Air Seasoning of California Redwood

Seventy percent of the redwood that is kiln-dried is sinker stock with moisture content in excess of 150 percent. Kiln-drying redwood results in some degrade which increases with increasing initial moisture content. Suitable equations for calculating degrade loss on kiln-drying are given. To reduce the cost of removing the 1 billion pounds of water from 300 million board feet of lumber that is kiln-dried, it is desirable to resort to preseasoning. Some of the factors involved in preseasoning are width of package, height of piles, sticker thickness, orientation, and spacing between piles. The optimum conditions for the first four factors are readily established for each yard, since available handling equipment is a strong determinant. Generally, the packages are 4 feet wide and 4 feet high and are stacked four to five packages high. Sticker thickness is commonly 3/4 inch. The remaining important yard characteristic is spacing between piles. This determines the turnover rate or volume of lumber dried per year per acre. Turnover rate is especially important where land is limited. Rates are computed for different pile spacings and different final moisture contents for 1-inch sinker stock. Because of opposing effects, the turnover rate is a maximum at some particular pile spacing; in the work reported here, it is 6-8 feet. To keep drying costs at a minimum, the moisture content at which it becomes more costly to air-dry than kiln-dry must be determined. With 1-inch sinker stock, this occurs at moisture contents below 55 percent.

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