An Australian test for decay in painted timbers exposed to the weather for a total of 6 years

Timber panels consisting of seven untreated timber species and two species treated with chromated copper arsenate (CCA) were assessed after exposure aboveground for two separate periods, which each had a duration of 3 years. Each panel was inspected and scored for the presence of decay in the vicinity of its top, middle, and bottom position. Painting of the top and bottom end grain was deliberately avoided. Decay was found to be most severe at the unpainted bottom position of panels. As each panel type was represented by only a single replicate at each site, a statistical analysis was performed using the data from 20 sites after grouping the latter into four distinct climate types (tropical, subtropical warm summer, subtropical dry summer, marine cool summer). None of the four panel types: radiata pine (Pinus radiata D. Don) sapwood treated with CCA, mountain ash (Eucalyptus regnans F. Muell.) CCA-treated heartwood, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) heartwood, and messmate (E. obliqua L’Herit.) heartwood had progressed to a condition considered to be unserviceable. Untreated heartwood of brush box (Tristania conferta R. Br.), radiata pine, red meranti (Shorea spp.) as well as mountain ash were not significantly different from each other within each of the four climate types. Untreated ramin (Gonystylus spp.) heartwood and untreated radiata pine sapwood were rated as having the worst condition and were not significantly different from each other in any of the four climate types.

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