Influence of basic catalyst and organosilane types on dimensional stability and durability of exterior wood cladding

To extend service life in exterior cladding applications, wood must be treated and/or coated. White spruce (Picea glauca (Moench) Voss) is a common wood species used in Canada for exterior cladding applications. White spruce is a refractory species and can be hard to treat with conventional approaches. Organosilanes could be an interesting wood treatment as condensation between organosilanes and wood hydroxyls can occur leading to a decrease in hydroxyl content, which are responsible for the dimensional instability of the wood. White spruce was pressure-treated with different formulations of organosilanes using acid and basic catalysts as well as hydrolysed and non-hydrolysed organosilanes. Weight percent gains were quite low (up to 11%) due to white spruce anatomy, and also because the organosilanes were located only in the cell wall. White spruce treated with organosilanes showed the best anti-swelling efficacy (up to 30%) for a nonhydrolysed formulation using an acid catalyst and the smallest organosilane molecule. The basic catalyst did not improve the anti-swelling efficacy compared to the acid catalyst because of its low mass gain. Three types of commercial coatings were applied on the treated wood and untreated control. The coated samples were submitted to accelerated UV exposure for 1,500 h to evaluate colour change and adhesion. The opaque stain exhibited the smallest total colour change (Delta E-ab*) with or without the modification of organosilanes.