Effective preservative treatments for Canadian glulam products are needed to maintain markets for mass timber on building facades, access markets with significant termite hazards, and expand markets for wood bridges. For all three applications, borate-treatment of lamina before gluing would be preferred as it would lead to maximum preservative penetration. However, the need to plane after treatment and prior to gluing removes the best-treated part of the wood, and creates a disposal issue for treated planer shavings. The present research evaluates the block shear resistance of glulam prepared from untreated and borate-treated lamina with a polyurethane adhesive. Borate treatment was associated with a small but statistically significant loss in median shear strength when evaluated dry; however, there was no difference between the performance of untreated and borate-treated samples when exposed to the vacuum-pressure soak/dry or the boil-dry-freeze/dry procedures. Further work is needed to modify the composition or application of the resin to improve shear strength for glulam applications and ensure consistent performance. However, overall, these data indicate that samples prepared from borate-treated lamina perform similarly in terms of block shear resistance to those prepared from untreated lamina.
Cross-laminated timber (CLT) may require preservative treatment in markets with severe termite hazards. Given the size of CLT panels, conventional pressure treatment would not be feasible. We therefore assessed the treatability of CLT panels with an alternative low moisture uptake surface-applied penetrating process for applying termiticides. Hem-fir panels were selected for the initial tests on the grounds that western hemlock and amabilis fir are relatively treatable. Nine test panels were dip treated and stored for 7, 14, or 21 day activation periods. Borate retention ranged from 1.2 to 6.5 kg/m3 and penetration ranged from 3 to 9 mm. Longer activation periods did not result in improved penetration. Greater penetration would likely be needed to meet performance-based standards.