Effect of Kerfing on Checking of Untreated Douglas-Fir Pole Sections

The effect of kerfing untreated, unseasoned, unincised Douglas-fir pole sections on checking during weathering for 44 months is discussed. Twenty-nine of the pole sections 1.8 m in length were kerfed full length to their pith, with a saw kerf 4 mm wide and the remaining 26 pole sections were unkerfed controls. During weathering at a test site near Vancouver, B.C., Canada, the depth and width of the major checks were monitored. The mean depth (68.4 mm) of the most penetrating checks in the unkerfed pole sections was almost 2.4 times that of the kerfed pole sections. A comparison with published data for kerfed (3-mm) and unkerfed (6-mm) poles pressure treated with creosote or pentachlorophenol showed that the mean width of the widest check in the treated poles was almost identical to that determined in this work (2.4 mm kerfed, 5.8 mm unkerfed). In the unkerfed pole sections, most of the worst checks developed during the first 2 years of weathering. For the kerfed pole sections, the saw kerf widened rapidly (5 mm to almost 12.5 mm) during this period, while the deepest check showed hardly any variation. More than 50 percent of the tangential shrinkage anticipated as a result of drying in the kerfed material was accounted for by the increase in the kerf width. There were more numerous severe checks in the unkerfed pole sections than in those which were kerfed, although the large variation in the number of the secondary checks, combined with the small sample number, prevented a detailed analysis of this observation.

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