-5

fire-retardant treated, 17-12

grain, 10-6

HPVA grade stamp, 10-8, 10-9fig

in light-frame construction, 16-3

plies, 10-6

preservative retention levels, 14-5t

to 14-6t

product standard, 10-5 to 10-6, 10-

5t, 10-6fig, 10-7

protecting form decay, 13-8

shear strength, 10-12

sheathing-grade, property values,

10-12t

specialty panels, 10-13

specifications, 10-8 to 10-9

softwood logs, processing, 10-7

standards, 10-8

splitting resistance, 10-12

strength and stiffness, 10-11t, 10-

12

types:

construction and industrial, 10-

7

hardwood and decorative, 10-7

veneers, 10-7 to 10-8

weathering of, 15-16fig

Plywood curved members:

bent after gluing:

common hardwoods for, 19-3

procedure for, 19-2

bent and glued simultaneously:

advantages, 19-2 to 19-3

procedure for, 19-2

Poisson's ratio:

discussion, 4-2

values, 4-3t

Pole buildings, 16-4 to 16-6, 16-5fig,

16-6fig, 18-3

Poles:

availability, 18-2

characteristics relating to:

Douglas-fir, 18-2, 18-4t

glued-laminated, 18-3

jack pine, 18-4t

lodgepole pine, 18-2, 18-4t

ponderosa pine, 18-2, 18-4t

red pine, 18-4t, 18-5

southern pine, 18-2, 18-4t, 18-5

western hemlock, 18-4t

western larch, 18-2

western red cedar, 18-2, 18-4t,

18-6

control of mold, stain, and decay,

13-6

form and taper, 18-3 to 18-4

preservation and seasoning, 18-2

preservative treatment:

and sapwood, 18-4

retention levels, 14-5t to 14-6t

specifications, 18-6

service life, 18-6

species selection, 18-2

standards and specifications, 18-2t,

18-7

strength properties, 18-7

uses, 18-3fig

weight and volume, 18-5

Polymeric methylene diphenyl

diisocyanate (PMDI) adhesives, 9-10

Polymerization, effect on mechanical

properties, 4-43

Polymers, organic and synthetic, and

adhesion, 9-9 to 9-10

Polymers, analytic chemical and

mechanical testing, 9-20

Polyurethane bonding with wood and

nonwood composites, 9-5

Polyurethane adhesives:

performance over time, 9-22

structural performance, 9-11t

working and strength properties,

and uses, 9-14t

Polyvinyl adhesives:

structural performance, 9-11t

working and strength properties,

and uses, 9-13t to 9-14t

Porches:

cleaning before refinishing, 15-23

finishing, 15-21

pests, 13-13

Pores. See Vessels

Portland-cement-bonded composites,

10-25 to 10-26, 10-26t

Post-frame buildings, 16-4 to 16-6,

16-5fig, 16-6fig

Posts, preservative retention levels,

14-5t to 14-6t

Pre-drying, 12-6

Prefinished wood products, 15-24

Preservative penetration:

heartwood, 14-12, 14-16t, 14-21,

14-24

incising, effect of, 14-21

sapwood, 14-12, 14-21, 14-24

softwoods, 14-16t

Preservative-pressure-treated wood,

EPA-approved customer information

sheets, 14-3t to 14-4t

Preservative retention tests, pressuretreated, 14-13t to 14-15t

Preservatives:

copper-containing, control of

marine borers with, 13-15

finishing, 15-6

effect on mechanical properties, 14-

24

effect on paintability, 15-22

effect on strength of oil-type, 4-41

EPA regulations 14-1 to 14-2

inorganic arsenicals:

EPA-approved information

sheet, 14-3t

handling precautions, 14-3t

use site precautions, 14-4t

oilborne, various types:

alkyl ammonium compound:

effectiveness, 14-9

in ammoniacal copper quat,

14-11

solubility, 14-9

bis(tri-n-butyltin) oxide:

concentration values, 14-8

inappropriate uses, 14-8

paintability, 14-8

recommended uses, 14-8

toxicity, 14-8

chlorothalonil:

effectiveness, 14-8

solubility, 14-8

stability, 14-8

chlorothalonil/chlorpyrifos:

component rations, 14-8

effectiveness, 14-8

chlorpyrifos:

effectiveness, 14-9

in combination, 14-9

copper naphtehnate:

color transfer and changes, 14-

8

effectiveness, 14-8

retention levels for various

wood products, 14-5t

solution values, 14-8

Southern pine sapwood

stakes retention and life span

test results, 14-14t

treatment for cutting

pretreated wood, 14-24

creosote, coal-tar:

advantages, 14-2

appearance, 14-2

composition variability, 14-2

EPA-approved customer

information sheet, 14-3t

effect on mechanical

properties, 14-24

for non-pressure treatments,

14-7

handling precautions, 14-3t

in pressure treatment process,

14-19

odor and vapors, 14-2

retention levels for various

wood products, 14-5t

standards, 14-2

temperature for pressure

treating, 14-21

treatment for cutting

pretreated wood, 14-25

use site precautions, 14-3t

volatility, 14-7

creosote-coal-tar solutions:

properties, 14-7

retention levels for various

wood products, 14-5t

standards by volume, 14-7
I–24

temperature for pressure

treating, 4-21

creosote-petroleum oil

solutions:

retention levels for various

wood products, 14-5t

naphtalene:

