Self-adhesive flashing tapes are an integral part of virtually every drainage plane we inspect. Primarily used as window and door flashing, they are also used to flash wall penetrations and sheathing seams as well as a variety of not so cost-effective, humorous applications. It is rare to encounter a drainage plane without some degree of improper bonding. Flashing tapes could be considered a builder’s best friend, yet they provide a false sense of security if not bonded correctly. It is important to understand just how dependent they are on proper installation, in the right weather conditions, to keep moisture out.
A common perception is that the presence of self-adhesive flashing will do the job, but the question to ask is will it stand the test of time and moisture; performing as it needs to perform. A prevalent installation defect of self-adhesive flashing tapes is poor bonding of the tape to the substrate. Of particular concern is the upper edge of flashing tape, which if un-bonded can actually trap and hold moisture. Not only are we concerned with preventing moisture from entering openings, we are also concerned with limiting the flow of moisture-laden air into the wall cavity, as energy performance is also part of the equation. We hold other contractors accountable to install products according to the manufacturer’s recommendations and something as important as the drainage plane should not be an exception.
Self-adhesive flashing tapes are generally made with PSAs (pressure sensitive adhesives) and rely upon the installer to apply significant pressure to securely adhere them. As the name “pressure sensitive” indicates, the degree of bond relates to the amount of pressure applied. Most, perhaps all, self-adhesive flashing tape manufacturers recommend that a roller or special dispenser be used when flashing tape is applied, otherwise bonding is not fully achieved and may be temporary. It is important to review and follow the manufacturer’s installation guidelines; nonetheless, a few adhesion-related items to look for on the jobsite include:
Air Temperature – The ambient temperature should be within the application range published by the manufacturer.
Clean and Dry surface – The surface should be both clean and dry, so the adhesive has the opportunity to bond.
Priming - If applying over material such as OSB (oriented-strand board), a primer may be required. Our experience has been that self-adhesive tapes do not bond well to un-primed wooden surfaces such as OSB or dimension lumber. Refer to the manufacturer’s guidelines to determine if this is required.
Roll It – A factory approved roller or dispenser should be used as this alone may make the difference as to whether or not water enters the wall.
Use Gravity and Shingle-Style Lap Techniques – Whenever possible, avoid using flashing tape as the sole line of defense against water intrusion. If gravity and shingle-style lap can be utilized then we recommend this as the first option.