When it’s time to cover wall sheathing with a water-resistive barrier (WRB), most residential builders choose plastic housewrap, asphalt felt, building paper, or rigid foam sheathing. Some commercial builders, however, choose a fifth option: a liquid-applied building wrap.
Liquid-applied WRBs come in a bucket and are applied to wall sheathing or concrete blocks with a roller or a spray rig. These products cure to form a tenacious, flexible coating that seals small cracks and penetrations.
Although liquid-applied WRBs cost more than housewrap, they also perform better. Once cured, these rubbery coatings have a major advantage over housewrap or asphalt felt: they provide a very high level of airtightness. While the cured films are highly resistant to water penetration, they are fairly permeable to water vapor. In other words, a wall coated with a liquid-applied WRB can still dry to the exterior.
For builders who prefer to establish a home’s air barrier at the sheathing layer, liquid-applied WRBs are a good alternative to Zip System sheathing.
The Sto Corporation was the first manufacturer to develop a liquid-applied WRB (StoGuard) that is vapor-permeable. Released in 2000, StoGuard remains the market leader. Sto’s competitors include W. R. Grace (the manufacturer of Perm-A-Barrier VP), Henry Company (the manufacturer of Air Bloc 31), DuPont Tyvek (the manufacturer of the Fluid Applied WB System), and Tremco (the manufacturer of Enviro-Dri). GBA’s review of Enviro-Dri was published in July 2012.
I’ll take an in-depth look at two of these products — the ones manufactured by Sto and DuPont.
According to the ICC Evaluation Service, StoGuard is an acceptable alternative to water-resistive barriers specified in the International codes. (Manufacturers interesting in getting code approval for a liquid-applied WRB must submit evidence to the ICC-ES that their product complies with AC212, Acceptance Criteria for Water-Resistive Coatings Used as…