Treatment of wood by diffusion

Abstract

Too often in wood preservation, a diffusion treatment has been seen only as some process, inferior to pressure impregnation, in which green wood is slowly penetrated by a water-borne preservative applied by long soaking or other economically unattractive method. In some cases this may be a fair judgement but there are important exceptions where a diffusion treatment has technical and economic advantage. One example is in the utilization of rainforest hardwoods where many species may need sapwood or heartwood treatment for better use as plywood, joinery or building timber. Often a sufficient, and sometimes a better treatment, especially of heartwood, can be given by a cheap, simple diffusion process than by pressure impregnation. Also, apart from such practical uses, it is now becoming recognized that diffusion within the wood is a fundamental factor affecting the distribution and performance of water-borne preservatives applied by pressure treatment. This is particularly so with hardwoods where the initial impregnation may not reach the fibres and may leave the cell walls unpenetrated unless subsequent diffusion occurs.