/

ß^ f^^k^

l<}2>')

Storage of

Lumber

Agriculture Handbook

No. 531

U.S. Department of Agriculture

Forest Service

::^ K
STORAGE OF LUMBER

By

Raymond C. Rietz

Formerly Research Engineer

Forest Products Laboratory

Forest Service

U.S. Department of Agriculture

(Maintained at Madison, Wisconsin,

in cooperation with the University of Wisconsin.)

AGRICULTURE HANDBOOK NO. 531

September 1978

Library of Congress Catalog Card No. 78-600012
Rietz, Raymond C.

1978. Storage of lumber. U.S. Dep. Agrie, Agrie. Handb. 531

63 p.

Surveys the most effective current techniques for protecting

the quality of stored lumber. Physical properties of wood which are

basic to the storing of lumber in commerce are explained. Causes of

storage losses in lumber are discussed. Individual chapters deal with

protection of wood in specific storage environments, such as in

yards, at manufacturing plants, or in transit.

KEYWORDS : Degrade, drying, lumber, storage, wood properties

The Forest Products Laboratory is maintained by the Forest Service, U.S. Department of Agriculture, at Madison, Wis., in cooperation with the University of Wisconsin.

Mention of chemical treatment in this handbook does not constitute a specific recommendation ; only those chemicals registered by the U.S.

Environmental Protection Agency may be recommended, and then only for uses as prescribed

in the registration—and in the manner and at

the concentration prescribed. The list of registered chemicals varies from time to time ; prospective users, therefore, should get current

information on registration status from the

Environmental Protection Agency, Washington,

D.C. 20460.

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 001-000-03768-4
CONTENTS

Page

Preface iv

Chapter 1. Protecting Lumber in Storage 1

Green and Partially Dried Lumber 1

Dry, High-Grade Lumber 1

Lumber During Transport and Handling 3

Unprotected Lumber Outdoors 3

Benefits of Protective Storage 4

Hazards of Careless Storage 4

Chapter 2. Moisture Changes in Stored Lumber __ 5

Wood Properties and Moisture Movement 5

Determining Wood's Moisture Content 9

Predicting and Controlling Moisture Change 12

Chapter 3. Effects of Climate on Lumber Storage __ 17

Relative Humidity 17

Temperature 17

Rainfall 17

Average EMC Conditions by Region and Season _ 17

Chapter 4. Techniques for Storing Lumber 21

Storing Lumber Outdoors 21

Storing Lumber in Sheds 24

Storing Plywood 24

Chapter 5. Treating Stored Lumber 31

When is Chemical Treatment Needed? 31

When and Where is Treatment Applied? 32

Applying Chemical Treatment 32

Precautions with Chemicals 33

Page

Chapter 6. At Sawmills—Lumber Handling

and Storage 34

Softwood Sawmills 34

Hardwood Sawmills 35

Recommendations 36

Chapter 7. In Transit—Lumber Handling

and Storage 37

Truck Transport 37

Rail Transport 38

Ship Transport 40

Recommendations 42

Chapter 8. At Lumber Distributing Yards—

Handling and Storage 43

Outdoor Storage 43

Indoor Storage 45

Recommendations 46

Chapter 9. At Woodworking Factories—

Lumber Handling and Storage 48

Storage Facilities -48

Handling Equipment 50

Recommendations 50

Chapter 10. At Building Sites—Lumber

Handling and Storage 52

Hazards from Moisture Regain 52

Minimizing the Risks 53

Recommendations 54

Additional Information 55

Glossary 57

Index 62

Illustration Requests

Requests for copies of illustrations contained in this Handbook should be directed to the Forest

Products Laboratory, U.S. Forest Service, P.O. Box 5130, Madison, Wis. 53705.
PREFACE

"How can I cut down grade loss in my stored

lumber?" Forest Service specialists in wood

drying receive similar questions by phone or

mail in research centers across the Nation. But

such questions cannot be answered without more

information. Are we talking about^ green or

dried lumber? Air dried or kiln dried? What

species? How long will the storage period be?

What is the intended end use of the lumber?

What climate prevails in the storage region?

Questions of lumber storage can lead into the

largersubject of lumber processing, and are often

too complex to permit simple answers. Yet such

questions are of crucial importance because

degrade and decay during storage are a major

cause of lumber losses. Such lumber waste

becomes intolerable as demands increase upon

our Nation's Umited supplies of sawtimber. The

issue demands a comprehensive, practical publication, and thus researchers from the Forest

Service, U.S. Department of Agriculture, have

compiled this handbook. It should help to fulfill

the Forest Service's objective of conserving, and

thereby extending, our Nation's forest resources.

Studies have shown that lumber can be stored

with little waste if techniques are applied based

on a scientific knowledge of wood properties.

Chapters 1 through 4 of this handbook explain

physical properties of wood which are basic to

storing lumber commercially. The first four

chapters will help answer such questions as

these: Why does wood gain or lose moisture?

What conditions must be met to keep kiln-dried

lumber dry? What causes staining, decay, or

warp? How do hardwoods and softwoods differ

in their storage properties?

The remaining chapters of this handbook deal

with specific storage situations. Through text

and photographs, they give practical details of

the better handling, packaging, and storage

procedures used in the lumber industry today.

Specific problems are discussed, such as the

merits and limitations of package wrapping, the

protection of lumber when in transit, and ways

of protecting lumber from rain soaking at

construction sites.

This book also gives recommendations for

better storage at the end of several chapters,

suggestions for additional reading, and a

glossary of terms.
CHAPTER 1: PROTECTING LUMBER IN STORAGE

A flatcar piled high with packages of lumber

moves across the Midwest, each package protected in its own jacket of wrapping. Millwork

awaits use at a construction site, covered by a

tarpaulin and resting on small timbers to prevent ground contact. Workmen dip packages of

green lumber into a fungicide solution prior to

shipment. These are examples of effective storage

and handling in today's lumber industry.

When is lumber said to be in storage? Between

cutting and use, lumber undergoes a complex

series of stages in processing and transport.

During this time, lumber is frequently stored.

After drying and planing, softwood lumber may

be stored before shipping, and then stored again

in trucks, railroad cars, or a ship's hold as it

moves toward a destination. Hardwood lumber

is usually dried at the producing sawmill and

moves as rough lumber to the using factories.

Finally, lumber may be stored at wholesale and

retail distribution yards, at woodworking plants,

and at the construction site.

The moisture content of lumber must be

controlled in storage. Moisture changes in lumber may at times be the direct cause of grade

loss. For example, the best lumber will be unsuitable for many uses if its moisture content

goes too high. Also, moisture changes in lumber

may be an indirect cause of deterioration. For

example, rapid and uneven moisture changes

can cause checking and warpage. Also, lumber

with a moisture content of over 20 percent may

develop stain or decay. (The figure of 20 percent

includes a safety factor ; lumber's moisture content is measured as a percentage by weight of

the completely dried wood substance.) Most

insect damage to lumber can be avoided if it is

well dried.

Controlling moisture content in stored lumber,

as it moves from sawmill to its final destination,

should be the major concern of the processor,

agent, and user.

Green and Partially Dried Lumber

Green or partially dried lumber usually undergoes controlled drying when in storage, and is

usually stickered and given some protection from

weather (fig.l). Green lumber bulk-piled for

extended storage during warm weather is in

danger from decay, stain, and insect attack. For

this reason, green lumber should be stickered

for drying as soon as possible after sawn. When

such lumber must remain bulk-piled in warm

weather, such as when shipped in the green

state, it is often protected by chemical treatment

(chapter 5).

Dry, High-Grade Lumber

At times the maximum moisture content

acceptable for construction lumber is set by

industry practice, and at other times by standards

and codes. Certain industry grading rules, for

example, require that softwood dimension lumber

used in the framing of houses be below 19 percent

moisture content. Lumber for use in the heated

interiors of buildings should properly be still

drier; its moisture content should not exceed 8

percent.

Therefore, those who handle dried high-grade

lumber must be careful that it not take on

excessive moisture in storage or transport. For

example, finished lumber at a construction site

should not be allowed to undergo soaking from

rain because this would jeopardize its structural

performance.

The problem is especially acute with kiln-dried

lumber to be used in an interior location. If such
M 136 715-7

Figure 1.—Green lumber will lose moisture when it is stored, and should be stickered as shown here for controlled,

even drying.

M 144 031

Figure 2.—Pallet packages of lumber stored in an open

shed. Some packages have been unitized with iron

bands (center). Others are clad in plastic film for

additional protection.

M 142 877

Figure 3.—Kiln-dried, finished softwood lumber stored

in a large closed shed. The strapped packages are

transported by an overhead gantry crane.
lumber becomes wet enough to require redrying,

additional labor and expense are required. Also,

the lumber will again undergo some degrade

from the drying process and refinishing may be

required.

Dry, high-grade lumber is best protected from

moisture regain when stored as solid packages

under roof (fig. 2). Closed storage sheds offer

the best protection from moisture regain during

long-term storage (fig. 3).

Lumber During Transport and

Handling

Lumber handling has become mechanized to

reduce overall costs at sawmills, distribution

yards, factories, and construction sites. Transport methods have changed to speed up the

loading and unloading of trucks, boxcars (fig.

4), flatcars, and ocean-going vessels. The merits

of mechanized handling will diminish if lumber's

moisture content increases during this handling.

High-quality lumber can be protected in

several ways during transport. Tight boxcars

and dry ship holds can minimize moisture regain.

Packages of lumber exposed during transport,

such as on open ñatcars or tractor-trailer trucks,

can be temporarily protected by sheet wrapping

(fig. 5). Sheet wraps can also protect lumber at

unloading points or during temporary storage at

distribution yards (fig. 6).

M 144 078

Figure 4.—A forkloader places a wrapped package of

lumber in a wide-door boxcar. The paper wrap will

temporarily protect the lumber when stored outdoors

at its destination.

Unprotected Lumber Outdoors

High-quality lumber will endure for a short

time storage conditions which, if sustained,

would cause grade and footage losses. How

tolerant any given lot of lumber may be to lack

of protection, such as when transported on open

trucks, depends upon the time exposed, the

weather, and qualities of the lumber itself.

Generally, thicker pieces of wood, such as dimension lumber, will regain moisture more slowly

than thinner pieces, such as nominal 1-inch

boards. Hardwoods are more resistant to moisM 144 033

Figure 5.—Wrap of waterproof paper protects packages of dried softwood lumber on a railroad flatcar.
ture regain than softwoods, dense woods more

resistant than less dense, and heartwood more

resistant than sapwood.

Benefits of Protective Storage

Control of atmospheric conditions during

lumber storage, principally relative humidity,

can create a moisture balance in the lumber

suited to its end use. Thus the lumber's commercial quality can actually be improved by

storage.

Dry lumber is usually bulk-piled when stored

so that the overdried boards can absorb moisture

from adjacent underdried boards. Moisture content differences between boards of the lot are

thereby lessened. The moisture gradient within

individual boards also tends to flatten out during

storage. That is, the difference in moisture content between the shell and core of each board is

lessened.

Storing dry, casehardened lumber in an

atmospherically controlled shed or warehouse

will usually result in only slight stress relief.

However, if such lumber is stickered in an open

shed the regain of moisture by the surfaces will

reduce casehardening stresses. At one time this

was called "tempering."

Hazards of Careless Storage

Well-dried lumber that becomes saturated with

water, such as from rain, melting snow (fig. 7),

or contact with wet ground, can warp and otherwise deteriorate. Bulk-piled lumber is in more

danger from wetting than when stickered because water cannot easily evaporate from the

bulk pile.

High relative humidity alone will not elevate

moisture levels of dried lumber sufiiciently to

cause serious decay, but may permit some mold

to develop. High humidity may also raise the

moisture content of kiln-dried lumber enough so

that the lumber must be redried to be used in an

interior service location.

Bulk-piled lumber in bins or unit packages

absorbs moisture at all exposed faces of the pile.

This moisture moves toward the pile interior.

Movement is more rapid along the grain, and

the penetration of moisture absorbed at the open

cell ends will be the greatest. Moisture entering

through the ends of the boards will cause swelling, increasing the width and thickness of the

ends over the rest of the board. Moisture regain

by the boards on the top, bottom, and edges of

the pile increases the moisture content range of

the lot. Damp outside boards may create problems in subsequent processing.

When 1-inch softwood lumber, kiln dried to 8

percent or less, is solid piled outdoors under a

pile roof in humid weather, average moisture

content can increase at the rate of about 2 percent per month during the first 45 days. An

absorption rate of about 1 percent per month

then may be sustained throughout a humid

season.

Comparable rates for open sheds are about 1

percent per month and for closed sheds 0.3

percent per month. Total lack of protection, with

wetting by rain, will considerably increase these

rates.

Figure 6.—Wrap which protected a package of kilndried lumber during transport is being removed prior

to storage in a closed shed.

M 143 86&^

Figure 7.—Finished lumber being stored outdoors in

bad weather without adequate protection. Such storage

results in needless waste.

4
CHAPTER 2: MOISTURE CHANGES IN STORED LUMBER

If moisture content in stored lumber becomes

greater than about 25 percent, lumber becomes

susceptible to decay, stain, or insect attack.

Furthermore, uneven wetting or drying of lumber will cause warp. Grade loss due to moisture

change can be prevented, but methods differ for

green, air-dry, and kiln-dry lumber.

Green lumber loses moisture to the air during

storage, and if dried unevenly will warp. Stickering green lumber prevents warp by allowing

air to circulate through the pile. Moisture can

then evaporate evenly from all faces of the

boards, and uneven shrinkage stresses are

prevented.

Kiln-dry lumber tends to take on moisture

from the air; storage procedures should thus

minimize or prevent moisture regain. If kiln-dry

lumber regains much moisture, the expense and

effort of the kiln-drying process may have been

wasted.

Techniques for controlling moisture movement in lumber fall into three categories:

(1) determining the moisture content of stored

lumber; (2) predicting and, in some instances,

controlling moisture loss or regain; and (3) calculating the dimensional changes in lumber

caused by changes in moisture content.

Wood Properties and Moisture

Movement

Wood will either lose or absorb moisture when

exposed to certain conditions of temperature and

relative humidity; this property is known as

hygroscopicity. Changes in moisture content

cause wood to shrink and swell, creating problems

during processing and final use.

Free Water and Bound Water

The moisture in freshly cut (green) lumber

is often called sap. Sap is simply water with

certain materials in solution. Water in green

wood exists in two forms : As liquid in the cell

cavities, known as "free water," and as moisture

in the cell walls, known as "bound water."

The moisture content of wood is the weight of

the water which wood contains divided by the

weight of the completely dried wood substance.

Wood's moisture content is always expressed as

a percentage. Average moisture content of living

trees will vary by species from about 30 percent

to more than 200 percent (table 1).

Green moisture content of wood from different locations within the same tree can vary

considerably. For instance, in softwood species

green moisture content for sapwood is much

higher than for heartwood. Green moisture content of sapwood and heartwood does not differ

so much in hardwoods; some green hardwoods

will even have a higher moisture content for

heartwood.

Growing conditions of the individual tree will

also affect green moisture content. These conditions include soil characteristics, climate of the

locale, and, in some instances, the altitude of the

growth site.

Fiber Saturation Point

When green lumber dries, free water in

cavities of the surface cells will leave first. No

bound water will leave a cell until all the free

water has evaporated. Wood's moisture condition when all free water has evaporated but the

cell wall remains saturated is called the fiber

saturation point (FSP). In general, the FSP

prevails at a cell moisture content of about 30

percent ; it may vary to some extent from species

to species. When the cell walls are dried below

the FSP, shrinkage begins. As adjacent cells in

the wood dry below the FSP, changes in the

physical and mechanical properties of the wood

occur.

Moisture Diffusion Characteristics

The rate at which lumber loses or regains

moisture is directly affected by the moisture

diffusion characteristics of the particular wood.

Understanding moisture movement in wood can

help avoid grade losses caused by uneven moisture changes, such as warp, checking, and

splitting.
Table 1.—Average moisture content of green wood by species

Species Moisture content ^

Common name Botanical name Heartwood Sapwood Mixed

heartwood

and

sapwood

Pet Pet Pet

Baldcypress

Cedar:

Alaska—

Atlantic white—

Eastern redcedar

Incense—

Northern white—

Port-Orford—

Western redcedar

Douglas-fir :

Coast type

Fir:

Balsam

California red

Grand

Noble

Pacific silver

Subalpine

White

Hemlock :

Eastern

Western

Larch, western

Pine:

Eastern white

Jack

Lodgepole

Ponderosa

Red

Southern :

Loblolly

Longleaf

Shortleaf

Slash

Sugar

Western white

Redwood :

Old-growth

Young-growth

Spruce :

Engelmann

Red

Sitka

White

SOFTWOODS

Taxodium distiehum 121 171

Chamaecyparis 32 166

nootkatensis

Chamaecyparis thyoides ___ ___

Juniperus virginiana 33 —^

Libocedrus deeurrens 40 213

Thuja oeeidentalis

Chamaecyparis lawsoniana 50 98

Thuja plieata 58 249

Pseudotsuga menziesii

Abies balsamea

A, magnifica

A, grandis

A, procera

A, amabilis

A. lasiocarpa

A, concolor

Tsuga canadensis

T, heterophylla

Larix oeeidentalis

Pinus strobus

P, banksiana

P. contorta

P, ponderosa

P. resinosa

P. taeda

P. palustris

P. echinata

P. elliottii

P. lambertiania

P. monticola

Sequoia sempervirens

S. sempervirens

Picea engelmannii

P. rubens

P. sitchensis

P. glauca

37

120

98

97

85

54

115

140

91 136

34 115

55 164

160

119

170

110

35

55

108

47

68

70

41 120

40 148

32 134 —

33 110

31 106

32 122

30 100

98 219

62 148 — -

86 210

100 200 ---

51 173

55

41 142

55
Table 1.—Average moisture content of green wood by species—continued

Species Moisture content *

Common name Botanical name Heartwood Sapwood Mixed

heartwood

and

sapwood

Alder, red

Ash:

Black

Green

White

Aspen :

Bigtooth

Quaking

HARDWOODS

Alnus rubra

Fraxinus nigra

F. pennsylvanica

F, americana

Populus grandidentata

P, tremuloides

Basswood, American Tilia americana

Beech, American Fagus grandifolia

Birch :

Paper

Sweet

Yellow

Betula papyrifera

B. lenta

B. alleghaniensis

Butternut Junglans cinérea

Cherry, black Prunus serótina

Cottonwood :

Black

Eastern

Populus trichocarpa

P. deltoides

Elm:

American

Rock

Ulmus americana

U, thomasii

Hackberry Celtis occidentalis

Hickory Garya spp.

Magnolia, southern Magnolia grandiflora

Maple :

Bigleaf

Red

Silver

Sugar

Acer macrophyllum

A. rubrum

A. saccharinum

A, saccharum

Oak:

Northern red

Northern white

Southern red

Southern white

(chestnut)

Quercus rubra

Q. alba

Q. falcata

Q, prinus

Pecan Carya illinoensis

Sweetgum Liquidambar styraciflua

Sycamore, American Platanus occidentalis

Tanoak Lithocarpus densiflorus

Pet

11

Pet

97

138

58 97

65 72

80 69

64 78

83 75

72 —

71 62

79 137

114 130

Pet

95 —

58

46 44 —

95 113

95 113 -----

81 133 —

55 72 —

89 72

75 70

74 72 —

— — 104

58 — 65

162 146

160 145 --

95 92

44 57 — -

61 65 —

71 49 —

80 104 __..

