Wood Laminating Comes of Age

The development of new and improved glues has been important for the growth of the laminating industry. Important improvements have been made in the resistance of glue bonds to water, heat, and decay as well as in strength properties and use characteristics of the glues. Suitable glues are now available for all forms and types of laminating and all service conditions. Animal glue and casein glue are excellent adhesives for wood; the resin glues have been used in the hardwood plywood and furniture fields; the resorcinol and phenol-resorcinol glues are used to bond any species of wood, and are fully durable under any exposure to moisture and durable against heat and chemicals, and set slowly so that large wood members can be assembled. Research on laminating of wood by gluing was begun at the Forest Products Laboratory 36 years ago. It began with a study in laminating wood for production of airplane propellers. Up to World War I non- water-resistant animal and vegetable glues were the principal ones used in wood gluing. Casein and blood-albumin glues with improved water resistance and working properties were developed. After World War I, gluing research led to an expansion of laminating processes to commercial products. The study was expanded to glue more than 300 bent laminated southern pine members and to test them for strength properties. The results of these tests gave information on the strength of members glued, the effect of end joints, the deflection under load, and the shear stress developed under load. Such specific information resulted in improved designs of wood structures. In the 1930’s came the development of the synthetic-resin glues, urea and phenol. In 1939 the Laboratory extended its weathering tests to laminated beams of southern pine, Douglas-fir, and hard maple with casein, urea and the acid-catalyzed phenol resins. In 1941 a research program was undertaken to seek new glues and to develop new methods. During the World War II period, the use of high frequency electric heating gained prominence in curing resorcinol glue. Methods for evaluating the quality and durability of glue bonds in laminated members and an accelerated test were found. Laminated products can maintain their size, shape, and condition best when glued at a moisture content equal to that which they will reach in service. Studies also showed that resorcinol and phenol-resorcinol glue bonds are not affected by later treatment of the laminated timber by any of the chemicals used for preserving wood against decay. Preservative-treated laminated members can also be produced by gluing treated lumber.

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