Warp reduction of red pine two-by-fours via restrained drying
2005
Erickson, R.W. | Shmulsky, R.
Warp in 2 by 4 lumber is a significant cause of loss in grade and value. Crook and twist are two of the largest factors. The softwood lumber grading standards (WWPA 1998)1 for red pine Stud grade list maximum crook and twist deviations from true as 0.25 and 0.375 inches, respectively, for 8-foot material. Acceptable bow is stipulated as three times the value for crook, that is, 0.75 inch. Two-by-four material sawn from young trees, forest thinnings, and stem tops contains a significant proportion of juvenile wood and is particularly notorious for warp. At the planer mill, warped 2 by 4's represent a significant loss in value. In-service, replacement of warped 2 by 4's as wall studs or truss members is costly. In this research, a drying restraint system was evaluated as a means of warp reduction in red pine lumber. Boards were dried to approximately 7 percent moisture content, representative of final in-service conditions. Results showed a significant improvement in Stud grade recovery.
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