This study investigated the mechanical properties of western hemlock plywood after treatment with waterborne preservatives and redrying. Unlike previously reported results for southern pine plywood, western hemlock plywood was more sensitive to redrying temperature than to preservative treatment. Generally, western hemlock plywood was affected by temperature and other variables. Losses in mechanical properties were generally higher than for similarly treated and redried southern pine plywood. Treatment of the plywood with either acidic (CCA-type C) or alkaline (ACZA) solutions resulted in adequate preservative gradients. Western hemlock tended to be affected more by acidic solutions than by alkaline solutions. Based on this research, treated western hemlock plywood should not be redried at temperatures in excess of 60°C without applying some design stress reduction factor.

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