Effect of Plywood Glue Lines on the Accuracy of Moisture-Meter Indications

The objective of this study was to determine the errors of moisture-meter indications when used or plywood. Five panels were made for each of two species, Douglas fir and yellow birch (of two, three, and five plies,) and for each of ten different glues, making a total of 300 panels. After curing and conditioning, four 5-inch squares were cut from each test panel. These specimens were conditioned to approximately 6-1/2, 12, 15, and 19 percent moisture contents. After equilibrium had been attained the percent moisture content was measured using one radio-frequency power-loss and four resistance-type moisture meters. The specimens were then ovendried and the true percent moisture content determined. The results of this study indicated that the moisture meter indications were unreliable and usually too high. The magnitude of the error depended on the glue used in the plywood and its moisture content, and also on the type of moisture meter used.

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