Estimating the moisture excluding effectiveness of surface coatings on Southern Yellow pine using acoustic emission technology

In this research, acoustic emission technology was used to estimate the moi sture excluding effectiveness of coatings on wood. Moisture interaction wit h wood causes damage, and coatings such as paints and varnishes can effecti vely limit this interaction. Over time, the moisture excluding effectivenes s of wood is reduced by the actions of weathering and the resulting wood-wa ter interaction leads to problems due to the dimensional instability of the wood. Five coating types, at two spreading levels, were applied to samples of southern yellow pine. The samples were exposed to three weathering cond itions to simulate the effects of exposure then immersed in water while the moisture interaction was monitored using acoustic emission monitoring equi pment. Cumulative counts as well as changes in size and moisture content we re measured or calculated. The results show that acoustic emission technolo gy is an effective and sensitive estimator of the moisture excluding effect iveness of coatings on wood. The acoustic emission method is sensitive to l ocal changes and coating fractures whereas the more traditional methods are sensitive to gross changes in sample characteristics. Of five coatings tes ted, the most effective one was found to be an oil-based paint, and the wor st performance was by a water-based, clear poly-urethane.