Penetration of boron in Douglas-fir and western hemlock lumber

The penetration and retention of disodium octaborate tetrahydrate in Douglas-fir heartwood and western hemlock sapwood were evaluated at concentrations of 0.5, 1.0, 2.5, 5.0, 10.0, and 20.0 percent (boric acid equivalent) with dip, full-cell, and empty-cell treatments. After a 1-month diffusion period, boron penetration in Douglas-fir heartwood was less than in western hemlock. Only western hemlock treated with higher concentrations of boron was completely penetrated. As expected, pressure treatments resulted in the highest retention, but there was little difference between full- and empty-cell processes. The results suggest that borates can be delivered to the outer shell in sufficient quantities to permit subsequent diffusion. Further studies with higher solution strengths combined with heating or steaming are recommended.

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