Southern pine sapwood

stakes retention and life span

test results, 14-14t

oxine copper:

composition, 14-8

corrosiveness, 14-8

retention levels for various

wood products, 14-5t

Southern pine sapwood

stakes retention and life span

test results, 14-13t

toxicity, 14-8

pentachlorophenal solutions:

and nonpressure treatments,

14-24

solution standards, 14-7

solution performance, 14-7

pentachlorophenol:

approved uses, 14-7

effect on mechanical properties

of wood, 14-24

effectiveness, 14-8

EPA-approved consumer

information sheet, 14-3t

handling precautions, 14-3t,

14-8

ineffective against marine

borers, 14-8

paintability, 14-7

retention levels for various

wood products, 14-5t

Southern pine sapwood

stakes retention and life span

test results, 14-15t

use site precautions, 14-4t

propiconazole:

effectivenss, 14-9

solubility, 14-9

uses, 14-9

tebuconazole:

effectiveness, 14-9

solubility, 14-9

zinc naphthenate:

effectiveness, 14-8

inappropriate uses, 14-8

properties, 14-8

3-iodo-2-propynyl butyl

carbamate:

effectiveness, 14-8

paintability, 14-8

retail marketing, 14-8

use in combination, 14-9

uses, 14-8

4, 5-dichloro-2-N-octyl-4-

isothiazolin-3-one:

effectiveness, 14-9

inappropriate uses, 14-9

solubility, 14-9

waterborne, general:

and non-pressure treatment, 14-

24

application and maintenance of

exterior wood finish, 15-14t

effectiveness, 14-9 to 14-10

effect on mechanical properties,

4-41 to 4-43

effect on strength, 4-41 to 4-43

finishing, 15-6

for marine piles, 14-10

initial kiln-drying temperature,

4-42

paintability, 14-10

post-treatment kiln drying

temperatures, 4-42 to 4-43

retention levels effect of strength,

4-24

retention levels for various

wood products, 14-6t

retentions necessary for marine

borer protection, 14-10t

temperature considerations, 14-

10

waterborne, various types:

acid copper chromate (ACC):

components, 14-10

effectiveness and leaching, 14-

10

retention levels for various

wood products, 14-6t

Southern pine sapwood

stakes retention and life span

test results, 14-13t

temperature for pressure

treating, 14-21

ammoniacal copper citrate (CC):

retention levels for various

wood products, 14-6t

solution percentages, 14-12

temperature for pressure

treating, 14-21

ammoniacal copper quat (ACQ):

common types, 14-11

composition of common types,

14-11t

retention levels for various

wood products, 14-6t

uses, 14-11

ammoniacal copper zinc arsenate

(ACZA):

composition, 14-11

replacement for ACA, 14-11

retention levels for various

wood products, 14-6t

temperature for pressure

treating, 14-21

use, 14-10

use with Douglas-fir, 14-10 to

14-11

chromated copper arsenate

(CCA):

common types, 14-11

component substitutions, 14-

11

composition of common types,

14-11t

effectiveness of common types,

14-11

effect on adhesion, 9-6

finishing wood treated with,

15-22

resistance to marine borers,

14-11

retention levels for various

wood products, 14-6t

Southern pine sapwood

stakes retention and life span

test results, 14-13t

temperature for pressure

treating, 14-21

use with Douglas-fir, 14-11

copper azole - Type A (CBAType A):

retention levels for various

wood products, 14-6t

solution percentages, 14-12

temperature for pressure

treating, 14-21

copper

bis(dimethyldithiocarbamate)

(CDDC):

retention levels for various

wood products, 14-6t

solution percentages, 14-11

to 14-12

temperature for pressure

treating, 14-21

uses, 14-12

inorganic boron (borax/boric

acid):

acceptable compounds, 14-12

effectiveness, 14-12

solubility, 14-12

temperature for pressure

treating, 14-21

uses, 14-12

Preservatives, recommended

retentions, 14-21, 14-5t

Preservatives, water-repellant, and

non-pressure treatments:

effectiveness, 14-9

federal specifications, 14-9

uses, 14-9

Preservative-treated wood:

best management practices, 14-25

cut surfaces, protection of, 14-24 to

14-25

effect on adhesion, 9-6

finishing, 15-6, 15-25

handling, 14-24

inspection, 14-25, 14-26fig

quality assurance, 14-25 to 14-26,

14-26fig

seasoning required, 14-25

service life, 15-22

specifications, 14-25

strength as affected by

preservatives, 14-24

timing of use, 14-24

Preservative treatment for:

composite products, 1-24

light-frame construction 16-2
I–25

Preservative treatment, effect on

strength, 6-13

Preservative treatment, preparing for:

air-drying practices, 14-17 to 14-18

conditioning green lumber, 14-18

Boulton or boiling-undervacuum process, 14-18

steaming-and-vacuum process,

14-18

cutting and framing:

common uses, 14-19

potential size changes, 14-19

timing, 14-18

drying, 14-17 to 14-18

incising:

method, 14-18, 14-18fig

purpose, 14-18

primary species, 14-18

peeling, 14-17, 14-17fig

preventing decay while drying, 14-

18

Preservative treatments, nonpressure:

