Effect of water repellents on long-term durability of millwork treated with water-repellent preservatives

This report describes the long-term effect of water repellents (WRs) on durability of painted window units that were placed outdoors near Madison, Wis., in 1956. It includes the final evaluation of the windows and an analysis of their water repellency during the first 6 years of exposure. Also, swellometer test results for the treating formulations are compared with water repellency and durability of the window units treated with those formulations. The wooden windows were originally treated with several water-repellent preservatives (WRPs) that contained different amounts of WR. Following the WRF treatment, the windows were primed, top coated, and left to weather for 28 years without maintenance. Analysis of the dimensional changes of the WR-treated windows showed that during the first 6 years of exposure, the water-repellent effectiveness (WRE: decreased with time. A least squares fit of this decrease in WRE with time had r2 values in the range of 0.6 to 0.8 for most treatments. Extrapolation of this trend showed that the effectiveness dropped to zero at about 20 years. There was little correlation between the long-term durability of the windows and the initial swellometer values for the various treatments. There was, however, a slight correlation (r2 = 0.64) between the original swellometer measurements and the time for the WRE to reach zero.

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