Treating Hardwood Posts By the Double-Diffusion Method

The double-diffusion process is one of the newer non- pressure methods for treating wood by means of relatively simple equipment. It consists of soaking green wood first in one chemical solution and then in a second chemical solution. The two chemicals diffuse into the wood and then react with each other to form a compound that is toxic to termites and wood-destroying fungi. Since the compound that is formed in the wood is practically insoluble, it shows little tendency to leach from wood exposed to wet condition. The method appears especially promising for the treatment of round wood products such as fence posts. There are several methods for applying the treatment. Posts may be treated by being completely immersed in the solutions contained in tanks, or they may be stood upright in barrels. The barrel method offers the advantage of low investment in equipment and appears to be practical for treating a limited number of posts on a farm. The chemicals selected for test were zinc sulfate mixed with arsenic acid in a proportion of approximately 6:1 in the first bath, and only sodium chromate in the second bath. Tables are presented giving the retention of the chemicals in posts, lumber, and crossties treated by double diffusion at Athens, Georgia in June 1955.

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