70

89
Table 1.—Average moisture content of green wood by species—continued

Species Moisture content ^

Common name Botanical name Heartwood Sapwood Mixed

heartwood

and

sapwood

Pet Pet Pet

HARDWOODS—continued

Tupelo:

Black

Water

Nyssa sylvatiea

N. aquatica

87

150

115

116

—

Walnut, black Juglans nigra 90 73 —

Willow, black Salix nigra — — 139

Yellow-poplar Liriodendron tulipifera 83 106 —

' Based on weight when ovendry.

Moisture diffuses through wood from zones

of higher to zones of lower moisture content.

Thus, when lumber is drying the moisture in the

wet interior of a board moves towards the drier

surface. If dry lumber is exposed to high relative humidity or wetting while in storage,

moisture diffuses from moist surfaces of the

boards to the drier interior. The greater the

difference in moisture concentration, the more

rapid will be the diffusion rate in both desorption

and absorption.

The moisture diffusion rate varies with wood

temperature. Cold wood in storage responds

more slowly to changes in atmospheric conditions, but moisture will move more rapidly in

warm wood.

Moisture diffusion in wood is also influenced

by the wood's specific gravity. In general, the

moisture diffuses more rapidly in the lighter,

low specific gravity woods than in the heavier,

high specific gravity woods. This accounts for

faster moisture regain by softwoods in situations where dry lumber is stored under humid

conditions.

Moisture content changes more rapidly in

permeable than in impermeable woods. Thus, the

sapwood of most species dries faster than the

heartwood and, conversely, regains moisture

more rapidly.

Equilibrium Moisture Content

Wood at or above the fiber saturation point,

such as green wood, will lose moisture when

exposed to any relative humidity below 100 percent. Also, totally dry (ovendried) wood will

absorb moisture when exposed to any relative

humidity except zero. At a constantly maintained

temperature and relative humidity, any wood

will reach a point where it neither loses nor

gains any moisture. When wood is in moisture

balance with the relative humidity of the air

surrounding it at a given temperature, the wood

is said to have reached its equilibrium moisture

content (EMC).

The relationship between wood EMC and the

temperature and relative humidity of air is

shown in figure 8. The graph shows that at

temperatures below 120° F (49° C) the EMC

of wood is closely related to the relative

humidity.

Air temperature is of secondary importance

when determining EMC. For example, at 20

percent relative humidity and a dry-bulb temperature of 40° F (5° C), the wood EMC

condition is about 414 percent. Elevating the

temperature 60° F (or 33° C) would reduce

EMC by only half a percent (to 4 pet).

On the other hand, if the relative humidity

varies from low to high at the same temperature.

8
the EMC will change considerably. For example,

at 70° F (21° C) and 20 percent relative

humidity, the EMC is just under 4Vè percent;

but at the same temperature and 80 percent

relative humidity, the EMC is 16 percent.

(Determining EMC so as to control moisture

changes in stored lumber will be explained later

in this chapter.)

Determining Wood's Moisture

Content

The moisture content of wood is expressed as

a percentage by weight of the dry wood substance. Moisture content is usually determined

by one of two methods fOvendrying or use of

electric moisture meters. The ovendrying method

involves determining the weight of the wood

substance after complete drying in an oven (i.e.,

until constant weight is attained). Ovendrying

has the advantage of being the more accurate

method, but is time-consuming and requires that

a piece be cut from the wood to be tested.

Electric moisture meters give rapid and

reasonably accurate readings throughout the

range of 7 to 25 percent moisture content, but

are subject to error if improperly used. Some

models do not damage the wood being tested;

lU'J

80

ii..

20

.

__

. — —

lO

I Ilk

Í

'II

.1

50 60 70

TEMPERATURE CF.)

M 144 246

others require that needlelike electrodes be

driven into the wood.

Wood that contains large amounts of volatiles

such as pitch or preservatives must be tested for

moisture content by a distillation method.

Ovendrying Method

The ovendrying method requires that a cross

section be cut from the board at some distance,

say 18 inches, from an end. This cross section

must remain in the oven for at least 12 hours

and usually more. The ovendrying method is

accurate throughout the whole range of moisture

content. It consists of the five following steps:

(1) Cut a cross section about 1 inch thick

along the grain.

(2) Immediately after sawing, remove all

loose splinters and weigh the section.

(3) Put the section in an oven maintained

at a temperature of 217.4° ± 3.6° F (103° ±

2° C), and dry until a constant weight is

attained.

(4) Weigh the dry section to obtain the

ovendry weight.

(5) Subtract the ovendry weight from the

initial weight, and divide the difference by the

ovendry weight, multiplying the result by 100

to obtain the percentage of moisture in the

section. This is the moisture content of the

section and is usually assumed to be representative of the board. The formula for this

computation is:

Moisture content in percent

X 100. _ Initial weight — ovendry weight

Ovendry weight

A shortcut formula convenient to use with

slide rules or calculators is:

Moisture content in percent

= (

Initial weight

Ovendry weight ~ 1) X 100

Figure 8.—Equilibrium moisture content of wood as

related to air temperature and relative humidity.

Balances used in weighing specimens for

moisture content determinations include the

triple-beam balance (fig. 9) and the pan-type or

torsion balances. Where a considerable number

of specimens are weighed in and out of the

drying oven, a direct-reading automatic balance

is very convenient.

The oven used for drjring the moisture sections should be large enough to accommodate a
M 136 717-12

Figure 9.—Layout for determining moisture content of

wood samples by ovendrying. Shown are a triple-beam

balance and a small electric oven.

number of specimens, with room to provide

spaces between them. The temperature of the

oven needs to be controlled with a reliable

thermostat at a setting within the limits of

217.4° ± 3.6° F (103° ± 2° C). Excessive temperatures will char the specimens, introducing

errors in the moisture analysis. Too low a

temperature may not evaporate all the moisture

in the specimen. The oven should be well ventilated to allow the moisture being evaporated to

escape.

Electric ovens are most generally used. When

the volume of specimens to be ovendried daily is

relatively small, a natural-circulation electric

oven is adequate. Some ovens contain fans to

circulate the heated air ; when large numbers of

specimens are being ovendried, electric ovens

with fans are recomfnended.

Microwave ovens are sometimes used to dry

the sections. Drying time is reduced to minutes,

but destructive distillation of the wood may

introduce errors in moisture content calculations. With experience in operating the microwave oven, however, these errors can be avoided.

Electrical Methods

Electric moisture meters are being extensively

used, particularly the portable or hand meters.

Two types, each based on a different fundamental relationship, have been developed:

(1) The resistance type, which uses the relationship between moisture content and direct

current resistance (fig. 10) ; and (2) the dielectric type, which uses the relationship between

moisture content and the dielectric loss factor of

the wood (fig. 11).

Resistance-type moisture meters are widerange ohmmeters. Portable, battery-operated

models are available. Most models have a directreading meter calibrated in percent for one

species; the manufacturer provides correction

tables for other species. The manufacturer

usually provides a temperature-correction chart

or table when tests on wood warmer than 90° F

(32° C) or cooler than 80° F (27° C) are made.

Electrical resistance of wood decreases as

wood warms and increases as it cools. A rule-ofthumb temperature correction is to subtract 1

percent moisture content from the meter reading, corrected for species, for every 20° that the

wood temperature is above 80° F. Add 1 percent

for every 20° that the wood is below 80° F.

Resistance-type meters are generally supplied

with pin-type electrodes that are driven into the

wood being tested. The most common consist of

four needles that extend about ^e inch beyond

their mounting chucks. Long, two-pin electrodes

which have insulated shanks except for the tip

are also available for use on lumber thicker than

1% inches.

When lumber with a normal drying distribution is tested, valid estimates of the average

moisture content of the cross section are obtained

by driving the pins deep enough in the lumber

so that the tip reaches one-fifth to one-fourth

the thickness of the board. If the lumber is regaining moisture or the lumber surface has been

wetted, the meter indications are îikely to be

much higher than the actual average moisture

content. In this case, insulated shank pins should

be used.

The useful range of resistance-type moisture

meters is from about 7 to 25 percent moisture

content. Meter readings greater than 30 percent

can only be considered as gross approximations

of the real moisture content of the wood. When

the electrodes are withdrawn, care is essential

to prevent pin breakage or bending.

The dielectric moisture meter uses surface

contact-type electrodes. The electrode is an

integral part of the instrument (fig. 11). The

lumber being tested is penetrated by the electric

field radiating from the electrode about % inch

into the wood, so that thicknesses to about l^/^

inches may be tested. The moisture content of

the surface layers of the lumber, however, has

10
M 134 790

Figure 10.—Moisture meters of the resistance type.

11
a predominant influence on the meter readings

because the electric field is stronger near

the electrode. The roughness of the lumber and

the electrode design may also influence meter

readings.

The effect of wood temperature on the dielectric loss factor and dielectric constant is not

well understood, so temperature correction charts

or tables are not provided with dielectric meters.

The manufacturers do, however, provide species

correction tables for converting the meter scale

reading of the instrument to moisture content.

The useful range of the dielectric moisture

meter is from 0 to 25 percent moisture content.

Predicting and Controlling

Moisture Change

Being able to derive the equilibrium moisture

content (EMC) of lumber in storage,can be

very useful to those responsible for the storage

facility. Average temperature and relative humidity of a locale can be used to determine the

EMC, and thus the eventual moisture content

which lumber will attain when stored outdoors

in that locale.

Furthermore, calculations involving EMC can

be used to determine the temperature required

in a heated, closed shed to attain a desired

moisture content in lumber stored there.

Determining EMC

The EMC may be determined for lumber at

any ambient temperature and relative humidity.

Where atmospheric conditions are constant, such

as in heated or air-conditioned sheds, temperaM 133 689

Figure 11.—A dielectric moisture meter.

M 144 087

Figure 12.—Humidity-measuring instruments (left to

right) : Electric hygrometer showing sensor head

and three adsorbent-salt cartridges; blower-type

psychrometer which is portable and battery powered ;

two sling psychrometers which are twirled to aerate

the wet-bulb wick.

ture and relative humidity may be measured with

a sling- or blower-type psychrometer or a

hygrometer (fig. 12). Readings of the psychrometer's dry-bulb and wet-bulb thermometers

must be interpreted by a chart supplied with the

instrument to give the relative humidity. An

electric hygrometer can give relative humidity

directly within seconds of being turned on.

To approximate the EMC of wood stored in

outdoor areas, it is possible to obtain average

values of temperature and relative humidity for

the geographical area and season (chapter 3).

With such figures, the approximate EMC for

lumber stored under exterior conditions can be

simply derived.

Controlling EMC in a Heated or

Air-Conditioned Shed

A desirable EMC for lumber can be prescribed

when the storage environment can be controlled,

such as in a heated or air-conditioned shed.

Kiln-dry lumber can then be stored without

significant change in moisture content.

For example, assume that the outdoor air is

at 50° F (10° C) and the relative humidity is

about 80 percent. From figure 13, the wood

EMC condition is seen to be about 17 percent.

Further assume that kiln-dry lumber averaging

7 percent moisture content is stored in a closed

shed, and that the shed will be heated to prevent

moisture regain.

When indoor shed air is heated, its absolute

humidity remains the same as that of outdoors.

The absolute humidity of outdoor air at 50° F

12
100

90

80

i

I

70

60

50

40

30

20

10

\

\

\

\ \

\\ w \\A\\\\

\

\

\

\á

-V—A

1 \ \V\\\\\

\\W\\\

\

\ \ \

\^

^\ \^vv^ r\ \

\ \ 2Íi^

\

\ \ \. \\

\ \ ^ w

\

2

\

\ '\

^ \

• \

• \

\^ i^ ^

\

\

\ .

\

\ •

\\\\x\\ \\

5 -X \

\^

——-\

^

;\ vv

\, \,

^^ 1

^

h \-VN\^xW

\ ^^^

10^ \

x^ ^

^^ --Jí^

X \

\^

^^ -^^

^

\.^^^ ^.^^^ >>

"\

^

~-^-~-^ r

1 r~~ ^ =^

^ -

20

15

lit

I

'I

I

s

10 20 30 40 50 60

TEMPERATURE

70 80 90 100 110 120

M 133 676

Figure 13.—Psychrometric chart illustrating the temperature elevation required to attain 7 percent EMC conditions, given an air temperature of 50" F (10° C) and relative humidity of 80 percent.

(10° C) and 80 percent relative humidity is

about 3.5 grains per cubic foot (fig. 13). At this

absolute humidity and a wood EMC value of 7

percent, the dry-bulb temperature is about 75° F

(25° C). This means that if the closed shed

air is heated 25°—from 50° to 75° F (10° to

24° C)—and circulated around the dry lumber,

moisture regain by the lumber is prevented.

The heating in a closed storage shed may be

regulated manually or with automatic control

equipment. Because the EMC is far more dependent upon humidity than upon temperature,

a humidistat rather than a thermostat is the

best automatic system to use. (See "Closed,

Heated Shed," chapter 3.)

If the weather is warm and humid, heating

the shed air will effectively depress its relative

humidity but may increase the temperature to

an uncomfortable level for workers inside.

Assume that the outdoor temperature is 90° F

(32° C) and the relative humidity is about 78

percent. The EMC condition of the outdoor air

is then 15 percent. To attain a 7 percent wood

EMC condition in the shed requires a temperature increase to 115° F (46° C). But workmen

may object to working in that warm a shed.

One solution is air-conditioning, but the increased costs may not be justified. However, at

some woodworking plants, year-around airconditioning is installed to control the temperature and relative humidity where wood is

processed. Storage rooms for kiln-dry lumber

are often included in these temperature- and

relative humidity-controlled areas.

13
Predicting Dimensional Changes in Wood

When the cells in the surface layer of a board

dry below the fiber saturation point (FSP)—

that is, below about 30 percent moisture content—^the cell walls shrink. This shrinkage is

restrained by the wet core of the board, yet the

stresses in the surface layer caused by cell-wall

shrinkage can be sufficient to squeeze the wet

core. Thus, a slight overall shrinkage of the

board can be observed although its average

moisture content is still considerably greater

than 30 percent. For most practical purposes,

however, the shrinkage of wood is considered as

being proportional to the moisture lost below 30

percent.

Shrinkage Characteristics

The shrinkage of wood varies with species

and with the orientation of the cells—^tangential,

radial, or longitudinal (fig. 14). Shrinkage

across the width of a board sawed tangentially

to the annual growth rings (plain sawed) is

about twice as much as in a board sawed radially,

or parallel to the rays (quartersawed). Longitudinal shrinkage or shrinkage in length is

generally very small (0.1 to 0.2 pet of the green

dimension).

Reaction wood, such as compression wood in

softwoods and tension wood in hardwoods,

shrinks considerably more in the longitudinal

direction than normal wood. Juvenile wood found

near the pith of the tree also has an appreciable

longitudinal shrinkage. Table 2 gives the total

tangential and radial shrinkage values for many

commercial species. The values are expressed as

a percentage of the green dimension. Thus

a plain-sawed board that is 10 inches wide when

green, of a species having a 10 percent total

RADIAL

M 136 889

Figure 14.—Shrinkage directions in a plain-sawed board.

tangential shrinkage, will shrink about 1 inch in

width when dried to 0 percent moisture content.

Dimensional Change Formula

The values of table 2 can be used to calculate

the radial or tangential dimensional change of

wood in going from one moisture content condition to another. The wood species, essential

grain pattern, present dimension, and moisture

content must be known to calculate the shrinkage

or swelling that will occur if the item changes

moisture content.

The formula is

AD =

AD

(MF-M,)D

(l?^*-«-)^M.

= The shrinkage or swelling in

any unit of length.

MI = the initial moisture content in

percent,

MF = the final moisture content in

percent,

D = the dimension at the initial

moisture content in units of

length,

FSP = the fiber saturation point in

percent (30 for most

woods 1), and

SrandSn = the total tangential or radial

shrinkage values.

Neither the initial nor the final moisture content values can exceed the FSP. Examples of the

use of this formula to determine dimensional

changes follow:

Example No. 1.—Determine the width of the

ends of packaged flat-grained oak flooring strips

machined to 2l^ inches at a moisture content of

6 percent, then stored in a warehouse where

moisture pickup causes the exposed end grain to

reach 12 percent moisture content. Some pieces

are of northern red oak and some of southern

red oak. Because the pieces are flat grained, the

total tangential shrinkage values of 8.6 percent

for northern red oak and 11.3 percent for

southern red oak are used (table 2). A value of

30 is used for FSP. The initial moisture content

is 6 percent and the final moisture content is 12

percent. The dimension at the initial moisture

content is 2.25 inches.

^Twenty-two percent is used for redwood, northern

white-cedar, and western redcedar.

14
Table 2.—Total shrinkage values of domestic woods ^

Species Shrinkage to 0 percent moisture content Species Shrinkage to 0 percent moisture content

Radial Tangential Radial Tangential

Pet

SOFTWOODS

Baldcypress 3.8

Cedar:

Alaska— 2.8

Atlantic white— 2.9

Eastern redcedar 3.1

Incense— 8.3

Northern white— 2.2

Port-Orford— 4.6

Western redcedar 2.4

Douglas-fir :

Coast 4.8

Fir:

Balsam 2.9

California red 4.5

Grand 3.4

Noble 4.8

Pacific silver 4.4

Subalpine 2.6

White 3.3

Hemlock :

Eastern 3.0

Western 4.2

Larch, western 4.5

Pine:

Eastern white 2.1

Jack 3.7

Lodgepole 4.3

Ponderosa 3.9

Red 3.8

Southern :

Loblolly 4.8

Longleaf 5.1

Shortleaf 4.6

Slash 5.4

Sugar 2.9

Western white 4.1

Redwood :

Old-growth 2.6

Young-growth 2.2

Spruce :

Engelmann 3.8

Red 3.8

Sitka 4.3

White 4.7

HARDWOODS

Alder, red 4.4

Ash:

Black 5.0

Green 4.6

White 4.9

Pet

6.2

6.0

5.4

4.7

5.2

4.9

6.9

5.0

7.6

6.9

7.9

7.5

8.3

9.2

7.4

7.0

6.8

7.8

9.1

6.1

6.6

6.7

6.2

7.2

7.4

7.5

7.7

7.6

5.6

7.4

4.4

4.9

7.1

7.8

7.5

8.2

7.3

7.8

7.1

7.8

Aspen :

Bigtooth

Quaking

Basswood, American

Beech, American

Birch:

Paper

Sweet

Yellow

Butternut

Cherry, black

Cottonwood :

Black

Eastern

Elm:

American

Rock

Hackberry

Hickory, pignut

Magnolia, southern

Maple: ,

Bigleaf

Red

Silver

Sugar

Oak:

Northern red

Northern white

Southern red

Southern white

(chestnut)

Pecan

Sweetgum

Sycamore, American

Tanoak

Tupelo:

Black

Water

Walnut, black

Willow, black

Yellow-poplar

Pet

8.3

3.5

6.6

5.5

6.8

6.5

7.8

8.4

3.7

8.6

8.9

4.2

4.8

4.8

7.2

5.4

8.7

4.0

3.0

4.8

4.0

5.6

4.7

5.3

4.9

5.3

5.0

4.9

5.1

4.2

5.5

3.3

4.6

Pet

7.9

6.7

9.3

11.9

8.6

9.0

9.5

6.4

7.1

8.6

9.2

9.5

8.1

8.9

11.6

6.6

7.1

8.2

7.2

9.9

8.6

10.5

11.3

10.8

8.9

10.2

8.4

11.7

8.7

7.6

7.8

8.7

8.2

* Expressed as a percentage of the green dimension.

