Performance of Softwood Plywood During 10 Years’ Exposure to Weather

The performances of laboratory-made southern pine and Douglas-fir plywood bonded with a phenol-formaldehyde adhesive were compared after 10 years of exposure in Wisconsin and Mississippi. Panels of both non-overlaid and resin-treated paper-overlaid surfaces were painted with two coats of high-quality commercial acrylic latex paint and refinished with another coat of latex paint after 5 years. After exposure the panels were examined for gluebond integrity, decay, face checking, and paint performance. Wood failure in initial plywood shear tests indicated well-bonded plywood. After 10 years of exposure neither species showed areas of delamination of as much as 1/4 inch in depth by 2 inches in length on any of the panels. Some decay showed in two of the panels exposed in Mississippi. One was of Douglas-fir and contained sapwood, and the other was of southern pine. Face checking occurred in both species on panels not overlaid with resin-treated paper. The acrylic latex paint showed no evidence of separation from the wood by peeling on either kind of plywood. Paint eroded in a natural manner but was discolored by fungal growth, particularly in Mississippi, and by a yellow exudate on the decayed panels. Unpainted southern pine plywood made in a plant trial run in 1963 showed serious delamination in three out of four panels after 10 years’ exposure. Delamination was less on painted panels.

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