A METHOD OF SEASONING SMALL 

QUANTITIES OF LUMBER 

Information Reviewed and Reaffirmed 

August 1958 

No. 1608 
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A METHOD OF SEASONING SMALL QUANTITIES OF LUMBER 

By 

E. F. RASMUSSEN, Engineer 

Forest Products Laboratory, 1 Forest Service 

U. S. Department of Agriculture 

The owner of a small quantity of green lumber or logs is often confronted 

with the problem of seasoning it to a state of dryness suitable for use in 

furniture, wood carving, or other handiwork. He cannot follow the practice of commercial mills, which employ dry kilns for the purpose, as 

kilns are too costly. On the other hand, air seasoning outdoors usually 

does not bring lumber to a sufficient state of dryness for such uses, although it is sufficient for structures that will in use be exposed to outdoor 

conditions, 

Green lumber can be seasoned to the necessary dryness for the purpose 

by combining outdoor air seasoning with subsequent further drying in a 

heated room. Studies at the Forest Products Laboratory show that, 

while this method is essentially simple, it is not without pitfalls for the 

inexperienced handler of green wood. Unless certain precautions are 

observed, such defects as checking, warping, and splitting may occur. 

If reasonable care is exercised, however, well-seasoned lumber can be 

obtained by this method. 

Seasoning Lumber 

Various factors must be considered if good results are to be obtained by 

seasoning. Among these are the size of the lumber to be dried, the use 

of end coatings to retard end drying, proper piling, and other practices. 

Above all, thorough seasoning is essential. If wood is not at a uniform 

1

Maintained at Madison, Wis., in cooperation with the University of 

Wisconsin. 

Report No. 1608 -1-
moisture content throughout at the time of fabrication, subsequent 

machining may expose surfaces of unequal moisture content. Surfaces 

with a high moisture content, when exposed to a drying atmosphere of 

low relative humidity, will begin to lose moisture rapidly, unequal drying stresses will develop, and further checking or warping may occur. 

This may be overcome by coating the article with a moisture-resistant 

coating and storing in a cool room until thoroughly dry. The best solution, however, is to allow the wood to season until it is at a uniform 

moisture content throughout before fabrication is attempted. 

Size of Lumber 

Thin, narrow lumber dries much more rapidly and with fewer seasoning 

checks than does thick, wide lumber. Warp, however, is increased. 

Thick planks or timbers containing the pith of the tree, commonly called 

boxed-heart timbers, are very difficult to dry without checking. Wide 

boards are more likely to surface check than narrow boards. Thick 

boards are also more susceptible to checking than thin boards. To obtain fast drying with a minimum of seasoning defects, the lumber should 

be cut into boards of about the thickness and width required for final use, 

with due allowance for shrinkage and warp. 

The handling and piling of a large amount of material, of course, involves more time and work if cut into small pieces than if it is in larger 

sizes. Where a large amount of material is to be seasoned, therefore, 

two alternative procedures present themselves : 

1. Cutting the material to the smallest size required for final 

use, thereby increasing the time, work, and space required for 

handling and piling, but reducing drying time and lessening the 

likelihood of seasoning defects, 

2. Drying the material in a larger size than is required for 

final use and cutting it to the required size after it has reached 

the desired moisture content. This will decrease the time, work, 

and space required for handling and piling but the drying time 

will be increased and seasoning defects will be more likely to 

develop. 

Where ultimate use requires wide or thick stock, seasoning defects can 

be held to a minimum by cutting the stock into narrow or thin boards and 

drying these to the desired moisture content, then gluing them together 

to form a laminated member of the size required, 

Report No. 1608 -2 -
-- -- 

Bark will retard the drying rate of thick wood items and may introduce 

a decay hazard under slow drying conditions. 

End Coating 

Lumber loses moisture much more rapidly from the ends than it does 

from the sides. This results in end checking, which may become very 

severe. 

To reduce excessive end drying, which will in turn reduce the amount 

and severity of end checks, lumber particularly thick, short stock 

should be end coated with a water -resistant coating as soon as possible 

after it is cut (1, 2).2 

Outdoor Piling 

All lumber should be carefully piled. In general, outdoor piles should 

conform to the practice shown in figure 1. A solid foundation constructed 

so as to permit free circulation of air through and beneath the pile is 

essential. The front of the foundation should face either toward the south 

or west if possible, because the front of the pile has no overhanging ends 

of boards jutting out irregularly and, therefore, is better protected from 

rain and snow by the stickers (crosswise strips between layers of boards) 

and the forward pitch of the pile, The foundations should be high enough 

so that the pile will slope from front to back 1 inch per foot and still be 

at least 18 inches above ground level at the back end. Cross supports 

should be placed under each tier of stickers. 

