A Laboratory Soil-Contact Decay Test: An Accelerated Method To Determine Durability of Treated Wood Shakes

Rodney C. De Groot, Bessie Woodward


In this study, cross sections of preservative-treated shakes were evaluated in soil-contact decay tests using Gleophyllum trabeum. The number of preservatives by species combinations used allowed evaluation of procedural aspects of this method. We conclude that the soil-contact decay test is a good tool for an accelerated evaluation of the durability of treated shakes. Experimental designs need to be structured so that each wood species can be analyzed separately. Interpretation of results requires consideration of both the distribution and median or mean of weight loss data for each treatment. Levels of retention should be well dispersed so that the effects of retention upon distribution of weight loss data for individual treatments can be determined. Selection of a sufficient sample size to represent the variation within the population of each wood species by treatment combination is judged to be more important than duration of the incubation period in excess of 12 weeks. Stated differently, a rigorous experimental design permits discrimination of major differences without a need to achieve a weight loss of 50% in untreated materials. Wood species utilized in this study were western hemlock (Tsuga heterophylla (Raf.) Sarg.), Pacific silver fir (Abies amabilis Dougl. ex Forbes), grand fir (Abies grandis Dougl. ex D. Don Lindl.), western white pine (Pinus monticola Dougl. ex D. Don), southern pine spp., and red alder (Alnus rubra Bong.).


preservative;method;shake;roofing;hemlock;pine;alder;wood decay;durability

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