"^W^

Handbook No. 72

U. S. DEPARTMENT OF AGRICULTURE

Forest Products Laboratory Forest Service
^0Mdll>^

Basic Information on Wood

as a Material of Construction

with Data for Its Use in

Design and Specification

Prepared by

The Forest Products Laboratory

Forest Service

U. S. Department of Agriculture

AGRICULTURE HANDBOOK NO. 72

(Supersedes an unnumbered publication of the

same title and a later slightly revised edition)

For sale by the Superintendent of Documents

Washington 25, D. C.

1955

U. S. Government Printing Office

Price $2.00 (paper cover)
PREFACE

FORESTS, distinct from all their other services and benefits,

supply a basic raw material—wood—which from the

earliest times has furnished mankind with necessities of

existence and with comforts and conveniences beyond

number. To return maximum values, however, forests

must not only be maintained in vigorous condition for the

continuous production of timber crops but must be fully

and profitably utilized.

As an aid to better and more efficient use of wood as a

material of construction, this handbook was prepared by

the Poorest Products Laboratory, a unit of the research

organization of the Forest Service, U. S. Department of

Agriculture. The Laboratory, which w^as established in

1910, is maintained at Madison, Wis., in cooperation with

the L^niversity of Wisconsin. It was the first and for

several years the only institution in the world conducting

general research on wood and its utilization. The vast

accumulation of information that has resulted from its

engineering and allied investigations of wood and wood

products during the past 40 years is the chief basis for this

handbook.
CONTENTS

Page

Structure of wood _ ]

Bark, wood, and pith 1

Growth rings 2

Springwood and summerwood 3

Sapwood and heartwood __ 4

Wood cells 4

Hardwoods and softwoods 5

Chemical composition of wood 5

Characteristics of some important coiumorcial woods ,ü;rc)wn in the United

States 7

Hardwoods 9

Softwoods 23

Literature cited 35

Physical properties of wood 37

Decorative features of common woods 37

Identification of wood 37

Grain and texture of wood 40

Plainsaw^ed and quartersaw^ed lurnbiT 41

Weathering of wood 42

Decay resistance of heartwood of native sjx'cies 44

Thermal conductivity of wood 46

Thermal expansion of wood 47

Electrical properties of wood 48

Effect of chemicals on wood 52

Weight of various woods 54

Working qualities of wood 62

Literature cited 63

Strength values of clear wood and related factors 67

Strength values _ . 67

Elastic properties of wood 78

Compression perpendicular to grain 78

Compressive strength on surfaces inclined to tlie grain _ 80

Shear parallel to grain 81

Tension parallel to grain -_ 81

Torsional properties 81

Toughness 82

Fatigue resistance 82

Variability in strength — . 83

Moisture content and strength 85

Specific gravity and strength 88

Temperature and strength -_ 89

Duration of stress -^ 93

Strength-reducing factors 93

Value of timber from live aiul from dearl tn^es 101

Resin 102

Turpentining 102

Extractives 102

Literature cited 103

Grades and sizes of lumber 105

Agencies promulgating grading rules 105

Hardwood lumber grading 106

Softwood lumber grading HI

Standard lumber patterns 126

Lumber items usually carried in retail yards _ - 126

Grade-marked lumber and moisture content provisions, 130

Points to consider when ordering softwood ]uml)er or timber 131

Standard lumber abbreviations ^31

Literature cited 135

JIT
IV CONTENTS

Page

Stress grades and working stresses j^^

Factors influencing strength f^/i

Principles of stress grading j^V

Use classes of structural lumber ^j^

General requirements for stress grades j|z

Optional requirements for stress grades |4»

Values of strength ratios j'*^

Recommended basic stress values ^^^

Adjustment of working stresses |^^

Manufacturers' standard grades |^^

Literature cited |^^

Timber fastenings ;^2

Nails : IS^

Spikes 174

Drift bolts \i^^

Wood screws |^^

Lag screws ]l^

Bolts 1^2

Timber-connector joints 187

Literature cited 201

Sohd and built-up structural members 203

Solid beams of rectangular cross section 203

Solid beams of circular section and of square section with a diagonal

vertical 210

Built-up beams with mechanical fastenings 211

Lateral support of beams ._ 215

Solid wood columns of rectangular cross section 216

Built-up columns with mechanical fastenings 220

Columns of circular cross section - 226

Built-up wood arches with mechanical fastenings 226

Lamella roofs 227

Tension members 229

Pole framing 229

Literature cited 230

Gluing of wood 233

Gluing properties of dififercnt woods 233

Glues used in woodworking 233

Glues for bonding wood to metal 235

Drying and conditioning wood for gluing 235

Machining lumber for gluing 238

Preparing veneer for gluing 239

Proper gluing conditions 239

Types of glued joints 240

Conditioning glued joints 241

Durability of glued members 244

Literature cited 245

Glued structural members 247

General characteristics of glued laminated construction 247

vStrength of glued laminated members 25U

Design of glued laminated members 258

Design of wood-plywood beams and girders 263

Literature cited 273

Plywood and other crossbanded products 275

Arrangement of plies 275

Quality of plies 277

Grades and types of ph^wood 277

Determination of strength of plywood 279

Splitting resistance 285

Shrinkage of plywood 286

Hollow-core construction 288

Literature cited 289

Structural sandwich construction 291

Fabrication of sandwich panels 292

Structural design of sandwich construction 293

Dimensional stability and bowing of sandwich panels 295

,M
CONTENTS V

Structural sandwich construction—Continued Page

Thermal insulation of sandwich panels 295

Fire resistance of sandwich panels 297

Literature cited 297

Bent wood members i 299

Steam bending of solid pieces 299

Steam bending of laminated members 303

Production of bent laminated members without steam treatment 303

Veneered curved members 304

Plywood curved members 304

Literature cited 308

Control of moisture content and shrinkage of wood 311

Equihbrium moisture content 311

Shrinkage of wood 311

Determination of moisture content 320

Seasoning of lumber 321

Storage of lumber at yards 325

Recommended moisture content 326

Design factors affecting shrinkage in the structure 329

Care of lumber and finish during construction 334

Literature cited 336

Fire resistance of wood construction 337

Improvement of fire resistance of wood construction through design. 337

Fire-retardant treatments for wood 346

Literature cited 349

Painting and finishing wood 351

Painting characteristics of woods 353

Choice of paints for exterior woodwork 360

Application of paint 365

Repainting 367

Abnormal paint wear 369

Back priming 371

Natural finish for exterior woodwork 373

Uncoated exterior woodwork 374

Interior finishing 374

Effectiveness of moisture-excluding coatings suitable f(jr interior use_ 377

Literature cited 377

Protection from wood-destroying organisms 381

Molds and stains 381

Decay 382

Control of molds, stains, and decay 383

Insects 386

Marine borers 393

Literature cited 397

Wood preservation 399

Wood preservatives 399

Preservative effectiveness 409

Preparing timber for treatment 409

Apphñng preservatives 411

Pressure processes 412

Treating conditions and specifications 415

Handling and seasoning of timVjcr after t reatment 418

Inspection 419

Effect of treatment on strength 420

Nonpressure processes 421

Literature cited 427

Poles, piling, and ties 429

Principal species used for poles 429

Weight of species used for poles 430

Volume of poles and piles 431

Engineering design of poles 431

Preservative treatment of poles 435

Treatment to stop decay in standing poles 436

Life of poles 436

Choice of species for piling 437

Bearing loads for piles 437
VI CONTENTS

Poles, piling, and ties—Continued Page

Eccentric loading and crooked columns 438

Driving of f)iles as affected by seasoning 438

Decay resistance and preservative treatment.of piling 438

Strength and other requirements for ties 439

Decav resistance and j^reservative treatment of ties 440

Life ¿f ties 441

Relation between percentage tie renewals and average life 441

Literature cited 443

Thermal insulat ion 445

Lisulating materials 445

Methofls of heat transfer 447

Heat loss t hrough different types of walls 449

Heat loss through different ty])es (^f doors and wind(nvs 452

Where to insulate ' 452

Literature citerl 454

Building fil^erl)oards 457

Classification of building fiber!:)oarfls 457

Semirigid insulation boards 458

Rigid insulation boards 458

Intermediate-density fibrous boards 462

Intermediate-density resin-bonded ])article boards 463

Fii)rous hardboards 463

Resiu-l)onded particle hardboards 464

Special densified liardboards 464

Literature citefl 465

Modified woods and pa])er-l)as(' laminates 467

Modified woods 467

Paper-!)asr' laminates 473

Literature cited __ 477

Glossarv 479

Index ___ 491
S'r

STRUCTURE OF WOOD

BARK, WOOD, AND PITH

A cross section of a tree shows the following- well-defined features

in succession from the outside to the center: (1) Bark (fig. 1), which

may be divided into (a) the outer, corky, dead part that varies greatly

in thickness with different species and'with age of trees, and (b) the

thin, inner, living part; (2) wood, which in merchantable trees of

M 83620. F

FIGURE 1.—The tree trunk: A, Cambium layer (microscopic) is inside of inner

bark and forms wood and barli cells. B, Inner bark i.s moist and soft. Carries

prepared food from leaves to all growing parts of tree. C, Outer bark or corky

layer is composed of dry dead tissue. Gives general protection against external

injuries. D, Sapwood is the light-coloiod wood beneath the bark. Carries

sap from roots to leaves. E, Hcartwood (inactive) is formed by a gradual

change in the sapwood. Gives the tree strength. F, Pith is the soft tissue

about which the first wood growth takes place in the newly formed twigs.

G, Wood rays connect the various layers from pith to bark for storage and

transference of food.
2 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

most species is clearly differentiated into sapwood and heartwood;

and (3) the pith, indicated by a small -entrai core, darker m color,

which represents primary growth formed when woody stems or

branches elongate. Pith is not separated from the wood m rough

lumber and timbers, but it is excluded from finished surfaces.

Most branches originate at the pith, and their bases are mtergrown

with the wood of the trunk as long as they are ahve. These hving

branch bases constitute intergrown knots. After the branches die,

their bases continue to be surrounded by the wood of the growmg

trunk Such enclosed portions of dead branches constitute the loose

or encased knots. After the dead branches drop off, the dead stubs

become overgrown, and, subsequently, :dear wood is formed. In a

tree, the part containing intergrown knots comprises a cyhnder,

extending the entire length of the tree; the part containing loose knots

forms a hollow cylinder, extending from the ground to the base of the

green crown. Clear wood constitutes an outer cylinder covering

overgrown branch ends. In second-growth trees, the clear zone and

even^the zone of loose knots may be absent.

GROWTH Rmcs

Between the bark and the wood is a layer of thin-walled living cells,

invisible without a microscope, called the cambium, in which all

growth in thickness of bark and wood arises by cell division. No

growth in either diameter or length takes place in wood already formed ;

new growth is purely the addition of new cells, not the further development of old ones. New wood cells are formed on the inside and new

bark cells on the outside of the cambium. As the diameter of the

woody trunk increases, the bark is pushed outward, and the outer

bark layers become stretched, cracked, and ridged in patterns often

characteristic of a species.

With many species in temperate climates, there is suflficient difference between the wood formed early and that formed late in a growing

season to produce well-marked annual growth rings. 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 (fig. 2). If the growth of

trees in diameter is interrupted by drought or defoliation by insects,

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 lost most of their foliage accidentally may form

only an incomplete growth layer, sometimes called a discontinuous

ring, until the crown is restored.

Growth rings are most readily seen in such native ring-porous

hardwood species as ash and oak,^and among softwoods in the several

species belonging to the yellow pine group owing to the sharp contrast

between spring\vood and summerwood in these species. In some

other species, such as water túpelo, sweetgum, and soft maple,

differentiation of early and late growth is slight, and the annual growth

rings are difl&cult to recognize. In some tropical regions, growth

may be practically continuous throughout the year, and no well-defined

annual rings are formed.
WOOD HANDBOOK

M 10712 F

FIGURE 2.—Cross section of a los showing annual growth rings. Each light

ring is springwood. PJach dark ring is summerwood.

SPRINGWOOD AND SUMMERWOOD

The inner part of the growth ring formed first in the growing season

is called spring-wood or earl3^ wood, and the outer part formed later

in the growing season, smnmerwood or late wood. Actual time of

formation of these two parts of a ring may vary with environmental

and weather conditions. Hpringwood is characterized by cells having

relatively large cavities and thin walls. Siunmerwood cells have

smaller cavities and thicker walls. The transition from springwood to

summerwood may be gradual or abrupt, depending on the kind of

wood and the growing conditions at the time it was formed. In some

species, such as the maples, gums, and yellow-poplar, there is little

difference in the appearance of the inner and outer parts of a growth

ring.

When growth rings are prominent, as in the southern yellow pines

and ring-porous hardwoods, spring^vood differs markedly from summerwood in physical properties. Springwood is lighter in weight,

softer, and weaker than summerwood; it shrinks less across and more
4 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

lengthwise along the grain of the wood. Because of the greater

density of summerwood, the proportion of summerwood is sometimes

used to judge the quality or strength of wood. This method is useful

with such species as the southern yellow pines, Douglas-fir, and the

ring-porous hardwoods, ash, hickory, and oak.

SAPWOOD AND HEARTWOOD

Sapwood contains living cells and has an active part in the life

processes of the tree. It is located next to the cambium and functions

in sap conduction and storage of food.

The sapwood layer may vary in thickness and in the number of

growth rings contained in it. Sapwood commonly ranges from 1}^

to 2 inches in radial thickness. In certain species, such as chestnut

and black locust, the sapwood contains very few growth rings and

sometimes does not exceed one-half inch in thickness. The maples,

hickories, ashes, some of the southern 3^ellow pines, and ponderosa

pine mav have sapwood 3 to 6 inches or more in thickness, especially in

second-growth trees. As a rule, the more vigorously growing trees of

a species have wider sapwood layers. Many second-growth trees of

merchantable size consist mostly of sapwood.

Heartwood consists of inactive cells formed by changes in the living

cells of the inner sapwood rings, presumably after their use for sap

conduction and other life processes of the tree have largely ceased.

The cavities of heartwood also may contain deposits of various

materials that frequently give much darker color to the heartwood.

All heartwood, however, is not dark colored. Species in which heartwood does not darken to a great extent include the spruces (except

Sitka spruce), hemlock, true firs, Port-Orford-cedar, basswood,

cottonwood, and buckeye. In some species, such as the ashes,

hickories, and certain oaks, the pores become plugged to a greater or

lesser degree with ingrowths, known as tyloses, before the change to

heartwood is completed.

Heartwood having pores tightly plugged by tyloses, as in white oak,

supplies lumber suitable for tight cooperage. The infiltrations or

materials deposited in the cells of heartwood usually make lumber cut

from it more durable when used in exposed situations than that from

sapwood. Unless treated, all sapwood is nondurable when exposed to

weather.

There is no consistent difference between sapwood and heartwood

in weight when dry and in strength. These properties are influenced

more by growth conditions of the trees at the time the wood is formed

than they are by the change from sapwood to heartwood. In some

instances, as in redwood, western redcedar, and black locust, considerable amounts of infiltrated material may somewhat increase the

weight of the wood and its resistance to crushing.

WOOD CELLS

Wood cells that make up the structural elements of wood are of

various sizes and shapes and are quite firmly grown together. Dry

wood cells may be empty or partly fiUed with deposits, such as gums

and resins, or with tyloses. Many cells are considerably elongated
WOOD HANDBOOK 5

and pointed at the ends; they are customarily^ called fibers or tracheids.

The length of wood fibers is highly variable within a tree and among

species. Hardwood fibers average about one twenty-fifth of an inch

in length; softwood fibers range from one-eighth to one-third of an

inch in length.

In addition to their fibers, hardwoods have cells of relatively large

diameter known as vessels. These form the main arteries in the

movement of sap. Softwoods do not contain special vessels for conducting sap longitudinally in the tree; this function is performed by

the tracheids.

Both hardwoods and softwoods have cells that are oriented horizontally in the direction from the pith toward the bark. These cells

conduct sap radiall}^ across the grain and are called rays or wood rays.

The rays are most easily seen on quartersawed surfaces. 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.

Wood also has other cells, known as wood parenchyma cells, that

function mamly for the storage of food.

HARDWOODS AND SOFTWOODS

Native species of trees are divided into two classes—hardwoods,

which have broad leaves, and softwoods or conifers, which have

scalelike leaves, as the cedars, or needlelike leaves, as the pines.

Hardwoods, except in the warmest regions, are deciduous and shed

their leaves at the end of each growing season. Native softwoods,

except cypress, tamarack, and larch, are evergreen. Softwoods are

known also as conifers, because all native species of softwoods bear

cones of one kind or another.

The terms ^^lardwood'^ and ^^softwood^' have no direct application

to the hardness or softness of the wood. In fact, such hardwood trees

as cottonwood and aspen have softer wood than the white pines and

true firs, and certain softwoods, such as longleaf pine and Douglas-fir,

produce wood that is as hard as that of basswood and yellow-poplar.

CHEMICAL COMPOSITION OF WOOD

The four major components of wood are extractives, ash-forming

minerals, lignin, and cellulose. The extractives are not part of the

wood structure, but they contribute to the wood such properties as

color, odor, taste, and resistance to decay. They include tannins,

starch, coloring matter, oils, resins, fats, and waxes, and can be

removed from the wood by neutral solvents, such as water, alcohol,

acetone, benzene, and ether.

Ash-forming minerals, lignin, and cellulose make up the wood

structure. Due to their uniform distribution throughout the wood

structure, any one of these three components when isolated retains

the microstructural pattern of the wood.

Cellulose, the most abundant constituent, comprises about 70 percent of wood. It may be subdivided into alpha-cellulose and hemicelluloses. Alpha-cellulose is the main basis of the useful products,

such as paper, explosives, synthetic textiles, and plastics, obtained
6 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

from cellulose. Further research is needed before complete and

profital)le utilization of the hemicelluloses can be realized.

Lignin comprises from 18 to 28 percent of the wood. It cements

the structural luiits of wood together and thus imparts rigidity to the

wood.

The ash-forming minerals, which are left as ash when the lignin

and cellulose are burned, make up from 0.2 to 1.0 percent of the wood

and comprise the nutrient plant-food elements of the tree.
CHARACTERISTICS OF SOME IMPORTANT COMMERCIAL WOODS GROWN IN THE UNITED

STATES

The commercial forest laml (table 1) of the United vStates iiicliules

about 622 mihion acres, of which about 8 percent is classed as oldgrowth sawtimber. Second-growth sawthnber comprises nearly 25

percent. Thus, sawtimber areas having sufficient volume for economic

sawlog operation constitute slightly more than one-third of the total

commercial forest area. The greater part of the remaining forest

land supports immature second growth.

The principal hardwoods may be classified in about 25 groups of

individual or closely related species and the softwoods in the same

number of similar groups. In the case of the oaks and southern yellow

pines, a considerable number of species are included in one group.

A map showing distribution of the general forest types in the United

States is shown in figure 3.

TABLE 1.—Forest land area of the United States hij elass of forest, eharacter of

growth, and region and State

Total

forest

land

('oninu'rcial forest '

Rescryed

for

parks 5

Xoncomniercial

forests ''

Region and State

Total

Oldgrowth

sawtimber -

Youncerowth

sawtimber -

Restocking3

Poorly

stocked

and denuded ^

New England:

Connecticut

Thousand

acres

1,907

16, 788

3. 310

4, 848

452

3. 835

Thoiisa n d

acres

1,900

16, 605

3. 297

4, 682

447

3.820

Thousand

acres

150

2

Thousand

acres

403

9,189

930

1,808

28

1. 588

Thousand

acres

1,264

5. 905

1, 842

2, 248

355

1.745

Thousan d

acres

233

1,421

523

626

64

471

Thousand

acres

103

12

25

5

Thousand

acres

Maine

Massachusetts

20

1

New Hampshire ^ 141

Rhode Island . „

Vermont 16 15

Total 31.140 30.811 168 13. 946 13. 359 3. 338 152 177

Middle Atlantic:

Delaware 442

2,742

2. 348

13.500

15,228

9, 954

442

2,722

2, 329

11,114

15,127

9, 852

2

4

2

49

20

84

200

848

423

5, 327

3. 725

4,129

195

1 495

1.494

4, 2,38

8, 100

5, 392

45

375

410

1,500

3. 282

247

Maryland 18

17

2,358

96

o

New Jersey o

New York 28

Pennsylvania

West Virginia 102

Total.. _ 44,214 41,586 161 14, <i52 20. 914 5, ,S,59 2, 489 139

Lake:

Michigan 19,000

19, 700

17,000

55, 700

17, 380

16, 700

16, 265

1, 125

260

125

1, 645

1,340

1,975

10.810

10. 100

9, 075

3, 800

5, 000

5, 090

552

500

86

1.06S

Mirmesota

Wisconsin

2, 500

649

Total 50, 345 1. 510 4, 9()0 29, 985

—-

13. 890 1, 138

— —

4,217

See footnotes at end of table.
HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

TABLE 1.—Forest ¡and area of the United States hy class of forest, character of

growth, and region aiid State—Continued

l^otal

forest

land

1 Commercial forest i

Reserved

for

parks «

Noncommercial

forests 6

Region and State

Total

Oldgrowth

sawtimber 2

Younggrowth

sawtimber 2

Restocking3

Poorly

stocked

and denuded^

rentrai:

Illinois 7

Tfioiisa 11 d

acres

3. 9íír.

3.445

2, 21S

1,121

11.857

15. IHS

1. 112

621

4.831

Thousand

acres

.3.941

3. 358

2 220

1.011

11,094

1.^074

987

470

4,779

Thousand

acres

Thousand

acres

1,824

1,448

1, 108

350

4, 073

2,034

240

110

2, 079

Thou,-

sand

acres

1.712

1,480

734

4.50

5, 900

11,203

480

220

1,892

Thousand

acres

405

424

324

111

1, .570

1,777

180

140

808

Thousand

acres

55

87

22

10

80

114

25

15

52

Thousand

acres

Indiana

Iowa -

Kansas -- -- 110

145

100

Kentucky . .. 83

Missouri^ -- - - ---

Nebraska

North Dakota _ . _. ...

75 100

136

Ohio

Total 44.419 4.3. 540 320 13.332 24,143 5, 745 460 419

South Atlantic:

North Carolina

South Carolina ^

18.40(1

11,943

14, 832

17,997

11.900

14, .377

9, .588

5, 042

7.1.38

0, .584

5, 909

0, 402

1,825

889

332

40

271

71

3

Virginia 1,84

Total 45. 175 44, 274 21,708 19.015 3.491 043 258

South:

Alabama

Arkansas

Florida 7

Georgia

I»uisiana

18. 87H

20. 03()

23. 047

21,4.32

Ifi,190

10, .533

10, 040

12, 105

30, 553

18,800

19, 928

21,451

21.107

10,109

10. .509

4,308

11,8.50

10, 788

80

180

150

189

25

143

10.071

12,047

3. 233

11,2,52

9. 8.52

5, 945

2, 034

0, 500

0. 960

.5, 107

5, 004

5, 820

5. 300

2, 902

8, 004

1,127

4, 513

2, 091

3, 482

2,097

12, 392

4,405

3. 22(!

1,900

1,122

771

1,,588

61

16

46

227

10

24

7

254

8

17

92

1, 5.50

98

17

Mississippi ^

Oklahoma

Tennessee ___

6,331

61

Texas 25, 7.57

Total 175,480 140, 910 707 fi8. ,500 40,594 30. 9S3 6.53 33. 923

Total East 390, 1.34 351,400 2, 920 137, 224 148,010 03, 30(i 5, ,5.35 39,133

Pacific Northwest:

Douglas-fir subregion

Pine subregion. _

29,145

24,710

20, 027

20,177

9,348

9,171

3.810

3. 909

7. 4.34

0, 222

5, 435

815

1,032

472

2,086

4,061

Total 53. 8.'í5 40,204 18, 519

11,904

6,015

7. 779 13. 0.50 0, 250 1..504 6,147

29,755

24, 100

20, 330

19, 874

Oregon . . _ 4, 810

2,969

0. 409

7, 1,S7

3,147

3,103

448

1,056

2.977

Washington 3.170

Total ,53, 855 40, 204 18,519 7, 779 13. 0,50 0,250 1,.504 6,147

California 45, 515

18,813

24,238

10, 405

10,149

14, 7.58

8,400

2,236

3,445

2,497

2,530

1. 503

3. 451

4,333

9,327

2,057

1,050

483

705 28,405

North Rocky Mountain:

Idaho _ 269

673

8,395

Montana 8.807

Total 43. 051 24,907 5, 081 4,033 13,000 1, 533 942 17,202

See footnotes at end of t able.
WOOD HANDBOOK 9

TABLE 1.—Forest land area of the United States by class of forest, character of

growth, and region and State—Continued

Total

forest

land

Coniinereial forest i

ReserviMl

for

parks ''

Noncommercial

forests ' '

Region and State

Total

Oldgrowth

sawtimber 2

Younggrowth

sawtiinber 2

Restocking'^

Poorly

stocked

and denuded ^

South Rocky Mountain:

Arizona _

Colorado

Thousand

acres

19,538

19, 902

4,720

20, 001

1,979

8,494

8, 878

Thousand

acres

2, 815

7, 874

98

3, 4(15

1, 705

1,530

3, 102

Thousand

acres

1,909

2, 324

31

1,834

392

987

1,244

77/0»-

sand

acres

000

1,052

9

300

388

251

404

Thousand

acres

221

3, 584

58

872

770

270

1.317

Thousand

acres

25

914

Thousand

acres

332

800

Thousand

acres

10,391

11 228

Nevada 4,022

New Mexico .._ 399

215

10

47

710

05

41

1, 809

15, 820

South Dakota 149

Utah . . 0,923

Wyoming 3, 997

Total 83, 512 20,559 8, 781 3, 004 7. 098 1.010 3,817 59,130

Tf>tal West 225. 933 108, 075 41,381 17,373 37. K05 11.450 0, 908 110,890

Total United States . (i22, 0C.7 459,541 44,307 154,597 185, 875 74,702 12, 503 150,023

Source: Forest Service, U. S. Department of Agriculture. Estimates as of Jan. 1,1945, from a Reappraisal

of the Forest Situation, except as noted in footnote 7.

1 Land capable of producing timber of commercial (luantity and quality and available now or prospective! y

for commercial use.

2 Includes areas characterized by timber large enough for sawlogs (lumber) and in sufficient volume jx-r

acre for economic operation.

3 Includes areas characterized by timber of cordwood size (diameter breast high 5 inches and larger) but

too small for sawlogs and seedling and si.\pling ari'as on which at least 40 percent of the growing spaci« is

occupied by commercial species predominantly below polctimber size and below mininunn volume per acre

for sawtimber or for polctimber.

^ Includes lands that do not qualify in any previous class.

6 Commercially valuable land in parks, preserves, and other holdings withdrawn from timber use.

6 Land chiefly valuable for purposes other than timber productirn, such as watershed protection, reducing

soil erosion, and pretecting wildlife.

7 Data from the Forest Survey, 1940-49.

The following brief discussion of the principal localities of growth,

characteristics,"and uses of the main commercial species or groups of

species will aid in selecting woods for specific purposes. IMore detailed

information on the properties of these and other species is given in

various tables throughout this handbook. The publications listed

in references (1) to (7) ^ may also be helpful.

The common and botanical names given for the different species

conform to the oflBcial nomenclature for trees of the U. S. Forest

Service.

HARDWOODS

Most of the commercial hardwood species ia the United States grow

east of the Great Plains. The hardwoods of the West, which grow

principally in California, Oregon, and Washington, amount to only

about 6K billion board-feet of the 315 billion total. Hardwoods

^ Italic numt^ers in parentheses refer to Literature Cited, p. 35.
F-463921

FIGURE S.-Forest vegetation of the United States (adapted from Shantz and Zon's natural vegetation map of the

United States m the Atlas of American Agriculture).
WOOD HANDBOOK H

comprise less than 20 percent of the total timber resources of the

United States.

The predominant hardwood species are the oaks, constituting a])ont

7 percent of the total sawtimber volume. Oth(U' hardwoods make

up 12 percent of the total.

Alder, Red

Red alder (Alnus ntbra) grows along the Pacific coast betwcn^n

Alaska and California. It is used conmiercially along the coasts of

Oregon and ^yashington and is the most abundant commercial hardwood species in these two States.

The wood of red alder varies from almost white to pale pinkish

brown and has no visible boundary l^etween heart wood and sapwood.

It is moderately light in weight, (5) intermediate in most strength

properties, but low in shock resistance. Red alder has relatively low

shrinkage.

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

for sash, doors, and millwork.

Ash

Important species of ash are white ash (Fraxinvs amfricana), green

ash {F. pennsylvanica), blue ash {F. quadrangulata), l)lack ash (F.

nigra)j pumpkin ash {F. profunda), and Oregon ash (F. latifolia).

The first five of these species grow in the eastern half of the United

States. Oregon ash grows along the Pacific coast.

States with the greatest production of ash are Louisiana, Pennsylvania, Wisconsin, Michigan, Ohio, and Tennessee.

Commercial white ash is a group of species that consists mostly

of white ash and green ash. Blue ash is also included in this group.

Heartwood of commercial white ash is brown; the sapwood is light

colored or nearly white. Second-growth trees have a large proportion

of sapwood. Old-growth trees with little sapwood are scarce.

Second-gi'owth commercial white ash is particularly sought because

of the inherent qualities of chis wood; it is heavy, strong, hard, stiff,

and has high resistance to shock. Because of these qualities, such

tough ash is used principally for handles, oars, vehicle parts, and

sporting and athletic goods. Some handle specifications call for

not less than 5 or more than 17 growth rings per inch for handles of

the best grade. The addition of a weight requirement of 43 or more

pounds a cubic foot at 12-percent moisture content will assure excellent

mac erial.

Oregon ash has somewhat lower strength properties than whit('

ash, but it is used locally for the same purposes.

Black ash is important commercially in the Lake Staters. The wood

of black ash and pumpkin ash runs considerabl}^ lighter in weight

than that of commercial white ash. Ash trees groA\ing in southern

river bottoms, especially in areas that are frequently flooded for long

periods, produce buttresses that contain relatively lightweight wood.

Such wood is sometimes separated from tough ash when sold.

Ash wood of lighter weight, including black ash, is sold as cabinet

ash, and is suitable for cooperage, furniture, and shipping containers.

Some ash is cut into veneer.

303747°—55 2
12 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Aspen

^^Aspen" is a generally recognized name applied to bigtooth aspen

(Populus grandidentata) and to quaking aspen (F. tremuloides).

Aspen does not include balsam poplar (P. balsamifera) and the species

of Populus that make up the group of cottonwoods. In lumber statistics of the U. S. Bureau of the Census, however, the term ''cottonwood" includes all of the preceding species. Also, the lumber of

aspens and cottonwood may be mixed in trade and sold either as

poplar or cottonwood. The common term ''popple" is sometimes

applied to the aspens. The name "popple" or "poplar" 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. There is 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

heartwood without being clearly marked. Aspen wood is usually

straight grained ^^dth a fine, uniform texture. It is easily worked.

Well-seasoned 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, moderately low in resistance to shock, and has a

moderately high shrinkage.

Aspen is cut for lumber, boxes and crating, pulpwood, excelsior,

matches, veneer, and miscellaneous turned articles.

Basswood

American basswood (Tilia ameñcana) is the most important of the

several native basswood species; next in importance is white basswood

{T. heterophylla). Other species occur only in very small quantities.

Because of the uniformity of the wood of the different species, no

attempt is made to distinguish between them in lumber form. Other

common names of basswood are linden, linn, and beetrec.

Basswood gi-ows 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. In commercial usage,

the term "white basswood" is used to specify white wood or sapwood

of either species.

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 the 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 large;

however, basswood sta^^s in place well and does not warp while in use.

Basswood lumber is used mainly in Venetian blinds, sash and door

frames, moldings, apiary supplies, woodenware, and boxes. Some

basswood is cut for veneer, cooperage, excelsior, and pulpwood.

^^¿^
WOOD HANDBOOK 13

Beech, American

Only one species of beech, American beech (Fagus granclifolia), is

native to the United States. The terms ^'red beech'' or ^'red-heart

beech'^ are applied to the darker colored heartwood and ^Svhite

beech" or ^Svhite-heart beech" to the lighter colored heartwood.

Beech grows in the eastern one-third of the United States and

adjacent Canadian provinces. Greatest production of beech lumber

is in the Central and Middle Atlantic States.

Beech wood varies in color from nearly white sapwood to reddishbro\vn heartwood in some trees. Sometimes there is no clear line of

demarcation between heartwood and sapwood. Sapwood may be

3 to 5 inches thick. The \vood 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 adaptable for steam bending. Beech has

large shrinkage and requires careful dr3nng. It machhies smoothly,

wears well, and is rather easily treated with preservatives.

Largest amounts of beech go into flooring, furniture, handles,

veneer, woodenware, containers, cooperage, and laundry appliances.

When treated, it is suitable for railway ties.

Birch

The important species of birch are yelloAV birch (Betula alleghaniensis), sweet birch {B. lenta), and paper birch {B. papyrijera). Other

birches of some commercial importance are riv(T birch {B, ivigra),

gray birch {B. populifolia), and western paper birch {B. papyrijera

var. Commutata).

Yellow birch, sweet birch, and paper birch grow principally in the

Northeastern and Lake States. Yellow^ and sw^eet birch also grow

along the Appalachian Mountains to northern Georgia. They ar(^

the source of most birch lumber and veneer.

Yellow birch has w^hite sapw^ood and light red(Ush-bro\vn heartw^ood.

Sweet birch has light-colored sapwood and dark-brown heartwood

tinged with red. Wood or yellow birch and sweet birch is heavy,

hard, strong, and has good shock-resisting ability. The w^ood is fine

and uniform in texture. Paper birch is low^er in wa^ght, softer, and

lower in strength than yellow and sweet birch. Birch shrinks considerably during drying.

Yellow and sweet birch lumber and veneer go principahy into the

manufacture of furniture, boxes, baskets, crates, w^oodenw^are, cooperage, interior finish, and doors. Birch veneer goes into plywood used

for flush doors, furniture, radio and television cal)inets, aircraft, and

other specialty uses. Paper birch is used for turned products, including spools, bobbins, and toys.

Cherry, Black

Black cherry {Prunus serótina) is sometimes known as cherry, wdld

black cherry, wild cherry, or choke cherry. It is the only native

species of the genus Prunus of commercial importance for lumber
14 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

production. It occurs scatteringly from southeastern Canada

throughout the eastern half of the United States. Production is

centered chiefly in the Middle Atlantic States.

The hearlwood of black cherry varies from light to dark reddish

brown and has a distinctive luster. The sapwood is narrow in old

trees and nearly white. The wood has a fairly uniform texture and

very satisfactory machining properties. It is moderatel}^ heavy.

Black cherry is strong, stiff, moderately hard, and has high shock

resistance and moderately large shrinkage. It stays in place well

after seasoning.

Black cherry is used principally for furniture and for backing blocks

on which electrotype plates are mounted. Other uses include burial

cask(^ts, wood(*nware novelties, patterns, and paneling in buildings

and railway coaches. It has proved satisfactory for gunstocks.

Chestnut, American

American chesnut (Castanea dentata) is known also as sweet chestnut. Before chestnut was attacked by a blight, it grew in commercial

quantities from New England to northern Georgia. Practically all

standing chestnut has been killed by blight, and supplies come from

dead timber. There are considerable quantities of standing dead

chestnut in the Appalachian Mountains, which may be available for

some time because of the great natural resistance to decay of its

heartwood.

The heartwood of chestnut is grayish brown or brown and becomes

darker with age. The sapwood is very narrow and almost white.

The wood is coarse in texture, and the 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.

It is moderately hard, moderately low in strength, moderately low in

resistance to shock, and low in stiffness. It seasons well and is easy

to work with tools.

Chestnut is used for poles, railway ties, furniture, caskets, boxes,

crates, and core stock for veneer panels.

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. heterophyUa), also known as cottonwood, river cottonwood, and

swamp poplar; and black cottonwood (P. trichocarpa).

Eastern cottonwood 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 in the

West Coast States and in western Montana, northern Idaho, and

western Nevada.

The heartwood of the three cottonwoods, eastern, black, and swamp,

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

seasoned.
WOOD HANDBOOK 15

Eastern cottonwood is moderately low in bendinc^ and compressive

strength, moderately limber, moderately soft, and moderately low in

ability to resist shock. Black cottonwood is slightly below' eastern

cottonwood in most strength properties. Both eastern and black

cottonwood have moderately large shrinkage. Some cottonwood is

difficult to work with tools because of fuzzy surfaces. Tension wood

is largely responsible for this characteristic^

Cottonwood is used principally for lumber, veneer, pulpwood,

excelsior, and fuel. The lumber and veneer go largely into boxes,

crates, and baskets.

Elm

There are six species of ehn in the United States: American elm

(Ulmus americana), slippery elm {U. rubra), rock elm (U. thoinasii),

winged elm (U. alata), cedar elm (t7. crassijidia), and September elm

{U. serótina). American elm is also known as white elm, water elm,

and gray elm; slippery elm as red elm; rock elm as cork elm or hickory

elm; winged elm as wahoo; cedar elm as red elm or basket elm; and

September elm as red elm.

American elm grows throughout the eastern half of the United

States, except in higher elevations of the Appalachian Mountains.

Slippery elm occupies about the same area, excepting the Atlantic

Coastal Plain, most of Florida, and alongé the gulf coast. Rock elm

occurs from New Hampshire to northern Tennessee and Nel)raska.

Winged elm grows from the Ohio Valley southward to the gulf and

westward to Texas. Cedar elm extends from southern Arkansas and

eastern Mississippi into Texas. September elm is most abundant in

the central Mississippi Valley.

The sapwood of the elms is nearly white and the heartwood light

brown, often tinged with red. The elms may be divided into two

general classes, hard elm and soft elm, based on the weight and

strength of the wood. Hard elm includes rock elm, winged elm,

cedar elm, and September elm. American elm and slippery elm are

the soft elms. Soft elm is moderately heavy, has high shock resistance,

and is moderately hard and stiff. Hard elm species are somewhat

heavier than soft elm. Elm has excellent bending qualities.

Production of elm lumber is chiefly in the Lake, Central, and

Southern States.

Elm lumber is used principally in boxes, baskets, crates, and slack

barrels; furniture; agricultural supplies and implements; caskets and

burial boxes; and vehicles. For some uses the hard elms are preferred.

Elm veneer is used for fruit, vegetable, and cheese boxes, baskets, and

panels.

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 range of hackberry and grows throughout

the Southern and South Atlantic States.
16 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

The sapwood of both species varies from pale ^^ellow to greenish or

grayish yellow. The heartwood is commonly darker. The wood

resem})les elm in structure.

Hackberry lumber is moderately heavy. It is moderately strong

in bending, moderately weak in compression parallel to the grain,

moderately hard to hard, high in shock resistance, but low in stifTness.

It has moderately large to large shrinkage but keeps its shape well

during seasoning.

Most hackberry is cut into lumber, with small amounts going into

dimension stock and some into veneer. Most of it is used for furniture

and some for containers.

Hickory, Pecan

Species of the pecan group include bitternut hickory (Carya cordiformis), pecan (f\ illinoensis), water hickory {C\ aquatica), and nutmeg

hickory (i\ myristicaeformis). Bitternut hickory grows throughout

the eastern half of tíie United States. Pecan hickory grows from

central Texas and Louisiana to Missouri and Indiana. Water hickory

grows from Texas to South Carolina. Nutmeg hickory occurs principally in Texas and Louisiana.

The wood of pecan hickory resembles that of true hickor^^ It has

white or nearly white sapwood, which is relatively wide, and somewhat darker heartwood. The wood is heavy and sometimes has very

large shrinkage.

Heavy pecan hickory finds use in tool and implement handles and

flooring. The lower grades are used in pallets.

Hickory, True

True hickories are found throughout most of the eastern half of

the United States. The species most important commercially are

shagbark (f'arya ovata), pignut (C. glabra), shellbark {C. laciniosa),

and mockernut (C\ tomentosa).

The greatest commercial production of the true hickories is in the

Middle Atlantic and Central States. The Southern and South

Atlantic States produce nearl}^ half of all hickory lumber.

The sapwood of hickory is white and usually quite thick, except in

old, slowly growing trees. The heartwood is reddish. From the

standpoint of strength, no distinction should be made between sapwood and heartwood having the same weight.

The wood of true hickor}^ is ver}^ tough, heav}^, hard, and strong, a

combination not found in any other native commercial wood. Hickory

shrinks considerably in drying.

About three-fourths of the hickory production is used for tool

handles, which require high shock resistance. It is also used for

ladder rungs, athletic goods, agricultural implements, dowels, gymnasium apparatus, poles, shafts, well pumps, and furniture.

A consicku^able quantity of lower grade hickory is not suitable,

because of knottiness or other growth features and low density, for

the special uses of high-quality hickory. It appears particularly

useful for pallets, blocking, and similar items.
WOOD HANDBOOK 17

Holly, American

American holly {Ilex opaca) is sometimos calhni white holly, evergreen holly, and boxwood. The natural range of holly extcnuls along

the Atlantic coast, gulf coast, and Mississippi Valley^

Both heartwood and sapwood are white, the heartwood with an

ivory cast. The wood has a uniform and compact texture; it is

moderately low in strength when used as a beam or cohunn and low

in stiffness, but it is heavy and hard, and ranks high in shock ri^sistance.

It is readily penetrable to liquids and can be satisfactorily dyed. It

works well, cuts smoothly, and is used principally^ for scientific and

musical instruments, furniture inla3^s, and athletic goods.

Locust, Black

Black locust (Robinia pseudoacacia) is sometimes called yellow

locust, white locust, green locust, or post locust. This species grows

from Pennsylvania along the Appalachian Mountains to northern

Georgia. It is also native to a small area in northwestern Arkansas.

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 high in resistance to shock, and ranks

very high in strength and stiffness. It has moderately small shrinkage.

The heartwood has high decay resistance.

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

timbers and for fence posts, poles, railroad ties, stakes, and fuel. An

important product manufactured from black locust is insulator pins,

a use for which the wood is well adapted because of its strength, decay

resistance, and moderate shrinkage and swelling. Other uses are for

rough construction, crating, ship treenails, and mine equipment.

Magnolia

Three species comprise commercial magnolia—southern magnolia

{Magnolia grandiflora), sweetl)ay {M. virginiana), and cucumbertree

{M.'acuminata). Other names for southern magnolia are evergreen

magnolia, magnolia, big laurel, bull bay, and laurel bay. vSweetbay

is sometimes called swamp magnolia, or more often simply magnolia.

The natural range of sweetbay extends along the Atlantic and gulf

coasts from Long Island to Texas, and that of southern magnolia,

from North Carolina to Texas. Cucumbertree grows from the Appalachians to the Ozarks northward to Ohio. Louisiana leads is production of magnolia lumber.

The sapwood of southern magnolia is yellowish white, and the

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

The wood, which lias close, uniform texture and is generally straight

grained, closely resembles yellow-poplar. It is moderately heavy,

moderately low in shrinkage, moderately low in ))ending and compressive strength, moderately hard and stiiï, and moderately high in

shock resistance. Sweetbay is reported to be much like southern
18 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

mao;nolia. The wood of ciicumbertree is similar to that of yellowpoplar, and cucumbertree growling in the yellow-poplar range is not

separated from that species on the market.

Magnolia liunber is used principally in the manufacture of furniture, boxes, Venetian blinds, sash, doors, veneer, and millwork.

Maple

Commercial species of maple in the United States Include sugar

maple (Acer sacchanim), black maple (A. nigrum), silver maple

(A, sacchannum), red maple (A. rubrum), boxelder (A. negundo), and

bigleaf maple {A. macrophylhim). Sugar maple is also known as

hard maple, rock maple, sugar tree, and black maple; black maple as

hard maple, black sugar maple, and sugar maple; silver maple as

white maple, river maple, water maple, and swamp maple; red maple

as soft maple, water maple, scarlet maple, white maple, and swamp

maple; boxelder as ash-leaved maple, three leaved maple, and cutleaved maple; and bigleaf maple as Oregon maple.

Sugar maple grows from Maine to Minnesota, and southward to

northern Georgia, Alabama, Louisiana, and Texas. Black maple

occupies mainly a belt from New York through southern Michigan,

southward to Kentucky, and westward through Iowa. Silver maple

grows through most of eastern United States except the southern

Atlantic and gulf coasts. Red maple grows east of the Great Plains

and south to the Gulf of Mexico. Boxelder grows from Minnesota

to Texas and eastward to the Middle Atlantic States. Bigleaf maple

grows along the Pacific coast.

Maple lumber comes principally from the Middle Atlantic and

Lake States, which together account for about two-thirds of the

production.

The wood of sugar maple and black maple is known as hard maple;

that of silver maple, red maple, and boxelder as soft maple. The

sapwood of the maples is commonly white with a slight reddishbrown tinge. It is from 3 to 5 or more inches thick. Heartwood is

usually light reddish brown, but sometimes is considerably darker.

Hard maple has a fine, uniform texture. It is heavy, strong, stiff,

hard, resistant to shock, and has large shrinkage. Sugar maple is

generally straight grained. Soft maple is not so heavy as hard maple.

Maple is used principally for lumber, veneer, crossties, distillation

wood, and pulpwood. A large proportion is manufactured into

flooring, furniture, boxes and crates, shoe lasts, handles, woodenware,

novelties, motor-vehicle parts, spools, and bobbins.

Oak (Red Oak Group)

Among the numerous species of red oaks in the LTnited States, 10

have considerable commercial importance.

( 1 ) Northern red oak (Quercus rubra), also known as eastern red oak,

grows in the eastern half of the United States to the lower Mississippi

Valley, Florida, and the Atlantic Coastal Plain. It is the most

important lumber tree of the red oak group. (2) Scarlet oak (Q.
WOOD HANDBOOK 19

coccínea) grows in the eastern third of the United States, except the

southern border States. (3) Shumard oak {Q. skumrinlii), also known

as Schneck oak, Texas oak, and southern red oak, grows chiefly alonji;

the Atlantic and gulf coasts. (4) Pin oak {Q. palustris), also'known

as swamp oak, grows principally in the central Mississippi Valley.

(5) Nuttall oak (Q. nuttaUii) grows in the lower Mississippi Valley

region from Missouri southward and from Alabama to Texas.

(6) Black oak {Quercus velutina), also known as yellow oak, grows

in the eastern half of the United States to northern Horida. (7)

Southern red oak {Q. falcata) grows from New Jersey to Missouri,

Arkansas, and Texas. (8) Water oak ((>. /y?V/m) grows in the South

Atlantic and Gulf States from Maryland to Texas. (9) Laurel oak

{Q. laurifolia) grows in the South Atlantic and Gulf Coastal Plains

from Maryland to Louisiana. (10) Willow oak (Q. phellos) grows

along the Atlantic and gulf coasts and the lower Mississippi Valley.

Most red oak lumber comes from the Southei-n States, the southern

mountain regions, and the Atlantic Coastal Plain.

The sapwood is nearly white and usually 1 to 2 inches thick. The

heartwood is brown with a tinge of red. Sawed lumber of red oak

cannot be separated by species on the basis of the characteristics of

the wood alone. Red oak lumber can be separated from white oak

by the number of pores in summerwood and because, as a rule, it

lacks the hairlike growth known as tyloses in the pores. The open

pores of the red oaks make these species unsuitable for tight cooperage.

Quartersawed lumber of the oaks is distinguished by the broad and

conspicuous rays, which add to its attractiyeness.

Wood of the red oaks is heavy. Rapidly grown second-growth oak

is generally harder and tougher than finer textured old-growth timber.

The red oaks haye fairly large shrinkage in drying.

The red oaks are largely cut into lumber, railroad ties, mine timbers,

fence posts, veneer, 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 and crates, agricultural implements, caskets and coffins,

woodenware, and handles. It is also used in railroad cars and boats.

Oak (White Oak Group)

There are nine commercially important species of the white oak

group, and all grow mainly in the eastern United vStates.

(1) White oak (Quercus alba) grows throughout the eastern half of

the United States and adjacent Canada. It is the most important

lumber tree of the white oak group. (2) Chestnut oak {Q. prinus),

also known as rock chestnut oak or rock oak, grows from southern

Vermont and New Hampshire, southward along the Appalachian

Mountains to central Georgia and Alabama. (3) Post oak (Q.

stellata) grows throughout the eastern half of the United States from

southern New England to the Great Plains. (4) Overcup oak (Q.

lyraia), also known as swamp white oak, grows in the Atlantic Coastal

States and westward to Texas through southern Illinois and Indiana.

(5) Swamp chestnut oak {Q. inichauxii), also known as basket oak
20 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

and cow oak, grows along the Atlantic coast and westward to Texas

through southern Illinois and Indiana.

(6) Bur oak (Querxus macrocarpa) grows mainly from New York

to Montana and southward through Kentucky to Texas. (7) Chinkapin oak {Q. muehlenbergii) grows from New York, southern Michigan,

and southern Minnesota southward to the Gulf of Mexico, except

for the Atlantic Coastal Plain. (8) Swamp white oak (Q. bicolor)

grows from southern Maine through the Central States to the Great

Plains. (9) Live oak {Q. inrginiana) is limited to the Atlantic Coastal

Plain, Florida, and the gulf coast.

White oak lumber comes chiefly from the South, South Atlantic,

and Central States, including the southern Appalachian area.

The heartwood of the white oaks is generally grayish brown, and

the sapwood, which is from 1 to 2 or more inches thick, is nearly white.

The pores of the heartwood of white oaks are usually plugged with

the hairlike growth known as tyloses. These tend to make the wood

inpenetrable by liquids, and for this reason most white oaks are

suitable for tight cooperage. Chestnut oak lacks tyloses in many of

its pores.

The wood of white oak is heav}^, averaging somewhat higher in

weight than that of the red oaks. The heartwood has moderately good

decay resistance.

White oaks are used for lumber, railroad ties, 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 was

formerly used extensively for ship timbers. An important use of

white oak is for planking and bent parts of ships and boats, heartwood

often being specified because of its decay resistance. It is also used

for flooring, agricultural implements, railroad cars, furniture, doors,

millwork, and many other items.

Sweetgum

Sweetgum (Liquidambar styraciflua) grows from southwestern

Connecticut westward into Missouri and southward to the gulf.

Lumber production is almost entirely from the Southern and South

Atlantic States.

The lumber from sweetgum is usually divided into two classessap gum, the light-colored wood from the sapwood, and red gum, the

reddish-brown heartwood.

Sweetgum has interlocked grain, a form of cross grain, and must be

carefully dried. The interlocked grain causes a ribbon stripe, however, that is desirable for inside finish and furniture. The wood is

rated as moderately heavy and hard. It is moderately strong,

moderately stiff, and moderately high in shock resistance.

Sweetgum is used principally for lumber, veneer, pl^^vood, slack

cooperage, railroad ties, fuel, and pulpwood. The lumber goes

principally into boxes and crates, furniture, radio and phonograph

cabinets, interior trim, and millwork. Sweetgum veneer and plywood

are used for boxes, crates, baskets, and interior woodwork.
WOOD HANDBOOK 21

Sycamore, American

American sycamore {Platanus occidentalis) is also kno\\*n as sycamore and sometimes as buttonwood, buttonball tree, and planetree.

Sycamore grows from Maine to Nebraska, Texas, and northern Florida. In the production of sycamore lumber, the Central States rank

first.

The heartwood of sycamore is reddish brown; sapwood is lighter in

color and from 1}^ to 3 inches thick. The wood has a fine texture and

interlocked grain. It shrinks moderately in drying. Sycamore wood

is moderately heavy, moderately hard, moderately stiff, moderately

strong, and has good resistance to shock.

Sycamore is used principally for lumber, veneer, railroad ties,

cooperage, fence posts, and fuel. Sycamore lumber is used for furniture, boxes (particularly small food containers), flooring, handles, and

butcher's blocks. Veneer is used for fruit and ve2:etable baskets. -'&'-

Tupelo

The túpelo group includes water túpelo (Nyssa aquatica), also known

as túpelo gum, swamp túpelo, and gum; black túpelo (A^. sylvatica),

also known as blackgum and sour gum; swamp túpelo (A^. sylvatica

var. biflora), also known as swamp blackgum, blackgum, túpelo gum,

and sour gum; and Ogeechee túpelo (A^. ogeche), also known as sour

túpelo, gopher plum, túpelo, and Ogeechee plum.

All except black túpelo grow principally in the southeastern United

States. Black túpelo grows in the eastern United States from Maine

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

lumber is from the Southern States.

Wood of the different túpelos is quite similar in appearance and

properties. Heartwood is light brownish gray and merges gradually

into the lighter colored sapwood, which is generally several inches wide.

The wood has fine, uniform texture and interlocked grain. Tupelo

wood is rated as moderately heavy. It is 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. For some uses, as in the case of buttressed ash trees, this wood

should be separated from the heavier wood to assure material of uniform strength. Because of interlocked grain, túpelo lumber requires

care in drying.

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

railroad ties and cooperage. Lumber goes into boxes, crates, baskets,

and furniture.

Walnut, Black

Black walnut (Juglans nigra) is also known as American black walnut. Its natural range extends from Vermont to the Great Plains

and southward into Louisiana and Texas. About three-quarters of

the walnut timber is produced in the Central States.

The heartwood of black walnut varies from light to dark brown; the

sapwood is nearly white and up to 3 inches wide in open-grown trees.
22 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Black walnut is normally straight gi^ained, easily worked with tools

and stays in place well. ^ It is heavy, hard, strong, stiff, and has good

resistance to shock. Black walnut wood is well suited for natural

finishes. . m i

The outstanding use of black walnut is for furniture. Other important uses are gunstocks, cabinets, and interior finish. It is used

either as solid wood or as plywood.

Willow, Black

Black willow (Salix ni/jra) is the most important of the many willows that grow in the United States. It is the only one to supply

lumber to the market under its own name.

Black willow is most heavily produced in the Mississippi Valley

from Louisiana to southern Missouri and Illinois.

The heartwood of black willow is grayish brown or light reddish

brown, frequently containing darker streaks. The sapwoocl is whitish

to creamy yellow. The wood of black willow is uniform in texture,

with somewhat interlocked grain. The wood is light in weight. It

has exceedingly low strength as a beam or post and is moderately soft

and moderately high in shock resistance. It has moderately large

vhrinkage.

Willow is cut principally into lumber. Small amounts are used for

slack cooperage, veneer, excelsior, charcoal, pulpwood, artificial limbs,

and fence posts. Black willow lumber is remanufactured principally

into boxes, baskets, crates, caskets, and furniture. Willow lumber is

suitable for roof and wall sheathing, subflooring, and studding.

Yellow-Poplar

Yellow-poplar (Liriodeiidron tulipifera) is also known as poplar,

tulip poplar, tulipwood, and hickory poplar. 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.

Yellow-poplar sapwood is white and frequently several inches thick.

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. 01d-grov;th timber is m.oderately

light in weight and is reported as being moderately low in bending

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

It has moderately large shrinkage when dried from a gi^een condition

but is not diflñcult to season and stays íJ:I place well after seasoning.

Much of the second-growth yellow-poplar is heavier, harder, and

stronger than old gi'owth. Selected trees produce wood heavy enough

for gunstocks. Lum})er goes mostly into furniture, interior finish,

siding, core stock for plywood, radio cabinets, and musical instruments.

Boxes and crates are made from lower grade stock. Yellow-poplar

plywood is used for finish, furniture, piano cases, and various other

special products. Yellows-poplar is used also for pulpwood, excelsior,

and slack-cooperage staves.
WOOD HANDBOOK 23

Lumber from the cucumbcrtree {Magnolia acuminata) sometimes

may be included in shipments of yellow-poplar because of its similarity.

SOFTWOODS

Most of our softwood timber is west of the Great Plains, and nearly

three-fourths of our eastern softwood stands are in the South Atlantic

and Southern States. Western softwood timber stands of Washington

and Oregon contain more than three-fifths of the western softwood

timber, those of California about one-fifth, and another one-fifth is

scattered along the mountains from Idaho and Montana southward.

Alaska-Cedar

Alaska-cedar (Chamaecyparis nootkafensis) grows in the Pacific

coast region of North America from southeastern Alaska southward

through Washington to southern Oregon, In Washington and Oregon, it is confined to the west side of the Cascade Mountains, usually

above an elevation of 2,000 feet. It reaches its best development

along the coast and on the nearby islands of southern Alaska and

British Columbia.

The heartwood of Alaska-cedar is bright, clear yellow. The sapwood is narrow, white to yellowish, and hardly distinguishable from

the heartwood. The wood is fine textm^c^d and generally straight

grained. It is moderately heavy, mock^rately strong and stifi,

moderately hard, and moderately high in resistance to shock. Alaskacedar shrinks little in drying, stays in placc^ well after seasoning, and

the heartwood is very resistant to decay. The wood has a mild,

unpleasant odor.

Alaska-cedar is used locally for ulterior finish, furniture, small

boats, cabinetwork, and novelties.

Baldcypress

Baldcypress (Taxodium distichum) is commonly known as cypress,

also as southern cypress, red cypress, yellow cypress, and white

cypress. Commercially, the terms ''tidewater red cypress," ''gulf

cypress," "red cypress (coast type)," and "yellow cypress (inland

type)" are frequently used.

Baldcypress grows along the Atlantic Coastal Plain from Dela\yare

to Florida, westward through the gulf coast region to the Mexican

border in Texas, and up the Mississippi Valley to southern Indiana.

The heaviest stands are found in the extensive swamps of the lower

Mississippi Valley and in Florida. About one-half of the cypress

lumber comes from the Southern States and one-fourth from the

South Atlantic States.

The sapwood of baldcypress is narrow and nearly white. The color

of the heartwood varies widely, ranging from light yellowish brown

to dark brownish red, brown, or chocolate. The wood is moderately

heavy, moderately strong, and mod(^rately hard, and the heartwood

is one of our most decay-resistant woods. Shrinkage is mod(>rately

small, but somewhat grciiter than that of cedar and less than that of

southern yellow pine.
24 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Frequently the wood of certain cypress trees 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 arrested

when the wood is cut into lumber and dried. Pecky cypress therefore

is durable and useful where appearance is not important and watertightness is unnecessary.

Cypress is used principally for building construction, especially

where resistance to decay is required. It is used for beams, posts, and

other members in docks, warehouses, factories, bridges, and heavy

construction.

It is well suited for siding and porch construction. It is also used

for caskets, burial boxes, sash, doors, bhnds, and general millwork,

including interior trim and paneling. Other uses are in tanks, vats,

ship and boat building, refrigerators, railroad-car construction, greenhouse construction, cooling towers, and stadium seats. It is also

used for railroad ties, poles, piling, shingles, cooperage, and fence

posts.

Douglas-fir

Douglas-fir (Pseudotsuga menziesii and var. glauca) is also known

locally as red fir, Douglas spruce, and yellow fir.

The range of Douglas-fir extends from the Rocky Mountains to the

Pacific coast and from Mexico to central British Columbia. Most

of the Douglas-fir production comes from the coast States of Oregon,

Washington, and California, principally Oregon, and some from

Idaho and Montana.

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

as much as 3 inches wide in second-growth trees of commercial size.

Fairly young trees of moderate to rapid growth have reddish heartwood and are called red fir. Very narrow-ringed wood of old 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.

Wlien lumber of high strength is needed for structural uses, density

can be determined by applying the density rule. This rule uses

percentage of summerwood and rate of growth as a basis.

Douglas-fir is used mostly for building and construction purposes

in the form of lumber, timbers, piling, and plywood. Considerable

quantities go into fuel, railroad ties, cooperage stock, mine timbers,

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

various products, including sash, doors, general millwork, railroadcar construction, boxes, and crates. Small amounts are used for

flooring, furniture, ship and boat construction, wood pipe, and tanks.

Firs, True (Eastern Species)

Two of the true firs, balsam fir (Abies halsamea) and Fraser fir

{A. iraseri), grow in the East. In the United States, balsam fir

grows principally in New England, New York, Pennsylvania, and the

Lake States. Fraser fir grows in the Appalachian Mountains of

Virginia, North Carohna, and Tennessee.

The wood of the true firs, both eastern and western species, is creamy

white to pale brown. Heartwood and sapwood are generally indistinï^
WOOD HANDBOOK 25

guishable. The similarity of wood structure in the true firs makes it

impossible to distinguish the species by an examination of the wood

alone.

Balsam fir is rated as Ugh t in weight, low in bending and compressive

strength, moderately limber, soft, and low in resistance to shock.

The eastern firs are used mainly for pulpwood, although there is

some lumber produced from them, especially in New England and the

Lake States.

Firs, True (Western Species)

Six commercial species make up the western true firs: Sul)alpine

fir {Abies lasiocarpa), California red fir (A. magnifica), grand fir (A.

grandis), noble fir (A. procera), Pacific silver fir {A. amahilis), and

white fir {A. concolor).

White fir grows from the Rocky Mountains to the Pacific coast.

Subalpine fir grows at high altitudes in the Rocky Mountain region

and the Cascade Mountains of Oregon and Washington. Pacific

silver fir is found in Oregon and Washington. Grand fir's range is

western Montana, northern Idaho, northeastern Oregon, and along

the coast from Washington to northern California. Noble fir grows

in the mountains of northwestern Washington, western Oregon, and

northern California. California red fir is limited to the mountains

of southwestern Oregon and northern and eastern California.

The western firs are light in weight, but, with the exception of grand

fir, have somewhat higher strength properties than balsam fir.

Shrinkage of the wood is rated from small to moderately large.

The western true firs are largely cut for lumber and marketed as

white fir throughout the Western States. Lumber of the western

true firs goes principally into building construction, boxes and crates,

planing-mill products, sash, doors, and general millwork. In small

house construction, the lumber is used for framing, subfiooring, and

sheathing. A considerable amount goes into boxes and crates.

High-grade lumber from noble fir is used mainly for interior finish,

moldings, skiing, and sash and door stock. Some of the best material

is suitable for aircraft construction. Other special and exacting uses

of noble fir are for Venetian blinds and ladder rails.

Hemlock, Eastern

Eastern hemlock {Tsugi canadensis) grows from New England

southward along the Appalachian Mountains to northern Alabama

and Georgia, and in the Lake States. Other names are Canadian

hemlock and hemlock spruce.

The production of hemlock lumber is divided fairly evenly between

the New England States, the Middle Atlantic States, and the Lake

States. North Carolina, South Carohna, and Virginia also produce

considerable amounts.

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 light in weight,
26 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

moderatcl}^ hard, moderately low in strength, moderately limber, and

moderately low in shock resistance.

Eastern hemlock is used principally for lumber and pulpwood. The

lumber is used largely in building construction for framing, sheathing,

subflooring, and roof boards, and in the manufacture of boxes and

crates.

Hemlock, Western

Western hemlock {Tsiuja heterojyhylia) is also known b}^ several

other names, including west coast hemlock, hemlock spruce, western

hemlock spruce, western hemlock fir. Prince Albert fir, gray fir, silver

fir, and Alaska pine. It grows along the Pacific coast of Oregon and

Washington and in the northern Rocky Mountains, north to Canada

and Alaska.

The heartwood and sapwood of western hemlock are almost white

with a purplish tinge. The sapwood, which is sometimes lighter in

color, is generally not more than 1 inch thick. The wood contains

small, soimd, black knots that are usually tight and stay in place.

Dark streaks often found in the lumber and caused by hemlock bark

maggots as a rule do not reduce strength.

Western hemlock is moderately light in weight and moderately low

in strength. It is moderate in its hardness, stiffness, and shock resistance. It has moderately large shrinkage, about the same as Douglasfir. Green hemlock lumber contains considerably more water than

Douglas-fir, but it is comparatively easy to kiln-dry.

Western hemlock is used principally for pulpwood and lumber.

The lumber goes largely into building material, such as sheathing,

siding, subilooring, joists, studding, planking, and rafters. Considerable quantities are used in the manufacture of boxes, crates, and

flooring, and smaller amounts for refrigerators, furniture, and ladders.

Incense-Cedar

Incense-cedar (Libocedrus deeurrens) grows in California, southwestern Oregon, and to a small extent in Nevada. Most of the

incense-cedar lumber comes from the northern half of California and

the remainder from southern Oregon.

Sapwood of incense-cedar is white or cream colored, and the heartwood is light brown, often tinged with red. The wood has a fine, uniform texture and a spicy oclor. Incense-cedar is light in weight,

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

stifl'ness. It has small shrinkage and is easy to season with little

checking or warping.

Incense-cedar is used principall}^ for lumber, fence posts, and ties.

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

blinds. Some is used for chests and toys. Much of the incense-cedar

lumber 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 peck once^the

lumber is seasoned. This lumber is used locally for rough construction

where cheapness and decay resistance are important. Because of its

resistance to decay, incense-cedar is well suited for fence posts. Other

products are railroad ties, poles, and split shingles.
WOOD HANDBOOK 27

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. It is found at elevations of 2,000

to 7,000 feet. About two-thirds of the lumber of this species is produced in Idaho and Montana and one-third in Oregon and Wasliington.

The heartwood of western larch is yellowish brown and the sapwood

yellowish white. The sapwood is generally not more than 1 inch thick.

The wood is stiff, moderately strong and hard, moderately high in

shock resistance, and moderately heavy. It has moderately large

shrinkage. The wood is usually straight grained, splits easily, and is

subject to ring shake. Knots are common but small and tight.

Western larch is used mainly in building construction for rough

dimension, small timbers, planks, and boards and for railroad ties and

mine timbers. It is used also for piling, poles, and posts. Some highgrade material is manufactured into interior finish, flooring, sash, and

doors.

Pine, Eastern White

Eastern white pine (Pinus strobus) grows in the United States

from Maine southward along the Appalachian Mountains to northern

Georgia and in the Lake States. It is also known as white pine,

northern white pine, We3^mouth pine, and soft pine.

Lumber production of eastern white pine is confined largely to the

New England States, which produce about one-half the total. About

one-third comes from the Lake States and most of the remainder

from the Middle Atlantic and South Atlantic States.

The heartwood of eastern white pine is light brown, often with a

reddish tinge. It turns considerably darker on exposure. The wood

has comparatively uniform texture, and is straight grained. It is

easily kiln-dried, has small shrinkage, and ranks high in ability to stay

in place. It is also easy to work and can be readily glued.

Eastern white pine is light in weight, moderately soft, moderately

low in strength, and low in resistance to shock.

Practically all eastern white pine is converted into lumber, which is

put to a great variety of uses. The largest proportion, which is

mostly second-growth knotty lumber of the lower grades, goes into

boxes. High-grade lumber goes into patterns for castings. Other

important uses are sash, doors, furniture, trim, knotty finish, caskets

and burial boxes, shade and map rollers, toys, and dairy and poultry

supplies.

Pine, Jack

Jack pine (Pinus banksiana), sometimes loiown as scrub pine, gray

pine, or black pine in the United States, grows naturally in the Lake

States and in a few scattered areas in New England and northern

New York. In lumber, jack pine is not separated from the other

pines with which it grows, including red pine and eastern white pine.

The sapwood of jack pine is nearly white, and the heartwood is

light brown to orange. The sapwood may make up one-half or more

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

303747"—55 3
28 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

somewhat resinous. It is moderately light in weight, moderately low

in bending strength and compressive strength, moderately low m

shock resistance, and low m stiffness. It also has moderately small

shrinkage. Lumber from jack pine is generally Imotty.

Jack pine is used for pulpwood, box lumber, and fuel. Less important uses include railroad ties, mine timber, slack cooperage,

poles, and posts.

Pine, Lodgepole

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

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

Pacific coast regions as far northward as Alaska. The cut of this

species comes largely from 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 light in weight, faii^ly easy to work, and

has moderately large shrinkage. Lodgepole pine rates as moderately

low in strength, moderately soft, moderately stiff, and moderately

low in shock resistance.

Lodgepole pine is used for lumber, mine timbers, railroad ties, and

poles. Less important uses include posts and fuel. It is being used

in increasing amounts for siding, finish, and flooring.

Pine, Pitch

Pitch pine (Pinus rígida) grows from Maine and northern New York

south along the mountains to eastern Tennessee and northern Georgia.

The heartwood is brownish red and resinous; the sapwood is thick

and light yellow. The wood of pitch pine is medium heavy to heavy,

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

resistance. Its shrinkage is medium small to medium large. It is

used for lumber and fuel.

Pine, Pond

Pond pine {Pinus serótina) grows in the coast region from New

Jersey to Florida. It occurs in small groups or singly mixed with

other pines on low flats. The wood is heavy, coarse-grained, and

resmous, with dark, orange-colored heartwood and thick, pale-yellow

sapwood. At 12-percent moisture content it weighs 38 pounds per

cubic foot. Sln-inkage is moderately large. The wood is moderately

strong, stiff, medium hard, and medium high in shock resistance. It

is used for general construction, railway ties, posts, and poles.

Pine, Ponderosa

Ponderosa pine (Pinus ponderosa) is known also as pondosa pine,

western soft pine, western pine, California white pine, bull pine, and

black jack. Jeffrey pine (P. jerffreyi), which grows in close association

with ponderosa pine in California and Oregon, is usually marketed

with ponderosa pine and sold under that name.
WOOD HANDBOOK 29

Ponderosa pine has extensive distribution from Arizona and New

Mexico to South Dakota and westward to the mountains of the

Pacific Coastal States.

Major producing areas are in Oregon, Washington, Cahfornia, and

Nevada. Other important producing areas are in Idaho and Montana ;

lesser amounts come from the southern Rocky Mountain region.

Botanically, ponderosa pine belongs to the yellow pine group rather

than the white pine group. A considerable proportion of the wood,

however, is somewhat similar to the white pines in appearance and

properties. The heartwood 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 stift*, and moderately low in shock

resistance. It is generally straight grained and has moderately small

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

piling, poles, posts, mine timbers, veneer, and ties. The clear wood

goes into sash, doors, blinds, moldings, paneling, mantels, trim, and

built-in cases and cabinets. Lower grade lumber is used for boxes and

crates. Much of the lumber of intermediate or lower grades goes into

sheathing, subflooring, and roof boards. Knotty ponderosa pine is

used for interior finish.

Pine, Red

Red pine {Pinus resinosa) is frequently called Norway pine. It

is occasionally known as hard pine and pitch pine. This species

grows in the New England States, New York, Pennsylvania, and the

Lake States. In the past, lumber from red pine has been marketed

with white pine without distinction as to species.

The heartwood of red pine varies from pale red to a reddish brown.

The sapwood is nearly white with a yellowish tinge, and is generally

from 2 to 4 inches w4de. The wood resembles the lighter weight wood

of southern yellow pine. Summerwood 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 so uniform in texture as eastern white pine,

and somewhat resinous. The w^ood has moderately large shrinkage

but is not difficult to dry and stays in place well when seasoned.

Red pine is used principally for lumber and to a lesser extent for

piling, poles, cabin logs, hewed ties, posts, and fuel. The wood is

used for many of the purposes for which eastern white pine is used.

It goes mostly into building construction, siding, piling, flooring, sash,

doors, blinds, general millvvork, and boxes and crates.

Pine, Southern Yellow

There are a number of species included in the group marketed as

southern yellow pine lumber. The most important, and their growth

range, are:

(1) Longleaf pine {Pinus palustris), which grows from eastern

North Carolina southward into Florida and westward into eastern
30 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Texas. (2) Shortleaf pine (P. echinata), which grows from southeastern New York and New Jersey southward to northern Florida

and westward into eastern Texas and Oklahoma. Northern limits of

growth are the Ohio Valley and southern Missouri. (3) Loblolly

pine (P. taeda), which grows from Maryland southward through the

Atlantic Coastal Plain and Piedmont Plateau into Florida and westward into eastern Texas. The northern limit of growth west of the

Appalachian Mountains is near the southern Tennessee border. (4)

vSlash pine (P. elliottii), which grows in Florida and the southern parts

of South Carolina, Georgia, Alabama, Mississippi, and Louisiana

east of the Mississippi River.

Lumber from any one or from any mixture of two or more of these

species is classified as southern yellow pine by the grading standards

of the industry. These standards provide also for lumber that is

produced from trees of the longleaf and slash pine species to be classified as longleaf yellow pine if conforming to the growth-ring and summerwood requirements of such standards. The lumber that is classified

as longleaf in the domestic trade is known also as pitch pine in the

export trade.

vSouthern yellow pine lumber comes principally from the Southern

and South Atlantic States. States that lead in production are Georgia,

Alabama, North Carolina, and Texas.

The wood of the various southern yellow pines is quite similar in

appearance. The sapwood is yellowish white and the heartwood

reddish brown. The sapwood is usually white in second-growth

stands. Heartwood begins to form when the tree is about 20 3^ears

old. In old, slow-growth trees, sapwood ma}^ be only 1 or 2 inches

in width.

Longleaf and slash pine are classed as heavy, strong, stiff, hard, and

moderately high in shock resistance. Shortleaf and loblolly pine are

usually somewhat lighter in weight than longleaf. All the southern

yellow pines have moderately large shrinkage but stay in place well

when properly seasoned.

In order to obtain heav}^ strong wood of the southern yellow pines

for structural purposes, a density rule has been written that specifies

certain visual characteristics for structural timbers.

Dense southern yellow pine is used extensively in construction of

factories, warehouses, bridges, trestles, and docks in the form of

stringers, beams, posts, joists, and piling. Lumber of lower density

and strength finds many uses for building material, such as interior

finish, sheathing, subflooring, and joists, and for boxes and crates.

Southern yellow pine is used also for tight and slack cooperage.

\yiien used for railroad ties, telephone and telegraph poles, and mine

timbers, it is treated with preservatives.

Pine, Sugar

Sugar pine {Pinus lamhertiana) is sometimes called California

sugar pine. The range of sugar pine extends from the Coast and

Cascade Mountain Ranges of southern Oregon along the Coast Ranges

and the Sierra Nevada of California. Most of the sugar pine lumber

is produced in California and the remainder in southwestern Oregon.

The heartwood of sugar pine is buif or light brown, sometimes
WOOD HANDBOOK 31

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 small shrinkage, is readily seasoned without warping or

checking, and stays in place well. This species is hght in weight,

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

and low in stiffness.

Sugar pine is used almost entirely for lumber products. The largest

amounts are used in boxes and crates, sash, doors, frames, bUnds,

general millwork, building construction, and foundry patterns.

Like eastern white pine, sugar pine is suitable for use in nearly every

part of a house because of che ease with which it can be cut, its ability

to stay in place, and its good naiUng properties. It is readily available in wide, thick pieces practically free from defects.

Pine, Virginia

Virginia pine {Pinus virgin lana), known also as Jersey pine and scrub

pine, grows from New Jersey and Virginia throughout the Appalachian

region to Georgia and the Ohio Valley. The hoartwood is orange and

the sapwood nearly white and relatively thick. The wood is rated

as moderately heavy, moderately strong, moderately hard, and moderately stiff and has moderately large shrinkage and high shock resistance. It is used for lumber, railroad ties, mine props, and fuel.

Pine, Western White

Western white pine (Pinus monticola) is also known as Idaho white

pine or white pine. In the United States, it grows in western Montana, northern Idaho, and along the Cascade Mountains and Sierra

Nevada through Washington and Oregon to central California.

About four-fiftlis of the cut comes from Idaho with the remainder

mostly from Washington; small amounts are cut in Montana and

Oregon.

Heartwood of western white pine is cream colored to light reddish

brown and darkens on exposure. The sapwood is yellowish \vhite

and generally from 1 to 3 inches wide. The wood is straight grained,

easy to work, easily kiln-dried, and stays in place well after se^asoning.

This species is moderately light in weight, moderately low in

strength, moderately soft, moderately stiff, moderately low in shock

resistance, and has moderately large shrinkage.

Practically all western white pine is sawed into lumber and used

mainly for building construction, matches, boxes, patterns, and

millwork products, such as sash, frames, doors, and blinds. In

building construction, boards of the lower grades are used for sheathing,

subflooring, and roof strips. High-grade material is made into siding

of various kinds, exterior and interior trim, and knotty finish. It has

practically the same uses as eastern white pine and sugar pine.

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, Oreg., southward to California. It

does not extend more than 40 miles iidand.
32 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

The heartwood of Port-Orford-codar is light yellow to pale brown in

color. Sapwood is thin and hard to distinguish. The wood has fine

texture, generall}^ straight grain, and a pleasant spicy odor. It is

moderately light in weight, 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 stays in place w^ell after seasoning.

A large proportion of the high-grade Port-Orford-cedar is used in

the manufacture of battery separators and venetian-blind slats.

Other uses are mothproof boxes, sash and door construction, flooring,

interior finish, furniture, and boatbuilding.

Redcedar, Eastern

Eastern redcodar {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 red oi dull red, and the thin

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 small shrinkage and stays in place w^ell after seasoning.

The texture is fine and uniform. Grain is usually straight, except

where deflected by knots, which are numerous. 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, pencils, scientific instruments, and small

boats. Southern redcedar is used for the same purposes.

Redcedar, Western

Western redcedar {Thuja plicata) growls in northern California,

western Oregon, w^estern and northeastern Washington, northern

Idaho, and northwestern Montana. It grows also along the Pacific

coast northward to Alaska. Western redcedar is also called canoe

cedar, giant arborvitae, shinglewood, and Pacific redcedar. Western

redcedar lumber is produced principally in AVashington, followed by

Oregon, Idaho, and Montana.

The heartw^ood of western redcedar is reddish brown and the

sapwood nearly white. The sapwood is narrow, often not over 1

inch in wddth. The wood is generally straight grained and has a

uniform but rather coarse texture. It has very small shrinkage.

This species is light in weight, moderately soft, low in strength when

used as a beam or post, and low in shock resistance. Its heartwood

is very resistant to decay.

Western redcedar is used principally for shingles, lumber, poles,

posts, and piling. The lumber is used for exterior siding, interior

finish, greenhouse construction, ship and boat building, boxes and

crates, sash, doors, and millw^ork.
WOOD HANDBOOK 33

Redwood

Redwood (Sequoia sem/pervirens) is a very large tree growing on the

coast of California. Another sequoia, giant sequoia {Sequoia qigantea), grows in a limited are*a in the Sierra Nevada of California.

Other nanies for redwood are coast redwood, California redwood,

and sequoia. Production of redwood lumber is limited to California'

The heartwood of redwood varies from a light cherry to a dark

mahogany. The narrow sapwood is almost white. Typical oldgrowth redwood is moderately light in weight, moderately strong and

stiff, and moderately hard. The w^ood is easy to work, generally

straight grained,^ and shrinks and swells comparatively little. The

heartwood has high decay resistance.

Most redwood lumber is used for building. It is remanufactured

extensively into siding, sash, doors, blinds, finish, casket stock, and

containers. Because of its durability, it is useful for cooling towers,

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. The wood

splits readily and the manufacture of split products, such as posts and

fence material, is an important business in the redwood area.

Spruce, Eastern

The term ^'eastern spruce" includes three species, red (Picea ruhens),

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

spruce grow principally in the Lake States and New England, and red

spruce in New England and the Appalachian Mountains. All three

species have about the same properties, and in commerce no distinction is made between them. The wood dries easily, stays in place

well, is moderately light in weight and easily worked, has moderate

shrinlvage, and is moderately strong, stiff, tough, and hard. The

wood is light in color, and there is little difference between the heartwood and sapwood.

The largest use of eastern spruce is for pulpwood. It is used for

framing material, general millwork, boxes and crates, ladder rails,

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

sometimes known by other names, such 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.

Most of the remainder comes from 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 % inch to 2 inches in width

and is often difficult to distinguish from heartwood. The wood has

medium to fine texture and is without characteristic taste or odor.

It is generally straight grained. Engelmann spruce is rated as light

in weight. It is low in strength as a beam or post. It is limber, soft,
34 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

low in shock resistance, and has moderately small shrinkage. The

lumber contains small knots.

Engelmann spruce is used principally for lumber and for mine

timbers, railroad ties, and poles. It is used also in building construction in the form of dimension stock, flooring, sheathing, and studding.

It has excellent pulp- and paper-making properties.

Spruce, Sitka

Sitka spruce {Picea sitchensis) is a tree of large size growing along

the northwestern coast of North America from California to Alaska.

It is generally known as Sitka spruce, although other names may be

applied locally, such as yellow spruce, tideland spruce, western spruce,

silver spruce, and west coast spruce. About two-thirds of the production of Sitka spruce lumber comes from Washington and one-third

from Oregon. Small amounts are produced in California.

The heartwood of Sitka spruce is a light pinkish brown. The sapwood is creamy white and shades gradually into the heartwood; it

may be 3 to 6 inches 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 light in weight, moderately low in bending and compressive strength, moderately stiff,

moderately soft, and moderately low in resistance to shock. It has

moderately small shrinkage. On the basis of weight, it rates high in

strength properties and can be obtained in clear, straight-grained

pieces of large size.

Sitka spruce is used principally for lumber, pulpwood, and cooperage. Boxes and crates account for about one-half of the remanufactured lumber. Other important uses are furniture, planing-mill

products, sash, 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) is a small- to medium-sized tree with a

straight, round, slightly tapered trunk. In the United States it

grows from Maine to Minnesota, with the bulk of the stand in the

Lake States. It was formerly used in considerable quantity for

lumber, but in recent years production for that purpose has been

small.

The heartwood of tamarack is yellowish brown to russet brown.

The sapwood is whitish, generally less than an inch wide. The wood

is coarse in texture, without odor or taste, and the transition from

springwood to summerwood is abrupt. The w^ood is intermediate in

weight and in most mechanical properties.

Tamarack is used principally for pulpwood, lumber, railroad ties,

mine timbers, fuel, fence posts, telegraph poles, and scaffolding poles.

Lumber goes into framing material, tank construction, and boxes and

crates.
WOOD HANDBOOK 35

Whitecedar, Northern and Atlantic

There are two species of whitececlar in the eastern part of the

United States—northern whitececlar {Thuja occidentalis) and Atlantic

whitecedar (Chamaecyparis thyoides). Northern whitecedar is also

known as arborvitae, or simply cedar. Atlantic whitecedar is also

known as juniper, southern whitecedar, swamp cedar, and boat

cedar.

Northern whitecedar grows from Maine southward along the Appalachian Mountain Range and westward through the northern part

of the 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 whitecedar lumber is probably greatest in

Maine and the Lake States. Commercial production of Atlantic

whitecedar centers in North Carolina and along the gulf coast.

The heartwood of whitecedar is light brown, and the sapwood is

white or nearly so. The sapwood is usually thin. The wood is light

in weight, rather soft and low in strength, and low in shock resistance.

It shrinks little in drying. It is easily worked, holds paint well,

and the heartwood is highly resistant to decay. The two species are

used for similar purposes, mostly for poles, ties, lumber, and posts.

Whitecedar lumber is used principally where high degree of durability

is needed, as in tanks and boats, and for woodenware.

LITERATURE CITED

(1) BETTS, H. S.

1945. [Individual Leaflets on Tree Species, With Production Figures.]

U. S, Dept. Agr., Forest Serv. Amer. Woods Ser.

(2) BROWN, H. P., PANSHIN, A. J., AND FORSAITH, C. C.

1949. TEXTBOOK OF WOOD TECHNOLOOY. VOL. I. STRUCTURE, IDENTIFICATION, DEFECTS, AND USES OF THE COMMERCIAL WOODS OF THE

UNITED STATES. 652 pp., illus. New York.

(3) KOEHLER, A.

1924. PROPERTIES AND USES OF WOOD. 354 pp., illus. Ncw York.

(4)

1943. GUIDE TO DETERMINING SLOPE OF GRAIN IN LUMBER AND VENEER.

U. S. Forest Prod. Lab. Rpt. 1585, [56] pp., illus. [Processed.]

(5) MARKWARDT, L. J.

1930. COMPARATIVE STRENGTH PROPERTIES OF WOODS GROWN IN THE UNIL ED

STATES. U. S. Dept. Agr. Tech. Bui. 158, 39 pp., illus.

(6) and HECK, G. E.

1938. STANDARD TERMS FOR DESCRIBING WOOD. U. S. ForCSt Prod. Lai).

Rept. 111169, [b] pp. [Processed.]

(7) WANGAARD, F. F.

1950. MECHANICAL PROPERTIES OF WOOD. 377 pp., iUus. New York.
PHYSICAL PROPERTIES OF WOOD

DECORATIVE FEATURES OF COMMON WOODS

The decorative value of wood depends upon its color, figure, luster,

and the way in which it bleaches or takes fillers, stains, fumes, and

transparent finishes (20).'^ Because of the combinations of color

and the multiplicity of shades found in wood, it is impossible to

give detailed descriptions of the colors of the various kinds. The

sapwood of most species, however, is light in color, and in some species

it is practically white. The white sapwood of certain species, such

as maple, is preferable to the heartwood for specific uses. In some

species, such as hemlock, the true firs, basswood, cottonwood, and

beech, there is little or no difference in color between sapwood and

heartwood, but in most species the heartwood is darker and fairly

uniform in color. Table 2 describes in a general way the color of the

heartwood of the more common kinds of woods.

Some types of figure are moi'c ])ronounced in plainsawed lumber

and others in quartersawed (table 2). Often lumber is neither

strictly plainsawed nor strictlv quartersawed but rather is intermediate,

thereby losing some of its decorative efi'ect.

In plainsawed boards and lotary-cut veneer, the annual growth

rings frequently foi'm ellipses and parabolas that make striking

figures, especially when the rings are irregular in width and outline on

the cut surface. On quartersawed surfaces, these rings foi'm stripes,

which are not especially ornamental unless the}^ are irregular in width

and direction. The relatively large rays, often referred to as flakes,

form a conspicuous figure in quartersawed oak and sycamore. With

interlocked grain, which slopes in alternate directions in successive

layers from the center of the tree outward, quartersawed 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 plainsawed lumber.

In open-grained hardwoods, the appearance of both plainsawed

and quartersawed 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 more by appl3âng a stain.

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.

IDENTIFICATION OF WOOD

Famiharity with most kinds of wood makes it possible to identify

them by their general appearance. In the technical identification of

wood and for instruction purposes, specific differences must be

pointed out. Some woods, such as black walnut, can readily be

identified by their color; others, such as Douglas-fir, cypress, and the

cedars, can be distinguished by their odor. Many woods have a

pronounced difference in color between sapwood and heartwood,

2 Italic numbers in parentheses refer to Literature Cited, p. 63.
38 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLE 2.—Color and figure of common kinds of wood

HARDWOODS

Species Color of heartwood i

Type of figure in—

Plainsawed lumber or Quartersawed lumber or

rotary-cut veneer quarter-sliced veneer

Alder, red.

Ash:

Oregon.

WhiteAspen

Basswood--

Beech, American.

Pale pinkish brown_.

Moderately dark grayish

brown.

Grayish brown, sometimes with reddish

tinge.

.---do

Light brown

Creamy white to creamy

brown, sometimes reddish.

White with reddish

tinge, to reddish

brown.

Faint growth ring.-

Conspicuous growth ring;

occasional burl.

do

---.do

Faint growth ring.,

---.do

-doBirch:

Paper Light brown

Sweet ; Dark reddish brown.

Yellow Î Reddish brown

Butternut Light chestnut brown

-do..

with occasional reddish tinge or streaks.

Light to dark reddish

I brown.

Chestnut, American \ Grayish brown

Cherry, black.

Distinct, not conspicuous growth ring; occasionally wavy.

.--do

Faint growth ring

Cottonwood ' Grayish white to light

V j grayish brown.

Elm:

American and rock.. Light grayish brown,

usually with reddish

tinge.

Slippery Dark brown with shades

of red.

Light yellowish or greenish gray.

Reddish brown

Faint growth ring; occasional burl.

Conspicuous growth

ring.

Faint growth ring

Cherry red..

Hackberry. .

Hickory

HoneylocustLocust, black Golden brown, some

times with tinge of

green.

Magnolia Light to dark yellowish

brown with greenish

or purplish tinge.

See footnotes at end of table.

Distinct, not conspicuous, with fine wavy

pattern within each

growth ring.

Conspicuous growth ring,

with fine pattern within each growth ring.

Conspicuous growth ring.

Distinct, not conspicuous growth ring.

Conspicuous growth

ring.

Conspicuous growth

rings.

Faint growth ring

Scattered large flakes,

sometimes entirely absent.

Distinct, not conspicuous

growth-ring stripe; occa<5Íonal burl.

Do.

Do.

Xone.

Do.

Xumberous small flakes

up to \i inch in height.

None.

Occasionally wavy.

Do.

None.

Occasional burl.

Distinct, not conspicuous

growth-ring stripe.

None.

Faint growth-ring stripe.

Distinct, not conspicuous growth-ring stripe.

Distinct, not conspicuous

growth-ring stripe.

Faint growth-ring stripe.

Distinct, no conspicuous

growth-ring stripe.

Do.

None.
WOOD HANDBOOK 39

TABLE 2.—Color and figure of common kinds of wood—CoDtinucd

HARDWOODS

Species Color of hcartwood i

Maple: Black, biglcaf, red,

silver, and sugar.

Oak:

All species of red oak

group.

All species of white

oak group.

Sugarberry _

Sweetgum.

SycamoreLight reddish brown.

Grayish brown, usually

with fleshy tinge.

Grayish brown, rarely

with fleshy tinge.

Light yellowish or greenish gray.

Reddish brown

^i'y])e of fiuurr iiiI

Plainsawed lumb(>r or I (¿uartersaw(Ml luTnl)er or

rolary-rut veneer fiuarter-sliee<l veneer

Faint growth ring, occasionally birdse ye,

curly, and wavy.

Conspicuous growth

ring.

Flesh brown.

Tupelo: Black and water.

Walnut, black

Yellow-poplar

Pale to moderately dark

brownish gray.

Chocolate brown occasionally with darker,

sometimes purplish

streaks.

Light to dark yellowish

brown with greenish

or purplish tinge.

-do.

Faint growth ring; occas i o n a11 y irregular

darker strt^aks in

"figured" gum.

Faint growth ring

.do..

Distinct, not conspicuous growth rinu; occasionally wavy, curly,

burl, and other ty|)es.

Faint growth ring

Occasionally curly and

wavy.

I'ronounced flake; distinct, not conspicuous

growth-ring stripe.

Do.

Distinct, not consiñcuous

growth-ring stripe.

Distinct, not pronounced

ribbon; ocasionally irregular darker streaks

in "figured" gum.

Numerous pronounced

flakes up to Vi inch in

heik^ht.

Distinct, not pronounced

ribbon.

Distinct, not conspicuous

growth-ring stripe; occasionally wavy, curly,

burl, crotch, and other

types.

None.

SOFTWOODS

Baldcypress Light yellowish brown

to reddish brown.

Conspicuous irregular

growth ring.

Distinct, not conspicuous

growth-ring strij)e.

Cedar:

Alaska- Yellow Faint growth ring None.

Atlantic white- Light brown with red- Distinct, not conspicuous Do.

Eastern redcedar

dish tinge.

Brick red to deep reddish brown.

growth ring.

Occasionally streaks of

white sapwood alternating with heartOccasionally streaks of

white sapwood alternating with heartwood

Incense- Reddish brown

wood.

Faint growth ring.

do

Faint growth-ring stripe.

Northern whitePnrf-OrfnrdDo.

Light yellow to pale

brown.

Reddish brown

do None.

Western redcedar Distinct, not conspicuous Faint growth-ring stripe.

Douglas-fir Orange red to red; sometimes yellow.

Nearly white._.

growth riníí.

Conspicuous growth

ring.

Distinct, not conspicuous growth ring.

Distinct, not conspicuous

Fir:

Balsam

growth-ring strii)e.

Faint growth-ring ^tripe.

See footnotes at end of table.
40 HANDBOOK 72, U. S. DEPARTMENT OF AiiRICULTURE

TARLK 2.—f'olnr and fujiire of common kinrh of wood—Continued

so P^T WOODS

Type of fitiurc inS pecios Color of heartwood '

Plainsawed lumber or

rotary-cut veneer

Quartersawed lumber or

quarter-sliced veneer

Fir—Continucil

White Nearly white to pale re(l- Conspicuous erowth Distinct, not conspicuous

dish brown. riníí growth-ring stripe.

Ifeinlock:

Eastern Litfht reddish brown Distinct, not coivspicuous growth ring.

Faint growth-ring stripe.

Western

Larcii, western ..

do ... do Do.

Russet to reddish brown Conspicuous growth

ring.

Distinct, not conspicuous

Pine:

Eastern white

growth-ring stripe.

Cream to li;.;ht reddish Faint growth ring None.

brown.

Lodirepole Li!.dit reddish brown Distinct, not conspicuous growth ring; faint

Do.

"pocked" app<'arance.

Ponderosa Oran^'e to reddish brown Distinct, not conspicuous growth ring.

Faint growth-ring stripe.

Red do do Do.

Southern yellow - do Coiisi)icuous growth Distinct, not conspicuous

ring. growth-ring stripe.

Suuar - Eii;ht creamy brown

Cream to liidit reddish

bi-(»wn.

Faint growth ring.

do

None.

^\'estern white Do.

Redwood Clierry to deep reddish Distinct, not conspicu- Faint growth-ring stripe;

brown. ous growth ring; occa- occasionally wavy and

sionally wavy and burl.

burl.

Sijruce:

Black, EniTolmann, Nearly white Faint growth ring None.

red, white.

Sitka Liuht reddish brown Distinct, not conspicuous growth ring.

Faint growth-ring stripe.

Tamarack Russet brown Conspicuous growth Distinct, not conspicuous

ring. growth-ring stripe.

1 The sapwood of all species is light in color or virtually white unless discolored by fungus or chemical

stains.

2 Includes longleaf, loblolly, shortleaf, and slash pine.

whereas in others there is no difference in color. Pitch is found

normally onl^^ in the pines, Douglas-fir, the spruces, larch, and

tamarack. Frequently, it is necessar};^ to refer to the finer details of

the structure, such as the size of the rays, the size and arrangement

of the pores, and the presence or absence of resin ducts, for accurate

identification {17, IS, 20, 21, 28, 29),

GRAIN AND TEXTURE OF WOOD

The terms ''grain" and ''texture" are commonly used rather loosely

in connection with wood. In fact, the}^ do not have any definite

meaning. Grain is often used in reference to the annual rings, as in

finc^. grain and coarse grain, but it is also emplo^^ed to indicate the
WOOD HANDBOOK 41

direction of the fibers, as in straight grain, spiral grain, and curly

grain. Painters refer to woods as open grahied and close grained,

meaning thereby the relative size of the pores, which determines

whether the piece needs a filler. Texture is often used synonymously

with grain, but usually it refers to the finer structure of the wood

rather than to the annual rings. When the words '^grain" or ''texture'' are used in connection with wood, the meaning intended should

be made perfectly clear (10),

PLAINSAWED AND OUARTERSAWED LUMBER

Lumber can be cut from a log in two distinct ways: Tangent to the

annual rings, producing ^'plainsawed" lumber in hardwoods and

'^flat-grained" or '^slash-grained" lumber in softwoods; and radially

to the rings or parallel to the rays, producing '^quartersawed" lumber

in hardwoods and '^edge-grained" or '^vertical-grained" lumber in

softwoods (fig. 4). Usually so-called quartersawcd or edge-grained

lumber is not cut strictly parallel with the rays; and often in plainsawed boards the surfaces next to the edges are far from l)eing tangent

to the rings. In commercial practice, lumber with rings at angles oí

45° to 90° with the surface is called quartersawed, and lumber with

rings at angles of 0° to 45° with the surface is called plainsawed.

Hardwood lumber in which the annual rings make angles of 30° to 60°

with the faces is sometimes called '^bastard sawn."

A B

ZM 554 F

FIGURE 4.—Quartersawed {A) and plainsawed {B) boards cut from a lo^-.
42 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

For many purposes either plainsawed or quartersawed lumber is

satisfacto^^ Each type has certain advantages, however, that may

be important in a particular use. Some of the advantages oí plamsawed or flat-2:rained lumber are: , • i i i

(1) It is cheaper, as a rule, because less time is required and less

waste is involved in sawing it from the log. ,

(2) The figure patterns resulting from the annual rings and some

other types of figure are brought out more conspicuously.

(3) Round or oval knots that may occur in plainsawed boards

affect the surface appearance less than spike knots that may occur

in quartersawed boards. Also, a board with a round or oval knot is

weakened less by the knot than a board with a spike knot. A greater

percentage of the boards from a log sawed to produce the maximum

amount of plainsawed lumber will contain knots, however, than will

boards from a log sawed to produce the maximum amount of quartersawed material. i .i i. i

(4) Shakes and pitch pockets when present extend through lewer

boards.

(5) It does not collapse so easily m drying.

(6) It shrinks and swells less in thickness.

The principal advantages of quartersawed or edge-gramed lumber

are:

(1) It shrinks and swells less m width.

(2) It twists and cups less.

(3) It surface-checks and splits less in seasoning and m use.

(4) Raised grain caused by separation in the annual rings does not

become so pronounced.

(5) It wears more evenly.

(6) Types of figure coming from pronounced rays, interlocked gram,

and wa\^ grain are brought out more conspicuously.

(7) It does not allow hquids to pass into or through it so readily

in some species.

(8) It holds paint better in some species.

(9) The sapwood appearing in boards is at the edges and its width

is limited according to the width of the sapwood in the log.

WEATHERING OF WOOD

Boards exposed to the weather without a protective coating rapidly

become weathered. Weathering may involve change in color, roughening and checking of the surface, and, if one side of the board only

is fully exposed, cupping and tearing loose from fastenings, but it

does not include decay. With ah species, edge-grained boards check

less conspicuously and cup less than flat-grained boards of the same

species. Thin boards tend to cup more than thick boards do. To

resist weatheiing well, boards should be no more than 8 times as wide

as they are thick. Weathering may cause boards that are both too

thin and too short, say less than 2 feet long, to split.

Actual erosion of wood from the surface due to weathering takes

place very slowly ; approximately a century is required for one-fourth

inch of thickness to waste away. Twisting, another although less

common effect of weathering, is caused primarily by uneven shrinkage

resulting from spiral and interlocked grain; it is more pronounced in
WOOD HANDBOOK 43

plainsawed than in quartersawed boards. Wcathering;, as a rule,

changes all woods to a gray color, darker in some woods than in others,

and attractive when accompanied by a silvery sheen, as it often is.

Metal fastenings for wood that is exposed to the weather should be

highly resistant to corrosion.

Light-gray color

silvery sheen.

and

Woods

withthat weather

Light-gray color and

moderate sheen.

Dark-gray color and

little or no sheen.

Woods on which

weather checks are—

Inconspicuous.

ConspicuousÍBaldcypress

Cedar: AlaskaPort-OrfordAspen

Basswood

Birch

Cottonwood

Hemlock: Eastern

Western

Hickory

Maple

Pine: Eastern white

Ponderosa

vengar

Western white

Spruce: Eastern

Sitka

Sweetgum

Yellow-poplar

Ash

Chestnut

Douglas-fir

Fir, commercial white

Larch, western

Oak: Red

White

Pine, southern yellow

Redcedar, western

Redwood

.Walnut, black

^\spen

Baldcypress

Cedar: AlaskaPort-OrfordWestern redcedar

Redwood

Yellow-poplar

Ash

Basswood

Birch

Chestnut

Cottonwood

Douglas-fir

Fir, conmiercial white

Hemlock: Eastern

Western

Hickory

Larch, western

Maple

Oak: Red

White

Pine: Eastern white

Ponderosa

Southern yellow

Sugar

Western white

Spruce: Eastern

Sitka

Sweetgum

Walnut, })lack

303747°—55-
44 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Woods that cup and

tend to pull loose

from fastenings when

exposed to the weather

SlightDistinct.

'Baldcypress

Cedar: AlaskaPort-OrfordWestern redcedar

.Redwood

Aspen

Basswood

Douglas-fir

Fir, commercial white

Hemlock: Eastern

Western

Larch, western

Pine: Eastern white

Ponderosa

Southern yellow

Sugar

Western white

Spruce: Eastern

Sitka

, Yellow-popular

\ Chestnut

UValnut, black

Ash

Birch

Cottonwood

T. ] ^Hickory Very pronounced - | Mapj^

Oak: Red

White

^ Sweetgum

^ Birch

Cottonwood

Elm

/ Sweetgum

Sycamore

Tupelo: Black

Water

^Many tropical hardwoods

Spiral grain, another cause of twisting, may occur sporadically in any species

PronouncedWoods likely to twist because of interlocked grain

when exposed to the weather

DECAY RESISTANCE OF HEARTWOOD OF NATFS^E

SPECIES

Wood kept either constantly dry or continuously submerged in

water does not decay, regardless of species or of the presence of

sapwood. A large proportion of the 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 affecting

the rate of decay. Wlien exposed to conditions that favor decay,

wood in warm, humid areas of the United States deteriorates more

rapidly than that in cool or dr}^ areas. High altitudes, as a rule,

are less favorable to decay than are low altitudes because the average

temperatures are lower and the growing seasons for fungi, which

cause decay, are shorter.

The natural decay resistance of all common native species of wood

lies in the heartwood. When untreated, the sapwood of substantially

all species has low resistance to decay and usuall}^ has a short life

under decay-producing conditions. The decay resistance of heartwood in service is greatly affected b}^ differences in the character of
WOOD HANDBOOK 45

the wood, the attacking fungus, and the conditions of exposuie. A

widely different length of hfe may therefore be o))tained from pieces

of wood cut from the same species or even the same tree and used

under apparently similar conditions. Further, in a few species, such

as the spruces and the white firs (not Douglas-fh«), the colors of the

heartwood and of the sapwood are so similar that frequently the two

cannot be easily distinguished.

Precise ratings of the decay resistance of the heartwood of different

species are not possible because of differences within a species and

the variety of service conditions to which wood is exposed. However,

broad groupings of many of the native species, based on service records,

laboratory tests, and general experience, are helpful in choosing woods

for use under conditions favorable to decay. The following list shows

(1) species with heartwood that is high in decay resistance, giving

generally satisfactory service where decay hazards exist; and (2)

species with heartwood that is moderate to low in decay resistanse,

usually requiring some form of preservative treatment to give satisfactory service under conditions that favor decay.

GROUP 1.—Species with heart/wood of high reKÍstance to decay

Sofhvoods (conifers) Hardwoods

Baldcypress Catalpa Mulberry, red

Cedars Chestnut Osage-orange

Junipers T.ocust, V)lack Walnut, black

Redwood Mesquite

Yew, Pacific

GROUP 2.—Speciei< untJi heartwood of moderate to loiv resistance to decay

Softwoods (conifers) Ifard (roods

Douglas-ñr Alders Hickory

Firs, true Ashes Iloneylocust

Hemlocks Aspens Magnolia

Larch, western Basswood Maples

Pine, ponderosa Beech Oaks

Pine, white (several spe- Birches Sassafras

cies) Butternut Sweetguni

Pine, southern yellow Cherry, black Sycamore

(several species) Cot tonwoods Túpelos

Spruces Elms Willows

Tamarack Hackberry Yellow-poplar

The heartwood of such species as Douglas-fir, eastern white pine,

honeylocust, sassafras, southern yellow pine, sweetgum, western

larch, and white oak is usually classified as moderate in decay resistance and generally gives good service under mild decay conditions.

The heartwood of the other species of Group 2 is generally lower in

decay resistance and frequently gives unsatisfactory service where

decay hazards exist. The woods of lower decay resistance are improved

by some form of preservative treatment for use under mild decay

conditions; those with moderate decay resistance are usually treated

for exposure to more severe decay hazards; and even the highly

decay-resistant woods of Group 1 may requh-e preservative treatment

for important structural and other uses where high decay hazards

exist and failure would require expensive repairs.
46 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

THERMAL CONDUCTIVITY OF WOOD

The thermal conductivity of wood is affected little by species,

except as species differ with respect to factors that influence thermal

conductivity. It does, however, vary with (1) direction of grain; (2)

specific gravity; (3) moisture content and its distribution; (4) kind,

quantity, and distribution of extractives; (5) proportion of sprmgwood

and summerwood; and (6) such features as checks, knots, and cross

o-rain (23). In normal wood, the relative rate of heat flow is approxi2.0

1.3

1.8

Í.1

1.6

L5

L4

1.3

, I.Z

I.I

1.0

0.9

0.8

0.1

0.6

0.5

0.4

0.3

0.2

0.1

-

1 1 1 1 SPECIFIC GRAVITY [BASED ON

1 VOLUME-^< n(\

^^ -

HI LUKKtzNI lYIUI^IUKL LUH/t/y/ ñnu

WEIGHT WHEN OVEN-DRV)

0$

- ^^

~ ^

^^

^

-

"'"'^^ ^^:>^ Ä^

-

^

^:^

..--^ ^ '"^''^^^

^^o.&^ Ö_:^ ^

- ^

' ''''^^

^^^

^^

"^^^;;^:>r^ 03Ö

0.5^

0.42

0.5&

0^

Ó4U

^

^^^^

-^[[[l]^-^

^c^*-'^'\„^

L^:>^^::^ c^^

"""""^^

^^^^ ^^--^

r^

^

^^^^^:^:^ ^^^

^^s^;^C^ ^ ::::^ ---^ 0.36 036 ^

^^^ ^ ^

:::::::: ^'— 0.34

030

021

o.iß

0.32 z^

^^^ C^ ^ ;;;II!II ^:^;^

Ö.Z4

azo

û.lè

0.12

^

"^^^ ^

':^ rr: ^ '^

^^^r:i^ 2:;::; ==^ I^ —=

"^^^^ m^ 0.14

-

0.10

0.08

-

-

1 1

, 1

1 1 1 \ 1 1 1 1 1 1 1

0 6 Ô 10 12 14 16 16 20 22 24 26 28 30

MOISTURE CONTENT (PERCENT)

ZM 38147 F

FIGURE 5.—Relation between computed thermal conductivity and moisure

content for wood having different specific gravity values.
WOOD HANDBOOK 47

mately the same in the radial and tangential direction, ])iit thermal

conductivity is generally 2^ to 2% times faster along the grain than

in^ the transverse directions. Since thermal conductivity increast^s

with specific gravity, the lighter weight woods are the l)etter insuhitois.

Thermal conductivity values for various specii^s are giv(^n in labh's

3 and 4. If the specific gravity (based on volume at current moisture

content and weight when oven-dry) and the moisture cont(Mit of the

wood are known, the conductivity can also })e (h^tc^^mined l)v the

chart shown in figure 5. Conductivity was computed from the

formula

/: =S'[1.39 +0.028i\/] + 0.ir)5

where k is conductivity, S is specific gravity based on volume at

current moisture content and weight when oven-(h;y, and M is moisture

content in percent.

TABLE 3.— Thermal conductivity of oven-dry wood across the grain

Species

Hardwoods:

Aspen, bigtooth

Balsa

Basswood, American _ _

Elm, rock

Maple, sugar

Oak, red 3

Prima vera

Tangile

Softwoods:

Baldcypress

AverNum- age

ber of specific

tests gravity 1

0.41

4 . 16

7 .38

1 .76

i) .6H

5 . 67

1 .47

4 ..^8

5 .39

Aver- I

age con- j

ductivitv I

k 2

0.71

.41

. m

1. 16

1. 13

1. lit

. 82

1.00

Species

Softwoods—Continued

Douglas-fir ..

Fir, white -- --

Hemlock, western. _.

Larch, western

Pine :

Southern yellow '..

White 3

Redcedar, western...

Redwood

Spruce, Engelniann..

AverNum- age

ber of specific

tests gravity •

8 0. 46

2 . 4!

2 . 46

3 . .')7

7 . ')(•)

10 .40

3 .34

8 .40

4 ,34

Average conductivitv

/: -

.6.4

.74

1 Based on volume and weight when oven-dry.

2 k is the quantity of heat expressed in British thermal units that flows in 1 hour through a 1-inch thickness of material, 1 square foot in area, when the temperature dilTerence l')etween the 2 surfaces is 1° F.

3 Average of several species.

A more detailed discussion of the thermal conductivity and insulation values of wood and wood-base materials is given on pages 445-455.

THERMAL EXPANSION OF WOOD

Dry wood, like most other solids, expands on heating and contracts

on cooling. The coefficient of linear thermal expansion (the increase

in length per unit of length for a temperature rise of 1° F.) differs m

the three different structural directions of wood. In the longitudinal

direction (along the grain) the values are independent of the specific

gravity of the wood and vary from about 1.7X10"^ to 2.5X10 ' per

1° F. for different species. Across the grain, or in the radial and tangential directions, the values, in general, vary directly with the specific

gravity (based on weight and volume when oven-dry) (35). The data

for several softwoods (Douglas-fir, Sitka spruce, redwood, and white
48 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

fir) and two of the softer hardwoods (yellow-poplar and cottonwood)

can be closely approximated by the simple relationships

a,= 45Xspecific gravityX10~^ per 1° F.

a, = 31Xspecific gravityXlO"^ per 1° F.

where cii is the coefficient of linear thermal expansion in the tangential

direction and ö, is the coefficient in the radial direction. The values

for two of the denser hardwoods (yellow birch and sugar maple) can

be approximated from the relationships

ö,= 32Xspecific gravitvXlO"^ per l'^ F.

a,= 25Xspecific gravityXlO"^ per I'' F.

The coefficient of linear thermal expansion of wood varies slightly

with temperature but for all ordinary uses may be considered constant

The coefficient of linear thermal expansion in the longitudinal direction of wood is from one-tenth to one-third of the values for the

common metals, concrete, and glass. The values for wood in the

transverse directions are generally larger than those in the longitudinal

direction, but are usually less than those of other structural materials.

The coefficients of linear thermal expansion of resin-bonded birch

laminates and plywood made from both resin-treated and untreated

veneer (imprc^g, compreg, and normal laminates and plywood) were

measured and compared with the values calculated by theoretical

equations involving the values for wood, the values for the resin, and

the modulus of elasticity values for wood in compression in the three

diñ*erent structural directions (84). The calculated values agreed

closely with the measured values. The values for the coefficient of

linear thermal expansion of resin-bonded, rotary-cut birch plywood

in the sheet directions are about 3.0X10"^ per 1° F. parallel to the

face ply and 4.2XIO'^ per l"" F. across the face ply. These values

are not much greater than the longitudinal value for the normal wood

(2.0X10-^ per 1° F.).

The coefficient of thermal expansion of wood can be neglected in

most structural designs, because the thermal expansion is much smaller

than the swelling and shrinking of the wood that occurs under normal

exposure conditions. Thermal expansion is of importance only in

the case of special structures that are kept dry and are subjected to

considerable temperature change.

Green wood behaves difierentl}^ from dry wood when heated; it

expands tangentially and shrinks radially. A discussion of this behavior and of the rate of temperature change in wood w^hen heated

would be too involved for this handbook, but information on these

subjects may be found elsewhere (^4, 25, 26).

ELECTRICAL PROPERTIES OF WOOD

The most important electrical properties of wood are its resistance

to the passage of an electric current and its dielectric properties. The

electrical resistance of wood, which is the reciprocal of the conductance,

is utilized in electric meters for determining the moisture content of

wood {11). It is of importance in connection with the use of wood

poles and crossarms to carry high-voltage electrical powerlines and

wood handles on linemen's fools. The dielectric properties—dielec-
WOOD HANDBOOK 49

TABLE 4.— Thermal conductivity of wood across the grain at various moisture coaient

values

Species

Hardwoods:

Ash, white

Aspen, big tooth

Balsa

Basswood, American...

Beech, American

Birch, yellow

Cherry, black

Chestnut, American

Elm:

American

Rock

Greenhcart

Maple:

Silver

Sugar

Oak:

Red3

White3

Pecan

Prima vera

Sweetgum

Sycamore, American..

Tangile

Tupelo, black

Softwoods:

Baldcypress

Douglas-fir

Fir,white3

Hemlock, western

Juniper, bigberry

Larch, western

Pine:

Southern yellow 3.

Whites

Redcedar, western

Redwood

Spruce

Number

of tests

Average

specific

gravity i

0. 5()

.41

. 17

.37

.59

.04

. m

.42

.54

. 65

.85

1 .47

27 . 00

12 .02

IS .02

1 .07

9 .40

1 . 55

1 .52

r. .54

1 .40

30 .38

52 .40

2 .38

5 .44

1 .44

13 .40

59 ..53

2() .30

10 .32

15 .39

12 . 35

Average

moisture

content

(percent)

15.0

12.1

8.0

9.3

11. 1

10.8

7.8

11.0

9.4

17.9

18.4

9.9

11.7

Average

conductivity k '

1.19

.H7

.44

.78

1.17

1.25

1.20

.88

1.00

1.39

1.78

.95

1.30

12.4 1.24

11. 1 1.22

10.0 1.28

9.7 . 93

11.0 1.10

9.0 1.02

10.0 1.08

10.0 .93

11.7 .82

18.4 1. 04

11.7 .82

23.0 1.00

10. 0 .97

12.0 .97

13.8 1.11

9.8 .70

13.3 .73

11.7 . 8:-!

13.0 .78

1 Based on volume at current moisture content and weight when oven-dry.

2 k is the quantity of heat expressed in British thermal units that flows in 1 hour through a 1-inch thieknrss

of material, 1 square foot in area, when the temperature difference between the 2 surfaces is 1° F.

3 Average of several species.

trie constant and power factor—assume importance when wood is

heated in an oscillating high-frequency electric field, as in the curing

of glues, and in connection with some moisture meters.

Electrical Resistance

The direct-current electrical resistance of wood {H, 16, SI, 32)

varies greatly with moisture content, especially below the fiber saturation point of 30 percent, decreasing as the moisture content increases.

It also varies with species, is greater across the gram than along it,
50 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

and approximately doubles for each drop in temperature of 22.5° F.

The electrical resistance varies inversely with the density of the wood.

Fortunately, the electrical resistance is affected so much more by

variations in moisture content that the effect of density of the wood

on moisture content determinations by the resistivity method is not

highly significant. The variation among species is probably caused

by minerals or electrolytic materials in the wood or dissolved in water

present in the wood.

Table 5 lists the electrical resistance along the grain of some common

species, at different uniform values of moisture content, between needle

electrodes driven each time to the same depth. The specific resistance,

which is the resistance of a centimeter cube of wood, varies from

3X10^^ to 3X10^^ ohm-centimeters for oven-dry wood to 10^ ohmcentimeters for wood at 16-percent moisture content (34)-

Since the electrical resistance of wood may increase as much as 10 ^

times with a moisture content change from 25 to 7 percent, the

moisture content of wood used as an insulator, as in powerline poles

or tool handles, is highly important. The leakage of current from

powerlines increases with increase in the moisture content of the crossarms and poles. Salts should not be used as a preservative treatment

for powerline poles, since the salt dissolved in the water of the wood

causes an additional lowering of the electrical resistance.

Dielectric Properties

At a low moisture content, wood is normally classified as an electrical insulator, or dielectric, rather than as a conductor (30). A dielectric can be heated by using it as the medium between electrodes

carrying charges of oscillating high-frequency electricity or placing it

in an electrical field of like nature. This property is utilized in the

curing of glue lines on wood by high-frequency electric current. The

rate at which the wood is heated and electrical power is absorbed

depends on the dielectric constant and the power factor. The resistivity of a dielectric can be determined by formula (30) from the

relationship between the dielectric constant and the power factor, and

when wood and glue lines are heated, the relative power absorbed in

the wood and in the glue lines can be calculated from the resistivity

values and dimensions of the wood and glue lines.

The dielectric constant of wood is the ratio of the capacitance of a

condenser in which the wood is used as the dielectric to the capacitance

of a similar condenser in which a vacuum dielectric is employed. The

capacitance of a condenser is measured by the quantity of electricity

put into it by a given voltage. The dielectric constant for a vacuum

or dry air is unity, and the values for wood are all greater than unity.

Since the structure and chemical composition of the cell walls of all

speci^^s are essentially similar, it is not surprising that the dielectric

constants are proportional to density at a given moisture content.

The dielectric constant of wood increases with increase in density, and

since the dielectric constant of water is approximately 81 as compared

to 4.2 for oven-dry wood, it is evident that the dielectric constant of

wood also increases with increase in moisture content. Variations in

moisture content have a greater effect on the dielectric constant than
neasured at SO"" F. between 2 pairs of needle electrodes l}i inches apart TABLEO,—The average electrical resistance along the grain in megohíus, me ... , ,

and driven to a depth of Yie inch, of several species of wood at different values of moisture content

Electrical resistance in megohms when th I moisture content in percent is—

Species

7 8 9 10

250

180

1,290

110

815

340

2, 750

2, 040

870

690

630

415

80

1.820

890

1,260

11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Hardwoods:

Ash, commercial white 12.000

36, 300

S7, 000

2,190

1, 740

19,950

2, 000

6, J60

31.600

16. 200

12, 600

6, 760

13,800

4, 790

3, 550

690

12,600

9, 770

8.320

690

470

4, 470

350

2, 090

2, 190

6.310

5, 010

2. 290

3, 160

1.590

1, 100

220

5, 020

2, 630

3,170

105

85

470

45

345

115

1,260

910

380

250

265

170

35

725

355

525

55

45

200

20

160

50

630

435

180

105

125

80

15

275

155

250

28

27

96

12

81

21

340

205

85

5.3

63

42

9

120

78

140

14

16

53

7

45

11

180

105

43

29

32

22

5

58

41

76

8.3

9.6

30. 2

3. 9

25.7

6. 3

105.0

56. 2

22.4

16.6

18.2

12. 6

2.8

27. 6

22.4

43. 7

5.0

6.2

18.2

2.3

15. 1

3.7

60. 2

29. 5

12.3

10.2

11.3

7 2

1.7

13. 0

12.9

3.2

4.1

11.5

1.5

9. 3

2.3

35. 5

16. 2

7 2

6.8

7.3

4.3

1. 1

6. 9

7.3

14.5

2.0

2.8

7. 6

1.0

6. 0

1.5

21.9

9. 1

4.4

4.5

4.6

2. 7

. 7

3.7

4.9

8. 7

1.32

1.86

5.13

. 66

3.98

1.00

14. 10

5. 25

2. 69

3. 16

3.02

1. 70

.45

2. 19

3. 16

5.76

0.89

1.32

3. 55

.48

2.63

.71

9. 33

3.09

1.66

2.24

2. 09

1.15

. 30

1.38

2.14

3.81

0.63

.93

2.51

.42

1.78

.52

6. 16

1.86

1.07

1.62

1.45

. 79

.21

.95

1.48

2.64

0. 50 0. 44

.69 . 51

1.78 1.32

.40 .40

1.26 .87

.44 .40

4.17 2.82

1.17 .74

.72 .49

1.23 .98

.95 .80

.60 .49

. 16 .12

. 63 .46

1.02 .72

1.91 1.39

0.40

.39

.95

.40

.63

.40

1.99

.50

.35

. 75

.63

.44

.09

.33

.51

1. 10

0.40

Basswood

Birch

.31

.70

Elm, American 18.200

38, 000

.40

Gum, red .46

Hickory, true -

.40

Khaya i

Magnolia

44, 600

43.700

1.44

.32

Mahogany, American

Maple, sugar

Oak: Commercial red 2...

Commercial white

Shorea 3

Tunelo black •

20, 900

7';, 400

14.400

17,400

2. 890

31,700

51,300

24.UOO

.26

60

.50

.41

"Walnut, black

Yellow-poplar K

.38

.85

Softwoods:

Baldcypress 12,600

22.400

31,600

57, 600

3,980

4, 780

6, 760

15, .S50

1,410

1. 660

2. 000

3. 980

630

630

725

1, 120

265

265

315

415

120

120

150

ISO

60

(id

83

8;^.

33

33

48

46

18. 6

18. 6

28. 8

26,. 9

11.2

11.2

15. 2

16. 6

7.1

7.1

11.8

11.0

4. 6

4.6

7. 6

6). 6

3. 09

3. 09

5. 01

4.47

1.78

2.14

3.31

3. 02

1.26

1.51

2. 29

2.14

.91

1.10

1. 58 1

1.55 1

66

79

15

12

..51

.60

.83

.86

.42

Douglas-fir (coast type)

Fir: California red

White

.46

. 63

.62

Hemlock, western 22, 900 5. 620 2. 040 S 50 400 185 9S 51 28.2 16.2 10. 0 »). 0 3.89 2. 52 1. 58 1.05 72 . 51 . 01

Larch, western 39.800 11.200 3, 980 1.445 560 250 120 63 33. 9 19. 9 12.3 7. 6 5. 02 3. 39 2. 29 1.62 1 20 . 87 .66

Pine: Eastern white

Longleaf

20, 900

25. 000

5. 120

8, 700

2, 090

3. 160

850

1,320

405

575

200

270

102

135

58

74

33. 1

41.7

19. 9

24.0

12.3

14.4

7. 9

8.9

5. 01

5. 76

3.31

3. 72

2. 19

2. 46

1.51 1

l.t>6 1

05

15

. 74

.79

.52

. 60

ronderosa 39. SOO 8,910 3.310 1,410 645 300 150 81 44.7 25.1 14.8 9. 1 5. 6.2 3. 55 2. 34 1.62 1 15 . s7 . 69

Shortleaf 43,600 11,750 3. 720 1,350 560 255 130 69 3S. 9 22.4 13.8 8. 7 5. 7») .^ SO 2. 63 1.S2 1 29 .!K3 . 6()

Sugar - 22. 900 5, 250 1,6)60 645 280 140 76 44 25. 7 15.9 10. 0 6. 6 4. 36 3. 02 2. 09 1.48 1 05 . /O . 56)

Redwood 22 400 4, 680

5, syo

1,550

2. 140

615

S30

250 100

165

45

So

22

44

12.6

25. 1 15.5

4.7

9. S

3. 2

6. 3

2. 29

4.27

1.74

3. 02

1.32

2. 14

1.05

1. ,-)S 1

S 5

17

.71

.91

. 6)0

Spruce, Sitka - 22, 400 .71

1 Known in the trade los "African mahogany." - The values for this species were calculated frcm measurements on veneer.

3 A PhiUppine hardwood, identified as tangile or some similar species.

Oi
52 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

do variations in density. The parallel-to-grain dielectric constant of

wood is significantly greater than the corresponding perpendicular-tograin constant. The dielectric constant of wood decreases with an

increase in frequency of the oscillating current.

The power factor of wood is the ratio of the power absorbed in the

wood per cycle of oscillation of an electric current to the total apparent

power stored in the wood during that cycle. The power factor of wood

is less dependent on density than is the dielectric constant but generally increases with increase in moisture content. At moisture content values of 0 to 7 percent, the parallel-to-grain power factors are

greater than the corresponding perpendicular-to-grain po\yer factors.

The power factor varies with the frequency of the oscillating current

and is greater at high frequencies when the wood is at a moisture content of 15 percent or lower.

EFFECT OF CHEMICALS ON WOOD

Wood is highly resistant to a number of chemicals. For this reason,

it is used for various types of tanks, containers, and equipment in

which chemicals are used and for structures near such equipment that

may contact chemicals through spillage, leakage, or condensation.

Wood owes its extensive use in chemical equipment largely to its

superiority over cast iron and ordinary steel in resistance to mild acids

and solutions of acidic salts. Iron is far superior to wood in resistance

to alkalies, however, and wood is therefore seldom used in contact with

solutions that are more than weakly alkaline.

Experience has shown that the heartwood of cypress, southern yellow

pine, Douglas-fir, and redwood is the most suitable for water tanks

(13) j and heartwood of the first three species for tanks for use where

resistance to chemicals in appreciable concentrations is an important

factor. The four species combine moderate to high resistance to water

penetration with moderate to high natural resistance to decay and

hydrolysis.

Chemicals may afi'ect the strength of wood by three general types

of action. The first involves swelling and the resultant weakening of

the wood. This action is almost completely reversible, so that, if the

swelling liquid or solution is removed by evaporation or by extraction

followed by evaporation of the solvent, the original dimensions and

strength are practically restored. The second type of action involves

permanent changes in the wood, such as hydrolysis of the cellulose by

acids or acid salts. The third type of action, which is also permanent,

involves delignification of the wood and dissolving of hemicelluloses

by alkalies. Occasionally dilute sodium carbonate solutions show

some action of this type on the wood of cooling towers. There is

also some evidence that iron salts catalyze oxidation of wood and

precipitate toxic extractives, thus lowering its natural decay resistance.

The strength properties of water-swollen wood are in general

considerably lower, and in some cases more than 50 percent lower

(27, 36), than those for wood at 12 percent moisture content, which

is about the average moisture content in normal use. This must be

taken into account in designing tanks for water and dilute aqueous
WOOD HANDBOOK 53

solutions or other structures in which the wood memhers nre wet for

an appreciable time.

Alcohols and other wood-swelUng organic licjuids that do not react

chemically with wood reduce its compressive strengtli proportionally

to the extent of swelling (12). A hquid such as acetone that swells

wood 60 percent as much as water will cause 60 percent as much loss

in strength as is caused by swelling in water. Nonswehing liquids,

such as petroleum oils and creosote, liave a negligible effect upon woocl

strength (see p. 420). Castor-oil hydrauhc fluids swell wood to some

extent, and reduce bending and compressive strength to an extent

that depends upon the depth of penetration of the fluid and presumably the degree of swelling of the wood (10),

Acids have a hydrolytic effect upon the cellulose of wood and thus

cause some permanent loss in strength (tal)le 6). The weakening

effect of alkalies (table 6) appears to be caused by a combination of

excessive swelling and softening and dissolving of lignin and hemicelluloses. It appears however that acids with pH values above 2

or bases with pH values below 10 have little weakening effect upon

wood at room temperature if length of exposure is moderate {6, 22).

TABLE 6.—Ratios of loss in strength of wood specimens soaked for 4 weeks in acids

and bases at room temperature, to loss of strength of ivater-soaked specimens ^

Ratio 2 of modulus of rupture of specimens

indicated concentration 3

soaked in the following acids or 1

to that of specimens soaked in \vi

)ases 0

iter

f the

Species

Hydrochloric acid

Sulfuric

acid Nitric acid Lactic acid

_

Acetic acid Sodium

hydroxi<le

Ammonium

il yd ro .vide

2 10 2 10 2 10 2 10 2 10 2 10 2 10

percent

percentpercentpercentpercentpercentpercentpercentpercentpercent

percentpercent

percent

I percent

Larch 1.09 0.81 1. 11 1.00 1.07 0. 95 1.21 1.10 1.07 1.04 0. 96 0. 52 1.06 0. 92

Pine 1.08 .84 1.13 .84 1.07 .93 1.25 1. 11 1. 11 .88 . 96 .51 1.00 .79

Spruce 1.00 .82 1.02 .94 .98 .96 1.00 1.04 1.09 .99 .93 .44 .98 . 75

Beech .96 .55 .97 .87 .83 .71 1.13 1.02 .97 .93 .59 .31 .67 .43

Oak .93 .52 .97 .82 .82 .65 .99 1.05 .96 .87 .58 .29 .65 . 36

Basswood... .88 .48 .87 .81 .76 .57 1.08 .96 1.09 1.00 .55 .21 .61 .33

' Values greater than unity indicate greater penetration and swelling by water than y)y the chemical

solutions, thus causing greater loss of strength of water-soaked than of chemical-soaked specimens.

2 Percent by weight.

3 Data from "Technologie des Holzes" by F. Kollman (B<'rlin, 1936).

Highly acidic acid salts, such as zinc chloride, tend to hydrolyze

wood if they are present in appreciable concentrations. Fortunately,

the concentrations used in wood-preservative and fire-retardant

treatments are sufficiently small, so that the strength properties other

than impact resistance are not greatly affected under normal use

conditions (<?, 15). A significant loss in impact strength may occur,

however, if higher concentrations are used. When used in hot arid

regions, railroad ties containing relatively low concentrations of zinc

chloride show signs of migration of the salt to the surface caused by

occasional wetting and drying. This migration, combined witli the

high concentrations of salt relative to the small amount of water
54 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

present, causes an acidic condition sufficient to make the wood brittle.

None of the other common salt preservatives when used in high concentrations is as acidic as zinc chloride, so that their effect upon the

strength of the wood can be disregarded in most cases (see p. 420).

Iron salts are frequently very acidic and show hydrolytic action on

w ood in the presence of free water. The softening and discoloration

of the wood around corroded nails results from a partial h3^drolysis

of the wood. This action is especially pronounced in acidic woods,

such as oak, and in woods containing considerable tannin and related

compounds, such as redwood. It can be eliminated by using zinccoated aluminum or copper nails.

A process commonly known as niggerizing has been used for some

time to provide wood with increased acid resistance (5, 4, 5). In

this process wood is treated with a coke-oven coal tar having a viscosity between 1,250 and 1,450 Savbolt seconds at 200^ F., a flashpoint of 270"^ to 310°, and a fire point of 335° to 375°. Coal tar is

the preferred treating material and heartwood of baldcypress or

southern yellow pine the preferred wood for niggerizing {2). Acidresistant paints have not proved suitable for protecting wood in continuous exposure to acids {1,2). Tests on small laboratory specimens

show that phenol resin treatment greatly increases the acid resistance

of wood {S3), but the difficulty and cost of treating by this method

limit its use.

A new proprietary acid-resistant treating agent, somewhat similar

to niggerizing agents, is claimed to increase materially the acid

resistance of wood. Favorable service tests have been made on wood

treated with this material (5, 4, 5, 7) for use in filter plates and frames;

acid-storage tanks; ''duck boards," walks, and platforms subject to

acid spillage or drip; ducts for acid vapors; drainage boxes; and

lumber, in general, used near operations involving the use of acid.

WEIGHT OF VARIOUS WOODS

Calculated weights of sawed or round timbers are necessarily

approximate values owing to variations in moisture content, density,

sapwood thickness, and the like that occur in different parts of the

same timber. The calculated average weights obtained by the methods given in this section are not 100-percent accurate, but are more

accurate than the weights commonly given in grading rules as a

basis for estimating timber transportation costs or other exacting

transactions. The methods described here are also useful for roughly

determining truck capacity needed to haul a given lot of timbers or

the possibility of driving or towing logs. There is enough difference

between the weights of sawed and round timbers to require separate

methods for estimating their average weights.

Sawed Timbers

Table 7 gives the average weight per cubic foot of sawed timbers

of various species at moisture content values of 8 and 15 percent,

and the average weight of 1,000 board-feet when air-dry (15-percent

moisture content). Factors for adjusting values for each 1 percent

change in moisture content are given.
WOOD HANDBOOK 55

TABLE 7.—Average weights ^ of saived hardivood and softwood timbers

contents of 8 and 15 percent^ ivith adjustment factors for changes

content values

at moisture

moisture

Species

Hardwoods:

Alder, rod

Apple

Ash:

Black

Blue

Green

White.

Aspen:

Bigtooth

Quaking

Basswood, American

Beech, American

Birch:

Alaska paper

Paper

Sweet

Yellow

Buckeye, yellow

Butternut

California-laurel

Cherry, black

Chestnut, American

Chinkapin, golden

Cottonwood:

Black

Eastern

Cucumbertree

Dogwood:

Flowering

Pacific

Elm:

American

Cedar

Rock

Slippery

Hackberry

Hickory:

Mockernut

Pecan

Pignut

Shagbark

Shellbark

Water

Holly, American

Honeylocust

Hophornbeam, eastern

See footnotes at end of table.

Weight per cubic foot

Based on

weight

and volume

at a moisture content of 15

percent

Based on

wi'ight

and volunuat a moisture content of 8

perœnt

Pounmis Pounds

28.8 28. 0

48. 5 47.6

35.3 34. 3

40.7 39.2

40. 7 39.4

42.7 41.5

27.3 26.6

27.0 26. 1

2(\. 0 25. 5

44.3 43.2

38. 8 38. 0

38. 9 38. 2

47.2 46. 0

43.4 42.4

25. 5 24.8

27.4 26. 4

39. 5 38. 2

30. 1 34.8

30. 5 29.5

32. 3 31.3

24.5 23. 8

28.9 28.0

34. 3 33. 3

51.5 50. 7

45.9 44. 9

36. 3 35. 5

45.9 44. 6

44.2 42.7

37.8 36. 7

37.4 36. 2

51.4 50. 4

46. 5 45. 0

53. 4 52. 6

51.2 50. 3

49.0 47.8

44.6 42. 3

39.8 38.9

45.3 43. 6

50.0 48.8

Factor '-' for

adjusting

value for

each 1-percent change

in moisture

content

0.112

. 133

.142

. 208

. 179

.175

.104

. 129

. 175

. 142

.104

. 145

. 183

. 18:^

. 145

. 145

.104

.125

.142

. 120

. 142

.117

.187

. 20S

.154

.175

.145

.212

.120

. 129

.170

. 329

. 133

.250

.167

W(Mght per 1.000 boardfeet air-dry (15-percent moisture content)

Actual

board-feet

Pounds

2, 400

4, 040

2, 940

3, 390

3, 390

3, 560

2, 270

2, 250

2, 170

3.) "»90

3.230

3, 240

3, 930

3, »•,20

2.120

2. 280

3, 290

3. 010

2, 540

2. 690

2. 040

2.410

2, 860

4. 290

3, 820

3, 020

3, 820

3, fiSO

3.150

3. 120

4,280

3, 870

4, 450

4.270

4, 080

3. 720

3, 320

3. 770

4,170

Dressed

(1 by 8

dressed to

^ >:<2 by

7h)

Pounds

1, 7t')0

2,960

2, 150

2. 480

2,480

2,610

l,fl60

1,650

1,590

2, 700

2, 370

2,370

2, 8S0

2, ('»50

1.550

1.670

2,410

2, 200

1,860

1,970

1,490

1,770

2, 090

3,140

2,800

2.210

2.800

2, 700

2, 310

2, 290

3,130

2. 830

3.2C)0

3,130

2, 990

2, 720

2, 430

2. 760

3, 050
56 HANDBOOK U. S. DEPARTMENT OF AGRICULTURE

TABLE 7.—Average weights ^ of sawed hardwood and softwood timbers at moisture

contents of 8 and 15 percent^ with adjustment factors for changes in moisture

content values—Continued

Species

Hardwoods—Continued

Locust, black

Madrone, Pacific

Magnolia, southern

IMangrovo

Maple:

Bipleaf

Black

Red

Silver

Sugar

Mountain-laurel

Oak, red:

Black

rherrybark

Laurel

Northern red

Southern red

Water

Willow

Oak, white:

Bur

Post

Swamp chestnut

White

Osage-orange

Palmetto, cabbage

Persimmon, common

Poplar, balsam

Sugarberry

Sweetgum

Sycamore, American

Tupelo:

Black

Water

Walnut, black

Willow, black

Yellow-poplar

Softwoods:

Baldcypress

Cedar:

AlaskaAtlantic whiteEastern redcedar

IncenseNorthern whitePort-OrfordWestern redcedar

See footnotes at end of table

Weight per cubic foot

I Based on I Based on

weight weight

and volume land volume

at a mois- I at a moisture con- ture content of 15 tent of 8

percent percent

01in(Is

49.0

45. 6

35. 5

70. 0

34.2

40. 9

37.0

33. 9

44.5

4X. 8

44.0

47.2

45. 5

43. 8

41.1

44.6

44. 0

45. 0

47.9

48. 5

40. 8

57.3

29.6

50. 8

23.2

3r.. 5

30. 4

35. 7

30. 4

35.1

38. 0

27.6

30.3

32.6

3L6

23. 8

33.5

25.5

21.8

30.1

23. 4

Pounds

40. 7

44.6

34.4

68.3

33. 2

39. 8

35. 6

32. 8

43.4

47.7

43.0

45.8

44.7

42. 5

40. 1

43.8

43.8

43.5

47.1

47.9

45. 6

.54.9

29.0

49.7

22.5

35. 3

35.5

34.7

35. 5

34.0

37.0

26.9

29.2

3L4

30.4

23.0

32.2

24.2

20.8

28.9

22.4

Factor 2 for

adjusting

value for

each ] -percent change

in moisture

content

Weight per 1,000 boardfeet air-dry (15-percent moisture content)

0. 324

. 150

. 162

.241

.145

.150

.195

.154

.154

.158

.150

. 200

.108

.187

. 142

. 120

. 112

.208

.120

.087

.167

.337

.087

.158

.100

.167

. 133

.137

.129

.l(i2

. 233

.104

.150

.170

.120

.187

.183

.145

.175

.137

Actual

board-feet

Pounds

4, 080

3. 800

2, 960

5, 8.30

2,850

3,410

3, 080

2,820

3, 710

4,070

3, 670

3, 930

3. 790

3, 6.50

3, 420

3, 720

3, 720

3, 7.50

3, 990

4,040

3, 900

4,770

2, 470

4, 230

1, 930

3, 040

3, 030

2, 970

3,030

2, 920

3,220

2,300

2,520

2,720

2,630

1,980

2.790

2,120

1,820

2, 510

1,950

I Pressed

(1 by 8

dressed to

25fi2 by

7^^)

Pounds

2, 990

2, 780

2,170

4,270

2,090

2, 500

2. 260

2,070

2,720

2,980

2, 690

2,880

2.780

2, 670

2, 500

2,720

2,720

2,750

2,920

2,960

2, 860

3, 490

1,810

3,100

1,410

2,230

2, 220

2,180

2,220

2,140

2,360

1,680

1,850

1,990

1,930

1,460

2,040

1,550

1,330

1,840

1,430
WOOD HANDBOOK 57

TABLE 7.—Average lüeighís ^ of sawed hardwood and softwood timbers at moisture

contents of 8 and 15 percent, with adjustment factors for changes in moisture

content values—Continued

Species

Weight per cubic foot

Based on

we igilt

and volume

at a moisture content of 15

percent

Based on

weight

and volume ¡in

at a moisture content of 8

percent

Softwoods—Continued

Douglas-fir:

Coast typo

Intermediate type

Rocky Mountain type..

Fir:

Alpine

Balsam

California red

Grand

Noble

Pacific silver

White

Hemlock:

Eastern

Western

Juniper, alligator

Larch, western

Pine:

Eastern white

Jack

Lodgepole

Pitch

Ponderosa

Red

Southern yellow:

Loblolly

Longleaf

Shortleaf

Slash

Sugar

Western white

Redwood (old-growth) _

Spruce:

Black

Engelmann

Red

Sitka

White

Tamaracks

Yew, Pacific

J^onnds

34.3

31.8

30. 5

22. 5

20.9

28.3

28.3

27.1

28.1

20. 7

29.0

29.0

30. 7

39.4

25.4

30.3

29.2

34.9

28.0

31.4

30.3

41.0

35. 7

43.9

20. 0

28.0

28.0

28.8

24. 1

28.4

28.1

29.4

37.0

45.7

Factor ' for

adjusting

value for

each 1-percent change

moisture

Pounds

33. 1

30.8

29.2

21.3

20. 4

27.2

27.3

20.2

27.3

25.8

28.0

28.7

35.4

38.2

24.2

29.2

28.2

33. 8

27.5

30.4

35.2

40.3

34.0

42.0

24.9

27. 1

27.4

27.8

23.2

27.2

27.1

28.7

30. 3

44.0

content

0.170

.137

.179

.107

.071

.1.58

.145

.129

.117

.129

.150

.129

.179

.170

. 107

.158

.142

.150

. 102

.142

.154

.179

.154

.179

. 102

.129

.175

.142

.129

.175

.145

.104

.187

.250

Weiglit per 1.000 boardfeet air-dry (15-|)('rcent moisture content)

Actual

board-feet

Pounds

2, 800

2, 050

2, 540

1, 870

2, 240

2, 300

2, 3(i0

2, 200

2. 340

2,220

2, 420

2, 470

3, 000

3, 280

2,120

2, 520

2. 430

2.910

2, 380

2,020

3, 020

3, 470

2,970

3, 000

2,170

2, 330

2, 380

2,400

2,010

2, 370

2,340

2,450

3,130

3,810

Dressed

(1 by 8

dressed to

^^;U2 by

7h)

Poii.nds

2, 090

1,940

1,800

1,370

1,040

1,730

1,730

1,000

1.710

1,030

1,770

1,810

2, 240

2, 400

1,550

1,850

1.780

2,130

1,740

1,920

2,210

2, .540

2,180

2, 080

1, 590

1, 710

1, 740

1, 700

1,470

1,740

1,710

1,790

2, 290

2. 790

1 Based on the weights and volumes of 2- by 2-inch, clear specimens from the top 4 feet of 10-foot butt logs

of typical trees. . ^ ,

2 To adjust value to any desired moisture content, add factor to value to be adjusted for each 1 percent

increase in moisture content; subtract factor from value to be adjusted for each 1 percent decrease m moisture content. These factors take shrinkage or swelling with moisture changes into consideration.
58 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

In any lot of lumber of a given species in an air-dry condition at

15-percent moisture content, the weight per cubic foot will rarely vary

more than 10 percent from the figure given in table 7. The greatest

changes in weight are those which occur in the early stages of drying

of green wood. Changes in the moisture content of air-dry wood are

attended by only relatively small changes in weight per cubic foot,

owing to the coiintereffect of change in volume as a result of accompanying shrinkage and swelling.

The values given in table 7 for w^eight per 1,000 board-feet at 15-

percent moisture content were determined by multiplying the values

per cubic foot at 15 percent by 83.3. Weights per 1,000 board-feet

in column 5 apply to actual board-feet and not to 1,000 board-feet

lumber scale. Rough lumber is generally oversized and dressed lumber undersized with respect to thickness. Therefore, the values in

column 5 usually need to be adjusted for actual shipments of lumber.

The adjustment for 1- by 8-inch boards dressed to '^%i inch in thickness

and 7}^ inches in width is as follows:

25/^ V 71/

=0.7324. /32 A / /2

1 X^

Values in column 5 (actual board-feet at 15-percent moisture content)

multiplied by the constant 0.7324 give the weights of the dressed lumber shown in column 6 for various species. Similarly, constants for

an}^ dressed size may be worked out and the weight per 1,000 boardfeet computed. An adjustment for rough oversized lumber is made

in a like manner, that is, actual size divided by nominal size.

Round Timbers

The weight per unit volume of green round timbers, such as logs,

pulpwood, posts, poles, and piling, may be estimated by means of

tables 8 and 9 when the average specific gravitv of the wood and the

moisture content of its sapwood and heartwood are known or are obtainable from standard reference tables. Table 8 gives the percentage

of sapwood in round timbers for various thicknesses and diameters.

Table 9 gives the weight per cubic foot of green wood at various

specific gravity and moisture content values.

All four tables are necessary for estimating the weight per cubic

foot of round timbers, because in round timbers the proportions of

sapwood and heartwood in the total volume often difi'er widely.

Furthermore, the sapwood generally contains more water than the

heartwood, and both the sapwood and heartwood contain more

moisture in the butt logs than in the top logs.

The following example illustrates how to determine the approximate

weight per cubic foot of green round timber b}^ using tables 8, 9, 12,

and 40.

For black túpelo, the average specific gravity is found from table

12 to be 0.46. The moisture content of the sapwood can be determined

by actual measurement or estimated from table 40 as 115 percent.
WOOD HANDBOOK 59

The moisture content of the heartwoocl can be determined by actual

measurement or estimated from table 40 as 87 percent.

Measure the average diameter of the timber and average width of

sapwood. If, for example, the average diameter is 10 inches and the

average sapwood thickness is 1% inches, then from table S the percentage of the volume of the round timber occupied by the sapwood

is found to be 58 percent. The percentage of the volume occupied

by the heartwood will therefore be 42 percent (100 pcMcent minus

58 percent).

TABLE 8.—Sapivood, in percent of volione, of round tiïnbers

Sapwood thickness I

Percent of sapwood in tiinVuT in which the averajie diameter in inches is-

(inches) 1

4 5 G 7 8 9 10 11 12 13 14 15 16

H 23 19 10 14 12 11 10 9 8 8 7 7 6)

1,^ 44

01

30

51

31

44 38

23

34

21

31

19

28

17 10

23

15

22

14

20

13

19

12

H IS

1 75 64 50 49 44 40 36) 33 31 28 27 25 23

m 8H 75 60 59 53 48 44 40 37 35 33 31 29

1 V;^ 94

98

84

91 83

07

75

61

68

56)

03

51

58

47

54

44

50

41

47

38

44

36

41

34

\H 39

2 . 100 9r.

99

100

89

04

97

99

82

87

92

95

81

SO

90

( >9

80

85

6)4

70

75

SO

6,0

(•>5

70

56

61

06

71

52

62

67

49

54

59

6)3

46

51

56

60

44

2K 4S

2^4 53

m 57

3 100 9 S 94 SO H4 79 75 71 ()7 64 61

:í^ 99 90 92 88 S3 79 75 71 68 65

31 o loo 98

100

100

95

97

99

100

100

91

94

90

98

99

loo

loo

87

90

93

95

97

98

99

S3

S6

S9

91

94

96

97

79

82

S5

88

91

93

95

75

78

S2

S5

S7

90

92

72

75

78

81

84

87

89

6S

'i% 72

4 . _ 75

\yi 7S

41^2 81

4^ 83

5 86

In table 9 under a specific gravity of 0.40 for a sapwood moisture

content of 115 percent, the weight per cubic foot is found to be 61.7

pounds. Under the same specific gravity value and a moisture

content of 87 percent, the weight of the heartwood is estimated to be

halfway between that given for moisture content values of 8G percent

and 88 percent, or 53.7 pounds per cubic foot. (Moisture content

values in the left column may be applied to either sapwood or heartwood.)

To find the weight in pounds per cubic foot of the round timber,

multiply the weight of sapwood by the percentage of sapwood divided

by 100, and similarly for heartwood.

Thus: 61.7 X 58/100 = 35.8 pounds

53.7 X 42/100 = 22.6 pounds

The total weight of the round timber per cubic foot is 35.8 plus 22.6,

or 58.4 pounds.

303747 -55-
TABLE 9.— Weight in poNfids per cubic foot of green wood at varions values of specific gravity and moisture content

iMoisture content

of wood

(p(Tcont)

30

32

34

3r).

38.

40.

42.

44.

46.

48.

50.

52.

54.

5(5.

58.

iO.

02.

04.

(Hi.

m.

70-

72.

74-

7ti.

78.

80.

82.

84.

86-

88-

90.

92.

o

0.32

2{\. 0

26. 4

26. 8

27.2

27. 6

28. 0

2S. 4

28.8

29.2

29. 6

30. 0

30.4

30. 8

31.2

31.5

31.9

32.3

32.7

33. 1

33. 5

33. 9

34.3

34.7

35.1

35.5

35. 9

3i). 3

36.7

37.1

37.5

37.9

38.3

0.34

27. 6

28.0

28.4

28.9

29. 3

29. 7

30. 1

30. 6

31.0

31.4

31.8

32 2

32.7

33. 1

33. 5

33. 9

34.4

34.8

35.2

35. 6

36. 1

36. 5

36.9

37.3

37.8

38.2

38.6

39.0

39.5

39.9

40.3

40.7

0. 36

29.2

29.7

30. 1

30. 6

31.0

31.4

31.9

32. 3

32. 8

33. 2

33. 7

34.1

34. 6

35. 0

35.5

35.9

36. 4

36. 8

37.3

37.7

38.2

38. 6

39.1

39.5

40.0

40.4

40.9

41.3

41.8

42.2

42.7

43.1

0. 38

30.8

31.3

31.8

32 2

32. 7

33.2

33. 7

34.1

34. 6

35.1

35. 6

36. 0

36.5

37. 0

37.5

37. 9

38.4

38.9

39.4

39.8

40.3

40. 8

41.3

41.7

42.2

42.7

43.2

43.6

44.1

44. 6

45.1

45.5

Weight in pounds per cubic foot when the si)eciiic gnivity i is

0.46

32.4

32.9

33. 4

33. 9

34.4

34. 9

35.4

35. 9

36. 4

36. 9

37.4

37. 9

38. 4

38. 9

39.4

39. 9

40.4

40.9

41.4

41.9

42.4

42.9

43.4

43.9

44.4

44.9

45.4

45.9

46. 4

46.9

47.4

47.9

0.42

34.1

34. 6

35. 1

35.6

36. 2

36. 7

37.2

37.7

38. 3

38. 8

39. 3

39. 8

40.4

40. 9

41.4

41.9

42.5

43.0

43.5

44.0

44.6

45.1

45. 6

46. 1

40. 7

47.2

47.7

48.2

48.7

49.3

49.8

50.3

0.44

35.7

36. 2

36. S

37.3

37. 9

38. 4

39. 0

39. 5

40. 1

40. 6

41.2

41.7

42.3

42.8

43.4

43.9

44.5

45.0

45. ()

46.1

46. 7

47.2

47.8

48.3

48.9

49.4

50.0

50.5

51.1

51.6

52.2

52.7

37.3

37. 9

38. 5

39. 0

39. 6

40.2

40.8

41.3

41.9

42.5

43.1

43. 6

44.2

44.8

45.4

45.9

46. 5

47.1

47. 6

48.2

48.8

49.4

49.9

50. 5

51.1

51.7

52.2

52.8

53.4

54.0

54.5

55.1

0. 48

3S. 9

39. 5

40. 1

40.7

41.3

41.9

42.5

43. 1

43. 7

44.3

44. 9

45.5

4(5.1

46. 7

47.3

47.9

48.5

49.1

49. 7

50. 3

50. 9

51.5

52.1

52.7

53. 3

53. 9

54.5

55.1

55.7

56.3

56.9

57.5

0. .^0

40. (i

41.2

41.8

42.4

43.1

43. 7

44. 3

44. 9

45. 6

46. 2

46. 8

47.4

48.0

48.7

49.3

49. 9

50.5

51.2

51.8

52.4

5;î.O

53. 7

54.3

54. 9

55.5

56.2

56.8

57.4

58. 0

58.7

59.3

59.9

0. 52

42.2

42. 8

43. 5

44. 1

44.8

45.4

46. 1

46.7

47.4

48. 0

48.7

49. 3

50. 0

50. 6

51.3

51.9

52. 6

53.2

53. 9

54.5

55. 2

55.8

5(1. 5

57.1

57.8

58.4

59.1

59.7

60.4

61.0

61.7

62.3

0. 54

43.8

44.5

45.2

45.8

46.5

47.2

47.8

48.5

49. 2

49.9

50. 5

51.2

51.9

52.6

5.3.2

53.9

54. 6

55.3

55.9

56. 6

57.3

58.0

58. 6

59.3

60. 0

60. 7

01.3

62.0

62.7

63.3

64.0

64.7

0. 56

45.4

4(î. 1

46. 8

47.5

48.2

48.9

49. 6

50. 3

51.0

51.7

52.4

5.3.1

5.3.8

54.5

55. 2

55.9

56. 6

57.3

58.0

58.7

59.4

60. 1

60.8

61.5

62.2

62.9

63.6

64.3

65. O

65. 7

66.4

67.1

47. O

47.8

48. 5

49. 2

49.9

50. 7

51.4

52.1

52. 8

5:5. 6

54. 3

55. O

55.7

56. 5

57.2

57.9

58. 6

59.4

60.1

(30.8

61.5

62.3

63.0

63.7

64.4

65.1

65.9

66. 6

67.3

68.0

68.8

69.5

0. 60 0. 62

50.3

0. 04

51.9

0. 6(5 0. OS

55. 2

0. 70

48.7 5(5. 8

49.4 51.1 52. 7 54.4 56. 0 57. 7

50. 2 51.8 &i. 5 55. 2 56. 9 58. 5

50. 9 52. 6 54. 3 5(5. 0 57.7 59. 4

51.7 5.3. 4 55. 1 56. 8 5S. 6 (50. 3

52. 4 54. 2 55. 9 57. 7 59.4 61.2

53. 2 .54. 9 5(5. 7 58. 5 60. 3 (52. 0

5:3. 9 55. 7 57. 5 59. 3 61. 1 (52. 9

54.7 56. 5 58.3 60. 1 62. 0 (53. 8

55.4 57.3 59. 1 61.0 62. 8 (54. (5

5(5. 2 58.0 59. 9 61.8 63. 6 (55. 5

5(5. 9 58.8 (50.7 62. (5 (54.5 (56. 4

57.7 59.6 01.5 63.4 65. 3 67. 3

58. 4 60. 4 02.3 (54.2 (56. 2 68. 1

59. 2 61. 1 (53. 1 65. 1 67. 0 69. 0

59. 9 61.9 03. 9 65. 9 67. 9 (59.9

60. 7 02. 7 04. 7 66. 7 68. 7 70.8

61. 4 63. 4 05. 5 (57.5 (59. 6 71.6

62. 2 64.2 00. 3 08.4 70.4 72.5

(52.9 65. 0 67.1 69.2 71.3 73.4

(53. 6 05. 8 67. 9 70. 0 72. 1 74.3

64.4 (50. 5 68.7 70.8 73.0 75.1

65. 1 07. 3 69.5 71.7 73.8 76. 0

65. 9 (58.1 70.3 72.5 74.7 7(5.9

66. 6 08.9 71.1 73.3 75.5 77.8

67. 4 09. 6 71.9 74.1 76. 4 78.6

08.1 70.4 72.7 75.0 77.2 79.5

68.9 71.2 73.5 75.8 78.1 80.4

69. 6 72. 0 74.3 76.6 78.9 81.2

7(3.4 72.7 75.1 77.4 79.8 82.1

71. 1 73.5 75.9 78.2 80.6 8:3.0

71.9 74.3 76.7 79.1 81.5 83.9
94.

