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Fundamentals of Flashing Tapes

Flashing tape, when used in window and door installations, provides an added layer of protection to the rough opening. It is an important redundancy that helps prevent water from penetrating into the home and causing mold, mildew, rot, and/or other complications with the structural integrity of the wall. Not all contractors are familiar with the options available with flashing tape, so let's review some basic information.

4 min.
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Flashing tape can be broken down into three main components: the facer, adhesive, and the release liner (see below). Knowing more about each layer will help you better understand how current products in the market might affect the speed, ease-of-application, and long-term performance of your installation.

us osi main image 1 flashing tape

Facer Materials

There are many variations of facer materials, two of which are most commonly used in the building industry. First is an aluminum-based membrane. It is thin and easily moldable around edges and corners. Much like aluminum foil, once formed, it tends to hold its shape well and provides a great, air and water barrier. The product also has great UV resistance which is necessary due to occasional delays in construction sequence resulting in extended periods of exposure. However, this material generally lacks elasticity, and it is prone to cracking or tearing during the installation process. These cracks can provide opportunities for water penetration.

Many brands are using a more-elastic, plastic-based facer which is usually comprised of a polypropylene or polyethylene technology. In addition to forming around edges and corners with less likelihood of tearing, its pliability seals around fasteners like screws and nails used during the window installation process. When coated properly, these facers can withstand damage from UV rays for long periods of time - some for 180 days or longer.

Adhesive Technology

There are three primary adhesive technologies used in most, current product offerings: asphalt, butyl and acrylic. There are also a few newly developed technologies beginning to surface, but availability is limited, and long-term performance and installation feedback are still being evaluated.

Asphalt is the oldest technology of the three offerings. Its most notable limitations are initial adhesion, compatibility issues with some sealants and cold-temperature application with a more limited range of approximately 40F (4C) - 120F (49C). This is often used in southern regions of the United States where fewer days of extreme cold weather and less than average annual rainfall are experienced. It once had a cost advantage, but as other adhesive technologies have become more mainstream, the savings gap has decreased significantly over time.

Acrylic offers very strong initial tack and adhesion to a wide variety of substrates. It can, however, be very unforgiving to both novice and experienced installer alike because of it tenacious adhesion its tolerance for repositioning after contact to the surface is very low. It has an extremely wide application and service temperature range, 0F (-40C) to 120F (80C) and -40F (-18C) to 240F (49C) respectfully, making it good for extreme temperature applications.

Butyl is currently the most common adhesive technology used in flashing tape products because it offers an optimal combination of performance attributes and cost benefits. It can be applied on most substrates – including masonry and brick. Depending on the exact formulation, you may need to enhance the strength of the bond under certain circumstances with use of a spray adhesive. It can be applied easily in temperatures as low as 20F and as high as 120F. Butyl will provide outstanding "self-healing" performance to seal around fastener penetrations made during the window or door install process. When combined with a poly-based facer, you’re install will benefit from optimal protection. While butyl formulations can vary a bit, they all generally provide good initial tack with some forgiveness – enabling installer to reposition or adjust during the install process.

Tape Liners

Located on the adhesive side of the flashing tape, the liner is peeled off and discarded during the installation process. They are usually made from either a coated paper or poly-based material. If coated properly, paper liners can be relatively easy to remove. However, in some instances, cheaper coatings are used to reduce product costs. This can result in repeated tearing during the removal process leaving installers with a frustratingly long installation. This is not ideal in any situation, but certainly not when you’re positioned on a ladder, 10 feet off the ground, trying to complete a second story window install. The more reliable choice here is the poly-based liner. Almost completely resistant to micro-tearing and certain to peel off fast and easy.

Disclaimer: the information provided is intended to offer a general understanding. OSI recommends you seek out technical data sheets, speak further with an expert and/or gather additional performance information before making any final product decisions.

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