The Critical Role of Sealants

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Sealants are a building product most homeowners rarely pay attention to until something starts to leak. Architects and contractors, on the other hand, know that sealant selection is critical to making a home weather resistant and energy efficient. Though sealants are a relatively minor cost in the scheme of any construction project, they play a major role in the success of that endeavor.


Not only do sealants get little respect from the public at large, but they are constantly being confused with caulk, adhesives and liquid waterproofing products. Technically, a sealant goes in between two different substrates (wood, glass, metal, brick, etc.) and joins them together.  Their job is to fill a gap—often at a place where two building elements need to be joined together—and form a barrier. 

They also must, depending on the materials being joined and the location of the structure, have some degree of elasticity to allow for the impact of heating and cooling and seismic movement. Sealants are termed elastomeric, which means they allow for flexibility, elongation and contraction. They help prevent structural damage from materials entering the joints, help prevent mold development and function as an air and water barrier. 

In contrast, adhesives bond two elements together without any flexibility, and are not used to for joint locations. Waterproofing products add a layer of protection but do not hold any elements together or fill any gaps.

Sealants are categorized by the chemistry they use. Each formula has different performance characteristics, such as weathering ability, temperature range for application, movement capability, life expectancy, odor during cure, curing time, potential to bubble during cure, need for a primer, stain resistance, paintability, ease of application and clean up, water resistance, different substrate adhesion properties and UV resistancy.

Though most of the emphasis is on qualities for exterior use, sealants also are found doing the same job of joining substrates together in the interior of the home as well. Inside potential for chemical exposure is even greater depending on the ventilation configuration during application.

Meanwhile, caulks are sealants’ cheaper cousin. They also fill a gap, but have fewer special qualities than sealants. They tend to be less expensive and last one-quarter of the service life of sealants, which runs around 20 years. Nonetheless, many think the terms sealant and caulk are interchangeable.

One thing both sealants and caulks have in common is potentially harmful chemicals in their makeup. This article will look at products that fall into both categories, and what hazards they may contain.