This report reviews current research dealing with the effects of waterborne preservative treatment and redrying on the mechanical properties of wood. In general, waterborne preservative treatments reduce average mechanical properties. This effect is exaggerated when treated wood is kiln-dried after treatment, especially at elevated temperatures. For lumber, recently completed research at the Mississippi Forest Products Laboratory (MFPL) and the US Forest Products Laboratory (USFPL) has shown that few negative treatment effects exist in the lower tails of the strength property distribution. An arbitrarily chosen -10% effect seems to begin somewhere between the 5th to 40th percentile of the strength distribution depending upon the grade of lumber and the severity of post-treatment redrying. As a result, the American Wood-Preservers' Association has recently initiated an across-the-board redrying temperature limit of 88°C (190°F) for all solid-sawn lumber and timbers. This report discusses recent research results and documents the reasoning behind the AWPA redrying temperature limit.

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