Delayed Shrinkage After Surfacing of High-Temperature Kiln-Dried Northern Aspen Dimension Lumber

Delayed shrinkage can develop in high-temperature kiln-dried northern aspen lumber (Populus tremuloides and Populus balsamifera) which has been classed as dry according to normal metering procedures for softwood lumber. As they are presently used, the resistance meter with short electrodes and the power-loss meter are incapable of detecting wet pockets in lumber. When the lumber is in storage or in later use, the wet pockets dry out and collapse develops in the form of severe shrinkage, often accompanied by internal checks. This study shows that 1 1/2-inch kiln-dried, surfaced, dimension lumber may shrink in thickness by up to 0.24 inch. Based on the frequency of occurrence in laboratory tests these defects can be expected to develop in up to almost 30 percent of each kiln charge. Attention is drawn to the possible adverse effects of these defects on the acceptance of the species group for dimension lumber. More rigorous moisture-content metering is suggested, preferably with an in-line continuous meter, so that wet pockets may be detected.

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