Boucherie process for green

unpeeled poles, 14-24

brushing:

application, 14-22

choice of preservative, 14-22

effectiveness, 14-22

penetration obtained, 14-22

cold-soaking process:

effectiveness, 14-22

method, 14-22

retentions and penetrations, 14-

22

compared to pressure treatment, 14-

21

diffusion processes:

butt or groundline treatment of

poles or posts, 14-23, 14-23fig

double diffusion, 14-22, 14-

22fig

wood used, 14-22

dipping:

effectiveness, 14-22

method, 14-22

penetration obtained, 14-22

steeping process:

effectiveness, 14-22

method, 14-22

wood used, 14-22

tire-tube method for green, unpeeled

fencepost, 14-24

vacuum processes:

contrasted to pressure treating,

14-24

effectiveness, 14-23

methods, 14-23 to 14-24

uses, 14-23

Preservative treatments, pressure:

advantages, 14-10

and preservative temperature, 14-21

empty-cell processes:

Lowry process, 14-20

Rueping process, 14-19 to 14-20

full-cell process:

description, 14-19

following other conditioning,

14-19

modified full-cell, 14-19

penetration and retention levels,

14-21

pressures used, 14-21

Primavera:

availability, 1-29

characteristics, 1-29

dimensional change coefficient, 12-

17t

locality of growth, 1-29

machineability, 1-29

mechanical properties, 4-18t, 4-22t

resistance to fungi, 1-29

shrinkage values, 3-10t

uses, 1-29

Propiconazole:

effectiveness, 14-9

solubility, 14-9

uses, 14-9

Purlins and glulam beam construction,

16-8

Purpleheart:

characteristics, 1-29

decay resistance, 9-8t

ease of bonding, 9-8t

locality of growth, 1-29

machineability, 1-29

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

uses, 1-29

Pycnanthus. See Ilomba

Quartersawn lumber:

advantages, 3-2t

color and figure:

hardwoods, 3-3t

softwoods, 3-4t

method of producing, 3-2

shrinkage, 3-11

Quality control in preservative-treated

wood, 14-25 to 14-26, 14-26fig

Rafters in light-frame construction 16-

4

Ramin:

characteristics, 1-29 to 1-30

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-29

mechanical properties, 4-18t, 4-22t

resistance to decay, 1-30

shrinkage values, 3-10t

uses, 1-30

workability, 1-30

Rays:

definition, 2-1

discussion, 2-3

effect on figure, 3-4

function, 2-1, 2-3

Reaction wood:

compression wood, 4-31

increase in density, 4-31

machining, 3-15

shrinkage, 3-8, 4-32

tension wood, 4-31

Redcedar, eastern. See Cedar, Eastern

red

Redcedar, western. See Cedar, Western

red

Redwood:

characteristics, 1-16

characteristics for painting, 15-3t

color and figure, 3-4t

charring rate date, 17-11t

connector joint strength, 7-21t

decay resistance, 1-16, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

flame spread index, 17-3t

flammability data, 17-7t

for finish board, 5-17

for siding, 5-17

heat release data, 17-9t

locality of growth, 1-16

moisture content, 3-6t, 4-34t

nomenclature, 5-13t

paintability rating, 15-4

penetration, 14-16t

plywood stiffness and strength, 10-

11t

preservative pressure and

temperature, 14-21

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

tensile strength, 4-24t

thermal conductivity, 3-20t

toughness values, 4-25t

uses, 1-16

workability, 1-16

Relative humidity:

equilibrium moisture content, 3-5

moisture content of wood, 3-7t, 15-

9 to 15-10

Remedial treatment, 13-8

Resorcinol adhesives:

performance over time, 9-21 to 9-22,

9-22fig

structural performance, 9-11t

working and strength properties,

and uses, 9-14t

Roble:

characterisitcs, 1-30

ease of bonding, 9-8t

locality of growth, 1-30

machineability, 1-30

mechanical properties, 4-18t, 4-22t

resistance to decay, 1-30

shrinkage values, 1-30

uses, 1-30

Rolling shear strength, defined, 4-24

Roof beams and water ponding, 8-9

Rosewood, ease of bonding, 9-8t

Rosewood, Brazilian:

characteristics, 1-30

locality of growth, 1-30
I–26

machineability, 1-30

mechanical properties, 4-18t, 4-22t

resistance to fungi and insects, 1-30

shrinkage values, 3-10t

uses, 1-30

Rosewood, Indian:

characteristics, 1-30

characteristics affecting machining,

3-17t

locality of growth, 1-30

machineability, 1-30

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

uses, 1-30

Round timber and ties:

availability, 18-2 to 18-3

durability, 18-6 to 18-7

efficient use, 18-1

form, 18-3 to 18-5

material requirements, 18-1

standards and specifications, 18-1,

18-2t

strength properties, 18-7 to 18-8

weight and volume, 18-5

Sande:

characteristics, 1-30

characteristics affecting machining,

3-17t

decay resistance, 3-18t

locality of growth, 1-30

machineability, 1-30

mechanical properties, 4-18t, 4-22t

resistance to decay and insects, 1-

30

shrinkage values, 3-10t

uses, 1-30

Sandwich panels:

advantage, 11-16

construction:

adhesives, 11-17

cores, 11-16 to 11-17, 11-17fig

core configurations, 11-17fig

description, 11-16, 11-16fig

manufacture, 11-17

resin treatment, 11-17

showthrough, 11-17

design:

bending stiffness, 11-18, 11-

18fig

bond strength, 11-19

buckling load, 11-18, 11-19, 11-

18eq, 11-19eq

core modulus, 11-18

deflection and beam loading, 11-

18, 11-18eq, 11-18t

dimpling of facings, 11-19, 11-

19eq, 11-19fig

facing stress, 11-19, 11-19fig

failure modes, 11-19, 11-19fig

minimum weight, 11-20, 11-

20fig

shear instability, 11-19

shear stiffness, 11-18, 11-18fig

wrinkling of facings, 11-19, 11-

19eq, 11-19fig, 11-20

dimensional stability:

bowing, 11-20

durability, 11-20

fire resistance, 11-21, 17-5

thermal insulation, 11-20 to 11-21

Santa Maria:

characteristics, 1-31

characteristics affecting machining,

3-17t

dimensional change coefficient, 12-

17t

locality of growth, 1-31

machineability, 1-31

mechanical properties, 4-18t, 4-22t

resistance to insects, 1-31

uses, 1-31

Sapele:

characteristics, 1-31

characteristics affecting machining,

3-17t

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-31

machineability, 1-31

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

uses, 1-31

Sap stain, 12-10, 12-13fig, 13-2

Sapwood:

color, 3-2

decay resistance, 2-2

function, 2-2

in visual stress grading, 6-5

location, 2-2

moisture content, 3-6t

moisture content and drying, 12-7

preservative retention and stake

lifespan, 14-13t to 14-15t

thickness, 2-2

Sassafras:

characteristics, 1-8

decay resistance, 1-8, 3-18t

dimensional change coefficient, 12-

16t

locality of growth, 1-8

nomenclature, 5-5t

shock resistance, 1-8

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

uses, l-8

Screws, lag:

description, 7-11

post-1991 lateral load, yield model

theory, 7-13 to 7-14, 7-6t, 7-13t,

pre-1991 lateral loads, 7-12 to 7-

13, 7-12eq, 7-12t, 7-13fig

lateral resistance, 7-12, 7-13, 7-13t

lubrication, 7-12, 7-13

prebored lead hole, size required, 7-

11, 7-12fig

spacing, 7-13

withdrawal resistance, 7-11 to 7-

12, 7-11eq

Screws, tapping:

described, 7-9

use in particleboard, 7-10

withdrawal loads, 7-10, 7-10eq

withdrawal resistance, 7-10

Screws, wood

gauges, 7-11t

lateral load coefficients, 7-6t

lateral resistance, 7-10 to 7-11, 7-

10eq

lead hole and load, 7-11

lubrication, 7-10

penetration depth and load, 7-11

sizes, 7-10t

types, 7-9, 7-9fig

withdrawal loads for particleboard,

7-10, 7-10eq

withdrawal resistance, 7-9 to 7-10,

7-10eq

yield model theory, 7-8t, 7-11

Seasoning and lumber purchasing

considerations, 5-18

Selangan Batu. See Balau

Select lumber availability, 5-16 to 5-

17

Sepetir:

characteristics, 1-31

decay resistance, 3-18t

locality of growth, 1-31

mechanical properties, 4-18t, 4-22t

shrinkage values, 3-10t

uses, 1-31

workability, 1-31

Seraya, white:

characteristics, 1-31

decay resistance, 3-18t

locality of growth, 1-31

machineability, 1-31

uses, 1-31

Shakes:

in glued structural members, 11-10

in lumber stress grading, 6-4 to 6-5

Shear deflection, of sandwich panels,

11-18

Shear stiffness:

of box and I beams, 11-12

of sandwich panels, 11-18

of stressed-skin panels, 11-14

Shear strength parallel to grain:

coefficient of variation, 4-23t

defined, 4-3,

Shear stress of beams, 8-6

Sheathing and light-frame

construction, 16-3, 16-4fig

Shingles and shakes, availability, 5-

17

Shingles, finishes, suitability and

expected service life, 15-15t

Shipworms, 13-13

Shrinkage:

adjustment for design use, 6-11

affect on painting, 15-4

coefficients for changing moisture

content by species, 12-16t, 12-17t

coefficient of variation, 3-8, 3-11

compression wood, 3-8

discussion, 3-7 to 3-11

fiber saturation point as related to,

3-8
I–27

longitudinal, 3-8

moisture content curves, 3-11fig

of domestic woods, 3-9

of imported woods, 3-9, 3-10

radial, 3-9, 3-10

reaction wood, 3-8

species, 3-9, 3-10

tangential, 3-9, 3-10

tension wood, 3-8

volumetric, 3-9, 3-10

Siding:

and mill glaze, 15-26

availability, 5-17

backpriming, 15-23

finishes, suitability and expected

service life, 15-15t

lumber finishing, 15-4, 15-13, 15-

20

prefinished at the factory, 15-24

removing weathered surface, 15-9

use of plywood, 15-5

Silverballi, brown, See Kaneelhart

Size factor:

for design use, 6-11 to 6-12

procedures for design use:

in-grade test, 6-11 to 6-12

small clear, 6-11

Skin stresses, stressed-skin panels,

11-14 to 11-15

Slash-grained lumber. See Flat-grained

Slope of grain:

determination, 4-29 to 4-30, 4-29eq

in visual sorting, 6-4

relationship to fiber orientation, 4-

30fig

types, 4-29 to 4-30

Smoke:

approaches for dealing with, 17-9

carbon monoxide, 17-10

defined, 17-9

release rate, 17-10

tests for determining yield, 17-9 to

17-10

toxicity, 17-10

Soft rot, 13-5

Softwood lumber:

