With more flexible flashing products on the market than ever before—some formulated for specific substrates or climates—today’s contractors have far more choices than they did 10 to 15 years ago.

Performance for asphalt-based flashing tapes has improved, and rubberized asphalt has been supplemented by pricier and higher-performing butyl- and acrylic-based products.

The biggest question with these products has always been what substrates they are or aren’t compatible with. The good news, according to experts, is that today’s asphalt-based products have fewer compatibility issues than did the products of a decade ago, making the current offerings a great choice for all-around flashing work.

Of course, just because compatibility is less of an issue doesn’t mean that the issue has completely disappeared. Flashing manufacturers tweaking their formulations to help their products stick to a wider array of substrates may lead some contractors to believe that any flashing is appropriate for any substrate. Not so.

“Compatibility is still the No.1 issue,” according to Bill Robinson of Train2Build, a well-known consultant and trainer who helps builders prevent moisture problems. Robinson says that there are two parts to this: how a particular flashing will react with a particular substrate, and how it will interact with other parts of the weatherization system, including doors and windows.

Although most flashings will adhere to a wide variety of substrates, there are some caveats, which are often mentioned in door and window manufacturers’ installation instructions. But many manufacturers are confident in the ability of today’s asphalt-based products.

“A majority of flashings being made today are compatible with most window products,” says Mark Waddell, an installation and applications specialist with PlyGem Windows. However, he does admit that installers who want to play it safe tend to choose butyl because, he says, it has more across-the-board compatibility with all building components.

Some companies offer less leeway. Eric Klein, an installation trainer with Marvin Windows and Doors, says that some asphalt-based adhesives can discolor the vinyl nailing fins used in the Marvin and Integrity window lines, discoloring the vinyl and causing it to run. Most of these problems seem to occur with bargain-basement tapes, but to be safe, the company recommends that contractors steer clear of asphalt tapes entirely. “We say that any tape used with our windows must not contain asphalt,” Klein says.

The other part of compatibility is how the flashing tape will interact with the rest of the weatherization system. This includes the WRB (weather resistant barrier, or housewrap) and any caulks or sealants. For instance, most WRB manufacturers will only honor the warranty if their product is installed using the recommended flashing tape—usually one made by the same manufacturer. The WRB and tape are formulated for maximum adhesion to eliminate compatibility problems.

In cases where sealants must be used, window and WRB manufacturers specify which ones are acceptable. No one seems to recommend silicone: its high surface tension means that even the best tape can’t get a grip on it. “The silicone surface is too slick; there’s nothing for the adhesive to grab onto,” says Floris Keverling of 475 Building Supply, a Brooklyn, N.Y.–based importer of high-performance building products. Klein has confirmed this with his own field-testing. “I did a test using a silicone sealant with an asphalt-based flashing and a flexible vinyl window flange,” he says. “It failed in a very short time. It was a disaster waiting to happen.”

Regardless of tape choice, the installer needs to pay special attention to surface conditions. For instance, most flashings stick better to the smooth side of OSB than to the rough side. There can also be adherence problems with masonry-based substrates. The best solution is to apply a primer, which will fill in any irregularities in the substrate and will provide some extra adhesion.

Unfortunately, this is where many builders fall short. Few heed this advice either because they aren’t aware of it or because it’s an extra step. But having a primer available in the store could encourage best practice. Most manufacturers have a primer that’s designed to work specifically with their flashing, so for every flashing tape you stock, it’s a good idea to also stock the recommended primer.

Roll It On
Another common problem with flashing installation is that many installers don’t use a roller to seat the flashing onto the substrate. “You can’t just use a hand to smooth it on,” Robinson says. Rolling is crucial, regardless of tape type.

Asphalt and butyl tapes have a natural stickiness, while acrylic-based tapes are pressure-activated. When the release paper on an acrylic tape is pulled, the surface doesn’t feel as sticky as that of an asphalt or a butyl tape, but the tape sticks like crazy and is difficult to dislodge once the adhesive has been activated. And all tapes need to be rolled in order to properly adhere.

“I use a J-roller to mash [the tape] onto the substrate,” Robinson says. And that’s a good case for dealers to place J-rollers next to the flashing tape, so that when installers are buying tape, they’re reminded about using the roller as well.

—Charles Wardell