15
Substituting in the formula will yield the

northern red oak dimensional change:

AD (12 - 6) 2.25

(SOgOO) _ 30)+ 6

13.50

325 == 0.041 inch

The positive value denotes swelling. The ends of

the pieces of strip flooring are 0.041 inch wider

than the inner portion due to moisture absorption

by the end grain.

The total tangential shrinkage value for

southern red oak is greater than northern red

oak ; substituting in the formula :

AD =

(12 -6) 2.25 13.50

242

The endwise moisture absorption gradient with

its accompanying swelling may create difficulties

in the installation of the flooring.

Example No. 2.—Determine the shrinkage in

width of a nominal 2- by 8-inch Douglas-fir

plain-sawed joist machined to a width of 71/^

inches at a moisture content of 19 percent and

then dried to 12 percent moisture content in a

retail lumberyard. In this example, FSP = 30,

MI = 19, MF = 12, D = 7.5, and, from table 2,

ST = 7.6 percent. Substituting in the formula:

iD =

(12 - 19) 7.5 _-52.5.

/30(100) 384

7.6

(?M|0)_3„).e-

= 0.056 inch

30V 19

= -0.137 inch

The width of the joist at the lower moisture

content is 7.500 - 0.137 inches or 7.363 inches.

16
CHAPTER 3: EFFECTS OF CLIMATE ON LUMBER STORAGE

Air temperature, relative humidity, and rainfall of the ^storage region affect procedures to

protect lumber stored outdoors.

Relative Humidity

Relative humidity has a much greater effect

on wood's equilibrium moisture content (EMC)

than does temperature (fig. 15). That is, the

more humid a region, the more rapidly dry lumber will take on moisture when yarded there.

Seasonal estimates of the average wood EMC

for a region can be helpful whenjtrying to control moisture change in lumber stored outdoors.

Such estimates are supplied later in this chapter.

Storage methods to retain low moisture content in kiln-dry lumber will differ sharply

between humid regions such as Florida and dry

regions such as New Mexico. Likewise, storage

requirements may differ from month to month

in regions where average relative humidity

varies considerably with seasons, such as in

inland California. Procedures explained in this

handbook should be qualified in terms of average

relative humidity of the storage region, especially

where relative humidity differs greatly from the

national average.

Temperature

Air temperature affects stored lumber because

warming speeds up moisture diffusion and thus

increases lumber's rate of moisture change.

Thus, if moisture differences between boards in

the lot need to be reduced, storage of lumber in

warm air temperatures is advantageous.

Warm temperatures also increase the hazard

of fungal infection in stored lumber. All lumber

is practically immune to fungal infection below

30^^ F (-1° C). When green lumber is solid

piled, mold, stain, and decay fungi will grow at

temperatures from 40° to 100° F (about 5° to

38 ' C) with rate of attack increasing rapidly at

higher temperatures in this range. Dipping or

spraying freshly sawed lumber with an approved

fungicide appreciably reduces the likelihood of

fungal growth. If, however, treated lumber is

held too long in the bulk pile in warm weather,

fungi can grow rapidly (chapter 5).

Rainfall

When lumber is stored outdoors with good

protection, rainfall does not greatly affect its

moisture content. Bulk-piled green lumber is

often temporarily stored outdoors unprotected

before stacking for air drying or kiln drying.

Some wetting of green lumber is not considered

hazardous. If, however, green lumber has been

treated with a fungicide for extended green

storage or shipment, protection from rain is

needed. Rain would leach the chemicals from the

exposed boards.

Bulk-piled dry lumber should be protected

from rain, preferably in storage sheds. Redrying

bulk-piled lumber that has been wetted by rain

is difficult. Bulk-piled lumber that was thoroughly

soaked must be stickered before it is redried,

and redrying will bring further shrinkage and

drying loss. Also, if rain-soaked lumber increases

its moisture content to 20 percent or more, fungi

may grow, causing stain and decay.

Average EMC Conditions by

Region and Season

The estimated wood EMC conditions for

spring, summer, fall, and winter for the United

States are given in table 3. Average temperatures and relative humidities reported by the

Weather Bureau for the four seasons have been

converted to wood EMC values. The States of

Alaska, Washington, Oregon, California, and

Texas are divided into coastal and inland

regions ; Arizona into a lowland and a highland

area; and Hawaii into windward and leeward

locations.

Five designations—arid, dry, moist, damp, and

wet—are arbitrarily established for classifying

the average wood EMC conditions of the outdoor

air. In a specific location, actual EMC values

may differ from the table 3 values in some years.

More localized EMC values can be determined

17
Table 3.—Estimated average wood EMC conditions for the United States

Spring* Summer * Pall* Winter*

State Aver- Desig- Aver- Desig- Aver- Desig- Aver- Desigage na- age na- age na- age naEMC^ tion» EMC^ tion* EMC^ tion» EMC» tion»

Pet Pet Pet Pet

Alaska

Coastal 16.3 Wet 18.1 Wet 19.0 Wet 17.2 Wet

Inland 14.2 Damp 15.6 .. do .. 16.8 .. do.. 14.7 Damp

Alabama 13.7 ..do.. 13.9 Damp 14.4 Damp 13.3 do.

Arizona

Lowland 6.7 Arid 6.6 Arid 8.0 Arid 8.9 Dry

Highland 7.2 .. do .. 7.0 . . do .. 8.5 Dry 9.2 do.

Arkansas 13.3 Damp 13.7 Damp 13.9 Damp 13.4 Damp

California

Coastal 13.5 ..do.. 14.0 ..do .. 13.1 ..do.. 14.1 do.

Inland 11.5 Moist 8.4 Dry 10.7 Dry 16.1 Wet

Colorado 10.8 Dry 8.7 .. do.. 9.6 .. do .. 10.5 Dry

Connecticut 12.4 Moist 13.8 Damp 15.0 Damp 12.2 Moist

Delaware 13.3 Damp 13.4 .. do .. 14.6 .. do .. 14.1 Damp

Florida 14.2 .. do .. 15.7 Wet 15.5 Wet 14.2 do.

Georgia 13.7 .. do .. 14.2 Damp 14.5 Damp 13.2 do.

Hawaii

Leeward 12.4 Moist 12.1 Moist 13.4 ..do .. 13.2 do.

Windward 15.6 Wet 16.8 Wet 16.8 Wet 16.1 Wet

Idaho 11.7 Moist 8.3 Dry 10.1 Dry 16.2 Wet

Illinois 12.4 .. do .. 13.3 Damp 12.9 Moist 14.9 Damp

Indiana 13.5 Damp 14.0 ..do .. 14.2 Damp 15.1 Wet

Iowa 11.9 Moist 13.4 .. do .. 12.9 Moist 14.2 Damp

Kansas 14.1 Damp 11.9 Moist 12.6 Moist 12.9 Moist

Kentucky 13.4 .. do .. 13.7 Damp 13.5 Damp 14.6 Wet

Louisiana 13.6 .. do.. 13.9 .. do .. 15.0 ..do .. 14.0 Damp

Maine 13.7 .. do .. 14.9 ..do .. 16.2 Wet 13.2 do.

Maryland 12.9 Moist 13.4 .. do.. 14.0 Damp 14.2 do.

Massachusetts 13.5 Damp 14.4 .. do .. 14.2 .. do.. 13.2 do.

Michigan 12.5 Moist 13.0 Moist. 14.0 .. do .. 15.5 Wet

Minnesota 12.0 .. do . . 13.7 Damp 14.5 ..do.. 13.8 Damp

Mississippi 13.7 Damp 14.3 .. do .. 15.2 Wet 13.6 do.

Missouri 12.9 Moist 13.2 .. do .. 12.6 Moist 13.5 do.

Montana 11.4 .. do .. 9.4 Dry 11.4 ..do.. 13.4 do.

Nebraska 13.0 .. do.. 12.3 Moist 12.5 .. do .. 13.0 Moist

Nevada 9.4 Dry 6.4 Arid 8.8 Dry 11.7 do.

18
Table 3.—Estimated average wood EMC conditions for the United States—continued

Spring* Summer * Fall* Winter*

State Aver- Desig- Aver- Desig- Aver- Desig- Aver- Desigage

EMC*

nation'age

EMC^

nation*

age

EMC*

nation'

age

EMC*

nation»

Pet Pet Pet Pet

New Hampshire 12.2 Moist 11.1 Moist 14.5 Damp 13.6 Damp

New Jersey 11.8 ..do.. 12.0 .. do .. 12.8 Moist 12.7 Moist

New Mexico 9.0 Dry 7.9 Arid 9.3 Dry 10.1 Dry

New York 13.1

Pet

Damp 12.8

Pet

Moist 14.1

Pet

Damp 14.8

Pet

Damp

North Carolina 13.3 Damp 14.8 Damp 14.7 Damp 13.2 Damp

North Dakota 11.4 Moist 11.3 Moist 13.2 ..do.. 13.6 do.

Ohio 12.9 .. do .. 13.4 Damp 14.0 ..do.. 15.2 Wet

Oklahoma 14.6 Damp 12.6 Moist 13.3 .. do.. 14.3 Damp

Oregon

Coastal

Inland

14.7

11.9

.. do..

Moist

12.4

8.1

..do..

Dry

14.9

9.6

..do..

Dry

18.7

16.0

Wet

do.

Pennsylvania 12.5 .. do.. 12.7 Moist 13.6 Damp 13.3 Damp

Puerto Rico

Windward 14.9 Damp 15.7 Wet 16.0 Wet 16.6 Wet

Rhode Island 12.4 Moist 13.4 Damp 13.6 Damp 12.7 Moist

South Carolina 13.8 Damp 14.6 ..do.. 14.6 .. do .. 13.6 Damp

South Dakota 12.4 Moist 11.7 Moist 11.7 Moist 12.8 Moist

Tennessee 13.3 Damp 13.7 Damp 14.2 Damp 13.8 Damp

Texas

Coastal

Inland

15.1

12.0

Wet

Moist

14.2

10.2

.. do..

Dry

16.1

12.5

Wet

Moist

16.6

12.3

Wet

Moist

Utah 10.1 Dry 7.2 Arid 9.7 Dry 13.9 Damp

Vermont 12.0 Moist 42.7 Moist 14.2 Damp 14.0 da.

Virginia 12.9 Moist 13.9 Damp 14.0 Damp 12.2 Meist

Washington

Coastal

Inland

14.2

11.6

Damp

Moist

13.8

9.6

..do ..

Dry

15.7

12.5

Wet

MoiBt

17.0

17.9

w«t

<tev

West Virginia 11.8 ..do.. 13.5 Damp 12.7 ..a©.. l?.l MQi«t

Wisonsin 13.2 Damp 13.5 ..do.r "14.B **l!äfimp* * i4:r iÖamp

Wyoming 12.1 Moist 9.7 Dry 10.8 Dry 11.5 Moist

* Spring is March, April, and May; summer is June to August; fall is September, October, and November; and

winter is December, January, and February.

® The EMC values were compiled by E. C. Peck of the Forest Products Laboratory from normal temperature

values and 1957-58 relative humidities for geographically distributed cities in each State or area (U.S. Weather

Bureau, Climatological Data, National Summary).

^Arid—8 pet wood EMC and less; dry—8.1 to 11.0 pet wood EMC; moist—11.1 to 13.0 pet wood EMC; damp—

13.1 to 15.0 pet wood EMC; and wet—15.1 pet wood EMC and higher.

19
from average temperature and relative humidity

values supplied by the closest major weather

station.

During the spring months, Arizona is designated arid. The rest of the Southwestern States,

except for Texas and California, fall into the dry

designation. The coastal areas of Texas and

Alaska are designated wet. The remainder of

the country is divided almost equally between

the moist and damp designations.

During the summer months, the States west

of the Mississippi River are much drier than

during the spring months. East of the Mississippi

River, conditions are a trifle damper than in the

spring months. Florida is the only Eastern State

rated wet. During the same season, the Southern

States, Lake States, and the Atlantic coastal

areas are generally designated damp. The Great

Plains States and the Northeast generally fall in

the moist category.

Fall is considerably damper than spring and

summer throughout the whole country. Many of

the Western States shift from arid to dry in fall

while some even change from dry to moist. The

regions rated moist and damp change little

between fall and other seasons.

For the United States as a whole, the weather

is damper during the winter months than in the

fall. No States are arid in winter and only three

States are designated dry. The greatest change

occurs in States west of the Rocky Mountains

and south of the Great Lakes. A considerable

portion of the Pacific Northwest shifts to the

wet designation in winter.

The climate of Alaska is generally wet throughout the year. All parts of that State exceed an

EMC of 15.0 percent, except that the inland

region in the spring and winter has EMC conditions just under 15.0 percent.

The climate of Hawaii is relatively moist overall, but varies widely depending on location in

the State. The hot, humid climate of Puerto Rico

places this island in the wet designation much of

the year despite localized variations.

The potential of a locale for lumber drying or

moisture regain is established by its average

wood EMC values. Rate of moisture change,

however, is influenced by the temperature of the

storage location. Local conditions may shift the

average EMC conditions to some extent. Weather

data published in local newspapers can be used

to determine the local EMC conditions.

I. I. l—l \ I I I I I

15ITTTTTT1

O

EQUILIBRIUM IHOISTUR£ CONTENT OF WOOD

I 1 i I rTTTTTÎ

B

J I L

^ I ^

K K* ^ Vi

§ ^ § ^

M 119 434, M 119 431, M 119 437

Figure 15.—Wood EMC is determined more by relative

humidity, less by temperature. This principle is illustrated for: (A) California's redwood region; (B) the

North Central States; and (C) Colorado, Utah,

Arizona, and New Mexico.

20
CHAPTER 4: TECHNIQUES FOR STORING LUMBER

Between cutting and use, lumber will probably

be stored a number of times: At the sawmill,

during transport, at lumberyards, and at the

construction site. During each of these storage

periods, the goal of. the manager or supervisor

should be to minimize grade and footage losses.

At sawmills, green lumber is stored before

being stacked for air drying or kiln drying, or

before shipment. Softwood sawmills store rough

lumber before finishing in the planer mill. Once

the lumber has been planed it is often stored

indoors, but outdoor storage with protective

packaging is also becoming common.

At hardwood sawmills, green lumber is usually

not stored long before stickering because of the

danger of fungal staining. Air-dry rough hardwood lumber is usually bulk-piled and stored in

open sheds, or outdoors under a protective cover.

Kiln-dry rough hardwood lumber usually awaits

shipment or factory processing in closed sheds.

Green, rough lumber is seldom protected when

transported from sawmill to drying yard. However, dry lumber, whether rough or finished, is

usually protected by tarpaulins during truck

transport, by waterproof paper packaging during

flatcar shipment, or by being loaded into tight

boxcars (fig. 16).

Dry lumber at woodworking plants is most

often stored in sheds, although unit packages of

softwood lumber in waterproof wrap are stored

outdoors for limited periods (fig. 17). Lumber

stored at construction sites is seldom adequately

protected, but should be. By scheduling lumber

shipments the contractor can at least keep the

volume of exposed lumber to a minimum until

the roof of the structure is installed and lumber

storage space in the building becomes available.

Storing Lumber Outdoors

Lumber is often stored outdoors, sometimes

because shed or warehouse facilities are not

available. Unprotected storage outdoors is satisfactory for such lumber items as small timbers

and lumber for less exacting uses, although precautions to prevent stain, decay and insect infestation may be necessary. But kiln-dry lumber

stored outdoors without protection will show a

rapid increase in moisture content. Rain wetting

of any dried lumber is detrimental and tends to

increase the degree of checking.

Protection against rain is more important for

solid-piled lumber than for stickered packages,

because rainwater cannot evaporate readily from

solid piles. Furthermore, rain that penetrates

bulk-piled lumber may in time increase the

moisture content of the wood to a point where

stain and decay fungi can grow. Some rain is

likely to penetrate outdoor piles of lumber despite protecting pile covers. Consequently, extended outdoor storage of dry lumber, especially

in solid piles, is hazardous.

If green or partially dried lumber is to be

stored outdoors for some time, the processes of

Figure 16.—Wide-door boxcar loaded with packages of finished lumber. The sides close completely, minimizing

moisture regain during shipment.

21
M 120 954

Figure 17.—Waterproof kraft-paper wrap being installed on a package of lumber. The wrap does not

cover the package bottom, and thus will not be

damaged by forklift handling.

yarding lumber for air drying are involved and

the recommendations in Agriculture Handbook

407, "The Air Drying of Lumber," apply.

Temporary Protection

Plastic-coated paper wrap for the unit packages of lumber (fig. 17) will adequately protect

kiln-dried softwood lumber under short-term

storage conditions such as the following: Longhaul transport on flatcars; interim storage at

distribution centers; and short-term outdoor

storage, such as at construction sites.

But coated paper wrapping should not be

considered a substitute for storage sheds when

long-term storage of dried lumber is involved.

The wrap can deteriorate during long-term exposure. The fragility of paper wrap must also

be taken into account during handling. At the

least, lumber which is stored outdoors for any

length of time in a protective wrap should be

periodically inspected, and rips in the wrap

taped or otherwise mended.

Dilapidated wrapping that holds rainwater

may increase moisture regain more than if the

lumber had no protection. To avoid such water

retention and to avoid tearing during forklift

handling, the bottom of wrapped packages is

often left uncovered. However, dampness from

ground water can enter such packages if not

enough ground clearance is provided by the pile

foundation. The safe storage period with waterproof wrap will depend on the weather (chapter

3), and upon the rate of wrapper deterioration

due to exposure, mechanical handling, or damage

by birds and animals.

M 144 023-2

Figrure 18.—Single-film polyethylene serves as a tarpaulin to protect dried lumber packages during

short-term storage.

Tarpaulins are often used for protecting bulked

dry lumber temporarily stored outdoors. Waterrepellent-treated canvas, single-film polyethylene

(fig. 18), and laminated polyethylene films

with scrim reinforcing are used as protective

tarpaulins.

Lumber Storage Yards

The outdoor storage yard can be located at

the sawmill, the wholesale or retail lumberyard,

the custom kiln-drying plant, or the woodworking factory. Conventional air drying is often

M 134 963

Figure 19.—Stickered lumber yarded for air drying.

