Sealant joints: don’t ignore this small component and its big mission

Anyone who has put in their time in our industry has most likely experienced this scenario on several occasions: A building owner or general contractor calls to report that water stains or other indications of water infiltration are appearing around window or door openings, and a site visit is requested to review this situation. You arrive at the site, meet with the owner, inspect the interior, and confirm that the interior materials around several window and door openings are indeed stained and wet. Then, the first thing you observe during an exterior review is wide open perimeter joints between the glazing system frames and the surrounding wall cladding materials. In many cases, it is obvious that no perimeter sealant was ever installed, and in many others, there are widespread failures of the sealant joints that have created the open joints (see Fig. 1-4). Either way, the result is the same: a direct path for water to enter the wall system around the glazing system.

It seems that the brainpower of a rocket scientist, or even a fenestration expert, should not be needed to determine that open exterior joints can allow large amounts of water into the wall system, but for many owners, experienced assistance is required. Years of evidence have shown that improperly installed, poorly maintained or completely absent sealant joints are often a major contributor to the water infiltration problems occurring in many structures. There are also other factors involved, because a properly designed envelope system should include secondary protection to control incidental water within the wall system. However, the exterior sealant joints are the first line of defense against the elements, and should not be overlooked.

In every type of building, clad with any combination of exterior wall and fenestration systems, there are multiple joints at transitions, penetrations and expansion-control locations that require proper seals. In order to achieve good performance in sealing these joints, four major factors must be addressed:

• Selection of appropriate materials
• Good joint details and laboratory testing
• Professional installation and field testing
• Regular maintenance.

Sealant selection

Unfortunately, it often seems that an over-emphasis on low price, coupled with limited knowledge regarding the properties of various sealant materials, drive product selection. The attitude seems to be that "a tube of caulk is a tube of caulk" whether it is bathroom sealant purchased from the local hardware store or a high-quality, construction-grade sealant. Thus, "whatever is the cheapest" and readily available is often selected. This approach often leads to adhesive and cohesive sealant joint failures due to several factors, including: chemical compositions that are not suited for the environmental conditions, sealants applied to substrates to which they are not intended to adhere, and sealant movement capabilities that are not sufficient for the joint and substrate conditions.

Selected products should be high quality, construction-grade sealants specifically designed for the joint location and type, and these materials should be tested and certified according to ASTM C920 – Standard Specification for Elastomeric Joint Sealants. This standard includes requirements for testing and classification of sealants by type, grade, movement capability, use, approved substrates and various other material characteristics. Generic adhesive sealants, painter's sealants and bathroom sealants are typically not tested or certified to these rigorous standards. The largest portion of the cost of a sealing job is typically tied to the installation labor and equipment, not to the sealant material. Thus, the up-front savings of a few dollars per tube of sealant are miniscule when compared to the potential expense of a re-sealing job necessitated by an improper sealant that has failed.

Joint details and laboratory testing

Once the appropriate sealant material is selected, proper joint sizes and configurations must be designed in accordance with industry standards and the manufacturer's requirements. No matter how good the sealant material, failures can occur if the joints are not properly formed. ASTM C1193 – Standard Guide for Use of Joint Sealants provides extensive and detailed standards for proper joint dimensions, application, backing materials and many other factors. The manufacturers of all high quality sealants further supplement this standard with their own published requirements for application. These manufacturers will also perform pre-construction, laboratory adhesion and compatibility testing of the sealant contact materials. There is typically no charge for this testing, and it should be performed as part of the design process.

Installation and field testing

An experienced, professional sealant installer is then required to take the selected material and properly apply it in accordance with the designed details. The installer must be familiar with all manufacturer and industry installation requirements, must assure that all substrates are properly cleaned and primed, must verify that all joint dimensions are within product and project specifications, and must properly install the sealant and backing material to provide proper joint formation. Field adhesion testing should be conducted as installation begins, and then periodically throughout the installation process, to verify proper joint performance. The Appendix to ASTM C1193 includes standardized procedures for this field adhesion test (see Fig. 5). In the real world, joint dimensions are often not as consistent as those shown in drawing details, and a common type of failure occurs when sealant is applied to overly narrow joints with no backing material. Products and methods are available to properly address almost any field condition, but the installer must bring these conditions to light to allow for revised details and products as required.

Maintenance

The responsibility for the final leg supporting a successfully sealed envelope lies with the building owner or manager. Although some high grade silicone sealants carry up to a 20-year warranty, every product has a finite life span and must be regularly inspected and maintained as required for continued and effective performance. Even a relatively small sealant void can allow a large amount of water into the wall system during a wind-driven rain, and regular maintenance can prevent much greater problems in the future.

Other considerations

In addition to the four major components of a successful sealing job, a glazing contractor should give careful consideration to some other factors. First, is the decision to either self-perform or subcontract the perimeter sealing work. Either method can be successful, but the glazing contractor is ultimately responsible for the job and will receive one of the first phone calls if there are problems. Even when subcontracting the work, it is critical to remain involved in product selection, to actively supervise the installation and to insist upon documentation of laboratory and field testing as verification of proper installation and performance.

You should also learn about the wall cladding materials surrounding the glazing system, to which the opposite side of the perimeter sealant will be adhered. For example, the sealant manufacturer might recommend one of their products as best for sealing to masonry walls, but another for sealing to a metal panel system. Another example involves the manufacturers of Exterior Insulation and Finish Systems. These companies typically require the perimeter sealant be adhered to the base coat, rather than the finish coat of their system. This requires awareness by the glazing contactor and coordination of perimeter sealant installation with the general contractor and other trades. You should not assume that everything on the far side of the sealant joint will be worked out by others, because once again, if there is a problem, you will be one of the first to receive a call.

When compared with the square footage of the entire building envelope, the sealant joints are a very small percentage of the total. This leads many in the industry to ignore or neglect these joints, but their importance should not be underestimated. The performance of the intricately designed and tested systems on each side of a joint can be compromised if the sealant is not doing its part. By properly selecting, installing and maintaining the exterior sealant, you provide that crucial first line of defense (see Fig. 6). Take good care of these small parts of the whole, and it will lead to substantial, longterm returns in building performance.