Sealant Types and Uses
Whether undertaking a new build or refurbishment project sealant joints are rarely given the attention and budget they require. This is surprising considering the array of tasks that sealants are used for.
Traditional constructions use mass walls and drainage channels to absorb and shed water before it reaches their inner surfaces. Whereas modern constructions utilise lightweight masonry wall, rainscreen, render, and curtain wall systems and these rely heavily on sealant joints, to provide air and weather seals whilst accommodating building movements such as thermal expansion, settlement, creep, sway, differential slab edge deflections, etc.
It is common for these joints to frequently suffer from poor design and/or installation. To preserve their effectiveness sealant joints have to be maintained and periodically replaced.
If a failure occurs in a sealant joint, it can affect the performance of the building envelope, the structure and internal finishes and furnishings. Special attention must be given to the design and specification of concealed joints, as these will be far more difficult to access for repair or replacement.
Taking the time to ensure that good quality products are selected and installed correctly is repaid many times during the life of the building by the reduction in costs associated with the damage caused by failed sealants and of frequent remediation works.
The majority of modern sealants are composed of an elastomeric compound for flexibility together with a filler product. Sealants are usually polymers, these pliable compounds allow gaps to be bridges and the sealant to resist a degree of movement, if required.
There are many different sealant products available, each designed for a different application, including structural applications e.g. for structural glazing, or bonding façade elements together.
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 is can be prone to shrinkage and can pull away from the substrate creating gaps, allowing water to penetrate.
These are UV stable making them suitable for exterior applications, and are not prone to shrinkage. Acrylics can be difficult to apply and cannot accommodate significant movement.
Adheres well to a broad variety of substrates but can be hard to apply due to their stringier consistency. They have poor resistance to abrasion and struggle to accommodate movements that introduce shearing forces. They are not suitable for demanding building applications.
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 have higher levels of volatile organic compounds (VOCs). Though, a life expectancy of 10 to 20 years does compensate for the price somewhat.
Has excellent thermal resistance, good dynamic movement capability and good adhesion. They can be easily vandalised and tend to collect dirt. For certain substrates (such as stone), staining may also be an issue, in some cases making the use of primers a necessity.
As weather proofing and air sealing applications silicones can be used structurally e.g. for bonding glass or metal to frames. Silicones are generally the most expensive but quality silicones have very good durability performance.
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.
Adhere well to the majority of different surfaces with little substrate preparation, and are generally the go-to choice for contractors. They have excellent resilience to abrasion and shear forces as well as having strong adhesion and movement capability.
No singular sealant type is universally superior or inferior to another. Some are simply better at certain applications than others are due to their innate physical and chemical properties.
When making a choice on sealant, it is important to consider the properties that most impact the area of the build you will be using the sealant for. The following are the key properties of sealant for evaluation on your build.
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.
A sealants 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.
Speaking generally, silicones have the longest service life (around 20 years or more). Some acrylics and butyls last little more than 5.
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
Movement capability is shown as a percentage of the joint width e.g. a sealant with ±10 percent movement capability in a 25-mm joint can stretch to 28 mm or contract to 23 mm and still recover without failing.
Is an abbreviation of modulus of elasticity. Low-modulus sealants usually have high movement capability and vice versa although it’s important to note that this isn’t always the case. Low-modulus sealants are often used with delicate substrates. High-modulus sealants are often used in static and non-moving joints. Medium-modulus sealants are general purpose products and balance stress at the surface the sealant is adhering to and the stiffness of the sealant.
How well a sealant will adhere to the construction material is an essential factor to consider. Test methods (e.g. ASTM C794 Standard Test Methods of Adhesion-in-Peel of Elastomeric Joint Sealants) evaluate the adhesion of elastomeric sealants. Manufacturers also provide adhesion data for various substrates.
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. The majority of sealant manufactures have developed them with low levels of VOC. Solvent based sealants generally have a higher level of respiratory irritants and environmental toxins and these should be avoided. However, VOC content varies widely by product.
- Ease of Application
A sealants 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. Noting that some cure quickly while there are others which are specifically designed to remain uncured.
As with most construction products, cheaper does not mean better. Higher cost products come with a higher performance. Replacing failed sealants is, almost always more expensive than selecting the correct sealant in the first place. However buy wisely and concentrate efforts on matching the performance requirements
Please Note: Every care was taken to ensure the information in this article was correct at the time of publication. Any written guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. However, for the most up to date LABC Warranty technical guidance please refer to your Risk Management Surveyor and the latest version of the LABC Warranty technical manual.