An Australian test for decay in painted timbers exposed to the weather for a total of 9 years

Ten timber panels (eight untreated and two treated with chromated copper arsenate (CCA)) were manufactured from seven timber species and subjected to a total of 9 years of aboveground exposure. Following exposure, each panel was inspected, evaluated for the presence of decay in the vicinity of the top, middle, and bottom positions, and given a score on a scale of 0 to 8. In most cases, decay was found to be most severe at the unpainted bottom position of the panels. A statistical analysis was performed on the scores of the bottom position of the 6 best-performing panel types at 22 exposure sites, which have been grouped into 6 distinct climate types. The climate-panel type interaction was not statistically significant. However, there was a significant panel type effect. Radiata pine (Pinus radiata D. Don) sapwood treated with CCA gave the best performance against decay in all climate types. Untreated heartwood of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), brush box (Lophosternon confertus (R.Br.) Peter Wilson & Waterhouse), messmate (Eucalyptus obliqua L’Herit.), and CCA-treated mountain ash (E. regnans F. Muell.) heartwood performed similarly to each other. Two of these panel types (Douglas-fir heartwood and brush box heartwood) performed significantly better (1% level) than radiata pine heartwood. Four panel types [red meranti (Shorea spp.) heartwood, mountain ash heartwood, radiata pine sapwood, and ramin (Gonystylus spp.) heartwood] were unserviceable at 10 or more (45% to 82%) of the sites so were not included in the statistical analysis.

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