Performance of wax-impregnated timber out of ground contact: results from long-term field testing

While, for instance, oils and waxes were found to be promising for protecting wood under laboratory test conditions, long-term outdoor experience with these materials is limited. This study aimed at investigating the performance of wax-treated wood exposed aboveground in double-layer and lap-joint configurations. Wetting resistance, susceptibility to checking and durability were investigated over several years. All wax-treated wood performed better in the lap-joint exposure than in double layer, which was characterized by severe moisture trapping. However, durability and moisture performance were considerably better compared to untreated controls, but diminished with increasing exposure time. Already after 1 year of exposure, the number of cracks on lap-joint specimens was nearly identic between treated and untreated samples. Due to the wax migration observed during exposure, the formation of checks, accumulation of water in treated samples and partial infection, it can be concluded that the chosen synthetic wax types are not recommendable for practical applications. On the other hand, the principle of wood protection through moisture protection became evident in the aboveground field tests: As long as moisture exclusion was assured, the development of decay was inhibited.