Importance of Moisture in Wood

The most important reason for drying wood is to prevent shrinkage and swelling during use and manufacture. Dimensional change in wood occurs at or below the fiber saturation point (about 30 percent moisture content) and is roughly proportional to the amount of moisture lost. If wood is properly selected, dried, and taken care of, it will hold its shape remarkably well. Drying prevents or reduces staining, insect attack, and decay. Drying facilitates wood preservation and fireproofing processes and increases wood strength; improves nailability, gluing, painting, and insulating properties; and decreases weight and electrical conductivity. As a rule, wood should be dried to or slightly below the moisture content it will have in use since a little swelling is less detrimental than the same amount of shrinkage. The conditions to which manufactured articles might be subjected varies greatly between regions in this country. Lumber conditioned to between 5 and 7 percent moisture content prior to production is suggested, with interior finish and flooring being 2 or 3 percent higher. Sample data from sample boards subjected to ambient conditions in various areas in California yielded moisture contents from 7.2 to 15 percent depending on wood type, season, and location.

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