A field trial was established at four locations in Australia to assess the effect of CCA and CCA-wax treatment on the checking (cracking) of radiata pine decking timber exposed to natural weathering. Untreated decking timber and timber that had been pressure treated with water acted as controls. After 1 year's exposure the number and sizes of checks occurring in treated timber and controls were assessed. Timber treated with CCA-wax had fewer checks, which were significantly smaller in size than those in CCA treated timber and the untreated controls (except for check length in untreated timber). Checking in CCA treated decking timber resembled that occurring in water treated controls in that checks tended to be larger (longer and wider) and fewer in number than those found in untreated (exposed) boards. This finding tends to suggest that the pressure treatment process may have influenced the susceptibility of wood to check during exterior exposure. The difference in check number and size between CCA treated and untreated controls was, however, statistically insignificant. The effect of the different treatments on checking was consistent across the four exposure sites. The implications of these findings for the development of preservative formulations that reduce the checking of wood during exterior exposure are discussed.

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