96-.

98-

100.

105.

110.

115.

120,

125.

130

185

140

145

150

36.3 38.7 41.2 43.6 46.0 48.4 50.8 53.3 55.7 58.1 60.5 62.9 65.4 67.8 70.2 72.6 75.1 77.5 79.9 82.3

36.7 39.1 41.6 44.0 46.6 48.9 51.4 53.8 56. 3 58.7 61.2 63.6 66.0 68.5 70.9 73.4 75.8 78.3 80.7 83.2

37.1 39.5 42.0 44.5 46.9 49.4 51.9 54.4 56.8 59.3 61.8 64.2 66.7 69.2 71.7 74.1 76.6 79.1 81.5 84.0

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 77.4 79.9 82.4 84.9

38.4 40.9 43.5 46.1 48.6 51.2 53.7 56.3 58.8 61.4 64.0 66.5 69.1 71.6 74.2 76.8 79.3 81.9 84.4 87.0

39.3 41.9 44.6 47.2 49.8 52.4 55.0 57.7 60. 3 62.9 65.6 68.1 70.8 73.4 76.0 78.6 81.2 83.9 86.5 89.1

40.2 42.9 45.6 48.3 51.0 53.7 5'i. 3 59.0 61.7 64.4 67.1 69.8 72.4 75.1 77.8 80.5 83.2 85.9 88.5 91.2

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 79.6 82.4 85.1 87.9 90.6 93.4

42.1 44.9 47.7 50.5 53.4 56.2 59. 0 61.8 64. 6 07.4 70.2 73.0 75.8 78.6 81.4 84.2 87.0 89.9 92.7 95.5

43.1 45.9 48.8 61.7 5-1.5 57.4 Ui). 3 63. 1 ()6. 0 68.9 71.8 74.6 77.5 80.4 83.2 86.1 89.0 91.9 94.7 97.6

44.0 46.9 40. 9 52.8 55.7 58.7 61.6 64. 5 67. 5 70. 4 73.3 76. 3 79.2 82.1 85.1 88.0 90.9 93.8 96.8 99.7

44.9 47.9 50.9 53. 9 56. 9 59.9 62. 9 65. 9 (i8. 9 71.9 74.9 77.9 80.9 83.9 80.9 89.9 92.9 95.8 98.8 101.8

45.9 48.9 52.0 55. 0 58.1 61.2 64. 2 67.3 70.3 73.4 76. 4 79.5 82.6 85.6 88.7 91.7 94.8 97.8 100.9 104.0

40. 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 87.4 90.5 93. 6 96.7 99.8 103.0 106.1

84.7

85.6

86.5

87.4

89.5

91.7

93.9

96.1

98.3

100.5

102.6

104.8

107.0

109.2

O

O

ö

' Ba^iüd on woitiht when oven-dry and volume when green.

Ü

W

O

O

Ci
62 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

WORKING QUALITIES OF WOOD

In selecting- wood for a given purpose, the ease with which it may

he worked is sometimes a factor, especially when handtools are to

be used. No test has been devised for definitely classifying woods as

to workability with handtools, but a classification based on the

experience of the Forest Products Laboratory together with the general

I'cputation of the wood is given in table 10.

Woodworking nowadays is largely done with machines rather than

with handtools. Difl'erent woods vary in their machining properties

just as they do in other properties. In addition, several machining

operations are involved, all of which must be considered in appraising

the machinability of anv given wood. Table 11 summarizes the

results of a long series of machining tests with hardwoods (9). The

comparisons are based on quality of surface produced, which is the

most important consideration when woodworking is done by machine.

Comparable data on softwoods are not available.

TABLE 10.-—Classification of certain harchvood and softwood species according to

ease of icorking loith handtools ^

HARDWOODS

iiroup 1—Easy

to work

Grou[) 2- Relatively

easy to work

Group 3—Least easy

to work

Alder, red Birch, paper Ash, commercial white

Tiasswood Cottonwood Beech

Butternut Magnolia Birch

Chestnut

Yellow-poplar

Sweet gum

Sycamore

Cherry

Elm

Tupelo: Hackberrv

Black Hickory, true and pecan

Water Honeylocust

Walnut, black Locust, black

Maple

Oak:

Commercial red

Commercial white

SOFTWOODS

Cedar:

Atlantic whiteBaldcy{jress

Fir:

Douglas-fir

Larch, western

IncenseNorthern whiteBalsam

Wi)ite

Pine, southern yellow

Port-Orford- Hemlock:

Western red cedar Eastern

IMne: Western

Eastern white Pine, lodge pole

Ponderosa Redcedar. eastern

Sugar

Western white

Redwood

Spruce:

Eastern

Sitka

1 The groupings in the table indicate the approximate order of ease of working based on the experience of

the Forest Products Laboratory and the general reputation of the wood. Direct comparison of species

within a group and comparison of hardwoods and softwoods is not intended.
WOOD HANDBOOK 63

TABLE 11.—Some machining and related properties of hardwoods

Kind of wood

Nail

Shap- Turn- Bor- Mortis- Sand- Steam splitting- Pian- ing- ing- ing- ing— ing— bendino— good to good to good to fair to good to ing— free

from IHTloCt excel- excel- excel- excel- excel- unpieces lent lent lent lent lent broken

pieces pieces pieces pieces pieces l)ieces plete

si)Iits

Ash

Percent

Basswood

Beech

04

Birch f>3

Buckeye

Chestnut 74

Cottonwood- - 21

Elm '¿:i

Hackbcrry

Hickory

74

Magnolia t)5

Mahogany

Maple:

Hard

SO

54

Soft

Oak:

Chestnut

41

Red 91

White 87

Pecan 8S

Sweetgum

Sycamore_ _ .

51

90

Tupelo:

Black 48

Water.-

Walnut, black 02

Willow 52

Yellow-i.>oplar

Average

70

Pe Tcent

51

9

21

53

6

24

3

11

10

19

25

68

23 90

21 84

28 85

31 89

21 8(;

8 85

23 75

43 79

34 91

5 58

12 81

Percent Per

94

75

99

98

75

91

70

94

99

100

, 09

100

99

80

100

99

95

100

92

98

82

()2

100

71

cent Percent

02 75

51 17

93 49

97 34

IS

72 04

52 19

75 (;o

70

9S 80

32 37

100

95 38

30 37

100 75

100 81

Screwsplittingpieces

free

from

coinI)lete

sidits

Percent Percent Percent

i-ü : (« ! 71

2 79 j OS

75 I 42 I .5S

72 32 48

100 78

5s 23 ('>7

9(i 21 2i>

24 21 42

35 34 40

98 7S

24 24 73

00

82

SO

0)3

35

73

74

03

03

52

01

49 70

flO 7S

0.9 74

47 0.9

09 0.9

79 74

05 : <i3

04 03

50 1 59

89 i2

'" 1

07

LITERATURE CITED

(1) ANONYMOUS.

1929. RESISTANT WOODS SATISFY MOST CORROSION REQUIREMENTS

Chem. & Metall. Engin. 36 (9): 567-568, illus.

WOOD FOR CHEMICAL EQUIPMENT. Chem. Engin. 49 (9): 104.

y^)

1942.

(3)

1946.

(4)

1947.

(5)

1948.

(6) ALLIOTT

1926.

REPORT OF COMMITTEE 7-10

Amer. Wood-Preservers'

DIVERSIFIED USES OF TREATED WOOD.

Assoc. Proc. 42: 255-265, illus.

REPORT OF COMMITTEE 7-10. DIVERSIFIED USES OF TREATED WOOD.

Amer. Wood-Preservers' Assoc. Proc. 43: 317-330, illus.

REPORT OF COMMITTEE 7-10. DIVERSIFIED USES OF TREATED WOOD.

Amer. Wood-Preservers' Assoc. Proc. 44: 343-352, illus.

E. A.

EFFECTS OF ACIDS ON THE MECHANICAL STRENGTH OF TLMBER! A

PRELIMINARY SiUDY. Soc. Chem. Indus. Jour. 45 (53): 463T466T, illus.
64 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

(7) BESCHER, R. H. O -D I I oru

1947. ACTD-PROOFiNG OF WOOD. Forest Prod. Res. boc. l^roc. i: izu123, illus.

(S) BETTS, H. S., AND NEWLIN, J. A.

1915. STRENGTH TESTS OF STRUCTURAL TIMBERS TREATED BY COMMERCIAL WOOD-PRESERVING PROCESSES. U. S. Dept. Agr. Bui. 286,

15 pp., illus.

(9) DAVIS, E. M.

1942 MACHINING AND RELATED PROPERTIES OF SOUTHERN HARDWOODS.

U. S. Dept. Agr. Tech. Bui. 824, 42 pp., illus.

(10) DROW, J. T.

1945. EFFECT OF HYDRAULIC-EQUIPMENL OILS ON THE BENDING AND

COMPRESSIVE STRENGTH OF SITKA SPRUCE. U. S. FOFCST PROD.

Lai). Rpt. 1520, 8 pp., illus. [Processed.]

(11) DUNLAP, M. E., AND BELL, E. R. TT n -n T^ J

1951. ELECTRICAL MOISTURE METERS FOR WOOD. U. S. Forest Prod.

Lab. Rpt. 1660, 10 pp., illus.

(12) ERICKSON, H. D., AND REES, L. W.

1940. EFFECT OF SEVERAL CHEMICALS ON THE SWELLING AND THE CRUSHING STRENGTH OF WOOD. Jour. Agr. Res. 60 (9): 593-603,

illus.

(13) HARTE, C. R.

1936 WOOD TANKS. EQUIPMENT FOR THE CHEMICAL PROCESS INDUSTRIES. Indus, and Engin. Chem. 28 (2): 176-179, illus.

(14) HASSELBLATT, M.

1926. VAPOR PRESSURE AND ELECTRIC CONDUCTIVITY OF WOOD AT DIFFERENT MOISTURE CONTENTS. Ztschr. f. Anorgan. u. Allg. Chem.

154: 375, illus.

(15) HATT, W. K. TT Q T. .

1906 EXPERIMENTS ON THE STRENGTH OF TREATED TIMBER. U. B. DEPT.

Agr. Forest Serv. Cir. 39, 31 pp.

(16) HTRUMA, J.

1913. EXPERIMENTS ON THE ELECTRICAL RESISTANCE OF WOOD. BUL.

Forest Expt. Sta., Meguro, Tokyo, 10: 59-65.

(17) KOEHLER, A.

1917. GUIDEBOOK FOR THE IDENTIFICATION OF WOODS USED FOR TIES

AND TIMBERS. U. S. Dept. Agr, Misc. RL-1, 79 pp., illus.

(18)

(19)

(20)

(21)

1922. IDENTIFICATION OF TRUE MAHOGANY AND CERTAIN SO-CALLED

MAHOGANIES. U. S. Dept. Agr. Bul. 1050, 18 pp., illus.

1924. PROPERTIES AND USE OF WOOD. 354 pp., illus. New York.

1926. IDENTIFICATION OF FURNITURE WOODS. U. S. Dept. Agr. Misc.

Cir. 66, 78 pp., illus.

1932. IDENTIFICATION OF LONGLEAF PINE TIMBERS. South. Lumberman

145 (1841): 36-37, illus.

(22) KOLLMANN, F.

1936. TECHNOLOGIE DES HOLZES. 764 pp., illus. Berlín.

(23) MACLEAN, J. D.

1941. THERMAL CONDUCTIVITY OF WOOD. Heating, Piping and Air Conditioning 13 (6): 380-391, illus.

(24)

(25)

(26)

1946. TEMPERATURES OBTAINED IN TIMBERS WHEN THE SURFACE TEMPERATURE IS CHANGED AFTER VARIOUS PERIODS OF HEATING.

U. S. Forest Prod. Lab. Rpt. R1609, 30 pp., illus. [Processed.]

1951. RATE OF DISINTEGRATION OF WOOD UNDER DIFFERENT HEATING

CONDITIONS. Amer. Wood-Preservers* Assoc. Proe. 47: 155-

169, illus.

1952. EFFECT OF TEMPERATURE ON THE DIMENSIONS OF GREEN WOOD.

Amer. Wood-Preservers' Assoc. Proc. 48: 136-157, illus.
WOOD HANDBOOK 65

(27) MARKWARDT, L. J., AND WILSON, T. R. C.

1935. STRENGTH AND RELATED PROPERTIES OF WOODS CROWN IN THE

UNITED STATES. U. S. Dept. Agr. Bill. 479, 99 pp., illus.

(28) RECORD, S. J.

1934. IDENTIFICATION OF THE TIMBERS OF TEMPERATE NORTH AMERICA,

INCLUDING ANATOMY AND CERTAIN PHYSICAL PROPERTIES OF

WOOD. 196 pp., illus. New York.

(29) RENO, J., AND KUKACHKA, B. F.

1950. WOOD IDENTIFICATION CHART. Woofl 5 (1): 25-27, illus.; (2):

28-29; (3): 22-23, illus.; (4): 24-25; (5): 20-27; (6): 2(5-27;

(7): 22-23; (8): 20-21; (9): 24-25. Chicago.

(30) SKAAR, C.

1948. DIELECTRIC PROPERTIES OF WOOD AT SEVERAL RADIO FREQUENCTES.

N. Y. State Col. Forestry, 36 pp., illus.

(31) STAMM, A. J.

1927. ELECTRICAL RESLSTANCE OF WOOD AS A MEASURE OF THE MOISTURE

CONTENT. Indus, and Engin. Cheni. 19 (9): 1021-1025, illus.

(32)

1930. ELECTRICAL CONDUCTIVITY METHOD FOR DETERMINING THE MOISTURE CONTENT OF WOOD. Indus. and Engin. Chem., Analvt.

Ed. 2 (3): 240-244, illus.

(33) AND SEBORG, R. M.

1939. RESIN-TREATED PLYWOOD. Indus. and Engin. Chem. 31 (7):

897-902, illus.

(34) WEATHERWAX, R. C, AND STAMM, A. J.

1945. ELECTRICAL RESISTIVITY OF RESIN-TREATED WOOD, LAMINATED

HYDROLIZED WOOD, AND PAPER-BASE PLASTICS. ElcCt. Engin.

64; 833, illus.

(35) AND STAMM, A. J.

1946. COEFFICIENTS OF THERMAL EXPANSION OF WOOD AND WOOD PRODUCTS. U. S. Forest Prod. Lab. Rpt. 1487, 24 pp., illus. [Processed.]

(36) WILSON, T. R. C.

1932. STRENGTH-MOISTURE RELATIONS FOR WOOD. U. S. Dept. Agr.

Tech. Bui. 282, 88 pp., illus.
STRENGTH VALUES OF CLEAR WOOD AND RELATED FACTORS

STRENGTH VALUES

The strengtli properties for any species of wood, or the properties

that enable wood to resist apphed forces, are truly representative only

when obtained from tests on small, clear piecc^s of \vood, because the

effect of such thino-s as knots, cross grain, checks and splits, and compression wood is then eliminated. Table 12 gives these strength

properties for some of the commercially important s])ecies; additional

information is presented in U. S. De])artment of Agricultui'e Technical

Bulletins 158 and 479 (15, 16)} The data are based on tests of specimens 2 by 2 inches or smaller in cross section and of different lengths,

depending on the test. Standard testing procedures of the American

Society for Testing Materials were followed {1).

Since there is a considerable differeuce in the strength of small,

clear pieces of wood when green and when air-dry, strength values

are given for both conditions. The normal increase in strengtli with

loss of moisture shown in table 12, however, does not hold for large

pieces, l)ecause the development of checks in and around knots and

of shakes and checks along the neutral axis during seasoning usually

offsets the increase in strength caused by drying. For allowable

working stresses for various species, see page 137.

Common and Botanical Names of Species, Column 1

The species listed m table 12 are grouped for convenience into hardwoods and softwoods, (The terms are not correlated with the hardness or softness of the wood.) Many of the species have numerous

common names, and frequently one common name is applied to

several species. In order to eliminate confusion, the common and

botanical names in the ta))les of this report conform to the standard

nomenclature of the U. S. Forest vService.

Moisture Content, Column 2

Moisture content is the weight of the water contained in the wood

expressed as a percentage of the weight of the oven-dry wood.

The moisture content given for green wood is the average for specimens taken from the pith to the circumference of the log. It includes

the moisture found in both the heartwood and the sapwood and is

the approximate moisture content of the living tree. In many species,

there is much more moisture in the sapwood than in the heartwood.

The moisture content of seasoned wood when tested varied somewhat among the different species. To facilitate comparison of the

strength properties, the test values were adjusted to coiiform to the

uniform moisture content of 12 percent, in accordance with standard

procedures outhned in the section on moisture content.

Italic numbers in parentheses refer to Literature Cited, p. 103.

67
68 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Specific Gravity, Column 3

Specific 2:ravitV is the ratio of the weight of a given vohime of wood

to that of an equal vohime of water at a standard temperature.

Since the weight of wood in a given vohime changes with the shrinkage and swelhng caused by changes in moisture content, specific gravity is an indefinite quantity unless the conditions under which it is

obtained are specified. The 2 specific gravity values presented for

each species are based on the weight of tlie wood when oven-dry and

its volume when green and at 12-percent moisture content.

Static Bending, Columns 4, 5, 6, 7, and 8

Fiber Stress at Proportional Limit

The fiber stress at proportional limit in static bending or flexure is

the computed stress in the wood specimen at wiiich the strain (or

deflection) becomes no longer proportional to the stress (or load).

It is therefore tlie stress in the specimen at which the load-deflection

curve departs from a straight line.

Modulus of Rupture

The modulus of rupture is a measure of the ability of a beam to

support a slowly applied load for a short time. It is an accepted

criterion of strength, although it is not a true stress, since the formula

by which it is computed is onl}^ valid to the proportional limit.

Modulus of Elasticity

The modulus of elasticity of wood is a measure of its stiflFness or

rigidity. For a beam, the modulus of elasticity is a measure of its

resistance to deflection. The modulus of elasticity as determined

from bending tests includes deflection due to shear distortion. The

moduli of elasticity in compression parallel to grain may be taken as

10 percent higher than the figiu'es in column 6.

Work in Bending to Proportional Limit

Work to proportional limit in static bending is a measure of the

energy absorbed by a beam when it is stressed to the proportional

limit. It is a comparative property that indicates the ability of the

wood to absorb shock without permanent damage.

Work in Bending to Maximum Load

Work to maximum load in static bending represents the ability of

the timber to absorb shock with some permanent deformation and

more or less injury to the timber. It is a measure of the combined

strength and toughness of wood under bendino; stresses.
WOOD HANDBOOK 69

Impact Bending, Column 9

Height of Drop Causing Complete Failure

In the impact l)endino; test, a hammer of o-iven weig-lit is dropped

upon a beam from successively increased hei(>:hts until complete

rupture occurs. The height of the maximum ch-op, or the (h'op that

causes failure, is a comparative figure representing tlie ability of wood

to absorb shocks that cause stresses l)eyond the proportional limit.

This ability of wood is important in tool liandles, basebnll bats, and

other articles subjected to frequent shocks.

Compression Parallel to Grain, Columns 10 and 11

Fiber Stress at Proportional Limit

The fiber stress at proportional limit in compression parallel to the

grain is the stress in the specimen at the limit of proportionality

between stress and strain. It is the stress at which the stress-strain

curve for compression specimens having a ratio of length to least

dimension of less than 11 departs from a straight line.

Maximum Crushing Strength

The maximum crushing strength is the maximum stress sustained

by a compression specimen having a ratio of length to least dimension

of less than 11 under a load slowly applied parallel to the grain.

This property permits evaluation of the strength of posts or short

blocks.

Compression Perpendicular to Grain, Column 12

Fiber Stress at Proportional Limit

The fiber stress at proportional limit in compression perpendicular

to the grain is the maximum across-the-grain stress of a few minutes'

duration that can be applied through a plate covering only a portion

of a timber surface without causing injury to the timber.

Shearing Strength Parallel to Grain, Column 13

Shearing strength is a measure of the ability of timber to resist

slipping of one part upon another along the grain.

Tensile Strength Perpendicular to Grain, Column 14

Tensile strength perpendicular to the grain is a measure of the resistance of wood to forces acting across the grain that tend to split a

member.

Hardness, Columns 15 and 16

Hardness represents the resistance of wood to wear and marring.

Values are presented for end-grain surfaces and side-grain surfaces

(average of radial and tangential values). It is measured by the load

required to imbed a 0.444-inch ball to one-half its diameter in the

wood.
TABLE 12.—Strength properties of sottte eonimereially important woods grown in the United States

[Rpsults of tests on small, cli.'ar spccinions in the green and air-dry condition i]

St itic bending Impact

bendComi)ression

pirallel to grain Coming—

height

pression

perpenS heir

parallel

Tension

perpenHardness—load

required to embed a 0.444-inch

ball to ^ 2 its

diameter

Common and botanical names of species

Moisture Specific

gravity '

FilH-r

Modn us of— Work to- of drop

causing

com- Fiber Maxidicular

to

grainto

grainma.\idicularto

graincontent str(>ss at I)lete stressât mum fiber nuun maxiItropor- Proportional

linut

Maximum

load

failure propor- crush- stress at shear- mum

tional Rup- Elastic- (50- tional ing proi)or- ing tensile

limit ture ity pound

hamlimit strength tional

limit

strength strength

mer) End Side

(1> (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)

In.-Lh. In.-Lh.

HAKDWOODS ¡,000 per cu. per en.

Pet. P. s. i. P. S. .. p. s. i. in. In. In. P. s. i. P. s. i. P. s. i. P. s. i. P. s. i. Lb. Lb.

Alder, red (Alruts rubra) j

98 U. 87 3, 800 0, 500 1.170 0. 70 8.0 22 2.020 2, 960 310 770 390 5,50 440

Ash:

Black (Froxin?/.<? »igra).

1 12 .41 0. 900 9, 800 1,380 1.85 8.4 20 4, 530 5, 820 540 1,080 420 980 590

I

85 .45 2, 000 0,000 1,040 .41 12.1 33 1. 090 2, 300 430 80.0 490 590 520

( 12 .49 7, 200 12.600 1,600 1.57 14.9 35 4. .520 5, 970 940 1,570 700 1,150 850

Groen (F. })ejinsytranica) 1

1

48

12

.53

. 50

5, 300

8, 900

9, 500

14. 100

1.400

1,600

1. 14

2. 72

11.8

13.4

35

32

3. 5'10

5. 120

4, 200

7, OHO

910

1,620

1,260

1,910

590

700

960

1,()30

870

1,200

Oregon (F. latifolia) 48

12

.50

.55

4, 200

7, 000

7,000

12,700

1,130

1,300

.92

2. 08

12.2

14.4

39

33

2, 700

4, 100

3,510

6, 040

650

1,540

1.190

1. 790

590

720

850

1,430

790

1,10)0

Whitü (F. americana) 1 42

12

.55

. 00

5, 100

8, 900

9, 0)00

15, 400

1,400

1,770

1.04

2. (iO

K). 6

17.6

38

43

3, 190

5, 790

3, 990

7, 410

810

1,410

1,380

1,950

590

940

1,010

1. 720

960

1,320

Aspen, quaking (Populusfreinuloi(üs) 94 .35 3, 201) 5, 100 8(i0 .69 0.4 22 1,070 2, 140 220 660 230 280 300

12 .38 5, 600 8, 400 1, 180 1.53 7.0 21 3, 040 4,250 460 850 200 510 350

Basswood, American (Tilia americana) (1

105 .32 2, 700 5. 000 1,040 .40 5.3 10 1,690 2, 220 210 600 280 290 250

12 .37 5, 900 8, 700 1,460 1.37 7.2 10 3, 800 4, 730 450 990 350 520 410

Beecli, American (Fagns grandifolia) f 54 .50 4, 300 8, 600 1,380 .85 11.9 43 2. 550 3, 550 (;7o 1. 290 720 970 850 i

12 .64 8,700 14,900 1,720 2. 63 15.1 41 4,880 7,300 1,250 2, 010 1, 010 1, 590 1,300

Birch:

Paper (Bcfula papyrifira) 1

1

05 .48 3, 000 (), 400 1.170 .45 10.2 49 1, 640 2. 360 340 840 380 470 500

12 .55 0, 900 12, 300 1, 590 1.80 10. 0 34 3, 610 5, 690 740 1,210 890 910

o

>

Ö

w

o

o

>

g

¿;

H

O

>

2

o

c¡

d

id
Sweet (F. lenta)

Yellow (P. alleghaniensis)...

Butternut (Jiiglans cinérea)

Cherry, black {Prunus serótina).

Chestnut, American (Castanea dentata).

Cottonwood:

Black (Populus frichocarpa)

Eastern (P. deltoides).

Cucumbcrtree {Magnolia acuminata).

Elm:

American {Ulmus americana)

Cedar {U. crassifolia).

Rock (Ü". thomasii)-.-

Slii)pery {U. rubra)...

Winged (17. alata)....

Hackberry {Ceîtis occidentnlis)

Hickory, pecan:

Bitternut {Carya cordiformis)-

Nutmeg (C. myrisficaeformis).

Pecan (C ilUnoensis)

Water {€'. aquatica)

See footnotes at end of table.

1 53 .60 4.800 9,400 1. 650 .94 15.7 48 2. 680 3,740 580 1.240 430 1.070 970 I 12 .65 10, 100 16. 900 2.170 2.72 18.0 47 6,330 8, 540 1,340 2,240 950 1, 960 1.470 1 67 .55 4, 200 8. 300 1. 500 .70 10.1 48 2. 620 3, 380 530 1, 110 430 810 780 1 12 .62 10, 100 16. 600 2. 010 2.89 20.8 55 6, 130 ' 8, 170 1,190 1,880 920 1,480 1, 260 1 104 .36 2, 900 5. 400 970 .52 8.2 24 2, 020 j 2,420 270 760 430 410 390 1 12 .38 5. 700 8. 100 1,180 1.59 8.2 24 4, 200 1 5, 110 570 1.170 440 570 490 f 55 .47 4, 200 8, 000 1. 310 .80 12.8 33 2, 940 3, 540 440 1, 130 570 750 660 1 12 .50 9, 000 12. 300 1, 490 3.11 11.4 29 5. 960 7, 110 850 1, 700 560 1,470 950 f 122 .40 3. 100 5. 600 930 .59 7.0 24 2. 080 2. 470 380 800 440 530 420 I 12 .43 6, 100 8, 600 1, 230 1.78 6.5 19 3.780 5, 320 760 1, 080 460 720 540 ( 132 .32 2, 900 4. 800 1, 070 .44 5.0 20 1, 760 2, 160 200 600 270 280 250 1 12 .35 5, 300 8. 300 1,260 1. 25 6.7 22 3, 270 4, 420 370 1. 020 330 540 350 Í 111 .37 2, 900 5, 300 1.010 .49 7.3 21 1, 740 2, 280 240 680 410 380 340 I 12 .40 5, 700 8. 500 1,370 1. 39 7.4 20 3, 490 4, 910 470 930 580 580 430 1 80 .44 4, 200 7. 400 1, 560 . 6)6 10.0 30 2,810 3. 140 410 990 440 600 520

^

I 12 .48 8, 000 12,300 1,820 1.98 12.2 35 4,840 6, 310 710 1.340 660 950 700

OO

Í 89 .46 3, 900 7. 200 1,110 .81 11.8 38 1, 920 2, 910 440 1. 000 590 680 620

ö

I 12 .50 7, 600 11.800 1. 340 2. 53 13.0 39 4, 030 5. 520 850 1. 510 660 1. 110 830

M

(iO .59 3. 900 9, 200 1,170 .75 20.0 60 2, 350 3. 730 600 1. 320 690 1, 160 1, 100

12 .64 5. 700 13. 500 1, 480 1.24 18.6 59 2, 600 6. 020 950 2. 240 1, 220 1, 640 1,320

d

Í 48 .57 4, 600 9. 500 1, 190 1.05 19.8 54 2. 970 3. 780 750 1.270 980 940

w

I 12 .63 8, 000 14,800 1,540 2.45 19.

2 56 4, 700 7. 050 1,520 1. 920 1.510 1.320

oo I 85 .48 4, 000 8. 000 1,230 .82 15.4 47 2. 790 3. 320 510 1,110 640 750 660 1 12 .53 7, 700 13.000 1, 490 2.35 16. 9 45 4, 760 6, 360 1,010 1, 630 530 1, 120 860 Í 59 .60 4. 000 9. 200 1.210 .81 21.7 73 1. 980 3. 700 630 1.300 850 1. 100 1. 140 1 12 . 66 6.300 14.800 1,650 1.36 23. 1 69 2, 920 6. 780 1,020 2. 370 1,210 1. 850 1.540 Í 65 .49 2, 900 6. 500 950 .58 14.5 48 2. 070 2. 650 490 1.070 630 760 700 I 12 .53 5, 900 11.000 1. 190 1.72 12.8 43 3, 710 5. 440 1, 100 1, 590 580 1, 110 880 f 66 . 60 5. 500 10 300 1, 400 1. 22 20. 0 66 4. 330 4, 570 990 1,240 1 U .66 9, 300 17. 100 1. 790 2 73 18.2 66 9, 040 2, 070 \ 74 .56 4, 900 9. 100 1. 290 1 0(i 22. 8 54 3. 620 3, 980 940 1, 030 I 12 . 60 8. 100 It», 600 1. 700 2. 04 25. 1 6. 910 1. 930 1 63 . 60 5, 200 9, 800 1. 370 1.18 14.6 53 3. 100 3. 990 960 1, 480 680 1,270 1.310 1 12 . 60 9. 100 13, 7(10 1, 730 2.81 13.8 44 5. ISO 7, S50 2, 130 2, 080 1,930 1.820 1 80 .61 6.000 10. 700 1. 5(>() 1.29 18.8 56 3, 240 4, 6(^)0 1.090 1,440 I 12 . 62 10. 200 17,800 2, 020 2. 88 19. 3 53 6, 400 8. 600 1.910 •<r
TABLE 12.—Strength properties of some commercially important woods grown in the United States—Continued

[Results of tests on small, clear specimens in the ereen and air-dry condition i]

to

>

Ö

O

O

d

w

Ö

w

>

§

O

O

O

c!

d

Common and botanical names of species

(1)

ir AKD WOODS—continued

Hickory, true:

Mockermit (Carya fomentosa)

Pignut (C. glabra)

Shagbark (C. ora(a)

Shellbark (C. laciniosa)

Honeylooust (Oledifsia triacanthos)

Locust, black (Robinia pseudoacacia)

Magnolia,southern (Magnolia grandiflora).

Maple:

Bigleaf {Acer macrophyllum) -

Black (.4. nigrum).

Red (A. rubrum)..-

Mois

ture

content

IM

59

12

54

12

m

12

61

12

»33

12

40

12

105

12

Specific

gravity'

72 .44

12 .48

65 .52

12 .57

'.3 .49

12 .54

Static bending

Fiber

stress at

proportional

limit

P. s. I.

6. 300

11.900

ñ, 200

11,300

5, 900

10. 700

5, 000

8, 900

5. (»00

8, 800

8. 800

12, 800

3, 600

0, 800

4, 400

6, 600

4,100

8, 300

3,800

8, 700

Modulus of—

Rupture

Elasticity

(5) (6)

P. S. 1.

11,100

1,000

p. s. i.

1, 570

19. 200 2.220

11,700 1. 650

20, 100 2. 260

11.000 1.570

20, 200 2. 160

10, 500 1.340

18, 100 1,890

10.200 1. 290

14, 700 1,6.30

13,800 l.,850

19, 400 2, 050

6, 800 1,110

11,200 1,400

7,400 1,100

10, 700 1,450

7, 900 1,330

13, .300 1, 620

7. 700 1,390

13,400 1,640

Work toProportional

limit

In.-Lb.

per cu.

in.

1.38

3.41

1.34

3.23

1.28

3.01

1.36

2.29

1.40

2. 74

2. .3()

4. 62

.67

1.90

1.02

1.66

.70

2.39

.71

2.84

Maximum

load

Impact

bending—

height

of drop

causing

complete

failure

(50-

pound

hammer)

(9)

In.-Lb.

per ca.

in.

26.1

22.6

31.7

30.4

23.7

25.8

29.9

23.6

12.6

13.3

15.4

18.4

15.4

12.8

8.7

7.8

12.8

12.5

11.4

12.5

Fiber

stress at

proportional

limit

(10)

In.

89

74

74

67

104

88

47

47

44

57

54

29

23

28

48

40

32

32

Compression

parallel to grain

P. s. i.

3.900

3, 950

3,430

2, 740

3, 320

6, 250

6, 120

6, 800

2,160

3. 420

2, 510

4, 790

2, 800

4, 600

2, 360

4, 650

Maximum

crushing

strength

Compression

perpendicular

to

grainfiber

stress at

proportional

limit

3, 240

5, 950

3, 270

6, (»80

3, 280

6, 540

P. s. i.

1,000

2. 140

1.140

2, 450

1.040

2, 170

1. 000

2, 220

1,420

2, 280

1,430

2, 260

570

1,060

550

930

740

1,250

500

1,240

Shear

parallel

to

grainmaximum

shearing

strength

(13)

Tension Hardness—load

per pen-, required to emP. s. i.

1.280

1.740

1,370

2,150

1,520

2,430

1,190

2,110

1,660

2, 250

1,760

2, 480

1,040

1,530

1.110

1,730

1,130

1.820

1,150

1,850

dicular

to

grainmaximum

tensili

strength

(14)

P.S. I.

930

900

770

640

610

740

600

540

720

670

bed a 0.444-inch

ball to ,i^!ts

diameter

End

(1."»)

Lb.

1.440

1,860

1,(»40

1,580

780

1,280

7(»0

1,330

940

1, 700

780

1,4.30

Lb.

1,390

1,580

1,570

1,700

740

1,020

620

8.50

840

1,180

700

950
Silver (A. saccharin um)

(-j

Su^ar (A. sacchanim) '^

Oak, red:r

Black (Quercus velutina) ¡ i

l|

Cherrybark( Q. fakata var. pagodaefolia) j >

Laurel (Q. lanrifolia) ,)

Northern rovl (Q. r¿/ora) . »

Fin (Q. palustris) - i

ScQ.y\et (Q. coccínea) . >

'í

Southern red (Q./rt/caía) . j

Water (Q./?i(7ra) . \\ Willow {Q.phtllos) :

Oak, white: ¡f

Bur (Quercus 7nacrocarpa)I

Chestnut (Q. prinns)n

Overcup (Q. hjrata)^

Post (Q. s^f//rt^a)'

Swamp chestnut (Q. 7nichüuxii)-j

Swamp white( Q. hicolor)i

White (Q. a/^</)

See footnotes at end of table.

66 .44 3.100

12 .47 0, 200

58 .56 5,100

12 .63 9, 500

SO .56 4, 000

12 .01 7, 900

78 .01 0, 500

12 .08 11.200

84 .56 4, 500

12 . 03 7, 700

SO .50 4,100

12 .03 8, 500

75 .58 4,000

12 .03 8. 000

05 .00 4, 500

12 .07 9, 700

i»0 .52 4,200

12 .59 0, 000

SI .50 5, 000

12 . 03 8. 900

94 . 50 4,400

12 .h9 9, 300

70 .58 3. 600

12 . 04 0, 400

72 . 57 4, 000

12 . 00 9. 000

S3 .57 4, 000

12 .03 5, 500

69 . 0)0 5. 000

12 .07 7. 000

76 . (^.0 4, 800

12 .07 7.300

74 .04 5, 400

12 . 72 10,200

OS . 00 4,700

12 .as 8. 200

5, 800 940 .01 11.0 29 1.930 2.490 400 1.050 560 670

8,900 1,140 1.90 8.3 25 4,360 5.220 910 1,480 500 1,140

9,400 1, 550 1.03 13.3 40 2,850 4.020 800 1.460 1,070

15,800 1, 830 2.70 16.5 39 5. 390 7, 830 1,810 2,330 1,840

8, 200 1,180 1.02 12.2 40 2,720 3. 470 870 1,220 1,000

13,900 1,040 2.15 13.7 41 4. 750 0. 520 1.150 1,910 1,380

10. 800 1.790 1.32 14.7 54 3. 820 4. 020 940 1.320 800 1,270

18,100 2, 280 3.09 18.3 49 0. 350 8. 740 1.540 2, 000 840 1,570

7, 900 1,390 .80 11.2 39 2. ()50 3.170 710 1. 180 770 1,020

12, 0)00 1.090 2.02 11.8 39 4. 040 0. 980 1.310 1,830 790 1,230

S, 300 1.350 .73 13.2 44 2. 300 3.440 760 1.210 750 1.060

14.;^00 1.820 2.33 14.5 43 4, .580 0, 700 1.250 1.780 800 1.580

8, 300 1.320 .71 14.0 48 3, 080 880 1.290 800 1.000

14,000 1,730 2.22 14.8 45 4. 020 0, 820 1.200 2,080 1,050 1,600

10.400 1,480 .81 15.0 54 2. 840 4,090 1.030 1.410 700 1,170

17,400 1,910 2.92 20.

5 53 5. 550 8. 330 1.380 1.890 870 1,690

0. 900 1.140 .93 8.0 29 2, 220 3. 030 680 930 480 910

10,900 1,490 1.44 9.4 20 2,910 0. 090 1.080 1.390 510 1,020

S, 900 1.550 1.14 11.1 39 3.2r,o 3, 740 770 1.240 820 1,050

15.400 2. 020 2.24 21.5 44 3. 900 0, 770 1.260 2. 020 920 1,400

7. 400 1.290 .88 8.8 35 2, 340 3, 000 750 1.180 760 1,020

14.500 1.900 2. 01 14.0 42 4, 380 7. 040 1.400 1,0.50 1.420

7.200 880 .89 10.7 44 2.3S0 3. 290 840 1.350 800 1,160

10.300 1.030 2.37 9.8 29 3. 580 0.0(>0 1.4S0 1.820 680 1,410

8,000 1.370 .90 9.4 35 2. S90 3. 520 060 1,210 690 970

13.300 1..590 2.88 11.0 40 4. 420 0, S30 1,040 1,490 1,250

8, 000 1.150 . 79 12.

6 44 2. 270 3. 370 540 1.320 730 1.010

12,000 1.420 1.20 15.7 38 2.010 0. 200 810 2.000 940 1.410

S, 100 1,090 1.31 11.0 44 2. 840 3, 480 1,000 1.280 790 1,160

13.200 1.510 2. 25 13.2 40 3, 700 0. cm 1. 7()0 1.840 780 1,350

8, 500 1.350 1.00 12.8 45 3, 000 3. 540 710 1.20)0 670 1,100

13,900 1.770 1. OS 12.0 41 4, 400 7. 270 1.370 1.990 690 1,290

9, 900 1,590 1. 05 14.5 50 3, 580 4.300 940 1.300 860 1,200

17.700 2, 050 2. 88 19.2 49 5. 830 S. 000 1.470 2. 000 830 1,680

S. 3(H> 1,250 l.OS 11.6 42 3. 090 3. 500 S30 l,2.-.0 770 1, 120

15.200 1,7802 27 14.8 37 4, 700 7.440 1.320 2. 000 800 1.520 \

590

700

97Í)

1,450

1, 000

1,210

1,240

1,480

1,000

1,210

1,000

1,290

1,070

1,510

1,200

1.400

860

1,060

1,010

1,190

980

1.460

1,110

1.370

890

1,130

960

1,190

1.130

1.360

1.110

1.240

1. 10)0

1. 620

1.0(^0

1,360

00
TABLE 12.—Strength properties of sofne eowmereially important woods g

[Results of tests on small, clear specimens in the green and a

rown in the United States—Continued

ir-dry conditii^i ']

Common and botanical names of species

HARDWOODS—continued

Sugar berry (C'elfis laa inaln ). - - -

Sweetgum {Liqu'ulaviUar sfijracillno)

Sycamore, American {Plantanus occidenialis).

Tupelo:

Black (Ni/ssa sijliafica)

Wa(er (AT. at;natica)

Walnut, black (Jiiglans nigra)

Yellow-poplar (Liriodendron fiilipifcra).

SOFTWOODS

Baldcypress (Tun^dinin distichmn)

Moisture

content

(2)

Pet.

12

llf)

Specific

gi'avity 2

(; !)

0. 17

. ')!

.4H

Static bending

Modulus of— ' A

Fiber

stress at

proportional

limit

(4)

P. s. i.

; {, 200

( ), 21)0

;_ {, fioo

(), (iOO

:-{,.'-;()()

(), 400

4,000

7,300

4.200

7, 200

-^, 400

10. "lOO

8. 400

0, 200

4, 200

7, 200

Kupt ure

(M

P. s. i.

(>, 000

It, 000

7, 100

i2.riOo

fi, .'lOO

10,000

7,000

<»,rtOo

7,300

O.CiOO

0,,^,00

14.000

0, 000

10.100

(t. f)00

10, (;oo

tional

limit

Elasticity

(H)

/ ,000

p. s. i.

S10

1. 140

1.200

1,010

1.000

1. 420

1,030

1.200

1, or.o

1. 2f )0

1, 420

l.OSO

1,220

1, ñSO

1,1S0

1, 4 10

(7)

In.-Lh.

per en.

in.

0. 7S

2. IS

. 00

.91

2. r>4

.9S

2.41

1. 10

3.70

1.39

.01

2. If)

Maxinmm

load

(X)

In.-Lh.

per en.

in.

12. 0

11.2

10. 1

11 9

8.3

0. 9

14.0

10.7

8. S

Impact I Compression

bend- ' parallel to grain ¡ Corn

ing—

height

of drop

causmg

com- Fiber Maxiible te stress at nuim

failure propor- crush-

(,S()- tional Ulg

pound limit strength

hammer)

(9) (10) (in

In. P. .s\ /. P. N. /.

33 1. 990 2, 800

30 3.970 5.020

30 2.040 3, 040

32 3. (>70 0, 320

2() 2. 400 2, 920

20 3.710 f), 3S0

30 2.490 3. 040

22 3, 470 •:,, 520

30 2. 090 3. 370

23 4. 280 5, 920

37 3, 520 4. 300

34 ;■■). 780 7. 5SO

2(» 2, 070 2, 600

24 3, 730 5. 540

•).- 3, 100 3. 580

24 4,740 0. 300

Com- 1 W

pression Shear Tension Ilardiu-s-l,.ad >

perpen- l)arallel perpen- reuinrec to (>m- y^

dicular to dicular beil a 0.4U-inch Ü

to

graingram—

maxit.o 1

grainball to(.lian

'o its

et er

td

O

fiber mum maxi- o

stress at shear- mum

proi)or- Ulg tensile

tional streneth strength <ï

limit

End Side

to

(12) (13) (14) ' (15) (16)

P. s. i. P. .S-. /. P. 6-. /. Lh. Lh.

5S0 1,050 (i()0 840 740

1. 240 1,280 1. 2S0 960 Ui

380 990 540 070 ()00

000 1,000 700 1,080 850

450 1,000 630 700 610

800 1.470 720 920 770 H

000 1.100 570 790 640 O

1. 150 1.340 500 1.240 sio

> 590 1. 190 600 800 710

1,070 1,590 700 1. 200 880 W

0)00 1, 220 570 9(i0 900 O

1.250 1,370 6W 1.050 1.010 r¡

300 790 510 480 440 5

560 1,190 540 (i70 540

500 810 300 440 390

900 1.000 270 OtiO 510
Cedan

Alaska- (Chainaeci/paris nooflcatensis)

Atlantic white- (C. íhijoides)

Eastern rcdcedar {Juniperus lir/jiniana)

Incense- (Lihocedrns deoirrens)

Northern white- (Thuja occidenfalis)

Port-Orford- (Cha^naecjparis lansoniana)

Western rcdcedar( Th aja plkifa)

Douslas-fir:

Coast type {Pseudotsuija vienziesii)

Intermediate type (P. men:ies}i)

Rocky Mountain type (P. menziesii va:

gla uca)

Fir:

Balsam (.4. balsa mea)

California red (.1. jywgnifica)

Grand (.1. graiidifi)

Noble (.1. procera). _.

Pacific silver (.1. amabilis)

White (.1. concolor)

Ilendock:

Eastern( Tsuga canadensis)

Western( T. heterophylla).

See foot notos at ond of table.

38

12

48

12

38

12

117

12

IKi

12

94

12

3(1

12

115

12

111

12

74

12

.42 3, 800

.44 7. 100

.31 2, 500

.32 4, 800

.44 3, 400

.47 3. 800

.•sr^ 3.000

.37 5,000 . 2i) 2, (iOO

.31 4. 000

.40 4.000

.42 7, 700

.31 3, 200

.33 5, 300

.4,^ 4,500

.48 7, 800

.41 3, 800

.44 7, 400

.40 3. (100

.43 (1, 300

.34 3, 000 . 3(» 5, 200 . 37 3, 400 . 3i> (1, 300

.37 3. (100

.40 5, SOO

.35 3, (100 . 3 S ('). (100

.35 3,500

.3S 0, 200

.35 3, 800

.37 (1, 500

.38 3, 800

.40 0, 100

.38 3,400

.42 ), 800

(j. 400

11,100

4, 700

6, S(>0

7, 000

8, 800

0, 200

8, 000

4, 200

(i, 500

0, 200

11, 300

5, 100

7, 700

7. ()0<1

12,200

(Í. 800

11,200

(1, 400

9, ("»00

4. 900

7, (100

(), 000

10,800

(1, 100

9, 300

5, 800

10,000

5, 700

9, 400

5, 700

9, 300

P., 400

8, 900

(.1, 100

10, 100

1 140 . 77

1.420 2. 06

750 .51

930 1.46

650 1.08

880 1.01

840 .94

1,040 1.67

(i40 .60

800 1.72

1. 420 .65

1, 730 1.97

920 . 63

1, 120 1.44

1,570 .75

1,950 1.77

1.350 . 63

1.040 1.87

1,180 .65

1,400 1.60

900 .52

1,230 1.23

210 .59

540 1.48

300 . 58

030 1.22

270 .61

5S0 1.59

2(10 . 60

530 1.40

030 .84

380 1.72

070 . 76

200 1.79

220 .57

490 1.82

9.2

10.4

5.9

4.1

15.0

8.3

6.4

5.4

5.7

4.8

7.4

9.1

5.0

5.8

9.8

6.6

8.8

6.8

6.4

4.7

5.1

6.4

8.9

5.6

7.5

6.0

8.8

6.0

9.3

5.1

6.8

6.8

7.5

27 2, 500 3, 050 430 840 330

29 5, 210 6,310 770 1,130 360

18 1,660 2,390 300 690 180

13 2,740 4,700 500 800 220

35 2, 540 3, 570 860 1.010 330

22 f). 020 1, 140

2. 940 3, 150 460 830 280

17 4, 760 5, 200 730 880 270

15 1,490 1,990 290 620 240

12 2, 630 3. 96)0 380 850 240

21 2, 770 3, 130 350 830 180

28 5, 890 6, 470 760 1,080 400

17 2,470 2, 750 340 710 230

17 4. 360 5,020 610 860 220

26 3,130 3, 8'10 440 930 300

31 5, 850 7, 430 870 1,160 340

22 2. 570 3.300 480 840 300

27 5, 510 6, 720 920 1, 130 340

20 2. 540 3, 000 4.50 880 350

26 4. 660 t). 060 820 1,070 330

16 2, 080 2, 400 210 610 180

20 3, 970 4,530 380 710 180

21 2,350 2,850 3(.0 800 3S0

24 4. 220 5,650 6.50 1. 090 3!»0

22 2, 640 3, 020 340 760 240

28 4, 420 5, 430 620 930 240

19 2. 420 2. 740 340 750 230

23 4.9(i0 5. 550 640 980 220

21 2, 380 2, 670 290 670 240

24 4.660 5. 550 490 1,050

22 2. 390 2.710 370 750 290

17 3, 590 5.350 600 930 260

21 2. 600 3. 080 440 S50 230

21 4, 020 5.410 800 1,060

22 2, 4S(.) 2, 990 390 810 310

26 5, 340 6, 210 6S0 1.170 310

540

790

400

520

760

900

570

830

320

450

460

730

430

660

570

900

510

710

450

740

290

510

430

880

420

6(K)

330

690

360

620

380

730

500 S10

520

940
TABLE 12.—Sfre?igth properties of some eommereially important woods grown in the United States—Continued

(Results of tests on small, elear specimens in the green and air-dry condition ']

Cornnion and botanical names of species

(1)

SOFTWOODS—continued

Larch, western {Larix occidentalis)

Tine:

Eastern white {Pinus strobus)

Jack (P. banksiana)

Lodfiepolo (P. contorta)

Ponderosa {P. ponderosa)

Rod (P. resinosa)

Pino, southern yellow:

Loblolly (P. taeda)

Longleaf (P. palustris)

Shortleaf (P. ectiinata)

Moisture

content

Specific

gravit y 2

(2) (3)

Pet.

\ 58 0.51

I 12 .55

Í 73 .34

I 12 . 35

1 60 .40

[ 12 .43

f r,5 .38

I 12 .41

1 91 .38

I 12 .40

92 .41

J 81 .47

I 12 .51

63 .54

12 .58

Í 81 .46

I 12 .51

Static bending

Fibrr

stress at

proportional Ruplimit ture

(4) ( =>)

P. 5. /. P. s. i.

4, (UK) 8, 200

8, 300 13,900

3, 000 4, 900

5. 700 8, 600

3, 400 (), 000

5. 800 9, 900

3, 000 5, 500

6, 700 9, 400

3. 100 5. 000

6, 300 9. 200

3, 200 5. 800

4,100 7. 300

7. 800 12, 800

5, 200 8, 700

9, 300 14,700

3, 900 7. 300

7, 700 12, 8ltO

Modulus ofElastic

ity

Propor-: Maxitional mum

limit load

(6) (7) i^)

Impact

bending—

height

of drop

causing

complete

failure

(50-

pound

hammer)

(9)

Compression . parallel to grain ' Compression

perpendicular

Fiber

stress at

proportional

limit

(10)

In.-Lb. In.-Lh.

1,000 per cu. per cu.

p. s. i. in. in. In,

1,530 0. SI 10.3 29

1.960 1.99 12.6 35

990 .53 5.2 17

1,240 1.51 6.8 18

1.070 .63 7.2 2(1

1,350 1.43 8.3 27

1,080 .49 5.6 20

1,340 1.97 6.8 20

970 .59 5.1 20

1,260 1.85 6. 6 17

1,280 .46 6.1 26

1.410 .68 8.2 30

1,800 1.92 10.4 30

1,600 .95 8.9 35

1,990 2.44 11.8 34

1.390 .63 8.2 30

1, 700 1.93 11.0 33

D

s. i.

3 OKI

5, 620

2 040

3 ()70

2 360

3 550

2 110

4 310

2 070

4, OfiO

2 1('»0

2 550

4 820

3 430

6» 150

2 500

5 ("190

Maximum

crushing

strength

to

grainfiber

stress at

proportional

limit

(11) (12)

p. 5. i. P.S. i.

3, 990 420

8. 110 980

2, 440 260

4. 800 510

2, 950 310

5. 660 600

2.610 310

5. 370 750

2. 400 360

5, 270 740

2. 730 280

3, 490 480

7. 080 980

4, 300 59'

8, 440 1.190

3, 430 440

7, 070 1,000

parallel

to

graiti—

maximum

shearing

strength

periH-n-!

dicular \

to

grain—

maxi- j mum I

tensile j

strength 1

(13) (14)

P. s. /. P. 5. i.

900 330

1.410 430

680 250

900 310

750 360

1, 170 420

680 220

880 290

680 290

1, 160 400

690 300

850 260

1,370 470

1,040 330

1,500 470

850 320

1,310 470

Hardness—load

required to embed a 0.444-inch

ball to loits

diameter

End Side

(15) (16)

Lb. Lb.

580 510

1,120 8:BO

300 290

480 380

440 400

800 570

320 330

530 480

300 310

550 450

350 340

420 450

750 690

550 590

920 870

410 440

750 690

o

o

a

>

O

>

S

o

d

C¡

S3

W
Slash (P. elliottii)

Pine:

Sugar (P. lambertiana)

Vii'ginia (P. virginiana)

Western white (P. monticola)..

Redwood, old-growth {Sequoia sempervirens)

Spruce:

Black (Pècea wan'ana)

'Englama.nniP.engelmannn)

Red (P. rubens)

Sitka (P. suchensis)

White (P. glauca)

Tamarack (Larix laricina)

1 6G .56 5,100

I 12 .61 9,800

1 137 .35 3,400

12 .36 5,700

88 .45 4, 000

12 .48 7,100

54 .36 3.400

. 12 .38 6, 200

112 .38 4, 800

1 12 .40 6,900

( 38 .38 2, 900

12 .40 5, 800

8Ü .32 2, 600

12 .34 5, 500

1 ^'^ .38 3, 400

I 12 .41 6, 800

1 42 .37 3, 300

i 12 .40 6, 700

50 .37 3, 300.

12 .40 6, 500

Í 52 .49 4, 200

I 12 .53 8, 000

8.900

15,900

5,100

8, 000

7, 300

13,000

5, 200

9, 500

7, 500

10,000

5. 400

10. 300

4, 500

8, 7O0

5. 800

10, 200

5, 700

10,200

5, 600

9, 800

7, 200

11,600

1,580 1.02 9.5 36 3,040 4,340 680 1.000

2,060 2.76 12.6 36 6,280 9,100 1,390 1,730

940 .70 5.4 17 2,330 2,530 350 680

1,200 1.53 5.5 18 4,140 4,770 590 1,050

1,220 .75 10.9 34 2, 500 3,420 390 890

1.520 1.86 13.7 32 3. 820 6. 710 910 1.350

1.170 .56 5.0 19 2. 430 2, 650 290 640

1.510 1.47 8.8 23 4, 480 5.620 540 850

1.180 1.18 7.4 21 3, 700 4. 2O0 520 800

1,340 2.04 6.9 19 4, 560 6,150 860 940

1,060 .45 7.4 24 1.540 2. 570 180 660

1.530 1.34 10.5 23 4. 520 5. 320 650 1.030

9(>0 .42 5.1 16 1.850 2. 190 250 590

1,280 1.34 6.4 18 3. 580 4.770 540 1,030

1.190 .58 6.9 18 2.380 2, 650 340 760

1,520 1.73 8.4 25 4,610 5,890 580 1,080

1.230 .53 6.3 24 2. 240 2. 670 340 760

1.570 1.62 9.4 25 4. 780 5.610 710 1.150

1.070 . 60 6.0 22 2. 130 2, 570 290 690

1.340 1. 76 7. 7 20 3. 700 5, 470 570 1.080

1,240 .84 7.2 28 2, 930 3, 480 480 860

1.640 2. 19 7. 1 23 4, 780 7.160 990 1.280

400

570

270

350

400

380

260

260

240

100

240

350

220

350

250

370

220

360

260

400

320

530

590

980

310

440

570

790

430

700

310

560

410

640

430

760

350

610

400

()70

630

1,010

310

380

540

740

310

370

410

370

520

260

350

350

490

350

510

320

480

380

590

O

O

>

a

2

c

1 The values in tht first Ime for each species are from tests of green material; those in the second line ar^ from tests of seasoned material adjusted to an average air-dry condition

of 12-percent moisture coTitent.

2 Bavsed on weight when oven-dry and volume when green or at 12-percent moisture content.
78 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

ELASTIC PROPERTIES OF WOOD

Certain elastic properties of wood that are necessary in design,

particularly when ph^vood is used, are presented in table 13 (^).

The modulus of elasticity of wood perpendicular to the grain is

designated as ET when the direction in which the deformation takes

place is tangential to the annual growth rings and as ER when the

direction is radial to the annual growth rings. These properties were

evaluated for a few species, and the results are presented as ratios

ETIEJ^ and ERJEL in table 13, where EL is the modulus of elasticity

parallel to the grain. These ratios vary among species and are

considerably affected by differences in specific gravity and moisture

content. For species not Hsted in the table, approximate values of

ETIEL= ^.()^ and £'ä/£'L = 0.10 may be used. Values of EL may be

obtained by ad(Ung 10 percent to the modulus of elasticity value in

cohmm 6 of table 12.

The modulus of elasticity in shear, called the modulus of rigidity,

must be associated with shear deformation in 1 of the 3 mutually

perpendicular planes defined by the L (longitudinal), T (tangential),

and /? (radial) directions and with shear stresses in the other 2 planes.

The symbol for modulus of rigidity has subscripts denoting the plane of

deformation. Thus, the modulus of rigidity GLT refers to shear

deformations in the LT plane resulting from shear stresses in 1.he LB

and ET planes. Values of these moduli for a few species are given in

table 13, and their variations among species and with changes in

specific gravity and moisture content are shown. For species not

listed in the table, approximate values of GLT/EL= OM, (TrÄ/^L=0.075,

and GRT/EL=0.018 may be used.

The Poisson's ratio relating to the contraction in the T (tangential)

direction under a tensile stress acting in the L (longitudinal) direction

and thus normal to the RT plane is designated as ^LT- The symbols

MLÄ1 i^RT, fJ'RLi ¡J^TR, ^ud IXTL havc siuillar significance, the first letter of

the subscript in each relating to the direction of stress and the second

to the direction of Lateral deformation under that stress. The Poisson's ratios appear to be independent of specific gravity but are

variously affected b}^ differences in moisture content. Information on

Poisson's ratios for wood is meager, and values for only a few species

are given in table 13.

COMPRESSION PERPENDICULAR TO GRAIN

Effect of Bearing Area on Stress

Proportional limit stresses in compression perpendicular to the grain

given in table 12 are from tests in which the load was applied through

a plate 2 inches wide placed on the central 2 inches of a specimen 6

inches long. The supporting action of the wood fibers adjacent to the

plate in the unloaded area caused an increase in stress over that which

would have resulted if the entire area of the specimen had been covered.

The test results indicate that the stress obtained in the standard test

procedure is about 50 percent greater than that obtained in loading

the entire area of a 2-inch cube. As the ratio of loaded to unloaded
TABLE 13.-—Flasiic constan is of various species

Young's modulus Modulus of ricridity ratios Poisson 's ratios

Speck's Specific

gravity i

Moisturo

content '

(percent)

ratios

1

0. SOI

ETIEL EHIEL

0. 109

GLHIEL

0. 057

OLT/EL GHTIEL ^LÄ ^'LT ^'RT ßjR ^RL ^'TL

Ash 13. 0 0. 00-1 0.041 0.0105 0. 533 0.053 0.050 0. 380 0. 0582 0. 0421

Balsa 2 . 131 U. 4 .016 . 040 .054 .037 .005 . 229 . 488 . 005 .231 .018 . 009

Birch, yellow .(14

.»'.5

13. 3

12. 0

. 050 . 078 . 420 .451 .097 . 420 . 043 .024

Do . 074 . 008 .017

Douglas-fir .

Do .

5()t) 7 5 001 090 . 295 .441 .447 . 3r,8 . 030 .023

. F,{)C^ 12. 9 . 050 . 008 . 292 . 449 . 390 .374 . 036 .029

Do . 506 10. 9 . 032 .056 .274 . 490 . 500 .396 .018 . 019

Do_.. .45 11.2 .004 . 078 .007

Khaya - .45 11.3 . 050 .111 .088 . 059 .021 . 297 .041 . 004 . 204 . 033 . 032

Mahogany ^ . 50 11.7 .004 . 107 . 08(:i . OfiO . 028 .314 . 533 . 000 . 320 . 033 . 034

Quipo 3 . 1.17 11.2 . 055 .182 . 082 .055 . 032 .210 . (')(il) .455 .128 .047 . 032

Sitka spruce - _ . :'>7h 7. 1 . 050 . 089 .375 . 43Ô . 4»i8 .248 . 034 . 022

Do .o7S 12. 8 . 043 . 078 . 372 . 407 . 435 .245 . 040 . 025

Do ; ! 7S If). 3 . 03 f> . 004 . _ - - .374 . 504 .527 .278 . 030 . 020

Do . - . ;:!7S 21.0 . 029 . 053 .371 . 539 .512 . 278 . 022 .017

Do . o 9

.3ií

. 530

. 530

. 5! »3

. 370

0 S . 070

. 004

. 008

. 001

. 044

Do 11.1 . 003

11.2

10. 2

11.0

10.7

Swretgum . 050 .115 . 325 .403 . 082 . 309 . 044 . 023

Do . 0S9

. OS 5

. 075

.001

. 002

. 009

.021

.0209

.011

Walnut - - - - - - - . 050

. 043

. 100

. 092

. 495

.318

. o:r2

. 392

.718

. 703

. 307

. 329

. 0520

. 030

. 0300

Yellow-poplar. .

. 019

1 Specific gravity based on volume at test and weight when oven-dry. The \alues shown to 2 decimal places and the corresponding moistun^ content values are tentative and

subject to revision.

2 The balsa in these tests varied in specific gravity fi-oni O.06 to 0.22, in wliich range EL is given approximately by the cfpiation /•:L = 5.50O.0()0Xspecific gravity-20O.OO0.

3 The quipo in these tests varied in si^ecific gravity fi-om 0.08 to 0.20, in which range EL is given appro.ximately by the equation ¿.L = 3.20o,000Xspecific gravity-170,000.

O

O

ö

>

ü

W

O

CO
80 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

area is (locreased, further increases in proportional limit stresses are

obtained. This factor is further discussed in arriving at safe working

stresses for bearing perpendicular to the grain, wherein higher working

stresses are permitted for bearing areas less than 6 inches in length

(p. 163).

Effect of Ring Placement on Stress

Investigations at the Forest Products Laboratory and elsewhere

have sho\\Ti that properties in compression perpendicular to the grain

are affected by the angle of growth rings with respect to the direction

of load (fig. 6) and that properties of hardwoods and softwoods are

affected differently l)y the orientation of growth rings. In softwoods, the lowest stress at proportional limit is obtained when the

growth rings are at an angle of 45° to the applied load, and it is

approximately one-half to two-tliirds of the value o])tained with the

rings at 0*^, or parallel, to the direction of load. Stress values at the

90° rmg position are approximately the same as those at the 0° position. At a 45° ring orientation, modulus of elasticity values are decreased somewhat more than are proportional limit stresses but are

about one-fourth greater for the 90° than for the 0° orientation. For

hardwoods, the 0° and 45° positions give about the same values for

proportional limit stress and modulus of elasticity, but values at 90°

are higher by about one-third.

FIGURE 6.—The direction of the load

in relation to the direction of the

annual growth rings: A, 90°, or

perpendicular; B, 45°; C, 0°, or

parallel.

ZM 22154 F

CoMPREssivE STRENGTH ON SURFACES INCLINED TO THE

GRAIN

A formula for determining the compressive strength of wood on

surfaces at an angle to the grain, known as the Hankinson formula,

is recommended for general use in timber framing. The formula is:

N-T. PQ

Pshi' e+Q cos^Ö

in which A^represents the allowable unit stress on the inclined surface;

Q, the unit stress in compression perpendicular to the grain; P, the

unit stress in compression parallel to grain; and 6, the angle between

the direction of the load and the direction of the grain (fig. 7).
WOOD HANDBOOK 81

FicuRE 7.—The angle 6 between the

direction of the load and the direction

of the «rain.

ZM 22153 F

For safe working stresses, the unit stress constants in the formula

would be the working stresses in compression parallel and perpendicular to the grain for the species.

SHEAR PARALLEL TO GRAIN

In the block shear tests (1) upon which the values in table 12 are

based, a 2- by 2-inch portion that projects % inch from a block 2 inches

wide and 2}^ mches long is sheared from the block. The specimen

is supported at the base, so that a )^-inch offset exists between the

adjacent edges of the support and the loading plate. The results

obtained are influenced to some extent by a nonuniform stress distribution throughout the depth of the shear area and by components of

stress perpendicular to the grain. The values presented, however,

indicate the relative shearing strength of the various species and

may be considered as reliable estimates of true shearing strength.

TENSION PARALLEL TO GRAIN

Relatively few data are available on the tensile strength of various

species parallel to the grain. In the absence of sufficient tensile test

data on which to base values for use in design, the modulus of rupture

values are also used for tension. Wliile it is recognized that those

values are conservative, the pronounced effect of stress concentration,

slope of grain, and other factors upon tensile strength make the use

of conservative values desirable. Furthermore, it is practically impossible to devise attachments that permit the tensile strength of

the full cross section of a wooden mem})er to ])e developed.

ToRSiONAL PROPERTIES

The torsional strength of w^ood is seldom needed in design, but

data are available that permit calculation of torsional properties if

they are required.

The torsional deformation of wood is related to the moduli of

rigidity in the longitudinal-radial (LR), longitudinal-tangential (LT),

and radial-tangential (RT) planes. These moduli were discussed

under elastic properties of wood. Wlien a wood member is twisted

about an axis parallel to the grain, the modulus in the AT plane is not

involved. Since the moduli in the LR and LT planes do not differ

greatly, the ''mean modulus of rigidity," taken as one-sixteenth of

the modulus of elasticity parallel to the grain, may be used safely in

standard formulas for computing the strength and rigidity of wood

members twisted in this manner.
82 HANDBOOK 12, U. S. DEPARTMENT OF AGRICULTURE

For solid wood members, the allowable ultimate torsional shear

stress may be taken as the shear stress parallel to the grain in table

12, and two-thirds of this value may be used as the allowable torsional

shear stress at the proportional limit. Information on critical

buckhng and twisting due to torsional instability is presented in a

bulletin on Design of Wood Aircraft Structures {23).

TOUGHNESS

Although a numl)er of the properties given in table 12 indicate

the ability of wood to absorl) shock or impact loads, a simple test has

been developed with a Forest Products Laboratory machine by which

the toughness of relatively small samples can be determined {21).

This test afl'ords a means of comparmg species and a basis for selecting

stock of known properties, particularly when used in conjunction with

specific gravity. Toughness values for some species of wood are

listed in table 14. These data are based on specimens % inch square

and 10 inches long, supported over a span of 8 inches. That size

was used as a standard by the Forest Products Lal)oratory until 1949

when, by international agreement, a specimen 2 centimeters (0.79

inch) square by 28 centimetei's (11 inches) long was adopted {1).

FATIGUE RESISTANCE

The fatigue i-esistance of wood is a measure of the ability of wood

to sustain repeated, reversed, or vibrational loads without failure.

Its resistance to fatigue, like that of metals, is an important consideration m design and niay be adversely afl'ected by abrupt changes

in cross section, l)olt holes, slope of grain, knots, and other strengthreducmg factors.

Tests to date indicate that wood, a fibrous material, is less sensitive to repeated loads than are more crystalline structural materials,

such as metals. Endurance limits are likely to be higher in proportion

to the ultimate^ strength values for wood than for some of the metals.

For example, tests in fatigue hi tension parallel to the grain indicate

an endurance load for 30 million cycles of stress of about 40 percent

of the strength of air-dry wood as determhied by a standard static

test. Similar results were obtained on tests of aii^-dry wood with

glued scarf joints. The minimum repeated load for each cycle was

one-tenth of the maximum for each cycle.

Tests of small cantilever bending specimens of ah*-dry solid wood

and plywood {S), subjected to fully reversed bending stresses, indicated an endurance limit for 30 million cycles of stress of about 30

percent of the modulus of rupture of the specimens.

Fatigue tests in repeated l)ending of green, standard-size wood

static l)ending specimens indicate that, if maximum repeated stresses

are below the proportional limit (60 percent of the modulus of rupture

or less), the specimens will withstand 30 million repetitions of stress

without failure and with only superficial damage at points of loading.

Tests of small rotating beam specimens {3) indicate an endurance

load for wood at 30 million cycles of stress of about 28 percent of the

modulus of rupture for specimens of this type.
WOOD HANDBOOK 83

TABLE 14.—Avei^age toughness values for some species of wood

Species

Birch:

Paper

Yellow

Catalpa, northern. .

Cedar:

AlaskaWestern redcedar

Moisture

content

Chestnut, Japanese

Douglas-fir:

Coast type

Intermediate

type

Elm, winged

Fir:

California red.

Corkbark

Noble.

Hemlock:

Eastern _

Western

Juniper:

Rocky Mountain

Percent

10

12

G6

12

10

9

90

I 14

( 43

36

10

56

12

132

12

55

10

62

11

12

1 12

Specific

gravity 1

Toughness

Radiar¿

0.56

.65

.40

.41

.48

.33

.53

.54

.46

.48

.43

.46

.60

.66

.36

.39

.31

.31

.36

.40

.39

In.-lb.

180

260

180

100

no

40

190

140

Tangential 3

In.-Ih.

180

330

180

120

120

70

220

200

Species

120 200

110 200

80 110

90 150

350 360

250 290

70 90

60 90

40 50

40 50

130

100

120

Juniper— Continued

Utah..

100

70

90

90

130

Larch, western

Mai)lo, sugar

Oak, pin

Pino:

Eastern white..

Jack

Red

Southern yellow

Loblolly

"Moisture

content

Longleaf _.

Shortleaf..

Slash

Virginia

Redwood:

Old-growth.

Second-growth.

Spruce:

Engelmann

Sitka

Willow, black..

Yellow-poplar..

Percent

51

12

61

12

14

12

99

12

49

12

111

12

86

12

90

13

88

13

78

12

124

103

11

138

12

60

11

153

11

110

Specific

gravity 1

Toughness

0.48

.48

.51

55

.64

.64

.33

.34

.41

.42

.40

43

.47

.51

.54

.57

.48

.50

.55

59

.45

.39

.39

.32

.33

,34

.39

.38

.40

.43

Radian

In.-lb.

130

100

140

110

190

230

60

60

100

80

110

80

140

90

180

90

140

80

180

110

180

60

50

60

40

60

Tangential • '

160

110

170

In.-lb.

120

100

210

180

190

220

80

60

200

130

190

150

180

1.50

230

140

190

120

240

170

250

110

80

80

50

80

140

190

120

1 m

1 Based on oven-dry weight and volume at test.

2 Load applied to radial face of specimen.

3 Load applied to tangential face of specimen.

Tests on a glued, double-shear type of specimen (9) indicate an

endurance load for 30 million cycles of stress of about 40 percent oí

the strength of the joint. The specimens were loaded repeatedly so

that the minimum repeated stress for each cycle w^as one-tenth ol the

maximum for each cycle.

VARIABILITY IN STRENGTH

Variability, or variation in properties, is common to all materials,

including rope, steel, concrete, and wood, but the degree of variability,

or spread of propertv values, differs markedly with the type oí material.

Since wood is a natural material and subject to numerous constantly
84 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

changing influences, such as moisture, soil conditions, and growing

space, it may show a decided variation in properties even in clear

material.

The property values tabulated in table 12 were obtained by averaging individual test values for each tree and then averaging the individual tree averages to arrive at the value for the species. Obviously,

some values obtained in individual tests were higher than the average,

and others were lower. Normally, the fact that the piece selected

may be stronger, harder, or stiffer than the average is of less concern

to the user than if it is weaker, although this may not be true if lightweight material is selected for a specific purpose. It is desirable,

however, that some indication of the spread of property values be

given. If a frequency distribution curve were presented for each

property and species, it would show a large number of property values

from the individual tests grouped around the average, and a smaller

number varying widely from higher to lower levels.

Magnitude of variation can also be indicated by standard deviation.

Standard deviation is the square root of the mean of the squares of

individual deviations from the average value. Since it is affected by

every value, it is a better measure of variability than the range of all

or any part of the values. The result is in units for each property,

and to facilitate comparisons, it is divided by the average value to

get a percentage figure that is termed the ^^coefficient of variation.'^

Coefficient of variation values for strength properties of green wood

are presented in the following tabulation:

Coefficient of

variation i

(percent)

Specific gravity 10

Shrinkage:

Radial 15

Tangential 14

Volumetric 16

Static bending:

Fiber stress at proportional limit 22

Modulus of rupture 16

Modulus of elasticity 22

Work to proportional limit 38

Work to maximum load 34

Impact bending, height of drop causing complete failure 25

Compression parallel to grain:

Fiber stress at proportional limit 24

Maximum crushing strength 18

Modulus of elasticity 29

Compression perpendicular to grain, fiber stress at proportional limit 28

Shear parallel to grain, maximum shearing strength 14

Tension perpendicular to grain, maximum tensile strength 25

Hardness:

End 17

Side 20

Toughness 34

1 Values given are based on results of tests of approximately 50 species of green wood. Values for wood

in the air-dry condition (12-percent moisture content) may be assumed to be approximately of the same

magnitude.

In a normal frequency distribution, about two-thirds of the individual values lie within the range encompassed by the sum and the

difference of the averag:e value and the product of the coefficient of
WOOD HANDBOOK 85

variation times the average value. Also, 95 percent of the individual

results will lie in the range of the sum and the diflerence of the average^

value and twice the same product. Thus, if the average value is 50

and the coefficient of variation is 6 percent, then two-thirds of tiie

pieces tested could be expected to have values between 47 and 53,

and 95 percent would have values between 44 and 56. Varial)ility

from the average must be considered in establishing working stiesses

for a species; this is discussed further on page 137.

MOISTURE CONTENT AND STRENGTH

Wood increases in strength as it (h'ies (26). With small, clear

pieces, the strength in endwise compression, for example, is about

twice as great for a moisture content of 12 percent as for green wood,

and drying to about 5-percent moisture content will sometimes triple

this property. Increase in strength does not begin, however, until

the fiber saturation point is reached. The fiber saturation point,

which is at approximately 30-percent moisture content, is reached

when the free water in the cell cavities has been evaporated and the

cell walls are still saturated.

Not all the strength properties of wood increase with a decrease in

moisture content; in fact, properties that represent toughness, or shock

resistance, sometimes actually decrease as the wood dries. This is

because dried wood will not bend so far as green wood before failure,

although it will sustain a greater load, and because toughness is

dependent upon both strength and pliability.

Frequently, strength values are obtained for pieces at different

moisture-content values, and the results are recorded as obtained.

It is then necessary to adjust some values before a true comparison

of results can be made. An approximate adjustment for the property

in question can be made by using the values given in the following

tabulation (22). These values represent the average increase (or

decrease) in wood strength properties for a 1-percent decrease (or

increase) in moisture content.

Change per

l-percerit

change in

moisture

content

Static bending: ^^^^^^"'^

Fiber stress at proportional limit 5

Modulus of rupture 4

Modulus of elasticity 2

Work to proportional limit 8

Work to maximum load -5

Impact bending, height of drop causing complete failure .5

Compression parallel to grain:

Fiber stress at proportional limit 5

Maximum crushing strength i>

Compression perpendicular to grain, fiber stress at proportional limit 5. 5

Shear parallel to grain, maximum shearing strength 3

Tension perpendicular to grain, maximum tensile strength 1.5

Hardness:

End - 4

Side 2.5
86 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

A more arcurate adjustment can be made by using the following

''exponential formula," devised by the Forest Products Laboratory:

LosS.=losS.+(^¡^io,^

where S^ and Mi are one pair of corresponding strength and moisture

content values as found from test, S2 and ^K are another pair, and

^3 is the strength value adjusted to the moisture content M3.

If one strength value is for green wood, the moisture content that

must be used is that corresponding to the intersection of straight

lines givmg strength-moisture content relations when strength values

are plotted as ordinates and moisture content values as abscissas on

semilogarithmic paper (26). This value, which is somewhat lower

than the fiber saturation point, is designated as Mp. As previously

stated, the strength undoubtedly increases when the moisture is

lowered below the fil)er saturation point, but, because of limitations

in test procedure, it is not practical to obtain a strength-moisture

content relation starting at this point. Experimentally determined

values of Alp for certain species follow:

Mr

(percenf)

Ash, white 24

Birch, yellow 27

Chestnut, American 24

Douglas-fir 24

Hemlock, western 2<S

Larch, western _ 28

Pme, loblolly 21

(percenf )

Pine, lon^leaf 21

Pine, red 24

Rcflwood 21

Spruce, red 27

Spruce, Sitka 27

Tamarack 24

For other species, a value of 25 percent is assumed for Mp.

The exponential formula is not applica1)le to results of tests on wood

in which there is a large variation in moisture content from one part

of the cross section to another.

Examples of Application of Formula

Case 1.—Strength values Si and So from matched specimens tested

green, il/i, and air-dry, AL are known, and the strength, ^3, at another

air-dry moisture content, il/g, is desired. Then

LogSs=losSi+(^i {Mi-MA

\MI-AL) loc S2

S,

Example: Tests of matched specimens of Sitka spruce gave values

of maximum crushing strength of 2,600 and 5,770 pounds per square

inch, respectively, for green wood and wood at 8.9-percent moisture

content. A^liat is the strength value for a moisture content of 12

percent?

Log S3=log 2,600+^

97- -12

27-8.9 loc 5,770

2,600

5^3=5,030 pounds per square inch.
WOOD HANDBOOK 87

Case ^ —The strength value, S2, at some air-dry moisture content,

M2, only is known, and the strength value, S:^,\.i another air-dry

moisture content, Mg, is desired. A good estimation of the true

strength value S^ can be obtained from the formula

log ^-''

Log Ss^log ^'^+(^^^2-^1/3) ^,^£^2)

where Sg and ^12 are values pertaining to gj-een wood and wood at

12-percent moisture content, respectively, as found in table 12 for

the species in question.

Example: Some tests of eastern hemlock at 8-percent moisture

content gave a value of modulus of rupture of 10,000 pounds per

square inch. Estimate the value that would have been ol)tained had

the tests been made at 13-percent moisture content.

. 8,900

^^^r.400

Log S3=log io,000+(8-i:])-^-¿^'

53=8,810 pounds per square inch.

(Since M-p has not been determined experimentally for eastern hemlock, the value of 25 percent is taken.)

Case S.—The strength value at some air-dry moisture content,

M2, only is known, and the strength value at another air-dry moisture

content, M3, is desired. The species is not included in table 12 as in

case 2, and hence, only an approximation of the true strength value

can be obtained. The formula is

[QCr

Log S,=log S,+{M2-MÙ^^J^

Average values of S12 over Sg, based on many different species and

for use in the preceding formula, are given in the following tabulation:

Ilardwnods Soft woods

(average (average of

of 113 54 species)

Static bending: species)

Fiber stress at proportional limit 1.80 1.81

Modulus of rupture 1. 59 1.61

Modulus of elasticity 1. 31 1. 28

Work to proportional limit 2. 49 2. 5()

Work to maximum load 1. 05 1.13

Impact bending, height of drop causing complete failure . 89 1. 03

Compression parallel to grain:

Fiber stress at proportional limit 1. 74 1. 80

Maximum crushing strength 1. 95 1. 97

Compression perpendicular to the grain, fiber stress at proportional Hmit 1. 84 1. 96

Hardness:

End 1.55 1.67

Side 1. 33 1.40

Shear parallel to the grain, maximum shearing strength 1. 43 1. 37

Tension perpendicular to the grain, maximum tensile strength. 1. 20 1. 23
88 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Example: A piece of Central American mahogany at 9-percent

moisture content tested 11,700 pounds per square inch in modulus of

rupture. Estimate the value for the same piece at 12-percent moisture

content.

lo^r 1 59

LogSa-log ll,700+(9-12)^|^^

83=10,510 pounds per square inch.

SPECIFIC GRAVITY AND STRENGTH

The substance of which wood is composed is actuall}^ heavier than

water, its specific gravity being about 1.5 regardless of the species of

wood. In spite of this fact, the dry wood of most species floats in

water, and it is thus evident that a large 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 ceh walls cause

some species to have more wood substance than others and therefore

to have higher specific gravit}^ values. Specific gravity thus is an

excellent index of the amount of wood substance a piece of dry wood

contains and hence is an index of its strength properties. It should

be noted, however, that specific gravity values are also affected by

gums, resins, and extractives, which contribute little to strength.

The relationships of specific gravity and various strength properties

of wood are expressed as equations in the following tabulation, which

is based on average results of strength tests of more than 160 species:

Specific gravify-strength relation 1

Air-dry wood {12-

percent moisture

Static bendinp;: ^^^een wood content)

Fiber stress at proportional limit.__p. s. i__ 10,200^1-25 16,700(71-^

Modulus of rupture p. s. i_ _ 17,600^1-25 25,700(7^-25

Work to maximum load. _in.-lb. per cu. in_ _ 35.6(zi-75 32.4G^i-75

Total work in.-lb. per cu. in__ 103(?2 72.7^2

Modulus of elasticity- _ 1,000 p. s. i_ .2,360(7 2,800(7

Impact bending, height of drop causing complete

failure in _ _ 114(7i -^s 94.6(7i -^^

Compression parallel to grain:

Fiber stress at proportional limit p. s. i__ 5,250(7 8,750(r

Maximum crushing strength p. s. i_ _ 6,730G 12,200(Î^

Modulus of elasticity 1,000 p. s. i__ 2,910(7 3,380(7

Compression perpendicular to grain, fiber stress

at proportional limit p. s. i__ 3,000(^2.25 4,630(?2-25

Hardness:

End lb_. 3,740G2-25 4,800(?2.25

Side lb-_ 3,42002-25 3,770(72-25

1 The properties and values should be read as equations; for example, modulus of rupture for green wood =

17,600(71.25^ where G represents the specific gravity of oven-dry wood, based on the volume at the moisture

condition indicated.

Some properties, such as maximum crushing strength in compression

parallel to the grain, increase approximately in proportion to the

increase in specific gravity, whereas other properties increase at a more

rapid rate. Because these general relations vary considerably, they

cannot be expected to give exact strength values, although they do

o'ive reliable estimates.
WOOD HANDBOOK 89

Strength values for pieces of wood within a species vary by a higher

power of the specific gravity values than do average strength values of

different species. If the exponents to specific gravity in the prececUng

tabulation are increased by 0.25, they will indicate the variation within

a species.

TEMPERATURE AND STRENGTH

Immediate Effect of Temperature

In general, when the temperature of wood is raised above normal, it

tends to become weaker in most strength properties, and when the

temperature is lowered, it becomes stronger. This effect on strength

is immediate, and its magnitude depends upon the moisture content of

the wood and, when the temperature is elevated, upon the time of

exposure. For most structural uses under ordinary atmospheric conditions, wood exposed to temperatures above normal, if the exposure is

for a limited period and the temperature is not excessive, can be

expected to recover essentially all of its original strength when the

temperature is reduced to normal. Experiments indicate that air-dry

wood can probably be exposed to temperatures up to nearly 150° F.

for a year or more without an important permanent loss in most

strength properties, but its strength while heated will be temporarily

reduced as compared to the strength at normal temperature.

The approximate immediate effect of temperature on most static

strength properties of dry wood (12-percent moisture content) within

the range of 0° to 150° F. can be estimated as an increase or a decrease

in the strength at 70° of about % to }^ percent for each 1° decrease or

increase in temperature (^, 5, 7, 19, 20). The change in properties

will be greater if the moisture content is high and less if the moisture

content is low. In some geographical locations fairly high temperatures are commonly experienced, but the accompanying relative

humidity is ordinarily quite low. Wood exposed to such conditions

will generally have a low moisture content, and the immediate effect

of the high temperature is not so pronounced as in locations where

wood has a higher moisture content.

Figure 8, A shows the approximate temperature and moisture content relations that apply for modulus of rupture in bending.

Tests of wood conducted at about —300° F. show that the important

strength properties of dry wood in bending and in compression,

including stiffness and shock resistance, are much higher at the

extremely low temperature than at normal temperature.

Permanent Effect of Exposure to High Temperatures

When wood is exposed to temperatures of 150° F. or more for

extended periods of time, it will be permanently weakened {12, 13,14) y

even though the temperature is subsequently reduced and the wood is

used at normal temperatures The permanent or nonrecoyerable

strength loss will depend upon a number of factors, including the

moisture content and temperature of the wood, the heating medium

and time of exposure, and to some extent upon the species and the

size of the piece. In the following discussion it should be understood
90 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

J40

120

100

A

40 80

TEMPERATURE (°F.)

120 160

100 r

^. MODUL

1 1

US OF ELASTICITY

90

FIBER

'-^PROPO/^

1

STRESS AT

niONAL LIMIT

80 ' ——L 1

\

MODULUS OF RUPTURE

1 1

'

70

60

\

^

WORK TO

.^MAX/MUM LOAD

50

v ~~~—~

"V ^. MODUL.US OF RUPTURE - HARDWOiODS

40

30

'— —

ß

100 200

HEATING PERIOD (DAYS)

300 400

2M 92547

FIGURE 8.—A, Approximate immediate effect of temperature on modulus of

rupture at several moisture content conditions. B, Effect of heating on bending properties of wood exposed to water at 200° F. for various periods and

then tested at normal temperature and 12-percent moisture content. All

curves are for softwoods unless otherwise indicated.
WOOD HANDBOOK 91

that losses in strength are permanent losses, measured at normal

temperature, after exposure to high-temperature conditions for various

periods. Reductions in strength would be substantially higher if

measured at the elevated temperature.

Broadh^, the available data indicate tliat exposure of wet wood for

a period of 1 year to a temperature of 180° F. will result in a substantial

permanent loss in strength, and in wet wood an important strength

loss will occur even at 150°. Exposure to higher temperatures will

result in increasingly greater strength loss(^s in shorter periods of time

as the temperature is increased. Strength properties are affected differently by exposure to high temperatures (fig. 8, />'). The shock

resistance of wood (work to maximum load) is the first bending strength

property affected to a measurable degree regardless of the species,

temperature, or heating medium. Modulus of elasticity, a measure

of stiffness, is least affected.

The effect of high temperatures on various species is different, but,

in general, hardwoods are affected to a considerably greater extent

than softwoods (fig. 8, B).

The heating medium used ho s a considerable bearing on the amount

of reduction of strength that results from exposure of wood at a particular temperatm^e for various periods of time. At all temperatures,

exposure to hot water causes somewhat less strength loss in a given

period of time than steam; the efl'ect of exposure to a hot press is

considerably less than it is for hot water, and the least effect results

from exposure to hot, dry air.

The important interrelation of temperature and time of exposure is

illustrated in figure 9, which shows the great reduction in modulus of

rupture of wood soaked in hot water as the temperature and time of

exposure are increased. Similar curves showing different rates of

deterioration would apply for other properties and heating media.

The relatively greater effect on hardw^oods is clearly evident. For

instance, the modulus of rupture of a hardwood shows an insignificant

reduction at 260° F. if exposed for 2 hours, but a reduction of about

13 percent if exposed for 4 hours and 22 percent if exposed for 8 hours.

Lowering the temperature to 250° F. results in no measurable reduction in modulus of rupture after 2 hours of exposure, only about 4

percent reduction after 4 hours, and about 14 percent after 8 hours.

Thus, 4 hours of exposure to hot water at 260° may be considered

essentially equivalent to 8 hours of exposure at 250° so far as the effect

on modulus of rupture is concerned. The effect of time of exposure

becomes very large with a substantial difference m temperature. For

example, 32 hours of exposure to hot water at 250° is no more harmful

than only 2 hours of exposure at 300°.

The effect of time and temperature on shock resistance is greater

than on modulus of rupture. Wlien a softwood is exposed to hot

water for 10 hours at a temperature of 300° F., the reduction in

modulus of rupture would approximate 30 percent, whereas in work

to maximum load, a measure of shock resistance, the corresponding

reduction would be more than 40 percent.

The effect of exposure to high temperatures on the strength of wood

is cumulative. For example, if wood at a particular moisture content

is exposed 6 different times to a temperature of 180° F. for 1 month

303747°—55 7
92 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

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TEMPERATURE CT.)

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ZM 92548 F

FIGURE 9.—Variation in modulus of rupture with temperature for softwoods

and hardwoods soaked in hot water for various periods. Strength tests were

made at normal temperature and 12-percent moisture content.
WOOD HANDBOOK 93

each, the overall effect would be approximately the same as for a

single exposure of 6 months.

The shape and size of wood pieces can be expected to influence tlu^

overall temperature effect in relation to the heatino; medium, exposure

time, moisture content, and the strength properties consid(u\Ml. If

the exposure is for only a short time, so that the inner parts of a laro;(^

piece do not reach the temperature of the surrounding medium, the

immediate effect on the strength properties of the inner parts will ])e

less than for the outer parts. On the other hand, the outer fibers of

a piece stressed in bending are subjected to the greatest load and will

ordinarily govern the ultimate strength of the piece; hence, the fact

that the inner part is at a lower temperature may be of little advantage.

For long-extended exposures, it can be assumed that the entire piece

reaches the temperature of the heating medium and will, therefore, be

subject to permanent, nonrecoverable strength losses throughout the

volume of the piece, regardless of size. It should be recognized,

however, that in ordinary construction service, such as in buildings,

the temperature of the air surrounding the wood varies substantially

during the day and the seasons of the year and that the wood itself,

or at least any substantial part of a member, is not likely to reach the

maximum temperature of the surrounding air. This is true particularly of the larger or structural members.

DURATION OF STRESS

The duration of stress, or the time during wliich a load acts on a

wood member, is an important factor in determining the load that a

member can safely carry. For members that carry a load continuously

for a long period of time, such as posts or beams in a warehouse, the

load-carrying capacity is much less than that determined from the

strength properties of table 12. A wood member continuously loaded

for 10 years can carry only about 60 percent of the load required to

produce failure in a standard strength test of only a few minutes'

duration (fig. 26) (27).

Conversely, if the loading rate is very rapid, as it might be in certain

aircraft members during flight or maneuvers, the load-carrying capacity is increased. This increase is approximately 25 percent over

that indicated by standard strength tests when the load is applied in

1 second. As an approximate indication of variation in strength of

wood members with duration of stress, the strength may be said to

increase or decrease 7 to 8 percent as the duration of loading time is

decreased or increased by a factor of 10 (10). The duration of stress

must be considered in establishing safe working stresses for timber

and is further discussed on page 160.

STRENGTH-REDUCING FACTORS

Knots

As a knot appears on a sawed surface, it is merely a section of the

entire knot, aiid its shape depends upon the direction of the cut.

When a knot is sawed through at right angles to its length, a round

knot results; when cut diagonally, an oval knot; and when sawed

lengthwise, a spike knot.
94 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Knots are further classified as intergrown or encased (fig. 10). As

long as a limb remains alive, there is continuous growth at the junction of the limb and the trunk of the tree, and the resulting knot is

called intergrown; after the limb has died, additional growth on the

trunk encloses the dead limb, and an encased knot results. The

encased knot and the fibers of the trunk are not continuous, and consequently, the distortion of the grain around the knot is less than for

intergrown knots. Encased knots and knotholes are accompanied

by less cross grain than are intergrown knots and hence have no more

effect on the bending strength of lumber than do intergrown knots.

Knots decrease strength because their grain is at a large angle to

the grain of the piece, and because the grain around them is distorted.

Also, checking may occur in and around them in drying. The weakening efl'ect of knots is greater on the tensile than on the compressive

strength.

In structural beams, the effect of knots on the bending strength is

largely dependent upon the location of tlie knot {17, 24). For

example, in a beam simply supported, knots on the lower side are

placed in tension, those on the upper side in compression, and those

at or near the neutral axis in horizontal shear. On the lower side at

the point of maximum stress, a knot has a marked effect on the maximum load a beam will sustain; knots on the compression side are somewhat less serious. In any location knots have little effect on shear.

The stiffness of beams is also affected but little by knots.

FIGURE 10.—A, Encased knot; B, intergrown knot.
WOOD HANDBOOK 95

In long columns, in which stiffness is the controlling factor, knots

are not of importance. In short or intermediate columns, the rechiction in strength caused by knots is approximate!}^ proportional to the

size of the knot. However, large knots have a somewhat greater relative effect than small knots.

Knots in round timbers, such as poles and pihng, have less efl'ect

on strength than knots in sawed timbers. Although the grain is

irregular around knots in both forms of timber, its angle with the

surface is less in naturally round than in sawed timber. Furthermore,

the round piece is often sufficiently enlarged at a knot to compensate,

at least partially, for the effect of the irregular grain.

Observation of trees and poles bent or broken by windstorms or in

felling or handling, as well as observations in tests of round timber,

shows that first failure often occurs between, rather than at knots.

Cross Grain

The fibers in a cross-grained piece of wood lie at an angle to the axis

of the piece {25). The principal types of cross grain are spiral grain

and diagonal grain (fig. 11). Other less important types are wavy,

dipped, interlocked, and curly grain.

ZM 48832 F

FIGURE 11.—Interior views of two pieces of wood showing inclination of the

annual rings (diagonal grain) and inclination of fibers in the plane of the annual

rings (spiral grain). The line do indicates the direction of the fibers in each

piece with respect to a longitudinal corner. A, A piece of wood with radial

{R) and tangential {T) surfaces and with left-handed spiral grain. B, A piece

of wood without radial and tangential surfaces and with right-handed spiial

grain. If spiral grain were not present, the direction of the fibers would be

parallel to a line from d' to o, d' being at the base of a perpendicular line from

the corner a to the annual ring be.

Spiral grain (fig. 12) is caused by the fibers growing in a winding or

spiral course about the bole of a tree instead of in a vertical course.

Spiral grain is not always jeadily detected by ordinary visual

inspection. The best test foî spiral grain is to split a sample section

from the piece at right angles to the annual rings. Another method

of determining the presence of sphal grain is to note the alinement of
96 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

f

FIGURE 12.—Spiral-grained and straight-grained forest trees.

pores, rays, and resin ducts on flat-grained faces. Checks on a flatsawed surface also follow the fibers and when present indicate the

direction of grain.

Diagonal grain results from sawing a piece of lumber at an angle

other than parallel with the bark. One of the frequent causes is sawing a log having a pronounced taper parallel with the axis of the tree

rather than parallel with the bark. It also occurs in sawing crooked or

swellcd-butt logs and from careless sawing. Diagonal grain is easily

detected by noting the slope of the annual rings on an edge-grain

surface. Its presence but not the slope is evidenced on a tangential

surface by the numerous hyperbolas produced by the intersection of

growth rings with the surface.

The slope of grain is usually expressed by the ratio between a 1-inch

deviation of the grain from the edge or axis of a piece and the distance

within which this deviation occurs (6). When a piece contains both

spiral and diagonal grain, the combined slope must be considered

rather than the greater of the two slopes. The combined slope is

determined by taking the square root of the sum of the squares of the

slopes of the two types of cross grain. For example, if these slopes

are 1 in 18 and 1 in 12, the combined slope is

Vils)+(¿) =10 "^ ^ ^^°P^ ""^ ^ ^^ 1^

.nM
WOOD HANDBOOK 97

Because of practical considerations in commercial stress grading,

slope of grain limitations in structural timbers are measured in the

face having the greatest slope of grain. This fact is taken into account

in the reduction factors applied for slope of grain in establishing

working stresses for various grades (p. 149).

Relationships between strength properties and the actual combined

slope of grain, determined for several species in tests by the Forest

Products Laboratory, are given in table 15.

TABLE 15.—Strength of wood members with various grain slopes compared to

strength of a straight-grained member, expressed as percentages

Maximum slope of grain in member

Static bending

Modulus of

rupture

Modulus of

elasticity

Percent Percent

100 100

96 97

93 96

89 94

81 89

55 67

in pact bending

—height of drop

causing complete failure

(50-pound

hammer)

romi)ression

parallel to

grain—maximum crushing

strength

Percent Percent

Straight-grained

lin 25

lin 20

linio

linio

lino

100

95

90

81

62

36

100

100

100

100

99

93

Compression Wood

Compression wood is an abnormal type of wood that is characteristic

of softwood trees or logs in which the pith is off center, as might

occur in leaning trees. Compression wood may occur in all softwood

(coniferous) species. It is denser and harder than the normal wood,

is characterized by wide annual growth rings that are usually eccentric,

and includes what appears to be exceptionally large proportions of

summerwood growth (fig. 13, A). The contrast in color between

springwood and summerwood, however, is usually less in compression

wood than in normal wood.

Compression wood has larger shrinkage along the grain than normal

wood, and low strength for its weight. When compression wood is

present in the same board with normal wood, the unequal longitudinal

shrinkage causes internal stresses that result in warping, sometimes

in rough lumber, but more often in planed, ripped, or resawed lumber.

The seriousness of the effects of compression wood is generally related

to its widely varying forms. The most serious effects occur in pronounced compression wood that can be readily detected by ordinary

visual examination, as compared to borderline forms that merge with

normal wood and frequently are only detected by microscopical examination. Warping is serious in millwork and cabinets in which

compression wood is limited to small tolerances. Moldings that are

securely fastened in place usually are not seriously affected by warping

caused by compression wood. Its reduced strength as compared

with normal wood, however, requires that compression wood be restricted to only small amounts for uses such as aircraft in which

safety of life and property are involved.
98 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

WWWWfaS^E;

FIGURE 13.—A, The darker areas shown are compression wood; B, compression

failure is shown by the irregular lines across the grain.

Tension Wood

Tension wood is an abnormal type of wood that occurs in many

hardwood species, mainly on the upper side of leaning trees but sometimes distributed entirely around some trees. Its presence in lumber

causes excessive longitudinal shrinkage and warping when moderate

to large numbers of its abnormal fibers are present. In addition,

these abnormal fibers hold together tenaciously, so that sawed surfaces

usually have projecting fibers and planed surfaces often are torn or

have raised grain. The undesirable characteristics vary in seriousness

in relation to the presence of small to large numbers of tension wood

fibers.

Compression Failures

Excessive bending of standing trees from wind or snow, felling trees

across boulders, logs, or irregularities in the ground, or the rough

handling of logs or lumber may produce excessive compression stresses

along the grain that cause minute compression failures. In some

instances, such failures are visible on the surface of a board as minute

lines or zones formed by the crumpling or buckling of the cells (fig.

iaÊà
WOOD HANDBOOK 99

13, B), although usually they appear only as white lines or may even

be invisible to the naked eye. Their presence frequently is indicated

by fiber breakage on end grain (fig. 14).

The strength of a piece containing visible compression faihu'es is

seriously reduced, especially in tensile strength and shock resistance;

such a piece may break suddenly along the compression failure when

subjected to shock or tension, in which event the failure will have a

brittle appearance. Even when compression failures are so small

that they are not visible with favorable lighting, they are known to

reduce shock resistance seriously and cause brittle fractures {18).

' .~~." .JK*

M 81195 F

FIGURE 14,—End-fírain surfaces of spruce lumber showing fiber breakage caused

by compression failures confined to the part below the dark line. Slightly

magnified.

Molds and Staining Fungi

Molds and staining fungi (p. 381) do not ordinarily appreciably

affect the strength of wood. Wliere molding or Stauung of wood is

intensive, the shock resistance may be greatly reduced, but even then

such properties as strength in compression parallel to the gram and

bending strength are usually but little affected.
100 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Al(.hoiio;h molds and stains themselves are usually not important

as reo-ards stronotb, conditions that favor the developnient of these

funo-i are likewise ideal for the growth of wood-destroying fungi (p.

382). Since decay even in its incipient stage may greatly reduce some

strength properties, stained lumber should be regarded with suspicion

when strength is an important factor.

Decay

Unlike the sap-staining fungi, the decay-producing fungi cause a

serious reduction in strength. Even apparently sound wood adjacent

to obviously decayed parts ma}^ contain incipient decay that is decidedly weakening, especially in shock resistance.

Different wood-destroying fungi affect wood differently. The fungi

that cause an easily recognized pitting of the wood, for example, may

be less injurious to the strength than those that, in the early stages,

give a slight discoloration of the wood as the only visible effect.

No method is known for estimating from the appearance of decayed

wood the amount of reduction in its strength. Therefore, when

strength is an important consideration, the safe procedure is to discard

every piece that contains even a small amount of deca}^ (p. 383), with

the exception of 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 unseasoned

or seasoned luml)er. Damage in the standing tree is difficult to control, but otherwise insect damage can be largel}^ eliminated by proper

control methods.

Insect holes are generally classified as pinholes, grub holes, and

powderpost (p. 386). The powderpost larvae by their irregular burrows may destroy most of the interior of a piece, while the surface

shows only small holes, and the strength of the piece may be reduced

virtually to zero.

No method is known for estimating from the appearance of insectdamaged wood the amount of reduction in strength, and, when strength

is an important consideration, the safe procedure is to discard every

piece that contains insect holes.

Pitch Pockets

A pitch pocket is a well-defined opening extending parallel to the

annual rings, substantially flat toward the pith and curved on the

bark side, which contains more or less free resin. Pith pockets are

confined to the pines, spruces, Douglas-fir, tamarack, and western

larch.

The eft'ect of pitch pockets on strength depends upon their number,

size, and location in the piece; their effect on strength has often been

overestimated. A large number of pitch pockets indicates a lack of

bond between annual growth layers, and a piece containing them

should be inspected for shakes, or separations along the grain.
WOOD HANDBOOK 101

Mineral Streaks

Maple, hickory, white ash, and a number of other species are often

damaged by small holes made by sapsuckers. These holes or bird

pecks are often placed in horizontal rows, sometimes encirchno; the

tree, and a brown or a black discoloration known as a ^'mineral streak"

has its origin at such holes. 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 importaDt defects as regards

strength, although they do impair tlie appearance of the wood. However, if several bird pecks occur in a row across the outer surface of a

piece of wood that is to be used in a bent product, such as a handle,

the holes would appreciably w^eaken the piece.

Seasoning Degrade

Seasoning degrade (p. 323) that influences strength is confined

mostly to surface and end checking. Some loss in strength, especially

in shock resistance, may occur when wood is dried at excessively

high temperatures, although such wood may show no visible signs of

degrade. Even improperly seasoned wood, however, may be considerably higher in strength than green wood, since properly seasoned

wood in the form of small, clear specimens may more than double in

strength in seasoning from a green to a dry condition; the increase

depends upon the strength property and the final moisture content.

Different drying conditions are required for different s])ecies of

wood, because the strength of wood is aft'ccted by the temperature

and the time of exposure in relation to its moisture content (p. 89).

Therefore, suitable kiln-drying schedules have been w^orked out for the

various species. These kiln-drying schedules result in no significant

difference in the strength properties of the wood as compared to those

obtained when careful air-drying practices, where temperature is not a

factor, are followed. Proper kiln-drying offers better control of

drying conditions than is usually the case with air-drying, and less

degrade due to drying can be expected.

VALUE OF TIMBER FROM LIVE AND FROM DEAD TREES

Sound timber from trees killed by insects, blight, wind, or fire is

undoubtedly as good for any structural purpose as that from live trees,

provided additional injury from further insect attack, staining, decay,

or seasoning degrade has not occurred.

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 in time the heartwood wall be similarly aff'ected. Such deterioration occurs also in logs that have been cut from live trees and improperly cared for afterwards. Because of variations in climatic and local

weather conditions and in other factors that affect deterioration, tlie

length of the period during which dead timber may stand or lie in the

forest without serious deterioration varies.
102 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

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 as

strong as wood from live trees. Also, logs of some of the more durable

species have had thoroughly sound heartwood after lying on the ground

in the forest for many years.

On the other hand, decay may cause great loss of strength within a

very brief time, both in trees standing dead on the stump and in logs

that have been cut from live trees and allowed to lie on the ground.

Consequently, the important consideration is not whether the trees

from which timber products are cut are alive or dead, but whether

the products themselves are free from decay or other defects that would

render them unsuitable for use.

Specifications for some timber products sometimes require that

only live trees be used; this requirement, however, is difficult to

enforce unless inspection is made in the forest, because wood cut

from fire-killed, wind-fahen, or otherwise naturally killed trees before

weathering, seasoning, discoloration, decay, insect attack, or similar

change has occurred cannot be distinguished from wood taken from

live trees. All specifications should omit the live-tree requirement

and depend entirely upon inspection to determine the suitability of

the timber for use.

RESIN

Resin is formed in some of the conifers, especially the southern

yellow pines. It is common in amounts up to 6 percent of the dry

weight of the wood, and pieces with a resin content up to 50 percent

are sometimes found.

Tests at the Forest Products Laboratory on southern j^ellow pine

indicate that resin will slightly increase some strength properties, but

the effect is too small to be of any particular significance; that is,

any additional strength resulting from the presence of resin is very

small as compared to that wdiich would normally result from an equal

additional weight of wood substance. An excessive amount of resin

is sometimes associated with an injury that may have greatly reduced

the strength.

TURPENTINING

Some species of southern yellow pine trees are frequently tapped

for turpentine, and if the turpentining is properly handled, the trees

are not unduly damaged for lumber purposes. Comparative tests

on mature turpentined and unturpentined trees have sho^\^l that

(1) turpentined timber is as strong as unturpentined timber of the

same weight, (2) the w^eight and shrinkage of wood are not affected

by turpentining, and (3) practically speaking, properly turpentined

trees contain neither more nor less resin than unturpentined trees.

EXTRACTIVES

Extractives, the part of a piece of wood that dissolves when the

piece is placed in an inert solvent, occur in many species and are

especially abundant in redwood, western redcedar, and black locust

(11). The three species mentioned are also relatively high in certain
WOOD HANDBOOK 103

strength properties for the amount of wood substance they contain,

and tests at the Forest Products Laboratory have shown that the

presence of extractives is probably accountabk\ The extent to

which extractives affect the strength is apparently de])endent upon

the amount and nature of extractives, the moisture condition of the

piece, and the mechanical property under consideration.

Of the strength properties examined, maximum crushing strength

in compression parallel with the grain showed the greatest increase

from the infiltration of extractives in the change of sapwood into

heartwood, the modulus of rupture came next, and shock resistance

showed the least. In fact, under some conditions, shock resistance

appears to be actually lowered by extractives. That the extractives

found in different species may affect the strength differently is indicated by the fact that they change the strength of western redcedar

less than the strength of black locust, although black locust has a

smaller percentage of extractives {11).

LITERATURE CITED

(1) AMERICAN SOCIETY FOR TESTING MATERIALS.

1952. STANDARD METHODS FOR TESTINC SMALL CLEAR SPECIMENS OF TIMBER. Amer. Soc. Testing Mater. Standard D. 143-52. Ft. 4:

720-757, illus.

(2) DOYLE, D. V., DROW, J. T., AND MCBURNEY, R. S.

1945. ELASTIC PROPERTIES OF WOOD: THE YOUNG'S MODULI, MODULI OF

RIGIDITY, AND POISSON'S RATIOS OF BALSA AND QUIPO. U. S.

Forest Frod. Lab. Rpt. 1528, IG pp., illus. [Frocessed.] (See

supplementary Rpts. 1528A through 1528H for elastic properties

of other species.)

(3) FULLER, F. B., AND OBORG, T. T.

1943. FATIGUE CHARACTERISTICS OF NATURAL AND RESIN-IMPREGNATED

COMPRESSED LAMINATED WOODS. Jour. Acrouaut. Sci. 10 (3):

81-85, illus.

(4) GEORGE, H. O.

1933. EFFECT OF LOW TEMPERATURES ON THE STRENGTH OF WOOD. N. Y.

State Col. Forestry, Syracuse Univ., Tech. Fub. 43, 18 pp., illus.

(5) GREENHILL, W. L.

1936. STRENGTH TESTS PERPENDICULAR TO THE GRAIN OF TIMBER AT

VARIOUS TEMPERATURES AND MOISTURE CONTENTS. Austral.

Council Sei. & Indus. Res., Jour. 9 (4): 265-276, illus.

(6) KOEHLER, A.

1943. GUIDE TO DETERMINING SLOPE OF GRAIN IN LUMBER AND VENEER.

U. S. Forest Frod. Lab. Rpt. 1585, 25 pp., illus. [Frocessed.]

(7) KOLLMAN, F.

1941. MECHANICAL CHARACTERISTICS OF VARIOUS MOIST WOODS WITHIN

TEMPERATURE GRADIENTS FROM —200° TO +200° c. Translation,

U. S. Nati. Advisory Com. Aeronaut. Tech. Memo 984, 37 pp.,

illus.

(8) KOMMERS, W. J.

1943. FATIGUE BEHAVIOR OF WOOD AND PLYWOOD SUBJECTED TO REPEATED

AND REVERSED BENDING STRESSES. U. S. Forcst Frod. Lab. Rpt.

1327, 11 pp., illus. [Frocessed.]

(9) LEWIS, W. C.

1951. FATIGUE OF W^OOD AND GLUED JOINTS USED IN LAMINATED CONSTRUCTION. Forest Frod. Res. Soc. Froc. 5: 221-229, illus.

(10) LiSKA, J. A.

1950. EFFECT OF RAPID LOADING ON THE COMPRESSIVE AND FLEXURAL

STRENGTH OF WOOD. U. S. Forcst Frod. Lab. Rpt. 1767, 10 pp.,

illus. [Frocessed.]

(11) LUXFORD, R. F.

1931. EFFECT OF EXTRACTIVES ON THE STRENGTH OF WOOD. Jour. Agr.

Res. 42: 801-826, ilhis.
104 HANDBOOK 72, Ü. S. DEPARTMENT OF AGRiCÜLTÜHE

(12) MACLEAN, J. D.

1958. EFFECT OF STEAMING ON THE STRENGTH OF WOOD. Amer. WoodProserver.^' Assoc. Proc. 49: 88-112, illus.

(18)

1951. KATE OF DISINTEGRATION OF WOOD UNDER DIFFERENT HEATING

CONDITIONS. Amer. Wood-Preservers' Assoc. Proc. 47: 155-168,

illus.

(14)

1945. EFFECT OF HEAT ON THE PROPERTIES AND SERVICEABILITY OF WOOD.

U. S. Forest Prod. Lab. Rpt. R1471, 12 pp., illus. [Processed.]

(15) MARKWARDT, L. J.

1930. COMPARATIVE STRENGTH PROPERTIES OF WOODS GROWN IN THE

UNITED STATES. U. S. Dept. Agr. Tech. Bui. 158, 39 pp., illus.

(10) and WILSON, T. R. C.

1935. STRENGTH AND RELATED PROPERTIES OF WOODS GROWN IN THE

UNITED STATES. U. S. Dept. Agr. Tech. Bui. 479, 99 pp., illus.

(17) NEWLIN, J. A., and JOHNSON, R. P. A.

1924. STRUCTURAL TIMBERS: DEFECTS AND THEIR INFLUENCES ON

STRENGTH. Amer. Soc. Testing Mater. Proc. 24, Pt. II; 975-989,

illus.

(18) PILLOW, M. Y.

1949. STUDIES OF COMPRESSION FAILURES AND THEIR DETECTION IN

LADDER RAILS. U. S. Forcst Prod. Lab. Rpt. D1733, 10 pp.,

illus. [Processed.]

(19) SULZBERGER, P. H.

1943. EFFECT OF TEMPERATURES ON STRENGTH PROPERTIES OF WOOD,

PLYWOOD, AND GLUED JOINTS. Austral. Council Sci. Indus. &

Res. Jour. 16 (4): 263-265.

(20) THUNELL, B.

1940. EFFECT OF TEMPERATURES ON THE BENDING STRENGTH OF SWEDISH

PINE WOOD. (Sweden) Govt. Testing Inst. Med. 80: 38 pp.,

illus. (English summarjO-

(21) U. S. FOREST PRODUCTS LABORATORY.

1941. FOREST PRODUCTS LABORATORY'S TOUGHNESS TESTING MACHINE.

U. S. Forest Prod. Lab. Rpt. 1308, 13 pp., illus. [Processed.]

(22)

1941. MOISTURE CONTENT-STRENGTH ADJUSTMENTS FOR WOOD. U. S.

Forest Prod. Lab. Rpt. 1313, 9 pp., illus. [Processed.]

(23)

1951. DESIGN OF WOOD AIRCRAFT STRUCTURES. ANC Bul. 18, 234 pp.,

illus. (Issued by Subcommittee on Air Force-Navy-Civil Aircraft Design Criteria, Aircraft Committee, Munitions Board.)

(24) WANGAARD, F. F.

1950. MECHANICAL PROPERTIES OF WOOD. 377 pp., illus. Ncw York.

(25) WILSON, T. R. C.

1921. EFFECT OF SPIRAL GRAIN ON THE STRENGTH OF WOOD. JOUR.

Forestrv 19: 740-747, illus.

(26)

1932. STRENGTH-MOISTURE RELATIONS FOR WOOD. U. S. Dept. Agr.

Tech. Bul. 282, 88 pp., illus.

(27) WooD^ L. W.

1947. BEHAVIOR OF WOOD UNDER CONTINUED LOADING. Engin. NeWSRec. 139 (24): 108-111, illus.
GRADES AND SIZES OF LUMBER

A log when sawed into lumber often ^nelds boards of widely var^âng

quality. To enable a user to buy the quality that best suits his purpose, the product of a log is divided into several lumber grades, each

having a relatively narrow range in quality.

Except as noted later, the grade of a piece of lumber is based on the

number, character, and location of features that may lower the

strength, durability, or utilit}^ value of the lumber. Among the more

common of such features are knots, checks, pitch pockets, shake, and

stain, some of which are a natural part of the tree. The best grades

are free or practically free from them, but the other grack^s comprising

the great bulk of lumber contain fairly numerous knots and other

features that affect quality. These features, however, do not prevent

such lumber from giving satisfaction for many widespread uses.

AGENCIES PROMULGATING GRADING RULES

Name and address

Hardwood Dimension Manufacturers'

Association, 230 Heyburn Bldg.,

Louisville, Ky.

Maple Flooring Manufacturers' Association, 35 E. Wacker Dr., Chicago,

111.

National Hardwood Lumber Association, 59 E. Van Buren St., Chicago,

ni.

National Oak Flooring Manufacturers' Association, 814 Sterick Bldg.,

Memphis, Tenn.

California Redwood Association, 576

Sacramento St., San Francisco, Calif.

Northeastern Lumber Manufacturers'

Association, 271 Madison Ave., New

York, N. Y.

Northern Hemlock & Hardwood Manufacturers' Association, (3shkosh, Wis.

Northern Pine Manufacturers' Association, 4329 Oakland Ave., Minneapolis,

Minn.

Southern Cypress Manufacturers' Association, Barnett National Bank Bldg.,

Jacksonville, Fla.

Southern Pine Inspection Bureau,'

National Bank of Commerce Bldg.,

New Orleans, La.

Woods covered by grading rules i

Hardwoods (hardwood dimension lumber, squares and laminated stock) (:2) .-

Maple (northern liard), beech, birch

(flooring) (3).

Hardwoods^ cypress, aromatic redcedar,

hardwood veneer (4).

Oak and pecan (flooring) (5).

Redwood (1).

Balsam fir, northern white pine, eastern

hemlock, and eastern spruce (6, 7).

Northern white })ine, Norway pine,

jack pine, eastern spruce, balsam,

eastern hemlock, tamarack, northern

whitccedar (5, 9).

Northern white l)ine, Norway pine,

eastern spruce, and jack ])ine.

Southern cvpress (upland and tidewater

types) {10).

Southern yellow pine and longlcaf yellow

pine (11),

1 Species names in this list are those used in the gradinj^: rules of the

2 Italic numbers in parentheses refer to Literature Cited, [). 135.

3 Affiliated with the Southern Pine Association.

different agencies.

105
106 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Name and address Woods covered by grading rules

West Coast Bureau of Lumber Grades Douglas-fir (coast region), west coast

& Lispection,4 1410 S. W. Morrison hemlock, Sitka spruce, western redSt., Portland, Greg. cedar, white fir, noble fir {13).

Western Pine Association, Yeon Bldg., Ponderosa pine, Idaho white pine,

Portland, Greg. sugar pine, lodgepole pine, western

larch, Douglas-fir, white fir. Engelmann spruce, incense cedar, and

western redcedar {14)-

Rod (Y-dar Shingle Bureau, White Western redcedar (shingles).

Bldg., Seattle, Wash.

4 Affiliated with the West Coast Lumbermen's Association.

HARDWOOD LUMBER GRADING

Hardwood Lumber (All Species)

Most hardwood boards are not used in their entirety but are cut

into smaller pieces to make furniture or some other fabricated product.

The rules that are considered standard in grading hardwood lumber

in the United States are those adopted by the National Hardwood

Lumber Association (4) .'* In these rules the grade of a piece of hardwood

lumber is determinecl by the proportion of the piece that can be cut

into a certain number of smaller pieces of material clear on one side

and not less than a certain size. In other words, the grade classification is based upon the amount of usable lumber in the piece rather

than upon the number or size of growth features that characterize

softwood yard grades. This usable material, commonly termed

''cuttings," must have one face clear and the reverse face sound, which

means free from such things as rot, heart center, and shake that materially impair the strength of the cutting. The lowest grade requires

only that cuttings be sound.

The highest grade of hardwood lumber is termed 'Tirsts^' and the

next grade ''Seconds." Firsts and Seconds, or, as they are generally

written^ 'TAS," nearly always are combined in one grade. The third

grade is termed "Selects," followed by No. 1 Common, No. 2 Common,

Sound Wormy, No. 3A Common, and No. 3B Common.

A brief summary of the standard hardwood lumber grades follows.

This summary should not be regarded as a complete set of grading

rules, as there are numerous details, exceptions, and special rules for

certain species that are not included. The complete official rules of

the National Hardwood Lumber Association should be followed as

the onl}- full description of existing grades. The summary is intended

only as a preliminary guide in distinguishing between the general

qualities to be expected under the various grades.

^ This association publishes a booklet that contains detailed grading rules for

various hardwood products, such as lumber, car stock, and vehicle stock. The

association maintains bonded lumber inspectors in various hardwood producing

and consuming centers who issue inspection certificates on shipments. The

correctness of the grades as shown on these certificates is guaranteed by the

association.
WOOD HANDBOOK 107

Summary of Standard Grades of the National

Hardwood Lumber Association

Alder, red

Ash

Aspen

Basswood

Beech

Birch

Boxelder

Buckeye

Butternut

Cedar, red

Cedar, Spanish

Cherry

Chestnut

Cottonwood

Cypress

Woods Included

Elm:

Rock (or cork)

Soft

Gum:

Black

Red and sap

Tupelo

Hackberry

Hardwoods (Pliilij^pine)

Hardwoods (Troi)ical

American other than

mahogany and Span- Pecan

ish cedar) Poplar

Hickory Sycamore

Locust Wahuit

Magnolia ^^'illow

Mahogany:

African

Cuban and San

Dominican

Philippine

Hard (or sugar)

Soft

Oak:

R(^d

White

1 Species names are those used in uradin^i rules of tlie association. Two of tlir woods

included, namely, cedar (east<'rn r«Mlc'edar) and cyprt'ss ( haldcypirss ). are not hardwoods.

Cypress lumber has a different set of ^'rading rules from those'used for the hardwoods.

Standard Lengths

Standard lengths are 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 10

feet, but not more than 50 percent of odd lengths will b(^ admitted.

Standard Thicknesses

Standard thicknesses for hardwood lumber are given in table IG.

TABLE 16.—Standard thicknesses for hardwood lauiber

Rough (inches)

Surfaced

1 side

(SIS)

Surfaced

2 sides

(S2S)

Koush (inches)

Surfaced

1 side

(SIS)

Surfaced

2 sides

(S2S)

3^

Inches

M

•3 8

I'; 8

11^16

Inches

9, 1 ,;

1)10

2'-.'

3_-

4.-

4I2

5_.

5Î2

6,.

Inches

2M.;

21 •!.•,

3' 1.;

31-M.;

(')

(')

(')

(')

Inches

21/4

1/ 2-1

H 3>i

34 3v'4

1 . _ (')

IM (0

lU (0

2 (0

1 Finished size not specified in rules. Thickness suhject to special contract.

Description of Standard Hardwood Grades

A description of the standard hardwood grades is given in table 17.

The highest grade, Firsts, calls for pieces that will allow 91 K percent

of their surface measure to be cut into clear-face material; that is,

303747°—55-
108 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

TABLE 17.—Standard hardwood grades ^

Grade and lenpths allowed

(feet)

Widths

allowed

Firsts: -

8 to 16 (will admit 30 percent of 8- to 11-foot, \2 of

which may be 8- and 9-

foot).

Seconds: -

8 to 16 (will admit 30 percent of 8-to 11-foot, H of

which may be 8- and 9-

foot).

Selects:

6 to 16 (will admit 30 percent of 6- to 11-foot, Ya of

which may be 6- and 7-

foot).

No. 1 Common:

4 to 16 (will admit 10 percent of 4- to 7-foot, V'l of

which may be 4- and 5-

foot).

No. 2 Common:

4 to 16 (will admit 30 percent of 4- to 7-foot, H of

which may be 4- and 5-

foot).

Xo. 3A Common:

4 to 16 (will admit 50 percent of 4- to 7-fcot, \<¿ of

which may be 4- and 5-

foot).

Xo. 3B Common:

4 to 16 (will admit 50 percent of 4- to 7-foot, Vi of

which may be 4- and 5-

foot).

Inches

0+

6-f

4+

3+

3+

Surface meassure of

pieces

Square feet

4 to 9

10 to 14

15+

'4 and 5

6 and 7

6and 7

8 to 11

8 to 11

12to 15

12to 15

116+

2 and 3.

.4+-..--

1

2

3 and 4

3 and 4

(5 to 7

5 to 7

8 to 10

11 to 13--..

U4+

1

2 and 3-.-

2and3-.-

4 and 5

4 and 5

6 and 7..-

6 and 7..-

8 and 9,.-

10 and 11.^

12 and 13..

14+

3+ 1 +-

3+ l-hAmount of

each piece

that must

work into

clear-face

cuttings

Percent

mi

mi

mi

831/3

831/^3

91^3

83 H

912/3

831/3

912 3

83 HI

Maximum

cuttings

allowed

91^3

(3)

100

75

66^^

75

75

my¿

662/á

66 2 á

50

662/3

50

662,3

50

66^

50

50

50

50

^331.:

ö 25

Minimum size of

cuttings required

/.I

4 inches by 5 feet, or

3 Inches by 7 feet.

Do.

Do.

4 inches by 2 feet, or

) 3 inches by 3 feet.

(')

>3 inches by 2 feet.

Do.

ÍH inchest by 2 feet.

1 Inspection to be made on the poorer side of the i)iece, excei)t in Selects.

2 Firsts and Seconds are combined as 1 grade (FAS). The percentage of Firsts required in the combined

grade varies from 20 to 40 percent, depending on the species.

3 Same as Seconds.

4 This grade also admits pieces that grade not below No. 2 Common on the good face and have the reverse

face sound.

fi Not specified.

6 The cuttings must be sound; clear face not required.
WOOD HANDBOOK IQQ

not more than 8% percent of each piece can be wasted in making the

required cuttings. In the grade of Seconds 83K percent of the surface^

measure of the pieces must yield clear-face cuttings.^ Both Firsts and

Seconds require pieces not less tha,n 6 inches wide and 8 feet lono-.

In the grade Selects the minimum width is 4 niches and the mininuim

length 6 feet. Both Firsts aud Seconds and the face side of Selects

must, in addition to cutting requirements, meet specified requirements

as to Imots, holes, and other imperfections. The cutting requirements

of Selects are 91K percent of clear face in pieces with 2 and 3 surface

feet. In larger pieces the cutting requirements are the same as for

Seconds on the face side. The reverse side of the cuttings in Selects

must be sound or the reverse side of the piece not below No. 1

Common.

The next 2 grades, No. 1 Common and No. 2 Common, call for

lumber not less than 3 mches wide and 4 feet long and require 66^^

percent and 50 percent of clear-face cuttings, respectively.^ The

minimum size of cuttings in these 2 grades is reduced from 4 inches

by 5 feet or 3 inches by 7 feet in Firsts, Seconds, and Selects to 3 inches

by 2 feet. The number of allowable cuttings in grades No. 2 Common

and better are limited by the hardwood grading rules (4) according

to the surface measure of each piece.

A grade of hardwood lumber called Sound Wormy has the same

requh'ements as No. 1 Common except that wormholes and limited

sound knots and other imperfections are allowed in the cuttings.

The grade of 3A Common admits pieces that will furnish 33}^

percent of clear face in cuttings not less than 3 inches wide and 2 feet

long. This grade will also admit pieces that grade not l)elow No. 2

Common on the good face and have the reverse face of the cutting

sound. The lowest grade. No. 3B Common, allows pieces that will

cut 25 percent in sound material not less than l}^ inches wide by

2 feet long.

Hardwood Flooring

Hardwood flooring is generally graded under the rules of the

Maple Flooring Manufacturers^ Association (3) and the rules of the

National Oak Flooring Manufacturers' Association (5). Tonguedand-grooved and end-matched hardwood flooring is commonly

furnished. Square-edge and square-end strip flooring is also available,

as well as parquetry flooring suitable for laying on a mastic base or

on an ordinary subfloor.

The Maple Flooring Manufacturers' Association grading rules

cover flooring manufactured from sugar maple (hard maple), beech,

and birch.

Each species has the three grades designated as First grade, Second

grade, and Third grade. Combination grades of Second and Better

and Third and Better are sometimes made. There are also four

5 Boards 6 to 15 feet surface measure will admit of 1 additional cutting to yield

91% percent of clear face.

6 Exceptions in No. 1 Common are pieces with 1 foot surface measure and 2

feet surface measure, which require 100 percent of clear face and 75 percent of

clear face, respectively, and in No. 2 Common pieces with 1 foot surface measure,

which require 66 percent of clear face.
lio HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

special grades—Wlúte Clear Northern Hard Maple, Brown Clear

Northei'n Hard Maple, Red Clear Northern Beech, and Red Clear

Northern Biixh, which arc made up of special stock selected for

uniformity of color. First grade flooring must have one face practically

free from all imperfections. Variations in the natural color of the

wood are allowed. Second grade flooring admits tight, sound knots

and slight imperfections but must lay without waste. Third grade

floormg has no restrictions as to imperfections in the grain but must

be of such a character that it can be properly laid and will give a

good servicoal)le floor. The standard thiclaiess of maple, beech, and

birch floornig is ^%2 inch. Face widths are IJo, 2, 2}^, and 3K inches.

Standard lengths are 2 feet and longer in First and Second grade

flooring and IK ft^'ct and longer in Third grade flooring.

The grading rules of the National Oak Flooring Manufacturers'

Association mainly cover quartersawed and plainsawed oak flooring.

Quartersawed flooring has three grades—Clear, Sap Clear, and Select.

Plainsawed flooring has four grades—Clear, Select, No. 1 Common,

and No. 2 Common. The Clear grade in both plainsawed and quartersawed flooring must have one face practically free from surface

imperfections except three-eighths inch of bright sap. Color is not

considered in any grade. Sap Clear quartersawed flooring must have

one face practically" clear but will admit unlimited bright sap. Select

flooring (plainsawed or quartersawed) ma}^ contain sap and will

admit a few features such as pin wormholes and small tight knots.

No. 1 Common plainsawed flooring must contain material that will

make a sound floor without cutting. No. 2 Common may contain

grain and surface imperfections of all kinds but must lay a serviceable

floor. Standard thicknesses of oak flooring are ^%2, %, and % inch.

Standard face widths are 1}^, 2, 2}^, and 3)^ inches. Lengths in upper

grades are 2 feet and up with a required average of 4K feet in a shipment. In the lower grades lengths are 1% feet and up with a requned

average of 2)2 or 3 feet.

The most recent rules of the National Oak Flooring Manufacturers'

Association also include specifications for flooring of pecan, hard

maple, beech, and birch. The grades of pecan flooring are: Fii^st

grade, practically clear but unselected for color; First grade red,

practically clear but made from all heartwood; First grade white,

practically clear but made from all bright sapwood; Second grade,

admits sound tight knots, pin wormholes, streak, and slight machining

imperfections; Second grade red, similar to Second grade but must

be made from all heartwood; Third grade, must make a sound floor

without cutting; and Fourth grade, must lay a serviceable floor. The

standard sizes for pecan flooring are the same as those for oak floormg.

The rules of the National Oak Flooring Manufacturers' Association

for hard maple, beech, and birch flooring are the same as those of

the Maple Flooring Manufacturers' Association.

Hardwood Dimension Stock

Hardwood dimension stock, as used by furniture and cabinet

manufacturers, is generally graded under the rules of the Hardwood

Dimension Manufacturers' Association (2). These rules apply pri-
WOOD HANDBOOK HI

marily to dimension stock cut from kiln-dried roiioh luml)er and covei'

three classes of material—kiln dried glued dimension, solid dimension

flat stock, and solid dimension squares. Each class may h(^ rough,

semifinished, or finished. Solid dimension flat stock has five grack's—^

Clear Two Faces, Clear One Face, Paint, Core, and Sound. Solid

dimension squares have three grades—Clear, Select, and Sound.

SOFTWOOD LUMBER GRADING

Softwood lumber, unlike hardwood lumber, is graded under a

number of different association rules. Not only are the diilerent

kinds of softwoods graded under different rules, but tlu^ same softwoods in a number of cases are graded under dift*er(4it association

rules.

The first industry-sponsored grading rules for softwoods were

established before 1900 and were comparatively simple because the

sawmills marketed their lumber locally and grades had only local

significance. As new sources were developed and lumber was transported to distant points, each producing region continued to establish

its own grading rules with the result that luml)er from the various

regions diff'ered in size, grade name, and, most impoi-tant of all, in

grade quality. When several diff'erent species graded under different

rules came into keen competition in the chief consuming areas, confusion and dissatisfaction were inevitable.

In order to eliminate unnecessary difl'erences in the grading rules

of the various softwood lumber manufacturers' associations and to

improve and simplify these rules, American lumber standards for

softwood lumber were formulated in the period from 1919 to 1925.

These standards were the result of a number of conferences organized

by the U. S. Department of Commerce and attended by representatives of lumber manufacturers, distributors, wholesalers, retailers,

engineers, architects, and contractors. The stanch^ixls themselves are

issued in pamphlet form as simplified practice recommenchations of

the U. S. Department of Commerce {12).

The agencies promulgating grading rides foi* commercial use have

based their rules on the American lumber standards for softwood

lumber. These include California Redwood Association, Southern

Cypress Manufacturers' Association, Southern Pine Association,

West Coast Lumbermen's Association, Western Pine Association,

Northern Hemlock & Hardwood Manufacturers' Association, and

Northeastern Lumber Manufacturers' Association.

Nomenclature of Commercial Softwoods

The names of lumber adopted by the trade as American lumber

standards are not always identical with the names of trees adopted

as official by the Fores^t Service. Table 18 has therefore been prepared to show the American lumber standards commercial name for

lumber corresponding to the Forest Service tree name used in this

handbook. Other names sometimes used locally but not in contracts

are also shown, as are accepted botanical names.
112 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLE 18.—Nomenclature of commercial softwoods

CEDARS AND JUNIPERS

Official Forest Service

tree name used in this

handbook

Alaska-cedar.

Allipator juniper

Atlantic whitec(>(lar

Eastern red cedar

Incense-cedar

Northern \vhitecedar_._

Port-Orford-cedar

Rocky Mountain juniper.

Utah juniper

Western juniper

Western red cedar

Name adopted as standard for lumber under

American lumber

standards

Alaska cedar.

Western juniper

Southern white cedar _ _ _

Eastern red cedar

Incense cedar

Northern white cedar. __

Port Orford cedar.

Western juniper...

do

.--.do

Western red cedarOther names sometimes

used

Yellow cedar, Sitka cypress, yellow cypress.

Juniper

White cedar, swamp cedar.

Red cedar, cedar, junii)er..

Cedar, white cedar

Arborvitae, cedar, swamp

cedar, white cedar.

Lawson's cypress, Oregon

cedar, white cedar.

Juniper

Juniper, white cedar

Juniper, cedar

Red cedar, cedar, western

cedar.

Botanical name

Chamaecyparis nootkatendis.

Juniperus deppeana.

Chamaecyparis thyoides.

Juniperus virginiana.

Libocedrus decurrens.

Ihuja occidentalis.

Chamaecyparis lav^soniana.

Juniperus scopuloruin.

J. osteosperma.

J. occidentalis.

Thuja plicata.

CYPRESS

Baldcypress- Red cypress (coast ty])e), Cypress, tidewater red

yellow cypress (inland

type), white cypress

(inland type).

cypress, fiulf coast red

cypress, Louisiana red

cypress, bald cypress,

black cypress.

laxodium distichum.

DOUGLAS-FIR

Dougla5-fir. Red fir, Ore^ïon ñr, Doujílas spruce, yellow fir.

Pupet Sound pine.

Pseudofsuga vienzicsii.

TRUE FIRS

Balsam fir

California red fir..

Fraser fir

Grand fir

Noble fir

Pacific silver fir...

Subalpine fir

White fir

Balsam fir..

White fir...

Balsam fir..

White fir...

Noble fir...

White fir...

do

do

Balsam, eastern fir_

Red fir

Balsam, eastern fir.

Yellow fir

Red fir

Red fir, fir

Balsam

Colorado white fir..

Abies balsamea.

A. magnifica.

A.fraseri.

A. grandis.

A. procera.

A. amabilis.

A. lasiocarpa.

.{. concolor.

HEMLOCKS

Carolina hemlock Eastern hemlock Hemlock, hemlock spruce,

spruce pine.

Tsuga caroliniana.

Eastern hemlock .... do do

Mountain hemlock Mountain hemlock Weeping spruce, Alpine

spruce, hemlock spruce.

T. mertensiana.

Western hemlock West coast hemlock Hendock, hemlock spruce.

Pacific hemlock, Alaska

pine.

T. heterophylla.
WOOD HANDBOOK 113

TABLE 18.—Nomenclature of commercial softwoorh—Continucd

LARCIÎ

Oílicial Forest Service

tree name used in this

handbook

Name adopted as standard for lumber under

American lumber

standards

Other names sometimes

use( 1 Botanical luime

Western larch. Western larch Tamarack, larch íAITíX occidentalis

PliXES

Eastern white pine Northern white ()in(". . Whit(i pine, cork pine, soft

pine, north(!rn pine,

Piiuis '•'frohvs.

Jack pine

Loblolly pino

Jack pine

Southern yellow i)ine...

pumpkin j)ine.

Scrub iñne

Old-field pino, slash ])mv.,

shortleaf pinci, Virginia

pine, sap pine, yellow

pino, North Carolina

P. hauksiana.

P. faeda.

Lodgepole pine

Longleaf pine .

Lodgepole pine

Longleaf yellow pine,'

southern yellow jdne.

Southern yellow pine

Scrub pine, spruce pine...

Southern pin*i, yellow

l)ine, hard pine, Georgia

¿)ine, |)itch i)ine, heart

pine, fat pine.

P. conforta,

P. patustris.

P. rigidn.

P. ponderosa.

P resinosa

Pitch pine

Ponderosa pine

Red pine

Ponderosa pine

Norway pine

Southern yellow pine...

Longleaf yellow pine,'

southern yellow pine.

Sugar pine

Southern yellow pine

Bull i)ine, Arizona white

pine, western soft pin(i,

western pine.

Hard j)ine, northern pin(!.

Yellow pine, S])ruco ])ine,

oldfif^ld pine, Arkansas

soft pine, North

Carolina pine.

Swamp i)ine, j)itch pine..

Big pine

Shortleaf pine P echinnla.

Slash pine P elliottii

Sugar pine

Virginia pine

Western white pine . _.

P. lfirnf)ertian,a.

P. nirqininna.

Idaho white pine .. White pine, soft pine P. nioiilicoln.

REDWOOD

Redwood. Redwood Sequoia, co-àsi redwood Sequoia sernperviren.

SPRITES

Black spruce

Blue spruce

Engelmann spruce.

Red spruce..

Sitka spruce.

White spruce.

Eastern spruce

Engelmann S[)rucc_

do

Eastern spruce.

Sitka spruce

Eastern spruce.

Whito spruce, silver

spruce, balsam, mountain spruce.

Si)ruce, tideland spruce,

western spruce, yellow

sj)ruce, silver spruce.

J^icea rnariana.

I', ¡junçrns.

P. engtlmanvii.

P. rubens.

P. Htciiensis.

P. glauca.

1 The commercial ref4Uirements for longleaf yellow pine lumber are that not only must it be produced from

the species Pinus elliottii and P. palvstris, but each piece must average either on one end or the other not

less than 6 annual rings per inch and not less than 3^^ summerwood. Longleaf yellow pine lumber is sometimes designated as pitch pine in the export trade
114 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

TABLE IS.—Nomenclafiire of commercial softwoods—Continued

Oilicia] Forest Service

tree n;inie used in this

handbook

I Xanie adopted as standard for lumber under

American 1 u m \) e r

standards

Other names sometimes

used Botanical name

' AM AR AC K

Laicli. hackmatack, red i Larir ¡uri-'in

larch, black larch.

Pacific ye\v_ I ^^'w, western yew, moun- 'rarus hra ifoJia.

tain nialio^any.

General Classification of Softwood Lumber

vSoftwood lumber is divided into tliree main classes—3^ard lumber,

structural lum])er (often referred to under the general term ^'timber"),

and factory and shop lumber. The folio^vhio; classification of softwood luml)er o¡vos the grade names in general use by lumber manufacturers' associations for the various classes of lumber.

Finisli (A inches and under thick and loinclies

and under wide).

Common boards (less

than 2 inches thick

and 1 or more inches

wide).

SOFTWOOD LCMBFK (This classification applies to

i-ough or drf^ssed

lumber; sizes iriven

are nominal.)

J'MP.EK (lumber

than 5 inclies

. inten<led for

;il building pur- <

; tnadin.u based

-e of the entire

-TKrCTUK.XL LUMBER

ilumber f) or more

inchesthick and wide,

e\cei)t joists an! (

planks; sirading based

on strength and on

use of entire piece).

FACTORY AND SIIOF

LUMBER (grading

based on area of i)iece

suitable for cuttings

of certain size and

quality).

Common dimension (2

inches and under 5

inches thick and 2 or

more inches vide).

'Joists and planks (2 to

4 inches thick and 4

or more inches w ide).

i^ean.s and stringers (.S

or more inches thick

and 8 or more inches

wide).

Posts and timbers (5 by

5 inches and larger).

Factory i>lank graded

for door, sash, and

other cuttings IM or

more inches thick and

5 or more inches wide.

8hop lumb(>r graded for

general cut-up i)urposes.

Planks (2 inches and

under 4 inchesthick

and 8 or more inches

wide).

Scantling (2 inches '

and under 5 inches

thick and less than

8 inches wide).

Heavy joists (4 inches

thick an<l 8 or more

inches wide).

oroaes

[A.

B.

C.

[D.

[No 1.

No 2.

No 3.

No. 4.

No 5.

No. 1

No. 2.

No. 3.

No. 1.

No. 2.

No. 3.

No. 1.

No. 2.

No. 3.

.\ssociation grading

rales should be referred to for standard grades and sizes.
WOOD HANDBOOK 115

Yard Lumber—Size Standards

Standard lengths of yard lumber are multiples of 1 foot as specified

in the manufacturers' association grading rules. In practice, however, even foot lengths are the rule.

Standard thicknesses and widths of various yard lumber products

are given in table 19. In commercial practice the (h'essed dimensions

are considered minimum dimensions, and some association rules

provide for thicker and wider sizes than American lumber standards.

TABLE 19.—Sutnmary of American standard thicknrsses and ividths ^ for softwood

yard lumber^ including finish, boardSj dimension, siding, flooring, ceidng, partition,

shiplap, and dressed and matched liaiiher

Item

Finish: Select or Common

Thickness

Inches

11 ,

2

2^''

3

3i_>

4

Bevel sidingBungalow siding

Rustic and drop siding (shiplapped, 'jn- inch lap).

Rustic and drop siding (shiplai)p('d, J-j-inch lap)--h

Rustic and drop siding (dressed and matched)

Flooring

Minimum dressed

' •^2

I'io

l^in

l^/ir,

V'i

2is_.......

2Í)¿___

V'H

3k'

l\p> butt, 'i

^^2 butt. •

^16 butt. ''¡

11 le butt. •

, til) -

ßtii»,

, tip

r, tip^

•^4 butt, -«lo tip-..

1116 butt, -'iti tip.

11 10.

Widths

1 Mini-

\ »minal mum

drcss(>d

7 nches Itic h es

2 l-'K

3 25x

4 31/.

5 Vr'

6 5 1 '2

7 (»1 j

8 71.,

9 81^1

10 91.1

11 I0l:i

12 11M

14 13

16 15

4 •i h

.5 W-i

6 .51- 1 8 lU

il 10 91.1

II 12 lilt 1 8 71.i

1

1

10

12

91.:,

111.1

4 311S

.5

()

41s

51.1 G

4 3

f) h

8 Oil Í6

1 10 8i'if>

12 1011,6

1 4 3t-4

1 ( )

4H

.5-^ 1 6

8 Bill 6

10 81116

1 2 1^2

3 , 2:'..

4 1 3I4

1 F) 1 4I4

1 6 5.M6

See footnotes at end of table.
116 HANDBOOK 72, U. 8. DEPARTMlCNT OF AGRICULTURE

TABLE 19.—Summary of American standard thicknesses and widths ^ for softwood

yard lumber, including finish, boards, dimension, siding, flooring, ceiling, partition,

shiplap, and dressed and matched lumber—Continued

I fern

Thickness

Xominal^

Inches

Ceiling..

Partition..

SteppinfîBoards "-.

Shiplap, H-inch lap.

Shiplap, î-'j-inch lap.

Center matched, H-inch tongue.

Dimension, plank, and joists

Minimum dressed

1 '^ •}':>,

VA V/\

V/2 1^/i

2 l'/8

1 25Í3

VA VA

V/2 VA

1

VA

VA2

2 H

3

4

25/^2-

25,52-

IMo

I'M G,

Inches

Widths

Xominal

Inches

3

4

5

6

3

4

5

O

See footnotes at end of table.

Minimum

dressed

Inches

3 H

m

2H

VA

4 H

5'M6

71/4

91/4

11H

Vyi

25i

3H

51/.

lOK'

1D/Í'

131/'

15î'i'

31.Í

5 H

7U

nu

13 H

15 H

3

5

7

9

11

13

15

31.4

5'Mfi

7

9

11

\%

2H

3H

71/2

91/^

11K>

13I/Ú

151/2

17H
WOOD HANDBOOK 117

TABLE 19.—Summary of American standard thicknesses and widths ^ for softwood

yard lumber, including finish, hoards, dimension, siding, flooring, ceiling, partition,

shiplap, and dressed and 'matched lumber—Continued

Item

Thieliiirss \Vi( Iths

Nominal Minimum dressed Nominal

Inches

0,')

4

t)

8

10

12

Minimum

dressed

Tlmhftrs

Inches

2

2 '2

3

4

\ 5

Inches

' ' otï

Inches

V- olT

heavy roofing, decking, and

19'H 7 3

Factory flooring, 2^^<

8 7

sheet piling •- _

3-ys 8 1)

4i^/K ni

» The thicknesses apply to all widths and the widths to all thicknesses excei^t as modified. In tonguedand-grooved flooring and in tongued-and-grooved shiplai)ped ceiling of -^io-, Mo-, and ••ic-inch dressed

thicknesses, the tongue or lap shall be Mo inch wide, with the overall widths Mc inch wider than the face

widths shown in this table. In all other worked lumber of dressed thickness Hie inch to IMe inches the

tongue shall be H inch wide or w^ider in tongued-and-grooved lumber, and the lap ^ó inch wide or wider in

shiplapped lumber, and the overall widths shall be not less than the dressed face widths shown in this table,

plus the widths of the tongue lap.

2 For nominal thicknesses under 1 inch, the board measure count is based on the nominal surface dimensions (width by length). With these cxcei)tions, the nominal thicknesses and widths in this table are the

same as the board measure or count sizes.

3 In some regions lumber thicker than 1H inch is graded according to board rules. When proi)er provision

is made for this in the applicable grading rules, such lumber may be regarded as American standard lumber.

4 In worked lumber of nominal thickness of 2 inches and over, the tongue shall be ^-i>. inch wide in tonguedand-grooved lumber and the laj) y¿ inch w^de in shiplapped lumber, with the overall widths 's inch and

K' inch wider, respectively, than the face widths showm in this table.

6 5 and thicker.

8 5 and wider.

7 Face width when shiplapped; when tongucd and grooved the face width is \^ inch greater ; when grooved

for splines the face width is H inch greater.

8 Face width when shij^lapped or tongued and grooved; when grooved for splines the face width is y>

inch greater.

Yard Lumber—Grade Standards

Ordinary building lumber is graded by lumber manufacturers'

associations as finish in grades A, B, C, and D; as common boards in

grades No. 1, No. 2, No. 3, No. 4, and No. 5; and as common dimension

in grades No. 1, No. 2, and No. 3. The general requirements of these

grades as used by lumber manufacturers' associations are summarized

in the following paragraphs.

Finish Lumber—Grade Qualities

Finish grades ^ of lumber provide for good appearance andfini shing

qualities; grades A and B are suitable for natural finishes and grades

C and D for paint finishes. In a few species where there is a pronounced difference in color between heartwood and sapw^ood and

where high natural resistance to decay is required, a grade of clear

heartwood is available.

7 Detailed descriptions and use recommendations for the various grades are

given in '^Lumber Grade-use Guide," issued by the National Lumber Manufacturers' Association, Washington, D. C.
118 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Grade A is practically clear wood. It is manufactured for such

items as finish, flooring, ceiling, partition, and siding. A large number of manufacturers do not segregate the grade even in these items,

and some of the lumber associations do not recognize the quality as a

separate grade. ^¥lien the grade is not segregated, it is combined

with B grade and sold as B and Better. Grade A lumber is used

almost entirely for interior and exterior trim and for flooring. The

demand is small and confined largely to high-class construction, such

as office l)uildings and the higher cost residences.

Grade B allows a few small imperfections. In practice these small

imperfections mainly take the form of minor skips in manufacture and

small checks or stain due to seasoning, and, depending on the species,

small pitch areas, pin knots, or the like. Grade A pieces in the mixed

grade are practically clear, but the average board contains 1 to 2 small

imperfections. Grade B and Better is the highest quality segregated

in a number of woods. In construction it is the grade most commonly

used for high-class interior and exterior trim, paneling, and cabinetwork, especially where these are to receive a natural finish. It is the

principal grade used for flooring in homes, oflRces, and public buildings.

In industrial uses it meets the special requirements for large-sized,

practically clear stock.

Grade C allows a limited number of small imperfections that can

be easily covered with paint. Specifically, the number of these per

board averages about twice that of B and Better, and the proportion

of small knots is greater than in B and Better. Grade C lumber is

especially adapted to use where the highest class paint finish is desired.

It is therefore popular for cornice and other exterior parts of dwellings,

porch flooring, porch columns, trim for bedrooms and kitchens,

built-in kitchen fixtures, and siding for the better class of structures.

It is used to some extent for natural finishes in medium-priced

dwellings and oflSces.

Grade D allows any number of surface imperfections that do not

detract from the appearance of the finish when painted. In practice

the number of such surface features per board averages 3 to 5 times

as many as in B and Better. Certain natural and manufacturing

imperfections are not much more numerous in grade D than in grade

C, but the number and size of the knots in grade D are considerably

greater than in grade C, and usually the back is of somewhat lower

quality. Commercial grading permits an occasional coarse knot or

hole in grade D that may be cut out with restrictions as to waste.

Grade D is used in construction for the same uses as grade C. It goes

into moderate- or low-priced houses, furnishing a medium-priced

lumber for casing, cornice work, shelving, and built-in fixtures that

are to be painted. It is also used extensively for millwork and molding and is adaptable to industrial uses requiring short-length clear

lumber.

The knots occurring in grade B and Better are predominantly under

one-half inch in diameter and have smooth, hard surfaces. A small

proportion of the knots in grade C are as large as 1 inch in diameter,

and a few are not of the best quality. A few knots in grade D lumber

are more than 1 inch in diameter and in quality are slightly soft, rough,

or loose.
WOOD HANDBOOK 119

Depending on the species, the highest commercially recognizc^d

grade may be C and Better or D and Better, but no such combination

of grades, except B and Better, is recommended in American lumber

standards.

Seasoning faults, such as checks, either in flat surfaces or at the ends

of boards, are among the more frequent imperfections in the finish

grades. Imperfect seasoning often causes a lowering of grade, but

the number of such occurrences is considerably reduced at plants of

careful manufacturers.

Pitch pocket is relatively common in the finish grades of several

species but occurs less frequently than knots in all the important

species except one. The variation among grades in the number and

size of pitch pockets is not so marked as in the case of knots. The

frequency of pitch pockets as compared with other forms of pitch

varies considerably among the species.

Among the other factors in the finish grades are stain and chipped

and torn grain.

Common Boards and Dimension—Grade Qualities

Common grades of boards contain features that detract from appearance, but the boards are suitable for general-utility and construction

purposes. The difi'erences between the various board grades are due

to the character more than to the number of such features as knots

and pitch. The number of knots and like features in a board averages

in different species about 5 to 20 per 8 board-feet regardless of grade.

No. 1 and No. 2 boards are for use without waste. No. 3, No. 4, and

No. 5 boards permit a limited amount of waste.

No. 1 boards are usually required to be sound and tiglit-knotted

stock, and the size of knots is limited. Such lumber is usually considered watertight. In most species practically all boards in the

grade contain knots, although in some species pitch is the predominant

feature of the grade. The size of the knots varies with the species.

From one-half to three-fourths of the knots are usually intergrown;

the remaining knots are encased, a small proportion of which are

unsound, broken, or checked.

No. 1 boards are used for siding, cornices, shelving, and paneling

in medium- and low-priced homes, and for sheathing and roof boards

in the more expensive type of buildings. They are well adapted to

coverage for farm buildings, especially where a weathertight structure

is required. In this grade it is difficult to entirely conceal the knots

with paint. The No. 1 board is a general-utility item in industrial use.

It is used extensively for door and window frames and for backing and

concealed parts of furniture and fixtures. Figure 15 illustrates the

appearance of No. 1 boards of four species.

No. 2 boards allow large and coarse features, such as knots, that

may be considered graintight. In practice, a smah amount of throughshake, through-pitch pocket, and decay is permitted in the grade.

The proportion of large knots is greater than in No. 1, and whereas

33 to 75 percent of the knots are intergrown, 10 percent or more are

usually unsound, loose, or otherwise partially open. Some commercial grading rules allow knotholes in the grade, provided they are
120 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

>w«U)^^«a»[&iii,.au

r-T

ML

FIGURE 15.—Typical No. 1 boards of four species.
WOOD HANDBOOK 121

strictly limited as to size and number. No. 2 boards are useil primarily as coverage where the wood is not painted or otherwise iinislied.

