Achieving shell or complete penetration of western hemlock and Pacific silver fir with borates by pressure/diffusion treatments

Due to their perceived environmental acceptability, there is renewed interest in borate-treated wood products. The objective of this work was to determine whether a larger dimension export product, Japanese “dodai,” used as sill plates for buildings, could be “shell-treated” or “completely penetrated” with borates using various pressure treating schedules and post-treatment diffusion periods. Hem-fir dodai were separated into the two component species and cut into test samples for pressure treatment by one of two processes: 1) a 2-hour full-cell; and 2) a 6-hour full-cell treatment. Test samples were assessed for boron penetration and retention directly after treatment and again after 2-week and 6-week diffusion periods. Results showed that complete- or shell-treatment of Canadian hem-fir dodai can be achieved by careful selection of pressure treatment schedule and diffusion period. The combination of treatment process and diffusion period selected would depend on the target penetration, analysis zone, or core loading required, and the species involved. For example, shell treatments of 80 percent at or exceeding 10-mm penetration were obtained in Pacific silver fir after a 2-hour pressure period. Western hemlock required a 2-hour pressure period and 2 weeks of diffusion. Complete penetration to core loadings of 1.2 percent boric acid equivalent were obtained with Pacific silver fir pressure treated for 6 hours and left for a 6-week diffusion period.

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