Durability ratings of post-treated wood-based composites after 14 years of field exposure

Abstract

Several commercial wood-based composites (softwood plywood [SWP], hardwood plywood [HWP], medium-density fiberboard [MDF], oriented strand board [OSB], and particleboard) [PB]) were post-treated with alkaline copper quat and copper azole at two different retention levels. The treated specimens were installed on concrete blocks covered with 5-sided PVC boxes simulating the crawl space conditions (protected above-ground) in Japanese houses in Southern Japan where decay and termite activity are high. The experimental variables are a comparison of treated versus untreated, preservative type and retention levels. During 14 years of exposure, the specimens were biannually visually rated. In general, termite damage became visible earlier and the harshness of attack was higher when compared to decay damage. The untreated and treated MDFs were the most resistant under the protected above ground conditions at the end of 14 years exposure. Particleboard durability performance followed the MDF rating during the same period. The untreated OSB, HWP, and SWP were the least resistant composite types. The treatments substantially increased the durability of the mentioned composite types by 317.6%, 80.5%, and 133% higher termite grading when correlated to their untreated controls, respectfully, yet they failed to maintain full protection. Based on statistical analysis, preservative types and retention levels did not significantly affect decay and termite ratings.