Subfloors, sheathing, and concrete forms are typical uses for the gra(h\

Dressed and matched, it is used for rough ilooring in inexpensive farm

and factory buildings, garages, and warehouses. The popuhir tyi)e of

knotty finish is largely selected from this grade. Typical No. 2 boards

of four species are shown in figure 16.

No. 3 boards (fig. 17) allow larger and coarser knots than No. 2

boards and also occasional knotholes. A larger part of large knots

and increased amounts of shake, decay, and holes distinguish No. 3

boards from No. 2 boards. No. 3 boards are used in construction for

concrete forms, sheathing, subfloors, roof boards, barn boards, and

temporary construction. They fill a demand from builders of less

exacting type of buildings for a cheaper material than No. 2 grade.

Industrially they are extensively used for boxes and crates, and in

some species for foundry fiasks.

Grades No. 4 and 5 boards are usually provided for in grading rules,

but grade No. 5 is not produced in some species. No. 4 is low-quality

lumber admitting the coarsest features, such as decay and holes. The

only requirement as to the quality of No. 5 lumber is that it must be

usable.

No. 4 boards (fig. 18) are not graded for use as a whole. They are

used for sheathing, subfloors, and roof boards in the cheaper types of

construction, but their most important industrial outlet is for boxes

and crates.

No. 5 boards are seldom shipped far from the mill and are therefore

not commonly available at retail yards in nonforested regions. They

are used for rough and temporary coverage of buildings, and for boxes,

crates, and dunnage.

The fact that all lumber manufacturers' associations do not divide

their lumber into five grades and that there are diflerences in inherent

properties of the various species makes it impossible to consider the

common grades of corresponding name for the diflerent woods as

interchangeable in use.

In most species one-third to two-thirds of the knots in the common

grades of boards are intergrown, whereas in the finish grades intergrown knots comprise only a small proportion of the total. Intergrown knots may check if large, but they are integral parts of the

wood and will not loosen or drop out.

In some species a large number of the encased knots remain tight,

but in other species many of them loosen. The loosening becomes

more pronounced in large knots and as the lumber becomes drier. As

a rule encased knots comprise a larger percentage of the total number

of knots in the small-knotted select grades than they do in the larger

knotted grades of boards.

A spike knot is formed by cutting a branch lengthwise rather than

crosswise as is the case with a round knot. Spike knots occur infrequently in grades better than No. 2.

Wood that contains small areas of clearly evident decay is not

permitted in grades better than No. 2.

Common dimension lumber is manufactured in Nos. 1, 2, and 3

dimension grades mainly, although stress grades are available in

several species.
122 f HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

"''^SäS:^

íj--,,. ,; '^., -;4*¿ifíÄííJ/i^S.J>,:Á^,^^;:•«Jla**fcíii'I-, i/i.ï..

'*ífl

M 90433 F

FIGURE 16.—Typical No. 2 boards of four species.
WOOD HANDBOOK 123

1 HH i nn HHm 1!>'

» *v

HP''' m i I^HMHP

- , •

n MMHNI PBI 1 W^^ * »

*h'

^H%

;^

• " «

-*

#

'

«■■r'«

- , «

? t.

•

_* »f V

*

%•

FiouRE 17.—Typical No. 3 boards of four species.

30:1747°--55 9
124 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 18.—Typical Xo. 4 boards of four species.
WOOD HANDBOOK 125

Grading is based principally on the requirements of framing for

buildings. The dimension grades are best adapted to use where

stiffness is the controlling factor, as in joists and studs or where the

size of the member is determined by common building practice rather

than by design to carry definite live and dead loads.^ Rafters for

houses are good examples of members whose size is generally determined by common practice rather than by special design.

No. 1 dimension is a sound grade allowing knots limited in size

depending on the size of the piece. The location of the knots in the

piece is important in grading dimension. Features, such as pitch,

torn grain, checks, and stain, that do not materially affect the strength

of the piece are not limited. Wane is limited to provide good nailing

on 1 side and 2 edges. The grade is for joists, rafters, and scaffolding

in light framing and for less exacting items in heavier framing. Likewise, it is used for planking for warehouses, platforms, and other

heavy-duty flooring, where the wearing surface rather than loadcarrying capacity is the important factor. The structural grades of

joists and plank or stress grades of dimension should be used for flooring

designed to carry heavy loads.

No. 2 dimension admits larger and coarser features than No. 1 but

each piece must be usable in its full dimensions for ordinary framing

purposes. It is used in construction for joists and rafters in mediumpriced light-frame construction and for plates, sills, studding, and other

vertical load-bearing members in high-priced light construction. It

is used as flooring to provide wearing surface where the load is not

carried by the wood floor. Industrially it is used for crating and other

uses where short lengths are required.

No. 3 dimension admits all features of No. 2 but in a more serious

degree. In general it is suitable for general-utility purposes in lowpriced and temporary light-frame construction. In small buildings,

where the members are short. No. 3 dimension may be cut and used

with considerable economy.

A grade of No. 4 dimension is made in some woods, but is lowquality lumber of limited utility.

Structural Lumber

Structural lumber is graded on the basis of strength and is intended

for use where working stresses are required. A full discussion of structural grades, sizes, and appropriate working stresses appears on

pages 137-164.

Factory and Shop Lumber

Factory and shop lumber is divided into two classes from the standpoint of use—factory plank and shop lumber—each of which has a

different set of grades. These grades are based on the percentage of

the area of each board or plank that will furnish cuttings of specified

sizes and quahties. Association grading rules give standard grades

8 Where strength rather than stiffness is the controHing factor, as in heavy

construction, the structural grades of joists and plaîiks or stress grades of dimension should be used.
126 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

for the various species, which differ somewhat in cutting requirements,

and standard sizes.

Factory plank is \% inches or more in thickness and is used hirgely

for door and sash cuttings. The Xo. 1 cuttings for factory phink as a

rule must be free of knots and other features that affect quality on

both sides. The Xo. 2 cuttings may contain any one of the folloAving

seven features: a limited amount of blue or brown stain, a small tight

knot, a small pitch pocket or streak, small seasoning checks, and

slightlv torn grain. The cuttings are of various lengths and widths,

depending on the door or sash parts for which they are used.

Shop lumber is used for general cut-up purposes. Two types of cuttings, (a) and (b), are recognized; (a) cuttings must l)e clear on both

faces, (b) cuttings equal in grade on one face to B and Better finish

lumber. The (a) cuttings for shop lumber as a rule must l)e at least

9K inches wide and 18 inches long, and the (b) cuttings at least 5 inches

wide ajid 3 feet long. Shop lumber grades hi some woods are available

in only 1-hich stock. Thick stock in these woods for cut-up purposes

is bought under factory plank rules.

STANDARD LUMBER PATTERNS

Figure 19 shows six typical patterns of hunber: Flooring, standard

match; ceiling, edge beading; drop siding, shiplapped; bevel siding;

dressed and matched, center" matched; and shiplap.

With softwood flooring, '^standard match" means that the upper lip

of the groove is thicker than the lower. The thickness of the lower lip

is the same for all standard thicknesses of flooring, and hence the difference between upper and lower lips becomes more pronounced in the

heavier thicknesses. Ceiling, which is thinner than 1 inch, is usually

machined with a V. Partition usually has the bead and V, also, î)ut

on both sides, and it is thicker than ceiling. Drop siding is usually

made from 1-inch lumber and prol)a))ly is nnide in more ])atterns than

any other product except molding. Some of these patterns are shiplapped, and others are tongued and grooved. Bevel siding is made by

resawhig 4/4- or 5/4-inch lumber on an angle. Square-edged lumber in

either boards, timbers, or dimension, of course, forms only rectangles

of difterent dimensions. Boards are frequently dressed and matched

(Dtl-M), in which event the tongue and groove are in the center, making the pieces center matched. For some uses it is considered preferable to shiplap boards.

LUMBER ITEMS USUALLY CARRIED IN RETAIL YARDS

The small retail yards throughout the United States carry softwoods

required for ordinary construction purposes and sometimes small

stocks of 1 or 2 hardwoods in the grades suitable for finishing or

cabinetwork. Any particular hardwood desired, however, may be

obtained by special order through the retail lumberyard. Hardwoods

are used in building chiefly for interior trim, cabinets, and flooring.

In modern practice, trim items are cut to size in standard pattern at

millwork plants and are sold in such form by the retail yards. Cabinets are usually made by the millwork plant ready for instaUation on
WOOD HANDBOOK 127

FLOORING (STANDARD MATCH)

^

CEILING (EDGE BEADING)

DROP SIDING (SHIPLAPPED)

BEVEL SIDING

DRESSED AA/Û MATCHED (CENTER M/JTCHED)

SH/PLAP

FIGURE 19.—Six typical patterns of lunil)er.

ZM 22047 F

the job by the carpenter. Hardwood flooring invariably is a phminomill product and is avaihible to the buyer only in standard patterns.

The assortment of species in general construction items carried by

retail yards depends largely upon geographical location. For instance,

in the Pacific Northwest local yards will, as a rule, stock Douglas-fir,

spruce, ponderosa pine, western hemlock, and western redcedar. An

Iowa yard may stock eastern hemlock, ponderosa pine, southern

yellow pine, and Douglas-fir. For some species only certain items of

various species may be available; for example, southern yellow pine

or Douglas-fir may^be stocked only in the form of dimension, eastern

hemlock only in sheathing and 1-inch boards, cypress and redwood in

finish boards or in siding. A New York market might stock eastern

spruce and hemlock, eastern white pine, cypress, ponderosa pine,
128 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

southern yellow pine, and Douglas-fir. In the eastern part of the

United States lumber from the Pacific coast is readily available because of low-cost water transportation via the Panama Canal.

Wliolesalers do not ordinarily stock lumber. However, some large

wholesalers located in extensive lumber-consuming districts have

yards stocked with many kinds of lumber, both of hardwood and

softwood. These wholesalers supply the varied needs of retail yards,

wood-using factories, and larger contractors, although purchases are

sometimes made directly from the lumber mills.

Lumber is sold in a numl)er of standard general-purpose items and

also in certain special-purpose items. Retail yards carry all of the

general-purpose items, but as a rule only the more important of the

special-purpose items. Some of these lumber items come in one

group of grades and some in another. There are not many items

made in the complete range of grades. Among the typical specialpurpose items are stepping, casing and base, silo staves, molding,

battens, window and door jambs, and porch columns. Descriptions

of lumber items commonly carried by all retail yards follow.

Common Boards

Common boards, so-called, or boards are a general-purpose item

available at all yards in one or more of the kinds of wood most frequently used in building. Boards are usually of nominal 1-inch

thickness dressed 2 sides to '^%i inch thick. Sometimes thinner stock

is offered, but it should not be classed as standard lumber. The

standard nominal widths are 4, 6, 8, 10, and 12 inches. Although

boards are manufactured in all grades from No. 1 to No. 5, No. 1,

No. 2, and No. 3 are the grades most generally available in retail

yards.

Boards are sold square edge, dressed and matched (tongued and

grooved) or with a shiplap joint. The largest uses for common boards

are subfloors, sheathing, barn boards, roofing boards, rough siding,

and concrete forms, and, in some species and grades, knotty finish.

Dimension

Dimension is primarily framing lumber, such as joists, rafters, and

studding. It also comprises the planking used for heavy floors.

Strength, stiffness, and uniformity of size are essential requirements.

It is stocked in all yards, frequently in only one of the general-purpose

construction woods, such as pine, fir, hemlock, or spruce. It is

usually nominal 2 inches thick dressed 1 or 2 sides to \% inches,

nominal 4, 6, 8, 10, or 12 inches wide, and 4 to 18 feet long in multiples

of 2 feet. Dimension thicker than 2 inches and longer than 18 feet

is manufactured but only in comparatively small quantities. The

grades in most common use are No. 1 and No. 2.

Finish

Finish, except for such special types as loiotty pine and pecky

cypress, is of select quality and is made to some extent in practically

all softwoods, although a local lumberyard usually stocks only 1 or
WOOD HANDBOOK 129

2 kinds. It is manufactured in all finish grades but principally B

and Better and C. It is usually nominal 1 inch, dressed 2 sides to ^%2

inch. The widths most usually stocked are 4 to 12 inches in even

inches. Finish goes principally into interior and exterior trim, although it has numerous other uses.

Siding

Siding, as the name implies, is made specifically for purposes of

exterior coverage. It is of two principal types, bevel siding and

drop siding; the latter also known as rustic siding or barn siding.

Bevel siding is ordinarily stocked only in the finish grades of white

pine, ponderosa pine, western redcedar, cypress, or redwood. Drop

siding is sometimes stocked both in finish and in sound, tight-knotted

utility grades of southern yellow pine, Douglas-fir, and hemlock, in

addition to the woods mentioned under bevel siding. Bevel siding

may be of the narrow t^-pe, V/i-, 4^-, or 5K-inch face width, or of the

wide type, 7^-, 9%-, or ll^-inch face width. The narrow type is

/i6,//á2, or YiQ inch thick, the wide type %& or % inch thick. Drop

siding is ordinarily 5-, 6-, or 8-inch nominal width and dressed to a

thickness of % inch. It ma}^ be either dressed and matched or shiplapped.

Ceiling and Partition

Ceiling and partition, which are usually in the finish grades, are

not made or stocked as commonly as in former years. Although, as

their name indicates, they are manufactured for a specific use, they

are often used for a variety of purposes where a finished appearance

is required and where a simple pattern is preferred to plain unbroken

surfaces. Ceiling and partition may be 2%-, 3}4-, 4}^-, and S^ie-inches

face width. Ceiling is %&, jU, %&, and ^Ke inch thick, and partition is

^%2 inch thick.

Flooring

Flooring is made chiefly in the harder softwood species, such as

Douglas-fir, western larch, and southern yellow pine, and in hardwoods, such as maple and oak. At least one of the softwoods and

one of the hardwoods are usually stocked in most yards. Flooringis usually nominal 1-inch dressed to '^%2 inch and 3- and 4-inch nominal width. Thicker flooring is available for heavy-duty floors both

in hardwoods and softwoods. Thinner flooring is available in hardwoods, especially for re-covering old floors. Vertical and flat grain

(also called quartersawed and plainsawed, respectively) are manufactured in both softwoods and hardwoods, and many dealers carr}^

both types in stock.

Vertical-grained flooring shrinks and swells less than flat-grained

flooring, is more uniform in texture, wears more uniformly, and the

joints do not open so much.

Softwood flooring is usually available in B and Better grade, C

Select, or D Select. The chief grades in maple are Clear No. 1 and

No. 2. The grades in quartersawed oak are Clear, Sap Clear, and

Select, and in plainsawed Clear, Select, and No. 1 Common. The

És¿^-.
130 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

quartersawecl has the same advantages that vertical-grained softwood flooring has. In addition the silver or flaked gram ol quartersawed flooring is frequentlv preferred to the figure of plamsawed

flooring. Beech, birch, and, for fancy parquetry floormg, walnut

and mahogany are also used.

Casing and Base

Casing and base is a standard item in the more important softwoods and is stocked in most yards in at least one species. The

chief grade is B and Better. It is made and graded to meet the

requirements of interior trim for dwehings. It is usually nominal

1-inch stock, dressed to % inch, of 5-, 6-, and 7-inch nominal widths.

Hardwoods for the same purposes, such as oak and birch, may be

carried in stock in the retail yard or may be obtained on special order

at the local planing mill.

Shingles

Shingles are made from western redcedar, cypress (baldcypress),

and redwood. Western redcedar furnishes the greater proportion.

The shingle grades of western redcedar are No. 1, No. 2, and No. 3;

cypress, No. 1—bests, primes, economy, and clippers; and redwood,

Ño. 1 and No. 2. The western redcedar No. 1 grade, tidewater red

cypress No. 1, and redwood No. 1 meet the requirements of No. 1

grade of commercial standards as promulgated by the Department of

Commerce. These highest grades, which are usually the most

economical grades for permanent construction, are all clear, all

heartwood, and all edge grained.

Shingles that are allheartwood give greater resistance to decay than

do shingles that contain sapwood. Edge-grained shingles are less

likely to warp than flat-grained shingles; thick-butted shingles less

than thin shingles; and narrow shingles less than wide shingles. The

standard thicknesses of shingles are described as 4/2, 5/2}^, and 5/2

meaning, respective!}'', 4 shingles to 2 inches of butt thickness, 5

shingles to 2)i inches of butt tliickness, and 5 shingles to 2 inches of

butt^ thickness. Lengths may be 16, 18, or 24 inches. Random

widths and specified widths (''dimension" shingles) are available in

western redcedar, redwood, and cypress (baldc^^press). Randomwidth shingles are usually packed })y the square, dimension by the

thousand shingles.

Lath

Lath are made in nearly all the important softwoods. The chief

grades are No. 1 and No. 2.

GRADE-MARKED LUMBER AND MOISTURE CONTENT

PROVISIONS

Grade-marked and trade-marked lumber is now available in most

softwood species and by lumber items. Each piece of such lumber

typically is stamped with its proper grade, a number identif3dng the
WOOD HANDBOOK 131

mill where it was made, and the mark of the inspection agency promulgating the grading rules, or with a certificate of inspection. The

grade designation stamped on a board indicates the quahty 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.

Lumber may be purchased under moisture content provisions. The

allowable moisture content is lower in the thinner lumber and in the

finish grades. In one specification of kiln-dried 4/4- and r)/4-inch

lumber of C and Better quality, for instance, the moisture content

must not exceed 12 percent in 90 percent of the pieces, and tlie remainder must not exceed 15-percent moistui'e content. For thicker

finish lumber and for kiln-(h'ied boards and dimension the allowable

moisture content values are from 15 to 20 percent. Specifications for

air-dried lumber are expressed similaily with the allowable moisture

content values ranging from 16 percent for 4/4-inch C and Better up

to 19 percent for 8/4-inch dimension.

POINTS TO CONSIDER WHEN ORDERING SOFTWOOD

LUMBER OR TIMBER

The following, based on a Federal specification, lists some of the

points to consider when ordering softwood lumber or timber.

1. Quantity.—Feet, board measure, number of pieces if of definite

size and length.

2. Size.—Thickness in inches—nominal and actual if surfaced on

faces. Width in inches—nominal and also actual if surfaced on edges.

Length in feet—may be nominal average length, limiting lengths, or

a single uniform length.

3. Grade.—As indicated in grading rules of lumber manufacturers'

associations.

4. Species of wood.—Douglas-fir, cypress, etc.

5. Product—Flooring, siding, timbers, boards, etc.

6. Condition of seasoning.—Air-dry, kiln-dry, commercially shipping

dry, etc. (Definite interpretation of requirements in this respect

necessitates specifying in terms of moisture content and how it is to

be determined.)

7. Surfacing.—Indicate whether rough (unplaned) or dressed (surfaced) stock is desired. SlS means surfaced on 1 side; S2vS, surfaced

on 2 sides; SlSlE, surfaced on 1 side and 1 edge; S4S, surfaced on 4

sides.

8. Association rules.—Southern Pine Association, Western Pine

Association, etc.

STANDARD LUMBER ABBREVIATIONS

The following standard lumber abbreviations are in common use in

contracts and other documents arising in the transactions of purchase

and sale of lumber.

AD—air-dried.

A. d. f.—after deducting freight.

A. 1.—all lengths.
132 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

ALS—American lumber standards.

Av. or avp:.—average.

Av. w.—average width.

Av. 1.—average length.

A. w.—all widths.

BIS—beaded one side.

B2S—beaded two sides.

BBS—box bark strips.

B&B or B & Btr.—B and better.

B&S—beams and stringers.

Bd.—board.

Bd. ft.-—board-foot (or board-feet); that is, an area of 1 square foot by 1

inch thick.

Bdl.—bundle.

Bdl. bk. s.—bundle bark strips

Bev.—bevel.

B/L—bill of lading.

Bm.—board measure.

Btr.—better.

CBlS—center bead one side.

CB2S—center bead two sides.

OF—cost and freight.

CG2E—center groove two edges.

GIF—cost, insurance, and freight.

CIFE—cost, insurance, freight, and exchange.

Clg.—ceiling.

Clr.—clear.

CM—center matched; that is, the tongued-and-grooved joints are worked

along the center of the edges of the piece.

Com.—common.

CS—calking seam.

Csg.—casing.

Ctg.—crating.

Cu. ft.—cubic foot or feet.

CVIS—center V one side.

CV2S—center V two sides.

DB. Clg.—double-beaded ceiling (E&CBIS).

DB. Part.—double-beaded partition (E&CB2S).

DET—Double end trimmea.

D&CM—dressed (1 or 2 sides) and center matched.

D&H—dressed and headed; that is, dressed 1 or 2 sides and worked to

tongued-and-grooved joints on both the edge and the ends.

D&M—dressed and matched; that is, dressed 1 or 2 sides and tongued and

grooved on the edges. The match may be center or standard.

D&SM—dressed (1 or 2 sides) and standard matched.

D2S&CM—dressed two sides and center matched.

D2S&M—dressed two sides and (center or standard) matched.

D2S&SM—dressed two sides and standard matched.

Dim.—dimension.

Dkg.—decking.

D/S or D/Sdg.—drop siding.

E—edge.

EBIS—edge bead one side.

EB2S—edge bead two sides.

E&CBlS—edge and center bead 1 side; surfaced 1 or 2 sides and with a

longitudinal edge and center bead on a surfaced face.

E&CË2S—edge and center bead 2 sides; all 4 sides surfaced and with a

longitudinal edge and center bead on the 2 faces.

EC M—ends center matched.

E&CVIS—edge and center V 1 side; surface 1 or 2 sides and with a longitudinal edge and center V-shaped groove on a surfaced face.

E&CV2S—edge and center V two sides.

EG—edge (vertical) grain.

EE—eased edges.

EM—end matched—either center or standard.

ESM—ends standard matched.
WOOD HANDBOOK 133

EVIS—edge V one side.

EV2S—edge V two sides.

Fac.—factory.

FAS—First and Seconds—a combined grade of the two upper grades of

hardwoods.

FAS—free alongside (named vessel).

F. bk.—flat back.

FBM—foot or feet board measure.

Fcty.—factory (lumber).

FG—flat (slash) grain.

Fig.—flooring.

FOB—free on board (named point).

FOHC—free of heart center or centers.

F. o. k.—free of knots.

Frm.—framing.

Frt.—freight.

Ft.—foot or feet. Also one accent (0-

Feet b. m.—feet board measure.

Feet s. m,—feet surface measure.

G M—grade marked.

G/R or G/Rfg.—grooved rooñng.

HB—hollow back.

Hdl.—handle (stock).

Hdwd.—hardwood.

H&M—hit and miss.

H or M—hit or miss.

Hrt.—heart.

Hrt. CO—heart cubical content.

Hrt. FA—heart facial area.

Hrt. G—heart girth.

Hrtwd.—heartwood.

ls&2s.—Ones and Twos—a combined grade of the hardwood grades of Firsts

and Seconds.

In.—inch or inches. Also two accent marks {'^).

J&P—joists and planks.

KD—kiln-dried.

K. d.—knocked down.

Lbr.—lumber.

LCL—less than carload.

LFT or LIN. ft.—linear foot (or feet);-that is 12 inches.

Lgr.—longer.

Lgth.—length.

Lin.—Linear.

Lng.—lining.

LR.—log run.

Lr. MCO—log run, mill culls out.

Lth.—lath.

M—thousand.

MB M—thousand (feet) board measure.

MC—moisture content.

MCO—mill culls out.

Merch.—merchantable.

M. 1.—mixed lengths.

Mldg.—molding.

MR—mill run.

M. s. m.—thousand (feet) surface measure.

M. w.—mixed widths.

No.—number.

NIE—nosed one edge.

N2E—nosed two edges.

Og.—Ogee.

Ord.—order.

P.—planed.

Par.—paragraph.

Part,—partition.

Pat.—pattern.
134 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Pc.—piece.

Pcs.—Pieces.

PE—j)lain end.

Pky.—pecky.

Pill.—plain, as plainsawed.

PO—i)urchase order.

P&T—post and timbers.

Qtd.—quartered—when referring to hardwoods.

Rfhn.—random.

Rc^.—regular.

Res.—resawed.

Rfg.—roofing.

Rfrs.—roofers.

Rgh.—rough.

Rip.—rip]:>ed.

R/L—random lengths.

Rnd.—round.

R. Sdg.—rustic siding.

R/W—random widths.

R/W&L—random widths and lengths.

S&E—surfaced 1 side and 1 edge.

SIE—surfaced one edge.

S2E—surfaced two edges.

SIS—surfaced one side.

S2S—surfaced two sides.

SI SIE—surfaced 1 side and 1 edge.

S2S1E—surfaced 2 sides and 1 edge.

S1S2E—surfaced 1 side and 2 edges.

S4S—surfaced four sides.

S4S&CS—surfaced four sides with a calking seam on each edge

S&M—surfaced and matched; that is. surfaced 1 or 2 sides and tongued and

grooved on the edges. The match may be center or standard.

S2S&SM-—surfaced two sides and standard matched.

S2S&CM—surfaced two sides and center matched.

S2S&]\I—surfaced two sides and center or standard matched.

S2S&S/L—surfaced two sides and shiplapped.

Sap.—sapwood.

SB—standard bead.

Sd.—seasoned.

Sdg.—siding.

Sel.—select.

SE Sdg.—square-edge siding.

SE&S—square edge and sound.

S. f.—surface foot; that is, an area of 1 scjuare foot.

Sftwd.—softwood.

Sh. D.—shipping dry.

Ship.—shiplap.

S. m.—surface measure.

S M—standard matched.

Smkd.—smoked (dried).

Smk. stnd.—smoke stained.

S. n. d.—sap no defect.

Snd.—sound.

Sq.—square.

Sqrs.—squarcSo

Std.^—standard.

Stnd.—stained.

Stk.—stock.

SW—sound wormy.

T&G—tongued and grooved.

TB(feS—top, bottom, and sides.

Tl)rs.—timbers.

Thi^ckness—4/4, 5/4, 6/4, S/4, etc.= l inch, 1)4 inches, 1K> inches, 2 inches, etc.

VIS—V 1 side; that is, a longitudinal V-shaped groove on 1 face of a piece

of lumber.
WOOD HANDBOOK 135

V2S—V on 2 sides; that is, a lon«;iturlinal V-shaped ííroove on 2 faces of a

piece of lumber.

VG—vertical grain.

W. a. 1.—wider, all lengths.

Wth.—width.

Wdr.—w^ider.

Wt.—weight.

LITERATURE CITED

(1) CALIFORNIA REDWOOD ASSOCIATION'.

1951. STANDARD SPECIFICATIONS FOR ORADES OF CALIFORNIA REDWOOD

LUMBER. 61 pp., illus. San Francisco.

(2) HARDWOOD DIME.NSION AIANUFACTURERS' ASSOCIATION.

1953. S'LANDARDS AND GRADING RULES FOR THE MEASUREMENT AND

INSPECTION OF GLUED AND SOLID HARDWOOD DIMENSION LX^MBER

FOR FURNITURE AND INDUSTRIAL WOOD PARTS. 15 pp. LouisviUc,

Ky.

(3) MAPLE FLOORING MANUFACTURERS' ASSOCIATION.

1953. GRADING RULES FOR NORTHERN HARD AL\PLE, BEECH, AND BIRCH

FLOORING. 11 pp. Chicago.

(4) NATIONAL HARDWOOD LUMBER ASSOCIATION.

1953. RULES FOR THE MEASUREMENT AND INSPECTION OF HARDWOOD

LUMBER, CYPRESS, VENEERS, AND THIN LUMBER. 104 pp. ChicagO.

(5) NATIONAL OAK FLOORING AIANUFACTURERS' ASSOCIATION.

1949. OFFICIAL FLOORING GRADING RULES, OAK, PECAN, BEECH, BIRCH,

HARD MAPLE. 10 pp. Memphis, Tenn.

(6) NORTHEASTERN LUMBER MANUFACTURERS' ASSOCIATION.

1950. STANDARD GRADING RULES FOR EASTERN SPRUCE AND BALSA]\I FIR.

IS pp. New York.

(7)

1948. STANDARD GRADING RULES FOR NORTHERN WHITE PINE AND NORWAY

PINE. 20 pp. New York.

(S) NORTHERN HEMLOCK AND HARDWOOD MANUFACTURERS' ASSOCIATION.

1947, OFFICIAL GRADING RULES FOR NORTHERN WHITE PINE, NORWAY

PINE, JACK PINE, EASTERN SPRUCE, BALSAM, ASPEN. 55 pp.

Oshkosh, Wis.

(9) NORTHERN HEMLOCK AND HARDWOOD MANUFACTURERS' ASSOCIATION;

APPLACHIAN HARDWOOD MANUFACTURERS INC.

1950. OFFICIAL GRADING RULES FOR EASTERN HEMLOCK LUMBER. 76 pp.

Oshkosh, Wis.

(10) SOUTHERN CYPRESS MANUFACTURERS' ASSOCIATION.

1950. STANDARD SPECIFICATIONS FOR GRADES OF TIDEWATER RED CYPRESS.

64 pp., illus. Jacksonville, Fla.

(11) SOUTHERN PINE INSPECTION BUREAU.

1948. STANDARD GRADING RULES FOR SOITTHERN PINE LUMBER. 124 pp.,

illus. New Orleans, La.

(12) U. S. DEPARTMENT OF COMMERCE.

1953. AMERICAN LUMBER STANDARDS FOR SOFTWOOD LUMBER. Simplified

Pracr. Recom. R16-5?. 26 pp. [Processed.]

(13) WEST COAST BUREAU OF LUMBER GRADES AND INSPECTION.

1947. STANDARD GRADING AND DRESSING RULES FOR DOUGLAS FIR, SITKA

SPRUCE, AVEST COAST HEMLOCK, WESTERN RED CEDAR LUMBER.

19 pp., illus. Portland, Oreg.

(14) WESTERN PINE ASSOCIATION.

1953. STANDARD GRADING RULES FOR PONDEROSA PINE, SUGAR PINE,

IDAHO WHITE PINE, LODGEPOLE PINE, LARCH, DOUGLAS FIR,

WHITE FIR, ENGELMANN SPRUCE, INCENSE CEDAR, AVESTERN RED

CEDAR LUMBER. 147 pp. Portland, Oreg.
STRESS GRADES AND WORKING STRESSES

Individual pieces of lumber, as they come from the saw, represent

a wide range in strength as well as other properties. The orderly

marketing of lumber, therefore, requires the establishment of grades

that permit the procurement of any required quality of lumber in any

desired quantity. Structural or stress grades of lumber are established

on the basis of features that relate to strength and strength uses.

They afford lumber of assured minimum strength to which working

stress values for structural design can be assigned. Factors that affect

stress grades and working stresses and their application in the grading

and use of structural lumber are discussed in this section.

FACTORS INFLUENCING STRENGTH

The most important factors that influence the strength of structural

lumber are the strength and variability of the clear wood, the moisture

content, the duration of load, and the size, number, and location of

strength-reducing features, such as knots, cross grain, and checks and

splits.

Strength of Clear Wood

Quality of Wood

The strength of the clear wood of any species varies over a considerable range (7).^ Pieces in the lower part of the range of strength for

a species are undesirable for strength uses; on the other hand, recognition of the higher strength of the better wood is desirable.

Strength is closely related to the weight or the density of the wood.

Higher working stresses can be assigned to lumber if pieces of low

strength are eliminated by excluding those that are of exceptionally

light weight and by using the rate of growth and the percentage of

summerwood to select pieces of superior strength from certain species.

Selection for rate of growth requires that the number of annual rings

per inch be within a specified range. Selection for density requires,

in addition to a specified rate of growth, a minimum percentage of

summerwood.

Decay

Decay in any form is severely restricted or prohibited in strength

grades because its extent is difficult to determine and its effect on

strength is often greater than visual observation would indicate.

Heartwood and Sapwood

Heartwood and sapwood of the same species are of equal strength,

and no heartwood requirement need be made when strength alone is

the criterion. Since heartwood of some species is more resistant to

^ Italic numbers in parentheses refer to Literature Cited, p. 164.

137
138 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

decay than their sapwood, heartwood may be required if the untreated wood is to be exposed to a decay hazard. On the other hand

sapwood takes preservative treatment more readily and should not

be limited in lumber that is to be treated.

Moisture Content of Wood

\Aaien wood is seasoned, the direct effect of the loss of moisture is

the stiffening and stren2:thening of the wood fibers. In large timbers,

however, this increase in strength may be largely offset by checking or

splitting that may occur in seasoning. Checks lessen resistance to

shear or to tension across the grain. Some net increase of strength

with drying is recognized in structural lumber not more than 4 inches

in thickness that is subjected to bending stresses (joists or beams) and

in posts or columns of any thickness. Glued laminated structural

members generahy are not subject to such checking, and larger increases of strength are recognized (p. 250).

Duration of Load

Both the elastic limit and the ultimate strength of wood are higher

under short-time loading than under long-time loading (8), Wood is

thus able to absorb overloads of considerable magnitude for short

periods or smaher overloads for longer periods. This property is important in strength uses because it directly affects working stresses.

A substantial reduction factor is applied to stress values obtained from

laboratory tests in which the load duration is a few minutes, to convert

them to working stresses suitable for long-time loading. Conversely,

stresses for shorter periods of loading in service are increased above

those for long-time loading.

Strength-Reducing Features

Structural lumber typicaUy contains knots, checks, and other

features that reduce its strength. The size and extent of these features are taken into account in ah structural grades.

Slope of Grain

In zones of cross grain, where the direction of the wood fibers is

not paraUel to the edges of the piece, longitudinal tensile and compressive stresses have components acting across the grain, the direction

in which wood is least strong. Cross-grained pieces are undesirable

also because they tend to twist with changes in their moisture content.

Stresses caused by shrinkage in seasoning are greater in structural

lumber than in smah, clear specimens and are increased in zones of

sloping or distorted grain. To provide a factor of safety,^ the reduction of strength due to cross grain in structural lumber is taken as

about twice the reduction observed in tests of small, clear specimens.

Knots

Knots interrupt the direction of grain and cause localized cross

grain with steep slopes. Intergrown or live knots resist some kinds
WOOD HANDBOOK 139

of stress, but encased knots or knotholes are ol)viously of little or no

value. On the other hnnd, distortion of grain is greater around an

intergrown knot than around an encased or dead knot. As a result,

overall strength effects are roughly equalized, and no distinction is

made in stress grading between live knots, dead knots, and knotholes.

Knots reduce tensile strengtli more than compressive or shear

strength.

The effect of knots on stiffness is small. Although the zone of

distorted grain around a knot has less stiffness than straight-grained

wood, such zones generally comprise only a minor part of the volume

of a piece of lumber, and stift'ness reflects the character of all parts.

The strength effect of a knot depends on the proportion of the cross

section of the piece of lumber occupied by the knot. Limits on knot

sizes are therefore made in accordance with the width of the face in

which the knot appears. The eflect of knots upon strength also

depends upon their location and upon the distribution of stress in

the piece. Compression members are stressed about equally throughout, and no limitation related to location of knots is imposed. In

structural members sui)jected to l)ending, stresses are greatest in the

middle part of the length and are greater at the top and bottom edges

than at midheight. These facts are recognized in differing limitations

on the sizes of knots in difl'erent locations. Since bending members

may be used with either edge uppermost, and since the effect of knots

on strength is greater in tension than in compression, knot requirements suitable for tensile stress are applied to both edges.

As knot size increases, the distortion of grain around the knot is

more than proportionally increased. For that reason, sizes of knots

in wide faces wider than 12 inches and narrow faces wider than G

inches are permitted to increase oidy in proportion to the square root

of the increase of the width of the face, whereas, below the 12- and

6-inch limits, the sizes permitted are generally proportioned to the

width of the face.

Cluster knots are prohibited because neither the sizes of the individual knots nor those of the cluster are good measures of the extent

of distortion of grain and the resultant effect on strength.

If two or more knots occur in tlie same cross section of a piece of

structural lumber there is a cumulative eflect on most of the strength

properties. Two or more knots of maximum size are not permitted

in the same cross section.

Knots in glued laminated structural members are not continuous

as in sawed structural luml)er, and different methods are used for

evaluating their efl'ect on strength (p. 251).

Shakes

Shakes in members subjected to bending reduce the resistance to

shear and are therefore limited most closely in those parts of a bending

member where shearing stresses are highest. In members subjected

only to longitudinal compression, shakes do not greatly affect strength;

they are limited because of appearance and because they permit

entrance of moisture that may make conditions favorable to decay.

Smaller shakes are permittecl in green than in seasoned lumber,

because they may be extended as the lumber dries.

303747°—55 10
140 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Checks and Splits

Wliereas shakes indicate a weakness of bond between annual rings

tliat is presumed to extend lengthwise without limit, checks and splits

are rated on the more restricted basis of the area of actual opening.

An end split is considered the same as an end check that extends

tlirough the full thickness of the piece. The effects of checks and

splits upon strength and the principles of their limitation are the same

as for shakes.

Wane

Requirements of appearance, fabrication, or bearing or nailing

surface generally impose stricter limitations on wane than does

strength. Wane is therefore limited in structural lumber on those

bases.

Pitch Pockets

Pitch pockets ordinarily have so little effect on structural lumber

that they can be disregarded in gi^ading for strength. The presence

of a large number of pitch pockets, however, may indicate a weakness

of bond between annual rings, and the piece should be carefully

inspected for shakes.

Holes

Since the strength effect of a knot depends more upon the distortions of the surrounding grain than upon the knot itself, knotholes

are considered to have the same effect as knots, Holes due to other

causes are not accompanied by distortion of grain, and the same

hmitations that apply to knotholes are sufficient.

Combination of Strength-Reducing Features

Where combinations of strength-reducing features are present,

their combined effects are taken into account in structural grading.

Lumber containing such combinations may be accepted if above

average in densit}^ and if the combinations are not too serious. Grading rules commonly prohibit any serious combination.

PRINCIPLES OF STRESS GRADING

Basic Stress

Basic stress is a generalized working strength value for the clear

wood of a species. It is reduced from the average laboratory value

obtained in strength tests in order to conform more closely to the

conditions of use of structural lumber. This reduction provides a

factor of safety, but it does not allow for the effect of any knots or

other strength-reducing features. Basic stress is thus independent

of grade and provides a measure of the inherent strength of the clear

wood of a species, from which any grade of that species can be evaluated.
WOOD HANDBOOK 141

Strength Ratio

The strength ratio of a piece of structural lumber or of a number

of similar pieces grouped in a structural grade represents the strength

remaining after allowance is made for the knots, cross grain, or other

strength-reducing features present. Thus, a strength ratio of 75

percent applies to a piece or a grade in which the maximum reduction

in strength from that of clear wood is 25 percent. If a grade permits

a range in sizes of strength-reducing features, the strength ratio is

based on the largest size permitted. Strength reductions from knots

and cross grain generally are not cumulative; thus, if the ratio from

knots is 75 percent and that from cross grain is 69 percent, the combined strength ratio is 69 percent.

Strength ratios are applied to stresses in transverse bending, tension

parallel to grain, compression parallel to grain, and horizontal shear

in beams. Modulus of elasticity and compression perpendicular to

grain are little affected by such features as knots, and strength ratios

of 100 percent are assumed for all grades. A piece or a grade may have

the same or differing strength ratios in bending, tension, compression,

or shear. Commonly, strength ratios in the various properties for a

single grade are adjusted to be approximately in balance under the

loading for which that grade is designed.

Working Stress

The basic stress for a species, when multiplied by the strength ratio

for a piece or a gi^ade, becomes the working stress for structural design

with that piece or grade of the species.

USE CLASSES OF STRUCTURAL LUMBER

The effects of knots, cross grain, and other strength-reducing

features on the strength of a timber var}^ with the loads placed on the

timber in use. Also, the effect of seasoning varies svith the size of the

timber. Consequently, efficiency in grading necessitates classifying

structural lumber according to its size and use as follows:

Beams and stringers.—Pieces of rectangular cross section, 5 by 8

inches (nominal dimensions) and up, graded with respect to their

strength in bending when loaded on the narrow face.

Joists and planks.—Pieces of rectangular cross section, 2 to 4 inches

thick and 4 or more inches wide (nominal dimensions), graded primarily with respect to their strength in bending edgewise or flatwise

but also used where tensile or compressive strength is important.

Dimension lumber (2 inches in nominal thickness) is sometimes

placed in stress grades separate from the grades of the thicker joists

and planks.

Posts and timbers.—Pieces of square or approximately square cross

section, 5 by 5 inches (nominal dimensions) and larger, graded primarily for use as posts or columns but adapted to miscellaneous uses

in which strength in bending is not especially important.

i^^^
142 HANDBOOK 72, U. S. DEPAHTATKNT OF AORICULÏUKE

('omhined n.ses.—The principles of stress gradinp; make possible the

assio;runent of strength ratios in compression or tension to the joist

and plank o^rades, in bending to the post and timber grades, or in

bending flatwise to the beam and stringer grades. The most comnion

of such combinations is in the assignment of compression or tension

values to joist and plank grades used in the fabrication of chord or

web members in wood trusses.

Round timbers.—Round timbers, such aspóles or piles fp. 429), are

not generally graded to a specific strength rating, although their

strength is afl'ected by such features as spiral grain and knots in

much the same way as is the strength of sawed lumber. Logs or

])oles are sometimes used in the framing of structures where strength

considerations govern their design.

Boards.—The increasing use of 1-inch boards in lightweight trusses

or other structural elements, or in glued laminated structural members, frequently requires that they be stress graded. Test data show

that a knot reduces the strength of a board in proportion to the pai"t

of the width occupied by the knot. The sum of sizes of knots is

limited in the same way as in joists and planks (p. 144). Effects upon

strength from cross grain are about the same as in thicker lumber.

Since any strength-reducing featui-es present appear in one or both

wide faces, the narrow faces, or edges, UCHMI not be considered in

o'i'adinii:.

GENERAL REQUIREMENTS FOR STRESS GRADES

Size Standards

The minimum dressed ^^ sizes (green) of structural lumber are

given in the grading rule })ooks of the various lumber manufacturers'

associations for industrial species. In general, these sizes are as follows, although the grading rule books should be consulted for a given

s])ecies:

Beams and stringers.—Nominal thicknesses, 5 or more inches; nominal widths, 8 or more inches; standard sizes, SlS, SlE, S2S, or S4S,

Yz inch oft* each way.

Joists and jüanks.—Nominal thicknesses, 2 inches to but not including 5 inches; nominal widths, 4 or more inches; standard thicknesses, SlS or S2S, /8 inch ofi'; standard widths, SlE or S2E, 4 inches,

/8 inch on', and 6 inches or more wide, Yz inch ofl".

Posts and timbers.—Nominal sizes, 5 by 5 inches and larger; standard sizes, SlS, SlE, S2S, or S4S, }•> inch ofl' each way.

Rough lumber should be sawed to full nominal dimensions, except

that occasional slight variation in sawing is permissible (6'). No shipment should contain more than 20 percent of pieces of minimum

dimension due to such variation in sawing. In any one shipment,

at least 80 percent of the pieces should be of full nominal dimensions,

and the remainder should be not more than one-sixteenth inch scant.

^^ Dressing- is specified as surfacing on 1 side (vSlS), 2 sides (82vS), 1 edge (SIE),

2 edges (S2E), or both sides and both edges (S4S) : }{> or % inch off means Yz or Ys

inch less than nominal.
WOOD HANDBOOK 143

General Quality of Lumber

No piece of exceptionally light weight should be permitted. All

lumber should be well manufactured.

Structural grades prohibit or severely restrict decay in any form.

Unsound knots and limited amounts of decay in its early stages are

permitted in some of the lower grades, which generally are not used

as primary structural elements. Sapwood decay, resulting from

im.proper seasoning practices, is not admitted unch^* this provision.

Slope of Grain

Slope of grain is measured and limited at whatever point in the

length of a structural timber that shows the greatest slope. It is

measured over a distance sufRciently great to define the general slope,

disregarding such short local deviations as those around knots.

Knots and Holes

Knotholes and holes from causes other than knots are measured

and limited as provided for knots. Cluster knots and knots in groups

should not be permitted.

Beams and Stringers

The size of a knot on a narrow face of a beam or stringer is taken

as its width between lines enclosing the knot and parallel to the edges

of the piece (fig. 20), except that, when a knot on a narrow face of a

side-cut piece extends into the adjacent one-fourth of the width of a

wide face, its least dimension is taken as its size. A corner knot in

a piece containing the pith should be measured either by its width

on the narrow face between lines parallel to the edges or by its smallest diameter on the wide face, whichever is greater.

The size of a knot on a wide face is measured by its smallest diameter. A knot at the edge of a wide face is limited to the same size

as a knot on a narrow face but is measured bv its smallest diameter.

ZM 22545 F

^^

FIGURE 20.—Moasurcnicnt of knots in

beams and stringers.

The sizes of knots on narrow faces and at the edges of wide faces

may increase proportionately from the size permitted in the middle

one-third of the length to twice that size at tlie ends of the piece (fig.

21), except that the size of no knot should exceed the size permitted

at the centerline of the wide face. The size of knots on wide faces may

increase proportionately from the size permitted at the edge to the

size permitted at the centerline.
144 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

ZM 22546 F

FIGURE 21—Maximum size of knots permitted in vaiious parts of beams and

strineers: A, Maximum size on narrow face or edge of wide face, middle third

of length with a gradual increase to 2A at ends of piece; B, maximum size at

centerline of wide face; L, length; W, width; T, thickness.

The sum of the sizes of all knots within the middle one-half of the

length of any face, when measured as specified for the face under consideration, should not exceed four times the size of the largest knot

allowed on that face. Two or more knots of maximum permissible

size should not be allowed in the same 6 inches of length on any face of

beams and stringers intended for stress in tension or compression.

Joists and Planks

The size of a knot on a narrow face of a joist or plank is taken as its

width between lines enclosing the knot and parallel to the edges of the

piece (fig. 22). A narrow-face knot that appears also on the wde

face of a side-cut joist (but does not contain the intersection of those

faces) is measured and graded only on the wide face.

The size of a knot on a wide face is the average of its largest and

smallest diameters; the size of a spike knot is the average of its length

and its greatest width (fig. 22).

A corner knot or a knot extending entirely across the width of a

narrow face in a side-cut joist is measured on its end or ends between

lines parallel to the edges of the piece and is graded mth respect to the

face on which it is measured (fig. 22). A corner knot in a joist containing the pith is measured either by its width on the narrow face

between lines parallel to the edges or by its smallest diameter on the

^\âde face, whichever is most restrictive.

If joists and planks are of square cross section, each of the four faces

should be graded as a narrow face.

The sizes of knots on narrow faces and at the edges of mde faces

may increase proportionately from the size permitted in the middle

one-third of the length to twice that size at the ends of the piece, except

that the size of no knot should exceed the size permitted at the centerline of the wide face (p. 152). The sizes of knots on wide faces may

increase proportionately from the size permitted at the edge to the

size permitted at the centerline.

The sum of the sizes of all knots in any 6 inches of length of the piece

should not exceed twice the size of the largest permitted knot. Two

or more knots of maximum permissible size should not be allowed in

the same 6 inches of len2:th on any face.

jMà
WOOD HANDBOOK 145

NOT MEASURED

ON NARROW FACE

B

ZM 91873 F

FIGURE 22.—Measurement of knots in side-cut joists and planks: A^ Narrow

face; B, wide face.

Posts and Timbers

The size of a knot on any face of a post or timber is taken as the

diameter of a round knot, the lesser of the two diameters of an oval

knot, and the greatest diameter perpendicular to the length of a spike

knot (fig. 23). A corner knot is measured wherever the measurement

will represent the true diameter of the branch causing the knot. In

compression members with greater width than thickness, the sizes of

knots in both narrow and wide faces are referred to the width of the

wide face for determination of the strength ratio.

The sum of the sizes of all knots in any 6 inches of length of a post

or timber should not exceed twice the size of the largest permitted

knot. Two or more knots of maximum permissible size appearing on

a face should not be allowed in the same 6 inches of length.

One-Inch Boards

Knots in 1-inch boards are measured by the average of the widths

on the 2 opposite faces of the board, each width being taken perpendicular to the length of the board. Narrow-face knots are ignored,

since they appear in one or both wide faces. A knot appearing in

both wide faces is considered to be only one knot. Sizes of knots are
146 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 23.—Measurement of knots i

posts and timbers or othei compren

sion members.

ZM 91872 F

limited to the sizes permitted in the center of the wide faces of joists

and phinks (p. 152). The sum of sizes should be limited in the same

way as in joists and ])lanks.

Shakes, Checks, and Splits

Joists and Planks or Beams and Stringers

Limitations on shakes, checks, or splits in joists and planks or

beams and stringers are based on the reduction of area effective in

resisting horizontal shear. Since shear stress in most joists or beams

is greatest near the ends, the restrictions are applied only for a distance

from each end equal to three times the height of the piece. (Height

equals width of wide face.) Since shear stress is greatest near the

neutral axis, the restrictions also are applied only in the middle

one-half of the height of the piece, and only the shakes, checks, and

splits in this section are measured.

Shakes are measured at the ends of the piece, and the size permitted

is determined by the width of the narrow face of the piece. The

size of a shake is the distance between lines enclosing the shake and

parallel to the wide faces of the piece (fig. 24).
WOOD HANDBOOK 147

FirîURE 2].—Mí^asurciiuMil, of sliíikcs

ill beams and stringers or joists and

])lanks.

Checks and splits are limited to tlie same nominal dimensions as

shakes (table 24) but are measured dift'erently. Tlu^ size of a chiM-k

is its average depth of penetration into tlu^ piece m(^asui'(Ml íVoiíi

and perpendicular to the sm-face of the wide face. The size of an

end split is one-third of its average length.

The grading of any combniation of shakes, checks, and sphts in

the middle one-half of the height is l)ased on the grad(4*'s judgment

of the prol)able effects of seasonuig or loading in service^ on tlie combination. WTiere a combination of two checks in oj)posit(^ faces, a

check and a split, a clieck and a shake, or a s])lit and a shake may la t(ubecome a single hoi'izontal shear plane, the sum of the sizes in the

combination should l)e restricted to the allowable size of shake.

^Vliere such a coml)ination is not additive in this wa}^^ onl}^ the largest

single characteristic is considered.

\'Vliere 2-inch dimcuision is to be used in light building construction,

in which the shear stn^ss is not critical, a moi'c lilx^'al pi'ovision

on end splits can be made. It is suggest(MI that the length of an end

split in such limiber be limited to 1)2 timers the width of the wide

face in a grade with a shear strength ratio of 50 pei'cent, oi* tliixH'-

quarters of the width of the wide face in a gi'ade with a shear strength

ratio of 75 percent.

Posts and Timbers

Shakes, checks, and splits have litth^ eifect on the strength of a

column. They are limit(Ml in posts and t im])ei-s for the sakc^ of ap[)c^arance and, in exterior exposures, to ]'e(bic(^ the opportunity for moisture

to enter and decay to start. It is suggestcMl that shakes (and si(h'

checks) be limited to one-tliird the width of unsi^asoned lunibiM* or

one-half the width of dry pieces of all post an'.l timbei* graces and be

measured in a direction perpendicular to tlie plane of the face in

which they appear (fig. 25). The width may be considei-ed to b(^,

cither of the two dimensions of a rectangidar cross section. The l(Migth

of an end split should not exceed Ijo times the allowable size of a shake

or side check, but this length may l)e permitted in addition to the

allowable sum of shakes and side checks.

Requirements for Continuous Spans

If beams and stringers or joists and planks are to ])e used as continuous beams, the restrictions for knots in the middle oiu^-third

of their length should be applied to the middle two-thirds of the length
148 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

ZM 22548 F

FIGURE 25.—Measurement of shakes in posts and timbers.

of pieces continuous over 2 spans and the full length of pieces continuous over 3 or more spans. Restrictions for checks applied only

in zones at the ends of the piece in simple spans should be applied to

zones of the same length and height anywhere in the length of continuous spans.

OPTIONAL REQUIREMENTS FOR STRESS GRADES

Certain optional requirements may be applied to stress grades if

the buyer and the seller agree. Some do not directly affect strength.

Heartwood

If heartwood is desired for decay resistance in untreated lumber,

a requirement may be made in terms of a minimum amount or percentage of heartwood on the girth, or on each face, side, or edge,

measured at the point where the greatest amount of sapwood occurs.

Lumber intended for preservative treatment should permit unlimited

amounts of sapwood.

Wane

The amounts of wane ordinarily permitted from considerations of

appearance and bearing or nailing surface are not large enough to

have a serious effect on the strength of structural lumber. It is

suggested that wane in the higher structural grades be limited to

one-fourth the nominal width of the face on which it appears, or that

an optional requirement of ^^free from wane" be specified if especially

high-grade timbers are desired for special purposes.

Density—Douglas-Fir and Southern Yellow Pine

Dense Douglas-fir or dense southern yellow pine averages on one

end or the other of each piece not less than six annual rings per inch

and one-third or more of summerwood (the darker, harder part of

the annual ring) measured on a representative radial line (5, 6) but

excluding the rapidly grown wood near the pith in boxed-heart pieces.

The contrast in color between springwood and summerwood must

be distinct. Douglas-fir pieces that average not less than 5 annual
WOOD HANDBOOK 149

rings per inch and southern yellow pine pieces that average less than 6

annual rings per inch meet the requirements of dense Douglas-fir

and southern yellow piue if they average one-half or more of summerwood. In case of disagreement, 2 radial lines are chosen, and the

decision is based on the average of measurements made on these 2 lines.

Lumber qualifying as dense Douglas-fir or dense southern yellow

pine is given basic stress values in bending, tension, compression

parallel to grain, and compression perpendicular to grain that are

about one-sixth higher than those for wood of these species without

such qualifications.

Close Grain—Douglas-Fir, Southern Yellow Pine,

and Redwood

Close-grained Douglas-fir or close-grained southern yellow pine

averages on one end or the other of each piece not less than 6 nor more

then 30 annual rings per inch, measured on a representative radial

line (5, 6), but excluding the rapidly grown wood near the pith in

boxed-heart pieces. Pieces averaging at least 5 or more than 30

rings per inch are accepted if they consist of one-third or more of

summerwood. In case of disagreement, 2 radial lines are chosen,

and the decision is based on the average of these 2 lines.

Close-grained redwood averages in each piece not less than 8 nor

more than 40 annual rings per inch (^).

Lumber qualifying as close-grained Douglas-fir, southern yellow

pine, and redwood is given basic stress values in bending, tension,

compression parallel to grain, and compression perpendicular to grain

that are about one-fifteenth higher than those for wood of these

species without such qualifications.

Medium Grain

Medium-grained southern yellow pine or Douglas-fir has not

less than four annual rings per inch, measured on a representative

radial line as with close grain. Since wood of faster growth than

four rings per inch in these species often has reduced strength as

compared to slower grown wood, most stress gTades, except those

based on close grain or density, carry the requirement for medium

grain.

VALUES OF STRENGTH RATIOS

Tables 20 through 24 can be used to estimate the strength ratio

of a known piece or grade or to determine specification limits for a

grade with a desired strength ratio. Limiting sizes of the various

strength-reducing features shown in these tables are related to the

methods of measurement described in the preceding sections.

Slope of Grain

Table 20 gives strength ratios for stress in extreme fiber in bending

and compression parallel to grain for various slopes of grain
150 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTT-^RE

TABLF. 20.—BcdïnR and stringers or joists arid planks, and posts and tmitjers:

strength ratios eorresponding to various slopes :J grain

Maxiiinini strength ratio

Slope of ^rain

1 in (;.

1 ill 8.

1 in 10.

1 in 12

i la M

TJranis and

strin'-!<'rs or

joisls and

planks I

Posts and

finihcrs -

Slope of irrain

Maximum strcnsith ratio

Beams and

strin^MTS or

joists and

planks '

'.r. 1 in 15 --

fit; 1 in 10 - --

71 1 in 18

s? 1 in 20

.S7

Posts and

timbers •

' Sfren.iitli ratios for siress in extreme fiber in f)endino" or in tensii)n paralhd 1o i/i-ain.

- Strenulti ratios for stress in comiJrossion parallel to urain.

Knots

Strength ratios for various combinations of size of knot and widtli

of face are given in tables 21, 22, and 23.

The use of these tables is illustrated by the following example.

The sizes of knots permitted in an S- by lO-inch (nominal) beam in

a grade liaving a strength ratio of 70 percent for stress in extreme

fiber in l)ending aiv desired. The smallest ratio in the column for

8-inch face in table 21 that equals or exceeds 70 percent is opposite

2}s inches in the size-of-knot colimm. A similar ratio in the column

for 16-inch face in table 22 is opposite 4}i niches. Hence, the permissible sizes are 2}s inches on the 8 inch face and 4% inches on the

lt)-inch face.

Shakes, Checks, Splits

Strength ratios for various combinations of width of face with size

of shakes, checks or splits are given in table 24.

RECOMMENDED BASIC STRESS VALUES ^^

Table 25 gives basic stress values for structural design with clear

lumber under long-time service at full design load. They are based

on the strength of green lumber and are applicable, with certain

adjustments, to lumber of any degree of seasoning. Adjustments for

seasonino-, short-time loading, and other factors are discussed on

pages 158-163.

'1 Acknowledgment is made to the Ottawa and Vancouver Laboratories, Forest

Products Division, Forest Service, Canada, who have made available their data

on strength values in s})ecies common to Canada and the United States and have

materially contrilnited to the discussions leading to the present system of basic

stresses.
WOOD HANDBOOK 151

TABLE 2\.—-Beams and stringers or joists and planks—knots on narrow faee irithin

niiddle third of length of piece: strength ratios i eorresponding to various eonthinaiions of size of knot and width of face

Size of knot

(inches)

Strcniitli latio \vlu>n nominal face width

2 in. ! 3 hi.

1_--

27^^

3...

31/8.

31/4-

3H31/2-

3H3:5/4.

3>'8.

4...

41/8.

414.

41-2.

474.

Pet.

71

(15

58

52

M\

2C.

Pet.

93

89

85

81

64

i-; s .--;

U2 i 51

l^K i 47

1^54 -- -- i 35

VÁ '----- 3(1

2 25

2U

21.4 --

2H i 21/'' ,

i^K ;

2^4 i--

Pe Pct.

I

h) in. 12 il). I 14 in. | 1(1 in

Pel. I J^ef.

73

88 I

8(1

84

83

81

80

78

57

54

52

H4

83

81

98

9(i

95

94 I

92 I

91

94

93

91

SI

83

81

71

7(1

f>3

(')2

(il

1 Strength ratios for stress in extreme hher in bending.

Strength ratios of 45 percent or higher are based on the relation oí the size of knot to the nonnnal widtli

of face; lower ratios arc based on the relation of the size of knot to the actnal width of face. In taf>ulating

the sizes of knots, the rule used in a[)i)ro.\iinating decimals by common fractions with 's-inch intervals has

the eíTect of subtracting 1.24 inch from the size of each knot. For exami)le, the strength ratios listed for a

312-inch knot are those which actually would obtain for a size of 3' I/24 inches. In view ol the allowance thus

introduced and the fact that nominal instead of actual widths of face are used, the strength ratios given

should be taken as maximum values.

Sizes of knots permitted for a given strength ratio in narrow faces wider than G inches in beams and

stringers are increased only in proportion to the square root of the increase of width of the face. Below

thest limits, the sizes permitted are proi)ortioned to the widtii of the face.
152 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

TABLE 22.—Beains and stringers or joists and planks—knots along centerline of

wide face at any point in length of piece; posts and timbers—knots at any point

on any face; and 1-inch boards—knots anywhere in wide face: strength ratios ^

corresponding to various combinations of size of knot and width of face

Size of knot -

(inches)

1.-.

IKIHIH2_--

2H23^-

2H.

3...

mm4.._

4K4H4^-

5.._

ÔH5H5MÖ._.

OK63^-

n^-

7H-.

73^-.

8.. .

8'^-.

Strength ratio when nominal face width is—

3 in. 4 in. 5 in. 6 in.

Pet.

93

85

76

68

60

51

35

25

Pd.

95

88

82

7t>

70

63

57

51

4,5

32

25

Pd.

96

91

86

81

76

71

66

61

56

51

46

36

31

25

Pd.

96

92

in. 10 in. 12 in. 14 in. 16in. 18 in. 20 in. 22 in. 24 in

Pd.

97

94

91

88

85

82

79

75

72

69

66

63

60

57

54

50

47

41

37

34

31

27

Pd.

98

95

93

90

88

85

83

80

78

75

73

70

68

65

63

60

58

55

53

50

48

45

40

37

35

32

29

27

Pd.

98

96

94

92

90

88

86

84

82

79

77

75

73

71

69

67

65

63

61

59

57

54

52

50

48

46

42

39

37

35

33

31

29

26

Pd.

98

96

94

93

91

89

87

85

83

81

79

77

75

73

71

69

67

66

64

62

60

58

56

54

52

50

48

46

42

40

38

36

34

32

Pd.

98

97

95

93

91

Pd.

99

97

95

93

92

90

88

87

85

83

82

80

78

76

75

73

71

70

68

66

65

63

61

59

58

56

54

53

51

49

48

46

42

40

Pd.

99

97

95

94

92

91

89

87

86

84

82

81

79

78

76

74

73

71

70

68

66

65

63

61

60

58

57

55

53

52

50

49

47

45

Pd.

99

97

96

94

93

91

Pd.

99

97

96

94

93

91

90

88

87

85

84

83

81

80

78

77

75

74

72

71

69

68

66

65

63

62

60

59

57

56

55

53

52

50

1 Beams and stringers or joists and |)lanks—strength ratio for stress in extreme fiber in bending; posts

and timbers—strength ratio for stress in compression parallel to grain; one-inch boards—strength ratio for

all stresses.

Strength ratios of 45 percent or higher are based on the relation of the size of knot to the nominal width

of face ; lower ratios are based on the relation of the size of knot to the actual width of face. In tabulating the

sizes or knots, the rule used in approximating decimals by common fractions with H-inch Intervals has the

effect ofsubtracting 3.^4 inch from the size of each knot. For example, the strength ratios listed for a 33^-inch

knot are those which actually would obtain for a size of 3n^4 inches. In view of the allowance thus introduced and the fact that nominal instead of actual widths of face are used, the strength ratios given should

be taken as maximum values.

Sizes of knots permitted for a given strength ratio in wide faces wider than 12 inches in beams and stringers

and joists and planks, or faces wider than 12 inches in posts and timbers, are increased only in proportion

to the square root of the increase of width of the face. Below these limits, the sizes permitted are proportioned to the width of the face.

2 Ratios corresponding to other sizes of knot can be found by interpolation.
WOOD HANDBOOK 153

TABLE 23.—Joists and planks—knots at edge of ivide face within middle \i of length

of piece: strength ratios ^ corresponding to various conibinations of size of knot

and width of face

Size of knot

Strength ratio when nominal face width is--

(inches)

2 in. 3 in. 4 in. 5 in. 6 in. 8 in. 10 in. 12 in. 14 in. 16 in. 18 in. 20 in. 22 in. 24 in.

Pet. Pet. Pet. Pet. Pet. Pet. Pet. PU. Pet. Pet. Pet. Pet. Pet. Pet.

H 80 8b 90 92 93 95 96 97 97 97 97 97 97 98

Vs 70 79 84 87 89 92 93 94 95 95 95 96 96 96

1/2 60 72 78 82 85 89 91 92 93 93 94 94 94 95

Vs 50

32

65

58

73

68

78

74

81

78

86

83

89

86

90

88

91

89

92

90

92

91

93

91

93

91

93

H 92

Vs 52 63 69 74 80 84 87 88 88 89 89 90 90

1 46 58 65 71 77 82 85 86 87 87 88 89 89

1^8 34 53 61 07 75 79 83 84 85 86 86 87 88

1^ 29 49 57 64 72 77 81 82 83 84 85 86 86

IH 40 54 60 69 75 79 80 82 83 83 84 86

IK2 36 50 57 67 73 77 79 80 81 82 83 84

m 32 47 54 64 71 75 77 78 80 81 81 82

\H 28 40 51 62 69 74 75 77 78 79 80 81

V/g 36

33

30

.48

45

40

59

57

55

67

65

63

72

70

68

74

72

70

75

74

72

75

74

78

76

76

79

77

76

80

2 78

2K8 77

2H 27 37 52 61 67 ()9 71 72 73 75 76

2H 34 50 59 65 67 69 71 72 73 74

2K2 32 48 57 63 66 68 69 71 72 73

2% 29 46 55 62 64 66 68 69 71 72

2H 27 41 53 60 63 66 66 fi8 69 71

2^8 25 39 51 58 01 63 65 67 68 69

3 37 50 57 60 62 64 66 67 68

m 35 48 55 58 60 62 64 t)6 67

3M 33 46 54 57 59 61 63 64 66

3H 31 42 62 55 58 f)0 ()2 63 65

m..- 29 40 51 54 56 58 60 (\2 63

3^8 27 39 49 52 55 57 59 61 62

3^ 26 37 48 51 54 56 58 60 61

•¿H. --- 36 46 50 52 55 57 58 60

4

11 34 45 48 51 53 65 57 59

4H 33 42 47 50 52 54 56 58

m 31 40 46 48 51 53 55 57

43/8 29 39 43 47 50 52 64 55

4M 28 37 41 46 48 51 53 54

iVs 27 36 40 45 47 50 61 53

iH--- 25 35 39 42 46 48 50 52

m5

1

34

32

37

36

41

40

45

42

47

46

49

48

51

- -

50

i strength ratios for stress in extreme fiber in bending.

Strength ratios of 45 percent or higher are based on the relation of the size of knot to the nominal width of

face; lower ratios are based on the relation of the size of knot to the actual width of face. In tabulating the

sizes of knots, the rule used in approximating decimals by common fractions with i/i-inch intervals has the

effect of subtracting Hé inch from the size of each knot. For example, the strength ratios listed for a 3Minch knot are those which actually would obtain for a size of S^yn inches. In view of the allowance thus

introduced and the fact that nominal instead of actual widths of face are used, the strength ratios given

should be taken as maximum values.

Sizes of knots permitted for a given strength ratio at the edges of wide faces wider than 12 niches in joists

and planks are increased only in proportion to the square root of the increase of width of the face. Below

these limits sizes are proportioned to the square of the remaining width of the face after the width of the knot

is subtracted.
TABI.H 24.— Bítuns rnid sln'ngcrs or joisls dad phi/iks—sfnikcs or cJiccks in middle ^2 of Ju i(jh(: slroKjth rotios ^ corrrspondinci to r(iri(n/s ^

coinliiiuilions of size of shake or check and iridfh of ( nd of piece ^

(îrcrll lllHllnT Scisoîici luinb'T

Size of -;h;ik(' (»r clicck - Stronpdi r;i(i(^ w h( Ml iionîiiial end wi^ltli ( I" nii'(,'(' is^ Sir n-ili r; lio \\h( 11 nonii nl on<l width 0 f pil'CC i

(inctirs)

j ill. ; ! ill. 1 in. r

Pc/. i

in. fl ill.

7V/.

S in. 10 in.

I'd.

12 in.

¡\¡.

14 in.

/v.

1(1 ill.

¡\t.

3 in.

¡\1.

1 in.

Pd.

5 in.

I\l.

Oin.

I'd.

s in.

I'd.

10 in.

Pd.

12 in.

Pd. Pd.

10 ii¡.

Pd.

'4 !»() m !l,'i !)(1 9(1 !^)7 OS OS OS 99 100 100 100 100 100 100 100 100 RIO 100

^S - - - - s;i S!) !*2 !»3 !»4 !)(1 07 07 OS 9S 94 100 100 100 100 100 100 100 100 100

^2 - . . 77 Sf) S S i)l !»2 V)4 05 0(1 '.»7 97 S 7 95 100 100 100 100 100 100 1(10 loi)

;' s - - — - 71 SI Sñ ss !)(! U3 04 05 00 90 so 91 90 !»9 100 100 100 100 100 100

^ i- ^ .--._._ Ü". 7(1 SL> S(l S S 1)1 03 04 i)5 90 7;^ SO 93 !»7 99 Kill 100 100 100 100

' s _ - F)S 72 7'J N3 Sf. !)() 02 03 94 95 (^.0 Si S!> 94 !*7 100 100 100 100 100

f)'' ( )S 7() SI S4 SS 00 02 93 94 5! 1 — S 5 91 94

92

(.lt» 100 100 loo loi)

WH 4(i (14 7;^ 7 s S 2 S(i SO 01 92 93 72 s 2 SS 97 100 100 100 100

I'-i - 2(; (iO 7(1 7(1 so s 5 SS 00 !>1 92 45 (17 7S 85 90 95 9!; 1(10 100 100

1 \s - - - fiii (17 73 7 s S3 s 7 SO !)() 92 20 02 75 82 87 94 97 100 100 100

1'2 - - - -- f)] (u-i 71 7(1 s 2 s 5 SS i'O 91 5S 71 SO S 5 92 9(1 99 100 100

1 f) 47 1)0 (18 74 so S4 87 SO 90 1 - 53 OS 77 S3 !'(l 95 9S 100 100

1^4 - - :\r) ri7 (1(^ 71 7!* S3 S() S8 S9 48 (Í4 74 SO S s !»3 90 99 100

1 ' 8 - •Ai) . ".4 (i;-; (19 77 S 2 85 87 SS 34 01 71 7S s 7 92 95 9S 100

O') 51 (11 (17 75 SO 84 8(1 SS 1 1 •)0 r^- os -, s"" 90

S9

SS

so

94

93

92

91

,,- 99

0),, 1 4S

;-¡()

(13

(11

74

71

70

7s

S3

S 2

SI

85

84

83

S7 i

I

so

S 5

54

50

47

0(1

03

00

73

71

0!)

S'A

SI

80

!)0

95

94

98

'>1,-, 1 ! 97

OH i 90

•)1., ;^2 r^i

4S

4<i 55

(i!>

()S

(1(1

74

73

79

78

82

SI

81

S 5

S4 1

83

30

32

28

57

54

52

00

(VI

02

78

70

74

85

S3

82

89

88

87

93

92

91

95

2''s

::'"" ':"

!M

'2\ 93

•)7 ^, 1 53

51

(15

03

00

70

(IS

7(3

75

73

80

79

77

S 2

SI

SO

25 49 59

57

73

71

07

81

79

7(1

80

85

82

90

S9

87

93

8 L- ...: L. 92

••-¡'.1 i 90

•¿^2 57 (15 71 75 7s 1 48 04 74 80 85 88

¿H 54 03 (^.9 73 77 00 71 78 83 1 K,

4 - . - - 50 (10 (17 72 75 57 08 75 81 ! Kr

4V.Í - . 5S 05 70 74 53 (V5 73 79 s;

4'2 - - 55 (13 ()S ''• 50 02 71 77 81

434 - - 5;í 01 00 71 59 08 75 7Í
5 50 59

57

54

52

50

65

63

61

59

57

56

54

52

50

69

67

66

64

63

61

60

58

56

55

53

52

50

57

54

51

66

64

61

59

57

54

52

50

73

71

69

67

65

63

01

59

57

55

53

51

78

5H 76

5}4 74

b% 72

6--- 71

6^ 69

ÖH-- - 67

ö54 65

7 64

714 62

7H

7^ -

60

68

8 56

%-% 55

%H 53

SH 51

9 49

• strength ratio for stress in horizontal shear.

Strength ratios of 45 percent or higher are based on the relation of the size of shake or check to the nominal u idth of face, lower ratios on the relation of the size of shake or check

to the actual width offace. In tabulating the sizes ofshakes or checks, the rule used in ai)prc-\imating decimals by common fractions with i^é-inch intervals has the effect of subtracting

Ir^A inch from the size of each shake or check. For example, the strength ratios listed for a 3} 2-inch shake or check are those that actually would obtain for a size of 31^4 inches. In

view of the allowance thus introduced and the fact that nominal instead of actual widths of face are used, the strength ratios in this table should as taken as maximum values.

- Ratios for sizes of shake or check ottier than those listed between 3 and 9 inches can be found by interpolation.

O

O

a

0

w

o

o

en
156 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Derivation of basic stresses involves consideration of a number of

factors representing the various circumstances that aflFect the adequacy

of structural lumber. Some of these factors are well understood or

can be accurately evaluated from available data; others are definable

only in the light of engineering judgment and experience. It is

therefore not possible to arrive at basic stresses by mathematical

calculation alone. Experience and judgment, backed by pertinent

test data, must be employed to formulate basic stresses that are applicable to certain specific conditions. With these specific conditions

defined, means may be suggested by which the stress values can be

adjusted by the engineer to meet other circumstances of design that

may be encountered.

TABLE 25.—Basic stresses for clear lumber under long-time service at full design

load,^ for use in determining working stresses according to grade of lumber and

other applicable factors

SOFTWOOD LrMBER

Species 2

(1)

Extreme

fiber in

bending

or tension

parallel

to grain

(2)

Maximum

horizontal

shear

(3)

Compression perpendicular

to grain 3

(4)

Compression

parallel

to grain

L/d = ll

or le^s

(5)

Modulus of

elasticity

in bending

(6)

Baldcypress (cypress)

Cedar:

AlaskaAtlantic white- (southern whitecet.ar)

and northern whitePort-Orford

Western redcedar

Douglas-fir:

Coast type

Coast type, close-grained

Rocky Mountain type ..

All types, dense..

Fir:

Balsam

California red, grand, noble, and white.

Hemlock:

Eastern

Western (west coast hemlock)

Larch, western

Pine:

Eastern white (northern white), ponderosa, sugar, and western white

(Idaho white)

Jack

Lodgepole

Red (Norway pine) .

Southern yellow

Dense

Redwood

Close-grained

Spruce:

Englemann

Red, white, and Sitka

Tamarack

P. s. i.

1,900

1,600

1,100

1,600

1,300

2,200

2,350

1,600

2,550

1,300

1,600

1, 600

1,900

2,200

1,300

1,600

1,300

1,600

2,200

2,550

1. 750

1,900

1,100

1,600

1,750

P. s. i.

150

130

100

130

120

130

130

120

130

100

100

100

110

130

120

120

90

120

160

160

100

100

100

120

140

220

130

185

145

235

250

205

275

110

220

220

220

235

185

160

160

160

235

275

185

195

130

185

220

. s. I.

1,450

1,050

750

1,200

950

1,450

1,550

1,050

1,700

950

950

950

1,200

1,450

1,000

1,050

950

1,050

1,450

1,700

1,350

1,450

800

1,050

1,350

1,000P.S. I.

1,200

1,200

800

1,500

1,000

1,600

1,600

1,200

1,600

1,000

1,100

1,100

1,400

1,500

1,000

1,100

1,000

1,200

1,600

1,600

1,200

1,200

800

1,200

1,300
WOOD HANDBOOK 157

TABLE 25.—Basic stresses for clear lumber under long-time service at full design

load,^ for use in determining working stresses according to grade of lumber and

other applicable factors—Continued

HARDWOOD LUMBER

Species 2

(1)

Ash:

Black

Commercial white

Aspen, bigtooth and quaking

Beech, American

Birch, sweet and yellow

Cottonwood, eastern

Elm:

American and slippery (soft elm).

Rock

Hickory, true and pecan

Maple, black and sugar (hard maple) _

Oak, commercial red and white

Sweetgum (gum, red gum, sap gum) .

Tupelo, black (black gum) and water.

Yellow-poplar (poplar)

Extreme

fiber in

bending

or tension

parallel

to grain

(2)

Maximum

horizontal

shear

C-J)

F.s. i.

1,450

2, 050

1,300

2. 2(.)0

2,200 i

1,100 j

1, 6(.)0

2, 200

2,800

2, 200

2, 050

1,600

1,600 i

1,450 i

130

185

100

185

185

90

150

185

205

185

185

150

150

130

Comi)ression perpendicular

to grain ^

(4)

220

365

110

3ti5

365

110

185

365

440

365

365

220

220

160

Compression

parallel

to grain

L/d=ll

or less

(5)

. S. K

850

1.450

800

1,600

1.600

800

1,050

1,600

2, 000

1.600

1.350

1,0.50

1,050

1, 050

Modulus ol

elasticity

in bending

(6)

1,000 p. ,s-. i.

1, 100

1,500

800

1.600

1.600

1,000

1.200

1,300

1.800

1,600

1.500

1, 200

1, 200

1, 200

• These stresses are based on the strength of green lumber and are applicable, with certain adjustments,

to lumber of any degree of seasoning or lumber used under any conditions of duration of load.

2 Species names approved by X^ S. Forest Service. Commercial designations are shown in parentheses.

3 Values given in previous editions of this handbook presumed some drying and were therefore at a higher

level than these for green lumber.

The following basic principles were assumed in arriving at the values

in table 25: (1) Each structural member to carry its own load; (2) consideration of lower range of strength values (7); (3) competent design

and fabrication (3)] (4) reliable stress grading; (5) supervision to

prevent gross overloading; (6) adequate maintenance; and (7) a

reasonable factor of safety.

The basic stress for a species is multiplied by the strength ratio

appropriate for a stress grade to give the working stress for structural

design with that grade of the species. Grade strength ratios are

determined from the size of knots or other strength-reducing features

permitted by the rules of the grade, evaluated in accordance with

tables 20 to 24. Strength ratios for use in evaluating working stresses

from the basic stresses in bending, tension parallel to grain, and compression parallel to grain (columns 2 and 5, table 25) are obtained

from tables 20, 21, 22, and 23. Strength ratios for use in evaluating

working stresses from the basic stresses in shear (column 3, table 25)

are obtained from table 24. vStrength in compression perpendicular

to grain and modulus of elasticity (columns 4 and 6, table 25) are but

httle affected by grade, and a strength ratio of 100 percent is assumed

for all grades; in other words, the basic stress is also the working

stress for use in design.
158 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Increases for density and close grain, as outlined on page 148, are

incoi'porated in the basic stresses of table 25 for dense and for closegrained material.

Tlie values for compression parallel to grain in table 25 apply to

posts, columns, or struts whose unsupported length does not exceed

11 times the least dimension of the cross section. For more slender

members, suitable intermediate- or long-column formulas (p. 216) are

to be used.

ADJUSTMENT OF WORKING STRESSES

The principal mo(Ufications made in working stresses for various

causes are summarized in table 26.

I'ABLIO 26.—Modification of working stresses by grade and use factors ^

Size classification

Working s

il rade ^^''^''""J '^ growth

tress modified byWork inJÍ stress

DensitySeasoning

Duration of

load

(1) (2) (3.

i

f4) (5) (<i) (7)

Extreme fiber in bending and j.Ioists and planks v. Yes N'es.- Yes 2 Yes.

tension parallel to grain. [lîeams and stringers

jJoists and planks __...-

[Beams and stringers

Yes "S'es Yes _ No . Yes.

Horizontal shear. ._. ._. _ Yes

Yes

No ... ! No - _

No .. No ..

^'es '

Yes .

Yes.

Yes.

(\)nij)ression perpendicular to

[Joists and i)lanks ...

•Beams and stringers

[Posts and timbers

L ^"es , Yes- - Yes .. Yes.

) 1

Compression parallel to grain _.

ÍJoists and i)lanks

[I'osts and timbers

^Joists and planks

Yes .

Yes...

Yes..

Yes...

Yes..

Yes...

Yes2 .

Yes._.

Yes.

Yes.

^Modulus of elasticity 1 Beams and stringers

[Posts and timbers

No. _. No .__ Yes--- No.3

' Modification for grade (column 3) is accomplished by application of the grade strength ratio. Modifications for rate of growth and density (columns 4 and 5) are shown under the appropriate species in the basic

stresses of table 25. Modifications for seasoning and duration of load (columns 6 and 7) are to be made by

the designer to fit the particular conditions for which the design is made.

Sec p. 161 for a discussion of possible adjustments of working stress for decay hazard.

2 Modification for seasoning in current commercial practice is accomplished by liberalizing gradclimitation

rather than increasing working stress.

3 If defiection under long-time load must be limited, it is common practice to provide for the long-time

increase of deformation by using one-half of the modulus of elasticity value in table 2.5 in calculating the

stiiTncss of the member. Modulus of elasticity, when considered as a measure of the basic stiffness of the

wood, is not affected by duration of load.

Seasoning Effects

The strength of clear wood increases as its moisture content decreases below the fiber saturation point, but in sawed structural

lumber this increase of strength is largely offset by seasoning degrade,

such as checks and honeycombuig. Basic stress values in table 25

are suitable for green lumber or lumber that is completely submerged

in use, provided no decay hazard exists (p. 161). Certain increases

above these values can be made for lumber that will be continuously
WOOD HANDBOOK 159

dr}^ in use, as in most covered structures. Larger increases for drying

are recognized in glued laminated lumber.

No increase for drying is made in working stresses for beams and

stringers.

The effect of seasoning on strength in bending or in tension ])arallel

to grain of joists and planks depends upon grade, the improvement

being greater for the higher than for the lower grades. For lumber

2 to 4 inches in nominal thickness (joists and planks) that will be

continuously dry in use, the strength ratio for bending stress in the

extreme fiber or for stress in tension or in compression parallel to

grain is increased by one-half of its excess over 50 percent. If, for example, the strength ratio for green lumber from tables 20, 21, 22, and

23 in a grade of joists and planks is 68 percent, the strength ratio for

dry wood is 77 percent ( QS-\ —=77 V Since many joists remain

continuously dry in use, it is common practice to take advantage of

the increase in strength from drying by increasing permissible sizes of

knots or other features rather than by increasing the working stress;

under this circumstance, the working stress may require reduction if

lumber with knots of these sizes is to be used under wet conditions.

Basic stresses for use in obtaining the working stresses for all grades

of 1-inch boards used under dr}^ conditions may be increased from the

values of table 25 by one-quarter in bending or tension parallel to

grain, one-eighth in horizontal shear, one-half in compression perpendicular to grain, three-eighths in compression parallel to grain, or

one-tenth in modulus of elasticity. Similar increases are included in

the values given in table 36 for basic stresses of glued laminated wood

under dry conditions, and the values in that table ma}^ also be used

for 1-inch boards.

Strength in compression parallel to grain is less affected by drying

degrade than is bending strength, and the increase in this strength

property on drying is significant in all grades of compression members.

A strength increase of 10 percent above the values of table 25 for

columns of all lengths may be taken for drying regardless of size or

grade.^^ If existing grades of joists and planks have a bonus foi'

drying m the permitted knot sizes, a 10-percent increase in the basic

stress values for compression parallel to grain (table 25) may also be

made.

Table 24 shows the increased sizes of shakes or checks permitted

in seasoned lumber as compared to green lumber.

Working stresses in compression perpendicular to grain may be

increased by 50 percent above the values in table 25 for lumber that

will be continuously dry in use.

An increase of 10 percent in modulus of elasticity from tlu^ values

of table 25 may be assumed for seasoned lumber.

^2 Since a column of thick cross section seasons very slowly in use, care must

be taken in applying this increase that the column is not overloaded before an

appreciable amount of seasoning can take place in the outer fibers. Seasoning

progresses inward from all exposed surfaces, and a moderate depth of seasoning

exerts a considerable influence on the strength of the column.
160 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Although drying results in an increase of strength in many structural timbers, designers of timber structures should consider that the

sizes assumed in design may be substantially reduced by the shnnkage

that usually accompanies drying. Increases of working stresses for

drying are based on strength properties related to the actual dimensions of the dry timbers.

Duration of Load

Design stresses derived from the basic stress values of table 25 are

suitable for long-time loading at full load. If the conditions of use

permit shorter periods of maximum load to be assumed, the working

stresses (except modulus of elasticity) can be increased in accordance

with the curve shown in figure 26. These increases apply to either

continuous or intermittent loading with a cumulative duration as

indicated.

In applying a stress increase for conditions of less than full duration

of load, the safe stress for the permanent part of a combined loading must not be exceeded. If the assumed loading conditions involve

an infrequent large load and a more frequent smaller load, the working

stresses and sizes of structural members should be safe for each of the

assumed loads. It is possible for sizes of members to be governed by

the permanent load or by some semipermanent load below the maximum load.

Working stress values, except modulus of elasticity, may be used

without allowance for occasional impacts up to 100 percent of the

220

^ 200

% 180

/60

140

to

^ 120

100,

\

\ U--— DURAIION OF sniNDARD

\

57REN6TH TEST

\

V

\,

\

V

DUR AT/ON LIM/T OF DATA

CURVE IS BASEL

1

^ ON WHICH '1

^\^

"^^ /

"^-^

^^

I

I

1^1 § ^ I

DURATION OF MAXIMUM LOAD

^

S

^ <A ^ U: ^ ^

Ui lii X X

c> 0>

«O

ZM 89380 F

FIGURE 26.—Relation of working stress to duration of load.
WOOD HANDBOOK 161

static load, provided that the sizes of structural members are safe for

the static loadings. Frequently repeated impacts, however, have

fatigue effects (p. 82).

In designing for wind loads in addition to dead and live loads, the

working stresses may be increased 50 percent above the level of the

basic stresses in table 25, provided the resulting structural members

are not smaller than those designed for dead and live load alone.

Wood under continuing load takes on a continuing increment of

deformation, usually very slow, but persistent over long periods of

time. The ''set'' or ''sag" of beams is an illustration. The deformation is greatest when green timbers season under load. It may

increase with time to as much as twice the initial deformation without

endangering the safety of the timber. This effect is most important

if the long-continued load or part of the load is at or near the

maximum design level. If deformation or deflection under long

periods of loading must be limited, the necessary extra stiffness can

be provided by setting the initial deformation limit at one-half the

long-time deformation limit. Values for modulus of elasticity in

table 25 will give the initial deflection of a beam, which will increase

under long-continued load. The increase may be somewhat greater

under varying temperature and moisture conditions than under

uniform conditions.

Modulus of elasticity, when used to calculate deflections or deformations, does not increase with time. Wlien used, however, in

calculating the strength of a long column, a reduction factor of 3 is

applied to the modulus of elasticity (p. 217) to give a working value

that is safe for long-time loading. Though the design of long columns

is predicted on an initial deflection, most long columns are in a state

of unstable equilibrium without deflection. A member in unstable

equilibrium is sensitive to long-time loading; that is, it may remain

in the unstable equilibrium for a period of time and then suddenly

deflect.

Since the reduction factor of 3 on modulus of elasticity has been

found satisfactory for long-time-loading conditions, the Avorking

stress for a long column based on that factor may receive the same

increases for shorter durations of load that are given to other working

stresses. In the case of an intermediate-length column (p. 216), the

increase for short-time loading is most conveniently made after the

long-time-loading stress for the column is calculated from the appropriate long-time working stresses for compression parallel to grain

and modulus of elasticity.

Decay

Since there is no satisfactory way of numerically appraising the

effect of decay on strength of wood (-4), decay is excluded from most

structural grades. No working stress can be assigned with assurance

to timber containing decay. Decay confined to knots and not present

in wood surrounding them is permitted in some structural grades.

Limited decay of pocket type is also permitted in the lowest dimension

grades of some species. Structural lumber exposed to the hazara of

decay should be inspected at frequent and regular intervals. If
162 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

decay is detected in or near highly stressed areas, the member should

be replaced. Special attention given to such features as drainage and

ventilation will help reduce or eliminate the necessity of removing

lumber because of decay. Treated wood or the heartwood of species

of high natural decay resistance should be used wherever conditions

are favorable to decay in order to prolong service life.

\Vlien untreated wood is used under conditions favorable to decay,

some loss of strength may occur before the decay is detected. A reduction of design stress may be in order so that the structure may

safely carry its design loads for the time until decay is detected and

the affected material can be removed. The amount of reduction is

a matter of choice for the structural designer. A general range from

a few percent up to 25 percent is adequate. Stiffness is affected less

than strength, and shock resistance is affected most.

Reductions of working stress for decay hazard are intended to

provide only temporary protection until repairs or replacements can

be made. It shoiüd be emphasized again that there is no safe working

stress for decayed wood.

Treating conditions specified by the American Wood-Preservers'

Association (1) should never be exceeded. The maximum temperatures and periods permitted by those specifications are seldom necessary in the treatment of partially seasoned structural lumber.

Preservative-Treated Timber

It may be necessary, when establishing allowable working stresses

for preservative-treated timber, to take into account possible reductions in strength that may result from the treating process (see p. 420).

Results of tests of treated timber show reductions in stress in extreme

fiber in bending and in compression perpendicular to grain ranging

from a few percent up to 25 percent, depending on the treating conditions. Compression parallel to grain is affected less and modulus of

elasticity very little. The effect on resistance to horizontal shear can

be estimated by inspection for shakes and checks after treatment.

These reductions in strength can be minimized by restricting

temperatures, heating periods, and pressures as much as is consistent

in obtaining the absorption and penetration required for proper

treatment.

Temperature

Stress values in table 25 are applicable to lumber used under

ordinary ranges of temperature. Special allowance should be made

for lumber subjected to abnormally high temperatures, particularly

for long periods of time (p. 89).

Other Conditions

Recommended stress values contain factors of safety that are

applicable to the usual conditions of design. The overall factor of

safety can be increased by reducing the design stress, or it can be

reduced by increasing the design stress. In structural design, the

engineer may weigh the factor of safety against the economics of the
WOOD HANDBOOK 163

specific project that is to be built. If an individual timber is in a

critical location where its failure might threaten the integrity of a

major structure or endanger human life, he may reduce its working

stress and thereby reduce the hazard of failure. Conversely, in

situations where failure of a member can result only in property

damage of limited extent and repair can easily be made, he may be

justified in economizing through the use of stresses higher than those

of table 25. The engineer's freedom to increase working stresses is

subject, of course, to restrictions in any applical)le codes or otlier

building regulations.

The values in table 25 for compression perpendicular to grain apply

to bearings 6 inches or more in length located anywhere in the length

of a structural member and to bearings of any length located at the

ends of beams or joists. For bearings shorter than G inches located

3 inches or more from the end of a member, the stresses may l)e

increased in accorchince with the followins: factors:

Length of bearing (inches) : H

1

m

2

Factor of

increase

1. 75

1. 38

1. 25

1. 19

Length of })earing (inches) Con.

3 :

4__

6 or more

Factor of

increase

L 13

1. 10

1. 00

For stress under a washer or other round bearing area, the same

factor may be taken as for a bearing whose length equals the diameter

of the waslier.

MANUFACTURERS' STANDARD GRADES

Standard stress grades are sponsored by various agencies of lumber

manufacturers. This sponsorship consists of (1) publication of detailed descriptions and grading rules for the various grades, (2) responsibility for mspection service either at the mill or at destination, and

issue of a certificate of inspection, and (3) application of a copyrighted grade mark to each graded piece. The following associations

and agencies offer some or all of these services:

California Redwood Association.

National Hardwood Lumber Association.

Northeastern Lumber Manufacturers Association.

Northern Hemlock and Hardwood Manufacturers Association.

Southern Cypress Manufacturers Association.

Southern Pine Inspection Bureau.

West Coast Bureau of Lumber Grades and Inspection.

Western Pine Association.

All published stress grades are listed with their recommended

working stresses in the current issue of '^National Design Specification for Stress-Grade Lumber and Its Fastenings," published by the

National Lumber Manufacturers Association (3).

Recommendations of working stresses made by lumber manufacturers' associations or agencies are worked out in accordance with the

principles of stress grading set forth in this section. Manufacturers'

recommendations are generally for the condition defined as ''continuously dry, such as in most covered structures" (^), and thus include

increases for drying (p. 158). Since many buildings may carry full
164 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

maximum design load for only short periods throughout a service

life of many years, an increase of 10 percent for less-than-long-time

loading is also included. This loading condition is designated as

normal loading (3) and assumes that the continuous or cumulative

duration of full maximum load will not exceed about 10 years during

the service life of a permanent structure (fig. 26). The manufacturers'

recommendations provide for removal of the 10-percent increase for

normal loading in the case of structures or structural elements on

which maximum load is applied for long periods. Specific increases

for snow, wind, earthquake, or other short-time loads, in accordance

with figure 26, are also recommended by the manufacturers (3).

LITERATURE CITED

(1) AMERICAN WOOD-PRESERVERS' ASSOCIATION.

1952. MANUAL OF RECOMMENDED PRACTICE. Standard Specif. (A looseleaf handbook, revised annually.)

(2) CALIFORNIA REDWOOD ASSOCIATION.

1952. STANDARD SPECIFICAIIONS FOR GRADES OF CALIFORNIA REDWOOD

LUMBER. 61 pp., illus. San Francisco.

(3) NATIONAL LUMBER MANUFACTURERS ASSOCIATION.

1953. NATIONAL DESIGN SPECIFICATION FOR STRESS-GRADE LUMBER AND

ITS FASTENINGS. 67 pp., illus.

(4) SCHEFFEI, T. C, WILSON, T. R. C, LUXFORD, R. F., AND HARTLEY, C.

1941. EFFECT OF CERIAIN HEART ROT FUNGI ON THE SPECIFIC GRAVITY

AND STRENGTH OF SII KA SPRUCE AND DOUGLAS-FIR. U. S. DEPT.

Agr. Tech. Bui. 779, 24 pp., illus.

(5) SOUTHERN PINE INSPECTION BUREAU.

1948. STANDARD GRADING RULES FOR SOUTHERN PINE LUMBER. 124 PP.,

illus. New Orleans, La.

(6) WEST COASI BUREAU OF LUMBER GRADES AND INSPECTION.

1947. STANDARD GRADING AND DRESSING RULES FOR DOUGLAS-FIR, SITKA

SPRUCE, WEST COAST HEMLOCK, WESTERN RED CEDAR LUMBER.

199 pp., illus. Portland, Oreg.

(7) WOOD, L. W.

1951. VARIATION OF STRENGTH PROPERTIES IN WOODS USED FOR STRUCTURAL PURPOSES. U. S. Forest Prod. Lab. Rpt. R1780, 11 pp.,

illus. [Processed.]

(8)

1951. RELATION OF STRENGTH OF WOOD TO DURATION OF LOAD. U. S.

Forest Prod. Lab. Rpt. R1916, 5 pp., illus. [Processed.1
TIMBER FASTENINGS

The strength and stabihty of any structure are in great measure

dependent upon the fastenings that hold its parts together. Among

structural materials, wood is exceptional because of the facility with

which structural parts made of it can be joined together with k wide

variety of fastenings, including nails, spikes, screws, bolts, lag screws,

drift pins, and metal connectors of various shapes. For utmost

strength and service, of course, each type of fastening requires joint

designs adapted to the varying strength properties of wood along and

across the grain and to the dimensional changes that occur with

changes in moisture content.

The allowable loads given in this section for various fastenings are

applicable under conditions of long-continued or permanent loading.

For loads of short duration, when the wood determines the load

capacity, the tabulated values and the equations for computing allowable loads can be modified in accordance with the provisions set

forth in the section on working stresses. The allowable loads given

for a particular loading condition for all fastenings are for one unit.

Loads for more than one unit, of either the same size or miscellaneous

sizes, are the sum of the loads permitted for each unit, provided that

the spacings, end distances, and edge margins are sufficient to develop

the full strength of each unit.

NAILS

Nails are the most common mechanical fastenings used in temporary and permanent construction (32, 34)-^^ There are many types,

sizes, and forms of standard nails (fig. 27) and, in addition, many

special-purpose nails. The formulas and tables presented here for

allowable loads apply for bright, smooth, common steel wire nails

driven into wood with no visual evidence of splitting. For nails

other than common wire nails, the allowable loads can be adjusted

in accordance with the provisions presented in subsequent paragraphs or by a factor that the designer considers to conform with the

character of the construction.

In general, nails give stronger joints when driven into the side

grain (perpendicular to the wood fibers) than into the end grain of

wood {13, 29). Also, nails should preferably be used so that their

lateral resistance, rather than direct withdrawal resistance, is utilized.

The withdrawal resistance of nails is greatly affected by such factors

as type of nail point, type of shank, time the nail remains in the

wood, siu-face coatings, and moisture content changes in the wood.

Withdrawal Resistance

The resistance of a nail to direct withdrawal from a piece of wood

is intimately related to the density or specific gravity of the wood,

the diameter of the nail, and the depth of penetration {31). The

surface condition of the nail at the time of driving also influences the

immediate withdrawal resistance.

Í3 Italic numbers in parentheses refer to Literature Cited, p. 201.

165
166 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

B C D F G H

ZM 57232 F

FiíiURE 27.—Nails with various surface conditions: A, Bright, smooth wire

nail; B, cement-coated; C, zinc-coated; /), chemically etched; E, annular

grooved; F, spirally grooved; G, spirally grooved and barbed; and //, barbed

nail.

For bright, common wire nails driven into the side grain of seasoned

wood that will remain dry or unseasoned wood that will remain wet,

the allowable withdrawal load is given by the formula:

p= 1,150 (?^^Z>

in which p represents the allowable load (one-sixth of the ultimate

load) per lineal inch of penetration in the member holding the nail

point; (7, the specific gravity of the wood based on oven-dry weight

and volume; and T), the diameter of the nail in inches. The average

specific gravity raised to the five-halves power is listed in table 27

for a numl)er of the common hardwood and softwood species. The

diameters of various pennv or gage sizes of nails are given in table

28. ^ *^ The relationship expressed by this equation is general, but certain

species give test values that are somewhat higher or lower than the

equation values. Usually common knowledge of the characteristics

of the nail, and of the species with particular reference to its splitting

tendencies, will aid in deciding whether the withdrawal resistance

will fall above or below the general equation values.

Although the general equation for nail withdrawal resistance indicates that the dense, heavy woods offer greater nail-holding power

than the lighter weight ones, lighter species are not disqualified for

uses requiring high holding power {2d). As a rule, the less dense

species do not split so readily as the dense ones {SS) and thus offer

an opportunity for increasing the diameter, length, and number of

the nails to compensate for tTie wood's lower holding power.

In practically all species, nails driven into green wood and pulled

before an}^ seasoning takes place offer about the same withdrawal

resistance as nails driven into seasoned wood and pulled soon after

driving. If, however, common smooth-shank nails are driven into

green wood that is allowed to season or into seasoned wood that is
WOOD HANDBOOK 1G7

subjected to cvoles of wetting and drying before the nails are pulled,

they lose a major part of their withdrawal resistance. In seasoned

wood that is not subjected to appreciable moistui'e eontcMit chang(^s,

the withdrawal resistance of nails may also diminish with lapse of

time. On the other hand, tests indicate that if, UIUKM- some conditions

of moisture variation and time, the wood filxn's are affcH'ted or tlu*

nail rusts, withdrawal resistance is very erratic and may be regained

or even increased over the immediate withdrawal resistance. ITnder

all these conditions of use, the withdrawal resistance of nails differs

TABLE 27.—Factors for calculating the alloivable strength of mechanical fastenings

in seasoned ivood

HARDWOODS

Specific gravity r; Allowable kit ral Basic strcssrs |

and powers • load constant {K) ' for bolts 2 Species ' 1 grouf)

Species 1

1 for con- 1 i T 'icr Parallel Perpen- nector

r; (73/2 (72 ; r;s/2 Xa i Is 3 1 Screws 3

ícrews ^

to dicular loads 5

---

grain to grain

Ash: 1 1

Black ' 0. 53 0.39 ' 0.28 ! 0.20 1. 2.^0 2.900 1.900 S50 300

Commercial whit .01 .48 .37 .29 1,700 4,000 2. 200 1, 450 500 4

Aspen:

Bigtooth .41 .26 .17 .11 900 2,100 1,700 800 150 1

Quakirm.. .40 .25 . 16 .10 900 2, 100 1,700 800 150 1

Basswood, American .40 .25 . 16 .10 900 2.100 1,700 1

Beech, American .67 .55 .45 .37 1,700 4.000 2. 200 1, 600 500 4

Birch:

Sweet - .71 .60 .50 .42 1,700 4, 000 2,200 1, 600 500 4

Yellow .6(3

. 45

.54

.30

.44

.20

.35

. 14

1,700

900

4, 000

2, 100

2, 200

1,700

1,600 500 4

Chestnut, American

Cottonwood:

2

Black

Eastern

. 37 . 22 . 14 .08 900 2,100 1,700 1

.43 .28 .18 .12 900 2,100 1,700 800 150 1

Elm:

American .55 .41 .30 .22 1, 2.50 2. 900 1,900 1,050 250 3

Rock .66 .54 .44 .35 1,70. 4, 000 2, 200 l,r.oo 500 4

Slippery .57 .43 .32 .25 1.2.^0 2, 900 1,900 1,0.50 250 3

Hackberry - .56 .42 .31 .23 1, 250 2,900

Hickory:

Pecan .65 .52 .42 .34 1,700 4, 000 2,200 2,000 600 4

True - .74 . 64 .55 .47 1, 70Ü 4,000 2,200 2, 000 6Üt) 4

Magnolia, southern _ ,53 .39 .28 .20 1, 250 2,900

Maple:

Black .02 .49

.41

.36

.38

.30

.26

.31

.22

.19

1,700

1, 250

1,250

4.000

2,900

2,900

2.200

1,900

1,600 500 4

Red -.

Silver

3

.51 1,900 3

Sugar .68 .56 .46 .38 1,700 4, 000 2, 200 1, (iOO .500 4

Oak:

Commercial red _ . 66 .,54 .44 .35 1,700 4. 000 2, 200 1,350 500 4

Commercial white .71 .60 .50 .42 1,700 4,000 2. 200 ' 1,350 501) 4

Sweetgum .53

.54

.39

.40

.28

.29

.20

.21

1,2,^.0

1,250

2, 900

2, 900

c: c:

' 1,050 1 ;^oo 3

Sycamore, American ..

3

Tupelo: 1 Black .55 .41 .30 .22 1,250 2, 900 ], 9(J0 1,0.'0 1 300 3

Water .52 .37 .27 .19 1,250 2, 900 1,900 1,0.')0 30!) 3

Yellow-poplar .43 .28 .18 .12 900 I 2, 100

i

1,700 ! 9.^0 ' 220

i 1

2

See footnotes at end of table.
168 HANDBOOK 7 2, IT. Ö. DEPARTMENT OF AGRICULTURE

TABLE 27.—Factors for calculating the allowable strength of mechanical fastenings

in seasoned wood—Continued

SOFTWOODS

Specific gravity 0

and powers ^

Allowable lateral

load constant (K)

Basic stresses

for bolts 2 Species

group

Species

G Ö3/2 (?2 Cf5/2 Nails 3 Screws 3

Lag

screws *

Parallel

to

grain

Perpendicular

to grain

for connector

loads *

RaldovDress 0.48

.46

.35

.32

.44

.34

.51

.45

.41

.41

.43

.44

.59

.37

.43

.42

.51

.59

.38

.42

.42

.35

.41

.42

.45

0.33

.31

.21

.18

.29

.20

.36

.30

.26

.26

.28

.29

.45

.22

.28

.27

.36

.45

.23

.27

.27

.21

.26

.27

.30

0.23

.21

.12

.10

.19

.12

.26

.20

.17

.17

.18

.19

.35

.14

.18

.18

.26

.35

.14

.18

.18

.12

.17

.18

.20

0.16

.14

.07

.06

.13

.07

.19

.14

.11

.11

.12

.13

.27

.08

.12

.11

.19

.27

.09

.11

.11

.07

.11

.11

.14

1

1,125

1,125

900

900

1.125

900

1,375

1,125

900

900

900

1,125

1,375

900

900

900

1,125

1,375

900

900

1,125

900

900

900

900

2,700

2,700

2.100

2,100

2,700

2,100

3,300

2,700

2,100

2.100

2,100

2,700

3,300

2,100

2,100

2,100

2. 700

3,300

2.100

2,100

2,700

2,100

2,100

2,100

2,100

1,700

1,700

1,500

1,500

1,700

1,500

1.900

1,700

1, 500

1,500

1,500

1,700

1,900

1,500

1,500

1.500

1,700

1,900

1,500

1,500

1,700

1,500

1,500

1,500

1,500

1,450

1,050

750

750

1,200

950

1,450

1, 050

950

950

950

1,200

1,450

1,000

950

1,000

1.050

1,450

1,000

1,000

1,350

800

1,050

1,050

1,050

300

250

180

180

250

200

320

280

150

300

300

300

320

250

220

250

220

320

250

250

250

180

250

250

250

2

Cedar:

\laska,- --

2

Atlantic white- -

Northern whitePort-Orford- -

2

Western redcedar

Douglas-fir:

Coast type 0

Rocky Mountain type.

Fir:

Balsam

C ommercial white

HemlockEastern -- -

1

3

2

1

1

1

Western - --

2

Larch, Western

Pine:

E'astern white

3

1

Lodgepole

Ponderosa 1

Red

Southern yellow «

Sugar --

2

3

1

Western white 1

Redwood (old-growth)

Spruce:

Enfflemann

2

1

Red 2

Sitka 2

White 2

1 Specific gravity based on weight and volume when oven-dry.

2 Basic stresses to be used in determining allowable bolt-bearing stresses.

3 Driven perpendicular to the grain of the wood and loaded either parallel or perpendicular to the grain.

4 Inserted perpendicular to the grain of the wood and loaded parallel to the grain.

5 Grouping to be used in determining allowable connector loads. Group 1 woods provide the weakest

and group 4 woods the strongest connector groups.

6 When graded for density, these species qualify for group 4 connector loads.

TABLE 2S.—Sizes of bright^ common wire nails

Penny Gage Length Diameter D

1)3/2 Peimy Gage Length Diameter D

D3/2

2d 15

12M

IIK2

10^

9

9

Inch

1

VA

2

2H

3

m

Inch

0.072

.098

.113

131

.148

.148

Inch

0.0193

.0307

.0380

.0474

.0570

. 0570

16d

Inch

8

6

5

4

3

2

Inch

3H

4

4M

5

5M

6

Inch

0.162

.192

.207

.225

.244

.262

Inch

0.0652

4d 20d .0841

6d 30d .0942

8d 40d .1068

lOd 50d .1205

12d 60d .1342
WOOD HANDBOOK 169

among species as well as within individual species, making it difficult

to evaluate their behavior. The withdrawal loads for nails driven

into wood that is subjected to changes in moisture content may be

as much as 75 percent below the values given by the general formula.

Factors That Affect Withdrawal Resistance

The withdrawal resistance of nails is affected by the surface condition of the nail, the types of head and point on the nail, the composition of the nail, the direction of driving, and whether the nails are

clinched or unclinched.

The surface condition of nails is frequently modified during the

manufacturing process to improve their withdrawal resistance. Such

modification is usually done by one of three methods, namely surface

coating, surface roughening, or deformation (10, 28) of the shank.

Other factors that affect the surface conditions 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 nail holding cannot be adequately

evaluated.

Surface-Coated Nails

A common surface treatment for nails is the so-called ^^cement

coating,'^ which if properly applied may double the resistance of

nails to withdrawal immediately after they are driven into the softer

woods. In the denser woods, like hard maple, birch, or oak, however,

coated nails have practically no advantage over plain nails, since

more of the coating is removed in driving. Some of the coating may

also be removed in the cleat or facing member before the nail penetrates the foundation member. 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, so that nails may sometimes be obtained that

show only a slight initial advantage over plain nails. The increase in

withdrawal resistance of cement-coated nails is not permanent but

drops off about one-half after a month or so for the softer woods.

Cement-coated nails are used extensively in construction of boxes,

which are usually built for rough handling and short-time service.

Nails that have special coatings, such as zinc, are intended primarily

for uses where corrosion and staining 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 zinc-coated nails

with an even, uniform coating may have over a plain nail in resistance

to immediate withdrawal is usually reduced under repeated cycles of

wetting and drying.

Surface-Roughened Nails

A chemically etched nail developed at the Forest Products Laboratory gives somewhat higher withdrawal resistance than other coated

nails and retains much of its superiority under var3áng moisture conditions (5, 16). Under impact loading, however, the withdrawal re-
170 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

sistance of the etched nails is Httle different from that of the plain or

cement-coated nails under various moisture conditions.

Sand-blasted nails perform in much the same manner as chemically

etched nails.

Form of Shank

Nail shanks are varied from a circular form to give an increase in

surface area without an increase in nail weight (11, 28), Special nails

with barbed, spirally grooved, annular grooved, and other kregular

shanks (fig. 27) are offered commercially. . i i .

The form and magnitude of the deformations along the shank influence the performance of the nails in the various species. The withdrawal resistance of these nails, except some types of barbed nails, is

in general somewhat greater than that of common wire nails in wood

remaining at a uniform moisture content. Under conditions involving

changes in the moisture content of the wood, however, some of the

special nail forms provide considerably greater withdrawal resistance

than the common wire nail {6, 7, 28). This is especially true of nails

driven into green wood that subsequently seasons. In general, annular grooved nails sustain larger withdrawal loads, and spirally grooved

nails sustain greater impact withdrawal work values than the other

nail forms.

Nail Points

A nail with a long, sharp point will usually have a higher withdrawal

resistance, particularly in the softer woods, than the common whe

nail, which usually has a diamond point {12). Sharp points, however,

accentuate splitting of certain species, which may reduce withdrawal

resistance (fig. 28). 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 than the common nail and, in the heavier woods, will provide

about the same withdrawal resistance. In the less dense woods, its

resistance to withdrawal is less than that of the common nail.

Nailheads

Nailhead classifications include flat, oval, countersunk, deep-countersunk, and brad. In general, 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.

Nail Composition

Nails of copper allo3^s, aluminum alloys, stainless steel, and other

alloys are used mainly where corrosion or staining is an important factor in appearance or permanence. Specially hardened nails are also
WOOD HANDBOOK 171

ZM 57967 F

FIGURE 28.—Characteristic filjcr distortion caused by nails with four different

t\'pes of points: A, Sharp; B, common; C, blunt"; and D, truncated. The

blocks of wood were split after the nails were driven.

frequently used where driving; conditions are difficult. In general,

the withdrawal resistance of copper nails is somewhat comparable to

that of common wire nails when pulled soon after driving.

Direction of 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, into the end of the

piece—withdrawal resistance in the softer woods drops to 75 or even

50 percent of the resistance obtained when the nail is driven perpendicular to the grain. The angle at which the nail is driven has less

effect on the withdrawal resistance in dense woods than in softer

woods. In most species, the ratio between the end-grain and sidegrain withdrawal loads of nails pulled after a time interval or after

moisture content changes have occurred is usually somewhat higher

than that of nails pulled immediately after driving.

The results of withdrawal tests at the Forest Products Laboratory

on slant and straight driving (14), when the piece attached is pulled

directly away from the main member, show that slant driving is

usually superior when nails are driven into dry wood 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.

30.3T47°^55 12
172 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

A^^ien nails are driven into green wood and pulled immediately,

straight driving is superior.

Cross slant driving of groups of nails is usually somewhat more

effective than parallel slant driving. The difficulties involved in

starting and driving either parallel- or cross-slanted nails, however,

and the loss in depth of penetration, the destruction and mutilation

of the wood fibers at the surface in starting the nail, and the breaking down of the wood under the hammer offset to a considerable

extent any advantages of slant nailing.

Toenailing, which is a common method of joining wood framework,

consists of slant driving a nail or group of nails through the end or

edge of an attached member and into a main member. Tests show

that the maximum strength of toenailed joints under lateral and

uplift loads is obtained by (1) using the largest nail that will not

cause excessive splitting; (2) 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; (3) driving the nail

at a slope of 30° with the attached member; and (4) burying the full

shank of the nail but avoiding excessive mutilation of the wood from

hammer blows (26),

Toenailing requires greater skill in assembly but provides joints of

greater strength and stability than does ordinary end nailing. In

tests of stud-to-sill assemblies with the number and size of nads frequently used in toenailed and end-nailed joints, a joint toenailed with

4 eightpenny common nails was superior to a joint end nailed with 2

sixteenpenny common nails. In such woods as Douglas-fir, toenailing with tenpenny common nails gave greater joint strength than the

commonly used eightpenny nails. The allowable withdrawal load

per nail in toenailed joints for all conditions of seasoning is equivalent to two-thirds of that calculated by the general formula for

withdrawal resistance of nails (17).

Prebored Lead Holes

Nails driven into lead holes with a diameter slightly smaller than

the nail have somewhat higher withdrawal resistance than nails

driven without lead holes. Lead holes also prevent or reduce splitting

of the wood.

Clinched Nails

The withdrawal resistance of smooth-shank clinched nails is considerably higher than that of unclinched nails. 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 withdra\vn, the species of wood, the size of nail, and the dkection

of clinch with respect to the grain of the wood (2).

In dry or green wood, a clinched nail provides from 45 to 170 percent more withdrawal resistance than an unclinched nail when withdrawn soon after driving. In green wood that seasons after a nail

IS driven, a clmched nail gives from 250 to 460 percent greater withdrawal resistance than an unclinched nail. However, this improved

strength of the clinched- over the unclinched-nail joint does not

justify the use of green lumber, because the joints may loosen as the

.^
WOOD HANDBOOK 173

lumber seasons. Furthermore, the 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. In such construction as boxes and crates, it is generally necessary to use both clinched and unclinched nails.

Nails clinched across the grain have approximately 20 percent

more resistance to withdrawal than nails clinched along the grain.

Nails in Plywood

The nailing characteristics of plywood are not greatly different from

those of solid wood except that plywood's greater resistance to splitting

when nails are driven near an edge is a definite advantage. The

nail-withdrawal resistance of plywood is from 15 to 30 percent 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 one-half inch thick, the high splitting resistance

tends to offset the lower withdrawal resistance as compared to solid

wood. The withdrawal resistance per inch of penetration decreases

with increase in the number of plies. The direction of the grain of

the face ply has little inñuence on the withdrawal resistance along the

end or edge of a piece of plywood.

Lateral Resistance

The allowable load for a bright, common wire nail in lateral resistance when driven into the side grain (perpendicular to the wood

fibers) of seasoned wood is expressed by the following general formula:

in which "p represents the allowable lateral load in pounds per nail; K,

a constant; and D, the diameter of the nail in inches. Values of K

for a number of the common hardwoods and softwoods are listed in

table 27. Values for converting the size of common wire nails from

penny to B^^'^ are listed in table 28.

The constants K listed in table 27 were obtained by dividing the

constants in general formulas for the proportional limit loads of

nailed joints in different species by a reduction factor of 1.6. The

ultimate lateral nail loads in softwoods will be about 6 times the

allowable loads expressed by the formula, and in hardwoods about 11

times. These loads apply only for conditions where the side member

and the member holding the nail point are of approximately the same

density and where the depth of penetration of the nail in the member

holding the point is not less than 10 times the diameter of the nail

for dense woods and 14 times the diameter for lightweight woods.

When metal is held to wood, an increase of about 25 percent can be

applied to the allowable lateral nail load.

The allowable lateral load for side-grain nailing given by the general

formula 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
174 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

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

percent of corresponding values for side-grain nailing.

It is therefore I'ecommended that the safe lateral loads for end-grain

nailing should be about 60 percent of those computed for side-grain

nailing in lightweight species and slightly higher in denser species.

If the"type of construction, method of loading, and hazard involved

are such that it appears safe to the designer to use higher loads, the

coefRcient preceding D^'~ in the equation may be raised accordingly.

It is not recommended, however, that smaller factors of safety be

used for permanent concealed joints.

Nails (Iriven into the side grain of unseasoned wood give maximum

lateral resistance loads approximately equal to those obtained in

seasoned wood, l)ut the proportional limit lateral resistance loads are

somewhat less. Since proportional limit loads are of prime importance

in establishing allowable loads, it is recommended that the allowable

lateral loads obtained by the general formula for seasoned wood be

reduced 25 percent 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 recommend an allowable lateral load

for a nailed joint under these conditions. Structural joints should be

inspected at intervals and, if it is apparent that a loss in joint strength

occurred during drying, the joint should be reinforced with additional

nails. Simply setting the original nails is not sufficient.

Nails m lateral resistance should be driven with sufficient end

distance, edge margin, and nail spacing to avoid any unusual splitting

of the wood.

Deformed-shank nails carry somewhat higher maximum lateral

loads than common wire nails, but both types perform similarly at

small distortions in the joint. In nailed joints subjected to vibration

or reversal of stress, as in boxes and crates that are handled roughly,

the deformed-shank nails with reduced sections, such as the spirally

and annular grooved nails, tend to break more easily than the smoothshank nails. The lateral loads for aluminum alloy nails are slightly

lower at small distortions in the joint than they are for uniform-shank

steel nails, but are somewhat higher at large distortions. Tests have

also indicated that an aluminum nail with a shank diameter 3 to 10

percent larger than that of a steel nail sustains lateral loads at small

distortions that are comparable to those for a steel nail.

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 3 to 12 inches. For corresponding lengths

(3 to 6 inches), they have larger diameters than the common wh^e
WOOD HANDBOOK 175

nails, and beyond the sixtypenny size they are usiiallv (h^siu-nated f)y

inches of length.

The allowable withdrawal and lateral resistance fornuihis and limitations given for common wire nails are also ai)plicable to spila^s,

except that, in calculating the withdrawal load for spikes, the depth'

of penetration should be reduced by two-thirds the length of the point.

DRIFT BOLTS

The ultimate withdrawal load of a round (h-ift. })olt or pin from the

side grain of seasoned wood is given by the formula:

p = 6,000 G-I)

in which jp is the ultimate withdrawal load per liui^al inch of penc^tration; G, the specific gravity based on the oven-chy weight and volume

of the wood; and D, the diameter of the drift boh in inclies.

This equation provides an average relationship for all species, and

the withdrawal load of some species may be above or below the

equation values. It also presumes that the bolts are driven into

prebored holes having a diameter one-eighth inch less than that of

the bolt diameter.

The allowable withdrawal load per lineal inch of penetration should

be determined by reducing the ultimate withdrawal load given by

the general formula by a factor consistent with the character of the

work. For general use, it is suggested that the ultimate withdrawal

load be divided by the factor 5.

In lateral resistance, the allowable 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 common bolt of the same diameter (p. 182).

The drift bolt should normally be of greater length than the common

bolt to compensate for the lack of washers and nut.

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 or when

countersinking is objectionable. Besides the head, the principal parts

of a screw are the shank, thread, and core (fig. 29).

Withdrawal Resistance

The resistance of wood screws to withdrawal from the side grain of

seasoned wood varies directly with the square of the specific gravity

of the wood. Tests indicate that, within certain limits, the withdrawal load varies directly with the depth of penetration and the

diameter of the screw (4). The effective length of a screw is limited

by the length at which the screw fails in tension; tliis limiting length

decreases as the density of the wood increases. The longer lengths

of standard screws should therefore be avoided in dense hardwoods.
176 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

/Q ^.-^

DIAMETER

BODY

A B

ZM 86795 F

FIGURE 29.—Common types of wood screws: A, Flathead; B, roundhead; and

C, ovalhead.

The allowable withdrawal load of common wood screws inserted

into the side grain of seasoned wood may be expressed as follows:

^=2,370 G^D

in which j) is the allowable \\athdrawal load (one-sixth of the ultimate

load) per lineal inch of penetration of the threaded part of the screw;

G, the specific gravity based on weight and volume when oven-dry;

and B, the shank diameter of the screw in inches. Specific gravity

values raised to the second power are given for a number of widely

used wood species in table 27.

This equation is applicable when screw lead holes in softwoods have

a diameter of about 70 percent of the root diameter of the threads,

and in hardwoods, about 90 percent. The root diameter for most

sizes of screws averages about two-thirds of the shank diameter. The

equation may be applied to all species, but inherent characteristics

may cause some species to give values 10 to 15 percent above or below

the equation values, and an occasional species may vary somewhat

more.

The equation values are applicable to the following sizes of screws:

Screw length (inches):

/2-

1%-

Gage limits

1-6

__ 2-11

_. 3-12

__ ^14

Screw length (inches)—Con. Gage limits

2 7-16

2/2 9-18

3 12-20

For lengths and gages outside of these limits, the actual values are

likely to be less than the equation values. The withdrawal loads of

screws inserted into the end grain of a piece are more or less erratic,

but, when splitting is avoided, they should average 75 percent of

the load sustained by screws inserted into the side grain.
WOOD HANDBOOK 177

Lubricating the surface of a screw is recommended to facilitate

insertion, especially in the dense woods, because it will have little

effect on ultimate withdrawal resistance.

Lateral Resistance

The allowable load in lateral resistance for wood screws in the side

grain of seasoned wood is given by the formula (S, 9)

p=KD'

in which p is the allowable lateral load in pounds; D, the diameter of

the screw shank in inches; and K, a constant depending on the inherent characteristics of the wood species. Values for converting

screw gage into D^ are given in the following tabulation:

Screw number or gage :

0 0. 060

1

2

3

4

5

6

7

D ¿)2

060 0. 0036

073 . 0053

086 . 0074

099 .0098

112 . 0125

125 . 0156

138 .0190

151 .0228

164 . 0269

Screw number or gage—Con. D

9-_

10.

11_

12.

14.

0. 177

190

203

216

242

16 . 268

18_ . 294

20 . 320

24 .372

i>2

0. 0313

. 0361

. 0412

. 0467

. 0586

. 0718

. 0864

. 1024

. 1384

Values for K for a number of the common species are given in

table 27. These values for K were obtained by dividing the constants in general equations for proportional limit loads by a reduction

factor of 1.6. They apply to wood at about 15 percent moisture

content. Loads computed by substituting these constants in the

equation are expected to allow a slip of from 0.007 to 0.01 inch,

depending somewhat on the species and quality of the wood.

The formula 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 cleat and the block holding the point

are approximately of the same density. This depth of penetration

gives an ultimate load of about six times the recommended allowable

load. 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 4 times the shank diameter, the

maximum load will be less than 4 times the load expressed by the

formula, and the proportional-limit load will be approximately equal

to that given by the formula. When the screw holds metal to wood,

the allowable load can be increased by about 25 percent.

In tests at the Forest Products Laboratory to determine the lateral

resistance of screws, the part of the lead hole receiving the shank, for

hardwoods such as oak, had the same diameter as the shank, and

that receiving the threaded part had the same diameter as the root

of the thread. For softwoods such as southern yellow pine and

Douglas-fir, the lead hole receiving the shank was about seven-
178 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

eighths the diaineter of the shank and that for the threaded parts was

a])Oiit seven-eighths the diameter of the screw at the root of the thread.

A larger coefficient K can be used m the formula for the allowable

lateral loads if it appears safe to allow larger loads and greater slips

in the design.

Sci-ews 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.

LAG SCREWS

Lag screws are commonly used l)ecause of their convenience, particularly where it would be difficult to fasten a bolt or where a nut on

the surface would be o})jectional)le. Lag screws range from about

0.2 to 1 inch in diaineter and from 1 to 16 inches in length. The

threaded part varies with the length and ranges from % inch with the

1- and l}4-inch screws to half the length for all lengths greater than

10 inches. The equations given herein for withdrawal and lateral

loads are based on lag sci'ews having an average yield point of about

45,000 pounds per square inch and an average tensile strength of

77,000 pounds per square inch. For metal lag screws having greater

or lower yield points and tensile strength, the withdrawal loads should

be adjusted in proportion to the tensile strength and the lateral loads

in proportion to the square root of the .yield-point stresses.

Withdrawal Resistance

The allowable load in dii'ect withdrawal of lag screws from seasoned

wood may be computed from the equation:

/>= 1,500 C?pi)''l'

in which j) is the allowable withdrawal load (one-fifth of the ultimate

load) in pounds per inch of penetration of the threaded part; T), the

shank diameter in inches, and G^ the specific gravity of the wood

based on weight and volume when oven-dry {19).

^ Lag screws, like wood screws, require prebored holes of the proper

size (fig. 30). The lead hole for the shank should be of the same

diameter as that of the shank. The diameter of the lead hole for the

threaded part varies with the density of the wood: For lightweight

softwoods, such as the cedars and white pines, 40 to 70 percent of the

shank diameter; for Douglas-fir and southern yellow pine, 60 to 75

percent; and for dense hardwoods, such as the oaks, 65 to ^h percent.

The smaller percentage in each range applies to lag screws of the

smaller diameters, and the larger percentage to lag screws of larger

diameters. Soap or similar lubricants should be used on the screws

to facilitate turning, and lead holes slightly larger than those recommended for maximum efficiency should be used with lag screws of

excessive length.

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 7 times
WOOD HANDBOOK 179

ZM 24964 F

FIGURE 30.—A, Clean-cut, deep penetration of thread made In' lag sciew turned

into a lead hole of proper size; B, rough shallow penetration of thread made

by lag screw turned into oversized lead hole.

the shank diameter in the denser species and 10 to 12 times the shanli

diameter in the less dense species will develop approximately the ultimate tensile strength of the lag screw.

The resistance to withdrawal of a lag screw from the end-grain

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

The allowable lateral loads for lag screws inserted in the side grain

and loaded parallel to the grain of a piece of seasoned wood can bo

computed from the equation:

p=KD'

in which p is the allowable lateral load in pounds parallel to the grain;

K, a constant depending on the species; and D, tlie sliank diameter of

the lag screw in inches (19). Values for K for a numlier of species

can be found in table 27. The values given by this fornuda apply

when the thickness of the attached member is 3.5 times the shank

diameter of the lag screw, and the depth of penetration in the main

member is 7 times the diameter in the harder woods and 11 times the
180 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

diameter in the softer woods. For other thicknesses, the computed

allowable loads should be multiplied by the following factors:

Ratio of (hickness of member to shank

diameter of lag screw

2__

3__.

4__

Factor

0. 62

. 77

.93

1.00

1.07

Ratio of thickness of member to shank

diameter of lag screw

4^2-

5_-

5/2-

6_-

6/2-

Factor

1. 13

1. 18

1. 21

1. 22

1.22

Wlien the lag screw is inserted into the side grain of wood and the

load is applied perpendicular to the grain, the allowable load given by

the lateral resistance formula should be multiplied by the following

appropriate factors:

Me

Shank diameter of lag screw

(i/iches) Factor

1. 00 1/

V¿'-

%--

l_-_

Shank diameter of lag screw

(inches) Factor

0 65

•MP

. 97

. 85

__ .60

55

__ . 76

-- . 70

__ .52

-- .50

For other angles of loading, the allowable loads may be computed

from the parallel and perpendicular values by the use of the Schölten

nomograph for determining the bearing strength of wood at various

angles to the grain (fig. 31) (18). The nomograph provides values

comparable to those given by the Hankinson formula:

A^= PQ

P sin'd+Q cos's

where P represents the allowable load or stress parallel to the grain;

Q, the allowable load or stress perpendicular to the grain; and N, the

allowable load or stress at an inclination 9 with the direction of the

grain.

Example: P, the allowable load parallel to grain is 6,000 pounds, and

Oy the allowable load perpendicular to the grain is 2,000 pounds.

A^, the allowable load at an angle of 40"" to grain is found as follows:

Connect with a straight line 6,000 pounds (a) on line OX of the nomograph with the intersection (b) on line OY of a vertical line through

2,000 pounds. The point where this Hne (ab) intersects the line representing the given angle 40° is directly above the allowable load, 3,285

pounds.

Working values for lateral resistance as computed by the preceding

methods are based on complete penetration of the shank into the

attached member but not into the foundation member. When the

shank penetrates the foundation member, the follomng increases in

allowable loads are permitted:

Ratio of penetration ofshank into foundation Increase

member to shank diameter in load

(percent)

1_-- 8

2 17

3 26

4 33

Ratio of penetration ofshank into foundation Increase

member to shank diameter in load

(percent)

5 36

6 38

7 39
WOOD HANDBOOK 181

§i

^^ ^' ¡5 <D

^ ^ ^ 5 "^ 5

r! ^ ^

K Vj ^

N ^ "^

^ c^ Ci» ^

V) S h i:^

s s s :^

k, '^j kj ^

CJ ^ -vi 5» ^ ^ ^ ^ ^ ^ 'i VJ

Q) ^ ^ ^

::i ^ ::i '^^ ^ ^ ^

-<TX

o

Ti

03

O rH

O .:í

^ c

•s ^

c3¿

JO o

bû

G

O

S

o

O

"o

O}
182 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Wlien lag screws are used with metal plates, the allowable lateral

loads parallel to the orain may be increased 25 percent, but no increase

sliould be made in the allowable loads when the applied load is perpendicular to the grain.

Lag screws should pr(^ferably not be driven into end grain, because^

s])litting may develop undei- lateral load. If lag screws are so used,

however, the allowable 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 gí'ain.

The spacings, end and edge distances, and net section for lag screw

joints should be the same as those for joints ^^âth bolts of a diameter

equal to the shank diameter of the lag screw.

Lag screws should alwa3^s be inserted by turning with a ^vrench, not

by driving. Soap, beeswax, or other lubricants applied to the screw,

particularly with the denser species, w411 facilitate insertion and

prevent damage to the threads, ])ut ^\âll not affect the lag screw's

holding power.

BOLTS

Bearing Strength of Wood Under Bolts

Basic bolt-bearing stresses (table 27) for calculating the allowable

loads for bolted joints acting parallel and perpendicular to the grain

were developed from general strength data published by the Forest

Products Laboratory {24, 30). The average ultimate crushing

strength pai'allel to the grain of small, clear, green specimens was

modified for softwoods and hardwoods for duration of loading, increase

in strength with dr3àng, variability of the wood, and a reduction

factor for safety. The average proportional limit stress perpendicular

to the grain of small, clear, green specimens was modified for inc^^ease

in strength with seasoning, variability of the wood, and a reduction

factor for safety. Special attention was given to the development of

the basic stresses for certain species that show abnormal strength,

splitting, or drying characteristics.

Basic stresses are listed in table 27 for a number of the common

species and are applicable for bolted joints in any grade of seasoned

lumber that is to l)e used in a dr}^ inside location. In locations where

the timber is occasionally wet but quickly dried and in locations that

are continuously damp or wet, the stresses listed in table 27 should be

reduced one-fourth and one-third, respectively. The limited test data

show that in multiple joints made with unseasoned members joined at

right angles to each other, the loads after the members had seasoned

were about 40 percent of those for joints made of seasoned members.

The allowable loads for correct!}^ spaced and alined bolts bearing

parallel ov perpendicida'' to the grain of the wood and with the load

applied through metal plates to both ends of the bolt are calculated by

multiplying the appropriate basic stress (table 27) by a percentage

factor (table 29) leased on the ratio of the length of bolt in the main

member to the bolt diameter (L/D). For loads acting perpendicular

to the grain, an additional factor, referred to as a diameter factor, is
WOOD HANDBOOK 183

applied to the basic stress values in accotdaiice with tlu^ following bolt

diametei's:

Diameter

Diameter of Imlt (inches) factor

M 2. 50

y% 1. 95

Vi 1. 68

H 1.52

% 1.41

]i 1.33

1 1. 27

Diaineler

Diameter of txilt (inches) factor

IV^ 1. U)

m 1.14

1^4 1. 10

2 1. 07

2% 1. 03

3 or over 1

TABLE 29.—Percentage of basic stress used in calculating allowahle hearing stresses

for common bolts when load is applied through metal splice plates

Ratio of bolt length to

diumctcr (L/D)

Bolts brariiiiï par

grain,' when basic s

illel to

tress is—

Bolts be iring i)orpen(licular to grain,2

when basic stress is—

750 to

950

p. s. i.

1,000 to

1,200

p. s. i.

1,300 to

2,000

p. s. i.

150 to

180

p. s. i.

200 to

280

p. s. 1.

300 1o

350

p. s. i.

400 to

600

p. s. i.

1

Percent

100.0

100.0

100. 0

99. 5

95. 4

85. 6

73.4

64.2

57.1

51.4

46.7

42.8

39.5

Percent

100.0

100. 0

100.0

97.4

88.3

75. 8

65. 0

56. 9

50.6

45.5

41.4

37.9

35.0

Percent

!00. 0

100. Í)

99. 0

92.5

80.0

67.2

57. 6

50. 4

44.8

40.3

36.6

33.6

31.0

Percent

100.0

100.0

100.0

100.0

100.0

100.0

100. 0

100. 0

94.6

85. 0

76.1

68. 6

62. 2

Percent

100.0

100. 0

100.0

loo.o

100.0

100.0

100. 0

96. 1

86.3

76.2

67. 6

61.0

55. 3

Percent

100.0

100.0

100.0

100. n

100.0

100. 0

97.3

88.1

76.7

67.2

59.3

52. 0

45. 9

Percent

100. 0

9 100. 0

3 - 100. 0

4 - - 100. 0

.5 100. 0

6 9(). 3

86. 9

8

9 -

75. 0

64.6

10 - - 55. 4

11

12

48.4

42. 5

13 37.5

1 For wood splice plates, each of which is ],i the thickness of the main member, the allowable loads should

be taken as ^i those computed for metal splice plates.

2 No reduction need be made when wood spHce plates are used except that the allowable load perpendicular to the grain should never exceed the allowable load parallel to the grain for any given size and r4uality of

bolt and timber.

Allowable Bolt Loads Parallel to

the Grain

The allowable load on a bolted timber joint aeting parallel to the

grain oif the wood through metal plates at both ends of the bolt is

calculated as follows:

(1) Select from table 27 the basic stress in compression parallel to

the grain for the particular species of wood and reduce in accordance

with the service condition if the joint is to be used in other than a

dry, inside location. Call this stress Si.

(2) Calculate the ratio of the length of the bolt in the main member

to the bolt diameter (L/D). Select the percentage r of basic stress

from table 29 for the calculated L/D.
184 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

(3) Multiply the basic stress Si by the percentage r to obtain the

allowable unit stress, S2, which is assumed to be uniformly distributed.

(4) Multiply S2 by the projected area of the bolt to obtain the

allowable load Pi for one bolt.

When the load is applied through wood splice plates, each of which

is one-half the thickness of the center member, the allowable load is

obtained by multiplying Pi by 0.8.

When the bolt holes aie properly centered and alined, the allowable

load on a number of bolts of the same or different diameters may be

taken as the sum of the individual load capacities.

Allowable Bolt Loads Perpendicular to the Grain

The allowable load on a bolted timber joint acting perpendicular to

the grain of the wood and at both ends of the bolt through metal

plates or wood side plates, each of which is one-half the thickness of the

main member, is calculated as follows:

(1) Select from table 27 the basic stress in compression perpendicular to the grain for the particular species of wood and reduce in accordance with the service condition if the joint is to be used in other than

a dry, inside location. Call this stress Si.

(2) Calculate the ratio of the length of bolt in the main member to

the bolt diameter (L/D). Select the percentage r of basic stress from

table 29 for the appropriate L/D.

(3) Select the diameter factor v for the appropriate size of bolt

(p. 183).

(4) Multiply the basic stress Si by the percentage factor r and the

diameter factor v to obtain the allowable average unit stress ^2 for the

particular L/D,

(5) Multiply the allowable unit stress S2 by the projected area of

the bolt to obtain the allowable load for a single bolt loaded through

either wood or metal splice plates.

When the bolt holes are properly centered and alined, the allowable

load on a number of bolts of the same or different diameters may be

taken as the sum of the individual load capacities.

The allowable bolt loads, both parallel and perpendicular to the

grain, determined by the preceding procedure are of such magnitude

as to prevent undue permanent distortion or other evident injury in

the joint under long-term loading or repeated application of the load.

For loads acting at an angle between the limits of parallel to the

grain and perpendicular to the grain, the allowable bolt load may be

obtained from the nomograph in figure 31 (18).

Effect of Quality of Bolt on Joint Strength

Both the quaUty of the wood and the quahty of the bolt are factors

in determining the proportional limit strength of a bolted joint. The

percentages of basic stresses given for calculating safe bearing stresses

apply to the common commercial bolts used in building construction.

For high-strength bolts, such as aircraft bolts, the reduction values

listed in table 29 would be somewhat larger for the larger L/D ratios.
WOOD HANDBOOK 185

Details of Design

The details of design required in the apphcation of the allowable

loads for bolts may be summarized as follows:

(1) A load apphed to only one end of a bolt, perpendicular to its

axis, may be taken as one-half the symmetrical two-end load.

(2) The center-to-center distance along the grain between bolts

acting parallel to the grain should be at least four times the bolt

diameter. 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 7 times the

bolt diameter for softwoods and 5 times for hardwoods. Wlien 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.

(3) For bolts bearing parallel to the grain, the distance from the

edge of a tünber 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 row^s, 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, w^hich 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 percent of the total area in bearing under all the bolts in

the particular joint under consideration; in hardwoods it should be

100 percent.

(4) 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. The minimum center-to-center spacing of bolts in the

across-the-grain direction for loads acting through metal side plates

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 bolt-bearing

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.

Effect of Bolt Holes

The bearing strength of wood under bolts is affected considerably

by the size and type of bolt hole into which the bolts are inserted.

A bolt hole that is too large causes nonuniform bearing of the bolt,

and, if the bolt hole is too small, the wood will split when the bolt is

driven. Normally, bolts should fit neatly, 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. 32).

Deformations accompanying the load also increase with increase in

the unevenness of the bolt-hole surface (fig. 33).
186 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

- f>-'' Ï1

w

t» 1

^^'' 1

ZM 9235 F

FrniRF S2 —Effect of rate of feed and drill speed on the surface condition of

Colt holes driUed in Sitka spruce. The hole on the left was bored with atwjst

drill potfltinL at a speed of 200 r. p. m.; the feed rate was 60 inches per minute.

The ¿oîeon'the right was bored w?th the same drill rotating at 800 r. p. m.; the

feed rate was 2 inches per minute.

I

4,000

y

/

/

/

/

/

3,000

/

/

/

<(S

A

/

^

/

/

/ ^^

1/ 0-

/

r

f^Ajr^

/

^

^'

/

^^

n

/^

0.010 0.020 0.030

DEFORMATION (INCHES)

ZM 56698 F

FIGURE 33.—Typical load-deformation curves showing the effects 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. Ihe

surface conditions of the bolt holes were similar to those illustrated in figure 32.
WOOD HANDBOOK 187

Rough holes result from the use of dull V)its and improper rates of

feed and drill speed, A twist drill, preferably machine sharpened, at

a 118"^ angle and operated at a recommended peri])heral speed that

corresponds to a speed of rotation of approximately 1,350 r. p. m.

divided by the diameter of the drill in inches produces uniform, smooth

holes. For carbon steel drills, the speed of rotation should be approximately one-half that used for high-speed drills. The rate of feed

depends upon the diameter of the drill and the speed of rotation but

should enable the drill to cut rather than tear the wood. The drill

should produce shavings, not chips (8).

TIMBER-CONNECTOR JOINTS

When timbers are joined with metal or other types of connectors,

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 tindjcr,

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 {17, 21, 22, 23, 27). Safe working long-time loads for metal

connectors in common use—split-ring (fig. 34), toothed (fig. 35), and

shear-plate (fig. 36)—and for a wood connector are discussed in this

section.

Derivation of Safe Working Loads for Long-Continued

Loading

The working loads for the split-ring, shear-plate, and toothed

connectors provided in tables 30, 31, and 32 were derived from the

results of tests of full-scale joints made from the more im])ortant

commercial species. The species were classified into foin^ groups in

accordance with their strength in connector joints. In establishing

the working loads, particular consideration was given to (1) the

effect of long-continued loading as against the brief loading period

involved in the test of joints (see p. 160 for effect of duration of lead

on working stresses) and (2) allowance for variability in timber

quality (1).

Since adequate data are not available on the effect of duration of

stress on the strength of connector joints, insofar as the w^ood is

considered, the relation between the load at failure in a standard

bending test of a few minutes' duration and the load that will cause

failure under long-time loading was assumed to apply. Undc^r constant load a beam will fail at a load only about nine-sixteenths as

great as the breaking load found in the standard bending test {1, 15).

Tests have demonstrated that the density or quality of the wood is

often the controlling factor in determining the strength of a joint.

Consequently, the load carried by a connector in the Laboratory test

employing wood of average quality for a species was adjusted to allow

for the lower than average material likely to be used in service.

The working loads listed in tables 30, 31, and 32 for connectors

acting parallel to the grain were derived by applying a reduction fac30.3747°—55 13
188 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

M 93396 F

FIGURE 34.—Split-rins conneftor assemljly—connector, piecut groove, bolt,

washor, and nut.

M 32890 F

FIGURE 35.—Toothed connector assembly.

,Mmâ
WOOD HANDBOOK 189

p«~"-

M 92355 F

FIGURE 36.—A, Shear-plate connector assembly with wood side plates; B, shearplate connector assembly with sleel side plates.

tor to the ultimate load, as found in tests. For split-ring and shearplate connectors, a reduction factor of 4 gave values that met the

provision that working loads for these connectors should not exceed

five-eighths of the proportional limit test load. Because load-slip

curves for the toothed connector do not exhibit a well-defined propor-
TABLE 30.—Safe ivorking loads ^ for 1 splil-ring connertor and bolt (Î connector unit)

Mininunn thickness of

member

Minimum

width all

members

Group 1 woods 2 Group 2 woods 2 Groui) 3 woods 2 (îrou[) 4 woods -

Connector unit

With 1

connector

only

With 2

connectors

in opposite

faces 1 bolt 3

Load at 0°

an^de to

grain

Load at 90°

angle to

grain

Load at 0°

angle to

grain

Load at 90°

angle to

grain

Load at 0°

angle to

grain

Load at 90°

angle to

grain

Load at 0°

angle to

grain

Loa<l at 90°

aîigl(^ to

grain

(1) (2) (3) (4) (5) (()) (7) (8) (9) (10) (11) (12)

In. In. In. Lh. Lb. Lb. Lb. Lb. Lb. Lb. Lb.

2'.j-inch connector and i^-inch bolt Í 1 m

2+ 3H

1, 490

1,7S5

880

l.Oñ.i

1.7Hñ

2,085

1,025

1,2::!0

2, 0H5

2, 480

1. 230

1, 475

2. 395

2, 875

1.435

1, 725

[ Px 15^ h ' •-> 2,41ñ 1,400 2, 795 l.()20 3. 355 1.945 3, 915 2. 270

4-inch connector und •'4-inch bolt I'l

1 11,

2

2H

51 :,

r, 1 ,^ 3.3S()

l,r,i(^

l,9(i0

3, 215

3,915

1. 8C.5

2, 270

3, 8()0

4. i'm

2, 240

2, 725

4.500

5. 480

2.010

3,175

[ 1-^M + 3+ 51.., 3. 44.S 1,995 3, 985 2.310 4. 780 2, 775 5.580 3. 235

' The safe working loads apply to seasoned timbers in dry, inside locations for a long-continued loa<l. It is assumed also that the joints are properly designed with resjiect to

such features as centering of connectors, adequate end distance, and suitable spacing.

2 Group 1 woods provide the weakest connector joints, and group 4 woods the strongest; s{>ecies included in the groups are given in table 27.

3 A 3-mcmber assembly with 2 connector units would therefore take double the safe working loads indicated in columns 6-12.

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TABLE S\.—Safc working loads ^ for 1 toothed connector and holt (1 connector unit)

romiector unit

(1)

2-inch connector with i^-inch bolt

25-8-inch connector with ^s-inch holt

3-^8-inch connector with vi-inch holt

4-inch connector with •'4-inch holt

Mininiimi thickness of

member

Minimum

Crroup 1 woods 2 Group 2 woods 2 Group 3 woods 2 (rroup 4 woods 2

With 1

connector

only

With 2

connc^ctors

in o{)i)osit.e

faces 1 bolt ;'

width all

members Load at 0°

angle to

grain

Load at 45°

to 00°

angle to

grain

Load at 0°

angle to

grain

Load at 45°

to 90°

angle to

grain

Loid at 0°

angle to

grain

Load at 45°

to 90°

angle to

grain

Load at 0°

angle to

grain

Load flt 45°

to 90°

angle to

grain

(2) (3) (4) (.")) (0) (<) (8) (0) (10) ill) (12)

///. i Ji>. ///. Lh. Lh. Lh. Lh. Lh. Lh. Lh. Lh.

1 1 1 I'^S 25 K 7S(l 520 000 (100 1,000 ; (>05 1,100 735

1 l's+ j 2+ 25 s St'iO 570 990 000 1,100 735 1,210 805

1 1 1 l^s 35 s 1. 171) 7sn 1,350 000 1,500 1,000 1,0>.50 1. 100

l.s ' 2 35 s 1.205 805 l,4ç:5 095 1.000 ' 1,105 1, 825 220

1 :-'s+ I 2',.-h 35 s l,4tll) 075 1,(>00 1,125 1,875 ' 1.250 2, 000 375

1 1 IS 45 s 1,520 1,015 1,755 1.170 1,050 . 1.300 2, 145 430

Ils ' 2 45 s l,Ht;5 1, 110 1,020 1.280 2, 135 1,425 2, 35(~ 505

1 ' ' 1 2^ s 45 s 1,010 1.270 2, 200 1,405 2,445 1,030 2, »lOO 705

i i's+ : 3+ 45 s 2,055 1,370 2,370 1, 580 2.030 ' 1,755 2. 805 930

1 15s 5 ^ _' 1,S35 1,220 2, 115 1,410 2, 350 : 1.505 2. 585 725

I's 2 51 • 1.0S5 1,320 2, 290 1,525 2, 540 1.095 2.795 8(>5

I'j ' 25s 51. 2,23ñ 1,400 2. 575 1,72;) 2, 80.". 1,910 3. 150 2 loo

[ I5s+ ! 8-h

1

51J 2, 385 1,50(1 2, 7.Î0 l,s;iô 3.05.-. 2.035 3, 300 2 240

1 The safe working loads api)ly to seasoned timbers in dry, inside locations for a long-continued load. It is assumed also that the joints are i)roi)erly designed with resiu'Ct to

such features as centering of connectors. ade(iuate end distance, and suitable si)acing.

2 Group 1 woods provide the weakest connector joints, and grouf) 4 woods the strongest; species inclu<led in the gn)ui)s are given in table 27.

3 A 3-member assembly with 2 connector units would therefore take double the safe working loads indicated in colunms 5-12.

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TABLE 32.—Safe workin ¡7 loads ^ for 1 shear- plate eon nerfor and bolt (Î connector i/n 7)

Mininnnn thickness of

member

Minimum

width all

members

(4)

(iroup 1 woods 2 (îroup 2 woods - ( iroup 3 woods ^ (troup 4 woods 2

Comiector unit

(1)

With 1

connector

only

(2)

With 2

connectors

in opposite

faces 1 bolt '^

(3)

Load at 0°

angle to

grain

(5)

Load at 90°

angle to

grain

(6)

Load at 0°

angle to

grain

(7)

Load at 90°

angle to

grain

(8)

Load at 0°

angle to

grain

(9)

Load at 90°

angle to

grain

(10)

Load at 0°

angle to

grain

(11)

Load at 90°

angle to

grain

02)

In. In.

1-?K

2

2's+

l>.i

l''s

3

3^K +

l'.l

2

2^H

I'^S

3

3>)K+

In.

31'j

3'j

3'.

51-2

51 j

5!J

5lj

5'2

51-2

oH

5 1/2

5»2

5K>

5 k'

5 k

Lh.

1.470

1.785

1.889

1.901

2. 12C

2. 486

2, 660

2. 705

2. 851

1,901

2. 120

2. 486

2. 66,0

2. 705

2. 851

Lh.

8.->-2

Lh.

1 704

Lh.

9S8

1,2;)0

1.271

1.27S

1.426

1.672

1.790

1.819

1.917

1.278

1.426

1.672

1.790

1.819

1.917

Lh.

2.045

2, 483

2, 6,29

2. 6,45

2, 950

3. 458

3, 700

3. 763

3, 967

2. 645

2, 950

3. 458

3. 700

3. 763

3. 967

Lh.

1. 186)

1.440

1,525

1.533

1,711

2, 006

2, 150

2.182

2, 301

1, 533

1,711

2,006

2, 150

2, 182

2. 301

Lh.

2, 386

2. 667

2. 66.7

3,086

3.442

4.035

4. 320

4. 391

4, 625

3, 086

3, 442

4.035

A •10l\

Lh.

1.384

1.680

1.779

1. 789

1.996

2. 340

2. 510

2, 547

2. 684

1,787

1,996

2. 340

2;K-inoli connector with •^:i-inch bolt . '

l'S+

1.035 1 2.669

1.096 2.191

1.102 2.204

1.229 2.458

1.442 2.882

1.540 3,080

1.568 ' 3. 137

1,653 0,306

1.105 2.204

1 OOd o jr,û

4-inch coimector with M-inch holt

1 1=4 +

4-incli connector with ^s-inch bolt 1.442

1.540

1 ^i\K

2, 882

3,080

4,391 2, ,547

4,625 2.684

1

1'4 + 1.6,53 j 3.306

1 The safe working loads apply to seasoned timbers in dry, inside locations for a long-continued load. It is assumed also that the joints are properly designed wdth respect to such

features as centering of connectors, adequate end distance, and suitable spacing. The tabulated loads apply for metal or wood side plates except that, for 4-inch shear plates with

metal side plates, the parallel-to-grain loads may be increased 5, 11, and 18 percent for groups 2, 3, and 4 wootls, respectively. The allowable loads for all loading except wind shall

not exceed 2,900 pounds for 2)s-inch shear plates or 4,970 pounds and 6,760 pounds for 4-inch shear plates with ):i- and ^s-inch bolts, respectively; for wind loading, the corresponding

allowable loads shall not e.vceed 3,870 pounds, 6,630 pounds, and 9,020 pounds.

2 Group 1 woods provide the weakest connector joints, and group 4 woods the strongest; species included in the groups are given in table 27.

3 A 3-member assembly with 2 connector units would therefore take double the safe working loads indicated in columns 5-12.

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WOOD HANDBOOK 193

tional limit, no factor based on proportional limit loads was consideied.

For this connector, the larger reduction factor of 4}^ was applied to

the ultimate load.

Tests of connectors under loads bearing perpendicular to grain,

although less extensive and less numerous than those for parallel

bearing, have been sufficient to establish a generally applicable relationship between the two directions. This relationship was used in

deriving allowable loads for perpendicular bearing. Ultimate load

was given less consideration for perpendicular than for parallel bearing, and greater dependence was placed on other factors, such as the

load at proportional limit and at given shps of the joint.

The figures quoted as the ratios between working loads and the

loads found in test are in no instance true factors of safety. For example, the reduction factor of 4 for split-ring and shear-plate connectors includes allowances for duration of stress and for variability as

well as a margin for safety. Thus, after the values from test are

multiplied by a factor of nine-sixteenths as an allowance for a longcontinued toad and by three-fourths to cover variability of the wood,

the actual factor of safety for a connector joint is on the order of

1% (4 x %6 X %=PK6) if the working load acts over a long period.

The tests from which working loads were derived were on specimens

carefully made from seasoned material, under favorable conditions,

and by experiencôd workmen (28).

In tabulating the safe working load for a connector joint of any

number of members, the unit is one connector with a bolt in shear.

For any joint assembly in which more than one connector unit is used

in the contact faces with the same bolt axis, the total safe working

load is the sum of the safe working loads of each connector unit. For

example, in tables 30, 31, and 32, minimum actual thickness of the

members is given for a joint assembly of 3 members employing 2

connectors in opposite faces with a common bolt; this assembly is

equivalent to 2 connector units, and, therefore, the safe working load

will be twice the corresponding value shown for a 1-connector assembly (columns 5 to 12). The loads as given apply only when the joints

are properly designed with respect to such jfeatures as centering of

connectors, adequate end distances, and suitable spacing of connectors.

Modification of Working Loads and Factors To Be

Considered in Their Use

Some of the factors that affect the safe working loads of connectors

were included in deriving the tabular values. Others require modification of the values listed in accordance with the provisions outlined in

the following paragraphs.