The well-braced pile foundations of stringers and

crossbeams prevent tipping. Most piles are covered

with a prefabricated board and batten roof.

22
practiced at such a yard (fig. 19). Thus the best

location is on high, level ground which is well

drained and not obstructed by trees or buildings.

A yard surface that is smooth and firm, particularly along the alleys, facilitates moving

lumber packages. The yard layout should be

oriented to the prevailing winds to accelerate the

drying of stickered lumber. Vegetation can be

controlled with weed killers. Routine maintenance

should remove debris, which harbors stain and

decay fungi and poses a fire hazard.

An air-drying yard for storing stickered lumber packages is often laid out so that rows of

piles run between main alleys. The rows may be

short or long depending upon the amount of

lumber to be stored in each row. A number of

rows between cross alleys constitutes a lumber

storage block.

A line-type storage yard may be used if a

large amount of lumber is stickered for air drying and accessibility is highly important. With

this type of layout, two lines of pile foundations

are built between two main alleys to accommodate packages of lumber (fig. 20). All piles of

packages are accessible from the main alleys. The

main alleys in both row-type and line-type forklift yards are usually 24 to 30 feet wide. The

cross alleys are often as much as 60 feet wide to

separate the blocks and check the spread of fire.

A lumber storage yard which is completely

paved facilitates lift-truck operation and allows

easier yard rearrangement with changes in

lumber inventory.

The main alleys are oriented in terms of the

yard site available. In a forklift yard of stickered

lumber, particularly a line-type yard, the movement of air through the packages is stimulated

by placing the main alleys parallel to the prevailing winds. Where rainwater evaporation or

snow and ice melt are important considerations,

however, the main alleys are usually oriented

north and south.

Use of Pile Covers

High-grade lumber stored in the yard, whether

solid piled or stickered, should be protected from

the weather. Lumber exposed to alternate wetting

and drying will check, split, warp, and discolor.

Piles of stickered lumber in the storage yard

can be provided with pile covers as in conventional air-drying yards (fig. 19). Pile covers of

various designs and materials are placed on the

pile's top package before lifting that package

into place.

Panel-type pile covers can also be used to roof

stored, solid-stacked packages of rough or

finished dry lumber. The covers must be raintight and project beyond the pile ends and sides

to prevent rain entry into the bulked packages.

Piling Methods

Whether lumber should be solid piled or

stickered depends upon its moisture content,

intended use, and estimated duration of storage.

Lumber with an average moisture content of 20

percent or more which is to be held in storage

Figure 20.-

yard.

M 135 029

-Stickered unit packages of hardwood lumber pijed on permanent foundations in a "line-type" forklift

23
for some time, particularly in warm weather,

should be stickered as for conventional air drying. Such lumber is likely to seriously deteriorate

if held very long in a solid pile. Mold and stain

will develop, followed by decay.

If the moisture content of stored lumber

averages less than 20 percent, mold, stain, and

decay fungi will not grow. The intended use of

this lumber, however, may be such that further

drying is required. If so, stickering for outdoor

storage may effect further drying depending

upon initial moisture content of the lumber and

the prevailing climate.

Kiln-dried lumber will tend to regain moisture

when stored outdoors, particularly during cool,

damp periods. Thus solid piling may be preferable to stickering. But kiln-dry lumber which is

solid piled must be protected from rain.

Pile Foundations

A pile of air-drying lumber requires some type

of foundation to insure ample ground clearance

for good ventilation under the pile. A line-type

forklift yard will have permanent foundations

(figs. 19, 20), whereas a row-type yard can have

either permanent or portable foundations (fig.

21). Foundations should be strong, resistant to

decay, and high enough to provide a clearance of

at least 12 to 18 inches between the lumber and

the ground. More clearance is needed if the yard

is not paved.

In a line-type yard, posts or piers support

stringers of timbers or railroad rails. The

stringers are parallel to the lumber. Crossbeams

placed on the stringers support the lumber

packages.

In a row-type yard, posts on footings support

the stickered packages at the outer sticker tiers.

A removable foundation is used to support the

center of the pile to prevent sagging and permit

forklift entry (fig, 21).

Storing Solid Packages

Unit packages of bulk-piled lumber intended

for forklift truck or carrier handling are often

built with tie strips to keep the edge boards

from falling off. In addition, the unit package is

often strapped at two or more points to make a

compact, rigid-handling parcel. The tie strips

are also used to separate quantities of lumber

within the package.

The tie strips should be vertically alined if a

number of layers are stripped, and should also be

alined with the supporting beams of the pile

foundations or carrier bunks. Packages in the

pile should be separated by bolsters—usually 4

by 4's—alined with the supporting beams.

Sagging is thereby prevented.

The size of the unit-handling package is determined by the weight-carrying capacity of the

lumber-handling equipment being employed.

When forklift trucks are used, the height that

packages can be piled is limited by the reach of

the fork-elevating mechanism, seldom more than

30 feet. Piles higher than this of 4-foot-wide

packages tend to tip over unless tie bolsters are

used. Excessive loading may crush tie strips or

boards in the lower levels of the pile.

Storing Stickered Packages

Stickered packages are seldom strapped because they do not have the stiffness that a solid

package exhibits. A stickered package must be

well supported by a good foundation that has

supporting crossbeams at most of the sticker

tiers. Bolsters between the packages in the pile

should bè in good vertical alinement with the

sticker tiers to effectively restrain warp.

Storing Lumber in Sheds

storage sheds offer lumber the best protection

from weathering, and also eliminate the expense

of making, storing, handling, and maintaining

pile covers. Losses in grade and footage through

outdoor air drying have stimulated an increased

interest in using open sheds for drying. Open

sheds provide permanent roofs, and can also be

used for storing air-dry lumber. Further modification—by closing up open sheds, installing

fans to create air circulation around the stored

lumber, and adding heat—can appreciably lower

the moisture content of stored lumber.

M 98792 F

Figure 21.—Foundations of a row-type forklift yard.

Piers on footings have painted marks to aline lumber

packages. A removable center foundation permits

forklift entry.

24
Open Sheds

An open shed is a roofed lumber storage yard.

All lumber items except those kiln dried to

moisture contents of less than 12 to 14 percent

can be stored in open sheds. The atmospheric

conditions within an open shed are substantially

those found outdoors. If the outdoor air can

circulate through and around stickered padcages,

the lumber will dry to as low a value as it does

in an exposed air-drying pile. The dr3áng period

in an open shed is usually shorter and the lumber

brighter than if stored outdoors because wetting

and rewetting are prevented.

Bulk-piled, kiln-dry lumber will regain moisture with extended storage in an open shed,

although more slowly than if stored unprotected.

Increase will be greatest in the outer tiers of a

solid pile. For example, surfaced boards of 1-by

8-inch kiln-dry Douglas-fir averaged 6.9 percent

moisture content when put in storage at a

western sawmill. Moisture content of the boards

increased by 3.4 percent when stored for 1 year

as a carrier package in an open shed. The two

outer tiers of boards in the five-tier package

increased 3.8 percent in moisture content, the

center tier 2.7 percent (fig. 22).

A shed may be open on all sides or on one side

only (fig. 23). Where unit packages are handled

by forklift truck, access to the shed is provided

by one or two open sides. The rows of piled

packages may run across the shed in bays between the roof supports. Where lumber is handled manually in and out of bins, as at some

retail lumberyards, a driveway between the open

sheds provides access. The roofs of these open

sheds usually extend far enough over the driveway so that trucks can be loaded and unloaded in

rainy weather.

Open sheds at the larger lumber-producing

sawmills are usually paved for forklift trucks

and other carrier vehicles. Cranes operating

within open storage sheds for dry, rough lumber

are generally of the monorail or bridge tjrpe, and

pile foundations are built up on the graded

ground. At small sawmills and retail lumberyards, open sheds are not always paved, although

the roadways may be graded or graveled. Open

storage sheds at wholesale lumberyards and

woodworking factories usually have paved floors

and driveways.

^^ —

/

/-

/

/

OUTER TIER. /

/

A

^^""

/

/

y

y

-/

/

\ISIDE TIER

^ /y

/

^

APR. UAf JME JULY AUG. SEPT. OCT NOV. DEC. MN. FEB. MAR. APR.

M 144 058

Figure 22.—Change in the average moisture content of

surfaced 1- by 8-inch Douglas-fir boards stored as a

carrier package in an open shed.

Closed, IJnheated Sheds

Closed, unheated sheds (fig. 24) are generally

used for storing kiln-dry lumber. The object

during storage is to maintain the percent moisture content attained by the drying process.

Thus, lumber should be solid-piled in closed,

unheated sheds, with only enough tie strips to

stabilize the package or to designate species,

quantities, grades, or items within it.

Kiln-dry lumber stored in an unheated, closed

shed will absorb some moisture, but less than

if it were stored outdoors. For example, 1-inch

southern pine boards in a solid pile went from

71/^ to 10l^ percent average moisture content

during 1 year of storage in a closed shed. Similar

lumber which was solid-piled outdoors for the

same period reached a moisture content of 13i^

percent.

M 142 874

Figure 23.—Open storage shed for packages of dry,

surfaced lumber.

25
100

90

80

70

I

60

50

40

30

20

10

M 135 003

Figure 24.—Closed, unheated storage shed at a distributing yard.

/

tr<r

JÎ

IJ

11

111

Vi 1

4

}

I

/7

8 12 16 20 24

MOISTURE CONTENT (PERCENT)

28

M 144 057

Figure 25.—Range of moisture content in Douglas-ñr

1- by 6-inch boards before and after 1 year of storage

in a closed, unheated storage shed. The lumber was

stored as unit packages 8 tiers wide and 45 layers

high.

Storage in an unheated, closed shed will also

decrease the moisture gradient in stored lumber—that is, the difference between the most

moist and least moist boards in the package. For

example, solid-piled packages of rough 1- by

6-inch kiln-dry clear Douglas-fir boards were

stored in a large, unheated storage shed for 1

year. Curves showing the range of moisture content before and after the storage period are seen

in figure 25. The range in the lumber's moisture

content before storage was about 20 percent ; it

was 13 percent after storage. Although the

range was reduced, the reduction was generally

at the expense of the dry boards in the unit

packages. Ninety-five percent of the boards in

the packages underwent an increase in moisture

content.

The roof and walls of a closed shed absorb

solar radiation and in turn heat the air inside.

The warmed air, however, tends to remain in the

upper parts of the shed. To be effective in lowering the equilibrium moisture content conditions around the stored lumber, the warm air

must be moved downward and circulated by

fans. Forced circulation, even without additional

heating, is beneficial. Forced circulation, together

with an additional source of heat, will convert a

closed, unheated shed to a closed, heated shed.

Closed, unheated sheds for lumber storage

should be floored or paved if the handling equipment operates on the floor surface. If the closed

shed is not paved, it should be located on a high,

26
well-drained site. Sometimes the closed shed will

have an elevated wood-decked tramway and

wood floor if it is built over low ground. In that

case, good ventilation of the space under the floor

is essential.

Large, closed, unheated sheds with overhead

bridge cranes (ñgs. 26, 27) are not floored

except where surface equipment operates to load

railroad cars and tiiicks. The pile foundations in

unpaved sheds should be so designed and constructed that air can circulate freely under the

bottom packages.

At some sawmills, lumberyards, and woodworking factories, limiber is moved in and out

of racks or bins in the unheated, closed sheds.

Aisles or driveways are provided for transporting the lumber to and from the bins, so that it

can be solid piled in the bins without difficulty.

Some items at sawmills and wholesale and retail

yards are placed on end in stalls (fig. 28).

Paving the floor of these stalls assures dry ends.

Closed, unheated sheds beside railroad sidings

often have an elevated floor to facilitate lumber

handling in and out of boxcars. The crawl space

under the elevated floor needs to be well

ventilated.

Closed, Heated Shed»

If the air in a shed is heated, EMC conditions

are lowered. Moisture regain by stored dry

lumber can thereby be prevented (chapter 2).

Closed lumber sheds can be heated to lower

the wood EMC by steam-heating coils, radiators.

M 142 876

Figure 26.—Dry, finished softwood lumber stored as unit packages in a large, unheated shed at a western sawmill.

High, close-spaced stacks are made possible by use of an overhead crane.

27
il^ ^^^-'\

^^^^^^

-!, '■■:>- ^

M 145 873

Figure 27.—Bridge crane servicing a large, unheated

storage shed.

or unit heaters. Gas-fired unit heaters are sometimes installed. It is essential that some air circulation be created by strategically located fans.

The heat supply can be controlled manually or

automatically. Manual control requires frequent

observations of outdoor and indoor wet- and

dry-bulb temperatures so that the relative humidity in the shed can be estimated and valve

settings adjusted accordingly.

Temperature control in closed, heated sheds

is often by a simple thermostat which regulates

either the heater or the heater fan. With changing outdoor temperature and relative humidity,

the thermostat in the storage area needs to be

frequently reset to maintain the desired wood

EMC.

Differential thermostats require less adjustment than simple thermostats in controlling

shed heating. They automatically maintain shed

temperature a fixed number of degrees higher

than the outdoors temperature. Differential

thermostats will maintain an approximate EMC

level without periodic readjustments. They are

inexpensive, and are available from a number of

national suppliers.

Humidistats will initiate heating when the

relative humidity goes above the adjusted set

point, and can control the EMC of lumber accurately enough to seldom need readjustment. For

example, a 7 percent EMC can be maintained in

a closed storage shed over a wide temperature

range if the relative humidity is kept at about

35 percent.

Kiln-dried lumber is often stored in cooling

sheds pending removal for factory processing or

shipment. Cooling sheds may be either open

sheds or closed, unheated sheds (fig. 29). Excessive moisture regain can occur when open cooling

sheds are used for temporary lumber storage.

However, open cooling sheds can be converted

to closed sheds ; if this is done, humidistat control of heated, circulated air is often desirable.

Such humidistat control will maintain low moisture levels indefinitely in kiln-dry lumber.

Closed, heated sheds are seldom insulated

because generally they are heated only 10 or 15

degrees above the temperature of the outside air.

Such a temperature elevation will usually protect

even kiln-dry lumber from moisture regain.

If closed, heated sheds are used for air drying,

the shed should not be so tight that all air

exchange Math the outside is prevented. In that

event, humidity from the drsáng lumber would

M 142 875

Figure 28.—Molding stock stored on end and in bins

at a retail lumberyard.

28
elevate the EMC and defeat the purposes of the

heating.

Storing Plywood

Plywood in storage must be protected from

changes in moisture content. A closed, unheated

shed is fully satisfactory for storing plywood

except for certain times of the year in humid

areas such as the Gulf Coast, where storage in a

closed and heated shed would be better. Plywood

must not be stored outside except for very short

periods unle^ fully protected by a good pile roof

or by complete coverage with a waterproof

wrapper.

Plywood's moisture content is normally below

20 percent, so tiie material is usually stored in

solid packages. Occasionally, however, some plywood may be received that has a moisture content of 20 percent or more. Such material must

be stickered sheet by sheet.

Plywood, especially the thinner sheets, has a

tendency to sag between supports. If the storage

period is quite long, this sag may develop into

permanent deformation. Therefore, plywood

sheets should be stored on a platform foundation

M 105 855

Figure 29.—Stickered lumber undergoing conditioning

in a closed, unheated cooling shed.

(fig. 30). A platform should also be used between

packages in the pile.

OPEN PILING

4 PLYWOOD SHEET LAID

LOOSE ON PLYWOOD BASE

}"PLYWOOD SHEET FOUNDATION

BASE NAILED TO CROSS SUPPORT

FOUNDA TION CROSS SUPPORT

SOLID PILING

'AME AS FOR OPEN PILING

M 118 853

Figure 30.—Plywood correctly piled on a platform foundation. Solid piling is adequate unless plywood is over 20

percent moisture content.

29
When solid piling all thicknesses of plywood,

the spacing of the cross supports must not exceed 2 feet on centers. Stickered packages of

plywood may require closer spacing of cross

supports, depending on the plywood sheet thickness. If the wet pljrwood is less than i^-inch

thick, the maximum spacing of stickers is 18

inches on center for plywood to be open piled.

If the plywood is V2-inch thick or thicker, a

sticker spacing of 2 feet is permissible. All

stickers must be vertically alined so that the

weight of the plywood will be transmitted

directly to the foundation supports. This spacing

prevents deformation of the sheets.

30
CHAPTER 5: TREATING STORED LUMBER

Fungal infection and insect attack both pose

serious hazards to stored lumber. Fungal infection was found to be the principal cause of degrade in a study of grade loss in 1-inch southern

pine lumber. Insect infestation also causes serious losses in stored lumber, particularly in the

warmer parts of the U.S.

For protection from fungi and insects, lumber

may require a dip or spray treatment in a

chemical solution at the storage installation. In

some cases this treatment will supplement an

earlier dip or spray at the sawmill.

To minimize fungal and insect attacks on

stored lumber, air-drying yards should be kept

sanitary and as open as possible to air circulation. Recommended practice includes locating

yards and sheds on well-drained ground.; Remove

debris, which is a source of infection, and

weeds, which reduce air circulation. Piling

methods should permit rapid drying of the lumber and also protect against wetting.

Open sheds should be well maintained with an

ample roof overhang to prevent wetting from

rain. In areas where termites or water-conducting fungi may be troublesome, stock to be held

for long periods should be set on foundations

high enough to be inspected from beneath.

When Is Chemical Treatment

Needed?

Prompt drying will often protect untreated

lumber from attack by stain, decay, and some

insects. For instance, untreated material uni-

^ Mention of chemical treatment in this chapter does

not constitute a specific recommendation. Only those

chemicals registered by the U.S. Environmental Protection Agency may be recommended, and then only for

uses prescribed in the registration, and in the manner

and at the concentration prescrbed. The list of registered chemicals varies from time to time. Prospective

users, therefore, should get current information on

registration status from the Environmental Protection

Agency, Washingon, D.C.

formly below 20 percent moisture content is

immune from attack by fungi. With protective

storage it will keep that immunity. However,

dried lumber which regains moisture to a

level of more than 20 percent again becomes

susceptible to stain and decay.

The sapwood of all wood species is more susceptible than heartwood to decay, stain, or

insects. Therefore, the hazards are highest for

woods which usually contain a high percentage

of sapwood. The heartwood of such species as

redwood, the cedars, and some white oaks has

high natural resistance to fungi and most insects. But few products—even from these

woods—are of heartwood only.

Damp weather can increase the damage from

stain and decay fungi. Rainfall and humid conditions increase the hazard to unprotected wood

in both open and solid piles.

Air temperature is highly important: The

stain and decay fungi grow most rapidly at 70°

to 90° F (21° to 32° C), no more than one-fifth

as rapidly at 50° to 60° F (10° to 16° C), and

cease growth at about 32° F (0° C). As a result,

wood at about 25 to 30 percent moisture content,

stored in solid piles in warm weather, may show

evidences of stain within a week and early decay

infection within a month. The initial infections,

which are not visible, probably started shortly

after the wood was sawed. With temperatures

of 50° to 60° F (10° to 16° C), similar deterioration requires five or more times as long. At 32°

F (0° C) or below, the lumber can remain in

solid piles indefinitely without adverse effects.