American Lumber Standard, 5-7

classification by grades:

factory and shop lumber:

factory (shop) grades, 5-10

industrial clears, 5-10

ladder and pole stock, 5-10

moulding stock, 5-10

tank stock, 5-10

structural lumber:

dimension lumber, 5-8

structural laminations, 5-8 to

5-9

yard lumber:

select lumber, 5-7 to 5-8

common lumber, 5-8, 5-8fig

development of grading rules, 5-7

drying targets, 12-5

grading organizations, 5-9t, 5-12

kiln drying schedules, 12-8 to 12-

9, 12-11t

manufacture:

size, 5-10 to 5-11, 5-11t

surfacing, 5-11 to 5-12

patterns, 5-12, 5-12fig

species, 5-12

Softwoods:

availability, 1-2

bending properties, 19-3

charring rates, 17-11t

color and figure, 3-4t

definition, 1-2

flame spread index, 17-3t

flammability data, 17-7t

heat release data, 17-9t

imported, 1-33 to 1-34

moisture content, heartwood and

sapwood, 3-6t

preservative penetration, 14-16t

relationship of mechanical

properties to specific gravity, 4-28t

species by region, 1-2t

stained, 3-4fig

thermal conductivity, 3-20t

uses, 1-2

Sorption hysteresis, discussed, 3-7

Solvents and adhesion, 9-10

Sound, speed of, 4-25 to 4-26

Southern pine sapwood stakes,

preservative retention and life span

tests, 14-13t to 14-15t

Soybean adhesives:

structural performance, 9-11t

working and strength properties,

and uses, 9-13t

Spanish-cedar:

characteristics, 1-31

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

locality of growth, 1-31

mechanical properties, 4-19t, 4-23t

shrinkage values, 3-10t

uses, 1-32

workability, 1-32

Specific gravity:

and paintability of wood, 15-1, 15-

4

and weathering of wood, 15-7

coefficient of variation, 3-11, 4-23t

definition, 3-11

density as a function of, 3-13t, 3-

14t

influence on mechanical properties,

4-27, 4-28t

moisture content, 3-5, 3-12fig

of reaction wood, 4-31

workability of wood, 3-15

Speed of sound, 4-25 to 4-26

Sphaeroma, 13-14

Spikes, 7-8

Spiral grain, 4-29 to 4-30, 4-32fig

Splits:

in glued structural members, 11-10

in lumber stress grading, 6-4

Spruce, black:

color and figure, 3-4t

dimensional change coefficient, 12-

17t

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

thermal conductivity, 3-20t

Spruce, Eastern:

characteristics, 1-16

flame spread index, 17-3t

locality of growth, 1-16

nomenclature, 5-13t

species, 1-16

uses, 1-16

workability, 1-16

Spruce, Engelmann:

characteristics, 1-16

characteristics for painting, 15-3t

charring rate data, 17-11t

color and figure, 3-4t

connector joint strength, 7-21t

dimensional change coefficient, 12-

17t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

locality of growth, 1-16

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ration, 4-3t

shock resistance, 1-16

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

tensile strength, 4-24t

thermal conductivity, 3-20t

toughness values, 4-25t

uses, 1-16

Spruce, red:

color and figure, 3-4t

connector joint strength, 7-21t

dimensional change coefficient, 12-

17t

fracture toughness, 4-26t

mechanical properties, 4-14t, 4-15t

moisture content, 4-34t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

thermal conductivity, 3-20t

Spruce, Sitka:

characteristics, 1-16

color and figure, 3-4t

connector joint strength, 7-21t

dimensional change coefficient, 12-

17t

ease of bonding, 9-8t

elastic ratio, 4-2t
I–28

flame spread index, 17-3t

locality of growth, 1-16

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t, 4-34t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ration, 4-3t

shock resistance, 1-16

shrinkage values, 3-9t

strength properties, 1-16, 4-8t

tensile strength, 4-24t

thermal conductivity, 3-20t

uses, 1-16

Spruce, white:

color and figure, 3-4t

connector joint strength, 7-21t

dimensional change coefficient, 12-

17t

mechanical properties, 4-14t, 4-15t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

strength properties, 4-8t, 4-13t

thermal conductivity, 3-20t

Stability:

beams:

water ponding, 8-9, 8-9eq

lateral-torsion buckling, 8-9 to

8-10, 8-9eq, 8-10t

deck support, effect of, 8-10, 8-

10eq, 8-10fig

built-up and spaced columns, 8-9,

8-9eq

column flanges, 8-9, 8-9eq

long columns, 8-8, 8-8eq

interaction of buckling modes, 8-10

to 8-11, 8-10eq, 8-11eq

short columns, 8-8 to 8-9, 8-8eq, 8-

8fig

Stain:

penetrating:

use on exterior plywood, 15-5

semi-transparent:

application and maintenance, 15-

14t, 15-20

discussed, 15-17

refinishing, 15-23

solid color:

