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Extending the Service Life of Elastomeric Joint Sealants

FRIDAY, APRIL 28, 2017

By Wiss, Janney, Elstner Associates Inc.


More items for Building Envelope

Elastomeric joint sealants are most commonly used in building construction as a primary (and sometimes as the sole) weather seal to prevent water infiltration, and air infiltration and exfiltration, through the joints in the building envelope.

When they fail, the construction industry and many building owners are accustomed to regularly replacing joint sealants on buildings, without considering modifications that can aid long-term weathering durability.

Where practical, using the elastomeric sealant as part of a weather seal system—and not as the sole weather resistive component—can improve long-term performance.

Images: Wiss, Janney, Elstner Associates Inc.

Tthere are certain joint positions and locations that can remain wet for long periods, particularly those at surfaces that can pond water, or which receive little or no sunlight to aid drying.

The most damaging conditions for elastomeric joint sealants are prolonged exposure to moisture, UV radiation and heat. Fortunately, most joint sealant applications do not expose the sealant to prolonged moisture because the sealant materials typically remain wet for a few days after precipitation. However, there are certain joint positions and locations that can remain wet for long periods, particularly those at surfaces that can pond water, or which receive little or no sunlight to aid drying.

Additionally, if the sealant is adhered to a porous substrate such as masonry, which remains wet for long periods, the sealant at the bond line will also remain wet. Sealants on the south—and sometimes east and west—sides of buildings and on upward-oriented surfaces generally receive significantly more exposure to UV than do sealants in more sheltered areas.

Applying coatings to the sealant or concealing the sealant joint can offset the effects of exposure to the elements, as described in the following project examples.

Service Life Improved by Coatings

On a tilt-up concrete wall panel system of a warehouse/distribution building, the polyurethane joint sealant had been in place for 18 years. A contractor informed the owner that the sealant would fail soon based on the sealant’s age, and should be replaced. Like many precast concrete buildings of this type, the concrete had been coated subsequent to erecting the tilt-up panels, and the sealant in the joints between panels had also been coated.

An investigation of the condition of the sealant revealed it was still well adhered to the concrete substrate, and remained flexible and resilient—most likely due to its lack of exposure to sunlight and moisture, having been protected by the coating.

Sealants on the south—and sometimes east and west—sides of buildings and on upward-oriented surfaces generally receive significantly more exposure to UV than do sealants in more sheltered areas.

The building owner was advised that sealant replacement was not necessary and that the installed weather seal “system” (i.e., the sealant and a coating applied over the joint sealant) was effective and would likely continue to perform satisfactorily for several more years.

Adding a coating over joint sealants in horizontal joints may be particularly prudent in parking structures and other applications where moisture, UV rays and heat are likely to result in an abbreviated service life of the sealant.

Service Life Improved by Altering the Wall Details

On an EIFS-clad facade at a hotel, the sealant at wide horizontal joints at the floor lines was exposed to UV rays and heat from the sun at some locations. At other locations, where it was shielded from direct sunlight due to the orientation and building configuration, the sealant was subjected to prolonged wetting. The wide sealant joints were regularly deteriorating because of these exposures.

Repairs at these locations not only included replacing the joint sealant, but also redesigning the EIFS wall details at the horizontal joint locations to shed water and shield the sealant from exposure to UV rays, heat and water.

This was accomplished by adding a belt course to the EIFS at the floor lines so that the sealant could be installed in a downward-oriented joint so that it was not directly exposed to moisture and sunlight. The sealant was present to prevent water and air infiltration at the EIFS manufacturer’s required floor line movement joints.

A fix was accomplished by adding a belt course to the EIFS at the floor lines so that the sealant could be installed in a downward-oriented joint so that it was not directly exposed to moisture and sunlight.

The modified joint configuration made the sealant bead a part of a “system” repair that allowed the sealant to perform as a second line of defense against water entry through the joint (good detailing that shed the water being the first line of defense). Similar detailing can be accomplished in masonry construction by projecting the masonry course above the horizontal sealant joints so that the sealant is shielded from moisture, heat and UV rays.

Not all joints can be designed to protect the sealant, such as when incorporating a coating or reconfiguring the wall detailing. However, when possible, designing joints based on a comprehensive wall system approach that better protects the joint sealant may provide longer service life for these applications.

About the Author

Christopher Sass, an associate principal-level architect with Wiss, Janney, Elstner Associates Inc., has worked on a variety of projects related to the investigation and repair design of distressed conditions in buildings. He has directed and participated in numerous investigations and design of repairs involving plazas, roofing, masonry walls, EIFS cladding, curtain walls, windows, sealants and water infiltration. His work has been focused on water infiltration, masonry, curtain walls and roofing. Sass is the Chairman of ASTM C24 Building Seals and Sealants, and the president of the board of the Masonry Institute of Michigan.

You can reach him at csass@wje.com.

ABOUT THE BLOGGER

Wiss, Janney, Elstner Associates Inc.

“Solving for Why” is written by professionals at Wiss, Janney, Elstner Associates Inc. Since 1956, WJE’s primary goal has been to provide the best solutions for its clients’ new and existing construction-related problems. The firm’s highly qualified engineers, architects, and materials scientists possess a collective knowledge gained from solving, as well as helping clients avoid, thousands of problems. Author information is available at the bottom of each blog entry.

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Tagged categories: Elastomeric coatings; Exposure conditions; Outdoor weathering; Sealant; Water-resistive barrier; Weathering

Comment from ROY CANNON, (7/31/2017, 8:33 AM)

Excellent summary of why it is important to design joints with exposures as well as sealant capability in mind. Too often, sealants are utilized as a stand alone "fix" to a breach of the building envelope by design or otherwise. Expansion joint spacing, size, and configuration, as well as choice of sealant type are all important considerations during the facade design phase.


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