Fluoride movement through Douglas-fir and hem-fir lumber following dipping in potassium/ammonium bifluoride
J J Morrell, C S Love
The ability of ammonium and potassium fluoride to diffuse through Douglas-fir and hem-fir lumber was evaluated over a 90 day period. Boards were dipped in a solution containing 10% (by weight) of ammonium and potassium bifluoride, then stored under cover for 90 days. Samples removed 30, 60 and 90 days after treatment indicated that the fluoride was unable to completely penetrate the wood. Penetration was markedly better in hem-fir, reflecting the greater permeability of this species. Increasing the dipping time had only a marginal effect on chemical uptake. Longer diffusion periods also had little effect on fluoride movement. Chemical assays of increment cores removed from the boards indicated that most of the chemical was detected in the outer 5 mm, although fluoride was present 5 to 15 mm from the surface. The results suggest that fluoride treatment can not completely diffuse through freshly sawn lumber at levels which would confer protection against many wood inhabiting organisms.