UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 552 
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Contribution from the Forest Service 
HENRY S. GRAVES, Forester 
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Washington, D. C. 
PROFESSIONAL PAPER 
July 9, 1917 
THE SEASONING OF WOOD. 1 
By Harold S. Betts, M. E., in charge, Office of Industrial Investigations. 
CONTENTS. 
Page. 
Importance of proper seasoning methods 1 
Fiber saturation point and shrinkage 2 
How wood may be injured in seasoning 11 
Checking 11 
Casehardening 11 
Honeycombing 11 
Warping 12 
Collapse 12 
Page. 
Air seasoning 12 
Crossties, poles, and sawed timbers 12 
Lumber 17 
Rules for piling lumber 20 
Kiln- drying 22 
Types of kilns 22 
Preliminary treatments 25 
The process of drying 26 
IMPORTANCE OF PROPER SEASONING METHODS. 
Practically all wood before being put to use is either seasoned in the 
air or dried in a kiln. The main objects of seasoning are to increase 
the durability of the wood in service, to prevent it from shrinking 
and checking, to increase its strength and stiffness, to prevent it 
from staining, and to decrease its weight. The sooner wood is sea- 
soned after being cut the less is the chance that it will be injured by 
the insects, which attack unseasoned wood, 2 or decay before the time 
comes to use it. Wood that is to be treated witH preservatives needs 
in nearly all cases to be seasoned as much as wood that is to be used 
in the natural state. 
Wood has a complicated structure. The walls of the cells of 
which it is made up shrink and harden when moisture is removed 
from them, and unless timber that is to be air-seasoned is piled in 
the right way, or conditions in the dry kiln are maintained in accord- 
ance with certain well-defined physical laws, the material is likely to 
warp or check, or in some way to be damaged seriously. Until 
recently proper methods of seasoning received comparatively little 
attention from manufacturers, and large losses, especially among 
i For assistance and suggestions given in connection with the preparation of this bulletin, the author is 
indebted to Mr. D. P. Sexton, of John B. Ransom & Co., Nashville, Tenn., and to Messrs. R. K. Helphen- 
stine, jr., and N. de Witt Betts, of the Forest Service. 
2 The sapwood of seasoned hardwood is subject to attack and frequently to serious damage by powder- 
post insects. See Farmers' Bulletin 778, "Powder- Post Damage by Lyctus Beetles to Seasoned Hard- 
wood," by A. D. Hopkins and T. E. Snyder, 1917° 
87732°— Bull. 552—17 i 