and mill glaze, 15-26

application and maintenance, 15-

14t, 15-20

discussed, 15-18

reconstituted wood products,

15-6

refinishing, 15-23

use on floors, 15-32

Stains. See also Discoloration

Stains, chemical, discussed 13-3

Stains, fungal:

blue, 15-29

discussed, 13-2

distinction from mold, 13-2

during drying, 12-10, 12-13fig

effect on wood, 13-3

Stains, iron, 15-23, 15-29, 15-32

Stake tests with preservatives,

pressure-treated, 14-13t to 14-15t

Standard lengths of lumber, 5-2

Standard lumber abbreviations,

Standard thicknesses of lumber:

for flooring, 5-5

table, 5-4

Standard widths of lumber, 5-4

Staples, 7-8 to 7-9

Starch adhesive, structural

performance, 9-11t

Staybwood, 19-10

Staypak:

appearance, 19-10

dimensional stability, 19-9t

properties, 19-6t, 19-9 to 19-10

purpose, 19-10

strength properties, 19-7t to 19-8t

uses, 19-10

Sticker stain during drying, 12-10, 12-

14fig

Stiffeners and glued members, 11-13

Stiffeners and glulam beam

construction, 16-8

Stiffeners, wood-plywood glued

structural members, 11-13

Stiffness, affected by knots, 6-4

Storage of lumber:

care in yards, 12-14 to 12-15, 13-7

green or partially seasoned, 12-14

storage shed temperature, 12-14t

Storing lumber:

finish and factory items, 12-15

sheathing and structural items, 12-

14

Strength and duration of load

adjustments, 6-13

Strength ratio:

definition, 6-3

equations, 6-5, 6-6fig

estimating, 6-5

ranges in visual grading, 6-6

Strength properties:

bird pecks, effect of, 4-33

compression failures, effect of, 4-33

creep, 4-37 to 4-39

dead trees, 4-33 to 4-34

derived for small clear wood, 6-5 to

6-6

duration of load, effect, 4-39 to 4-40

extractives, effect of, 4-33

fire-retardant treatments, 4-41

for commercially important woods,

4-3t to 4-8t

insect damage, effect of, 4-43

juvenile wood, 4-32

knots, effect of, 4-27 to 4-28, 4-34

moisture content as related to, 4-34

nuclear radiation, 4-43

pitch pockets, effect of, 4-33

rate of loading, 4-37

slope of grain, 4-28 to 4-30

treatment, effect of 6-13

Strength, related to slope, 4-30fig

Stress equations:

axial load:

tensile stress, 8-4, 8-4eq

short-block compressive stress,

8-4, 8-4eq

bending:

notches, slits and holes, effect 8-

6 to 8-7

size effect, 8-6, 8-6eq

straight beam stresses, 8-5

tapered beam stresses, 8-5 to 8-6,

8-5fig, 8-5eq, 8-6eq

time effects, 8-7

water ponding, 8-7

combined bending and axial load:

concentric load, 8-7, 8-7eq

eccentric load, 8-7, 8-7eq

torsion, 8-8, 8-8fig, 8-8eq

Stress-graded lumber, American

Standard lumber sizes, 5-5t

Stress grading:

American Lumber Standard

Committee (ALSC):

accredited rules-writing and

independent agencies, 6-2t

American Softwood Standard, 6-

2

National Grading Rule, 6-2, 6-3,

6-3t

American Society of Testing and

Materials (ASTM):

calculating clear wood

properties for visual stress

grades, 6-3

design properties, 6-1

strength ratio, 6-3

U.S. responsibility structure, 6-2,

6-2fig

Stress, relationship between constant

load and failure, 4-39 to 4-40, 4-39fig

Structural composite lumber (SCL) in

bridges, 16-10

Structural flakeboard and light-frame

construction, 16-3

Sucupira:

characteristics, 1-32

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-32

mechanical properties, 4-19t, 4-23t

resistance to fungi and insects, 1-32

shrinkage values, 3-10t

uses, 1-32

workability, 1-32

Sugarberry (See also Hackberry):

size of pores, 15-31t

Suradan. See Pilon

Sweetgum:

characteristics, 1-8

characteristics for painting, 15-3t

color and figure, 3-3t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t
I–29

flame spread index, 17-3t

interlocked grain, 1-8

locality of growth, 1-8

machining and related properties, 3-

16t

moisture content, 3-6t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shock resistance, 1-8

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

thermal conductivity, 3-19t

toughness values, 4-24t

uses, 1-8

Swelling, coefficient for changing

moisture content, by species, 12-16t to

12-17t

Sycamore:

characteristics for painting, 15-3t

color and figure, 3-3t

decay resistance, 3-18t

ease of bonding, 9-8t

machining and related properties, 3-

16t

nomenclature, 5-5t

size of pores, 15-31t

Sycamore, American:

characteristics, 1-8

connector joint strength, 7-21t

dimensional change coefficient, 12-

16t

locality of growth, 1-8

moisture content, 3-6t

penetration, 14-16t

shock resistance, 1-8

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

thermal conductivity, 3-19t

uses, 1-8

Tamarack:

characteristics, 1-16

characteristics for painting, 15-3t

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

17t

locality of growth, 1-16

mechanical properties, 4-14t, 4-15t

moisture content, 3-6t, 4-34t

nomenclature, 5-13t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

shrinkage values, 3-9t

strength properties, 4-8t, 4-13t

uses, 1-16, 1-17

Tangare. See Andiroba

Tanoak:

characteristics, 1-32

decay resistance, 3-18t

dimensional change coefficient,

12-16t

locality of growth, 1-8

machineability, 1-9

machining and related properties,

3-16t

nomenclature, 5-5t

plywood stiffness and strength,

10-11t

shrinkage values, 3-9t

strength properties, 1-9, 4-6t, 4-11t

uses, 1-9

Teak:

characteristics, 1-32

characteristics affecting machining,

3-17t

decay resistance, 3-18t

dimensional change coefficient,

12-17t

ease of bonding, 9-8t

locality of growth, 1-32

machinability, 1-32

mechanical properties, 4-19t, 4-23t

shrinkage values, 3-10t

uses, 1-32

Tebuconazole:

effectiveness, 14-9

solubility, 14-9

Temperature blisters, avoiding while

painting, 15-21

Temperature, effect on:

fatigue strength, 4-40 to 4-41

mechanical properties:

irreversible effects, 4-36 to 4-37,

4-38fig

reversible effects, 4-35 to 4-36,

4-36fig

properties, 6-14, 6-14t

relative humidity and moisture

content, 3-7t

Tensile strength, end-grain bonded

joints, 9-18 to 9-19

Tensile strength parallel to grain:

average values, 4-24

coefficient of variation, 4-23t

defined, 4-3

Tensile strength perpendicular to

grain, 4-3

Tension wood:

definition, 4-31

density increase, 4-31

description, 4-31

effect on strength, 4-31

machining, 3-15

shrinkage, 4-32

Texture of wood, 3-1 to 3-2

Texture, effect on paintability, 15-5

Termites:

damage caused by, 13-9t, 13-10fig

nonsubterranean, 13-12

subterranean, 13-11 to 13-12

termite-resistant wood, 13-12 to

13-13

Thermal, conductivity of wood:

definition, 3-15

determination, 3-17

factors affecting, 3-17

selected species, 3-19t to 3-20t

Thermal diffusivity of wood, 3-17

Thermal expansion, 3-21

Thermal properties of wood, 3-15

Thermoplastics and adhesion, 9-9 to

9-10

Ties:

availability, 18-3

preservative penetration levels, 14-

5t to 14-6t

service life, 18-6 to 18-7

sizes, 18-5

standards and specifications, 18-2t

strength properties, 18-8

weight and volume, 18-5

Timber:

inventory, 1-2

resources, 1-2

Timber bridges:

glulam, 16-10, 16-10fig

log stringer, 16-9

sawn lumber, 16-9

structural composite lumber, 16-10

Timber buildings:

arch structure, 16-8

dome, 16-8 to 16-9, 16-8fig

glulam beam, 16-8

mill-type construction:

fire resistance, 16-7

specifications, 16-7

timber frame houses, 16-6 to 16-7,

16-8fig

Timbers, recommended moisture

content, 12-3

Timber from dead trees, properties of,

4-33 to 4-34

Time, effect on strength:

creep, 4-37 to 4-39

duration of load, 4-39 to 4-40

Tornillo:

characteristics, 1-32

decay resistance, 3-18t

locality of growth, 1-32

mechanical properties, 4-19t, 4-23t

uses, 1-32

workability, 1-32

Torsion, strength, 4-24

Toughness:

average values, 4-24t, 4-25

coefficient of variation, 4-23t

defined, 4-24

Tracheids, description and function,

2-3

Transverse and volumetric shrinkage

of wood, 3-7 to 3-8

Trebol. See Macawood

Trim, exterior:

care during construction, 12-19

recommended moisture content,

12-5t

Trusses:

care during construction, 12-8 to

12-19

in light-frame construction, 16-4

in pole and post-frame construction,

16-6

Truss plates, 7-25, 7-26fig

Tupelo:

characteristics, 1-9
I–30

connector joint strength, 7-21t

locality of growth,

nomenclature, 5-5t

shock resistance, 1-9

species, 1-9

uses, 1-9

Tupelo, black:

color and figure, 3-3t

dimensional change coefficient, 12-

16t

machining and related properties, 3-

16t

moisture content, 3-6t

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

thermal conductivity, 3-19t

Tupelo, swamp, moisture content, 3-6t

Tupelo, water:

color and figure, 3-3t

dimensional change coefficient, 12-

16t

machining and related properties, 3-

16t

moisture content, 3-6t

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

thermal conductivity, 3-19t

Tupelo, white, color and figure, 3-3t

Urea and dimethylol urea for

plasticizing wood, 19-2

Urea adhesives:

performance over time, 9-21 to 9-22,

9-22fig

structural performance, 9-11t

use with composite products, 10-4

working and strength properties,

and uses, 9-14t

Van der Waal’s forces, 9-2

Varnish:

application and maintenance, 15-

14t

clear, 15-18

use on boats, 15-22

use on floors, 15-22

Veneer:

and adhesion, 9-4 to 9-5, 10-8

drying, 10-8

grading, 10-9, 10-10t

HPVA grade stamps, 10-8, 10-9fig

use with plywood, 10-7 to 10-8

Veneered curved members, 19-3

Ventilation and anobiids, 13-10

Vertical-grained lumber. See Edgegrained lumber

Vessel:

definition, 1-2

function, 2-3

texture, 3-1 to 3-2

Vibration properties, 4-25

Virola. See Banak

Visual grades in the National Grading

Rule, 6-3t

Visual grading:

