The weatiering resistance of twelve commercial pigmented stains on Douglas-fir plywood and glulam (glue laminated timber) was evaluated by exposing coated specimens at six test sites (Hokkaido, Tsukuba, Toyama, Kyoto, Kagoshima, and Okinawa) in Japan. The stains which were of two types, penetration and film forming, differed in their mode of failure during exposure. The penetration type failed through the development of cracks in the wood surface whereas the film forming type failed via film failure. Deterioration of coated wood surfaces was evaluated by calculation on a defected area using transparent squared sheet and a water repellency test. In the case of the film forming stains the development of even a small defect in the film affected the appearance of the treated wood surface. Kagoshima was the most severe site for the exposure tests whereas Hokkaido was the least severe. one However, differencs between the exposure sites were not great. Glue line failure occurred in more than 70% of the glulam specimens after 3.5 years exposure and the maximum depth of delamination was approximately 7 mm.
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