High humidity favors subterranean termites,

but does not affect drywood termites or powderpost beetles. The influence of temperature on insect activity, however, is pronounced. Insects are

inactive at temperatures of 50° F (10° C) or

below, but increase their activity rapidly as the

temperature rises about this level. Insects will

approximately double their activity with each

increase of 10° above 50° F, reaching maximum

activity levels at about 80° F (27°C).

31
when and Where Is

Treatment Applied?

Stain and decay in lumber are normally controlled at sawmills, collection points, and drying

yards by drying the wood as rapidly as possible

below 20 percent moisture content. Lumber to

be air-dried may be treated with fungicidal

solution by dip or spray before the drying period

begins. Sometimes an insecticide is mixed into

the solution if insects are likely to be a problem.

The layer of wood chemically protected by a

dip or spray is only "skin deep," and will not

stop fungi or insects that have already entered

the wood. This is why stock is dipped as soon as

possible after it is sawed. To illustrate how

quickly the dipping must be accomplished, the

safe times are estimated as: 1 day with temperatures of 80° F or above; 2 days at 70° F:

1 week at 60° F ; and 1 month at 50° F. Longer

delays at these temperatures progressively lower

the benefit from surface treatments.

Generally, dip or spray treatments immediately after cutting are designed to protect green

stock only when it is drying. If treated green

lumber is not air-dried to below 20 percent moisture content, prolonged storage may require

redipping or respraying of the lumber.

Efficient management of a lumber storage

yard can eliminate situations which encourage

growth of stain or decay fungi in stored lumber.

When lumber is brought to a yard, an estimate

should be made as to how long the storage period

will be. The superintendent, using this estimate,

will be able to prescribe recommended storage

practices. He should also consider the time

needed to ship the lumber to destination points,

for during this time protection is also needed.

Lumber properly dipped in an antistain solution at the sawmill can be stored in solid piles

for up to 1 month in warm weather if further

drying is not required. If longer bulk storage is

anticipated, dip-treated stock should be redipped.

Additional dipping can protect pines and hardwoods from stain and decay for 6 to 8 weeks in

warm weather and western softwoods other than

pines for 4 to 6 months.

If the lumber was not dipped at the sawmill,

dipping at the storage yard may still protect it

from fungi during bulk storage provided the

stock is not already infected. Infection would not

occur if daytime temperatures in the interval

between sawing and receipt at the yard did not

exceed about 40° F (5° C). If temperatures

were higher, however, fungus infection may

have already taken place, and solid piling should

be avoided. Instead, lumber may be dipped in a

fungicidal solution and open-piled.

Because a number of factors affect safe

storage time, all dipped bundles should be labeled

with the date on which they were treated. Representative ones should be opened from time to

time to determine the condition of the stock.

Any lumber that shows signs of being inadequately protected should be designated for early

use, redipped, or stickered for air drying.

Applying Chemical Treatment

Lumber to be dipped at the storage installation

will probably be in unit packages. Thus the

dipping procedures explained here will be for

unit packages. When lumber is dipped, the

amount of solution absorbed will be about 4 to 8

percent of the wood weight, depending on type

of wood and moisture content at the time of

treatment.

Treating Area and Equipment

Location of the treating plant affects the costs

and efficiency of the treating operation. Ready

access of the plant to packaging and storage

areas—and to railroad spurs or shipping docks—

will keep costs to a minimum and insure an

efficient handling operation.

Equipment for treating lumber often includes

an electric hoist that runs on a monorail attached

to the ridge of a long, open shed. The treating

vat can be installed in or above the ground but

should be located in the center of the shed. This

leaves protected areas in both ends of the shed

where untreated packages can be brought in or

the treated packages loaded out. Dead or electrically operated rollers are often used in both

ends of the shed.

The vat should be sufficiently large to admit

the largest unit package to be dipped and should

hold sufficient solution to treat a number of

packages without replenishment. Provision also

should be made for easily adding and removing

the treating solution. A well-designed vat would

32
be about iy2 times the height and width of the

largest package to be dipped and about 3 feet

longer. A drainboard wide enough to accommodate several packages should be provided at the

removal side of the vat to free the hoist for

continuous treating.

Some type of hold-down device, such as weights

or a heavy iron cradle, is required to keep the

packages submerged in the solution. Weights

should be attached to the pallet that supports the

packages, not to the load in such a way as to

compress the packages against the vat bottom.

In fact, the boards should be compressed against

one another as little as possible to allow the

treating solution to penetrate between them.

The vat should be supplied from a mixing

tank of known capacity. This tank will carry

extra treating solution which can be prepared

without interrupting treating operations. Steam

or electrical heating coils would be a desirable

supplement to the mixing tank to insure that

chemicals dissolve rapidly and completely.

Dipping Operation

Packages of lumber should be submerged in

the protective solution for at least 5 minutes,

and for up to 15 minutes if long storage periods

are expected. Packages treated in a waterborne

solution should be turned on edge with the board

faces parallel to the sides of the vat. This can be

done as the packages are placed in the vat. Packages treated with an oil-borne solution need not

be turned entirely on edge during treatment.

However, some means should be provided to tilt

the bundles as they are immersed to let air

escape from the voids and to allow solution to

flow in.

Packages removed from the treating solution

should be drained for a sufficient time to recover

most runoff. A drainage period at least as long

as the treating period usually will be adequate.

Treating for Insect Control

Insects can extensively damage stored lumber

under certain conditions. Treatment may be

needed to control such damage in both dry and

green wood, regardless of the wetness or dryness

of the storage location.

The principal insects that attack stored wood

vary in their need for moisture. Ambrosia or

pin-hole beetles invade green or partially dried

wood, but usually are only a minor hazard in

lumber stored away from forested areas or

sawmills.

Among the most troublesome insects are those

belonging to the powder-post beetle group. These

insects chiefly attack partially dried sapwood and

are particularly damaging to such large-pored

hardwood species as oak, ash, hickory, walnut,

and pecan.

The principal other insect that might attack

stored lumber is the termite. There are two

general types—the subterranean and the drywood termite. Practically all woods are susceptible to their attack. Subterranean termites are

by far the most prevalent type in the United

States. They must have contact with some source

of moisture, almost always the ground. Drywood

termites occur only in limited areas along the

Gulf and Pacific Southwest coasts, particularly

in Florida and southern California. Drywood

termites and powder-post beetles are the only

pests that primarily attack dry wood.

Properly applied treatments which are commercially available generally provide ¡protection

to stored lumber against powder-post beetles

and termites.

It is important to realize that the dip treatments described here apply only to the protection

of the products in storage. Preservation of wood

for use requires different types of solutions and

methods of application.

For wood that might be treated only because

of a subterranean termite hazard, a more efficient

method of protecting the lumber would be to

treat the ground under the storage piles or sheds.

Precautions With Chemicals

All treating solutions should be so handled that

none, or as little as possible, gets on workers'

skin and clothing. In particular, contact of the

skin with the dry chemicals should be avoided.

When lumber dipped in water solutions is to

be painted, sufficient time must be allowed

during storage or before painting to allow the

wood to dry adequately. Only rather short drying

periods will be necessary to remove excess

moisture resulting from treatment with waterborne chemicals because the increase in moisture

content from dipping or spraying will be small.

Residual oil should be cleaned from any dry

hardwood lumber to be painted.

33
CHAPTER 6: AT SAWMILLS—LUMBER HANDLING AND STORAGE

Lumber storage ^varies from total outdoor

exposure at small, portable sawmills to a high

degree of protection under roof at large, permanent sawmills. Procedures will differ according to whether hardwood or softwood lumber is

being sawn, and whether the sawmill uses a

central yard or does its own drying and planing.

The mill's degree of modernization will also

affect procedures.

Softwood Sawmills

Small Sawmills

Portable or semipermanent sawmills producing softwood lumber are usually located near the

source of logs. The rough green lumber is

usually assembled into a unit package for transport to an air-drying yard near the mill site, or

is trucked to a central yarding location. The

solid-piled unit packages of green lumber are

exposed to the weather.

Green lumber at these small mills is seldom

treated with a fungicide, but often should be,

because extended storage in the bulked handling

package increases the hazards of stain development (chapter 5). If the lumber is air dried at

the sawmill, the rough, dry lumber is trucked to

the buyer without protection. If the small sawmill

owner also operates a planer, the finished lumber

should be tarpaulin-protected on the delivery

trucks, but is not so protected in most cases.

Green lumber is often trucked from small

softwood sawmills to a central yard. The lumber

is sorted and stacked at this yard for either air

drying or kiln drying. A sorter is usually used

to segregate thicknesses, widths, lengths, and

sometimes grades. The sorted lumber is usually

built into solid packages and moved by lift truck

to the stacker station. There, the solid packages

are made into stickered packages for drying.

These stickered packages may be placed on piles

in the air-drying yard, or may be stacked on kiln

trucks for drying in track-type dry kilns. The

stickered packages may also be placed in a

package-loaded kiln for drying.

Portable softwood sawmills not delivering

their lumber to a concentration yard either sell

green lumber or air dry the sawed lumber at the

mill location. Mill-run lumber to be air dried is

trucked to a yard site where hand-built airdrying piles are erected. The lumber may be fiat

piled, crib piled, or end piled.

Large Sawm^ills

At large softwood sawmills, lumber moves

through two separate sequences of procedures,

or "processing flows". First, fresh-cut lumber

moves in a series of steps from the saw to

either dry kilns or an air-drying yard. Then the

completely dried lumber moves through another

processing flow to be finished, regraded, packaged, strapped, and stored for shipment as

remanufactured lumber.

Lumber sawn at the larger softwood sawmills

is immediately sorted. The lumber is usually

stacked mechanically for kiln drying soon after

sorting. The kiln truckloads or stickered unit

packages often stand outdoors awaiting kiln

space or the accumulation of a kiln charge.

Degrade from exposure in the upper courses of

such packages or kiln truckloads has justified

the construction of open sheds at many softwood

sawmills. After kiln drying, rough softwood

lumber is usually stored in open cooling sheds

before processing in the planer mills.

Dry, rough lumber to be held for some time is

stored in sheds. Lumber to be processed and

shipped is taken to the planer mill, usually by

lift truck or carrier. Dry, finished lumber is held

in a closed shed.

At large softwood sawmills, green lumber is

transported from sorter to stacker by transfer

chains or transfer-track-type dump buggies.

Conventional green chains may be roofed, but

the pulled lumber is often exposed to the

weather. Edge, drop, and tray sorters are not

usually roofed. Rough, dry lumber is moved

from a dry sorting chain to storage in closed

sheds by lift truck, carrier, or monorail.

34
In softwood operations which are large and

modernized, the rough kiln-dried lumber is

transferred from the unstacker to the planer by

transfer chains. The finished and remanufactured

lumber is regraded, packaged, strapped, and is

then stored in closed, unheated storage sheds.

Kiln-dry rough lumber is usually kept under

roof. However, outdoor areas between the planer

mill and finished lumber sheds are sometimes

used for storing finished lumber as wrapped

carrier packages (fig. 31).

Some of the larger softwood sawmills enclose

the sorting equipment and store stickered kilntruckloads of lumber under cover at the loading

end of the battery of dry kilns. Kiln-dry rough

lumber is sometimes left on sticks and stored in

an open shed until needed in the planer mill.

Most often, however, the rough, dry lumber is

regraded, packaged, and stored in a closed

"rough dry shed."

At the larger softwood sawmills, however, the

trend is toward a reduction in dry, rough lumber inventory Avith an increasing inventory of

finished planer-mill products. The rough dry

shed is being eliminated. The finished lumber is

packaged and strapped to stabilize the package,

and stored in large closed sheds equipped with

bridge cranes. The loading dock for both railroad car and trailer truck loading is part of

these closed sheds.

Hardwood Sawmills

Sawmills cutting hardwood lumber are usually

permanently located and set up. Green lumber at

hardwood sawmills, large and small, is almost

M 142 881

Figure 31.—Wrapped unit packages of dry, finished

softwood lumber stored outdoors at a sawmill. Note

roofs on top of piles to provide additional protection.

M 140 707

Figure 32.—Forklift truck placing stickered package of

hardwood lumber on pile bottom in line-type air-drying

yard.

always handled and stored outdoors. The sawmill and green chain may be under roof, but the

bulk-piled sorted lumber is exposed without protection until transferred either to the air-drying

yard, with or without a pile roof, or to the dry

kiln.

Small Satcmill»

At small hardwood sawmills, the sawed lumber is often sorted into three or four segregations at the back end of the mill. This sorted

lumber is then stacked into unit-handling packages in stalls which are sometimes provided

with sticker guides. The unit packages are

transported from the stacking location to the

air-drying yard by forklift truck and placed on

the pile foundations (fig. 32).

A forklift truck transports the stickered, airdried packages to a station where inspection for

grade and tally is carried on while unstacking.

Air-dried rough hardwood lumber often awaits

shipment outdoors in solid piles or packages

without protection. The air-dried lumber is

usually shipped from the sawmill by truck without protection

The small hardwood sawmill seldom has indoor

storage facilities for air-dried lumber. A small

remanufacturing plant to trim and rip air-dried

hardwood lumber may be located in an open shed,

but lumber storage space is usually quite limited.

35
Large Sawmills

At larger hardwood sawmills, the lumber is

sorted into various classifications on a green

chain (fig. 33). Some lumber items may be

stickered in stalls with sticker guides set up

alongside the green chain. The packages are built

up on kiln trucks and tracks so that the completed package can be rolled out for forklift

truck pickup and transport to the air-drying

yard. When hardwood lumber is to be stacked on

kiln trucks for kiln drjing or air drying (fig.

34), a forklift moves solid-piled packages from

the green chain to the stacker.

At sawmills where the hardwood lumber is

stacked in hand-built piles for air drjáng, the

lumber is solid-piled on dollies or carts at the

green chain and pulled by tractor to the pile

location. At a hardwood mill with dock-type

air-drjdng yards, the bulk-piled sorted lumber on

carts or wagons is tractor-drawn on the elevated

tram to the pile location. All too often, more

concern for protective storage would reduce

degrade in the yarded lumber.

Large hardwood sawmills may have a closed

shed for storing air-dried rough lumber. Lumber

not meeting the requirements of a shipment is

accumulated there until ordered. Hardwood sawmills with dry-kilns will have sheds for cooling

and storing kiln-dried rough lumber awaiting

shipment. Kiln-dried hardwood lumber is not

ordinarily stored for inventory purposes at

hardwood sawmills unless a factory, such as a

flooring plant, is operated in connection with the

M 140 709

Figure 33.—Green chain at a hardwood sawmill. The

graded lumber is bulk piled on dollies that can be

moved out far enough for a forklift truck to pick up

the parcel and transport it to the stacking stalls.

M 142 891

Figure 34.—Green hardwood lumber being air-dried on

kiln trucks.

sawmill. Kiln-dried rough hardwood lumber is

usually kept under cover until loaded into tight

boxcars.

Recommendations

Softwoods

Green lumber.—Treat green lumber with a

fungicide if bulk storage is extended, particularly

during the warmer months (chapter 5). Species

like the white pines must be stacked for drying

soon after sawing to avoid brown stain.

Kiln-dried lumber.—Store dry lumber, both

rough and finished, under cover. Keep shed

access doors closed during off-work periods.

Inspect wrapped packages of finished lumber

stored outdoors for wrapper breaks and tears.

Redry wetted lumber.

Hardwoods

Green lumber.—Stack for air drying or kiln

drying soon after sawing. Treatment with a

fungicide may be necessary during warmer

months to prevent sap stain (chapter 5).

Air-dried lumber.—Store under cover to prevent moisture regain. Covers on outside bulkpiled stock should effectively prevent rainwater

entry. Keep bulked piles off of the ground to

allow ventilation. Air-dried lumber can be stored

in closed sheds, either bulked or on sticks. Keep

shed doors closed when possible.

Kiln-dried lumber.—Store as bulked lumber in

closed, heated sheds.

36
CHAPTER 7: IN TRANSIT—LUMBER HANDLING AND STORAGE

If carelessly shipped, dry lumber can regain

enough moisture to require redrying, and green

lumber can stain or decay. Such waste is totally

unnecessary. With proper transport procedures,

even kiln-dried lumber can cross the United

States—or be shipped to foreign ports—^without

any appreciable loss of quality.

Nationwide, a vast inventory of lumber is in

transit at any one time by railroad, truck, or

ship. Lumber moves from sawmills to locations

of end use either directly or through wholesale

and retail lumberyards. Softwoods are usually

shipped as finished lumber. Hardwoods more

often move from the sawmill to the woodworking plant as rough lumber, although kiln drying

and surfacing in transit may sometimes be

involved. Coastal sawmills ship lumber by oceangoing vessels to domestic and foreign ports.

Present-day lumber shipments are usually

unitized for mechanical handling. The strapped

unit-handling packages are loaded by forklift

into wide-door railroad boxcars, onto flatcars,

and onto trucks. Ocean-going vessels are loaded

by ship gear.

On the eastern seaboard of the United States,

lumber from the Pacific Coast is readily available because of low-cost sea transport via the

Panama Canal. Often green lumber is shipped

by sea because weight is not a major expense in

this tjTDe of shipping. On the other hand, lumber

crossing the United States by rail is usually kiln

dried because rail rates are based on weight.

Railroads place southern and northeastern suppliers in a favorable shipping cost position for

Eastern markets.

Generally, when 1-inch dry softwood lumber

is shipped in tightly closed boxcars (fig. 35), in

enclosed trucks, or in packages with complete

and intact wrappers, average moisture content

changes can generally be held to 0.2 percent per

month or less. In holds of ships, dry material

usually absorbs about 1.5 percent moisture

during normal shipping periods. If green material

is included in the cargo, the moisture regain of

the dry lumber may be doubled. (On deck, the

moisture regain may be as much as 7 percent.

However, dried lumber is seldom stowed on

deck.)

Truck Transport

Changing transportation costs have led to

increased use of trucks for transport of lumber

and wood-based products. Trucks have become a

major means of lumber transport for regional

remanufacture plants, for retail supply from

distribution yards, and for hauls where the distance from primary manufacture to customer is

within about 1,500 miles.

Considerable quantities of air-dried lumber are

shipped by truck from sawmills to factories or

custom kiln-drying plants. Tractor-trailer units

are usually used for this purpose, and in most

instances the trailer is a ñatbed unit that can be

loaded and unloaded by lift truck. The lumber is

anchored to the trailer by chains tightened with

load binders.

Few data are available on moisture changes

during truck shipment. Time in transit is short,

M 144 032

Figure 35.—Dry, finished softwood lumber being loaded

into a tight boxcar. A straddle carrier prepares tc

deliver additional lumber.

37
seldom exceeding a week even on longer hauls,

so little change in lumber's moisture content

would be expected from atmospheric humidity.

However, trucked lumber can be wet by rain or

splashed-up road water.

High value, air-dried lumber is often protected

by covering the load with canvas tarpaulins (fig.

36). Lower grade lumber is seldom protected at

all, especially on short hauls. Some protection is

recommended during truck transport within a

wet or moist climate zone during wet periods.

