Effects of redrying schedule on preservative fixation and strength of CCA-treated lumber

Southern pine and western hemlock dimension lumber specimens were pressure treated with chromated copper arsenate (CCA) and then redried using one of seven post-treatment schedules. The influences of these seven kiln- or air-drying schedules on chemical leachability, decay resistance, and wood strength were evaluated to better understand the relationship between the severity of the redrying process and CCA fixation. For southern pine, six kiln-drying schedules exhibited less leaching of chromium and arsenic than did CCA-treated material air-dried after treatment. Depending on the temperature in initial kiln-drying, chromium and arsenic leaching were significantly reduced after a two-step post-treatment kiln-redrying schedule having an initial 12-hour fixation and a small wet-bulb depression followed by a drying period. Further work is needed to optimize the fixation and drying period and the appropriate wet-bulb depression to ensure complete fixation. Leaching of copper in southern pine or chromium, copper, or arsenic in western hemlock was not affected by redrying schedules. No significant reduction in strength or decay resistance in southern pine or western hemlock lumber redried by any schedule was detected. Southern pine dimension lumber, which was initially kiln-dried at a high temperature and treated with CCA preservative, experienced a faster rate ofredrying than did lumber initially kiln-dried at conventional temperature schedules.