courtesy DAP Products

Last fall, DAP introduced SmartBond, a polyurethane subfloor adhesive that goes on like a foam sealant but collapses to a sticky gel (see photos) after two to five minutes, depending on jobsite humidity. According to DAP product engineer Steve Padget, the foam presents millions of tiny cells—a lot of surface area—to the air. Those cells pull moisture out of the air, which allows the material to cure. The more humid it is, the less ti me you have. In a moderate climate, you have about 20 minutes before the glue sets up. In a hot, muggy climate, this “open time” is about 10 to 12 minutes—still time to get sheathing in place, but you’ll want to stay in front with measuring and cutting.

Delivering adhesive to the top edge of the joist is reportedly faster with pressurized foam. Like any adhesive, the rate at which you move the gun determines how thick a bead gets applied. Ideally, Padgett says, you’re looking for full coverage over the top edge of a 2-by joist (this is how the ASTM spec reads). With SmartBond, a 1/2-inch foam...

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