Properties and Kiln-Drying Characteristics of Young-Growth Western Hemlock Dimension Lumber

Sinker heartwood occurs in both old- and young-growth trees. Two classifications of sinker were found and characterized as heavy, with floccosoids, and light, without floccosoids. Green moisture content (MC) of sapwood and sinker heartwood averaged above 140 percent while normal heartwood averaged about 80 percent. However, the range in MC for sinker heartwood varied from 80 to more than 200 percent. Specific gravity of sinker may or may not be higher than normal heartwood depending on growth rate and extractive content. During kiln-drying, normal heartwood reached fiber saturation point in one-half the time of sapwood and sinker heartwood. Total drying time to 15 percent MC for normal heartwood was about 30 percent less with a conventional schedule (180?F) and 40 percent less with a high-temperature schedule (230?F) than for sinker heartwood and sapwood. High-temperature drying reduced kiln time from conventional drying by 50 percent or more for the four board types.

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