The metal components in metal buildings are subject to significant expansion and contraction, so the correct sealants must be used for these applications. Also, sealants should be chosen based on their specific application and purpose in the building.
Sealant Purposes
Sealants used in metal buildings are used to achieve several goals, including weatherproofing, adhesion, and corrosion prevention.
Weatherproofing
External sealants are designed to create a weathertight barrier to prevent infiltration of water, humidity, air, dust, and dirt.
Adhesion
Metal sealants join panels and help provide structural strength yet retain the flexibility to expand and contract without cracking.
Corrosion Prevention
Sealants for metal buildings also help prevent corrosion that can give them a service life of 30 years or more.
Sealant Types
There are three commonly used types of sealants and a fourth hybrid type that’s less commonly used but is becoming more popular.
Butyl
Butyl is the most widely used metal building sealant and is available in tape and gunnable forms. It is non-curing, so it remains flexible throughout its lifespan to allow cyclical joint movement in all temperatures and weather conditions. While butyl is used for exterior applications, it is not meant to be used where exposed to sunlight because it’s not UV resistant. It has a long service life, designed to last as long as the metal panels that it seals.
Polyurethane
Polyurethane has excellent adhesive properties but is not as flexible as butyl. Unlike butyl, it cures and hardens, which makes it more susceptible to cracking and failure. It can be used to connect dissimilar materials such as concrete to metal. It is UV-resistant so it can be used in external applications exposed to sunlight. It is waterproof and available in a wide variety of colors for exterior applications where color matters.
Silicone
Silicone is gunnable, easy to apply, and cures quickly. It isn’t as strong as butyl and polyurethane, however, so it can fail more easily. Silicone is used to seal gaps in joints where different materials meet. Because it is UV stable and available in a clear form, it’s good for sealing windows. Most silicones are not paintable, but they are available in many colors. Silicone is noncombustible and those that are USDA compliant can be used in food processing areas, such as kitchens with stainless stee food prep surfaces.
Polyether
Polyether combines some of the attributes of polyurethane and silicone but is newer and not as widely used. It has strong adhesive qualities but is more flexible like silicone. It is UV-resistant, so it can be used in applications exposed to sunlight. It is available in many colors, so it is an option for exterior use where color is important. It is paintable if its color eventually fades.
Sealant Features
A number of factors should be considered when selecting a sealant, including compatibility, strength and flexibility, class, service life, and UV resistance.
Compatibility
It’s important that a sealant is not only chemically compatible with its substrate, but it also meets adhesion requirements for that substrate. It must be able to withstand the metal’s constant cycling of expansion and contraction without peeling off.
Strength and Flexibility
The sealant must be strong enough for its intended use and yet not brittle. It has to endure the stretching needed to adhere firmly to the substrate yet accommodate the expansion and contraction of metal without cracking, splitting, or tearing.
Class
Sealants are classified according to their level of flexibility that ranges from 12.5 to 100. The number corresponds to the percentage that the sealant can expand and contract. A single number means that the percentage of expansion and contraction is the same. For example,12.5 means the sealant can expand 12.5% and contract 12.5%. Two numbers mean that expansion and contract rate are different. A 100/50 sealant can expand 100% and contract 50%.
Service Life
Since the cost of sealant is a relatively small part of a building’s overall cost, it is worth investing in high quality sealant from a reputable company.
UV Resistance
A sealant’s intended application and placement will determine whether or not it needs to be UV-resistant. A sealant that will be exposed to sunlight will need to be UV-resistant to prevent breakdown and failure of the sealant.
Sealant Application
Builders should follow the building component manufacturer’s instructions to avoid voiding product warranties. Correct application will take into account joint characteristics, temperature and humidity, surface preparation, application techniques and tooling, and cure time.
Joint Characteristics
The sealant requirements for joints will be affected by factors such as the type of metal, required adhesion strength, and the joint width, depth, and expansion and contraction tolerances.
Surface Preparation
The sealant will have surface preparation requirements for the metal substrate, including cleaning the surface with specific solvents to remove contaminants and ensuring it is completely dry before applying the sealant. Roll formers use lubrication to form metal panels, which will need to be removed to ensure proper adhesion between the sealant and metal surface. In addition, primer is recommended for some metal substrates.
Temperature and Humidity
Another factor to consider is the temperature and humidity at the time of application. While sealants are designed to have wide tolerances, in some cases, it may be necessary to coordinate the timing of the application to suitable conditions.
Application
Manufacturers provide guidelines for how sealants should be applied, including the amount to be applied. Using too much or too little can dramatically decrease the effectiveness of the sealant. It’s critically important that the job is done correctly and supervised and inspected properly to avoid the cost of having to redo a job.
Cure Time
The cure time for sealants can vary widely. Silicone’s surface may “skin” over in 15 to 20 minutes and cure in 24 hours. Full cure time for polyurethane and polyether can range from 24 to 48 hours.
Conclusion
To ensure the maximum performance and lifespan of metal components in a metal building, it’s crucial to select the right sealants based on their unique characteristics and the specific applications in which they are intended to be used. Equally important is making sure they’re applied correctly, carefully following the manufacturers and building component supplier’s directions to achieve the desired results for the client. MB
Sources
Dynamic Fastener www.dynamicfastener.com
EPDM Coatings www.epdmcoatings.com
Lakeside Construction Fasteners www.lakesideconstructionfasteners.com
Nationwide Protective Coatings www.nationwideprotectivecoatings.com
Novagard www.novagard.com
Red Dot Products www.reddotprocucts.com
Triangle Fastener www.trianglefastener.com
