Durability of Adhesives in Plywood

Seven plywood adhesives were evaluated for durability by exposing panels and shear test specimens to weathering at the Madison exposure site for nearly 8 years. Wet strength loss and wood failure changes were measured as a function of exposure time. The method of exposure accelerated the degradation that would have resulted in most service environments. Results were compared qualitatively with the information obtained by accelerated aging in the laboratory and analyzing wet strength loss as a rate process. The rapid, initial strength loss that had been observed with acid-catalyzed adhesives on Douglas-fir by dry-heat aging in the laboratory was also detected in their behavior on the test fence. The tendency for some adhesives to hydrolyze during laboratory aging by water soaking ‘as also reflected in test fence performance. A more precise measure of a correlation between test fence results and laboratory-derived data was not possible because of the high variability in the shear strength values.

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