EFFECTS OF REDRYING SCHEDULE ON PRESERVATIVE FIXATION AND STRENGTH OFCCA-TREATED LUMBER

Southern pine and western hemlock dimension lumber specimens were pres sure treated with chromated copper arsenate (CCA) and then redried usi ng one of seven post-treatment schedules. The influences of these seve n kiln- or air-drying schedules on chemical leachability, decay resist ance, and wood strength were evaluated to better understand the relati onship between the severity of the redrying process and CCA fixation. For southern pine, six kiln-drying schedules exhibited less leaching o f chromium and arsenic than did CCA-treated material air-dried after t reatment. Depending on the temperature in initial kiln-drying, chromiu m and arsenic leaching were significantly reduced after a two-step pos t-treatment kiln-redrying schedule having an initial 12-hour fixation and a small wet-bulb depression followed by a drying period. Further w ork is needed to optimize the fixation and drying period and the appro priate wet-bulb depression to ensure complete fixation. Leaching of co pper in southern pine or chromium, copper, or arsenic in western hemlo ck was not affected by redrying schedules. No significant reduction in strength or decay resistance in southern pine or western hemlock lumb er redried by any schedule was detected. Southern pine dimension lumbe r, which was initially kiln-dried at a high temperature and treated wi th CCA preservative, experienced a faster rate of redrying than did lu mber initially kiln-dried at conventional temperature schedules.