Synopsis: This article is an introduction to a new class of window and door flashing that is applied as a liquid instead of a tape. Product details from several manufacturers of these liquid-applied flashings are included.

By now, conscientious builders know that window and door openings need to be flashed carefully to keep out water. For residential builders, the most common way to flash openings is with peel-and-stick membrane.

However, a growing number of builders are looking at liquid-applied flashings (LAFs). Common in commercial construction, LAFs haven’t been seen much in residential work. Their advertised advantages—a small learning curve and fast installation—seem to warrant a closer look. LAFs come in various forms from eight different manufacturers. (Two others, Dryvit and Vapro Shield, make LAFs but require them to be used only as part of a proprietary WRB system. A third, Dow Corning, says that its product “isn’t designed for use in single-family residential construction.”) Some products are dispensed from cartridges like caulk; others come in a pail and have the consistency of mayonnaise.

Application is simple

All LAFs share the base chemicals used in the manufacture of caulks and sealants. Most are formulated from silyl-terminated polyether (STPE), but some, such as Pecora XL-Flash, are formulated from silyl-terminated polyurethane (STPU).

Once cured, they form a rubbery layer that manufacturers claim to be waterproof and airtight. Unlike most peel-and-stick flashings, most LAFs are vapor permeable; when used on the exterior side of wall sheathing, they won’t create a wrong-side vapor barrier.

Builders have discovered that liquid flashings work particularly well with inset windows. They don’t require any tricky origami at corners, and they avoid the problem of thick buildup caused by multiple layers of folded peel-and-stick.

To use an LAF, you squeeze or spread a generous…