deriving strength properties for

small clear wood, 6-5 to 6-6, 6-6fig

deriving modulus of elasticity for

small clear wood, 6-6, 6-7fig

in-grade procedures, 6-6 to 6-7

sorting criteria, 6-3 to 6-4

Visual sorting criteria in lumber stress

grading:

checks and splits, 6-4

decay, 6-5

density, 6-5

explanation, 6-3

heartwood and sapwood, 6-5

knots, 6-4

pitch pockets, 6-5

shakes, 6-4 to 6-5

slope of grain, 6-4

wane, 6-5

Waferboard, obsolescence, 10-5

Waika. See Manni

Walele. See Ilomba

Wallaba:

characteristics, 1-33

decay resistance, 3-18t

ease of bonding, 9-8t

locality of growth, 1-32 to 1-33

machinability, 1-33

mechanical properties, 4-19t, 4-23t

resistance to insects, 1-33

shrinkage values, 3-10t

uses, 1-33

Walnut, black:

availability at retail yards, 5-16

characteristics, 1-9

characteristics for painting, 15-3t

color and figure, 3-4t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

kiln drying schedule, 12-11t

locality of growth, 1-9

moisture content, 3-6t

nomenclature, 5-5t

Poisson ratio, 4-3t

shock resistance, 1-9

shrinkage values, 3-9t

size of pores, 15-31t

strength properties, 4-6t, 4-11t

uses, 1-1, 1-9

workability, 1-9

Wane in lumber stress grading, 6-5

Wapa. See Wallaba

Warp:

and finishing, 15-13

and weathering, 15-7

during drying, 12-7

Waterborne preservatives. See

Preservatives, waterborne

Waterponding, effect on bending

stress, 8-7

Water repellants (See also water

repellant preservative):

application and maintenance, 15-

14t, 15-20

discussed, 15-10

moisture-excluding coatings,

different from, 15-11

used as a finish, 15-18

Water-repellant preservatives:

application and maintenance, 15-

14t, 15-19 to 15-20

as a first step in finishing, 15-11,

15-20

backpriming, 15-23 to 15-24

caution in use, 15-18

effect of use on window sash and

frame, 15-17fig

on wood exposed to marine

environments, 15-22

paintability, 15-6, 15-16

refinishing, 15-23

used as a finish, 15-16

use on edges of reconstituted wood

products, 15-6

use on end grain, 15-13

Wax in composite products, 10-4

Weathering of wood:

effect on extractives, 15-6

effect on lignin, 15-7

effect on paint adhesion, 15-8 to

15-9

and mill glaze, 15-25

artist’s rendition of, 15-7fig

as a natural finish, 15-16

erosion rates for hardwoods and

softwoods, 15-8t

in marine environments, 15-22

of finishes, 15-9

process, 15-6

warp, 15-8

Web stresses, glued members, 11-13

Western redcedar, used for poles, 18-2,

18-4t, 18-6

White-cedar:

Atlantic. See Cedar, Atlantic white

Northern. See Cedar, Northern

white

White rot, 13-5

Willow, black:

characteristics, 1-9

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

locality of growth, 1-9

machining and related properties, 3-

16t

nomenclature, 5-5t

penetration, 14-16t

shock resistance, 1-9

shrinkage values, 3-9t

strength properties, 4-6t, 4-11t

toughness values, 4-24t

uses, 1-9

Withdrawal resistance:

of lag screws, 7-11 to 7-14

of nails, 7-2 to 7-5

of wood screws, 7-9 to 7-11
I–31

Wood buildings, consideration:

moisture control:

effect on heat flow, 16-12

mold, mildew, mites and health,

16-12

moisture control strategies, 16-

12 to 16-13

paint failure and appearance

problems, 16-12

structural failure, 16-12

sound control, 16-13, 16-13t

structural performance and

servicability, 16-10 to 16-11

thermal insulation and air

infiltration control, 16-11 to 16-12

Wood cells. See cells of wood

Wood cleaners and brighteners, 15-33

Wood Components Manufacturers

Association, 5-2, 5-4t

Wood fillers,15-30, 15-31

Wood identification, 2-4

Wood screws. See screws, wood

Work to maximum load in bending, 4-3

Working qualities of wood, 3-15

Yang. See Keruing

Yellow-cedar. See Cedar, yellow

Yellow-poplar:

characteristics, 1-9

characteristics for painting, 15-3t

charring rate data, 17-11t

color and figure, 3-4t

connector joint strength, 7-21t

decay resistance, 3-18t

dimensional change coefficient, 12-

16t

ease of bonding, 9-8t

elastic ratio, 4-2t

erosion of planed surfaces, 15-8t

flame spread index, 17-3t

fracture toughness, 4-26t

locality of growth, 1-9

machining and related properties, 3-

16t

moisture content, 3-6t

penetration, 14-16t

plywood stiffness and strength, 10-

11t

Poisson ratio, 4-3t

shock resistance, 1-9

shrinkage values, 3-9t

size of pores, 15-31t

strength properties, 4-6t, 4-11t

thermal conductivity, 3-19t

toughness values, 4-24t

uses, 1-9

Zinc-coated nails, 7-4,

Zinc naphthenate:

effectiveness, 14-8

inappropriate uses, 14-8

properties, 14-8