Modified double-diffusion is suggested as a method of impregnation for mixed tropical hardwoods for certain types of ground contact use in less developed countries. Compared with vacuum/pressure impregnation, capital costs are low and little skill is needed for the operations involved. Treatment of messmate (Eucalyptus obliqua L'Herit) rounds involving pre-heating in water prior to their immersion in the first stage solutions is described. Preliminary indications are that (i) there is a deeper penetration of arsenic when a compound of this element is used in the first stage solution (ii) a more even and deeper penetration of chromium is obtained when sodium chromate, rather than sodium dichromate, is used in the second stage solution. It is concluded that quality control in double-diffusion may be a limiting factor in the adoption of the process for the treatment of wood unless a simple but effective method is found to control solution concentrations and elemental ratios.

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