Degrade of Oak Lumber as Influenced By Drying

Two thicknesses (4/4 and 8/4) of two species ( red and white oak) were airdried in central Pennsylvania to determine effective drying seasons and degrade. A total of 110 packages (600 to 800 bd ft each) were exposed, under package roofs, during a 5-year period. Defect type and location relative to top and bottom courses, sides and interior boards were analyzed. The air-dried, monetary losses were less than 2 percent for 4 by 4 and greater than 3 percent for 8 by 4 red and white oak. The top courses for 8 by 4 red and white oak showed the highest percentage of degrade, about 75 percent of which was from checks. Interior boards of white oak had relatively high degrade from warpage. Red oak appeared more defect-sensitive to the drying season than white oak. Much 4 by 4 degrade was from rapid spring drying. Partially-dried packages exposed to winter conditions had the greatest air-dried degrade. Packages dried to 20 percent by erroneously exposed to winter conditions degraded as much as those which were partially dried. Green lumber did not appreciably degrade from winter conditions, and 8 by 4 white oak may have benefited from the freezing. The effective air-drying season in central Pennsylvania was from early March to late November, when the mean temperature is above the freezing point. Additionally, 20 packages were kiln-dried from the green condition .and 20 from the airdry condition to determine kiln-drying time and influence on degrade. The least degrade was found for 8 by 4 white oak (l.7 percent) because of reduction of checking and warpage. Airdried lumber required one-fourth the kiln-drying time to 6 percent moisture content of green lumber. The kiln-drying-time” for 8 by 4 lumber was three times that of 4 by 4 lumber in a green or airdried state.

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