UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 552 



'^SajVJjS^' Contribution from the Forest Service ^3 



J^^^^i. HENRY S. GRAVES, Forester J&&*^3L 



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 



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 

 hi 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 



1 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 1 



