Laboratory durability testing of preservative treated wood products - first attempts and observations

In the past, durability classes (DC) had been assigned to wood species, sometimes also to homogenously modified wood-based materials such as thermally modified wood. More recently, some standards allow for classifying the biological durability of chemically modified wood, preservative treated wood and wood composites. Even treated products may be subject to durability classification, but necessary methods for representative sampling and testing of treated products are lacking. This study aimed at examining the feasibility and suitability of product testing for a durability classification of treated wood products. Sections of untreated and preservative-treated terrace decking and palisades were incubated with pure cultures of brown and white rot causing basidiomycetes under laboratory conditions. Instead of mass loss, the decayed cross-sectional area was determined and used for comparison. The spatial distribution of fungal decay and wood moisture content had been investigated. The effect of end-grain sealing and pre-stressing of the specimens on the decay development were examined as well. The handling of large specimens, e.g. sections of poles or other products, under sterile lab conditions was challenging, but specimens were successfully inoculated and incubated for a period of 16 weeks. Contamination of test containers and specimens with mould were negligible. Compared to mass loss measurements, the quantitative evaluation of decayed areas on the specimen sections was more laborious and time-consuming. Mass loss measurements on the specimens were not possible, but information about infestation pathways and decay patterns were extracted from the measurements. While the application of end-grain sealants hindered fungal decay, pre-drying of the specimens led to the formation of checks which expedited decay.