Moisture Meter Calibrations for Untreated and ACQ-Treated Southern Yellow Pine Lumber and Plywood

Abstract

Abstract This study investigates the effects of alkaline copper quaternary (ACQ) preservative treatment and of plywood glue lines on resistance-based moisture content (MC) measurements. Moisture meter readings using stainless steel screws as electrodes were acquired over a range of moisture conditions in Southern Yellow Pine (SYP) lumber and plywood. Calibration equations are presented for predicting gravimetric MC from meter readings taken in SYP lumber and SYP plywood with or without ACQ treatment. These corrections assume that the meter has been set for SYP. Correlation equations are also presented for directly relating resistance to gravimetric MC, which may be useful for automated data collection systems employed in monitoring moisture levels in buildings. The conductance of SYP lumber was raised by treatment with ACQ, particularly at higher moisture contents, but was unaffected by vacuum-pressure treatment with water. The conductance of untreated SYP plywood, measured with electrodes penetrating the glue lines, exceeded that of untreated SYP lumber. The conductance of SYP plywood was lowered by treatment with ACQ, by vacuum-pressure soaking with water, and by exposure to rain. We suggest that electrolytes in the plywood glue lines increase the conductance of untreated plywood relative to that of untreated lumber, and that the concentration of these electrolytes is lowered by the (aqueous) preservative treatment process, thereby lowering the conductance of these high-conductance pathways.