Precautions should also be taken when a shipment is going to cross several climate or elevation

zones.

Rail Transport

Some years ago both the U.S. Forest Products

Laboratory and the Canadian Western Forest

Products Laboratory studied the changes in

moisture content of softwood lumber shipped in

tight railroad boxcars from West Coast sawmills to Midwestern United States and Eastern

Canadian markets.

The U.S. Forest Products Laboratory studies

involved five boxcar loads of 1-inch clear

Douglas-fir shipped from a West Coast sawmill

to the Chicago, 111., area during late winter and

spring months. The time in rail transit averaged

18.5 days, the shortest period being 14 days and

the longest 22 days. Table 4 shows the average

moisture content at the time of loading and the

change while in transit.

Average moisture content of the five carloads

of kiln-dry boards at the time of loading was 8

percent, and the average gain in moisture content was 0.2 percent. These values are based on

an average of 18 test boards distributed throughout the boxcar load in each shipment. The test

boards were checked for moisture content by the

ovendry method both before loading and when

unloaded. Moisture content changes in the test

boards did not correlate with their position in

the boxcar.

In a different study, test boards in a carload

of Douglas-fir quarter-round and crown molding,

which were at 8 percent moisture content when

loaded, regained 0.8 percent in moisture in a

20-day transit period from the West Coast to

the vicinity of Chicago. Thus, no significant

change in moisture content of dry lumber need

be expected during the usual haul in tight

boxcars.

Table 4.—Gain in lumber moisture content during

U.S. rail shipment

Average Gain in

Carload moisture moisture

shipment Month content when content in

No. shipped loaded transit

Pet Pet

1 January 8 0,2

2 February 8 ,3

3 February 10 ,3

4 March 9 ,1

5 March 7 .8

Average 8 -t-0.2

M 142 893

Figure 36.—Packages of kiln-dried hardwood lumber

on a truck-trailer are covered with a tarpaulin.

The rail shipments studied by the Canadian

Western Forest Products Laboratory involved

19 boxcar loads of softwood lumber with an

average transit time from Vancouver to Montreal or Ottawa of 20 days. The shortest transit

period was 12 days and the longest 25 days.

Shipments were made during each season of the

year. The test boards for each shipment, 18

to 33 in number, were distributed uniformly

throughout the lumber in each boxcar. The

changes in moisture content during these rail

shipments of kiln-dried lumber are presented in

table 5. It was concluded that kiln-dried lumber

will arrive at its destination in eastern Canada

in satisfactory condition.

A study of moisture changes in rail shipments

of kiln-dried hardwood lumber was conducted

by the U.S. Forest Products Laboratory. These

shipments were of kiln-dried pecan lumber,

transported in wide-door boxcars (fig. 37) from

38
Table 5.—Gain in lumber moisture content during

Canadian rail shipment

M 142 879

Figure 37.—Wide-door box car designed for fork truck

handling of packages of kiln-dried lumber. Note

comer irons and ratchet-tj^e load binders.

midsouth Mississippi to a furniture company in

North Carolina, a distance of about 900 miles.

Each load of unitized lumber packages contained

four test boards for moisture analysis. Test shipments were made from June through November,

with the results summarized in table 6.

Changes in moisture content were not considered commercially significant, and the lumber

was moved into furniture production without

additional processing. Since these studies were

conducted, the furniture company has utilized

Species Size

Number

of

shipments

Average moisture

content

Loaded Unloaded Gain

In. Pet Pet Pet

Douglas-fir 1 7 7.4 8.8 1.4

Douglas-fir 2 4 9.7 10.6 .8

Western hemlock 1 4 8.6 9.4 .8

Sitka spruce 1 4 7.8 8.2 .9

roller-bed boxcars for these shipments of kilndried pecan lumber (fig. 38).

Some shippers use "chain" flatcars for lumber

shipments (fig. 39). These ñatcars are loaded

with unit packages of bulked lumber by lift

truck. When the carload is in place, it is anchored

or bound to the car by chains thrown over the

load and tightened with ratchet load binders.

These chain cars may or may not have bulkheads

at the flatcar ends.

M 144 081

Figure 38.—Roller beds of another wide-door boxcar are shown in action. After the center of the car has been

unloaded, a truck draws a roller bed of lumber out of the car end, using a cable that passes through a pulley in

the left section of the car.

39
Table 6.—Gain in moisture content of

rail-shipped pecan lumber

Month of

shipment

Moisture content

At point

of shipment

At point

of receipt Gain

Pet Pet Pet

June 6.6 6.66 0.41

July 6.23 6.38 .16

August 6.23 6.21 -.02

September 5.59 6.05 .46

October 6.24 6.63 .29

November 6.29 6.71 .42

Air-dried hardwoods are often unitized and

shipped on chain flatcars without protection.

These cars move to woodworking plants where

the stock is kiln dried. Air-dried hardwood lumber is often shipped on chain cars to custom

kiln-drying plants. Gondola cars are also sometimes used for bulk-shipping lumber.

Conventional flatcars have become more widely

used for the transport of dried lumber because

of several advantages. Improvements in unitized

package wrapping have made it possible to

obtain these advantages without much increase

ïj|gy<^^ .^^ÊÊ1^>«aiH .JÉÊI^n' í-k^i^^^' MH ^ ' W^^^9'^Ê í ; :|||ÄJ WBS^ »»«'* '**

5" ;. ;£ **'SMSS%ä^^

" S ' ■■■"" J¿'S» -*«»» SiSim . -^^HB

• ' 2 W~ "r « .^•«■■tl.^ii^ ^-

1 %

- - ' '—:'" '*'^'*'"-^31-'1J¿XÍ'^^JJ¡ÍL

m

J^M

M 135 004

Figure 39.—Strapped unit packages of air-dried hardwood lumber loaded on a bulkhead chain car.

of moisture content, even on long hauls. Flatcars

can save handling time and shipping cost. The

load of lumber per flatcar may be twice that per

conventional boxcar. Flatcars tend to offer lower

per-unit freight rates and can be loaded by lift

trucks to save handling time.

Unitized packages on flatcars are usually protected, either partially by tarpauUns or entirely

by flexible, waterproof packaging which completely "tailor-wraps" each package. One common

type of waterproof packaging uses composite

kraft paper that is glassfiber-reinforced and

polymer-coated (fig. 40). The packaging is frequently supplied with additional reinforcement

at stress points such as edges and corners.

Improvements in packaging materials have

made possible the shipment of kiln-dry lumber

with little change in moisture content and a

good retention of brightness by the boards.

Wrapping for unitized packages of lumber

should be free from rips to be effective. Rain

which enters the rips is held by the sheeting and

the package may act as a humidifier. If so,

moisture regain may be higher than if the

lumber were unprotected (chapter 3).

Ship Transport

Lumber transported from the United States

by ship falls into one of two categories: (1)

Pacific Coast softwood lumber, usually green,

destined for the U.S. Eastern Seaboard States;

(2) dried, finished lumber for foreign ports.

Green lumber is often stored on deck, exposed

to the weather; seasoned lumber is usually

stowed below decks in ship holds, either by itself

or together with green lumber.

A study conducted in Canada involved 33

shipments of lumber from the Canadian west

coast to five different ports. The study concluded

that seasoned lumber stored below decks, either

by itself or together with green lumber, will not

undergo moisture regain of serious proportions.

This study indicates that well-dried lumber

may undergo significant moisture regain if

stored on deck, although it is not commonly so

stored.

Each test shipment consisted of one or more

strapped unit packages containing 48 end-coated,

4-foot sample boards. Moisture content and

weight of each board in the package were determined when the test packages were assembled.

Douglas-fir and western hemlock were used in

40
CUSHION OF CREPED

KRAFT PAPER

CREPED CUSHION

-PLASTIC COATED

KRAFT PAPER

M 143 905

Figure 40.—Details of one type of plasticized kraft-paper wrapping. This reinforced wrap protects utilized packages

of lumber during shipment on railroad flatcars and beds of open trailer trucks.

the tests. The test packages were stored in the

ships' holds or below decks with commercial

shipments of dry or green lumber. Test packages

of kiln-dried lumber were stowed on deck with

green lumber in ocean shipments to South Africa

and Montreal, Canada.

Upon arrival at the port of destination, the

individual boards making up the test packages

were weighed and their moisture content determined. The moisture gains for the various

shipments are presented in table 7.

Stowage of 1-inch kiln-dried lumber together

with green lumber below decks resulted in almost

twice the overall gain in moisture content as

compared with dry lumber stowed alone. But

even when green and dry were stored together,

moisture regain in the dry lumber was not

enough to seriously impair lumber quality.

Kiln-dried lumber stowed on deck, even though

protected from direct contact with the weather,

regained almost four times more moisture than

did dry lumber stowed with other dry lumber

below decks. However, on-deck storage of kilndried lumber is not a common practice.

Similar tests were made with 2-inch instead

of 1-inch Douglas-fir lumber. The 2-inch kilndried lumber had a moisture content of 9 to 10

percent when stowed. Shipments were to the

41
same ports as with the 1-inch lumber, except not

to Trinidad. The overall average moisture gains

for these shipments of 2-inch lumber were as

follows :

Stowed below decks with dry lumber 1.3 percent

Stowed below decks with green lumber-_2.4 percent

Stowed on deck with green lumber 4.2 percent

The average moisture content of this 2-inch

lumber at the time the test packages were loaded

was slightly higher than the 1-inch lumber, and

the moisture regain somewhat less. The moisture

increase for 2-inch kiln-dried lumber stowed

with green lumber below decks and on deck is

about the same as for the 1-inch kiln-dried

lumber.

The Canadian Laboratory concluded that when

well-dried lumber was stowed below decks the

lumber would arrive at its port of destination at

a satisfactory moisture content. The data indicate the advantage of stowing dry lumber

separate from green lumber below decks.

No data are available on moisture content

changes in present-day ocean shipments of

unitized dry lumber.

Recommendations

Softwoods

1. Green lumber is unitized and shipped,

sometimes without protection, by truck, railway

flatcar, or ocean-going vessels. Extended transit

time may result in degrade from mold, stain,

and decay fungi, especially during warm

weather. Green lumber may need to be treated

with a fungicide before shipping during the

warmer months (chapter 5).

2. Dry, finished lumber should be shipped in

tight boxcars, as wrapped unit packages on

flatcars, or below decks in ships. Protection may

not be necessary during short truck hauls during

dry weather; otherwise, tarpaulin coverage

should be used.

Hardwoods

1. Green lumber shipments can be made

without protection when the transit periods are

short. The lumber should be air dried prior to

long periods of rail, truck, and ship transport.

2. Air-dried lumber can generally be shipped

by truck, rail, or ocean-going vessel without

protection.

3. Kiln-dried lumber requires protection

during transit. Use tight boxcars or package

wrappers for rail shipments. Use watertight

tarpaulins on open truck shipments. Stow below

decks on vessels.

Table 7.—Average gain in lumber ^ moisture content during ocean shipment

Number of

shipments

Shipment

destinations

Time in

transit

Lumber moisture content increase

Stowed with dry

lumber below decks

Stowed with green

lumber below decks

Stowed on deck

with green lumber

Days Pet Pet Pet

11 England 54 2.9 4.7 —

10 Australia 66 1.7 3.2 —

6 South Africa 85 2.2 1.8 7.6

3 Eastern Canada 47 .7 3.7 6.5

3 Trinidad 37 1.7 3.2 —

Average _ 1.9 3.3 7.1

' 1-in. kiln-dried Douglas-fir.

42
CHAPTER 8: AT LUMBER DISTRIBUTING

YARDS—HANDLING AND STORAGE

Lumber distributing yards may be either

wholesale or retail. Handling systems at these

yards will depend upon the volume of lumber

being stored and the quantity moving in and out

of the yard.

At the larger distributing yards, lift trucks,

including side loaders and end loaders (fig. 41),

are used for unit-package handling. Incoming

boxcar shipments of loose dry lumber are usually

unitized when unloaded for yarding. The unitized

packages are often stored outdoors briefly,

without protection (fig. 42) ; extended storage

is often in open or closed sheds (fig. 43). Lumber

on incoming railroad chain cars, flatcars, and

gondola cars is usually unitized for forklift truck

or crane unloading. Shipments to the larger

distributing yards in open-top trucks are often

strapped packages that can be unloaded by

forklift.

Straddle carriers (fig. 44) may be used in the

larger yards where haul distances justify the use

of these more rapid transport vehicles. Larger

distribution yards are usually wholesale operations which ship to woodworking plants, retail

lumberyards, or construction sites. Their shipments are usually unitized. Shipping is by truck,

both enclosed and open-bed.

At the smaller distributing yards, lumber is

unloaded from boxcars onto trucks and moved

to open or closed sheds where the lumber is piled

in bins. Facilities for unit-package handling are

not often available. Shipments out of these

smaller yards, usually retail operations, are

often on a job-lot basis. Thus the inventory of

any one lumber item is relatively small. Hauls to

a building site are usually by open truck without

protection. If such shipments will be exposed

outdoors upon delivery, some sort of temporary

protection, as a sheet wrapping, is recommended

(chapter 10).

Outdoor Storage

Lumber is often stored outdoors if shed or

warehouse space is not available (fig. 45).

Unprotected outdoor storage is satisfactory,

although not ideal, for such lumber items as

timbers and lumber to be used for less exacting

requirements. However, kiln-dried lumber should

not be stored outdoors unprotected. Such lumber,

even if protected from rain by a cover, will

dampen excessively for interior uses when

stored outdoors for long periods in most parts of

the United States. If the storage period is to be

brief, piled packages of dry, solid-stacked lumber

are often protected by canvas or plastic tarpaulins. Strapped packages of lumber wrapped

with waterproof paper are often stored outdoors

without additional protection.

Outdoor storage may become an air-drying

process if incoming lumber in a green or only

partially dried condition is stickered rather than

bulk piled. Whether lumber yarded outdoors

should be bulk piled or stickered for further drying depends upon the lumber's moisture content

and intended use. Lumber at a moisture content of

20 percent or more that is to be held for some

time, particularly in warm weather, should be

stickered for additional air drying. Piles of

stickered packages should be roofed to keep

moisture regain during rainy weather to a

minimum (chapter 4).

Solid-piled green lumber is likely to deteriorate

if held for an extended time. Stain and mold will

develop first, followed by decay. Dry lumber in

43
M 142 894

Figure 42.—Packages of dry, finished softwood lumber

are piled in a staggered manner for pick-up by an

end loader.

M 142 883

Figure 43.—Strapped unit packages of lumber stored

in a closed shed at a wholesale distributing yard.

M 144 217

Figure 41.—The end loader, or end picker, is equipped

with a hydraulic clamping device (A) for grasping

the ends of lumber parcels (B). The lumber can then

be easily transported (C).

M 144 221

Figure 44.—Straddle carrier transporting a bulk package of finished lumber. These carriers can move

lumber more rapidly than forkloaders or endloaders

can.

44
solid packages, if not protected from wetting by

wrappings or pile roofs, will take on excessive

moisture with extended storage.

Indoor Storage

All dry lumber items can be protected in the

three types of shed detailed in chapter 4: (1)

open sheds, (2) closed, unheated sheds, and

(3) closed, heated sheds.

Open Sheds

An open shed at a distribution yard provides

a permanent roof over the stored lumber (flg.

46). The atmospheric conditions within the open

shed are the same as outdoors, and provide

equilibrium conditions for air-dried lumber.

Stickered packages can be stored in open sheds

for further air drying.

The shed may be open on all sides or on one

side only. The lumber is piled and unpiled from

the open sides. At the larger distributing yards,

forklift trucks are used to handle packages of

lumber placed in rows of piles across the shed.

Certain grades and sizes of lumber are often

hand-stacked in bins set up in the bays (fig. 47).

Lumber kiln dried to moisture content levels of

10 percent or less is not often stored in open

sheds unless the storage period is expected to be

short.

M 142 897

Figure 46.—Outdoor storage of dry, finished softwood

lumber. Note the use of pile roofs to provide some

protection from rain and sun.

Closed, Unheated Sheds

Closed sheds are used primarily for the storage

of well-dried lumber items. The object of this

type of indoor storage is to prevent excessive

regain of moisture by the dry stock. The lumber

is solid piled (fig. 48).

At the larger distributing yards, unit packages

are handled with forklift trucks. Blocks of

packages of similar lumber items are built up

for ready accessibility. The shed is often paved.

Patterned and specialty grades of lumber may

be hand-stacked in bins from a central aisle or

roadway (fig. 49). Moldings of various sizes and

I

M 136 779-5

Figure 46.—Strapped packages of lumber in an open shed. The lift truck can operate from both sides of the center

posts.

45
patterns which have been bundled and wrapped

at the producing mill are often stored upright at

the distributing yard (fig. 50).

Kiln-dried lumber stored in an unheated,

closed shed will absorb some moisture because

the wood's average moisture content is usually

lower than the prevailing wood equilibrium

moisture content (EMC) in the shed. The lumber tends to come to equilibrium with the higher

EMC conditions, with the outer parts of the piles

gaining moisture the most rapidly (chapter 2).

The temperature inside of the closed, unheated

shed will be somewhat higher than outdoors

because of heat radiating from a roof warmed

M 136 780-12

Figure 47.—Storage of lumber in bins in an open shed.

by solar radiation. The increased shed temperature will lower the average or effective EMC

conditions to some extent.

Closed, Heated Sheds

EMC conditions in a closed shed can be lowered

by heating the air being circulated in the building. A closed shed can be heated with steamheating coils, steam radiators, steam unit heaters,

or gas-fired unit heaters. The heated air should

be circulated around the stored lumber continuously. Unit-heater operation is often thermostatically controlled by on-and-oif operation of the

unit-heater fan. But a better procedure is to

attain full-time fan operation by using an automatic valve on the steam or gas line. This valve

is controlled by the thermostat or humidistat.

Then, with changing outdor temperature and

relative humidity the indoor shed temperature is

automatically set to maintain the desired EMC

condition.

M 144 021

Figure 48.—Packages oí dried, finished lumber being

stored in a closed, unheated shed.

Recommendations

Softtcoods

1. Green lumber can be stored outdoors without protection in cool weather, provided that the

storage periods are not extended. In warm

weather, the risk of fungal stain, decay, or insect

infestation makes prompt stickering, and perhaps chemical treatment, advisable before storage (chapter 5).

2. Dry lumber requires protection from

weathering and moisture regain. Wrapped packages stored outdoors need to be inspected for

M 142 882

Figure 49.—Storage of dry lumber in bins in a closed,

unheated shed.

46
wrapper deterioration ; torn wrappers should be

repaired or the package quickly moved under

roof. Open or closed shed storage offers the best

protection.

Hardwoods

1. Green or partially dried rough lumber

should be stickered and stacked for air drying.

High value lumber should be air dried in an open

shed.

2. Air-dried lumber when bulked requires

protection from weathering and moisture regain. Outdoor storage requires suitable raintight

cover and some elevation off the ground. Storage

in open sheds is ideal.

3. Kiln-dried lumber should be bulk piled and

stored in a closed shed. Heated storage is

advantageous.

M 136 780-11

Figure 50.—Wrapped bundles of molding stored upright

in segregated stalls.

