BORON-DIFFUSION TREATMENT OF ASPEN LUMBER STORED UNDER VARIOUS RELATIVE HUMIDITIES

This study was designed to determine if boards of a relatively refract ory wood species, quaking aspen, could be effectively treated with a b erate preservative using traditional dip-diffusion methods. In additio n, various solution concentrations and storage conditions were tested and their effects on diffusion were compared. Boards dipped in Tim-Bor (R) (U.S. Borax, Inc.) were stored uncovered and stickered in controll ed rooms set at various relative humidities (RHs) to provide different equilibrium moisture contents. Chemical analysis of boron content fro m aspen boards indicated that after 8 weeks of storage in controlled r ooms of 86 and 92 percent RH, boards had core retentions of 0.01 to 0. 37 percent boric acid equivalent. The final moisture contents of treat ed lumber were 54 and 49 percent for boards treated with a 15.6 percen t BAE solution and 70 and 58 percent for boards treated with a 34.7 pe rcent BAE solution when stored in rooms at 86 and 92 percent RH, respe ctively, indicating that diffusion could still be occurring. After 4 w eeks of storage, 61 percent or greater of the board cross section was penetrated at a concentration of 0.25 percent or higher as determined by spot test indicators for the two dip solutions. Results from this s tudy indicate that aspen boards can be adequately treated with Tim-Bor using traditional dip-diffusion methods. Under restricted drying cond itions of high humidity and high temperature, a sufficient preservativ e loading was obtained for control of wood decay fungi and wood-destro ying insects.