Water Repellency and Dimensional Stability of Southern Pine Decking Treated with Waterborne Resin Acids

Abstract Many residential consumers prefer that wood used in above‐ground exterior applications be protected by environmentally benign biocide systems and have good dimensional stability. To help achieve these two properties we are employing resin acids, a by‐product from the kraft pulping of pines, in a waterborne formulation. In an extremely harsh above‐ground exterior exposure, two sets of decking boards treated with the resin acid system had water repellent properties that were still effective after up to two years of exposure. The increased water repellency reduced the moisture gain following summer rainstorms by about one‐third compared to untreated matched samples, and this was sufficient to significantly reduce splitting by about half and cupping by one‐third. A wide variation in moisture gain following rain was observed for the untreated sapwood flatsawn decking, with the moisture gain positively and significantly correlated to the extent of checking. The optimal use of resin acids may be to provide some limited dimensional stability and, in combination with antioxidants and organic biocide(s), as a benign wood preservative system.