Laboratory evaluation of wood-based composites treated with alkaline copper quat against fungal and termite attacks

Vacuum-impregnation with alkaline copper quat (ACQ) was applied as a post-treatment to five commercially-available wood-based composites (approximately 12-mm thick), including softwood plywood (SWP), hardwood plywood (HWP), medium density fiberboard (MDF), oriented strand board (OSB) and particleboard (PB). In general, ACQ-treated wood-based composites were not as resistant to biological attack as treated Cryptomeria japonica sapwood blocks, possibly due to the uneven distribution of preservative in the composites. Untreated and treated composites were tested for their resistance to two decay fungi (brown-rot fungus Fomitopsis palustris and white-rot fungus Trametes versicolor) and the subterranean termite Coptotermes formosanus by Japanese standardized laboratory test methods. Untreated MDF was the most resistant to both biological attacks, followed by PB, which was less resistant to C. formosanus. ACQ did not adequately protect SWP from F. palustris or termite, or OSB from F. palustris or T. versicolor even at the highest test retention of 5.2 kg/m3, whereas the biological resistance of HWP was reasonably improved by ACQ. Since cut-end-coated composites treated at higher retentions of both ACQ and copper azole performed much better than uncoated materials, cut-ends were considered to provide decay fungi and termites with easy access or penetration. These findings support the importance of remedial treatment of processed building components at construction sites.