Effects of Moisture on the Hardness of Selected Commercial Wood-Base Panel Materials

Hardness tests were run on twenty-nine selected wood-base panel materials; six plywoods, eleven particleboards, nine hardboards, one insulation board, one aluminum siding material, and one waste-paper board at four moisture conditions. The resistance to indentation of selected commercial wood-base panels was in the order of hardboard, particleboard, plywood, wastepaper board sheathing, aluminum siding, and insulation board sheathing. The surface dent-resistance of most of the hardboards and particleboards was two to three times greater than plywoods, and was superior to or comparable with that of the oaks and maple wood species. Aluminum siding was about one-tenth, one-fifth, and one-third as hard as hardboard, particleboard, and plywood sidings, respectively. The greatest variability in face hardness was among the results for aspen flakeboard and the least among results for both dry-process hardboard sidings (S2S) and particleboard made from Douglas-fir. Tempered 1/4-inch thick hardboard, high density Douglas-fir 3/4-inch and 3/8-inch particleboard floor-tile showed excellent property of resistance to indentation and wear at all conditions. After exposed to a humidity of 90 percent, and soaked in water for twenty-four hours, the average face hardness values of hardboards, plywoods, and particleboards were about 90, 80, and 70 percent; and 80, 60, and 50 percent of those at normal 50 percent humidity condition, respectively. In spite of these -loses, the residual dent-resistance of most of the particleboards and hardboards still meets or exceeds that of the Commercial Standards. Ovendrying the panels from 50 percent humidity condition changed little in their hardness values. As a result of horizontal shear and split failures occurred in the core, the dent-resistance at the end of most particleboards and hardboards was about one-half of that on the board surface. The effect of moisture on the end hardness values of five hardboards, six particleboards, and five plywoods was twice as much as that on the face hardness values. The end hardness, Y was positively correlated with face hardness, x value (Y = 258 0.25x).

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