Performance of a rigid and a flexible adhesive in lumber joints subjected to moisture content changes

Abstract

Experimental work was undertaken to investigate the extent and magnitude of deterioration that can occur in typical plywood-to-lumber glue joints subjected to stresses resulting from changes in the moisture content of the wood, and to compare the performance of a somewhat flexible or deformable adhesive to that of a rigid adhesive in these joints. Results showed that the degradation of lumber-to-plywood joints can be very severe as a result of one cycle from 80° F. and 30 percent relative humidity, to 80° F. and 97 percent relative humidity, returning to a low moisture condition. Failure included physical destruction of the lumber, glue, or plywood, or only a weakening of the joint, depending on the orientation of the plywood face grain to the grain of the lumber. Losses in shear strength of exposed joints exceeded 30 percent in some cases when compared to control joints. In joints where conditions of specific gravity and wood quality permitted direct comparison of the rigid resorcinol-resin glue and the somewhat deformable modified epoxy-resin adhesive, the deformable adhesive showed distinct superiority.

Citation

Krueger, G. P.; Blomquist, R. F. 1964. Performance of a rigid and a flexible adhesive in lumber joints subjected to moisture content changes. Research note FPL no. 076. Madison, WI : USDA, Forest Service, Forest Products Laboratory. 38 pages.