On-Site Preservative Treatments; Their Effectiveness for Exterior Millwork of Different Species Used in Various Climates

Results of 7 years of exposure tests are presented which show the effectiveness of a variety of short-soak preservative treatments on exterior wood millwork of a number of wood species. Mill-run western hemlock, Douglas-fir, and white fir, heartwood of ponderosa pine and western redcedar, and sapwood of ponderosa pine, Douglas-fir, and southern pine were treated by a 3-minute dip. Treatments were: a) Pentachlorophenol in mineral spirits (Fed. spec. TT – W – 570, b) Pentachlorophenol plus water repellents in mineral spirit (Fed. spec. TT – W – 572), c) Copper naphthenate in mineral spirits – a 1 percent solution. The treatments are applied to sections of porch flooring and a step rail attached to a post located in Wisconsin, Mississippi, and Oregon. A 3-minute dip of precut stock with 5 percent pentachlorophenol gave good protection against decay, especially at the end grain. Results indicated that ponderosa pine sapwood, southern pine sapwood, mill-run western hemlock, and mill-run white fir would derive the largest improvement from treatment, due to their greater susceptibility to decay. Treatment was most beneficial in Mississippi and least beneficial in Wisconsin.

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