Wind or Earthquake Loads

In designing for wind or earthquake forces acting alone, or acting

in conjunction with dead and hve loads, the safe working loads for

the various connectors may be increased by the following percentages.
194 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

provided the nunilxM- and size of connoctors is not less than that required for the eombination of dead and Uve loads alone:

IncTcase

(percent) i

Split-riiiíí connector, any size, bearing in any direction 50

Shear-plate connector, any size, l)earing parallel to grain 33}^

Shear-plate connector, any size, bearing perpendicular to grain 50

Toothed-ring connector, 2-inch, })earing in any direction 50

Toothed-ring connector, 4-inch, bearing in any direction,. _ 25

1 Pcrcoiitafrcs for sh(>;ir-plate connectors bearing at intermediate angles and for toothed-ring connectors

of other sizes can ^)e o^)tained by interpolation.

Impact Forces

Impact may be disi'egarded up to the following percentage of the

static effect of the live load producing the impact:

Impact

uUoumnces

(percent) i

Split-ring connector, any size, bearing in any direction 100

Shear-plate connector, any size, bearing parallel to grain 66%

Shear-plate connector, any size, bearing perpendicular to grain 100

Toothed-ring connector, 2-inch, i)earing in any direction 100

Toothed-ring connector, 4-inch, Ijearing in any direction 50

1 Percentages for shear-plate connectors t)earing at intermediate angles and for toothed-ring connectors

of other sizes may be obtained by interj^olation.

One-half of any impact load that remains after disregarding the

percentages indicated should be included with the other dead and live

loads in obtaining the total force to be considered in designing the

joint.

Factor of Safety Not Reduced

The procedures described for mcreasing the allowable loads on

connectors for forces suddenly applied and forces of short duration

do not reduce the actual factor of safety of the joint but are recommended because of the favorable behavior of wood under such forces.

The differentiation among types and sizes of connector and directions

of bearing is due to variations in the extent to which distortion of the

metal, as well as the strength of the wood, affects the ultimate strength

of the joint.

Special Design Considerations

Conditions of design may be encountered, with respect to the kind

of load on a structure and the period of its continuation, that are

neither ''long continued" nor ''suddenly applied.'' These conditions

requh^e or justify special consideration and possible modifications,

other than those that have been indicated, of the working loads listed

in tables 30 to 32. For such conditions, it may be assumed that 90

and SO percent of the stress that causes failure in 5 minutes (time

usually assumed for wind load) will cause failure in 50 minutes and

10 liours, respectively (see p. 160 for effect of duration of load on working stresses). Special considerations are also involved when connectors are used in pl^nvood (27),
WOOD TTANDBOOK 195

Exposure and Moisture Condition of Wood

The loads listed in tables 30, 31, and 32 apply to seasoned timbers

used where they will remain dry. If the timbers will be more or less

continuously damp or wet in use, two-thirds of the tabulated values

should be used. The amount by which tlîe 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 pi'oportion of sapwood and the

durability of the heartwood of the species if untreated, and the character and efficiency of the treatment if treated. These factors should

be evaluated for each individual design. Industry recommendations

for the use of connectors when the condition of the lum))er is other

than continuously wet or continusously dry are given in National

Design Specification for Stress-Grade Luml)er and Its Fastenings

Ordinarily, before fabrication of connector joints, timbers 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 timber for roof trusses and other structural units used in dry

locations and in which shrinkage is an important factor. Urgent

needs for some types of construction sometimes result in the erection

of many timber-connector structures and structural units employing

green or inadequately seasoned lumber. Since such lumber subsequently dries out in most buildings, causing shrmkage and opening

the joints, it is essential that adequate maintenance measures 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. Frequently,

the first inspection should be made within 3 to 6 months after erection.

Grade and Quality of Lumber

The timber for which the working loads for connectors are applicable

should conform to the general requirements in regard to the quality

of structural lumber given in the grading rule books of lumber manufacturers^ associations for the various commercial species.

With the recommended safe loads for connectors, it is assumed

that the wood at the joints is clear and relatively free from checks,

shakes, and splits. The wood should be either free from knots, or,

if knots are assumed to be 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. It is also assumed that

cross grain at the joint does not exceed a slope of 1 in 10.

Loads at an Angle With the Grain of Wood

The safe working loads for the split-ring and shear-plate connectors

for intervening angles of 0° to OO"" between direction of load and grain

may be obtained by the formula given under the heading Compressive
196 HANDBOOK 7 2, U. S. DEPAPVTMP:NT OF AGRICULTURE

StrcMio-tli on Surfaces Inclined to the Grain on page 80 or by the

nonK)0'r;i])li in figure 31 (18). With tlie toothed connectors, the safe

working load at\in inclination to the grain of 0"" to 45"^ may be obtained with the previously mentioned formula; but from 45'' to 90°

it is equal to the working load perpendicular to the grain.

Thickness of Member

The ri^lationshi]) between the loads for the different thicknesses of

lum1)er is basi^l on test results foi* cormector joints. The least thickness of memlx'r given in tables :>0, ol, and 32 for the various sizes

of comiectors is, in general, the minimum that should l)e used. The

loads listed for th(^ gi'eatest tliickness of meml)er in each type and

size of coiiueclor unit are the maximum h)ads to l)e used for all thicker

IUIUIKU'. The loads for wood meml)ejs of tliicknesses hitermediate

to those listed can be obtained )jy dii'ect interpolation.

Width of Member

The width of mimilxM* listed for each type and size of connector is

the minimum that should be used. When the comiectors are bearing

parallel to the grain, no increase in load occurs with an increase in

width over the minimum. When they are bearing perpendicular to

tlu^ grain, the load increases about 10 perceiit for each 1-incli increase

in ^^^dth of member over the miiiiminn widths i-equired for each type

ami size of comiector, up to twice the diameter of the connectors.

When the comu'ctor is i)laced off center and the load is applied contimiously iîi one direction only, the proper working load can be determini^l l)y considering the width of mem1)er as equal to twice the

edge distaiu'c (the distance l)etween the center of the connector and

the cCii^r of the mem1)er toward which the load is acting), but the

distance l)etween the center of the connector and the opposite edge

should not be less than one-half the permissible minimum width of

the member.

End Distance and Spacing

The working load values in tables 30, 31, and 32 appl}^ when the

distance of the comiector from the end of the member (end distance

e) and the s])acing (s) between connectors in multiple joints arc not

factors in the strength of the joint (fig. 37, A). When the end distance or spacing for connectors l)earing parallel to the grain is less

than that required to develop the full load, the proper reduced working

load for design may be obtained b}^ multiplying the working loads in

tables 30, 31, and 32 l)y the appropriate sti'ength ratio given in table

33. For example, the load for a 4-inch split-ring connector bearing

parallel to the grain, when placed 7 or more inches from the end of a

Douglas-fir tension member that is 1% inches thick, is 4,780 pounds.

When the end distance is only b% inches, the strength ratio obtained

by direct interpolation from the vahu^s given in table 33 is 0.81, and

the load equals 0.81 times 4,780 or 3,870 pounds.
WOOD HANDBOOK 197

A

k

LEGEND:

e - END DISTANCE

S - SPACING PARALLEL TO GRAIN

a- EDGE DISTANCE

C - CLEAR DISTANCE

2M 39253 F

FIGURE 37.—Types of multiple-connector joints: A, Joint strength flep^Mirlcnt

upon end distance e and connector spacing a; B, joint strength flcpendcnt

upon end e, clear c, and edge a distances; C, joint strength dependent upon end

€ and clear c distances; D, joint strength dependent upon end e, clear c, and

edge a distances.
198 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Placement of Multiple Connectors

PrelimiDary investigations of the placement of connectors in a

multiple joint, together with the observed beliavior of single connector

joints tested with variables that simulate those in a multiple joint,

furnish a basis for some suggested design practices.

When two or more connectors in the same face oí a member arc in

a line at right angles to th^ grain of the m<^mber and are bearing parallel to the grain (fig. 37, (7), the clear distance (c) between the connectors should not l)e less than one-half inch.

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. 37, B), the rules for the width of meml)er and edge distances

(p. 196) used with one connector are applicable to the edge distances

for multiple connectors. The clear distance between the connectors

(c) should l)e equal to the clear distance from the edge of the timber

toward which the load is acting to the connector neai'est this edge (c).

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.

37, D), the available data indicate that the load for multiple connectors is not equal to the sum of the loads for individual connectors

and that somewhat more favorable results are o])tained in tests if the

connectors are stai^írered so that they do not act along the same line

TABLE 33.—Strength ratio for connectors for various longitudinal s pacings and end

dista nees ^

Connector and diameter (inches) .Strcn^nh

ratio

End distance ^

Tension

nK.'mher

! Strength

Compres- ratio

sion member

Split-ring:

21.,

21 j

4

4

Shear-plate:

2^8--- ..

4

4

Toothcd-rinp

2

2

2^/i;

29 B

i-^%

-iH

4

4

^1%

9+

41.

4+

2

29 s

8+

4

Percent

100

50

100

50

100

50

100

50

100

50

100

50

100

50

Inches

5^24

7+

3>2

7+

Inches

4+

2I2

5k'+

3y4

4+

2' •'

5I2+

' Percent

3I2+ 2+

2 ; 4^^+ ' 2H+

'2H

0^8+ I 3-}B+

3^8 \

7+ 4+

100

62

100

62

100

62

100

62

100

67

100

67

100

67

100

67

1 Strength ratio for spacings and end distances intermediate to those listed may be obtained by interpolation, and multiplied by the loads in tables 30, 31, and 32 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.

2 Spacing is distance from center to center ol connectors (fig. 37, .4).

3 End distance is distance from center of connector to end of member (fig. 37, A).
WOOD HANDBOOK 199

with respect to the grain of the transverse member. Industry recommendations for various angle-to-the-grain loadings and spacings are

given in reference (i 7).

The phicement of connectors m joints with meml)ers at right angles

to each other is sul)ject to the minimum limitation of either member.

It is vii'tually impossible to set up general rules regarding the alhiement, spacing, and margin of connectors to cover all possible directions

of the applied load. The designer must rely upon a sense of proporJon

and fitness in applying the rules set forth to a condition of loading

that is within the limits discussed.

Cross Bolts

Cross bolts placed at or near the end of timbers joined with connectors, or at hitermediate panel pouits will provide additional safety.

They may also be used to reinforce members that have, through change

in moisture content in service, developed checks to an undesirable

degree.

Net Section

The stress in the net area (whether in tension or compression) of

sawed timbers, which 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, should not exceed the safe stress

of clear wood in compression parallel to the grain. In using this

stress, it is assumed that knots do not occur in the longitudinal projection of the net section within a length of one-half the diameti^^ of

the connector from it.

In laminated timbcu^s, 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 safe

stress at the net section is limited to the safe compressive stress for

the member, which takes account of the effect of knots.

Examples of Connector-Joint Design

(1) Calculate the safe working strength of a tension joint of seasoned coast-type Douglas-fir in which 2 pieces 3% inches thick and

5K inches wide are joined end to end by means of side plates l^g inches

thick, 5K mches wide, and 28 inches long, when four 4-inch split-ring

connectors and two %-inch bolts are used. In this arrangement, 2

connectors and a concentric bolt are placed symmetrically on either

side oiF the butt joint at a distance of 7 inches from the ends of the

members and side plates. This end distance, as shown in table

33, is adequate to develop the full design load.

The working load given in table 30 for one 4-inch split-ring connector, when used in 1 face of a Douglas-fir member 1% inches thick

or as 1 of 2 connectors used in opposite faces of a member 3 inches

thick, is 4,780 pounds. The safe load of the joint for 2 connectors

equals 2 times 4,780 or 9,560 pounds.

(2) Calculate the safe working strength of the joint in example (1)

when the side plates are 16 mches instead of 28 inches in length. By
200 HANDBOOK 72, U. ft. DKPAHTAIEXT OF ACRICULTURI.

placina" (lu> coiinectoi's lialfway l)etween tlic ends of the sides plates

aiul tlTe but I joiiU, tlie end dislanee is 4 inelies. The strength ratio

as ¡nterp()hU('d from vahies given in table 33 for a 4-ineh end distance

is O.nS, and tlie safe load accordingly equals 0.68 times 9,560 or 6,500

pounds.

(:]) C^dculate the safe woi'king strength of a joint of seasoned

southern vcdlow pin" in which 2 tension side members 1% inches thick

and 5): inches \vu\v are joined at right angles to opposite faces of a

center timber 3% inches thick and 5}^ inches wide by means of two

4-in(*h s])ht-ring connectors and a ^^4-inch bolt.

The load U)v 1 of two 4-inch split-i'hig connectors used in opposite

faces of a memlx'i' :] inches thick and r>]f> inches wide and bearing

])erpendicidar to the giain is 2,775 ])ounds (table 30). The load for 1

connectoi- Ix^ai'ing parallel to the grain in 1 face of a side member \%

inch(S thick and with an end distance of 7 inches is 4,780 pounds

(ta])l(^ :]()). Th(^ sab' load of the joint, which is governed b}^ the load

ill the center mend)er, equals 2 times 2,775 or 5,550 pounds.

(4) Calculate the safe working sti-ength of the joint in example (3)

wlu^i the distance from the end of the side plates overlapping the

center memlx'j- to the center of the bolt hole is 3M instead of 7 inches.

The strength ratio for an end distance of 3t^ niches is 0.62 (table 33).

The load for one 4-inch s])lit-ring connin-tor in the side member, hence,

e(|uals 0.62 times 4,780 or 2,964 ])ounds. This is lai'ger than the

woi'king load h)r one connectoi- in the center niemlxM'. The strength

of the joint, therefore, is still governed bv the load in the center

member and, as 1)efoi-e, is 5,550 pounds.

Other Connector Types

In addition to the connectors discussed, the Forest Products

Laboratory made an exjiloratory investigation of several other types

of coniKH'tors intended for use in building construction, such as the

bulldog, claw-plate, circular-spike, and Kül)ler wood-dowel connector

(20). Many of these connectors are of European origin. Some of the

niet.al connectors are no longer manufactured, and others have a very

limited use. A l)rief presentation is in(4ud(Ml here on the Kultier wood

dowel in ord(M' to provide information on the load-carrying capacity

of a wood connector.

The Kübl(M' doubly coned dow(4s were originally made of cast iron.

Later, oak Mas tri(Ml and found satisfactory in Europe. Two sizes

were tested by tlu^ Laboratory, one approximat(4v 2% inches and the

other approximately 4 inches in diauKqc^". Bolts Y: inch in diameter

were used with each size of do\\'el, and the bolt holes in the test specimens Were l)ored /io-inch larger than the bolts.

The recommended working load for one Kühler wood dowel is as

follows: 2U-inch dowel paralhd to grain, 1,650 pounds; perpendicular

to grain, 990 pounds; 4-inch dowel parallel to grain, 3,750 pounds;

perpc^ndicular to grain, 1,425 pounds. These loads are for oak dowels

US(M1 in seasoned southern vellow pine or Douglas-fir (coast type).

They can be safely used with all the species in groups 3 and 4 listed

in table 27 and are based on a factor of 4 on ultimate loads of specimens tested at the Forest Products Laboratory. For group 1 woods

use 80 percent and for group 2 use 90 percent of these values.
WOOD HANDBOOK 201

LITERATURE CITED

(1) AMERICAN SOCIETY FOR TESTINíí MATERIALS.

1949. TENTATIVE METHODS FOR ESTARLISIIINC STUM^TKAL CRADES OF

LUMBER. Amer. Soc. Testing Mater. Standard I)24r)-40T, 27

pp.

(2) BORKENIIAGEN, E. H., AND KuELLINO, II. J.

1948. CLINCHING OF NAILS IN CONTAINER CONSTRUCTION. \\ S. ForCst

Prod. Lab. Rept. 111777, 4 ])])., illus. [Processed.]

(3) DEWELL, II. D.

1917. TIMBER FRAMING. 275 p})., illus., Sail Fraiicisco.

(4) FAIRCHILD, I. J.

1926. HOLDING POWER OF WOOD SCREWS. U. S. Nati. I5iir. Slaiidards

Techiiol. Paper 319, 2S i)p., illus.

(5) GAHAGAN, J. M.. AND BEOLINGER, K.

1932. NEW NAIL-TREATING PROCIOSS INC LILO ASIOS HOLDING I'OWKII. F. S.

Forest Prod. Lab. Kpt. R97(), 3 i)p. (Processed.]

(6) GiESE, H., AND HENDERSON, S. M.

1947. EFFECTIVENESS OF ROOFING NAILS FOR AI^PLICATION O !'^ MIOTAL

BUILDING SHEETS, lowa Aij;r. Isxpt. Sta. Pes. Bui. )>r>o; 525-592,

illus.

(7) BODY, L. L., AND DALE, A. C.

1950. EFFECT OF MOISTURE CONTENT OF WOOD ON WITHDRAWAL lilOSlSTANCE

OF ROOFINí; NAILS. A^^v. IMI.íííII. 31 (4): 178-181, 18;], illus.

(8) GOODELL, H. R., AND PlIILIl'PS, R. S.

1944. BOLT-BEARINCi STRENGTH OF WOOD vVND MODIFIED WOOD: EFFIOCT

OF DIFFERENT METHODS OF DlilLLING BOLT HOLES IN WOOD AND

PLYWOOD. F. S. Forest Prod. Lai). Rpt. 1523, 10 pj)., illus.

[Processed.]

(9) KOLBERK, A., AND BlllNBAUM, M.

1913. TRANSVERSE STRENCJTH OF SCREWS IN WOOD. Cornell Civ. ICu^ill.

22: 31-41, illus.

(10) MARKWARDT, L. J.

1952. HOW SURFACE CONDITION OF NAILS AFFECTS THEIH IIOLDINM; I'OWER

IN WOOD. F. S. Forest Prod. Lab. lli)t. D1927, 4 |)p., illus.

[Processed.]

(11) AND GAHAGAN, J. M.

1929. THE GROOVED NAIL. Packin^i and Shipping- 56 (1): 12-14, illus.

(12) AND GAHAGAN, J. M.

1930. EFFECT OF NAIL POINTS ON flESlSTANCE TO WITIIDIÍAWAL. F. S.

Forest Prod. Lab. Rpt. R1220, 3 pp., illus. [Processed.]

(13) AND GAHAGAN, J. M.

1931. MECHANISM OF NAIL HOLDING. Barrel anil Bo.x and Packa.ues ;;(3 (S):

26-27, illus.

(14) AND GAHAGAN, J. M.

1952. SLANT DRiviN(i OF NAILS. DOES IT PAY? Packing and Slii]>piii^-

56 (10): 7-9, 23, 25, illus.

(15) AND WILSON, T. R. C.

1935. STRENiiTH AND RELATED PROPE liTI JOS OF WOODS ORoW.V IN THE

UNITED STATES. F. S. Dcpt. A^T. Tceh. Bul. 47*.), 99 pp., illus.

(16) MARTIN, T. J., AND VAN KLEECK, A.

1941. FASTENING. F. S. Patent No. 2,268,323. l\ S. Pat. Oilice, OIF

Gaz. 533: 1226.

(17) NATIONAL LUMBER MANUFACTURERS ASSOCIATION.

1953. NATIONAL DESIGN SPECIFICATION FOR STRESS-GRADE LUMBER AND

ITS FASTENINGS. 66 pp., illus.

(18) NEWLIN, J. A.

1939. BEARING STRENGTH OF WOOD AT ANGLE TO THE GRAIN. L. S.

Forest Prod. Lai). Rpt. R1203, 1 p., illus. [Processed.]

(19) AND GAHAGAN, J. M. T^ U T^ + A

1938. LAG SCREW JOINTS: THEIR BEHAVIOR AND DESIGN. I. S> Uept. A^^r.

Tech. Bul. 597, 26 pp., illus.

(20) PERKINS, N. S., LANDSEM, P., AND TRAYER, G. \\ . i^ o r^ f

1933. MODERN CONNECTORS FOR TIMBER CONSTRUCTION, b. S. F'i'ptCom., Nati. Com. Wood Ftil., and F. S. Dept. A^r.. l^orest

Service. 147 pp., illus.
202 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

(21) SCHöLTEN, J. A. .

19::)8. MODKHN Ci)NNECTORS IN WOOD CONSTRUCTION. Agr, Lllgin. lU

(oj: 201-203, illus.

(22)

(23)

(24)

(25)

1940. CONNECTOR JOINTS IN WOOD CONSTRUCTION. Railwav PurchasGS

and Stores 33 (9): 431-435, illus.

1944. TIMBER-CONNECTOR JOINTS, THEIR STRENGTH AND DESIGN. U. S.

Dept. Agr. Tech. Bui. 865, 106 pp., illus.

1946. STRENGTH OF BOLTED TIMBER JOINTS. U. S. Forcst Prod. Lab.

Rept. R1202, 2 pp., illus. (Revised.) [Processed.]

1950. NAIL-HOLDING PROPERTIES OF SOUTHERN HARDWOODS. South.

Lumberman 181 (2273): 208-210

(26) AND MOLANDER, E. G.

1950. STRENGTH OF NAILED JOINTS IN FRAME WALLS. Agr. Engin.

31 (11): 551-555.

(27) STERN, E. G.

1940. A STUDY OF LUMBER AND PLYWOOD JOINTS WITH METAL SPLIT-RING

CONNECTORS. Pa. Eugiu. Expt. Sta. Bui. 53, 90 pp., illus.

(28)

1950. IMPROVED NAILS FOR BUILDING CONSTRUCTION. Va. Polvtech.

Inst., Engin. Expt. Sta. Bui. 76, 23 pp.

(29)

1950. NAILS IN END-GRAIN LUMBER. Timber News and Machine A\ oodworker 58 (2138): 490-492, illus.

(30) TRAYER, G. W.

1932. BEARING STRENGTH OF WOOD UNDER BOLTS. U. S. Dcpt. Agr.

Tech. Bui. 332, 40 pp., illus.

(31) U. S. FOREST PRODUCTS LABORATORY.

1931. NAIL-HOLDING POWER OF AMERICAN WOODS. U. S. ForCSt Prod.

Lab. Tech. Note 236, 4 pp., illus. [Processed.]

(32)

1940. GENERAL OBSERVATIONS ON THE NAILINCi OF WOOD. I. S. ForCSt

Prod. Lab. Tech. Note 243, 2 pp. [Processed.]

(33)

1941. NAILING DENSE HARDWOODS. U. S. Forcst Prod. Lab. Tech. Note

247, 3 pp. [Processed.]

(34) U. S. HOUSING AND HOME FINANCE AGENCY.

1947. TECHNIQUE OF HOUSE NAILING. 53 pp., iUuS.
SOLID AND BUILT-UP STRUCTURAL MEMBERS

Wood structures take many forms, and it is beyond the scope of

this publication to treat each one in detail. This section deals only

with fundamental considerations related to the simplei* structural

elements, such as beams and columns. Industry recommenihations

covering' the design, fabrication, and erection of timber structures are

discussed in Standards for Timber Construction (7).^^

SOLID BEAMS OF RECTANGULAR CROSS SECTION

Wood beams are usually of rectangular section and of uniform

depth throughout their span. They should be so designed that the

following stresses do not exceed the allowable unit values: (1) The

extreme fiber stress caused b}^ flexural loads; (2) the maximum

horizontal shear stress; and (3) the stress in compression across the

grain at the end bearings. Beams should also be so designed that their

deflection under load will not exceed the limit fixed by the intended

use of the structure. If actual and nominal sizes of lumber differ, the

allowable unit values must be used with the actual sizes.

Extreme Fiber Stress

Either the ultimate bending strength or the safe load for a wood

beam of rectangular cross section ma}^ })e calculated from the formula

o

where M is the bending moment in inch-pounds, 7^ is a form or depth

factor,/is the unit flexural stress in the extreme fiber in pounds per

square inch, and b is the width and d is the depth of the beam in inches.

If the ultimate bending strength is desired,/ is the modulus of rupture.

If the safe load is desired,/is the safe flexural stress for the kind and

grade of material used. In either case, M must be expressed in terms

of the load and the span in order to calculate the stress. For example,

if a simply supported beam has a total load W uniformly distributed

over a span i,

^^^^

If the beam has a concentrated load P at the center of the span,

-^^ 4

1^ Italic numbers in parentheses refer to Literature Cited, p. 2;i0.

203 303747°—55 14
204 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Depth Factor

A depth factor is introduced in the basic design formula for rectangular beams to take into account the somewhat lower unit strength

developed in deep beams as compared to shallow beams. In arriving

at the basic stress values for bending strength in table 25, a depth

factor was assumed that corresponds approximately to a 12-inch depth

of beam. In most designs of structural lumber beams of rectangular

shape, if working stresses derived from the basic stress values of that

table are used, no further adjustment for depth is necessary; that is,

the basic formula can be used in the form

6

If the depth of a rectangular beam is more than 16 inches, an additional depth factor should be calculated by the formula of page 258.

That formula is for use with the basic stress values of table 25 and

therefore gives a factor of unity when the depth is 12 inches.

Combined Loading Effects

If flexural stress in the extreme fiber is combined with direct stress

resulting from the application of end compression or tension, the

combined stress is determined by algebraic addition of the acting

stresses. For example, compressive stress is added to bending stress

in the upper fiber of a beam and subtracted from bending stress in

the lower fiber of the beam. Stresses so combined should not exceed

allowable values given by the following formulas.

If a transversely loaded beam is also under end compression and is

stayed against lateral buckling, the allowable stress is such that

PIA MIS_^

c + /

where FjA is the unit direct stress induced by axial load in compression

parallel to gram (P is the axial compressive load and A is the area of

the cross section), AIjS is the flexural stress induced in bending (i\/is

the bending moment and S is the section modulus, equal to 6¿76 in a

rectangular beam), c is the allowable working stress in compression

parallel to grain, and / is the allowable working stress in bending.

PIA As the end compression approaches zero, the term —^ also approaches

c

zero and the preceding equation approaches

MIS^

/

or

O

the basic formula for flexural stress.
WOOD HANDBOOK 205

If the unit stress from end compression is large in comparison

with the flexural stress and lateral buckling is possil)le, the beam

should be designed as a column with side loads bv the methods o-iven

on page 219. ' ^

If a transversely loaded beam is also in axial tension, tlie allowable

stress is such that

t '^ f

where P/A is the unit direct stress induced by axial load in tension,

t is the allowable working stress in tension parahel to grain, and M/S

and/are as previously defined. In many cases / and f have the same

value ftable 25), and the equation becomes

P/A+ .\f/S=l=J

Horizontal Shear in Beams

The general formula for horizontal shear in beams is

VQ

in which all units are in inches or pounds, q is the maximum liorizontal shearing stress, Q is the statical moment of the area either

above or below the neutral axis and about that axis (as used here,

statical moment is a product of an area and the distance from the

center of gravity of that area to an axis), Fis the external or vertical

shear, / is the moment of inertia of the section about the neutral

axis, and t is the width of the beam at the neutral axis.

For a rectangular beam b inches wide and d inches (hu^p, the general

formula becomes

_3F

^ 267/

Stress Concentration Effects

Shearing stress is increased at certain locations in a beam l)ecause

of stress concentration effects. The most common concentration of

stress is at the base of shakes, checks, or s])lits, where there is an

abrupt change of cross section. This concentration causes slunir failures in beams at relatively low stress values, even when calculated

on the net cross section after deduction of the area of actual opening.

Since checking occurs to some extent in practically all striu'tural

beams, a large factor for stress concentration was introduced in the

basic shear stress values of table 25.

Another shear stress concentration may occur immediately adjacent

to points of application of a concentrated load or reaction. Such a

concentration is not common, because allowal)le bearing values in

compression perpendicular to grain ordinarily require fairly large

bearing areas; furthermore, building regulations usually specify
206 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

minimum lengths of bearing that do not result in critical stress

concentrations. Special cases involving apphcations of load or

reaction to aieas measuring one-half inch or less in length should be

examined for stress concentration effects (16).

Shear in Checked Beams

Because the upper and lower parts of a beam checked near the neutral

axis act partly as two beams and partly as a unit, a part of the end

reaction is resisted internally by each half of the beam acting independently and consequently is not associated with shearing stress at

the neutral plane (12). In using the basic formula for horizontal

shear, in which b is the full width of the beam and q the allowable unit

shear stress based on the assumption that checks are present, allowance for two-beam action should be made in calculating the allowable vertical shear V.

The following procedure is recommended for calculating the

horizontal shear on the neutral plane in checked beams:

(1) Use the basic shear formula as given.

(2) Use for the allowable shearing stress a working stress value

derived from the appropriate basic sti'ess in table 25.

(3) In calculating the reactions represented by the vertical shear

value V in the formula, (a) take into account any relief to the beam

under consideration resulting from the load being distributed to

adjacent parallel beams by flooring (p. 209) or other members of the

construction, (b) neglect all loads within a distance from both supports equal to the height of the l)eam, (c) if there are any moving

loads, place the largest one at a distance from the support equal to

three times the height of the l)eam, and (d) treat all other loads in

the usual manner. If a timber does not qualify for shear resistance

under the foregoing procedure, which under certain conditions may

be overconservative, the reactions for the concentrated loads should

be more accurately determined by the following equation:

91

in which r' is the reaction to be used as due to a load P' ; Z, the span

in inches; x\ the distance in inches from the reaction to the load P';

and h, the height of the beam in inches.

Compression Across the Grain

The area of end bearing should be such. that the unit stress in

compression perpendicular to grain does not exceed the allowable

value given in table 25. The stresses in compression perpendicular

to grain given in that table apply to bearings of any length at the

ends of a beam and to bearings 6 inches or more in length at any other

place along the beam. They may be increased when applied to

small plates and washers as explained on page 163. In calculating
WOOD HANDBOOK 207

the bearing area at the ends of beams, no allowance need be niadc^ for

the fact that, as the beam bends, the j^ressure upon the inside edge of

the bearing is greater than that at the opposite edge. The wood

yields enough so that the pressures become eciualized before serious

damage occurs.

Deflections of Beams

When service conditions require that l)eams be designed for stiiïness, the dimensions are determined })y applying the usual deflection

formulas, the deflection being kept within a prescribed fraction of the

span. The deflection is often limited to one three-bun(h-ed-sixtieth

of the span of framing over plastered ceilings and over unplastered

ceilings to one two-hundred-fortieth of the span. A ratio of one

two-hundreth of the span has been used for highway bridges, but some

engineers advocate a more severe limitation. A commonly I'ccorded

limitation for stringers in railroad bridges and trestles is one threehundreth of the span. For floors that support shafting, deflection

limitations much more severe than the preceding are sometimes

required.

Wood l)eams usually sag in time; that is, the deflection increases

beyond what it was immediately after the load was first applied.

Green timbers, especially, will sag if allowed to season under load,

although partially seasoned material will also sag to some extent.

In thoroughly seasoned beams, there are small changes in deflection

with changes in moisture content but little pennanent increase in

deflection.

Calculations from the values for modulus of elasticity in table 25

will give the initial deflection of a beam. If deflection under longtime load is to be limited, it is customary to design for an initial

deflection of about one-half the value permitted for long-time deflection. This can be done by doubling any long-tijue loads when calculating deflection, by using one-half the values given in table 25 for

modulus of elasticity, or by any equivalent method.

Notched Beams

Beams are often notched at the ends to improve clearance or to

bring the top surfaces level with adjacent beams or girders (flg. 38).

Occasionally they are also notched at intermediate points, either

bottom or top, in order to clear other parts of a structure or to receive

other members.

When notched on the lower side at the ends (flg. 38, A), the strength

of a short, relatively deep beam is decreased by an amount depending

on the shape of the notch and on the relation of the depth of the notch

to the depth of the beam. It is recommended that in designing

beams with square-cornered notches at the ends of the beams the

desired bending load be checked against the load o})tained by the

equation

y^22/öde~J\ /bde'rr

"3W y
208 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

^ - ,-

f

1

1 1 Si

h^i

NET DEPTH

ZM 91876 F

FIGURE 38.—Notched beams: A, Notched at ends to one-half depth of beanij

B, beam with gradual change in cross section at ends to eliminate concentration

of stress; C, notched on the upper side; D, beveled on the upper side; E^ notched

to one-half depth of beam at center.

where V is the vertical shear, 6, the width of the beam; dg, the actual

end depth above the notch; c/, the total depth of the beam; and g, the

w^orking stress in horizontal shear.

In setting up this equation the actual end depth is used as the

effective depth to resist shear, and the safe shear stress is reduced by

multiplying it by the ratio of the effective depth to the total depth.

Experiments made at the Forest Products Laboratory on short deep

beams with relatively high shearing stresses substantiate this recommendation {IS), The experiments also showed that by cutting away
WOOD HANDBOOK 209

the lower corner at the end notches, in order to obtain a gradual

change m cross section, the breaking loads were raised very markedly

(fi^. 38, 5).

Beams are occasionally notched or beveled on the ui)per side

(figs. 38, C, 38, D), and these beams present a less sevei'e condition

from the standpoint of stress concentration eíF(H*ts than b(^ams

notched or beveled on the lower side. Expt^riments with notches on

the upper side indicate that shear stress should be checked with the

formula

'-^''[-("/)']

where V is the vertical or ext(4'nal shear; q is the working stress m

shear; b is the width and d is the (h^pth of the beam; d^ is the (h'pth

below the notch; and e is the distance that the notch extends insi(h^

the inner edge of the support. If e exceeds c/, this formuhi is not

used; rather, the shear strength is evaluated on the basis of the depth

of the beam below the notch, de. For a beam with a bevel on tlie

upper side (fig. 38, D) instead of a square notch, de is taken as the

height of the beam at the inner edge of the support and e as the

distance from the support to the start of the bevel. The depth of a

notch on the upper side should in no case exceed 40 percent of the

depth d of the beam.

AVhen notches are at or near the middle of the length of a beam

(fig. 38, E), the net depth should be used in determining the bending

strength. Tests have shown that, as far as breaking loads ai-e concerned, this rule is sufficiently conservative. The general tendency,

however, of a notch on the top or bottom of a beam and near the

point of maximum moment is to lower the proportional limit load and

to start compression or tension failure at lower loads than would be

expected of an unnotched beam of a depth equal to the net depth of

the notched beam.

The stiffness of a beam is practically unaffected by notches.

Distribution of Concentrated Load Between Joists

Tests at the Forest Products Laboratory indicate that loads up

to 400 pounds concentrated on an area of ]i square foot of a conventional dwelling floor system are distributed laterally for a consick^-able

distance with only 20 to 30 percent carried by the joist directly uncU^r

the load. The floor system in the tests consisted of joists, bridging, a

diagonally laid subfloor, and a 1-inch finish floor laid across the

joists. The load was applied at midspan.

The general problem of load distribution has been extensively

investigated, particularly with reference to moving loads on brklge

floor systems (5, 10). Recommendations from those investigations

indicate that about YA to V2 of a concentrated load on a joisted floor may

be carried by the joist under the load. The proportion is higher when

the loaded joist is near the side of the floor system than when it is

at the center. Plank floors on beams that are spaced 5 or more feet

apart show Httle or no distribution of load to beams other than the

one directly under the load.
210 ÏÎAXDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

SOLID BEAMS OF CIRCULAR SECTION AND OF SQUARE

SECTION WITH A DIAGONAL VERTICAL

Such wood members as poles and masts usually have circular cross

sections, and sometimes ordinaiy beams and columns are of circular

section. For architectural effects, a wood beam of square cross section

is sometimes placed with a diagonal of the section vertical. Iri calculating the bending- stn^ngth of such members, it is necessary to include

a form factor in the beam formula.

The design formula for a beam of circular section is

4

where 1\I is the bending moment, F is the form factor,/ is the unit

ilexural stress in the outer liber, and r is the radius of the cross section.

The form factor F for a circular wood beam has a value of 1.18, and

the formula then becomes

4

If circular wood beams have an api)reciable taper, the maximum

value for stress in the outer fiber under uniformly distributed load, as

in a joist or rafter, occurs away from the center of the span toward the

small end of the beam. The location of maximum stress varies with

the taper, being at midspan with no taper and at a distance from the

small end of 0.27 times the span if the small end has one-half the

diameter of the large end. With a single concentrated load a t midspan,

the maximum stress occurs at mids])an unless the small end has less

than one-half the diameter of the large end.

Wood poles set in the ground are designed as vertical tapered cantilever beams. It can be shown that, if a horizontal force is applied at

the top end of the pole, the maximum stress occurs where the diameter

is 1/2 times the top diameter. With forces uniformh^ distributed along

the pole, the maximum stress occurs where the diameter is 3 times the

top diameter. If application of either of these rules indicates that

the maximum stress is below the ground line, the maximum stress will

occur at the ground line.

The design formula for a beam of square cross section placed so that

a diagonal of the section is vertical is

where M is the bending moment, F is the form factor, / is the unit

flexura! stress in the outer fiber, and a is the side of the square.

The form factor F for a square beam \y'\Ú\ a diagonal vertical has a

value of 1.414, and the formula then becomes

.. 1.414 fa^ fa^ M=—_—^ - =- —
WOOD HANDBOOK 211

It can be shown from the preceding formulas that a beam of sqiiaîc

cross section has the same bending strength whether placed in the

usual manner or with a diagonal of the section veitical and that a

circular beam (without taper) has the same strength as a square beam

of the same cross-sectional area.

BUILT-UP BEAMS WITH MECHANICAL FASTENINGS

Beams are sometimes built up from lumber of relatively small

dimensions in order to (1) utilize small pieces of lumber, (2) reduce

seasoning degrade, and (3) eliminate knots or other strength-reducing

features. Two general methods are emplo3^ed: (1) Several pieces of

the same depth, but relatively thin, may be placed side by side and

spiked or bolted together, either with or without intervening spaces;

(2) two or more pieces of the same width may be placed on top of each

other and bolted or otherwise fastened together with keys to transmit

the shear stress, or fastened together by continuous sheathing on the

sides, or glued.

The following discussion is restricted to built-up beams with

mechanical fastenings. Glued laminated beams are discussed on

pages 247-263.

Vertically Laminated Beams

Laminated beams with the laminations vertical and bolted together,

in tests at the Forest Products Laboratory (4), were as strong and stiff

as solid beams of the same external dimensions. The laminated

beams tested consisted of 5 nominal 2- by 12-inch planks each 16 feet

long fastened together side by side with bolts spaced as indicated in

figure 39. They were practically free from such features as knots,

but about one-half of the pieces contained seasoning checks. The

solid beams were dense and of a high structural grade.

As a rule, the stiffer planks in a vertically laminated beam take a

larger percentage of the load than those less stiff. First failure, however, usually occurs in the piece with the largest knot or other strengthreducing feature, regardless of its stiffness.

The planks must be well fastened together in order to prevent

buckling of individual planks. If spikes are employed, through bolts

or bolts and connectors should be provided. Spikes are seldom used

for beams more than 10 inches in depth without through bolts. It is

-45

Ô'O -

—>1< 45-r'- -45

- 8-0

>\< 45 ^6

\--^^í- 45 -45 45' -^^ZZiZM 22052 F

FIGURE 39.—Bolt spacing of beams with vertical laminations used in tests at

the Forest Products Laboratory.
212 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

good practice also to place two bolts at each end of the beam, as shown

in figure 39. i_ • i.

A girder is sometimes built of one or more full-length members with

narrow pieces nailed or spiked between or on the side of the members

in a diagonal position, forming a flat inverted V (fig. 40, A). Tests

show that narrow pieces so nailed add little or nothing to the strength

or stiftness of the girder (5). If a girder consists of two full-length

outside laminations with a full-width center lamination butt-jointed

at the center of the span (fig. 40, B), the butt-jointed lamination adds

to the girder about one-half as much strength and stiffness as a fullleno-th lamination would add.

/I

SIDE VIEW

TOP VIEW

B

SIDE VIEW

ZM 91877 F

FIGURE 40.—yl, girders with narrow pieces nailed diagonally; B, a butt-jointed

center lamination.

Sheathed Beams

A sheathed compoimd beam may be made of diagonal boards or

planks nailed to each side of two timbers placed one on top of the

other (fig. 41). The diagonal sheathing runs in opposite directions

on the tw^o sides. In tests (7), the efficiency of beams of this type

for a span-depth ratio of 12 was about 70 percent and for a ratio of 24

about 80 percent as compared to the strength of solid beams of the

same size. Deflections of the sheathed beams, however, were about

double those of the solid beams.

Long before a beam broke in these tests, the diagonals split open

or the nails were partly drawn out or bent over the wood, thereby

permitting the two timbers to slide on each other. Beams of this type

should not be used where the increased deflection would be objectionable.
WOOD HANDBOOK 213

2M 22050 F

FIGURE 41.—A sheathed compouncl i)eani com]:>ose(l of cUa^onal boards or planks

nailed to each side of two tiinl>ers.

Keyed Beams

In a keyed compound l)eani the shear l)etween adjacent timl)ers is

taken by wood or metal k(\ys, and the timbei's are fastened together

with bolts, as in figure 42. Kidwell (7) tested several types of keyed

beams and recommended that for ordinary piuposes an efficiency of

75 percent be allow^ed when oak keys are used and 80 percent when

cast iron keys are used. He gave formulas for the number and spacing

of keys. This information may also be found in books on timber

framing (6). The keys are sometimes tapered like wedges, so that

a driving fit may be obtainc^d (fig. 42), but they are also made of

flat plates or blocks without taper, sometimes known as tables.

Connectors of the toothed-plate, toothed-ring, or split-ring type

(p. 187) are suitable for keys of compound beams. Tests at the Forest

Products Laboratory indicated efficiencies up to 85 percent in strength

for keyed beams with split-ring connectors spaced 6 inclues along the

beam length. Deflections were apprecialfly greater than for one-piece

beams.

Well-seasoned timber should be used in the construction of keyed

beams and o'reat care exercised in framing.

1 ' /' 1

1 1 / ' 1 0 /

'i ' '1

/ @ /

1 Mi 1 ^ j_

_.Q^ .Ci_ r^^^. _£i.

--o- -CZK4

"W

--o--

^^ ~^^

ZM 22075 F

FIGURE 42.—A keyed compound beam in which the shear between adjacent

timbers is taken }\y wood or metal keys.
214 PTAXDBOOK 72^ U. S. DEPARTMENT OF AGRICULTURE

Composite Beams or Slabs

Composite beams or slabs can be made of lumber in combination

with other structural materials {15). Bridge decks have been made

with a base of lamijiated luml)er covered with a concrete mat several

inches thick. The luml)er base is composed of alternating wide and

narrow longitudinal i)lanks, spiked, l)olted, or dowx^ed together and

sometimes prefabricated in panels 2 to 4 feet wide. The wide planks

a;i'e grooved and milled, with concrete filling the recesses to form keys

that transmit horizontal shear and prevent uplift of the concrete from

the wood. The concrete^ is lightl}^ reuiforced against temperature

and shriidvage stresses, or, in continuous spans, may be reinforced for

tensile sti'esses. The hnnber base must be d(^signed to carry the load

of green concr(»te until the concrete has set and can contribute to the

strength of the deck. The ])laiiks should have preservative treatment,

since moisture may enter the joints and provide conditions favorable

to decay. Figure 43 shows a typical cross section of such a composite

deck.

•:'^-".'-é-'.^

c

p' '.'>'. ' '^

• •^' .'

. : .

^-^1.

-m. • '<> •

ïm-ïr

m

'^'^^w'^

TRANSVERSE SECTION

DETAIL OF WIDE PLANK

M 93470 F

FIGURE 43.—Construction of a composite wood-concrete deck. The transverse

section shows: .1, Laminated him])er base of wide and narrow planks; B,

twisted transverse dowel for holdino; planks together; C, concrete mat with

remforcmg- bars. The upper portions of tlie wide planks are milled and k)ngitudmally grooved, as shown in the detail, to provide kevs that transmit horizontal shear and prevent separation of the concrete from'the wood.
WOOD HANDBOOK 215

Trussed Beams

Trussed beams can be economically used for long- spans and Inrg-e

loads when headroom permits. In the simplest I'oi-m (iio-. 44, .1) the

wood beam is supported at the center by a single wood strut or kingpost, which in turn is supported by metal tie rods ])assing up to^a

thick steel pkte at each end of the beam. To avoid secojidary stresses

the centerhnes of beam, rod, and end su])port should int(M-sect in a

point. If the avaihi.bk^ headroom is above the beam the trussed l)eam

ilhistrated in figure 44, B may ])e USIHI.

For the greater spans, or whert^ headroom is snuill or loads ar(^

concentrated at two intermediate^ l)oints, queen trussc^s (Hgs. 44, C,

44, D) are preferable to king trusses.

Sometimes 2 tie rods are used with a single beam, 1 being placed on

each side. Also, 2 beams may have a. single^ rod between them or :>

beams may have 2 rods between them. It is desirable to give the

assembly as much depth as conditions permit in order to rechice the

stresses. Greater stability is obtained with beams continuous for tlu'

full span than with beams jointed over the struts.

Stresses in the beam itself and in tlu* reinforcing struts or rods (tig.

44) can be calculated in terms of loads or reactions by the principles of

stress analvsis as set forth in textbooks on sti'uctural design.

t:^

^^-^.

' M ZM 22073 F

FIGURE 44.—.4 and B, ]vin,ü¡ types of trussed l^eanis; C and D, queen types.

LATERAL SUPPORT OF BEAMS

Deep narrow beams are laterally unstable and require resti'aint

against sidewise buckling. In floor joists, buckling is prevented by

diagonal or other bridging between joists or by the flooring nailed to

the joists. The following approximate rules are I'cconunended:

(1) If the ratio of depth to breadth does not exceed 2, no lateral support is needed.
216 HAXDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

(2) If the ratio is :3, the ends shoukl be hekl in position.

(:]) If the ratio is 4, the piece should be held in line by spiking or

bolting as in a vei'tically laminated beam.

(4) If the ratio is 5, one edge should be held in line, as by flooring

nailed to the edge of a joist.

(5) If the ratio is 6, diagonal bridging as in floor joists should be

used.

(G) If the ratio is 7, both edges should be held in line.

(7) If a beam is subject to both flexure and compression parallel to

grain, the ratio of depth to breadth may be as much as 5, if one edge

is held firmly in line, for example, by rafters (or by roof joists) and

diagonal sheathing. If the dead load is sufficient to induce tension

on the under side of rafters, the ratio may be as high as 6.

Additional rules apply to the design of roof truss membc^rs that are

subjected to com})ine(l flexure and compression {10).

Special conditions of lateral instability may require a more refined

method of analysis {17) than is afforded b}^ the foregoing approximate

rules.

SOLID WOOD COLUMNS OF RECTANGULAR CROSS

SECTION

Length Classes

Solid wood columns fall into three length classes characterized by

the type of failure. When the length does not exceed 11 times the

least dimension, failure is by crushing. At lengths between 11 and K

times the least dimension, failure is a combination of crushing and

lateral buckling {11). The significance of K is explained in the following paragraphs. Beyond this range, wood columns generally fail

by lateral deflection or buckling, behaving essentiall}^ as Euler columns.

Since most wood columns are rectangular or square in section, the

ratio of unsupported length to least dimension, or the slenderness

ratio, is commonly expressed as Ljd, in which L is the unsupported

length in inches and d the least side in inches.

For short columns or posts, that is, the first class of columns with

Ljd ratios of 11 or less, the same unit stress is recommended for all

lengths. For these columns

P

in which PIA is the working stress for the column and c is the safe unit

compressive stress parallel to the grain for the grade of material and

the loading condition under consideration. Basic stresses from which

safe working stresses {c) are derived are given in table 25.

For columns of the intermediate class, that is, with Ljd ratios

between 11 and Kj the following formula {11) is recommended:

5^c.r.-ic¿ v-nm
WOOD HANDBOOK 217

in which PIA and c have the same meaning- as b(^fore and K is a constant depending upon c and the modiiUis of eLasticity. The vahu^ K

is the minimum vahie of Lid at which the cohimn will behave as a

Euler column. This value is obtained when

A :^

In the Euler formula for lono- columns (S(M^ followino- paraoranh)

PIA has th(^ valu(^ 2c/:] when ^ i . i ^

L

1 2 V (>^*

where Z? is the modulus of elasticity. If this value oï Lid is desio-natcd

as K and a rechiction factor of :> is introduced foi' E, tlu^n

Ë

^^-iVi--Vf

Values of E are given in table 25.

Foi' columns with Lid ratios equal to /v or greater, the Euler formula

with a recbiction factor of :] is:

P_0. 274/Í

.1"" mÍLX'~

The values of c (table 25) used in the formulas for short and for intermediate columns have safety factors about equivalent to that in the

Euler formula.

The reduction factor of 3 is applied to the Euler maximum load and

in the formula for determining K to convert from laboratory test conditions to the conditions of use (including long-time loading) and to

provide a factor of safety. Conditions of ordinary hazard to columns

as primary structural members are assumed. Conditions of extraordinary hazard or danger to human life may require that a larger

safety factor be obtained through a reduced working stress value.

Conversely, in situations of more limited hazard, or where property

damage only may be involved, the designer may economize with a

smaller factor of safety by increasing the working stress. Columns

to be used continuously dry or subjected to short-time periods of

loading may be designed with somewhat less reduction from the Euler

breaking load (see pp, 158-161) without encroaching on the safety

factor.

The slenderness ratio (Lid) of a solid wood column should in no case

exceed 50.

Exam/pies: Calculate the safe load for a 10- by 10-inch column if its

grade and loading condition are such that c and E are 1,300 and

1,600,000 pounds per square inch, respectively, and the column is (1)

8 feet long; (2) 14 feet long; (3) 20 feet long. The actual dhnensions

of the 10- by 10-inch timber are 9}^ by 9}^ inches.
218 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

For a length of S feet the column has a slenderness ratio of 10 and

is therefore within the sliort-cohunn class. The unit stress c is multiplied l)y the area to give the safe load:

9)^X9)^X1,300=117;300 pounds

In calculating the safe load for the 14-foot column, Ä'must first be

determined and then the Ljd ratio, which if less than K places the

column in the intermediate-length class. Since i? is 1,600,000 pounds

per square inch,

^=^^-^^W 1,:U)0 =-^

For a l(Migth of 14 feet the Ljd ratio is

14X12 ,^^

wdiich is between 11 and 22.4. The column is therefore in the intermediate class and

P

-r=l,:]()()

[>-i(M)l

1,130 pounds per square inch.

The safe load is:

9)^X0)^X1,130=102,000 pounds

With a 20-foot length Ljd is 25.3, wdiicli is gi'eater than K, and the

column is in the Euler class. Then

P^O. 274X1,000,000

.1" (25.3)^

= GS5 pounds ])er square inch

and the safe load is:

9):;X9UX685 = 61,800 pounds

Alternate Design Method

W[\ÚQ ultimate str(4igth values in wood columns show that the

three length classes exist, design at the working stress level is sometimes simplified by omitting the intermediate class and using the longcolumn formida for all lengths that give values not exceeding the safe

stress on short columns {10). Working stresses by this method range

from 0 to 15 percent higher than those calculated by the preceding

formulas for intermediate columns.
WOOD HANDBOOK 219

Side Loads and Eccentricity

The general formulas for safe eccentric or combined side and end

loadmgs of wood columns as developed by Newlin (21) are

P/A(^)+M/S+,P/A

J c

for columns with slenderuess ratios of 11 or less, and

f-P/A + c -^

for columns with slenderness ratios of 20 or more, where P/A is the

direct compressive stress induced by axial load; AÍ/S, the flexuralstress

induced by side loads that are independent of end load; c, the allowable unit working stress in compression parallel to grain for a column

of the slenderness ratio under consideration, but with centrally applied

axial load and no side load ; /, the allowable unit working stress in

flexure that is permitted where only flexural stress exists; e, the eccentricity; r/, the width of column, measured in the direction of side loads

or eccentricity (equivalent to the depth when the column is considered

as a beam subject to flexural forces); and z, the ratio of flexural to

direct compressive stress when both result from the same loading

(remains constant while load varies).

Stresses for columns with slenderness ratios between 11 and 20 are

determined by straight-line interpolation between the formula for a

slenderness ratio of 11 and the formula for a slenderness ratio of 20.

These formulas may be simplified for some conditions of loading

by dropping out certain terms; for example, if there are side loads and

a concentrically applied end load, e becomes zero, and the first term

in the numerator of the equations disappears. The formulas can be

solved for P/A or for M/S if this will facilitate their use. Solution of

the second formula for P/A leads to a quadratic equation with two

roots; the root giving the smaller numerical value to P/A should be

used.

These formulas are applicable only to columns of square or rectangular cross section.

If the side loads are such that maximum deflection and maximum

flexural stress do not occur at midlength of the column, it is generally

satisfactory to consider M/S as the maximum flexural stress due to the

load or loads, regardless of its position in the length of the column.

When the point of this maximum stress is near the end of the column,

a slight error on the side of overload will occur.

Columns With Side Brackets

Formulas for eccentric loading assume that the eccentric load is

applied at the end of the column. If an eccentric load is applied

by a bracket at some point below the upper end, conditions of stress

808747° -55 15
220 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

and deflection are somewhat more favorable. An exact solution of

the problem is difficult, but the following simple rule is safe and, for

brackets in the upper quarter of the length of the column, is quite

acciu'ate.

Assume that a bracket load P at a distance a from the center of a

colunm (fig. 45) is replaced by the same load P centrally applied at

the top of the column plus a side load P] applied at midheiglit.

Calculate Pi from the foi'mula

P.=

:kiL,P

where L is the hwigtii of (lie column and Li is (he h^ngtli from the

})ottom of the column to tlu^ toj) of the l^i'acket. Take care that a, Z,

and Zi are expi'essed in the sanu.^ units of measurement.

The assumed centrally applied load P can be added to other column

loads, and the assumed side load Pi is US(M1 to calculate flexural stress

AIIS in the formula for side loads.

-t^i

ZM 91879 F

FicuRE 45.—A, Actual t)racket loading

of a column; B^ assumed equivalent

loading".

A B

BUILT-UP COLUMNS WITH MECHANICAL FASTENINGS

This section refers to built-up columns with pieces joined by nails,

bolts, or other mechanical fastenings. Glued laminated columns are

discussed on pages 252, 25G, 2G1, and 263.

Design of Rectangular Sections

No arrangement of pieces with any kind of mechanical fastenings

will make a built-up column fully equal in strength to a one-piece

column of comparable material and dimensions (^4)- Arrangements

with parallel planks and cover plates (fig. 46, ^4) or with planks boxed

around a solid core (fig. 46, B) give the following percentages of the

strength of a one-piece column of the same dimensions and quality:

L\d ratio:

6

10_-_

]4___

Slrenglh of

1-piece cofumn

{perce It!)

82

71

L/d ratio:—Continued

18

22

26__

SIreng/h of

I-piece column

{percent)

65

. 74

_._ 82
WOOD HANDBOOK 221

ZM 22045 F

FIGURE 46.—Two types of l)uilt-up columns: .1, K(l«;es

plates; B, })()xed solid core.

tied together with cover

For Ljd ratios of 10 or p^roater, these pcM-eentages appl}^ to both

built-up columns in which the individual pieces are full length and

columns in which butt-jointed pieces are used.

Compression Joints

Butt joints in comj^ression members shouhl be perpendicuhir to

the direction of stress and should be accurately cut and closely fitted.

In short posts {Ljd less than 10), pieces butted end to end fail at 75

to 80 percent of the crushing strength of full-length pieces. If the

joint in a short cohmin has full lateral support (such as ma}^ occur

in the compression members of trusses) and a metal plate not thinner

than 20 gage is tightly fitted between the butted pieces, no reduction

of compressive strength need be assumed {10).

Wrinkling or Twisting of Compression Members With

Thin Outstanding Flanges

Columns whose cross section includes thin outstanding Hanges or

parts (fig. 47) are elastically unstable {17). They can fail by wrinkling

of the outstanding part or l)^^ torsion of the whole section about its

own axis at loads less than those indicated b}^ the formulas on pages

216-218 for crushing or bending failure.

If an outstanding flange under a compressive load projects from a

column section that is high in torsional stifl'ness, the wrinkling stress

may be critical; that is, the outstanding part may wrinkle and make

the remaining section unsafe. The stress at which wrinkling may

occur is given by

p =0.07£p

where p is the critical wrinkling stress, E is the modulus of elasticity,

and h is the thickness and b the width of the outstanding flange.
222 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

B

'///,

ZZvVTZ///,///

////

ZM 23108 F

FIGURE 47.—Typical cross sections of compression members that may fail

through elastic instability: A, L-section: B, U-section; C, T-section; D, isection.

If one or more relatively wide and thin parts project from a compression member that does not have great torsional stiffness, the

member may twist about its own longitudinal axis. Such twisting is

likely to occur with sections like A of figure 47. The critical stress

is given by

p =0.044£' ^1

with notation as in the preceding equation. Resistance to twisting

can be increased above the value indicated in this equation by using

generous fillets in the internal angles of the section. ^ ^ The coefficients given in the equation for wrinkling and twistmg

were obtained from tests of Sitka spruce, but they are appUcable to

other species of wood without appreciable error. The rigidity of the

section may, in some instances, be such that the critical stress occurs
WOOD HANDBOOK 223

at a value between the values given by the wrinkling and twisting

formulas. For circumstances requiring precise design, reference

should be made to a more comprehensive discussion of the subject (17).

Stresses given by the formulas for wrinkling or twisting are critical

or failing stresses, and the unit stress on the compression member must

be kept below them. The amount of reduction or the factor of safety

required on the critical values is left for the structural designer to

determine on the basis of the particular conditions under which the

member is to be used.

Box Columns of Wood

Tests for strength of box columns of wood made at the Virginia

Polytechnic Institute (S) indicate that the dc^sign formulas for shoi't,

intermediate, and long columns, as on pages 21G-218, are applicable

to box columns of square cross section. Where L/d appears in the

formulas for intermediate or long solid columns, it is replaced by

L

for square box columns, c/i being the outside dimension and do the

inside dimension of the cross section of the box column. The formulas

were adapted, b}^ means of suitable reduction coefficients related to

the arrangement and fastening of members and the condition of end

fixity, to allow for load capacities somewhat lower than those of solid

columns of equal cross section. It was recommended that the ratio

of width to thickness of the side members of the 1)0X should not exceed

10. The work included an analysis of economics in the use of lumber

made possible by box-column design.

Spaced Columns

Spaced columns (fig. 48) consist essentiall}^ of two parallel compression members separated by spacer blocks and joined through those

blocks by means of timber connectors. The compression members

and the spacer blocks are often of the same thickness. The spaced

column may be used for the direct support of vertical loads, but often

appears as a chord or other member in a wood truss.

The compression members in spaced columns are characterized by

their slenderness ratio L/d, the ratio of the length, i, to the thickness

of one member, d (fig. 48). This ratio should not exceed 80. The

length L is the full length of a free-standing column, or the length

between panel points or other points of lateral support in a truss. A

load may be applied directly to the ends of the compression members,

in which case the end spacer blocks do not extend beyond the ends of

the column. In trusses, however, the end spacer blocks may extend

beyond the ends of the column, and the load may be applied through

them and their connectors to the compression members.

Connectors should be of a size and number to restrain differential

movement between the compression members. Since the forces

causing differential movements are less in short than in long spaced
224 HAXÜBOOK 72, U. S. Dí^PARTMEXT OF AGRICULTURE

FT

d^

d

Eim.

FicuRE 48.—A spaced column made

from two compression members

joined through spacer blocks by

means of timl)er connectors.

ZM 91880 F

columns, tiic coiiucctor reciuirements are correspondingly less. The

connector or connectors on each face of each end spacer block should

bear safely a load (p. 187) calculated by multiplying the cross-sectional

area of one compression member (without deduction for cuts made

to receive connectors) by the following unit stress values:

(1) For slenderness ratios of 11 or less, use 0 unit stress.

(2) For slenderness ratios of GO to 80, use one-fourth of the basic

stress value in compression parallel to grain for the species (table 25).

(3) For slenderness ratios between 11 and 60, use a unit stress

obtained by straight-line interpolation between 0 for a slenderness

ratio of 11 and tlie value for a slenderness ratio of 60.

Spacer blocks joined to the compression members by means of

connectors are required at both ends of the spaced column. A spacer

block at midlength or, in long coliunns, tw^o blocks at the one-third

points of length are also required. All spacer blocks must be of equal

thickness and at least as thick as the compression members. They

should, if possible, have the grain of w^ood running parallel to the

length of the compression members. The minimum length of the end

spacer blocks is determined by the end distances required by the

connectors (p. 196), and their width should be equal to or greater than

the width of the compression members. Middle blocks should be of

such size and so fastened as to insure that the compression members

will maintain their spacing under load. Spiking or bolting is generally

adequate for joining the middle blocks to the compression members.

Truss joint members may take the place of end or middle spacer

blocks if they meet the requirements for size, location, and number

and size of connectors.
WOOD HANDBOOK 225

Spaced columns are designed from the ordinary eokinm formulas of

pages216-218,considering each compression member as an misupported

simple column and taking the sum of the side loads for the two compression memhei-s. Certain modifications of the formulas are mad(^

to convert to spaced-column conditions. Test values show that loads

supported by compression members in the short-column class art^

limited by the net section of the meml)ers aiU^v (Unhiction of the cuts

made to receive the connectors and bolts. Loads on long cohimns

are not so limited. Further, there is a fixity factor that increpases the

strength of members in the long-cohinm but not in the short-column

class. The fixity factor is 2.5 if coimeciors in the erul spacc^r blocks

are at a distance of L/W or less from the end of the column and 3.0

if the connectors are between L/20 and L/W horn the end of the column

and the end blocks extend to the end of the column.

The fixity factor is most conveniently recognized in design by applying it to the value for E in the column formulas of pages 216-218.

The column formulas ])ecomc

for loníí columns, and

p, . ^0.274 FE

'^^~ ' (L/Jf

'''•'-« ['4 (¿,)'] P,

for intermediate columns, where

where 7^ is the fixity factor.

The load P calculated by either of these fornuilas must not CXCCîMI

the safe load on a short column of the same grade, and of net cross

section as reduced by connector or bolt hoicks. Where it is practical

to exclude knots from the connector areas, somewhat higher values

of P can be realized (10).

The compression members in spaced columns are usually of such

proportions that critical loads for long columns are governed by the

stiffness in a direction perpendiculai* to the wudth of those members.

If the compression members are not much wider than they are thick,

the stiffness in a direction parallel to their width may govern. It can

be shown that the strength of a long spaced column is the same for

both directions of bending when the ratio of width to thickness of the

compression members equals the square root of the fixity factor.

The required cross-sectional area and basic stress value for the

compression members are used as previously described to determine

the required number and size of connectors in the end spacer blocks.

These connectors in turn determine the minimum length of the end

spacer blocks.

The formulas for spaced columns give safe load values for long-time

loading and are subject to increase for shorter durations of load

(p. 160). Increases for drying (p. 158) are refiected in the values

chosen for E and c.
226 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

COLUMNS OF CIRCULAR CROSS SECTION

Round and square wood members of the same cross-sectional area

will carry the same loads in both bending and compression and will

have approximately the same stiffness. To compute the required

size of a round column, design first for a square column and then use

a round column of a diameter that will give an area equivalent to the

area of the square. If the column is tapered, the diameter for use as

(1 and for computing A in the Euler formula sliould be taken as the

diameter at a distance of one-third of the length from the smaller end.

This will give a diameter of a round column necessary to prevent

failure from buckling. The unit compressive stress at the small end

of the column that will result from the calculated load should also be

computed, since it must not exceed the allowable stress for a short

column.

BUILT-UP WOOD ARCHES WITH MECHANICAL

FASTENINGS

Horizontally Laminated Arches

Arches with mechanically joined laminations whose width is horizontal generally lack efficiency against thrust and ilexural loads.

Glued construction (p. 247) is best for horizontalh^ laminated arches.

If mechanical fastenings are used, horizontally laminated arches have

greater lateral stability than vertically laminated arches and are

occasionally alternated with the latter where this stability is an

important factor.

Vertically Laminated and Segmented Arches

Curved segmented rafters or roof arches can be made b}^ joining

with bolts or spikes relatively short pieces of lumber with their width

vertical and upper edges bandsawed to a curved outline. A common

construction for rafters of this type is of 3 thicknesses of nominal

1-inch lumber (fig. 49).

Transverse joints at the ends of the segments of vertically laminated and segmented arches ti'ansmit no bending stress and only

limited compressive stress, so that design should be based on the net

unjointed section of the arch. Working stresses suitable for the

design of one-piece members of the same species and grade ma}^ be

used with that net section. For bending strength and stiffness, all

segments should extend through the full effective depth of the cross

section of the arch. Owing to the curvature of the member, stresses

at the ends of the segments are not parallel to the direction of grain;

if the radius of curvature is short, this fact should be taken into account

(p. 253) in setting the working stresses.

A segmented, laminated arch does not have a high degree of lateral

stability. If 1 of its edges is held firmly in line by the roof deck, the

ratio of the depth to the thickness of its cros*s section should not

exceed 5,
WOOD ITANDBOOK 227

ZM 91881 F

FIGURE 49.—Perspective view of a ])art of a vertically- laminatefl segmeiited

arch.

Tests of curved rafters at the Forest Products Lahoratoiy (20)

indicate that the same amount of lumber when hc^nt and g\\wd in

horizontal laminations is somewhat stiffer and consick^rably stronger

than when nailed in vertical laminations. Gluing of the nailed vertically laminated rafters improved both their strength and their

stiffness.

LAMELLA ROOFS

The lamella roof (fig. 50) is a curved roof framed by a system of

intersecting skewed arches made up of short segments of lumber

bolted at their intersections. The intersection of arches in two

directions adds to the strength and stübility against horizontal forces.

The multiplicity of joints in a lamella roof system permits considerable

vertical deformation under load, which should be taken into accoimt
228 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

in the design (19). Since the arches are skewed, their thrust has

components in both the transverse and longitudinal directions of the

huihiing. Transverse components are resisted by tie rods and braces,

as with conv(Mi(ional arches. Longitudinal components are resisted

by the longitudinally placed roof decking and by sill planks extending

h^igthwise of the buikhng.

-2-OR 3-PLY VERTICALLY

LAMINATED END ARCH

JOINTS BOLTED

AND NAILED

LAIVIELLA5

ROOF SHEATHING

(TONGUED AND

GROOVED)

SPACERS

-WEDGES ^SILL 2-INCH SILL PLANK

A

B ZDJ

FiouRE 50.—.1, Lam(41a roof plan; ß, side view of a lamella.

To minimize deformations in a lamella system, all joints should be

carefully fitted and well tightened. If lamellas are of unseasoned

wood, shrinkage in drying will permit slippage in each joint, which has

a cumulative effect of shortening the arch s^^stem. Such shortening

can be compensated by an additional camber or crown in the system
pwf

WOOD HANDBOOK 229

as first constructed. Use of well-seasoned lumber minimizes sueli

joint slippage and consequent change in shape.

Since lamella arches are commonly rather flat, it is im])ortaiit Ihnl

the}' be built to accurate line and contour if design assumptions are to

be valid (19). Falsework under the full length of span is i^etpiired for

support of the system during construction, as with other types of

built-in-place arclies.

TENSION MEMBERS

Unit design stresses for tension members ai'e derived from the basic

stress values in column 2 of table 25. Care should l)e taken that tlie

net cross section of tension membei-s at points cut or l)Oi'ed to receive

fastenings is adequate for the loads imposed. Tension naendjers,

unless very long, ordimirily do not require latei-al suppoi't.

POLE FRAMING

Pole framing (fig. 51) is one of the simplest types of building frames

used to give shape and stability to a building. In genei-al, it can be

adapted to any type of building (2, 9, 13, 22). It was used extensively by the pioneers of this country, but (hie to the short service life

of the poles and the cruch' construction methods, it bowed to other

types of construction as sawed luml)er and othei- materials became

available. In recent years, l)ecause of rising building costs and the

availability of methofls for making wood more diu-able, tiie use of pole

FIGURE 51.—A modern pole-frame V)arn under construction.

University of Wisconsin.)

(Plioto courtesy
230 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

framing' lias Ix'on revived. Because no foundation is needed and the

amount of bracing required is small, both labor and material costs arc

less for pole framing than for other types of framing'.

Pole-frame buildings are generally 1-story buildings with the poles

spaced from 10 to lo feet apart and set from 4 to 5^2 f('ot in the ground,

depending on the type of soil and the height of building. Plates and

girts are secured and braced to the poles to provide a skeleton frame

for the attachment of roof rafters and end and side wall sheathing.

Proper preservative treatment of the poles to resist decay and

termites (see p. 435) is essential if they are to serve as long as the other

parts of the structure. Firm soil oi- concrete footings are needed to

support the poles against settlement, and firm packing of the soil

about the poles is required for anchorage and stability. In general,

mechanical fastenings, such as nails and bolts, are used to secure the

plates, girts, and braces to the poles.

Poles in building frames act as columns in carrying the building

loads and as vertical beams in resisting wind or other horizontal forces.

Engineering principles of design for round columns (p. 226) and round

beams (p. 210) can be used where loads and stresses are known.

LITERATURE CITED

(1) AMICRICAX IXSTITCTE OF TIMBER COXSTRICTIOX.

11)54. TIMBER CONSTRUCTION STANDARDS 58 pj)., illus.

\\'a.sliinn;toii, I). (\

(2) BlCALOW, I. W.

1950. POLE BARX roxsTRicTiox. X. Y. Aí2;r. Col. (( orncll) Bui. 401,

0 pp., illus. [Processed.]

(o) BOOMSLITER, G. p., (\\THER, C. M., AXD \\oRRELL, D. T.

1951. DISTRIBUTIOX OF WHEEL LOADS OX A TIMBER BRIDO.E FLOOR. ^^'.

Va. Kiiiiiii. Kxpt. 8ta. Res. Bui. 24, 31 pp., illus.

(4) HECK, G. E.

1921. BUILT-UP SOUTHERX YELLOW PIXE TIMBERS TESTED FOR STREXOTH.

Nati. Lumber Mfrs. Assoc. Wood Construct. Inform. Serv. Ser.

E-2B, 9 pp., illus.

(5) —

1950. COMPARATIVE TESTS OF XAILED BUILT-UP BEAMS OF VARIOUS (OXsTRUCTioxs. South. Lumberman 180 (2260): 58, 60.

(6) JACOBY, H. S., AXD DAVIS, R. P.

1930. TIMBER DESIGX AXD COXSTRUCTIOX. Ed. 2, 234 pp., illus. New

York.

(7) KiDWELL, E.

1898. EFFiciEXCY OF BUILT-UP wooDEX BEAMS. Amer. lust Mining

Engin. 27: 732-818.

(8) KixzEY, B. Y., JR.

1950. WOOD BOX coLUMXs AXD THEIR DEsiox. Va. Polvtech. Inst.,

Wood Res. Lab., 15 pp., illus.

(9) MILLER, T. A. H.

1931. USE OF LOGS AND POLES IN FARM COXSTRUCTIOX. U. S. Dept. Agr.

Farmers' Bui. 1660, 25 pp., illus. (Slightly rev. 1948.)

(10) NATIONAL LUMBER MANUFACTURERS ASSOCIATION.

1953. NATIONAL DESIGN SPECIFICATION FOR STRESS-GRADE LUMBER AND

ITS FASTEXINGS. 66 pp., illus.

(11) XEWLIN, J. A,, AND GAHAGAN, J. M.

1930. TESTS OF LARGE TIMBER COLUMNS AND PRESENTATION OF THE

FOREST PRODUCTS LABORATORY COLUMN FORMULA. U. S. Dept.

Agr. Tech. Bui. 167, 44 pp., illus.
WOOD HANDBOOK 231

(12) NEWLIN, J. A., HECK, G. E., AND MARCH, H. W.

1934. NEW METHOD FOR CALCULATING LONGITUDINAL SHEAR IN CHECKED

WOODEN BEAMS. Atuer. Soc. Mech. Knjjin. Trans. 56 (lOV.

739-744.

(13) ROBINSON, D. D., AND ROSS, C. R.

1947. POLES AND FENCE POSTS FOR OREGON FARMS. OrCÍÍ. Ao;r. ('ol

Ext. Bui. 681, 24 pp., illus.

(14) SCHöLTEN, J. A.

1931. BUILT-UP WOOD COLUMNS CONSERVE LUMBER. 1MIü;ÍH. NoWS-lleC.

107 (9), 11 pp., illus.

(15) SCOFIELD, W. F. ,AND O'BRIEN, W. K.

1949. MODERN TIMBER ENGINEERING. Ed. 3, 147 pp., illus. South. Pino

Assoc.

(16) SMITH C. B., AND VOSS, A. W.

1948. STRESS DISTRIBUTION IN A BEAM OF ORTHOTROPIC MATERIAL SUBJEC'IED TO A CONCENTRATED LOAD. Xatl. AdvisOrV ConUH.

Aeronaut. Tech. Note NS6, 37 i)])., illus.

(17) TRAYER, G. W., AND MARCH, IE W.

1931. ELvVSTIC INSTABILITY OF MEMBERS HAVING SECTIONS COMMON IN

AIRCRAFT CONSTRUCTION. Nati. Advisorv Gonuu. Aeronaut.

Rpt. 382, 42 pp., illus.

(18) I^ S. FOREST PRODUCTS LABORATORY.

19)^5. ROUNDING NOTCHES MAKES STRONGER JOISTS. Auicr. Lumberman

3039: 46, illus.

(19) VON KARMAN, T.

ANALYSIS OF THE LAMELLA ROOF! (L) VERTICAL FORCES! (2) HORIZONTAL FORCES. 29 pp., illus. Gugtienheiin Aeronaut. La)).,

Galif. Inst. Teehnol., Pasadena.

(20) WILSON, T. R. C.

1939. GLUED LAMINATED WOODEN ARCH. U. S. Dei)t. A^r. Tech. Bui.

691, 122 pp., illus.

(21) WOOD, L. W.

1950. FORMULAS FOR COLUMNS WITH SIDE LOADS AND ECCENTRICITY.

U. S. Forest Prod. LaV). Rpt. R1782, 17 v)p., illus. (l^rocessed.]

(22) WOOLEY, J. G.

1952. REPAIRING AND CONSTRUCTING FARM BUILDINGS. 261 pp., illUS.

New York, N. Y.
GLUING OF WOOD

Gluing is done extensively in woodworking and in the pi'oduetion

of laminated wood (p. 247), plywood (p. 275)/and sandwich materials

(p. 291). Modern glues, processes, and techniques vary as widely as

the products made, and developments have been many in recent

years. In general, however, it remains true that the quality of a

glued joint depends upon (1) the khid of wood and its preparation for

use, (2) the kind and quality of the glue and its pi'eparation for use,

(3) the details of the gluuig process, (4) the types of joints, and (5)

the conditioning of the joints (7).^^ Depeiuling on the glue used,

service conditions also affect the performance of the joint to a greater

or lesser extent.

GLUING PROPERTIES OF DIFFERENT WOODS

Table 34 gives the gluing properties of the woods most widely used

for glued products. The classifications are based on the avei^agc

quality of side-grain joints of wood that is approximate!}^ average in

density for the species, when glued with animal, casein, starch, urea

resui, and resorcinol resin glues. A species is considered to be glued

satisfactorily when the strength of the jomt is approxmiately equal to

the strength of the wood (7).

Whether it will be easy or difficult to obtain a satisfactory joint

depends upon the density of the wood, the structure of the wood, the

presence of extractives or infiltrated materials in the wood, and tin*

kind of glue. In general, heavy woods are more difficult to glue than

lightweight woods, hardwoods are more difficult to glue than softwoods, and heartwood is more difficult than sapwood. Several species

varv considerablv in their gluing characteristics with difierent glues

(table 34).

GLUES USED IN WOODWORKING

Table 35 describes briefly the characteristics, prei)aiation, and uses

of the types of glue most commonly used to make joints in wood.

Animal glues (10) have long been used extensively hi woodworking;

starch glues came into general use, especially for veneering, early in

this century; casein glue (11) and vegetable protein glues, of which

soybean is the most important, gained commercial importance during

and immediately following World War I for gluing lumber and venetMinto products that required moderate water resistance. Synthetic

resin glues were developed more recently but now surpass many of

the older glues in importance as woodworking glues. Phenol resin

glues (9) are widely used to produce plywood for severe service conditions. Urea resin glues (12) are used extensively hi producing

plywood for furniture and interior paneling. Resorchiol (9) and

pÈenol-resorcinol resin glues are useful for gluing lumber into products

that will withstand exposure to the weather. Polyvinyl resm emulsion glues are used in assembly joints of furniture.

^^ Italic numbers in parentheses refer to Literature Cited, p. 245.

233
234 HANDBOOK

TABLE 34

í2, U. DEPARTMENT OF AGRICULTURE

Clas^ifivatioïi of various hordivood and softwood, species according to

(jliiing properties

HARDWOODS

(îroup 1

(fJliie very easily with

(lilïcrcnt íilucs under

wide r;iiip:e of gluing

conditions)

CJroui)

(i;iue well with diíTerent plues under a moderately wide range of , gluing eonditioris)

Tiroup 3

(Tilue satisfactorily under well-con tri)lled

gluing conditions)

Group 4

CRequire very close control of gluing conditions, or si)ecial treatment to obtain best

results)

vVspen.

Chestnut, American.

Cot ton wood.

Willow, black.

Yellow-poplar.

Alder, red.

BasswGod.i

Butlermit.' 2

Elm:

American. 2

Rock.' 2

Ilackberiy.

Magnolia,' 2

Mahogany.2

Sweet gum.1

Ash, while.2

Cherry, black.'

Dogwood. 2

Maple, soft.' 2

Oak:

Red.2

White.

Pecan.

Sycamore.' 2

Tupelo:

Black.'

Water.' 2

Walnut, black.

Beech, American.

lUrch, sweet and yellow.2

Hickory. 2

Maple, hard.

Osage-orange.

Pcrsinunon.

SOFTWOODS

Baldcyi>ress.

Cedar, w(>stern red-.3

Fir, white.

Larch, wester .

edwood.

Spruce, Sitka.

Cedar, eastern red-.2

1 Vjuglas-fir.

Hemlock, western.'^

Pine:

liastiM'u while.-^

Southern yellow.'

Ponderosa.

Cedar, Alaska

1 Species is more subject to starvecl joints, particularly with animal glue, than the classification would

()t.[ierwis(> indicate.

2 Cilued more easily with resin glues than with nom-esin glues.

3 Crliicd more easily with nonresin glues tlian with resin glucs.

Broadly, synthetic resin glues are of two types—tliermosetting and

thermoplastic. Thermosettiníí resins, once cured, are not softened by

heat. Thermoplastic resins will soften when reheated.

In addition to the major woodworking ghies listed in table o5, glues

made from a base of blood albumin have had vei'v limited use in the

United States but are more commonly used in Europe in the production

of plywood. They are mixed at the time of use and are applied at

room temperatures, but most of them require hot pressing. They are

highly water resistant but not so durable as some of the synthetic

resin glues. Defibrinated blood is sometimes used as a filler or extender for phenol resin glues.

Many brands of glues made from fish, animal, or vegetable derivatives are sold in liquid form, read}^ for application. Their principal

use in w^oodw^orking is for small jobs and repair work. They are variable in quality and low in w^ater resistance and durability under damp

conditions. The better brands are moderate in dry strength and set

fairly quickl}^ They are applied cold, usually by brush, and are

pressed cold. They stain w^ood only slightly, if at all.
WOOD HANDBOOK 235

GLUES FOR BONDING WOOD TO METAL

Glues capable of prodiicing bonds of hioh sUength and durability

between wood and metal are comparatively nc^w in woodworking.

Many of them are combinations of a thei-mosetting resin, often of ihc

phenolic type, and a thermoplastic resin oi- ehistonier, such as a polyvin3d resin or synthetic rubber (3). The vehicle may be wntw, alcohol,

eth}^ acetate, or some other solvent.

Some of these wood-metal adhesives are si)read on one or both of the

surfaces to be bonded, the solvent is evapoi'ated, and the bonding opcM'-

ation is completed under heat and prc^ssure. With other wood-metal

adhesives, the bonding is done in 2 steps, usually with 2 diirei'ent adhesives. In the first step, one* adhesive is s¡)rea(l as a pi'imer on the

metal and cured at elevated temperatures. In the second step, the

primed metal is bonded to the wood with a room-tcmperature-si^ting

resin adhesive of the woodworking type. The metal svu-face nuist be

thoroughly cleaned, and genei-ally more care is I'ecjuired in removing

solvents before bonding than is required in wood-wood bonds.

Adhesives formulated with casein and rubber latex, both natural

and synthetic, have been used for several year's to bond wood to metal.

These formulations have the advantage of curing at room t(^mp('ratui-e,

and the bonds are satisfactory where highest strength and dui'abilit}^

are not essential.

DRYING AND CONDITIONING WOOD FOR GLUING

The moisture content of wood at the time of gluing lias much to do

with the final strength of joints, the development of checks in the wood,

and the warping of the glued members. Glues will adliere to wood

with an}^ moisture content up to 15 percent; water-resistant glues will

adhere to wood with even higher moistiu'C content. Lai'ge changes

in the moisture content of the wood after gluing, however, cause shrinking or swelling stresses that ma}^ seriously weaken both the wood and

the joints.

The most satisfactory moisture content of wood at the time of gluing

is that which, when increased by the moistui'c of the glue, appi'oximately equals the average moisture content that the glued member

will have in service. In gluing 1-inch boards or thicker pieces, this

relation can be attained b}" proper' seasoning. In veneer oi* other

thin pieces, however, the moisture added by the glue IVequently (exceeds the moisture content of the wood ui sei-vice (7). Under these

conditions the wood cannot be dried enough before gluing to avoid

redrying after gluing. The amount of moisture added to wood in

gluing varies from less than 1 percent in lumber to 45 percent or more

in thin plywood. The thickness of the wood, the number of plies, the

density of the wood, the glue mixture, the quantity of glue spread,

and the gluing procedure (hot pressing or cold pressing) all affect the

increase in moisture content of the wood.

In general practice, adjustments cannot be made for all these widely

var3dng factors, and it is seldom necessary to dry lumber to a moisture

content below 5 percent or higher than 12 percent. Lumber with a

30;J747°—55 16
(^lass

Animal

Oascin and vee;etable protein.

Starch

Trca resin

Melaniine rrsin.

Phenol resin

TABLE 35.—Charaden'stirs, preparation, and uses; of (he

Form and testing , Pro|)rrtirs

)nost eonn)ionh/ used woodwork i n{f glnef^

I'n'paration and application

A'lany grades sold in dry foi'in; liquid

glues available; (luality determined

by tests on solutions of the glue.'

Several l)rands s(dd in dry powdrr

form; may also be prepared fiom

raw materials by user; quality deterndned by tests on glue and by

tests on wood joints.^

DilTerent grades sold in dry form;

also available in liquid form ready

to use; quality deternuned chiefly

by tests on wood joints.

Several brands sold as dry ])owdrrs,

others as liquids; may be blendcii

with melamine or otlier resins;

(luality determined by tests on glue

and by tests on wood joints.'^

Comi^aratively few brands available;

usually marketed as a powder with

or without catalyst; «luality determined by tests on glue and t>y tests

on wood joints.^

Several brands available, some dry

powders, others as liquids, and one

as dry fdm; quality determined by

tests on glue and by tests en wood

joints.-»

High <lry strength; low resistance to

moisture and damj) conditions;

stain wood very slightly, if at all.

Jligh to low dry strength; moderate

to low water resistance and moderately durable under danq) conditions; pronounced dulling elYect on

tools; stain some woods l>adly.

High in dry strength; low resistance

to moisture and damp conditions;

stain some woods moderately.

High in both wet and dry strength;

moderately dnral>le under damp

Ci'Uditions; moderate to low resistance to temperatures in excess of

l.'iO^ F.; white or tan in color; stain

wood very slightly if at all.

High in t)oth wet and dry stivngth;

very resistant to moisture and damp

conditions; stain wood very slightly,

if at all; whiti> to tan in color.

iligh in both wet and dry strength;

very resistant to moisture and damj)

conditions, more resistant than

wood to high temi)eratures; stain

wood very slightly; dark red in

color.

Tsed extensively in furniture assembly joints, cabinetmaking. aiui

nnllwork.

Dry form mixed with water, soaked,

and melted; solution kept warm

during application; liquid forms

a])plied as received; both pressed at

room tenijieratures. i

Mixed with cold water, ai)plied and i Used for gluing lumber an<l vtMieer

pressed cold. I for purposes requiring modi'rate

; moisture resistanc<\

Dry forms mixed with water, usually

with addition of caustic soda, and

fieated; applied cold; liquid form

applied as recf^ived; both pressed

cold.

Dry form mixed with water; hardeners, hllers, and extenders may be

added by user to either dry or liipiid

form; api)lied at room temperatures,

some formulas cure at room tenijieratures, others require hot ])ressing

at about 250^ F.

Afixed with water and ai)])lied at room

temperatures; heat recpiired to cure

(2"H)^ to :-!()()"-' F.).

Film form used as receivini; powchnform mixed with solvent, often alcohol and water, at rocín temperature;

hardeners and fillers often added by

users; most common tyi)es require

hot pressing at about 30t)° F.

Tsed primarily in gluing veneer.

Used extensively in gluing veneer for

furniture and oth(>r int(>rior uses

and to some extent in gluing luml>er ai\d assembly j(-ints.

Used to a limited extent in bag

molding and in gluing lumber and

veneei' for jiurposes re(|uiring colorless and highly resistant glue lines.

Used primarily for production of

highly resistant plywood.

to

CO

X

>

y,

a

Dd

o

o

M

>

H

y,

H

O

>

O

s

o

d
Rcsorciiiol resin.

Polyvinyl resin

emulsion.

Several brands available in liquid

form; catalyst supplied separately;

some brands arc combinations o^'

phenol and resorcinal resins; relatively high priced; quality determined by tests on glue and by tests

on wood joints^

Several brands are available, varying

to some extent in properties; marketed in liquid form ready to use; fpiality determined largely by tests on

glue joints.

High in both wet and dry strength;

very resistant to moisture and damp

conditions; mere resistant than

wood to high temperatures; stain

wood very slightly; dark red in

color.

ricnerally high in dry strength; low

resistance to moisture and elevated

temi)eratures; joints tend to yield

under continued stress; white in

color; stain wood little if at all.

Mixed with catalyst and a]»plied at

room temperatures; resorcinal glues

cure at room temperatures; some

resorcinol-phenol blends cure best

under moderate heat (100° to 200°

F.).

Marketed as a liquid ready to use;

a])plicd and pressed at room tem-tera tures.

Used primarily for gluing lumber or

assembly joints that must withstand severe service conditions.

\^sv(\ in assembly joints in furniture,

cabinetmaking, and mill work.

1 Federal Specification C-(i-4ril. (Hues; animal. Io;.-!l.

2 Federal Specification C-(t-45(3. Glue; casein. 1941.

3 Federal Specification 0-0-496. Glue; Resin-type (Liquid and Powder), i;»44.

* Military Si)ecification MIL-A-397A. Adhesive, room-temperature and intermediate-temperature setting, resin (phenol, resorcinol, and melamine base). lOol. O

>

Cd

r^

to

CO
238 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

moisture content of 5 to 6 percent is generally satisfactory for gluing

into fuiniture, interior millwork, and similar items. Lumber for outside use should generally contain 10 to 12 percent of moisture before

gluing. A moisture content of 3 to 5 percent in veneer at the time of

gluing is satisfactory even for thin plywood in furniture, interior millwork, and similar products. For certain uses, such as plywood for

boxes, veneer at a moisture content of 10 to 12 percent or even higher

is acceptable and may be desirable from a manufacturing standpoint.

Lumber that has been dried to the approximate average moisture

content desired for gluing may still show differences bet^veen various

boards and between the interior and the surfaces of individual pieces.

Large differences in the moisture content of pieces that are glued together result eventually in considerable stress on glue joints and tend

to produce warping of the product. For this reason, it is desirable

for many purposes to condition wood to a relatively uniform moisture

content after (hying and before gluing. Variations of 1 percent or

less between boards of the same species and size may be disregarded,

since they may occur even after a long conditioning period. Lumber

that is to be glued should also be free from drying degrade, such as

casehai-dening, warp, checks, and splits, although, if quality is of secondary^ importance, some types of degrade may be permitted.

MACHINING LUMBER FOR GLUING

Wood surfaces that are to be glued should be smooth and true, free

from machine marks, chipped or loosened grain, and other surface irregularities. Preferably, machining should be done just before gluing,

so that the surfaces do not become distorted from subsequent moisture

changes. For uniform distribution of gluing pressure, each lamination or ply should be uniform in thickness. A small variation in thickness in each lamination or ply may cause a considerable variation in

the thickness of the pile when a number of similar pieces are piled in

the same order as they come from the surfacer.

Surfaces made by saws are usuall}^ rougher than those made by

planers, jointers, and other machines equipped with cutterheads.

vSaws perfected recently, however, produce a smoother cut than older

types. B}^ making it possible to glue sawed joints more extensively,

these new saws save both labor and material. Joints can be maáe

between smoothly sawed surfaces that are approximately equal in

strength to those between planed surfaces. Unless the saws are very

well maintained, however, joints Ijetween sawed surfaces are generally

weaker than those between well-planed or jointed surfaces.

In cabinet work and other constructions where joints are exposed

to view, the sawed joint is often more conspicuous than the planed

joint.

Wood surfaces are intentionally roughened by some operators

by tooth planing, scratching, or sanding wdth coarse sandpaper in

the belief that rough surfaces are better for gluing. Tests of joints

made using good gluing practices, however, show no benefit from

roughening the surfaces.
WOOD HANDBOOK 239

PREPARING VENEER FOR GLUING

Veneer is eut by saAving^ slieino-, or rotary ])r()('esses (5). Sawed

veneer is produeed in long narrow strips, usually from flitches scheeled

for figure and grain. The two sides of the sheet are equally firm and

strong, and either side may l)e glued or exposed to view witii tlie same

results.

wSlieed veneer is also eut in the form of long strips l)y moving a flit eh

or bloek against a heavy knife. Beeause the venenar is forci^l abruptly

away from the fliteh by the knife, it tends to have \\m^ eluu'ks oibreaks on the knife side. The eheeked side is ealknl the o|)en or loosc^

side, the other side the elosed or tight side. The o])(^n sid(' is likcdy to

show imperfections in finishing and thend'orc^ should b(^ the glue side

whenever possible. For nuiteiiing face stock where the eheeked side

of part of the sheets must be the finish side, the veiu^er must be W(41 eut.

The rotary-cut process producers continuous sluH'ts of flat-grained

veneer b}^ revolving a log against a knife. The half-i-oimd pi-ocess,

the back-cut process, and other modifications of straight rotarycutting are used to produce highly iigui'tnl vencM'r from stum])s,

burls, and other irregular parts of logs. In these processes a part of a

log, stump, or burl is placed off center in a lathe and is rotaiy-cut into

small sheets of veneer. All rotary-cut veneer has an open and a CIOSíMI

side (4), although it may be difficult to distinguish one fi'om the other

if the veneer is well cut. When rotary-cut veneer is us(ul for faces,

the checked or open side should if possil)le, Ix^ the ghu^ side.

Because veneer usually is not resurfaced Ixd'on^ it is glued, it must

be carefully cut. Provided the veneer is well cut, tlu^rc^ is no appreciable diñ'erence in any property except appearance of plywood nuide

from veneer produced by any of the three processes. VencHU' selected

to be glued should be (1) uniform in thickness, (2) smooth and flat,

(3) free from large checks, decay, or other quality-reducing features,

and (4) straight grained. For plywood of the lowaT grades, however,

some of these requirements may be modified.

PROPER GLUING CONDITIONS

To insure a strong joint in wood, a film of glue unl)roken by air

bubbles or foreign particles should be in contact with the wood surfaces

over the entire joint area. This result is obtained by controlling the

details of the gluing operation {2, 7, 8).

Making strong glue joints with glues applied in liquid condition

depends primarily upon a proper correlation between gluing pressure

and glue consistenc}^ during pressing. The consistency of the glue

mixture, once it is spread on the wood, is extremely variable. It

depends upon such factors as the kind of glue, glue-w^ater proportion

of the mixture, quantity of glue spread, moisture content of the wood,

temperature of the glue, room, and w^ood, the time between spreading

and pressing, and the extent to which the glue-coated surfaces are

exposed to the air. Room-temperature-setting glues usually thicken

and harden steadily after spreading until they are cured. Hot-press

glues often thin out during the initial heating period and then thicken

and harden as curing progresses.
240 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Pressure is used to squeeze the glue out into a thin continuous film

between the wood layers, to force air from the joint, to bring the wood

surfaces into intimate contact with the glue, and to hold them in this

position during the setting or curing of the glue. A light pressure

should be used with a thin glue or one that becomes thin during curing,

a heavy pressure with a thick glue, and corresponding variations in

pressure should be made with glues of intermediate consistency. 1'he

strongest joints usually result when the consistency of the glue permits

the use of moderatel}^ high pressures—100 to 250 pounds per square

inch (7).

Joints should be kept under pressure at least until the}^ have enough

strength to withstand the interior stresses tending to separate the

wood pieces. In cold-pressing operations, under favorable gluing

conditions, this stage will be reached in 2 to 7 hours, depending upon

the curing characteristics of the glue and upon the thickness, density,

and absorptive characteristics of the wood. A longer pressing period

is advisable as a precautionary measure when operating conditions

permit (13).

In hot-pressing operations the time required varies with the temperature of the platens, the thickness and kind of material being

pressed, and the kind of glue. The variation in time in actual practice

is from about 2 minutes to as much as oO minutes. Depending somewhat upon the size of the joint and the type of glue, the time under

pressure may be reduced to a few seconds l)y heating the glue joint with

high-frequency electric current.

Gluing with the (h\v forms of glues requires special conditions that

vary somewhat with the particular glue and the product.

TYPES OF GLUED JOINTS

Side-Grain Surfaces

With most species of wood, straight, plain joints between side-grain

surfaces (fig. 52, A) can be made substantially as strong as the wood

itself in shear parallel to the grain, tension across the grain, and

cleavag(\ The tongued-and-grooved joint (fig. 52, B) and other

shaped joints have tlie theoretical advantage of lai'ger ghiing surfac s

than the straight joints, but in practice th(\v do not give higher

strength with most woods. Furthermore, the theoretical advantage»

is often lost, wholly or partly, because the shaped joints are more

difficult to machine than straight, plain joints so as to obtain a perfect

fit of the parts. Because of poor contact, the effective holding area

and strength may actually be less on a shaped joint than on a flat

surface. The principal advantage of the tongued-and-grooved and

other shaped joints is that the parts can be more quickly alined in

the clamps or press. A shallow tongue-and-groove is usually as useful

in this respect as a deeper cut and is less wasteful of wood.

End-Grain Surfaces

It is practicallv impossible to make end-butt joints (fig. 53, A)

sufficiently strong or permanent to meet the requirements of ordinary

service. With the most careful gluing possible, not more than about
WOOD HANDBOOK 241

M 93137 F

FIGURE 52.—Sido-to-si(le-t;rain joints: .4, Plaii»; B, tonoiK^d-and-oroovcd.

25 percent of the tensile strength of the wood paralk4 with the grain

can be obtained in })utt joints. In order to approximate the tensile

strength of various species, a scarf, serrated, or other form of joint

that approaches a side-grain siu'face must be used (fig. 53). The

plain scarf is perhaps the easiest to glue and entails fewer machining

difficulties than the many-angle forms. The efficiencies of scarf joints

of different slopes are discussed in the section on strength of glued

structural members (p. 255).

End-to-Side-Grain Surfaces

End-to-side-grain joints (fig. 54, A) are also difficult to glue properly

and, further, are subjected in service to unusually severe stresses as

a result of unequal dimensional changes in the two members of the

joint as their moisture content changes. It is therefore necessary to

use irregular shapes of joints, dowels, tenons, or other devices to

reinforce such a joint in order to bring side grain into contact with

side grain or to secure larger gluing surfaces (fig. 54). All end-to-sidegrain joints should be carefulh^ protected from changes in moisture

content.

CONDITIONING GLUED JOINTS

When boards are glued edge to edge, the wood at the joint absorbs

water from the glue and sw^ells. If the glued assembly is surfaced

before this excess moisture is dried out or distributed, more wood is

removed along the swollen joints than elsewhere. Later, when the

joints dry and shrink, permanent depressions are formed that ma}^

be very conspicuous in a finished panel {6).

When pieces of lumber are glued Qi\gQ to edge or face to face, the

glue moisture need not be dried out but simply allow^ed to distribute
242 HAXDBOÍJK r. s. DEPARTMENT OF AGRICULTURE

K

>>*L:

B E

A

c F

íí4-^í.-íí-e-.

D

M 92377 F

FIGURE 53.—End-to-end-grain joints: A, End butt; B, plain scarf; C, serrated

scarf; D^ finger; E^ Onsrud; F^ huoked scarf; G, double-slupe scarf.

itself uniforml}^ throughout the wood. Approximately uniform

distril)ution of glue moisture can usually be obtained by conditioning

the stock after gluing for 24 hours at Í60° F., 4 days'at 120° F., or

at least 7 days at room temperature with the relative humidity, in

each case, adjusted to prevent significant drying.
WOOD HANDBOOK 243

B

I.

£j^

/

M 92376 F

FIGURE 54.—End-to-side-grain joints: yl, Plain; B^ n^iter; C, dowel; I), mortise

and tenon; £J, dado tongue and rabl^et; F, slip or lock corner; G', dovetail;

//, blocked; /, tongued-and-grooved.

In plywood, veneered panels, and other eonstiuctions made by

gluing together thin layers of wood, it is advisable to condition the

panels to average service moisture content. In cold-ghiing operations,

it is frequently necessary to dry out at least a part of the moisture
244 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

added in gliiino;. The diying is most advantageously done under controlled conditions and time schedules (7).

Drying such glued products to excessively low moisture content

materially increases warping, opening of joints, and checking. Following hot-press operations, the panels will often be very dry, and

it may be desirable to recondition them under circumstances that

will cause them to regain moisture.

DURABILITY OF GLUED MEMBERS

Tlie durability of glue joints in wood members depends upon the

type of glue, the service conditions, the gluing technique, and the

design or construction of the joints. Moisture conditions are particubirly important not only because of the effect of moisture on the

glue itself but because of the effect of moisture content on the internal

stresses developed on the glue joint. These internal stresses, and

consequently the behavior of the joints in service, are also dependent

upon the design of the joint, the thickness of the plies or laminations,

and the density and shrinkage characteristics of the species used.

Available evidence indicates that joints well designed and well

made with any of the commonly used woodworking glues will retain

their sti-ength indefinitely under conditions such that the moisture

content of the woofl does not exceed approximately 15 percent and

the temperature remains within the range of human comfort.

Low temperatures seem to have no significant effect on the strength

of glue joints, but some glues have shown evidence of deterioration

when exposed to temperatures of about 158° F. Joints that were

w(41 made with phenol resin, resoix'inol resin, or melamine resin glues

have ])roved more durable than the wood when exposed to water, to

warmth and dampness, to alternative wetting and drying, and to

temperatmx's sufficiently high to char the wood (14). These glues are

sufficiently durable for use in products that are exposed to the weather.

Tests have shown that joints made with urea resin glues are highly

resistant to water and to wetting and drying but that they tend to

\\eak(^n when subjected to temperatures of al)Out 158° F. or higher.

Data considered adequate for predicting the retention of strength

of urea resin glue bonds exposed to temperaturi^s between 158° F.

and the hiunan-comfort zone are not available. Casein and soybean

glue joints will withstand temporary exi)osure to dampness or water

without permanent loss in strength, but if the moisture content of

the wood continuously or repeatedly exceeds a])out 18 percent,

they will eventually lose strength ; the rate of loss of strength may

vary, however, depending upon such factors as species and

construction.

Polyvinyl resin emulsion glues have moderate resistance to dampness, but low resistance to water; the tendency of the joints to yield

under stress generally increases as the temperature increases. Joints

made with animal glue or with stanch glue are not suited to damp

service conditions. If toxic materials are added to animal glues,

serviceability of the glued products in warm, damp environments

is increased slightly.

Treatments that can be used to increase the durability of glued

members include: (1) Coatings that reduce the moisture content
WOOD HANDBOOK 245

changes in the wood and (2) impregnation of the wood with piTS(^rva-.

tives. Moisture-exchiding coatings reduce the rate of moisture content changes in wood and lessen the sweUing stresses that occur

during temporary periods of exposure to damp conditions; the}^ do not

protect wood effectively during prolonged exposiu-e to damp conditions. By impregnating glued meml)ers with preservatives, the deteriorating eft'ects of prolonged exposure to damp conditions can be

reduced. The useful life of casein-bonded plywood may be doubled

or tripled by impregnating it with preservative chemicals, such as

coal-tar creosote, that protect Ijoth glue and wood (1).

LITERATURE CITED

(1) BROUSE, D.

1932. METHODS OF INCREASINO DURABILITY OF PLY\\'()OD. WoodwOrk¡n<;

Indus. 11 (2): 3U-31, 33, illus.

(2) DoucLASS, W. D., and PETTI FOR, C. I^.

1932. THIRD AND FINAL REPORT OF THE ADHESIVES RESEARCH COMMITTEE

(OT. BRIT.). Dej)t. Sei. Indus. Res., 109 pp., illus., London.

(3) EICKNER, H. W., and BLOMQUIST, R. F.

1950. ADHESIVFS FOR BONDINO WOOD TO METAL. U. S. Forest Prod. Lab.

Rl)t. 1768, 15 i)p., illus. [Processed.]

(4) FLEISCHER, H. O.

1949. EXPERIMENTS IN ROTARY VENEER CUTTINO. Forest Prod. Res.

Soc. Proc. 3: 20 i)p., illus.

(5) KNIGHT, E. V., and WULPI, M.

1927. VENEERS AND PLYWOOD, THEIR CRAFTSMANSHIP VVND ARTISTRY. 372

I)p., illus., New York.

(6) SELBO, M. L.

1952. EFFECTIVENESS OF DIFFERENT CONDITIONING SCHEDULES IN REDUCING SUNKEN JOINTS IN EDGE GLUED LUMBER PANELS. Forest

Jour. 2 (1): 8 pp., illus.

U. 8. Dept. Agr. Bui. 15Ü0, 78 pp., illus.

1930. GLUING AVOOD IN AIRCRAFT MANUFACTURE, L^. 8. Dcpt. Agr. Tech.

Bul. 205, 58 pp., illus.

(9) U. S. DEPARTMENT OF DEFENSE.

1951. ADHESIVE, ROOM-TEMPERATURE AND INTERMEDIATE-TEMPERATURE

SETTING, RESIN (PHENOL, RESORCINOL, AND MELAMINE BASE).

Mil. Spec. MIL-A-397A, 15 pp., illus.

(10) U. 8. FEDERAL SPECIFICATIONS BOARD.

1931. GLUE; ANIMAL. Fed. Spec. C-G-451, 7 pp., illus.

(11)

(12)

194G. GLUE; UREA-RESIN. Ferl. Spec. C-G-490, ]OI)P., illus.

(13) U. S. FOREST PRODUCTS LABORATORY.

1951. WOOD AIRCRAFT INSPECTION AND FABRICATION. ANC Bul. 19,

335 pp., illus. Issued by Sut^committee on Air P'orce-Xavy-Civil

Aircraft Design Criteria, Aircraft Committee, Munitions Board.)

(14) WANGAARD, F. F.

1946. SUMMARY OF INFORMATION ON THE DURABILITY OF WOODWORKING

GLUES. U. S. Forest Products Laboratory Rpt. 1530, 36 pp.,

illus. [Processed.]

(7)

Prod. Res. Soc.

TRUAX, T. R.

(8)

1929. GLUING OF AVOOD.

1941. GLUE; CASEIN. Fed. Spec. C-G-456, 7 i)p., illus.
GLUED STRUCTURAL MEMBERS

Glued structural members are of two tyi)es --glued laminated

members and wood-plywood members of built-up cross section.

Both types offer certain advantages.

GENERAL CHARACTERISTICS OF GLUED LAMINATED

CONSTRUCTION

Parallel-grain or laminated construction (fig. 55) refers to two oi*

more layers of wood glued together with the grain of all layers approximately parallel. The laminations ma}^ vary as to s]:>ecies, mmiber,

size, shape, and thickness.

Parallel-grain or laminated construction has long been used for

furniture parts, for cores of veneered panels, and for sporting goods.

The first use of glued laminated structural members was in Europe,

where it is reported that as early as 1907 laminated arches were

made of dry softwood lumber and casein glue. Improvements in

casein glue during World War I aroused further interest in the fabrication of glued laminated structural members, at first for aircraft

and later extending to the framing members of l)uil(bngs. One of

the early examples of the use of glued laminated arches in the United

States was in a building erected in 1934 \)j the Forest Prochicts

Laboratory. This installation was followed by many others in gymnasiums, churches, halls, factories, hangars, and barns. The development of the highly moisture-resistant synthetic resin glues permitted

expansion of glued laminated construction into such uses as bridges,

trucks, and marine construction where a high degree of resistance to

severe service conditions is required (4)^"^- With increased public

acceptance of glued laminated construction, laminating has increased

steadily until it now forms an important segment of the woodworking

industry.

Advantages of Glued Laminated Members

If glued laminated members are made of dry lumber, they will

remain relatively constant in dimensions under normally dry use

conditions. Hence, the development of splits, checks, and loosened

fast(3nings and connections is greatly reduced.

Another advantage of laminated members is that they can be

produced in a thoroughly dry condition in a relatively short tune.

Laminating also permits more nearly complete utdization of avadable supphes, because larger members can be built up of short-length

and narrow lumber. Moreover, selective placement oí the laminations to disperse knots and other natural characteristics results m

improved strength.

' Italic numbers in parentheses refer to Literature Cited, p. 273.

247
248 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

H

ZM 92379 F

FIGURE 55.—Types of parallel-grain (laminated) construction: A, Section of

arch; B, section of table top; C, section of door stile or rail; Z), section of grand

piano; E, section of air})lanc propeller hub; F, section of beam; (j, section of a

column; //, chair leg; /, bowling pin; J, baseball bat.
WOOD HANDBOOK 249

Laminating structural members by gluing, however, involves certain economic considerations and fabricating techniques not encountered in producing solid timbers. The cost of preparing lumber for

gluing and of the laminating operation, for example, usually raises

the ftnal cost of the product above that of solid green timbers. For

constructions in which green timbers are satisfactory, thc^-efore,

more time and higher costs are required to cut and season lumbt^^

and to laminate than to cut solid green timbers. In addition, th(^

laminating process itself requires equipment, plant facilities, and

fabricating skills not required for producing solid grcMMi timbers.

Avoiding Internal Stresses

For best results in making glued laminat(^d members, it is important to avoid the development of internal stresses when the member

is exposed to conditions that change its moisture content. Diflerences in shrinking and swelling are the fundamental causes of internal

stresses, and laminations should be of such character that they shrink

or swell similar amounts in the same direction. If laminations are

of the same species or of species with similar shrinkage characteristics, if they are all flat-grained or all edge-grained material, and if

they are of the same moisture content, the assembly will be reasonably

free from stresses on the glued joints and have little tendency to

change shape or to check or open at the joints. Laminations that

have an abnormal tendency to shrink endwise ])ecause they have

excessive cross grain or compression wood (p. 97) should not be

included in constructions that must remain flat, because serious

bowing or cupping may result.

While observance of these principles is desirable, practical considerations may prevent exact conformance. In softwood structural members intended for interior use, for example, segregation of flat-grained

from edge-grained material is generally imnecessary, and a range in

moisture content among the laminations in the same assembly no

greater than 5 percent may be permitted without significant effect

on serviceableness.

Preservative Treatment of Laminated Members

If the laminated member is to be used under conditions that raise

its moisture content to more than about 20 percent, either the heartwood of durable species should be used or the wood should be treated

with preservative chemicals and only highly moisture-resistant glues

should be used. If the size and shape of the members permit, laminated members can be treated with preservatives after gluing, but

penetration perpendicular to the planes of the glue joints will be

distinctly retarded at the first glue line. Providing suitable precautions are observed, laminations may be treated and then glued.

The treated laminations should be conditioned and must be resurfaced

just before gluing. Not all preservative-treated wood can be glued

with all glues, but, if suitable glues and treatments are selected and

if the gluing is carefully done, laminated members can be produced that are entirely serviceable under moist, warm conditions

favoring deeply.
250 HANDBOOK 72, U. S. DEPAHTMI^NT OF AORICULTURp:

Species for Laminating

Softwoods, principally Douglas-fir and southern yellow pine, are

Tuost commonly used for laminating such structural members as

arches and beams. Boat timbers, on the other hand, are often made

of white oak because it is moderately durable under wet conditions.

Other species can also be used, of course, when their mechanical and

physical properties are suited for the purpose.

Quality of Glue Joints

The quality of glue joints in laminated members intended for

service und(4'^ dry conditions is usually evaluated by means of the

block shear t(^st()). Acceptable criteria are often based on unit

slu^ar strcaigtli and percentage of wood faihn-e considered satisfactory

for the species Ixûng used. For lammated meml)ers that must withstand severe service conditions, however, the block shear test alone

does not in-ovide an adequate evaluation. To serve satisfactorily

imder severe conditions, the glue joints should be capable of withstanding, without significant (k'lamination, high internal stresses that

develop as a r(^sult of rapid wetting and drying (2). Industry standards (13, IJi, 20) covering the design and fabrication of glued structural

laminated wood have ])een issued, and at least two military specifications cover structural glued laminated items for specific uses {16, 17).

STRENGTH OF GLUED LAMINATED MEMBERS

From the standpoint of strength and design, glued laminated members have certain definite advantages. For example, a laminated

member made of thoroughly seasoned wood for use under continuously

dry conditions may be designed on the basis of the strength of the dry

wood, regardless of the size of the finished member, while large, onepiece sawed members must be designed on the basis of gTeen strength,

regardless of service conditions. In a laminated member designed to

resist bending loads, high-grade laminations may be placed in the

outer portions of the l)eam, where their high strength may be effectively used, and lower grade laminations in the inner portion, where

their low strength will not greatly afi'ect the overall strength of the

member. By selective placement of the laminations, the knots can

be S(\attered and im])rove(l strength can be obtained. Even with

random assembly of laminations, studies have indicated that knots

are imlikely to occur one above another in several adjacent laminations.

Aside from the beneficial effect of dispersion of imperfections that

results from laminating, however, available test data do not indicate

that laminating improves strength properties over those of a comparable solid piece. That is, the simple act of gluing together pieces

of wood does not, of itself, improve strength properties, unless the

laminations are so thin that the glue bonds significantly affect the

strength of the member. For most laminating, where material in

luml)er thicknesses is used, that would not occur.
WOOD HANDBOOK 251

The various factors affecting strength are discussed in the following

paragraphs. The principal determinants of strength are knots, cross

grain, and end-joint efficiency. It should be noted that the eifec^ts of

these 3 factors are not cumulative; that is, the lowest of the 3 controls

the strength. Where other effects, such as those of curvature or beam

depth, are applicable, they should be applied in addition to those for

knots, cross grain, and end joints.

Effect of Knots on Bending Strength and Stiffness

The effect of knots on the bending strength and stiffness of laminated

members depends upon the number, size, and position, with res|)ect

to the neutral axis of the member, of the knots close to the critical

section. Specifically, the bending properties depend upon the sum

of the moments of inertia, about the gravity axis of the full cross

section, of the areas occupied by all knots weithin 6 inches to either side

of the critical section. This sum may be represented by the symbol

IK- The moment of inertia of the full (or gross) cross section of the

member about its own gravity axis is represented by IQ- The relations

between bending strength and stiffness and the ratio IKIIQ are shown

in figures 56 and 57.

The curves shown in figures 56 and 57 were empirically derived

from tests of laminated beams containing knots in various concentrations {22).

i.o

"^\

^- r

\ 1

i 1

1

1 v_. . .

11

!

i

\ : 1 :

1 \^ y--{/*3X)(l-xñl-'/2X}

1 ^\ 1

j

! \ ! 1 i i

i \^ 1 1

! i 1 i 1 X

1 1

! 1 \[

1 ! !^

i

1

! 1

! i 1 1 1^^^^.^

ZM 75226 F

FIGURE 56.—Design curve relating allowable flexural stress to moment of inertia

of areas occupied by knots in laminations of laminated ):>eams.

30.-^747
252 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

t:: i^ 100

90

80

70

"^ 60

50

^vN

1

-y-[i-(iK/iGi']

\

\

\^

0.1 0.2 0.3 0.4 0.5 0.6 0.7

X-IK/IG

2M 81023 F

FIGURE 57.—Design curve relating allowal)le modulus of elasticity to moment

of inertia of areas occupied by knots in laminations of laminaterl beauis.

Effect of Knots on Compressive Strength

The compiTssive strength of himinated members depends upon

the proportion of the cross-sectional area of each lamination occupied

l)y the largest knot in the lamination. Figure 58 shows an empirically

derived relationship between compressive strength and K\h, where h

is the lamination width and K is the average of the largest knot sizes

in each of the himinations [22).

Effect of Knots on Tensile Strength

Test data relating knot size to tensile strength are not available.

Figure 59, however, represents a relation between tensile strength and

K¡h derived from figure 58.

Effect of Cross Grain on Strength

The effect of cross grain on strength is given in table 15. For

laminated beams, it is possible to vary the cross-grain requirements at

dift'erent points in the depth of the beam in accordance with the stress

requirements. That is, steeper cross grain may be permitted in

laminations in the interior of the beam than in the laminations at and

near the outside. The permitted variation should be based on the

assumption of linear variation of stress across the depth.
WOOD HANDBOOK 253

ÍOO

M

90

80

70

SO

50

¡^^y^Pu K/b)^][l - ^ (K/b)J

x.

1

\ ¡

\^ 1

i \

11

^

O.i 0.2 0 3 0.4 0.5

K/b

0.6

ZM 81025 F

FIGURE 58.—Design curve relating; allowable conipressive stress to size of kn«

in laminations of laminated short columns.

>U

Effect of Curvature of Laminations on Bending

Strength

Stress is induced when laminations are bent to curved forms, such

as arches and curved rafters. While much of this stress is quickly

relieved, some remains and tends to reduce the strength of a curved

member. The ratio of the allowable design stress m curved members

to that in straight members is

1.00-

2,000

{Rltf

where t is the thickness of a lamination and R is the radius of the curve

to which it is bent, both R and t being hi the same units {21).

Effect of Lamination Thickness on Strength

Tests (22) have indicated that lamination thickness has no effect on

the strength of straight laminated members. Lamination t.hickne^^^^

does, however, affect the strength of curved members dependmg upon

the radius to which the lamination is bent (see preceding section).
254 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

100

90

80

70

60

50

40

30

20

10

\

\

^y--[i-2.5(K/b)^jLn-^iK/b}]

.

\

\

\

0.1 0.2 0.3

X = K/b

0.4 0.5 0.6

ZM 81026 F

FIGURE 59.—Design curve relating allowable tensile stress to size of knots in

laminations of laminated tension members.
WOOD HANDBOOK 255

Effect of End Joints on Strength

For a largo proportion of laminated meml)ors, Ixvauso of thoir size,

pieces of wood will need to be jointed end-to-end to provide laminations

of sufficient length. In most cases, the strength of mc^mlxTs is rechieed

by the presence of end joints (./^, 21, 22).

Scarf Joints

Laminations containing scarf joints (fig. 53) and located in the

tension portion of bending members or in tension members should not

be stressed to more than the following percentages of the stn^ss permitted in an unjointed member:

ri /. 1 Joint fador Scarf slope: (percent)

1 in 12 or flatter _ _ _ 90

1 in 10 __ 85

1 in 8 80

1 in 5 65

These limitations apply to interior laminations as well as to the

lamination at the tension face. In a beam with 40 equal laminations,

for example, the stress at the outer face of the second lamination is 95

percent of that at the outer face of the bottom lamination. Hence, if

the bottom lamination is continuous, and the second lamination contains a scarf joint sloping at 1 in 12 at the critical section, the working

stress (stress in extreme fiber) should be restricted to about 95 percent

of the basic value, in order not to exceed the 90 percent permissible at

the outer face of the second lamination.

Working stresses need not be reduced if laminations containing

scarf joints are located in the compression portion of bending members

or in compression members.

Stepped or hooked scarf joints (fig. 53) may be assumed to have the

same strength as a plain scarf joint of the same slope, except that the

area occupied by the step or hook should be considered as ineffective

in transmitting stress. The slope of a stepped scarf should be taken as

the slope of the plane portion of the scarf, not as the distance between

tips divided by the lamination thickness.

A double-slope scarf joint (patent applied for), as illustrated in

figure 53, has been used to some extent for end-jointing laminations.

If made by comparable fabricating techniques, a joint of this type

should have the same strength as a plain scarf joint of the same slope.

Scarf joints in tension and bending members should be well scattered.

It is suggested that, in highly stressed areas, scarf joints in adjacent

laminations be spaced, center to center, at intervals of not less than 24

times the lamination thickness. In bending menibers spacing of scarf

joints may vary linearly from 24¿ in areas of maximum allowable stress

to Oí in areas of zero stress.

Where it is not feasible to maintain a specific pattern of scarf-joint

distribution, joints should be well scattered—that is, a conscious

effort should be made to prevent concentration of joints—and somewhat lower strength should be assumed for scarf joints stressed in
256 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

tension than was given previously. Under such conditions, the

following joint factors are suggested in lieu of those given previously:

Joint factor

Scarf slope: ^P''''''^^

1 in 12 or flatter |^

1 in 10 fl

1 in 8 ¿X

lin 5 Ö0

The slope of scarf joints in compression members or in the compression portion of bending members should not be steeper than 1 m 5;

a similar limitation of 1 in 10 is suggested for tension members and the

tension portion of bending members. Because there is some question

as to the durability of steep scarf joints for exterior use or other severe

exposure, scarf joints with a slope steeper than 1 in 10 should not be

used.

Butt Joints

Butt joints can transmit no tensile stress and can transmit compressive stress only after considerable deformation or if a metal bearing

plate is tightlv fitted between the abutting ends. In normal assembly

operations, such fitting would not be done, and it is therefore necessary

to assume that butt joints are ineff'ective in transmitting both tensde

and compressive stresses. Because of this ineffectiveness, and because

butt joints cause concentration of both shear stress and longitudinal

stress, they are not recommended for use in structural members.

If butt Joints are used in the compression portion of bending members, all laminations at a particular cross section containing butt

joints should be disregarded in computing the moment of inertia of

that cross section. If butt joints occur in the tension portion of a

l)ending member, the efi'ective moment of inertia should be computed

l)y subtracting from the moment of inertia of the full cross section 1.2

times the moment of inertia of those laminations containing butt

joints at the particular cross section.

If butt joints are used in compression members, the effective crosssectional area should be computed by subtracting from the gross

cross-sectional area the area of all laminations containing butt joints

at a single cross section. In addition, laminations that contain butt

joints and that are adjacent to others containing butt joints should

be considered only partially effective if the spacing of the joints in

adjacent laminations is less than 50 times the lamination thickness.

The effective area of such adjacent laminations should be computed

by multiplying their gross area by the following percentages:

Buti-joint spacing Effectiveness factor

{v=iamination thickness) {percent)

30Í 90

20¿ 80

10¿ 60

Butt joints are not recommended for use in tension members. If

they are used, the effective cross-sectional area may be computed as

indicated for compression members, except that 1.2 times the area of

laminations containing butt joints at a particular cross section should

ble subtracted from the gross area.

.jM
WOOD HANDBOOK 257

Other Types of End Joints

In addition to scarf joints and butt joints, other types of end joints

may be used in laminated members. In general, however, few data

are available on their effect on strength. When data are not availa})le

for establishing spacing requirements, strength, and like factors for

these joints, they may be treated as butt joints.

Effect of Edge Joints on Strength

It is sometimes necessary to joint pieces edge-to-edge to provide

laminations of sufficient width. For tension members, compression

members, and horizontally laminated bending members, the strength

of such joints is of little importance to the overall strength of the

member. Therefore, from Ihe standpoint of strength alone, it is

unnecessary that edge joints be glued. Other considerations, however, such as the appearance of face laminations or the possibility

that water mil enter the unglued joints and promote decay, may

dictate that edge joints should be glued.

In vertically laminated beams, sufficient laminations must be edge

glued to provide adequate shear resistance in the beam. Not only is

adequate initial strength required of such joints, but they must })e

durable enough to retain that strength under the conditions to which

the beam is exposed in service.

Effect of Shakes, Checks, and Splits on Shear Strength

In general, shakes, checks, and splits have little effect on the shear

strength of laminated beams. Shakes generally occur infrequent!}^

but should be excluded from material for laminations or placed only

in positions of low shear. Most laminated members are made from

laminations that are thin enough to season readily without developing

checks and splits. Since checks and splits lie in a radial plane, and

since the majority of laminations are flat grained, checks and splits

will be so positioned in horizontally laminated beams that they will

not affect shear strength.

In cases where shakes, checks, and splits affect the shear strength

of a beam, as in vertically laminated beams, their effect may be taki^n

into account in the manner described for one-piece sawed membeis

(p. 206).

Vertically Laminated Beams

The effect of knots on the strength of vertically laminated beams

may be taken into account by determining the strength ratio of each

lamination by the method described in the section on stress grades

and working stresses and averaging these ratios to determine the

strength ratio for the beam (22). The eflects of cross grain on strength

and limitations on end joints are as described on pages 252-257.

Effect of Beam Depth on Bending Strength

Unit strength values, computed by the usual engineering methods

from test data on wood beams, decrease as the depth of the beam increases. Basic stresses for extreme fiber in bending have l)een taken
258 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

to corin^spond to beams of 12-inch depth, so that the effect of depth

on strength is not a serious problem for one-piece sawed members.

Laminated members, however, can be of considerable depth, and the

effect of this factor on strength should be considered.

An empirical formula for the depth-effect factor, Fhy is

F,=O.S\ 7/^+143

7/^+88'

where 77 is the depth of the beam.

The form of the beam has a similar effect, as discussed under

structural members of lumber (p. 210).

DESIGN OF GLUED LAMINATED MEMBERS

Engineering formulas applicable to solid wood structures are applicable also to structures of laminated wood. The fact that laminated

members can be made in curved form, hoAvever, introduces some

circumstances not ordinarily met in the design of wood structures.

The application of ordinary engineering formulas to deep, sharply

curved bending members may introduce appreciable error in the calculated stresses. For such cases, the methods applicable to curved

beams, as described in standard text books on mechanics, should be

used.

Wlien bending moments are applied to curved members, stresses

are set up in a direction parallel to the radius of curvature (perpendicular to grain). Stresses so induced should be appropriately

limited.

Procedures for establishing design stresses and factors affecting the

design of glued laminated structural members are discussed in detail

by Freas and Seibo (4)-

Basic Stresses

Basic stresses for use in determining working stresses for the design

of laminated members to be used under dry conditions, as in most

covered stinactures, are given in table 36. For structures to be used

under wet conditions of service, as in most exterior service, the basic

stresses are the same as those given for solid sawed timbers (table 25).

Estimation of IR/IG for Bending Members

Unless the location of knots is controlled when laminations are

assembled in beams and arches, an assumption must be made as to

the concentration of knots near the critical cross section, in order to

estimate the factor IKIIG for the determination of the appropriate

strength ratio. A conservative assumption would place a knot of

maximum permitted size at the critical cross section in every lamination. Experience with lumber grades indicates that such a concentration of knots is unlikely to occur.

^'NTien data on the frequency of occurrence of the sums of knot

sizes in 1-foot lengths for a specific grade are available, it is possible

to apply statistical procedures to these data and to arrive at a value
WOOD HANDBOOK 259

^LIA'^Ù '"^'^^t ^^. ^ basis for design. The same procedure may be

used for members in which two grades of lumber are used. Values

ot IK/I G and of the strength ratio, based on a statistical approach

have beeil deve oped for a limited number of grades of Douglas-fi,'

and southern yellow pine (I4, 20). ^^^^^<^»

When a statistical analysis is not available for a grade or speci(^s

it IS suggested that either definite limitations on knot concentrations

be imposed in assembly of laminations or, if random assembly of

laminations is used a conservative assumption as to knot concentration be used as a basis for design. If specific limitations on knot

TABLE 36 —ßaszc stresses for structural members laminated from clear material

and under long-time service at maximum design load and under dry conditions (as

m most covered structures)—for use in determining working .tresses according to

grade of laminations and other applicable factors

SOFTWOODS

Species 1

Baldcypress (cypress)

Cedar:

AlaskaAtlantic (southern whitecedar) and

northern white-...

Port-OrfordWestern redcedar .

Douglas-fir:

Coast type

Coast type, close-grained

Rocky Mountain type

All types, dense

Fir:

Balsam

California red, grand, noble, and

white

Hemlock:

Eastern

Western (west coast hemlock)

Larch, western

Pine:

Eastern white (northern w^hite),

ponderosa, sugar, and western white

(Idaho white)

Jack

Lodgepole

Red (Norway pine)

Southern yellow

Dense

Redwood

Close-grained

Sprue«:

Engelmann

Red, white, and Sitka

Tamarack

Extreme

fiber in

bending

or tension

parallel

to grain

P. s. I.

2, 4()U

2, 000

1,400

2,000

1, 000

2,750

2,950

2.000

3,200

1,600

2,000

2,000

2,400

2,750

1,600

2,000

1,600

2, 000

2,750

3,200

2,200

2,400

1, 400

2,000

2,200

Maximum

longitudinal shear

P. s. i.

170

115

150

135

in)

150

135

150

115

115

115

125

150

135

135

100

135

180

180

115

115

115

135

160

Compression perpendicular

to grain

330

275

195

275

220

350

375

310

410

165

330

330

330

350

Compression parallel to

grain

Modulus

of elasticity in

bending

P s. i.

2, 000

1,450

1.050

1,650

1,300

2, 000

2, 150

1, 450

2, 350

1,300

1,300

1,300

1,650

2,000

275 1,400

240 1,450

240 1, 300

240 1,450

350 2, 000

410 2, 350

275 1,850

295 2, 000

195 1,100

275 1,450

330 1.850

1,000 p. s. i.

1,300

1,300

900

1.600

1, 100

1,800

1,800

1,300

1,800

1,100

1,200

1,200

1,500

1,600

1, 100

1, 200

1. lüo

1,300

1,800

1,800

1,300

1,300

900

1,300

1,400

See footnote at end of table.
260 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

TABLE 36.—Basic stresses for structural members laminated from clear material

and ander lotKj-titne service at ynaxirnum design load and under dry conditions {as

in )n<>st covered structure^)—for use in determining ivorking stresses according to

grade of laminations and other applicable factors—Continued

HARDWOODS

Species 1

?]xt renie

fiber in

bendiníí

or tension

[)arallel

to grain

Ash:

Black. ..

Commercial white..-

Beech, American _.

Birch, swet't and yellow

('(jttonwood, (eastern

Klni:

American and slippery (soft elm).

Rock.

Hickory, true and pecan

Maple, black and sugar (hard maple).

Oak, commereial re(l an<l white_.

Svvcetgum (gum, red gum,sai) gum) _

'I'upelij, black (black gum) and water

>'ell(jw-p<>plar ([loplar). ... ._. . . .

I Speeies names from api)r<)\('(i i-heck lisl, 1'

I)areid,heses.

Maximuni

longitudinal shear

s. I.

].'()

210

21(1

210

Kill

170

210

210

210

170

IT)!!

Compression perI>endicular

to grain

Compression parallel to

grain

330

550

1. 150

2, 000

550 2, 200

550 2. 200

105 1, 100

275 1,450

550 2. 200

<ie>o 2, 750

550 2, 200

550 1,«.5<J

330 1,450

330 1,450

24(J 1,450

Modulus

of elasticity in

bending

i,oœp.s.i.

1, 200

1,600

1,800

1,«00

1, 100

1, 300

1,400

2, 000

1,.SOO

i.noo

1,300

1,300

1,300

F<)n\><t Ser\ ice Commercial «lesi.tinations are shown i

concentration are imposed, the limitations adopted may be nsed as a

basis for calculation of IKIICJUnder a conservative assumption, each lamination would contain,

at the critical cross section, a knot of the maximum size permitted

in the grade. Then, for members containing lammations of a single

grade, the value of IRIIG will be numerically equal to the ratio Kjb,

where K is the maximum permitted knot size and h is the finished

width of the lamination. Where two grades are combined—for

example, in a member with an outer group of laminations on each

side^of higher grade than the central group of laminations—the value

of Kjb for the member, in computing IKIIG^ depends upon the contribution of all the groups to the moment of inertia of the member.

For example, assume a member having 15 laminations, of which the

central 9 have a Kjb value of 0.50 and the outer 3 on each side have

üKlh value of 0.25. It may be assumed that for all laminations

KJh equals 0.25 and that the central 9 laminations have an additional

Kjh of 0.25. The central group, however, contributes to the moment

of inertia only in the proportion (9/15)^ Therefore, the value of

IKIIG will be:

0.25 +0.25 (9/15)^= 0.304

\Miere it is feasible to establish a specific pattern of knot locations

during assembly of the member, IKIIQ may be evaluated from the

knot locations specified by the pattern.
WOOD HANDBOOK 261

Estimation of K/b for Axially Stressed Members

Unless the location of knots is controlled when axially stressed

members are assembled, some assumption must be made as to the concentration of large knots in a member. A conservative assumption

would be that a knot of maximum permissible size occurs in each 3-foot

length of each lamination.

A statistical method based on the frequency of occurrence of the

largest knots in 3-foot lengths of lumber has been developed for

estimating the average of the largest knot sizes in a member. This

method has been applied to a limited number of Douglas-fir and

southern yellow pine grades (1/^, 20).

If grades or species are to be used for which a statistical analysis

has not been made, it is suggested that the conservative assumption

for concentration of large knots be used as a basis for design stresses.

Under this assumption, the factor Kjb, for use with figure 58 or figure

59, will involve a value of K equal to the size of the largest knot

permitted in the grade. For members composed of laminations of

more than one grade, the stress applicable to the lower grade should

be used.

Bending Members

In designing bending members, a number of factors are involved

in choosing an appropriate working stress—the effects of knots, cross

grain, end joints, height or depth of the beam, and curvature of the

laminations. The first four factors apply to either straight or curved

members and are not to be combined. The basic stress is multiplied

by the lowest of these four factors to obtain the working stress of

straight members.^^ For curved members, the resulting value is

multiplied also by the curvature factor.

Moment of Inertia

If scarf joints w^ith slopes not steeper than 1 in 5 are present, the

moment of inertia of the full cross section of the beam may be considered in design. If butt joints are present, the moment of inertia

should be reduced as described for them.

Deflections

Experience wdth figure 57 and statistically derived values of IKIIG

indicates that, for the majority of cases, the reduction of modulus of

elasticity below the basic value will be less than 5 percent. In most

instances, therefore, it will be sufficiently accurate to base calculations

of deflection on basic values of modulus of elasticity. Use of either

basic values of modulus of elasticity or values derived from figure 57

will give only immediate values oi deflection. Where deflection is

critical, consideration must be given to the added deflection that

occurs under long-time loading (see p. 161).

17 This may be unconservative for members having span-depth ratios of less

than about 14. That is, for such members, it may be necessary to modify the

lowest of the other three strength ratios by multiplying by the height factor.
262 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Radial Stresses

When curved members are subjected to bending moments, stresses

are set up in a direction parallel to the radius of curvature (perpendicular to grain). If the moment increases the radius (makes the

member straighter), the stress is tension; if it decreases the radius

(makes the member more sharply curved), the stress is compression

(21). The stress is a maximum at the neutral axis and is approximately

o _3 M

where M is the bending moment, R is the radius of curvature of the

centerline, and b and h are, respectively, the width and height of the

cross section.

For compression perpendicular to grain, values of SR should be limited to those shown in tables 25 and 36. For tension perpendicular to

grain, the stress should be limited, for softwoods, to about one-third

and, for hardwoods, to about three-eighths of the working stress in

shear.

Deep, Curved Members

It is known from the principles of mechanics that the stresses in

sharply curved members subjected to bending are in error when computed by the ordinär}^ formulas for straight beams. The amount of

the error depends upon the relation of the depth of the member to the

centerline radius. In solid timber construction, of course, this is not

a problem. In laminated construction, however, deep, sharply curved

members, such as arches with abrupt knees, may be used. It is probable that limitations on the sharpness to which laminations can be

bent will limit the curvature of deep beams or arches. The analytical

methods applicable to curved beams should be used, however, to determine whether or not the usual engineering formulas may be applied

without significant error to deep, sharply curved members of glued

laminated wood.

Axially Stressed Members

Three factors must be considered in choosing working stresses for

axially stressed members—the effects of knots, cross grain, and end

joints. The factor giving the lowest strength ratio is the one that determines the working stress; the three factors are not to be combined.

For compression members, the effect of plain scarf joints need not be

considered, since they are assumed to be 100 percent efficient in transmitting compression stress.

Effective Cross-Sectional Area

If plain scarf joints with slopes not steeper than 1 in 5 are present,

the full cross section may be considered effective. If butt joints are

present, the cross-sectional area should be reduced as was described

for these joints.
WOOD HANDBOOÏC 263

Columns of Different Classes

The usual formulas for determining the load-carrying capacities

of wood columns may be used for laminated columns. For short and

intermediate columns, the proper value of the compressive strength

should be calculated. For all classes of columns, the effect of joints

should be considered in arriving at the proper value of the effective

area.

Fastenings

Design loads or stresses for fastenings that are applicable to solid

wood members (p. 165) are applicable also to laminated members.

Since greater depths are possible with laminated members than witli

solid members, however, design of fastenings for deep laminated members requires special consideration. In these members, considerable

shrinkage may occur between widely separated bolts, and, if the bolts

are held in position by metal shoes or angles, large splitting forces

may be set up. It is desirable, therefore, to have the moisture content

of the member as near as possible to that which it will attain in service.

Slotting of the bolt holes in the metal fitting will tend to relieve the

splitting stresses. Cross bolts will assist in preventing separation if

splitting does occur; they will not, however, prevent splits.

DESIGN OF WOOD-PLYWOOD BEAMS AND GIRDERS

Glued structural members of built-up cross section, with pl^^vood

webs and either solid or laminated flanges, may be designed to carr>'

the same loads as members of rectangular cross section. The cross

sections of such wood-plywood beams and girders may have the form

of a box, an I, or a double I, as shown in figure 60.

Because the design of members with built-up cross sections places

material where it may be stressed to the best advantage, considerable

• UPPER FLANGE

LOAD BLOCK

OR ST IF FENER

ZM 89772 F

FIGURE 60. -Typical cross sections for wood-plywood beams: A, Box l)ean)s

B, double I-beam; C, I-beam.
264 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

savings of wood and weight are possible. Fabrication costs, however,

are higher than for members of rectangular cross section and may offset

the savings in material.

The design of a wood-plywood beam or girder is similar to that of

a steel-plate girder: (1) The flanges are designed to withstand bending moments; (2) the plywood webs are designed to withstand shear;

(:^) the joints between the webs and the flanges are designed to transfer stresses from the webs to the flanges; and (4) stift'eners and load

blocks are provided to distribute concentrated loads and to limit the

lengths of the unsupported panels in the webs. The design of such

a girder is a ''cut and try" procedure, but, once a trial section is

selected and loads are known, stresses can be calculated by using conventional formulas.

Limiting Considerations in the Design of WoodPlywood Beams

The overall height of a wood-plywood beam or similar structural

member is governed by one of the following considerations: Í1)

Clearance or other headroom limitations. (2) Width of the plywood

economically available for use in a beam. This is usually 4 feet or

some even fraction, such as one-half, one-third, or one-fourth, of 4 feet,

so that waste will be minimized. (3) Ratio of height to width and

span. The member must not be laterally unstable under design

loads when it is not restrained.

The choice of the type of cross section that should be used in a

given application depends upon several factors. If plywood of sufficient thickness is not available to permit utilization of single-web

members (I-beam), members with multiple webs may be required.

For some architectural appearances, the smooth surface of the box

l)eam may be desired. In certain exposures, however, because of the

danger that moisture may condense on or otherwise enter the interior

of a box beam, it may be desirable to select an I-beam. The I-beam

is easier to inspect for deterioration while in service than multiple-web

beams, because all parts of the I-beam are exposed.

Design of Flanges

The flanges of a wood-plywood member carrying bending moments

are designed so that the compressive stresses in compression flanges

at design load do not exceed the compressive working stress of the

wood and so that the tensile stresses in the tension flange do not exceed

the tensile working stress of the wood. For flanges that are of laminated construction, the working stresses and limitations for scarf

joints given in the section on glued laminated members (p. 255) should

be used as the limiting values of stress.

Calculation of Stress in Tension and Compression

The stress in the extreme fiber in compression is calculated by the

following formula:

o _MCc

^c— J

i11^
WOOD HANDBOOK 265

where Sc is the fiber stress in compression, in pounds per square inch;

M, the bending moment at the section under investigation, in inchpounds; Cc, the distance from the neutral axis to the extreme fiber

in the compression flange, in inches; and /, the moment of inertia of

the section about the neutral axis, in inchest

The stress in the extreme fiber in tension is calculated by the following formula:

o Ma

where St is the fiber stress in tension, in pounds per square inch; M

the bending mommt ot the section under investigation, in inchpounds; Ct, the distance from the neutral axis to the extreme fiber

in the tension flange, in inches; and I the moment of inertia of the

section about the neutral axis, in inches^.

The neutral axis of a box beam or an I-beam is at midheight if the

tension and compression flanges are of the same size, but if flanges of

unequal size are used, it is necessary to locate the neutral axis by a

summation of the moments of the areas of the cross section. Unequal

flanges are more economical of material than those of equal size,

because the tensile strength of wood is much higher than the compressive strength. The location of the neutral axis of a beam with

unequal flanges may be computed by the formula:

^h [t, (d-tc)-ft id-td]

where e is the distance from midheight of the beam to the neutral axis;

n the number of webs in the cross section of the beam; and k the modular ratio between the webs and flanges. For plywood with the grain

of some plies paraUel and the grain of other plies perpendicular to

the grain of the flanges, the modular ratio k is equal to the ratio of

the combined thickness of the plies with grain parallel to the grain

of the flanges to the thickness of the plywood. For plywood with

the grain oriented at 45"^ to the grain of the wood in the flanges, the

modular ratio k is approximately %. The symbols 6, tc, it, tw, and

(/ are the dimensions shown in figure 61.

Customarily, for preliminary calculation, the webs are ignored both

in locating the neutral axis and in computing the moment of inertia.

When this is done, the formula simplifies to

Jtc {d-Q-it (d-tt)

^ 2 (tc +t,)

The moment of inertia for a member with a built-up cross section

is computed by the summation of the moments of inertia of the

elements of the cross section about their respective gravity axes and

summation of the areas of the elements multiplied by the square of

the distances from the neutral axis to the respective gravity axes.

The two summations are added to give the general formula

i=i:io+^Ax'
266 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

where / represents the moment of inertia of the entire cross section;

/o the moment of inertia of each element about its gravity axis; A the

area of each element; and x, the distance from the neutral axis of the

entire cross section to the gravity axis of an element.

The specific formula for computing the moment of inertia / of the

cross section of a wood-pl3^wood member may be written as follows:

The symbols are the same as used in previous formulas or are shown

in figure 61.

Again, for preliminary computations, the contribution of the webs

to the moment of inertia is often neglected. Then the specific formula

is simplified to

/^*['--t''+.(c4-y+,,(c,-!jy]

When there are holes in the flanges for attaching other parts of the

structure or for other purposes, the moments of inertia should be calculated on the net cross section (gross cross section minus area occuNEUTRAL

AXIS

ZM 89773 F

FIGURE 61.—Component parts of a wood-plywood beam and symbols for use

in forminas when the component parts have essentially equal moduli of

elasticity.
WOOD HANDBOOK 267

pied by holes) for computing stresses, but the location of the neutral

axis should be calculated on the gross cross section. Additional

information on the design of flanges ma}^ be found in Forest Products

Laboratory Report 1513 (7).

The preceding formulas for calculating the position of the neutral

axis and the moment of inertia for built-up beams are based on the

assumption that the moduli of elasticity for the component parts are

essentially equal. If these moduli differ materially, the formulas

will give values that are in error, and the magnitude of the error

will vary with the difference in moduli of elasticity. The following

calculations are more exact, since they take into account differences

in moduli of elasticity.

The product of the modulus of elasticity and the moment of inertia,

El, is calculated by the following formula:

EI=E, Y2 f>tc'+E, ^ bt,'+E, ^ ntJ-'+E, ht, {a-^~)

+E, ht, (a-(/+^y+£:3 ntj (ö-£)'

where terms previousl}^ used have the same meanings and apply to

the cross section shown in figure 62, J^i, £2, and £'3 are the compressive

moduli of elasticity of the compression flange, tension flange, and

web, respectively, in pounds per square inch, and a is the distance from

the outside of the compression flange to the axis about which statical

moments are taken.

When the axis in question coincides with the neutral axis of the

built-up beam, the sum of the statical moments will equal zero.

To find the distance a at this point, the expression for El is difl'erentiated with respect to a and set equal to zero, giving the following

equation:

Ex btc (2a-tc^+Eo htt (2a-2(l+ t,) + E, ntj {2a-d)=0

Solving this equation for a gives:

E, ht,'+2E2 htt(l-E2 btt'+E,ntJ'

^~ 2 {E, bt.+Eobtr+E.nt^rl) '

This value of a can then be substituted in the formula for determination of El, and the El value for the built-up beam can be computed.

To compute stresses m the component parts of the beam, the proper

moment of inertia value / can be obtained by dividing the El value

for the beam by the modulus of elasticity for the part ni question.

For example, the formula for the stress in the extreme fiber m compression is:

_MCcE,

^c- El

where the symbols have the meanings previously indicated.

303747°—55 18
268 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 62.—The component parts of

a wood-plywood beam and the formula symbols for computing stress

when the component parts have

different moduli of elasticity.

ZM 89774 F

Design of Webs

The webs of a wood-plywood member are designed so that shear

sti'esses in the webs will not exceed design allowables when expected

maximum loads occur in service. Shear webs w^itli the grain of the

veneers in the pl>^vood oriented at 45"^ to the principal axis of the

member have considerably higher shear strength for a given thickness

than do webs with the grain of the veneers in the pl^nvood oriented

at 0'^ and 90° to the axis of the member. The manufacture of 45°

])lywood is wasteful of material, however, and ply^vood with this grain

orientation is used only in structures where weight is of paramount

importance, such as wing beams in aircraft.

The allowable working stresses in shear for the plyAvood webs

should be determined as given for phnvood elsewhere in this handbook

(p. 281).

Calculation of Shear Stress in Webs

The stress in shear in the webs is calculated by the following

formula:

S.

where Ss is the shear stress in the pl3^vood webs, in pounds per square

inch; F, the total shear at the location under investigation, in pounds;

Q, the statical moment of the area external to the axis of maximum

——.^^^ 3

shear stress, in inches ; n^ the number of webs; /, the moment of

: 4

inertia of the cross section about the neutral axis, in inches , based on
WOOD HANDBOOK 269

the gross section and computed as outlined in the section on calculation of stress in tension and compression; and ¿^ the thickness of one

web, as shown in figure 61, in inches.

The statical moment of the area external to the neutral axis is

calculated by a summation of the moments of the areas of the elements external to the neutral axis. Either those areas above or those

below the neutral axis may be summed. The two statical moments

ai'e equal and may be represented by the following formulas:

or

Q=~[bf^C2C-td + nkf,X'r]

where Q is the statical moment of the area external to the neutral

axis in inches ; ii, the number of webs; and K, the modular ratio 1)Ctween webs and flanges (see section on calcidation of stress m tension

and compression). The symbols b, tc, Cc, tw, it, and Ct are the dimensions shown in figure 61. More detailed information on the design of

webs may be found in material published earlier (5, 6, 9, 10, 18, 19).

The statical moments should be calculated on tlie gross section.

No corrections should be made for holes or similar reductions in the

area of the flanges.

Design of Joints Between Flanges and Webs

Stresses in the flanges must be transferred to the webs when a woodplywood member is under load. Usually, the wood-plywood member

is glued, and stresses are transferred in shear along the glue line.

Members should be designed so that these stresses do not exceed

design allowables under expected loads.

Mechanical fastenings (such as split-ring connectors) may be used

in large members to transfer the shear stress. When this is done,

the total shear force between flanges and webs should be distributed

among the fastenhigs according to design allowables given in the

section on timber fastenings.

The allowable stress at the glue lines between flanges and webs is

limited by the strength of the plywood in shear acting in tlie plane of

the plywood. This type of shear is designated as roUing shear, and

the allowable shear stress is approximately three-eighths of the allowable unit stress for horizontal shear of the species of wood in the

plywood if the grain of the wood in the plies is parallel or perpendicular to the principal axis of the member. If the grain in the

plywood is oriented at 45^ to the principal axis of the member, the

allowable shear stress is approximately one-half of the allowable unit

stress for horizontal shear of the species of wood used in the plywood.

Further information on these allowable stresses is given on page 275

and in Forest Products Laboratory Report 1630 {11).
270 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Calculation of Shear Stress Along the Line Between

Flanges and Webs

The shear stress along the line })etween the flanges and webs is

calculated by the following foi-mula:

where Sç is the shear stress at the lines between the webs and the

flanges, in pounds per square inch; V, the total vertical shear, m

pounds; Qf, the statical moment of the area external to the Imes

between the webs and the flanges, about the neutral axis, in inches ;

71, the number of glue lines between the webs and the flanges; /, the

rnoment of inertia of the gross cross section of the member about the

neutral axis, in inches ; and tt, the thickness of the tension flange, m

inches.

The statical moment of the area external to the Ihies between the

webs and flanges, about the neutral axis, may be expressed by the

following formula, since the tension flange is the area external to the

lines between the webs and component parts of the tension flange:

These formulas for shear stress and statical moment are applicable

to wood-plywood members of box or I cross section and to double-I

members when the total amount of tension-flange material on the

outsides of the webs is equal to the total amount between the webs.

When the amounts are not equal, the shear stresses are greater along

the lines adjacent to the greater flange areas, and stresses must be

investigated for these portions separately.

If the compression flanges are larger than the tension flanges, the

shear stresses along the lines between the webs and the compression

flanges are less than those along the lines between the webs and the

tension flanges, and it is not necessary to investigate these stresses.

Examples of this type of calculation'are given in Forest Products

Laboratory Report 1551 (8).

Design of Stiffeners and Load Blocks

The design of stiffeners and load blocks as to number and sizes

does not lend itself to a rational procedure (5), but certain general

rules can be given that will help the designer of a wood-plywood

structure obtain a satisfactory structural member.

Stift'eners serve a dual purpose in a structural member of this

type. One function is to limit the size of the unsupported panel in

the plywood web, and the other is to restrain the flanges from moving

toward each other as the beam is stressed.
WOOD HANDBOOK . 271

Stiffeners should be glued to the webs and should be in contact

with both flanges, as shown in figure 60. A rational way of determining how thick the stiffener in contact with the web should be is not

available, but it appears, from tests of box beams made at the Forest

Products Laboratory, that a thickness of at least six times the thickness of the plywood web is sufficient. Because stiffeners must also

resist the tendency of the flanges to move towards each other, the

stiffeners should be as wide as the flanges.

The spacing of the stiffeners is relatively unimportant for the shear

stresses that are allowed in plywood webs in which the grain of the

wood in some plies is parallel and the grain of the wood in other

plies is perpendicular to the axis of the member. Maximum allowed

stresses are below those which will produce buckling. Stiffeners

placed with a clear distance between stiffeners equal to or less than

two times the clear distance between flanges are adequate.

Load blocks are special stiffeners placed along a wood-plywood

structural member at points of concentrated load. Load blocks

should be designed so that stresses caused by a load that bears against

the side-grain material in the flanges do not exceed the design allowables for the flange material in compression perpendicular to grain.

Deflection of Wood-Plywood Members When Used as

Beams

The deflection of a wood-plyw^ood beam is produced by bending

stresses (compression stresses in the compression flange and tension

stresses in the tension flange) and by shear stresses in the plywood

webs. For solid wood beams, the deflection due to shear is smafl,

as compared to the deflection due to bending, for the spans usually

used.

The deflections due to bending stresses in a wood-plywood beam

can be calculated from the conventional formula for flexure:

y- El

where y is the center deflection, in inches; k\ a constant depending on

the t3rpe of loading and support; W, the total load, in pounds; /,

the span, in inches; E, the modulus of elasticity in compression, in

pounds per square inch; and /, the moment of inertia of the section

about the neutral axis, in inches.

The deflection due to shear in a beam is more difficult to estimate

than the deflection due to bending. Tests of a large number of woodplywood beams loaded at the third points indicate that the actual

stiffness of beams with plywood webs in which the grain was oriented

at 45° was about 80 percent of the stiffness calculated for bendmg

alone. For beams with plywood webs in which the grain was oriented

at O'' and 90° to the axis of the beam, the actual stiffness of the beams

averaged about 40 percent of the stiffness calculated for bendmg alone.

Third-point loading does not produce a relation between bendmg

and shear in a beam that is too greatly different from that usually
272 HANDBOOK 72, U. S, DEPARTMENT OF AGRICULTURE

oncountored in service. Therefore, to estimate the total deflection

of a wood-plywood beam, it is usually satisfactory to calculate the

deflection due to bending and increase this deflection by 25 percent

if 45° plywood webs are used and by 150 percent if 0° or 90 webs

are usedf Other means of estimating the deflections due to shear can

be used (5, 12). . ^ - . .

If several beams or girders of the same size are used m a structure,

and deflections are important, it is desirable to check the deflection

characteristics of actual members by test loading them and observing

the deflections. If mechanical fastenings are used to connect the

webs and flanges, it is necessary to test load typical members, because

it is not possible to calculate the accumulative slip in the mechanical

fastenings.

Lateral Stability of Beams and Girders

The resistance of a box or I member to buckling in a lateral direction

when loaded is important if the member is not restrained and forced

to deflect in a plane by other parts of a structure. A deep, narrow

beam may fail by buckling (in much the same manner as a long

column) before the ultimate bending strength is reached if it is not

restrained and forced to deflect in the plane of the load. The calculation of critical loads for any beam with a built-up cross section,

like a box beam or I-beam, is complex and involved. Tests at the

Forest Products Laboratory indicate that box beams and I-beams

of usual proportions are not critical in this respect at stresses allowed

by design, if the spans are not excessive, and the ratios of moments of

inertia about the neutral axis to moments of inertia about an axis

perpendicular to the neutral axis do not exceed 30 to 1.

The following rules for lateral deflection are conservative and can

be used to check a design for lateral stability:

(1) If the ratio of the moment of inertia of the cross section about

the neutral axis to the moment of inertia about the axis perpendicular

to the neutral axis does not exceed 5 to 1, no lateral support is required.

(2) If the ratio of the moments of inertia is between 5 to 1 and 10

to 1, the ends of the beam should be held in position at the bottom

flange at supports.

(3) If the ratios of the moments of inertia are between 10 to 1 and

20 to 1, the beams should be held in line at the ends. (Both the top

and bottom flanges should be restrained from horizontal movement in

planes perpendicular to the axis of the beam.)

(4) If the ratio of the moments of inertia is between 20 to 1 and

30 to 1, one edge should be held in line.

(5) If the ratio of the moments of inertia is between 30 to 1 and 40

to 1, the beam should be restrained by bridging or other bracing at

intervals of not more than 8 feet.

(6) If the ratio of the moments of inertia is greater than 40 to 1, the

compression flanges should be fully restrained and forced to deflect

in a plane.

A more exact analysis of lateral stability which may be used for design if desired, is given by Trayer and March {15),
WOOD HANDBOOK 273

LITERATURE CITED

(1) AMERICAN SOCIETY FOR TESTING MATERIALS.