47
CHAPTER 9: AT WOODWORKING FACTORIESLUMBER HANDLING AND STORAGE

Woodworking factories buy lumber either

directly from sawmills or from wholesale distributing yards. Green, partially air-dried, airdried, and kiln-dried lumber—all is delivered to

such plants. The storage conditions at the plant

are adjusted to further dry the lumber if necessary, or to prevent moisture changes. Lumber is

stored both outdoors and in sheds. In many

instances, the lumber is kiln dried at the factory.

If so, cooling sheds and indoor storage rooms are

often used to store the lumber before use.

Storage Facilities

Green lumber often arrives at a woodworking

factory as solid packages (fig. 51) which are

then stickered for drying. Slower drying hardwoods like oak are built into unit packages for

drying in a conventional air-drying yard or in

specially built open sheds (fig. 52). However,

some woodworking plants air dry hardwoods

such as oak on kiln trucks prior to kiln drying

(fig. 53). The faster drying hardwoods are

usually stickered for kiln drying while green,

although the thicker sizes may require air drjang

first. Green softwoods are stickered for immediate kiln drying.

Some woodworking factories do not have dry

kiln equipment, but employ the facilities of custom kiln-drying operations. Lumber shipments

are kiln dried and often surfaced at the custom

kiln-drying plant while enroute from the sawmill

to the factory.

M 142 900

Figure 52.—Air-drying sheds at a furniture factory.

M 136 715-10

Figure 51.—Temporary outdoor storage of green hardwood lumber at a furniture factory.

M 142 913

Figure 53.—Stickered hardwood lumber air drying on

kiln trucks prior to kiln drying.

48
Air-drying yards at woodworking factories

should be located at sites favoring good drying.

Such yards should be laid out to facilitate lumber

handling. The alleys or roadways are often paved

and the pile foundations permanent, particularly

in line-type yards. Pile covers should be used.

Yarding is usually done with forklift trucks

because most woodworking factories have converted their air-drying yards from hand-built

piles to unit-package handling.

Partially air-dried lumber, either softwood or

hardwood, is usually stickered for kiln drying.

Stickered unit packages are sometimes stored

outdoors without protective cover before loading

into a package-loaded dry kiln, or are placed on

kiln trucks for drying in a track-type dry kiln.

Kiln-truckloads of green, partically air-dried, or

well air-dried lumber are sometimes stored in a

"green" end storage shed of a dry-kiln installation

before loading into the dry kiln. Such storage

under roof protects high value lumber.

If kiln-dried lumber must be stored outdoors,

it should be bulk piled well off the ground on

supporting foundations. Sheet plastic covers on

these piles will cut down moisture regain. If the

storage period is extended, redrying may be

necessary, requiring that the lumber be stickered.

Unit packages of softwood lumber, kiln dried

and wrapped, are often stored outdoors at millwork factories (fig. 54). The storage period is

usually brief. In extended outdoor storage, the

wrappers on kiln-dried packages of lumber

should be periodically inspected and repaired

(chapter 4). Extended exposure of unit packages

with damaged wrappers can increase losses due

to stain and decay.

Open Sheds

Lumber stored in an open shed is protected

from weathering. The shed roof shields the

lumber from exposure to direct sunshine and

rain. Green and partially air-dried lumber can

be stickered, placed in the open shed, and dried.

Well air-dried lumber can be bulk piled and

stored in an open shed. The range of moisture

content in the package may be reduced with

duration of storage if at the time of bulk piling

the range was fairly high.

Kiln-dried lumber is sometimes stored in open

sheds at woodworking plants with the realization that moisture regain will take place. The

storage period must be reasonably short if redrying is not planned. Waterproof paper wrapin 144 022

Figure 54.—Wrapped unit packages of kiln-dried

finished softwood lumber stored outdoors at a millwork factory.

ping will retard moisture regain during shortterm storage of kiln-dried lumber in open sheds.

At many woodworking factories, cooling sheds

to relieve stresses in lumber after kiln drying

are essentially open sheds. Stickered kiln-charges

of lumber should not be left long in such

sheds, or moisture regain may become so great

that the limiber cannot meet manufacturers'

requirements.

Closed, Unheated Sheds

The open shed provides protection from sun

and rain, but the closed shed, in addition, protects the lumber from winds. Thus, the closed,

unheated shed is not suited to air drying. Well

air-dried stock is bulk piled for storage in these

sheds. The range in moisture content will be

reduced with extended storage. Kiln-dried lumber is stored in closed, unheated sheds ^with the

expectation that some moisture regain will take

place, but less rapidly than in an open shed.

Reduced air circulation and some heating of the

shed by solar radiation help to keep the lumber's

moisture regain low.

Many dry-kiln cooling sheds at woodworking

factories (fig. -55) can be classified as closed,

unheated storage sheds. The access doors, however, must be kept closed most of the time or

they are essentially open sheds. Warming by

both solar radiation and heat from the dry kilns

can reduce the wood EMC conditions in the

cooling shed. Stickered lumber can be stored

there for some time without excessive moisture

regain.

49
Kiln-dried lumber in closed, unheated sheds

requires bulk piling during extended storage to

keep moisture regain limited. Redrying may

become necessary to reduce the moisture gradient

within and between boards of the lot when the

duration of storage in the closed, unheated shed

is greatly extended.

Closed, Heated Sheds

Cooling sheds for kiln-dried lumber at woodworking factories are sometimes heated during

cool, damp weather — generally during the

winter—to keep the lumber EMC low (fig. 56).

However, heating of such sheds is seldom

thermostatically controlled, and all heat is turned

off during the summer months.

Some woodworking plants include heated

storage rooms where lumber is held until needed

in the rough mill. Heat in these rooms is often

regulated by thermostat, but is turned off during

the summer. Such rooms are not used for drying

lumber.

Handling Equipment

Factories using track-type dry kilns arrange

the plant layout so that the stickered kiln truckloads of lumber can be transferred and moved

into the rough mill. Here the loads are usually

placed on a lumber lift. As the layers are removed by the cutoff sawyers, stickers are removed by hand and turned to the lumberstacking area by conveyor. Stickers may also be

placed in staked dollies, trucks, or pallets for

transfer to the stackers.

-i-SS.«*är^

M 142 I

At some factories, forklift trucks serve an

air-drying or storage yard (fig. 57), serve

package-loaded dry kilns, or load kiln trucks for

track-type kilns. At such factories the stickered

packages are placed on a roller or chain conveyor feeding a breakdown hoist. The lumber

slides off onto a conveyor feeding the sawyers

in a rough mill. The stickers are conveyed to

the stackers or into a bin pallet. A modification

of the system is to unstack the packages at an

unstacker station and perhaps do some sorting.

Then the bulked packages of dry lumber are

moved by conveyor or lift truck to the rough

mill or the cutup department of the factory.

Recommendations

Softwoods

1. Green lumber must be stickered for drying

if deterioration due to stain and decay is to be

avoided.

B

Figure 55.—Kiln-dried lumber stored in a cooling shed

on kiln trucks. The doors at the two ends of the

transfer track are usually closed.

M 136 715-9, M 136 715-6

Figure 56.—Kiln-dried lumber stored in a heated shed

at a furniture factory. A. Sliding doors provide

access for lift trucks with packages of lumber. B.

Kiln-dried lumber on stickers stored in an insulated,

heated storage shed. Note the unit heater in the

shed's upper right-hand comer.

50
2. Partially dry lumber can be bulked and

stored in an open shed if its moisture content is

less than 20 percent. If the moisture content is

above 20 percent, either sticker for additional

drying or plan immediate use, particularly in

summer months.

3. Kiln-dried lumber should be bulk piled and

stored in a heated shed. Wrapping unit packages

with waterproof paper and storing outdoors is

satisfactory for temporary storage. Repair torn

wrappers.

Hardwoods

1. Green lumber must be stickered for drying.

If the stickered units are air dried outdoors, pile

covers on high-value lumber are inexpensive.

Storage of stickered lumber in an open shed

gives better protection than with pile covers.

2. Air-dried lumber can be bulked and stored

in an open shed. If the lumber exceeds 20 percent moisture content, stickering and further

drying in a conventional air-drying yard or in

an open shed is beneficial.

3. Kiln-dried lumber should be stored in a

heated cooling shed if the stock is left on sticks

pending transport to the rough mill or cutup

M 143 998

Figure 57.—Forklift truck removes a wrapped package

of lumber to be used at a manufacturing facility.

plant. If the stock is bulked for storage outdoors,

protection from weather is essential and the

storage period must be limited. Bulked indoor

storage should be in an EMC-controUed storage

shed.

51
CHAPTER 10: AT BUILDING SITES—LUMBER

HANDLING AND STORAGE

Lumber is not often protected from the

weather at construction sites, although in many

instances it should be. Lumber is commonly

placed on the ground in open areas near the

building site as bulked and strapped packages

(fig. 58). Supports under such packages are

useful to prevent wetting from mud and ground

water. At large construction locations, such as

apartment buildings, office buildings, and condominiums, the strapped unit packages are delivered to the area on roller bed trucks and

rolled off onto the ground (fig. 59). Sometimes

these packages are still wrapped with waterproof paper. However, protection is lost if

wrappers are torn.

Hazards From Moisture Regain

Prefabricated building parts such as roof

trusses are sometimes dumped on the ground at

the building site and left lying unprotected (fig.

60). In warm, rainy weather, moisture regain

can result in fungal staining. Wetting of the

lumber also results in swelling. Subsequent

shrinkage of the framing may contribute to

structural distortions. Extended storage of lumber over about 20 percent moisture content

without drying can allow decay to develop.

M 142 919

Figure 68.—Strapped packages of lumber at a construction site. Supports under the packages prevent

ground contact.

jt»* ffimJ0^

M 142 918, M 142 915, M 142 871

Figure 59.—Construction lumber stored at a building

site. A. Strapped unit packages of studs are stored

near the building being constructed. No protection is

provided against rain, and little protection from

ground mud. B. Unit package of studs being broken

down and pieces selected for wall framing. C. Joists

being cut for installation.

52
A partially erected building is often exposed

to rains that wet the framing and subflooring

during the construction period (fig. 61). The

effect is not serious because the surface-wetted

wood is dried by the sun and warm winds. However, if such wetting is frequent due to construction delays before the building's roof and

siding are in place, water-repellent treatment to

protect the framing and other exposed wood is

beneficial. The water repellent effectively reduces the amount of water absorbed by the

wood.

Minimizing The Risks

At small home building sites, the contractor

often has most of the building materials delivered after the foundation is completed. These

deliveries often include millwork, such as window

and door frames, for which swelling or warp

can be critical. Such a delivery schedule may be

far from ideal in many instances.

M 142 878

Figure 61.—Partially completed house. Framing' and

subflooring are exposed to rain. Delivered materials

have been placed on supports to keep them from

contacting the mud.

M 142 920, M 142 8S8

Figure 60.—Storage of prefabricated roof trusses at a

residential building site. A. Strapped unit of roof

trusses placed directly on ground. B. Partially constructed home having ample storage space for roof

trusses. Here the problem is the lack of handling

equipment to lift and move the heavy packages of

roof trusses into the basement area.

So far as possible, deliveries of materials

should be arranged to minimize onsite storage

time. Delivery of millwork, for instance, might

be deferred until the partly completed building

offers a source of protection. Once the materials

have been delivered construction should proceed

rapidly. As soon as the house is completed,

exterior surfaces should be primed with paint.

When weather is bad, such as during winter

in the northern sections of the country, some

protection is afforded by plastic sheeting (fig. 62).

M 142 896

Figure 62.—Prefabricated panels and framing lumber

stored at a building site in winter. Plastic tarpaulins

are used to provide some protection from snow.

58
Recommendations

The following recommendations, if followed,

should help minimize lumber deterioration at the

building site:

(1) Do not unload the lumber in the rain if

possible. Delivery by the distributor may need

to be delayed.

(2) Try to avoid unloading lumber directly

onto the ground. Delivery of unit packages of

lumber by roller bed trucks may result in the

packages being dumped onto the ground. If the

construction project is large enough to warrant

use of a lift truck, have stringers laid on the

ground to support the packages of lumber.

(3) Protect millwork from the weather and

from damage such as glass breakage.

(4) Schedule deliveries to keep exposedstorage times as short as possible.

54
ADDITIONAL INFORMATION

American Society-for Testing and Materials

1965. Standard methods of test for moisture

content of wood. ASTM D 2016-65. Philadelphia, Pa.

Brown, N. C, and J. S. Bethel

1958. Lumber—The stages of manufacture

from sawmill to consumer. Ed. 2, John

Wiley and Sons, N.Y.

Brown, W. H.

1970. Keeping it dry! One of the problems

with kiln-dried lumber. Woodwork. Ind.

27(3), p. 27-28.

Canadian Department of Resources and

Development

1952. Moisture content changes in seasoned

lumber in storage and in transit. Forest

Branch Bull. No. 102. Ottawa.

Cech, M. Y.

1966. New treatment to prevent brown stain

in white pine. Forest Prod. J. 16(1) : 23-27.

Clark, Joe W.

1957. Comparative decay resistance of some

common pines, hemlock, spruce, and true fir.

Forest Sei. 3(4) :314-320.

Comstock, G.L.

1966. Dimensional changes in kiln-dried softwood lumber after surfacing and during

storage. U.S. Forest Serv. Res. Note

FPL-0144, Forest Prod. Lab., Madison,

Wis.

Cuppett, D. G.

1965. How to determine seasoning degrade

losses in sawmill lumber yards. U.S. Forest

Serv., Res. Note NE-32. Northeast. Forest

Exp. Stn., Upper Darby, Pa.

Gill, T. G., D. V. Robertson, and R. J. Miller

1956. Handbook for the preservative treatment of packaged lumber and fabricated

wood products for long-term storage. Timber Eng. Co., Washington, D.C.

Glesne, N.

1959. Small sawmill lumber handling. Forest

Prod. J. 9(7): 9A-10A.

Hickman, L.

n.d. Protection of lumber for exterior storage. Western Pine Assoc. Res. Note 6.711.

Portland, Oreg.

Host, John R.

1969. Economics of producing and handling

packaged lumber. U.S. Forest Serv. Res.

Pap. INT-66. Forest and Range Exp. Stn.,

Ogden, Utah.

Hunt, George M. and George A. Garratt

1967. Wood Preservation. Ed. 3. McGrawHill, N.Y.

James, William L.

1975. Electric moisture meters for wood.

USDA Forest Serv. Gen. Tech. Rep. FPL-6.

Forest Prod. Lab., Madison, Wis.

Little, Elbert L., Jr.

1953. Check list of native and naturalized trees of the United States (including

Alaska). U.S. Dep. Agrie, Agrie. Handb.

41, 472 pp. Washington, D.C.

McMillen, John M.

1961. Coatings for the prevention of end

checks in logs and lumber. U.S. Forest Prod.

Lab. Rep. 1435.

McMillen, John M.

1963. Stresses in wood during drying. U.S.

Forest Prod. Lab. Rep. 1652.

Panshin, Alexis J., and Carl DeZeeuw

1970. Textbook of wood technology. Vol. 1,

Ed. 3. McGraw-Hill, N.Y.

Rector, Ray M.

1972. Dry storage operations. S. Lumberman

224(2782) p. 21.

Rice, W. W.

1964. Learn profitable lumber stacking.

Hitchcock's Woodworking Dig. 66 (2) :

44-46.

Rietz, Raymond C, and Rufus H. Page

1971. Air drying of lumber: A guide to

industry practices. U.S. Dep. Agrie, Agrie.

Handb. 402. 110 pp.

55
U.S. Department of Commerce

1970. American softwood lumber standard.

National Business Standard. Voluntary

Product Stand. PS 20-70. 26 pp. Washington, D.C.

U.S. Department of Defense

1968. Lumber: Unitizing and Loading of.

Military Specification MIL-.L-14362C.

U.S. Forest Products Laboratory

1967. Factors inñuencing decay of untreated

wood. USDA Forest Serv. Res. Note

FPL-0154. Madison, Wis.

U.S. Forest Products Laboratory

1972. Methods of controlling humidity in

woodworking plants. USDA Forest Serv.

Res. Note FPL-0218. Madison, Wis.

U.S. Forest Products Laboratory

1974. Wood Handbook. U.S. Dep. Agrie,

Agrie Handb. 72, Rev. 528 pp. illus.

56
GLOSSARY

Airdried.—The dried condition of lumber, usually 12 to 20 percent moisture content, reached

by exposing it for a sufficient period to the

prevailing atmospheric conditions.

Air drying.—The process of drying green lumber by exposure to prevailing atmospheric

conditions.

Board.—1. Yard lumber which is less than 2

inches thick and which is 2 or more inches

wide. 2. A term usually applied to 1-inch-thick

lumber of all widths and lengths.

Bolster.—A square piece of wood usually 4 by

4 inches in cross section, placed between

stickered packages of lumber to provide space

for the entry and exit of the forks of a lift

truck.

Bound water.—Syn : Adsorbed moisture, hygroscopic moisture, imbibed moisture. Moisture

that is intimately associated with the finer

wood elements of the cell wall by adsorption

and held with sufficient force to reduce the

vapor pressure.

Bright.—Syn: Unstained. The term is applied

to wood that is free from discolorations. The

term "bright sapwood'' is sometimes used to

describe sapwood of natural color or in which

the stain or discoloration can be removed by

surfacing to standard thickness.

Bulk pile.—Syn: Solid pile. The stacking of

lumber onto dollies or pallets, into unit packages, or into bins without vertical spaces or

stickers between the layers for air circulation.

Bunk, carrier.—Specially designed wood beams

on which parcels of lumber or other wood

items are placed, enabling the straddle truck

or carrier to pick the unit up for transport.

Casehardening.—A condition of stress and set

in dry wood in which the outer fibers are

under compressive stress and the inner fibers

under tensile stress, the stresses persisting

when the wood is uniformly dry.

Cell.—In wood anatomy, a general term for the

minute units of wood structure having distinct

cell walls and cell cavities. Includes wood

fibers, vessel segments, and other elements of

diverse structure and function.

Check.—Syn : Cracks, drying check, checking. A

separation of the wood fibers within or on a

log, timber, lumber, or other wood product

resulting from tension stresses set up during

drying, usually the early stages of drying.

Circulation, air.—In drying wood, the movement

of air by either natural or mechanical means.

Forced circulation.—The movement of air

by mechanical means.

Conditioning.—1. A storage procedure that reduces differences in moisture concentration

within lumber, thereby reducing the drying

stresses. This usually follows the final stage of

drying. 2. Adjustment of the moisture content

of wood to that which is expected to prevail

under the lumber's condition of use.

Correction, temperature.—An adjustment of the

readings of the resistance-tjrpe electrical

moisture meter to compensate for changes in

the temperature of the wood.

Decay.—Syn: Rot, dote. 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, ring-shaked, pitted, or crumbly.

Decided discoloration or bleaching of the

rotted wood is often apparent.

Incipient decay.—The early stage of decay

which 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.

