The current investigation was conducted to develop environmentally sound fixed wood preservatives for ensuring a long service life of pressure-treated wood products. Inorganic compounds such as zinc borate, basic copper carbonate and sodium silicate were selected to formulate wood preservatives (CBZS), which were expected to replace chromated copper arsenate (CCA). Both basic copper carbonate and zinc borate were first dissolved in the aqueous solution of volatile amine to contain 9.5% (m/m) copper, 3.4% (m/m) zinc and 9.5% (m/m) boric acid in the preservative concentrate. This concentrate was dissolved in water with an anti-leaching agent, sodium sili-cate.
Following the vacuum impregnation of sugi (Cryptomeria japonica D. Don) sapwood specimens [10(L) X 20 (R) X 20 (T) mm] with the treatment solution, the treated specimens were dipped in an aqueous solution of high concentrations of some rare earth chloride or alkali earth metal chloride in order to neutralize alkaline component of sodium silicate in wood.
Active components of CBZS in the treated wood were proved to be highly resistant to leaching process, which was thought to be equivalent to outdoor ground contact exposure for two years. The residual proportions of copper, boric acid and zinc were 80-88%, 60-80% and approximately 99%, respectively. Laboratory biological tests according to JIS K 1571-2004 clearly demonstrated that the treated materials were satisfactorily resistant to decay fungi and subterranean termites.

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