1947. METHODS OF TESTING PLYWOOD, VENEER, AND OTHER WOOD-RASE

MATERIALS. Amer. Soc. Testing Mater. Standard DcS05-47 Pt

4: 691-713, illus.

(2)

1950. METHOD OF TEST FOR INTEGRITY OF GLUE JOINTS IN LAMINATED WOOD

PRODUCTS FOR EXTERIOR SERVICE (TENTATIVE). Anier SoC T(\sting Mater. Standard D1101-50T. Pt. 4: 847-848.

(3) DOUGLAS-FIR PLYWOOD ASSOCIATION.

1948. TECHNICAL DATA ON PLYWOOD. Sec. 7: 1-4, illus.; Sec. 9: 1-15,

illus. Tacoma, Wash.

(4) FREAS, A. D., and SELBO, M. L.

1953. FABRICATION AND DESIGN OF GLUED LAMINATED W^OOD STRUCTURAL

MEMBERS. U. S. Dept. Agr. Tech. Bui. 1069, 220 pp., ilhis.

(5) LEWIS, W. C, and DAWLEY, K. R.

1943. STIFFENERS IN BOX BEAMS AND DETAILS OF DESIGN, V. S. Forest

Prod. LaV). Rpt. 1318-A, 4 pp., illus. [l^rocessed.]

(6) ——-— HEEBINK, T. B., and COTTINGHAM, W. S.

1944. BUCKLING AND ULTIMATE STRENGTHS OF SHEAR WEBS OF BOX BEAMS

HAVING PLYWOOD FACE GRAIN DIRECTION PARALLEL OR PERPENDICULAR TO THE AXIS OF THE BEAMS. F. S. Forest l^rod. Lai). Ri>t.

1318-D 16 pp., illus. [Processed.]

(7) HEEBINK, T. B., and COTTINí;HAM, W. S.

1944. EFFECTS OF CERTAIN DEFECTS AND STRESS CONCENTRATING FACTORS

ON THE STRENGTH OF TENSION FLANiJES OF BOX BEAMS. U. S.

Forest Prod. Lab. Rpt. 1513, 10 pp., illus. [Processed.]

(S) — HEEBINK, T. B., and COTTINGHAM, W. S.

1945. EFFECT OF INCREASED MOISTURE CONTENT ON THE SHEAR

STRENGTH AT GLUE LINES OF BOX BEAMS AND ON THE GLUE-SHEAR

AND GLUE-TENSION STRENGTHS OF SMALL SPECIMENS. U. S. FORCST

Prod. Lab. Rpt. 1551, 11 pp., illus. [Processed.]

(9) — HEEBINK, T. B., COTTINGHAM, W. S., and DAWLEY, E. R.

1943. BUCKLING IN SHEAR WEBS OF BOX AND I-BEAMS AND THE EFFECT

UPON DESIGN CRITERIA. Ü. S. Forcst Prod. Lab. R])t. 1318-B, 7

pp., illus. [Processed.]

(10) — HEEBINK, T. B., COTTINGHAM, W. S., and DAWLEY, K. R.

1944. ADDITIONAL TESTS OF BOX AND I-BEAMS TO SUBSTANTIATE FURTHER

THE DESIGN CURVES FOR PLYWOOD WEBS IN BOX BEAMS. U. S.

Forest Prod. Lab. Rpt. 1318-C, 9 pp., illus. [Processed.]

(11) MARKWARDT, L. J., and FREAS, A. D.

1950. APPROXIMATE METHODS OF CALCULATING THE STRENGTH OF PLYWOOD.

U. S. Forest Prod. Lab. Rpt. 1630, 5 pp., illus. (Rev.) [Processed.]

(12) NEWLIN, J. A., and TRAYER, G. W.

1941. DEFLECTION OF BEAMS WITH SPECIAL REFERENCE TO SHEAR DEFORMATIONS. IT. S. Forest Prod. Lab. Rpt. 1309, 19 pp., illus.; rei)riiit

from Nati. Advisory Com. Aeronaut. Rj^t. 180. [Processed.]

(13) SOUTHERN HARDWOOD PRODUCERS INC.; APPALACHIAN HARDWOOD MANUFACTURERS, INC.; AND NORTHERN HEMLOCK AND HARDWOOD MANUFACTURERS ASSOCIATION.

1952. STANDARD SPECIFICATIONS FOR THE DESIGN AND FABRICATION OF

HARDWOOD GLUED LAMINATED LUMBER. 12 pp., illuS. Memphis,

Tenn.

(14) SOUTHERN PINE ASSOCIATION.

1951. STANDARD SPECIFICATIONS FOR DESIGN AND FABRICATION OF STRUCTURAL GLUED LAMINATED SOUTHERN PINE, 12 pp., illuS. NcW

Orleans, La.

(15) TRAYER, G. W., and MARCH, H. W.

1931. ELASTIC INSTABILITY OF MEMBERS HAVING SECTIONS COMMON IN AIRCRAFT CONSTRUCTION. Nati. Advisorv Com. Aeronaut. Rpt.

382, 42 pp., illus.
274 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

(16) U. S. DEPARTMENT OF DEFENSE.

1950. LAMINATED WHITE OAK (FOR SHIP AND BOAT USE). Mil. Specif.

]MIL-0-15154, 10 pp., illus.

(17)

1952. LAMINATED DOUGLAS FIR (FOR SHIP USE). Mil. Specif. MIL-F2038, 11 pp., illus.

(18) U. S. FOREST PRODITCTS LABORATORY.

1943. DESIGN OF PLYWOOD WEBS FOR BOX BEAMS. U. S. Forest Prod. Lab.

Rpt. 1318, 7 pp., illus. [Processed.]

(19) and ANC-23 PANEL ON SANDWICH CONSTRUCTION FOR AIRCRAFT.

1951. DESIGN OF WOOD AIRCRAFT STRUCTURES. ANC Bul, 18, 234 pp.,

illus. (Issued by Subcommittee on Air Force-Navy-Civil Aircraft

Design Criteria, Aircraft Committee, Munitions Board.)

(20) WEST COAST LUMBERMEN'S ASSOCIATION.

1951. STANDARD SPECIFICATIONS FOR THE DESIGN AND FABRICATION OF

STRUCTURAL GLUED (SOFTWOOD) LAMINATED LLTMBER. 12 pp.,

illus. Portland, Oreg.

(21) WILSON, T. R. C.

1939. GLUED LAMINATED WOODEN ARCH. U. S. Dept. Agr. Tcch. Bul. 691,

123 pp., illus.

(22) and COTTINGHAM, W. S.

1947. TESTS OF GLUED LAMINATED WOOD BEAMS AND COLUMNS AND DEVELOPMENT OF PRINCIPLES OF DESIGN. \]. S. Forcst Prod. Lab. Rpt.

R1687, 36 pp., illus. [Processed.]

^
PLYWOOD AND OTHER CROSSBANDED

PRODUCTS

Plywood is a term generally used to designate glued wood panels

that are made up of layers, or plies, with the grain of 1 or more layers

at an angle, usually 90°, with the grain of the others (1, 4, 5, 6, 7, 5).^'

The outside plies are called faces or face and back, the center ply or

pUes are called the core, and the plies immediately below the face

and back, laid at right angles to them, are called the crossbands (fig.

63). The essential features of plywood are embodied in other glued

constructions with many variations of details (3). The core may be

veneer, lumber, or various combinations of veneer and lumber; the

total thickness may be less than Ke inch or more than 3 inches; the

different pues may vary as to number, thickness, and kinds of wood;

and the shape of the members may also vary. The crossbands and

their arrangement largely govern the properties, particularly the

warping characteristics, and the uses of all such constructions (2).

As compared with solid wood, the chief advantages of pl^^vood are

its approach to equalization of strength properties along the length

and width of the panel, greater resistance to checking and splitting,

and less change in dimensions with changes in moisture content.

The greater the number of plies for a given thickness, the more nearly

equal are the strength and slirinkage properties along and across the

panel and the greater the resistance to splitting.

ARRANGEMENT OF PLIES

The tendency of crossbanded products to warp as the result of

stresses caused b}^ shrinking and swelling is largely eliminated by

balanced construction. This construction consists of arranging the

plies in pairs about the core, so that for each ply there is an opposite,

similar, and parallel ply. Matching the plies involves a consideration of (1) thicloiess, (2) kind of wood with particular reference to

shrinkage and density, (3) moisture content at the time of gluing,

and (4) angle or relative direction of the grain.

The use of an odd number of plies peraiits an arrangement that

gives a substantially balanced effect; that is, when 3 plies are glued

together with the grain of the outer 2 plies at right angles to the

grain of the center ply, the stresses are balanced and the panel

tends to remain flat with moisture content changes. With 5, 7, or

some other uneven number of plies, the forces may be similarly balanced. If only two plies are glued together with the grain of one at

right angles to the grain of the other, each ply tends to distort the

other when moisture content changes occur, and cupping usually results. Similar results are likely when any even number of plies are

used, unless the 2 center plies are parallel and act essentially as 1

plyThe use of balanced construction is highly important in thm panels

that must remain flat. In thicker members some deviation from

balanced construction is possible without serious consequences. For

example, with lumber cores that are properly crossbanded the face

^^ Italic numbers in parentheses refer to Literature Cited, p. 289.

275
276 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

A

FACES - _5^ CORE

CORE.

FACES - ^ CORE

. //////.v/.Y^/.: zzzzzzzzzzz.

CROSSBANDS

c

FACE CORE

^CROSSBANDS

D

FACE FIVE-PLY CORE

FACE

E

ZM 92378 F

FIGURE 63.—Types of plywood and cro.ssbanded construction: A^ 3-ply (all

veneer) ; ß, 3-ply (lumber core) ; C 5-ply (all veneer) ; D, 5-ply (lumber core) ;

E, 7-ply (all veneer) ; F, 5-ply bent work (all veneer) ; G, 5-ply, spirally wrapped

(all veneer) ; //, section of hollow-core door.
WOOD HANDBOOK 277

and back plies may be dissimilar without any noticeable effect;

whereas if dissunilar face and back plies were used in thin three-ply

panels, the warping might be very objectionable. In certain curved

members, the natural cupphig tendency of an even number of plies

may even be used to advantage.

Since the outer or face plies of a crossbanded construction are restramed on only one side, changes in moisture content inchice relatively large stresses on the outer glue joints. The magnitude of

stresses depends upon such factors as thickness of plies, density and

shrinkage of the wood hivolved, and the amount of change in nioisture content. In general, one-eighth inch is about the maxinunn

thickness of face plies that can be held securely in place when dense

woods are used and large changes in moisture content occur, and

thinner faces are advisable under such conditions of service.

QUALITY OF PLIES

In thin plywood the quahty of all the plies affects the shape and

permanence of form of the panel. All plies should be straight grained,

smootlily cut, and of sound wood.

In thick, five-ply lumber-core panels the crossbands, in particular,

añ'ect the quality and stabihty of the panel. Imperfections in the

crossbands, such as marked differences in the texture of the wood or

irregularities in the surface, are easily seen in the panel through thin

surface veneers. Cross grain that runs sharply through the crossband veneer from one face to the other causes the panels to cup.

Cross grain that runs diagonally across the face of the crossband

veneer causes the panel to twist unless the two crossbands ai"e laid

with their grain parallel. Lack of observance of this simple precaution accounts for much warping in crossbanded construction (2),

The best woods for cores of high-gi-ade panels are those of low

density and shrinkage, of slight contrast between springwood and

summerwood, and of species that are glued easily. Edge-gi*ained

cores are better than flat-grained cores because they shrink less in

width. In softwoods with pronounced summerwood, moreover,

edge-grained cores are better because the hard bands of summerwoo(l

are less likely to show through thin veneer and the panels show

fewer irregularities in the surfaces. In most species, a core made

entii-ely of either quartersawed or plainsawed material remains more

uniform in thickness with moisture content changes than one in

which the two types of material are combined.

Distinct distortion of surfaces has been noted, particularly in

softwoods, when the core boards were neither distinctly flat grained

nor edge grained.

GRADES AND TYPES OF PLYWOOD

Broadly speaking, two classes of plywood are available—hardwood

and softwood. Most softwood plywood is made of Douglas-fir, but

western hemlock, white fir, ponderosa pine, redwood, and other

species are used. Hardwood plywood is made of many species.
278 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Various grades and types are manufactured. ''Grade'' is determined by the quality of veneer, and ''type" by the moisture resistance

of tlie giue jomts. The types and grades in general use are listed in

commercial standards established by the industry with the assistance

of tlie Department of Commerce. Separate commercial standards

cover Douglas-fir plywood, western softwood plywood, ponderosa

])ine and sugar pine plywood, and hardwood plywood (4, 5, 6, 7).

DougJasi-fir jyJytooocL—Two types of Douglas-fir ply^vood are listed

in Commercial Standard CvS45-48—Interior and Exterior. The

Interior type is expected to retain its form and practically all of its

strength when occasionally subjected to a thorough wetting and subsequent normal drying. It is commonly bonded with soybean glue or

with an extended resin glue of the phenol type. Exterior-type plywood

is expected to retain its form and strength when repeatedly wet and

dried and otherwise subjected to the elements and to be suitable for

permanent exterior use. It is commonly bonded with hot-press,

phenol resin glue.

Within each type, several grades are established by the quality of

the veneer on the two faces of a panel. In descending order of quality,

the veneer is designated as A, B, C, or D. Grade A-A plywood, for

example, has Grade A veneer on both faces, and Grade A-D plywood

has Grade A veneer on one face and Grade D on the other. As a

general rule, Grade C is used for the inner plies of the Exterior type

and Grade D for the inner plies of the Interior type.

Softwood plywood other than Douglas-fir.—The requirements of

Commercial Standard CS122-49 for western softwood plywood

resemble those of the commercial standard for Douglas-fir. The same

two types—Interior and Exterior—are provided for, and the grade is

determined by the quality of veneer used on the two faces of each

panel. The grades of veneer are designated A, B, C, and D, as with

Douglas-fir veneer, but one higher grade, A-1, is provided.

Commercial Standard CS157-49 provides for only an Interior type

of ponderosa pine and sugar pine plywood. The grades of veneer are

designated in descending order of quality as Good, Sound, Solid,

Sheathing, and Backs. Provisions are made for eight grades of

plywood, as for example "Good 2 Sides'' and "Solid 1 Side," depending

upon the quality of veneer used on the faces and backs.

Hardwood plywood.—Four types of hardwood plywood—Technical,

Type I, T^^pe II, and T^^pe III—are described in Commercial Standanl

CS35-49. For the most part the difference between the types is

based on the resistance of the glue bond to severe service conditions,

although Technical differs from Type I in the permissible thickness

and arrangement of plies. Glue bonds conforming to the requirements

of both Technical and Type I pl^^wood are high in durability and

correspond closely to those required for Exterior-type Douglas-fir

plywood. In general, resistance of the glue bonds of Type II hardwood

plywood resembles that of Interior-type Douglas-fir plywood. Good

dry strength but no water resistance is required of the glue bonds in

T3^pe III hardwood plywood.

The grade of the plywood is determined by the quality of the

veneers used on the faces and backs of the panels. The veneer is

graded 1, 2, 3, and 4 in order of descending quality. The requirements

are the same for all hardwood species for Grades 2, 3, and 4; Grade 1
WOOD HANDBOOK 279

requirements are described separately for each species. The plywood

grade is designated by combining the designation of the grade^of the

veneer on the face and back, as Grade 1-2 or Grade 2-3. Veneers of

Grade 2 or 3 are generall}^ used for mner plies.

Plywood for special purposes.—Most of the plywood produced in

this country conforms in general to the commercial standards. Some

plywood, however, is produced to meet specific demands or to conform

to specifications that were drawn to secure a product suitable for

a special purpose.

A considerable quantity of plywood is produced with overlays of

paper or fabric impregnated with synthetic resins. Frequently, an

overlay is applied to one face to provide a desired decorative effect

combined with good wearing characteristics. This product is widely

used for counter and table tops. If a decorative type of overlay is

applied on one face, a plain overlay is usually applied on the l)ack to

reduce the tendency to warp that would otherwise result. Often the

overlay is applied primarily to improve general serviceability, to

improve painting characteristics, or to reduce face checking. In such

cases, the decorative layer is omitted, and the same overlay of plain

color is used for both face and back. As a general rule, decoi-ativc^

overla3^s are laid in a separate operation after the plywood panel has

been fabricated, while plain overlays are laid at the time of gluing

the veneer into plywood.

Specifications for aircraft structural plywood sharply define glue-line

quality, species, thickness of plies, and mechanical properties of the

veneer in order to insure a product suitable for use in the structural

elements of aircraft (8). Large corporations likewise may develop

their own specifications for plyw^ood for special purposes.

Unless very large quantities are involved, procurement of specialpurpose plywood is difficult, costly, and often wasteful. For most

purposes, plywood conforming to commercial standards is adequate.

DETERMINATION OF STRENGTH OF PLYWOOD

Determination of the strength properties of plywood by testing all

of the many possible combinations of ply thickness, species, and

number of plies is impractical. For this reason, formulas relating

the strength properties of plywood to the construction of the plywood and to the properties of the component plies were developed

mathematically and checked by tests to verify their applicability.

Plywood strength properties are therefore not given directly but

are given as formulas that permit calculations for any specific case.

Plywood may be used under loading conditions such that stiffeners

will be required to prevent it from buckling. It may also be used in

the form of cylinders or curved plates. Such uses are beyond the

scope of this handbook, but they are discussed in ANC Bulletin 18 (^).

It is obvious from its construction that a strip of plywood cannot

be so strong in tension, compression, or bending as a strip of solid

wood of the same size. Those plies having their grain direction

oriented at 90^ to the direction of stress can contribute only a fraction

of the strength contributed by the corresponding area_s of a solid strip,

since they are stressed perpendicular to the grain. Strength proper-
280 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

ties in the directions parallel and perpendicular to the face grain tend

to be equalized in plywood, since in some interior phes the grain

direction is parallel to the face grain and in others it is perpendicular.

The formulas given in this handbook may be used, m general, tor

calculating the strength properties of plywood at proportional limit

or ultimate or for estimating working stresses, depending upon ttie

strenc-th property that is substituted in the formulas for the property

of the veneer. Procedures for evaluating the effect of such features

as knots and cross grain on the strength of veneer are not available.

Factors by which basic stresses must be reduced to obtain safe working

stresses must therefore be a matter of judgment based on each individual case. Strength properties at proportional limit and ultimate

that are suitable for use in the formulas are given in table 12. Basic

stresses are given in tables 25 and 36.

Properties in Edgewise Compression

Modulus of Elasticity

The modulus of elasticity of plywood in compression parallel, to or

perpendicular to the face-grain direction is equal to the weighted

average of the moduli of elasticity of all plies parallel to the applied

load. That is,

E^ or E,=l 2 Eihi

where Ey, is the modulus of elasticity of plywood in compression

parallel to the face grain; Ex, the modulus of elasticity of plywood in

compression perpendicular to the face grain; Ei, the modulus of

elasticity parallel to the appUed load of the veneer in ply i; hi, the

thickness of the veneer in ply i; h, the thickness of the plywood; and n,

the number of plies.

Those plies whose grain direction is perpendicular to the apphed

load contribute so little to the value of E^ and Ex that they may be

omitted from the calculation with httle error.

The modulus of elasticity in compression at angles to the facegrain direction other than 0° or 90° is given approximately by:

A_^ cos^ e+^ sin^ <9+7^- sin' 0 cos' 6

Ee Ey, rLx ^wx

where EQ is the modulus of elasticity of a plywood strip in compression

at an angle d to the face grain; Gy^x is the modulus of rigidity in shear

for the conditions in which all 4 of the shear stress components are

directed parallel to the plane of the plywood (1 pair of components

parallel to and 1 pair perpendicular to the face grain) ; and the other

terms are as defined in the previous formula. Formulas for computing values of Gy^ are elsewhere in this section.

When compressive loads are applied at an angle to the face grain

of plywood elements, shear strains (angular displacements) result in

.^
WOOD HANDBOOK 281

addition to the direct compressive shortening. ANC Bulletin 18 (9)

gives methods for calculating these shear strains as well as the dimensional changes resulting from the effect of Poisson's ratio.

Strength Properties

The compressive strength of plywood subjected to edgewise forces

is given by:

rp ^ w rp

" cic 171 " < F

cL

cL

K

^ ex LT ^ CL

where Few is the compressive strength of plywood parallel to the face

grain; F ex. the compressive strength of plywood perpendicular to

the face grain; F^L. the compressive strength of the veneer parallel to

the grain; and KCL, the modulus of elasticity of the veneer parallel

to the grain.

Values of modulus of elasticity in bending for solid wood are given

in table 12. These values, increased by 10 percent, may l)e used for

y?cL- If niore than one species is used in the longitudinal plies, values

for the species having the lowest ratio of FCLIECL should be used in

the formulas given.

When plywood is loaded at an angle to the face grain, its ultimate

compressive strength or working stress in compression may be computed from:

/cos^ö , sin^ e .

\'FJ ^ CW"^+"F^" ^ Cl +

where FCB is the compressive strength of plywood at an angle B to the

face grain, and Fswx is the shear strength of plywood for the condition

with all 4 of the shear stress components directed parallel to the plane

of the plywood (1 pair of components parallel and 1 pair perpendicular

to the face grain); and the other terms are as previously defined.

Properties in Edgewise Tension

Modulus of Elasticity

Values of modulus of elasticity in tension will be the same as those

in compression.

Strength Properties

The strength of a plywood strip in tension parallel or perpendicular

to the face grain may be taken as the sum of the strength values of

the plies having their grain direction parallel to the applied load.

For this purpose, the tensile strength may be taken as equal to the

modulus of rupture.
282 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

The tensile strength parallel to the face grain will be designated as

Ff and the tensile strength perpendicular to the face gram as rtxThe tensile strength at an angle to the face grain may be computed

from:

F, lcos^e.sm'_

\M F '^^F. J- (If ^ IX

0 . sin^ öcos^(9

2 ~r j^ 2

-* AWT

where Fte is the tensile strength of plywood at an angle 6 to the face

o-i'ani.

Properties in Edgewise Shear

Modulus of Rigidity

The modulus of rigidity of plywood may be calculated from:

Gicx'^T 2—1 ^i'^'i

fi i=}

1 /=1

where Gy,x is the modulus of rigidity of plywood subjected to shear

but not to bending; Gfu^,, the modulus of rigidity of ph^vood subjected

to bending as well as shear; and Gi, the modulus of rigidity of the ith

ply in the plane of the sheet; It, the moment of inertia of the ith ply

about the neutral plane of the pl3^vood ; and /, the moment of inertia

of the total cross section about its centerline.

When the plywood is made of a single species of wood:

Gfy,i^Gy.^=G^T for rotary-cut veneers;

Gjy,^-=^Gy,x^Gj^R for quarter-sliced veneer.

Values of G^T and GJ^R are given in terms of the modulus of elasticity

parallel to grain (Ei) in table 13.

The modulus of rigidity at an angle to the face grain ma}^ be computed from:

-[e+¿] ^=^ cos^ 29+1 ^^4- I sin^ 2Ö

Strength Properties

The ultimate strength of plywood elements in shear, with the shearing forces parallel and perpendicular to the face-grain direction, is

given by the empirical formulas

F — ^^ ^^~^-u ^- T" F • //.

h ' 16/¿ tr

.j.d
WOOD HANDBOOK 283

where n is the number of phes and F,y,:ci is the shear strength of the

ith ply.

In using this formula, the factor (n — l)/h should not be assigned a

value greater than 35.

To convert Fswx to a basic stress, divide it by 4, thus taking into

account variabilit}^, long-time loading, and factor of safety.

In some commercial grades of plywood, gaps in the core or crossbands are permitted. These gaps reduce the shear strength of plywood, and the formula just given shoukl be corrected to accoinit for

this effect. This may be done by subtracting from the number of

plies (T?) in the first term twice the number of plies containing openings

at any one section and omitting from the summation in the second

term all plies containing openings at any one section. Since the lirst

term represents the contribution of the glue hivers to shear, twice

the number of plies containing openings at any one section is sul)tract(H1

to account for the lack of glue on each side of the opening. The

modification for the effect of core gaps just outlined represents a

logically derived procedure not confirmed by test. When test data

become available, this procedure may be modified.

When the ph^wood is stressed in shear at an angle to the face grain,

ultimate shear strength with face grain in tension or compression is

given by the following formulas:

¡Í Í' , 1 \ • "o/i^cos^^Ö

F,Bc^

1

1 . 1 \ . , ^^ . COS" 26

2 v(¿+¿)^"'^'^+'

For the special case in which the shear stresses are applied at 45*^

to the face grain:

F ^'-

MB'

F ^'

MkJ

Properties in Flexure

Modulus of Elasticity

The modulus of elasticity in bending is equal to the average of the

moduh of elasticitv parallel to the span of the various plies weighted

according to their ^moment of inertia about the neutral plane. That

is,

303747^—55 19
284 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

where Ef,^ is the modiihis of elasticity of plywood in bending w^ien

the face grain is parallel to the span; Efx, the modulus of elasticity of

plywood in bending when the face grain is perpendicular to the span;

Ku the modulus of elasticity of the 7th ply in the span direction; /<,

the moment of inertia of the /th ply about the neutral plane of the

])lywoo(l ; and I, the moment of inertia of the total cross section about

its cent(M-line.

For syiTunetrically constrnctíMl ])lywoo(], the n(Mitral plane will

be at the centíMÜne. For unsynnnetrically constructcul plywood,

the neutral plane is usually not at the centerline of the geometrical

section. For such cases, the distance from the neutral plane to the

extreme compression (or tension) fiber, c, is given by:

i = l

where d is the distance from the extreme compression (or tension)

liber to the centerline of the iÚ\ ply.

When all plies are of the same thickness and species, these general

formulas reduce, for pl^^wood made from rotary-cut veneer, to:

3-ply,AV.=g(^>+26)

-ply,/i..-/^(26^+99)

/,,,.^ ( 26 + 99 f;)

7-ply,/^..-^|| (99 1^+244)

9-ply, E,u=^(244 ^{+485)

i?.=^(244 + 485 1^)

For quarter-sliced veneer, the formulas will be the same, except

that ET!E:^ will be replaced by E^^JEL. The symbols ET and £«

denote the moduli of elasticity in the tangential and radial directions,

respectively. Values of ETJËL and ERJEL for some species are given

in table 13.
WOOD HANDBOOK 285

For species for which vakies of the ratio are not avaihvbl(\ it is

suggested that ETJEL be taken as 0.05 and EKIEL as 0.10.

Strength Properties

The resisting moment of plywood strips having face grain paralh^l

to the span is given by:

W FT

M=0.85-;("^

EL C

For face grain perpendicular to the span,

7l/=1.10 Ç^ ^for 3-ply plywood

EL c 1 ^ 1 J

TP ^ TP T

^/=0.90 -^—^ —^ for plywood having 5 or more phes

LLL C

where M is the resisting moment of the plywood; i\, th(^ strength

property of the outermost longitudinal ply; c, the distance from the

neutral plane to the outer fiber of the outermost longitudinal ply;

and E'f^ is the same as Efjc, except that the outermost ply in tension

is neglected, and the other terms are as defined previously.

For plywood having five or more plies, the use of Efj in place of

E'f^ in calculating the resisting moment will result in negligible error.

It should be noted that E'f^ is used only in strength calculations and

is not to be used in deflection calculations.

Formulas are not available for calculating bending strength at an

angle to the face grain.

Approximate Methods

Table 37 gives approximate methods of calculating the strength

and stiffness of plywood. The methods given therein will be us(^ful

in estimating properties and, in some cases, may be expected to give

values sufficiently accurate for general use. The methods are not

apphcable to cases where the plywood may be expected to buckle.

SPLITTING RESISTANCE

Plywood permits fastening with nails or screws close to the edges

because it oflers much greatei- resistance to splitting than ordinary

wood. Also, because of the ecpialization of strength properties along

and across a sheet and the resistance to splitting resulting from the

crossbanded construction, plywood panels covering relatively large

areas are less liable to damage from concentrated or impact loads

than similar panels made of ordinary lumber.

In removing nails from plywood, some care must be used to pull

them straight out, or nearly so, because splintering of the outside ply

may result if the nails are pulled or pried out at an angle.
286 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

SHRINKAGE OF PLYWOOD

The shrinkage of plywood varies with the species, the ratios of ply

thicknesses, the numÍ3er of plies, and the combination of species.

The average shrinkage values obtained at the Forest Products Laboratory in drying, from a soaked to an oven-dry condition, 3-ply panels

having all plies in any one panel of the same thickness and species

was about 0.45 percent parallel to the face grain and 0.67 percent

perpendicular to the face grain, with ranges of from 0.2 to 1 percent

and 0.3 to 1.2 percent, respectively. The panels tested ranged in

thickness from Ko to K inch. For all practical purposes, shrinkage of

plywood in thickness does not differ from that of solid wood.

TABLE 37.—Design method a tul allowable stresses for ealculating the strength and

stiffness of plywood ^

Property, and direction of

stress with resiK'Ct to direction of face grain

Tension:

I'arallel or |>eri)endiciilar

±4.5'

Compression:

Parallel or perpendicular

±45°..

BearLnp at ripht angles to

plane ol plywood.

I>oad in bending, parallel or

perpendicular.

Area to be considered I'nit stress to be used

Deflection in bending, parallel or perpendicular.

Deiomiation in tension or

compression, parallel or

perpendicular.

Shear through thickness:

Parallel or perpendicular

±4.5°.

Parallel plies '- only

Full cross-sectional area.

Parallel idies - only

Full cross-sectional area

Loaded area

Bending moment M = Ksl!c where .^'=unit

stress for e-Xtreme fiber in bending; /=nioment of inertia computed on basis of

parallel plies only; c = distance from neutral axis to outer fiber of outermost ply

having its grain in the direction of the

span; A"=1..5n lor 3-ply plywood having

the grain of the outer plies perpendicular

to the si)an; A'=().8.S for all other plywood.

Deflection may be calculated by the usual

formulas, takine as the monnmt of inertia

that of the parallel plies plus I/20 that of the

perpendicular plies. (When face plies are

parallel, the calculation may be simplified,

with but little error, by taking the moment

of inertia as that of the parallel plies only.)

Parallel plies - only

Tnit stress for extreme fiber

ill bending,

' ^ unit stress for extreme fiber

in bending.

T'nit stress in compression

parallel to grain.

^{^ unit stress in compression

parallel to grain.

I'nit stress in compression

perpendicular to grain.

I'nit stress for extreme fiber

in bending.

Tnit value for modulus of

elasticit>'.

Full cross-sectional area.

Unit value for modulus of

elasticity.

Double unit stress in horizontal shear.3

4 times unit stress in horizontal shear.

( otnutes at (Mid of table
WOOD HANDBOOK 287

TABLE 37.—Design method and alloioable stret^e^s for calculating the strength and

stiffness of plywood ^—Continuod

Property, and direction of

stress with respect to direction of face grain

Shear in plane of plies:

Parallel or perpendicular

Area to be considered Vnit stress to be used

Full shear area: Plywood beams. Horizontal shear.

Area oí contact between plywood and llanKC

or íraniinK member:

I- or box-bearns with plywooti webs

Shear between i»lies of web or between

web and l'ange:

•,'4 unit stress in horizontal

shear.

•'s unit str(>ss in horizontal

shear.

Panels having ])lywood eovers

stressed in com¡)ression or tension,

or both. Shear between plies or

between cover and framing members when depth of member

e.xceeds twice its width and end

headers are used or when depth is

not more than twict^ the width

and no headers are used.

Interior framing members M unit stress in horizontal

shear.

Framing members at eflge of panel-. '^íí nnit stress in horizontal

shear.

±45° Area of contact between plywood and flange

or framing member:

I- or box-beams with plywood webs

Shear between plies of web or between

web and fange:

See footnote at end of table.

M' unit stress in horizontal

shear.
2SS HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

TABLE 37.—Desitjn meuiod and alloivahle s/resses for calculating the strengtii and

stiffness of plywood '—Coiitiniied.

Vro\n rtv, and (liicctioii of

St rc <s with csjM-c( fo «liI('Cl on (»f fa( • ^lain

Aica fo hf COllsiiiricrl Unit stress to be used

Area oí contact hctwcci) plywood

and flaiific or framirifi nicmhcrCoTitinucd

Shear bet.vvceii i)lies of web or

between web and ilan^M'—

Continued

Panels having plywood covers

stressed in compression, or tension,

or l)oth. Shear between filies or

between cover and framing nienib<'rs when dei)th of inenil>er

exceeds twice its width and end

liea<lers are used or when depth is

not more than twice tlie width

and no hea<h'is ire useil.

Interioi'fiaminti niemfxTS _ ... T'nit stress in fiorizontal

Framing meiTibers at edjic of inniel ^j unit stress in horizontal

shear.

1 The suggested! simidified methods of calculation apply reasonably well ^^ ith usual i)lywood types under

ordinary conditions of service. It is recognized, however, that they are not entirely valid for all types of

plywood and plywood constructions, or (or all spans and span-depth ratios. Also the methods given are

not applicable to structures so proiiortioned that the i)ly\vood is in the buckling range, in which event the

results will be too high.

2 By "parallel plies" is meant those idies whose grain direction is parallel to the direction of i)rincipal

stress.

' This value shouM Vie reduced if gaps occur at edge joints (see j). 283).

HOLLOW-CORE CONSTRUCTION

The term ''hollow-core" refers to a type of crossbanded construction,

somewhat resembling lumber-core plywood, in which the center ply

or core is not solid but built up of wood strips, wood lattice, sections

of paper cylinders, or other materials offering only partial support

to the facings. Perhaps the most common application of the constructiiDn is the hollow-core, flush door (fig. 63, H) in which the space

between the stiles and rails contains a lattice and the facings are

three-ply plywood. The lattice or other supporting material used in

the core space must be spaced so as to provide suflficient mchanical

support to prevent buckling or distortion of the facings, and, as in

conventional plywood, the construction as a whole must be balanced

to prevent waTping. When properly fabricated, the construction is

lightweight in relation to its strength.
WOOD HANDBOOK 289

LITERATURE CITED

(1) AMERICAN SOCIETY FOR TESTINC MATERIALS.

1949. DEFINITIONS OF TERMS RELATING TO VENEER AND PLVWIX^D (TENTATIVE), Amer. Soc. Testing Mater. Standard D1038 49T. Pt. 4,

733-738.

(2) BROUSE, D.

1940. SOME CAUSES OF WARPINC IN PLYWOOD AND VENEERED PRODICTS.

U. S. Forest Prod. Lab. Rpt. R1252, 8 pp., illus. [Processed.]

(3) PERRY, T. D.

1942. MODERN PLYWOOD. 366 pp., illus. New York.

(4) U. S. DEPARTMENT OF COMMERCE.

1948. DOUCLAS-FiR PLYWOOD. Coni. Standard CS45-48, 25 pp., illus.

(5)

1949. HARDWOOD PLYWOOD. Coui. Standard CS35-49, 27 pj)., illus.

(6)

1949. w^ESTERN SOFTWOOD PLYWOOD. Coin. Standard CS122-49, 22 pp.,

illus.

(7)

1949. PONDEROSA PINE AND SUC AR PINE PLYWOOD. Coni. Standard CS157-

49, 13 pp.

(8) U. S. DEPARTMENT OF DEFENSE.

1950. PLYWOOD AND VENEER: AIRCRAf T I^LAT PANEL. Mil. SpCCif. MIL-P -

6070, 12 pp., illus.

(9) I^. S. FOREST PRODUCTS LABORATORY.

1951. DESICN OF WOOD AIRCRAFT STRUCTURES. ANC Bul. 18, 234 pp.,

illus. (Issued by Subconiniittee on Air Force-Navy-Civil Aircraft

Design Criteria, Aircraft Connnittee, Munitions Board.)
STRUCTURAL SANDWICH CONSTRUCTION

Structural sandwich construction is a layered construction formed

by bonding two thin facings to a thick core (fig. 64). The thin facings

are usually of a strong, dense material, since they are the principal

load-carrying parts of the construction. The core, which is of a

weaker, lightweight material, separates and stabilizes the thin facings

and carries shearing loads. The entire assembly provides a structural

element of high strength and stiffness in proportion to its weight.

Sandwich construction is also economical, since only small amounts of

the relatively expensive facing material are used and the core materials

are usually inexpensive. The materials are positioned so that each

is used to its best advantage.

FinuRE 64.—A cutaway section of sandwich construction with plywood facings

and a paper honeycomb core.

Specific nonstructural advantages can be incorporated in a sandwich

construction by proper selection of facing and core materials. An

impermeable facing can be employed to act as a moisture barrier for

a wall or roof panel in a house; an abrasion-resistant facing can be

used for the top facing of a floor panel; and decorative effects can be

obtained by using panels with plywood or plastic facings for walls,

doors, tables, and other furnishings. Core material can be chosen to

provide thermal insulation, fire resistance, and decay resistance.

291
292 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

The component parts of the sandwich construction should be

compatible with service requirements. Moisture-resistant facings,

cores, and adhesives should be employed if the construction is to be

ex])osed to adverse moisture conditions. Similarly, heat-resistant or

(lecay-resistant facings, cores, and adhesives should be used if exposure

to elevated temperatures or decay organisms is expected.

FABRICATION OF SANDWICH PANELS

Facing Materials

One of the advantages of sandw^ich 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. Some of the

different facing materials used include plywood, single veneers or

])lywood overlaid with a resin-treated paper; hardboard; asbestos

board; metals, such as aluminum, enameled steel, stainless steel, or

magnesium sheet; wallboard; fiber-reinforced plastics or laminates;

and veneer bonded to metal.

Core Materials

Many lightweight materials, such as balsa wood, rubber or plastic

foams, ^and formed sheets of cloth, metal, or paper, have been used

as core for sandwich construction. From the standpoint of economy,

availability, and other advantages for mass production, the type of

core made from paper treated with synthetic resin (5, 9) ^^ appears

to be promising. The paper core is made by forming flat sheets of

dense paper in various ways to yield a much larger volume of lowdensity honeycomblike material (fig. 64).

Since sandwich panels are likely to be subjected to damp or wet

conditions, the presence of resin in the paper core is necessary to

yield a product that is permanently strong and stiff in the wet condition. Treatment with 15 percent of resin provides paper of good

strength when wet, decay resistance, and handling characteristics

during fabrication (10). Resin amounts in excess of about 15 percent

do not seem to produce a gain in strength commensurate with the

increased quantit}^ of resin required.

Manufacturing Operations

The principal operation in the manufacture of sandwich panels is

the bonding of the facings to the core, usually in hot-press equipment.

Special presses are indicated for sandwich panel manufacture, because

the pressures required are usually lower than can be obtained in the

range of good pressure control on ordinary ply^vood or plastic presses.

Since pressure requirements are low, however, simple and perhaps

less costl}^ presses could be used. Continuous roller presses or bagmolding equipment may also be suitable. Certam special problems

^^ Italic numbers in parentheses refer to Literature Cited, p. 297.
WOOD HANDBOOK 293

arise in the pressing of sandwich panels, but their niaimfaclure is

basically not complicated (9).

The facing materials may need to be cleaned and primed befoic

the adhesive is applied, especially if they are metallic.

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 be placed more easily in the panel during manufacture than

after it is completed.

Some of the most persistent difficulties in the use of sandwich panels

are caused by the necessity for edges, inserts, and connectors foipanels. In some cases, the problem involves tying together thin

facing materials without causing severe stress concentrations, and in

other cases, such as furniture, the problem is caused by ''showthrough'' of core or hiserts through decorative facings. These difficulties are minimized by the choice of materials in which the rate and

degree of diñerential dimensional movement between core and insert

are at a minimum.

Further information on fabrication of sandwich ])an(4s is given in

other Laboratory papers (4, 9, 12, 14).

STRUCTURAL DESIGN OF SANDWICH CONSTRUCTION

The structural design of sandwich construction may be compared

to the design of an I-beam ; the facings of the sandwich represent th(*

flanges of the I-beam, and the sandwich coie represents the I-beam

web. The core of the sandwich serves, through the bonding adhesive,

to carry shearing loads and to support the thin facings against lateral

wrinkling caused by compressive loads in the facings.

In general, the procedure is to provide facings thick enough to

carry the compression and tension stresses and then to space the

facings with a core thick enough to impart stiffness and bending

strength to the construction. The core should be strong enough to

carry the required shearing loads. The construction should l)e

checked for possible buckling, as for a column or panel in compression,

and for possible wrinkling of the facings.

The core material itself is assumed to contribute nothing to the

stiffness of the sandwich construction, because it usually has a lowmodulus of elasticity. The facing moduli of elasticit}^ are usually at

least 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 constructions sul)-

jected to bending and decreased buckling loads of columns and edgeloaded panels, compared to constructions in which the core shear

modulus is large. The effect of this low shear modulus is greater foishort beams and columns and small panels than it is for long beams

and columns and large panels.

The stiffness of sandwich construction having facings of equal or

unequal thickness is given by:

i,f,E,EAh+cf

4 (/i^^+M\>)
294 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

where D is the stiffness per unit width of sandwich construction

(product of moduhis of elasticity and moment of inertia of the cross

section); /i, Í2 are the facing thicknesses; E,, E2 are the moduh oí

elasticity'of tlie facings; h is the total sandwich thickness; and c is the

core thickness. The stiffness is used to compute the deflections and

the buckling loads of sandwich panels.

The midspan deflection of a panel of sandwich construction, with

simply supported ends and free edges, under a uniform transverse

load is given by:

bPa'' r . 192 cZ)

w- 384Ö6

where w represents the midspan deflection; P, the total load on sandwich panel; a, the span length; G^, the shear modulus of core material;

and 6, the width of the sandwich panel.

In a strip of sandwich construction subjected to both bending

moments and shear loads the mean facing stresses are given by:

^1.2"

2M _

yK^(h+c) b

where Si, 2 is the mean compression or tension stress in facing 1 or 2;

fi, 2, the thickness of facing 1 or 2; and M, the bending moment.

Under the same conditions, the shear stress in the core is given by:

_ 2V

'^ {h+c)b

where q is the shear stress in the core and V, the shear load on the

sandwich.

The buckling load of a sandwich panel at least twice as wide as it is

thick and loaded as a simply supported column is given by:

and

^=^^'^^f-a^W(^^l-0

where a is the column length and 6, the panel width.

The preceding formulas are basically those needed for the design of

sandwich constructions. Formulas have been derived for various

loading and edge conditions for constructions of orthotropic or Isotropie materials. The behavior of thin facings in regard to wrinkling

and core shear failure has also been investigated. Analyses of these

more specific problems of design may be found in other laboratory

papers (7, 2, 3, 6, 7, S, IS).
DIMENSIONAL STABILITY AND BOWING OF SANDWICH

PANELS

In a sandwich panel any dimensional movement of one facing with

respect to the other due to changes in moisture content and temperature causes bowing of an unrestrained panel (9). 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

dimensions of the panel will increase or decrease but bowing will not

result.

The problem of dimensional stability is chiefly rehited to the facings,

because the core does not have enough stift'ness to cause bowing of the

panel or to cause it to remain flat. The magnitu(U> of the bowing

effect, however, depends on the thickness of the core.

It is possible to calculate mathematically the bowing of a sandwich

construction if the percent expansion of each facing is known. The

maximum deflection due to bowing caused by the expansion of one

facing resulting from temperature or moisture differential is given

approximately by

SOOh

where k is the percent expansion of one facing as compared to the

opposite facing; a, the length of the panel; and h, the total sandwich

thickness.

In conventional construction, vapor barriers, usually of asphaltimpregnated paper or metal foil, 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 include bonding of metal foil within the sandwich

construction; blending aluminum flakes with the resin bonding adhesives; and use of plastic vapor barriers between veneers, overlay

papers, special finishes, or metal or plastic facings. Because added

cost is likely, some of these should not be resorted to unless their need

has been demonstrated.

A large test unit (14) simulating use of sandwich panels of various

kinds under housing conditions has been constructed at the Laboratory

for the purpose of observing bowing of panels and general performance. The experimental assembly shown in figure 65 represents the

type of construction used in the test unit.

As a generalization, the bowing of sandwich panels is probably

neither greater nor less than that of stressed-skin prefabricated housing panels having similar facings.

THERMAL INSULATION OF SANDWICH PANELS

Satisfactory thermal insulation of sandwich panels can best be

obtained by using cores having low thermal conductivity, although the

use of reflective layers on the facings is of some value. Paper cores

295
296 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 65.—Experimental assembly used to investigate the performance of

sandwich panels for house construction.

of the types previously mentioned have thermal conductivity values

(k values) ranging from 0.30 to 0.65 British thermal units per hour

per 1° F. per square foot per inch of thickness, depending on the particular core construction (5, 9, 11). The k value is also affected by

the cell size, density, and resin content of the core.
WOOD HANDBOOK 297

An improvement in the insulation value can be realized l)y fillino;

the honeycomb core with insulation or a foamed-in-plac(^ resin. A

reduction in the k values of a corrugated core from 0.46 to 0.40 British

thermal units per hour per IT. per square foot per inch of thickness

was obtained when a phenolic resin was foamed into the core. A

slightly lower value was obtained through the use of fill insulation.

FIRE RESISTANCE OF SANDWICH PANELS

In tests at the Laboratory, the fire resistance of wood-faced sandwich panels was appreciabl}' higher than that of hollow panels faced

with the same thickness of plywood {9). 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 alinement of the flutes in the core. In panels having

flutes perpendicular to the facings, only slight spread of flame occurred (9). In corrugated core in which one-half of the flutes were

parallel to the length of the panel, the spread of flame occurrc^d in the

vertical direction along open channels. This could no doubt 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, l)y simply

turning the length of the core blocks at 90° to the vertical direction.

LITERATURE CITED

(1) BoLLER, K. H., and XORRIS, C. B.

1950. EFFECT OF SHEAR STRENGTH ON MAXIMUiM LOADS OF SANDWICH

COLUMNS. U. S. Forest Prod. Lab. Rpt. 1815, 12 pp., illiis.

[Processed.]

(2) ERICKSEN, W. S.

1950. DEFLECTION UNDER UNIFORM LOAD OF SANDWICH PANELS HAVINO

FACINGS OF UNEQUAL THICKNESS. U. S. Forest Prod. Lab. Rpt.

1583-C, 32 pp., illus. [Processed.]

(3) and MARCH, H. W.

1950. COMPRESSIVE BUCKLING OF SANDWICH PANELS HAVING FACINGS OF

UNEQUAL THICKNESS. U. S. Forest Prod. Lai). Rpt. 1583-B,

30 pp., illus.

(4) HEEBINK, B. G., MOHAUPT, A. A., and KUNZWEILER, J. J.

1947. FABRICATION OF LIGHTWEIGHT SANDWICH PANELS OF THE AIRCRAFT

TYPE. U. S. Forest Prod. Lab. Rpt. 1574, 30 pp., illus. [Processed.]

(5) KuENzi, E. W.

1951. PAPER HONEYCOMB AS A CORE FOR STRUCTURAL SANDWICH CONSTRUCTION. Amer. Soc. Testing Mater. Symposium on Structural Sandwich Constructions, Spec. Tech. Pub. 118, illus.

(6) and ERICKSEN, W. S.

1951. SHEAR STABILITY OF FLAT PANELS OF SANDWICH CONSTRUCTION.

U. S. Forest Prod. Lab. Rpt. 15(;0, 42 p]).. illus. [I^rocessod.]

(7) MARCH, H. W., and SMITH, C. B.

1949. FLEXURAL RIGIDITY OF A RECTANGULAR S'l^R] P OF SANDWICH CONSTRUCTION. U. S. Forest Prod. Lai). Rpl- 1505, 19 pp., illus.

[Processed.]

(8) NoRRis, C. B., ERICKSEN, W. S., MARCH, IL W., SMITH, C. B.,and BöLLER,

K. H.

1949. WRINKLING OF THE FACINGS OF SANDWK:H CONSTRUCTIONS SUBJECTED TO EDGEWISE COMPRESSION. U. S. Forest Prod. Lab.

Rpt. 1810, 68 pp., illus. [Processed.]
298 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

(9) SEIDL, R. J.

1952. PAPER-HONEYCOMB CORES FOR STRUCTURAL SANDWICH PANELS.

U. S. Forest Prod. Lab. Rpt. R1918, 21 pp., ilhis. [Processed.]

(10) KuENZi, E. W., FAHEY, D. J., and MOSES, C. iS.

1951. PAPER-HONEYCOMB CORES FOR STRUCTURAL BUILDING PANELS:

EFFECT OF RESINS, ADHESIVES, FUNGICIDES, AND WEIGHT OF

PAPER ON STRENGTH AND RESISTANCE TO DECAY. U. S. Forest

Prod. Lab. Rpt. R1796, 16 pp., illus. [Processed.]

(11) TEESDALE, L. V.

1949. THERMAL INSULATION MADE OF WOOD-BASE MATERIALS: ITS APPLICATION AND USE IN HOUSES. U. S. Forest Prod. Lab. Rpt.

R1740, 40 pp., illus. [Processed.]

(12) U. S. FOREST PRODUCTS LABORATORY.

1951. SANDWICH CONSTRUCTION FOR AIRCRAFT, PART I: FABRICATION,

INSPECTION, DURABILITY, AND REPAIR. ANC Bulletin 23, 120

pp., illus. (Issued by Subcommittee on Air Force-Navy-Civil

Aircraft Design Criteria, Aircraft Committee, Munitions Board.)

(13)

1951. SANDWICH CONSTRUCTION FOR AIRCRAFT, PART II : DESIGN CRITERIA

FOR SANDWICH CONSTRUCTION. ANC Bulletin 23, 101 pp., illus.

(Issued by Subcommittee on Air Force-Navy-Civil Aircraft

Design Criteria, Aircraft Committee, Munitions Board.)

(14) U. S. FOREST PRODUCTS LABORATORY.

1948. PHYSICAL PROPERTIES AND FABRICATION DETAILS OF EXPERIMENTAL HONEYCOMB-CORE SANDWICH HOUSE PANELS. U. S.

Housing and Home Finance Agency Tech. Paper 7, 23 p., illus.
BENT WOOD MEMBERS

Curved members of wood are produced by bandsawing or b}^ bending. Bandsawing often wastes considerable wood and produces curved

members that have cross grain, or grain that runs out along the curved

surfaces. Bending produces curved members that are free from this

type of cross grain and, if well done with propeily selected lumber, is

also less wasteful of wood. Bending is used particularly for producing

members of sharp curvature, such as parts of fmiiitm-e and ship and

boat frames.

The bending may be done with or without a plasticizing treatment,

such as steaming. The bent member may be solid or laminated.

The grain of all laminations may be parallel, or that of adjacent

laminations may be perpendicular. The laminations ma}^ be individually bent and then glued together in the curved shape, or glued

together and then bent.

STEAM BENDING OF SOLID PIECES

Principles of Bending

Wood of certain species steamed or soaked in boiling water can l)e

compressed as much as 25 to 30 percent parallel to the grain. The

same wood can be stretched only 1 to 2 percent. Because of the relation between attainable tensile and compressive deformations, it is

necessar}^ if bending involves severe deformation, that most of the

deformation be forced to take place as compression. The inner or

concave side must assume the maximum amount of compression and

the outer or convex side, zero strain or a slight tension. To accomplish this, a metal strap equipped with end fittings is 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 (6).^^

Selection of Stock

In general, hardwoods possess better bending (juality than softwoods, and certain hardwoods surpass others in this quality. The

species commonly used to produce bent members are: White oak, red

oak, elm, hickory, ash, beech, birch, maple, walnut, sweetgum, and

mahogany. Softwoods have poor bending quality, as a rule, and are

not often used in bending operations. Yew and yellow-cedars are

probable exceptions to this rule. Douglas-fir, southern yellow pine,

the cedars, 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 greater than about 1 to 15. Decay, knots, shake, pith, surface

checks, and exceptionally light or brashy wood should be avoided.

20 Italic numbers in parentheses refer to Literature Cited, p. 308.

303747°—55 20 ^^^
300 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Such irrogiilaritios tend to cause the pieces of wood to fail during

Ixniding, paiticuLnrly if they are on the face that is to be the inner or

concave side at the time of bending and if the piece is to be bent to a

sharp curvature.

Seasoning Bending Stock

Although green wood can be bent to produce most curved members,

difficulties are introduced in the drying and fixing of the bent piece and

in reducing the moisture content of the bent piece to a figure suited for

the end use. Another disadvantage with green stock is that hydrostatic pressure may be developed during bending. Hydrostatic pressure may 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 requires

a long 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 percent before it is steamed. The

preferred moisture content 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 a

moisture content of 12 percent. The moisture content values desired

for the bending of chair parts fall within the range of those for partially

or thorouglily air-dried stock.

Plasticizing of Bending Stock

Heat and moisture make certain species of wood sufficiently plastic

for bending operations. Steaming at atmospheric or a low gage

pressure (fig. 66) or soaking in boiling or nearly boiling water are

satisfactory methods of plasticizing wood. Wood at 20- to 25-percent

moisture content needs to be heated without losing moisture; at

lower moisture content heat and moisture must be added. As a consequence, the recommended plasticizing processes are steaming or

boiling for about ji hour per inch of tliickness for wood at 20- to

25-percent moisture content and steaming or boiling for about 1 hour

per inch of thickness for wood at lower moisture content values.

Steaming at high pressures causes wood to become plastic, but wood

treated with high-pressure steam generall}^ does not bend so successfully as wood treated at atmospheric or low pressure. Certain chemicals plasticize wood, but wood so plasticized seldom bends as successfully as wood plasticized with steam at atmospheric pressure.

Bending Operation and Apparatus

After being plasticized, the stock should be quickl}^ 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
P»;

WOOD HANDBOOK 301

FIGURE 66.—Rcninviiiíj a stick from a steaniitig retort.

of steamed wood against the form. If the curvature to be obtained

demands a difference of much more than 3 percent between lengtlis

of the outer and inner sm-faces of the pieces, then the apparatus

should include a device for applying end pressm-e. This generally

takes the form of a metal strap or pan provided with end blocks, end

bars, or clamps (figs. 67, 68).

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

dried to a moisture content suited 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 dried, the curvature will be maintained

unless the wood undergoes changes in moisture content. An increase

in moisture content causes the piece to lose some of its curvature.

A decrease in moisture content causes the curve to become sharper,
302 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

FicuKE 67.—A pan loaded ^vith steamed stock, between the plates of a hot-plate

l)ress, ready for bending into chair-ljack posts.

FIGURE 68.—Apparatus for bending heavy members. The end blocks of the

metal strap are equipped with reversed levers made from I-beams, which prevent the end blocks from overturning and sliding off, help to regulate end pressure, and reduce the tendency of the stick to assume reverse or back bends

near the ends.
WOOD HANDBOOK 303

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 possesses less strength than a similar but

unbent piece. The reduction in strength brought about by bending,

however, is seldom serious enough to affect the utility value of the

member.

STEAM BENDING OF LAMINATED MEMBERS

Straight laminated members can be steamed and bent after they

are glued by operations similar to those used for solid meml)ers (5).

The glue used for laminating should be one that will not be affected

by the steaming or boiling treatment. In asseml)ling the laminations

for a member that is to be bent, the best pieces should preferably be

selected for the outer laminations. It is especially important to place

a high-qualit}^ piece on the side that is to ])e concave after l)ending.

Butt joints within the member should be designed to resist longitudinal

compression.

PRODUCTION OF BENT LAMINATED MEMBERS WITHOUT

STEAM TREATMENT

Laminated curved members are produced from (h-y stock by bending and gluing together in one operation several comparatively thin

pieces without softening them b}' steam or hot water. This process

has the following advantages over the bending of single-piece members:

(1) The laminations can be made so thin that bending to the required

radius involves only moderate stress and deformation of the wood

fibers; consequently, the use of steam or hot water is unnecessary and

less subsequent drying and conditioning is required; (2) because of

the moderate stress induced in bending, stronger parts are produced ;

(3) the tendency of laminated members to change shape with changes

in moisture content resulting from changes in relative humidity is less

than that of single-piece bent members; (4) ratios of thickness of

member to radius of curvature that are impossible in bending single

pieces can readily be obtained by laminating; also members having

reversed curvature are more readily made by laminating thin plies,

and curved parts of any desired length can be produced l)y staggering

the joints in the laminations.

Both softwoods and hardwoods can be used for laminated bent

structural members, and thin material of any species can be satisfactorily bent for such purposes. The choice of species and glue is

dependent primarily upon the cost, required strength, and demands

of the application.

Laminating of curved pieces in the United States was originally

apphed chiefly to comparatively small parts, such as those m furniture and pianos. The principle has been extended rapidly, however,

to the construction of wood arches for use as roof su])])orts in farm,

industrial, and public-assembly buildings, and to the construction of

ship timbers {4, 12),
304 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

VENEERED CURVED MEMBERS

Veneered curved members are usually produced by gluing veneer

to on(^ or both faces of a curved solid wood base (7, 8, 9, 10). The

l)ases are ordinarily bandsawed to the desired shape or bent from a

]uece grooved with saw kerfs on the concave side at right angles to the

directions of bend. Sometimes series of curved pieces are bandsawed

contiguously from the same block of wood and reassembled in a gluing

operation in the same relative position with glue-coated pieces of

veneer between, thus producing a number of similar veneered curved

pieces in one operation. Pressure is then applied to the whole series.

In other assemblies single members are bandsawed to the desired

ciu'vature and then faced with a layer of veneer, and pressure is applied

l)y means of flexible bands and clamps while the glue sets. Pieces

bent by making saw kerfs on the concave side are commonly reinforced

and kept to the required curvature by gluing splines, veneer, or other

pieces to the curved base.

Veneering over curved solid wood finds use mainly in furniture.

The grain of the veneer is commonly laid in the same general direction

as the grain of the ciu'ved wood base. The use of crossl^and venec^rs,

that is, veneers laid with the gi*ain at right angles to the grain of the

base and face veneer, reduces the tendency of the member to split.

PLYWOOD CURVED MEMBERS

Curved plywood is produced (1) by l)ending and gluing the plies in

one operation, or (2) by bending previously glued flat plywood.

Ciu^ved ph^wood made by method (1) is more stable in curvature

than plyAvood curved by method (2).

Plywood Bent and Glued Simultaneously

In bending and gluing plywood in a single o])eration, glue-coated

|)i(^ces of veneer are ass(unbled and pressed over or between ciu'ved

forms, and pressure and sometimes heat applied until the glue sets and

liolds the assembly to the desired ciirvature {3, 11). Some of the

himinations 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 in order to

facilitate bending.

The advantages of bending and gluing plywood simultaneously to

form a curved shape are similar to those for curved laminated members,

and in addition the cross plies give the curved members properties

characteristic of cross-banded plywood.

Molded Plywood

Although any piece of curved plywood may properly be considered

to be molded plywood, the term ''molded'' is usually reserved for plywood that is glued to the desired shape, either between curved forms,

as described previously, or, more commonly, by means of fluid pressure. The molding of ])lywood by means^ of fluid pressure applied

with flexible bags or blankets of some impermeable material (bag
WOOD HANDBOOK 305

molding) is used in making plywood parts of various degrees of compound curvature (1,2). These parts vary in size from small aircraft

fairings to complete boat hulls.

Misnomers, such as ''plastics pl^^wood," ''plastic planers/' or just

''plastics" have been applied to structm-(^s of mohhul ])lywood that

are actually made from wood VCIKHM-S 1)ond(Ml with synth(^tic i'(^siu

adhesives. By w^Mght, th(^s(^ structuj-(^s contain about .SO ])ei-c(Mit of

wood and 20 percent of i'(^sin adli(^siv(\ Excerpt for vaiiations in

shape, the prochict is essiMitially tlu^ same as i]a.t-j)i(^ssed plywood.

Plywood Bent After Gluing

After the plies are glued together, flat plywood is ofti^i bent b}^ methods that are somewhat similar to those used in bending solid wood.

To bend plywood properly to shape, it must be plasticized l)y sonu^

means, usually moisture or heat, or a combination of l)oth. The

amount of curvatiux^ that can ])e 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 introducing the bend. Plywood

is normally bent over a form or a bending mandrel.

Limited data are available on the relation between approximate

breaking radius and thickness of plywood, veneer, and luml)er under

several conditions. vSome of these were derived from actual factory

practice and some from tests at the Forest Products Laboratory. An

approximate relation between thickness and breaking radius of plywood of aircraft quality is presented in flgure 69, A and B. These

graphs are based primarily on tests of plywood between 0.035 and 0.375

inch in thickness, but it is believed that the curve for the 90° angle and

10 percent moisture content may also be applied in estimating th(^

breaking radius of veneer or air-dry lumber between 0.01 and 1 mch

in thickness. The angle referred to on each graph is the angle between

the grain direction of the face plies and the axis of the bend.

Most of the tests were made at th(^ 0° or 90° angle, but a few tests

on wider strips of plywood at 45° indicated that there was little or

no difference between the results at 0° and 45° conditions. The term

"hot soaked" means that the plywood is thoroughly soaked in hot or

boiling water until it sinks, after which it is bent over a mandrel

heated to approximately 300° F.; the term "10-percent moisture content" means plywood of this moisture content bent over a cold mandrel. The tests were made by slowly bending 1-inch-wide strips of

aircraft pl3rvvood around a series of mandrels of decreasing size until

fracture occurred. Soaking in water at room temperature would

probably produce a degi'ee of flexibility or a breaking radius intermediate between that shown for dry plywood and that for hot-watersoaked plywood. Bending plywood at 10-percent moisture content

over a hot mandrel also might be considered an intermediate treatment, and a breaking radius between those of dry and hot-soaked

plywood anticipated.

In applying these data, it is desirable to multiply the approximate

breaking radius obtained from figure 69 by a factor of safety in order

(1) to obtain a working radius that will provide against overstressing

in bending, (2) to allow for inapplicability of figure 69 to the case
306 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

HARDW00D5

T-THICKNE55 OF PLYWOOD (INCH)

ZM 48523 F

FIGURE 69, A.—Hardwoods. Approximate relation between thickness and breaking radius of plywood between 0.035 and 0.375 inch in thickness, of aircraft

construction and quality. Tests made l^y slowly bending plywood strips 1

inch wide over njandrels with no support on the tension side. Angle referred

to on the graph is the angle between the grain direction of the face plies and the

axis of the bend. Broken line a refers to the example given in the text.
WOOD HANDBOOK 307

SOFTWOODS

I

I

5!

2

I

5

1^

'^ 0,09

II 0.08

Qt: 0.07

00/ 0.01 0-OS 004 0.0b 0Û6ÔJ 02 Ö.S Ö.4 Oh OS 1.0

T-TH/CKN555 Of" PLYWOOD (INCH)

ZM 48523 F

FIGURE 69, B.—Softwoods. Approximate relation between thickness and breaking radius of plywood between 0.035 and 0.375 inch in thickness, of aircraft

construction and quality. Tests made by slowly bending plywood strips 1

inch wide over mandrels with no support on the tension side. Angle referred

to on the graph is the angle between the grain direction of the face plies and

the axis of the bend. Broken line 6 refers to the example given in the text.
308 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

in hand, (3) to avoid face checking of plywood, and (4) to reduce the

forces required to form the bend and hold the bent part in position.

Values of 2 to 3 are suggested for the factor of safety against breakage

applied to the radius in adapting these data to the bending of commercial plywood.

Examples showing the use ojfigure 6'5.—After soakmg m hot water,

to what radius can 0.160-inch birch plywood be bent on a hot mandrel,

with the face grain parallel to the axis of bend and allowing a factor

of 3 against breakage? Starting at r=0.160 inch on the graph for

hardwoods, R is found (line a on graph) to be 0.37 inch, which, multiplied by 3, gives 1.11 inches as the safe bending radius.

What thickness of Douglas-fir plywood can be safely bent to a

9-inch radius dry and unheated, with the face grain parallel to the

axis of the bend? Using a factor of safety of 3, the breaking radius

is read on the softwood curve as 3, which is 9 divided by the factor

of safety. From this radius, the thickness is found (line h on graph)

to be about 0.125 inch.

Flat plywood glued with a waterproof adhesive can be bent after

gluing or postformed to compound curvatures. No simple criterion,

however, is available for predetermining whether a specific compound

curvature can be imparted to flat plywood. Soaking the pl3rvvood

and the use of heat during forming are aids in manipulation. Normally

the plywood to be postformed is first thoroughly soaked in hot water

and then dried between heated male and female 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.

Plywood has been postformed to compound curvatures that require

an upset of about 8 percent in compression without evidence of

\\T^inkling or shear failures. It should be remembered that in postforming plywood to compound curvatures, all of the deformation

must be by compression or shear, as plywood cannot be stret<ched.

Hardwood species, such as birch, poplar, and gum, are normally used

in plywood that is to be postformed.

LITERATURE CITED

(1) HEEBINK, B. G.

1945. METHODS OF BAG-MOLDING PLYWOOD. InduS. PlasticS 1 (4).

(2)

(3)

1946. FLUID-PRESSURE MOLDING OF PLYWOOD. U. S. FoiGst Prod. Lab.

Rpt. R1624, 19 pp., illus. [Processed.]

1950. SOME METHODS OF GLUING LIGHT LAMINATED OR PLYWOOD CURVED

SHAPES FROM VENEER. U. S. Forest Prod. Lab. Rpt. R1485,

3 pp., illus, [Processed.]

(4) KNAUSS, A. C, and SELBO, M. L.

1948. LAMINATING OF STRUCTURAL WOOD PRODUCTS BY GLUING. U. S,

Forest Prod. Lab. Rpt. D1635, 63 pp., illus. (Revised.) [Processed,]

(5) MCKEAN, H. B., BLUMENSTEIN, R. R., and FINNORN, W. F.

1952. LAMINATING AND STEAM-BENDING OF TREATED AND UNTREATED OAK

FOR SHIP TIMBERS. South. Lunibemian 185 (2321).

(6) PECK, E, C.

1950, BENDING SOLID WOOD TO FORM. U. S. Forest Prod. Lab. Rpt.

D1764, 29 pp., illus. [Processed.]

(7) PERRY, T. D,

1930. METHODS USED IN VENEERING CURVED WOOD FORMS. VencerS 24 (9).
WOOD HANDBOOK 309

(8) PERRY, T. D.

1930. INSTRUCTIONS FOR BUILDING CURVED PLYWOOD. VcilCerS 24 (10).

(9)

1930. PRINCIPLES INVOLVED IN RENDIXC PLV\V()OD. N'oiK'i'TS 24 (11).

(10)

1951. CURVES FROM FLAT PLYWOOD. Wood PpOfl. ;")() (4).

(11) 4^RnAX, T. II.

1929. í:LUINí¡ OF WOOD. U. S. I)('})i. Agr. Hul. 1500, 7S pp., illus.

(12) r. S. FOREST PRODUCTS LARORATORV.

1945. WOOD A MANUAL FOR ITS USE IN WOODEN VESSELS. IsSVlCcl by

Navy Bureau of Ships, 235 i)p., illus.
CONTROL OF MOISTURE CONTENT AND

SHRINKAGE OF WOOD

EQUILIBRIUM MOISTURE CONTENT

Any piece of wood will give off or take on moisture from the surrounding atmosphere until the amount of moisture in the wood balances that in the atmosphere. The moisture content of the wood at

the point of balance is called the equilibrium moisture content and is

expressed as a percentage of the oven-dry weight of the wood.

Assuming constant temperature, the ultimate moisture content

that a given piece of wood will attain depends entirely upon the

relative humidity of the atmosphere surrounding it. The relationship

between equilibrium moisture content and relative humidity at

different temperatures is shown in table 38. For practical use in

control of dry-kiln or storage-room conditions, comparative values are

shown for different dry-bulb temperatures and for different wet-bulb

depressions. For example, at a dry-bulb temperature of 70° F. and

a wet-bulb depression of 9° below dry-bulb temperature, which corresponds to a relative humidity of 59 percent, the equilibirum moisture

content of the wood is 10.9 percent. Changes in relative humidity in

the higher ranges cause greater changes in equilibirum moisture content than do corresponding changes in the lower ranges of relative

humidity. Although different species exhibit some differences in

their reactions to relative humdity, for practical purposes table 38

applies to the wood of any species.

Wood in service is exposed to daily and seasonal changes in relative

humidity. Thus, wood is virtually always undergoing at least slight

changes in moisture content because of its tendency to come to a

balance with the relative humidity of the surrounding air. The

changes are gradual and may be further retarded by protective

coatings, such as varnish, lacquer, or paint. The practical object of

all correct seasoning, handling, and storing methods is to minimize

moisture content variations in wood in service by fabricating or

installing the wood at a moisture content corresponding to the average

atmospheric conditions to which it will be exposed.

SHRINKAGE OF WOOD

Wood, like many other materials, shrinks as it loses moisture and

swells as it absorbs moisture.

Wood from the tree may contain from 30 to 300 percent of water

{3, 11),^^ based on the weight of the oven-dry wood. This water may

be separated roughly into two parts, that contained as free water in

the cell cavities and intercellular spaces of the wood and that held as

absorbed water in the capillaries of the walls of such wood elements

as fibers and ray cells. The absorbed water is of primary interest in

the consideration of shrinkage. When all of the free water is removed

but all of the absorbed water remains, wood is said to have reached

21 Italic nunibors in parenthèses refer to Literature Cited, p. 336.

311
TABLE 38.—Relative humidity ^ and equilibrium ?uoisture eonteni- table for use with dry-bulb temperatures and wet-bulb depressions CO

to

Wot-bulh (lopression C^F.)

30

3^

50

55

00

65

70

75

80

85

90

95

92

l.í 93

1 94

I

Í9,

I -

I 95

1 -

I 95

lÍ9n

1 --

I 9(^,

I -

Í 9C>

lf 9r,

78' 67'

1.5.9 i2. 9

81 72

iß.8'' í^.9\

8:3 75

/7. 6'i í/f.S'

S5, 7H

}8.3' 1,5. fí

86, 80i

19.0 16. S'

88 82-

19.5 16.9

89; 83

19.9. 17. Jf,

90 84

20. S 17. H

90 8»i

20.6 IS. 2

91 m

20.9 18.5

91 87

21.0 18.1

92 88

21.2 18.8

92 89

21.3 18.9

92 89

21.3 19. 0\

93 89'

2Í.3 /9.O.

57

m

11.9

68

;.?. iv

13.7

74

7()

/.5, /

7S

15.6

80

/(5. /

81

16. 5

82

16.8

83

/7.^^

84

/?. p'

85:

/7..?

85

/7.4

86

17.5

7 I 8 i 9 ¡ 10 11 12 13 I 14 , 15 16 17 18 l!í 20 21 , 22 23 24 25 26 ¡ 27 28 29 30 32 34 36 38 40

.L i

"1

45 .50

46' 3r,' 27 17 6' I '

P,r¡ 7.4, 5.7\ 3.9\ ;.^ , M 45 37' 2<8' 19 11 ' 3 .. _

10.3 8.8 7. 41 ^. ^;! If. 5. ¿.P| 0.8

50 52 45 37 29' 22' 15 8 _.._!

//..? 9.9 8.6 7.41 6. i 5.0 3.5 }.9i ^ \ 64 58 511 44 37, 31 25 19 12 6

n. O 10. 7 9. 5' 8. 5 7. 5^- 6. ,5' ,5. 3 4. ?' 2. 9 1. 5

68 62 56: 50| 44: 38¡ 32^ 27i 21, 16, 10 5,__

12.7 11.5 10.3 9.4' 8.5 7.6 6.7 5.7' 18 3.9 2.8 1.5

70 (i5! 601 54| 49i 44' 39: 34¡ 28| 24¡ 19 14 9 5

I3.jfl2.m.()l0.l 9..r 8.4 7.6 6.8 6.0] 5.3 15 3.6 2.5 1.3

73' 68' ()3 58Í 53 48' 43 39 34Í 30Í 2(>i 211 17' 13' 9 5 1 _

ll9 12.7 11.6 10.7 9.9 9.1 8.3 7.6 6.9 6.3 5.6 4.9 4./ o. 2 2.3 1.3 0. 2 _ ^

75 70 {\i\^ 61 56' 52* 48 44' 39' 36' 32 27' 24 20 16 13 8 6 2

llf.J, 13..] 12.1\11.2\}O.J, P.7| 8.9 8..y\ 7.7j 7./, 6.5 5.8 5.2 í,.5 3.8 o.O. 2.3 /. 4 0,4

77 72 68¡ 64' 59 55 5l 48' 44' 40 36 33 29 25 22 19 15 12 9 6 3

1J,.9 Í3.7\12.5\1Í.6\ÍC.9\10.1 9.1 8.8\ 8.3, 7.7 7.2\ 6.6\ 6.i' 5.5\ 2,.9 4.;í; 3.7 2.9 2.2> 1.5 0.7 _

7S 74 70 66, 62' ,58 54 51, 47 44 41 37 34 31 2.S 24 21 18 I", 12 10

15.:12,.O'l2.í)U2.0\lí.2l0.5\^ 9.8 9.3\ 8.7'. 8.2 7.7 7.2: 6.7 6.2 5.0 5.1 4.7 4./ ,?. .r 2.9 2.3 1

79 75 72. 68j 64j 611 57 54 50| 47 44, 41 38 35 32 29 26 23 20 18 15

15.5íJt.3 13.2''í2.:V<lí.5\l0.9 10.}^ 9.7 9. r 8.6' 8.1] 7.?' 7..' 6.8 6.3 5.8 5.4 5.0 4.5 4.0 3.5 3.

80, 76i 73 70j ()6j 63j 59 56, 53 50, 47j 44| 41, 38, 36 33 30 28 25 23 20

15.7 ¡4.5 13.5 12.5 í 1.8 II. 2\lO. 5 10.0 9.5 9.0' 8.5 8.1] 7.0 7.2 6.7 6.3 6.(, 5.6 5.2 J,.8 4..? 3.

81 78i 741 71! 68¡ 65! 61 ¡ 5H\ 55| 52i 49! '^Á '^^ 'il' '^^' •"!»' '^^ '^^ 29, 26, 24

15.9 14.7 13.7.12.812.0 11.4 10.7.10.2 9.7 9.3 8.8 8.4 8.0 7.6 7.^ 6.8 6.5 6.1 5.7 5.3 4.9 4

82¡ 79' 75I 72I 69' 66| 63 6o| 57! 55| 52 49l 4()¡ 44l 42' 39 37 34' 32 30i 28

16.1 14.9 13.9,12.9^12.2.11.6 11.0 10.5 10.0 9.5 9. L 8.7 8.2 7.9 7.5.7.1 6.8 6.', 6.1 5.7 5.3 5.

H:V 80! 77! 73 70' 68' 65' 62 59' 56 54' 51 49' 46 44* AV 39 37 35 33' 30

16. 1 15. O 13. 9\13. 1 Í2. 4 11.811. 2 10. 6 10. 1, 9. 6 9. 2 8. 9 8. 5 8. 1 7.8 7.4 7.(1 6.7 6. 4 6. 1 5. 7

7 i 1

7 C. 9 0. 2

2 10 7 5 3 . .

O 2.4 1-8 1.1 O.3....

8, 15 13 11, 9 4

9' 3.4 3.0 2. 4 1.7 0.9

!2Í 19, 17i 15i 13 9¡ 5 1

6 4.2 3.8 3.3 2.8 2.1 1.3 0.4

261 23 22I 20' 17' 14! lol o' 2

/ 4-S 4-4: 4-0, 3.6 3.0 2.3 1.5 0.6

28 26 24' 22' 21' 17' 13' 10 7 4

5.2 4.9 4.6 4.2. 3.6 3.1, 2.4 1.6 0.7

X

>

DÖ

O

O

(O

a

ü

w

>

S

w

:^

o

>

o

2

o

d

d
105

110

115

120

125

130

140

150

160

170

180

190

200

210

96

97

97

97

1"

(97

l-

|97l

l-í

I 98¡

!l«

98,

98

93

2Í.4

93

21. I^

93

21. J,

94

21.S

94

2Í.2

94

21.0

95

20.7

95

20.2

95

95

19. I^

96

18.9

9f

1S.Ö

96

/8. Í

9ê

17.7

90

90

90

19.G

91

91

18.9

91

;8.8

92

921

/8. 4

93 i

/8./:

93;

;?.7|

94!

94,

941

16. J!

94

87

17.5

87

77.0

88

Í7.5

88

17. J,

88

;7..s

89

17.2

891

90^

901

16. 2 ^ 91 :

i5. 8i

911

15.5,

92,

92,

1I,.9^

92'

i4-o'

83 80 77 74| 711 69 66' 63

16.2 15.1 11 O 13. 2\12. 6111. 9 11.3 10.8

84 81 78 751 73| 70 67 65

16.2^15.1 l4.l'lS.3J2.6J2.0 11.4 10. 8

&5¡ 82 791 76j 741 71 68 66

16.2 15.1 I4.IJS.4 12.7^12.1^11.5 10.9

85: 82', 80| 77¡ 74J 72¡ 69 67

16.2 15.1 14. 1 13.412.7 12. Uli. 5 11.0

86' 83 80 ' 771 75| 73 70 68

16.1^15.0^14.0 13.4 12.7'12. }\ll. 5 11.C

86l 83! 81, 78' 76: 73' 71 69

16.0 14.9\í4.0'l3.4'12.7h2.ril.5 íl.O

87Í 84' 82' 79^ 77| 75 73 70

15. S'Í4. s'/.5. 8 13. 2 12. 5 11. í? //. 4 10. 9

87' 851 82 80 ' 78' 76! 74 72

15. 4 14- 5U3. 7 13. 0 12. 4'í}. 8'11. 2:10. 8

60

10.3

62

10.4

63

10.4

65

10.5

65

10.5

67

10.5

68

10.4

70

10.3

88' 86' 83' 81 79i 77 75! 73! 71

15.2 14. 2 13:4 12.7 Í2.U11.5\11.0\10.6

89 86| 84! 82 80¡ 78( 76! ''^

14.8 13.9^13.2 12.4 11-8 11.3 10.8\Í0.4

89, 87i 85i 83 81 791 77! 75

14.5 13.7\12.9.12.2 11.6 ll.l\lC.6\lO.Í

90 881 85, 84 82 80 78 76

14.2 13.4 12.7 12.0 11.4 10.9\10.5

90 88

14-0 13.2

90 .8.8

13. 8 13. O

86, 84 82, 80 ¡ 79

12.411.8 11.2 10.8^10.3

86' 85 S3 811 79

12. 2 11.7 11. 1 10.6 10.0

10.1

72

9.9

73

9.7

75

/0.0| 9.6

77¡ 75

9. .Sj 9.4

781 76

5.7, 9.2

58

9.8

60

9.9

61

10.0

62

10. C

63

10.0

64

10.0

66

10.0

68

9.9

69

9.7

70

9.6

72

9.4

73

9.¿

74

9.1

75

9.0

53

9.0

55

9.a

56

9.5

58

9.4

59,

601

9.4^

62¡

9.4'

64l

9.,^!

65

9.1

67

í'. O

68

8.8\

69!

8. Öl

701

S.4\

71|

8. .5,

541

8.9|

55

9.0^

571

58

9.0

60|

9.()

621

8.9!

641

8.8'

651

8.6'

8. .3 7.9

50 48

8.41 8./

52! 50

7.6

46

7.7

48

7.8

53; 51 49

í.7| 8.3 7.9

55, 53 j 51

8.7] 8.5j 8.0

561 .541 52

8.7| 8.3^^ 8.0

58 56, 54

8.7] 8.4' 8.0

60' 58' 57

8.6' 8..?' 8.0

62 60 ' .58

8. ,5' 8.2^ 7.9

63 62' 60

8.4 8.0! 7.8

65 fôl 62

8./1 7.8! 7.Ö

68! 661 65

7.7

66

7.5

68 j 67 j 65,

7.^1 7.4\ 7.1

7.9

67

7.?

&3

7.4.

64,

7.15,

42

7.3'

44!

7.5!

45]

7.ÖJ

47|

7.7\

is\

7.7^

50,

7.8\

531

7.8

.55'

7.8

57!

7.7|

591

7.6\

601

7.4\

621

7.5

63 i 7.C1

64,

6.9,

37

6.7

40

6.8

41

7.0'

43

7. i

45

7. .^

47|

7. .51

49

7. .3

51'

7.;5'

53

7..?

55'

57 i 7.0'

58!

6.8^

60 i 6.6

61

6.5

35

6.-i

38

6.6

40

6.7

41

6.8

43,

451

7.0,

7.1

49

7./

52

7.0'

.53'

6.9

55

6.8

57!

6.6

58

6.4

60

34 31

6. i .5. 7

36 34

6.3 6.0

381 36'

6. ó I 6.2,

40; 381

6.6 6.3i

39,

41,

6.6,

44

6.6

48! 46!

6.9^ 6.7[

50, 49'

6.8: 6.7

52' 51

6.7! 6.6

54I 52'

6.-5' 6.4

56' 54^

6.4' 6.2'

.57, 55'

6. ? 6. O

59 57;

6. / ; .5. 9

29 28

.5.4 '5. .2

32 30

5.7 5.4

34 32

.5. 91 -5.6

36! 34

6.1] 5.8

381 36

6..?l 6.0

401 38

6.4¡ 6./

43 j 41

6.4\ 6.2

45 43

6.4] 6.2

47' 46'

6.4' 6.2\

49' 48

6.4' 6.r

261 24

4.8^ 4-Ö

26

4.8

29

5. .1?

31

5.4

33

.5..^

35

5.6

38

51 50

6. ¿ 6.0

53 51

6.0 .5.9

54 53

5.9 -5.7

56 54

28

5.2

31

5.4

33

,5.6

3,

5.8

3

-5.9

40

6.0 .

42, 41

6.0' 5.8

44 43

6.o\ 5.8

47 45

6.C; 5.7

48' 47

-5.8' .5.7

50l 49

5.7 5.5

52 51

5.6 .3.4

.53 52

5. 4, 5. 3

20 17

.',.2 3.6

23 20

4.-51 4-0

26' 23

4.7! 4-S

281 251

5. Oí 4.^'

30| 27

5.2 4-8

32, 29

.5.J, 4--9.

35 32

5. 4! 5. /

38 36

5. 4, -5. ?

41 ' 38

5.5 5.2

43 40

5.5 5.2

45 42

•5. 4 -5. i'

46 44

5.3 5.0

48 46

5.?' 4-9

.50 47

5. / 4- 8

14 11

.3.7 2.4

17 14

.3.-5^ 5.0

20 17

3.9' 3.4

221 19

4.^1 3.7

24, 22

I f I r

-f. -f > 4- '-'

26 24

4.6 4.^^i

30 27,

4.S, 4.4^

.33 301

4.9 4.Ó

35 33

4..y^ 4.Ö

38' 35

4.9 4.6'

40 38

4.8 4.6

42 .39

4. O -f. '5 -í. ^

43 41 39'

4.7 4-5 4.5'

45 43 41 ! 4.6 4.4 4.^!

1.8

11

:?.5

14

2.9

17

5.5

19

3.6,

21|

.3.8

25

4./

28

31

4.3

33

4. 4

35

....

4

/.;

8 2

1.7 0.4

10 5

.15 lA

13 8

2.7 /.e

15 10

3.0 2.0

19 14

5.4 ;g.6

23 18

5.6 2.9

25 21

3.7 , 3.2

28 1 24

5.7 5.2

30 26

3.8 3.3

32 28

.3.8 ,3.5

34 30

5.8 5. 5

36 32

3.7 ,5. .3

o

o

Ö

tí

td

O

O

1 Relativo humidity values in roman type.

2 Equilibrium moisture content values in italic type.

CO

CO
314 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

the fiber saturation point. The fiber saturation point is approximately 30-percent moisture content for all species.

Shrinkage occurs if the moisture content is reduced to a value

below that of the fiber saturation point and is proportional to the

amount of moisture lost below 30-percent moisture content (7, 15).

Wood dried to 15-percent moisture content has attained about one-half

of the total shrinkage possible. For each 1-percent loss in moisture

content below the fiber saturation point, the wood shrinks about onethirtieth of the total. Lilvewise, for each 1-percent increase in moisture content the piece swells about one-thirtieth of the total swelling

possible. The total swelling is equal numerically to the total shrinkage. Shrinking and swelling are expressed as percentages based on

the green dimensions of the wood.

As a piece of wood dries, the outer parts are reduced to a moisture

content below the fiber saturation point considerably sooner than the

inner parts. Thus, the whole piece may show some shrinkage before

the average moisture content reaches the fiber saturation point.

Wood shrinks most in the direction of the annual growth rings

(tangentially), somewhat less across these rings (radially), and ver}^

little, as a rule, along the grain (longitudinally) {2). The combined

effects of radial and tangential shrinkage on the shape of various

sections in drying from the green conditions are illustrated in figure 70.

Wood that contains cross grain or irregular grain will shrink more

longitudinally than straight-grained wood. Local shrinkage in such

pieces may cause distortion.

ZM 12494 F

FIGURE 70.—Characteristic shrinkage and distortion of flats, squares, and rounds

as affected by the direction of the annual rings. Tangential shrinkage is about

twice as great as radial.
WOOD HANDBOOK 315

Table 39 gives the average tangential, radial, and volumetric

shrinkage for numerous species during (h*ving from the gr(H^n condition

to 20-, 6-, and 0-percent moisture content. The ratio of total radial

to total tangential slu'inkage ranges from 1:1.1 to lii).?.

In general, the heavier species of wood shrink mor(^ acioss the grain

than lighter ones. Heavier pieces also shrink more than Hghter pieces

of the same species. Hardwoods generally shrink more than softwoods. Species, however, do not always conform to the genei-al

shrinkage pattern. For example, l)asswood is a light wood but shrinks

considerablv more than black locust, a heavv wood.

TABLE 39.—Shrinkage vdhie^i of wood ¡xised on its (Uniensions when, gre^'n

Species

Shrinkage

Dried to 2n-perceiit

moisture content i

SOFTWOODS

Baldcypress

Cedar:

AlaskaAtlantic whiteEastern redcedar .

IncenseNorthern white- --

Port-OrfordWestern redcedar.

Douglas-fir:

Coast type

Intermediate type

Rocky Mountain type

Fir:

Alpine

Balsam

California red

Corkbark

Grand

Noble

Pacific silver

White

Hemlock:

Eastern

Western

Larch, western

Pine:

Eastern white

Jeffrey

Limber

Lodgepole

Pitch

Pond

Ponderosa

Red

Southern yellow:

Loblolly

Longleaf _.

Shortleaf.--

Slash...

Seo footnotos at ond o

Radial

Percent

.9

LO

1.0

1. 1

1.4

1.2

.9

1.Ü

1.3

.9

1. 1

1.Ó

1.5

1. 1

l.U

1.4

1.4

1.3

1.7

1.3

1.5

1.8

table.

Tan- Volugential | metric

Dried to (i-percent

moisture content 2

Percent

2.1

2.0

1.8

1.6

1.7

1.6

2.3

1.7

2.6

2.5

2. 1

2.5

2.3

2.4

2.5

2.5

2.7

3.3

2.4

2.3

2.6

2.7

2.0

2. 2

1.7

2.2

2.4

2.4

2.1

2.4

2.5

2.6

2.6

2.6

Percent

3.5

3. 1

2.9

2.6

2.5

2.4

3.4

2.3

3.9

3.6

3.5

3.1

3.7

4.1

3. 0

4.6

4.6

3.3

3.2

4.0

4.4

2.7

?>. 3

2.7

3.8

:i. 6

3.7

3.2

3.8

4.1

4.1

4.1

4.1

Radial

Percent

?,. 0

2.2

2.3

2.5

2.6

1.8

3.7

1.9

4.0

3. 3

2.9

3.2

2.2

2.7

3.6

3. 7

2.6

2.4

3.4

3.4

1.8

3. ó

1.9

3.6

3.2

4.1

3.1

3.7

3.8

4.1

3.5

4.4

Tangential

Volumetric

Percent Percent

5. 0 8. 4

4.8

4.3

3.8

4.2

3.9

5.5

4.0

6.2

6. 1

5.0

5.9

5.5

5.8

5.9

6.0

6.6

7.8

5.7

5.4

6.3

6.5

4.8

5.4

4. 1

5.4

5.7

5.0

5.8

5.9

6.0

6.2

6.2

7.4

7.0

6.2

6. 1

5.8

8.1

5.4

9.4

8.7

8.5

7.5

9.0

9.8

7.2

8.8

11.0

11.0

7.8

7.8

9.5

10.6

6.6

7.9

6.6

9.2

9.2

9.8

9.8

9.8

9.8

Drii'd to O-piMccnt

moisture content

Radial Tangential

Percent Percent

3.8

2.8

2.9

3.1

3.3

2.2

4.6

2.4

5.0

4. 1

3. 6

2.6

2.9

4.0

2.8

3.4

3.0

4.3

4.2

2.3

4.4

2.4

4.5

4.0

5.1

3.9

4.6

4.4

5.6

6.0

5.4

4.7

5.2

4.9

6.9

5.0

7.8

7.6

6.2

7.4

6.9

7.2

7.4

7.5

8.2

9.8

7.1

6.8

7.9

8.1

6.0

6.7

5.1

6.7

7.1

7.1

6.3

7.2

7.4

7.5

7.7

7.8

Volumetric

Percent

10. 5

9. 2

8.8

11.8

10.9

10. 6

9.4

11.2

12.2

9.0

11.0

13. 8

13. H

9.8

9.7

11.9

13.2

8.2

9.9

8.2

11.5

10.9

11.2

9.6

11.5

12.3

12.2

12. 3

12.2

30:;747''—55- -21
310 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLK 3i).—Siirinkage values of wood leased on its diniensions when green—Con.

s()FT\vof)i>s con.

I'ino Continued

Su.u:ir ...

Tahlc-niountam.

Western white.. -

Pinyoii.

Kc'lwood:

01(l-KT0\vth

Sccotid-gTO\vth___

^^prucc:

Black

En^'^clniann

Kc<l

Sitka

Tamarack

^'c\v, Pacific

Shrinkai!<'

HARDWOODS

Alder, red.

A(.i.le..._.

Ash:

Black

Blue

Green

Oreuon

Pumpkin

White

Asi)en:

BiL'tooth

Quakinc

Basswood, American

Beech, A merican

Tiirch:

Alaska paper

Gray

Pai)er

Sweet

Yellow

Buckeye, yellow

Butternut

Calilornia-laurel

Catalpa, northern..,

Cherry:

Black

Pm

Chestnut, American

Cottonwood:

Eastern and southern

Black

Cucumhertree

Dopwfiod, ílo^^'erin£ i

See footnotes at end of t.

Dried 1o 20-|)ercent Dried to B-perceiit

moisture content i moisture content -

Dried to 0-ijercent

moisture content

TÍ..1; 1 ' Tan- Volu- : ,, ,. , , Tan- I Volu- ^, ^.. , Tan- I Volu-

^^^^^^'^'^ I ííential ' melrie ^^-'^'^'^'^ \ ^ential metric I ^^""'^'''^^ I ffcntial I metric

J'ercfii/ I'crcfi/f /'<rrni/ I'frcfnl

2. 1

l.S

JJI i.'J 2. 1')

1.4 2.5 ''>. U

1.5 1.7 :;.;]

.9 l.f. 2.:-!

•' 1.0 2.4

1.4

1. 1

2..'{

2 2

?,. S

1.4 2 5 ;^s

1.2 2. 5 4.5

1.::! l.h a. 2

1.5 2.4 4.2

2.0 .-;. 5 ;. 1

1.7 2. * ) 5. 1

1.3

1.2

1.7

2.5

ible.

2.2

2.4

2.1

2. fi

2. C,

2.2

2.9

2. S

3. 1

2.4

3.1

2. 9

2.9

3.9

•':. O

;;. 4

4.(1

3. 1

3.7

3. o

3. s

2. n

2.8

4.2 '

5. o

5.2 Î

5.8

2.9

2. 7

2.3

2.0

3.0

2.2

3.1

2.9

4.2

5.9

rcTCf'iii

\. 5

5. 4

5. 9

3.5

3. 9

0. 2

0. O

5.9

4.3

5.8

8.4

0.5

5.0

0.2

0.3

5.4

7.4

8.8

0.9

0.8

7.4

0. 5

5.1

0.8

3.9

5.7

8.2

5.4

7.4

0.9

7.0

9.4

9.4

7.9

9.0

8. 3

9.4

9.2

10. 1

14.7

12 2

9.4

10.0

10. O

9.0

10.7

9.4

9.2 ! 12.0 : 13.0 I

13.4

11.8

13.0

12. 5

13. 4

10.0

8. 5

9.9

5.8

9.2

10.2

9. 3

11.3

9.9

10. 9

16.6

l'(TC( ni

2. !> j

3. I

4. 1

4.0

2.0

2.2

4. 1

3. 4

3. 8

4.3

4.4

5. 9

5. O

3. 9

4. f.

4.1

3.7

4.8

3. 3

3.5

6.0

5.1

0. 5

5.2

0.3

0. 5

7.2

3. O

3.4

2.9

2.8 j 3.4 !

3.9 i

3.6

5.2

7.4 I

PcTccnt Pira III

0. S

7.4

5.2

4.4

4.9

0.8

0. (^.

7.4

5.4

10.:

6.5

7.1

8.1

0. 3

7.8

7.9

0.7

9.3

11.0

9.9

8.0

8.5

9.2

8.1

0.4

8.5

4.9

10.3

0.7

9.2

8.0

8.8

11.8

10.9

11.8

9.9

0.8

7. 1

11.3

KU

11..S

11.5

13.0

9. 7

12.0

18.4

11.7

12.5

13.2

12.0

13. 4

11.8

11.5

15. 8

10.3

10. 7

14.7

10.2

15.0

10.7

12.5

10. O

12.4

11.5

12.8

11.0

14.1

12.4

13.6

20. 8
WOOD HANDBOOK 317

TABLE 39.—Shrinkage values of ivood based on its (/imensions ivJien green.—Con.

Shrill kago

bpecies

Dried to 20-perc('nt

moisture content '

Radial

HARDWOODS—COn.

Eim:

American

Rock

Slippery

Greenheart .

Ilaekberry

Hickory.

Pecan ^ . -

True:

Moekernut

Piirnut

Shafîbark

Shellbark

Holly. American .

I ioneylocust

Ilophornbeam, eastern

Iroko - - -

Iron bark, eray _.

Khaya

Lauan, red

Locu-^t, black. _

jMadrone, I'aeific

IMaifnolia, southern

M ahosany

Manqrove

Maple:

BiGfleaf

Black

Red

Silver

Sugar

Oak:

Black

Bur

California black

Canyon live

Chestnut

Laurel

Live

Oregon white

Pin -

Post

Northern red

Rocky Mountain white

ScarletSouthern red

Swamp chestnut

Swamp red ..

Water

White -

Willow

See footnotes at end o

Tan- Volugcntial I metric

Percent

1.4

L6

L6

1.1

1.0

1.0

2.0

2.4

2. o

2. 5

1. 0

1.4

2. S

1. 1

L9

1.4

1. 1

1..'.

l.'J

1.8

1.2

1.8

1.2

1.0

1.3

1.0

LO

1.5

L.5

1.2

1.8

L8

1.3

2.2

1.4

1.4

1.8

1.3

1.4

1.5

1.5

1.7

L8

1.4

1.8

1.7

Itérée ni

3. 2

3.0

f tabh.'

3.7

3.8

3.3

4.2

3.3

2.2

3.3

1.0

2.8

1.9

2.7

2.4

4. 1

2.2

1.7

2.4

3.1

2.7

2.4

3.2

3.2

2.9

2. 2

3.2

3.2

3.3

3. 0

3.2

3 3

2.7

2.4

3. 2

2.9

3.0

3.5

3.1

3.0

3.2

Dried to 0-i)ercent

moisture content 2

Dried to 0-percent

moisture content

U'i.li.^ll '^'^^"- I ^'''^''- ' R'uli'il! '^^^"- ' ^''*^'^- ^^^''^^^^' ! gential ! m(>tric ' ^^'^'''^^' gential ; metric

4.9

4.7

4.0

2.7

5. 0

0.0

0.0

5. 0

0. 4

5. 0

3.0

0. 5

2.8

4.7

2. 9

3.9

3.4

0.0

4. 1

3.9

4.7

4.4

4.0

5.0

4.7

4.2

4. 0

5.4

5. 0

0.3

4.9

4.5

4.8

5.4

4.5

4.2

4.0

5.4

5.5

5.9

5.5

5.3

0.3

3.8 0. 5

3.9 7.1

2.7 3.4

3.8 7.1

3.9 7.1

0.2 8.8

5.8 9.2

5. 0

0. 1

3.8

3.4

0.8

2.7

4.5

3. 3

2.0

4.5

4.3

2.9

4.3

3.0

3. 8

3.2

2.4

3.9

3. 0

3. 5

2.9

4.3

4.4

3.2

5.3

3.4

3.4

4.3

3.2

3. 0

4.2

4.4

3.4

4.2

4.0

8.0

10.1

7.9

5.3

8.0

3.8

0.7

4.0

0. 4

5.8

9.9

5.3

4.0

5.7

7.4

0.0

5.8

7.0

7.8

7.0

5.3

7.0

7.8

7.9

7.0

7.2

7.0

7.8

0.0

5.8

7.8

7.0

8.0

8.5

7.4

7.2

7.7

J^ercenf Percent Percent

11.7

11.3

11.0

0.4

13.5

10.9

14. 3

14. 3

15.4

13. 5 I

8. 0 I

15.5 '

0.8

11.2

7.0

9.4

8.2

14.5 !

9. 8

(). 4

12.0

9. 3

11.2

10. 5

9. 0

11.9

11.4

10.2

9. 7

13.9

13.4

15. 2

11.8

10.7

11.0

13. 0

10. 8

10.0

11.0

13.0

13. 1

14.2

13.1

12.0

15.1

Percent

4.2

4.8

4.9

3.4

4.8

4.9

7.8

7.2

7.0

7.0

4.8

4.2

8.5

3.4

5.0;

4.1 I

3.3 '

4.0 ¡ 5. 0 I 5.4

3.0

5.4

3.7

4.8 I

4.0 I

3.0 '

4.9

4.5

4.4

3. 0

5. 4

4.0

0.0

4.2

4.3

5.4

4.0

4.1

4.0

4.5

4.2

5.3

5.0

Percent

9. 5

8. 1

8. 9

4.2

8.9

8.9

11.0 i

11.5 I 10.0

12.6 . 9.9

0. f.

10.0

4.8

8. 4

8.0

12.4

0.0

5.0

9.7 I 8.8 '

9.7

9.9

9.5 I 9.0 I 9.5 I 9.8 '

8.2

7.2

9.7

8.7

10.8

10. 6

9.3

9.0

9.6

Percent

14.0

14. 1

13.8

8.0

10.9

13.0

17.9

17.9

10.7

19.2

10.9

10.8

19.4

8 5

14.0

8.8

11.7

10.2

18. 1

12.3

8.0

15.8

11.0

14. 0

13. 1

12.0

14 9

14.2

12.7

12. 1

1(1.2

10.7

19.0

14.7

13.4

14.5

16.2

13. 5

12.5

13.8

10. 3

10.4

17.7

10.4

15. 8

18.9
318 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLE 39,—Shrinkage values of wood based on its dimensions when green Con.

--

Shrinkage

Sijecics

Dried to 20-percent

moisture content i

Dried to 6-percent

moisture content 2

Dried to 0-percent

moisture content

Radial Tan- Volugential metric

Percent Percent

.3.1

Radial

Percent

Tan- Volugential metric

Percent Percent

1 7.4

Radial Tan- Volugential metric

HARDWOODS—con. Percent Percent Percent Percent

9.2

19 1

10.3

15. 0

14.2

13. 3

Persimmon, common

Sassafras

SweetRum

Sycamore, American

Tanpile - - - - -

2.6

1.3

1.7

1.7

1.4

.8

1.5

1.4

1.8

.9

1.0

1.3

3.7 6.4

2. 1 3. 4

3.3 5.0

2.5 1 4.7

3.0 4.4

1.4 2.3

2.6 4.6

2.5 4.2

2.6 4.3

2. 7 4. 8

3.0 4.6

2. 4 4. 1

6.3

3.2

4.2

4. 1

3.4

1.8

3.5

3.4

4.4

2. 1

2.3

3.2

9.0 1 15.3

5.0 i 8.2

7.9 12.0

6.1 11.4

7.3 ¡ 10.6

3.4 5.4

6.2 11.1

6. 1 10. 0

6.2 1 10.2

6.5 1 11.5

7.2 ' 11.0

5. 7 9. 8

7.9

4.0

5.2

5.1

4.3

2.3

4.4

11.2

6.2

9.9

7. 6

9.1

Teak

Tupelo:

Black

4.2 6 8

13.9

WatcT 4. 2 7. 6 12.5

AValnut, black

Willow:

Black

5. 5

2.6

2.9

4.0

7.8 1 12.8

1

8.1 ' 14.4

Pacific 9.0 ' 13.8

Vellow-DODlar 7.1 ¡ 12 3

1 These shrinkage values have been fak(>n as V^ the «^hrinka'.'-e to \\w oven-dry condition as eiven in th<"

last 3 colurrin^ of this table.

2 These shrinkage values have been taken as is of the sh^inka'-'.' to th(^ ovi^n-dry condition as given in the

last 3 columns of this tab^e.

'- Average of butternut hickory, iiutmeu hickory, water hickory, and pecan.

Values for longitudinal shrinkage are not given in table 39. The

total longitudinal shrinkage of normal wood usuaUy ranges from 0.1

to 0.3 percent of the green dimension. Exceptionally lightweight

wood of any species tends to shrink abnormally in length.

Wood containing compression wood and tension wood also shrinks

more along the grain than does normal wood. Compression wood

occurs in softwoods and tension wood in hardwoods. Longitudinal

shrinkage varies widely with the form of compression wood. In

borderline forms that differ only slightly from normal wood, lengthwise shrinkage is but a little more than that of normal wood. Pronounced forms, on the other hand, shrink 5 to 10 times as much along

the grain as normal wood of the conifers. In the same way, pieces

of hardwoods with onh^ a few tension wood fibers have nearly the

same longitudinal shrinkage as normal wood, but if many of these

fibers are present, longitudinal shrinkage is considerably greater than

that of normal wood.

Compression wood or tension wood may occur in the same board

with normal wood, so that internal stresses are set up that cause

lengthwise distortion. If the boards contain moderate to pronounced

forms of compression wood or moderate to large numbers of tension

wood fibers, these stresses are large and serious warping usually

results. Even borderline forms of compression wood or tension wood

may interfere mth the usefulness of pieces in products that permit

only small tolerance with respect to warping. In addition, cross

breaks may occur in bands of compression wood or tension wood.
WOOD HANDBOOK 319

Although theoretically the normal moisture content-shrinkage relation may be considered a direct one from ?;ero slu'inkage at filx^r saturation point to maximum shrinkage at z(^ro moisture^ content, actually

the relationship is more like that shown in iigui-e 71. For some

shrinkage calculations, however, a straight-line relation may l)e assumed without too great an error. Foi' exami)le, assume that a piece

0IZ54567Ô9I0

SHRINKAGE fPERCENT OF GREEN DIMENSION)

ZM 22048 F

FIGURE 71.—Typical moisture content-shrinkage curves. These curves are for

Douglas-fir and southern .yello.v pine and may be used for est.inatn.g the

amount of change in dimension that will take place with change in the moisture

content of the wood.
320 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

of flat-sawed southern yellow pine sheathing at 12-percent moisture

content is dried to 7 percent. According to the curve in figure 71

marked tangential, the shrinkage from the green condition to a moisture content of 7 percent would be 5 percent and that from green to

12 percent would be VA percent, for a difference of 1}^ percent. If

a straight-line relation is used, the shrinkage would equal five-thirtieths

or one-sixth of the total tangential shrinkage of 6.67 percent, or 1.11

percent of its width. Since the shrinkage values and curves represent

averages, the actual shrinkage of a })oar(l may vary somewhat from

them.

DETERMEVATION OF MOISTURE CONTENT

The amount of moisture in wood is ordinarily expressed as a percentage of the weight of the wood when oven-dr3^ Two methods of

(U^termining moisture content are described in the following paragraphs. The oven-dry method is probably the most nearly exact

but is slow and necessitates cutting the wood; the electrical method

is the more rapid and does not necessitate cutting the wood. A distillation method is used on woods containing volatile oils, such as

pitchy southern yellow pine (5).

Oven-Drying Method

In the oven-drying method (5), cross sections, about 1 inch long in

the direction of the grain, are cut from representative boards of a lot

of lumber. These sections should be cut at least 1 foot from the ends

of the boards to avoid the effect of end drying and should be free from

knots and other irregularities, such as bark and pitch pockets.

Each section is nnmediately weighed, before any diying or adsorption

of moisture has taken place, and is then placed in an oven heated to

214"^ to 221° F. and kept there until it reaches constant weight. If

the section cannot be weighed immediately after it is cut, it should

be wrapped in metal foil until it can be weighed. In the oven, a

section will reach a constant weight in 12 to 48 hours. For weighing

ordinary moisture content sections, balances having a capacity of

about 200 grams and sensitive to 0.05 gram are recommended.

Both steam and electric ovens are in common use for drying moisture-determination sections. The sections, with either type of oven,

should be open piled in order to permit good circulation of air, especially around the end-grain surfaces, and thus hasten dr3âng.

The constant or oven-dry weight and the weight of the section when

cut are used to determine the percentage moisture content wâth the

following formula :

-p. , . , , , iveiqht uuen ciit—oven-dnj iveiqht^^ ,„^

rercent moisture content= -. . ,, —X 100 oven-dry weight

Electrical Methods

Electrical methods for determining the moisture content of wood

make use of such electrical properties of wood as its electrical resistance, dielectric constant, and power-loss factor (1). Electrical

^
WOOD HANDBOOK 321

moisture meters appeared on the market al)Out 1930. Instrumenls

are made that determine the moisture content through its eflect upou

the direct-current electrical resistance of wood and its effect on

capacity and losses of a condenser in a high-frequency circuit in which

the wood serves as the dielectric material of the condenser.

Although some meters are calil)rated to cover a range of 4 to 120

percent, the operating range of most meters is 7 to 25 percent. Above

and below these values the readings are inaccurate. Within the rauge

ot 7 to 25 percent, electrical moisture meters should read within d= 1

percent of the moisture content, as determiníHl by the oven-drying

method. To obtain accurate readmgs, the instruments should be iu

good adjustment and used accorduig to the manufacturer's instructions, which include corrections for various species and cover luml^er

up to lYo inches thick or thicker lumber that is known to be of uniform

moisture content.

Some judgment must be exercised in the use of electrical meters.

They should not be used on dry luml)er that has been wet by rain or

exposed to damp conditions that have caused the surfaces to become

wet. Preferably, meters should not l)e used on very cold or hot luml)ei-.

Most meters are calil)rated at 70"^ F. An approximate temperature

correction for resistance-type meters is the adding of 1 percent to the

meter reading for each 20° below 70° and the subtracting of 1 percent

for each 20° above 70° F.

The principal advantage of the electrical method over the ovendrying method is its speed and convenience. The time required to

determine the moisture content of any piece of wood is onl}^ a few

seconds. The electrical method is therefore adaptable to sorting

lumber on the basis of moistiu'c content and can be used to measure

the moisture content of wood installed in a building. With this

method, the piece of wood is not cut or mutilated except for the driving

of a few small needles into the wood to serve as electrodes for the

resistance-t3'pe meters.

SEASONING OF LUMBER

Moisture in Wood

The moisture in wood, commonly called ''sap," may for most

practical purposes in the drymg of wood (5, 9) he considered as water

alone. Table 40 gives some moisture content values for green heartwood and sapwood of various species. The values shown may be

considered average, and considerable variation from these values may

be expected in individual tr(^es and single boards, particularly hi

sapwood.

Sawmill Practice

Methods of seasoning softwood lumber vary with the use requirements. It is common practice at most sawmills to kiln-dry all upper

grade lumber intended for finish and flooring. Ordinarily dimensio]i

and lower grades used for framing lumber are sent to a yard for air-drying or, in the case of some species, are shipped without being seasoned.

Timbers are generallv not held long enough to be seasoned, thougli
322 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLE 40.—Average moiaiure content of green wood, by species

SOFTWOODS

Baklcypress

Cedar:

AlaskaAtlantic whiteEastern redcedar

IncenseNorthern whitePort-OrfordWestern redcedar. -.

Douglas-fir:

Coast type

Intermediate type..

Rocky Mountain

type

Fir:

Alpine

Balsam

California red

Cirand

Noble

Pacific silver

White

Hemlock :

Eastern

Western

Larch, western

Pine:

Eastern white

Lodgepole

Ponderosa

Red

Southern yellow:

loblolly.

LongleafShortleaf.

Sugar

Western white

Redwood, old-growth

Spruce:

Eastern

Engelmann

Sitka

Tamarack

Percent

121

HARDWOODS

Alder, red

Apple

Ash:

Black

Green

White

Aspen

Basswood, American.

Percent

171

9S

249

115

154

13fi

115

IM

160

119

170

119

120

148

134

110

lOfi

122 I 219 j

14K

210

128

173

142

58

44

113

133

47

117

lOK

Beech, American

Birch:

Paper

Sweet

Yellow

Buckeye, yellow

Buttonmt

California-laurel

Cherry, black

Chestnut, American

Chinkapin, golden

Cottonwood, black

Dogwood, flowering

Elm:

American

Cedar

Rock

Hackberry

Hickory:

Bitteniut

Mockenmt

Pignut

Red

Sand __

Water

Holly, American

Hophombeam, eastern _

Locust, black

Madrone, Pacific

Magnolia

Maple:

Silver (soft)

Sugar (hard)

Oak:

California black

Live

Northern red

Southern red

Tan

Water

White

Willow

Osage-orange

Persimmon, common

Sweetgum

Sycamore, American.. _

Tupelo:

Black

Swamp

Water

Walnut, black

Willow, black

Yellow-poplar

5S i_

120 !.

95

00

44

61

80

70

71

69

68

80

79

114

87

101

150

90

83

92

61

57

65

.54

52

49

52

50

62

97

72

75

69

75

81

78

74

137

130

115

108

116

73

106

1 Based on weight when oven-dried.
WOOD HANDBOOK 323

some drying may take place between the time tliev are sawed and the

time of shipment.

Sawmills cutting hardwoods commonly classify for size and giade

at the time of sawing and then send all stock to'the air-(hying yard.

After yard seasoning, the stock may h(^ kiln-th-ied at the sawniill or

shipped to a remanufacturing plant whei-e it is kiln-(h*ied before ben)g

made up into finished products, such as furniture, cabinet work"^

interior finish, and flooring.

Air-Drying

The principal advantages of air-dried wood over green wood

(S, 9) are: Reduction in weight, with a resulting descréase hi ship])ing

costs; reduction or elimination of shrinkage, checking, honeycombing,

and warping occurring in service; increase in strength; increase in

nail-holding power; decrease in the tendency for blue stain and other

forms of fungi to attack the wood; reduction in likelihood of attack

by some forms of insects; and improvement in the capacity to hold

paint or to receive preservative treatment.

Kiln-Drying

Among the advantages of kiln-drying over air-drying are the

following: Greater reduction in weight and consequently in shipping

charges; reduction in moisture content to any desired value, which

may be lower than that obtainable through air-drying; reduction

in drying time below that required in air-drying; the killing of any

stain or decay fungi or insects that may be in the wood; setting of the

resins in resinous woods; and less degrade, in most cases, if proper

kiln schedules are used.

Seasoning Degrade

Obtaining lumber practically free of seasoning degrade in the higher'

grades is insured by adherence to approved grading rules on the part

of the manufacturer and knowledge of the lumber and its grades

on the part of the user. Degrade that sometimes develops in seasoning

may be classified (3) into two main groups: (1) That caused by

unequal shrinkage, which includes checks, honeycomb, warp (fig. 72),

loosening of knots, and collapse; and (2) that caused by the action

of fungi, namelv, molds, stains, and decay. Chemical brown stain,

frequently known as yard or kiln brown stain, may also occur in some

softwoods. It is a yellow to dark-brown discoloration and is apparently caused by the oxidation of water-soluble materials in the

wood. It has no effect upon strength and general usefulness of the

wood except in the case of upper grade stock with a natural finish.

So-called sticker stain is common in the air-drying of both softwoods

and hardwoods and presumably is also caused by the concentration

and oxidation of water-soluble materials in the wood.

Seasoning degrade, with the exception of chemical stains, can

be largely eliminated by proper practice in either air-drying or kilndrying. Drying lumber too rapidly will cause checking and splitting,
324 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

TWIST

POINT OF GREATEST

DEFLECTION

DIAMOND CUP

Fi(¡URE 72.—Varidiis kinds of w.arp.
WOOD HANDBOOK 325

whereas drying it too slowly under favorable temperatures will permit

stain or decay to develop. Honeycombing and collapse are more

common in hardwoods than in softwoods and are more likely to

occur during improper kiln-drying than during air-drying.

The grading rules of the various lumber associations specify the

amount of degrade permitted for the various graders of lumber.

Moisture Content of Seasoned Lumber

The trade terms ''shipping-dry," ''air-(hy/' and "kihi-dried,"

although widely used, may not have icU^ntical ineaning as to moisture

content in the different prochicing regions. The wide limitations

of these terms as ordinarily used are covered in the following statements, which, however, are not to be construed as exact definitions:

Shipping-dry liimber.—humhQT that is partially dried to prevent

stain and mold in transit.

Air-dry lumber.—Lumber that has been dried l)y exposure to the

air either outdoors or in an unheated shed for any length of time.

If exposed for a sufficient length of tim(\ it may have a moisture

content ranging from 6 percent, as in summer in the arid vSouthwcst,

to 24 percent, as in winter in the Pacific Northwest. For the Unitinl

States as a whole, the minimum moisture content range of thoroughly

air-dry lumber is 12 to 15 percent, and the average is souK^what highei\

Kiln-dried lumher.—Lumber that has been kiln-dried, particularly

the finish grades of softwoods and hardwoods, to a moisture content

of 6 to 12 percent. Kiln-dried softwood lumber of the common yard

grades is likely to have a somewhat higher moistui'e content.

The importance of suitable moisture content values is recogniz(^d,

and provisions covering them are now incorporated in some grading

rules. It should be noted, however, that the moisture content values

in the general grading rules may or may not be suitable for a sp(H'ific

use, and, if not, a special moisture content provision should be made

in the specifications.

STORAGE OF LUMBER AT YARDS

Lumber when received at a distributor's lumberyard may be j)ra,ctically green, partially seasoned, or throughly seasontnl. It can

easily be protected from stain or decay if good storage practices are

followed.

If green or partially seasoned, the lumber should be open piled

on stickers and protected from sunshine and precipitation by a tight

roof (5, 9, 15). If the lumber is seasoned to a moisture content

of less than 20 percent, it is good practice to pile it ^'solid," board on

board, in a shed that will afford ample protection against sunsliine

and precipitation. If it is desired to reduce the moisture content

still further, however, the lumber should be open piled on stickers:

If dry lumber is stored in the open, it is best to pile it on strmgers

and to use stickers between the layers of lumber. The pile should

have a roof that will shed water. Dry lumber can be piled solid in

the open for relatively short periods but should be protected from rain

with suitable pile covers. Because it is diflñcult to keep ram out completely, long storage of solid-piled lumber is not recommended.
c

326 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

The foregoing relates primarily to such items as sheathing, shiplap,

studs andloist's. Such kiln-dried items as exterior finish and sidmg

can be stored in a closed but unheated shed. The equihbrium moisture

content of such a shed would be higher than that of the atmosphere

within an occupied house, however, and items kiln-dried to a moisture

content suited for interior finish would absorb moisture if stored there.

For this reason, interior trim, flooring, and cabinet work should be

stored in a closed shed where some heat can be provided during cold

or damp weather to maintain the lumber at the desired moisture

content (^,10). i • . i

The moisture content of lumber items m storage can be mamtamed

by control of the temperature within the shed. If there is no source

of moisture except that contained in the air, the proper shed temperature required to maintain a given moisture content can be determined

by the use of figure 73. This chart shows equilibrium moisture content values of wood obtained on heating or cooling air at various

temperature and relative humidity conditions. For example, if the

outdoor temperature is 30° F., the relative humidity is 75 percent,

and the desired moisture content of the lumber is 8 percent, proceed

as follows: From the intersection of the (vertical) 30° temperature

line and the (horizontal) 75 percent relative humidity line, extend a

line midway between the adjacent (concave) vapor pressure lines

until it intersects a line midway between the 7- and 9-percent moisture

content lines indicated on the right-hand ordinate. The reading on

the bottom scale below the point of the second intersection is about

45°. (See dotted lines in figure 73.) In other words, under the conditions stated, the moisture content of the flooring can be maintained

at S percent merely by heating the air to 45°.

Heat is required in storage sheds when the outdoor relative humidity

is high. If the temperature of the shed is kept almost 10° F. higher

than the outdoor temperature, the lumber will usually be brought to

or maintained at 10-percent moisture content. If the temperature

is increased 20° the moisture content will be about 7 percent. During cold weather, if the storage shed contains any water lines the

temperature should not be allowed to drop below 32°. A method of

automatic control of equilibrium moisture content in a lumber shed

is described in reference H).

RECOMMENDED MOISTURE CONTENT

The percentages of moisture content recommended here for wood

are selected primarily for the purpose of reducing changes in moisture

content to a minimum, thereby minimizing dimensional changes after

wood is put into service {8). The service conditions to which the wood

will be exposed, whether outdoors, m unheated buildings, or in heated

buildiugs^ should be considered in determining seasoning requirements.

Timbers

Ordinarily, timber should be seasoned to as low a moisture content

îis it will ultimately come to in service, or as near this condition as

practical. While this optimum is possible with lumber less than 3

^iM
100

30 40

TEMPER/^TURE ( ^F. )

^ CO

FIGURE i6.—Kelationship of relative liuinidity, vapor pressure, equilibrium moisture content, and temperature. ^
328 HANDiBOOK 72, V. S. DEPARTMENT OF AGRICULTURE

inches thick, it is seldom possible to obtain fully seasoned timbers or

thick joists and planks. Wliere it is necessary to use thick members,

as in warehouses, bridges, trestles, and derricks, some shrinkage of

the assembly should be expected, and the design of the structure

should minimize shrinkage effects. In the case of built-up assemblies,

such as roof ti'usses, it may be necessary from time to time to tighten

the bolts or other fastenings as the members shrink.

Lumber for Exterior or Interior Service

The moisture content requirements for finish lumber or wood products used uiside heated buildings are more exacting than those for

lumber used outdoors or in unheated buildings. This is due to the

higher character of the service required and also to the lower relative

humidity conditions encountered within heated buildings than outdoors. Table 41 and figure 74 show the recommended moisture content values and tolerances for wood used in interior parts of heated

buildings. The values for exterior trim and siding can be applied to

lumber used outdoors and in unheated buildings. Table 41 also gives

corresponding values for exterior parts of heated buildings.

General commercial practice is to kiln-dry some wood products,

such as flooring {13} and furniture wood, to a slightl}^ lower moisture

content than service conditions demand, counting on a moderate

mercase in moisture content during the storage and manufacturing

periods. This practice is intended to assure uniform distribution of

moisture among the individual pieces. Common grades and dimension are sometimes but not ordinarily seasoned to the moisture content

values indicated in table 41. Wlien they are not, the design of the

structure should take account of this condition in such a way as to

minimize shrinkao-e effects.

// PrPCSNT

AVERAGE

MOISTURE CONTENT

ZM 20143 F

FIGURí: 71.—Recommended moisture content averages for interior-finishing

woodwork for use in various parts of the United States.
WOOD HANDBOOK 329

TABLE 41.—Recommended ynoisture content values for various wood items at time of

installation

Use of lumber

Moisture content (percentage of wcifiht of oven-dry wood)

for—

Dry southwestern

States I

Averag(

Interior-finish woodwork and softwood

flooring - -

Siding, exterior trim, sheathing, and

framing 3

Percent

^.J Individ-

" I ual pieces

Percent.

4-9

Damp southern

coastal States '

Averages

Percent

11

Individual pieces

I^ercent

S-l.S

Rimiainder of the

TTnited States i

Average^ I

., , Individual pieces

Percent \ Percent

1 For limiting range see fig. 71.

2 If the average moisture content is within ±1 percent of that recoirnnended and the moisture content

values of all the pieces tested fall within the prescribed range, the entire lot will proba))ly be satisfactory.

To obtain a realistic average, test at least 10 percent of each item. If the amount of a given item is small,

several tests should be made. For exaniple, iîi an ordinary dwelling having about 60 floor joists at least 10

tests should be made on joists selecte«! at random.

3 Framing lumber of higher moisture content is commonly used in ordinary construction because lunjbcr

of the moisture content specified may not be available except on special order.

Veneer and Plywood

When veneers are glued together with cold-setting glues to make

pljAvood, they absorb comparativel}^ large quantities of moisture. To

keep the final moisture content low and to minimize rediying of the

pl\^vood, the initial moisture content of the veneer should be as low

as practical. Very dry veneer, however, is difficult to handle without

cracking, so that the minimum practical moisture content is about 4

percent. After being ghied, plywood intended for interior service

should be conditioned to the moisture content values given in table

41 for interior lumber. If the plywood is glued by hot-press processes,

the veneer may need conditioning to a moisture content dependent

upoD the water content of the glue. It is often desirable to add water

to the pl}^vood by conditioning (p. 241).

DESIGN FACTORS AFFECTING SHRINKAGE IN THE

STRUCTURE

Framing Lumber in House Construction

The most effe(*tive method of minimizing settlement oi* dimensional

change due to shrinkage in the house frame would be to us(^ frammg

lumber seasoned to the moisture content it would reach m use (6', 12,

14, 16). There are practical aspec'ts, however, that make it dithcult,

if not impossible, to meet this optimum condition, but, iortunately,

some shrinkage of the frame may take place without visible evidence

appearing after the house is completed. If the moisture content o

the frammg hunber at the time the wall and cei mg finish is ai)plied

is not more than about 5 percent above that which it will reach m
330 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

servir-e 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 perhaps ceiling joists may reach a moisture

content as low as 6 to 7 percent. In mild climates the minimum

moisture content will be higher. i • i i

The most common evidences of shrinkage are cracks m plastered

walls, open joints and nail pops in dry wall construction, distortion

of door openings, unlevel floors, loosening of joints and fastenings,

or the occasionfil distortion in drying of some individual members

that mav push a wall out of alinement. Wliere incompletely seasoned

framinglumber is used, the extent of vertical shrinkage after the house

is completed is proportional to the amount of wood used as supports

in a horizontal position, such as girders, floor joists, and plates. On

this basis more evidence of shrinkage would appear in the second than

in the first floor of a 2-story house; more in a 2-story than in a 1-story

house; and more in a house with a heated basement than one without

a basement.

If framing lumber has a higher moisture content Avhen installed

than that re'commended for framing in table 41, some shrinkage may

be expected. Framing lumber, even thoroughly air-dried stock, will

generally have a moisture content higher than that recommended

when it is delivered to the building site. If carelessly handled in

storage at the site, it may take up more moisture. There are certain

practices, however, that the builder can follow which will protect the

stored lumber (see p. 334). He can also plan his work so that an

appreciable amount of seasoning will take place during the early part

of the construction period and thus minimize the effects of further

drying and shrinkage after completion.

The builder's objective should be to follow a practice that provides

time for the framing lumber to lose moisture before it is covered or

enclosed. 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. If

the application of the wall and ceiling finish is delayed for about 30

days during warm, dry spring or summer weather, air-dried yard

stock should lose enough moisture so that any further drying in place

will be relatively unimportant. During this period the builder can

proceed with the application of outside wall covering, the installation

of plumbing, heating, and wiring equipment, and any other work that

does not enclose the framing. The basement floors should be installed during this period. In cool, damp weather, or if unseasoned

lumber is used, the period of exposure should be extended. 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 any

defects that may have developed during drying, such as warped or

distorted studs, shrinkage of lintels over openings, or loosened joints,

should be corrected.

Consideration should be given to the type of framing best suited

to the building and particularly to construction methods that minimize the use of wood across the grain in vertical supports.

The platform type of construction (fig. 75) is intended to equalize

but not to minimize shrinkage. This method is used generally for
WOOD I-IANDBOOK 331

first floors and for the second story of hoiisc^s having wood sidiji<r or

shingle wall œvering. Vertieal shrinkage at the scn^ond-íloor lin(^

presents a problem at chimneys and on outside walls of brick or stone

veneer or stucco that are unbroken, miovc the design calls for a

break, such as an overhanging second floor or a change m mat(M-ials

provision lor shrinkage is readily made.

H/P RAFTER^

SOLE PLATE^

HEADER^

PLATE'

SUBFLOOR

SOLE PLATE

HEADER -

SILLSOLID BRIDGING

SOLE PLATE

GIRDER

LEDGER STRIP

BRIDGING

SHEATHING

MASONRY WALL

FIGURE 75.—Platfornj type of fraiue construction.

ZM 88257 F

Vertical shrinkage in the exterior walls is held to a minimum in the

balloon (fig. 76) type of construction, and this system is preferable

where exterior walls are of brick or stone veneer or stucco without a

break at the intervening floor line.

Girders built up of seasoned 2-inch lumber will shrink less than

solid girders, since it is not customary to season lumber thicker than

nominal 2 inches. Potential shrinkage in joists and girders is less if

the joists bear on ledger strips nailed to the side of the girder (fig. 77)

303747°—55 22
332 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

HIP RAFTER^

RAFTER

PLATE

SU8FL00R/NG^

LEDGER BOARD

DIAGONAL BRACES

LET INTO STUDS

FIRE STOP

ROUGH FLOORING

SILL

BUIL T-UP

GIRDER

SHEATHING

CORNER POST MASONRY WALL

ZM 88258 F

FiouRE 76.—Balloon type of frame construction

.-^GIRDER

CLEARANCE

A

^^^-—jo/sr

LEDGER STRIP

CLEARANCE

SOLID BLOCKING—'t

SPACE FOR UTILITIES

- JOIST

LEDGER STRIP

B

M 87429 F

FIGURE 77.—Joists l)ear on ledger strips to minimize shrinkage: A, Ledger strip

nailed on girder to support joists; B, spaced girder.
WOOD HANDBOOK 333

than if the joists run over the top of the girder (fio-. 78). TIK^ use of

metal post caps instead of wood holstVrs Hkç\vis(^ ivduccs total

shrinkage.

FULL BEARING

JOIST

BUILT-UP GIRDER

GONGRE TE

M 93742F

FKíURK 78.—Joists run over top of i^inler increase tlie vertical hei^iit of tli(.

wood used across the airain and increase subséquent shrinkai^i'.

Heavy Timber Construction

In heavy timber construction, a certain amount of shrinkage is to

be expected. If not provided for in the desigii, it may causi^ weakening of joints, affect floor levels, and be otherwise objectionable. On(^

means of eliminating part of the shrinkage in mill l)uildings and similar

structures is the use of metal post caps, whereb}' the upper column is

separated from the lower column only by the metal in the post caj).

This method eliminates the shrinkage that occurs if the wood girder

is used as a bearing for the upper column. The same thing is accomplished by supporting the upper column on the lower column with

wood corbels bolted to the side of the lower column to support the

girders.

Where joist hangers are used, the top of the joist, when installed,

should be slightly 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. Laminated floor material can easily

be properly seasoned and shrinkage minimized accordingly, beciuise

each piece is of relatively small cross section.
334 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Interior Finish

The normal seasonal changes in the moisture content of interior

finish are not enough to cause serious dimensional change if the stock

is properly seasoned and the woodwork is carefully designed and assembled. * Large members, such as ornamental beams, cornices, newel

posts, stair stringers, and handrails, should be built up from comparatively small pieces. Wide, plain surfaces, such as table tops, counter

tops,^ and panels, should be crossbanded. Door and window trim

and base should be hollowbacked. Backband trim, if mitered at the

corners, should be glued and splined before erection; otherwise butt

johits should be used for the wide faces. Large, solid pieces, such as

knotty pine panels, should be stained and finished as much as possible

before erection and should be so designed and installed that the panels

are free to move across the grain.

CARE OF LUMBER AND FINISH DURING CONSTRUCTION

Lumber and Dimension

Lumber received at the building site should be protected from wetting and other damage. Construction lumber in place in a structure

before it is enclosed may be wet during a storm, but the wetting is

mostly on the exposed surface, and the lumber can dry out quickly.

Dry lumber may be solid piled at the site, but the piles should be at

least 6 inches off the gi'ound and covered with canvas or waterproof

paper laid so as to shed water from the top, sides, and ends of the

pile. If such protection is not provided, the lumber should be open

piled on stickers to avoid the slow redrying that would result from

solid piling.

Lumber that is received in the green or nearly green condition, or

lumber that has been used for concrete forms, should be piled with

stickers for more thorough drying before it is built into the structure.

Lumber, whether dry or green, should be protected from alternate

wetting by rain and drying by direct sunshine in order to reduce

checking and warping. Frequently in the construction of houses, the

garage, if detached, can be built first and will serve as an excellent

storage space for sheathing, siding, studs, and joists.

Finish Floor

Cracks develop in flooring if it absorbs moisture either before or after

it is laid and then shrinks when the building is heated (13). Such

cracks can be greatly reduced, if not entirely eliminated, by observing

the following practices: (1) Specify flooring manufactured according to

association rules and sold by dealers that protect it properly; (2) do

not allow the flooring to be delivered on a damp or rainy day or before

the masonry and plaster walls are dry; (3) have the heating plant installed before the flooring is delivered; (4) break open the flooring

bundles and expose all sides of the flooring to the atmosphere; (5)

close up the house at night and raise the temperature about 15° F.

above the outdoor temperature for perhaps 3 days before laying the
WOOD HANDBOOK 335

floor; (6) after laying the floor keep the house elosecl at night or during

damp weather and supply some heat if necessary.

Better and smoother sanding and finishing can l)e done when the

house is warm and the wood has been kept dry.

Interior Finish

In a building under construction, the relative humidity will average

higher than it will in an occupied house because of the moisture that

evaporates from wet concrete, brickwork, and plaster, and even from

the structural wood members. The average temperature will also be

lower, because workmen prefer a lower temperature than is agreeable

in an occupied house. Under such conditions the finish tends to hav(»

a higher moisture content during construction than it will have later

during occupancy.

Before any interior finish is delivered, the outside doors and windows

should be hung in place so that they may be kept closed at night and

in this way hold the conditions of the interior as close as possible to

the higher temperature and lower humidity that ordinarily prevail

during the day. Such protection may be sufficient during the dry

summer weather, but during damp or cool weather it is highly desirable that some heat be maintained in the house, particularly at

night (13). Whenever possible, the heating plant should l)e placfnl

in the house before the interior trim goes in, so as to be availal)le for

supplying the necessary heat. Portable heaters also may be used.

The temperatures during the night should be maintained at about 15°

F. above outside temperatun^s and not be allowed to drop l)elow about

70° during the summer or 62° to 65° when outside temperatures are

below freezing.

After buildings have thoroughly dried, there is less need for heat,

but unoccupied houses, new or old, should not be allowed to stand

without some heat during the winter. A temperature of about 15° F.

above outside temperatures and above freezing at all times will be

sufliicient to keep the woodwork, finish, and other parts of the house

from being affected by dampness or frost.

Plastering

0

IT

During a plastering operation in a mod(^rate-siz(Hl 6-rooni hous(

approximately 1,000 pounds of water are used, all of which must b(

evaporated before the house is ready for the interior finish. Failure

to provide ventilation adequate to remove this evaporated moisture

means trouble later because of the moisture absorbed by the framework. In houses plastered in cold weather the moisture may also

cause paint on exterior finish and siding to blister. During warm,

dry, summer weather with the windows wide open, this moisture is

practically gone within a week after the final coat of plaster is applied.

During damp, cold weather, drying is retarded accordingly. Adequate

ventilation should be provided at all times of the year, as the evaporated moisture is airborne, and a large volume^ of air is require^d to

cany away the amount of water involved.
336 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

When the he<ating system or portable heaters are used to prevent

iVe(^zing: of plaster and to hasten its drying, the windows should be

])roperly adjusted to allow the escape of the evaporated moisture.

liven in the coldest weather, the windows on the leeward side of the

house should be opened 2 or 3 inches, preferably from the top.

LITERATURE CITED

(1) DuxLAP, M. E., and BELL, E. R.

1940. ELECTRICAL MOLSTURE METERS FOR WOOD. U. S. Forest Procl. Lab.

Rpt. R1660, 10 pp., illus. (Rev.) [Processed.]

(2) KOEHLER, A.

1046. LONciTUDiNAL SHRINKAGE OF WOOD. U. 8. Forcst Prod. Lab. Rpt.

R1Ü03, 8 pp., illus. (Rev.) [Processed.]

(3) AÍATFEWSON, J. S.

1030. AIR SEASONING OF w^ooD. U. S. Dept. AgT. Tecli. Bui. 174, 55 pp.,

(4)

illus.

1053. ELECTRICALLY OPERATED WOOD-ELEMENT HYGROSTATS FOR CONTROL OF MOISTURE FLUCTUATIONS IN LUMBER STORED IN CLOSED

SHEDS. U. 8. Forest Prod. Lab. Rpt. R1140, 10 pp., illus. (Rev.)

[Processed.]

(5) AlcATiLLEN, J. M.

1050. METHODS OF DETERMINING THE MOISTURE CONTENT OF WOOD. U. 8.

Forest Prod. Lab. Rpt. R1640, 8 ])p., illus. (Rev.) [Processed.]

(6) XAIIONAL LUMBER MANUFACTURERS ASSOCIATION.

1020. HOUSE FRAMING DETAILS. 24 pp., illus. Washington, D. C.

(7) PEGK, E. C.

1047. SHRINKAGE OF WOOD. U. 8. Forest Prod. Lab. Rpt. R1650, 6 pp.,

illus. [Processed.]

(8)

(0)

(10)

1050. MOISTURE CONTENT OF WOOD IN USE. U. 8. Forest Prod. Lab.

Rpt. R1655, 8 pp., illus. (Rev.) [Processed.]

1050. AIR DRYING OF LUMBER. U. 8. Forest Prod. Lab. Rpt. R1657,

18 pp,, illus. (Rev.) [Processed.]

1052. STORAGE AND HANDLING OF LUMBER (AT WHOLESALE AND RETAIL

YARDS AND AT CONSUMER PLANTS). JJ. 8. Forest Prod. Lai).

Rpt. RIOIO, 17 pp., illus. [Processed.]

(11) R.ASMUSSEN, E. F.

1051. PROPERTIES OF WOOD RELATED TO DRYING. U. 8. ForCSt Prod. Lab.

Rpt. RlOOO-l, 25 pp., illus. [Processed.]

(12) TEESDALE, L. V.

1034. HOW PLASTERING AFFECTS THE MOISTURE CONTENT OF STRUCTURAL

AND FINISH WOODWORK. U, 8. Forest Prod. Lab. Rpt. R1274,

4 pp., illus. (Rev.) [Processed.]

(13) and IMATHEWSON, J. 8.

1052. PREVENTING CRACKS IN NEW WOOD FLOORS. U. 8. Dept. Agr.

Leaflet 56, 6 pp., illus.

(14) LT. 8. FOREST PRODUCTS LABORATORY.

1047. TECHNIQUE OF HOUSE NAILING. 53 pp., illus. (Lssued by U. 8.

Housing and Home Finance Agencv.)

(15) —

1052. SHRINKAGE AND SWELLING OF WOOD IN USE. U. 8. Forest PrOd.

Lab. Rpt. R.736, 10 pp., illus. (Rev.) [Processed.]

(16) WEYERHAEUSER 8ALFS CO.

1050. HIGH COST OF CHEAP CONSTRUCTION. 71 pp., illus. St. Paul, Minn.
FIRE RESISTANCE OF WOOD CONSTRUCTION

Acceptable fire resistance in wood construction is obtained t)y takingadvantage of the self-insulating qualities of wood and by enii)lovino:

good structural details. The performance of wood in struct\u-es

under fire conditions may be further improved by impregnation

treatments and surface coatings with fire-retardant niaterials.

IMPROVEMENT OF FIRE RESISTANCE OF WOOD

CONSTRUCTION THROUGH DESIGN

Wood construction for many years has been identified in standard

buildhig codes with 1 of 3 standard types (9).- These are the heavytimber, ordinary (p. 339), and light-frame ty])es. The first two have

been widely used for industrial or commercial buildings and the third

for dwellings and some smaller commercial buildings. With the

recent development of the wood roof truss or arch and the glued

laminated structural member, a new type of construction, the onestory industrial or commercial building, has appeared. General

principles of design of these types of construction, particularly as

they affect fire prevention and control, are presented here.

Heavy-Timber Construction

Heavy-timber construction, also known as mill-type construction,

has been extensively built, and man}^ structures of this ty])e are still

in use (fig. 79) (10). It is a multistory construction with exteiior

walls of masonry and interior columns, beams, and floors of wood in

solid masses with a minimum of surface or projections exposed to fire.

The present tendency is away from large, solid sawed timbers and

toward glued laminated structural members with longer spans that

permit larger unobstructed floor areas.

In heavy-timber construction, wood columns are not less than

nominal 8 inches thick, with rounded or chamfered corners. Beams

and girders are not less than nominal 6 inches thick and not less than

nominal 10 inches deep. Built-up beams are permitted, when closely

jointed by gluing or bolting. Beams made of two members with an

intervening air space are not permitted in floor framing for heavytimber construction. Floors are constructed of splined or matched

planks nominal 3 inches thick with a nominal 1-inch finish floor or of

planks nominal 4 inches wide set on edge with a nominal 1-inch finish

floor. Roof decks are of similar construction but may have spUned or

matched planks nominal 2}^ inches thick (nominal 2 inches thick if the

buildmg is sprinklered) or planks nominal 3 inches wide set on edge.

Roof orders are not less than 6 inches (nominal) in least dimension.

Italic numbers in parentheses refer to Literature Cited, p. 349.

337
33S HAXDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

M 9357') F

FIGURE 79.—Heavy-timber, or niill-type, construction.
WOOD HANDBOOK 339

Roof arches or trusses may be nominal 4 hy 6 or laro;er meinl)ers,

except that spaced members may be nominal 3 inches thick if properly

blocked or covered or single members nominal 3 inches thick if the

building is sprinklered.

Heavy-timber construction is fire resistant because of the slow

rate of burning of wood in massive form. The average rale of penetration of char under standard time-temperature fire conditions (1)

is of the order of l}^ inches per hour.'^^

The resistance of heavy timber to fire is shown in the following

results of fire tests of wood columns under design load:

•

Type of column i (tim})er, longleaf piiic or Douglas-fir; crosssection, /o fanmr

11% by Huinches) with— ' HHiniftcs)

Steel plate cap 35-38

Cast iron cap and pintle 45-50

Reinforced concrete cap 78-112

Steel plate cap; cap and column protected with %-inch gy])sum

wallboard ' 73

Cast iron cap; cap and column Drotected with 1-inch layer of portland cement plaster or metal lath 135

^ Data for triiiiber colnnms with reiuforco<l foncicte raps arp from HniKlltook of Vivo

Protection {10) ; all other data are from Fire Exposure Tests of Loaded Timber Columns

(12).

Ordinary Construction

The term ^'ordinary construction'^ was originally defined for buildings 2 to 4 stories high with exterior walls of masonry and interior

wood-joist frames with members not less than 2 inches (nominal)

thick. This type of construction has been widely employed in commercial or public buildings in villages and small cities. Ordinary construction differs from heavy-timber construction in that exterior walls

are not so heavy and interior framing is less massive. These differences

are reflected in smaller heights and areas allowed. It diners from lightframe construction in its larger allowable heights and areas, its selfsupporting masonry walls, and in a number of interior requirements

appropriate to public occupancy. There are detailed code requirements for firestops (nominal 2-inch-thick wood or the equivalent) in

concealed spaces in walls or ceilings through which fire may spread.

Large attic spaces are divided by ''draft stops," partitions made of 2

thicknesses of 1-inch lumber or the equivalent.

One-Story Industrial Buildings

In recent years, the one-story industrial or commercial building has

largely superseded other types of wood-frame industrial construction.

Typically, this building has side walls 12 to 20 feet high, supporting

wood roof trusses or arches with spans of 40 to 100 feet or more (fig. 80).

Truss or arch members are often of glued laminated construction.

23 Wood chars a little more rapidly when a fresh surface is exposed to fire than

it does under a laver of charcoal, about Yzo inch per minute in the first 5 minutes

and }io inch per rainute after >^ hour of exposure (7).
340 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE
WOOD HANDBOOK 341

Larger buildings are simply multiples of such units placed side bv side,

separated by fire walls as required by building codes. In some instances, a ceiling is hung below the roof framhig, but the space above

the ceilmg is usually unoccupied. This type of construction is popular

because it provides large unobstructed working areas.

One-story industrial construction with masonrv walls and roof

framing members not less than nominal 2 inclies thick often cpialific^s

in building codes as ordinary construction. vSmaller buildings without

masonry walls may qualify as light-frame construction. The masonry

walls and the interior wood construction generally are not massive

enough to give fire resistance equivalent to that of heavy-timber

construction.

Fire-fighting operations in such one-story buildings are facilitated

by the limited height, the large unobstructed areas, and the general

absence of inaccessible spaces. It is easy to provide any number of

exits for personnel in case of fire. From the standpoint of fire safety,

this construction ranks favorably with ordinary construction.

In construction of this type, provision for fire protection around

basement heating units and maintenance of automatic fii-e s(*])aration

between basement and main floor are commonly required by code.

Unused attic spaces are accessible to firemen, often from the roof as

well as from below. Metal connections at joints of roof trusses or at

the crest of arches, embedded in the wood so that deep charring must

take place before the connection is destro^^ed, provide greater fire

resistance.

Light-Frame Construction

Most residential and some commercial or industrial buildings of

wood are of light-frame or, as more commonly known, frame (*onstruction. Originally restricted to the conventional type of building

with stud walls, joisted floors and ceilings, and raftered roofs, lightframe construction has more recently been diversified by the introduction of prefabricated, panelized, or stressed-skin structural

elements.

Light-frame wood buildings do not have the fire resistance of the

heavier wood frames. Therefore, in these buildings, attention to

good construction details is important to retard the spread of fire

and reduce hazards to occupants and property damage in case of

fire. The fire resistance of light-frame construction depends in large

part on construction details, of which firestops; separation of wood

from masonry around chimneys and fireplaces; and walls, ceilings,

floors, roofs, stairways, and doors are important {9, 13, 15).

Firestops

Firestops are obstructions provided in concealed air spaces and are

designed to interfere with the passage of flames up or across a buildhig.

Fh'e in buildings spreads by the movement of high-temperature air

and gases through open channels. In addition to halls, stairways,

and other large spaces, heated gases also follow the concealed spaces

between floor joists, between studs in partitions and walls of frame

construction, and between the plaster and the wall where the plaster
342 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

is carried on furring strips. Fire may quickly find its way through

these hidden channels to every part of the structure if they are not

obstructed at suitabk» points.

Wood of 2-inch nominal thickness or some noncombustible insuhxting material not k^ss than 1 inch thick are effective firestops. Good

practice inchuU^s: Firestops at exterior walls, each floor level, and the

level where the roof connects with the wall; firestops at each floor

level in partitions that are continuous through two or more stories;

headers at the top and bottom of the space between stair carriages;

mineral wool, as})estos, or an equivalent material packed tightly

around pipes or ducts that pass through a floor or a firestop; and selfclosing doors on vertical shafts, such as clothes chutes. Figure 81

shows applications of firestops in an exterior wall.

2"x4" FIRESTOP

2"x 4"

SPACER BLOCK

ANCHORED S/LB

SECOND-FLOOR

JOISTS

1X4 RIBBON

(LET IN)

STUD

I"X 4" DIAGONAL

BRACE (LET IN)

FIRST-FLOOR JOIST

2"x 4"FIRESTOP

ZM 87434 F

FIGURE 81.—Firestops in frame construction.

Wood Construction Around Chimneys and Fireplaces

Good practice in the protection of wood from ignition by heat

conducted through chimneys and fireplaces includes the following

details: If smoke pipes from furnaces pass through walls, they are
WOOD HANDBOOK 343

protected by thimbles at least 8 inches larger in diameter than th(^

pipe. No smoke pipe passes through a floor or ceiling but joins the

chimney on the same floor where it originates. Wood ))eams, joists,

or rafters are separated from any chimiu^y l)y a 2-inch space. ' Woo(Í

furring strips placed around chimneys to' support base or oth(4- trim

are insulated from the masonry l)y asbestos paper at h^ast ji inch tliick,

and metal wall plugs or approved noncombustible nail-hohling devicc^s

attached to the wall surface are used for iiaiHng. Wood construction

is separated at least 4 inches from the l)ack wall of any fireplace, and

wood header beams supporting trimuK^r arches at fireplaci^s are placed

at least 20 inches away from the face of the chimney breast. A wood

mantel or other woodwork is placed not less than S'inches from either

side nor less than 12 inches from the top of any fireplac(> opening.

Fireplace^ hearths are of noncombustible material, not less than fs

inches wide, measured from the face of the opi^iing. All spaces

between the masonry of chimn(\ys and wood joists, beams, headers,

or trimmers are filled with noncom})ustible material.

Partitions

A fire starting in one room of a building will be confined to that

room for a yariable period of time, depending on the fire resistance of

the walls, partititions, ceilings, and doors. The fin^ resistance of

wood frame walls and partititions depends to a consid(^rable oxivni

upon the materials used for faces, the method of joining wall and

partition units, the quality of workmanshij), and the ty])e and quantity

of any insulation that may be used.

The following tabulation gives the fire resistance of non-bearing

l)uilt-up prefabricated wood partitions:

vit i mal c

ftre-rcsisfni/ce

period '

(mill ules)

Solid partitions of l^Mfi- by 3M-inch, to]iRuefl-and-<irooved, beaded wood

boards placed vertically with staggered joints:

2 board layers 15

2 board layers with asbestos paper weighing •^>0 pounds per 100 square

feet between layers 25

Solid panels of %-inch wood boards, 2'íí to (> inches \\'ifle, grooved, and joined

with wood spliîies, nailed together; i)oards placed vertically with staggered joints:

1 board layer 10

2 board layers 25

3 board layers 40

Solid panels with •)i,rinch plywood facings glued to l^/.i-inch solid wood core

of glued tongued-and-grooved construction for both sides and ends of core

pieces, with tongued-and-grooved rails in the core about 2'2 feet apart—

2^-inch-thick panels 60

Hollow panels with plywood facings on both sides glued to wood frame;

thickness of framing not less than 1% inches:

K-inch plywood faces 10

%-inch plywood faces 15

H-inch plywood faces 20

%-inch plywood faces 25

Hollow panels with plywood facings, '4 inch thick on one side and % inch

thick on the other side, glued to 2H- by =^4-inch wood studs set edgewise;

panels filled with mineral wool batts weighing 2 pounds per square foot of

filled space—3-inch-thick panel 15

• Data obtained from National Bureau of Standards Report (///).
344 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

The following tabulation gives the fire resistance of well-constructed

load-bearing wood-frame partitions:

Ultimate

fire-resistance

period '

Faciiii^s of boards without plaster: (miriu/es)

V^-inch fiberboard weighing 0.7 pound per square foot 10

^^-inch fiberboard weighing 1.1 pounds per square foot 15

^-inch flameproofed fiberboard weighing 1.6 pounds per scjuare foot

as treated ^' 30

^4-inch tongued-and-grooved wood boards 20

%-inch tongued-and-grooved wood boards with mineral-wool fill 35

%-inch tongued-and-grooved wood boards with asbestos paper weighing 30 pounds per 100 square feet between boards and studs 45

%-inch gypsum wallboard 25

M-inch gypsum wallboard — . 40

i^-inch gvpsum wallboard with mineral wool fill 45

U-inch gypsum wallboard with mineral wool batts nailed to studs 60

Facings of plaster on wood lath:^—

tf-inch gypsum plaster (1:2, 1:3) 30

i/-inch gypsum plaster (1:2, 1:3) with mineral wool fill . . 60

Facings of plaster on board plaster base:^

H-inch gypsum plaster (1:2, 1:2) on H-ii^ch fiberboard weighing 0.7

pound per square foot 35

i^-inch gypsum plaster (1:2, 1:2) on %-inch flameproofed fiberboard

w^eighing 2.8 pounds per square foot as treated 60

^/2-inch neat gypsum plaster on %-inch plain gypsum lath 60

^X-inch gypsum plaster (1:2, 1:2) on H-inch perforated gypsum lath,

1 hole of %-inch or larger diameter per not more than 16 square

inches of lath surface 60

^-^-inch gypsum plaster (1:2, 1:2) on %-inch gypsum lath, plain,

indented, or perforated other than as above 45

1 Data are from National Bureau of Standards Report (16). Fire-resistance values are for nominal 2- by

4-inch wood studs (No. 1 common or better) set edgewise and having 2- by 4-inch wood plates at top and

bottom and stayed transversely at midheight with wood blocks. Partitions were loaded on the basis of

360 pounds per square inch of the net area of the studs. "Mineral wool fill" can be taken as rock wool batts

weighing not less than 1.0 pound per square foot of wall surface, glass wool batts at 0.6 pound per square

foot, or rock wool blown in and weighing not less than 2.0 pounds per square foot of wall surface. "Wall

surface" applies only to surface of filled space.

2 Plaster proportions (in parentheses) are given as weights of dry plaster to dry sand, the first ratio being

for the scratch coat and the second for the brown coat.

The fire tests upon which the fire-resistance values in the preceding

tabulations are based were conducted in substantial accord with

Standard Specifications for Fire Tests of Building Construction and

Materials, No. A2-1934, American Standards Association.

Basement Ceilings

Since fires may start from heating plants located in basements, it is

desirable that a fire-resistant separation of the basement from the

remainder of the building be provided. Gypsum board, asbestos

board, or plaster on metal or gypsum lath placed on the basement

joists affords an eff'ective means of increasing thé fire resistance of the

basement ceiling and of retarding the rapid spread of flames, but such

material is usually omitted to reduce cost. Less expensive fireretardant coatings applied to all exposed wood surfaces also provide

protection from rapid spread of fire. Particular attention should

be given to the wood floor members directl}^ above and near the

furnace.

If, as is common, a basement stairway is directly under the stah^way

leading from the fii^t to the second floor, it is good practice to protect
WOOD HANDBOOK 345

the underside of the upper stairway with iu-e-iu^sistant coverinos, as

suggested for basement ceihngs, and to phxcc^ ñrí^stops between the

wood carriages at the top and bottom.

Floors

Tlie conventional (looi* construction of joists, sul)floor, and finisli

floor offers consi(UM-al)k^ resistance^ to th(^ ])enetration of fu-o and will

retain some supporting capacity in fire exposuin^s u]) to 15 minutes

(16). Prefabricated floor panels, in which tlu^ supporting power

depends upon stressed covers, and floor systems supported by box

girders mth thin plywood webs are more vulnerable to fire penetration.

Doors and Stairways

If a fire-resistant ceiling is placed on the basement joists, it is

desirable to have a door leading to the basement with fire resistance

e(iual to the combined resistance of the ceiling and floor over the bas(^-

inent.

Enclosed stairways retard rapid spread of fire from floor to floor.

If the interior d(^sign calls for an open stairway below, it can often

be closed at the top with a solid flush door. Hollow-core flush doors

oft'er little resistance to the penetration of fire vmless the space between

covers is packed with an insulating material.

