SYMPOSIA PAPER Published: 01 January 2004

Comparison of Butyl versus Modified Asphalt Window Flashing Adhesives


In the last few years, using window flashings to keep moisture out of wall systems has become an increasingly used practice. Builders have identified moisture intrusion as a key reason for callbacks. Window flashing products are expected to keep moisture from entering a wall system, around windows in particular, over the life span of a home. Traditionally, felt splines have been used to flash flanged windows, but now flexible flashings are emerging as the industry standard. Peel-and-stick flexible flashing integrates the window into the wall system by creating a seam between the window flange and wall system. Because the flashing product relies on its adhesive to create and maintain this seam over the life of the home, the durability of the flashing adhesive is very important There does not seem to be a good understanding of the in-use performance aspects of the typical adhesives, butyls and modified asphalts, used in flashing materials. This study characterizes key attributes of these different adhesive systems, which can be related to performance differences between typical butyl and modified asphalt adhesives used in window flashing products.

There are a number of key aspects that are important when considering what adhesive system to choose for a window flashing material. This study targets some of these parameters as ways to compare butyl and modified asphalts. The properties that will be tested are:- long term durability (simulated aging and exposure), - staining tendencies, - peel adhesion over a wide temperature range, and — compatibility to vinyl (a common window material).

Choosing the correct window flashing product is an important decision when it comes to keeping moisture out of wall systems over the life span of a home. The results of this study will help the building science community decide on the best way to protect homes from moisture intrusion.

Author Information

Zima, AD
DuPont, Richmond, VA
Weston, TA
DuPont, Richmond, VA
Katsaros, JD
DuPont, Richmond, VA
Hagood, R
DuPont, Wilmington, DE
Price: $25.00
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Developed by Committee: C24
Pages: 262–279
DOI: 10.1520/STP12568S
ISBN-EB: 978-0-8031-5498-8
ISBN-13: 978-0-8031-3480-5