Reducing the surface checking of deck-boards exposed to natural weathering: effects of wood species and surface profiling

Surface checking is a defect in wood decking that is highly disliked by consumers. Surface checking can be reduced by selecting species that are more resistant to checking, or profiling deck-boards with a series of V(rib) or U(ripple) shaped grooves. Most literature on checking of decking focuses on species that are already used as exterior products. This provides an opportunity to investigate the use of other under-utilized species as deck-boards. Surface profiling has been applied to deck-boards to reduce checking, but there is little research on why it is effective. I hypothesize that both species and the geometry of surface profiles will significantly influence checking of deck-boards exposed to natural weathering. To test this hypothesis I exposed deck-boards made from 9 untreated softwoods and 8 untreated hardwoods outside for one year and measured the checking of the boards. None of the species performed as well as western red cedar and ipe, durable species that resist checking. However, some diffuse porous hardwoods performed quite well and further improvements might be achieved with chemical or physical treatments. Profilometry was used to classify and identify the geometry of commercially profiled deck-boards. The ratio of the surface grooves (R1) to those of peaks (R2) classified profiles into two categories mentioned in the literature (rib and ripple). A new category of profile (ribble) was also identified that had intermediate characteristics of both rib and ripple profiles. New profiles with various R1/R2 and height to width (H/W) ratios of profile peaks and grooves were tested to examine the effect of profile geometry on the checking of Pacific silver fir boards exposed to natural weathering. Profiling reduced the width of checks but increased cupping of the boards. There was no consistent trend of R1/R2 and H/W ratios on checking, but rib profiles were better than ribble or ripple profiles at restricting checks. Therefore, I conclude that species and profile geometry influence checking. Furthermore, some of the rib profiles could be used with diffuse porous hardwoods and some softwoods to enable them to compete more effectively with decking made from durable wood species or wood plastic composites.Forestry, Faculty ofGraduat