Roof Coverings

The better gi-ades of wood shingles are edge grained and thick

butted with 5 butts measuring at least 2 inclies. Edge-grained

shingles warp or curl less than flat-grained ones, thick-butted shingles

less than thin ones, and narrow shingles less than wide ones. Fire

sparks are less likely to lodge beneath and ignite tight, flat shingles

than warped shingles. To follow accepted rules of good practice in

laying shingles not only makes a long-lived and economical roof but

markedly reduces fire hazards. Painting or staining shingles with the

materials customarily used for that purpose has little effect on their

fire resistance.

Surface Coverings and Finishes

Finishing or covering materials, such as paint, should be such as not

to promote rapid spread of flame, give off poisonous gases, or otherwise

cause an unusual or excessive fire hazard. Flame-spread tests suitable for evaluating surface coverings or treatments are available {2, 8,

19,20).

Glued Laminated Members

The fire resistance of glued laminated structural members, such as

arches, beams, and columns, is approximately equal to the fire resistance of solid members of similar sizes. Available information indicates that laminated members glued with phenol, resorcinol, or melamine glues are at least equal in fire resistance to a one-piece member of
346 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

the same size and that laminated members glued with casein glues

may have sht;-htlv less fire resistance.

in tests at tlu^ Forc^st Products T^aboratory, when the edges of the

himinations in s(M'tions of himinated members bonded with casein

o'hie wcvv (^X])OS(M1 to a gas fire, sHghtly (keeper charring resulted at the

o:hie joints than l)etwe(»n the glue joints. When the broad face of a

lami]uition was exposed to the fire, the outer lamination loosened

from the rest of the meml)er when the zone of char penetrated to the

depth of the glue line. The appearance of the joints and the results

of shear tests indicated, however, that little if any weakening of the

glue joints occurred beyond the charred surface as a result of the fire

exposure. Also, the performance of casein-glued laminated rnembers

in actual fires is reported to demonstrate the integiity of casein-glued

joints beyond the zone of char.

When the fire endurance required of a wood member is less than the

time required for the zone of char to penetrate through the outer

laminations, the presence of glue or the type of glue is unimportant.

Thus, on the basis of a rate of penetration of char of 1}^ inches per

hour of exposure to fire, casein-glued laminated lumber, with outer

laminations not less than 1^ inches thick (such as nominal 2-inch

lumber laminations) would be equivalent in fire resistance to solid

members of the same actual size with a fire resistance up to 1 hour.

For a casein-glued member whose thickness of laminations permits

penetration of the zone of char to the outermost glue line in a period

less than the required fire endurance of the member, the zone of char

will penetrate a little faster in the laminated member, after it reaches

the first glue line, than in a solid member. Available data indicate

that for a beam made of %-inch casein-glued laminations the char

may be as much as 10 percent deeper in the laminated beam than in

a solid beam of the same size after exposure to fire for 1 hour.

Thus, for lieav3^-timber-construction classification, laminated meml)ers glued with phenol, resorcinol, or melamine glues or laminated

members glued with casein glue and having nominal 2-inch outei

laminations are considered equivalent to solid sawed members in

comparable standard minimum sizes; for casein-glued members with

face laminations less than 1)2 inches thick, the dimension of the

member in the direction at right angles to the glue lines should be

increased at least 0.15 inch.

FIRE-RETARDANT TREATMENTS FOR WOOD

Two general kinds of treatments are available for improving the

fire resistance of wood: (1) Impregnation treatments that deposit

fire-re tardant chemicals within the wood (17) and (2) coatings or

layers of protective materials over the surface of the wood (19).

Good fire-retardant effects can be obtained by both methods. For new

wood construction and the repair of existing structures with new parts,

pressure impregnation with effective fire-retarding chemicals offers

the best possibility of obtaining lasting fire-retardant eft'ects in high

degree. For wood in existing structures, surface applications offer

the principal means of increasing the fire-retardant properties. Lumber, timbers, and pl}nvood impregnated with fire-retarding chemicals
WOOD HANDBOOK 347

now find many uses in a great variety of buildings (5). During

World War II, large quantities of impregnated lumber were used for

the construction of dirigible hangars and for shoring aboard ships.

Impregnation Treatment

Wood is impregnated with firc-retardant chemicals by methods

simdar to those used to inject preservatives (p. 411). The wood is

placed within a sealed treating c^dinder and the treatmg solution

forced in by means of pressure. Although additional hiformation is

needed on the effect of the treatments on the strength of wood, the

amounts required for a specified performance, and the permanence of

the treatments under adverse exposure, it is known that the fireretarding effect of impregnation treatments is closely related to the

quantity of chemical injected into the wood as well as to the chemical

used (S, 11). Absorptions up to 1 pound of fire-retardant chemical

per cubic foot of wood, quantities such as are used with toxic chemicals

for decay prevention, have only a small effect on the combustion of

wood. It is necessary to use much more chemical to obtain the best

fire-retardant results. For a high degree of efl'ectiveness, 5 to 6

pounds of the more effective chemicals per cubic foot of wood in

thicknesses less than 2 inches are required, or approximately 400 to 500

pounds per thousand board-feet. Lumber in thicknesses greater

than 2 inches requires proportionately less material (4, ^8).

Effectively treated wood can be charred or disintegrated by continuous exposure to intense heat from an outside source, but when the

heating is discontinued the burning ceases. The principal eft'ects of

fire-retardant impregnation treatments are to retard the normal

increase in temperature under fire conditions, to decrease the rate of

flame spread, to lessen the rate of flame penetration or destruction

of wood in contact with fire, and to make fires more easil}^ extinguished.

Impregnation treatments may be complete; that is, the treatment

may extend completely through the piece; or they may be only partial,

in which case only an outside zone of the piece is impregnated. Complete impregnation with an adequate quantity of fire-retardant

chemicals makes wood sufficiently resistant to fire so that it will not

of itself support combustion. Partial impregnation affords protection that is adequate for most purposes and under many conditions,

although the central part is unimpregnated. It obviously is cheaper

and generally more practical than complete impregnation. Only

partial impregnation is possible with some species of wood and with

most lumber and timbers of commercial size (6). When the lumber

must be cut into smaller sized pieces or machined after treatment in

such a way that the interior is exposed, however, the eft'ectiveness of

the treatment may be greatly reduced unless there has been practically complete penetration.

Many chemicals have a fire-retardant effect when wood is impregnated with them, but because of cost limitations or various objectionable characteristics, comparatively few are considered commercially

practical. Among the most commonly used chemicals are monoammonium phosphate, diammonium phosphate, ammonium sulfate,

303747^—55 23
348 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

sodium tetraborate (borax), boric acid, and zinc chloride. The

ammonium phosphates are effective in checkmg both flammg and

glowing. Borax, although elective in checking flammg, is not a

good slow retardant. Boric acid, on the other hand, is exceptionally

effective in stopping glow but is not so effective for retarding flaming.

Because of the different characteristics of the compounds and because

of cost considerations, fire-retardant treating formulations usually

ai-e mixtures of fire-retardant chemicals. Typical formulations arc

available {4, 5, 17). The fire-retarcHng effec^tiveness of numerous

chemicals other than tlie six listed is reported in Plxperiments in Fireproofing Wood {11).

Many chemicals that might be used as fire retardants may have

undesirable effects on the wood or be otherwise objectionable for

specific uses. Caution should be observed, therefore, in deciding

upon any treatment that has not had thorough trial in practice.

Among use characteristics of importance are permanence of the fire

resistance imparted to wood, effect on strength of wood, tendency to

corrode metals, effects on paint and glue, hygroscopicity, and toxicity

to occupants of buildings.

There are a number of formulations of fire-retardant chemicals of

high effectiveness that have been in commercial use over a sufl&cient

period of years to demonstrate that they are practical (4, 5),

Coatings and Surface Treatments

Many coating materials protect wood against fire in varying

degree (i7). As with impregnation treatments, the amount of protection provided by a coating is related to the amount and thoroughness of application, and to the severity of the fire exposure.

Fire-retardant coatings are of varying composition and properties.

Most available preparations are of value primarily for interior use

and are not durable when exposed to the weather. They usually

owe their effectiveness to one of the following water-soluble fireretardant chemicals: Ammonium phosphate, borax, or sodium silicate.

These fire retardants are combined with other constituents to provide

other properties required or desirable in a paint, such as adherence

to wood, appearance, and brushability. vSome good proprietary

fire-retarding coatings based on these chemicals are on the market.

The following nonproprietary formulations {17) are among those

which have shown good results in laboratory tests, when applied in

adequate amounts:

Percent by

i\\ weight

Basic carbonate white lead ^1

Borax - 32

Raw linseed oil ^?"^

Turpentine ^- ^

Japan drier -^

100.0

3 or 4 thick coats, or approximately 1 gallon per 125 square feet

of surface, are required for good protection.
WOOD HANDBOOK 349

(2)-

Sodium silicate solution (specific gravity 1.41 to 1.42, silica-soda Pounds

^ ratio 3.2 to 3.4) ' . _ _ ^ _ 112

Kaolin _ 1 50

Water ._ __ _ _ ^ ^ 100

3 to 4 coats are required to give good y)rotection. 1 gallon will

cover approximately 100 square feet (4 coats"). Parts hy

(3)— ireighf

Monoammoniuni phosphate___ _ _ . . _ , _ 50

Sodium alginate gel 2 percent _ _ _ _ _ 50

Prepare the alginate gel by adding 2 parts by weight of dry

sodium alginate to 98 parts by weight of hot water. Stir until a

uniform gel is obtained. Grind in a pebble mill equal parts by

weight of monoammonium phosphate and the alginate gel. A grinding period of 12 to 24 hours is sufficient. 2 to 3 coats are required

for good protection. 1 gallon will cover about 70 sf[uare feet (3

coats).

So far as is known, no water-insoluble compound has been found

that is equal in fire-retarding efïeetiveness to the three water-soluble

chemicals listed previously. Compounds of low water solubility that

have measurable fire-retardant properties are zinc borate, chlorinated

paraffin, and chlorinated rubber, and exterior proprietary preparations are on the market containing these constituents. Although

possessing moderate fire-retarding properties, these paints do not

give a performance equal to that of the better interior paints.

LITERATURE CITED

(1) AMERICAN SOCIETY FOR TESTINC; MATERIALS.

1950. METHODS OF FIRE TESTS OF BXTILDINF: CONSTRUCTION AND MATERIALS.

Amer. Soc. Testing Mater. Standard E-119-50. Pt. 4: 9!)3-100l,

illus.

(2)

1950. TENTATIVE METHODS OF FIRE HAZARD CLASSIFICATION OF RUILDINC

MATERIALS. Amcr. Soc. Testing Mater. Standard ]^-84-50T

(Tentative). Pt. 4: 1020-1022.

(3) AMERICAN WOOD-PRESERVERS' ASSOCIATION.

1944. REPORT OF COMMITTEE 9, FIREPROOFINC. Amer. \\'ood-Prcs(Tvrrs'

Assoc. Proc. 40: 261-348, illus.

(4)

1949. REPORT OF COMMITTEE P-5, FIRE-RETARDANT PRESEKVA'J'IVES.

Amer. Wood-Preservers' Assoc. Proc. 45: 46-54.

(5) ANGELL, H. W.

1951. PRODUCTION AND USE OF FIRE RETARDANT TREATED LUMBER.

Forest Prod. Res. Soc. Proc. 5: 107-114, illus.

(6) HUNT, G. M., and GARRATT, G. A.

1953. WOOD PRESERVATION. 402 })p., illus. New York.

(7) LAWSON, D. L, WEBSTER, C. T., and ASHTON, L. A.

1952. FIRE ENDURANCE OF TIMBER BEAMS AND FLOORS. Struct. Engin.

(England) 30 (2): 7 pp., illus.

(8) MCNAUGHTON, G. C., and VAN KLEECK, A.

1953. FIRE-TEST METHODS USED IN RESEARCH AT THE FOREST PRODUCTS

LABORATORY. U. S. Forest Prod. Lab. Rpt. R1443, 13 pp., illus.

[Processed.]

(9) NATIONAL BOARD OF FIRE UNDERWRITERS.

1949. NATIONAL BUILDING CODE. 258 pp., illus. New York.

(10) NATIONAL FIRE PROTECTION ASSOCIATION.

1948. HANDBOOK OF FIRE PROTECTION. 10th ed., 1544 pp., illus. Boston

(11) TRUAX, T. R., HARRISON, C. A., and BAECHLER, R. II.

1935. EXPERIMENTS IN FIREPROOFING WOOD—FIFTH PROGRESS REPORT.

Amer. Wood-Preservers' A^soc. Proc. 31: 231-248, illus.
350 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

(12) UXDERWRITERS LABORATORIES, INC.

1939 FIRE EXPOSURE TESTS OF LOADED TIMBER COLUMNS. Underwriters

Labs. Bui. Res. 13, 23 pp., illus.

(13) U. S. FEDERAL BOARD OF VOCATIONAL EDUCATION.

1931. LICHT FRAME HOUSE CONSTRUCTION. U. S. Fed. Bd. Vocat. Ed.

Bui. 145, Trade and Indus. Ser. 41, 216 pp., illus.

(14) U. S. NATIONAL BUREAU OF STANDARDS.

1921. FIRE TESTS OF BuiLDiNC COLUMNS. U. S. Nati. Bur. Standards

Technol. Paper 184, 373 pp., illus.

(15)

1932. RECOMMENDED MINIMUM REQUIREMENTS FOR SMALL DWELLING

CONSTRUCTION. U. S. Dept. Com., Rpt. Bldg. Code Com., Bldg.

and Housing 18, 107 pp., illus.

(16)

1942. FIRE RESISTANCE CLASSIFICATION OF BUILDING CONSTRUCTIONS.

Bldg. Mater, and Struct. Rpt. 92, 70 pp.

(17) U. S. NAVY.

1944. CHEMICALS, FIRE-RETARDANT, FOR LUMBER AND TIMBER. Navy

Dept. Specif. 51 C 38, 7 pp.

(18)

1944. CHEMICALS, FIRE-RETARDANT, FOR LUMBER AND TIMBER (RECOMMENDED TREATING PRACTICE). Navy Dept. Specif. 51 C 40,

8 pp.. illus.

(19) VAN KLEECK, A.

1948. FIRE-RETARDING COATINGS. U. S. Forcst Prod. Lab, Rpt. R1280,

11 pp. [Processed.]

(20)

1950. EVALUATION OF FLAME-SPREAD RESISTANCE OF FIBER INSULATION

BOARDS. U. S. Forest Prod. Lab. Rpt. D1756, 12 pp., illus.

[Processed.]

.J¡£ái
PAINTING AND FINISHING WOOD

The principal reason for coating woodwork is usually improvement

and maintenance of appearance. Immediate considerations in coating wood for appearance are: (1) Paint and enamel are opaque and

therefore conceal the gi-ain and color of the wood, substitiiting color,

sheen, and texture of their own. (2) Varnish, lacquer, oil, and wax

are transparent and thus reveal the grain of a piece more fully by

displacing the air at its surface with a medium of much higher refractive index. They intensify the natural color of the wood, the

more so the deeper they penetrate into the wood. In conjunction

with stain, they may alter the color of the wood. The sheen and

texture of these coatings are substituted for those of the wood.

(3) Stain without varnish or lacquer changes the color of wood without

greatly altering its sheen or texture.

Ultimate considerations in coating wood for appearance are:

(1) Unless protected by suitable coatings, wood exposed to the weather

undergoes weathering, which greatly alters its appearance and may

impair its usefulness (i, ^7).^^ (2) Uncoated interior wood surfaces are porous enough to absorb liquids quickly, to stain ami spot

readily, and to hold dnt tenaciously, Nonporous coatings or coatings that tend to shed liquids will protect wood from discoloration

and present a surface easily cleaned.

Other reasons for painting or finishing wood are to provide a

brighter surface for better lighting in dark rooms, to retard changes

in moisture content and dimensions of wood, and to make it more

difficult for wood to take fire and for the flames to spread. Moisture-retardant coatings are discussed on pages 371-373, fire retardant

coatings on pages 348-349.

Paints and finishes are not used primarily to prolong the life of

wood (1). Ordinary paints and varnishes are ineffective as preservatives against decay fungi. In addition, wood that is damp enough for

attack by fungi is likely to be difficult to keep painted (8). Decay

of wood and its prevention are discussed on pages 381-386. The

painting of wood that has been treated for the prevention of decay is

discussed on page 359.

Exterior woodwork that stays reasonably dry, except for wetting

of its exposed surfaces by rain or snow for short times, does not decay,

but, if left uncoated, it is subject to weathering. In weathering, wood

usually turns gray (at high altitudes, in the mountains, it may turn

brown), smoothly planed surfaces become rough and cracked, and

the wood wastes away at the exposed surfaces by about 0.25 inch a

century. In addition, boards may cup, warp, and pull at their

fastenings and, if too thin or too short, may split. Weathering can

be prevented by keeping wood always well painted (fig. 82), but since

the cost of repeated paintings soon exceeds the value of the wood, it

is uneconomical to paint merely to keep wood from weathering. But

if painting is to be done for the sake of appearance anyway, the protective power of paint makes it possible to use thinner pieces of wood

than would otherwise be advisable.

24 Italic numbers in parentheses refer to Literature Cited, p. 377.

351
352 HANDBOOK 7 2, U. S. DEPARTMENT OF ' AGRICULTURE

.„„>

FiGUBE 82.—Wood houses can be kept well painted for many decades if good

paints and painting practices are used. This house^ built in 1759, has been

occupied and kept in good condition ever since. The exterior woodwork is

undoubtedly the original, and it has never been necessary to remove the old

paint before repainting.
WOOD HANDBOOK 353

PAINTING CHARACTERISTICS OF WOODS

Wood may be finished by merely saturatino- ¡ts surface with

drymg-oil, sealer, or wax finishes, either with or without stain, and

without forming a continuous coating of appreciable thickness over

the surface. vSuch finishes may be called penetrating finishes or intrasurface finishes as distinguished from surface coatings, such as paint

and enamel. A surface coating forms a continuous skin ov(^r th(^ wood

seldom less than 0.001 inch and preferably not more than 0.005 inch

thick except in special cases, such as textured or sand finishes. It is

applied ovcT a suitable sealer or primer that makes the wood surface

nonabsorptive of liquids, so that the finishing coats will remain on

the surface. Hardwoods with relatively large pores (vessels) require

a heavily pigmented wood filler, to plug the pores, before they can

be painted smoothly.

Spreading Rates

The spreading rate of paint or other finish is the area of siu-face

covered by a unit volume of paint. On smoothly planed surfaces of

softwoods the spreading rate varies with species only for the first or

priming coat of paint applied on the new surface; the spreading rate

of subsequent coats does not vary with species (2).

Even for priming-coat paint the species of wood has less efi"ect on

spreading rate than the individuality of the painter or the kind and

proportion of ingredients in the paint. Some painters brush paint

out farther than others; the best painters apply paint in somewhat

thicker coats than unskilled painters are inclined to do. Priming

coats of house paint on new, smooth wood normally should be spread

at the rate of approximately 600 square feet a gallon if they are to be

followed by 2 coats of paint but not more than 450 square feet a gallon

if only 1 coat is to follow. Less viscous materials, such as varnish,

may be spread at 700 or 800 square feet a gallon. Some native softwoods tend to take 10 to 12 percent more or less priming-coat paint

than the average. By the time second- and third-coat paints have

been applied, however, the difference in paint consumed amounts to

only 3 or 4 percent above or below the average, a value that is probably within the limits of uniformity with which a good workman will

paint at different times. The woods that tend to take more than the

average amount of paint are generally lightweight, and those that

tend to take less paint are heavy and have a high proportion of summerwood. Rough surfaces, sucli as shingles, the sawed side of bevel

siding, weathered wood, or surfaces on which repainting has been

neglected for a long time, may consume twic(^ the amount of primingcoat paint required for smoothly planed surfaces.

Drying of Paint

The time required for a coating of paint or other finish to dry—that

is, to harden—usuallv depends almost entirely on the composition of

the paint, the intensity of the sunlight, and the temperature and
354 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

relative humidity of the atmosphere. Drying is retarded for a few

hours, however, if the wood is wet when painted; its moisture content

should therefore not exceed 20 percent. On wet redwood or cypress,

priming-coat paint may remain liquid for days, especially when the

paint contains little or no white lead or zinc sulfide pigment {16).

On air-dry redwood, paint hardens as rapidly as on any other wood.

On cypress boards that contain much more than the average amount

of the oily extractive characteristic of cypress, the hardening of paints

without white lead or zinc sulfide may be retarded even when the

boards are reasonably dry, unless the drying takes place in strong sunlight. Eastern redcedar, Spanish cedar, and, to a less extent, PortOrford-cedar also contain oily extractives that retard hardening of

coatings or that may even, in confined places with little light and

ventilation, resoften coatings after they have hardened {32),

The native hardwoods contain no constituent that delays hardening

of paints if the wood is reasonably dry. On wet oak or chestnut,

there may be some retardation of hardening when there is little

sunlight or when the weather is cold.

Filling Porous Hardwoods Before Painting

For painting purposes, the hardwoods may be classified as follows

{15):

Harduwods with large pores Ilardiooods with small pores

Ash Alder, red

Butternut Aspen

Chestnut Basswood

Elm Beech

Hackberry Cherry

Hickory Cottonwood

Khaya (African mahogan}-) Gum

Mahogany " Magnolia

Oak Maple

Sugarherry Poplar

Walnut Sycamore

Birch has pores large enough to take wood filler effectively when

desired but small enough, as a rule, to be painted satisfactorily

without filling.

Hardwoods having small pores may be painted with ordinary house

paints in' exactly the same manner as softwoods. Hardwoods with

large pores require wood filler before they can be covered smoothly

with paint or enamel. Without filler the pores not only appear as

depressions in the coating but become centers of early paint failure.

For interior woodwork ordinary wood filler, which is a paste made of

ground quartz, linseed oil or varnish, and paint drier, may be used.

For exterior woodwork, the filler may be made by thinning a gallon

of soft paste white lead with a gallon of turpentine or other paint

thinner. The mixture is brushed over the wood, allowed to stand

about 10 minutes, and wiped oft' with rags or cotton waste across the

grain of the wood, in order to pack the filler into the large pores as

thoroughly as possible and to remove excess filler from the surface.

When the filler is dry, the wood is ready for painting.
WOOD HANDBOOK 355

Effect of Nature of Wood on Wearing of Paint

During the first year or two after an exterior wood surface has been

painted properly the nature of the wood usually has very little effect

on the behavior of the paint coating. Later on, when the coating

has become sufficiently embrittled with age (7, 13), difl^erences between woods become important and largely determine how rapidly

the coating disintegrates {3, 20, 24). Under normal conditions of

exposure—that is, when the abnormal conditions discussed on page 369

do not pertain—paint coatings on wood (6, 18, 25) deteriorate most

rapidly where the greatest amount of sunshine falls (fig. 83), and

deterioration proceeds in successive but overlappuig stages as follows:

1. The soiling stage. The coating gradually becomes dirty.

2. The flattmg stage. The coating loses its gloss.

3. The chalking stage. Dirt may be thrown off more or less completely, but colors appear to fade. Loose pigment may be wiped oft'

the surface of the paint much like chalk.

4. The fissure stage. (Under the most favorable conditions, some

paints may skip this stage and pass to the stage of disintegration.)

Fissures are of two general types depending on the nature of the

paint:

a. Checking. The fissures are at first superficial but later may

penetrate entirely through the coatmg. Fissures formed in

checking are usually very inconspicuous.

b. Cracking. The fissures pass entireh^ through the coating

when first observed. The coating at the edges of the cracks

sooner or later comes loose from the wood and curls outward.

As a rule cracking comes at a more advanced stage of paint

embrittlement than checking.

5. The stage of disintegration. Behavior in the fissure stage determines the form in which disintegration takes place (fig. 84):

a. Erosion. When pairts that do not suffer checking waste

away by chalking or erosion fast enough to escape cracking,

the coating finally becomes too thin to hide the wood and

patches of the wood begin to be laid bare.

b. Crumbling, which develops from checking. Tin}^ fragments

of coating, cut off when the fissures become interwoven and

penetrate entirely through the coating, fall away.

c. Flaking, which develops from cracking and curling. The

loosened edges of coating that curl outward finally fall oft*,

after which the newly formed edges curl outward and the process continues. Flaking is usually a more rapid form of disintegration than crumbling.

6. The stage of advanced break-up or neglect. Dismtegration has

laid bare enough wood for the boards to begin to show serious weathering.

From the time that crackhig or disintegration begins the nature of

the wood painted dominates the further rate of wearing away of the

coating. On softwoods cracking, crumbling, and flaking progress

chiefly over the bands of summerwood (fig. 83). The wider the bands

of summerwood intersected by the painted surface the more rapidly

disintegration proceeds and the more conspicuous are the areas laid
350 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 83.—In normal paint deterioration, the bands of summerwood are laid

bare )>y crumbling or flaking of the coating long Ijefore the softer springwood

is exposed. Paint disintegrates more rapidly on surfaces that face south and

receive the most sunshine (A) than on surfaces that face north and receive less

sunshine (D). On each of the 8-year-old test panels shown, the right-hand

area was originally i)ainted with a house paint of slightly lower quality than

that used on the left-hand area.

bare. Repainted coatings behave in much the same way as coatings

apphed to new wood, provided the repaintings are spaced far enough

apart to avoid unduly thick coatings.

Certain wood characteristics {30, 24) largely determine the rate of

paint disintegration on softwoods: (1) On wood of hght weight (low

density) paint disintegrates relatively slowly because light wood contains little summerwood. (2) On narrow-ringed wood paint disintegrates more slowlv than on wide-ringed wood because the bands
WOOD HANDBOOK 357

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-i

1 i

' í

*

% 1

-t

tí i Ï i

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M 92357 F

FIGURE 84.—Three forms of normal paint dif^integration: A, Coating thinned

by erosion; B, checking penetrated to the wood surface, followed by crumbling;

C, cracking, followed by curling and flaking away of loosened ]iaint. Thre^

forms of abnormal paint disintegration: D, Cross-grain cracking, which results

from too thick coating; E, alligatoring, frequently caused by the use of dissimilar

paints for successive paintings; F, blistering, in this case caused by chemical

deterioration of one of the earlier laj'ers of paint.

of summerwood are narrower. (3) On edgc-graincd surfaces, with

narrower bands of summerwood, disintegration of paint is slower than

on flat-grained surfaces. (4) Flat-grained boards may hold paint

better on the bark side than on the pith side because on the pith side

there is sometimes a tendency for the edges of the bands of summerwood to loosen and curl outward, thus dislodging the coating. (5)

IE...
358 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

High-grade lumber holds paint better than low-grade because knots

and other grade-limiting features hold paint poorly and because the

low grades usually come from the center of the tree where the wood

is likely to be wider ringed.

Coatings begin to fail to protect wood against weathering when

deep fissures develop or when disintegration sets in, though weathering seldom becomes serious until the coating is well into the stage of

neglect. The consequences of inadequate protection depend upon

the characteristics of the wood. Edge-grained boards are less seri-,

ously affected than flat-grained boards of the same species. Woods

that hold their shape well and do not develop conspicuous checks or

cracks on weathering are less seriously affected than other woods.

Classification of Softwoods for Painting

Almost all native softwoods of com.m.ercial im.portance can be

kept well painted for long periods of time if proper care is given to

selection of primers and paints and to choice of programs of maintenance in accordance with the painting characteristics of the wood.

vSome woods are less exacting than others in their requirements.

Table 42 classifies native softwood species with respect to their

painting characteristics for exterior use. The classification is based

upon the average behavior of commercial shipments of select grades

of the difterent woods; that is, upon lumber of a quality that is

commonly used for house siding or millwork. Boards of any one

species may vary widely in the ease with which they can be kept

painted, so that, in general, boards selected for physical properties

that are least exacting will serve more satisfactorily than the average

run of the species rated in table 42. After several repaintings the

differences among species diminish and may disappear entirely if

such paint abnormalities as excessive coating thickness or incompatibility (p. 369) set in.

TABLE 42.—Grouping of softwoods for exterior painting

Group 1 ' Group 2 2 Group 3 3 Group 4 <

Alaska-cedar. Eastern white pine. Commercial white iir. Douglas-fir.

Atlantic whitecedar. Supar pine. Eastern heiûlock. Red pine.

Baldcypress. Western white pine. Eastern spruce. Southern yellow pine.

Incense-cedar. P'ngelmann spruce. Tamarack.

Northern whitecedar. Lodgepole pine. Western larch.

Port-Orford-cedar. Ponderosa pine.

Redwood. Sitka spruce.

Western redcedar. Western hemlock.

^ Woods on which paints of the widest range in kind and quality give good service.

2 Woods on which care is needed to select a suitable priming paint, such as pure white lead or a zincless

house-paint primer3 Woods more exacting than those of group 2 but less exacting than those of group 4 in requirements of

suitable priming paint, finish paint of high quality, and careful choice of program of maintenance.

* Woods that need most careful selection of suitable paints, and for which aluminum house paint is particularly desirable for priming when the wood is first painted, with a zincless house-paint primer as second

clioice if for any reason aluminum paint cannot be used.
WOOD HANDBOOK 359

Effect of Extractives in Wood on Paint

Behavior

In general, the extractives in wood have much less effect on paint

behavior than has been commoiüy supposed. They are far less

important than the width of the bands of summerwood.

Distinction must be made between piny resins, which are characteristic of pines but occur also in other softwoods, and other extractives.

Piny resins consist of a solid rosin and a volatile liquid, such as

turpentine. They affect paint unfavorably by exuding through

coatings, leaving unsightly encrustations. Exudation is minimiziul

by thorough seasoning of the lumber to drive out the turpentine and

thus render the resin less mobile, but more careful seasoning is necessary to remove turpentine than to remove moisture (28, 32). The

piny resins raay also be responsible for the fact that paints containing

zinc oxide fail somewhat more rapidly on the pines than they do on

other softwoods having bands of summerwood of similar width.

Other extractives in wood may have a favorable eft'ect on the

durability of paint {16)] there is evidence that such is the case with

extractives in redwood and cypress. Colored extractives in redwood

and redcedar that are soluble in water may exude through coatings

if the wood beneath the coating becomes very wet; under normally

dry conditions, however, these discolorations do not occur.

Effect of Impregnated Preservatives on

Painting

Wood treated with the water-soluble preservatives in common

use can be painted satisfactorily after it is redried. The life of the

coating may in some instances be slightly less than it would have

been on untreated wood, but the loss in durability is not enough to

offer any practical objection to the use of treated wood for purposes

where preservation against decay is necessary and the appearance

of painted wood and protection against weathering are desired {12).

Such treated wood when used indoors in textile mills, pulp mills, or

other places where the relative humidity may be above 90 percent

for long periods may give rise to discoloration of paint or to exudation

of preservative solution.

Coal-tar creosote or other dark oily preservatives tend to stain

through paint unless the treated wood has been exposed to the

weather for many months before it is painted {33). Aluminum paint

often serves well on wood freshly creosoted by an ''empty-ceir'

process or cleaned after treatment by steaming or vapor drying.

Fairly good results can also be obtained on creosoted wood with

rough surfaces (sawed or weatherbeaten surfaces) by applying exterior

water-thinned paints, such as casein pahits or resin-emulsion paints.

Wood treated with oilborne chlorinated phenols can be painted

without difficulty when the solvent oils have evaporated thoroughly

from the surfaces. If light oils that evaporate rapidly are used for

the treating solution, painting can be done soon after the treated

wood has dried {21).
3G0 HANDBOOK 7 2, U. Ö. DEPARTMENT OF AGRICULTURE

Plywood

Th(^ paintin^^ characteristics of plywood are essentially those of

solid luml)ei- of the kind used for the face ply. The most abundant

and least expensive plywood is usually faced with rotary-cut veneer

of woods in group 3 or group 4 of table 42. It therefore has flatgrained faces that display wide bands of summerwood and requires

careful choice of primers and paints for best results. Moreover, the

face plies of plywood are often more susceptible to checking or cracking than is lumber of the same kind of wood.

Plywood has been modified in different ways to improve the durability of paint coatings and to reduce the tendency to face checking

{29), The methods are applicable to lumber also but have not yet

been developed widely for that purpose.

Plywood made with face veneiTs that have been acetylated to make

(luun more sta})le dimensionally holds paint coatings longer and

resists checking and weathering better than ordinary plywood.

Similarly plywood faced with v(»neers trc^ated with phenolic resin

(impreg, p. 467) has superior painting characteristics and stability

against checking and weathering. Other coverings for plywood for

the same purposes are paper impregnated with phenolic resin and

finely groimd wood waste bonded together and to the plywood with

synthetic resin. Striating plywood by cutting parallel grooves,

ai)OUt eight to the inch, in the direction of the grain of the face plies

])i-eaks up the wide bands of summerwood and achieves significant

improvement in durability of coatings and in resistance to checking.

Consumption of paint is increased by about 10 percent, however.

CHOICE OF PAINTS FOR EXTERIOR WOODWORK

House paints of the best quality are recommended for nearly all

needs for exterior painting. Inferior paints made to sell at materially

lower prices must be appl'ied in greater amounts to accomplish the

same result, may not last so long, and are less reliable generally.

Even when low initial cost of painting is the chief consideration, it

usually proves cheaper to use high-grade paint in the minimum number

of coats because the labor for a paint job generally costs several times

as much as the paint.

For both low initial cost and great durability, whenever the colors

are acceptable, paints of good quality made ^\dth iron oxide pigments

are more economical than most other good paints. Two coats of

exterior aluminum paint make an exceedingly durable, highly protc^ctive coating when a metallic appearance is not considered undesirable. For very brief service or where very frequent repainting is

desired for some reason and protection against weathering is not

necessary, whitewash or exterior water or water-emulsion paints are

safer to use than linseed oil paints of very inferior quality. The

water paints give their best service on rough rather than on smoothly

planed wood.

For residences or buildings of architectural pretension white or

light-colored paints are most popular for the major painted surfaces,

supplemented if desired by deeply colored paints on minor surfaces.
WOOD HANDBOOK 361

When deep colors are appropriately dominant it is often ])etler and

more economical to use rough wood surfaces, such as shingh^s or the

sawed side of siding, and apply exterior stains rather than gloss paints.

Composition of Paint

The quality of a house paint depends upon tlie quality of the

liquids, the quality of the pigments, and the proportions of pigments

and liquids of which it is made {17, 18, 19, 22).

Quality of the Liquids

Linseed oil is the most widely accepted liquid ingredient for exterior

paints for wood. It is available in many degrees of refinement for

different purposes. Proper choice of the kind of linseed oil most

suitable for the pigments used is essential for making high-grade

paint, but as a rule the purchaser must rely upon the manufacturer's

judgment in selecting the kind of oil. Substitution of other drying

oils for part of the linseed oil is common practice and may not impair

the quality of the paint. Thus, many paints contain substantial

proportions of soybean oil. Moreover, some of the modern oils are

chemically treated to improve their drying characteristics. For the

painter's needs in thinning paints for application, raw or boiled lins(»ed

oil of good quality should be used.

Raw or refined linseed oil is oil that still has about the same viscosity

(consistency) that it had when first extracted from flax seed. Boiled

oil has nearly the same viscosity, but has very small quantities of

driers incorporated in it to make it dry faster, say in 16 hours inst(^ad

of 72 hours. The driers are soaps of lead, manganese, or col)alt and

are sometimes used with soaps of zinc or calcium. Concentrated

solutions of such driers in mineral spirits are available for painters to

use when needed, under the name of liquid paint drier. Bodied

linseed oil is refined linseed oil that has been heated at a high temp(a*-

ature, usually between 550° and 625° F., long enough to increase its

viscosity greatly. It can also be made by treating refined oil with

chemicals, such as sulfur chloride.

Before 1943 the liquid part of house paints of best quality contained

at least 85 percent of linseed oil, by weight. Such paints are called

oil-rich paints, but there are few of them left on the market. Oil-rich

paints may contain a little bodied oil, up to 10 or 15 percent, to

improve flow and leveling of brush marks. Shice 1943 most house

paints have been oil-restricted, that is, the liquid part consists typically of 33 percent of raw oil, 33 percent of l^odied oil, and 34 perccait

of volatile thinner. A gallon of oil-restricted paint costs less l)ut

normally covers less surface than a gallon of oil-rich paint. Th(^

liquid part of some brands of house paint have a composition between

the extremes of the typical oil-restricted and oil-rich paints.

Varnish is rarely a desirable ingredient in the liquid of good house

paint (except in aluminum paint, p. 367), but it is often used in inferior

paints because large proportions of inexpensive volatile thinners

can then be incorporated. On the other hand, good exterior varnish

or bodied linseed oil or tung oil is necessary to make exterior enamels,
362 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

trim paints of the deeper colors, or exterior floor paints, which must

stand mechanical wear as well as weather. In such enamels or floor

paints of good quality as much as 50 percent by weight of the liquid

may be volatile thinner.

The volatile thinner in most paints is mineral spirits, a petroleum

product. Paint users thin paint, when necessary, with turpentine,

mineral spirits, or prepared thinners sold by paint manufacturers.

There should be no more than 1 or 2 percent by weight of water in the

liquid of any good paint.

Quality of the Pigments

Differences in the behavior of linseed-oil paints during the successive stages in deterioration with age (p. 355) are determined largely

by the nature of the pigments (25). No kind of paint now known is

superior in all stages of deterioration; improvement in one stage is

usually effected at some sacrifice in other stages. In addition, some

paints require more careful spacing of repaintings for successful

maintenance than other paints. For these reasons the useras judgment about the relative importance of the different stages, and particularly about the stage at which he expects to repaint, determines

what kind of paint he can use to best advantage. For intelligent

paint niaintenance, therefore, the user should know the pigment

composition of the paint and its bearing upon behavior during

deterioration (17).

The opaque white pigments are of particular importance in white

paints and in paints of all but the deepest colors. Most of the colored

paints are tinted paints, that is, white paints in which

minor proportions of colored pigments are incorporated. White

lead, zinc oxide, and titanium dioxide are the principal opaque white

pigments, although zinc sulfide is used in a few paints, and lead

titanate and antimony oxide have been used in the past. There

are also inexpensive pigments of low opacity, called extending pigments, that are present in modern mixed-pigment paints, often in

large proportions. The white paints, white-base paints for the user

to tint, and tinted paints now generally available may be grouped

for convenience into pure white lead paint; mixed-pigment paints

containing titanium dioxide, white lead, and zinc oxide; and mixedpigment paints containing titanium dioxide and zinc oxide. Formerly

there were also lead and zinc mixed-pigment paints.

In pure white lead paint the pigment is entirely basic carbonate

white lead except for necessary addition of colored pigments when

the paint is tinted, During the soiling and flatting stages of its life

white lead paint may become dirtier than mLxed-pigment paints,

especially in congested urban locations or when apphed in the late

fall, winter, or early spring, or in deeply shaded places. Chalking of

white lead paint and apparent fading, if it is tinted, usually set in

fairly early, after which the dirt is thrown off promptly and evenly,

leaving a clean surface, which may, however, contrast strongly with

deeply shaded parts of the building that are still dirty and not yet

faded. Checking begins comparatively early, usually inconspicuously, and gradually works deeply into the coating, but probably

for that reason cracking and flaking rarely occur.

...^ài
WOOD HANDBOOK 363

The outstanding merits of pure white lead paint are its exceptionally

great resistance to adverse conditions of service (p. 369) and its wide

tolerance for differing programs of maintenance. White lead paint

can be repainted more frequently than other paints without suffering

impaired service from excessive thickness of coating, or repainting

may be postponed until the coating is far along in the stage of neglect

without having a difficult and expensive surface to prepare for satisfactory repainting (30, 81). Initial painting with white lead paint

provides a very satisfactory foundation for subsequent painting with

mixed-pigment paints, but it is seldom advisable to apply pure white

lead paint over mixed-pigment paints because checking may then

assume the conspicuous form known as alligatoring.

Mixed-pigment paints of the titanium-lead-zinc group vary widely

in composition. During the soiling and flatting stages of paint life

they remain much cleaner than pure white lead paint, particularly

if their content of white lead is not too high. On the other hand,

during the chalking stage there is a tendency for the white chalk to

wash off and be deposited on nearby surfaces of darker color, such as

brickwork or trim paints of dark color, unless the content of white

lead is relatively high. If the paint is tinted, unduly free chalking

also causes severe fading of the color. The titanium dioxide pigments,

however, are made in difl'erent grades from freely chalking to chalkresistant types. For white paints of greatest cleanliness in the soiling

stage, the freely chalking type is used, but such paints should never

be'tinted and are usually so marked on the label. For tinted paints

of moderate or low content of white lead, the chalk-resistant type or

a blend of the freely chalking and chalk-resistant types of titanium

dioxide is used.

In the fissure stage, titanium-lead-zinc paints high in white lead

may develop checking; later on the^^ crack and finally disintegrate by

flaking. If the content of white lead is lowered, checking may be

eliminated and cracking may be further delayed, though the cracking

and subsequent flaking tend to be coarser and more conspicuous the

longer they are postponed. Titanium-lead-zinc paints of low content

of white lead and lead-free titanium-zinc paints under very favorable

conditions may skip the fissure stage entirely and disintegrate by

erosion. Lead-free titanium-zinc paints are not discolored by hydrogen Sulfide, but that immunity ma}^ be lost if they are tinted because

most colored pigments in common use contain metals that form black

Sulfides.

Mixed-pigment paints that contain zinc oxide are more exacting

than pure white lead paint in their requirements for good maintenance

over a long period of years {29). If the mixed-pigment paints are

repainted too often the coating soon becomes unduly thick, cracks

conspicuously, and disintegrates in large scales. On the other hand,

if repainting is too long delayed, the advanced condition of cracking,

curling, and flaking leaves a rough surface that requires scraping and

sandpapering to prepare it for smooth repainting. With each successive painting the condition is likely to become worse until eventually

it becomes necessary to remove all old paint completely with a

painter's torch or with house-paint remover before further pamtmg

can be done satisfactorily.

303747^—55 24
364 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Dull red, brown, and yellow pigment paints are made most economicall}^ with iron oxide pigments, either natural earths or manufactured pigments. For good retention of color and maximum

durability, the content of iron oxide in the pigments may well be 50

percent or more by weight and should certainly not be less than 30

percent. Bright reds require organic lake pigments that are more

expensive and less durable than iron oxide reds. Bright yellows and

oranges are made with chrome yellows (lead chromate and basic lead

chromate), which are fully as expensive as white pigments but are

more durable. Greens are made with chrome green, which is a

mixture of chrome yellow and prussian or Chinese blue (iron ferrocyanide). Durable blacks are made with carbon pigments, such as

lampblack; asphalt paints make cheaper but less durable blacks for

exposure to the weather. The colored-pigment paints tend to be slow

in drying, to make unduly soft coatings, and to be subject to resoftening under some conditions of service unless there is a substantial

proportion of good varnish in the paint, ^^^len color permits, colored-pigment paints often retain color and protective power better

if they contain some zinc oxide or white lead. If they do not, it is

advisable to apply them over priming coats of white lead paint, housepaint primer, or aluminum paint.

Proportions of Pigments and Liquids

Durability as well as color and opacity are imparted to paint by

pigments. For that reason there is an optimum proportion of pigments and nonvolatile liquids in good paint. In the oil-rich paints,

in which most or all of the linseed oil is raw, refined, or boiled oil, the

total pigment is usually from 27 to 30 percent by volume of the total

nonvolatile ingredients. The total nonvolatile ingredients, which

remain in the coating after it drys, are 87 percent or more by volume

of the paint.

In typical oil-restricted paints, the total pigment commonly is 32

to 36 percent by volume of the total nonvolatile ingredients, and the

total nonvolatile ingredients are not more than 73 percent by volume

of the paint. Thus, it takes more oil-restricted paint than oil-rich

paint to cover a given area of surface with a coating of prescribed

thickness. As a rule the consistency of oil-restricted paints is such as

to lead the painter to apply just about the extra amount of paint

required.

The ratio of total pigment to total nonvolatile ingredients by volume

is called the pigment volume. Paints in which the pigment volume is

too low may become excessively dirty in the soiling stage and may

crack and scale badly in the fissure stage of paint life. Paints in

which the pigment volume is too high may chalk and fade badly and

wear out too soon.

Many paint manufacturers customarily print the composition or

formula on the labels of paints sold to the public; these formulas are

nearly always expressed in percentage of ingredients by weight rather

than by volume. Apart from the printing of such formulas there are

no generall}^ recognized standards of paint quality.
WOOD HANDBOOK 3f)5

Priming Paints

The first coat of paint applied on new wood or over well-worn old

paint, called the priming coat, should difl'er somewhat in composition

from the paint applied subsequently for finish coats. A o-ood primin»;

paint should contain white lead but no zinc oxi(k% it should have about

as much total pigment as finish-coat paint does, and the liquids sliould

contain enough volatile thinner to wet wood ciuickly and enougli

bodied linseed oil to prevent undue penetration of liquids into thc^

wood with consequent loss of oil l)y the priming ])aint. vSuch primers

cannot be mixed on the jol) by adding liquids to finish-c-oat paint.

For that reason most paint manufacturers sell special house-paint

primers as one of the items in their lines of house paints (23).

Exterior Stains

Exterior wood stains are essentially ])aints gi'eally dihited w^itli

linseed oil, a volatiU^ thinner, and sometimes cj-eosote. vStains ai-e

cheaper than paints, l)ut they do not protect wood against weatbei*-

ing and are therefore most suitable for rough surfaces, such as shingles or siding placed with the sawed side out. Good stains contain

only pure, finely divided, opaque pigments and are free from transparent pigments. The pure iron oxide, chrome, and carbon pigments

are very satisfactory; white pigments less so. The liquid part of the

stain should be at least one-third linseed oil b}^ volume, with twothirds recommended by some authorities. Particidar merits are

claimed for stains made with pigments gi'ound in very highly bodied

linseed oil, because the pigments are more highly dispersed in such

liquids and become more deeply embedded in rough wood surfaces.

Houses with shingles or siding with the sawed side out, stained with

colored-pigment stains, and with smoothly planed and painted wood

trim often have the trim painted twice for every time that the sick'

walls are stained.

APPLICATION OF PAINT

Wood shoidd not be painted when it is wet. If no free water is

present, however, the moisture content is of minor importance; wood

painted at 16 to 20 percent moisture content holds pahit slightly

longer than wood painted at lO-percent moisture content. Paint

dries very slowly at low^ temperatures. Painthig should therefore

not be done wdien there is danger of dew or frost or of a drop of more

than 20'' F. in temperature at night; application of paint at such

times should cease several hours before sunset. In clear, warm

weather coatings of paint can be applied within 24 hours of each

other if necessary, but it is better practice to allow at least 2 or 3

days. On the other hand, it is generally inadvisable to allow more

than 1 or 2 weeks to elapse between successive coats. When new

houses reach the stage for exterior painting in late fall or early winter, it is poor practice to apply a priming coat only and then to wait

for spring before finishing the job. A better way is to treat the

exterior woodwork with w^ater-repellent preservative (21) and then

wait until spring to do all of the exterior painting at one time.
366 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

On new wood surfaces or on painted surfaces on which the old

coating is not 3^et deeply cracked, paint may be apphed with a brush

or spray gun with equally serviceable results. Over old coatings

that have passed well into the fissure or the flaking stage of pamt

deterioration, however, paint applied with a brush may make a

somewhat smoother coating with better appearance and perhaps

have a little better durability than sprayed paint.

Best practice in painting new wood surfaces calls for the application

of three coats of paint, a priming coat, a second coat, and a finish

coat. Nevertheless, much if not most painting of new houses is

done with two coats only. If paint of sufficiently high quahty is

available and is properly applied, 2-coat work could be fully satisfactory (23), but most 2-coat work in recent years has been scanty

in the quantity of paint apphed and therefore less durable than a

more generous paint job.

A coating of house paint 4.5 to 5.0 mils (1 mil is 0.001 inch) thick

initially usually gives the best and longest service. A thinner coating wears out too soon, and a thicker one is inclined to crack too

soon and later to scale badly. If a house-paint primer containing 25

percent of total pigment and 73 percent of total nonvolatile ingredients by volume is used with an oil-rich finish paint containing 26

percent of total pigment and 87 percent of total nonvolatile ingredients, a coating approximately 4.5 mils thick can be obtained as

follows : Spread the primer at the rate of 1 gallon for 600 square feet

of surface and then spread 2 coats of finish paint, each at the rate of

1 gallon for 850 square feet of surface. If the finish paint is oilrestricted and contains only 73 percent of total nonvolatile ingredients, each coat of it should be spread so that 1 gallon covers only

725 square feet of surface.

To obtain the same coating thickness in 2-coat work, the primer

and the oil-rich finish paint must be applied about as generously as

is practicable even in good weather for painting; the primer may be

applied at 1 gallon to 450 square feet and the finish paint at 1 gallon

to 500 square feet. If the painting must be done in cold weather or

if the finish paint is oil-restricted a coating thickness of 4.5 mils is

too much to expect of 2-coat work. '''

Most paints of high quality are sold in the prepared or readymixed form. Ordinarily they are ready for application as soon as

the contents of the container have been thoroughly stirred. Whitebase paints for tinting may be colored by adding carefuUy the

necessary quantities of colors ground in oil or the special preparations

made by some manufacturers for that purpose. But as a rule, there

should be no need for adding thinner, oil, or so-called ^^fortifying''

oils. Unnecessary additions are made so often that it is wise to be

on guard to avoid them. In cold weather paint thickens in viscosity

and may then be thinned with no more than 1 pint of tm^pentine

or mineral spirits to a gallon to ease the brushing, but no oil should be

added because it increases the chances of the paint \viTnkling as it dries.

Although pure white lead paint is available in the prepared form,

it is more often purchased in a more concentrated form called soft

paste white lead, which requires substantial addition of liquids to

make it ready for application. Paint of highest quality can be mixed

from soft paste white lead, but when mixed-pigment paints are sold

.M
WOOD HANDBOOK 367

in the paste form, they are usually of cheaper quality than th(^ prepared paints of the same manufacturer. Use of paste paint has th(^

advantage that mixtures can be made with greater pigment volume

that that of the finish-coat paint. Thus, paint for the second of 3 coats

on new wood, or for the first of 2 coats over old paint in reasonably

good condition, can be mixed with 35 to 40 percent pigment volume,

when the pigment volume in the finish coat is to l)e 27 to 36 percent,

merely by thinning the paste with more turpentine and less oil than

are used for the last coat. Such adjustment of pigment volume in

successive coats favors better paint performance.

Soft paste white lead is sold by the pound rather than the gallon.

The 100-pound pail contains about 3 gallons of paste, which may be

mixed as follows: For the first or priming coat on new wood, add 4

gallons of raw linseed oil, 2 gallons of turpentine or mineral spirits,

and 1 pint of liquid paint drier; for the second coat add 1.5 gallons of

raw linseed oil, 1.5 gallons of turpentine or mineral spirits, and 1 pint

of liquid paint drier; for the final coat add 2.75 gallons of raw linseed

oil and 1 pint of liquid paint drier. Boiled linseed oil may be used in

place of raw oil, but in that case add only ji pint instead of 1 phit of

drier. For 2-coat work on new wood mix as follows: For the first

coat add 3 gallons of raw linseed oil, 3 quarts of turpentine or mineral

spirits, and 1 pint of liquid paint drier; for the final coat add no more

than 3 gallons of raw linseed oil and 1 pint of liquid paint drier.

To make the mixtures, first add only a small part, perhaps onetenth, of the total oil to the soft paste white lead and stir until the

paste is again smooth and uniform. Then twice pour in perhaps onefifth of the extra oil and stir until smooth. Finally add the rest of

the oil and the other liquids and stir well. If all the liquids are added

to the paste at once, it is very difficult to make a smooth mixture.

When painting woods of groups 2, 3, and 4 (table 42) with mixedpigment paints, it is particularly necessary to use a special priming

paint for the first coat (4). Pure white lead paint or a good zincless

titanium-lead house-paint primer may be used (23), For two-coat

work, one or the other of these is about the only choice because, with

a single finish coat, the primer must have about the same color. If

three coats of paint can be applied, the experience of the Forest Products Laboratory indicates that the most eft'ective special primingpaint on woods of groups 3 and 4 is exterior aluminum paint for wood

{9, 11, 14, 34)' iÖuminum priming paint for wood is made usually

with 1.75 pounds of commercial paste aluminum in 1 gallon of very

long-oil spar varnish made specifically for that purpose. The right

kind of varnish must be used. Neither ordinary spar varnish, which

is both unsuitable and too expensive, nor cheap bronzing liquid for interior use is acceptable for exterior aluminum paint. Suitable aluminum priming paints are sold for the one purpose of painting wood and

are not recommended for other uses. When properly applied the

aluminum primer hides the surface of the wood completely.

REPAINTING

The major problem in maintenance of paint coatings on exterior

surfaces is to keep reasonably good appearance at all times without

allowing the coating to become so thick that it cracks and scales badly
368 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

and eventually has to be removed completely (30, 31). To do so over

a long period of years, repainting must be spaced far enough apart for

weathering to take off as much coating thickness as is restored at each

repainting. Since no house paint fully meets these requirements, choice

must be made between two alternatives. One, which is the older and

better established practice, is to allow each paint job to go far enough

into the stage of disintegration or even of neglect to entail a few years

of somewhat shabby appearance before repainting is done. The other

alternative is to repaint as soon as the coating passes far enough into

the stage of disintegration to begin to look shabby, taking care to

apply as little new paint as is necessary for a satisfactory job, and

then to plan on having all old paint removed down to bare wood every

15 or 20 years. Old paint may be removed with a painter's blow

torch, with the newer electric torches, or with house-paint remover,

but in any case it is a costly job.

Coatings of pure white lead paint lose about % mil of thickness

annually on side walls fully exposed to sunshine at Madison, Wis.,

and their thickness can be built up to 15 mils before the normal

performance is impaired. By reason of its relatively rapid wear, high

critical thickness, and favorable behavior during the stages of disintegration and neglect, pure white lead paint makes the safest choice

for those who prefer the first alternative of keeping the coating from

ever getting thick enough to require complete removal. Suitable

maintenance programs for pure white lead paint range from repainting

with 1 coat every 3 years to repainting with 2 coats every 8 to 10

years, on the average.

Coatings of mixed-pigment paints that contain zinc oxide lose only

about /2 mil of thickness annually at Madison, Wis., and they become

too thick to perform normally long before the coating thickness

reaches 10 mils. Since it is difficult to repaint satisfactorily wthout

applying at least 2 mils of new paint, coatings of mixed-pigment

paints cannot be repainted safely more often than once in 4 years and

then with no more than 1 coat at a time. If 2 coats are applied at a

time, repaintings should be 6 to 7 years apart, on the average. On the

other hand, coatings of mixed-pigment paints can seldom be allowed

to go too far into the stage of disintegration without serious danger

of so much flaking or scaling that the surface becomes difficult to

prepare for repainting and to repaint smoothly.

Since coatings wear away even less rapidly on the shaded parts of

a house than they do on the sunny parts, in repainting correspondingly

less new paint should be applied on the protected areas. Unless that

is done, the paint may eventually crack, curl, and scale on the shaded

parts before it begins to disintegrate on the sunny parts.

In the maintenance of paint over a long period it is advantageous

to repaint always with paint of the same composition as that used for

finish coat in the first painting. Although some combinations of

dissimilar paints used successively are satisfactory or even beneficial,

such as special house-paint primers with finish-coat paints, other

combinations are harmful, such as white paint over most deeply

colored paints. Often the same combination of paints in reverse

order may serve well; thus, deeply colored paints may usually be

applied over previous coatings of white paint. But a combination of
WOOD HANDBOOK 369

dissimilar paints should be avoided whenever possible unless it is

known to be satisfactory.

Sometimes a relatively small number of boards on a house lose

their paint much sooner—within 1 or 2 years after painting—than

the rest of the boards. In such cases the^ average life of subsequent

coatings can often be increased by replacing these boards with new

ones chosen for good painting characteristics (p. 358). On the other

hand, if the less satisfactory boards hold their paint for 3 or more

years, they may be brought nearly to equality with the others merely

by removing all paint from them and priming them well with suitable

special priming paint.

ABNORMAL PAINT WEAR

Under certain conditions of service, the normal course of paint

deterioration (p. 355) gives way to one of several kinds of abnormal

paint wear.

As the thickness of a coating is built up beyond 5 mils, any cracking

during the stage of fissures and curling and flaking during the stage of

disintegration become coarser in pattern, larger in size, and more

conspicuous. Up to a critical thickness characteristic of the kind of

paint, most of the larger cracks run roughly parallel to the direction

in which the paint was last stroked with the brush during application.

As a rule, that is also the diiTction of the grain of the wood underneath, but, when it is not, the cracking follows the direction of

brushing rather than the grain of the wood. When the critical

thickness of the coating is passed, however, a new and much

coarser form of cracking sets in with its dominant direction at right

angles to that of the normal cracking. Even paints that normally

check and crumble without any cracking are subject to cross-grain

cracking when the coating becomes too thick. Cross-grain cracking

sets in earlier, becomes still more conspicuous, and leads to coarser

scaling the thicker the coating becomes from further repaintings {30,

81).

Heterogeneous coatings formed by using dissimilar paints for

successive paint jobs often behave abnormally. Difference in composition may result in variance in such properties as hardness, shrinkage with age, thermal expansion, and swelling on absorption of moisture. For example, paint coatings share with wood the property of

absorbing water and swelling, and the extent to which they do so

varies with the composition of the paint. Thus, a coating built up

of dissimilar layers may be subject to severe internal stresses that

impair its performance. Among the kinds of abnormal behavior

that may result are alligatoring (outer layer of coating develops

fissures and then shrinks until a lower layer is exposed), intercoat

peeling or scaling, some forms of blistering, and cross-grain cracking,

curling, and scaling (fig. 84).

Abnormal discolorations of paint may arise either in the soiling

stage or in other stages of paint life. In'^damp places, mildew, which

is a growth of fungi on the surface, may cause a blackening of the

coating that is often mistaken for dirt. Less often there may be pink,

red, purple, yellow, or brown discolorations according to the nature

of the infecting organism. Plenty of white lead and zinc oxide in
370 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

paint makes it resist mildew reasonably well. Resistance may also

be imparted by adding preservatives, such as phenyl mercury conapounds or chlorinated phenols, to the paint. The fungi of blue stain

growing in damp sapwood may push their fruiting bodies through

paint coatings, causing a bluish-black discoloration on the pamt as

well as in the wood.

Water-soluble colored ingredients in a few woods, such as redwood

and redcedar, may discolor paint coatings if the wood becomes thoroughl}^ wet (8) ; slight discoloration of this kind may occur temporarily

from wetting with rain or with a garden hose after the coating reaches

the stages of fissures and disintegration. A black discoloration with

a metallic luster appears on paints that contain lead, iron, chromium,

or manganese pigments when the air is contaminated with hydrogen

sulfide. Such atmospheric pollution is rare, but it may occur near

swamps, rivers overloaded with sewage, a few chemical processing

factories and oil refineries, smoldering fires in underground coal

mines, or natural sulfur springs. Sulfur dioxide, which is commonly

present in industrial fumes, does not blacken paint, though too much

of it shortens the life of most paints.

Paints may fail by blistering, often before the last paint job passes

out of the soiling stage, for a number of different reasons, some of

which are not yet well understood. Perhaps the most frequent cause

of blistering is excessive moisture, but there are other common causes

not connected with unusual conditions of dampness. A blast of heat

suddenly directed at a coating on wood causes blistermg by both

softening the paint and expanding the air in the cavities of the wood

underneath. Use of a painter's torch to remove paint depends on

this principle. But modest warming of painted surfaces by sunshine

can cause temperature blistering if there is a soft layer anywhere

within the coating or if dampness in the wood blocks free movement

of air through its capillaries until the pressure of the warm trapped

air becomes high. New paint applied in a thick coating may dry with

a hard skin on top and leave the bottom of the new la^^er soft enough

for temperature blistering for some time, especially if the new paint

is dark in color and therefore highly absorptive of the sun's heat.

Old layers of paint blanketed from sunshine and oxygen by more

recently applied paint may soften and reliquefy from a splitting of

the fatty acids in linseed oil into azelaic and other simpler acids. If

that process goes far enough, the backs of the blisters or the surfaces

under them are covered with a glossy material that looks like varnish

but is in fact largely azelaic acid or its metal salts. Such glossybacked blistering is frequently seen on older houses that have been

kept well painted.

Blistering of paint, often followed by peeling or scaling, is often

brought about by prolonged conditions of excessive moisture (8).

Moisture that gets into the side walls of houses is likely to be especially

harmful. One wa}^ in which moisture enters side walls is by condensation during cold weather because there is too much humidity within

the house or no vapor bamer on the warm side of the side walls (37).

Another way is by excessive seepage of storm water through faulty

or unguarded joints. During cold weather when the house is heated,

the temperature gradient through the walls tends to move the free

water through the wood toward the paint coating. Such movement
WOOD HANDBOOK 371

of water and trapped air develops a pressure under the coating, and

the coating is softened and weakened by absorption of water until it

yields to the pressure in the form of blisters.

Pure white lead paint and other zincless white paints are markedly

resistant to moisture bUstering because they absorb less water, swell

less, and thus are less seriously weakened than zinc-containing paints.

vSome manufacturers now sell blister-resisting house paints, sometimes

called ''breather type" house paints, for use where there is danger

that ordinary mixed-pigment paints may become blistered. But to

obtain the full benefit of the blister resistance of the special paints,

it is necessary to have any previous paint of the ordinary kind removed completely.

Wood side walls have always been subject to moderate penetration

by storm water, which gets in through both vertical and horizontal

joints between boards and especially at joints around windows and

doors and at comers. Early paint failures, whether or not they begin

by blistering, must not be atrributed to faults in the construction or

operation of a building unless it can be clearly established that more

water enters the side walls than is customary in well-built houses.

BACK PRIMING

Concealed surfaces are occasionally painted to retard changes in

the moisture content of the wood (34). More than one coat is rarely

applied for such purposes, and using the same priming-coat paint

that is applied to the exposed surfaces is often convenient. Siding,

shingles, and millwork are the principal items of building lumber

back primed at times in this way.

Although back priming has long been recognized as good practice,

it is usually dispensed with because of the expense and inconvenience

of doing part of the painting before the lumber has been erected. If

lumber must be cut and fitted in the course of erection, back priming is

best done immediately afterward, so that the freshly cut ends and surfaces can be coated. Prefabricated units are sometimes primed at the

mill, but slow-drying paints delay production schedules and fast-drying

paints are likely to prove incompatible with the paints and finishes

used later at the site. Mill priming often must include priming of the

surfaces to be left exposed if unbalanced protection and possible

warping and twisting during shipment and storage are to be avoided,

even though the kind of finish that may later be chosen for the exposed

surfaces may not be known.

No coating that completely prevents changes in the moisture content

of wood has been found ; the best that can be done is to retard the rate

of change (10). Good coatings furnish adequate protection against

rapidly changing atmospheric conditions or against alternate rain and

sunshine, but they are relatively ineftective against prolonged exposure

to extreme conditions and do not prevent seasonal fluctuations in the

moisture content of interior woodwork.

Table 43 gives the comparative effectiveness of various common

coatings in protecting wood at 11-percent moisture content against

absorption of moisture during 2 weeks' exposure to nearly saturated

air. Table 43 gives also the comparative effectiveness of 1, 2, and 3

coats when new. With age the effectiveness at first increases some-
372 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

what and then decreases as the coating deteriorates, so that the

coatings must be kept in good condition to maintain their effectiveness.

A similar comparison of coatings for interior use only is given on page

377.

The degree of protection attainable with a priming coat alone is

usually limited; at least 2 coats and often 3 are necessary to build

up an adequate barrier against moisture. Mill priming, therefore,

affords only a very moderate degree of protection against change in

moisture content before installation, and after woodwork has been

installed the benefit derived from back priming is probably limited.

Treatment of wood with water repellents or water-repellent preservatives in lieu of mill priming or back priming has been well established in the millwork industries for many years, and is finding use for

siding and other items of lumber {21). Water repellents are usually

applied by dipping. Although in moisture-excluding effectiveness they

TABLE 43.—Moisture-exchiding effectivepess of coatings, suitable for both exterior

and interior nse, during 2 weeks^ exposure of wood (initially at ll-percent moisture

content) to nearly saturated air

['FOT ordinary exterior house paints in their customary usos moisture-excluclinR efTectivene&s greater than

about 60 percent is not necessary. The data in this table should not be construed as an index of the servicx:^-

ableness of such paints in general]

Coating

No. '

Description

Effecti V

1 coat

Percent

eness ' found for—

2 coats 1 3 coats

i

1 Aluminum powder Ln asphalt or pitch pamt vehicle

Percent Percent

98

o Aluminum powder in No. 16 vehicle 39

78

15

62

39

24

9

88

92

81

86

86

85

61

95

94

93

91

4

Extra fine aluminum powder in No. 16 vehicle . Aluminum powder in "alkyd" type synthetic vehicle

White lead in a vehicle similar to No. 16

G

8

1 coat of No. 2 plus 2 coats of No. 17

White lead in No. 19 vehicle ,

Aluminum powder in No. 2.3 vehicle..- .._

91

91

90

90 9 Asi)halt or pitch paint

10

11

12

Aluminum powder in bodied linseed oil vehicle

1 coat of No. 8 plus 2 coats of Xo. 17

Wliite lead in No. 23 vehicle

Aluminum powder in linseed oiL . - _ .

26

9

14

30

6

20

15

f)

4

25

1

:5

84

62

62

57

65

69

49

67

56

37

58

53

25

14

5

89

86

8.3

77

75

73

73

70

67

65

64

14

15

16

17

18

19

20

Aluminum powder and red lead in linseed oil

Linseed oil house paint containing zinc oxide and other white pigments

with or without tinting colors

Phenol aldehyde synthetic resm, 50 gallon vamish 2

Linseed oil house paint containing no zinc oxide, such as common leadand-oil paint.

Red lead in linseed oil _._..

Ester gum resin, 33 gallon si^ar varnish 2.__.

Crraphite in linseed oil

24

Red linseed oil barn })aint, pigment 98 percent i)ure iron oxide...._-

Red linseed oil barn paint, pigment Venetian red containing 40 ])ercent

of iron oxide

Ester gum resin, 75 gallon long-oil spar varnish.

Linseed oil containing paint drier .. ..

56

45

35

21

1 Perfect protection would be reitresented by 100 ].)ercent effectiveness; complete lack of protection, as with

uncoated wood, by 0.

- A "50 gallon" varnish is made in the proportion of .50 gallons of drying oil to 100 pounds of resin; a "33

gallon" varnish is made with 33 gallons of drying oil to 100 i)ounds of resin.
WOOD HANDBOOK 373

Stand no higher than throe coats of Unseed oil, coating No. 24 in tal)U'

43, m practice they often prove moi-e effective than coatings of good

paints because the water repellents have exceptional ability to kee])

water from penetrating through joints and spreading over wood

surfaces.

NATURAL FINISH FOR EXTERIOR WOODWORK

Natural ñnishes that are traus])arent (Miougli to allow the grain

of the wood to show have been used si)aringly in the ymsi for exterioiwoodwork exposed to the weather bcn^ause such finishes are much h^ss

durable and require more frequent renewal than house paints (26).

Where surfaces are fully exposed to sun and raui, natural finishes mav

need renewal at least once a year. Nevertheless, there is an increasuig demand for natural fiiiishes on sidewalls of houses of some

modern styles.

Availabk^ natural finishes may be classified into two typt^s: Surfnri'-

coating finishes and penetrating finishes. Th(^ surfaces-coating finishes

inelude varnishes and synthetics. The penetrating finishes incluih'

oils, sealei'S, and water repellents.

The surface-coating finishes form a continuous coating that is

resinous in nature and usually glossy, possibly 1 mil or more thick,

over the wood.

After several renewals such finishes are inclined to crack l)adly or

to become opaque in spots, and then to curl and scale. It is then

necessary to strip them from the wood with varnish remov(U' l)efo]-e a

satisfactory finish can be restored. Such finishes are often preferred

for relatively small areas, such as front doors, but are chosen less

often for large areas, such as wood siding.

The penetrating finishes soak into the wood and do not leavi^ a film

of measurable thickness on the surface. Neither do they I'csult in a

highly glossy finish. One generous coat may suffice, though commonly

2 coats are put on at the outset and renewed at intervals with 1 coat

at a time. For best results care should be taken during application

to wipe off' any excess sealer that is not absorl)ed by the surface before

it dries. If that is not done, the finish is no longer a sealer finish but

becomes instead a varnish finish, that is, a coating.

A finish with even less gloss than the sealer finish may be obtained

by applying a drying od, such as boiled linseed oil or raw hnseed oil

to which a little liquid paint drier has been added. Oil finish should

be applied and maintained in the same way as a wood-sealer finish,

with care to see that unabsorbed oil is always wiped off before it (h'ies.

Water-repellent finishes, which usually contain wax and other

nonvolatile ingredients, give the wood an ap])earance similar to that

given by the drying-oil finislu^s. They penetrate wood so well that it

is seldom necessary to wipe off* excess material.

Some of the penetrating finishes are made with a small quantity

of pigment usually red or brown, which adds somewhat to the durability, evens up the variations in natural color of the wood, and

obscures slight grayness from weathering of the wood if renewal of

finish is delayed a little too long. In some commei'cial products the

pigment is gray to give the appearance of weathered wood.
374 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

All of the natural finishes are subject to blackening from mildew

in places where there may be lingering dampness. For that reason

the natural finishes usually should contain fungicides, such as chlorinated phenols or phenyl mercury compounds, If they do not, or if

additional protection seisms advisable, the wood may be treated with

a water-repellent preservative before the natural finish is applied.

UNCOATED EXTERIOR WOODWORK

Architectural design sometimes calls for the appearance of weatherbeaten wood {27), The best way to attain such appearance is to let

wood weather naturally, especially since uncoated exterior woodwork

is not necessarily lacking in durability. For weathered construction

it is advisable to choose woods that weather with a minimum of

cupping, twisting, and conspicuous checking, such as those of group 1

in table 42. Edge-grained boards weather better than flat-grained

boards, and thick boards better than thin ones. It is also best to

exclude boards containing pith and to place flat-grained boards with

the bark side (the side nearer the bark of the log) out. Weathered

construction should be fastened especially firmly with noncorrosive

metals, and joints should be designed to prevent retention of moisture

as far as that is possible.

INTERIOR FINISHING

Interior finishing differs from exterior chiefly in that interior woodwork usually requires much less adequate protection against moisture

and that more exacting standards of appearance and a greater variety

of effects are expected. Good interior finishes used indoors should

last much longer than paint coatings on exterior surfaces, but interior

finishes are not made to withstand the rigors of outdoor exposure.

Opaque Finishes

Interior surfaces may, if desired, be painted with the materials

and by following the procedures recommended for exterior surfaces.

As a rule, however, smoother surfaces, better color, and a more lasting

sheen are demanded for interior woodwork, and therefore enamels

rather than paints are used. These finishes differ from paints in that

linseed oil is replaced partly or entirely by bodied oils or by varnishes

in order to make a coating that does not show brush marks and presents a harder surface with a desired degree of gloss. They may also

be made of nitro-cellulose lacquers or S3rQthetic resins and drying oils

that dry much more rapidly than oleo-resinous enamels. Unless

made with expensive pigments of extraordinary opacity, such as

titanium dioxide or zinc sulfide, enamels are less opaque than paints

of the same color because they cannot be made with so large a proportion of pigment.

Before enameling, the wood surface should be made extremely

smooth. Imperfections, such as planer marks, hammer marks, and

raised grain, are accentuated by enamel finish. Raised grain is

especially troublesome on flat-grained surfaces of the heavier soft-
WOOD HANDBOOK 375

woods because the hard bands of summerwood are sometimes crushed

into the soft springwood in planing and later are pushed up again

when the wood changes in moisture content {35, 36). It is helpful

to sponge softwoods with water, allow them to dry thoroughly, and

then sandpaper them lightly with sharp sandpaper before enameling.

In new buildings woodwork should be allowed adequate time to come

to its equilibrium moisture content before finishing.

Hardwoods having large pores must be filled with wood filler before

the prirning coat. For all woods the priming coat may be white-lead

paint niixed according to directions for exterior priming-coat paint,

or special priming paints may be used. Knots in the white pines,

ponderosa pine, or southern yellow pine should be shellacked or sealed

with a special knot sealer after the priming coat is dry. A coat of

knot sealer is sometimes necessary also over the white pines and

ponderosa pine to prevent discoloration of light-colored enamels by

colored matter apparently present in the resin of the heartwood of

these species. One or two coats of enamel undercoat are next applied;

this should completely hide the wood and should also present a surface

that can easily be sandpapered smooth. For best results the surface

should be sandpapered before applying the finishing enamel, but this

operation is sometimes omitted. After the finishing enamel has been

applied, it may be left with its natural gloss or rubbed to a dull finish.

Transparent Finishes

There are many good ways of applying transparent finishes to

cither hardwoods or softwoods. Most finishing consists in some

combination of the following fundamental operations: Staining,

filling, sealing, surface coating, rubbing, and polishing. Before

finishing, planer marks and other blemishes of the wood surface that

would be accentuated by the finish must be removed.

Both softwoods and hardwoods are often finished without staining,

especially, if the wood is one with a pleasing and characteristic color.

When used, however, stain often provides much more than color alone

because it is absorbed unequally by different parts of the wood and

therefore accentuates the natural variations in grain. With hardwoods such emphasis of the grain is usually desirable; the best stains

for the purpose are dyes dissolved either in water or in oil. The water

stains give the most pleasing results but raise the grain of the wood

and require an extra sanding operation after the stain is dry. ''Nongrain-raising'' stains are now available that often approach the water

stains in clearness and uniformity of color. With softwoods, stains

color the springwood more strongly than the summerwood, reversing

the natural gradation in color in a manner that is often garish. Pigment-oil stains, which are essentially thin paints, are less subject to

this objection than are other stains and are therefore more suitable

for softwoods. Alternatively the softwood may first be coated with

clear sealer after which the pigment-oil stain may be applied to give

more nearly uniform coloring.

Hardwoods having large pores must be filled before varnish or

lacquer is applied if a smooth coating is desired. The filler may be

transparent and mthout effect on the color of the finish, or it may be
376 HANDBOOK 12, U. S. DEPARTMENT OF AGRICULTURE

colored to contrast with the surrounding wood. Usually colored

filler is darker than the rest of the wood.

Sealer is used to prevent absorption of subsequent surface coatings

and to prevent the bleeding of some stains and fillers into surface

coatings, especially lacquer coatings. Shellac is the oldest type of

si^aler. Varnish can be used as a sealer but is not so effective as

shellac or other suitable spirit varnish.

Transparent surface coatings may be of wax, shellac, varnish, or

nitrocellulose lacquer. Wax provides a characteristic sheen without

forming a coating of sensible thickness and without greatly enhancing

the natural luster of the wood. Coatings of a more resinous nature,

especially shellac and varnish, accentuate the natural luster of some

hardwoods and seem to permit the observer to look do^\^l into the

wood to a certain extent. Shellac applied by the laborious process of

French polishing probably achieves this impression of depth most

fully, but the coating is easily marred by water and is expensive.

Rubbing varnishes made with resins of high refractive index for light

are nearly as effective as shellac. Lacquers have the advantage of

drj^ing rapidly and forming a hard surface but require more applications than varnish to build a lustrous coating.

Varnish and lacquer usually dry with a highly glossy surface. To

reduce the gloss the 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 making a dull surface

and fine powders a bright sheen. For very smooth surfaces with high

polish the final rubbing is done with rotten-stone and oil. Varnish

and lacquer can be made to dry dull in the first place, but the result

is not quite the game as produced by rubbing.

Finishes for Floors

Finishes for wood floors are subject to severe mechanical wear and

consequently deteriorate more rapidly than finishes on most other

classes of woodwork. Floor finishes must, therefore, be renewed

frequently. Discussions of floor finishes usually place undue emphasis

upon the kind or quality of material used and pay far too little attention to the maintenance. Any of the comm.on types of floor finishes

will keep wood floors in excellent condition if properly maintained, but

no finish will do so if it is neglected. The essential problem is to adapt

a systematic program of maintenance to the requirements of the

finishing material chosen and of the degree of wear to which the fioor

is subjected.

The opaque and transparent interior finishes already described are

applicable to floor finishing, provided that the floor paints, floor

varnishes, or lacquers are made with the careful balance between

toughness and hardness necessary to make them resistant to mechanical wear. The essential point in maintaining any floor finish that

forms a surface coating is to renew it before the old coating has

actually worn down to the wood in conspicuous spots. Good floor

paints or varnishes may require less frequent renewal than woodsealer or sealer and wax finishes under similar conditions of wear, but

each renewal with paint or varnish is more expensive in material and
WOOD HANDBOOK 377

labor and keeps the floor from \nmig US(MI for a longer time than finishes

that do not include substantial surface coating.

Floor-sealer finishes, which are absorbed by the wood and do not

form substantial coatings, are widely used l)oth for residences and foi'

public and commercial buiklings where traffic is heavy. They may

furnish slightly less protection against moisture and dirt than coatings,

but they can be applied with less hxbor and inconveniencia In particular, floor-sealer finislu^s can be renewed more rapicUy, so tliat- floors

are kept out of service for a shorter time than coatings rc^quin^ Like

other wood seakn*s, fioor s(^a,h^rs look and s(^rv(^ l)est when they are

rubbed into the wood surface and any unal)sorb(Hl matc^rial is wipcul

oft. Bufliing the floor with fiiu^ stc^el wool shortly after the sealer

has been applied gives excc^Uent- rc^sults, and machines are available

for this purpose.

Floor wax is often applied ovca- floor si^alers, less often over varnish

or paint finishes, for additional luster and for periodically cleaning

and repolishing floors. Paste or liquid floor waxes rt^quire vigorous

rubbing, preferably with a power-driven polishing machine. Watia*-

emulsion waxes dry with reasonably good shtn^i without rubbing,

though the finish can be further improved by rubbing.

EFFECTIVENESS OF MOISTURE-EXCLUDING COATINGS

SUITABLE FOR INTERIOR USE

The comparative effectivenc^ss of various common coatings for

interior use in protecting wood at 11-percent moisture content against

absorption of moisture during 2 weeks' exposure to nearly saturated

air is given in the following tabulation:

FJfectireness^

(¡Hrcail

3 coats of aluminum powder in ^loss oil (quick flrying) or in varnish \)2

3 coats of aluminum powder in shellac. _ _ i)2

Heavy coating of paraffin 91

3 coats of rubbing varnish _ „ _ _ 89

3 coats of shellac . . _ _ . . 87

3 coats of enamel (cellulose-lacquer vehicle) ._ 76

3 coats of cellulose lacquer _ 73

3 coats of gloss oil bronzing liquid 12

3 coats of furniture wax 8

1 Perfect protection would he reprcsentecl by lOO-pcrccnt clTcctivcncss; complete lack of protection, as

with imcoated wood, by zero.

LITERATURE CITED

(1) BROWNE, F. L.

1925. ROLE OF PAINT AND VARNISH IN WOOD CONSERVATION. Drugs, Oils

and Paints 41(3): 17 pp., illus.

(2)

1926. SPREADING RATE OF OUTSIDE WHITE HOUSE PAINT ON DIFFERENT

WOODS. Drugs, Oils and Paints 42(7): 22 pp., illus./

(3)

1930. PROPERTIES OF WOOD THAT DETERMINE PAINT SERVICE OF EXTERIOR

COATINGS. Paint, Oil and Chem. Rev. 89(12): 24 pp., illus.

(4)

1930. EFFECT OF PRIMING-COAT REDUCTION AND SPECIAL PRIMERS UPON

PAINT SERVICE ON DIFFERENT WOODS. ludus. Eugill. Chem.

22(8): 29 pp., illus.
378 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

(5) BROWNE, F. L.

1930. DRYING OF EXTERIOR PAINTS UNDER VARIOUS WEATHER CONDITIONS

AND OVER DIFFERENT WOODS. Indus. Engin. Chem. 22(4): 400-

401.

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

1930. PROCEDURE USED BY THE FOREST PRODUCTS LABORATORY FOR

EVALUATING PAINT SERVICE ON WOOD. Amer. Soc. Testing Mater.

Proc. 30(11): 852-870.

1931. ADHESION IN THE PAINTING AND IN THE GLUING OF WOOD. InduS.

Engin. Chem. 23(3): 290-294.

1933. SOME CAUSES OF BLISTERING AND PEELING OF PAINT ON HOUSE

SIDING. U, S. Forest Prod. Lab. Rpt. R6, 9 pp., illus. (Rev.)

[Processed.]

1933. DURABILITY OF PAINT ON LONGLEAF AND SHORTLEAF PINE. Soutll.

Lumberman 146(1844): 20-22.

1933 and 1936. EFFECTIVENESS OF PAINT PRIMERS AND PAINTS IN RETARDING ABSORPTION OF MOISTURE BY WOOD. InduS.

and Engin. Chem. 25(8): 835-842, illus; 28(7): 798-809.

illus.

1934. ALUMINUM PRIMING PAINT, EFFECT ON THE DURABILITY OF HOUSE

PAINTS ON WOOD. Indus. and Engin. Chem. 26(4): 369-376.

1934. DURABILITY OF PAINT ON WOOD TREATED WITH ZINC CHLORIDE.

Amer. Wood-Preservers' Assoc. Proc. 30: 410-430.

1935. EFFECT OF CHANGE FROM LINOXYN GEL TO XEROGEL ON THE BEHAVIOR OF PAINT. Colloid Symposium Monog. 11: 211-222.

1935. SPECIAL PRIMING PAINTS FOR WOOD. Indus. and Engin. Chem.

27(3): 292-298.

1935. PAINTING CHARACTERISTICS OF HARDWOODS. Indus. and Engin.

Chem. 27(1): 42-47.

1936. EFFECT OF EXTRACTIVE SUBSTANCES IN CERTAIN WOODS ON THE

DURABILITY OF PAINT COATINGS. Indus. and Engin. Chem.

28(4); 7 pp., illus.

1937. PROPOSED SYSTEM OF CLASSIFICATION OF HOUSE PAINTS. InduS.

and Engin. Chem. 29(9): 1018-1026.

1938. WHEN AND HOW TO PAINT HOMES AND FARM BUILDINGS. U. S.

Forest Prod. Lab. Rpt. R962, 14 pp. (Rev.) [Processed.]

1946. POINTERS FROM YOUR PAINT FARM. Successful Farming 44(9):

28-29, 52, 54-55.

1947. WOOD PROPERTIES AND PAINT DURABILITY. LT. S. Dept. Agr. MiSC.

Pub. 629, 10 pp., illus.

1949. WATER-REPELLENT PRESERVATIVES FOR w^ooD. Architect. Rec.

105(3): 131-132, 174, illus.

1949. PAINTING THE FARM AND CITY HOME. U. S. Dept. Agr. Yearbook

1949: 625-630.

1950. TWO-COAT SYSTEM OF HOUSE PAINTING. U. S. Forest Prod. Lab.

Rpt. R1259, 21 pp., illus. (Rev.) [Processed.]

1951. W^OOD PROPERTIES THAT AFFECT PAINT PERFORMANCE. U. S. ForeSt

Prod. Lab. Rpt. R1053, 23 pp., illus. (Rev.) [Processed.]

'.i^
WOOD HANDBOOK 379

(25) BROWNE, F. L.

1952. TESTING HOUSE PAINTS FOR DURABILITY. V. S. FoiVSl Prod.

Lab. Rpt. RlOll, 15 pp., illus. (Heviewed and Heaffirinod.)

[Processed.]

(26)

1952. NATURAL WOOD FINISHES FOR EXTERIORS OF HOUSES. Architect.

Rec. 111(2): (Also issued as U. S. Forest Prod. Lab. Rpt. 190S,

9 pp.)

(27)

1952. WOOD siDiNo LEFT TO WEATHER NATURALLY. Architect. Rec.

112(5): 197-199, illus.

(28) and HRUBESKY, C. E.

1931. EFFECT OF RESIN IN LONOLIOAF PINE ON THE DURABILITY OF HOUSE

PAINTS. Indus, and Engin. Chein. 23(8): 874-877.

(29) and LAUOHNAN, D. F.

1952. MODIFICATION OF WOOD AND PLYWOOD TO IMPROVE PAl NTABILITY.

Jour. Forest Prod. Res. Soc. 2(3): 3-24. illus.

(30) and LAUOHNAN, D. F.

1952. HOW OFTEN SHOULD A HOUSE BE PAINTED AN EXPERIMENTAL

STUDY OF PROGRAMS OF PAINT MAINTENANCE. JOUT. I'^Orest

Prod. Res. Soc. 2 (5): 173-193.

(31) and LAUOHNAN, D. F.

1953. EFFECT OF COATING THICKNESS ON THE PERFORMANCE OF HOUSE

PAINTS UNDER DIFFERENT PROGRAMS OF MAINTENANCE. Off.

Digest Fed. Paint and Varnish Prod. Clubs 338: 137-159.

(32) and RIETZ, R. C.

1949. EXUDATION OF PITCH AND OILS IN WOOD. V. S. Forest Prod. Lab.

Rept. R1735, 11 pp., illus. [Processed.]

(33) DuNLAP. M. E.

1926. PAINTING OF TREATED WOOD. Indus, and Engin. Cheni. 18(10):

1091.

(34) EDWARDS, J. D., and WRAY, R. I.

1927. PROTECTING WOOD WITH ALUMINUM PAINT. Indus. and Engin.

Chem. 19 (9): 975-977.

(35) KOEHLER, A.

1930. CAUSES AND PREVENTION OF RAISED GRAIN. Timbcrman 31 (4):

162-166, illus.

(36)

1932. SOME OBSERVATIONS ON RAISED GRAIN. Aiiicr. Soc. Mcch. Engin.

Trans. Wood Indus. 54 (4): 27-30.

(37) TEESDALE, L. V.

1947. REMEDIAL MEASURES FOR BUILDING CONDENSATION DIFFICULTIES.

U. S. Forest Prod. Lab. Rpt. R1710, 14 pp., illus. [Processed.]

303747°—55 25
PROTECTION FROM WOOD-DESTROYING

ORGANISMS

Under proper conditions, wood has proved itself good for centuries

of service. Generally speaking, molds, stains, or decay appearing ii)

lumber may be traced to lack of proper precautions in yarding logs

and in piling, storing, and handling sawed material. The problems

of fungus attack in milling and merchandising stages have been

extensively studied by Government and other investigators, and

preventive measures are well known and widely practiced m the

industry. Decay should not be tolerated in lumber except in the

lower Common grades, and stain should be limited to lumber used

where appearance is secondary. It remains for the user to build

with his material in such a way as to insure the structure against the

inception and spread of decay.

Molds, stains, and decay in wood are caused by fungi, which are

microscopic plants that must have organic material on which to live,

and for some of them wood offers the required food supply. Their

growth, however, is dependent upon suitably mild temperature (50°

to 90"^ F.) and dampness. Most decay occurs in wood having a

moisture content above the fiber saturation point. Wood that is

continuously water soaked or continuously dry will not decay.

Usually, wood maintained at 20-percent moisture content or less,

typical of air-dried wood, is safe from fungus damage.

MOLDS AND STAINS

Molds and stains are confined largely to sapwood and are of various

colors. Little direct staining of the wood is caused by molds, since

the discoloration caused by them is largely superficial and is due for

the most part to cottony or powdery surface growths, which vary

from white or light colors to black. Such blemishes often are easilv

brushed or surfaced off.

Stains penetrate into the sapwood (not heartwood) and cannot be

removed by surfacing. The discoloration of the wood occurs as

specks, spots, streaks, or patches of varying intensities of color. The

so-called ''blue" stains, which vary from bluish to bluish black and

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 brown stain mentioned should

not be confused with chemical brown stain (p. 323).

Under favorable moisture and temperature conditions staining and

molding fungi may become established and develop rapidly in the

sapwood of wood products 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 subsequent 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 control measures are

given by Scheffer and Lindgren (22) ^' and on pages 325-326.

25 Italic numbers in parentheses refer to Literature Cited, p. 397.

381
382 HANDBOOK 72, U. 8. DEPARTMENT OF AGRICULTURE

Stains and molds should not be considered stages of decay, since the

causal fungi do not attack the wood substance appreciably. Ordinarily, they affect the strength of the wood only slightly; their greatest

effect is usually confined to those strength properties which determine

shock resistance, or toughness (p. 99).

Stained and molded stock is practically unimpaired for many uses

in which appearance is not a limiting factor. It is not entirely satisfactory for siding, trim, and other exterior millwork, however, because

the infected wood has greater water absorptiveness. Also, incipient

decay often is present in the discolored areas. Both of these factors

increase the hazard of decay in wood that is rained on unless the wood

has been treated with a suitable preservative.

DECAY

Decay-producing or wood-destroying fungi may, under conditions

that favor their growth, attack either heartwood or sapwood, causing

a condition that is variously designated as decay, rot, or dote (3).

The fresh surface growths of decay fungi are usually ffuffy or cottony

-seldom powdery like the surface growths of molds. They may

appear as fan-shaped patches, strands, or root-like structures, usually

white or brown. Sometimes fruiting bodies are produced that take

the form of toadstools, brackets, or crusts. The microscopic strands

or hyphae that permeate the wood use parts of the wood itself as food.

Some wood-destroying fungi live largely on the cellulose; others use

the lignin as well as the cellulose.

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. Many fungi 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 then undergone definite changes in color and properties,

depending upon the organism and the substances it removes. The

rotted wood may be white or brown in color—white if the decay

fungus consumes lignin as well as cellulose, and brown if the cellulose

primarily is removed. There are also intermediate types between

the white and brown rots.

Brown, crumbly rot, in the dry condition, is sometimes called ''dry

rot," but the term is incorrect because wood must be damp in order to

decay, although it may become dry subsequently. A few fungi,

however, have water-conducting strands and are therefore 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 the ''dry rot fungi,'' but they

nevertheless must have access to water in order to function.

Decay Resistance of Wood

For a discussion of the natural resistance of wood to wood-destroying

fungi and a grouping of species according to decay resistance,*^ see

page 45.
WOOD HANDBOOK 383

Certain wood-destroying fungi attack the heartwood, and rarc^v the

sapwood, of living trees, whereas others confine theii* activities to logs

or manufactured products, such as sawed lumber, structural timbers,

poles, and ties. A few of the first group may cease tlieir activiti(^s

after the trees have been cut, as in pecky cypress or pecky incensecedar.

Others may continue their destruction after the trees have been cut

and worked into products, provided conditions remain favorable for

their growth. In living trees the sapwood is less subj(^ct to attack

than the heartwood, presumably because of the nature of the attacking

fungi and the very high moisture content of living sapwood. The

sapwood of logs or wood products, on the other hand, usually decays

more readily than the heartwood, because the moisture content of the

sapwood becomes more favorable for the growth of decay fungi and

the heartwood often contains natural chemicals that retard the growth

of fungi.

Effect of Decay on Strength of Wood

Incipient decay induced by some fungi is reflected immediately in

pronounced weakening of the wood, whereas other fungi reduce

strength much less (p. 99). For example, the decay produced by

Fomes pini causes little or no reduction in strength in its incipient

stage. This is the most common decay in living softwood trees. On

the other hand, Polyporus schweinitzii, another common rot in standing

softwoods, greatly reduces the strength of wood at a very early stage.

In the later stages of decay any wood-destroying fungus will seriously

reduce the strength of wood (2S), as well as its fire resistance.

CONTROL OF MOLDS, STAINS, AND DECAY

Logs, Poles, Piling, or Ties

The species, section of the country, and time of the 3^ear will determine what precautions must be taken to avoid serious damage from

fungi in poles, piling, ties, and similar thick products during seasoning

or storage. In dry sections, rapid surface seasoning by first peeling off

the bark and then decking the peeled product on high skids or piling it

on high, well-drained ground in the open will retard molds, stains, and

decay; but checking must be guarded against with other measures. In

humid regions, such as the Gulf States, air-drying of these products

often is not sufficiently rapid to avoid losses from fungi. Therefore,

preseasoning treatments with antiseptic solutions sometimes are used,

but main reliance is placed on early preservative treatment or use of

the product (22).

For logs, rapid conversion into lumber or storage in water is the

surest way to avoid fungus damage. Antiseptic sprays promptly

applied to ends and places from which the bark is removed will protect

most timber species during storage for 2 to 3 months, provided woodinfesting insects are not prevalent. For longer storage, the addition

of an end coating is needed to prevent seasoning checks, through

which infection can enter the log (33).
384 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Lumber

Growth of fungi can be. prevented in lumber and other wood products that can be quickly dried to a moisture content of 20 percent or

less and kept dry. Kiln-drying is the most satisfactory and effective

method of rapidly reducing moisture content. Standard air-drying

practices are usually sufficient; end racking is used for some species.

Dip or spray treatment of freshly cut lumber with suitable antiseptic solutions, such as organic mercury compounds, chlorinated

phenols, and borax, alone or in mixture, will prevent fungus infection

durmg air-drying. Successful control by this method depends not

only upon immediate and adequate treatment but also upon the proper

subsequent handling of the lumber (33).

Air-dr3âng yards and sheds should be kept as sanitary as possible.

Recommended practice includes locating yards and sheds on welldrained ground; removing debris, which serves as a source of infection,

and weeds, which reduce air circulation; and employing proper piling

methods that permit rapid drying of the lumber. Proper piling

requires high, sloping foundations, the avoidance of close or solid

piling of unseasoned stock, watertight roofs raised several inches above

the top courses, and sound, dry stickers of heartwood or of preservative-treated wood {14, 20),

The user's best assurance of receiving lumber free from decay or

stain is to buy stock marked by a lumber association in a grade that

requires freedom from such quality-reducing features. If lumber is

to be used under conditions conducive to decay, it should be the

heartwood of a naturally durable species or should be adequately

treated with a good wood preservative (p. 399).

Buildings

The lasting qualities of properly constructed wood buildings are

apparent in all parts of the country. vSerious decay problems are

almost always a sign of faulty design or construction or of lack of

reasonable care in the handling of the wood. The conditions that

favor decay development are described on page 381.

Construction principles that assure long service and avoid decay

hazards in buildings include: (1) Build with dry lumber; (2) use

designs that will keep the wood dry and accelerate rain runoflF; or (3)

for parts exposed to decay hazards, use preservative-treated wood or

heartwood of a decay-resistant species {30).

A building site that is dry or for which drainage is provided will

reduce decay hazards. Stumps, wood debris, stakes, or wood concrete

forms frequently lead to decay if left under or near a building and

should be removed.

Unseasoned or infected wood should not be enclosed until thoroughly

dried. Unseasoned wood may be infected because of improper

handling at the sawmill, at retail yard, or after delivery on the job.

Untreated wood parts of substructures often are infected with decay

if in contact with the soil. Sills in contact with dirt fill under porches,

joists touching the ground under the house, and particularly siding or

skirting in contact with earth must be guarded against. If contact
WOOD HANDBOOK 385

with soil is necessary, as with foundation posts, heartwood of a decayresistant species should be used or the wood should be impregnated

with a reliable preservative (p. 399).

Sill plates and other wood in contact with concrete near the ground

should be protected by a moistureproof membrane, such as heavy

asphalt paper. In some cases, preservative treatment of the wood in

actual contact with the concrete is advisable. Girder and joist

openings in masonry walls should be big enough to assure an air space

around the ends of these wood members; if the members are below the

outside soil level, moistureproofing of the outer face of the wall is

essential.

In basementless buildings, wetting of the wood by condensation may

result in serious decay damage. A crawl space with at least an 18-inch

clearance should be left under wood joists and girders. Condensation

can be prevented either by providing openings on opposite sides of the

foundation walls for cross ventilation or by laying roll roofing on the

soil {SO).

Porches, exterior steps, and platforms present a decay hazard that

cannot be fully avoided by construction practices. Therefore, the

use of preservative-treated wood usually is advisable.

The prevention of decay in walls and roofs rests largely in designs

that prevent the entrance and retention of rain water. A fairly wide

roof overhang, with gutters and downspouts that are never permitted

to clog, is very desirable. Sheathing papers in the walls should be of

a ^'breathing" or vapor-permeable type. Vapor barriers, if installed,

should be near the warm face of insulated walls and ceilings. Roofs

must be kept tight, and cross ventilation in attics is desirable (28).

The use of sound, dry lumber is important in the exterior as well as

substructure parts of buildings (SI).

Where service conditions in a building are such that the wood

cannot be kept dry, as in textile mills, pulp and paper mills, and

cold-storage plants, properly treated lumber should be used unless

heartwood of naturally decay-resistant species is available (13).

In making repairs necessitated by decay, every effort should be

made to correct the conditions leading to the damage. If the conditions cannot be remedied, all infected parts should be replaced with

treated or naturally decay-resistant wood, and it is advisable to remove

surrounding material at least 2 feet beyond any evidence of decay.

If the sources of moistm^e that caused the decay are entirely eliminated, it is necessary to replace only the weakened wood with dry

lumber.

Other Wood Products and Structures

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 described for

buildings—dry the wood rapidly and keep it dry, or treat the wood

with accepted protective and preservative solutions. Interior grades

of plywood should not be used where the plywood will be exposed to

moisture since the glues, as well as the wood, may be dismtegrated

by fungi'and bacteria {6, 9). With either plywood or fiberboard of
386 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

the exterior t^^pe, joint construction should be carefulh^ designed to

prevent the entrance of rain water.

Wood boats present both a serious decay hazard and certain

problems that are not encountered in the ordinär}^ use of wood. The

parts especially subject to decay are the stem, knighthead, transom,

and frameheads that are reached by rainwater from above or condensation moisture from below. Faying surfaces are more liable to

decay than exposed surfaces, and in salt water service, hull members

just below the weather deck are more vulnerable than those below

the water line. In fresh water, members below the water line are

most subject to decay. Recommendations for avoiding decay include:

(1) Use only heartwood of durable species, preferably below 20

percent in moisture content and not airead}^ infected; (2) provide and

maintain ventilation in the hull and avoid paint coatings that lock in

moisture; (3) keep water out as much as is practicable, especially

fresh water; and (4) where it is necessary to use sapwood or nondurable

heartwood, impregnate the wood with a preservative (11),

INSECTS

The more common types of degrade caused by wood-attacking

insects are shown in table 44 (26). Methods of controlling and

preventing insect attack of wood are described in the following

paragraphs.

Beetles

Bark beetles (2, 24) may (himage log structures and other rustic

construction on whicli the bark is left. They are reddish brown to

black and vary in length from about Kb to K hich. They bore through

the outer bark to the soft iimer part, where they make tunnels in

which they lay their eggs. In making the tunnels, they push out

fine brownish-white sawdustlike particles. If man}^ beetles are

present, their extensive tunneling will loosen the bark and permit it

to fall off in large patches, making the structure unsightl3^

To avoid bark-beetle damage, the logs should be cut during the

dormant season (October or November, for instance) and piled at

once off the ground in the open or under cover to promote the rapid

drying of the iimer bark before the beetles begin to fly in the spring.

In almost every case, this will prevent damage by insects that prefer

freshly cut wood. \^^ien the logs cannot be cut or handled as recommended, it is advisable to immerse them in or thoroughly spray them

with a solution containing 0.075 percent (0.2 percent under severe

conditions) of gamma benzene hexachloride (BHC) in No. 2 fuel

oil (15, 17).

Ambrosia beetles, roundheaded and flatheaded borers, and some

powderpost beetles (2, 7, 24, 26) that get into freshly cut timber can

cause considerable damage to wood in rustic structures and some

manufactured products. Utilization of proper cutting practices and

spraying the material with a toxic chemical, as mentioned for bark

beetles, will control these insecte. Damage by ambrosia beetles can

be prevented in freshly sawed lumber by dipping the product in a
WOOD HANDBOOK 387

TABLE 44.—Classification of the more common types of degrade caused by woodattacking insects

PinholesGrub holes..

TT j V, 1 I Condition of

How and whore made ae^^aderl timber

Holes with dark streak in surrounding

wood, Yioo to yi inch in diameter,

usually circular and open (not

grouped in given space):

Hardwoods:

Stained area 1 inch or more

long.

Stained area less than I inch

long.

Softwoods: Stained area less than

1 inch long.

Holes usually without streak in surrounding wood of both softwoods |

and hardwoods (usually grouped in |

given space): |

Holes darkly stained, less than Vs I

inch in diameter.

Holes unstained, open, and vari- i

able in diameter:

Lined with a substance the ¡

color of wood; from Moo to I

Yï inch in diameter (hard j

woods rarely with streaks in

surrounding wood).

Unlined, less than H inch in

diameter (not grouped in

given space).

Holes Hto 1 inch in diameter, variable

in shape, oi)en or with boring dust:

Hole stained, usually open.

By ambrosia beetles in living trees.

By ambrosia beetles in recently felled trees and

green logs.

By ambrosia beetles in sapwood of peeled trees, green

logs, and green lumber.

By ambrosia beetles in

felled trees, green logs,

and green lumber.

By timberworms in living

and felled trees and green

logs.

Powderpost '

Hole? unstained, usually with boring dust present:

Bormgs fine, granular, or fibrous.

Borings variable in character,

sometimes absent.

Holes mostly VIQ to H inch in diameter, circular to broadly oval, filled

with granular or ijowdery boring

dust, and unstained:

Hardwoods _.. -

By ambrosia beetles in green

logs and green lumber.

By \\ood-boring grubs

living trees.

do.

Softwoods.

Wormh oles, no living worms.

1)0.

Do.

By adults and larvae of j

beetles and other woodboring insects in recently

felled softwoods and hardwoods.

By roundheaded borers and

])Owderpost beetles in

green or seasoned wood.

By flatheaded borers in living, recently felled, and

dead trees.

By roundheaded borers,

weevils, and Anobium

powderi^ost beetles in seasoned wood.

Do.

Do.

Do.

Do.

Do.

Do.

Wormholes, powderposted.

Do.

Do.

See footnotes at end of table.
'388 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLE 44.—Classification of the more common types of degrade caused by woodattacking insects—Continued

Type of

degrado Description

Pitch pocket.

Black check

Bluing . _

Pith fleck.

Gum spotRing distortions.

Stained area over 1 inch long

TTow and where iTiade Condition of

degraded timber

By various insects in living Worm holes, no iv

trees. ing worms.

By the grubs of various in- Do.

sects in living trees.

By fungus follow^ing insect Do.

wounds in living trees and

recently felled sawlogs.

By the maggots of flies or Do.

adult weevils in living

trees.

By the grubs of various In- Do.

sects in living trees.

By de-foliating larvae or flat- Do.

headed cambium miners

in living trees.

1 Powderpost or the so called "live worm" is of continuous injury; hence timber having this type of degrade cannot be used with safety before treatment with chemicals, kiln-drying, or steaming in a kiln. Powderpost can be prevented by proper handling of the stock.

solution containing 0.2 percent of gamma benzene hexachloride in the

form of a water emulsion (IS, 17). The addition of one of the sapstain preventives mentioned for controlling molds, stains, and decay

will keep the lumber bright.

Powderpost beetles {24, 25, 26) attack both hardw^oods and softwoods, both freshly cut and seasoned lumber and timber. The

powderpost beetles that cause most damage to dry hardwood lumber

belong to the Lyctus species. They attack the sapwood of ash,

hickory, and oak, in particular, as it begins to season. Eggs are laid

in pores of the wood, and the larvae burrow through the wood making

tunnels from Ke to K2 inch in diameter, which they leave packed with

a fine powder. Powderpost damage is indicated by holes left in the

surface of the wood by the winged adults as they emerge and by the

fine powder that may fall from the w^ood.

When selecting hardwood lumber for building or manufacturing

purposes, any evidence of powderpost infestation should not be overlooked, for the beetles may continue to be active long after the wood

is put to use. Sterilization of green wood with steam at ISO"" F. or

sterilization of wood with a lower moisture content at 180"^ F. under

controlled conditions of relative humidity for about 2 hours is efi'ective for inch lumber. Thicker material requires a longer time. A

3-minute soaking in a petroleum oil solution containing 5 percent of

pentachlorophenol, 5 percent of DDT, or 1 percent of lindane is also

effective for checking infestation or preventing attack of lumber up

to 1 inch thick. Small dimension stock also can be protected for

about a year by brushing or spraying with these chemicals. In the

case of infested furniture or finished woodwork in a building, these

same insecticides may be used, but they should be dissolved in a refined petroleum oil, like mineral spirits. Since the 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.
WOOD HANDBOOK 3g9

Susceptible hardwood lumber used for manufacturing purposes

should be protected from powderpost attack as soon as it arrives at

the plant Good plant sanitation helps check mfestation. Damage

to manulactured items frequently is traceable to infestations that

occur betöre the products are placed on the market, particularly if a

finish IS not applied to the surface of the items until they are sold

Once wood is mfested, the larvae will continue to work, even though

the surface is subsequently pauited, oiled, waxed, or varnished.

A roundheaded powderpost beetle, commonly known as the old

house borer, causes most msect damage to seasoned pine floor joists.

The larvae reduce the sapwood to a powdery or granular consistency

and make a ticking sound while at work. Wlien mature, the beetles

make an oval hole about one-fourth inch m diameter in the surface of

the wood and emerge. Infested wood should be drenched with a solution of 5 percent of DDT, 2 percent of chlordane, or 1 percent of

Imdane in a highly penetrating solvent; trichlorobenzene is preferable,

though a petroleum oil is satisfactory. Borers working in wood behind plastered or paneled walls can be eliminated by having a licensed

operator fumigate the building with a deadly poisonous gas like

hydrocyanic acid.

Termites

Termites (16, 18, 27, 29, 30) superficially resemble ants hi size, general appearance, and habit of living in colonies. About 56 species

of them are known in the United States. From the standpoint of

their methods of attack on wood, they can be grouped into two maui

classes: (1) The ground-inhabiting or subterranean termites; and

(2) the 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. Their occurrence

and damage are much greater m the Southern States than m the

Northern States where low temperatures do not favor their development (fig. 85). The hazard of infestation is greatest (1) beneath

basementless buildings that are poorly drained and ventilated and

(2) in houses with basements in the parts of the foundation that are

adjacent to enclosed porches, sun parlors, and terraces where filled

earth is close to the timbers.

The subterranean termites develop their colonies and maintain

their headquarters in the ground, from which they build their tunnels

through earth and around obstructions to get at the wood they need

for food. Each colony shuts itself off and lives in the dark, but the

termites must have a constant source of moisture or they will die. It

is the worker members of the colony that cause the destruction of

wood. At certain seasons of the year male and female winged forms

swarm from the colony, fly a short time, lose their wings, mate, and if

successful in locating a suitable place they 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

^^fl3âng ants'' are termites; therefore, suspicious insects should be

identified before money is spent for their eradication (fig. 86).
390 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

FIGURE 85.—A, The northern limit of recorded damage done by subterranean

termites in the United States; B, the northerr limit of damage done by drywood or nonsubterranean termites.

Â B

FIGURE 86.—A^ Winged termite; ß, winged ant (both greatly enlarged). The

wasp waist of the ant and the long wings of the termite are distinguishing

characteristics.

Subterranean termites do not establish themselves in buildings by

being carried there in lumber but by entering from ground nests after

the building has been constructed. Telltale signs of their presence are

the earthen tubes or runways built by these insects over the surfaces

of foundation walls to reach the wood above. Another sign is the

swarming of ^\nnged adults early in the spring or fall. In the wood

itself, the termites make galleries that follow the grain, leaving a shell

of sound wood to conceal their activities. Since the galleries seldom
WOOD HANDBOOK 391

show on the wood surfaces, probmg with an ice pick or knife is advisable if the presence of termites is suspected.

The best protection whero subterranc^an termites arc prevalent is to

build so as to prevent their gaining accc^ss to the building {16, SO).

The foundations should be of concrete or other solid material through

which the termites cannot penetrate. With l)rick, stone, or concrete

blocks, cement mortar should be us(^d, tor termiti^s can work through

some other kinds of mortar. Wood that is not impi'egnated with an

effective preservative must be kept well away from the ground. Tf

there is a basement, it should preferably })e floored with concrete.

Posts supporting the first-floor beams must be thoroughly treated if

they bear directly on the ground or on wood blocking. Untreated

posts should rest on concrete piers extending a few inches above the

basement floor if that floor is of concrete; if the basement floor is of

earth, the concrete piers should extend at least 18 inch(*s above it.

If the earth is not excavated beneath the building, and th(^ floor is of

wood construction, the floor joists and other woodwork, unless adequately treated with preservative, should be kept at least 18 inches

from the earth and good ventilation should be provided beneath the

floor.

Moisture condensation on the floor joists and subflooring, which

may cause conditions favorable to decay and thus make th(^ wood more

attractive to termites, can be avoided by covering the soil bellow with

roll roofing. In the case of ranch-st3de buildings or buildings with

radiant heating, where concrete-slab floors are laid directly over a

gravel fill, the soil directly beneath the expansion joints and around

utility openings in the floor should be poisoned before the concrete is

poured. Furthermore, insulation containing cellulose intended for

use as a filler in expansion joints should be impregnated with a chemical

toxic to termites. Sealing the top one-half inch of the expansion

joint with coal-tar pitch also provides effective protection from groundnesting termites.

All concrete forms, stakes, stumps, and waste wood should be

removed from the building site, since they are possible sources of

infestation. In the main, the precautions that are efl'ective against

subterranean termites are also helpful against decay.

Metal termite shields are used onl}^ to supplement good construction. They are employed mainly in the Deep South and in the

tropical lands. Unless well designed and correctly instalh^d, they

offer a false sense of security and are a waste of money. Shields made

of sisal kraft, roll roofing, and other building papers are not efl'ective

substitutes for metal because they are penetrable. Termiteproof

shields are made of 26-gage galvanized iron or 16-ounce (per square

foot) copper. They are used between the foundation and woodwork

and fitted tightly around pipes and other equipment connecting wood

with the ground. All metal joints must be soldered or tightly interlocked to be effective. The metal shields extend out from the foundation at an angle of 45'' for a horizontal distance of at least 2 inches

{29,80),

Where it is not feasible to install metal shields, and other protection

is needed in addition to that obtained by structural methods, a

thorough poisoning of the soil adjacent to the foundation walls and
392 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

piers beneath the building with a recognized soil poison will prove to

be beneficial {29, 30). A thorough treatment should last at least 5

years.

To control termites in a building, one of the main things to remember is to break any contact between the termite colony in the soil

and the woodwork. This can be done by blocking mechanically the

runways from soil to wood, by poisoning the soil, or by using both of

these methods. Wlien more difficult treatments are needed, such as

drilling of masonry foundations, the detailed instructions in U. S.

Department of Agriculture Farmers' Bulletin 1911 {29)^ should be

followed. Possible reinfestations should be guarded against by frequent inspections for the telltale signs that were listed previously.

Nonsubterranean Termites

Nonsubterranean termites have been found only in a narrow strip

of territory extending from central California around the southern

edge of the United States to Virginia (fig. 85). Their principal damage is confined to an area in southern Cahfornia and to parts of

southern Florida, notably Key West.

The nonsubterranean or dry-wood termites are fewer in number,

do not multiply so rapidly, and have colony life and habits somewhat

different from those of the subterranean termites. The total amount

of destruction they cause in the United States is very much less than

that caused by the subterranean termites. Their ability to live in

damp or 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 unmolested for a few years.

In constructing a building in localities where the nonsubterranean

termites are prevalent, it is well 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 at this season (18^ 27).

Since paint is a good protection against the entrance of dry-wood

termites, all exposed wood should be kept adequately painted. Fine

screen should be placed over any openings through which access

might be gained to the interior unpainted parts of the building. As

in the case of ground-nesting termites, 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 found to be infested with dry-wood termites, the

infested wood should be replaced if badly damaged. If the wood is

only slightly damaged or difficult to replace, further termite activity

can be arrested by blowing a teaspoonful of a poisonous dust, such as

finely divided Paris green, arsenical dust, or 50 percent DDT, into

each nest. Also effective are liquid insecticides, such as trichlorobenzene or the following dissolved in fuel oil at the strength indicated:

DDT, 6 percent; chlordane, 2 percent; pentachlorophenol, 5 percent;

and gamma benzene hexachloride, 0.4 percent. Detached houses

heavily infested with nonsubterranean termites have been fumigated
WOOD HANDBOOK 393

with success. This method is quicker and often cheaper than the

use of poisonous hquids and dusts, but it does not prevent the termites

from returning, since no poisonous residue is left in the tunnels.

Moreover, fumigation is very dangerous and should be conducted

only by licensed fumigators.

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 treatment with wood preservatives of recognized

value.

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 and baldcypress has

some resistance, especially when used above ground. Termites are

known to attack these woods at times, however. Very resinous

heartwood of southern yellow pine is practically immune, but wood

of this character is not available in large quantities or suitable for

many uses.

Carpenter Ants

Carpenter ants are large or small black or brown ants that are

found usually in stumps, trees, or logs but sometimes are found

doing damage in poles, structural timbers, or buildings. They use

the 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 fuel

wood. 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 mostly frequented by them are

porch columns, porch roofs, window sills, and sometimes the wood

plates in foundation walls. 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 or stumps, 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 attractive to

the ants.

When carpenter ants are found in a structure, badly damaged

timbers should be replaced. In wood not sufficiently damaged to

require replacement, the ants can be killed by dusting with 5 percent

chlordane; 4 percent rotenone (derris powder), or 10 percent DDT

(10). Where the colony is located in decaying wood in porches, soak

the wood with a solution containing 2 percent of chlordane or 5 percent

of pentachlorophenol (a wood preservative as well as an insecticide)

in petroleum oil.

MARINE BORERS

Damage by marine boring organisms to fixed or ñoating structures

of wood in salt or brackish waters is practically worldwide. Slight

attack is sometimes found in rivers even above the region of brackish-
394 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

ness. 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 piling may

be completely destroyed in a year or less. Along the coast of the

New England States the rate of attack is less rapid but still sufficiently

rapid generally to require protection of wood where long life is desired.

The principal marine borers from the standpoint of wood destruction

in the United States {1, 4, 1^) ^-re described in the following paragraphs.

Shipworms

Shipworms are mollusks of various species that superfically are

wormlike in form. The group includes several species of Teredo and

several species of Bankia that are readily distinguishable on close

observation but are all very similar in several respects. In the early

stages of their life they are minute, free-swimming organisms. Upon

finding suitable lodgement 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 anim.al grows

in length and diameter within the wood but remains a prisoner in its

burrow, which it lines with a shell-like deposit. It lives upon, the

wood borings and upon 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 a pile may be

completely honeycombed and ruined while the surface shows only

slight perforations. When present in great numbers the borers grow

only a few inches before the wood is so completely occupied that

growth is stopped, but when not crowded they can grow to lengths

of 1 to 4 feet according to species.

Limnoria

Limnoria are small crustaceans about )i to )i inch long that bore

small burrows in the surface of piling. They can move freely from

place to place if occasion requires but usually continue to bore in one

place. When great numbers are present their burrows are separated

by very thin walls of wood that are easily eroded by the motion of the

water and objects floating upon it. This erosion causes the animals to

burrow continually deeper; otherwise the burrows would probably

not become more than 2 inches long or more than K inch deep. Since

erosion is greatest between tide levels, piling heavily attacked by

Limnoria characteristically wears within such levels to an hourglass

shape. Untreated piling can be destroyed by Limnoria within a year

in heavily infested harbors.

Martesia

Martesia are wood-boring mollusks that resemble clams in general

appearance. Like the shipworms, they enter the wood when very

small, leaving a sm.all entrance hole, but grow larger as they burrow

into the wood. They generally do not exceed 2}^ inches in length and
WOOD HANDBOOK 395

1 inch in diameter but are capable of doing considerable damage.

Their activities in the United States appear to be confined to the

Gulf of Mexico.

Sphaeroma

Sphaeroma are somewhat similar to Limnoria but larger, sometimes

reaching a length of K inch and a width of )i inch. They resemble in

general appearance and size the common sow bug or pill bug that

inhabit damp places. They are widely distributed but not so plentiful

as Limnoria and do much less damage. Nevertheless piling in some

structures has been ruined by them. Occasionally they have been

found working in fresh water.

Resistance of Woods 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 turpentine, greenheart, jarrah, azobe, totara, kasikasi, manbarldak, and several others, has shown resistance to marineborer attack. Service records on these woods, however, do not

always show uniform results and are affected by local conditions.

Protection of Permanent Structures from

Marine Borers

The best practical protection for piling in sea water is heavy treatment with coal-tar creosote or creosote-coal tar solution. The

treatment must be thorough, the penetration as deep as possible,

and the retention high in order to give satisfactory results in heavily

infested waters. It is best to treat such piling by the full-cell process

^^to refusal'^* that is, to force in all the oil the piling can be made to

hold without using treatments that cause serious damage to the wood.

The retentions recommended on page 417 are minimum values.

When maximum protection against marine borers is desired, as much

more oil as is practicable should be injected. For highest retentions

it is necessary to air-dry the piling before treatment.

Limnoria, Martesia, and Sphaeroma are not always stopped even

by thorough creosote treatment. The average life of well-creosoted

structures is many times the average life that could be obtained from

untreated structures; nevertheless, well-creosoted structures arc

sometimes damaged seriously.

Shallow or erratic penetration affords but slight protection. The

spots with poor protection are attacked, and from them the borers

spread inward and destroy the untreated interior of the pile. Low

retention fails to provide a reservoir of surplus preservative to compensate for depletion by evaporation and leaching.

When wood is to be used in salt water, avoidance of cutting or

injury by sharp tools 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

303747°—55 20
396 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

pile. Where piling is cut to grade above the waterline, the exposed

surfaces should, of course, be protected from decay.

The life of treated piling is influenced by the thoroughness of the

treatment, the care and intelligence used in avoiding damage to the

creosoted shell during handling and installation, and the severity of

borer attack. 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 {5). The San Francisco Bay Marine Piling Committee estimated a range of 15 to 30 years for the life of creosoted piling on the

Pacific coast {12). More recent service records (<5) show average-life

figures of from 22 to 48 years on well-treated Douglas-fir piling in

San Francisco Bay waters. In South Atlantic and Gulf of Mexico

waters, creosoted piles are estimated to have an average life of 10 to

12 3^ears {1) and frequently last much longer {8). On the North

Atlantic coast longer life is to be expected.

Metal armor and concrete jacketing have been used with varying

degrees of success for the protection of marine piling (5). The metal

armor may be in the form of sheets, wire, or nails. Scupper-nailing

with iron or steel furnishes some protection, particularly against

Limnoria. Sheathing of piling 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 have sooner or later let in the borers, and in

onl}^ a few cases reported has long life been obtained. Attempts during

World War II to electroplate wood piling with copper were not

successful. Concrete casings are now in greater use than metal

armor and appear to provide better protection when high-quality

materials are used and are carefully applied. Applying concrete

casings to creosoted piling appears to be a practice worthy of consideration where the importance of a structure and the severity of

borer attack justify the expense of the two-way protection system.

Protection of Wood Boats from Marine-Borer Attack

Wood barges and lighters have been constructed with planking or

sheathing pressure treated with creosote to provide hull protection

from marine borers, and the results have been favorable. While

coal-tar creosote is the most effective preservative yet developed for

protecting wood against marine borers, it has disadvantages that

make its use objectionable 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 (31) protect boat hulls against marineborer attack, but the protection continues only while the coating

remains unbroken. Since it is difficult to maintain an unbroken

coating of antifouling paint, the U. S. Navy finds it desirable to

impregnate the hull planking of some wood boats with certain coppercontaining preservatives. Such preservatives, when applied with high

retentions (1.5 to 2.0 pounds per cubic foot), have limited effectiveness

against marine borers and should help to protect the huU of a boat

during intervals between renewals of the antifouling coating. These
WOOD HANDBOOK 397

copper preservatives do not provide protection equivalent to that

furnished by coal-tar creosote, and their effectiveness in protecting;

boats is therefore best assured if the boats are dry docked at regular

and frequent intervals and the maintenance of the antifouling coating

is not neglected.

Marine-borer tests on plywood show that improved service can be

obtained through preservative treatment of the plyA\^ood, acetylation

of the veneer, and the use of special adhesives, particularly those

containing sihceous extenders {19, 21). These developments have not

yet been fully explored in the building of ply^vood boats, however.

LITERATURE CITED

(1) ATWOOD, W. G., and JOHNSON, A. A.

1924. MARINE STRUCTURES, THEIR DETERIORATION, AND PRKSEU v ATlOiN.

Nati. Res. Council Rpt. Com. on Marine V\\'\\\^ Invest., 534 pp.,

illus.

(2) BEAL, J. A., and MASSEY, G. L.

1945. BARK BEETLES AND AMBROSIA BEETLES. Duke Univ. Forestry

Bui. 10, 178 pp., illus.

(3) BOYCE, J. S.

1923. DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. U. S. Dept.

Agr. Bui. 1128, 52 pp., illus.

(4) CALMAN. W. T.

1919. MARINE BORING ANIMALS INJURIOUS TO SUBMERCXED STRUCTURES.

Brit. Mus. Nat. Hist. Econ. Ser. 10. 35 pp.. illus.

(5) CHELLIS, R. D.

1948. FINDING AND FIGHTING MARINE BORERS. Engin. News Rec. 140

(12): 422-424, illus.; (14): 493-496, illus.

(6) CHRISTENSEN, C. M., and MOSES, C. S.

1945. MOLDS AND BACTERIA THAT DELAMINATE PLYWOOD BONDED WITH

CASEIN AND SOYBEAN GLUES. U. S. Dept. of Agr. Forest Path.

Spec. Release 25, 23 pp., illus.

(7) CRAIGHEAD, F. C.

1950. INSECT ENEMIES OF EASTERN FORESTS. U. S. Dept. Agr. Misc.

Pub. 657, 679 pp., illus.

(8) DANIELS, A. S.

1949. REPORT OF COMMITTEE U-6, MARINE AND FOUNDATION PILE SERVICE

RECORDS. Amer. Wood Preservers' Assoc. Proc. 45: 294-305.

(9) ENGLERTH, G. H.

1950. DECAY RESISTANCE OF PLYWOOD BONDED WITH VARIOUS GLUES.

Forest Prod. Res. Soc. Proc. 4: 14 pp., illus.

(10) FuRNiss, R. L.

1944. CARPENTER ANT CONTROL IN OREGON. Oreg. Agr. Expt. Sta. Cir.

158, 12 pp., illus.

(11) HARTLEY, C, and MAY, C.

1943. DECAY OF WOOD IN BOATS, U. S. Dept. Agr. Forest Path. Spec.

Release 8, 12 pp., illus.

(12) HILL, C. L., and KOFOID, C. A.

1927. MARINE BORERS AND THEIR RELATION TO MARINE CONSTRUCTION

ON THE PACIFIC COAST. San Francisco Bay Marine Piling Com.

Final Rpt., 357 pp., illus.

(13) HoxiE, F. J.

1930. DECAY OF WOOD IN INDUSTRIAL BUILDINGS. AsSOC. Factorv Mutual

Fire Insurance Co., Inspection Dept. 119 pp., illus. Boston.

(14) HUMPHREY, C. J.

1917. TIMBER STORAGE CONDITIONS IN THE EASTERN AND SOUTHERN

STATES WITH REFERENCE TO DECAY PROBLEMS. U S. Dept.

Agr. Bui. 510, 43 pp., illus.

(15) JOHNSTON, H. R.

Ig52 CONTROL OF INSECTS ATTACKING GREEN LOGS AND LUMBER. South,

Lumberman 184 (2307): 37-39, illus.
398 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

(16) KoFoiD, C. A., LIGHT, S. F., HORNER, A. C, RANDALL, M., HERMS, W. B.,

and HOWE, E. E.

1934. TERMITES AND TERMITE CONTROL! A REPORT TO THE TERMITE

INVESTIGATIONS COMMITTEE. 734 pp., illiis. Berkeley, Calif.

(17) KowAL, R. J.

1049 CONTROL OF WOOD BORING INSECTS IN GREEN LOGS AND LUMBER,

Forost Prod. Res. Soc. Proc. 3: 469-479.

(18) LIGHT, S. F.

1929. TERMITES AND TF.RMITE DAMAGE. Calif. Agr. Expt. Sta. Cir. 314,

28 pp., illus.

(19) IMACLEAN, J. D.

1950. RESULTS OF EXPERIMENTS ON THE EFFECTIVENESS OF VARIOUS

PRESERVATIVES IN PROTECTING WOOD AGAINST MARINE-BORER

ATTACK. U. S. Forest Prod. Lab. Rpt. D1773, 19 pp., illus.

[Processed.]

(20) PECK, E. C.

1952. STORAGE AND HANDLING OF LUMBER. U. S. Forest Prod. Lab. Rpt.

D1919, 17 pp., illus. [Processed.]

(21) RICHARDS, A. P., and CLAPP, W. F.

1946. CONTROL OF MARINE BORERS IN PLYWOOD. Amer. Soc. Mech.

Engin. Wood Indus. Div. Paper 46-A-43, 6 pp., illus.

(22) SCHEFFER, T. C., and LINDGREN, R. M.

1940. STAINS OF SAPWOOD AND SAPWOOD PRODUCTS AND THEIR CONTROL.

U. S. Dept. Agr. Tech. Bui. 714, 123 pp., illus.

(23) WILSON, T. R. C, LUXFORD, R. F., and HARTLEY, C.

1941. EFFECT OF CERTAIN HEART ROT FUNGI ON THE SPECIFIC GRAVITY AND

STRENGTH OF SITKA SPRUCE AND DOUGLAS-FIR. JJ. S. Dept. Agr.

Tech. Bui. 779, 24 pp., illus.

(24) ST. GEORGE, R. A.

1943. PROTECTION OF LOG CABINS, RUSTIC WORK, AND UNSEASONED WOOD

FROM INJURIOUS INSECTS. U. S. Dept. Agr. Farmers' Bui. 1582,

19 pp., illus. (Rev.)

(25) SNYDER, T. E.

1926. PREVENTING DAMAGE BY LYCTUS POWDER POST BEETLES. U. S.

Dept. Agr. Farmers' Bui. 1477, 12 pp., illus.

1927. DEFECTS IN TIMBER CAUSED BY INSECTS. U. S. Dept. Agr. Bul.

1490, 46 pp., illus.

(26)

(27)

1950. CONTROL OF NONSUBTERRANEAN TERMITES. U. S. Dept. Agr.

Farmers' Bul. 2018, 16 pp., illus.

(28) TEESDALE, L. V.

1949. THERMAL INSULATION MADE OF WOOD-BASE MATERIALS, ITS APPLICATION AND USE IN HOUSES. U. S. Forest Prod. Lab. Rpt.

R1740, 40 pp., illus.

(29) U. S. DEPARTMENT OF AGRICULTURE.

1949. DAMAGE TO BUILDINGS BY SUBTERRANEAN TERMITES AND THEIR

CONTROL. U. S. Dept. Agr. Farmers' Bul. 1911, 38 pp., illus.

(Rev.)

(30)

1951. DECAY AND TERMITE DAMAGE IN HOUSES. L^. S. Dept. Agr. Farmers' Bul. 1993, 26 pp., illus. (Rev.)

(31) LT. S. FOREST PRODUCTS LABORATORY.

1945. WOOD: A MANUAL FOR ITS USE IN WOODEN VESSELS. 235 pp., illus.

(Issued bv Navy Bureau of Ships.)

(32) VERRALL, A. F.

1952. CONTROL OF WOOD DECAY IN BUILDINGS. Agr. Engin. 33 (4):

217-219, illus.

(33) and SCHEFFER, T. C.

1949. CONTROL OF STAIN, MOLD AND DECAY IN GREEN LUMBER AND OTHER

WOOD PRODUCTS. For. Prod. Res. Soc. Proc. 3: 9 pp., illus.
WOOD PRESERVATION

Wood can be protected from attack by decay funcri, harmful insects,

or marme borers by the application of selected chemicals, or wood

preservatives. The degree of protection obtained depends on the

kmd of preservative used and the thoroughness of the method of

appUcation. Some preservatives are moiT effective than others,

and some are more adaptable to certain use requirements. P'urthermore, the wood is well protected only when the preservative sul)-

stantially penetrates it, and some methods of treatment assure

better penetration than others. There is also a difference in the

treatability of various species of wood, particularly of their heartwood, which generally resists preservative treatment more than

sapwood {19)}^

Good wood preservatives, thoroughly applied w^ith standard retentions (see pp. 417-418) and with the wood satisfactorily penetrated,

substantially increase the life of wood structures, often as much as

five times {2Jf). On this basis the annual cost of treated wood in

service is greatly reduced below that of similar wood without treatment {16, 17). ^

WOOD PRESERVATIVES

Wood preservatives fall into two general classes: Oils, such as

creosote and petroleum solutions of pentachlorophenol; and waterborne salts that are applied as water solutions.

Preservative Oils

Preservative oils generally have high resistance to leaching and

are therefore suitable for outdoor exposures. They do not cause

the wood to swell, but some shrinkage may result if a loss of moisture

occurs in the wood during the treating process. Creosote and solutions with the heavier, less volatile petroleum oils often help protect

the wood from weathering but ma^^ adversely influence its cleanness,

odor, color, paintability, and combustibility. Preservative oils

sometimes travel from treated studs or subflooring along nails and

discolor adjacent plaster or finish flooring.

CoaUTar Creosote

Coal-tar creosote is a black or brownish oil made by distilHng coal

tar. The character of the tar used, the method of distillation, and

the temperature range in which the creosote fraction is collected all

influence the character of the creosote oil. The character of th(^

various coal-tar creosotes available, therefore, may vary to a considerable extent. Small dift'erences in character, however, do not

prevent creosotes from giving good service, and satisfactory results

in preventing decay may be expected, as a general rule, from any

26 Italic numbers in parentheses refer to Literature Cited, p. 427.

399
400 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

coal-tar creosote that complies with or closely approaches the requirements of standard specifications.

Coal-tar creosote is the most important and most generally useful

wood preservative {25). Its advantages are (1) its high toxicity to

wood-destroying organisms, (2) its relative insolubihty in water and

its low volatility, which impart to it a great degree of pernianence

under the most varied use conditions, (3) its ease of application, (4)

the ease with which its depth of penetration can be determined, (5)

its general availability and relatively low cost (when purchased in

wholesale quantities),'and (6) its long record of satisfactory use.

Although for general outdoor service in structural timbers and for

marine use there is, as yet, no better preservative than coal-tar

creosote, for some special purposes it has certain properties that are

disadvantages. Freshly creosoted timber can be ignited easily and

will burn readily, producing a dense smoke. After the timber has

seasoned some months, however, the more volatile parts of the oil

disappear from near the surface and the creosoted wood usually is but

little, if any, easier to ignite than untreated wood. Until this volatile oil has evaporated, ordinary precautions should be taken to

prevent fires. On the other hand, after untreated wood has started

to decay, often within a few years, it is easier to ignite than timber

that has been kept sound by creosote treatment. The only recommendation that can be made with respect to fire hazard is that sorne

preservative other than creosote should be used where this hazard is

considered of utmost importance, unless the treated wood is also

protected from fire.

The odor of creosoted wood is unpleasant to some persons. Foodstuffs that are sensitive to odors should not be stored where creosote

odors are present. Creosote vapors are harmful to growing plants.

Workmen sometimes object to the use of creosoted wood because it

soils their clothes and because it burns the skin of the face and hands

of some individuals, causing an injury similar to sunburn. There

need be no fear, however, that creosoted timber has a serious effect

on the health of workmen handling or working near it or on the health

of the occupants of buildings in which it is used. Creosoted wood can

very often be used in sills and foundation timbers and in floor sleepers

embedded in or resting on concrete with little danger of the odor

becoming objectionable.

The color of creosote and the fact that wood treated with it usually

cannot be painted satisfactorily make it unsuitable for finish lumber

or other lumber used where appearance and paint receptivity are of

major importance.

A number of specifications prepared by different organizations are

available for creosote oils of different kinds. Although the oil obtained imder most of these specifications will probably be sufficiently

effective in preventing decay, the requirements of some organizations are more exacting than others. Federal Specification TT-W00556b for coal-tar creosote, adopted for use by the U. S. Government,

will generally prove satisfactory and, under normal conditions, can

be met without difficulty by most creosote producers. The requirements of this specification are similar to those of the American WoodPreservers' Association Standard Pi for creosote (i), which is equally

acceptable.
WOOD HANDBOOK 4()1

Crystal-Free Coal-Tar Creosote

Crystal-free coal-tar creosote is creosote from which some of the

crystal-forming materials have been removed, so that the oil will flow

freely at ordinary temperatures and will not deposit crystals in its

container. Oils of this type are more convenient to handle than

ordinary creosotes, but their general properties and efi'ectiveness are

similar to those of the ordinary coal-tar creosote. They are intended

primarily for brush and spray applications. American WoodPreservers' Association Standard P7 (1) and Federal Specification

TT-W-560 cover crystal-free creosotes.

Anthracene Oils

Anthracene oils, sometimes referred to as carbolineums, are coaltar distillates of higher specific gravity and higher boiling range than

ordinary coal-tar creosotes, but their general properties and effectiveness as preservatives are similar to those of coal-tar creosotes. Highboiling distillates are advantageous to use in open-tank treatments

that involve heating, since losses through evaporation are likely to be

less than with low-boiling oils. Anthracene oils are usually sold

under proprietary or trade names and are covered b}^ American

Wood-Preservers' Association Standard P7 (1) and Federal Specification TT-W-531.

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 American Wood-Preservers' Association specifications. These include wood-tar creosote (table 45), 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

Tars

Coal tars are seldom used alone for preserving wood because good

penetration is usually difficult to obtain with them and because they

are less poisonous to wood-destroying fungi than the coal-tar creosotes.

Service tests have demonstrated that surface coatings of tar are of

little value. Coal tar has been used in the pressure treatment of

crossties, but satisfactory penetration of the wood is difficult to obtain with the highly viscose tar. When good absorptions and deep

penetrations are obtained, however, it is reasonable to expect a satisfactory degree of effectiveness from treatment with coal tar. The tar

is particularly effective in reducing checking in crossties in service.

Water-gas tar is used less extensively than coal tar, but, in certain

cases where the wood was thoroughly impregnated with it, the results

were good (table 45).
TABLE 45.—Condition of round southern yellow pine experimental fence posts on the Harrison Experimental Forest, Saucier, Miss., after about

llYi to 16 years of service

Preservative

Posts set late in 1936 to February 1937

Beta-napthol, 5 percent (by weight) in

oil mixture.

Borax-boric acid (50-50 mixture)

Celcure (acid cupric chromate)

Chromated zinc chloride.

Coaltar.-

Coal-tar creosote, grade 1

Coal-tar creosote, 50 percent; used crankcase oil, 50 percent (by volume).

Coal-tar creosote, 10 percent; used crankcase oil, 90 percent (by volume).

Crankcase oil (used)

Lignite coal-tar creosote

Mercuric chloride

No- D-K (hardwood-tar creosote)

Osmosar

P. D. A. (phenyldichlorarsine) 0.84 percent (by weight) in gas oil.

Pentachlorophenol, 4.82 percent (by

weight) in used crankcase oil.

Pentachlorophenol, 3.02 percent (by

weight) in used crankcase oil.

Sodium bichromate .

Sodium chromate

Posts

No.

100

100

96

94

Form of

preservativo

Solution. _

Salt

...do

-do

Oil

-do

Solution V

..do«

Oil 8

...do

Salt

Oil

Salt

Solution

-do

95 _._do

98 Salt90 I., do

Retention of preservative 2

Mininmm

LI), per

Cll.ft.

3.90

.64

.75

.37

1.60

1.90

1.60

2.50

1.10

.05

1.30

4.10

2.90

3.10

.59

.70

Maxinmm

Lh. per

cu.ff.

10.00

1.32

1.05

1.33

19.20

8.60

14.80

23.20

16. 80

11.60

.15

13. 00

11.00

9.50

11.40

i 1.14

Î. 19 I

Average

Standard deviation

Method

of

treatment

fj). per

cu.ff.

fji. per

Cll. ft.

6.20 1.30

.92 .11

.92 .08

.87 .19

6. 50 2.90

6.00 1.50

5.40 2.20

7.10 3.80

7.60 2.90

6. 30 3.20

.09 .03

6. 60 3.50

^30

5.90 .90

6.70 1.60

6.40 1.80

.88 .11

.93 .10

Pressure

do.

do.

do.

.do-

.do.

.do.

...do

-do

...do

Steei)ing.

Pressure _

Osmose..

Pressure.

...do

.--do

..do

--.do

Condition of posts December 1952

Serviceable

Pet,

19.4

7.2

90.4

74.2

90. 6

98.0

99.0

30.0

19.2

73.5

75.0

52.0

74.0

61.7

100.0

97.9

49.0

34.4

Removed on account ofDecay

Pet.

15.3

15.5

7.5

14.4

4.2

2.0

1.0

63.0

77.8

10.2

3.0

11.0

11.4

4.2

2.1

5.1

3.3

Decay

termites

Pet.

47.0

41.2

2.1

11.4

5.2

6.0

3.0

14.3

14.0

33.0

12.5

24.6

18.3

16.7

Termites

Pet.

18.3

36.1

1.0

2.0

8.0

4.0

2.1

9.6

27.6

45.6

Total removed

90

Pet.

80.6

92.8

9.6

25.8

9.4

2.0

1.0

7.0

80.8

26. 5

25. 0

48.0

26.0

38.3

2.1

51.0

65. 6

Average

life 3

O

to
Tanalith (Wolman Salts)

Tetrachlorophenol, 2.9 percent (by

weight) in used crankcase oil.

Tetrachlorophenol, 4.83 percent (by

weight) in used crankcase oil.

Water-gas tar

Zinc chloride

Zinc meta arsenite

Untreated posts (set Feb. 1937)

Posfft Sf't ill Î93S and 1941

Untreated i)osts (set Nov., Dec. 1938)

Copper sulfate and sodium arsenate (set

May 1941).

Osmoplastic ground-line treatment (set

Feb. 1941).

--.do .20 .47 .35 .07

Solution - 1.20 .10 7.10 3. 10

..do 3. 50 9.40 5.80 1.50

Oil 1.20 19.00 0. 30 3.00

Salt ,67 1.11 .94 .10

.- do .25 .54 .42 .06

Salt \ .35

I .16

Mixture.-- 8.34

.do.

..do.

.do.

do

do.

80. 4 12. 4

94.7 I 5.3

I

100.0

98.0

84.7

100. 0

None

Double 99.0

dillusion.

(«) 31.3

1.0

4.1

33. 3

1.0

1.0

11.2

93.8

63. 6

3.1

3.1

10.1 08

19.6

5.3

2.0

15.3

100.0

100. 0

1.0

<>8. 7

' Installation included 100 posts for each treatment. This number has since been reduced in some cases by fire ami pilferage.

2 Based on the 100 posts treated in each group, unless otherwise indicated.

3 Average life of all untreated posts is 3.3 years; other values are estimates taken from a mortality curve. Where percentage of posts removed is 10 percent or less,

average life is given.

< Retention values based on 97 posts.

* Retention values based on 89 posts.

Ö Retention values based on 99 posts.

' Average application.

« Average aiM»lication per i)ost to a 15-incli band (3 inches above and 12 inches below ground line) and to tO]) surface of i.tost.

23

3.1

no estiraato on

O

O

ö

>

ü

CO

o

o

5^

O

CO
404 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Creosote Solutions

For many years, either coal tar or petroleum oil has been mixed

with coal-tar creosote, in various proportions, as a means of lowering

preservative costs. These creosote solutions have a satisfactory

record of performance, mostly when used in the treatment of crossties.

Federal Specification TT-W-566a, ''Creosote-coal-tar Solution,''

places no limit on the quantities of coal-tar creosote and coal tar present in the solution, but the solution must meet definite requirements

as to physical and chemical composition. American Wood-Preservers' Association Standard P2 (1) includes 4 creosote-coal-tar solutions

that must contain, respectively, not less than 80, 70, 60, or 50 percent

by volume of coal-tar distillate and must also meet requirements as to

physical and chemical properties. Federal Specification TT-W-568

and American Wood-Preservers' Association Standard P3 (1) stipulate that creosote-petroleum oil solutions shall contain not less than

50 percent by volume of coal-tar creosote.

Creosote solutions not only cost less than straight creosote but also

tend to reduce weathering and checking of the treated wood. The

solutions may have a greater tendency to accumulate on the surface

of the treated wood (bleed) and may penetrate the wood with greater

difficulty, particularly since they generally are more viscous than

straight creosote. Higher temperatures and pressures during treatment, when they can safely be used, will often improve penetration of

solutions of high viscosity.

Since petroleum oil and coal tar are less toxic to wood-destroying

organisms than straight creosote, their mixtures with creosote are

also less toxic. The toxicity of a creosote-petroleum oil solutiou,

compared to that of straight creosote, is generally less, proportionately,

than the percentage of creosote in the solution. Creosotes of high

toxicity are therefore considered desirable for use in creosote-petroleum

solutions. Some preservative users, particularly in pole treatment,

fortify the petroleum oils in creosote solutions with such toxic materials as pentachlorophenol and copper naphthenate to increase the

preservative effectiveness of the solution.

Creosote-petroleum solutions with favorable performance records

generally contain petroleum oils of the comparatively heavy, highboiling, high-viscosity residuum types, such as covered by American

Wood-Preservers' Association Standard P4 (1). The protective

qualities of solutions containing lighter, distillate fuel oils have not

been adequately demonstrated.

Pentachlorophenol Solutions and Copper Naphthenate

Solutions

The use of petroleum oils fortified with chlorinated phenols, principally pentachlorophenol, or with copper naphthenate \l3,22) as wood

preservatives became large scale following World War II, because of

the shortage of coal-tar creosote. These preservatives were first

used prirnarily for surface applications. The chlorinated phenols in

volatile light-colored solvents, such as mineral spirits, were first used

for window sash and millwork that requfi-ed a clean, nonswelling, and
WOOD HANDBOOK 405

paintable treatment. Commercial treatment of poles and lumber

with pentachlorophenol solutions began in 1941.

The petroleum oil used in these solutions varies from the diesel-oil

type to the heavier types ordinarily used in creosote-petroleum solutions. American Wood-Preservers^ Association Standard P9 (/)

covers petroleum oils for use in pentachlorophenol or copper naphthenate solutions.

Federal Specification TT-W-571c covers the treatment of wood

with solutions of pentachlorophenol; other large-scale users, such as

telephone companies and the Rural Electrification Administration,

also have specifications covering the formulation and use of these

solutions. Federal Specification TT-W-570 covers pentachlorophenol, and the American Wood-Preservers' Association Standard P8

(1) covers both pentachlorophenol and copper naphthenate,

Pentachlorophenol solutions for wood preservation generally contain 5 percent of this chemical; copper naphthenate solutions have a

copper metal concentration varying from 0.5 to 3.0 percent for

different use requirements. The performance of these preservatives

is influenced by the character of the petroleum oil in the treating

solution, and experience to date indicates that best results are obtained

with fairly heavy oils of low volatility. Petroleum oils that remain

in the wood in substantial quantities after treatment, however, are

likely to interfere with painting.

Service and field tests on wood treated with petroleum oils containing 5 percent of pentachlorophenol or copper naphthenate equivalent

to 0.5 percent or more of copper metal show that these preservatives

provide a high degree of protection against decay fungi and termites

when the wood is properly treated. It is too early to predict their

utlimate protective properties in comparison with coal-tar creosote.

They are known, however, to provide much less protection than

creosote against marine borers.

Pentachlorophenol does not appreciably alter the natural color of

the wood, but copper naphthenate gives it a green color. The properties of the wood treated with petroleum oils containing these preservatives, with respect to cleanness, paintability, color, odor, and

combustibility, depend largely upon the properties of the petroleum

oil used. Pentachlorophenol in the dry form and in solutions irritates

the skin of workers, but with careful handling and the use of suitable

protective clothing it is possible to avoid harmful effects. The use

of ^'bloom'' preventives, such as ester gun, is required in pentachlorophenol solutions with volatile solvents to prevent the formation of

crystals of the preservative on the surface of the wood after treatment.

Water-Repellent Preservatives

Preservative oils containing water-repellent components are sold

under various trade names, principally for the treatment of window

sash and other millwork. Federal Specification TT-W-572 stipulates

that such preservatives consist of volatile solvents, such as mineral

spirits, that do not cause appreciable swellmg of the wood and not

less than 10 percent or more than 25 percent of nonvolatile matter,

including the preservative and water-repellent components. The
406 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

preservative chemicals may be not less than 5 percent of pentachlorophenol or not less than 2 percent of copper in the form of copper

naphthenate.

Effective water-repellent preservatives retard moisture changes m

the wood but do not prevent them. They therefore help reduce

dimensional changes in the wood due to moisture changes when the

wood is exposed to rainwater or dampness for short periods but not

when it is in contact with the ground or other sources of prolonged

dampness. As with any wood preservative, their effectiveness in

protecting wood against decay and insects depends upon the thoroughness of the method of application.

Waterborne Preservatives

Standard wood preservatives used in water solution include zinc

chloride, chromated zinc chloride, copperized cln'omated zinc chloride,

Tanalith (AVolman Salts), acid copper chromate (Celcure), zinc meta

arsenite, ammoniacal copper arsenite (Chemonite), chromated zinc

arsenate (Boliden salt), and ckromated copper arsenate (Greensalt

or Erdalith). These preservatives are employed principally in the

treatment of wood for uses where it will not be in contact with the

ground or water and where the treated wood requires painting. As a

general rule, they are less resistant to leaching and do not perform so

satisfactorily as the preservative oils under conditions favorable to

leaching. The leaching resistance of some of these preservatives has

been developed to the extent that good performance can be expected

in ground contact or in other wet installations, but they are still not

considered equal in effectiveness to creosote when used under such

conditions. On the other hand, waterborne preservatives are generally

preferable to creosote for indoor use and can give indefinitely long

life where not subject to leaching.

Waterborne preseiwatives leave the wood surface comparatively

clean, paintable, and free from objectionable odor. With several

exceptions, they must be used at low treating temperatures (100° to

160° F.) because of their instability at the higher temperatures common with preservative oils. This may involve some difficulty when

higher temperatures are needed to obtain good treating results in such

woods as Douglas-fir. Since water is added during treatment, the

wood must be dried after treatment to the moisture content required

for use.

Zinc chloride and chromated zinc chloride are frequently used as fire

retardants for wood but at retentions higher than those used onl}^ for

wood-preserving purposes.

Zinc Chloride and Its Improved Forms

Zinc chloride and chromated zinc chloride are covered in Federal

Specifications TT-W-576a and TT-W-551, respectively, and in

American Wood-Preservers' Association Standard P5 (1). Copperized

chromated zinc chloride and chromated zinc chloride (FR)^^ are

included in American Wood-Preservers' Association Standards P5

-^ (FR) for fire retardant.

:aLiS
WOOD HANDBOOK 407

and PlO (1), respectively. Copperized chromated zinc chloride is

covered by Interim Federal Specification No. TT-W-00562.

Until 1938, zinc chloride was the most extensivel}^ used waterbornc

preservative in the United States. Its principal advantages are its

low cost, cleanness, and lack of fire hazard. Zinc chloride solutions

were at one time mixed with creosote for the treatment of crossties

and construction timbers, but this use has been discontinued because

the zinc chloride does not give so satisfactory performance as some of

the other extenders for creosote already mentioned. Since 1938,

zinc chloride has been gradually displaced by other waterborne preservatives.

Chromated zinc chloride was developed and promoted about 1934.

The specifications require that it contain not less than 77.5 percent of

zinc chloride and not less than 17.5 percent of sodium dichromate

dihydrate. The claim that chromated zinc chloride has greater

resistance to leaching than plain zinc chloride is supported by the

results of some field tests but not b}^ others.

More recently developed forms of chromated zinc chloride are

copperized chromated zinc chloride (14) and chromated zinc chloride

(FR) (S). Copperized chromated zinc chloride contains approximately 73 percent of zinc chloride, 20 percent of sodium dichromate,

and 7 percent of cupric chloride. This preseiwative has been in commercial use for a limited time, but in laborator}^ and accelerated field

tests it has shown better permanence than chromated zinc chloride.

These tests indicate that the two preservatives compare favorably in

other properties. Chromated zinc chloride (FR) contains 80 percent

of chromated zinc chloride, 10 percent of boric acid, and 10 percent of

ammonium sulfate. Retentions of from 1}^ to 3 pounds per cubic foot

of wood provide combined protection from fire, decay, and insect

attack.

Tatialith (Wolman Salts)

Tanalith (Wolman Salts) is covered by U. S. Patent No. 1,957,873

(1934). Its approximate composition, according to Federal Specification TT-W-573 and American Wood-Preservers' Association Standard

P5 (i), is 25 percent of sodium fluoride, 25 percent of disodium hydrogen arsenate, 37.5 percent of sodium chromate, and 12.5 percent of

dinitrophenol. Service records on various types of above-ground

wood structures treated with this preserv^ative show good performance.

Acid Copper Chromate (Celcure)

Acid copper chromate (Celcure) is covered by U. S. Patents Nos.

1,684,222 (1926) and 2,041,655 (1936). It contains, according to

Federal Specification TT-W-546, approximately equal quantities of

copper sulfate and sodium dichromate and a sufficient quantity of free

acetic acid or chromic acid to maintain the preservatives in solution

under operating conditions. Tests on stakes and posts exposed to

decay and termite attack indicate that wood well impregnated with

Celcure gives good service. Tests by the Forest Products Laboratory

and the U. S. Navy showed that wood thoroughly impregnated with

at least 1 pound of Celcure per cubic foot has some resistance to

marine borer attack. The protection against marine borers furnished
408 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

by this preservative, however, is much less than that provided by a

standard treatment with creosote.

Zinc Meta Arsenite (ZMA)

Zinc meta arsenite is covered by U. S. Patents Nos. 1,659,135 (1928)

and 1,984,254 (1934). Federal Specification TT-W-581 and American

Wood-Preservers' Association Standard P5 (1) require that the zinc

meta arsenite in treating solutions be composed approximately of 60

parts of arsenious acid and 40 parts of zinc oxide, with sufficient acetic

acid to keep the preservative in solution under operating conditions.

Zinc meta arsenite has been in limited use for nearly 25 years. Service

records on treated crossties, poles, and posts show that it provides

good protection.

Ammoniacal Copper Arsenite (Chemonite)

Ammoniacal copper arsenite (Chemonite), which was developed

about 1925, is covered by U. S. Patent No. 2,149,284 (1939) and has

been in commercial use for about 14 years. According to Interim

Federal Specification No. TT-W-00549b, Chemonite should contain

approximately 57.7 percent of copper hydroxide, 40.7 percent of

arsenic trioxide, and 1.6 percent of acetic acid. These ingredients

should be dissolved in a solution of ammonia and water with the

weight of the ammonia not less than 1.5 times nor more than 2.0

times the weight of the copper hydroxide in the final solution. The

solution strength is adjusted as necessary according to the retention

of dry chemicals desired in the treated wood. The net retention of

preservative is calculated as pounds of copper hydroxide plus arsenic

trioxide per cubic foot of wood treated within the proportions as

limited in the specification.

Service records on Chemonite-treated structures show that this

preservative provides good protection against decay and termites (8).

Chemonite adds somewhat to the life of wood exposed to attack by

marine borers, but it cannot be recommended as a substitute for

creosote when long service is required or when the treated structure

is to be used in heavily infested waters.

Chromated Copper Arsenate (Greensalt or Erdalith)

Chromated copper arsenate (Greensalt or Erdalith) was developed

in India under the name of Ascu and is covered by U. S. Patent No.

