a plywood - patching composition is provided based on a non - cellular polyurethane elastomer prepared by reacting a polyether or polyester polyol with a polyisocyanate in the presence of a catalytic amount of a co - catalyst system comprising an organo - bismuth compound , preferably a bismuth salt of a carboxylic acid , and at least one organo - metallic compound , preferably a metal salt of a carboxylic acid , wherein the metal is selected from the group consisting of zinc , antimony and lithium and wherein the bismuth and metal are present in an effective mole ratio ; and process for preparing same . the catalysts utilized are relatively non - toxic , yet they promote rapid polymerization with essentially no foaming for a wide variety of non - cellular polyurethane elastomeric applications , particularly in plywood - patch applications where even small amounts of foaming are deleterious to the properties thereof .