57
Defect,—Any irregularity or imperfection in a

tree, log, bolt, or lumber which reduces its

volume or quality or lowers its durability,

strength, or utility value. Defects may result

from knots and other growth conditions and

abnormalities ; from insect or fungus attack ;

from milling, drying, machining, or other

processing procedures.

Degrade.—A loss in adjudged quality which

drops lumber to a lower commercial grade.

Density,—The weight of a body per unit volume,

usually expressed in pounds per cubic foot or

grams per cubic centimeter. In wood, density

changes in terms of moisture content.

Dipping,—Process of submerging lumber in a

vat containing fungicides or other chemicals

to prevent stain or decay, to impart water

repellency, or to color the product.

Discoloration,—Syn : Stain. Change in the color

of lumber due to fungal and chemical stains,

weathering, or heat treatment.

Drying,—Syn: Seasoning, curing. The process

of removing moisture from wood to improve

its serviceability.

Electrodes,—Devices made of electrically conducting material, usually steel pins, for connecting wood into the electric circuit of an

electric moisture meter.

Insulated electrodes,—Special electrodes,

used with resistance-type electric moisture meters, that are coated with an insulating material to limit or control the

point of contact between the electrode

and the wood.

EMC,—see "equilibrium moisture content."

Endloader,—A carrier vehicle for bulked lumber, so named because the lift mechanism

grasps lumber packages from the end.

Equilibrium moisture content,—Abbr: EMC.

The moisture content at which a material

neither gains nor loses moisture when surrounded by air at a given relative humidity

and temperature.

Extractives,—Substancesin 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 which do not react

chemically with wood substances.

Fiber saturation point,—Abbr: FSP. The stage

in the drying or wetting of wood at which the

cell walls are saturated with water (bound

water) and the cell cavities are free of water.

It is usually considered to be approximately

30 percent moisture content, based on the

weight of the wood when ovendry.

Forkloader,—Syn : Forklift truck. A vehicle that

handles and transports lumber, so named because of its power-elevated forks.

Foundation, open,—In air drying, structural supports for the pile designed to facilitate air

circulation under the pile.

Free water.—Syn : Capillary water. Water that

is held in the cell cavity of the wood.

Fungi,—Low forms of plants consisting mostly

of microscopic threads that traverse wood in

all directions, coverting the wood to materials

they use for their own growth. Fungi cause

decay and staining of lumber.

Grade,—A classification or designation of the

quality of manufactured pieces of wood or of

logs and trees.

Gantry,—A framework supported at the ends so

that it spans a distance. Used to support a

traveling crane, or for other purposes.

Grain,—The direction, size, arrangement, appearance, or quality of the fibers in lumber.

When used with qualifying adjectives the

term designates the orientation of fibers

and/or growth rings in lumber.

Cross grain,—Lumber 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.

Diagonal grain.—Lumber in which the annual rings are at an angle with the axis

of a piece as a result of sawing at an

angle with the bark of the log. A form of

cross grain.

Edge grain.—Syn: Comb grain, edge-sawn,

quarter grain, quarter-sawed, rift grain,

rift sawed, stripe grain, vertical grain.

Lumber that has been sa*wed or split so

the wide surfaces extend approximately

at right angles to the annual growth

rings, exposing the radial surface. Lumber is considered edge-grained when the

rings form an angle of 45° to 90° with

the wide surface of the piece.

End grain.—The ends of wood pieces that

are cut perpendicular to the fiber direction.

Flat grain,—Syn: Flatsawn, plain grain,

plain-sawed, slash grain, tangential cut.

58
Lumber sawed or split in a plane approximately perpendicular to the radius

of the log. Lumber is considered flatgrained when the annual growth rings

make an angle of less than 45° with the

surface of the piece.

Straight grain.—Lumber in which the

fibers and other longitudinal elements

run parallel to the axis of a piece.

Green chain.—A conveyor for moving green

lumber at sawmills, generally from the saw

to a sorting or stacking area.

Green lumber,—1. In general, lumber just as cut

from freshly felled trees. 2. In accordance

with the American Softwood Lumber Standard, lumber above 19 percent moisture content.

Hardwoods,—Generally, one of the botanical

groups of trees that have broad leaves—e.g.,

oak, elm, basswood—in contrast to the conifers

or softwoods. Also, the wood produced from

such trees. (The term has no reference to the

actual hardness of the wood.)

Heartwood.—The inner layers of wood in the

growing trees that have ceased to contain

living cells and in which the reserve materials,

e.g., starch, have been removed or converted

into resinous substances. It is generally darker

in color than sapwood, though the two are not

always clearly differentiated.

High-temperature drying,—In kiln-drying wood,

use of dry-bulb temperatures of 212° F or

more.

Humidity, absolute.—The weight of water vapor

per unit volume of air at a specified temperature and pressure.

Relative humidity.—Ratio of actual to saturation vapor pressure of water in air at

a given temperature and pressure. Always

expressed as a percentage.

Hygrometer.—Any of several instruments for

measuring atmospheric humidity.

Hygroscopidty.—The property of a substance,

such as wood, that permits it to absorb and

retain moisture readily.

Infection.—The invasion of wood by fungi or

other micro-organisms.

Infestation.—The establishment of insects or

other animals in wood.

Kiln charge.—^Lumber properly packaged and of

suitable quantity for insertion in a dry kiln.

Kiln drying.—The process of drying lumber in

a closed chamber in which the temperature

and relative humidity of the circulated air can

be controlled.

Kraft.—A tough brown paper made from sulfite

pulp. When faced with a waterproof film, this

paper is often used for wrapping lumber

packages.

Lumber.—The product of the sawmill and planing mill not further manufactured than by

sawing, resawing, passing lengthwise through

a standard planing machine, cross cutting to

length, and matching.

Lumber storage room.—Usually a room maintained within specified equilibrium moisture

content limits so that lumber stored in it will

not gain or lose moisture beyond fixed limits.

Meter, electric moisture.—An instrument used

for rapid determination of the moisture content in wood by electrical means.

Microwave heating.—Heating a material by

using electromagnetic energy alternating at a

frequency from 915 megahertz to 22,125

megahertz.

Moisture content of wood,—^Weight of the water

contained in the wood, expressed as a percentage of the weight of the ovendry wood.

Average moisture content,—1. The percentage moisture content of a single sample

of wood which is representative of a

larger piece. 2. The average of several

moisture content determinations taken of

samples from a single piece or lot of wood

products.

Core moisture content.—The moisture content of the inner portion of a moisture

content section which remains after a

shell one-fourth the thickness of the

section has been removed.

Determination of w^oisture content.—The

testing of lumber to determine the amount

of moisture present. This is usually expressed in terms of percent of the ovendry

weight.

Final moisture content.—The average moisture content of the wood at the end of

the drying process.

Green moisture content.—The moisture

content of wood in the living tree.

Initial moisture content.—The moisture

content of the wood at the start of kilndrying or air-drying.

Shell moisture content.—The moisture con59
tent of the outer one-fourth of the

thickness of a moisture section.

Moisture distribution.—The variation of moisture content throughout a piece of wood,

usually from face to face but sometimes from

end to end, or from edge to edge.

Moisture gradient.—A condition existing during

drying in which the moisture content uniformly varies from the more moist inside

toward the drier surface of a piece of wood.

Also a term used specifically to denote the

slope of the moisture content distribution

curve.

Moisture range.—The difference in moisture content between the driest and wettest boards in

a shipment or lot, or between representative

samples of the lot.

Mold.—A fungus growth on lumber at or near

the surface and, therefore, not typically resulting in deep discolorations.

Ovendry.—A term used to describe wood that

has been dried in a ventilated oven at 100° to

105^ C until there is no further loss in weight.

Pervious wood.—A wood through which moisture moves readily.

Pile.—Syn: Stack, rack. Stacking lumber layer

by layer, separated by stickers or self-stickering, on a supporting foundation (hand

stacking) or placing stickered unit packages

by lift truck or crane, one above the other on

a foundation and separated by bolsters.

Pile roof.—Syn : Pile cover, cover boards, stack

cover. A cover on top of the pile to protect the

upper layers from exposure to the degrading

influences of sun, rain, and snow. The sides

and ends of the roof may project beyond the

pile top provide added protection.

Psychrometer.—A type of hygrometer which

measures relative humidity by subjecting wetbulb and dry-bulb thermometers to a stream

of moving air. The difference in readings,

interpreted by means of a chart supplied with

the instrument, yields relative humidity.

Rot.—See Decay.

Sap.—The moisture in green wood, containing

nutrients and other chemicals in solution.

Sapwood.—The outer layers of the stem that in

the living tree contain living cells and reserve

materials, e.g. starch. The sapwood is generally lighter in color than the heartwood.

Shrinkage.—The contraction of wood fibers

caused by drying below the fiber saturation

point. Shrinkage—radial, tangential, and

volumetric—is usually expressed as a percentage of the dimension of the wood when

green.

Sideloader.—A carrier vehicle similar to a forklift truck.

Softwoods.—Generally, one of the botanical

groups of trees that, in most cases, have

needlelike to scalelike leaves; the conifers;

also, the wood produced by such trees. (The

term has no reference to the actual hardness

of the wood.)

Specific gravity.—The ratio of the ovendry

weight of a piece of wood to the weight of an

equal volume of water at 4^ C (39° F).

Specific gravity of wood is usually based on

the green volume and ovendry weight.

Stack.—1. To make a pile on a suitable foundation by hand-placing layers of lumber on

stickers, or similar stock (self-stickered).

2. To construct by hand or with mechanical

equipment, unit packages of the item to be

dried, by separating layers of the stock with

stickers.

Stacking rack.—Syn: Stacking jig, stacking

stall. In hand building stickered unit packages

of lumber, guides are provided to produce

good sticker alinement and square sides.

Stain.—A discoloration in wood that may be

caused by micro-organisms, metal, or chemicals. The term also applies to materials used

to impart color to wood.

Sticker.—Syn : Grosser, strip, piling strip, stick.

A wood strip placed between courses of lumber in a pile or unit package and at right

angles to the long axis of the stock, to permit

air to circulate between the layers.

Sticker alinement.—The placing of stickers

in a pile, package, or truckload of lumber

so that they form vertical tiers.

Sticker spacing.—The distance between

stickers measured from center to center.

Straddle carrier.—A transport vehicle for lumber, so named because its arched frame straddles the lumber package being transported.

Stress, drying.—An internal force, exerted by

either of two adjacent parts of a piece of wood

upon the other during drying, caused by uneven drying and shrinking, and influenced by

set.

Compressive stress.—The stress that develops in the interior region of wood

60
during the early stages of drying, caused

by the shrinking of the outer shell ; also

the stress in the outer layer at a later

point in drying caused by the shrinking

of the interior.

Tensile stress,—The stress that develops in

the outer layers of wood during the early

stages of drying when these layers are

trying to shrink but are restrained by the

still-wet interior region; also the stress

later in drying as the interior layers try

to shrink and are restrained by the outer

shell.

Stresses, relief of.—The elimination of normal

drying stresses as a final step in drying by

applying the appropriate conditioning treatment.

Swelling.—Increase in the dimensions of wood

due to increased moisture content. Swelling

occurs tangentially, radially, and, to a lesser

extent, longitudinally.

Temperature, dry-bulb.—Temperature of air as

indicated by a standard thermometer or comparable temperature-sensing device.

Temperature, wet-bulb.—The temperature indicated by any temperature-measuring device,

the sensitive element of which is covered by a

smooth, clean, soft, water-saturated cloth

(wet-bulb wick).

Temperature, wet-bulb depression.—The difference in the readings of the wet- and dry-bulb

thermometers.

Tier.—In air drying or kiln drying, lumber or

other wood products stacked in vertical alinement. Usually refers to sticker alinement from

layer to layer.

Thermostat.—A device for automatically regulating temperature.

Thermostat, differential.—A device which

keeps the temperature of a building a

fixed number of degrees above outdoors

temperature.

Unitized packages. — Syn: Unit packages.

Bundles of lumber bound as units with steel

strapping or by other means. Lumber is usually packaged in this way to facilitate mechanical handling.

Warp.—Distortion in lumber causing departure

from its original plane, usually developed during drying. Warp includes cup, bow, crook,

twist, and kinks, or any combination thereof.

Water, bound (adsorbed, hygroscopic).— Moisture that is bound by adsorption forces within

the cell wall ; that is, the water in wood below

the fiber saturation point.

Free water.—Moisture that is held in the

cell cavities of the wood, not bound in the

cell wall.

Weathering.—The mechanical or chemical disintegration and discoloration of the surface of

lumber which 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 continual variation in

moisture content brought by changes in the

atmosphere. Weathering does not include

decay.

Wood.—Syn: Xylem. The tissues of the stem,

branches, and roots of a woody plant lying

between the pith and cambium, serving for

water conduction, mechanical strength, and

food storage, and characterized by the presence of tracheids or vessels.

61
INDEX

Absorption rate, stored lumber, 3, 4

Air-conditioned lumber storage, 13

Air-dry lumber, storage of, 21, 23, 36, 40, 51

Air drying, 23, 43, 49

Air-drying yard, layout of, 23

Air temperature—see temperature

Alley arrangement in yards, 23, 49

Ambrosia beetles, 33

Bins, storage using, 27, 45

Bolsters, 24

Bound water, 5, 57

Boxcar shipment, 37

Building sites—see construction sites

Bulkhead flatcars, 39

Bulk-piled lumber, 4, 21, 34, 43, 50

Casehardened lumber, 4

Chain flatcars, 39

Chemical treatment of lumber, 31, 46

Chemicals, precautions with, 33

Climate affecting lumber storage, 17, 38

Construction sites, 21, 52

Cooling sheds for storage, 29, 34, 50

Cranes, 25, 27, 35

Damp weather, effect on lumber, 4, 31

Decay, prevention of, 5, 17, 21, 34, 50

Deck-stored lumber, 4

Delivery schedules, 21, 53

Determining moisture content, 9

Dimensional changes in wood, 5, 14, 53

Shown by species, 15

Dip treatment, 33

Discoloration, 23

Distributing yards, 3

Drying oven for moisture determination, 9

Drying process, 5

Electric moisture meters—see moisture meters

EMC—see equilibrium moisture content

End loaders, 44

Equilibrium moisture content, 8, 13, 17, 49

Regional values for, 18

Extractives, 9

Fiber saturation point, 5

Flatcars, railroad, 40

Forced circulation in sheds, 26

Forklift trucks, 50

Foundations for piled lumber, 24

Framing materials, 52, 53

Free water, 5, 58

FSP—see fiber saturation point

Fungal attack on wood, 17, 31

Fungal infection, prevention of, 17, 31, 34, 50

Fungicidal treatment, 31

Furniture factories, 39

Geographical factors in storage, 12, 38

Glossary of terms, 57

Gondola railroad cars, 40

Green chains at sawmills, 34, 36

Green lumber, storing, 1, 21, 32, 34, 40, 51

Green moisture content, 5

Ground water, decay risk from, 52

Handling—see mechanical handling

Heartwood, 5, 18, 33

Heated storage sheds, 27

Heaters for storage sheds, 28, 46

Automatic control of, 13, 28

Home building sites—see construction sites

Humidistats for storage sheds, 28, 46

Hygrometer, electric, 12

Hygroscopicity, 5

Indoor storage—see sheds

Infection, 31

Insect attack on wood, 31

Insecticidal treatment, 33

Juvenile wood, 14

Kiln-dry lumber, 21, 24, 28, 36, 43, 51

Kiln drying, 48

Kiln trucks for storage, 34, 48

Kraft-paper wrap—see paper wrap

Local conditions—see climate

Lumber storage yards, 22

Line type, 23

Row type, 23

Advantages of paving yards, 23

Mechanical handling, 3, 23

Microwave oven for moisture determination, 10

Millwork, 53

Millwork factories, 49

Moisture change, 8, 12

62
Moisture content, 5

Moisture diffusion characteristics, 5, 8

Moisture gradient, 4, 8, 16

Moisture meters, 10

Moisture range, 4, 26, 49

Mold, 17, 42

Moldings, storage of, 28

Ocean shipment of lumber, 37, 40

Outdoor storage, 3, 21, 35, 43

Outdoor storage yards—see lumber storage yards

Ovendrying to determine moisture content, 9

Paper wrap for lumber packages, 3, 22, 36, 40,

49,52

Permeability of wood, 8

Pile covers, 23, 45

Pile foundations, 22, 24

Piling methods, 22, 24, 34, 43

Pin-hole beetles, 32

Pitch, 9

Plastic sheeting, 22, 49, 53

Platform foundation for plywood, 29

Plywood, storage of, 29

Polyethylene sheets to protect lumber, 22

Portable sawmills, 34

Powder post beetles, 32

Predicting moisture loss or regain, 12

Prefabricated building parts, 53

Psychrometer, 12

Psychrometric table for EMC determination, 9

Rail shipment of lumber, 38

Rail sidings, handling at, 27, 35

Rainfall, 17

Rainfall levels by State, 18

Rain-soaking of lumber, 17, 21, 31, 52

Reaction wood, 14

Redrying wet lumber, 3

Regional conditions—see climate

Relative humidity, 4,17

Related to EMC, 8

Roller bed trucks, 52

Rough, dry sheds, 35

Row spacing in yards, 23

Sapwood, 5, 8, 33

Sawmill handling procedures, 21, 34

Sawmills, 21, 25, 27

Hardwood, 35

Softwood, 34

Sea transport—see ocean shipment

Sheet wrapping—see paper wrap

Sheds for lumber storage, 24

Open, 4, 25, 34, 45

Closed and heated, 12, 27, 46

Closed and unheated, 4, 25, 36, 44

Ship, transporting lumber by, 40

Shrinkage—see dimensional change

Snow, protecting lumber from, 4, 23

Solar radiation, effect of, 26, 49

Solid-piled lumber, 4, 21, 34, 43, 50

Sorting lumber at mills, 34

Specific gravity of different woods, 8

Spray treatment of lumber, 31, 32

Stacking plywood, 29

Stain, fungal, 17, 21, 31, 50, 52

Staining, prevention of, 17, 31, 36, 50

Stalls for storing special lumber, 27

Steam heating coils, 27, 46

Stickering, 5, 24, 34, 43, 46

Straddle carrier, 44

Stress, drying, 49

Swelling—see dimensional change

Tarpaulins, 22, 38

Temperature, 8,17, 32

Temperature correction chart for moisture

meters, 12

^'Tempering,*' 4

Tension wood, 14

Termites, 31, 33

Thermostats for storage sheds, 28, 46, 50

Transporting lumber, 3, 37

Treating lumber^—see chemical treatment

Treating shed, design of, 32

Truck transport, procedures for, 37

Trucks, 3, 37, 43, 52

Trusses, 53

Unit heaters, gas fired, 28, 46

Unit-package handling, 35, 40, 43, 52

Volatile elements of wood, 9

Warp, 1, 4, 5, 23, 53

Waterproof packaging—see paper wrap

Water-repellent treatment for lumber, 53

Weathering, 23, 46

Wind effects, 23, 53

Woodworking factories, 22, 40, 48

Yard operation and maintainance, 22, 49

"SÎr U.S. GOVERNMENT PRINTING OFFlCEt 1978 O 263-698

63