Warp reduction of red pine two-by-fours via restrained drying

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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