Shelling is a severe type of raised grain that occurs at the surface of deck-boards made from wood species that have growth rings with pronounced differences in density between earlywood and latewood, for example southern pine (Pinus spp.). Shelling is more severe in deck-boards fixed with their growth rings oriented pith-side-up (concave) rather than bark-side-up (convex). Far less is known about shelling than the other types of physical deterioration (checking and cupping) that affect consumer acceptance of wooden deck-boards. Furthermore, it is not known if shelling occurs in profiled wood decking, which is commonly used in Australia, Europe, Japan and New Zealand. We carried out a designed experiment to examine shelling in flat and profiled deck-boards made from western larch (Larix occidentalis Nutt.), a species with large earlywood-latewood density contrast. Deck-boards were oriented pith-side-up or bark-side-up, fixed to a sub-frame and exposed to natural weathering for 7 months. The roughness of weathered deck-boards was characterized using a confocal profilometer, and photography was used to observe the morphological features of shelling. Flat western larch deck-boards oriented pith-side-up were significantly rougher than boards oriented bark-side-up, confirming suggestions in the literature that growth ring orientation influences shelling of deck-boards. Shelling of flat deck-board was caused by the separation of earlywood and latewood, creating ridges and occasionally splinters of latewood projecting from the surface of boards. Shelling of profiled deck-boards also resulted from the separation of earlywood and latewood. Shelling was less pronounced in profiled deck-boards that were oriented bark-side-up, and in boards with wavy (ribble) rather than rib profiles. Shelling of profiled deck-boards created slivers that projected from the peaks of profiles. Some of these slivers were quite sharp, and for this reason we suggest that profiled deck-boards should be oriented bark-side-up rather than pith-side-up.

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