Sealant joints are rarely given the attention and budget they deserve when undertaking a new construction or renovation project. It is surprising considering the many functions sealants perform.

To absorb and shed water before it reaches its inner surfaces, traditional constructions employ mass walls and drainage channels. Modern constructions use lightweight masonry walls, rainscreens, renders, and curtain walls, which rely heavily on sealant joints to provide air and weather seals while accommodating movements of buildings, such as thermal expansion, settlement, creep, and slab edge deflections, among others.

In many cases, these joints are poorly designed and/or installed. Maintenance of sealant joints is essential to maintaining their effectiveness.

When a sealant joint fails, it can affect the performance of the building envelope, the structure, and the finishes and furnishings within. As concealed joints are far more difficult to repair or replace, special attention must be paid to their design and specification.

In the long run, choosing good quality products and installing them correctly reduces costs associated with failed sealants and frequent remediation works many times over the life of a building.

Most modern sealants are composed of an elastomeric compound for flexibility along with a filler. Sealants are usually polymer compounds, which bridge gaps and resist movement to some extent if needed.

It is possible to use a variety of sealants, each designed for different applications, including structural applications, such as gluing façade elements together.  

Sealant Types

 In construction, the seven most common types of sealants are:

• Water based Latex
  Popular for residential use because of the ease of application and ability to adhere to most substrates. These can be painted on and are suitable for situations where gaps / voids are very small and movement is minimal. Latex can be prone to shrinkage and can pull away from the substrate creating gaps, allowing water to penetrate.
• Acrylic
  These are UV stable making them suitable for exterior applications, and are not prone to shrinkage. They can be challenging to apply and cannot accommodate significant movement.
• Butyl
  Adheres well to a broad variety of substrates but can be hard to apply due to their stringier consistency. Their abrasion resistance is poor and they cannot accommodate movements introducing shearing forces. This makes them unsuitable for demanding building applications.
• Polysulfide
  Excellent flexibility even at low temperatures with little shrinkage or UV degradation, and can be used for underwater applications. Polysulfides are more expensive than similar sealants and have a tendency to emit higher levels of volatile organic compounds (VOCs). Even so, a life expectancy of 10 to 20 years somewhat compensates for the price.
• Silicone
  Has excellent thermal resistance, good dynamic movement capability and good adhesion. However, they are easily vandalized and tend to collect dirt. It may also be necessary to use primers on certain substrates (such as stone) to prevent staining.
  Silicones can also be used structurally to bond glass or metal to frames, for example, as weatherproofing and air sealing materials. Quality silicones are generally the most expensive, but they also offer very good durability.
• Polyisobutylene
  Have similar properties to natural rubber but with improved durability, good resistance to chemical attack, and have very low permeability. These are commonly used as the primary seal for insulating glazing units (IGU) as they are capable of resisting the transmission of vapour and gases. The products are normally factory applied, rather than site applied.
• Polyurethane
  Adhere well to the majority of different surfaces with little substrate preparation, and are generally the go-to choice for contractors. Moreover, they have excellent resistance to abrasion and shear forces, as well as good adhesion and mobility.

There is no one sealant type that is universally better or worse than another. Because of their innate physical and chemical properties, some are better suited to certain applications than others.

Sealant Properties

When selecting a sealant, it is important to take into account the properties that will most affect the area of the build you will be using it on. Below are the key properties to evaluate when selecting a sealant.

• Consistency
  Pourable sealants have a fluid consistency and are generally used in horizontal joints, and can be self-levelling. Non-sag sealants are thicker and do not run, even on vertical joints.
• Durability
  A sealant’s expected life cycle under ideal conditions is unlikely to be the same as the actual lifespan, this is especially true if the sealant was misapplied to the surface or is incompatible with the substrate it is applied to.
  In general, silicones have the longest service life (around 20 years). Acrylics and butyls generally last for less than 5 years.
• Hardness
  A harder sealant is more resistant to damage. However, as hardness increases the flexibility decreases.
• Exposure Resistance
  High performance sealants continue to perform well and remain flexible in the sun, temperature extremes and moisture.
• Movement Capability
  The movement capability is expressed as a percentage of joint width. For example, a sealant with a movement capability of 10% in a 25-mm joint can stretch to 28 mm or contract to 23 mm and still recover.
• Modulus
  Is an abbreviation of modulus of elasticity. Generally, low-modulus sealants have high movement capabilities and vice versa, but this is not always true. Delicate substrates are commonly treated with low-modulus sealants. In static and non moving joints, high-modulus sealants are often used. Sealants of medium modulus are general-purpose products that balance stress at the surface the sealant is adhering to with the stiffness of the sealant.
• Adhesion
  How well a sealant will adhere to the construction material is an essential factor to consider. The adhesion of elastomeric sealants is evaluated using test methods (for example, ASTM C794 Standard Test Methods of Adhesion-in-Peel of Elastomeric Joint Sealants). Adhesion data is also provided by manufacturers for various substrates.
• Staining
  The components within sealants can leach into porous substrates (such as natural stone) and may leave a visible stain. You must ensure sealants are tested on an unobtrusive area before putting into use, even if the sealant claims to be non-staining.
• VOC Content
  Any emission of volatile organic compounds from products needs to be understood. Many sealant manufacturers have developed low-VOC sealants. Solvent-based sealants usually contain a higher level of respiratory irritants and environmental toxins, and these should be avoided. Product-specific VOC contents vary widely.  
• Ease of Application
  A sealant’s curing and tooling (ease of getting a smooth surface of correct/required geometry) characteristics are important when it comes to judging a sealants ease of application. It should be noted that some diseases heal quickly while others are y designed to remain uncured.
• Cost
  As with most construction products, cheaper does not mean better. Higher-cost products come with higher performance. It is almost always more expensive to replace failed sealants than to select the correct sealant in the first place. So buy wisely and make sure you match performance requirements.