The service life of moderately durable species can be extended significantly if the challenge of effective treatment of refractory wood species can be overcome. Along with preservative effectiveness, the performance of preservative in treated wood depends on factors such as retention and penetration in treated wood, the wood anatomy, the uniformity of penetration and micro-distribution within the cell lumen and cell wall. Since 1960 treatability of alternative species research has been conducted at Scion. This manuscript summarises results from various preservative treatment trials of roundwood and timber from alternative plantation species to radiata pine such as common softwood species like Douglas-fir and cypresses plus hardwoods such as eucalyptus species and New Zealand indigenous beech species. Preservative treatment testing followed by durability testing of treated products eventually determines whether preservative treatment will be beneficial. Results showed none of the alternative softwood species tested were able to be treated to meet the minimum requirements of the standard (NZS3640:2003) using conventional full-cell process with CCA preservative. In most cases preservative penetration and uptake in the sapwood of the Eucalyptus species was satisfactory. However, the need for higher preservative retention to combat soft-rot decay, sapwood depth and heartwood durability must be considered before any hardwood species is treated and used in higher decay hazard situations.

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