Loss in Stiffness Evaluates Decay Resistance of Wood Treated with Copper Naphthenate

Inception of wood decay was measured by loss in stiffness of western white pine beams exposed to wood-destroying fungi. Beams 12 cm. long and 4 by 7 mm. in cross section were treated with 0.5 to 5.0 percent solutions of copper naphthenate in varsol solvent by dipping. The beams were placed in decay chambers and inoculated with the decay organism. Six fungi were used, namely Poria monticola, P. xantha, P. incrassata, Fomes roseus, Lenzites saepiaria, and L. trabea. Deflection of each beam was measured weekly under static bending load of fixed value (1.6 kg.). The bending tests showed that a high concentration of the preservative was required to inhibit certain fungi associated with decay in boats. The strength loss as indicated by increased deflection of the beams appeared applicable for use in toxicity tests of wood preservatives which are to be applied without pressure. A concentration of 5 percent by weight of copper applied by dipping inhibited most test organisms.

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