Many of us do not install sealants in our expansion and control joints, but we install our fair share in other locations. We install sealant with our coping installations, flashing installations, and our side work installations for some.
Sealants, caulking, and adhesives are sometimes used interchangeably in site conversations, without the need for corrections, but they represent three separate products. Historically, caulking represented a product used on the interior of the building, which was formulated for approximately 10% expansion and compression movement. Adhesives are formulated to have superior bond strength for holding two individual substrate materials together.
Sealants, which could be used inside of a structure or to hold substrate materials together, are primarily designed for our industry to seal exterior control, expansion, dowel pins, flashing laps, and door frames. Sealants have a far greater ability to expand and contract when placed properly in a range, not uncommon from 50% compression to 100% expansion, typically far greater than the design movement of the joint being sealed.
Overall our sealant joints need to have a few standard applications to perform for what we do. The sealant must perform in a manner that allows only biaxial stress to function properly or simply needs to move back and forth, only in compression or expansion. The use of a bond breaker tape or backer rod is a major key to allowing this to happen. A bond breaker does a few things for the installer. First, it prevents sealant bond to the inside of the joint, allowing the sealant to stick to the left and right side of the substrate (when discussing the substrate(s), this conversation refers to the joint as the substrate). This two-sided adhesion allows the sealant to move only back and forth.
Second, the installer will be able to shoot the sealant into the joint more consistently and even, keeping the sealant estimate more accurate and controlling cost. Third, it will prevent what is known as a cohesive failure because the sealant will not have to endure the triaxial stresses that a three-sided adhesion would create. Triaxial stress is where the stress of moving back and forth is combined with the stress of moving in and out from the back of the joint. Sealants are not designed for this and will rip down the center of the joint over time. An old timer’s rule of thumb for elastomeric sealants, more is not always better, is 2:1 width to depth, with exceptions for silicones where you can do a 1:1 width to depth in ¼ inch by ¼ inch installations.
Adhesive failure is when the sealant peels off the substrate either soon after installation or over the service period. Once an adhesion failure has occurred, one of two things needs to happen, the surface of the substrate needs to be reviewed for bond (proper preparation of substrate before re-applying the newly selected sealant product), or the selection of material must be checked for proper compatibility. Technical support from all the manufacturers can easily assist you with making the proper selection if this occurs.
Tooling the joints is important in proper placement; it compresses the sealant properly into the joint and provides a slick finish. Some folks like to wet their tools or fingers, or better yet, use dish soap to finish the joint; this should be avoided when possible.
Adhesion to a substrate is critical when selecting a product. In many cases, this is decided before bidding on a project, but any old product will no longer perform under all installation conditions when it becomes a contractor’s decision. Understanding the substrate is the key. Granite panels against aluminum window frames will be a completely different application than a brick veneer to the steel door frame. Any of the polymer-modified flashings found today to change the game even more. Surface energy is a fundamental property found in all products. Polymer-modified flashing products will have lower surface energy n the flashing lap joint than in a brick expansion joint. Matching the surface energy properties to the chemical properties of the sealant will save you trouble and callbacks when you take the time upfront. As mentioned before, technical teams at any of the companies where you purchase products are typically able to assist you in this selection process. One word of note, sometimes a product can be applied to a substrate and seem like it installs perfectly, but in some cases where products are not compatible, the sealant may just peel off without a bit of residue 24 hours later, 23 hours after you covered up your work in some cases.
Hopefully, this gives you a look at sealant issues that may not be commonly discussed; hopefully, this information will prevent a problem on your job one day.