When lumber reaches its destination it is sorted and graded according to lumbermen’s standards, after which, it is loaded upon trucks and hauled to the storage yards.
Here, it is so placed that air can get at the four sides of each piece and evaporate the water held by the “green” lumber. This is called air seasoning. The time necessary to season a piece of lumber so that it may be used for high-grade work depends upon the kind of wood, its shape and size, the condition of the atmosphere, etc.
Two, three, and even four years are often required; the longer the better, provided it is kept dry.
Fig. 217.
KILN DRYING TUPELO, IONIA, MICHIGAN.
It will never become perfectly dry because of the moisture in the air itself. Because of the slowness of this method of seasoning, millmen resort to artificial means. The lumber, as it is needed, is shut up in a room heated by steam. [Fig. 217] shows the method of “sticking” lumber in preparing it for the kiln.
High temperature, no matter how much moisture may be contained in the air, will evaporate water from wood.
Green, or fresh sap-wood may be partially seasoned by boiling it in hot water or by steaming it.
Pine, spruce, cypress, cedar, etc., may be placed in the kiln as soon as sawed, four days for one inch thick boards being sufficient to dry them. Hard woods, such as oak, maple, birch, etc., are usually allowed to “air season” for a period of from three to six months before being placed in the kiln. Six to ten days additional kiln-drying is allowed them.
The usual temperature for kilns is from 158 to 180 degrees Fahr. Hardwoods lose moisture so slowly that to place them in the kiln directly from the saw would cause them to shrink very unevenly and hence make them subject to serious “checks”.