Field-Glued Plywood Floors

Eight of 12 elastomeric construction adhesives which were tested for shear strength and durability appeared suitable for field-glued plywood floor applications. A total of 1,860 tests were conducted, demonstrating that adhesives form strong bonds with both dry and unseasoned lumber, even when surfaces are damp or frosty. Adhesive shear strength generally averaged from 150 to 450 pli under most conditions. Gluing should be avoided in subfreezing weather unless temperatures rise above 40?F shortly after assembly. An adhesive performance specification was developed for field-glued plywood floors. Floors were 20 to 80 percent stiffer than the joists alone when a single layer of 5/8 inch plywood was glued to the joists. The increase in stiffness depends on the plywood face-grain direction, the size of the joists, plywood thickness, and especially whether or not T&G plywood joints are glued. Gluing T&G joints between panels increased floor stiffness about 15 to 25 percent when compared to similar floors with unglued joints. The floor is stiffer when plywood is installed with the face grain parallel to the joists, rather than perpendicular. A design method for determining floor stiffness was developed. Joist stiffness increased less than 5 percent when plywood was nailed to them with a normal nailing schedule. This increase was only temporary, diminishing as the joists seasoned. A nail spacing closer than normal would be required to obtain a substantial increase in stiffness without using adhesives. The creep resistance of field-glued floors is about equivalent to nailed-only construction using dry lumber, but significantly better than nailed construction with green lumber.

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