The purpose of this article is to briefly discuss sealants and design considerations for restoration and maintenance projects. The replacement of your building’s sealants should be treated as a scheduled maintenance item, just like an oil change on your car. The life expectancy of a sealants varies, but replacement should be evaluated every 10-15 years. Commonly confused with caulking, sealants accommodate movement whereas caulk is used to simply fill a void within a component. Sealants are used in exterior wall construction to prevent the passage of liquids, light, or gases between two materials despite differential movement between those components. It is important for anybody considering a sealant restoration project to understand the different types of joints, sealants, design considerations, and installation procedures.
Types of Joints & Function
Joints are installed throughout structures in many different locations and configurations as needed to strategically accommodate movement in the structure while maintaining a watertight envelope. Common locations of joints are where two components of a structure meet, such as expansion joints, control joints, building transitions, fenestration perimeters, curtain walls, and glazing. Each application may require a different style of joint. Common joint types are construction joints, isolation joints, expansion joints, and control joints.
These joints function in two ways: either dynamic or static. Dynamic joints are those which are intended to move, and static joints are those which are not intended to move. Depending on the intended function, joints may be configured as butt joints, fillet joints, bridge joints, or lap joints.
Types of Sealants
Selecting the proper sealant can affect the service-life of the joint and the weathering envelope of your structure. In selecting a sealant type, remember that the primary function of any sealant is to maintain a positive seal between the substrates of the joint opening. The joint helps resist the passage of heat, light, sound, air, rain, snow, wind, odor, dust, and chemical and biological contaminants, while at the same time withstanding the effects of thermal cycles, UV radiation, moisture, and structural movement.
There are many different types of sealants with varying chemical and physical properties. The most common types of sealants are acrylics, butyls, latex, polysulfides, polyurethanes, silicones, and other high performance joints such as preformed expansion joints or joint bridging tape. In selecting a sealant type for your project, there are important considerations you must take into account:
- Joint Function: Is the joint dynamic or static? Is it going to experience thermal cycles? A static joint can use a wider range of sealants that will fill the joint and adhere to the substrates, while dynamic joints often require a high performance sealant to accommodate the anticipated movement.
- Movement: The anticipated movement of the joint must be calculated and then compared to the movement capability of the sealant. A high modulus sealant is relatively stiff whereas a low modulus sealant is relatively elastic.
- Geometry: The joint should be configured with the proper geometry so as to not allow three-sided adhesion. Depending on the type of joint, the configuration may vary. For example, an hour-glass shape is preferred when installing a butt joint.
- Backing Material: Be sure to select the proper backing material: closed-cell backer rod, open-cell backer rod, hybrid backer rod, bond-breaker tape, etc. Each of these has their own advantages and disadvantages.
- Compatibility: It is important to evaluate which materials the joints are being adhered to. Certain sealants require an adhesion promoter whereas others do not. Likewise, certain sealants are not compatible with certain substrates.
- Exposure: Sealants are designed to withstand different environments. For example, exterior sealants which will remain exposed to sunlight must be UV stable.
- Location: It is important to consider where the joint is located and what it may be subjected to, such as below grade, immersion, chlorides, foot traffic, or vehicular traffic.
- Odor: Almost all liquid sealants give off some type of odor during the installation and curing processes. This can be a problem when working in confined spaces or around building occupants.
- Aesthetics: The final appearance of liquid sealants lies solely with the installers and their craftsmanship. Proper joint tooling does not permit the use of soaps or solvents, which requires the joint to be tooled by hand.
- Safety & Security: Sealants are designed to provide supplemental benefits such as fireproofing or security. For example, many designers will specify a “pick proof” sealant for use in a prison.
Even the best barrier, drainage, and diversion systems will not work if the sealant joints are not properly designed, configured, and installed. The majority of sealant failures are due to faulty joint installation or the use of the wrong sealant. For more information about how to begin your sealant restoration project, please contact Trisco Systems, Inc. at 419-339-3906.
Information for this article was obtained from Sealant, Restoration, and Waterproofing Institute’s publication: “Sealants: The Professional’s Guide”, as well as their Technical Bulletin #7 “Sealant Types and Uses”. Conproco’s “Dictionary of Moisture Protection and Restoration”, 2008 Edition, was also referenced.