Kiln- and Boulton-Drying Douglas-Fir Pole Sections At 220 to 290F

Eight-foot-long sections of poles were kiln-dried at 220?, 260?, and 290?F and Boulton-dried at 220?F. The kiln schedule at 220?F duplicated the temperature conditions of end-matched sections that were Boulton-dried and pressure treated with a commercial charge of poles. Moisture distribution was determined by oven-drying cores. Temperatures during and after drying were recorded at various depths in sections dried at 220? and 290?F. Drying at all temperatures reduced greatly moisture content in the outer 1 to 3 inches but not at greater depths. Very long times would be required to dry large poles to moisture contents that they eventually attain in service. Because such drying times probably would be prohibitively long, kiln-drying should attempt only to season the outer portion of large Douglas-fir poles to moisture contents that are conducive to preservative treatment. Because of the lengthy times involved, prudence suggests that maximum temperatures not exceed 200?F to prevent excessive reductions in wood strength. The problem of continued checking of some large poles in service must rely on other solutions such as deep incising, through boring, or kerfing to the center.

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