Exposure Test of Painted, Pressure-Treated Millwork

Improvement to make millwork a more dimensionally stable product, a more resistant product to fungi and insects, and a more serviceable product is important. To investigate phenomena of these properties, an experiment was run on a test building in Illinois which contained millwork of pressure treated Douglas-fir and ponderosa pine. Controls, specimens treated at 3 pounds per cubic foot, and specimens treated at 6 pounds per cubic foot were studied. The preservative used contained 12.86 percent by weight of water repellent and 5 percent by weight of pentachlorophenol. Fluctuations in moisture contents were observed over the seasons tested. Water repellents showed they did not affect moisture absorption, but did affect the rate of absorption and the rate of dimensional change. It was concluded that pressure treatment provided a surface that prevented the formation of a tight bond between the paint and the treated wood. Higher concentrations showed no effect of reducing the bond between the paint and the wood. The aluminum, primer proved to be an inferior primer compared to standard primers. When the paint cracked, the bond breakage between the paint and the wood was attributed to the action of the solvent, and not to the method of treatment, primer formulation, or to the toxicant.

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