The premature removal of treated wood from service, due to weathering rather than decay, has led to increased acceptance of alternative products promoted as “low maintenance”. Wood-plastic and pure plastic products threaten to take considerable market share from the approximately 2 million cubic metres of preservative treated softwood lumber production. These competing products have raised the bar for performance and price of decking. Profiling lumber shows promise to provide a makeover with a new look and reduced checking. Application of a durable coating should reduce the effects of weathering and reduce leaching of preservatives. A service trial was therefore initiated of various profiles and coatings.
Pacific silver fir and lodgepole pine lumber, both Mountain Pine Beetle-affected (MPB) and non-MPB, were used. Five different profiles were applied: rippled-flat edge, rippled to edge, ribbed-eased edge, ribbed-flat edge and centre, and flat radius edge. Two preservative systems were tested: coated or uncoated ACQ and a pigmented or coated carbon-based preservative. Five different types of fasteners were used, and the new boards were built into a deck in the Forintek courtyard.
This report provides results after one year of exposure. All types of profiling significantly reduced check length compared to flat boards for both species, however, the pattern with the central flat strip showed checking down that strip. The ribbed profile was best for hiding the checks that did occur. Post-MPB pine, rippled-flat edge showed the lowest check length and depth compared to any other profile, for both heartwood up and sapwood up. Pacific silver fir, ribbed-eased edge showed the lowest check length compared to any other profile for both heartwood up and sapwood up. Pacific silver fir showed lower check depths than post-MPB-pine, for all profiles and orientations with one minor exception and lower check length on flat radius edge sapwood up. Heartwood up showed less checking than sapwood up in Post-MPB pine for all profiles, but the same was not true for Pacific Silver Fir. At this stage the effect of coating on checking was not statistically significant.