Durability of exterior natural wood finishes in the Pacific Northwest

Abstract

There is a growing demand for natural exterior wood finishes that retain the original attractive appearance of wood with the least change in color and masking of grain. A number of experimental finishes are being evaluated for their performance in the cool, moist climate of Olympia, Wash. This study, started in 1966, has included observations on the weathering performance of 48 experimental finishes, both transparent and pigmented. Of these, 36 are still on exposure and inspected annually. Generally, water-repellent preservatives are the least durable of the natural finishes. Pentachlorophenol was the most effective mildewcide used in these finishes. Semitransparent, penetrating stains provide greater durability as compared to the transparent water repellent preservatives. Stains containing only 20 percent binder provided excellent protection even after 8 years’ exposure. Latex stains containing copper chromate were excellent durable natural finishes. Simple water solutions of chromium containing chemicals acted as durable “natural” finishes and were especially effective after one refinishing. These exposure results indicate that natural finishes for wood can be used successfully in climates where mildew growth is a problem and service lives of at least 6 years could be expected.

Citation

Feist, William C.; Mraz, Edward A. 1980. Durability of exterior natural wood finishes in the Pacific Northwest. Research Paper FPL-RP-366. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 8 pages