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SEASONING OF WOOD 



RAYMOND C. RIETZ 



The living tree holds gallons and 

 gallons of water in the walls and 

 cell cavities of the fibers that make up 

 the structure of its wood. The fibers 

 dry out and shrink when they are ex- 

 posed to air. Thus the rough products 

 of the tree poles, posts, ties, boards, 

 ax-handle blanks, barrel staves shrink 

 as the water evaporates from the wood. 

 This is the seasoning process drying 

 and shrinking. 



The use to which the seasoned wood 

 is to be put determines how much 

 water is to be removed in drying. 

 Lumber for a barn, which is exposed 

 only to changing outdoor air condi- 

 tions, need not be dried to as low a 

 moisture content as hardwood boards 

 for fine furniture, which is exposed to 

 heated indoor air in winter. Another 

 example: Wood for a croquet ball, 

 which has to stay round despite knocks 

 and dampness, must be dried and 

 shrunk more than wood that is to be 

 used in a rough packing crate. 



Two principal seasoning processes 

 are in common use, air drying and kiln 

 drying, each of which is better adapted 

 to some uses than the other. 



The air drying of wood is much 

 like drying the family washing, except 

 that the boards cannot be so simply 

 hung on lines or directly exposed to the 

 sun and the wind. It consists of piling 

 the lumber outdoors so that air cur- 

 rents can circulate through the pile and 

 carry away the moisture from the sur- 

 face of the wood. As the surface dries, 

 moisture from within the board re- 

 places it and, in turn, is carried away 

 by the air. It is a slow process, but on 

 the whole is quite satisfactory. For 

 some special uses, such as hardwood 

 furniture, flooring, and millwork, air 

 drying in most parts of the United 

 States does not dry wood to a low 

 enough moisture content for satisfac- 

 tory use. In such cases the hardwood 

 lumber is usually first air-dried at the 



producing sawmill and then kiln-dried 

 to a still lower moisture content at the 

 woodworking factory. 



With a little care and attention to 

 details, lumber can be piled so that it 

 will not warp, check excessively, or be- 

 come infected with decay while air 

 seasoning. 



First, the air-drying yard should be 

 laid out to make full use of the pre- 

 vailing winds, because the greater the 

 air movement through the pile, the 

 quicker the lumber will be dried. The 

 bottom of the pile should be designed 

 to allow free movement of air under- 

 neath, and this pile should usually be 

 arranged so that it slopes from front 

 to rear in order that rain water will 

 drain away readily. The slope of the 

 pile is determined by the arrangement 

 of the piers, those at the front being 

 higher than those at the rear of the 

 pile. To reduce yarding costs, some 

 producers are experimenting with hor- 

 izontal lumber piles built up from 

 "packages" of lumber moved about 

 with lift trucks. The pile piers are all 

 of the same height to accommodate 

 the handling equipment, and the built- 

 up seasoning piles are flat. 



As the pile goes up, it should have a 

 forward pitch of about an inch to each 

 foot of height. Over each layer of 

 boards, narrow strips, called stickers, 

 should be laid crosswise, about 2 to 4 

 feet apart, to keep the layers separated. 

 An inch or two of space should be al- 

 lowed between the edges of boards for 

 air to move up or down through the 

 pile. Boards should be placed carefully, 

 so that the various air channels are un- 

 obstructed. Stickers likewise should be 

 lined up one above the other; other- 

 wise the boards lying on them may be 

 bent by the weight of the boards above 

 and warp in drying. Finally, a roof 

 consisting of a double layer of boards, 

 the upper layer overlapping the lower, 

 should be put over the pile so that it 