2,106,978 (1S38) (8). It has been used in the United States since

1938 to a limited extent for the treatmenc of poles, posts, and lumber. A standard of the American Wood-Preservers' Association stipulates that Greensalt contain 56 percent of potassium dichromate, 33

percent of copper sulfate, and 11 percent of arsenic pentoxide. Service data, on poles, posts, and stakes treated with this preservative

and installed in the United States, show good protection against

decay and termites over a period of 12 years or less. Favorable

records for a somewhat longer period are available outside the

United States.
WOOD HANDBOOK 409

Chromated Zinc Arsenate (Boliden Salt)

Chromated zinc arsenate (Boliden salt) was developed in Sweden

and has been used there since 1936 for the commercial treatment of

various wood products (8). It has been used commercially in the

United States since 1951 and is covered by U. S. Patent No. 2,139,747

(1938) Interim Federal Specification Ño. TT-W-00538 stipulates

that chromated zinc arsenate contain approximately 20 percent of

arsenic acid, 21 percent of sodium arsenate, 16 percent of sodium

dichromate, and 43 percent of zinc sulfate (30), Test data on stakes

installed in Sweden in 1936, in South Africa in 1937, and in the

United States and Panama Canal Zone in 1940 show that chromated

zinc arsenate, in retentions of 0.33 pound (anhydrous basis) per

cubic foot or higher, provides good protection against decay and

against termites (4, 8).

PRESERVATIVE EFFECTIVENESS

Results of service tests on various treated products showing the

effectiveness of different wood preservatives are published in the

annual Proceedings of the American Wood-Preservers' Association.

There are few service tests, however, that include a variety of preservatives under comparative conditions of exposure. Some Forest Products Laboratory stake tests (4) show such comparative data under

similar exposure conditions, and table 45 shows comparative data on

test posts treated with a number of preservatives in general use, as

well as several in less extensive use.

PREPARING TIMBER FOR TREATMENT

For satisfactory treatment and good performance thereafter, the

timber must be sound and suitably prepared for treatment. Except

in a few specialized treating methods involving unpeeled or green

material, the timber should be well peeled and either seasoned or

otherwise conditioned before treatment. It is also highly desirable

that all machining of timber be completed before treatment. Machining may include incising to improve the preservative penetration in

woods that are resistant to treatment, cutting, framing, or boring

of holes.

Peeling

Peeling round or slabbed timber is necessary to enable it to season

quickly enough to avoid decay and insect damage and to permit the

preservative to penetrate satisfactorily.^^ Strips of even 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 timber. Careful peehng

is especially important for wood that is to be treated by a superficial

method. In the more thorough processes some penetration will take

28 Processes in which a preservative is forced or diffuses through green wood

lengthwise do not require peeling of the timber.
410 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

place both leno:tliwise and tangentially in the wood, and consequently

small strips of bark are not quite so harmful. Machines of various

types have been developed for peeling round timbers, such as poles.

pilino;, and posts (10).

Seasoning

For treatment with waterborne preservatives by certain diffusion

methods, the wood should be as green and as full of water as possible.

For treatment by other methods, however, and particularly for treatment with preservative oils, seasoning before treatment is desirable.

Plants treating timber by pressure processes can condition green

timber by other means than air-drying to make it more absorptive

and thus avoid a long delay and possible deterioration of the timber

before treatment. Nevertheless, air-drying, despite the greater time,

labor, and storage space required, is a widely used method of conditioning and is generally the cheapest and most effective, even for

pressure treatment. Kiln-drying is often used for the seasoning of

lamber before treatment and has been used experimentally as a means

of seasoning poles (16, 21).

How long the lumber must be air-dried depends on the chmate,

location, and condition of the seasoning yard, methods of pihng, season

of the year, and size, species, and character of the timbers (16). It

is not uncommon in commercial practice to air-dry railway ties and

larger timbers for 8 to 12 months if conditions permit the timber to

be kept that long mthout deterioration, but the desirability of so long

a drying period is not fully established. A great deal can be accomplished even with large pieces in 3 to 6 months of good seasoning

weather. Small pieces season more quickly than large pieces and sapwood more quicldy than heartwood. The most satisfactory seasoning

practice for any specific case mil depend on the individual drying

conditions and the preservative treatment to be used and must be

determined by experience. Treating specifications therefore are not

generally specific as to moisture content requirements.

It is not necessary that the timber be seasoned to a uniform moisture

content throughout, but the part that is to be penetrated by the

preservative must have enough water removed to make room for the

preservative to enter. It is also important that the timbers be seasoned suflñciently, so that any checking that may occur subsequent

to treatment wll not expose unpenetrated wood.

Hardwood ties and timbers tend to check and split seriously during

air-drying. These defects can be reduced by careful piling to avoid

rapid drying and by appl^nng antichecking irons or dowels before

seasoning. Split ties are also salvaged by pressing the split ends together in a hydraulic jack and holding them with bolts or spiral

dowels (16).

To prevent decay and other forms of fungus infection during airdrying, the timbers should be cut and seasoned when conditions are

less favorable for fungus development (see p. 381). If this is impossible,

chances for infection can be minimized by prompt conditioning of the

green timbers (see p. 414), careful piling and roofing during air-drying,

and pretreatment of green timber with preservatives that will protect

the timber during air-drying (20).
WOOD HANDBOOK 411

Incising

^ Wood that is resistant to penetration by preservatives is often incised (fig. 87) before treatment to permit deeper and more uniform

penetration. To accomplish this, sawed or hewed timber is passed

through a machine having horizontal and vertical rollers equipped

with teeth that sink into the wood to a predetermined depth, usually

% to % inch. ^ The teeth are spaced so as to give the desired distribution

of preservative with the minimum number of incisions. A machine

of different design is required for incising the butts of poles. The

effectiveness of incising depends on the fact that preservatives usually

penetrate into wood much farther in a longitudinal direction than in

a direction perpendicular to the faces of the timber. The incisions

expose end-grain surfaces and thus permit longitudinal penetration.

Incising is practiced chiefly on Douglas-fir, western hemlock, and

western larch ties and timbers for pressure treatment and on poles

of cedar and other species. Itis especially effective in improving penetration in the heartwood areas of sawed or hewed surfaces.

Cutting and Framing

All cutting, framing, and boring of holes should be done befoi'e

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. It is much more practical

than is commonly supposed to design wood structures so that all

cutting and framing may be done before treatment. Railroads are

are now following the practice extensively and find it not only practical

but economical {26). 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 the framing of material for bridges

and for many specialized structures, such as water tanks and barges.

Treatment of the wood with preservative oils involves little or no

dimensional change. In the case of treatment with waterborne preservatives, however, some change in the size and shape may occur

even though wood is reseasoned to its original moisture content. If

precision fitting is necessary, the wood is cut and framed before treatment to its approximate final dimensions in order 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, although this is not always necessary.

APPLYING PRESERVATIVES

Wood-preserving methods are of two general types: (1) Pressure

processes, in which the wood is impregnated in closed vessels under

pressures considerably above atmospheric pressure, and (2) nonpressure processes, which vary widely as to procedures and equipment used. Pressure processes generally provide a closer control

over preservative retentions and penetrations, and to this extent they

usually provide greater protection than nonpressure processes.

Some of the nonpressure methods, however, are better than others

and are occasionally as effective as pressure processes in providing

good preservative retentions and penetrations.

303747°—5i5 27
412 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTUHE

FIGURE 87.—Pneumaticalh' controlled timber incisor with large-size timber

leaving machine.

PRESSURE PROCESS

In commercial practice, wood is most often treated by surrounding

it with preservative in high-pressure apparatus and applying pressure

to the preservative (25). A number of pressure processes {1, 16, 19)

differ from one another in a few details, but the general principle is

the same in all. The wood, placed on steel cars, is run into a long

steel cylinder (fig. 88), which is then closed and filled with preservative. Pressure then forces preservative into the wood until it has

absorbed the desired amount. A considerable amount of preservative is absorbed resulting in a relatively deep penetration. Two principal types of pressure treatment, the full-cell or Bethell process and

the empty-cell process, are in common use.

Full-Cell Process

The full-cell process is used when the retention of a maximum

quantity of preservative is desired. For timbers to be treated with

creosote and exposed to marine borers it is standard. Water-borne

preservatives are generally applied by the full-cell process, and

control over preservative retention is obtained by regulating the
WOOD HANDBOOK 413

M 92948 F

FIGURE 88.- -Exterior view of treating cylinders at wood-preserving plant under

construction.

concentration of the treating solution. The steps in this process arc

essentially as follows:

1. The charge of timber is sealed in the treating cylinder, and a

preliminary vacuum is applied for Yi hour or more to remove the air

from the cylinder and as much as possible from the wood.

2. The preservative, previously heated to somewhat above the

desired treating temperature, is admitted to the cylinder without

the admission of air.

3. After the cylinder is filled, pressin-c is applied until the required

retention of oil is obtained.

4. When the pressure period is completed, the preservative is

withdrawn from the cylinder.

5. A short final vacuum may be applied immediately afterward to

free the charge from dripping preservative.

When the timber 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.

Empty-Cell Process

The object of empty-cell treatment is to obtain deep penetration

with a relatively low net retention of preservative. For treatment

with oil preservatives, the empty-cell process shoidd always be used

if it will result in the desired retention. Two empty-cell treatments,
414 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

the Rueping and the Lowry processes, are commonly employed, both

of which use the expansive force of compressed air to drive out part

of the preservative absorbed during the pressure period.

The Rueping empty-cell process has been widely used for many

years, in both 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 timber. The air penetrates some species easily,

requiring but a few minutes' application of pressure. In the treatment

of the more resistant species, common practice is to maintain air

pressure from % to 1 hour before admitting the preservative, but the

necessity for long air-pressure periods doe¿ not seem fully established.

The air pressures employed generally range between 25 and 100

pounds per square inch, depending on the net retention of preservative desired and the resistance of the wood.

2. Following the application of preliminary air pressure, the preservative is forced into the cylinder. During the filling process the air

in the treating cylinder interchanges with preservative at the same

pressure in an equalizing or Rueping tank, or it is gradually allowed

to escape from the treating cylinder as the preservative is pumped

in, at a rate that keeps the pressure within the cylinder constant.

When the treating cylinder is filled with preservative, the treating

pressure is raised above that of the initial air and is maintained until

the point of refusal is reached, or until the gross absorption is sufficient to leave the required net retention of preservative in the wood

after the completion of the treatment.

3. At the end of the pressure period the preservative is drained

from the C3dinder, and a final vacuum removes the surplus preservative from the wood. The amount recovered may be from 20 to 60

percent of the gross amount injected.

The Lowry process is often called the empt3^-cell process mthout

initial air. The chief difference between it and the Rueping process,

which employs initial air pressures above atmospheric, is that in the

Lowr}^ process the preservative is admitted to the cylinder mthout

either an initial air pressure or a vacuum, and the air originally in the

wood at atmosphere 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 the equipment for the

full-cell process can be used without other accessories, while the

Rueping process usually requires additional equipment^ such as an

air compressor and an extra cylinder or Rueping tank for the preservative or a suitable pump to force the preservative into the cylinder

against the air pressure. Both processes, however, have advantages,

and both are widely and successfully used.

Conditioning Green Timber for Pressure Treatment

When green timber is to be treated under pressure (19), either of

two commonly used methods for conditioning may be selected. One

is the steaming-and-vacuum process, which is employed mainly for
WOOD HANDBOOK 415

southern yellow pine, and the other is the Boulton or boihno:-iindcrvacuum process, which is used for Douglas-fir and to some extent for

hardwoods. In the steaming process the green timber is steamed hi

the treatmg cylinder for several hours, usually at 20 pounds gage

pressure (259° F,), and when the 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,

and the subsequent vacuum lowers the boiling point so much that

part of the water is evaporated or is forced out of the wood by the

steam produced when the vacuum is applied. The steaming and

vacuum periods employed depend upon the size, species, and moisture

content of the wood. The steaming method usually reduces the

moisture content of green wood somewhat, and the heating assists

greatly in getting the preservative to penetrate, but it does not dry

the wood to the ''seasoned'' condition. If the steaming period is

sufficient, it will also sterilize the wood.

In the Boulton or boiling-under-vacuum method of partial seasoning, the timber is heated in the preservative oil under vacuum, usually at temperatures of about 180"^ to 220° F. 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, however, usually

removes only a very limited amount of moisture from the heartwood.

A third method of conditioning known as ''vapor drying" {15) has

been patented and has recently come into commercial use for the

seasoning of railroad ties, poles, and other products. The green wood

is seasoned by subjecting it in the treating cylinder to the vapors pi'oduced by boiling an organic chemical, such as xylene, and removing

the mixed vapors of water and the chemical from the drying chamber.

A small quantity of the chemical remains in the wood, but the balance

is recovered and reused. The wood is treated by standard pressure

methods after the seasoning is completed.

TREATING CONDITIONS AND SPECIFICATIONS

Specifications on the treatment of various wood products by

pressure processes and on the hot-and-cold-bath treatment of cedar

poles have been developed by the American Wood-Preservers' Association {1). These specifications limit pressures, temperatures, and

time during conditioning and treatment in order to avoid conditions

that will cause serious injury to the wood. They also contain minimum

requirements as to preservative retensions and penetrations and

recommendations for handling wood after treatment, as means of

providing a quality product. The specifications are rather broad in

some respects, allowing the purchaser some latitude in specifying the

details of his individual requirements. The purchaser should exercise

great care, however, to avoid limiting the operator of the treating

plant so closely that he cannot do a good treating job, and to avoid

requiring treating conditions so severe that they will damage the

wood. Federal Specification TT-W-571 {27) recommends treatment

practices for use on U. S. Government orders for pr(^ssure-treated

wood products; other purchasers have specifications similar to those

of the American Wood-Preservers' Association.
416 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Treating Pressures and Preservative Temperatures

The pressures used in the full-cell and Lowry (empty-cell) treatments vary from about 100 to 200 pounds per square inch, depending

on the species and the ease with which the wood takes the treatment,

but are most commonly about 150 to 175 pounds per square inch.

Pressures applied in the Rueping (empty-cell) treatment are usually

between 150 and 200 pounds per square inch; depending more or less on

the preliminary air pressure employed. Many woods are sensitive to

high treating pressures, especially when hot. American WoodPreservers' Association Standards (1), for example, permit a maximum

pressure of 150 pounds per square inch in the treatment of Douglas-fir

and 125 pounds per square inch for western redcedar poles. In commercial practice even lower pressures are frequently used on such

woods.

Specifications of the American Wood-Preservers' Association

commonly require that the temperature of preservative oils during

the pressure period shall not be more than 210° F. and shall average

at least 180° F. Since high temperatures are much more effective

than low temperatures for treating resistant wood, better results are

obtained by using average temperatures between 190° and 200° F.

with both preservative oils and water solutions that are not injured

by high temperatures. With a number of waterborne preservatives,

however, especially those containing chromium salts, maximum

temperatures are hmited to 160° F. or less to avoid partial precipitation of the preservative.

Preservative Retention and Penetration

Preservative retentions are generally specified in terms of the

weight of preservative per cubic foot of wood treated, based on total

weight of preservative retained and the total volume of wood treated

in a charge. Some specifications, however, stipulate a minimum

retention of preservative as determined from chemical analysis of

borings from the treated wood (9).

The preservatives and minimum retentions recommended for

various products in Federal Specification TT-W-571 (28) are shown

in tables 46, 47, and 48. Since the figures given in tables 46, 47, and

48 are minirnum retentions, it may often be desirable to use retentions

somewhat higher. For lumber of small sizes, retentions should be

higher than those for larger timbers in order to compensate for the

increased surface area per unit volume (18). It is customary to

increase retentions of waterborne preservatives about 50 percent

when the treated wood is used under moist conditions that may

result in leaching of the preservatives.

Somewhat higher retentions of preservative oils are justified in

products to be installed under severe climatic or exposure conditions.

Heavy-duty poles and other items with a high replacement cost are

also often treated with higher than the minimum retentions. It may

be necessary to increase retentions in order to assure 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
WOOD HANDBOOK 417

TABLE 46.—Recommended minimum net retentions of creosote and solutions containing creosote for various wood products '

Product and service condition Coal-tar

creosote

Creosote-coaltar solutions

Creosote-petrolouiii oil

solution

Ties (crossties, switch ties, and bridge ties)

LI), per at. ft.

8

14

2 20

10

6

14

2 20

12

8

6

Lh. per cu.ff.

8

14

2 20

10

0

14

2 20

12

Lb. per en. ft.

9

Lumber and structural timbers:

For use in coastal waters:

Douglas-fir (coast type)

Southern yellow pine.

For use in fresh W;ater, in contact with ground, or for important structural members not in contact with ground

or water 12

For other use not in contact with ground or water . ^

Piles:

For use in coastal waters:

Douglas-fir (coast type)

7

Southern yellow pine

For land or fresh-water use 14

Poles .. - --_..._ ...

Posts - .... 6 7

1 As stipulated in Federal Specification TT-W-571. Requirements of American Wood-Preservers'

Association standards as to penetrations and treating conditions are to be followed with minor exceptions

noted.

2 The greater retention specified for southern yellow pine is due to the fact that this species has thicker

sapwood and it is thus easier to get a heavier retention than with Douglas-fir.

TABLE 47.— Recoynmended minimum net retentions of oilborne preservatives for

various wood products '

Product and service condition

Lumber and structural timber:

For use in contact with ground

For use not in contact with ground or water

Poles

Posts

Pentacnlorophenol, 5 percent in petroleum oil

Lb. per cu.ft.

10

6

Copper naphthenate (0.75

percent copper

metal) in petroleum oil

Lb. per cu.ft.

10

6

1 As stipulated in Federal Specification TT-W-571. Requirements of American Wood-Preservers'

Association standards as to penetrations and treating conditions are to be followed with minor exceptions

noted.

retentions lower than the stipulated minimum. Treatment to refusal

is usually required for woods that are resistant to treatment and will

not absorb sufficient preservative to meet the mhiimum retention

requirements.

Penetrations 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; the red heartwood of beech and the heartwood of white oak and Rocky-Mountain-type Douglas-fir, for

example, are exceptionally resistant to penetration by commercial

treating processes, even when incised. Penetrations in unincised
418 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLE 48.—Recovimended minivium net retenliojis of waierborne preservatives for

various wood products '

Product and service condition

Cel cure

(acid cupric chromate)

Lb. per

cu.ft.

0.75

.50

.75

Chemonite (ammoniacal

copper

arsenite)

Chromated

zinc

chloride

Tanalith

Boliden

salt (chromated

zinc

arsenate)

Lb. per

cu.ft.

1.00

.50

1.00

CopperIzed chromated

zinc

chloride

Lumber and structural timber:

For use under moderate leaching conditions

For use not in contact with ground or

water

Posts - - -

Lb. per

cu.ft.

0.50

.30

.50

Lb. per

cu.ft.

1.15

.75

1.15

Lb. per

cu.ft.

0.55

.35

.55

Lb. per

cu. ft.

1.15

.75

1.15

1 As stipulated in Federal Specification TT-W-571. Rerjuirements of American Wood-Preservers'

Association standards as to penetrations and treating conditions are to be followed.

heart faces of these species may occasionally be as deep as }i inch, but

usually are less and often are not more than Ke inch. Long experience has shown that even these slight penetrations have value,

although deeper penetrations are highly desirable. The heartwood

of coast-type Douglas-fir, southern yellow pine, and various hardw^oods, wdiile highly resistant, can be made to take transverse penetrations of K to K inch on the average and sometimes considerably

more. Incising is beneficial for many resistant species. The white

heartwood of beech and the heartwood of the red oaks, black túpelo,

and ponderosa pine can usually be penetrated without difficulty.

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 piling, ties, and structural timbers.

Practically, however, the operator cannot always insure complete

penetration of sapw^ood in every piece when treating large pieces of

round material having thick sapwood, for example, poles and piling.

Specifications therefore permit some tolerance, as in American WoodPreservers' Association Standard C4 (1) on southern yellow pine

poles, which, for a retention of creosote of 8 pounds per cubic foot,

requires that 2.5 inches or 85 percent of the sapwood thickness be

penetrated in not less than 18 out of 20 poles sampled in a charge.

The requirements vary somewhat depending on the species and

specified retentions.

HANDLING AND SEASONING OF TIMBER AFTER

TREATMENT

Treated timber should be handled with sufficient care to avoid

breaking through the treated part. 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 sawed timber in

rope or cable slings may crush the corners or edges of the outside

pieces. Breakage or deep abrasions may also result from throwing

the lumber or dropping it any considerable distance. When damage

results through carelessness or otherwise, the exposed places should
WOOD HANDBOOK 419

be re-treated as thoroughly as conditions permit. Treated wood

that must be stored before use should be protected in order to avoid

checking or mechanical injury.

Although cutting wood after treatment is highly undesirable, it

cannot always be avoided. When cutting is necessary, the damage

may be partly overcome in timber for land or fresh-water use by

thoroughly brushing the cut surfaces with coal-tar creosote. Two

coats of hot creosote should be applied if practicable, but cold

application will be better than none. Brush-coating cut surfaces,

however, gives little protection against marine borers. A special

device is available for applying pressure treatment to bolt holes

bored after treatment. For wood treated with water-soluble preservatives, where the use of creosote on the cut surfaces is not practicable,

a strong solution of the preservative in use may be substituted.

For treating the end surfaces of piles where they are cut off after

driving, at least two generous coats of creosote should be applied with

great care and thoroughness. A coat of asphalt or similar material

may well be 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 top treatment and the entrance of storm water.

American Wood-Preservers' Association Standard M4-52 (1) contains

instructions for the care of pressure-treated wood after treatment.

Timber treated with creosote and other oils may be used immediately after treatment, if desired, but a period of seasoning may help

dry the oily surfaces and make the timber less unpleasant to handle.

The removal of petroleum-oil solvents is particularly important in the

case of wood that requires painting after treatment with oilborne

preservatives, such as pentachlorophenol.

With waterborne preservatives, seasoning after treatment is important for the timbers that are to be used in buildings or in any other

place where shrinkage after placement in the structure would be

undesirable. Injecting waterborne preservatives puts large amounts

of water into the wood, and considerable shrinkage 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.

With some waterborne preservatives, seasoning after treatment is

recommended for all treated timber in order to complete the chemical

reactions that are intended to take place within the wood and, thus,

to increase the resistance of the preservative to leaching by water.

INSPECTION

Inspection of timber for quality and grade before treatment is

desirable. Grade-marked lumber and timber can be specified and

obtained in many instances. Such material is graded at the mills

and is usually dependable without additional inspection. When

inspection previous to treatment is impractical, the purchaser can

usually inspect for quality and grade after treatment; if this is to be

done, however, it should be made clear in the purchase order.
420 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Currently, there are no generally accepted procedures for accurately

(leterniiiiing retention of various preservatives, other than measurement of quantity of preservative used in treatment. As previously

mentioned, some specifications (9) provide for a determination of

minimum retentions by chemical analysis of borings from the treated

wood, but such sampling and analysis have not been used to determine

the overall retention of a charge, as it is commonly specified. Furthermore, the nature and quantity of the preservative in the wood change

as the period of service increases, so that samples of treated wood

taken sometime after treatment may not be representative of those

taken when the treatment was completed. The purchaser, therefore,

must either accept the statements or affidavit of the treating-plant

operator or have an inspector at the treating plant to observe the

treatments and insure compliance with the specifications. Railroad

companies and other corporations that purchase large quantities of

treated timber usually maintain their own inspection services. Commercial inspection and consulting service is available for purchasers

willing to pay an inspection fee but not using enough treated tinber

to justify employing inspectors of their own. Care should be taken

to choose experienced, competent, and reliable inspectors, since

premature failures of treated structures can often be attributed to

faulty inspection.

Penetration measurements should be made at the treating plant

if inspection service is provided but can be made by the purchaser

at any time after the timber has been treated. They give about the

best single measure of the thoroughness of the treatment. Rejection

of treated timber for insuflfiicient penetration is hardly enforceable,

however, unless there was a previous agreement with the plant

operator on minimum penetration requirements.

The depth of penetration of creosote and other dark-colored

preservatives can be determined directly by observing a boring

removed by an increment borer. The boring should usually be taken

at about midlength of the piece, or at least several feet from the end of

the piece, in order to avoid the umepresentative end portion that is

sometimes completely treated by end penetration. Since preservative

oils tend to creep over cut surfaces, the observation should be made

promptly after the boring is taken. Holes made for penetration

measurements should be tightly filled with a thoroughly treated wood

plug.

The penetration of preservatives that are practically colorless must

be determined by chemical dips or sprays that show the penetration

by color reactions.

EFFECT OF TREATMENT ON STRENGTH

Coal-tar creosote, creosote-coal tar mixtures, and creosote-petroleum oil mixtures are practically inert to wood and have no chemical

mfluence upon it that would affect its strength. Likewise, solutions

containing standard waterborne preservatives, in the concentrations

commonly used in preservative treatment, and solutions of toxic

chemicals in petroleum apparently have no important* effect on the

streno:th of wood.

JÉ
WOOD HANDBOOK 421

Although wood preservatives are not regarded as harmful in themselves, the treatment necessary to inject them into the wood, if unusually severe or if not properly carried out, may result in considera])le

loss in strength of the wood. Among the factors tliat influence the

effect of the treating process on strength are (1) the species of wood,

(2) the size and moisture content of the timhei's treated, (3) the heating

medium used and its temperature, (4) the length of the heathig period

used in conditioning the wood for treatment and the length^of timr

the wood is in the hot preservative, and (5) the amount of pi'c^ssure

used. Of these factors, the most important are the severity and diuation of the heating and pressure conditions used. Information on the

efi'ect of temperature on the strength of wood is covered on pages 89-93.

Working stresses for treated timber are discussed on pages 161-162.

NONPRESSURE PROCESSES

The numerous nonpressui*e processes differ widely in the retentions

and penetrations of preservative o])tained and consí^ciuently in the

degree of protection that they provide to the treated wood. When

similar retentions and penetrations are achieved, wood treated by a

nonpressure method should have a service life comparable to that of

wood treated by pressure. It should be recognized, nevertheless, that

the results of nonpressure treatments, particularly those involving

superficial applications, are not so generally satisfactory as the r(^sults

of pressure treatment. The less effective superficial nonpressure

processes, however, serve a useful purpose when more thorough

treatments are impractical.

Nonpressure methods, in general, consist of: (1) Superficial applications of preservative oils by spraying, brushing, or brief dipping;

(2) soaking in preservative oils or steeping in water solutions; (l\)

diffusion processes with waterborne preservatives; (4) various a(hi])tations of the hot-and-cold-bath process; (5) vacuimi treatment; and

(6) a variety of miscellaneous processes (16).

Superficial Applications

The simplest treatment is to apply the preservative—cj'eosote or

other oils—to the wood with a brush or a spray nozzle. Oils that are

thoroughly liquid when cold should be selected, unless it is possible to

heat the preservative. The oil should be flooded over the wood,

rather than merely painted upon it, and every check and depression

in the wood should be thoroughly filled with the preservative, since

any untreated wood left exposed provides ready access for fungi. At

least two coats should be apphecl, the second one after the first has

dried. Rough lumber may require as much as 10 gallons of oil to

1,000 square feet of surface, but surfaced lumber requires consideral)ly

less. The transverse penetrations obtained will usually be less than

one-sixteenth of an inch.

Brush and spray treatments should be used only when more effective

treatments cannot be employed. The additional life obtained by

such treatments over that of untreated wood will be aft\'cted greatly

by the conditions of service; for wood in contact with the ground, it
422 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

mñy he from 1 to :] .years. Brushing with solutions of water-soluble

preservatives is seldom worth while for wood that is exposed to the

weather, to soil, or to water and is likely to be less effective than

brushing with preservative oils in protected situations.

Dipping for a few seconds to several minutes in a preservative oil

gives greater assurance than brushing or spraying that all surfaces and

checks are thoroughly coated with the oil, and it usually results in

slightly greater penetrations. It is a common practice to treat Avindow

sash, frames, and other milhvork, either l)efore or after assembly, by

dipping for approximately o minutes in a water-repellent preservative

(23). The amount of preservative used may vary from about 6 to

17 gallons per thousand board-feet (0.5 to 1.5 pounds per cubic foot)

of milhvork treated. The penetration of preservative into end surfaces of ponderosa pine sapwood is, in some cases, as much as 1 to

o inches. End penetration in such woods as southern yellow pine and

Douglas-fir, however, is much less, particularly in the heartwood.

Transverse penetration of the preservative applied by brief dipping is

very shallow, usuall}^ onl}^ a few hundredths of an inch. Since the

exposed end surfaces at joints are the most vulnerable to decay in

milhvork products, good end penetration is especially advantageous.

Dip applications provide very limited protection to wood used in

contact with the ground or under ver3^ moist conditions (4). They do

have value, however, for exterior woodwork and milhvork that is

painted, that is not in contact with the ground, and that is exposed

to moistiu-e onl}^ for brief periods at a time (29).

Cold Soaking and Steeping

Cold soaking well-seasoned wood for several hours or da3^s in lowviscosity preservative oils or steeping green or seasoned wood for

several days in waterborne preservatives, such as zinc chloride, are

limited-purpose processes that have been tried with varying degrees

of success on fence posts, lumber, and timbers (7, 28).

Pine posts treated by cold soaking in a solution containing 5 percent

of pentachlorophenol in No. 2 fuel oil for 24 to 48 hours or longer, in

most cases, were in good condition after approximate!3^ 10 years of

service test. These posts were well penetrated in the sapwood and

had preservative-solution retentions of from 2 to 6 pounds per cubic

foot. Most species are not treated so satisfactorily as the pines b}^

cold soaking, and test posts of such woods as birch, aspen, and sweetgum treated by this method have failed prematurely (7). Preservative

retentions and penetrations obtained by cold soaking lumber for

several hours are considera})l3^ better than those obtained by brief

dipping of similar species. Preservative retentions, however, seldom

equal those obtained in pressure treatment unless the wood is infected

with fungus at the time of treatment (5).

vSteeping with waterborne preservatives has very limited use in

the United States but has been employed for many years in Europe.

In treating seasoned w^ood both the water and the preservative salt

in the solution soak into the wood. With green wood, the preservative

(^ntei's the water-saturated wood by diffusion. Preservative retentions

and penetrations vary over a wide range, and the process is not
WOOD HANDBOOK 423

generally recommended when more reliable treatments are practical.

Tests on posts also show variable results depending upon the preservative, the species of wood, and the severity of the exposure conditions. When mercuric chloride ^^ is used as a preservative, as is fairly

common in Europe, the steeping process is known as Kyanizing.

Zinc chloride, copper sulfate, sodium fluoride, and other \vàterl)orne

preservatives also may be used. Preservative-solution concentrations

vary with different preservatives; 1 percent solution is common with

mercuric chloride and 5 percent for zinc chloride. Tlie wood is soaked

in the solution from 1 to 2 weeks.

Diffusion Processes

In addition to the steeping process, difl'usion processes are used

with green or wet wood. These processes employ vvaterborne preservatives that will dift'use out of the water of the treating solution into

the water of the wood. The end-difl'usion process is a simple, low-cost

process of limited effectiveness that can be applied to unpeeled,

unseasoned fence posts. A newer difl'usion process of considerable

promise, called double difl'usion, is under development by the Forest

Products Laboratory (2). It consists of steeping green wood first in

one chemical and then in another. The two chemicals difl'use into

the wood and then react to deposit toxic compounds with high resistance to leaching. Service tests on posts treated by this method and

installed as early as 1941 are showmg very satisfactory results (6).

Other diffusion processes consist of applying preservatives to the

butts or around the ground line of posts or poles. In standing-pole

treatments the preservative may be injected with a special tool into

the pole, applied as a paste or bandage, poured into holes bored in

the pole at the ground-line zone, or poured on the surface of the pole

and into an excavation several inches deep around the ground line

of the pole. These treatments have recognized value for application

to untreated standing poles.

Adaptations of the Hot-and-Cold-Bath Process

The hot-and-cold-bath treatment with coal-tar creosote and otlier

oil preservatives is the most effective of the nonpressure processes,

and the thoroughness of the treatment obtainal)le most nearly

approaches that of the pressure processes. The treatment consists

of heating the wood m the preservative in an open tank for several

hours, and then quickly submergmg it in cold preservative and

allowing it to remain several hours in this cold bath. Two methods

may be used: (1) Transferring the wood at the proper time from a

hot-bath tank to a cold-bath tank; or (2) draining the hot preservative

from a single tank and quickly refilling the tank with cold preservative. The same result can also be accomplished, although more slowly,

by shutting off the heat at the proper time and allowing the wood and

the hot preservative to cool together.

The principle involved is the same in each procedure. Durmg

the hot bath, the heating causes the an m the wood to exnand and

2ö This preservative is very poisonous and therefore dangerous to handle.
424 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

some to be forced out. Heating the wood also helps improve the

penetration of the preservative. When the cooling takes place,

whether it is sudden or slow, the air in the wood contracts, and a

partial vacuum is thus created that results in the forcing of liquid

into the wood by the pressure of the atmosphere. Some preservative

is a))sorbed during the hot bath, but most of the preservative is taken

up 1)V the wood during the cooling bath.

The chief use of the hot-and-cold-bath process is for treatmg poles

of some of the thin-sapwood species, such as western redcedar, for

telegraph, telephone, and power lines (fig. 89). The process is also

useful for fence posts and for lumber or timbers for other purposes

when circumstances do not permit the more effective pressure treatments. Coal-tar creosote and pentachlorophenol solutions are the

preservatives ordinarily chosen for posts and poles, but water solutions of preservatives, such as zinc chloride solution, may also be

-mployed if the solution is kept at uniform strength and the watersolul)le preservative is not adversely affected by heating. For the

preservatives that cannot safely be heated, the process must be

modified.

With coal-tar creosote, hot-bath temperatures up to 235° F. may

be employed, but usually a temperature of 210° to 220° is suflficient.

In the commercial treatment of cedar poles, temperatures of from

212° to 235° are specified with creosote and pentachlorophenol solution (1). If the temperature is too high, a considerable percentage

of the oil may be lost by evaporation, especially if a creosote with a

relatively low boiling range is used. In the cold bath the desired

temperature is usually approximately 100°. This temperature usually

keeps the oil fiuid but is much lower than that of the hot bath. If

the oil is not sufficiently fluid at 100°, however, the temperature of

the cold l)ath should be increased. Specifications for treating poles

set a cold-bath t'^mperature limit between 90° and 150° (1).

The length of both baths must be governed by the ease with which

the timber takes treatment. With well-seasoned timber that is

moderately eas}^ to treat, a hot bath of 2 or 3 hours and a cold bath of

like duration will probably be sufficient, but much longer periods are

required with resistant woods. With preservative oils, the object is

to obtain as deep penetration as possible, but with a minimum amount

of oil. If the penetration is not sufficient, either the hot or the cold

bath should be lengthened. If the penetration is satisfactory, but too

much oil is absorbed, the cold bath should be shortened.

In the hot-and-cold-bath treatment of posts of some woods, such as

southern yellow pine, particularly those posts containing molds, blue

stain, and incipient decay, preservative retentions are often excessively high. One method of reducing preservative retentions is to

employ a final heating or ^^expansion^^ bath with the creosote at 200°

to 220° F. for an hour or two and to remove the wood while the oil is

hot. This second heating expands the oil and air in the wood, and

some of the oil is thus recovered. The expansion bath also leaves the

wood cleaner than when it is removed directly from cold oil. Another

means for reducing retentions of creosote is to use water, zinc chloride

solution, or steam as a heating medium before the cold bath in creosote.

By such heating methods, some water is absorbed that tends to reduce

retention of preservative, and some sacrifice in penetration may also

result.
WOOD HANDBOOK 425

M 92433 F

FIGURE 89.—Tanks for butt treatment of poles by hot-and-cold-bath process.
426 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

The best combination of treating conditions in any instance will

vary with the character and the condition of the timber and must be

learned by trial. The penetration cannot always be controlled at will

})y manipulating the treating conditions, however, for some woods are

highly resistant to treatment and at best may permit a depth of only

one-eighth inch or less, especially in heartwood faces. The sapwood

of most species is less resistant to penetration than the heartwood and

transverse penetrations of % to 1 inch are often obtained in sapwood.

Certain preservative chemicals in water solution cannot safely be

heated to high temperatures, because, at such temperatures, reactions

nuiy take place that precipitate some of the chemicals out of solution

or otherwise reduce the value of the solution. Such solutions are not

practical for use in the hot bath. This difficulty has been solved in

some open-tank plants by heating the wood with steam instead of in

the preservative. The tank is covered after the wood is in place, and

steam is applied at atmospheric pressure for a few hours. At the

conclusion of the steaming period, cold preservative solution is pumped

into the tank and absorption takes place as the wood cools [see U. S.

Patent No. 2,235,822 (1941)].

Preservatives consisting of toxic chemicals in volatile organic

solvents cannot safely be heated in open tanks because of the loss of

solvent by evaporation and the considerable danger of fire or explosion.

Steaming is unsuitable because it wets the surface of the wood and thus

interferes with the penetration of preservative oils. The obstacle is

sometimes overcome by heating the wood in a dry kiln or hot box and

til en immersing it quickly in cold preservative. A kiln-heating

process for this purpose, in which the relative humidity in the kiln is

controlled during the heating process, is covered by U. S. Patent

1,991,811 (1935).

Vacuum Processes

Two vacuum processes, in which the wood is either subjected to a

vacuum alone or to steaming and a vacuum before it is submerged in a

cold bath of preservative, have had some commercial use in the

treatment of lumber, timbers, and millwork. In the treatment of

millwork, a vacuum is applied, the wood is immersed in an unheated

water-repellent preservative, anrl, after the wood is removed from the

preservative, a final vacuum is used to remove surplus preservative

from the surface {11). In the treatment of mine timbers and lumber,

the wood is subjected to an initial vacuum, steamed, subjected to a

second vacuum, and immersed in an unheated waterborne preservative {12). Good penetrations and retentions of the preservative can

be obtained by these processes in woods that are not resistant to

treatment. Even with easily penetrated woods the results will vary

within wide limits according to the magnitude and time of initial

vacuum, the time the wood is immersed in the preservative, and, to

some extent, the magnitude and time of the final vacuum. In treating

millwork by the vacuum method, the treating time used and the

retentions and penetrations of preservative obtained are similar to

those with the brief dipping treatment of millwork. The vacuum

treatment, however, leaves tlie wood in drier condition, so that there

is no delay at the plant in the further processing of the millwork.
WOOD HANDBOOK 427

Miscellaneous Nonpressure Processes

A number of other nonpressure methods of various types have been

used to a hmited extent. Several of these involve the application of

waterborne preservatives to living trees (31). The Boucherie process

for the treatment of green, unpeeled poles {16) has been used for many

years in Europe. The process consists of attaching liquid-tight caps

to the butt ends of the poles and through a pipe line or hose leading to

the cap, a waterborne preservative, such as copper sulfate, is forced

into the pole under hydrostatic pressure.

The tire-tube process (32) 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 tightly around the butt

end of the post to make a bag that is used to hold a solution of waterborne preservative, such as zinc chloride.

LITERATURE CITED

(1) AMERICAN WOOD-Preservers' ASSOCIATION.

1952. MANUAL OF RECOMMENDED PRACTICE. STANDARD SPECIFICATIONS.

(A looseleaf handbook, revised annuall^^)

(2) BAECHLER, R. H.

1953. HOW TO TREAT FENCE POSTS BY DOUBLE DIFFUSION. V. S. FOFCST

Prod. Lab. Rpt. R1955, 4 pp., illus. [Processed.]

(3) BESCHER. R. H., HENRY, W. T., and DREHER, W. A.

1948. A STUDY OF PERMANENCE OF COMMERCIAL FIRE RETARDANTS.

Amer. Wood-Preservers' Assoc. Proc. 44: 369-379, illus.

(4) BLEW, J. O., JR.

1952. COMPARISON OF WOOD PRESERVATIVES IN STAKE TESTS (1952

progress report). U. S. Forest Prod. Lab. Rpt. R1761, 7 pp.,

illus. [Processed.]

1952. TREATABILITY OF SOUTHERN YELLOW PINE AS INFLUENCED BY

FUNGUS INFECTION. Jour. Forest Prod. Res. Soc. 2 (3): 85-86,

illus.

1952. COMPARISON OF WOOD PRESERVATIVES IN MISSISSIPPI POST STUDY

(1952 progress report). IT. S. Forest Prod. Lab. Rpt. R1757,

11 pp. [Processed.]

(5)

(6)

(7)

1950. TREATING WOOD IN PENTACHLOROPHENOL SOLUTIONS BY THE

COLD-SOAKING METHOD. V. S. Forest Prod. Lab. Rept. R1445,

9 pp., illus. (Rev.) [Processed.]

(8) BucKMAN, S. J., and COMMITTEE.

1949. REPORT OF COMMITTEE P-4, NON-STANDARD PRESERVATIVES. Amcr.

Wood-Preservers' Assoc. Proc. 45: 28-45.

(9) EDISON ELECTRIC INSTITUTE.

1952. SPECIFICATIONS FOR THE FULL-LENGTH, NONPRESSURE, PRESERVATIVE TREATMENT OF POLES. 12 pp.

(10) FoBES, E. W.

1949. BARK PEELING MACHINES AND METHODS. V. S. Forest Prod. Lai).

Rept. D1730, 22 pp., illus. [Processed.]

(11) GARLICK, G. G.

1948. NEW VACUUM WOOD TREATING PROCESS. Timberman 49 (8):

58-62.

(12) GRIFFITH, E. M.

1950. INITIATION AND OPERATION OF A TIMBER TREATMENT SYSTEM FOR

A GROUP OF PENNSYLVANIA ANTHRACITE MINES. 5 pp., illuS.

Glen Alden Coal Co., Wilkes-Barre, Pa. [Processed.]

303747°—55-
428 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

HATFIELD, I.

1944. INFORMATION ON PENTACHLOROPHENOL AS A WOOD-PRESERVING

CHEMICAL. Amer. Wood-Preservers' Assoc. Proc. 40: 47-67.

HENRY, W. T., and KEPFER, R. J.

1949. coppERizED CHROMATED ZINC CHLORIDE. Amer. Wood-Preseivers'

Assoc. Proc. 45: 66-75, illus.

HUDSON, M. S.

1947. VAPOR DRYING. THE ARTIFICIAL SEASONING OF WOOD IN VAPOR

OF ORGANIC CHEMICALS. Forest Prod. Res. Soc. Proc. 1: 32 pp.,

illus.

HUNT, G. M., and GARRATT, G. A.

1953. WOOD PRESERVATION. 402 pp., illus., New York.

MACLEAN, J. D.

1925. THE RELATIVE COST OF TREATED AND UNTREATED TIMBER. AMER.

Wood-Preservers' Assoc. Proc. 21: 111-122.

1929. ABSORPTION OF WOOD PRESERVATIVES SHOULD BE BASED ON THE

DIMENSIONS OF THE TIMBER. Amer. Wood-Preservers^ Assoc.

Proc. 25: 129-142.

1952. PRESERVATIVE TREATMENT OF WOOD BY PRESSURE METHODS.

U. S. Dept. Agr. Handb. 40, 160 pp., illus.

MAYFIELD, P. B., and COMMITTEE.

1948. REPORT OF COMMITTEE 6-5 SEASONING PRACTICE. Amer. WoodPreservers' ASSOC. Proc. 44: 313-320.

and COMMITTEE.

1949. REPORT OF GENERAL COMMITTEE ON SEASONING PRACTICE. Amer.

Wood-Preservers' Assoc. Proc. 45: 236-241.

MiNiCH, A., and GOLL, M.

1949. TECHNICAL ASPECTS OF COPPER NAPHTHENATE AS A WOOD-PRESERVING CHEMICAL. Amer. Wood-Preservers' Assoc. Proc. 44:

72-81.

NATIONAL WOODWORK MANUFACTURERS ASSOCIATION.

1951. MINIMUM STANDARDS FOR WATER REPELLENT PRESERVATIVES FOR

MiLLwoRK. 2 pp., illus. Chicago.

SHIPLEY, G. B.

1951. WOOD PRESERVERS' CONTRIBUTION TO CONSERVATION. Amer.

Wood-Preservers' Assoc. Proc. 47: 339-345, illus.

STEER, H. B.

1952. WOOD PRESERVATION STATISTICS 1951. Amer. Wood-Preservers'

Assoc. Proc. 48: 363-404., illus. (Published annually.)

STIMSON, E.

1928. ECONOMY OF FRAMING STRUCTURAL TIMBERS BEFORE TREATMENT.

Amer. Wood-Preservers' Assoc. Proc. 24: 106-113.

U. S. FEDERAL SUPPLY SERVICE.

1950. WOOD PRESERVATIVE, RECOMMENDED TREATING PRACTICES. Fed.

Specif. TT-W-571, 11 pp. (See yearly index for specifications

on individual preservatives.)

U. S. FOREST PRODUCTS LABORATORY.

1945. PRESERVATION OF TIMBER BY THE STEEPING PROCESS. U. S

Forest Prod. Lab. Rpt. R621, 10 pp., illus. (Rev.) [Processed.]

VERRALL, A. F.

1949. DECAY PROTECTION FOR EXTERIOR WOODWORK. South. Lumberman 178 (2237): 74, 76-78, 80, illus.

ViNsoN, J. C, and COMMITTEE.

1950. REPORT OF COMMITTEE P-4, NON-STANDARD PRESERVATIVES. Amer.

Wood-Preservers' Assoc. Proc. 46: 33-49.

WiLFORD, B. H.

1944, CHEMICAL IMPREGNATION OF TREES AND POLES FOR WOOD PRESERVATION. U. S. Dept. Agr. Cir. No. 717, 30 pp., illus.

WiRKA, R. M.

1945. TIRE-TUBE METHOD OF FENCE POST TREATMENT. U. S. Forest

Prod. Lab. Rpt. R1158, 16 pp., illus. (Rev.) [Processed.]
POLES, PILING, AND TIES

PRINCIPAL SPECIES USED FOR POLES

The more important factors to l)e coiisiih^Tcl in judging the

suitability of a species for poles are:

1. Abundance. An adequate timber supply must be availa])le if a

species is to be seriously considered as a potential source for poles.

2. Treatability. Since poles generall}^ require preservative treatment, it is desirable to use woods that can be satisfactorily penetrated

during commercial wood-preserving processifs.

3. Location of timber. Transportation costs from forest to treating plant or from treating plant to destination may be more favorable^

to one species than to another.

4. Strength. Poles must be sufficiently strong to support the

weight of the wire, ice coatings on the wire, and wind pressure.

5. Weight. Light weight is desirable from the standpoint of shipping costs and ease of handling and erection. Since the lightei*

species of wood are not so strong as the heavier species, the larger sizes

of poles required in some instances may offset this advantage.

6. Form. The poles should be reasonably straight, with a gradual

taper, and with strength-reducing features, such as knots, limited so

as to insure sufficient strength. The good appearance resulting from

smoothness, straightness, and uniform taper is particularly desirable

in urban districts.

The principal species used for poles in telephone, telegraph, and

powerlines are southern yellow pine, the cedars, lodgepole pine,

Douglas-fir, western larch, and ponderosa pine {9, 15).^^

Southern Yellow Pine

The southern yellow pines now furnish the major part of the tim1:)er

used for poles throughout most of the LInited States. The disappearance of chestnut, the diminishing supply of northern whitecedar, and the cost of western redcedar in the East and South are

factors in the increased use of treated southern 3^ellow pine poles.

Southern yellow pine accounted for about 75 percent of the total

number of poles treated in 1951. The supply of southern ^^ellow

pine poles in lengths over 40 feet is diminishing and is being supplemented by Douglas-fir, larch, and other western species.

Southern yellow pine poh^s are pressure treated full length with

preservatives.

Cedar

Western redcedar and northern whitecedar are extensively used for

poles; western redcedar furnishes the bulk of the cedar used for this

purpose. The Lake States furnish most of the northern whitecedar

poles, and Idaho, Washington, and British Columbia most of the

western redcedar poles. The cedars have comparatively thin sapwood, and the heartwood is naturally decay resistant. The butts of

30 Italic numbers in parentheses refer to Literature Cited, ]). 443.

429
430 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

western redcedar and northern whitecedar poles are usually treated

wdth creosote or other oil preservatives to increase their decay resistance. A considerable number of poles of these species are also treated

full length, particularly for use under climatic conditions that favor

decay or ''shellrot" in the tops of butt-treated poles.

Lodgepole Pine

Lodgepole pine is \videly used in the Rocky Mountam area because

of its desirable shape, treatabUity with preservatives, and availability.

Lodgepole pine poles are given either full-length or butt treatment,

depending upon the climatic conditions. In the dry sections of the

Rocky Mountain area, decay in the tops of poles is not rapid, and

butt treatment only may be sufficient.

Douglas-Fir

Until World War II, the use of Douglas-fir poles was confined

principally to the Pacific coast. The limited supply of southern

yellow pine poles in long lengths, however, has created a market for

Douglas-fir poles throughout the United States. Douglas-fir poles

compare favorably with southern yellow pine poles in strength. They

are generally treated full length.

Other Species

Western larch, ponderosa pine, Atlantic whitecedar, jack pine, red

pine, eastern redcedar, redwood, spruce, and hemlock are occasionally

used for poles.

Western larch poles produced in Montana and Idaho came into

use following World War II because of their favorable size, shape,

and strength properties. Western larch requires preservative treatment full length for use in most areas but is butt treated for use in

dry areas of the Rocky Mountain States.

Ponderosa pine has been used to some extent because of its availability, favorable shape, and good qualities for being treated.

Redwood, Atlantic whitecedar, jack pine, red pine, eastern redcedar, spruce, and hemlock poles are used to a slight extent, for the

most part locally in the areas where they are produced. All of these

species generally require preservative treatment.

Other species having limited use, mostly local, include tamarack,

baldcypress, black locust, ash, elm, and cottonwood. With the exception of black locust, none of these last long without preservative

treatment.

WEIGHT OF SPECIES USED FOR POLES

The weight of poles is a factor in freight charges and, except where

machines are used, in the ease with which they can be handled and

erected. Table 49 gives the weights per cubic foot for the more

important pole woods groAvn in the United States. The weight values

for green wood were determined by the method given in the section on

weight of round timbers (p. 58).
WOOD HANDBOOK 431

TABLE 49.— Weight per cubic foot and specific gravity of the more important species

used for potes

Species

Baldcypress

Douglas-fir:

Coast type ..

Rocky Mountain type

Hemlock, western.

Larch,western ---

Pine:

Jack

Loblolly 2

Lodgepole

Longleaf2.

Ponderosa

Green

Air-dry

(15-

percent

moisture

content)

Specific

gravity i

Lb. per

cu.ff.

Lb. per

en. ft.

50 32 0. 42

39 34 .45

34 30 .40

41 29 .38

50 38 .51

40 30 .40

53 3fi .47

39 29 .38

55 41 .54

45 28

1

.38

Species

Pine—Continued

Red

Shortleaf2

Red cedar:

Eastern

Western .

Redwood . . -

Spruce (red, Sitka, and

white)

Whitecedar:

Atlantic

Northern

Oreen

Lb. per

cu. ft.

49

52

37

27

50

34

25

27

Air-<lrv

(15-

percent

moisture

content)

. per

ft.

Specific

giiivit>' '

0.41

.40

,44

.31

.38

.31

.29

' Based on volume when green and weight when oven-dry.

2 These 3 species belong to the southern yellow pine group.

VOLUME OF POLES AND PILES

Volumes of polos or piles may be computed by measurino; live

lengths and diameters and appl3nng a formula or a volume tal)le.

The values in table 50 were computed by the cone-frustum formula

F=0.001818i(Z)^+d^+o¿)

where V is the volume in cubic feet, L the length in feet, D the top

diameter in inches, and d the butt diameter in inches.

The values are accurate for pieces of uniform taper and circular

cross section. Errors from irregularities of shape and taper may be

minimized by taking diameter measurements at short intervals and

computing the volume of each short section separately.

American Wood-Preservers' Association Standard Specification

F3-51, Standard Volumes of Round Forest Products, provides two

methods for the calculation of pole and pile volume, one of which us(»s

the cone-frustum formula but with the application of correction factors

for some species {10).

ENGINEERING DESIGN OF POLES

Poles are selected on the basis of the loads that must be supported

and are specified by class, length, and species. The prmcipal load is

in bending from horizontal wind forces on ice-covered wires. The

horizontal pull from dead-end or unbalanced wires is important m

some cases. Compressive stresses from the vertical loads on the pole

are of little consequence unless transformers or other heavy objects

are supported. If this is the case, consider-ation must })e given to

bending stresses resulting from the vertical loads when the pole is

deñected from the vertical.
TABLE 50.— Cubical contents of poles and piling

[To determine the volume of a pole or pile find the average diameter at each end of the piece to the nearest half inch. Multiply the number in the table correspondin<î to these 2

diameters by the length of the piece in feet. The result is in cubic feet]

5>^-

6...

7...

73 2-

ö>2-

10...

10} 2-

11...

1132-

12...

123^-

13...

133i.

14..'.

1432-.

15-...

153Í-.

16....

163'^--

17....

1732--

18_..,.

18} i".'.

Diameter of large end (inches)

0. 087

.099

.111

.124

.138

. 153

.169

.186

.204

.222

.242

.262

.284

. 306

.329

.353

.378

.404

.431

.459

,487

517

547

579

611

644

678

713

749

786

Cubic feet per lineal foot when diameter of small end in inches is41 2 5 .^»2 6 6^2 71 2 8 m 9 9^2

0.110

1 :

.123 0. 136

.150

. 165

.181

.198

.216

.235

.254

.275

. 296

.137 0. 165

.180

. 197

.214

.232

. 251

.271

.292

.314

.151 0. 196

.213

.231

.250

.269

.290

.311

.333

1

.167 0.230

.249

. 268

.'2SS

.309

.330

.353

.183 0. 267

.287

.307

.329

.351

. 374

.200 0. 307

. 328

.350

.372

.396

.219 0.349

.371

.395

.419

. 238 0.394

.418

.442

. 258 0.442

.467 .279 0.492

.300 .318 .337 .356 .377 .398 .420 .444 .468 .493 .519

.323 .341 .360 . 380 .401 .423 . 446 .470 .494 .520 .546

.347 . 365 .385 .405 .427 .449 .472 .496 .521 .547 .574

.371 .390 .410 .431 .453 .476 .500 . 524 .550 .576 .603

.397 .416 .437 .458 .480 . 504 .528 .553 .579 . 605 .633

.423 .443 . 464 . 486 .509 .532 .559 .582 .609 . 636 .664

. 450 .471 .492 .515 .538 . 562 .587 . 613 .640 . 667 .696

.479 . 500 .521 .544 . 568 .592 .618 .644 .671 .700 .729

.508 .529 . 551 .575 . 599 .624 . 650 . 676 .704 .733 . 762

. 538 . 560 .582 . 606 .630 . 656 .682 .710 .738 .767 .797

. 569 .591 .614 .638 .663 . 689 .716 .744 .772 .802 .832

.600 . 623 .647 .671 .697 .723 .750 .779 .808 .838 .869

. 633 . 656 .(>80 .705 .731 .758 .786 . 815 .844 .875 .906

.667 .690 .715 .740 .767 .794 .822 .851 .881 .912 .944

.701 .725 .750 .776 .803 .831 .860 .889 .920 .951 .983

.737 .761 .787 .813 . 840 .809 .898 .928 .959 .990 1.023

.773 .798 .824 .851 .879 .907 .937 .967 .999 1.031 1.064

.810 . 836 . 862 .890 . 918 .947 .977 1.008 1. 039 1.072 1.106

CO

to
19..

19H

20-.

20H.

21...

21M

22..

22M

23_.

233Í

24..

^4H

25..

.824

.862

.902

.942

.984

1.026

1.069

1.113

1.158

1.204

1.251

1.299

1.347

10...

lOH.

11...

12...

1212-

13...

13H.

14...

Uli.

15...

1532-

16---

163-^.

17__.

17H18.--

tS.i 2-

19-.-

1932-

.849

.888

.928

.969

1.010

1.053

1.097

1.141

1.187

1.233

1.280

1.329

1.378

.875

.914

.955

.996

038

081

125

170

216

263

311

359

409

.901

.941

.982

1.024

1.067

1.110

1.155

1.200

1.247

1.294

1.342

1.391

1.441

.929

.969

1.011

1.053

1.096

1.140

1.185

1.231

1.278

1.326

1.374

1.424

1.474 . 958

.999

1.040

1.083

1.127

1.171

1.217

1.263

1.310

1.359

1.408

1.458

1. 509

.987

1.029

1.071

1.114

1.158

1.203

1.249

1.296

1.344

1.392

1.442

1.492

1. 544

1.018

1.059

1,102

1.146

1.190

1.236

1.282

1.329

1.378

1.427

1.477

1.528

1.579

1.049

1.091

1.134

1.179

1.224

1.269

1.316

1.364

1.413

1.462

1.513

1.564

1.616

1.081

1.124

1.168

1.212

1.258

1.304

1.351

1. 399

1.449

1.499

1.549

1.601

1.654

1.114

1.158

1.202

1.247

1.293

1.339

1.387

1.436

1.485

1.536

1.587

1.639 1 693

1.149

1.192

1.237

1.282

1.329

1.376

1.424

1.473

1.523

1.574

1.626

1.679

1.732

Ciibic feet pe lineal foot when diameter of small end in inches is—

10 101/2 11 111/2 12 1232 13 13 3è i 1^ ' 143'2 1 1 ^^

0. 545 1 , !

.573 0. 601

.630

.660

.691

.723

.756

.790

.824

.860 . 896 1 !

.602 0. 660

.690

.722

.754

.787

.821

.856

.892

.929

'""'""""

.631 0.721

.753

.786

.819

.8.54

.890

.926

.963

.662 0. 785

.819

.853

.888

.924

.960

.998

.693 0.852

.887

.922 . 959

.996

1.034

.725 0.922

.958

.994

1.032

1.071 . 756 0. 994

1.031

1.069

1.109

.793 1.069

1.108

1.147

.828 1.147

1.187 .864 1.227

.900 .933 .967 1.001 1.037 1.073 1.110 1.149 1.188 1.228 1.269

.938 .971 1.005 1.040 1.076 1.113 1.151 1.189 1.229 1.269 1.311

.977 1.010 1.045 1.080 1.117 1.154 1.192 1.231 1.271 1.312 1.354

1.016 1.050 1.085 1.121 1.158 1.196 1.234 1.274 1.314 1.356 1.398

1.057 1.091 1.127 1.163 1.200 1.239 1.278 1.318 1.359 1.400 1.443

1.098 1.133 1. 169 1.206 1.244 1.282 1.322 1.362 1.404 1.446 1.489

1.140 1.176 1.212 1.249 1.288 1.327 1.367 1.408 1.449 1.492 1. 536 1.184 1.219 1.256 1.294 1.333 1.372 1.413 1.454 1.496 1.539 1. =^84

1. 228 1.264 1.301 1.339 1.379 1.419 1.459 1.501 1.544 1.588 1.632

ooö

Cd oo

4^

00

CO
TABLE 50.— Cubical contents of poles and piling—Continued

CO

>

o

Cd

O

o

Dkimeter of large end (inches)

20.-

20» 2

21..

21}/2

22.-

223^

23..

23M

24.-

2412

25...

,273

319

,3fi5

413

462

511

562

613

665

719

773

Cubic feet per lineal foot when diameter of small end in inches is1.309

1.356

1.403

1.451

1.500

1.550

1.601

1.653

1. 706

1.759

1.814

1.347

1.394

1.442

1.490

1.540

1.590

1.642

1.694

1.747

1.801

1. 856

1. 38(1

1.433

1.481

1.530

1.580

1.631

1.683

1.736

1.789

1.844

1.899

1. 425

1.473

1.522

1.571

1.622

1.673

1.725

1.779

1.833

1.888

1.943

1.466

1.514

1.563

1.613

1.664

1.716

1.760

1.822

1.877

1.932

1.988

1. 507

1.556

1.605

1.656

1.707

1.759

1.813

1.867

1.922

1.978

2. 034

13^

1. 637

1.687

1.738

1.789

1.842

1.896

1.950

2. 006

2.062

2.119

2.178

1.682

1.732

1.784

1.836

1.889

1.943

1.998

2.054

2.111

2.168

2.227 Ö

>

O

>

s

o

d

d

fc.
WOOD HANDBOOK 435

Required factors of safety are sometimes applied as multipli(u-s of

the expected load. The selected multiple of the design load is tlien

used with the rated ultimate strength of the pole.

Pole classes set up by the American Standards Association (4) nn^

used in the National Electrical Safety Code (21, 22) and in numerous

State and other codes. Sizes of poles in those classes are so arranged

that all poles of the same class, regardless of length or species, will

resist the same horizontal force applied 2 feet from the top end of the

pole. The pole species are placed in six groups, each group having

its own rating for ultimate stress in the outer fiber in bending. Stress

ratings apply to treated or untreated poles. Required sizes 6 feet

from the butt are calculated on the basis that the ultimate stress

will be reached at the ground line with the followin^: horizontal forces:

Class:

1.

2_

3-

Pouná8

4, 500

3, 700

3, 000

4 2, 400

Class:

5

6

7

Pounds

1, !)00

1, 500

1, 200

Three classes smaller than the precedhig are also esta])lislied on the

basis of required top sizes only (for attachment of crossarms or otlier

services).

Fiber stresses for poles are discussed more fully in a Forest Products

Laboratory publication (26).

These loads and stresses are related to poles with knots and othei*

strength-reducing features limited as provided in the specifications of

the American Standards Association (4). Since permitted strengthreducing features are essentially the same in all species, tlie stress

ratings show about the same relations among species as art» shown

in tests of small clear specimens. The design of the smaller pole lines

is usually more or less standardized on the basis of a certain class of

pole for a certain type of line, without specific reference to loads or

stresses. Such designs are often more conservative than the American

Standards Association specifications, to provide for future load

increases or for other reasons.

PRESERVATIVE TREATMENT OF POLES

Federal Specification TT-W-571c (23) and American WoodPreservers' Association Standard C4 (12) cover the general tieatment

of poles.

The great majority of the poles of species other than the cedars arc

given full-length, empty-cell, pressure treatment. In 1951, 89

percent of the poles were treated with coal-tar creosote and 7 percent,

were treated with pentachlorophenol solution. Waterborne preservatives have been employed to some extent. Poles so treated are

cleaner than creosoted poles, but it has not been d^^monstrated that

they will have equivalent serviceability. A minimum retention of 8

pounds of coal-tar creosote or of a 5-percent solution of pentachlorophenol per cubic foot of wood by an empty-cell process is commonly

specified. Retentions of 10 or 12 pounds per cubic foot are frequently

specified, especially in the South. The higher retentions cost more

but give greater assurance of satisfactory penetration and long life.
436 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Wien butt treatment only is required, poles are treated with

preservative oils by the hot-and cold-bath, open-tank process. In

cedar poles, the best penetration is obtained by incising them before

treatment. Special machines are used for incising, so as to give the

distribution of preservative with the minimum number of incisions

(see p. 411). Specifications covering butt treatment of the incised

cedar poles by the hot-and-cold bath have been adopted by the

American Wood-Preservers' Association (11). Lodgepole, pine,

Douglas-fir, and western larch poles are commonly incised before

treatment by the hot-and-cold-bath process.

Some treated poles exude preservative suflficiently to make the

surface oily in spots. This bleeding is not likely to reduce the life of

the poles, but it may prove objectionable to men who work on the

poles or to anyone who may come in contact with a bleeding pole.

Methods of completely preventing bleeding have not been established.

The use of lower retentions, low-residue creosotes or selected oil

solutions of pentachlorophenol as preservatives, and a final heating or

expansion bath following treatment, however, will help to produce

clean poles.

TREATMENT TO STOP DECAY IN STANDING POLES

Poles in service that have started to decay are sometimes treated

to arrest the decay and extend their life. Several ground-line treatments for standing poles are employed in the United States (6).

These methods require excavating around the pole to a depth of 12

to 18 inches and then applying a preservative to the exposed surface.

One patented method involves the application of the preservative

in paste form. A waterproof paper bandage i^ used to hold the

preservative against the pole. In another patented method, the

preservative paste is injected into the wood with a heavy, hollow

needle. Both of these methods use waterborne preservatives, which

will diffuse in the wet wood of the pole.

Another commonly used method involves first spreading sodium

fluoride in the trench around the pole and partially refilling the

trench with soil. Coal-tar creosote is then poured against the surface

of the pole about 18 inches al)Ove the ground line and allowed to run

into the checks and around the ground line. Petroleum oil containing

5 percent of pentachlorophenol has been used instead of the sodium

fluoride and creosote.

Butt-treated poles that have started to decays in the untreated tops

are often sprayed with a No. 2 fuel oil containing 5 percent of

pentachlorophenol.

LIFE OF POLES

The life of poles is so greatly influenced b}^ their species; size and

amount of sapwood ; the soil, climate, and use conditions; the t3^pe of

preservative used and the method of treatment; and the loads carried

that an average lite figure is not reliable and wide variations from the

average are to be expected in individual installations. Service records

arc not available in sufficient quantity to determine a mathematical

avera.o-e.

.^
WOOD HANDBOOK: 437

Roughly, it may be said that avorage-sized poles of northern whitecedar, western redcedar, Port-Ortord-cedar, redwood, and ])aldcypress,

when the sapwood is less than 1 inch thick, will last about 12 to 17

years without treatment. Good butt treatment with cj'eosote will

give a life of 20 to 25 years or more in territory where failure fi*om

top decay is infrequent and dry-wood termites arc not active. Poles

of baldcypress, Port-Orford-cedar, and redwood with sapwood much

thicker than 1 inch, if untreated, will have a much shorter lih^

Douglas-fir and western larch poles, when used untreated, arc

likely to last only about 9 years or less. Southern yellow pine poles

used wthout treatment under the warm, damp conditions prevailing

throughout most of the Southern States would be likely to fail in

a year or two. On the other hand, with a retention of 8 to 10 pounds

or more of creosote thorougbl}^ hijected by an empty-cell process,

southern yellow pine poles of good quality should last :'>5 yeai's or*

more. Equally good results can be expected from othec pole species

when similarly treated.

In the dry Rocky Mountain region, lodgepole pine thoi'oughly butttreated with coal-tar creosote should have an average life of 20 yc^ars

or more. With full-length treatment and good sapwood penetration,

lodgepole pine poles should compare favorably with similarly treated

southern yellow pine and Douglas-fir poles.

CHOICE OF SPECIES FOR PILING

The properties desirable in piles include sufficient strength and

straightness to withstand driving and to carry the weight of structures built on them, and in some instances to resist bending stresses.

Decay resistance or ease of penetration by preservatives is also important except in piles for temporary use or piles that will be in Iresh

water and entirely below the permanent w^ater level.

Southern j^ellow pine, Douglas-fir*, and oak are among the principal

species used for piling {9), but western redcedar and numerous other

species are also used.

Specifications for timber piles covering kinds of wood, general

quality, resistance to decay, dimensions, tolerance, manufacture, inspection, delivery, and shipment have been published in the American

Railway Engineering Association Manual {2). Specifications for

timber piles have also been prepared by the American Association of

State Highway Officials (7), the American Society for Testing

Materials^ (5), and the Federal Supply Service {24-).

BEARING LOADS FOR PILES

Bearing loads on piles are sustained by earth friction along the

sides of the pile, by bearing of the tip on a solid stratum, or by a combination of the two. Wood piles, because of their tapered form, are

particularly efficient in supporting loads by side friction. Bearing

values that depend upon side friction are related to the stability of

the soil and generally do not approach the ultimate strength of the

pile (5, 18, 20). Engineering handbooks give formidas {18, pp.

730-741) for estimating bearing values from the penetration under

blows of known energy from the driving hammer. Some enginetvrs
438 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

prefei' to estimate bearing capacity from experience or observation of

the Ix^iavior of pile foundations under similar conditions or from the

results of static-loading tests.

Where wood piles sustain foundation loads by bearing of the tip

oil a solid stratum, loads may be hmited by the compressive strength

of the wood parallel to the grain. Working stresses in compression

parallel to gi'ain should not exceed 75 percent of the basic stress values

of table 25. If a large proportion of the length of a pile extends above

^.^Tound, its bearing value may be limited by its strength as a long

column. Side loads may also be applied to piles extending above

gi'ound. In such uistances, however, bracing is often used to i*educe

the unsupported column length or to resist the side loads.

ECCENTRIC LOADING AND CROOKED COLUMNS

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 so great as might be expected. Tests

have shown that a timber, when subjected to combined bending and

compression, develops a higher stress at })oth the elastic limit and

maximum load than when subjected to compression only {19). 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 common in piling.

DRIVING OF PILES AS AFFECTED BY SEASONING

Under usual conditions of service wood piles will be wet, but they

may be driven in either the green or the seasoned condition. Because

of the increased strength resulting from drying, seasoned piles either

treated or untreated are likely to stand driving better than are green

or unseasoned ones. This is particularly true of treated piles, inasmuch as tests have demonstrated that, while the strength of green

wood may be considerably reduced by treatment, thoroughly seasoned

treated wood may be but little weaker than seasoned untreated wood.

Under the same drying conditions, however, untreated wood loses

moisture more rapidly than does treated wood.

DECAY RESISTANCE AND PRESERVATIVE TREATMENT OF

PILING

Piles in general have rather wide sapwood and consequently low

decay resistance. High natural decay resistance will be found only

when the piles have thin sapwood and are of species that have decayresistant heartwood.

Since wood that remains completely submerged in water does not

decay, decay resistance is not necessary in piling so used, but it is

necessary in any part of the piling that may extend above the permanent water level. When piling that supports the foundations of

bridges or buildings is to be cut off above the permanent water level,

it should, as a safety precaution, be pressure creosoted, usually by the

empty-cell process, with not less than 12 pounds of creosote per cubic
WOOD HANDBOOK 439

foot (7, IS, 23) (see p. 417). The untreated surfaces exposed at the

cut-offs should also be given protection by thoroughly brushing the

cut surfaces 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, fitted over

the pile head.

Piling driven into earth that is not constantly wet is subject to about

the same service conditions as apply to poles, but is generally expected

to last longer and therefore requires higher preservative retentions

than poles (see p. 416).

Piling used in salt water is, of course, subject to destruction by

marine borers even though it does not decay below the waterline.

The best practical protection against marine borers is heavy treatment

with coal-tar creosote or creosote-coal-tar solution. The piling should

be treated by the full-cell process ''to refusal"; that is, to force in all

the oil the piling can be made to hold without using treatments that

cause serious damage to the wood (see p. 412) {8).

STRENGTH AND OTHER REQUIREMENTS FOR TIES

Many species of wood are used for ties. Their relative suitabilitv

depends largely upon their strength, wearing qualities, treatability

with wood preservatives, and to some extent their natural resistance

to decay and tendency to check, although availability and cost must

also be considered.

The chief strength properties considered in a wood for crossties are

(1) bending strength, (2) end hardness and strength in compression

parallel to grain, which are indicative of resistance to spike pulling

and the lateral thrust of spikes, and (3) side hardness and compression

perpendicular to the gi^ain, which indicate resistance to wear under

the rail or the tieplate.

The composite tie-strength figures given in table 51 consist of a

combination of the strength properties listed above as necessary for

satisfactory service {17). Average values of specific gravity are also

given. Table 51 shows that a species of high specific gravity usually

has a high composite tie-strength value, and hence in the absence of

other strength data, the specific gravity is a good criterion.

The relative importance of the several mechanical properties

involved for ties changes with conditions of track installation and

maintenance and with service conditions. For example, the requirejnent for ties under heavy traffic will be greatly different than for light

traflSc. Consequently, the composite tie values should be regardecl as

indicative, rather than an exact measure of the relative mechanical

suitability of species for crossties.

Sizes of ties range from 6 by 7 to 7 by 9 inches ; lengths are usually

8 or 8)^ feet. With heavier traffic and higher speeds of trains, the

present tendency is toward increasing use of the larger sizes.

Specifications for crossties covering general quality, resistance to

wear, resistance to decay, design, manufacture, inspection, delivery,

and shipment have been published in the American Railway Engineering Association Manual {2) and in Federal Specification MM-T371a {25),
440 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLE 51.— Comporte strength figures and speeific gravity values of crosstie woods

S pecios

HAKnWf)ODS

Ash, commercial white

Aspeii.

Aspen, Big:tooth.. . .

Beech, American

Birch:

Sweet

Yellow

Catalf)a, iiorthcni

Cherry:

Black

Pin

Chestnut, American

Cottonwood:

Black

Eastern ^

Elm:

A merican

Rock

Slippery

Hackberry

Hickory:

IVcan

True

Hone ylocust

Locust, hlack

Maple:

Silver

Sugar

Oak:

Commercial red

Commercial white._

Poplar, balsam

Sassafras

Compositestrength

fifiure

SweetRuni

Sycamore, American

108

4P.

53

97

108

94

52

84

52

59

45

49

Specific

gravity i

Species

0.54

.35

.35

.50

.00

.55

.38

.47

.36

.40

.32

.37

HARDWOODSTupelo:

Black .. ..

Water

Walnut, black...

73 .46

103 . 57

81 .48

74 .49

127 .59

141 .65

133 .60

161 .66

67 .44

112 .56

100 .57

103 .59

36 .30

66 .42

71 .44

69 .46

SOFTWOODS

Baldcyprcss

Cedar:

Eastern redcedar

Xortheni whitePort-OrfordWestern redcedar

Doußlas-fir:

Coast type

IntiTmediate type ,.

Rocky Mountain tyi)e_

Fir, commercial white

Hemlock:

Eastem

Western

Larch, western

Pine:

Jack

Loblolly 2

Lodgepole

Longleaf 2

Ponderosa

Red

Shortleaf 2

Pin yon

Redwood

Spruce:

Englemann

Red, Sitka, and white. _

Tamarack

Compositestrength

figure

79

81

100

78

40

67

52

78

71

65

58

63

64

82

Specific

gravity i

0.4G

.46

.51

.44

.29

.40

.31

.45

.41

.40

.36

.38

.38

.51

59 .40

73 .47

56 .38

90 ..54

54 .38

58 .41

72 .46

60 .48

72 .38

47 .32

57 .37

71 .49

1 Based on volume wdien green and weight when oven-dry.

- These species belong to the southern yellow pine group.

DECAY RESISTANCE AND PRESERVATIVE TREATMENT OF

TIES

Although the majority of ties used are given preservative treatment

before mstallation, a few are used untreated, and for these natural

decay resistance is important. In ties given preservative treatment,

variations in natural decay resistance are of less importance than

susceptibility to treatment.

The majority of ties treated are pressure treated with coal-tar

creosote, creosote-coal-tar solutions, or creosote-petroleum mixtures.

Minimum retentions of 8 to 9 pounds per cubic foot, injected by an

empty-cell process, are most commonly employed.

Federal Specification TT-W-571c \23) includes recommendations

for the treatment of crossties, swdtch ties, and bridge ties. Specifica-
WOOD HANDBOOK 441

tions covering the preservative treatment of ties liave been adopted

and published by the American Wood-Preservers' Association (I4) and

the American Railway Engineering Association (2).

LIFE OF TIES

The service conditions under which ties are exposed are severe.

The life of ties in service therefore depends on their ability to resist

decay and the extent to which they are protected from mechanical

destruction by breakage, loosening of spikes, and rail or plate wear.

Under sufficiently light traffic, heartwood ties of naturally durable

wood, even if of low^ strength, may give 10 or 15 years' service w^ithout

preservative treatment, but under heavy ti'affic without adequate

mechancial protection, the same ties might fail through mechanical

wear in 2 or 3 3^ears. The life of treated ties is affected also by the

preservative used and the thoroughness of treatment. As a result,

the life of individual groups of ties may vary widely from the general

average depending on the local circumstances.

With these preceding limitations, the following rough estimates are

given: (1) Ties well penetrated with 8 pounds or more per cubic foot

of coal-tar creosote, creosote-petroleum mixture, or creosote-coal-tar

solution should last 25 years or more when protected against mechanical destruction. (2) Ties treated with zinc chloride should last 10 to

15 years except in very wet or very dry climates, where their life

would be shorter. (3) Untreated heartwood ties of cedar, cypress, or

redwood may last 12 to 15 years and sometimes longer, under light

traffic conditions. (4) Heartwood ties of Douglas-fir, white oak,

tamarack, and w^estern larch should last 6 to 10 years without treatment. (5) Regardless of species, ties that contain a large proportion

of sapw^ood are not likely to last longer than 2 to 4 years without

preservative treatment.

Records on the life of treated and untreated ties are published from

time to time in the annual proceedings of the American Railway

Engineering Association and the American Wood-Preservers' Association.

RELATION BETWEEN PERCENTAGE TIE RENEWALS AND

AVERAGE LIFE

If, after the installation of a group of ties, accurate records are kept

of the percentage of the grouplhat are removed each year, figure 90

can be used to estimate the average life that will be obtained.

There is a fairly definite relation (16) between the rate of renewals

and the average life of any particular group of ties of simdar quality

and subjected to similar conditions of service. The accuracy with

which the average life can be predicted by means of figure 90 is greater

with large groups of ties than with small groups and increases as the

percentage of renewals increases. Since very early renewals are often

caused by unusual conditions, the average life indicated by renewal

percentages below 10 or 15 is not so reliable as that indicated by somewhat higher percentages. The average life of a group of ties is

usually reached when about 60 percent have been removed.
442 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

«. V

" i \

-^—

LEGEND

DIAGONAL LINES REPRESENT AVERAGE LIFE

INDICATED BY RESPECTIVE FIGURES

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WOOD HANDBOOK 443

LITERATURE CITED

(1) AMERICAN ASSOCIATION OF STATE HIGHWAY OFFICIALS.

1949. STANDARD SPECIFICATIONS FOR HIGHWAY BRIDGES 284 pp Washington, D. C.

(2) AMERICAN RAILWAY ENGINEERING ASSOCIATION.

1950. MANUAL OF THE AMERICAN RAILAVAY ENGINEERING ASSOCIATION.

,^, , yl^is., Chicago. (Looseleaf manual, revised annually )

(3) AMERICAN SOCIETY FOR TESTING MATERIALS.

1952. TENTATIVE SPECIFICATIONS FOR ROUND TIMBER PILES Amer Soc

^ ^ ^ Testing Mater. Standard D25-52T. Pt. 4: 681-685, illus

(4) AMERICAN STANDARDS ASSOCIATION.

1948. STANDARD SPECIFICATIONS AND DIMENSIONS FOR WOOD POLES

Amer. Standards Assoc. Specif. 05.1-1948, 14 pp., illus.

(5) AMERICAN WOOD-PRESERVERS' ASSOCIATION.

1932. USE OF CREOSOT^ED WOOD PILING FOR BUILDING FOUNDATIONS.

Amer. Wood-Preservers' Assoc. Proc. 28: 10 pp.

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

1942. REPORT OF COMMITTEE 5- 5-2-POLES, NON-PRESSURE METHODS.

Amer. Wood-Preservers' Assoc. Proc. 38: 400-409.

1951. STANDARD FOR CREOSOTED-WOOD FOUNDATION PILßS. Amer.

Wood-Preservers' Assoc. Specif. C12-51, 1 p.

1951. STANDARD FOR PRESSURE-TREATED PILES AND TIMBERS IN MARUXE

CONSTRUCTION. Amer. Wood Preservers' Assoc. Specif. C18-51,

Ip.

1952. WOOD PRESERVATION STATISTICS 1951. Amer. Wood-Preservers'

Assoc. Proc. 48: 363-404, illus. (Published annually.)

1952. STANDARD VOLUMES OF ROUND FOREST PRODUCTS. Amer. WoodPreservers' Assoc. Specif. F3-51, 8 pp.

1952. PRESERVATIVE TREATMENT OF INCISED POLE BUTTS BY THE NONPRESSURE PROCESS, WESTERN REDCFDAR AND NORTHERN WHITECEDAR POLES. Amer. Wood-Preservers' Assoc. Specif. C7-53,

3 pp.

1952. PRESERVATIVE TREATMENT OF POLES BY PRESSURE PROCESSES.

Amer. Wood-Preservers' Assoc. Specif. C4-53, 7 pp.

1952. PRESERVATIVE TREATMENT OF PILES BY PRESSURE PROCESSES. Amer.

Wood-Preservers' Assoc. Specif. C3-53, 5 pp.

1952. PRESERVATIVE TREATMENT OF CROSSTIES AND SWITCH TIES BY

PRESSURE PROCESSES. Amer. Wood-Preservers' Assoc. Specif.

C6-53, 7 pp.

(15) ANDERSON, I. V.

1947. TRENDS IN THE UTILIZATION OF POLE SPECIES AND THEIR EFFECT

ON FOREST MANAGEMENT. Soc. Amer. Forestcrs Proc. 1947:

128-140, illus.

(16) MACLEAN, J. D.

1926. PERCENTAGE RENEWALS AND AVERAGE LIFE OF RAILWAY TIES.

Engin. News-Rec. 97 (9): 336-339.

(17) MARKWARDT, L. J.

1930. COMPARATIVE STRENGTH PROPERTIES OF WOODS GROWN IN THE

UNITED STATES. U. S. Dcpt. Agr. Tech. Bui. 158, 39 pp., illus.

(18) MERRIMAN, M., MERRIMAN, T., and WIGGIN, T. H.

1930. AMERICAN CIVIL ENGINEERS' HANDBOOK. Ed. 5., 2,263 pp., illus.

New York. (Reprinted 1942.;

(19) NEWLIN, J. A., and TRAYER, G. W.

1924. STRESSES IN WOOD MEMBERS SUBJECTED TO COMBINED COLUMN

AND BEAM ACTION. Xatl. Advisory Com. Aeronaut. Rpt. 188,

13 pp., illus.

30:^747°—55 29
444 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

(20) TLRZAGHI, C.

1929. SCIENCE OF FOUNDATIONS ITS PRESENT AND FUTURE. Amer.

Soc. Civ. Engin. Trans. 93 (1704): 270-301, illus.

(21) U. S. DEPARTMENT OF COMMERCE.

1948. NATIONAL ELECTRIC SAFETY CODE. Nati. Bur. Standards Handbook

H30, 408 pp., illus. Washington, D. C.

(22)

1944. DISCUSSION OF NATIONAL ELECTRICAL SAFETY CODE. Nati. Blir.

Standards Handbook 39, 162 pp., illus. Washington, D. C.

(23) U. S. FEDERAL SUPPLY SERVICE.

1950. WOOD PRESERVATIVE, RECOMMENDED TREATING PRACTICES. Fed.

Specif. TT-W-571, 11 pp.

(24)

1947. PILES: WOOD. Fed. Specif. MM-P-371, 10 pp., illus., and

Amend. 1, 1 p., Oct. 20, 1949.

(25)

1950. TIES, RAILROAD, WOOD (CROSS AND SWITC?!). Fed. Specif. MM-T371a, 4 pp.

(26) WILSON, T. R. C, and DROW, J. T.

1953. FIBER STRESSES FOR WOOD POLES. U. S. Forest Prod. Lab. Rpt.

D1619, 10 pp. illus. (Rev.) [Processed.]

^
THERMAL INSULATION

The inflow of heat through outsi(k- walls and roofs in hot weather

or Its outflow during cold weather has important efl'ects upon the

comfort of the occupants of a building. During cold weather, such

heat flow also governs fuel consumption to a great extent. Wood

itself is a good insulator but commercial insulating materials are often

incorporated into exterior walls, ceilings, anrl floors to increase resistance to heat passage {10)}^

Commercial insulating materials are manufactured in a number of

forms and types {6). Each has advantages for specific uses, some are

more resistive to heat flow than others, and no one type is best for all

applications {S).

INSULATING MATERIALS

For purposes of description, materials commonly used for msiilation may be grouped in the following general classes: (1) Rigid insulation, (a) structural, (b) nonstructural; (2) flexible insulation, (a)

blanket, (b) batt; (3) fill insulation; (4) reflective insulation; and (5)

miscellaneous types.

Rigid Insulation

Structural Insulating Board

Structural insulating board is made by reducing wood, cane, or

other vegetable fibers to a pulp and then assembling the fibrous pulp

LQto large lightweight or low-density boards that combine strength

with thermal and acoustical insulating properties. Such boards

may also be used for decorative purposes. The finished board as

generally made is 6 to 12 feet long, 4 feet wide, and ){ to 1 inch thick.

Boards of greater thickness are produced by laminating sheets of

standard thickness together. The most common fiberboard products are general-use board, sheathing, lath, tile board, planks, and

roof insulation. A more detailed discussion of these products is given

in the section on building fiberboards (p. 457).

General-use insulatmg board is available in sizes 4 feet wide, 6 to

12 feet long, and y% to 1 inch thick. Sheathing is used on walls and

is available in widths of 2 and 4 feet, lengths of usually 8 feet, and

thicknesses of K and ^^^2 inches. It may be obtained with or witliout

surface coatings, which usually have an asphalt base. Lath made of

fiberboard is 18 inches wide, 48 inches long, and K to 1 inch thick.

Fiberboard has better insulating properties than most materials used

for a plaster base and is commonly used for that purpose on exterior

walls and under roofs or attics. Some fiberboard lath has an asphalt

coating that serves as a vapor barrier. Tile board produced from

Italic numbers in parentheses refer to Literature Cited, p. 454.

445
446 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

fiberboard is made in small squares or rectangular patterns, generally

with interlocking edges, and is used for interior finish, particularly

on ceilings. It is available for thermal insulation purposes in sizes

from 12 by 12 inches to 16 by 32 inches and in thicknesses of %, Vi, and

1 inch.

Plank is another type of interior finish and is frequently used in

conjunction with tile board. It is 8 to 16 inches wide, 6 to 12 feet

long, and K iiich thick. Tile board and plank may be obtained as

manufactured or with a factory-applied surfacing. These materials

are often used where a decorative finish is desired and insulating

properties are of secondary importance. They are sometimes combined with sound insulation. Roof insulation is used on flat roofs

under composition roofing and under certain types of roofing on

pitched roofs. It is also used under concrete floors. It is 23 to 24

inches wide, 47 to 48 inches long, and K to 2 inches thick.

Slab Insulation

Nonstructural rigid insulation is often called ''slab insulation,"

The slabs or blocks are small, rigid units sometimes 1 inch thick but

generally thicker and vary in size up to 24 by 48 inches. The types

made from wood-base materials are cork blocks, wood fiber bonded

with cement, magnesite, or other adhesive, and fiberboard slabs.

Cork blocks are made by bonding small pieces of cork together in

blocks or slabs ranging from 12 by 36 inches to 36 by 36 inches and

1 to 6 inches thick. They are used widely for cold-storage insulation

and for insulating flat roofs of industrial and commercial buildings.

Wood-fiber blocks are made by bonding wood fibers similar to

excelsior, but coarser, with some suitable bonding agent, such as

magnesite cement. They are made in thicknesses of 1 to 3 inches

and in various widths and lengths. The principal uses are for roofdeck insulation in industrial buildings, structural floor and ceiling

slabs, and nonbearhag partitions.

Fiberboard slabs are made by laminating fiberboard products to

produce rigid blocks and are used for cold-storage insulation. Mineralwool slabs or blocks are made of both rock wool and glass wool with

suitable binders for low-temperature insulation and specialty uses.

Other types of blocks and slabs include cellular glass, insulation board,

cellular-rubber products, and vermiculite or expanded mica with

asphalt binder.

Flexible Insulation

Flexible insulation is manufactured in two types, (1) blanket or

quilt and (2) batt. Blanket insulation is furnished in rofls or strips

of convenient length and in various widths suited to standard stud

and joist spacing. The usual thicknesses are from K to 2 inches.

The body of the blanket is made of loosely felted mats of mineral or

vegetable fibers, such as rock, slag, or glass wool, wood fiber, cotton,

eel grass, and cattle hair. Organic fiber mats are usually chemically

treated to make them resistant to fire, decay, insects, and vermin.

Most blanket insulation is provided with a covering sheet of paper
WOOD HANDBOOK 447

on one or both sides and with tabs on the edges for fastening the

blanket in place. The covering sheet on one side ma}^ be of a type

intended to serve as a vapor barrier. In some cases the covering

sheet is surfaced with aluminum foil or other reflective insulation.

Batt insulation also is made of loosely felted fibers, generally of

mineral-wool products. It is made in small units, in widths suital)le

for fitting between standard framing spaces, and in thicknesses of 2,

3, and 3% inches. Some batts have no covering; others are covered

on one side with a paper similar to that used for blanket insulation.

Fill Insulation

Loose-fill insulation is usually composed of materials used in bulk

form, supplied in bags or bales, and intended to be poiu'ed or blown

into place or packed by hand. It is used to fill stud spaces or to

build up any desired thicknesses on horizontal surfaces. Loose-fill

insulation includes rock, glass, and slag wool, wood fibers, shredded

redwood bark, granulated cork, ground or macerated wood pulp

products, vermiculite, perlite, powdered gypsum, sawdust, and wood

shavings.

Reflective Insulation

Most materials reflect radiant heat, and certain ones have this

property to a high degree. Some radiate or emit less heat than

others. For reflective insulation, high reflectivity and low emissivity

are required, as provided by aluminum foil, sheet metal coated with

an alloy of lead and tin, and paper products coated with a reflective

oxide composition. Aluminum foil is available in sheets mounted

on paper, in corrugated form supported on paper, or mounted on the

back of gypsum lath or paper-backed wire lath. Reflective insulation is installed with the reflective surface facing or exposed to an air

space preferably three-fourths inch or more in width. Reflective

surfaces in contact with other surfaces lose their reflective properties.

Miscellaneous Insulation

Some insulation does not fit in the classifications described, such as

(1) confettilike material mixed with adhesive and sprayed on the

surface to be insulated, and (2) multiple layers of corrugated paper.

Lightweight aggregates, such as vermiculite and perlite, are sometimes used in plaster as a means of reducing heat transmission.

Lightweight aggregates made from blast-fiuiiace slag, burned-cla}^

products, and cinders are used in concrete and concrete blocks. The

conductivity of concrete products made of such lightweight aggregates

is substantially lower than that of gravel and stone aggregates.

METHODS OF HEAT TRANSFER

Heat seeks to attain a balance with surrounding conditions, just as

water will flow from a higher to a lower level. When occupied buddings are heated to maintain inside temperature in the comfort range,

there is a dift'erence in temperature between inside and outside.
448 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Heat will therefore be transferred through walls, floors, ceilings,

windows, and doors at a rate that bears some relation to the temperature difference and to the resistance to heat flow of intervenmg

materials. The transfer of heat takes place by 1 or more of 3 methods—

conduction, convection, and radiation. i r i

Conduction is defined as the transmission of heat through sohd

materials; for example, the conduction of heat along a metal rod one

end of which is heated in a fire. Convection is the term apphed to

the transfer of heat by air currents from a warm zone to a colder zone;

for example, air moving across a hot radiator carrying heat to other

parts of the room or space. Heat also may be transmitted from a

warm body to a cold body by wave motion through space, and this

process is called radiation because it represents radiant energy. The

waves do not heat the space through which they move, but when they

come in contact with a colder surface or object a part of the radiant

energy is absorbed and converted into sensible heat, and a part is

reflected. Heat obtained from the sun is radiant heat.

Heat transfer through a structural unit composed of a variety of

materials may include any one or more of the three methods described.

In a frame house having an exterior wall of plaster, lath, 2- by 4-inch

studs 16 inches on center, sheathing, sheathing paper, and bevel siding,

heat is transferred from the room atmosphere to the plaster by radiation, conduction, and convection, and through the lath and plaster b}^

conduction. Heat transfer across the stud space is by radiation from

the back of the lath to the colder sheathing, and by convection, the

air warmed by the lath moving upward on the warm side of the stud

space, and that cooled by the sheathing moving downward on the

cold side. Heat transfer through sheathing, sheathing paper, and

siding is by conduction. Some small air spaces will be found back of

the siding, and the heat transfer across these spaces is principally by

radiation. Through the studs from lath to sheathing, heat is transferred by conduction and from the outer surface of the wall to the

atmosphere, it is transferred by convection and radiation.

The thermal conductivity of a material is an inverse measure of

the insulating value of that material. The customary measure of

heat conductivity is the amount of heat in British thermal units that

will flow in 1 hour through 1 square foot of a layer 1 inch thick of a

homogeneous material, per 1° F. temperature difference between

surfaces of the layer. This is usually expressed by the s3rmbol k.

Where a material is not homogeneous in structure, such as one containing air spaces like hollow tile, the term conductance is used instead

of conductivity. The conductance, usually designated by the symbol

C, is the amount of heat in British thermal units that will flow in 1

hour through 1 square foot of the material or combination of materials

per 1^ F. temperature difference between surfaces of the material.

Resistivity or resistance, a direct measure of the insulating value,

is the reciprocal of transmission (conductivity or conductance) and is

represented by the s^^mbol i?. The overall coefficient of heat transmission through a wall or similar unit, including surface resistances,

is represented by the symbol U and deflnes the movement in British

thermal units per hour, per square foot, per 1° F. The resistance of

the unit would be R=jj*
WOOD HANDBOOK 449

HEAT LOSS THROUGH DIFFERENT TYPES OF WALLS

The heat loss through walls and roofs made of different materials

can be compared by comparing the overah coefficients of heat transmission, or U values, of the construction assemblies. To determine

the U value by test would be impractical in most cascas, ])ut it is a

simple matter to calculate this value for most combinations of materials commonly used in building construction whose thermal properties are known.

Table 52 gives conductivity and conductance values with corresponding resistivity and resistance values used in calculating the

thermal properties of construction units {1).

To compute the U value: Add the resistance of each material, exposed surface, and air space in the given section, using values given in

table 52.' The sum of these resistances divided into 1 (reciprocal of

the sum) gives the coefficient U. For reflective insidation, the value

given in the table for an air space bounded by aluminum foil is used.

Example: The overall U value through the stud space of a conventional frame wall consisting of plaster, gypsum lath, air space,

wood sheathing, sheathing paper, and siding where heat flow is

horizontal is calculated as follows:

Interior surface resistance 0. 61

Gypsum lath and plaster . 42

Air space • ÍH

Wood sheathing, sheathing paper, and bevel siding 2. 00

Exterior surface resistance (wind movement 15 miles per hour) .17

Overall resistance 4. 11

The overall coefficient of thermal transmission through the stud

space becomes:

4.11

For the U value through the stud, substitute the resistivity of

wood based on the depth of the stud for the resistance value of the

air space. For example, a species of wood that has a k value of 0.9

at 10-percent moisture content has a resistivity of 1.11. The resistance of a nominal 2- by 4-inch stud is:

35/Xl.ll=4.02

Substituting the value of 4.02 for the air-space value of 0.91 gives an

overall resistance value of 7.22 or a U value of 0.138. Assummg the

area of the stud represents 15 percent of the waU area, the corrected

transmission value becomes :

0.243X85 +0.138X15^^ ^97

Too

If 1-inch blanket insulation, bounded by two %-inch air spaces, is

used in the stud space, the resistance becomes 5.52 mstead of the an--

space value of 0.91; and the overall resistance of the wall through

the stud space is 8.72, compared with 4.11 without msulation. The

replacement of 25//2-inch wood sheathing with filx^rboard of the samc^

thickness increases the overall resistance from 4.11 to 5.47.
450 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

The heat-transmission formula is appHed to top-floor ceihngs in

the same manner as for side walls, but the coefficients used for surface

and air-space resistances depend upon the direction of heat flow.

TABLE 52.— Values ^ recommended for coin-puting overall coefficients of thermal

transmission ^

M atcrial Description

Conductivity

k

Conduct

ancc

C

Resistivity

1

i k

Resistance

1

C

Air spaces:

Bounded by ordinary

materials.

34 inch or more in width:

Vertical . 1.10

1.31

. 945

.46

.54

.20

.23

.27

.09

.25

.13

2.27

0 91

! Horkontal, heat flow up 76

Horizontal, heat flow down.. 1 06

Bounded by aluminum Vertical 1 2 17

foil.

Do Horizontal, heat flow up 1.85

Do Horizontal, heat flow down 5.00

Do Space Uiinches or more divided

by material reflective on both

sides:

Vertical 4 35

Horizontal, heat flow up 3 7(1

Horizontal, heat flow down. _ 11 11

30° slope, heat flow up 4 00

30° slope, heat flow down 7 ö*"'

Exterior finish, frame walls:

Brick veneer . 4 inches thick (nominal) 44

Stucco - - 1 inch thick 12. 50 0.08

Wood shingles 1.28

1.28

.50

6.00

3 2.70

78

Southern yellow pine lap 78

siding.

Wood sheathing, paper, Fir sheathing—2^32 inch, yellow

pine lap siding.

2 00

and siding.

Asbestos shingles 17

Plywood siding _ 3-ply, H inch 3 37

Stone veneer.. Sandstone or limestone

Made from mineral or vegetable

fiber, or animal hair; enclosed

or open.

No added binder

12.00

.27

.30

.33

.41

.27

.46

.26

.28

.27

.48

.24

.08

3.70

3.33

3.03

2.44

3.70

2.17

3.84

3.57

3.70

2.08

4.17

Insulating materials:

Fill and blankets

Corkboard

Insulating board Made from vegetable fiber

Sawdust and shavings _. Various species..

Macerated paper Ground newsprint and other

pulp products.

Slab insulation made from shredded wood with cement binder.

Fill insulation made from redwood bark at density of 5

pounds per cubic foot.

Shredded paper and asbestos

fiber with emulsified asphalt

binder.

Fiber made from rock, slag or

glass.

Expanded

Shredded wood and cement.

Shredded redwood bark.

Paper and asbestos fiber.

Mineral wool

Vermiculite

Cotton Batt or blanket

See footnotes at end of table.
WOOD HANDBOOK 451

TABLE 52— Values ^ recommended for comvutzTig overall coefficients of thermal

transmission 2— Continued

Material Description

Conductivity

AConductance

C

Resistivity

1

k

Resistance

1

C

Interior finish:

Composition wallboard,. ^6 toHincb thick- 0.50

3.80

2.00

Oypsnm plaster .80

Oypsum wallboard Hhichthick 3.70

2.^iO

.66

.60

.31

4.40

3 4. 00

2.50

1.25

2.27

1.00

.64

.60

.58

.40

0 27

Gypsum lath and plaster Pla^t^r assumed >^ inoh .42

Insulating fiberboard (H Plain or decorated ) 52

inch).

Insulating board lath Plaster assumed H inch 1 67

(H inch) and plaster.

Insulating board lath (1 do 3 18

inch) and plaster.

Metal lath and plaster. ,. Plaster assurn^d ^ tn<^h 23

Plywood 3-ply, H inch thick 3 25

Wood lath and plaster... 40

Masonry materials:

Brick Common, assumed 4 inches

thick.

Face, assumed 4 inches thick

SO

Do ... ... 44

Cement mortar. . 12.00 .08

Clay tile:

4-inch Hollow 1 00

6-inch do 1.57

8-inch do 1.67

10-inch - - - - - . do 1.72

12-inch do 2.50

Concrete Lichtweight aggregate ^ 2.50

4.09

12.00

.40

.22

.08

Do C^inder acßrreeate -

Do Sand and gravel aggregate

Hollow, lightweight aggregate ^.-

do ^

Concrete blocks:

8-inch - - - - .50

.47

1.00

.60

.53

1 00

.80

.61

.46

2.00

12-inch.. --- . 2. 13

4-inch Hollow, cinder aggregate. 1.00

8-inch do - -,- 1.66

12-inch do - - 1-88

8-inch Hollow, sand and gravel aggregate.

do -

1.00

12-inch 1.25

03TÇ>sum tile:

3-inch Hollow 1.64

4-inch do 2.18

Tile and terrazzo

Stonft12.00

12.00

.08

.08

Roofing materials:

6.00

6.50

3.53

6.50

20.00

1.28

2.82

.42

33.22

.17

.15

Built-up roofing — .28

.15

^}fítí^ Ass^nn*^ t-hickneas V> inch .05

.78

Sheathing:

.35

Insulating fiberboard

(2^ inch).

Plywood

2.37

3-ply, Mo inch thick 3.31

See footnotes at end of table.
452 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

TABLE 52. — Values ^ recommended for computing overall coefficients of thermal

transmission 2-—Continned

Material Description

Conductivity

k

conduct- ^

Resistance

1

C

Sheathing—Continued

Wood (2^2 inch;.

Wood (2^2 inch) plus

building paper.

Surfaces:

Inside

For known species and moisture

content see values for wood

(fig. 5).

i.n2

.86

1.65

1.95

1.21

6.00

5.25

0.98

1.16

Ordinary materials, still air:

Vertical .61

Horizontal, heat flow up . 51

Horizontal, heat flow down_

Ordinary materials, 15 miles-perhour wind.

Reflective materials, 15 miles83

0utside . 17

.19

per-hour wind.

' Values are expressed in British thermal units per hour per square foot per 1° F. temperature difference

on opposite sides of the material. Conductivity values (k) are per inch of thickness; conductance values

(C) are for thickness or construction stated.

2 Table based chiefly on data from 1952 American Society of Heating and Ventilating Engineers Guide.

3 Calculated values based on tests made at the Forest Products Laboratory.

* Expanded slag, burned clay, or pumice.

HEAT LOSS THROUGH DIFFERENT TYPES OF DOORS

AND WE>íDOWS

In determining heat loss for houses, the loss through doors and

windows should be included in the computations. Table 53 gives

heat transmission values for doors and windows.

WHERE TO INSULATE

Insulation is used to retard the flow of heat through ceilings, walls,

and floors if wide temperature differences occur on opposite sides of

these structural elements (4, 6, 7, 10), In dweUings, for example,

insulation should be used in the ceiling of those rooms just below an unheated attic. If the attic is heated, the insulation should

be placed in the attic ceiling and in the dwarf walls extending from

the roof to the floor. All exterior walls should be insulated. Floors

over unheated basements, crawl spaces, porches, or garages should

also be insulated.

Condensation

Two types of condensation create a problem in buildings during

cold weather; that which collects on the inner surfaces of windows,

ceilings, and walls, and that which collects within walls or roof spaces

{8, 9). Smiace condensation is quite common in industrial buildings

where relative humidity is high. In a factory or warehouse, water

dripping from a ceiling may seriously damage manufactured materials and machinery. ''Sweating^^ walls and windows also are a

:M~
WOOD HANDBOOK 453

TABLE 53.~ Coefficients of transmission (U) commonly used for doors, windows

and glass blocks '

Item

iHe-inch door

IH-inch door

iH-inch door

2i/Mnch door

Single

With storm sash, spaced 1 inch.

Double glazing 3

Glass blocks ^

Door 2

0. 5)9

.51

.4f)

Door plus

storm door

0.32

.30

.28

25

Window

1.13

.53

-,.61

1 Table based upon data from 1952 American Society of Heating and Ventilating Engineers' C^uide.

2 For doors containing thin wood panels or glass, use the same U values as shown for single windows.

3 2 thicknesses of glass in 1 sash spaced H inch apart.

* Blocks are 7% by 7^4 by 3^^ inches.

serious nuisance. Condensation may collect on the indoor surface

of exterior walls of houses, particularly behind furniture or in outside

closets, causing damage to finish, furniture, and flooring. It may also

collect on windows, particularly those unprotected by storm sash.

Water running off the windows may create conditions favorable to

decay in wood sash, cause rust in steel sash, and damage window

finish and walls and floors below the windows.

To prevent surface condensation, the relative humidity in the

building must be reduced or the surface temperature must be raised

above the dew point of the atmosphere. Adding insulation to a wall

or roof reduces heat transfer through the unit, and the inside surface

temperature is increased accordingly. The amount of insulation

required for given conditions can be calculated. Storm sash or

double glazing reduces condensation on windows.

Moisture sometimes condenses wdthin the walls or roof spaces

of buildings if relative humidity is comparatively high during cold

weather. In walls, this type of condensation may result in decay of

wood, rusting of steel, and damage to exterior paint coatings {2). In

roofs and ceilings it may cause stained finish and loosened plaster and

increase the chances of decay in structural members.

Under certain conditions when outdoor temperatures are low,

water vapor will pass through permeable inner-surface materials and

condense within a wall or roof space on some cold surface havmg a

temperature below the dew point of the atmosphere on the w^arm side.

When the condensing surface is considerably below the dew pomt,

differences in vapor pressure between the cold and warm sides cause

vapor to move from the high-vapor-pressure zone to the low-pressure

zone. The rate of movement is more or less proportional to the

difference in vapor pressure and inversely proportional to the resistance

of interposed materials. The amount of condensation that collects

on the condensing surface depends upon the resistance of mtervenmg

materials, differences in vapor pressure, and time. There will also

be some difference in vapor pressure between the condensing surlace

and the ou4door atmosphere. Some part of the water vapor reaching

the condensing surface wdll therefore escape outside-through materials

that are permeable. Materials comnmnly used for side wall covermgs
454 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

are usually permeable. Roofing materials are generally highly

resistant to vapor transmission. Wood shingles applied over narrow

roof boards are not resistant to vapor transmission.

Insulation can cause increased condensation under certain conditions. Heat flow is reduced by insulation, and consequBntly the

temperature of those parts of a wall or roof on the cold side of the

insulation is lower during cold weather than if no insulation were used.

This in turn means a greater diffei^ence in vapor pressure between the

warm side and the condensing surface and a greater amount of condensation. Insulation is important, however^ as a means of conserving

heat and creating comfortable hving conditions and its influence on

condensation can be largely mitigated.

The rate of vapor transmission thj-ough inner siu*faces may be

controlled by the use of materials having h%h resistance to vapor

movement. Such vapor barriei^ should be located on or near the

warm surface so that the temperature of the barrier will always be

above the dew point of the heat^ space.

For new construction, the barrier may be any one of several materials, such as asphalt-impregnated and surface-coated paper applied

over tne face of the studs, gypsum lath with alimiinum-foil backing,

fiberboard lath with vapor-resistive coating, blanket insulation with

vapor-resistive cover, and reflective insulation. For existing construction, certain types of paint coatings add materially to the resistance

to vapor transfer. One coat of äumlnum primer followed by two

decorative coats of flat paint or lead and oil seems to offer satisfactory

resistance (5, 8,10).

Ventilation

Attics and roof spaces are generally provided ^vith suitable openings

for ventilation, partly as a means of summer cooling and partly as a

means oí preventing winter condensation {10). For gable roofs,

louvered openings are provided in the gable ends, allowing at least 1

square foot of louver opening for each 300 square feet of projected

ceUing area. For hip roofs, inlet openings are usually provided under

the overhanging eaves with a globe ventimtor at or near the peak for an

outlet. The inlets should equal 1 square foot to each 900 square feet

of projected ceüing area and the outlets 1 square foot to each 1,600

squa,re feet. Ventilation for flat roofs should be developed to suit

the method of construction.

LITERATURE CITED

(1) AMERICAN SOCIETY OF HEATING AND VENTU^ATING ENGINEERS.

1962. HEATING, VENTnATING, AIR CONDITIONING GUIDE. Ed, 30, 1496

pp., fllus. New York.

(2) BROWNF, F.ll

1927. SOME CAUSES OF BLISTERING AND PEELING OF PAINT ON HOUSE

SIDING. Amer. Paint and Varnish Mfrs. Assoc, Sei. Sec. Cir.

317: 480-486.

(3) CLOSE, P.D.

1946. BUILDING INSULATION. Ed. 3, 372 pp., illus. Chicago.

(4) DILLER.J. D.

1946. DECAY, A HAZARD IN BAßEMENTLESS HOUSES ON WET SITES: PROTECTION OF THE SUBSTRUCTURE TIMBERS í ROM EXCESSIVE

M0I9TUBB BY THE USE OF AN ASPHALT ROLL ROOFING AS A SOIL

COVER. Amer. Btiilder 68 (7): 92, 122, 124.
WOOD HANDBOOK 455

(5) DuNLAP, M. E.

1949. CONDENSATION CONTROL LN DWELLING CONSTRUCTION. U. S.

Housing and Home Finance Agency, 73 pp., illus.

(6) SHUMAN, L.

1950. INSULATION. WHERE AMD HOW MUCH. U. S. Houslng and Home

Finance Agency, Tech. Reprint 8er. 4, 9 pp., illus.

(7)

1960. INSULATION OF CONCRETE FLOORS IN DWELLINGS. U. S. Housing

and Home Finance Agency, Tech. Reprint Ser. 8, 8 pp., illus.

(8) TEESDALE, L. V.

1947. REMEDIAL MEASURES FOR BUILDING CONDENSATION DIFFICULTIES.

U. S. Forest Prod. Lab. Rpt. R1710, 27 pp., illus. [Processed.]

(9)

1941. CONDENSATION PROBLEMS LN MODERN BUILDING. U. S. Forest

Prod. Lab. Rpt. R1196, 9 pp., illus. [Processed,]

(10)

1949. THERMAL INSULATION MADE OF WOOD-BASE MATERIALS. U. S.

Forest Prod. Lab. Rpt, R1740, 40 pp., illus. [Processed.]
BUILDING FIBERBOARDS

A building fiberboard is a sheet material maiuifaetured of refined or

partially refined vegetable fiber, principally from wood, although fiber

from bagasse, waste paper, straw, licorice root, and cornstalks is used to

some extent. Binding agents and other materials may be added during manufacture to increase strength, resistance to moisture, fire, or

decay or to improve some other property. Among the materials added

are rosin, alum, asphalt, paraffin, various cements, preservative and

fire-resistant chemicals, synthetic resins, and drying oils.

Building fiberboards are manufactured primarily for use as panels,

insulation, and cover materials in buildings, for components of cabinets, cupboards, doors for millwork and furniture, and other constructions where flat sheets of moderate strength are desh^ed. The

use of fiberboards as a structural material is increasing.

These board products are manufactured in densities ranging from

2 to about 90 pounds a cubic foot. The lower density boards are used

primarily as insulation and the higher density boards as structural

materials or wearing surfaces. Since the classification of building

boards used in this handbook is based on density, rather than on

method of manufacture or form of raw material used in manufacture,

it is essentially a classification based on end uses, rather than manufacturing processes.

Building boards may be essentially fibrous in character, as are most

of the conventional insulation boards and hardboards; or they may be

composed of distinct particles bonded together in a flat sheet with a

synthetic resin. Some boards are not definitely either a fibrous or a

particle type but are a combination of the two types. Most of the

fibrous boards are manufactured by an adaptation of a papermaking

process; that is, the fiber raw material is reduced to a pulp and formed

into a mat from a water slurry on the screen of a paper machine. The

wet mat is then dried in a continuous drier or simultaneously compressed and dried into a compact sheet. In a modification of the conventional wet-felting process, known as the semidry process, the fibers

are carried in an air suspension rather than a water suspension and

are air felted into the mat. The resin-bonded particle boards are

made by blending wood particles or chips with various resins and

consolidating the mixture under heat and pressure.

CLASSIFICATION OF BUILDING FIBERBOARDS

The following classification by. density may be used to define the

different classes of building boards:

Density

(gin. per cc.)

Semirigid insulation board 0.02 to 0.15

Rigid insulation board ' Ín î^ en

Intermediate-density board -^^ ^o -^0

Hardboard, untreated or treated '^21^ I'V^

Special densified hardboards 1-35 to 1.45

457
458 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Classification of building fiberboords by density is not ideal, particularly when there is a considerable ov¿1ap in both properties and

uses. When details of manufacture are considered, however, a classification by density can be used with better success than classifications

based on strength, thickness, or some other mechanical property.

The strength and physical properties of the different types ofIbuüding fiberboards are given in table 54. These values can he considered

as only approximate, since the properties of different proprietary

products vary, depenaing on the land of fiter and its degree of refinement and the binders, imprégnants, and method of manufacture used.

Published data from actual tests should be consulted for comparisons

of different products or when the contemplated use requires a particular strength or physical property. The test procedures given in

reference (7)^^ mav be used to evaluate the different properties of

building fÎDerboaras.

SEMIRIGID INSULATION BOARDS

Semirigid insulation board is the term apphed to fil:>erboard products

manufactured primarily for use as insidation. These very low

density fiberboards have about the same heat-flow characteristics

as conventional blanket or batt insulation but have sufficient stiffness

and strength to maintain their position and form without being

attached to the structure proper. They may be bent around curves

or comers, and when cemented, mechanically fastened, or placed

between framing members will hold their shape and position even

though subjected to considerable vibration.

The senurigid insulation boards are mamifactured in sheets from

K to IK inches thick. When greater thicknesses are required, two

or more sheets are cemented together. Sheet sizes vary from 1 by 2

feet to 4 by 4 feet.

Semirigid insidation boards are used for heat insulation in truck

and bus bodies, automobiles, refrigerators, railway cars, on the

outside of duct work, and wherever vibrations are so severe that loosefill or batt insvdation may pack or shift. They are also used as

soimd insulation for the walls of telephone booths and around speakers

in radios, pubhc-address systems, and phonographs and as cushioning

in utihty-quahty furniture and for packaged material.

RIGID INSULATICW BOARDS

About two-thirds of the footage of building fiberboard produced

may be classed as rigid insulation boards. These boank are used

in housing and many aUied applications where their economy, structural strength, and insulation (p. 445) and sound-absorbing quahties

satisfy a particular use requirement. They are usually subdivided

into the following use classifications: Class A, general-use boards;

Class B, lath for plaster base: Class C, roof insuLa^on board; Class D,

interior boards, factory-finished; Class iL sheathfaig; and Qass F,

interior board, flame-resistant, finished surface. Physical and

strength properties of rigid insulation board are summarized in

table 54,

32 Italic numbers in parentheses refer to Literature Cited, p. 465.
TABLE 54.—Physical properties and general classifications o/ building fiberboa '^ds^

o

* General classification of

Thicknesses

generally

available

Specific

gravity Density

Thermal

conductivity (/:)2

Modulus of

rupture

Modulus of

elasticity

in bending

Tensile

strength

parallel to

surface

Tensile

strength

perpendicular to

surface

Compression

strength

parallel to

surface

Water absorption

(24-hour immersion) Maximum

linear

expansion 3

Hard-

"^ building fiberboards

By

wei^t

By

volume

ness

CO

^ Semirigid insulation board.

Rigid insulation boaixi *

Intermediate-density fiIn.

Vz-VA-..

3/Í6-H—

H-H....

H-l

H-2

0.02-0.15 .-

0.15-0.40-.

0.40-0.80-.-

0.40-0.80-..

0.88-1.04...

0.95-1.15...

0.80-1.05...

1.35-1.45.-.

Lb. per

cu. ft

1.5-9..-.

9-25

25-50....

25-50....

50-65..--

60-70..._

50-70

0 24-0 27

P. 5. Í.

1,000

P. 8, L P. s. i. P. s. i. P. s. i. Pet. Pet. Pet.

0.27-0.40 .-

0.40-0.80.--

0.40-0.80...

0.80-1.40..-

1.50

250-700

400-4,000-..-

400-1.000

25-90

90-700

200-500--..

800-2,000

10-25 5-10 0.6

.75

.4

700-3,400

intermediate-density resinbonded particle board

Fibrous hardboard (un100-350 100-150.-

9-18

45-60--..

3,000-6,000-.

7,500-10,500..

3,000-3,500_-.

10,000-12,500

400-800._..

800-1,000.-

40C-Ó00....

1,250

1,000-3,000

4,000-5,500-

300-600-.-.

7,700

2^00-4,000-

4,200-5,300.

3,500-4,000.

26,500

Fibrous hardboard (treated).

Resin-bonded particle hardboard

6-13

300

500

15-40.-. .85 9 2, 100

Special densiñed hardboard. 85-89...- 1.85 0.3-1.2.-. 7 90

1 Values presented in this table must be considered as approximate, since properties between different products vary, depending on density, base materials, binders, imprégnants,

and method of manufacture; for accurate values for any product, actual tests are required.

2 British thermal units oí heat passing through 1 square foot of 1-inch-thick material in 1 hour for each 1» F. difference in temperature between the surfaces of the material.

3 Expansion produced by the change in moisture content from equilibrium at 50 percent relative humidity to equilibrium at 97 percent relative humidity.

^ Includes general-use boards (class A); lath for plaster base (class B); roof insulation (class C); interior board, factory-finished (class D); sheathing (class E); and interior board,

flame-resistant finished surface (class F).

5 Sheathing boards are generally available in thicknesses of h and ^y^z inch.

* Load in pounds required to imbed a 0.444-inch-diameter steel ball to H' its diameter.

' Hardness as determined on the "M" scale of the Rockwell hardness tester.

O

O

ö

>

dd

o

o

CO
460 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Basically, the material in the different products from any one

manufacturer may be the same. Because of end use, the board may

})e modified to sonie extent by adding imprégnants, coating or painting

its surface, or cutting it to*^some special size. The edges and ends

may be tongued and grooved, shiplapped, V jointed, beveled, or

shaped instead of square for tight or decorative construction. Acoustical i)oard is a special type of insulation board that has multiple

holes drilled or punched'in the surface to break the sound-wave

pattern. Additional information on rigid insulation boards is given

in Commercial Standard 42-49 (4) and Federal Specification LLL-F321b (5).

General-Use Boards

Some rigid insulation boards are manufactured for multiple uses

or for remanufacture into boards for specific uses. These boards

are classified as general-use boards. They are % to 1 inch thick and

are usually available in sizes of 4 by 8 feet or larger. Some of these

products may be used as exterior wall coverings for temporary buildings. Some have satisfactory durability when protected with paint,

so'^that they may be used for panels, siding, or other exterior covering

in low-cost housing. A few products, including some sheathing

boards, are available that are impregnated with cleca^^-inhibiting

chemicals to increase their resistance to deterioration when used

where the moisture content and temperature are favorable for decay.

vSome general-use boards have a prime coat of paint that reduces

bleed-through of asphalt imprégnants when ordinary paints are used.

These prime-coated boards may be given successive coats of paint

in the same wa}^ as other materials.

Fiberboard Lath

Rigid insulation board is often used as lath for plaster base. Such

lath is usually manufactured in }^-inch-thick sheets, 18 by 48 inches

in area, with shiplapped or otherwise matched edges. Some brands

are provided with metal clips that aid in transferring forces from one

sheet to another. Some are impregnated with an asphaltic or similar

material, so that the board has high strength retention when wet.

Fiberboard lath may have a heavy bituminous coating that acts

as a vapor barrier.

Fiberboard lath is nailed to the studding of a house with the

vertical joints staggered in the same manner as for gypsumboard

lath. Large sheets 4 by 8 feet, are occasionall}^ used as plaster base.

When this is done, strips of expanded metal lath should span all joints

to reduce plaster cracking at joints.

Fiberboard lath is superior to other plaster base in thermal and

sound insulation properties, and, because of its thermal insulation

qualities, dirt patterns are claimed to develop more slowly on the

final painted plaster surface.

Roof Insulation

Roof insulation boards (Class C) also comprise a substantial part

of the production of rigid insulation board. They are manufactured
WOOD HANDBOOK 461

in sheets 2 by 4 feet in area and }^ to 2 inches thick. Roof insulation

boards are used to insulate flat or slightly sloped, built-up roofs.

i hey may be used m single and multiple thicknesses and are laid

on the deck ol the roof as a base for the layers of mopped roll roofing.

Sheathing Board

The biggest growth in the use of rigid insulation board has been as

sheathmg for houses. Sheathing boards are manufactured usually

m a 2%2-mch thickness and are either 2 by 8 feet or 4 by 8 feet in area.

The 2- by 8-foot sheathing boards are furnished with shiplappod^

V-jomted, or otherwise matched edges and are applied lionzoutally

to the outside framework of a house. The 4- by 8-ioot board is

apphed with the long dimension vertical and, when adequately nailed,

imparts considerable rigidity to the wall of a house. When properly

attached 4- by 8-foot sheathing is approved by the Federal Housing

Authority for use in a house without further bracing. With 2- by

8-foot sheathing, additional bracing of the wall is required.

Fiberboard sheathing generally is impregnated or coated with

materials that increase its strength retention when wet. In general,

it furnishes low-cost coverage, is easy to apply, öfters good protection

from air infiltration, and has a greater insulation value than heavier

sheathing material. The principal disadvantage in using fiberboard

sheathing is that, if beveled siding is used for exterior cover, joints in

the siding can occur only at studs, because the fiberboard sheathing

has Httle resistance to nail withdrawal. If some other siding material,

such as wood shingles, is used, furring strips of wood are usuall}^

provided to which the covering material is nailed. Some manufacturers recommend the use of a ''shingle backer construction'' with

special nails to attach the shingles.

The moisture content at which framing lumber, for use with either

fiberboard or wood sheathing, should be installed is discussed on

page 329.

Interior Board

Interior-finish boards are classified as Class F boards if they are

finished with a paint or impregnated with chemicals that retard the

spread of flame and as Class D boards if they have a natural finish or

are painted with an ordinary paint. Both classes are used for interior wall and ceiling coverage and are manufactured in a wide range

of sizes in tile and plank form. Thicknesses most generally available

are ji, %, and 1 inch. Tiles are manufactured in 8-, 12,- and 16-inch

squares and 12- by 24-inch and 16- by 32-inch rectangles and are

generally applied to ceilings. All edges are tongued and grooved, or

otherwise matched, so that adjacent tiles will produce an even surface.

The edges also are usually beveled for decorative purposes. Planks

are manufactured in widths of 8, 10, 12, and 16 inches and in lengths

of 6, 8, 10, and 12 feet and are usually used for walls. They are

usually applied vertically. Their edges are tongued and grooved, or

otherwise matched, and may have decorative beveling and beading.

Interior-finish insulation board is used in new construction (drywall) and for repair and remodeling of existing structures. The

boards can be cemented to existing plaster that is not loose or uneven,
462 HANDBOOK 12, U. S. DEPARTMENT OF AGRICULTURE

or attached to furring strips by concealed fasteners. Because interiorfinish boards have good thermal insulation characteristics, dirt

patterns are likely to develop more slowly than on conventionally

plastered surfaces. Moreover, large expanses of plaster in ceilings

are likely to crack in time, but, since ceihngs of insulation board tile

have numerous joints, they do not develop other cracks. Interiorfinish insulation board usually should not be apphed in large sheets

with masked joints, as is done with g3Tsum board, because the

linear expansion caused by increase in moisture content with seasonal

changes in relative humidity may produce objectionable compression

buckling of the panel.

The principal disadvantage of interior-finish insulation board for

use as wall covering is its softness and poor resistance to scufläng or

abrasion. For that reason, insulation board planking is often used

for the upper parts of walls and denser and more abrasion-resistant

materials, such as pl^^vood, for the lower parts.

Acoustical board is a special form of interior board tile manufactured with numerous holes, about one-eighth inch in diameter, in the

exposed surface of the tile. These tile ai^ to improve the acoustical

properties of rooms and are usually applied to ceilings.

INTERMEDIATE-DENSITY FIBROUS BOARDS

Building fiberboards of the intermediate-density classification

include boards weighing between about 25 and 50 pounds a cubic

foot. They are sometimes called wallboards, but because rigid

insulation board and hardlx)ard are also used as wall covering, the

term ^^intermediate-density" is more restrictive. The large range in

strength and other physical properties for intermediate-density

fiberboard is shoA\Ti in table 54. Included in the intermediatedensity boards are the laminated-paper wallboai^s and the partially

densified hardboards.

The primary use for intermediate-density fibrous boards is for

interior wall covering. Because the}^ are denser than the rigid

insulation boards, they usually have more resistance to abrasion or

other surface damage than lower density boards. These boards also

have limited use in furniture manufacture. They can be used to

advantage as drawer bottoms and dividers in chests, as backs in

cabinets and similar items, and as core stock in utility-grade furniture.

Intermediate-density fibrous boards are manufacture<l in %^- to J^-

inch-thick sheets up to 4 by 12 feet in size. When used as paneling,

they may be cemented or nailed in place. Decorative molding often

is used at joints. Standard woodworking tools can be used for fabrication. The boards take and hold paint well, though the surfaces

sometimes must be sealed to prevent paint from soaking into them.

The laminated-paper wallboards often have a large linear expansion

with changes in moisture content. If large increases in moisture

content may be expected in service, the panels should be attached in

such a way that they are free to expand; otherwise, they may buckle

between supporting members and even pull loose from the framing.

Pertinent standards and specifications for intermediate-density fibrous

boards are cited in Commercial Standard 112-43 {3) and Federal

Specification UU-W-1 Ola {6).
WOOD HANDBOOK 463

INTERMEDIATE-DENSITY RESIN-BONDED PARTICLE

BOARDS

Production of intermediate-density resin-bonded particle boards is

increasing, because more manufacturers are realizing that it is a

profitable way to utilize residues from millwork, furniture, or similar

operations. They are marketed for use as interior paneling in houses

and for use in furniture and millwork. Because the resin-bonded

particle boards of intermediate density stay flat with changes in

moisture content, they are being used as alternates for solid lumber

cores in veneered construction. The linear expansion with changes

in moisture content may be large, but it is not greater than the values

for wood across the grain.

FIBROUS HARDBOARDS

Most hardboaixls can be classified as fibrous in nature. They

include boards made by the conventional wet-felting process, by

forming a wet mat as in the conventional process but drying it before

pressing, and by air-felting of dry or partially dry fibers. Hardboard

manufactured by the conventional process is characterized by 1

smooth face and 1 face with a screen impression. The ^^screen back"

results because a screen must be used to allow steam to escape from

the wet fiber sheet when hot-pressed. With the m,odification of the

conventional process in which the mats are dried before hot-pressing

it is possible to produce a hardboard with two smooth faces. In the

air-felting process, a board with two smooth faces is produced if the

moisture content of the fiber is kept low; otherwise, it is necessary to

produce a screen-back board.

Hardboards are classified as untreated or treated. The treated

boards are often called tempered boards. The tempering process

consists of impregnating pressed boards in drying oils and then baking

them in an oven. This treatment increases the strength and water

resistance above tliat of untreated hardboard. The comparison of

the strength properties given in table 54 indicates the superiority of

the treated hardboards over the untreated boards. The untreated

hardboards are manufactured in densities ranging from 50 to 65

pounds a cubic foot; the treated hardboards usually are slightly

heavier, from 60 to 70 pounds a cubic foot.

Hardboards are manufactured in }i- to ^e-inch-thick sheets as large

as 4 by 16 feet. They are dense, uniform, usually smooth surfaced

can be worked with ordinary woodworking tools, take finishes well,

can be bent to single curvature, and can be punched or die-cut. Some

material is embossed or scored during the pressing operation to simulate a leather or tile surface.

Hardboards have many of the same uses thin plywood has. In

housing, hardboards are used for interior paneling, floor surfacmg,

and exterior siding (in the form of either lapped sidmg or panels). It

millwork, they are used for insert panels in conventional doors; surface

panels for flush doors; backs, counter tops, and dividers for cabmets;

and bottoms in drawers. Hardboards are used as facing material for

reusable concrete forms, especially where a smooth finished surface is
464 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

desired. Other uses of hardboard include window displays, store and

office fixtures, paneling for railway passenger cars, and furniture

paneling, drawer bottoms, dividers, and exterior surfaces. Hardl)oards are used for crossbands in veneered construction when decorative veneers are glued to solid lumber cores, and as facing for plywood.

In manufacturing operations, templates and assembly jigs are made

from hardboards.

Added information on fibrous hardboards is given in Hardboard

Industry in the United States (2). The applicable specification is

cited in Federal Specification LLL-F-311b (7).

An important part of the hardboard industry is the remanufacture

of hardboards by scoring and pamting to produce panel material

with a highly decorative, factory-applied paint or enamel finish.

These hardboard materials are called ''prefinished wall panels^' and

are sold for wall covering in kitchens and bathrooms of houses where

dry-wall construction is used. Metal moldings and a means

of attachment are provided, so that the prefinished wall panels can

be used successfully in these rooms where high humidity is common

without objectionable buckling due to expansion of the hardboard.

CS 176-51 (5) is the appropriate commercial standard for this material.

RESIN-BONDED PARTICLE HARDBOARDS

Production of resin-bonded particle boards of densities between 50

and 70 pounds a cubic foot is limited. These boards are becoming

available in greater quantity, however, and may be used for many of

the same applications as the conventional fibrous hardboards. They

are uniformly light in color and have a surface that is hard and resists

damage. Hardboards of this type are made in panels as thick as 1

inch and as large as 4 by 12 feet. Their approximate strength and

physical properties are given in table 54. The boards take paint and

stain finishes well and can be glued and worked by methods and equipment used for fabricating with wood. Veneers or lithographed-paper

overlays simulating wood grain are sometimes glued to the surface of

the panels.

The resin-bonded particle hardboards have adequate strength

(table 54) for interior applications in housing or for furniture. They

are not usually recommended for use in exterior or other severe exposure, because they shrink and swell more than desirable. Because

the wood particles are compressed to more than their usual density

during pressing, these boards are also subject to springback (thickness

swelling) when moisture content changes occur in service. This

springback may be as much as 20 percent in some products. Special

design considerations must be made when the sizes of the panels are

large enough for the linear change to be appreciable.

SPECIAL DENSIFIED HARDBOARDS

A ne^v group of very dense hardboard products has been developed

for specialized uses. These hardboards are manufactured from fibrous

mats formed in the same manner as for the conventional.hardboards

and are available in densities from 85 to 89 pounds a cubic foot and
WOOD HANDBOOK 465

in thicknesses up to 2 inches. A summary of their important strength

properties is presented in table 54. *^

These high-density hardboards can be used to make dies, for either

press formmg or stretch forming of metals, that have adequate wearing qualities and are economical. Because these boards are lighter in

weight than metals, manufacturing jigs made from them are handled

and moved more easily then metal jigs. Because their electrical

resistance is high, and because they are durable and can be cut and

drilled easily, they can be used satisfactorily for bases and panels in

electrical apparatus.

LITERATURE CITED

(1) AMERICAN SOCIETY FOR TESTING MATERIALS.

1952. TENTATIVE METHODS OF TEST FOR EVALUATING THE PROPERTIES OF

FIBER BUILDING BOARDS. Aiuer. Soc. Testing Mator. Standard

D1037-52T: 831-846, illus.

(2) LEWIS, W. C.

1952. HARDBOARD INDUSTRY IN THE UNITED STATES. Jour. Forest Prod.

Res. Soc. 2 (4): 3-6, 68.

(3) U. S. DEPARTMENT OF COMMERCE.

1943. HOMOGENEOUS FIBER WALLBOARD. Com. Standard CS 112-43,8 pp

(4)

1949. STRUCTURAL FIBER INSULATING BOARD. Coin. Standard CS 42-49,

17 pp., illus.

(5)

1951. PREFiNisHED WALL PANELS. Com. Standard CS 176-51, 10 pp.

(6) U. S. FEDERAL SUPPLY SERVICE.

1935. WALLBOARD, COMPOSITION. Fed. Specif. UU-W-lOla, 4 pp.

(7)

1939. FIBERBOARD. HARD PRESSED, STRUCTURAL. Fed. SpCCif. LLL-F311, 4 pp.

(8)

1942. FIBERBOARD, INSULATING. Fed. Specif. LLL-F~321b, 11 pp.
MODIFIED WOODS AND PAPER-BASE LAMINATES

Materials with properties quite different from those of the original

wood are obtained by chemically treating wood, compressing it, or

combining the two treatments. Likewise, sheets of paper treated with

chemicals can be laminated into thick, hard structural materials.

These modified woods and paper-base laminates are considerably

more expensive than normal wood because of the cost of chemicals and

the amount of processing required to produce them. They should

therefore be used only for special purposes where their increased cost

is offset by improvements in critica] properties and better service.

MODIFIED WOODS

Chemical Treatments

Wood is treated with chemicals to increase its decay, fire, and

moisture resistance. Application of water-resistant chemicals to the

surface of wood, or impregnation of the wood with such chemicals

dissolved in volatile solvents reduces the rate of subsequent swelling

and shrinking of the wood but does not affect the final dimension

changes caused by seasonal humidity changes. Paints, varnishes,

lacquers, and wood-penetrating water repellents have this type of

effect. These chemical treatments for wood are discussed elsewhere

in this handbook.

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 mthin the swollen structure of the wood fibers (26).^^

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 (i, 20,

21, 23), No thermoplastic resins have been found that effectively

stabilize the dimensions of wood.

Wood treated \\dth a thermosetting fiber-penetrating resin that is

cured without compression is known as impreg. The wood (preferably veneer) is soaked in the aqueous resin-forming solution or

impregnated with the solution under pressure until the resin content

is equal to 25 to 35 percent of the weight of the dry wood. It is

allowed to stand under nondrying conditions for a day or two to

permit uniform distribution of the solution throughout the wood.

The resin-containing wood is dried at moderate temperatures to

remove the water and then heated to higher temperatures to set the

reún {21, 23).

Uniform distribution of the resin has been effectively accomplished

with solid wood only in the case of the sapwood of readily penetrated

species in lengths up to 6 feet (15). The drying of resin-treated solid

wood also introduces checking and honeycombing (15). For these reasons, it is recommended that the treatments be confined to veneer and

the treated and cured veneer be used to build up the desired objects.

33 Italic numbers in parentheses refer to Literature Cited, p. 477.

467
468 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Any species of veneer except the resinous pines can be used. The

stronger the original wood, the stronger will be the product.

Impreg has a number of properties differing from those of normal

wood and ordinary plywood. These are given in table 55, together

with similar generalized findings for other modified woods. Table 56

gives data for the strength properties of birch impreg (2, 4)-

Impreg found limited use during World War II in plywood panels

used to make housings for special electrical control equipment where

high electrical resistivity was needed. It shows promise for the

facing of exterior plywood to eliminate face checking. It also could

be used to advantage in master patterns, such as master shoe lasts,

in which dimensional stabilit}^ is of major importance. It has been

given large-scale tests for use in patterns and die models for automobile parts.

TABLE 55.— Properties of modified woods

Property Impreg Compres Staypak

Specific gravity.. _ _

Equilibrium swelling

and shrinking.

Springback

Face checking

Grain raising

Surf'ice finish

Permeability to water

vapor.

Decay and termite resistance.

Acid resistance .

Alkali resistance

Fire resistance

H cat resistance

15 to 20 percent greater

than normal wood.

M to \^ that of normal

wood (21, 23).

NT one..

Practically eliminated

(23).

Greatly reduced.

Similar to normal wood.

About Mo that of normal wood (23).

Considerably better

than normal wood (23).

Considerably better

than normal wood (23).

Same as normal wood.

Same as normal wood

(23 K

Greatly increased.

Usually 1.0 to 1.4 f££)

Vi to H that of normal

wood at right angles to

direction of compression, greaterin direction

of compression but very

slow to attain (22, 2^).

Yevy small when properly made.

Practically eliminated

for specific gravities

below 1.3 (22, 20-

Greatly reduced for uniform-texture woods,

consi<lerable for contrasting-grain woods.

Varnished-like appearance for specific gravities above about 1.0.

Cut surfaces can be

uiven this surface by

sanding and buffing

(22).

No data but presumably

much lower than impreg.

Considerably better than

normal wood (22).

Better than Impreg because of impermeability.

Somewhat better than

normal wood because

of Impermeability.

Same as normal wood for

long e.xposure, somewhat better for short

exposure (20, 22).

Greatly increased

1.25-1.40 (in).

Same as normal wood at

right angles to compression, greater In direction

of compression but very

slow^ to attain (16).

Moderate when properly

made (16).

About the same as in

normal w^ood.

About the san)e as in

normal wood.

Varnished-like appearance, (^ut surfaces can

be given this surface

by sanding and buffing

ilO).

No data but presumably

lower than impreg.

Normal, but decay occurs

somewhat slower.

Better than normal wood

because of impermeability but not as good as

compreg.

Somewhat better than

normal wood because of

impermeability.

Same as normal wood for

long exposures, somewhat better for short

exposures.

No data.
Property

WOOD HANDBOOK 469

TABLE 55.— Properties of modified woods— Continued

Staypak

Electrical resistance

Heat conductivity..

Compresstvo strength.

Tensile strength..

Flcxural strength.

Impreg Compreg

Hardness..

Impact strength:

Toughness..-

Izod.

Abrasion resistance

(tangential).

Machinability

Moldability.

Gluability..

Mo that of normal wood

at 30 percent relative

humidity; Moioo that

of normal wood at 90

percent relative humidity (S3).

Slightly Increased (S3)...

Increased more than

proportional to specific gi-avity Increase

(2,1,).

Decreased significantly

(^,4).

increased less than proportional to specific

gravity increase (2, f^.).

Increased considerably

more than proportional to specific gravity increase (4,5^).

About \^ of value for

normal wood (2, 4)-

About M of value for

normal wood (Î, 4).

About \^ of value for

normal wood (4,35).

About the same as normal wood, but dulls

tools more.

Cannot be molded, but

can be formed to single

curvatures at time of

assembly.

Same as normal wood—

Slightly less than impreg

at low relative humidity values due to entrapped water (55).

Increased about in proj)ortion to specific gravity increase.

Increased considerably

more th;in proportional

to specific gravity increase (2, 4)'

Increased less than proportional to specific

gi-avity increase (2, 4)-

Increased less than proIjortional to specific

gravity increase parallel to grain, increased

more perpendicular to

grain (?, 4).

10 to 20 times that of normal wood (32).

Yi to VA of value for normal woofi i2,¿t).

y¿ to H of value for normal wood (2,4).

Increased about in proportion to specific gravity increase (4,55).

Requires metalworking

tools and metalworking-tool speeds.

Can be molded by compression and expansion

molding methods (20,

24).

Same as normal wood

after light sanding, or,

in the case of thick

stock, machining surfaces plane.

No data.

No data, but should increase about In proportion to specific gi-avity

increase.

Increased about in proportion to specific gravity increase parallel to

grain, increased more

perpendicular to grain

(2).

Increased about in proportion to specific gravity increase (2).

Increase* 1 proportional to

specific gravity Increase

parallel to grain, Increased more perpendicular to grain (2).

10 to 18 times that of normal wood (26).

Same to somewhat greater

than normal wood (2).

Same to somewhat greater

than normal wood (2).

Increase about In proportion to specific gravity increase (35).

Requires metalworking

tools and rnetalworkingtool speeds.

Cannot be molded.

Same as normal wood

after light sanding, or,

in the case of thick

stock, machining surfaces plane.

Resin-Treated Compressed Wood (Compreg)

Compres; is similar to impreg except that it is compressed before

the curing of the resin witliin the structure (22, 24). The resmformino- chemicals act as plasticizers for the wood so that it can be

apprecfably compressed under ply^vood-assembly pressures and compressed to a specific gravity of 1.35 under pressures of about 1,000
470 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

pounds per square inch (20, 22). Some of its properties are similar

to those of impreg, and others vary considerably (tables bb and 56).

Its advantages over impreg are its natural lustrous finish that can be

developed on an}^ cut surface by sanding with fine sandpaper and

buffing, its greater strength properties, and the fact that it can be

molded (tables 55 and 56) {2, 4, 5).

Compreg can l)e molded b}^ gluing blocks of uncured impreg with

a phenolic glue so that the glue lines and resin within the plies are

only partially set, cutting to the desired length and width but 2 to 3

times the dc^sired thickness and compressing in a split mold at about

TABLK 56.— Streniftii propertivs of normal and modified laminates ' of yellotv birch

and a laminated paper plastic

Piopi'ity

I'liickness it) of laminate .. in

Míñsture content at time of teyt -. percent

Specific ?ra\ity (l)ase(i on weight and xolunie at

test).._ .^ . . _,.

Normal -

laminated

wood

0.94

9.2

Impreíí 3

(impregnated,

uncompressed )

l.ir.

5.0

Compieg3

(impregnated,

highly

compressed)

5. 0

1. />

Staypaks

(unimpregnatcd,

highly

compressed)

0. 4S

4.0

1.4

Papreg ^

(impregnated,

highly

compressed)

0.12G.

0.512

P A R A L L K L L A MINA T E S

Kle.\ure—grain parallel to span (flatwise) : ^

Proportional limit stress.... p. s. i

Modulus (jf rupture. , _._ ]». s. i_

Modulus of elasticity.. 1,000 p. s. i.

KJc.xure—grain i)erpendicular to span (flatwise): ^

Proportional limit stress ... j). s. i

Modulus of rupture_.. , ... p. s. i.

Mijdulus of elasticity.. 1,000 i). s. i..

Compression parallel to grain (edgewise): ^

Pr(»p(^rtional limit stress . p. s. i.

Ultimate strength I), s. i. .

Modulus of elasticity 1,000 p. s. i..

Compression perpendicular to grain (edgewise) :8

Proportional limit stress p. s. i.

Ultimate strength p. s. i.

Modulus of elasticity 1,000 p. s. i..

Compression perpendicular to grain (flatwise) ,5

maxinmm crushing strength p. s. i.

n^ension parallel to grain (lengthwise):

Ultimate strength [). s. i..

Mt^dulus of elasticity 1,000 p. s. i..

Tension perpendicular to grain (crosswise):

Ultimate strength p. s. i..

M(;dulus of elasticity 1,000 p. s. i..

Shear strength parallel to grain (edgewise) :6

Johnson, double shear across laminations

p. s. i..

Cylindrical, double shear parallel to laminates

p. s. i-.

Shear modulus:

Torsion method 1,000 p. s. i..

Plate shear method (F. P. L. test).. 1.000 p. s. i..

See footnotes at end of table.

11.500 15.900

20, 400 18, 800

2. 320 2, 380

1,000 1.300

1.900 1. 700

153 220

6, 400 10,200

9, 500 15.4ÍJ0

2. 300 2.470

070 1,000

2,100 3, 600

162 243

4, 280

22,200 15,800

2, 300 2,510

1,400 1,400

166 227

2,980 3, 400

3.030 3. 560

182 255

2C>. 700

36,300

3.690

4. 200

4, 600

626

16), 400

26,100

3. 790

4, 800

H.OfJO

571

16,700

37, 000

3,950

3,200

622

7, 370

5. 690

454

20,100

39, 400

4. 450

3. 200

5.000

tJ02

9.700

19,100

4, 670

2, 600

9. 400

583

13.200

45, 000

4, 610

3,300

575

6.370

3,080

385

15.900

36. 600

3. 010

10, 5ÍJ0

24.300

1,480

7. 200

20.900

3, 120

4, 200

18,200

1.600

42.200

35. 600

3. 640

20, 000

1,710

17,800

3.000

909
WOOD HANDBOOK 471

TABLE 66.—Strength properties of normal and modified laminates ' of yellow birch

and a laminated paper plastic—Continued

PARALLEL LAMINATES

Property

Toughness (F. P. L. test, edgewise 6) in-lb

Do.. in.-lb. per in. of width

Impact strength (Izod)—grain lengthwise:

Flatwise (notch in face)

ft.-lb. per in. of notch

Edgewise (notch in face)

ft.-lb. per in. of notch

Hardness (Rockwell, flatwise s) 7V/-numbers

Load to imbed 0.444-inch steel ball to J-i its

diameter Ibs.

Hardness modulus (HM)^ p. s. iAbrasion-Navy wear-tist machine (flatwise)/ wear

per 1,000 revolutions in.

Water absorption (24-hour immersion), increase in

weight percentDimensional stability in thickness direction:

Equilibrium swelling percentRecovery from compression percentNormal 2

laminated

wood

2:^5

250

14.0

11.3

1,600

5,400

0.030

43.6

9.9

Impreg 3

(impregnated,

uncompressed)

2.3

1.9

-22

2, 400

9, 200

0.057

13.7

2.8

0

Comprep 3

(impregnated,

highly

compressed)

145

230

4.3

73.2

41,300

0.018

2.7

8.0

0

Staypakz

(unimpregnated,

highly

compressed)

250

515

43,800

0.015

4.3

29

4

Papre g <

(impregnated,

highly

compressed)

0.67

110

35, 600

0.018

2.2

CROSS-BANDED LAMINATES

Flexure—face grain parallel to span (flatwise) : ^

Proportional limit stress p. s. i.-

Modulus of rupture p. s. i--

Modulus of elasticity 1,000 p.s. i.-

Compression—parallel to face grain (edgewise) : «

Proportional limit stress p. s. i..

Ultimate strength p. s. i--

Modulus of elasticity 1,000 p. s. i--

Tension—parallel to face grain (lengthwise) :

ultimate strength p'. s. i - -

Modulus of elasticity 1,000 p. s. i.-

Toughness (F. P. L. test edgewise «)

in.-lb. per in. of width..

6, 900

13,100

1,310

3.300

5.800

1,360

12.300

1.290

8.100

11,400

1,670

5,200

11.400

1,500

7,900

1,460

14.400

22, 800

2,480

8,700

23,900

2,300

16,500

2.190

115

11,400

25,100

2, 900

5,200

14.000

2,700

24, .500

2, 570

320

12,600

31,:300

2.240

5, 000

18.900

2. 370

27, 200

2, 700

1 Laminates made from 17 plies of He-h^ch rotary-cut yellow birch veneer.

2 Veneer conditioned at 80° F. and 65 percent relative humidity before assembly with phenol resin film

glue.

3 Impregnation, 25 to 30 percent of water-soluble phenol-formaldehyde resin ba^sed on the dry weight of

untreated veneer.

< High-strength paper (0.003-inch thickness) made from commercial unbleached black spruce pulp

(Mitscherlich sulfite), phenol resin content 36.3 percent, based on weight of treated paper. Izod-impact,

abrasion, flatwise-compression, and shear specimens, all of î^i-inch-thick papreg.

« Load applied to the surface of the original material (parallel to laminating-pressure direction).

0 Load applied to the edge of the laminations (perpendicular to laminating-pressure direction).

7 Values as high as 10.0 foot-pounds per inch of notch have been reported for compreg made with alcoholsoluble resins and 7.0 foot-pounds with water-soluble resins.

8 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 0.444-inch steel ball expressed in pounds per square mch:

P P

HM=;r—c or 0.717 X- 2 Trrh
472 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

300'' F. (20, 22). Only a small flash squeeze-out at the parting hne

Ix'tween the two halves of the mold need be machined oft'. This

technique was used for molding- motor-test ''club" propellers and

airplane antenna masts during World War II.

A more generall}^ satisfactory molding technique, known as expansion molding, was recently developed {27). The method consists of rapidly precompressing dry but uncured single sheets of resintreated veneer in a cold press after preheating them to 200° to 240° F.

The heat-plasticized wood responds to compression before cooling.

The heat is insufl^cient to cure the resin, but the subsequent cooling

sets the resin temporarily. These compressed sheets are cut to the

desired size, and the asseml)ly of plies is placed in a split mold having

the final desired dimensions. Because the wood was precompressed,

the filled mokf can be closed and locked. A^lien 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 a])out half of the original compressing pressure.

On continued heating, the resin is set, and after cooling, the object

may be removed from the mold in finished form. Metal inserts or

metal surfaces can be molded to compreg or compreg handles molded

onto tools by this means. Compreg bands have been molded to the

outside of turned wooden cylinders mthout compressing the core.

Compreg tubes and small airplane propellers have been molded in

this way.

Solid compreg was used chiefly during World War II for trainer-plane

adjustable-pitch propellers, motor-test propellers, antenna masts,

spar and connector plates, refrigerator blocks for ships, and tooling

jigs. The flight propellers were carved from glued-up blocks of compreg made from compreg panels 1 ){inches thick. Compreg, because of

its high compressive strength, makes excellent spar and connector plates.

For this purpose, the crossbanded product is usuall}^ used. The combined load-bearing and thermal-insulating properties of compreg are

advantages in use as supporting blocks for refrigerators. Compreg

is extremely useful for aluminum drawing and forming dies, didling

jigs, and jigs for holding parts in place while welding because of its

excellent strength properties, dimensional stability, low thermal

conductivity, and ease of fabrication.

Solid compreg shows promise for use in silent gears, pulleys, waterlubricated bearings, fan blades, shuttles, bobbins and picker sticks

for looms, instrument bases and cases, clarinets, electrical insulators,

tool handles, knife handles, and various novelties. Compreg may

replace fabric-reinforced plastics in a number of uses because of its

better strength properties and lower cost. It should be significantly

cheaper because veneer is cheaper than fabric on a weight basis and

about 50 percent less resin is used per unit weight of compreg than for

fabric laminates.

Partially compressed compreg appears suitable for use as facing

materials for ordinary plyAvood. These facing materials could be

used in house, trailer, and boxcar exterior panels, boat siding, interior

panels, furniture, and flooring. A test floor was laid at the U. S. Forest

Products Laboratory consisting of 10-inch-square tongued-andgrooved panels, composed of 3-ply yellow-poplar compreg faces
WOOD HANDBOOK 473

compressed from ^e-inch to }^inch thickness, a single Ke-inch-thick

back ply of impreg to balance the construction from a swelling standpoint, and a }^-inch-thick 5-ply Douglas-fir core. All phes in the

panel were glued with phenol glues. The floor has a very attractive

greenish-tan natural finish and is in excellent shape after over 5 years'

service. Such a floor is more expensive than the normal oak strip

floor but should require less service to keep in good condition. The

original finish can be restored by sanding with fine sandpaper and

buffing.

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 (2). Up to the present

time, 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 was developed. It will not lose

its compression under swelling conditions as will ordmary compressed

untreated wood. This material, named staypak, is made b}^ modifying

the compressing conditions to cause the lignin cementing material between the cellulose fibers to flow sufficiently to eliminate internal

stresses {16, 25).

Staypak is not as water resistant as compreg, but it is about twice as

tough and has higher tensile and flexural strength properties, as shown

in tables 55 and 56. 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 for use in propellers, tool handles, forming dies, connector plates, and picker sticks

and shuttles for weaving, where high impact strength is needed. As

staypak is not impregnated, it can be made from soHd wood as well as

from veneer. It should hence be considerably cheaper than compreg.

Staypak is not being manufactured at the present time. Several

companies, however, are prepared to make it if the demand becomes

appreciable.

PAPER-BASE LAMINATES

Paper-base laminates are plastic laminates made by compressing together sheets of resin-impregnated paper into coherent solid panels.

Such panels have been made for years for electrical insulating purposes

{SJf) but for structural use they are comparatively new. The chief advantages of these panels over ordinary wood-flour-filled, resin-molded

materials are their greater toughness and strength, and the fact that

they can be made with a higher filler-to-resin ratio and can be pressed

at lower pressures without the use of confining molds.
474 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

High-Strength Laminates (Papreg)

improving the paper used has helped develop paper-base laminates

suitable for structural use. Cooking the pulp under milder conditions

and operating the paper machines so as to give optimum orientation

of the fibers in one direction, together with the desired absorbency,

contribute markedly to improvements in strength (<9,10^ 11,12, IS, 19).

Phenol 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) {3, 6). They are

also considerably cheaper than 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 unfortunately make the product brittle (low

impact strength). Advanced phenol resins fail to penetrate the fibers

as well as water-soluble resins and thus impart less water resistance and

dimensional stability to the product, but the product is considerably

tougher. In practice, compromise alcohol-soluble phenol resins are

generally used.

Table 56 gives the strength properties of high-strength paper-base

laminates, which have been given the class name papreg (5, H). The

strength properties compare favorably with those for the wood laminates, compreg and staypak, and are considerably superior to those

for fabric laminate, except for the edgewise Izod impact test. Fabric

laminates have one other advantage, namel}^, that of being moldable

to greater double curvatures. As paper is considerably cheaper than

fabric and can be molded at considerably lower pressures, the paperbase laminates should have an appreciable price advantage over fabric

laminates.

Papreg was used during World War II 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." It 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. An experimental papreg tail fin with modified

fittings was made for a trainer airplane that met all of the specified

loading tests required of its aluminum counterpart (7).

