The excellent field performance of copper-chrome-arsenate (CCA) treated timber has been accepted for many years. The preservative loadings used in practice have been based on field trial results, backed by service tests. The performance of treated hardwoods in trials and practice indicated that provided the required loading and penetration could be achieved the performance would be good. Recent unexpected failures in a few hardwoods treated to specification indicate that some hardwoods behave differently in ground contact from the normal test species with equal preservative loadings. Field evidence with creosote suggests that some discrepancies can occur with other preservatives as well. The immediate problem is confined to a vary few species and in all cases failure has been due to soft-rot at the ground line. Petty & Preston (1968) demonstrated that CCA preservatives penetrate deeply into the tracheid wall of conifers affording excellent protection to the timber. It was decided to investigate the micro-distribution of CCA preservative components in two problem hardwood species, Acer pseudoplatanus and Eucalyptus maculata. If the components were found to be distributed less uniformly than in softwood tissues this could possibly account for the unexpected field performance of these hardwoods in ground contact.

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