Preliminary Observations of the Effect of Kerfing on the Surface Checking and Warping of Flat Sawn Southern Pine Decking
R Ratu, J Weizenegger, P Evans
Checking and warping of decking timber are serious defects and methods of reducing their severity are required to ensure that wooden decking can compete with alternative decking materials. Kerfing is effective at reducing the checking and distortion of square cross-section lumber, and the checking of roundwood. In the past it has also been applied to preservative treated decking boards, however, there is no information on whether kerfing reduces the surface checking or warping of treated boards. In this study one, two or three kerfs were sawn to depths of 10, 13, or 20 mm into the underside of 140 mm (width) x 40 mm (thick) southern pine decking boards. Kerfed boards and matched unkerfed controls were exposed to natural weathering for 1 year and the surface checking and distortion of boards was measured. The aim was to determine whether sub-surface kerfing of decking boards could reduce the surface checking and distortion of boards, and the kerfing treatment (kerf number by depth) that was most effective at reducing both the checking and distortion of boards. Kerfing reduced the cupping of boards exposed to the weather, but had no significant effect on twist, or bow. Both the single and triple kerfs were effective at reducing the cupping, whereas the double kerfs were ineffective. There was a positive correlation between kerf depth and reduction in cupping, and the kerf sawn to a depth of 20 mm was particularly effective at reducing cupping. Kerfing had no statistically significant effect (p>0.05) on the surface checking of boards, although in most cases checking of boards containing kerfs was greater than that occurring in the unkerfed controls. Further research is needed to confirm these preliminary findings.