The maximum spacing between stickers should not exceed 4 feet. 

1-inch hardwood lumber, the sticker spacing should be 2 feet or less so 

For 

as to minimize warping. 

short distance out beyond the ends of the boards (approximately one -half 

The front tier of stickers should project a 

inch) and for this reason should be slightly wider than the intermediate 

stickers. The pile should pitch forward 1 inch per foot of height. If the

lumber is cut to uniform lengths, the rear tier of stickers should be of 

the same width as the front tier and should also project beyond the ends 

of the boards. Where the lengths vary somewhat, the rear stickers may 

have to be located so as to catch the shortest boards. The long boards

will then project beyond the rear stickers. 

2 Numbers underlined in parentheses refer to Literature Cited at the end 

of this report. 

Report No. 1608 -3-
Stickers for hardwoods are usually 1 by 1-1/2 inches in cross section 

(front tier of stickers 1 by 2 inches) and long enough to extend across 

the pile. All material used for stickers should be free of stain and decay so that the lumber will not become infected. Stickers should be at 

a low moisture content. Vertical flues provided in the pile (fig. 1) are 

desirable for easily dried species in order to obtain good air circulation 

and a fast drying rate. The flues should be not more than 2 inches wide 

for the more refractory species, such as oak and the heartwood of maple. 

All piles should be roofed (fig. 1) for the protection from the sun's rays 

and to exclude rain. The roof should be weighted down with heavy 

weights or extra lumber to reduce warping in the upper courses of 

lumber . 

Piling in Open or Closed Sheds 

or in Rooms 

The method of piling lumber in open or closed sheds or in rooms should 

conform to the practice shown in figure 2. The same procedures given 

for outside piling apply. It is not necessary, however, to slope the pile 

from front to rear or to provide a forward pitch, Furthermore, individual pile roofs will not be necessary, but it would be well to place 

some weights on top of the piles to reduce warping. 

Seasoning Procedure 

The initial drying can take place either in the open, in closed or open 

sheds, or in an unheated room, Some boards should be placed in the pile 

as samples in such a manner that they can be easily removed for periodic examination and weighing, 

Proper moisture content governed by use requirements. --Lumber that is 

to be used in structures in which it will be exposed outdoors can, as already noted, be air dried to a satisfactory moisture content without being 

repiled in a heated room. 

Lumber that is to be dried to a low moisture content, for example, to the 

6 or 8 percent required for interior trim, flooring, furniture, or novelties, should first be air dried to a moisture content of about 20 percent 

or lees and then repiled in a heated room to attain further drying. The 

temperature in this room should be maintained approximately 20° F. 

above the outside temperature at all times of the year. Because many 

Report No. 1608 -4-
variables, such as size, species, initial moisture content, and climatic 

conditions, affect the drying rate, it is impossible to state the period of 

time required to bring the lumber to a moisture content of 20 percent. 

Control of drying rate. --Modifications in piling that will reduce the drying rate and minimize checking are (1) decreased spacing between piles; 

(2) decreased width of vertical flues; (3) increased width of pile; (4) thinner stickers; (5) avoiding the use of stock for stickers (narrow, dry, 

special stickers are less conducive to checking); and (6) piling stock in 

a cool room having a high relative humidity. 

Methods of determining moisture content. --The simplest method of 

determining whether the lumber has reached the lowest moisture content 

attainable by air drying is by weighing the sample boards previously 

mentioned. As soon as these samples show little or no loss in weight 

over a period of a week or 10 days of drying under normal summer airdrying conditions, they will have reached a thoroughly air -dried moisture 

condition. At other times of the year, or during prolonged periods of 

rainy weather, the rate of moisture loss will be slower and under such 

conditions the samples should show no appreciable change in weight for 

3 to 5 weeks before the wood can be considered well air dried. 

The ovendrying method of moisture content determination is more nearly 

accurate but involves the use of special equipment (4). 

The air-dried lumber should remain in the heated room until dry enough 

for use (5). The time required will vary from a week or two for small, 

thin boards to possibly a year or more for large, thick pieces that will 

be used as carving stock, 

Two methods of roughly estimating when the material is at a moisture 

content of about 7 percent are outlined as follows: 

The first method consists of sawing a piece 1-1/2 to 2 feet long from 

several wider boards; the cut should be made at least 6 inches from any 

knot or other defect. From the freshly cut end of the board, cut off a 

section approximately 1 inch in length along the grain. Measure the 

width of this section (width of the board) to within 1/64 inch and then 

place it near a radiator, hot air register, or a stove for at least a day. 

If no checks appear on the ends and no measurable shrinkage in width 

occurs8 the wood is uniformly dry to a moisture content of about 7 or 8 

percent. 

