Strandboards were treated with a copper-boron water-based preservative at different points of manufacture process namely, green strand diffusion, vacuum, spray application in the resin blender and post manufacture heat and cold quench. Preservative was applied to achieve five different retentions (0, 1.5, 3, 6, 12 kg m-3). The modulus of rupture and modulus of elasticity were assessed before exposure to decay. Treated boards were then exposed to unsterilised soil at high level of relative humidity and temperature for 18 months at two different soil moisture contents. Assessment of results was based on weight losses and strength losses. At the lower moisture content decay was severe and brown rot was the predominant decay type at ineffective preservative retentions. At the higher soil moisture content soft rot decay predominated. Vacuum, diffusion and spray treatment achieved protection only at the highest preservative retention while the heat and cold quench failed to achieve protection. There was significant difference in terms of decay between the high and low moisture conditions. Weight loss and strength loss showed good correlations.

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