Select the Right Sealant for the Job

Sealants are an everyday essential for the majority of installers and fitters to join two surfaces, fill gaps and provide a seal / barrier that is typically waterproof and airtight. Although predominantly used to provide a seal that restricts the flow of water or air, many sealants will perform other tasks too. Such as providing noise insulation, protecting against the passage of fire and smoke, or being chemical resistant and preventing the growth of microorganisms like mould and mildew.

Sealants may have similar qualities to adhesives in that they join two surfaces, however they are quite different. Sealants’ primary purpose is to create a seal and this can be either markedly strong or quite weak. Different sealants will also offer varying degrees of durability and flexibility. These differences in performance coupled with the other specific tasks they can perform, means it may not be quite as straight forward as it seems to choose the right sealant for the job.

Sealants are used across numerous industries although here we will focus on those that can be used by MEP and HVAC installers.

Considerations:

Cost – although more expensive premium sealants will generally be more flexible, easier to work with and last longer. So, investing in a quality product first time may actually save money in the long run.

Ease and Conditions of Application – Sealants can differ in their application in terms of ease and conditions required. So, choosing the correct one can prevent poor application and seal failure.

Flexibility / Hardness – Various uses require different levels of hardness and movement in the seal. Ensure enough movement is allowed to suit your application. Low modulus sealants will be softer to the touch and provide greater movement. Where higher modulus sealants are stiffer and can absorb heavier loads.

Adhesion – some sealants have better adhesion than others, so it’s always worth checking product datasheets to check adhesion properties and ensure compatibility with the substrates used in the application.

Durability – consider what the seal will be exposed to such as abrasion, is there high movement / expansion, will the sealant need to be UV resistant or weather proof to maintain both its colour and effective seal.

Safety Measures - some sealants have more toxic compounds than others, so will require different levels of safety measures on application. For example, if working in confined spaces a water-based sealant will be best to use as these tend to have fewer toxic compounds also known as Volatile Organic Compounds (VOC’s).

Aesthetics – sealants are available in different colours, although many are also paintable once cured. If aesthetics are important make sure the sealant chosen can be painted over or is available in the required colour.

Resistance / Purpose – do you require the seal to be resistant to heat, noise, UV, chemicals or mould. Or indeed meet specific regulations for ductwork and pipe installation. If so, this will dictate the types of sealants required.

• Intumescent Sealants – will be tested for resistance to fire and smoke under BS EN 1634 in order to provide a fire-retardant seal. Intumescent sealants will usually have acoustic properties too. 
• Acoustic Sealants – will generally be rated to BS EN ISO 140-3 for sound insulation. They should stay relatively soft after application to help reduce sound transmission.
• Sanitary Sealants - will typically be certified under BS EN 15651-3 where sanitary joints are required, such as for washrooms, tiled areas, refrigeration units or areas of high humidity to prevent mould growth.
• Duct Sealants – should be tested to BS EN 13141-1 covering the ventilation of buildings or DW/144 the standard specification for ductwork manufacture and installation, including air leakage.
• Pipe Sealants – will generally be certified by Water Regulations Approval Scheme (WRAS) and / or BS 6920 covering non-metallic materials that will come in contact with drinking water.

Main Types of Sealants

There are many types of Sealants available with different formula’s, generally some will be more solvent-based whilst others are water-based. Water-based sealants are a good choice when a sealant is needed with low VOC’s, they are easy to work with, and don’t have the odour or clean-up issues that can be associated with solvent-based sealants.

The most common sealants used in the building industry are Silicone.

Silicone Sealants – have one of the higher life expectancies of the different sealant types, plus they offer good adhesion, are completely waterproof, provide decent temperature resistance and protect against UV fading. They also generally retain their flexibility over time. However, they are typically more expensive than other types and aren’t paintable. Silicone sealants are split into three main types with different cure and modulus; High Modulus Acetoxy, Low Modulus Neutral and Low Modulus Acetoxy.

Cure:

• Acetoxy - are fast curing but give off a vinegary odour.
• Neutral – generally take longer to cure but are almost odourless.

Modulus:

• Low Modulus – are softer to touch with greater elasticity which allows for more movement. Typically used for external applications.
• High Modulus – are harder and more rigid once cured, allowing for less movement. Generally best for internal applications.
• Mid Modulus – are a more recent addition to the market and offer a compromise between the more common low and high modulus sealants in terms of their elasticity and usage.

Acrylic Sealants – formed from water-based acrylic resins an environmentally friendly material with fewer VOC’s, which is also odourless. They are suitable for filling joints around wood, aluminium and UPVC, although offer less flexibility than other types. They are easy to apply, paintable and typically a lower cost option. Although if applied externally conditions must be dry and preferably warm.

MS Polymer Sealants – decent all-rounders especially where surfaces may experience vibration or strain. They offer flexibility, great durability and excellent adhesion to non-porous surfaces. They will bond to damp surfaces too and are paintable.

Polyurethane Sealants – can be difficult to apply and expensive to buy, but offer first rate water resistance and permanent elasticity under all climate conditions. They are one of the toughest sealants and particularly valued for their abrasion resistance. They provide excellent adhesion to metal and fibreglass. Low modulus Polyurethane sealants are also inert once fully cured with any harmful solvents having evaporated.

Polysulphide Sealants - can be used where a tough, flexible watertight seal is required for joints subject to movement, such as expansion joints. They can be applied in cold conditions and are available in both a; one-part system and two-part system. Two-part systems includes both a base and accelerator which need to be mixed before applying.

Although only a brief summary we hope the above will help choose the right sealant for the job. You can view our sealants range here, which includes general, premium, intumescent, duct and pipe sealants. Alternatively for further information contact our Sales team on 01322 274226 or via [email protected].