A recent development in processing wood with a gaseous preservative means that dry, treated wood can be produced in under 30 hours with the benefits of product diversification, faster stock turnover and the ability to respond to short term demand. About 400,000 m³ of wood are treated each year in New Zealand with boron salts to protect from borer infestation. Traditionally this treatment is effected by dipping the freshly sawn wood into a solution of boron salts and then stacking the wood while the salts diffuse through it. For 50 mm thick timber the diffusion process takes from 5 to 8 weeks. The Forest Research Institute has developed a new technique whereby the treatment is carried out in the gas phase effecting full impregnation within seconds. This process is carried out in a pressure vessel, which acts as both a kiln, preservation vessel and steam conditioning chamber. The wood is first high temperature dried to a low moisture content, exposed to a vapourised organoborate and then steamed. Total time in the vessel is about 30 hours. Preservative treatment in the gas phase is a novel development for the wood processing industry. An outline of the development of the process is presented and the implications for this industry are discussed.

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