Effect of Reversing the Loose and Tight Sides of Surface Veneer on Flexural and Shear Properties of Southern Pine Plywood

Placing the loose side of face veneers outside has only a small effect on the stiffness of uncycled southern pine plywood. However, the effect (reduction) could be 10 percent or more for plywood with face veneer 1/6″ thick and thicker (3-ply, 1/2-inch plywood). Results of flexure strip tests indicate that placing the loose side of face veneer on the outside reduced the flexural strength (MOR) approximately 20 percent. The effect was greater in plywood with thick 1/6″ face veneer. The relative position of the loose side of face veneers affects differently various flexural properties of plywood strips subjected to wet and dry cycling. For specimen with face grain parallel to span the placement of face veneer does not affect the MOR while MOE is reduced more if tight side is out. For specimens with face grain perpendicular to span placement of tight side out of face veneer reduces more all flexural properties. The placement of loose side of face veneers on the outside had a negative effect on edgewise shear modulus but had no effect on edgewise shear strength. The relative position of the loose side of face veneers had no effect on glue line shear strength or on percentage wood failure of either cycled or uncycled southern pine plywood. Finally, considering the appearance and paintability, it is recommended that the tight side of face veneers be kept on the outside unless placing the loose side on one surface would facilitate production and reduce costs.

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