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 bead will deliver that coverage once the foam collapses and the sheathing is pressed into place. DAP offers a “pro gun” with a knob that allows you to maintain a consistent flow rate to match your speed. (It also offers cans with a built-in nozzle cap that you operate with your finger. Most framers will want the pro-gun, but for occasional use, the DAP cap works decidedly better than the typical nozzle on a can of window sealant.)
Northwest framer Tim Uhler wasn’t convinced by the “easy application” claims. For Uhler, it was all about bending over. He and his crew have gotten used to the Milwaukee M12 Caulk and Adhesive Gun for delivering subfloor adhesive. A quart-size tube extends the cordless gun—not by a lot—but enough to make all the difference in how hunched they feel at the end of the day.
For Austin, Texas–based builder Matt Risinger, the reasons for using SmartBond are cost and performance. At first, he winced at the $20-per-can price tag … until he realized that one can delivers as much adhesive as six or so tubes. (DAP advertises eight 28-ounce tubes to one 20-ounce can at that perfect 1/2-inch-diameter bead size.)
Risinger and Uhler are both using Huber Engineered Wood’s AdvanTech, an “enhanced OSB” subflooring that requires a more expensive “premium” polyurethane adhesive. Regular subfloor adhesive won’t bond well to enhanced OSB. Risinger has done some interesting tests using a come-along and a scale to measure the force needed to yank off a piece of bonded subfloor (search YouTube for “Risinger subfloor adhesive test”), and found that SmartBond provides about three times more holding power than Loctite PL 400.
The only downside to SmartBond that Risinger reports is the lack of squeeze-out. Not a big deal; he trusts his framer. But he notes that if you’re looking for squeeze-out to verify that your framers actually used adhesive, you aren’t likely to see it with SmartBond.
Clayton DeKorne is executive editor of JLC.