For years, the most commonly used sealants and caulks in the commercial building industry included urethanes, solvent-borne silicones, and acrylics. For the most part, those types of sealants performed as expected, keeping air, water, insects, and dust out of buildings at windows or gaps in walls or joints. Although they have long been trusted in the industry due to their history, traditional solvent-borne sealants have several drawbacks, including shrinking, cracking due to ultraviolet (UV) exposure, odors, and high amounts of solvents.

A new technology that combines the best properties of urethanes and silicones has emerged and is beginning to make headway in the industry. Hybrid sealants can be applied anywhere traditional sealants can be applied and even offer additional application versatility, such as adhesion over coated surfaces or over residual silicone base products.

What Are Hybrid Sealants?

Hybrid sealants are best defined as a fusion of technologies — the best performance properties of both urethanes and silicones. And in that fusion process, their inherent weaknesses are limited. Urethane and silicone sealants are often referred to as high-performance sealants because they provide significant adhesion, movement capability, and durability. Hybrid sealants, therefore, combine the strength of polyurethanes with the weathering resistance of silicones to create a high-performance, functionally versatile sealant. Along with their high-performance properties, hybrid sealants are gaining in popularity due to their solvent- and isocyanate-free nature as well as their flexibility and adaptability, according to adhesives.org. Hybrid sealants bond with most construction materials, such as concrete, stone, wood, metal, plastic, polycarbonate, ceramic tiles, and gypsum boards. They also bond well with porous surfaces.

Additionally, most hybrid sealants contain very small amounts of volatile organic compounds (VOCs) or none at all, allowing them to be used on projects at odor-sensitive facilities such as hospitals, schools, and offices without causing major disruption to operations. Each year, VOC regulations get more and more stringent. New states are issuing VOC limitations and states with existing limitations are expanding the reaches of their regulations as well as issuing more aggressive restrictions for existing product categories. This, according to the International Sanitary Supply Association, has helped to drive the development of this new technology.

How Do Hybrid Sealants Perform?

Like most urethanes, hybrid sealants are moisture-assisted cure products. When the sealant is exposed to moisture, it will begin to cure from the outside in. Since there is moisture in the air, the product cures all the way through regardless of the application, substrate, or material temperatures. It is important to note that cure times are dependent on temperature as well as application thickness. Even when fully cured, hybrid sealants remain extremely flexible. The high solid content enables high elongating properties, which is critical to the performance of the product.

With traditional solvent-borne sealants, application rates can significantly impact cure. If applied too thick, the top of the sealant will skin over, but the product will never fully cure. Due to the high solvent content, traditional sealants also shrink as they cure, minimizing their effectiveness.

What Is UV Stability and Why Is It Important?

Many polymers as well as natural and synthetic ingredients are highly susceptible to damage from ultraviolet radiation, also known as UV degradation. When exposed to UV rays, most sealants and caulks will shrink and crack over time, rendering them almost useless as they no longer create a tight seal. A UV-stable product, though, can withstand even the harshest UV exposure. Hybrid sealants are the only products in this arena with stand-alone UV stable features, meaning the product won’t dry out and crack as it ages. The material will remain flexible for years, providing critical moisture and air penetration protection. Traditional urethane and silicone sealants will dry out as they age, requiring most to be painted to provide UV stability.

Along with shrinking and cracking, another problem that will arise if UV stability is not present is the possibility of water infiltration. Once water makes its way through the front line of a sealant and breaches the surface, numerous problems can follow, such as substrate damage, mold, and adhesion failure, among others.

Suitable Applications for Hybrid Sealants

Hybrid sealants can be applied in any areas where most other general sealants can be applied. Even with their low solvent content, the application range is not limited; this is because of the strong adhesive backbone of these products. Some hybrid sealants will even bond to high-performance coatings, which are often used to protect metal substrates. Another valuable feature of hybrid sealants is the ability to apply them over residual silicone materials. Typically, only another silicone product will stick to silicone. However, modified silane (MS) hybrid sealants will bond to clean residual silicone left in joint pores or between a glass window and its frame.

Some common applications for hybrid sealants include:

• Filling expansion joints between brick, block, exterior insulation and finish systems (EFIS), and concrete floors

• Joints between façade panels — metal and composite

• Door thresholds

• Window re-glazing

• Metal to masonry

• Chimneys

• Wood steps

The only real disadvantage of hybrid sealants is that they don’t bond very well to extremely smooth substrates. A simple, yet effective solution to increase adhesion to a smooth substrate is to use 100-grit sandpaper or a grinding wheel to roughen the surface.

A good rule of thumb before beginning any project is to ask the materials manufacturer to provide a sample tube to perform a test patch. This will help ensure correct color match as well as test the adhesion and suitability. It is also important to become licensed, as performance of the product is dependent upon proper installation.

Performance Properties

To summarize, hybrid sealants combine the strength of polyurethanes with the weathering resistance of silicones to create a high-performance, functionally versatile sealant. Most hybrid sealants contain very little VOCs, allowing them to be applied virtually anywhere without causing disruption. Hybrid sealants also have a high solids content, meaning they won’t shrink or crack even when exposed to harsh weather or strong UV radiation, which translates into higher performance and longer service life by protecting the building from moisture and air penetration. Hybrid sealants are gaining in popularity in the building industry due to their premium performance properties.

About the Author:

Richard Catley is the sealants and accessories product manager at The Garland Company, Inc. He has seven years’ experience in this industry and is highly knowledgeable in the field of construction-grade sealants. He helps to develop, modify, and introduce new products to the industry at The Garland Company, a more than 120-year-old manufacturer of high-performance solutions for the total building envelope. For more information, contact: Richard Catley, rcatley@garlandind.com, www.garlandco.com

For a real-world example using these sealants, check out this feature article.