InTrans / Aug 14, 2018

Moisture protection for timber members

This research evaluated sealers and coating systems for protecting softwood and hardwood bridge timbers treated with creosote and CCA preservative systems. Fractional moisture contents after 47 days of moisture adsorption for CCA treated southern pine end grain specimens was lowest for two coats of epoxy compared to the controls and the unfinished CCA treated control. All of the other finishes provided less moisture retardation. Similar results were obtained for the transverse grain CCA treated southern pine specimens. After 47 days of testing the CCA treated red maple results were somewhat different than the southern pine results. Two coats of epoxy provided the best protection from moisture gain through the end grain of CCA treated red maple followed by two coats of roof cement. Two coats of other finishes had higher moisture gain and similar retardation to each other. The best finish for transverse grain CCA treated red maple was two coats of epoxy. All other finishes had comparable 47-day factional moisture contents to the controls (untreated and unfinished). In general, the finishes provided some retdation in the moisture gain in the creosote treated specimens during the first one or two days of testing for both species and grain directions. After the first two or three days, the moisture gain was not retarded. Epoxy was the only notable exception to the moisture gain retardation of the finishes on creosote treated wood. One coat of epoxy on creosote treated southern pine and red maple end grain and transverse grain specimens produced substantial reductions in the rate of moisture gain and fractional moisture content values. Two coats of epoxy more than doubled the one coat reduction in the 47-day fractional moisture content for southern pine and red maple end grain and transverse grain speciments.