Structural Sealant
Structural sealant is used to bond window frames, curtainwalls, and other similar structural components together. These materials can be susceptible to failure if they are not properly installed or maintained.
To ensure performance, structural silicone joint sealants are tested and qualified to a number of specifications. One of the most rigorous is ASTM C920 Standard Specification for Elastomeric Joint Sealants.
Sealant Composition
Structural sealants are used to seal openings or gaps between substrates in a building structure. They perform several important functions, including providing weather protection, thermal and acoustical insulation, and fire barriers. They may also serve as a simple smoothing or filling material.
The selection of the right type of structural sealant depends on the application and the performance requirements of the end user. Among other factors, the polymer chemistry, chemical makeup, and tensile strength of the sealant must be considered. In addition, the joint design and movement capability of the sealant must be coordinated with the expected joint movements.
Sealants are available in a wide range of polymers and are made from a variety of additives, such as fillers or plasticizers. Some of these additives have a negative impact on the performance of the sealant, while others are beneficial.
A few of the most common polymers used to prepare structural sealants are silicone, acrylic, urethane, butyl, and others. All of these types have unique characteristics that make them appropriate for different applications.
Some of these characteristics include adhesive and cohesive strength, modulus of elasticity, recovery ability after deformation, and durability under the effects of weathering. These properties affect the bonding action and the effectiveness of a structural sealant.
Additionally, sealants must have the ability to adhere securely to specific substrates and to maintain a seal even under the effects of moisture. Adhesion is a very critical property of a sealant and must be determined prior to installation.
During installation, it is important to ensure that all the required materials are at the site and that the joint dimensions are correct. If the sealant is not installed correctly, it will not perform as intended and it may damage the construction material.
The performance of a sealant is also affected by its chemical composition and the amount of moisture in the environment. The polymer and the surface of the sealant must be able to withstand moisture from rain, dew, snow, fog, and sea spray. In addition, the sealant must be able to resist the effect of UV radiation from sunlight.
Sealant Performance
Structural sealants are liquid applied or pre-formed products that adhere to structural materials such as glass, metal and other panel materials. They are primarily used for bonding of structural glazing and curtainwall to building substrates and thereby provide a weatherproof barrier for exterior or interior applications. They exhibit excellent mechanical properties, high ultimate tensile strength, un-primed adhesion to most building substrates and are resistant to a variety of environmental conditions, including heat, light, moisture, and movement.
Sealant performance is evaluated by many different factors, but the Structural Sealant most important consideration is the ability of the product to meet the performance expectations of its application. This can be a function of the product’s chemical makeup, its mechanical properties, its ultimate tensile strength, and its adhesion to substrates.
Adhesion is tested by the ASTM C719 test method, which evaluates the sealant’s adhesion to a specified substrate under certain conditions of temperature, humidity and shear. This test can also be done in an immersion environment to evaluate the sealant’s ability to withstand movement.
This test method is a good choice for testing the sealant’s ability to handle the joint movement of an application and is often considered the most rigorous standard sealant specification in the world. However, it is not a long term test and will not give a user much insight into the sealant’s longevity in a field application.
Another important consideration for sealants is their compatibility with other materials in construction. This is a concern in the case where the sealant is to be bonded with a material such as a wood or concrete substrate. The sealant must not affect the cure profile of the other material or cause degradation or liquefaction.
Several industry test methods are available for evaluating compatibility with other building materials. These tests may be performed in a laboratory or at the site where the sealant is to be installed.
The most rigorous test method for determining the sealant’s ability to withstand joint movement is the ASTM C719 test method. This test method requires the sealant to be cured in the joint under conditions of temperature, humidity and shear.
Installation
Structural Sealant is used to assemble, install, and repair glazing or other components in windows and curtain walls. It can also be used to provide weatherproofing and to bond various types of metal (aluminum panels), enamel, and glass to a framing system such as steel or wood.
Installation requires the use of joint filler and sealant backing materials recommended by the manufacturer to match the sealant material and to allow optimal joint movement. Unless otherwise indicated, joint backing materials are to be installed at depths between 1/4 and 1/2 inch (6.4 and 12.7 mm).
If the joints will be moving, ensure that all substrates are properly primed using cement based primer. Applying a sealant to cement based substrates without a primer will result in “three-sided adhesion” that will not accommodate movement.
Almost all sealants require the application of cement based primers to achieve adequate adhesion for moving joints. Dow Corning recommends requiring primers on all substrates as a quality assurance process that will protect the long term integrity of your building.
When selecting the proper product for your application, consider a wide range of factors including: performance characteristics, aesthetics, schedule, and warranty. For example, one-component silicone sealants are often preferred over two-part systems because they are easier to install in the field.
The selection of a product can also affect the cost of the project. For example, the purchase of a high-quality sealant may be more expensive than purchasing a cheaper alternative.
For this reason, it is important to choose a sealant that will work well with the structural elements of your building. For example, a structural silicone sealant is better suited for securing steel and aluminum structural members than a standard weatherproof sealant.
If a sealant is installed improperly, it can lead to poor performance and deterioration of the structure. This is why it is critical that all the required preparation and testing be completed before installation begins.
The following procedures are typically followed for the installation of structural silicone sealants: Pre-Construction Compatibility Test: Ensure that joint substrates will be compatible with the selected Structural Sealant joint sealant and that it can withstand the environmental conditions expected on the job site. Adhesion Testing: Perform field-adhesion tests at intervals specified by the manufacturer on each joint sealant and substrate.
Maintenance
Structural Sealant is a dependable and durable material that will stand the test of time. To maximize its longevity, it’s important to properly maintain the adhesive layers. This includes the application of a suitable bonding agent, cleaning the surface and avoiding moisture or humidity intrusion. It’s also a good idea to periodically inspect the joint for signs of wear, such as scratches, nicks and dings.
In a pinch, some careful cleaning and buffing can get the job done. Ideally, it would be best to follow the manufacturer’s instructions closely to avoid any pitfalls that may occur from an improper application. The best way to do this is to consult a professional, like your local BSA or BSI representative who can provide you with the right information at the right time. This will result in a high quality, long lasting bond that will stand up to the test of time and provide your building with its coveted occupants for many years to come.
