The preservative treatment of green timber by diffusion is reviewed together with criteria which influence the economics of the process. New process options are described which should overcome some of the technical and economic disadvantages of double diffusion. These include the use of coagulating agents which increase the viscosity of the preservative solution and facilitate treatment by momentary immersion. It is anticipated that the main application for the diffusion treatment process will be for the treatment of refractory timbers for both ground contact and above ground exposure. The system is most suitable for low density and higher heartwood moisture content wood species - for example Sitka spruce, and is ideally suited for use in the tropics for treating both plantation grown softwoods and mixed tropical hardwoods.

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