Papreg has been used to some extent for heavy-duty truck floors,

industrial processing trays for nonedible materials,\nd in combination

with melamine-treated papers for decorative table tops. An experimental floor of papreg on a plywood base has been laid in the lobby of

the Forest Products Laboratory. Papreg also appears suitable for

pulleys, gears, bobbins, and many other objects for which fabric laminates are used. Because it can be molded at low pressures and is

made from thin papers, it is advantageous for use where very large single

sheets or accurate control of panel thickness are required

Lignin-Filled Laminates

The relatively high cost and limited availability of phenohc resins

have resulted in considerable effort to find cheaper, more available

impregnating and bonding agents. One of the most successful tried

M
WOOD HANDBOOK 475

is a lignin-filled laminate made with lignin recovered from the spent

Hquor of the soda pulping process. Lignin is precipitated from solution within the pulp or added in a preprecipitated form before the

paper is made {28, 29, SO, 31). 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 used.

The water resistance can also be improved by merely impregnating

the surface sheet with phenolic resin. It is also possible to introduce

hgnin, together with phenolic resin, into untreated paper sheets with

an impregnating machine (18).

The lignin-filled laminates are always dark brown or black. Their

strength properties except for toughness are, in general, somewhat

lower than those of papreg. The Izod impact values are usually

twice those for papreg. In spite of the fact that lignin is somewhat

thermoplastic, the loss in strength on heating to 200^ F. is proportionately no more than for papreg (14, SI).

Lignin-filled laminates are not as yet made on a very large scale.

They have a number of potential uses, however, where a cheaper

laminate with less critical properties than papreg can be used.

Paper-Face Overlays

Paper has recently found considerable use as an overlay material for

veneer or plywood. Overlays can be classified into three different

types according to their use, namely, (a) masking, (b) decorative, and

(c) structural (8, 17). 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, as the overlays need not add strength to the

product. For adequate masking a single surface sheet with a thickness of 0.015 to 0.030 of an inch is desirable. Paper impregnated

with phenolic resins to the extent of about 25 percent of the weight

of the paper gives the best all-around product. Higher resin contents

make the product too costly and tend to make the overlay more

transparent. Appreciably lower resin contents give 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 apphed at the same time that the veneer is

assembled into plywood in a hot press. Undue 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 face plies of the plywood.

Important uses for masking overlays are on exterior plywood siding

for houses, boxcars, and trucks where thay minimize checking and

improve paint-holding properties. Paper-faced plywood is admirably

suited for reusable concrete forms, especially if faced with paper

having somewhat higher than normal resin contents, because the

paper face provides a smooth, nonsticking surface and prevents

splintering. Overlays are applied to tops of tables on which parachutes are assembled, where absence of splintering is imperative.

They also are suitable for tops of tables for messhalls and for covering

various industrial trays because of their low absorbency of liquids

303747°—55 31
476 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

and freedom from checking. Overlays are of value on paneling used

where greater than normal moisture resistance is needed, such as

interior walls of l)arns, and where smoothness of surface is important,

such as bins and chutes.

In order to produce a highly glazed surface, paper-base overlays

used for decorative purposes are made with higher resin contents

than the masking overlays. Attractive colors and patterns are of

major importance in the appearance of these overlays. Unfortunately

if phenolic resins are used, the amber color of these makes it impossible

to obtain many of the desired pastel shades. Melamine resins are,

in general, the most suitable from the standpoint of obtaining light

colors combined with high water resistance, stability, and abrasion

resistance, and the top plies of most decorative laminates are made

from paper treated with these resins. The core plies are usually

treated with phenolic resins, because they are considerably cheaper

and easier to impregnate into the paper. The back of the decorative

overlay usually consists of a melamine backing sheet or a special

paper that inproves adhesion.

A typical assembly of thin impregnated sheets, which is normally

pressed separately and then glued to solid wood or plywood core, is

as follows: A melamine-impregnated back balancing sheet, several

plies of core sheet impregnated with phenol resin, a colored printed

sheet carrying the design, and a thin, transparent surface sheet with

a high content of melamine resin. The printed sheet may be impregnated with melamine resin or unimpregnated. If it is impregnated,

the face consists of only two plies, a printed sheet with the design

turned upward and a thin clear cover sheet highly impregnated with

resin. The clear sheet also inñ,j be used as a barrier and the design

sheet laid on top with the design facing do^^'^l. It is important not

to place the design on the outer surface, because it may be worn away

more easily.

Covering decorative veneers of cabinet woods with a thin sheet of

paper impregnated with melamine resin gives the veneer resistance to

scuffing and to marring by spilled water or alcoholic drinks. Decorative overlays for table tops are frequently made with a thin aluminum-foil sheet just beneath the barrier sheet to give added resistance

to marring or charring by cigarettes by conducting away excessive heat.

Service records of paper-base plastic overlays used extensively for

decorative table, bar, and counter tops, and bathroom paneling have,

in general, been excellent.

In structural overlays, laminated resin-treated faces contribute to

the strength properties of the product and form a structural sandwich material. These overlays are made from high-strength papers

and phenol resins of the type used for making papreg. The impregnated paper may be laminated and assembled with a wood core in

a single operation, or bonded subsequent to lamination. If the resin

content is 35 to 50 percent of the weight of the impregnated paper,

the uncured sheets are self-bonding to wood and do not require the

application of glue. If the papreg is laminated before gluing to the

wood core, the back should be sanded before gluing to remove the

surface glaze. A typical use for such sandwich material is for

aircraft cargo and truck flooring.
WOOD HANDBOOK 477

LITERATURE CITED

(1) BURR, H. K., and STAMM, A. J.

1945. COMPARISON OF COMMERCIAL WATER-SOLUBLE PHENOL-FORMALDEHYDE RESINOIDS FOR WOOD IMPREGNATION. U. S. Forest Prod.

Lab. Rpt. 1384, 12 pp., illus. (Rev.) [Processed.]

(2) ERICKSON, E. C. O.

1947. MECHANICAL PROPERTIES OF LAMINATED MODIFIED WOOD. U. S.

Forest Prod. Lab. Rpt. 1639, 16 pp., illus. [Processed.]

(3) and BöLLER, K. H.

1945. STRENGTH AND RELATED PROPERTIES OF FOREST PRODUCTS LABORATORY LAMINATED PAPER PLASTIC (PAPREG) AT NORMAL TEMPERATURES. U. S. Forest Prod. Lab. Rpt. 1319, 13 pp. illus.

(Rev.) [Processed.]

(4) and FAULKES, W. F.

1949. BASIC PROPERTIES OF YELLOW BIRCH LAMINATES MODIFIED WITH

PHENOL AND UREA RESINS. U. S. Forest Prod. Lab. Rpt. 1741,

14 pp. [Processed.]

(5) FiNDLEY, W. N., WoRLEY, W, J., and KACALIEFF, C. D.

1946. EFFECT OF MOLDING PRESSURE AND RESIN ON RESULTS OF SHORTTIME TESTS AND FATIGUE TESTS OF COMPREG. Amer. 80C.

Mech. Engin. Trans. 68 (4): 317-327, illus.

(6) INSTITUTE OF PAPER CHEMISTRY.

1943. A STUDY OF RESINS, OTHER THAN PHENOL-FORMALDEHYDE RESINS,

FOR USE IN PAPER-BASE PLASTICS. Office Prod. Res. and

Devlpmt., War Prod. Bd. 24 pp.

(7) JUNGMAN, E. C.

1945. DEVELOPMENT OF A COUNTERPART VERTICAL FIN OF PAPREG FOR

THE AT-6 AIRPLANE. U. S. Forest Prod. Lab. Rpt. 1594, 12

pp., illus. [Processed.]

(8) LAND, J. C, GROSS, E. A., and MORAN, T. H.

1945. PLASTIC OVERLAYS FOR DOUGLAS-FIR VENEERS AND PLYWOOD.

Douglas-fir Plywood Assoc. Rpt. 33, 22 pp. Tacoma, Wash.

[Processed.]

(9) IVIACKIN, G. E., SEIDL, R. J., and BAIRD, P. K.

1943. EFFECT ON PAPREG OF SIX WATER-ALCOHOL RATIOS USED AS

DILUENTS OF IMPREGNATING RESINS. U. S. ForCSt Prod. Lab.

Rpt. 1387, 4 pp., Illus. [Processed.]

(10) SEIDL, R. J., and BAIRD, P. K.

1943. CERTAIN PROPERTIES OF PAPREG AFFECTED BY CALENDERING

PRESSURE ON MITSCHERLICH BASE PAPER. U. S. ForeSt Prod.

Lab. Rpt. 1389, 4 pp., illus. [Processed.]

(11) SEIDL, R. J., and BAIRD, P. K.

1943. CERTAIN PROPERTIES OF PAPREG AFFECTED BY WET-PRESS PRESSURE ON MITSCHERLICH BASE PAPER. U. S. Forcst Prod. Lab.

Rpt. 1575, 3 pp., illus. [Processed.]

(12) McGovERN, J. N., and KELLER, E. L.

1943. SULFITE PULPS FOR HIGH-STRENGTH LAMINATED PAPER PLASTICS:

PULPING VARIABLES AND PROPERTIES OF BLACK SPRUCE PULPS,

PAPERS, AND PLASTICS. U. S. Forcst Prod.' Lab. Rpt. 1393, 6

pp., illus. [Processed.]

(13) and KELLER, E. L.

1943. SULFITE PULPS FOR PAPREG: BASE PAPERS AND LAMINATES FROM

BLACK SPRUCE, BALSAM KIR, WESTERN HEMLOCK, AND GRAND FIR.

U. S. Forest Prod. Lab. Rpt. 1399, 7 pp. [Processed.]

(14) IMEYER, H. R., and ERICKSON, E. C. O.

1945. FACTORS AFFECTING THE STRENGTH OF PAPREG. U. S. Forest Prod.

Lab. Rpt. 1521, 7 pp., illus. [Processed.]

(15) MiLLETT, M. A., and STAMM, A. J.

1947. WOOD TREATED WITH RESIN-FORMING SYSTEMS, A STUDY OF SIZE AND

SPECIES LIMITATIONS. IVIod. Plastics 25 (1): 125-127.

(16) SEBORG, R. M., MILLETT, M. A., and STAMM, A. J.

1945 HEAT-STABILIZED COMPRESSED WOOD (STAYPAK). Mech. Engin. 67

(1): 25-31.
478 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

(17) SEIDL, R. J.

1947. PAPER AND PLASTIC OVERLAYS FOR VENEER AND PLYWOOD. FOFCST

Prod. Res. See. Proc. 1: 8 pp., illus.

(18) BURR, H. K., FERGUSON, C. N., and MACKIN, G. E.

1944. PROPERTIES OF LAMINATED PLASTIC MADE FROM LIGNIN AND LTGNINpHENOLic RESIN-IMPREGNATED PAPERS. U. S. Forest Prod. Lab.

Rpt. 1595, 7 pp., illus. [Processed.]

(19) MACKIN, G. E., and BAIRD, P. K.

1943. CERTAIN PROPERTIES OF PAPREG AS AFFECTED BY LAMINATING

PRESSURE, RESIN CONTENT, AND VOLATILE CONTENT. U. S. Forest

Prod. Lab. Rpt. 1394, 9 pp., illus. [Processed.]

(20) STAMM, A. J.

1948. MODIFIED WOODS. Mod. Plastics Enc3'clopedia. 40 pp., illus.

New York.

(21) and SEBORG, R. M.

1950. FOREST PRODUCTS LABORATORY RESIN-TREATED WOOD (IMPREG).

U. S. Forest Prod. Lab. Rpt. 1380, 8 pp. (Rev.). [Processed.]

(22) and SEBORG, R. M.

1951. FOREST PRODUCTS LABORATORY RESIN-TREATED, LAMINATED, COMPRESSED WOOD (COMPREG). U.S. Forest Prod. Lab. Rpt. 1381,

12 pp., illus. (Rev.). [Processed.]

(23) and SEBORG, R. M.

1939. RESIN-TREATED PLYWOOD. Indus. Engin. Chem. 31 (7): 897, 902.

(24) and SEBORG, R. M.

1941. RESIN-TREATED, LAMINATED COMPRESSED WOOD. Amer. SoC. Chem.

Engin. Trans. 37: 17 pp., illus.

(25) SEBORG, R. M., and MILLETT. M. A.

1948. u. s. PATENT 2,453,679. U. S. Pat. Office, Ofif. Gaz. 616: 544.

(26) and TARROW, H.

1949. WOOD, A LIMITED SWELLING GEL. Jour. Phvs. Coll. Chem. 53:

251-260.

(27) and TURNER, H. D.

1945. u. s. PATENT 2,391,489. U. S. Pat. Office, Off. Gaz. 581: 568.

(28) U. S. FOREST PRODUCTS LABORATORY.

1943. LiGNIN-FlLLED, LA^MINATFD PAPER PLASTICS. IT. S. ForeSt Prod.

Lab. Rpt. 1576, 8 pp., ilhis. [Processed.]

(29)

(30)

1943. PREPARATION OF LIGNIN-FILLED PAPER FOR LAMINATED PLASTICS.

U. S. Forest Prod. Lab. Rpt. 1577, 11 pp. [Processed.]

1943. PHYSICAL AND MECHANICAL PROPERTIES OF LIGNIN-FILLED LAMINATED

PAPER PLASTIC. \J. S. Forcst Prod. Lab. Rpt. 1579, 3 pp., illus.

[Processed.]

(31) and HOWARD SMITH PAPER MILLS.

1946. LIGNIN-FILLED LAMINATED-PAPER PLASTICS. Paper Trade Joui*. 122

(14): 143-150, illus.

(32) WEATHERWAX, R. C, ERICKSON, E. C. O., and STAMM, A. J.

1948. A MEANS OF DETERMINING THE HARDNESS OF WOOD AND MODIFIED

WOODS OVER A BROAD SPECIFIC GRAVITY RANGE. Amer. SoC.

Testing Mater. Bui. 153: 84-89, illus.

(33) and STAMM, A. J.

1945. ELECTRICAL RESISTIVITY OF RESIN-TREATED WOOD (iMPREG AND

COMPREG), HYDROL17ED-WOOD SHEET (HYDROXYLIN) AND LAMINATED RESIN-TREATED PAPER (PAPREG). U. S. Forest Prod.

Lab. Rpt. 1385, 9 pp., illus. [Processed.]

(34) WEST, C. J.

1946. PAPEP-BASE PLASTICS. Inst. Paper Chem. Bibliog. Ser. 167, 102 pp.

(35) YouNGQUiST, W. G., and MUNTHE, B. P.

1948. ABRASIVE RESISTANCE OF WOOD AS DETERMINED WITH THE U. S.

NAVY AVEAR-TEST MACHINE. L^. S. Forest Prod. Lab. Rpt. 1732,

8 pp., illus. [Processed.]
GLOSSARY

Adhesive ~k substance capable of holding materials together bv surface attachment. It IS a general term and includes cements, mucilage, and paste as

well as glue.

Air-dried.—{See Seasoning.)

American hmiber standards.—American lumber standards embody provisions for

softwood lumber dealing with recognized classifications,^ nomenclature,

basic grades, sizes, description, measurements, tally, shipping provisions^

grade marking, and inspection of lumber. The primarv purpose of these

standards is to serve as a guide or basic example in the preparation or

revision of the grading rules of the various lumber manufacturers' associations. A purchaser must, however, make use of association rules, as

the basic standards are not in themselves commercial rules.

Annual growth ring.~The growth layer put on in a single growth year, including

springw^ood and summerwood.

Balanced construction.—A construction such that the forces induced by uniformly

distributed changes in moisture content will not cause warping. Symmetrical construction of plywood (which see) in which the grain direction of

each ply is perpendicular to that of adjacent plies is balanced construction.

Bark.—Outer layer of a tree, comprising the inner bark, or thin, inner living part

(phloem), and the outer bark, or corky laver, composed of drv, dead tissue.

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.

Basic stress.—(See Stress.)

Bastard sawn.—Hardwood lumber 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. In shape bird peck usually resembles

a carpet tack with the point toward the bark, and it is usually accompanied

by discoloration extending for a considerable distance along the grain

and to a much lesser extent across the grain. The discolorfition produced

by bird peck causes what is commonly known as mineral streak (which see).

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. Common in sugar mapíe

and used for decorative purposes, rare in other hardwood species.

Blue stain.—{See Stain.)

Boards.—{See Lumber.)

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.

Bow.—The distortion in a board that deviates from flatness lengthwise but not

across its faces.

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.—Unstained.

Broad-leaved trees.—{See Hardwoods.)

Brown stain.—{See Stain.)

479
480 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Building fiherhoard.—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.

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. {See Laminated wood.)

Bump.—A bark-covered protuberance whose bark pattern conforms with the

bark pattern of the log. A bump has a height-to-length ratio of at least

1 inch in height to 12 inches in length.

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 wood or veneer, a localized severe distortion

of the grain generally rounded in outline, usually resulting from overgrowth

of dead branch stubs, varying from one-half inch 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 root.—An adventitious root serving as an added prop or support for a

tree. Adventitious roots arise from pomts on the trunk that are not the

normal points of origin for roots.

Cambium.—The one-cell-thick layer of tissue between the bark and wood that

repeatedly subdivides to form new wood and bark cells.

Casehardening.—A stressed condition in a board or timber characterized by

compression in the outer layers accompanied by tension in the center or

core, the result of too severe drying conditions.

Cell.—A general term for the minute units of wood structure, including wood

fibers, vessel segments, and other elements of diverse structure and

function.

Celhdose.—The carbohydrate that is the principal constituent of wood and forms

the frame work 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.)

Close grain.—{See Grain.)

Coarse grain.—{See Grain.)

Collapse.—The flattening of single cells or rows of cells in heartwood during the

drying or prassure treatment of wood, characterized by a caved-in or

corrugated appearance.

Compartment kiln.—{See Kiln.)

Compound curvature.—Wood bent to a compound curvature has curved surfaces

no element of which is a straight line.

Compreg.—Wood in which the cell walls have been impregnated with synthetic

resin and compressed so as 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 fstanding 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 appear as fine wrinkles across the face of the piece.

Compression set.—Permanent compression of a group of wood fibers resulting from

restraint from swelling while taking on moisture or compressive stresses on

the wetter core of wood during drying imposed by adjoining fibers or an

external mechanical agency.

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, relatively large amount of

summerwood, sometimes more than 50 percent of the width of the annual

rings in which it occurs, and its lack of demarcation between springwood

and summerwood in the same annual rings. Compression wood shrinks

excessively lengthwise, as compared with normal wood.
WOOD HANDBOOK 481

Conifer.—{See Softwoods.)

Crook.—A distortion of a board in which there is a deviation edgewise from a

straight line from end to end of the board.

Crosshand.—To place the grain of layers of wood at right angles in order to

minimize shrinking and sweUing; also, in plvwood of five 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 strains resulting from unequal longitudinal shrinkage or

to external forces.

Cross grain.—{See Grain.)

Cup.—A distortion of a board in which there is a deviation flatwise from a straight

line across the width of the board.

Curhj grain.—(See Grain.)

Cut stock.—A term for softwood stock comparable to dimension stock in hardwoods. (See Dimension stock.)

Decay.—The decomposition of wood substance by fungi.

Advanced {or 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.

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.

Decayed knot.—(See Knot.)

Delamination.—Separation of plies through failure of the adhesive; often used in

reference to the durability of the glue line.

Density.—The weight of a body per unit volume. When expressed in the c. g. s.

(centimeter-gram-second) system, it is numerically equal to the specific

gravity of the same substance.

Density rules.—Rules for estimating the density of wood based on percentage of

summerwood and rate of growth. The rules at present apply only to

southern yellow pine and Douglas-fir and differ slightly.

Dew point.—Temperature at which a vapor begins to deposit as a liquid. Applies

especially to water in the atmosphere.

Diagonal grain.—{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.)

Dimension stock.—A term largely superseded by the term hardwood dimension

lumber. It is hardwood stock processed to a point where the maximum

waste is left at a dimension mill, and the maximum utility is delivered to

the user. It is stock of specified thickness, width, and length, in multiples

thereof. According to specification it may be solid or glued up; rough or

surfaced; semifabricated or completely fabricated.

Dimensional stabilization.—Reduction in swelling and shrinking of wood, caused

by changes in its moisture content with changes in relative humidity,

through special treatment.

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.

Dressed lumber.—{See Lumber.)

Dry-bulb temperature.—Temperature of air as indicated by a standard thermometer. {See Psychrometer.)

Dry kiln.—{See Kiln.)

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.

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.

Early wood.—{See Springwood.)

Edge grain.—{See Grain.)
482 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Edge joint.—[See Joint.)

Empty-cell process.—Any process for impregnating wood with preservatives or

chemicals in which air, imprisoned in the wood under pressure, expands

when pressure is released to drive out part of the injected preservative or

chemical. The distinguishing characteristic of the empty-cell process is

that no vacuum is drawn before applying the preservative. The aim is to

oVjtain good preservative distribution in the wood and leave the cell cavities

only partially filled.

EncaHed knot.—{See Knot.)

End joint.—{*SVé; Joint.)

Equilibrium tnoisture content.—The moisture content at which wood neither gains

nor loses moisture when surrounded by air at a given relative humidity

and temperature.

Extractives.—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.

Factory and shop lumber.—{See Lumber.)

Fiber, ivood.—A comparatively long (one twenty-fifth or less to one-third inch),

narrow, tapering wood cell closed at both ends.

Fiberboard.—(See Building fiberboard.)

Fiber saturation point.—The stage in the drying or wetting of wood at which the

cell walls are saturated and the cell cavities are free from water. It is

usually taken as approximately 30 percent moisture content, based on

weight when oven-dry.

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.

Fine grain.—{See Grain.)

Finish.—Wood products to be used in the joiner work, such as doors and stairs,

and other fine work required to complete a building, especially the interior.

Fireproofing.—Making wood resistant to fire. Wood cannot be treated chemically so that it will not char or decompose at temperatures of about 280°

F. and higher. What effective fireproofing does is to make wood difliicult

to ignite, keep it from supporting its own combustion, and delay the

spread of flame over the wood surface.

Fire-retardant chemical.—A chemical or preparation of chemicals used to reduce

flammability or to retard spread of fire.

Flakes.—{See Rays, wood.)

Flat grain.—(See Grain.)

Flitch.—A portion of a log sawed on two or more sides and intended for remanufacture into lumber or sliced or sawed veneer. The term is also applied

to the resulting sheets of veneer laid together in sequence of cutting.

Framing.—Lumber used for the structural members 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 absorption and retention of

preservative in the treated portions.

Gelatinous fibers.—Abnormal fibers in certain hardwoods. Thej^ are associated

with ''Tension wood," which see.

Girder.—A large or principal beam used to support concentrated loads at points

along its length.

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 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 springwood and summerwood.

The term is sometimes used to designate wood with large pores, such as oak,

ash, chestnut, and walnut, but in this sense the term ''coarse textured" 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.
WOOD HANDBOOK 483

Grain—Continued

Curly-grained t/^ooá.—Wood in which the fibers are distorted so that they have

a curled appearance, as in '^birdseye" wood. The areas showing curly

gram may vary up to several inches in diameter

Diagonal-grained wood.—Wood in which the annual rings are at an angle with

the axis ot a piece as a result of sawing at an angle with the bark of the tree

or log. A lorm of cross grain.

Edged-grained ¿wm6er.—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.

Fine-grained wood.—{See Close-grained wood.)

Flat-grained lumber.—LnmheT that has been sawed in a plane approximately

perpendicular to a radius of the log. 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.—Wood in which the fibers are inclined in one

direction in a number of rings of annual growth, then gradually reverse

and are inclined in an opposite direction in succeeding growth rings, then

reverse again.

Open-grained wood.—Common classification of painters for woods with large

pores, such as oak, ash, chestnut, and walnut. Also known as ''coarse

textured."

Plainsawed lumber.—Another term for flat-grained lumber.

Ouartersawed lumber.—Another term for edge-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 lumber, or lumber that has received no intentional drying;

unseasoned. The term does not apply to lumber that may have become

completely wet through waterlogging.

Growth ring.—(See Annual growth ring.)

Hardwoods.—Generally one of the botanical groups of trees that have broad

leaves in contrast to the conifers or softwoods. The term has no reference

to the actual hardness of the wood.

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 be

infiltrated with 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 diñ'erent simple sugars.

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.—A construction of thin sheet material, such as resin impregnated

paper or fabric, which has been corrugated and bonded, each sheet in

opposite phase to the phases of adjacent sheets, to form a core material

whose cross section is a series of mutually continuous cells similar to natural

honeycomb.

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.—{See Laminated wood.)

Imperfect manufacture.—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 themj, variation in sawing, misent lumber, machine burn, machine

gouge, mismatching, and insufficient tongue or groove.

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.
484 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Insnlation, thermal.—Materials that retard the transfer of heat when placed

between two heat-conducting materials.

Iniergroiirn knot.—(See Knot.)

Interlocked-grained ivood.—{See Grain.)

Joint.—The junction of two pieces of wood or veneer.

Butt joint.—An end joint formed by abutting the squared ends of two pieces.

Because of the inadequacy and variability in strength of butt joints when

glued, they are not generally glued.

Edge joint.—The place where two pieces of wood are joined 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.—The place where two pieces of wood are joined together end to

end, commonly by scarfing and gluing.

Lap joint.—A joint made by placing one adherend partly over another and

bonding the overlapped portions.

Scarf joint.—An end joint formed by joining with glue the ends of two

pieces that have been tapered or beveled to form sloping plane surfaces,

usually to a feather edge, 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 alinement 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 insufliicient

quantity of glue remained in the joint. Starved joints are caused by the

use of excessive pressure or insufficient viscosity of the glue, or a combination of these, which results in the glue being forced out from between the

surfaces to be joined.

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 heated chamber for dr3àng lumber, veneer, and other wood products.

Compartment kiln.—A dry kiln in which the total charge of lumber is dried

as a single unit. It is designed so that, at any given time, the temperature

and relative humidity are uniform throughout the kiln. The temperature

is increased as drying progresses, and the relative humidity is adjusted to

the needs of the lumber.

Progressive kiln.—A dry kiln in which the total charge of lumber is not dried

as a single unit but as several units, such as kiln-truckloads, that move

progressively through the kiln. The kiln is designed so that the temperature is lower and the relative humidity higher at the entering end than at

the discharge end.

Kiln hroivn stain.—{See Stain.)

Kiln-dried.—{See Seasoning.)

Knot.—That portion of a branch or limb which has been surrounded by subsequent growth of the wood of the trunk or other portion of the tree. As a

knot appears on the sawed surface it is merely a section of the entire knot,

its shape depending upon the direction of the cut.

Decayed knot.—A knot that, due to advanced decay, is softer than the surrounding wood.

Encased knot.—A knot whose rings of annual growth are not intergrown with

those of the surrounding wood.

Intergroivn knot.—A knot whose rings of annual growth are completely intergrown with those of the surrounding wood.

Large knot.—A knot more than lyi inches in diameter.

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.

Medium knot.—A knot more than % inch but not more than m inches in

diameter.

Pin knot.—A knot that is not more than >^ inch in diameter.

Round knot.—A knot whose sawed section is circular or oval.

Small knot.—A knot more than y2 inch but not more than % inch in diameter.

Sound knot.—A knot that is sohd 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 definiteh^ elongated.
WOOD HANDBOOK 485

Knot chister.—Three or more knots in a compact, roughly circular group, with

the grain between them highly contorted, originating from adventi-

?^u iu ^'^'^ ^^ ^^^^ knots laterally arranged and without contortion

oí the nbers between them do not constitute a knot cluster.

Lamtnate.~k product made by bonding together two or more layers (laminations)

of material or materials.

Laminate, paper-base.—A multilayered panel made by compressing sheets of

resin-impregnated paper together into a coherent solid mass.

Laminated wood.—-An assembly made by bonding layers of yeneer or lumber with

an adhesiye so that the grain of all laminations is essentially parallel.

(See Built-up timbers.)

Horizontally laminated wood.—Laminated wood in which the laminations are

so arranged that the wider dimension of each lamination is approximately

perpendicular to the direction of load.

Verticalhj laminated wood.—Laminated wood in which the laminations are

so arranged that the wider dimension of each lamination is approximately

parallel to the direction of load.

Lap joint.—(See Joint.)

Late wood.—(See Summerwood.)

Lignin.—The second most abundant constituent of wood, located principally in

the middle lamella, which is the thin cementing layer between the wood

cells. The chemical structure of lignin has not been definitely determined.

Log.—A section of the trunk of a tree in suitable length for sawing into commercial

lumber.

Longitudinal.—Generally, the direction along the length of the grain of wood.

Loose knot.—(See Knot).

Lumber.—The product of the saw and planing mill not further manufactured

than by sawing, resawmg, passing lengthwise through a standard planing

machine, crosscutting to length, and matching.

Boards.—Yard lumber less than 2 inches thick and 1 or more inches wide.

Dimension.—Lumber from 2 inches to but not including 5 inches thick and 2 or

more inches wide.

Dressed size.—The dimensions of lumber after shrinking from the green

dimension and being surfaced with a planing machine usually Ys or H iiich

less than the nominal or rough size; for example, a 2- by 4-inch stud actually

measures 1%, by 35^ inches under American lumber standards for softwood

lumber.

Factory and shop lumber.—Lumber intended to be cut up for use in further

manufacture. It is graded on the basis of the percentage of the area tliat

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-grooyed joint at the edges or ends when laid edge to edge or

end to end.

Nominal size.—As applied to timber or lumber, the rough-sawed commercial

size by which it is known and sold in the market.

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 as it comes from the saw.

Shiplapped lumber.—Lumber that is edge dressed to make a lapped joint.

Shipping-dry lumber.—Lumber that is partially dried to preyent stain and

mold in transit.

Structural lumber.—Lumber that is 2 or more inches thick and 4 or more inches

wide, intended for use where working stresses are required. The grading of

structural lumber is based on the strength of the piece and the use of the

entire piece.

Surfaced lumber.—Lumber that is dressed by running it through a planer.

Timbers.—Lumber 5 or more inches in least dimension. Timbers may be

classified as beams, stringers, posts, caps, sills, girders, purlins, etc.

Timbers, round.—Timbers used in the original round form, such as poles,

piling, posts, and mine timbers.

Yard lumber.—Lumber of all sizes and patterns that is intended for general

building purposes. The grading of yard lumber is based on the intended

use of the particular grade and is applied to each piece with reference

to its size and length when graded, without consideration to further

manufacture.
486 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

Afatched luinher.—{See Lumber.)

Medullary rays.—{See Rays, wood.)

Millwork.—Generally, all building naatehals made of finished wood and manufactured in millwork plants and planning mills. Includes such items as

inside and outside doors, window and door frames, blinds, porch work,

mantels, panel work, stairways, moldings, and interior trim. Does not

include flooring, ceiling, or siding.

Mineral streak.—An olive to greenish-black or brown discoloration of undetermined cause in hardwoods, particularly hard maples; commonly associated

with bird pecks and other injuries; occurs in streaks usually containing

accumulations of mineral matter.

Modified wood.—Wood processed to impart properties quite different from those

of the original wood by means of chemical treatment, compression, or

treatment with or without heat.

Moisture content of wood.—The amount of water contained in the wood, usually

expressed as a percentage of the weight of the oven-dry wood.

Moisture gradient.—A condition of graduated moisture content between successive

tnickness zones of wood that may be losing or absorbing moisture. During

seasoning the gradations are between the relatively dry surface zones and

the wet zones at the center of the piece.

Molded plywood.—{See Plywood.)

Naval stores.—A term applied to the oils, resins, tars, and pitches derived from

oleoresin contained in, exuded by, or extracted from trees chiefly of the

pine species (genus Pinus) or from the wood of such trees.

Niggerizing.—A process of treating wood with paraffin or a coke-oven coal tar to

increase its resistance to acids.

Nominal-size lumber.—[See Lumber.)

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.

Open grain.—{See Grain.)

Oven-dry wood.—Wood dried to constant weight in an oven or above the temperature of boihng water (usually 101° to 105° C. or 214° to 221 F.°).

Overlaid veneer.—A single sheet of veneer overlaid and bonded on one or both sides

with paper, resin-impregnated paper, or metal.

Overlays, paper-plastic.—One or more sheets of paper impregnated with resin and

used as face material usually for plywood, but sometimes for lumber or

other products. The paper-plastic material, when properly molded to the

surface of the plywood, forms an integral part of the panel and cannot be

peeled off. Overlays can be classified as masking, decorative, or structural,

depending on their purpose.

Papreg.—Any of various paper products made by impregnating sheets of specially

manufactured high-strength paper with synthetic resm and laminating

the sheets to form a dense, moisture-resistant product.

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 segments, sometimes for many years.

Two kinds of parenchyma cells are recognized, those in vertical strands,

known more specifically as wood parenchyma, and those in horizontal

series in the rays, known as ray parenchyma.

Peck.—Pockets or areas of disintegrated wood caused by advanced stages of

localized decay m the living tree. It is usually associated with cypress and

incense-cedar. There is no further development of peck once the lumber is seasoned.

Phloem.~{See Bark.)

Pin-knot.—{See Knot.)

Pit.—A relatively unthickened portion of a cell wall where a thin membrane

may permit liquids to pass from one cell to another. A ''bordered" pit

has an overhanging rim that is not present in a ''simple'' pit.

Pitch pocket.—An opening extending parallel to the annual growth rings containing, or that has contained, pitch, either solid or liquid.

Pitch streak.—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 in the structural center of a tree trunk,

branch, twig, or log.
WOOD HANDBOOK 487

Pith fleck.—A narrow streak, resembling pith on the surface of a piece; usually

brownish, up to several inches in length; resulting from burrowing of

larvae m the growing tissues of the tree.

Plainsawed.—{See Grain.)

Planing mill products,—Vroáncis worked to pattern, such as flooring, ceilins; and

siding. ^ ^'

Plank.—A broad board, usually more than 1 inch thick, laid with its wide dimension horizontal and used as a bearing surface.

Plasiicizing wood.—Soitening wood by hot water, steam, or chemical treatment

to increase its moldability.

Plywood.—A crossbanded assembly made of layers of veneer or of veneer in

combination with a lumber core or plies ^joined with an adhesive. Two

types of plywood are recognized, namely, (1) veneer plywood and (2)

lumber-core plywood. The grain of adjoining plies is usually laid at right

angles, and almost always an odd number of plies are used to obtain

balanced construction.

Molded 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 molding) or other means.

Postformed plywood.—The product formed by reshaping, by means of steaming or other plasticizing agent, flat plywood into a curved shape.

Pocket rot.—Advanced decay that appears in the form of a hole, pocket, or area of

soft rot usually surrounded by apparently sound wood.

Pore.—{See Vessels.)

Porous woods.—Another name for hardwoods, which frequently have vessels or

pores large enough to be seen readily without magniñcation.

Postformed plywood.—{See Plywood.)

Preservative.—Any substance that, for a reasonable length of time, is eñ"ective in

preventing the development and action of wood-rotting fungi, borers of

various kinds, and harmful insects that deteriorate wood.

Progressive kiln.—{See Kiln.)

Psychrometer.—An instrument for measuring the amount of water vapor in the

atmosphere and having both wet-bulb and dry-bulb thermometers. Since

the bulb of the wet-bulb thermometer is kept moistened, that thermometer

will be cooled as a result of evaporation and consequently will show a

temperature lower than that of the dry-bulb thermometer. The evaporation is less in moist air, hence the difi*erence between the thermometer

readings is greater when the air is dry; this difference constitutes a measure

of the dryness of the surrounding air.

Quartersawed.—{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.

Raised grain.—A roughened condition of the surface of dressed lumber in which

the hard summerwood is raised above the softer springwood but not torn

loose from it.

Rate of growth.—The rate at which a tree has laid on wood, measured radially in

the trunk or in lumber cut from the trunk. The unit of measure in use is

number of annual growth rings per inch.

RaySy wood.—Strips of cells extending radially within a tree and var3ing 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.

Medullary rays.—Wood rays that originate at the pith.

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.

Resin passage {or duct).—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.

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 springwood, and an outer zone with

smaller pores, known as the summerwood.
488 HANDBOOK 72, U. S. DEPARTMENT OF AGRICULTURE

Rot.—{See Decay.)

Rotarij-eiit veneer.—{See Veneer.)

Rough lumber.—{See Lumber.)

Round knot.—{See Knot.)

Round timbers.—{See Lumber.)

Sandwieh construction.—{See Structural sandwich construction.)

^i^fip—All the fluids in a tree, special secretions and excretions, such as oleoresin,

excepted.

Sapivood.—The living wood of pale color near the outside of the log. Under most

conditions the sapwood is more susceptible to decay than heartwood.

Sawed 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.)

Seasoning.—Removing moisture from green w^ood in order to improve its serviceabiUty.

Air-dried. Dried by exposure to air, usually in a yard, without artificial

heat.

Kiln-dried.—Dried in a kiln with the use of artificial heat.

Second groivth.—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.

Set.—A permanent deformation, either in compression or tension, of wood fibers

that are kept from shrinking or swelling, with loss or gain of moisture, by

adjoining fibers that are at a different moisture content.

Shake.—A separation along the grain, the greater part of which occurs between

the rings of annual growth.

Shear.—Slipping of one part of a piece of wood upon another along the grain.

Sheathing.—The structural covering, usually of boards or fiberboards, placed over

exterior studding or rafters of a structure.

Shiplapped lumber.—{See Lumber.)

Shipping-dry lumber.—{See Lumber.)

Shop lumber.—{See Lumber.)

Side cut.—The term used when the pith is not present in a piece.

Sliced veneer.—{See Veneer.)

*S'o/¿tí'oor/s.—Generally, one of the botanical groups of trees that in most cases

have needlclike or scalelike leaves; the conifers; also the wood produced

by such trees. The term has no reference to the actual hardness of the

wood.

Sound knot.—{See Knot.)

Specific gravit]/.—The ratio of the weight of a body to the weight of an equal

volume of water at 4° C. or other specified temperature.

Spike knot.—{See Knot.)

Spiral grain.—{See Grain.)

Split.—A lengthwise separation of the wood, due to the tearing apart of the wood

cells.

Springwood.—The portion of the annual growth ring that is formed during the

early part of the season's growth. It is usually less dense and weaker

mechanically than summerwood.

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 staÍ7i.—A rich brown to deep chocolate-brown discoloration of the

sapwood of some pines caused by a fungus that acts much like the bluestain fungus.

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.—{See Blue stain.)

Starved joint.— {See Joint.)

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.
WOOD HANDBOOK 489

Stickers.—Strips or boards used to separate the layers of lumber in a pile and thus

permit air to circulate between the layers.

Strength.—The term in its broader sense embraces collectively all the properties

of wood that enable it to resist different forces or loads. In its more

restricted sense, strength may apply to any one of the mechanical properties, in which event the name of the property under consideration should

be stated, thus: strength in compression parallel to grain, strength in

bending, hardness, and so on.

Strength ratio.—A ratio representing the strength of a piece of wood remaining

after allowance is made for the maximum effect of the permitted knots,

cross grain, shakes, or other strength-reducing features.

Stress.—Force per unit of area.

Basic stress.—The working stress for material free from strength-reducing

features, such as knots, checks, and cross grain. It has in it all the factors

appropriate to the nature of structural timber and the conditions under

which it is used except those that are accounted for in the strength ratio.

Working stress.—Stress for use in the design of a wood member that is appropriate to the species and grade. It is obtained by multiplying the basic

stress for the species and strength property by the strength ratio of the

grade.

Structural lumber.— {See Lumber.)

Structural sandwich -construction.—A layered construction comprising 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 of which

is the controlling element in their selection and use. Trestle timbers

(stringers, caps, posts, sills, bracing, bridge ties, guard rails) ; car timbers

(car framing, including upper framing, car sills) ; framing for buildings

(posts, sills, girders, framing joints); ship timbers (ship timbers, ship

decking) ; and crossarms for poles are examples of structural timbers.

Stud.—One of a series of slender wood structural members used as supporting

elements in walls and partitions.

Straight grain.—{See Grain.)

Sumrnerwood.—The portion of the annual growth ring that is formed after the

springwood formation has ceased. It is usually denser and stronger

mechanically than springwood.

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.

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. Flatgrained lumber is sawed tangentially.

Tension set.—A conditon of wood in which a group of fibers, owing to restraint

imposed by adjoining fibers or by an external mechanical agency, are fixed

or set in a condition of tension as a result of a restraint on normal shrinkage

during a drop in moisture content.

Tension wood.—An abnormal form of 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

tenaciouslv, so that sawed surfaces usually have projecting fibers and

planed surfaces often are torn or have raised grain. Tension wood may

cause warping. o • Texture.—A term often used interchangeably with gram, bometunes used to

combine the concepts of density and degree of contrast between sprmgwood

and sumrnerwood. In this handbook texture refers to the finer structure

of the wood {see Grain) rather than the annual rings.

Thermoplastic glues and resws.—Glues and resins that are cured by coolmg from

the heated condition but soften when subsequently subjected to high

temperatures. . ^^ ^ j -xu i. ^ i x

Thermosetting glues and resins.—Glues and resms that are cured with heat but

do not soften when subsequently subjected to high temperatures.

Timber, standing.—Timber still on the stump.

Timbers,— {See Lumber.)
490 HANDBOOK 7 2, U. S. DEPARTMENT OF AGRICULTURE

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,

Tran.svcrse.—Directions in wood at right angles to the w-ood fibers. Includes

radial and tangential directions. A transverse section is a section through

a tree or timber at right angles to the pith.

Truss.—An assembly of members, such as beams, bars, rods, and the like, so

combined as to form a rigid framework that cannot be deformed by the

application of exterior force without deformation of one or more members.

Twist.—A distortion caused by the turning or winding of the edges of a board so

that the four corners 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 oak and black locust. Tyloses are

formed by the extension of the cell wall of the living cells surrounding

vessels of hardwood or sometimes in a similar manner by the extension of

the cell wall into resin-passage cavities in the case of softwoods.

Vapor harrier.—A material with a high resistance to vapor movement, such as

asphalt-impregnated paper, that is used in combination with insulation to

control condensation.

Veneer.—A thin layer or sheet of wood cut on a veneer machine.

Rotary-cvt veneer.—Veneer cut in a lathe which rotates a log or bolt, chucked

in the center, against a knife.

Sawed veneer.—Veneer produced by sawing.

Sliced veneer.—Veneer that is sliced off a log, bolt, or ñitch with a knife.

Vertically laminated.—[See Laminated wood.)

Vertical grain.—{See Grain.)

Vessels.—Wood cells of comparatively large diameter that have open ends and are

set one above the other so as to form continuous tubes. The openings of

the vessels on the surface of a piece of wood are usually referred to

as pores.

Virgin growth.—The original growth of mature trees.

Wane.—Bark or lack of wood from any cause on edge or corner of a piece.

Warj).—Any variation from a true or plane surface. Warp includes bow, crook,

cup, and twist, or any combination thereof.

Wavy-grained ivood.—(See Grain.)

Weathering.—The mechanical or chemical disintegration and discoloration of the

surface of wood that is 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-hulh temperature.—The temperature indicated by the wet-bulb thermometer

of a psychromeler (which see). Theoretically, the wet-bulb temperature

is the temperature at which the atmosphere would become saturated by

evaporation of water without loss or gain in total heat content of the air and

vapor.

Wood flour.—Wood reduced to finely divided particles approximating those of

cereal flours in size, appearance, and texture, and passing a 40-100 mesh

screen.

Wood preservative.—{See Preservative.)

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 no wide variation in

chemical composition or specific gravity between the w^ood substance of

various species, the characteristic differences of species being largely due to

differences in infiltrated materials and variations in relative amounts of

cell walls and cell cavities.

Workability.—The degree of ease and smoothness of cut obtainable with hand or

machine tools.

Working stress.—{See Stress.)

Xylem.—The portion of the tree trunk, branches, and roots that lies between the

pith and the cambium.

Yard brown stain.—{See Stain.)

Yard lumber.—{See Lumber.)
INDEX

Abbreviations, standard lumber

Acid copper chromate. See Copper chrornate,

acid.

Acid resistance of wood, methods for increasing

Acoustical board, description and use ..

Aircraft plywood:

breaking radius in bending

specifications

Air-drying, advantages

Air-drying yards, recommended practices for_

Air-dry lumber:

breaking radius in bending

moisture content range..

Air-dry wood, strength properties, table

Air spaces, thermal conductivity:

bounded by aluminum foil, table

bounded by ordinary materials, table

Alaska-cedar:

characteristics

classification for painting, table

color and figure, table

factors for strength of mechancial fastenings,

table

gluing properties, table

locality of growth

moisture content, table

nomenclature, table

shrinkage values, table

strength properties of clear wood, table

stresses, basic:

clear lumber, table _ _

laminated members, table

toughness, table

uses

weathering

weight, table:

per cubic foot

per 1,000 board-feet

Alder, decay resistance

Alder, red:

characteristics

classification for painting

color and figure, table

gluing properties, table

locality of growth_ _ _

moisture content, table

shrinkage values, table

strength properties of clear wood, table

uses

weight, table:

per cubic foot

per 1,000 board-feetworking quality with hand tools, table

Alpha-cellulose, use

Aluminum foil reflective insulation

Aluminum priming paint, composition

Ambrosia beetles:

control measures

damage caused

303747°—55 32

Page

131 American lumber standards:

application

Page

nomenclature, table

origin

112

112

115 54 yard lumber sizes, table

462

30S

279

Ammoniacal copper arsenite. >Ve Topper

arsenite. ammoniacal.

Animal glues, characteristics, and preparation,

table 233

401

401

323

384

Anthracene oils:

effectiveness as preservative

properties

308 specifications 401

325 Ants, carpenter 393

70

449

449

Apple:

moisture content, table '.

shrinkage values, table

weight, table:

per cubic foot

322

316

55 23

per 1,000 board-feet 55

226

358

38

Arches, built-up with mechanical fasteners:

horizontally laminated:

lateral stability

167 strength 226 234

23

vertically laminated and segmented:

design of 226 322 lateral stabilitv .- 226 112 method of construction. _. 226 315 strength 226 bV

Asbestos fiber and paper, thermal conductivity, table 451

258

83

23

43

Asbestos shingles, thermal conductivity, table.

Ash:

classification for painting.

decay resistance

451

354

45

56

56

elastic constants, table

machining pro])erties, table

weathering-- ._-

79

63

43

45 Ash, black:

characteristics 1]^

11

354

38

234

11

322

316

70

11

55

color and figure, table _.

factors for strength of mechanical fastenings,

table

locality of growth

moisture content, table_. . _.

shrinkage values, table .

strength properties of clear wood, table

stresses, basic:

clear lumber, table

laminated members, table

uses

38

167

11

322

316

70

1*57

258

55

62

weight, table:

per cubic foot 55

5 per 1,000 board-feet 55

447

367

Ash, blue:

characteristics 11

locality of growth 11

386

386

shrinkage values, table

uses

316

11

491
492 INDEX

Page

Ash, blue—Tontinued

weight, table:

per cubic foot

per 1,000 board-feet

Ash, commercial white:

characteristics

electrical resistance, table

factors for strength of mechanical fastenings,

table

locality of growth

stresses, basic:

clear lumber, table

laminated members, table

ties, strength of, table.

uses

working qualitj^ with hand tools, table.

Ash-forming minerals

Ash, green:

characteristics

locality of growth

moisture content, table.

shrinkage values, table

strength properties of clear wood, table. , _ _

uses

weight, table:

per cubic foot

per 1,000 board-feet

Ash, Oregon;

characteristics

color and figure, table

locality of growth

shrinkage values, table

strength properties of clear wood, table... .

uses

Ash, pumpkin:

characteristics

locality of growth

shrinkage values, table

uses

Ash, W'hite:

characteristics.

color and figure, table

gluing properties, table

locality of growth

moisture content, table

shrinkage values, table

strength properties of clear wood, table

thermal conductivity across grain, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Aspen:

classification for painting

color and figure, table

decay resistance

gluing properties, table

moisture content, table

ties, strength of, table

weathering

Aspen, bigtooth:

characteristics

factors for strength of mechanical fastenings,

table

locality of growth

55

55

11

49

167

11

156

260

440

11

62

6

11

11

322

316

70

11

55

55

11

38

11

316

11

11

316

11

11

38

234

11

322

316

70

49

11

55

55

354

38

45

234

322

440

43

Aspen, bigtooth—Continued

nomenclature

shrinkage values, table

stresses, basic, table

thermal conductivity across grain, tables.. -

ties, strength of, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Aspen, quaking:

characteristics

factors for strength of mechanical fastenings,

table

locality of growth

moisture content, table

nomenclature

shrinkage values, table

strength properties of clear w^ood, table

stresses, basic, table

uses .

weight, table:

per cubic foot

per 1,000 board-feet

Asphalt shingles, thermal conductivity, table.

Back priming

Baldcypress:

characteristics

classification for painting, table

color and figure, table

decay resistance

electrical resistance, table

factors for strength of mechanical fastenings,

table

gluing properties, table

locality of growth

moisture content, table

nomenclature, table

pecky lumber

poles:

life of

weight per cubic foot, table

shrinkage values, table

strength properties of clear wood, table

stresses, basic:

clear lumber, table

laminated members, table

tanks, use for

termite resistance

thermal conductivity across grain, tables. .-

ties, strength of, table

weathering

weight, table:

per cubic foot

per 1,000 board-feet

\vorking quality with hand tools, table

Balloon type of construction, as related to

shrinkage. _,

Balsa:

thermal conductivity across grain, tables..

elastic constants, table

Bark, inner and outer

Bark beetles:

control measures

damage caused

Page

12

316

156

49

440

12

55

55

12

167

12

322

12

316

70

157

12

55

55

451

371

23

358

39

45

167

234

23

322

112

23

436

431

315

70

156

259

52

393

49

440

43

56

56

62

331

49

79

1

386

386
INDEX 493

Basic stresses:

adjustment for:

decay hazard _ 102

duration of load-_ l^n

seasoning efîects 158

temperature 152

clear lumber, table 15P,

definition 2 40

discussion _ I^Q

Basswood:

classification for painting 354

color and figure, table 3g

decay resistance 45

eiïect of acids and bases on strength 53

electrical resistance, table 51

gluing properties, table 234

weathering 43

working quality with:

hand tools, table 62

machines, table P3

Basswood, American:

characteristics 12

factors for strength of mechanical fastenings,

table 167

locality of growth 12

moisture content, table 322

nomenclature 12

shrinkage values, table 316

strength properties of clear wood, table 70

thermal conductivity across grain, table 49

uses 12

weight, table:

per cubic foot 55

per 1,000 board-feet 55

Basswood, white:

characteristics 12

locality of growth 12

nomenclature 12

uses 12

Bastard sawn lumber, definition 41

Batt insulation:

materials 446

thermal conductivity, table 449

Beams:

duration of load, effect on strength 160

in heavy-timber construction :__- 337

knots, effect on strength 93

Beams, built-up with mechanical fasteners:

advantages 211

composite, method of construction 214

keyed:

deflections 213

methods of constructing 213

strength 213

methods of constructing 211

sheathed compound:

deflections 212

methods of constructing 212

strength 212

trussed:

methods of constructing 215

stresses, calculation 215

vertically laminated:

butt-jointed lamination, effect on strength. 212

Page

Beams, built-up with mechanical fasteners—Con.

vertically laminated—Continued

construction 211

strength 211

Beams, laminated:

design of 258

strength, factors in .. 250

Beams, solid:

circular:

form factor in design 210

strength 21O

lateral support of, approximate rules for 215

rectangular:

bearing area at ends, calculation 206

bending strength, calculation 203

combined loading effects 204

compression across the grain 206

deflection calculations 207

deflection limitations 207

depth factor in bending strength calculation 204

horizontal shear, calculation 205

load distribution 2')9

notched beams, design 207

safe load in bending, calculation 203

shear in checked beams, calculation 200

stress concentration effects 205

square with a diagonal vertical:

form factor in design 210

strength 210

Beams, wood-plywood, design of 263

Beams and stringers:

description 141

dressed sizes, minimum 143

effect of seasoning on strength 158

knots:

method of measuring 143

stress-grade limitations, tables 143

shakes, checks, and splits:

method of measuring 146

stress-grade limitations, table 146,151

slope of grain permitted, table 150

Beech:

classification for painting 354

decay resistance 45

effect of acids and bases on strength, table. 53

ties, strength of, table 440

working quality with:

hand tools, table 62

machines, table 63

Beech, American:

characteristics 13

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

locality of growth----, 13

moisture content, table 322

shrinkage values, table 316

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

thermal conductivity across grain, table 49

uses 13
494 INDEX

Page

Beech, American—Continued

weifiht. table:

{¡er cubic foot 55

per 1.00(1 board-feet 55

Beetles:

ambrosia beetles:

control measures. 386

damage caused-- 386

bark beetles:

control measures 386

damage caused _ 386

powder}»ost beetles:

control measures 388

damage caused 388

Bending of solid wood:

advantages 299

ay)paratus for_. 300

compression obtainable -- 299

fixing the bend _. .-. 301

green stock, disadvantages in use 300

moisture content of stock, recommended -_ 300

plasticizing of stock, recommended processes.._ .._ 300

principles of 299

properties of wood, essential . _. 299

seasoning of stock.__ 299

species, selection of 299

stretch obtainable . 299

Bending strength, solid beams . 203,210

Bent wood:

characteristics of 301

moisture change, effect of . _ _ . 301

strength 303

Beta-napthol, eifectiveness as preservative,

table ... 402

Birch:

decay resistance 45

electrical resistance, table ._ 51

weathering 43, 44

working quality with:

hand tools, table 62

machines, table 63

Birch, Alaska paper:

shrinkage values, table 310

weight, table:

per cubic foot 55

per 1,two board-feet _ 55

Birch, gray:

shrinkage values, table. 316

Birch, paper:

characteristics 13

color and figure, table 38

locality of growth 13

moisture content, table. 322

shrinkage values, table . . 316

strength properties of clear wood, table 70

toughness, table 83

uses 13

weight, table:

per cubic foot 55

per 1,000 board-feet.. 55

working quality with hand tools, table. . 62

Birch, river 13

Page

Birch, sweet:

characterist ics 13

color and figure, table - 38

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

locality of growth 13

moisture content, table 322

shrinkage values, table 316

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

ties, strength of, table 44U

uses 13

weight, table:

per cubic foot 55

per 1,000 board-feet 55

Birch, western paper 13

Birch, yellow:

characteiistics 13

coeilicient of thermal expansion, calculation. 47

color and figure, table. 38

elastic constants, table 79

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

laminates, properties, table 467

locality of grow^th . 13

moisture content, table 322

shrinkage values, table . 316

strength properties of clear wood, table.... 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

thermal conductivity across grain, table .. 49

ties, strength of, table. . . 440

toughness, table 83

uses 13

weight, table:

per cubic foot. 55

per 1,000 board-feet 55

Bird pecks, eiïect on strength 101

Blanket insulation:

materials 446

thermal conductivity, table 451

Bleeding, poles 436

Blistering of paint coatings:

blister-resisting paints 370

causes 370

Blood albumin glues, characteristics, preparation, uses 236

Boards:

description and uses 119.128

efîect of seasoning on strength 158

knots:

method of measuring 145

stress-grade limitations, table 145,151

sizes, table 116

stress grading 142

Boats, w^ood:

control of decay in 385

control of marine borers 396

Boliden salt. See Zinc arsenate, chromated.
INDEX 495

Page

Bolts:

bearing strength of bolts under:

basic stresses for calculating, tables 167,183

bearing strength of wood under:

bolt holes, effect of 185

diameter factor 183

loads at an angle to the grain . 184

loads parallel to grain 183

loads perpendicular to grain . 184

design details _ 185

quality of bolt, effect on joint strength 184

Bolts, drift:

lateral resistance 175

withdrawal resistance 175

Borax-boric acid, effectiveness as i)reservative,

table 402

Boring properties of hardwoods, table. . 63

Botanical names of trees . 70,67

Boulton process for conditioning green timber

for preservative treatment 415

Box columns, design of 220

Boxelder:

characteristics 18

locality of growth 18

nomenclature 18

uses _ 18

Breaking radius in bending:

air-dry lumber 305

plywood 305

veneer 305

Brick, thermal conductivity, table 451

Brick veneer, thermal conductivity, table 451

Buckeye, machining properties, table . 63

Buckeye, yellow:

moisture content,-table -__ 322

shrinkage values, table 316

weight, table:

per cubic foot 50

per 1,000 board-feet-. 50

Building board, for insulation 445

Building fiberboards. See Fibert)oards, building.

Buildings, control of decay in 384

Butternut:

classification for painting 354

color and figure, table. 38

decay resistance. __ 45

gluing properties, table 234

moisture content, table.. 322

shrinkage values, table. 316

strength properties of clear wood, table 70

weight, table:

per cubic foot 50

per 1,000 board-feet.. 50

working quality with hand tools, table ... 62

Butt joints:

effectiveness factor in laminated members.. 256

transmission of stress... 256

Butt treatment, poles 436

California-laurel:

moisture content, table. 322

shrinkage values, table . ... 316

weight, table:

per cubic foot ^^

per 1,000 board-feet •'>•'>

Page

Cambium 1,2

Carbolineums. See anthracene oils.

Carpenter ants:

control measures 393

damage caused by . 393

Casein glue, characteristics, jjreparation, uses,

table .. 234

Casing and base, description . . 130

Catalpa, decay resistance 45

Catalpa, northern:

shrinkage values, table 316

ties, strength of, table. 440

toughness, table 83

Cedar:

decay resistance.. 45

poles:

incising 436

preservative treatment ... . 429,435

properties of ... . . 429

See also Alaska-cedar, Incense-cedar, Redcedar, and White-cedar.

Ceiling and partition:

description 129

patterns 126

sizes, table 115

Ceilings, basement, fire resistance of . 344

Cclcure. See Copper chromate, acid.

Cells of wood:

description 4

fibers . 5

functions of various types .._ 5

length .. 5

parenchyma.-. . ... 5

rays .. 5

tracheids ... 5

vesselsr 5

Cellulose, discussion 5

Cement mortar, thermal conductivity, table.. 451

Checks, elïect on strength of laminated members .. 257

Chemical brown stain, characteristics.. 323

Chemicals, effect on wood:

acids, table 53

acid salts .. 54

alkalies, table 53

discussion... .... 52

methods for increasingacid résistance of wood. 54

niggerizing.. ... .... . 54

nonswelling liquids 53

strength reduction, table . . 53

swelling liquids... . 53

types of action . . 52

Chemonite. See Copper arsenite, ammoniacal.

Cherry:

classification for painting.. . 354

working quality with hand tools, table 62

Cherry, black:

characteristic^ 13

color and figure, table... — 38

decay resistance.-. ... 45

gluing properties, table.. — ... . 234

locality of growth. 14

moisture content, table. 322

nomenclature . . - 13

shrinkage values, table 316
496 INDEX

Page

Cherry, black—Continued

slreriííth pro¡)eríies of clear wonrl, table ... 70

thermal conductivity across grain, table __ 49

ties, strength of, tah)le 440

uses 14

weight, table:

per cubic foot 55

per 1,000 board-feet 55

('herry, pin:

shrinkage values, table 31 P>

ties, strength of, table 440

Chestnut:

classification for painting. 354

decay resistance 45

ties, strength of, table 440

weathering 43, 44

working quality with:

hand tools, table iV2

machines, table. .-. 63

Chestnut, American:

characteristics 14

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

location of timber. 14

moisture content, table 322

nomenclature H

shrinkage value-s, table 316

strength properties of clear wood, table ... 70

thermal conductivity across grain, table .. 49

uses 14

weight, table:

per cubic foot 55

per 1,000 board-feet 55

Chestnut, Japanese, toughness, table 83

Chinkapin, golden:

moisture content, table 322

weight, table:

per cubic foot 55

per 1,000 board-feet 55

Chromated copper arsenate. See Co{)per

arsenate, chromated.

Chromated zinc arsenate. See Zinc arsenate,

chromated.

Chromated zinc chloride. See Zinc chloride,

chromated.

Circular beams:

design of 210

strength 210

Clay tile, thermal conductivity, table.... 449

Coal tar:

crosstie treatment with . _ 404

eiïectiveness as preservative, table 404, 409

penetrations obtained 404

Coal-tar creosote. See Creosote.

Coefficient of linear thermal expansion, discussion 47

Coefficient of variability 84

Color of w^ood, table 38

Columns:

duration of load, effect on strength 160

fire resistance of 339

heavy-timber construction 337

Page

Columns—Continued

knots, elTect on strength ^ ^

seasoning, effect on strength 158

Columns, built-up with mechanical fasteners:

box columns, design of 223

butt joints, effect on strength 221

spaced columns:

connector requirements 225

design of 225

method of construction 223

strength, compared to one-piece columns 220

Columns, circular:

design of 22G

strength, compared to square columns 226

Columns, laminated, design of 263

Columns, solid rectangular:

classification on slenderne.ss ratios 216

combined side and end lf)ads, calculation.._ 219

eccentric loading, calculation 219

formulas for design 217

safe load calculations 217

side bracket load, calculation 220

Common names of trees 70,67

Common boards:

description 128

sizes, table 119

uses 128

Composite beams or slabs, method of constructing 214

Compreg 469

Compressed wood, untreated Cstaypak):

finish 473

manufacture 473

properties, tables 468

uses 473

Compression failures:

appearance 99

cause 98

strength, effect 99

Compression members with thin outstanding

flanges:

twisting formula and discussion 221

wrinkling formula and discussion 221

Compression parallel to grain:

definition of:

fiber stress at proportional limit 69

maximum crushing strength 69

strength values:

coefficient of variability 84

fiber stress at proportional limit, table 70

maximum crushing strength, table 70

moisture content as related to 85.87

slope of grain as related to, table 97

specific gravity as related to 88

Compression perpendicular to grain:

bearing area at ends of beams 206

fiber stress at proportional limit:

coelficient of variability 84

definition 69

moisture content as related to 85,87

specific gravity as related to 88

values, table ._- 70

working stresses as related to:

annual grow^th ring direction ' ^ 80

bearing area _ 78
INDEX 497

Page

Compression wood:

characteristics 97

effects in lumber 97

occurrence 97

shrinkage 318

strength of 97

warping, cause 318

Compressive strength, surfaces inclined to

grain, formula 80

Concrete, thermal conductivity, tahle 451

Concrete blocks, thermal conductivity, table. 451

Condensation:

effect of insulation on 453

prevention in wall and roof spaces 453.454

prevention on surface 452

Conduction of heat 448

Conductivity, thermal:

definition 448

discussion and tables 40

insulating materials, table 451

Conifers, description 5

Connectors:

connector-joint design, examples of 199

cross bolts, use of 199

multiple connectors, placement of 198

strength ratios:

shear-plate, table 198

split-ring, table 190

toothed-ring, table 191

stress in net area 199

working loads:

derivation of 187

end distance and spacing, effect of 196

exposure conditions, effect of 195

factor of safety 193

grade and quality of lumber 195

impact forces, effect of 194

Kubier wood dowel 2(H)

loads at angle to grain 195

moisture content of wood, effect of 195

shear-plate connector, table 192

special design conditions, effect of 194

species classification, table 167,190

split-ring connector, table 167

thickness of member, effect of, tables... 192,196

toothed-ring connector, table 191

width of member, effect of 196

wind or earthquake loads, effect... 193

Continuous spans, limitation of knots and

checks 147

Convection of heat 448

Copper arsenate, chromated:

composition 408

effectiveness as preservative 408

use 408

Copper arsenite, ammoniacal:

composition 408

effectiveness as preservative 408

retentions recommended for various wood

products, table 418

specification 408

Copper chromate, acid:

composition 407

effectiveness as preservative, table 402

Page

Copper chromate, acid—Continued

retentions recommended for various wood

products, table 418

specification 407

Copper naphthenate:

composition 405

effect on properties of wood 405

effectiveness as preservative 405

oils for, specification 405

retentions recommended for various wood

products, table 417

specifications 405

uses 404

Copper sulfate and sodium arsenate, effectiveness as preservative, table 402

Copperized chromated zinc chloride. See Zinc

chloride, copperized chromated.

Corkboard, thermal conductivity, table 449

Cotton, thermal conductivity, table 449

Cottonwood:

classification for painting 354

coefficient of thermal expansion, calculation. 47

color and figure, table 38

decay resistance 45

gluing properties, table 234

weathering 43, 44

working quality with:

hand tools, table 62

machines, table 63

Cottonwood, black:

characteristics 14

Cottonwood, southern, shrinkage values,

table .- 315

Cottonwood, swamp:

characteristics 14

locality of growth 14

nomenclature 14

uses 14

Crankcase oil, effectiveness as preservative,

table 402

Creosote, coal-tar:

advantages 400

control of marine borers with 395

effect of character on service 399

effectiveness, table 402

fire hazard 400

health effect 400

odor 400

painting 400

pole treatment 435

retentions recommended for various wood

products, table 417

specifications 400

Creosote, crystal-free coal-tar:

efïectiveness as preservative. 401

properties 401

specifications 401

Creosote, oil-tar, effectiveness as preservative. 401

Creosote solutions:

with coal tar:

properties 401

retentions recommended for various wood

products, table 417

specifications 404

toxicity 404
498 INDEX

Page

Cr('().süto solutions—Contimied

with petroleum oil:

fortification of 404

elYecti\eness as preseivative, table... 4f)9

oils, specification for . 404

proi)erties - 404

retentions recommended for various wood

Itroducts, tat)le 417

specifications 104

toxicity - - 404

Creosote, water-gas-tar, elTecdveness as i)reservative - 401

Creosote, wof)d-tar, eíTectiveness as preservative, table 402,409

Crossbanded constiuction. See Plywood, IIollow-core construction, Sandwich construction.

Cross grain:

determination of combined slope of spiral

and diagonal grain . _ 90

diagonal grain, test for presence. 95

eíYect on strength of laminated members 252

factors for strength of mechanical fastenings.

table- - 107

locality of growth .. . 14

moisture content, table, -. . . 322

nomenclature . . 14

shrinkage values, table . 315

strength properties of clear wood, tat)le 70

ties, strength of, table. 440

uses . . 14

weight, table:

])er cubic foot 55

per 1,000 board-feet 55

Cottonwood, eastern:

characteristics . __.... 14

factors for strength of mechanical fastenings,

table. 107

locality of growth 14

nomenclat ure 14

shrinkage values, table ... 315

sti'ength properties of clear wood, table 70

stresses, basic:

clear lumber, table ]50

laminated members, table 2()0

ties, strength of, table.. 440

uses 14

weight, table:

I)er cubic foot 55

per 1.000 board-feet 55

shrinkage of cross-grained boards 31G

s{)rial grain, test for i)resence .. .. 95

strength as related to, table 96, 13S

twisting, cause 13K

t >'pes 95

Cross-grain cracking of paint, cause 309

Crossties. .sve Ties.

Crushing strength, maximum:

coetficient of varial)ility... 84

definition 09

moisture content as related to .. . 85,87

slofjc of gvain as related to, table 97

specific gravity as related to 88

values, table 70

Page

Curved wood members:

laminated:

design of 262

manufacture of 3^*3

plywood 304

solid 299

veneered 304

Cucumbertree:

characteristics 18

locality of growth 17

nomenclature 17

shrinkage values, table 316

strength properties of clear wood, table 70

uses 18

weight, table:

per cubic foot 55

per 1,000 board-feet 55

Cutting and framing before preservative treatment 411

Dead trees:

decay resistance 101

specifications for products from 102

strength 101

Decay:

appearance of fungi 382

cause of-. . 381

control in:

boats, wood 386

buildings 384

logs, poles, ijiling. or ties 383

lumber 384

plywood 385

dry rot fungi 382

effect on strength . 383

foofloffungi 382

heartwood. susceptibility to __ 382

incipient decay, api)earance 382

limitation in structural lumber 137. 142,162

occurrence 382

prevention of:

safe moisture content 381

sapwood, susceptibility to 382

strength, effect on 100

typical decay, appearance. 382

Decay resistance:

classification of species 45

conditions favoring decay 44

dead trees 101

heartwood 45

piling 437

poles - . 436

sapwood 44

ties 440

Decking, heavy, sizes, table. 117

Decorative features of wood:

color, table 38

figure, table 38

knots 37

luster 38

Deflection, beam:

calculation 207

limitation. 207

Degrade, seasoning:

chemical brown stain 323

classification 325
INDEX 499

Page

Degrade, seasoning—Continued

elimination 323

sticker stain 323

Density, criterion of strengtli 137,148

Depth factor:

in bending strength calculation 204

laminated beams 258

Diagonal grain, test for presence of 95

Dielectric constant:

definition 50

factors influencing 50

Dimension:

care during construction 334

description and uses. 121,128

sizes, table 116

Dimensional stabilization of wood, by resin

treatment 467

Dimension stock, hardwood, grades ._ 110

Discontinuous rings, definition 2

Dogwood, flowering:

gluing properties, table .. 234

moisture content, table 322

shrinkage values, table 316

weight, table:

per cubic foot 55

per 1,000 board-feet 55

Dogwood, Pacific:

weight, table:

per cubic foot 55

per 1,000 board-feet 55

Door, coeflBcient of heat transmission, table. _ _ 453

Door plus storm door, coefficient of heat transmission, table 452

Doors, fire resistance in frame construction 358

Dote. See Decay.

Double-diffusion process of preservative treatment:

effectiveness, table... 409, 423

method 423

Douglas-fir:

characteristics — -- 24

classification for painting, table.-- 358

coefficient of thermal expansion, calculation. 47

color and figure . 38

decay resistance — 45

elastic constants, table 79

gluing properties, table 234

laminated arches and beams, use for 247

locality of growth 24

nomenclature, table 24,112

piling suitability 437

plywood grades and types 278

poles:

life of 437

properties of 430

preservative treatment 430,435

stresses, basic:

clear lumber, table 150

laminated members, table 259

tanks, use for ^2

thermal conductivity across grain, tables.- 47,49

ties, life of 441

toughness, table ^^

uses ^

Douglas-fir— C ontinued

weathering

working quality with hand tools, table

Douglas-fir, close-grained:

requirements

stresses, basic:

clear lumber, table-. .

laminated members, table

Douglas-fir, coast type:

electrical resistance, table - - - _

factors for strength of mechanical fastenings,

table

moisture content, table

poles, weight per cubic foot, table -

stresses, basic:

clear lumber, table

laminated members, table. _.

shrinkage values, table

strength properties of clear wood, table

ties, strength of, table

toughness, table

weight, table:

per cubic foot

per 1,000 board-feet

Douglas-fir, dense:

requirements

stresses, basic:

clear lumber, table

laminated members, table-..

Douglas-fir, intermediate type:

moisture content, table

shrinkage values, table .

strength properties of clear wood, table ...

ties, strength of, table

toughness, table

weight, table:

per cubic foot

per 1,000 board-feet

Douglas-fir, medium-grained, requirements-..

Douglas-fir, Rocky Mountain type:

factors for strength of mechanical fastenings,

table

moisture content, table

poles, weight per cubic foot, table . .

shrinkage values, table.. - ..

strength properties of clear wood, table _

stresses, basic:

clear lumber, table

laminated members, table

ties, strength of, table

weight, table:

per cubic foot

per 1,000 board-feet

Dressed and matched lumber, sizes, table

Dressed sizes, minimum for structural lumber.

Drift bolts. See Bolts, drift.

Drying rates of paint

Dry rot:

appearance

fungi causing

Duration of load:

effect on load-carrying capacity .

effect on strength of structural lumber U

Early wood, description and properties

Page

. 43,44

62

149

. 156

259

167

322

431

156

259

316

67

440

83

55

55

149

156

259

322

316

70

440

83

55

55

149

167

322

431

315

70

156

259

440

55

55

115

142

353

382

382

93

1,160

2
500 INDEX

257

Page

Edge-grained lumber:

advantages 42

method of producing 41

Edge joints, effect on strength of laminated

members

Elastic constants of wood:

discussion

values of:

modulus of elasticity ratios, table

modulus of rigidity ratio?, table

Poisson 's ratio

Electrical properties of wood:

dielectric constant:

definition

factors influencingdielectric properties, uses

electrical resistance:

along the grain of diiïerent species, table

factors influencing

specific, values

uses

power factor:

definition

factors influencing

Elm:

classification for painting . 354

decay resistance 45

weathering 43

working quality with:

hand tools, table 62

machines, table 63

Elm, American:

characteristics 15

color and figure, table 38

electrical resistance, table 51

factors for strength of mechanical fastenings, table 167

gluing properties, table 234

locality of growth 15

moisture content, table 322

nomenclature 15

shrinkage values, table 316

strength properties of clear wood, table.. __. 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

thermal conductivity across grain, table.

ties, strength of, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Elm, cedar:

characteristics

locality of growth

nomenclature

strength properties oí clear wood,

uses

weight, table:

per cubic foot

per 1,000 board-feet

Elm, hard, species included

table.

Page

Elm, rock:

characteristics 15

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

locality of growth 15

moisture content, table 322

nomenclature 15

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

thermal conductivity across grain, tables... 49

ties, strength of, table _. 440

uses 15

weight, table:

per cubic foot . 56

per 1,000 board-feet 56

Elm, September:

characteristics 15

locality of growth 15

nomenclature 15

uses 15

Elm, slippery:

characteristics 15

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth 15

nomenclature. 15

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

ties, strength of, table. .. _ 440

uses 15

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Elm, soft:

species included 15

stresses, basic:

clear lumber, table 156

laminated members, table 260

Elm, winged:

characteristics 15

locality of growth 15

nomenclature 15

strength properties of clear wood, table 70

toughness, table •_ 83

uses 15

Empty-cell process for preservative treatment. 413

Enamels for interior finishes, characteristics- 351,353

Encased knots, definition 2

End joints, effect on strength of laminated

members 255

Equilibrium moisture content:

discussion 311

relative humidity as related to, table 311

Erdalith. See Copper arsenate, chromated.

Expansion, thermal, discussion 47
INDEX 501

Expansion molding of compreg 459

Exterior finisli, thermal conductivity, table. _ _ 449

Exterior woodwork:

natural finishes for:

durability 373

protection from mildew 374

types ;;;;; 3^3

uncoated:

choice of woods 374

fastenings suitable for 374

weathering 374

Extractives:

discussion 5

paint behavior, effect on 353 359

strength, effect on 102

Factory and shop lumber, use classes 125

False rings, definition 2

Fastenings:

design loads in laminated members 263

factors for calculating strength of, table 167

Fatigue resistance, endurance loads for various

types of test specimens 82

Fiberboard building:

classification 457

density range 457

description 457

hardboards:

fibrous 463

resin-bonded particle 464

special densified 464

treated 463

untreated 463

insulation board, rigid:

accoustical board 462

fiberboard lath 460

general-use boards 460

interior board - _. 461

roof insulation 460

sheathing board 461

insulation board, semirigid 458

intermediate-density board:

fibrous 462

resin-bonded particle 463

manufacture 457

strength and physical properties, table 457

uses 457

Fiberboard, fire resistance of 344

Fiberboard, insulatmg:

products 445

thermal conductivity, table 449

Fiberboard lath:

method of use 460

sizes and special features 460

thermal and sound insulation properties 460

Fibers:

description 4

function 4

Fiber-saturation point, shrinkage as related to. 314

Fiber stress at proportional limit:

coefficient of variability 84

definition 69

moisture content as related to 85,87

specific gravity as related to 112

values, table 70

Page

Figure of wood, table 39

Fill insulation:

materials 447

thermal conductivity, table 449

Fhiish floors:

air moisture conditions for proper laying,

determination 334

cracks, cause 334

methods to prevent cracks 334

Finish, softwood:

description and uses 117,128

sizes, table ii5

Finish, thermal conductivity:

exterior, table 449

interior, table 449

Finishes, floor:

kinds 376

pi-operties 376

upkeep 376

Finishes, interior:

characteristics 374

opaque:

enamels, characteristics 374

preparation of surface 374

transparent:

application procedure 375

fillers, purpose 375

preparation of surface 375

stains, purpose 375

surface coatings, kinds and effects 376

Finishes, natural:

for exterior woodwork:

durability 373

protection from mildew 374

types 373

Fir, alpine:

characteristics 25

locality of growth 25

moisture content, table 322

nomenclature, table 112

shrinkage values, table 315

uses 25

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Fir, balsam:

characteristics 24

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth 24

moisture content, table 322

nomenclature, table 112

shrinkage values, table 315

strength properties of clear wood, table. _ __ 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

uses 24

weight, table:

per cubic foot ,56

per 1,000 board-feet 56

working quality with hand tools, table.... 62
502 INDEX

Page

Fil-, California red:

charactf.Tistics ._ - 25

electrical resistance, table 41»

locality of growth.. ._ .. 25

moisture content, tal)le . • {22

nomenclature, table. . . 112

shrinkage values, table . . . -. 315

strenpth properties of clear wood, table . 70

stresses, basic:

clear lumber, table ..____....-- 150

laminated members, table -. .. 259

touglniess, table ... S3

uses. 25

weight, table:

lier cubic foot - _- 50

per 1,000 board-feet .... .. _. 50

Fir, conmiercial white:

classification for painting . . . 358

factors for strengtli of medianical fastenings,

table 107

ties, strength of, table . . -.. 440

weathering 43

Fir, corkbark:

slirinkage values, table ... 315

toughness, table 83

Fir, Fraser:

characteristics 24

locality of growth 24

nomenclature, table ........ .. 112

uses. __ ... . _ _. 24

Fir, grand:

characteristics ... .. 25

locality of growth.. .. ._ __.. 25

moisture content, table. .. . 358

nomenclature, tattle. - 112

shrinkage values, table ... .__ _. 315

strength properties of clear wood, table.. 70

stresses, basic:

clear lumber, table _. 150

laminated members, table 259

uses 25

weight, table:

per cubic foot ... 50

per 1,000 board-feet ... _ _. 50

Fir, noble:

characteristics __ 25

locality of growth _. 25

moisture content, table ._. _. .. 322

nomenclature, table. _ ... 112

shrinkage values, table ...... . ... 315

strength properties of clear wood, table .. 70

sti-esscs, basic:

clear lumber, table . . ... .. 150

laminated members, table ... 259

toughness, table . ... 83

uses 25

weight, table:

I^er cubic foot ... ... .50

per 1,000 board-feet. . ... _. 50

Fir, Pacific silver:

characteristics .... .... 25

locality of growth 25

moisture content, table 358

nomenclature, table 112

shrinkage values, table 315

Page

Fir, Pacific silver—Continued

strength properties of clear wood, table... 70

uses 25

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Fir, true:

decay resistance 45

eastern species 24

western species 25

Fir, white:

characteristics 25

coeihcient of thermal expansion, calculation. 47

color and figure, table . .. 38

electrical resistance, table 51

gluing properties, table . 234

locality of growth . 25

moisture content, table .. . 322

nomenclature, table ._ . 112

shrinkage values, table ._ . 315

strength properties of clear wood, table ... 70

stresses, basic

clear lumber, table 156

laminated members, table. 259

thermal conductivity across grain, table 47

uses 25

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table . . 62

Fire resistance of:

frame construction:

basement ceilings 344

chimneys .342

doors and stairways .. 345

fireplaces .342

fire stops .. ... 341

partitions, load-bearing.. 343

part it ions, nonbearing. 344

shingles 345

surface coverings and finishes 345

glued laminated members. . . _ 345

lieavy-timber construction 337

one-story industrial buildings 339

ordinary construction 339

sandwich construction.. 295

Fire-retardant chemicals:

characteristics 347

eiïectiveness 347

k inds 347

zinc chloride chromated:

composition _. 407

retentions 407

specification 406

Fire-retardant treatments for wood:

coatings and surface treatments:

efîectiveness 348

formulations 348

kinds 348

impregnation:

absorptions required 347

chemicals for.. 347

effectiveness 347

methods 347

uses.. 346
INDEX 503

Page

Fire stops 339,341

Flat-grained lumber:

advantages 42

method of producing 41

Flexible insulation 446

Flooring, storage at yards.. . 326

Flooring, hardwood:

availability . 129

grades 109

moisture content recommendini, table _ _ 329

Flooring, softwood :

description . . 129

grades available - ._. 129

factory sizes, table Un

moisture content recommended, table .. 329

sizes, table .. .- 115

standard match. . . . 126

Floors:

buckling of joists, prevention of_ . 215

care during construction 334

distribution of load bet\\et>n joists, 209

finishes for:

kinds 377

properties.. 377

upkeep 376

fire resistance in frame construction 345

requirements in heavy-timber construction. 337

Fames pini, effect on strength 383

Forest lands, amount, table . 7

Form factor:

circular beams

square beams with diagonal vertical. _. ..

Frame construction, fire resistance of _ _

Framing:

minimizing shrinkage

moisture content recommended, table

pole -- -----

Full-cell process for preservative treatmentFungi:

appearance of-- ... 382

conditions favorable to growth... 381

dry rot fungi 382

food of 381

occurrence 382

General-use, rigid insulation board:

sizes -- -

210

210

341

329

329

229

412

uses -

Glass blocks, coefficient of heat transmission:

ribbed surface, table .-.

smooth surface, table. . . -

Glossary .-

Glues for bonding wood to metal:

procedure for using

types

Glues, woodworking:

characteristics, preparation and uses of:

animal, table

blood albumin

casein, table

liquid

resin, table - -

starch, table--

vegetable protein, table. .

460

460

453

453

479

235

234

236

234

236

234

236

236

236

Gluing:

conditioning glued joints

conditioning wood for.

consistency of glue . . .

machining lumber for.

moisture content recommiMidtMl for:

lumber-- .. . .__

veneer..

pressure application:

cold-pressing.. . .

hot-pressing . ..

Gluing properties of diff(>rrnt woods:

classification of species, table... . ...

factors alTecting.. .

(irade-marked lumber, purpose .....

Grades of lumber:

American lumber standards _

factory and shop lumber.. . .

hardwood dimension stock

hardwood flooring

hardwood lumber, table .

softwood lumber... .. ... ....

structural lumber

yard lumber...

Grade-use examples for softwood lumber:

boards.. .

dimension

factory plank

finish

shop lumber ... . . Greenheart:

shrinkage values, table . .

thermal conductivity across grain, table

Greensalt. See ropi)er arsenate, chromated

Green wood:

effect of heating.. .. ..

moisture content, table..

strength i)roperties, table.

strengtli ratios, table... .. . .

weight per cubic foot, table ..

Grain of wood:

cross grain, eiïect on strength..

discussion..

strength as related to slope of giain, table

(xrowth rate, criterion of strength . . 1

Growth rings:

determination of tree age by..

discontinuous, definition.. . . .

discussion.. ... .. ...

false, definition.. .. ..

Gum. classification tor painting.. .

Gum, red:

description.. .

electrical resistance, table.. ..

Gum, sap, description

Gypsum board, fire resistance of.. ...

Gypsum lath and plaster, thermal conductiv

ity, table

Gypsum plaster, thermal conductivity, table

Gypsum sheathing, thermal conductivity

table. - -

Gypsum tile, thermal conductivity, table

Gypsum wallboard, thermal conductivity

table

Page

24]

238

23<>

238

235

235

240

240

234

233

130

111

. 126

110

. 109

108

111

125, 148

117

. 119

. 121

12fi

117

126

- 315

49

47

322

7(.)

150

56

95

40

97

37, 148

354

20

49

20

343

449

449

449

440
504 INDEX

Page

Hack berry:

characteristics 15

classification for painting 354

color and figure, table 38

decay resistance 45

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

locality of growth 15

moisture content, table 322

shrinkage values, table 315

strength properties of clear wood, table 70

ties, strength of, table 440

uses 16

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with:

hand tools, table 62

machines, table 63

Hankinson formula, for compressive strength

on surfaces inclined to grain 80

Hardboards:

fibrous:

density range 463

manufacture 463

prefinished wall panels 464

sizes 463

strength and physical properties, table.. 459, 463

tempering process, efifect 463

uses 463

resin-bonded particle:

density range 464

effect of moisture content changes. .. 464

sizes 464

strength and physical properties, table 464

uses 464

special densified:

density range 464

strength and physical properties, table 459

th icknesses 464

uses 465

Hardness:

coefficient of variability 84

definition 69

moisture content as related to 85, 87

specific gravity as related to . 88

values, table 70

Hardwood dimension stock, grade 110

Hardwood flooring, grades:

Maple Flooring Manufacturers' Association- 109

National Oak Flooring Manufacturers Association 110

Hardwood lumber:

availability 111

uses 112

Hardwood lumber grading:

grade classification, all species 106

summary of standard grades of the National

Hardwood Lumber Association:

description of standard hardwood grades,

table 108

standard lengths 107

standard thicknesses, table 107

woods included 107

Page

Hardwood lumber manufacturers' a-ssociations, woods covered by grading rules 105

Hardwood plywood, grades and types 278

Hardwoods:

definition 5

hardnei^s 5

length of fibers 4

locality of growth 9

machining properties, table 63

painting:

classification 354

filler 354

percent of total timber 9

vessels in, function of 4

Heartwood:

color, variation in different species 4

decay resistance in different species 45

durability in weather exposure 4

form ation 4

moisture content, table 322

preservative penetration in 416

strength 4

specification in structural lumber 137,148

tyloses in pores, use for cooperage 4

weight 4

Heat loss through different types of doors and

windows 452

Heat loss through different types of walls 449

Heat transmission, coefficient of:

definition 449

door, table 453

door plus storm door, table 453

double-glazed window, table 453

ribbed-surface glass blocks, table 453

single window, table 453

smooth-surface glass blocks, table 453

values for computing, table--. 449

Heat transmission, methods of 447

Heavy-timber construction:

description '. 337

fire resistance 339

shrinkage 333

specifications for construction 337

Hemicellulose 6

Hemlock, decay resistance 45

Hemlock Carolina, nomenclature, table 112

Hemlock, eastern:

characteristics 25

classification for painting, table ^... 358

color and figure, table. 38

factors for strength of mechanical fastenings,

table 167

locality of growth 25

moisture content, table 322

nomenclature 25,112

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table... 156

laminated members, table 259

ties, strength of, table 440

toughness, table 83

uses. 25

weathering 43^ 44
INDEX 505

Page

Hemlock, eastern—Continued

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

Hemlock, mountain, nomenclature, table 112

Hemlock, western:

characteristics 26

classification for painting, table 358

color and figure, table 38

electrical resistance, table 49

factors for strength of mechanical fastenings,

table 167

glumg properties, table 236

locality of growth 26

moisture content, table 322

nomenclature 26,112

poles, weight per cubic foot, table 431

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

thermal conductivity across grain, tables... 47

ties, strength of, table... 440

toughness, table 83

uses 26

weathering 43, 44

weight, table:

per cubic foot 56

per 1,000 board-feet 56

workmg quality with hand tools, table 62

Hickory:

classification for painting 354

color and figure, table 38

decay resistance 45

gluing properties, table 234

weathering 43, 44

Hickory, bitternut:

characteristics 16

locality of gi'owth 16

moisture content, table 322

strength properties of clear wood, table 70

uses 16

Hickory, mockernut:

characteristics 16

locality of growth 16

moisture content, table 322

shrinkage values, table 315

strength properties of clnar wood, table. 70

weight, table:

per cubic foot 56

per 1,000 board-feet 56

uses 16

Hickory, nutmeg:

characteristics 16

locality of growth 16

strength properties of clear wood, table 70

uses ^6

Hickory, pecan:

characteristics ^^

factors for strength of mechanical fastenings,

table 1Ö7

gluing properties, table 258

locality of growth 16

Page

Hickory, pecan—Continued

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated meml>ers, table 260

thermal conductivity across grain, table 49

ties, strength of, table 440

uses 16

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with:

hand tools, table 62

machines, table 63

Hickory, pignut:

characteristics 16

locality of growth 10

moisture content, table 322

shrinkage values, table 315

strength properties of clear wood, table 70

uses 16

weight, table:

per cubic foot 56

per 1,000 board-feet 50

Hickory, red:

characteristics 16

locality of growth 16

moisture content, table 322

uses 16

Hickory, sand, moisture content, table 322

Hickory, shagbark:

characteristics 16

locality of growth 16

shrinkage values, table 315

strength properties of clear wood, table 70

uses 16

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Hickory, shcllbark:

characteristics 16

locality of growth 16

shrinkage values, table 315

strength properties of clear wood, table 70

uses 16

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Hickory, true:

characteristics 16

electrical resistance, table.. 51

factors-for strength of mechanical fastenings,

table 167

locality of growth 16

shrinkage values, table _ 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table. - 156

laminated members, table 260

ties, strength of, table 440

uses. 16

working quality with:

hand tools, table 62

machines, table 63
506 INDEX

Page

Hickory, water:

characteristics _ . 16

locality of growth 16

moisture content, table . 322

strength properties of clear wooc , table. .. 70

uses .. 16

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Pioles:

effect on strength of structural lumber . 140

measurement in structural lumber._ - 143

Hollow-core construction:

description.. ._ 2R8

use _ . . 288

Holly, American:

characteristics 17

locality of growth 17

moisture content, table 322

nomenclature . 17

315

17

shrinkage values, table.

uses

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Honeylocust:

color and figure, table 38

decav resistance.. - 45

315

70

shrinkage values, table.

strength properties of clear wood table- ._

ties, strength of, table... 440

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools. table. .. 62

Hophornbeam, eastern:

moisture content, table 322

shrinkage values, table 315

weight, table:

per cubic foot 56

per 1,000 board-feet._ 5fi

Horizontally laminated members. See Laminated members, mechanically fastened.

Hot-and-cold-bath process of preservative

treatment... .. 423

Hot-soaked plywood 305

Identification of wood 37

Impact bending, height of drop ca ising complete failure:

coefliicient of variabihty 84

discussion 69

85, 87

97

moisture content as related to

slope of grain as related to, tablespecific gravity as related to 112

70

467

values, table... .

Impreg _

Incense-cedar:

characteristics 26

classification for painting, table.. . 358

color and figure, table 38

localitv of growth.. 26

moisture content, table 322

nomenclature, table 112

peck y lumber 26

shrinkage values, table 315

Page

Incense-cedar—Continued

strength properties of clear wood, table 70

uses : 26

weight, table:

per cubic foot 66

per 1,000 board-feet 56

working quality with hand tools, table 62

Incising for preservative treatment:

effect on penetration 418

method 411

poles 436

purpose 411

species requiring 411

Industrial buildings, one-story, fire resistance

of 339

Insect damage:

classification lOO, 387

strength, effect on lOO

Insulating materials:

batt 446

blanket 446

fill 447

miscellaneous 447

reflective 447

rigid nonstructural (slab) 446

rigid structural (fiberboard) 445

thermal conductivity, table 449

insulation, effect on condensation 452

Insulation board lath and plaster, thermal

conductivity, table 449

Insulation board, rigid:

classification 453

fiberboard lath:

method of use 460

sizes and special features 460

460

460

460

thermal and sound insulation properties,

general-use boards:

sizes

uses

interior board:

advantages and disadvantages 462

finishes 451

for sound insulation 452

linear expansion, effect 462

method of use 461

sizes and forms 46I

uses .-__ 461

roof insulation:

method of use 46O

sizes 460

uses, __ 460

sheathing board:

advantages and disadvantages 461

method of use 461

nail-withdraw^al resistance 461

rigidity 461

sizes 461

strength and physical properties, table.. 459

Insulation board, semirigid:

heat-flo^v characteristics 458

sizes 458

strength and physical properties, table 459

uses 458

Intergro\vn knots, definition 2
INDEX 507

Page

Interior finish:

care during construction 335

moisture content recommended, table 329

thermal conductivity, table 449

Interior-finish fiberboards:

advantages and disadvantages 4f)2

finishes 4^1

for sound insulation 402

linear expansion, effect 402

method of use 40i

sizes and forms 401

uses 401

Interior finishes:

characteristics 374

effectiveness as moisture-excluding coatings. 377

opaque:

enamels, characteristics 374

preparation of surface 374

transparent:

application procedure 375

fillers, purpose 375

preparation of surface 375

stains, purpose 375

surface coatings, kinds and effects 376

Intermediate-density building boards:

fibrous:

linear expansion, effect 462

method of use 462

sizes-- 462

strength and physical properties, table, 459, 462

uses 462

weight 462

resin-bonded particle:

strength and physical properties, table 459

uses 463

Iroko, shrinkage values, table 315

Ironbark, gray, shrinkage values, table 315

Joints, glued:

butt:

effectiveness factor in laminated members. 256

transmission of stress 256

durabihty, factors affecting 244

edge, effect on strength of laminated members 257

end, effect on strength of laminated members 255

end-grain surfaces 240

end-to-side-grain 241

laminated members, quality in.. 250

moisture content of 241

scarf:

advantages 241

joint factor 255.256

permitted stress 255

slope of grain 256

spacing... -- 255

serrated 241

side-grain surfaces 240

temperature, effect on durability 244

tongued-and-grooved 240

treatments to increase durability 244

water resistance 244

Joints, timber-connector. See Connectors.

Joints, toenailed, strength of 171

Joist hangers, shrinkage as related to 333

303747°—55 33

Page

Joists, sizes, table 117

Joists and planks:

description 141

dressed sizes, minimum. 142

effect of seasoning on strenptb . 159

knots:

method of measuring . _ 144

stress-grade limitations, tables 144,150

shakes, checks, and splits:

method of measuring.. _ 146

stress-grade limitations, table 146,150

slope of grain permitted, table 150

Juniper, decay resistance 45

Juniper, alligator:

nomenclature, table 112

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Juniper, bigberry, thermal conductivity

across grain, table 49

Juniper, Rocky Mountain:

nomenclature, table..- 112

toughness, table 83

Juniper, Utah:

nomenclature, table 112

toughness, table 83

Juniper, western:

nomenclature, table 112

Keyed beams:

deflections 213

methods of constructing 213

strength 213

Khaya:

classification for painting 354

elastic constants, table 79

electrical resistance, table 49

shrinkage values, table 315

Kiln-dried lumber, moisture content range... 325

Kiln-drying, advantages 323

Knots:

decorative features • 37

formation of 2

grades, effect on 118,121,125

kinds 93

laminated members, effect on strength of .. 251

location, effect on strength 139

shapes - 94

strength, effect on... 94,138

structural lumber:

methods of measuring 143

strength ratios corresponding to size,

tables 150

stress-grade limitations, tables 139, 143,150

Kubier wood dowel, working loads 200

Lag screws. See Screws, lag.

Lamella roof:

method of construction 227

strength 227

LaminatPd construction, definition 247

Laminated members, curved:

advantages 303

design 262

methods of producing . 303

species, choice of 303

uses .- - - 303
508 INDEX

Page

Laminated members, glued:

advantages 247

axially stressed members, design;

effective cross sectional area. . . ^ 362

knot concentration efïect.. 261

working stress 262

basic stresses:

for use under dry conditions, table 259

for use under wet conditions 258

bending members, design:

deflection calculation 261

knot concentration efïect. . 258

moment of inertia --- 261

radial stresses 262

working stress 258

butt joints:

efTective cross-sectional area of laminations 256

transmission of stress 256

columns, design 263

cost in comparison with solid timbers . 249

design based on dry strength 250

fastenings, design loads for 263

iire resistance of 345

glue joint quality, testing 250

placement of laminations 249, 250

preservative treatment of 249

scarf joints:

joint factor 255

permitted stress 255

slope of grain 256

spacing 255

shrinking and swelling, prevention of 249

strength as affected by:

cross grain. 252

curvature of laminations . 253

depth-effect factor 257

edge joints 257

end joints 255

knots 251

lamination thickness 253

shakes, checks, and splits 257

strength, compared to solid members 250

uses 247

vertically laminated:

edge gluing for shear resistance 256

effect of knots on strength 257

effect of shakes, checks, and splits on

strength 257

woods for-:

arches and beams 250

boat timbers 250

Laminated members, knots at connector

location 199

Laminated members, mechanically fastened:

horizontally laminated arches:

lateral stability 226

strength 226

vertically laminated beams:

butt jointed lamination, effect on strength. 212

construction 211

strength 211

Page

Laminated members, mechanically fastened—

Continued

vertically laminated and segmented arches:

design of 226

lateral stnbility 226

method of construction 226

strength 226

Laminates, paper base:

high strength (papreg) 473

lignin-filled 474

overlays 475

Laminate?, yellow birch, properties, table 470

Larch, effect of acids and bases on strength,

table 53

Larch, western:

charact eristics 27

classification for painting, table 358

color and figure, table 38

decay resistance 45

electrical resistance, table 49

factors for strength of mechanical fastenings,

table 167

gluing properties, table 235

locality of growth 27

moisture content, table 322

nomenclature, table 112

poles:

life of 436

preservative treatment 430, 435

properties of 430

weight per cubic foot, table 431

shrinkage values, table. 315

strength properties of clear wood, table.... 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

thermal conductivity across grain, table-s... 47, 49

ties:

life of 441

strength of, table 440

toughness, table 83

uses 27

weathering 43

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

Late wood, description and properties. 3

Lath, grades 130

Lath and plaster, thermal conductivity, table. 449

Lauan, red, shrinkage values, table 315

Light-frame construction, fire resistance of 341

Lignin-filled paper-base laminates 474

Limnoria:

damage by 394

life processes 394

Liquid glues, characteristics, preparation, uses 233

Locust, black:

characteristics 17

color and figure, table 38

decay resistance 45

locality of growth 17

moisture content, table 322

nomenclature 17
INDEX

Locust, black—Continued

shrinkage values, table

strength properties of clear wood, table"/.'

ties, strength of, table

uses

weight, table:

per cubic foot

per 1,000 board-feet '"'

working quality with hand tools, table

Logs, control of molds, stains, decay

Loose knots, definition

Lowry process for preservative treatment

Lumber;

care during construction

control of molds, stains, decay:

antiseptic solutions

seasoning practices

items available in retail yards

moisture content provisions, limitations

retentions of preservatives recommended for

various uses, tables 41

standard abbreviations

standard patterns

storage in yards

Machining properties of hardwoods, table

Madrone, Pacific:

moisture content, table

shrinkage values, table

weight, table:

per cubic foot

per 1,000 board-feet

Magnolia:

classification for painting

color and figure, table

decay resistance

electrical resistance, table

gluing properties, table

moisture content, table

working quality with:

hand tools, table

machines, table

Magnolia, southern:

characteristics

factors for strength of mechanical fastenings,

table

locality of growth

nomenclature

shrinkage values, table

strength properties of clear wood, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Magnolia, sweetbay:

characteristics

locality of growth

nomenclature

uses

Mahogany:

classification for painting

elastic constants, table

electrical resistance, table

gluing properties, table

machining properties, table

shrinkage values, table

Page

315

70

440

17

56

56

62

383

2

414

384

384

126

326

7,418

131

126

325

63

322

315

56

56

354

38

45

49

234

322

62

63

167

17

17

315

70

18

56

56

17

17

17

18

354

79

49

234

63

315

Mangrove:

shrinkage values, table

weight, table:

per cubic foot

per 1,000 board-feet

Maple:

classification for painting

decay rCvSistance

weathering

working quality with hand tools, table

Maple, bigleaf:

characteristics

color and figure, table

locality of growth

n omenclature

shrinkage values, table

strength properties of clear wood, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Maple, black:

characteristics

color and figure, table

factors for strength of mechanical fastenings,

table

locality of growth

nomenclature

shrinkage values, table

strength properties of clear wood, table

stresses, basic:

clear wood, table

laminated members, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Maple, hard:

gluing properties, table

machining properties, table

moisture content, table

species included

stresses, basic:

clear lumber, table

laminated members, table

Maple, red:

characteristics

color and figure, table

factors for strength of mechanical fastenings,

table

locality of growth

nomenclature

shrinkage values, table

strength properties of clear wood, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Maple, silver:

characteristics

color and figure, table

factors for strength of mechanical fastenings,

table

locality of growth

moisture content, table

509

Page

- 316

56

56

- 354

45

. 43,44

62

18

38

18

18

315

70

18

56

56

18

38

167

18

18

315

70

150

260

18

56

56

234

63

322

18

156

260

18

38

167

18

18

315

70

18

56

56

18

38

167

18

322
510 INDEX

Maple, silver—Continued

nomenclature

shrinkage values, table

strength properties of clear wood, table

thermal conductivity across grain, table

ties, strength of, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Maple, soft:

gluing properties, table

machining properties, table

moisture content, table

species included ...

Maple, sugar:

characteristics

coeiRcient of thermal expansion, calculation.

color and figure ...

electrical resistance, table

factors for strength of mechanical fastenings,

table

locality of growth

moisture content, table

nomenclature

shrinkage values, table

strength properties of clear wood, table

stresses, basic:

clear, lumber

laminated members, table

thermal conductivity across grain, tables

ties, strength of, table

toughness, table

uses

weight, table:

per cubic foot

per 1,000 board-feet :

Marine borers:

attack, rapidity

boats, wood, control on _

creosote treatment for protection against:

effectiveness

life expected of treated wood

retentions required

geographical distribution

Limnoria:

damage by

life processes

Martesia:

damage by

life processes

mechanical protection of piling

plywood, control on

resistance of woods to

shlpworms:

damage by

life processes

species

Sphaeroma:

appearance

damage by

Masonry, thermal conductivity, table

Melamlne-resln glue, characteristics, preparation, uses, table

Page

18

. 315

70

49

440

18

56

56

234

63

322

18

18

47

38

49

167

18

322

18

315

70

156

259

49

440

83

18

56

56

394

396

395

395

395

393

394

394

394

394

396

397

395

394

394

394

395

395

449

Page

Mercuric chloride, effectiveness as preservative, table 409

Mesquite, decay resistance 45

Metal lath and plaster, thermal conductivity,

table 449

Mill priming 372

Mill-type construction. See Heavy-timber

construction.

Minerals, ash-forming 5

Mineral streak:

description lOl

strength, effect on 101

Mineral wool, thermal conductivity, table 449

Mixed-pigment paints, maintenance program

for 368

Modified woods, properties, table 468

Modulus of elasticity:

coefficient of variability . 84

definition 68

moisture content as related to.. _ 85, 87

slope of grain as related to, table 97

specific gravity as related to 88

values, table 70

Modulus of rigidity:

discussion 78

ratios, table 79

Modulus of rupture:

coeiïicient of variability 84

defin ition 68

effect of acids and bases on, table 53

effect of temperature on 89, 90

moisture content as related to 85,87

slope of grain as related to, table 97

specific gravity as related to 88

values, table... 70

Moisture content:

definition 67

determined by:

distillation method 320

electrical method. 320

oven-drying method 320

distribution in tree 311

equilibrium:

discussion 311

relative humidity as related to, table 311

favorable for decay 381

green wood, table 322

heartwood, table 322

provisions for lumber, limitations.. 325

provisions for purchase of lumber 131

recommended for:

flooring, hardwood, table 329

flooring, softwood, table 329

framing, table 329

interior finish, table 329

lumber for gluing 235

plywood 329

sheathing, table 329

siding, table 329

timbers 326

trim, exterior, table 329

veneer 235,329

sapwood, table 322

seasoned lumber 325
INDEX 511

Page

Moisture content—Continued

shrinkage as related to 311,319

strength of wood as related to 85

Moisture-excluding coatings;

effectiveness 245

interior finishes, effectiveness 377

paints, table, 371

Molded plywood 304

Molds and stains:

appearance of 381

cause of 381

control in:

buildings 384

logs, poles, piling, or ties 383

lumber 384

plywood 385

rate of growth 381

strength of wood, effect on 100

use of stained and molded wood .. 382

Mortising properties of hardwoods, table 63

Mountain-laurel, weight, table:

per cubic foot 50

per 1,000 board-feet 50

Mulberry, red, decay resistance 45

Nails:

lateral load constant, table.. 167

lateral resistance:

direction of driving, effect of 173

green wood 174

nail composition, effect of 174

nail spacing 174

seasoned wood 173

shank form, effect of 174

sizes, table 167

toenailed joints, strength of 172

withdrawal resistance:

clinched nails 172

density of wood, effect of 167

direction of driving, effect of. 171

green wood 167

nail composition, effect of 170

nail heads, effect of 170

nail points, effect of 170

plywood 173

prebored lead holes, effect of.. 172

seasoned wood 167

shank form, effect of 170

surface coatings, effect of 169

surface roughening, effect of.. ^ 169

Natural finishes for exterior woodwork:

durability 373

protection from mildew 374

types 373

Niggerizing process for increasing acid resistance 54

Nomenclature 70

Notched beams, design 207

Oak:

classification for painting 354

decay resistance 45

effect of acids and bases on strength, table.. 53

piling suitability 437

Oak, black:

locality of growth 18

shrinkage values, table. 315

Page

Oak, black—Continued

strength properties of clear wood, table.. - 70

weight, table:

per cubic foot- 56

per 1,000 board-feet 56

Oak, bur:

locality of growth 20

shrinkage values, table 315

strength properties of clear wood, table. . .. 70

weight, table:

per cubic foot 56

per 1,000 board-feet - 56

Oak, California black:

moisture content, table .. 322

shrinkage values, table 315

Oak, canyon live, shrinkage values, table 315

Oak, cherrybark:

strength pro¡)erties of clear wood, table. _.. 70

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Oak, chestnut:

locality of growth 19

machhiing properties, table. 63

shrinkage values, table . 315

strength properties of clear wood, table. .. 70

Oak, chinkapin, locality of growth... 20

Oak, commercial red:

ties, strength of, tiible. 440

working quality with hand tools, table 62

Oak, commercial white:

ties, strength of, table.. 440

working quality with hand tools, table 62

Oak, laurel:

locality of growth. 19

shrinkage values, table. 315

strength properties of clear wood, table 70

weight, table:

per cubic foot.. . 56

per 1,000 board-feet 56

Oak, live:

loaility of growth 20

moisture content, table 322

shrinkage values, table. 315

Oak, northern red:

locality of growth 18

moisture content, table 322

shrinkage values, table. 315

strength properties of clear wood, table.... 70

weight, table:

per cubic foot . 56

per 1,000 board-leet 56

Oak, nuttall, locality of growth 18

Oak, Oregon white, shrinkage values, table .. 315

Oak, overcup:

locality of growth 19

strength properties of clear wood, table 70

Oak, pin:

locality of growth 17

shrinkage values, table 315

strength properties of clear wood, table 70

toughness, table --. 83

Oak, post:

loföility of growth 19

shrinkage values, table. 315
512 INDEX

Page

Oak post—Continued

strength properties of clear wood, table. ... 70

weight, table:

per cubic foot. 56

per 1,0()0 board-feet 56

Oak, red:

color and figure, table.. 38

electrical! resistance, table . 49

factors for strength of mechanical fastenings.

table 167

gluing properties, table 234

machming properties, table 63

stresses, basic:

clear lumber, table 156

laminated members, table 260

thermal conductivity across grain, tables . . 49

weathering 43, 44

Oak, red group:

characteristics 19

locality of growth. 18

nomenclature. 18

species included 19

uses 19

Oak, Rocky Mountain white, shrinkage values,

table 315

Oak, scarlet:

locality of growth 17

shrinkage values, table 315

strength properties of clear wood, table 70

Oak, Shumard, locality of growth 17

Oak, southern red:

locality of growth 18

moisture content, table 322

shrinkage values, table 315

strength properties of clear wood, table 70

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Oak, swamp chestnut:

locality of growth 19

shrinkage values, table. 315

strength properties of clear wood, table. 70

weight, table:

per cubic foot 5f3

per 1,000 board-feet 56

Oak, swamp white:

locality of growth 20

shrinkage values, table 315

strength properties of clear wood, table 70

Oak, tan, moisture content, table 822

Oak, water:

locality of growth 18

moisture content, table 322

shrinkage values, table 315

strength properties of clear wood, table 70

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Oak, white:

color and figure, table 38

electrical resistance, table 49

gluing properties, table 234

laminated boat timbers, use for 250

moisture content, table 322

shrinkage values, table 315

Page

Oak, white—Continued

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

thermal conductivity across grain, table 49

ties, life of 441

weathering 43, 44

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Oak, white group:

characteristics 20

locality of growth 19

nomenclature 19

species included 19, 20

uses 20

Oak, willow:

locality of growth 19

moisture content, table 322

shrinkage values, table 315

strength properties of clear wood, table 70

weight, table:

per cubic foot 55

per 1,000 board-feet 56

Osage-orange:

decay resistance 45

gluing properties, table 234

moisture content, table 322

shrinkage values, table 315

weight, table:

per cubic foot 56

per 1,000 board-feet 56

One-story industrial buildings:

description 339

fire resistance of 341

Ordinary construction:

code requirements for fire protection 339

description 339

Osmoplastic groundline treatment, efîectiveness, table 402

Osmosar, effectiveness as preservative, table-. 409

Overlays:

on plywood 278

paper-face 475

Paints:

abnormal wear, causes 369

as vapor barriers 454

acid-resistant, effectiveness.. 53

advantages 351

application:

coating thickness for best service 366

moisture content of wood, effect 365

number of coats 366

spray gun 365

temperature, effect 365

time interval between coats 365

back priming:

effectiveness 371

purpose 371

use, extent of 371

blistering of coating:

blister-resisting paints 370

causes.- .370
INDEX 513

Page

Paints—Continued

characteristics 351,353

choice for exterior woodwork 360

classification of hardwoods for painting 354

classification ofsoftwoods for painting, table. 358

coating thickness, efïect on wear 309

colored-pigment paints, properties.. 3G3

composition:

proportion of pigments and liquids .. . 304

quality of liquids .. 361

quality of pigments 362

cross-grain cracking, cause . 369

deterioration, course of _ _. . 355, 362

discoloration:

causes 369

prevention 370

drying rates:

extractives, effect of . 354

moisture content of wood, eiïect of... 354

on hardwoods 354

on softwoods 354

extractives, effect 359

filler for porous hardwoods 354

fire resistance 345

mill priming:

effectiveness 371

purpose 371

mixed-pigment paints, maintenance program for 368

moisture-excluding coatings, effectiveness,

table 371

nonpreservativc against decay 351

paste:

advantage 366

mixing 367

plywood, painting characteristics of 360

preservatives as affecting 359

priming paints:

aluminum 367

requirements 365

three-coat work 367

two-coat work 367

repainting:

paint composition, importance of 368, 369

procedures 367

spreading rates on softwoods 353

titanium-lead-zinc paints, properties 363

titanium-zinc paints, properties 363

wearing qualities as affected by kind of

wood 355

weathering, prevention with 351

white lead paint:

maintenance program for 368

properties 362

Palmetto, cabbage:

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Paper-base laminates:

high-strength (papreg):

experimental floor 474

properties, table 468

resins for manufacture 474

uses — ^^"^

Page

Paper-base laminates—Continued

decorative overlays:

resins for 470

typical assembly 476

uses 476

lignin-filled:

manufacture 475

potential use 475

properties 475

masking overlays:

application to plywood 475

resin content 475

uses 475

structural overlays .. 476

Papreg 474

Paper and asbestos fiber, thermal conductivity,

table .. 449

Paper honeycomb core, for sandwich construction .5. 292

Paper, macerated, thermal conductivity, table. 449

Parallel-grain construction:

definition .. 247

uses 247

Parenchyma cells, function 5

Particle boards. See Resin-bonded particle

boards.

Partition:

description 129

sizes, table 116

Partitions, fire resistance of:

load-bearing wood frame 344

nonbearing wood 343

Paste paint:

advantage 366

mixing 367

Pecan:

characteristics 16

locality of growth 16

uses 16

See also Hickory, pecan.

Peeling for preservative treatment 409

Penetration of preservative. See Preservatives.

Pentachlorophenol :

composition. , 405

crystal formation, prevention of _ _ 405

effect on properties of wood 405

effectiveness as preservative table. 405, 409

health effect 405

oils for, specification 405

pole treatment 435

retentions recommended for various wood

products, table 417

specifications 405

uses 404

Persimmon, common:

gluing properties, table 234

moisture content, table 322

shrinkage values, table 315

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Phenol-resin glue, characteristics, preparation,

uses, table... 234
514 INDEX

Page

Phenol-resin treatment to increase acid resistance of wood 54

Phenyldichlorarsine, effectiveness as preservative, table 402

PUing:

bearing loads for 437

control of marine borers 395

control of molds, stains, decay 383

crooked piling 438

decay resistance 438

driving as affected by seasoning 438

eccentric loading, reduction in strength 438

knots, effect on strength 95

properties important in 437

preservative treatment, retentions recommended, table 417

sheet, sizes, table 117

specifications 437

species used 437

trea,tment recommendations 438

Pine, effect of acids and bases on strength,

table 63

Pine, eastern white:

characteristics 27

classification for painting, table 358

color and figure, table 38

electrical resistance, table 49

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

locality of growth 27

moisture content, table. 322

nomenclature 27,112

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

toughness, table 83

uses 27

weathering 43

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality w^ith hand tools, table 62

Pine, jack:

characteristics- 27

locality of growth 27

nomenclature 27,112

poles, weight per cubic foot, table 431

strength properties of clear wood, table.. _. _ 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

ties, strength of, table 440

toughness, table 83

uses 28

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Pine, Jeffrey:

locality of growth 28

shrinkage values, table 315

Pine, lumber, shrinkage values, table 315

Page

Pine, loblolly:

characteilstics 30

locality of growth 30

moisture content, table 322

nomenclature, table 112

poles, weight per cubic foot, table 431

shrinkage values, table 315

strength properties of clear wood, table 70

ties, strength of, table 440

toughness, table 83

uses 30

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Pine, lodgepole:

characteristics 28

classification for painting, table 358

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth 28

moisture content, table 322

nomenclature 28,112

poles:

life of 437

preservative treatment 430, 435

properties of 430

weight per cubic foot, table 431

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

ties, strength of, table 440

uses 28

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

Pine, longleaf:

characteristics 30

classification 29

electrical resistance, table 49

locality of growth 29

moisture content, table 322

nomenclature, tab'le 112

poles, weight per cubic foot, table 431

shrinkage values, table 315

strength properties of clear wood, table 70

ties, strength of, table 440

toughness, table 83

uses 30

weight, table:

per cubic foot _ 56

per 1,000 board-feet 56

Pine, pitch:

characteristics. _ 28

locality of growth 28

shrinkage values, table 315

uses 28

weight, table:

per cubic foot 56

perl,000 board-feet. 56
INDEX 515

Page

Pine, pond:

characteristics. - 28

locality of growth 28

nomenclature, table 112

shrinkage values, table 315

uses 28

Pine, ponderosa:

characteristics 28

classification for painting, table 358

color and figure, table 38

decay resistance 45

electrical resistance, table 49

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

locality of growth 28

moisture content, table 322

nomenclature 28,112

plywood grades and types 278

poles:

properties of 430

weight per cubic foot, table 431

shrinkage values, table 315

strength properties of clear wood, table-. . 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

ties, strength of, table 440

uses 29

weathering 43

weight, table:

per cubic foot 322

per 1,000 board-feet 322

working quality with hand tools, table 62

Pine, red:

characteristics. 29

classification for painting, table 358

color and figure, table 38

factors for strength of mechanical fastenings,

table .• 167

locality of growth 29

moisture content, table 322

nomenclature 29,112

poles, weight per cubic foot, table. . 431

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 258

ties, strength of, table 440

toughness 83

uses 29

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Pine, shortleaf:

characteristics 30

electrical resistance, table 49

locality of growth 29

moisture content, table 322

nomenclature, table 112

poles, weight per cubic foot, table. _. 431

shrinkage values, table 315

strength properties of clear wood, table 70

ties, strength of, table 440

Page

Pine, shortleaf—Continued

toughness, table 83

uses 30

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Pine, slash:

characteristics 30

classification 30

locality of growth 29

nomenclature, table 112

shrinkage values, table 315

strength properties of clear wood, table. _ .. 70

toughness, table 83

uses 30

weight, table:

per cubic foot-- - 56

per 1,000 board-feet 56

Pine, southern yellow:

characteristics 30

classification for painting, table 358

color and figure, table 38

decay resistance 45

efí'ectiveness of preservatives in service tests,

table 409

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

laminated arches and beams, use for 250

lap siding:

thermal conductivity, table 449

thermal resistivity, table 449

locality of growth-- .._ 29

moisture content, table 322

piling suitability 437

poles:

extent of use 429

life of 436

presevative treatment 429

recommended preservative retentions for:

lumber, table 417

piles, table 417

structural timbers, table 417

shrinkage values, table 315

species included 30

standards 30

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated member, table. 259

tanks, use for 52

termite resistance.- 393

thermal conductivity across grain, tables-. - 49

toughness, table - 83

uses 30

weathering 43

weight, table: 56

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table- -... 62

Pine, southern yellow, close-grained:

requirements 149

stresses, basic, clear lumber, table.. 156

Pine, southern yellow, dense:

requirements 149
516 INDEX

Page

Pine, southern yellow, dense—Continued

stresses, basic:

clear lumber, table 156

laminated members, table 259

uses :i 30

Pine, southern yellow, medium-grained, requirements 149

Pine, sugar:

characteristics 30

classification for painting, table 358

color and figure, table 38

electrical resistance, table 49

factors for strength of mechanical fastenings,

table 167

locality of growth. .30

moisture content, table 322

nomenclature 30,112

plywood grades and types 278

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

uses 31

weathering 43

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

Pine, table-mountain, shrinkage values, table. 315

Pine, Virginia:

characteristics 31

locality of growth 31

nomenclature 31

strength properties of clear wood, table 70

toughness, table 83

uses 31

Pine, western white:

characteristics 31

classification for painting, table 358

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth 3i

moisture content, table 322

nomenclature 31,112

shrinkage values, table... 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table.. 259

uses 31

weathering 43

weight, table;

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

Pine, white:

decay resistance 45

thermal conductivity across grain, tables... 49

Pinyon:

shrinkage values, tables 315

ties, strength of, table 440

Page

Pitch pockets:

description.- _ 100

grades, effect on 119

occurrence 100

strength, effect on 100,140

Pith 1

Plainsawed lumber:

advantages 42

method of producing 41

Planing properties of hardwoods, table 63

Plank, sizes, table 116

Plaster, thermal conductivity, table 449

Plaster and lath, thermal conductivity, table. 449

Plaster board, fire resistance of 344

Plastering, care during construction 335

Platform type of construction, as related to

shrinkage... 330

Plywood:

advantages 275

arrangement of plies 275

balanced construction 275

bending strength, table 285

compressive strength, table 281,285

conditioning after gluing 243

control of decay in 385

control of marine borers.. 397

core woods, kinds of 277

description 275

grades and types:

aircraft structural 279

Douglas-fir 278

hardwood 278

ponderosa pine 278

sugar pine 278

western softwood 278

modulus of elasticity in:

bending 283

compression 280

tension 281

modulus of rigidity 282

moisture content recommended 329

nail-withdrawal resistance 173

odd number of plies, effect 275

overlays, types 279

painting characteristics of 360

quality of plies, effect 277

shear strength :

calculation, table 282, 285

correction for gaps in core or crossband... 283

shrinkage 275, 286

splitting resistance 275, 285

stiffness, calculation of, table 286

stresses from moisture content changes 277

strength, calculation of:

discussion 279

table 286

stresses, allowable, table 286

tensile strength, table 281, 285

thermal conductivity, table 449

Plywood curved members:

bent after gluing, procedure for 305

bent and glued simultaneously:

advantages 304

procedure for _ 304
INDEX 517

Page

Plywood curved members—Continued

breaking radius 305

hot-soaked plywood 304

molded by fluid pressure 304

post-formed to compound curvatures:

procedure for 308

species used . 308

working radius for bending 304

Plywood-faced panels, fire resistance of 343

Poisson's ratio:

discussion 78

values, table 79

Pole framing:

advantages 229

description 229

design and construction 210, 230

Poles:

characteristics relating to:

cedar ._ 429

Douglas-fir 430

lodgepole pine 430

ponderosa pine 430

southern yellow pine. 429

western larch 4:30

classes 435

control of molds, stains, decay 383

design of - 431

form 429

knots, effect on strength 94

life of:

baldcypress-- 437

Douglas-fir 437

lodgepole pine 437

northern white-cedar _ . 437

Port-Orford cedar 437

redwood 437

southern yellow pine 437

western larch 437

western redcedar 437

preservative treatment:

bleeding incident to. 436

butt 436

cedar 436

coal-tar creosote. 435

Douglas-fir 436

full length 435

incising preparatory to.. .. 436

lodgepole pine 436

pentachlorophenol 435

recommended retentions, table - 417

specifications 435

waterborne preservatives _. - 435

western larch - 436

species selection 429

strength 429.431

stress ratings 431

treatment to stop decay in standing 436

volume:

formula 431

table 431

weight:

importance 429. 431

table 431

Polyporus schweinitzii, effect on strength 383

Page

Polyvinyl-resin emulsion glue, characteristics,

preparation, uses, table 234

Poplar, classification for painting 354

Poplar, balsam:

ties, strength of, table -. 440

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Port-Orford-cedar:

characteristics 32

classification for painting, table 358

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth 31

moisture content, table 322

nomenclature 31,112

poles, life of.-. 437

shrinkage values, table. 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table . 259

ties, strength of, table. -. 440

uses 32

weathering 43

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

Post caps, metal, shrinkage as related to 333

Post-forming of plywood curved members 308

Posts, preservative treatment retentions

recommended, table 417,418

Posts and timbers:

description 141

dressed sizes, minimum _ 142

knots:

method of measuring ._, 145

stress-grade limitations, table 145,150

shakes, checks, and splits:

method oi measuring 147

stress-grade limitations 147

slope of grain permitted, table 150

Powderpost beetles:

control measures 388

damage caused 388

Power factor:

definition 52

factors influencing 52

Preservatives:

anthracene oils:

effectiveness 401

properties 401

specifications 401

beta-naphthal, effectiveness, table 402

borax-boric acid, effectiveness, table. 402

classes -- 399

coal tar:

crosstie treatment with 401

effectiveness, table 402, 409

penetrations obtained 401

copper arsenate, chromated:

composition - 408
518 INDEX

Page

Preservatives—Continued

copper arsenate, chromated—Continued

effectiveness 4()8

use 408

copper arsenite, ammoniacal:

composition 408

effectiveness 408

retentions recommended for various wood

products, table 417

specification 408

copper chromate, acid:

composition 407

effectiveness, table 407

retentions recommended for various wood

products, table 417

specification 407

copper-containing, control of marine borers

with 396

copper naphthenate:

composition 405

effect on properties of wood 405

effectiveness 405

oils for, specification 405

retentions recommended for various wood

products, table 417

specifications 405

uses 404

copper sulfate and sodium arsenate, effectiveness, table 402

crankcase oil, effectiveness, table 402

creosote, coal-tar:

advantages .399

control of marine borers with 395

effect of character on service 399

effectiveness, table 402

fire hazard 400

health effect 400

odor 400

painting 400

retentions recommended for various wood

products, table 417

specifications 400

creosote-coal tar solutions:

properties 404

retentions recommended for various wood

products 417

specifications 404

toxicity 404

creosote, crystal-free coal-tar:

effectiveness 401

properties 401

specifications 401

creosote, oil-tar, effectiveness 401

creosote-petroleum oil solutions:

effectiveness, table 402

fortification of 404

oils, specifications for 404

properties 404

retentions recommended for various

products, table 417

specifications 404

toxicity _ - 404

creosote, water-gas-tar, effectiveness 401

creosote, wood-tar, effectiveness, table 402, 409

effectiveness in service tests, table 402

Page

Preservatives—Continued

mercuric chloride, effectiveness, table 402

Osmoplastic groundline treatment, effectiveness, table 402

Osmosar. effectiveness, table 402

paint behavior, effect on 359

penetration:

heartwood 417

incising, effect of 417

inspection for 420

sapwood 418

species, effect of 417

pentachlorophenol :

composition 405

crystal formation, prevention of 405

effect on properties of wood 405

effectiveness, table 402

health, effect on 405

oils for, specification 405

retentions recommended for various wood

products, table 417

specifications 405

uses 404

phenyldichlorarsine, effectiveness, table 402

preservative oils, advantages and disadvantages 399

retentions recommended:

how specified 416

inspection for 420

lumber, tables 416.417

piles, table 417

poles, tables 417,418

posts, tables 417, 418

preservative oils, tables 417, 418

structural timbers, tables 417,418

ties, table 417

waterborne preservatives, table 417, 418

Tanalith:

composition 407

effectiveness 407

retentions recommended for various wood

products, table 418

specifications 407

sodium bichromate, effectiveness, table 402

sodium chromate, effectiveness, table 402

tetra<3hlorophenol, effectiveness, table 402

waterborne preservatives:

advantages and disadvantages 406

chemicals used as 406

leaching resistance 406

pole treatment 435

uses 406

water-gas tar, effectiveness in fence post

treatment, table 401,402

water-repellent preservatives:

effectiveness 405

specification 405

Wolmansalt. See Tanalith.

zinc arsenate, chromated:

composition 409

effectiveness 409

zinc chloride:

advantages 407

effectiveness, table _ 402
INDEX 519

Page

Preservatives—Continued

zinc chloride—Continued

retentions recommended for various wood

products, table 417

specification 406

use 407

zinc chloride, chromated:

composition 407

effectiveness, table 402

fire retardant 407

leaching resistance 407

retentions recommended for various wood

products, table 407. 402

specifications 406

zinc chloride, copperized chromated:

composition 407

effectiveness 407

specification 406

zinc meta arsenite:

composition 408

effectiveness, table 408

retentions recommended for various wood

products, table 418

specifications 408

Preservative-treated timber:

cut surfaces, protection of 418

handling 418

inspection for:

penetration 420

quality and grade 419

retention 420

seasoning required 419

strength as affected by:

preservatives 161,420

treatment necessary for injecting 421

working stresses for 161

Preservative treating pressures 416

Preservative treating specifications 416

Preservative treating temperatures 416

Preservative treatment:

laminated members 249

piling 4.38

poles. See Poles, preservative treatment.

ties 440

Preservative treatment, preparing for:

conditioning green timber:

Boulton or boiling-under-vacuum process. 415

steaming-and-vacuum process 415

vapor-drying process 415

cutting and framing 411

incising:

method 411

purpose 411

species requiring 411

peeling, purpose 409

seasoning:

air-drying practices 410

preventing decay and seasoning degrade... 410

purpose 410

Preservative treatments, nonpressure:

Boucherie process for green unpeeled poles. - 427

brushing or spraying:

application 421

effectiveness 421

penetration obtained , 422

Page

Preservative treatments, nonpressure—Con.

cold-soaking process:

effectiveness 422

method 422

retentions and penetrations.. _ 422

diffusion processes:

butt or groundline treatment of poles or

posts 423

double diffusion 423

end diffusion. 423

dipping:

effectiveness 422

method 422

penetration obtained 422

hot-and-cold-bath process:

effectiveness 423

methods 423

preservatives used 424

retentions and penetrations, control of 424

temperatures used 424

uses for.._ 424

steeping process:

effectiveness 422

method 423

preservatives used 423

tire-tube method for green, unpeeled fence

posts 427

vacuum processes:

effectiveness 426

methods 426

uses 426

Preservative treatments, pressure:

advantages _ _ 411

empty-cell processes:

Lowry process 414

Rueping process 414

full-cell process 412

Pressures, preservative treating 416

Prima vera, thermal conductivity across grain,

tables 47

Priming paints:

aluminum 367

requirements 365

three-coat work 367

two-coat work 367

Quartersawed lumber:

advantages 42

method of producing 41

Quipo, elastic constants, table 79

Radiation of heat 448

Rays:

definition 5

function 5

Redcedar, eastern:

characteristics 32

color and figure, table 38

gluing properties, table 234

locality of growth 32

moisture content, table 322

nomenclature, table 112

poles, weight per cubic foot, table 431

shrinkage values, table 315

strength properties of clear wood, table 70

ties, strength of, table 440

uses-, - - 32
520 INDEX

Page

Redcedar, eastern—Continued

weight, table;

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table -. 62

Redcedar, southern, locality of growth 32

Redcedar, western:

characteristics 32

classification for painting, table 358

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

gluing properties, table ... ___.-- 234

locality of growth 32

moisture content, table 322

nomenclature -. 32,112

piling suitability 437

poles:

life of 437

preservative treatment 430

properties of . 430

weight per cubic foot, table . . 431

shrinkage values, table _ 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

thermal conductivity across grain, table 49

ties, strength of, table.- . 440

toughness, table 83

uses 32

weathering _ 43

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

Redwood:

characteristics 33

classification for painting, table 358

coefficient of thermal expansion, calculation. 47

color and figure, table 38

decay resistance 45

electrical resistance, table 49

factors for strength of mechanical fastenings,

table 167

gluing properties, table 234

locality of growth 33

moisture content, table 322

nomenclature 33,112

poles:

life of 437

weight per cubic foot, table 431

shredded bark:

thermal conductivity, table 449

thermal resistivity, table 449

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

tanks, use for 52

termite resistance 393

thermal conductivity across grain, tables... 47, 49

ties, strength of, table 440

toughness, table 83

Page

Redwood—Continued

uses 33

weathering 43

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

Redwood, close-grained:

requirements 149

stresses, basic:

clear lumber, table 156

laminated members, table 259

Reflective insulation 447

Relative humidity, equilibrium moisture content as related to, table 311

Repainting:

maintenance program for:

mixed-pigment paints 368

white lead paint 368

paint composition, importance of 368, 369

procedures 375

Resin:

amount in conifers 102

strength, effect on. 102

Resin-bonded particle boards:

hardboards:

density range 464

effect of moisture content changes 464

sizes 464

strength and physical properties, table. 459, 464

uses 464

intermediate-density:

strength and physical properties, table 459

uses 463

Resin glues, characteristics, preparation, uses,

table 236

Resin-treated paper-base laminates 474, 475

Resin-treated wood, compressed (compreg):

fl ooring 472

manufacture by expansion molding 472

manufacture from impreg 469

properties, tables 468

uses 472

Resin-treated wood, uncompressed (impreg):

manufacture 467

properties, tables 468

uses 468

Resin treatment ofsandwich construction core- 292

Resistance, electrical, table 49

Resorcinol-resin glue, characteristics, preparation, uses, table 236

Retention of preservative:

how specified 416

inspection for 420

recommended for:

lumber 416

piles, table 417

poles, tables 417, 418

posts, tables 417

preservative oils, tables 417, 418

structural timbers 417. 418

ties, table 417

waterborne preservatives, table 417, 418

Rigid insulation 445
INDEX 521

Roofing:

heavy, sizes, table 117

thermal conductivity, table 449

Roof insulation:

method of use 461

sizes 460

uses 461

Roofs:

buckling of structural members, prevention of 216

control of decay in 335

lamella:

method of construction 227

strength 227

requirements in heavy-timber construction, 337

Rotary-cut veneer, characteristics 239

Round timbers:

not stress graded 142

percentage of sapwood, table 59

weight, determination 58

Rot. See Decay.

Rueping process for preservative treatment.-^ 414

Sanding properties of hardwoods, table 63

Sandwich construction:

advantages 291

bowing 295

buckling load 294

compression stress 294

core materials 292

deflection 294

dimensional stability 295

fabrication 292

facing materials 292

fire resistance 297

moduli of elasticity 293

resin treatment 292

shear modulus of core- 293

stiffness 293

tension stress in facings 294

thermal insulation of_.. 295

vapor barriers in 295

Sapwood:

decay resistance 44

durability 4

function 4

moisture content, table 322

percent of volume of round timbers, table-.- 59

preservative penetration in 418

specification in structural lumber 137,148

strength 4

thickness, different species 4

weight 4

Sassafras:

decay resistance 45

shrinkage values, table- 315

ties, strength of, table 440

Sawdust and shavings, thermal conductivity,

table -- 449

Sawed timbers, weight, table 56

Sawed veneer, characteristics 239

Scarf joints:

advantages 241

joint factor 255,256

permitted stress 255, 256

Page

Scarf joints—Continued

slope of grain 256

spacmg 255

Screws, lag:

description 178

lateral load constant, table 167

lateral resistance 179,182

prebored lead holes, size required 178

withdrawal resistance 178

Screws, wood:

lateral load constant, table 167

lateral resistance 177,178

sizes 176

types 175

withdrawal resistance 175,177

Seasoned lumber;

air-dry 325

kiln-dried 325

shipping-dry 325

strength ratios, table 150

Seasoning degrade:

amount permitted 323

classification 323

grade, effect on 119

methods of eliminating 323

strength, effect on 101

Seasonmg for preservative treatment 410

Seasoning of structural lumber 138,158

Seasoning practice;

air-drying, advantages 323

hardwood stock 323

high-grade lumber 321

kiln-drying 323

timbers 321

Shakes and checks;

structural lumber;

effect on strength 139

methods of measuring 146,147

strength ratios corresponding to size, table. 150

stress-gi-ade Hmitations, table 146

Shaping properties of hardwoods, table 63

Shavings, thermal conductivity, table 449

Shear strength, solid beams _ 205

Shear strength parallel to grain:

coefficient of variability 84

definition 69

factors affecting shear values 81

moisture content as related to 85,87

values, table 70

Shear-plate connector;

strength ratio, table 198

working loads, table 167

Sheathed compound beams;

deflections 212

methods of constructing 212

strength-. - 212

Sheathing;

moisture content recommended, table 329

thermal conductivity, table 440

Sheathing board:

advantages and disadvantages 461

method of use 461

nail-withdrawal resistance 461

rigidity 461

sizes 461
522 INDEX

Page

Shingles:

descript ion 130

fire resistance of 345

grades 130

sizes 130

species used 130

thermal conductivity, table. 440

Shiplap lumber, sizes, table... 116

Shipping-dry lumber 325

Shipworms 394

Shock resistance, efitect of tempt-rature on 89, 91

Shrinkage:

balloon type of construction 331

coefficient of variability 204

compression wood - 318

construction that minimizes 331

cross-grain boards .- 315

fiber-saturation point as related to :>14

framing lumber .-- 329

heavy timber 333

interior finish 334

joist hangers 334

laminated members, prevention in .. 249

longitudinal 318

moisture content as related to 311. 319

platform construction 330

plywood 275, 286

post caps, metal, to prevent.. 333

radial, table ..- - 315

seasonal variation in moisture content as

related to 311

species, various, table 315

tangential, table -- 315

tension wood -. 318

turpentining, effect 102

volumetric, table - 315

Siding:

description -- 129

moisture content recommended, table.. ... 329

patterns 126

sizes, table 115

Slab insulation 446

Slash-grained lumber. See Plainsawed lumber.

Sliced veneer, characteristics 239

Slope of grain:

determination 96

limitation in structural timbers, table. . 143,150

strength as related to. table 97

Sodium bichromate, table . - 402

Sodium chromate, table 402

Softwood lumber:

availability 127

grading classification 114

grading factory and shop lumber use classes. 125

grading nomenclature, table 112

standard lumber patterns 126

structural lumber grades.... 125,137,163

uses for various grades 117

yard lumber grades 117

yard lumber sizes, table 115

Softwood plywood, western, grades and types. 278

Softwoods:

definition.- _ 5

hardness 5

Page

Softwood s—Continued

length of fibers 5

locality of growth 23

painting classification, table 358

Sound insulation 462

Spaced columns:

connector requirements 223, 225

design of 225

method of construction 223

Special densified hardboards:

density range 464

strength and physical properties, table 459

thicknesses 465

uses 465

Specific gravity:

coefficient of variability 84

definition 68

strength as related to 88

values, table 70

Sphaero ma 395

Spikes 174

Spiral grain, test for presence of 95

Split-ring connectors:

strength ratios, table 198

working loads, table 167

Splits:

effect on strength of laminated members . -. 257

structural lumber:

effect on strength 140

methods of measuring 147

strength ratios corresponding to size, table. 150

stress-grade limitations, table - _ 146,147,150

Splitting resistance:

hardwoods:

nails, table 63

screws, table. 63

Splitting resistance of plywood 275, 286

Spreading rates of paint on softwoods 353

Springwood:

description 3

physical properties 3

Spruce:

decay resistance 45

effect of acids and bases on strength, table.. 53

Spruce, black:

characteristics 33

color and figure, table 38

locality of growth . 33

nomenclature, table 112

shrinkage values, table 315

strength properties of clear wood, table 70

weight, table:

per cubic foot 56

per 1,000 board-feet 56

uses 33

Spruce, eastern:

characteristics 33

classification for painting, table 354

locality of growth... 33

moisture content, table 322

species included 33

uses 33

weathering 43

working quality with hand tools, table 62
INDEX 523

Page

Spruce, Engelmann:

characteristics 33

classification for painting, table 354

color and figure, table 38

factors for strength of mechanical fastenings,

table 107

locality of growth 33

moisture content, table 322

nomenclature 33

nomenclature, table .. 112

shrinkage values, table 315

strength properties of clear wood, table.. . _ 70

stresses, basic:

clear wood, table 15(i

laminated members, table 259

ties, strength of, table 440

thermal conductivity across grain, table 49

toughness, table 83

uses 34

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Spruce, red:

characteristics 33

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth 33

nomenclature, table 112

poles, weight per cubic toot, table 431

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

ties, strength of, table.. 440

uses 33

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Spruce, Sitka:

characteristics 34

classification for painting, table 358

coefficient of thermal expansion, calculation. 47

color and figure, table 38

elastic constants, table 79

electrical resistance, table 49

factors for strength of mechanical fastenings,

table

gluing properties, table

locality of growth.

moisture content, table -

nomenclature

nomenclature, table

poles, weight per cubic foot, table ....

shrinkage values, table

strength properties of clear wood, table,

stresses, basic:

clear lumber, table - -

laminated members, table

ties, strength of, table

toughness, table

uses

weathering

303747°—55 34

Page

Spruce, Sitka—Continued

weight, table:

per cubic foot - 56

per 1,000 board-teet 56

working quality with hand tools, table 62

Spruce, white:

characteristics 33

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth 33

nomenclature, table 112

I)oles, weight per cubic foot, table . . 431

strength properties ol clear wood, table . .. 70

stresses, basic:

clear lumber, table. 156

laminated members, table 259

440

33

56

56

323

16'

234

34

322

34

112

431

315

70

156

259

440

83

34

43

ties, strength of, table

uses

weight, table:

per cubic foot

per 1,000 board-feet

Stain, chemical brown.__ .-

Stain, sticker 323

Stains, exterior:

properties 355

uses 365

Stairways, fire-resistant types 345

Standard deviation 84

Standard lumber patterns _.. 126

Starch glue, characteristics, preparation, uses,

table

Static bending:

definition of:

fiber stress to proportional limit

modulus of elavSticity

modulus of rupture

work in bending to maximum load

work in bending to proportional limit

strength values:

coefficient of variability .

fiber stress to proportional limit, table

modulus of ekisticity, table 70, 79

modulus of rupture, table 70

moisture content as related to 85,87

slope of grain as related to, table 97

specific gravity as related to 88

work to maximum load, table 70

work to proportional limit, table 70

Staypak 473

Steam bending properties of hardwoods, table. 63

Steaming-and-vacuum process for conditioning green timber for preservative treatment- 414

Stepping, sizes, table 116

Sticker stain 323

Stone, thermal conductivity, table 449

Storage of lumber:

care in yards 325, 326

dry lumber - 325

green or partially seasoned 325

storage shed temperature 326

Strength of preservative-treated timber:

preservatives, effect of 167,420

treatment necessary for injecting, effect of,.. 421

working stresses - 167

234

68

68

68

84

70
524 INDEX

Page

Strength properties:

air-dry wood (clear), table 70

bird pecks, effect ._ _. --- 101

chemicals, effect on, table— 52, 53

compression failures, effect.-. 98

compression wood 97

dead trees 101,102

decay, effect 100

duration of stress, effect .... 93

extractives, effect 102

green wood (clears table 70

insect damage, effect .. --- 100

knots, effect 93,94

mineral streaks, effect. _ __ 101

moisture content as related to 85, 88

molds and stains, effect on . _ 99

piling --- 437

pitch pockets, effect. 100

poles 429,431

resin, effect 102

seasoning degrade, effect 101

slope of grain as related to, table 97

specific gravity as related to 88

temperature, immediate effect 89

temperatm^e, permanent effect _ 89, 93

ties, table 440

turpentining, effect 102

variability as related to 83, 85

Strength ratio:

application to structural lumber 141

definition 141

values corresponding to:

knot sizes 150

shake, check, or split sizes, table.. _ 150

slope of grain, table 150

Strength-reducing features in structural

lumber 138,140

Stress concentration effects, in beams 205

Stress grades of lumber. See structural

lumber.

Stresses:

basic:

clear lumber, table 156

definition 140

discussion 156, 157

laminated members 258

working:

adjustment, table 158

definition 141

determination 1.57

laminated members 258

preservative-treated timber 161

Structural insulating board 445

Structural lumber:

checks and splits:

effect on strength 140

method of measuring 147

strength ratios corresponding to size.

table 150

stress-grade limitations, table 146,147.150

combination of strength-reducing features,

limitation 140

continuous spans:

limitation of knots and checks 147

Page

Structural lumber—Continued

cross grain:

effect on strength 138

decay limitation .... 137,143,161

dressed sizes, minimum 142

duration of load, effect on strength. _. 138

general quality required 143

grades 125.137.163

heartwood 137,148

holes 140

knots:

effect on strength 138

methods of measuring 143

strength ratio corresponding to size, table. 150

stress-grade limitations, tables 1.38.143,150

manufacturers' standard grades 163,164

pitch pockets 140

sapwood 137

seasoning 138,158

shakes 139,146,1.50

size standard 142

slope of grain, table 143,150

strength criteria:

close grain 137,149

strength ratios, tables 149,153

stresses, basic, table 156

stresses, working, table 158

use classification. 141

wane 140,148

Structural members:

built-up, strength of 265

glued laminated, strength of 250

wood-plywood, strength of 265

Structural timbers, retentions of preservatives, table 417

Stucco, thermal conductivity, table 449

Sugarberry:

characteristics 16

classification for painting 354

color and figure, table 38

locality of growth 15

strength properties of clear wood, table 70

uses 16

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Surnmerwood:

description 3

physical properties 3

strength criterion 4

Surfaces, thermal conductivity, table 449

Sweetgum:

characteristics 20

color and figure, table 38

decay resistance 45

elastic constants, table 79

factors for strength of mechanical fastenings,

table 167

gluing properties 234

locality of growth 20

moisture content, table 322

shrinkage values, table 315

strength properties of clear wood, table 70
INDEX 525

Page

S weetgum—Continued

stresses, basic:

clear lumber, table 156

laminated members, table 259

thermal conductivity across grain, table 49

uses 20

weathering 43,44

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with:

hand tools, table 62

machines, table 63

Sycamore:

classification for painting 354

color and figure, table 38

decay resistance 45

gluing properties, table 234

weathering 43

working quality with:

hand tools, table 62

machines, table 63

Sycamore, American:

characteristics 21

factors for strength of mechanical fastenings,

table 167

locality of growth 21

moisture content, table 322

nomenclature 21

shrinkage values, table 315

strength properties of clear wood, table 70

thermal conductivity across grain, table _ - 49

uses 21

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Tamarack:

characteristics 34

classification for painting, table 358

color and figure, table 38

decay resistance 45

locality of growth 34

moisture content, table 322

nomenclature, table 112

shrinkage values, table 315

strength properties of clear wood, table _.. 70

stresses, basic:

clear wood, table 156

laminated member, table 259

ties, life of 441

ties, strength of, table 440

uses 34

weight, table:

per cubic foot -56

per 1,000 board-feet 56

Tanalith 407.418

Tars. See Coal tar and Water-gas tar.

Tanks, species for 52

Temperature effects on strength 89

Temperatures, preservative treating 416

Tensile strength parallel to grain 81

Tensile strength perpendicular to grain:

coeflScient of variability 84

definition ^^

Page

Tensile strength perpendicular to grain—Con.

moisture content as related to 85,87

values, table 70

Tension members, design stresses, table 229

Tension wood:

effects in lumber 98

occurrence 98

shrinkage 318

warping, cause 318

Termites:

nonsubtenanean_ _ 392

subterranean 389

woods resistant to 393

Tetrachlorophenol, eíTectiveness as preservative, table 402

Texture of wood 40

Thermal conductivi y:

across grain of different woods, tables 47

definition 448

determination 47

factors afi'ecting 46

insulating materials, table 449

paper cores in sandwich construction 295

Thermal expansion 47

Thermal resistivity:

definition 448

insulating materials, table .___ 449

Thermoplastic resins, definition 234

Thermosetting resins, definition 234

Ties:

control of molds, stains, decay 383

decay resistance 440

life of naturally durable 441

life of treated 441

mechanical wear 440

preservative retentions, table 417

renewals 441

specifications. 439

strength properties of, table 440

strength requirements for 440

Timber-connector joints. See Connectors.

Timbers:

moistme content recommended 328

round:

percentage of sapwood, table 59

weight, determination 58

sawed, weight, table 55

sizes, table 117

Titanium-lead-zinc paints, properties 363

Titanium-zinc paints, properties 363

Toenailed joints, strength of 171

Tongued-and-grooved joint advantage 240

Toothed-ring connectors:

strength ratios, table 198

working Toads, table 167

Torsional rigidity, calculation 81

Torsional shear stress, allowable 81

Toughness:

coefficient of variability 84

method of determining 82

values, table 83

Tracheids 5

Treated wood:

piling - - - 438
526 INDEX

Page

Treated wood—Continued

poles. _ 435

ties 440

Trim .... 325,329

Trussed beams 215

Tupelo, black:

characteristics

color and figure, table

electrical rasistance, table

factors for strength of mechanical fastenings,

table

gluing properties, table 234

locality of growth 21

moisture content, table 322

nomenclature 21

shrinkage values, table 315

strength properties of clear woods, table 70

stresses, basic:

clear lumber, table 156

laminated members, table. 260

21

38

49

167

thermal conductivity across grain, table

ties, strength of, table .

47

440

uses 21

weathering .. ... 43

weight, table:

per cubic foot-.. .-. 56

per 1,000 board-feet

working quality with:

hand tools, table

machines, table--

Tupelo, ogeechee:

characteristics _

56

62

63

21

locality of growth.- _ 21

nomenclature 21

uses 21

Tupelo, swamp:

characteristics... 21

locality of growth 21

nomenclature _ 21

uses.. 21

Tupelo, water:

characteristics 21

color and figure, table 38

factors for strength of mechanical fastenings,

table . 167

gluing properties, table

locality of growth

234

21

moisture content, table

nomenclature

322

21

shrinkage values, table 315

strength properties of clear wood, table- _. 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

ties, strength of, table 440

uses

weathering .

21

43

weight, table:

per cubic foot . 56

per 1,000 board-feet 56

working quality with:

hand tools, table

machines, table

62

63

Turning properties of hardwoods, table -. 63

Turpentining, effects of 102

Page

Tyloses 4

Urea-resin glue characteristics, preparation,

uses, table 234

Vapor barriers

Vapor barriers in sandwich construction 295

Vapor drying process 415

Variability, coefiQcients of 84

Varnishes 351, 353, 376

Vegetable protein glue 233

Veneer:

breaking radius in bending 305

moisture content recommended 329

rotary cut 239

sawed 239

sliced 239

Veneered curved members 304

Veneered panels 243

Ventilation of roof space 454

Vermiculite, thermal conductivity, table 449

Vertically laminated beams. See Laminated

members, mechanically fastened.

Vessels 5

Wallboard, thermal conductivity, table 449

Walls, control of decay in 335

Walnut, black:

characteristics 21

color and figure, table 33

decay resistance 45

electrical resistance, table 49

gluing properties, table 234

locality of growth 2I

moisture content, table 322

nomenclature 21

shrinkage values, table 315

strength properties of clear wood, table 70

ties, strength of, table 440

uses 22

weathering 43,44

weight, table:

per cubic foot 55

per 1,000 board-feet 55

w^orking quality with:

hand tools, table 62

machines, table 63

Wane 140,148

Warping, causes 97, 318

Waterborne preservatives. See Preservatives.

Water-gas tar, effectiveness in fence-post treatment, table 401,402

Water-repellent preservatives. See Preservatives.

Water repellents 372

Wea,thering of wood 43, 351

Weight :

green wood per cubic foot, table 59

round timbers 5g

sawed timbers 55,58

turpentining, no effect 102

White-cedar, Atlantic:

characteristics 35

classification for painting, table 358

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth... 35
INDEX 527

Page

White-cedar, Atlantic—Continued

moisture content, table 322

nomenclature 35

nomenclature, table 112

poles, weight per cubic foot, table 431

shrinkage values, table 315

strength properties of clear woods, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

uses . 35

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

White-cedar, northern:

characteristics 35

classification for painting, table 358

color and figure, table 38

factors for strength of mechanical fastenings,

table 167

locality of growth 35

moisture content, table 322

nomenclature 35

nomenclature, table 112

poles:

life of 436

preservative treatment 429

properties of 429

weight per cubic foot, table_ 431

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 259

ties, strength of, table 440

uses 35

weight, table:

per cubic foot 56

per 1,000 board-feet 56

working quality with hand tools, table 62

White lead paint:

maintenance program for 368

properties 362

Willow:

decay resistance 45

machining properties, table 63

Willow, black:

characteristics 22

gluing properties, table 234

locality of growth 22

moisture content, table 322

shrinkage values, table 315

toughness, table 83

uses 22

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Willow, Pacific, shrinkage values, table 315

Window, coeflQcient of heat transmission, table. 453

Wolman salt. See Tanalith.

Wood cells 5

Wood, compressed 469

Wood lath and plaster, thermal conductivity,

table. 449

Page

Wood-plywood beams and girders:

deflection 271

flanges, design 264

joints between flanges and webs, design 269

lateral stability, rules for 272

limitations in design 264

stiffeners, design 270

webs, design 268

Wood preservative:

effectiveness, table 402

kinds 399

methods 411, 421

retentions for wood products, tables 417

Wood, resin-treated 467

Wood, thermal conductivity, table. 449

Work in bending to maximum load:

definition 68

moisture content as related to 85, 87

specific gravity as related to 88

values, table 70

Work in bending to proportional limit:

coefficient of variability 84

definition 68

moisture content as related to 85, 87

values, table 70

Working qualities, tables 62, 63

Working stresses:

adjustment for decay hazard 162

adjustment for density, table 158

adjustment for duration of load 160

adjustment for grade, table 168

adjustment for growth rate, table 158

adjustment for seasoning effects, table 158

adjustment for temperature 162

bearing area in compression perpendicular to

grain 163

columns 158

definition 141

determination 158

safety factors _ _ 162

Wrinkling of compression members 221

Yard lumber 115

Yellow-poplar:

characteristics 22

coefficient of thermal expansion, calculation. 47

color and figure, table 38

elastic constants, table ... 79

electrical resistance, table 49

factors for strength of mechanical fastenings, table 167

gluing properties, table 234

locality of growth 22

moisture content, table 322

nomenclature 22

shrinkage values, table 315

strength properties of clear wood, table 70

stresses, basic:

clear lumber, table 156

laminated members, table 260

toughness, table 83

uses 22

weathering 43

weight, table:

per cubic foot 56

per 1,000 board-feet 56
528 INDEX

Page

Yellow-poplar—Continued

working quality with:

hand tools, table 62

machines, table 63

Yew, Pacific:

decay resistance 45

nomenclature, table 112

shrinkage values, table 315

weight, table:

per cubic foot 56

per 1,000 board-feet 56

Young's modulus ratios, table 7^

Zinc arsenate, chromated "^

Zinc chloride:

advantages

Page

Zinc chloride—Continued

effectiveness as preservative, table 402

retentions recommended, table 417

specification 406

use 407

Zinc chloride, chromated:

composition 407

effectiveness as preservative, table 409

fire retardant 407

leaching resistance 407

retentions recommended, table 402,407

specifications 406

Z re chloride, copperized chromated 407

/ nc meta arsenite 408,417

U. S. GOVERNMENT PRINTING OFFICE: t955