Effect of prestain on the release rate of copper, chromium, and arsenic from western hemlock

Abstract

To enhance appearance, stains are often sprayed onto western hemlock (Tsuga heterophylla (Raf.) Sarg.) lumber prior to treatment with chromated copper arsenate (CCA-C). Recently, concerns have increased that prestaining may affect the rate of leaching of CCA-C components from the treated wood and that leaching data generated with prestained material may not reflect the rate of release from nonstained wood. A secondary concern is that copper naphthenate field treatments applied to wood exposed during construction may contribute to the amount of copper released from CCA-C-treated structures. This paper describes a study in which the release of copper, chromium, and arsenic was compared with end-matched nonstained and prestained CCA-C treated specimens exposed to artificial rainfall. The effect of copper naphthenate end coating on release of copper was also evaluated. The application of prestain prior to CCA-C treatment reduced the release rate of arsenic from the treated wood by approximately 28%. Most of the decrease in leaching appeared to occur early in the test, during the time when arsenic release was greatest. The prestain also appeared to slightly decrease the release of copper and chromium, but these differences were not statistically significant. The application of a copper-naphthenate end coating did significantly increase the amount of copper detected in the leachate. Results from this study indicate that release rate data generated from nonstained CCA-C-treated wood may overestimate the release of arsenic from wood that has been prestained. In addition, results suggest that the application of a prestain may be a valuable tool in minimizing the release of arsenic from CCA-C-treated wood.

Citation

Lebow, Stan T.; Evans, James W. 1999. Effect of prestain on the release rate of copper, chromium, and arsenic from western hemlock. (Research note FPL ; RN-0271):6 p. ill. ; 28 cm.