Report No. 1608 -5-
-- 

To use the second method, mark a line across several of the widest 

boards with a carpenter's square. Measure the width of each board 

along this line to the nearest 1/64 inch and record the measurement on 

the board. Pile the lumber on stickers in a room heated approximately 

20° F. above outdoor temperatures. Measure the width of the marked 

boards from time to time over a period of 3 months or more. When no 

further shrinkage in their width can be detected, the lumber is roughly 

at a moisture content of about 7 or 8 percent. 

Seasoning Special Items 

Special items, such as cross sections of trees, large carving blanks, or 

boards containing the pith of the tree, must be dried slowly in order to 

hold seasoning defects to a minimum, 

As soon as the material is cut from the log, it should be completely 

covered with a moisture-resistant coating (1, 2) to prevent rapid loss of 

moisture with subsequent checking. 

A coating that is easy to obtain and apply and yields good results is paraffin. It should be heated to a temperature of from 135° to 155° F., and 

applied to the material by brush or by dipping. All parts of the wood 

surface should be covered, and no bubbles should be present. The thickness of the coating will depend on the item to be dried; species extremely 

susceptible to checking require a thicker coating than do less susceptible 

species. Some idea of the susceptibility toward checking of the most 

common woods may be obtained from kiln-drying schedules (3); the 

species for which low temperatures and high relative humidities must be 

used in the initial stages of drying in kilns are the ones most susceptible 

to seasoning defects. 

After the coating is applied, the material can be piled on stickers in an 

unheated shed. The sticker thickness and the flues between the pieces 

of material can be increased or decreased to hasten or retard drying. 

After the material has reached a moisture content of approximately 20 

percent, which may take from several months to a year or more, it 

should be repiled for further drying on stickers in an attic or in a room 

heated to 20° F. above outdoor temperatures. During this period, Samples should be weighed at weekly intervals to determine the drying rate. 

As soon as the samples have reached a moisture content of 7 to 8 percent, the moisture-resistant coating can be removed. 

Report No. 1608 -6-
Material can be dried with the bark on, but during the drying process the 

bark will, in most cases, become loose and eventually fall off. If it is 

desired, therefore, to retain the bark on the material for such items as 

exhibit specimens or novelties, it can be nailed in place with small 

finishing nails, which will be hard to detect except by close examination. 

Winter Versus Summer Felling of Trees 

It is a commonly accepted idea that wood is more durable if the trees 

are felled during the fall or winter months than during spring or summer. 

This belief probably originated because logs cut in the late spring or 

early summer are more likely to be attacked by insects and fungi. Seasoning also progresses more rapidly because of low spring and summer 

humidity conditions, and the logs and lumber may become excessively 

checked . 

If the logs are cut immediately into lumber and the lumber is properly 

piled for air seasoning, the season of the year should be considered only 

as it affects drying. 

Many persons also believe that the moisture content of a tree is lower in 

winter than in summer because the "sap is down." This is not the case. 

Actually there is very little difference. 

Seasoning in the Log Form 

Wood in the log form dries slowly, especially through the bark. It is 

virtually impassible to season logs without decay and without severe surface and end checks. When checks have once started they are very hard 

to stop, usually increasing in size to the point where losses become 

excessive. 

These checks are due not only to normal drying stresses but also to 

stresses caused by the fact that the log tends to shrink twice as much 

around its circumference as it does along the radius. 

During the summer months, checking can be retarded by applying a 

moisture -resistant coating (1, 2) to all freshly cut surfaces. Bark will 

retard drying and subsequent checking. Therefore, if the bark is removed, the entire log should be covered with a moisture-resistant coating. 

Report No. 1608 -7-
If it becomes necessary to store loge for extended periods before cutting 

them into lumber, they can be kept free of decay and checking by submerging them completely in water. 

Literature Cited 

(1) Forest Products Laboratory 

1953. Coatings That Prevent End Checks. Forest Products 

Laboratory Technical Note No. 186. 

(2) 

1955. List of End Coating Manufacturers and Dealers. Forest 

Products Laboratory Report No. 1954. 

(3) Torgeson, O. W. 

1951. Schedules for the Kiln Drying of Wood. Forest Products 

Laboratory Report No. 1791. 

(4) Forest Products Laboratory 

1952. The Detection and Relief of Casehardening. Forest Products 

Laboratory Technical Note No. 213. 

(5) 

1955. Control of Moisture Content and Shrinkage of Wood. 

Separate from U. S. Dept. of Agri. "Wood Handbook." 

Report No. 1608 -8- .6-11 
Figure 1.--Essential features in piling lumber outdoors for rapid and uniform air seasoning. 

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