Vacuum Treatment of Lumber

Preservative penetrations and retentions were compared on 2-inch structural lumber treated by the long-cycle vacuum process or by conventional pressure impregnation. Two preservatives, pentachlorophenol in petroleum and acid copper chromate, were used on six commercially important construction species– coast Douglas-fir, white fir, western hemlock, lodgepole pine, ponderosa pine, and southern pine. Retentions of acid copper chromate determined by weight and by assay of the outer 5/8- inch zone correlate fairly well on pressure treatment but not on vacuum treatment. In the case of pentachlorophenol, the correlation is not close with either treatment. Penetration in vacuum treatment was significantly less than that obtained in pressure treatment of these species. Good penetration of preservative was noted primarily in sapwood of the three pines treated by vacuum.

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