Do Not Blame Adhesives When Veneers Are Guilty
Scientists have tested adhesive performance for making plywood and engineered wood flooring, assuming that smooth veneers of the same species were equal in properties. Work in Finland, however, in conjunction with the Forest Products Laboratory, has shown that this assumption is not a correct assumption. Therefore, perfectly good adhesives may be wrongly discarded after failing a performance test when in actuality the veneer caused the failure.
Thin sheets of wood (veneers) are bonded together with adhesives to make plywood and engineered wood flooring. In tests for wood adhesive quality, one assumes that all smooth veneers of the same species produce products with similar strength. In a joint program between the Forest Products Laboratory and Aalto University (Espoo, Finland), scientists have shown that two factors (log soaking temperature and check depth) make this assumption false.
Logs have traditionally been soaked in hot water first to make it easier to peel the veneer. Soaking logs in hot water were found to make a more bondable surface than room temperature water. Second, as the veneer is cut from the log, it develops checks (cracks) as it is bent going over the cutting knife. Deeper checks can give premature failure in the wood, resulting in low strength values.
The result of this work is that we can prevent veneer failure from causing a perfectly satisfactory adhesive to fail the test. Not only should this work lead to a general improvement in veneer quality, but also educate the users by adding notes to some of the wood adhesive standards.
Forest Service Partners