Strength Properties of Paper-Covered Veneer from True Fir and White- Speck Douglas-Fir

The types of paper-covered veneers investigated in this study included 1/8-inch Douglas-fir containing light, medium, and heavy amounts of white speck or honeycomb, 3/16-inch Douglas-fir with a medium amount of white speck, and 1/12-inch and 1/8-inch defect-free true fir. Ponderosa pine 5/16-inch apple-box shook was used as an additional comparative material in some of the tests. The material was tested after part of it had reached equilibrium moisture content in a high humidity of 85 percent and the remaining portion in an intermediate humidity of 65 percent. After conditioning, the specimens were tested for puncture resistance, nail-holding ability (direct and lateral withdrawal), stiffness, and bending strength. The test results were analyzed statistically. The results of the tests indicated that with the exception of the 1/8-inch Douglas-fir with a large amount of honeycomb, and the sound 1/12-inch true fir material, all materials tested were equal in modulus of rupture and modulus of elasticity. The 1/8-inch Douglas-fir veneer with a large amount of honeycomb was equal in strength to the 1/12-inch sound white fir product (both of these materials were approximately equal to the other 1/8-inch paper-covered veneers in nail-holding capacity, even though lower in bending strength.) All the paper-covered veneers gave the same average results as the pine shook in both nail-holding tests. At 65 percent relative humidity and 70?F., with the individual product thickness taken into consideration, the pine shook took a maximum load approximately 1-1/2 times greater than the 3/16-inch Douglas-fir product and deflected only one half as far. However, when the pine was compared in the same manner with the 1/8-inch Douglas-fir material with either light or medium amounts of white speck, the pine took a miximum load about 4 times greater and deflected only one seventh as far. The Douglas-fir veneer with light and medium amounts of white speck gave test values equal to or greater than those of the 1/12-inch true fir product for all properties evaluated. The 3/16-inch paper-covered Douglas-fir veneer with a medium amount of white speck compared favorably with the pine shook, although the additional thickness of the pine material made it stiffer and stronger.

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