What to consider when sealing expansion joints or movement joints
Movement of the joint
The biggest challenge is the different movement coefficients of the various materials that the joint is made from. For example, gypsum, concrete and aluminium all expand and contract at different rates. The sealant should not only strongly adhere with different substrates, but also accommodate different degrees of movement for the materials it joins.
Similarly, expansion joints in floors need to be able to withstand the pressure from high levels of foot traffic and constant movement and weight, without their functionality being affected.
Material and finish
The desired look of the surface or finish also matters. Building facades need to look immaculate without staining or streaking, despite the weather changes and precipitation they face.
Plus, with many applications featuring different materials, it’s important to know how the material will affect your decision in choosing the right expansion joint sealant. For example:
- Concrete joints require a durable sealant that is highly flexible and can accommodate the movement between concrete and other materials such as our Bostik PU91 Construction Polyurethane sealant.
- Wood floors typically experience a lot of movement and foot traffic. You need a sealant that is specifically developed for wooden and parquet floors such as the Bostik P26 Polymer sealant.
Building regulations and safety
Building regulations and safety will impact which sealant you need to use. For example, certain materials must comply with relevant legislation, such as the Construction Products regulations or Approved Document B.
For internal and external expansion joints which need to be fire retardant, we recommend using a sealant that is not only highly flexible but also offers passive fire resistance.
Our Bostik FP403 Fireseal Hybrid sealant is a one-component, fire resistant sealant, suitable for sealing linear joints up to 4 hours and offers a movement accommodation of 25%. It's perfect for both vertical and horizontal joints in walls, floors, ceilings, metal frames and more.
Before choosing which sealant to use, we strongly recommend that you check the integrity and insulation requirements for your project.
External expansion joints
Expansion joints in facades and floors consist of connections between exterior building elements. You need a sealant that can weather environmental stress and still offer a great finish – we have two options:
- The Bostik P26 Weatherproof Polymer sealant is perfect for weatherproofing exterior joints subject to high movement. It is high modulus, has high movement capacity and can be used in interior or exterior applications.
- The Bostik PU91 Construction Polyurethane sealant is perfect for sealing construction joints subject to high movement. It is durable in wetter conditions such as a warehouse floor or wall. It is high modulus, bubble and primer free and can be used in interior and exterior applications.
How to seal an expansion or movement joint
There are several kinds of expansion and movement joints. Since these joints should be able to absorb a lot of stress, they should be correctly designed. We advise that you contact our in-house experts if you have any doubts or queries.
The durability of a movement joint depends on three factors: pre-treatment, choosing the optimal product, and correct application.
- Check the substrates of your tiles or other materials before purchasing your sealants. Since a movement or expansion joint will probably undergo a lot of movement and pressure, using the most optimal product will ensure it stays durable and doesn’t crack. For instance, pure silicone sealants are very durable and can withstand UV exposure.
- Before applying any sealant, ensure the surface is clean, dust free and dry.
- The depth and width of joints should be in line with the movement coefficient of the building substrates.
Types of expansion joints and the recommended sealant
When it comes to construction facade applications, you should turn to professional grade polymers that offer durable, weatherproof joints with high movement properties. The addition of the ability to paint is often required. Look for a product meeting BS EN 15651-1: Sealants for facade elements. In some cases the sealant must also be robust and durable enough to cope well with trafficked joints in floors. Look for a product meeting BS EN 15651-4: Sealants for pedestrian walkways.
Bostik P26 Weatherproof Polymer Sealant
A professional grade polymer for weatherproofing exterior joints subject to high movement. High modulus, high movement capability and suitable for interior and exterior applications.
Bostik PU91 Construction Polyurethane Sealant
A professional grade polyurethane sealant developed for sealing construction joints subject to high movement. High modulus, bubble and primer free and suitable for interior and exterior applications.
Bostik FP403 Fireseal Polymer Sealant
A one-component, fire resistant hybrid sealant. It is suitable for fire resistant sealing of linear joints up to 4 hours and offers movement accommodation of 25%. It can be applied in both vertical and horizontal joints. This sealant can be used to seal walls, floors or ceilings, metal frames and all metal stud (gypsum) connections are certified too.
Bostik P26 Weatherproof Polymer Sealant
A professional grade polymer for weatherproofing exterior joints subject to high movement. High modulus, high movement capability and suitable for interior and exterior applications.
Bostik PU91 Construction Polyurethane Sealant
A professional grade polyurethane sealant developed for sealing construction joints subject to high movement. High modulus, bubble and primer free and suitable for interior and exterior applications.
Bostik P26 Weatherproof Polymer Sealant
A professional grade polymer for weatherproofing exterior joints subject to high movement. High modulus, high movement capability and suitable for interior and exterior applications.
Bostik PU91 Construction Polyurethane Sealant
A professional grade polyurethane sealant developed for sealing construction joints subject to high movement. High modulus, bubble and primer free and suitable for interior and exterior applications.
Bostik PU91 Construction Polyurethane Sealant
A professional grade polyurethane sealant developed for sealing construction joints subject to high movement. High modulus, bubble and primer free and suitable for interior and exterior applications.
Bostik P26 Weatherproof Polymer Sealant
A professional grade polymer for weatherproofing exterior joints subject to high movement. High modulus, high movement capability and suitable for interior and exterior applications.
Bostik PU91 Construction Polyurethane Sealant
A professional grade polyurethane sealant developed for sealing construction joints subject to high movement. High modulus, bubble and primer free and suitable for interior and exterior applications.
Bostik P26 Weatherproof Polymer Sealant
A professional grade polymer for weatherproofing exterior joints subject to high movement. High modulus, high movement capability and suitable for interior and exterior applications.
Bostik PU91 Construction Polyurethane Sealant
A professional grade polyurethane sealant developed for sealing construction joints subject to high movement. High modulus, bubble and primer free and suitable for interior and exterior applications.
Bostik P26 Weatherproof Polymer Sealant
A professional grade polymer for weatherproofing exterior joints subject to high movement. High modulus, high movement capability and suitable for interior and exterior applications.
Bostik PU91 Construction Polyurethane Sealant
A professional grade polyurethane sealant developed for sealing construction joints subject to high movement. High modulus, bubble and primer free and suitable for interior and exterior applications.
Frequently Asked Questions
Before starting your expansion joints in concrete project, prepare the surface by removing any old sealant and debris. Clean the joints thoroughly with a wire brush and vacuum to ensure excellent adhesion.
For the best results, measure the joint width and insert a foam backing rod slightly larger than the gap. This provides the perfect foundation for your sealant application.
Cut the sealant cartridge nozzle at a 45-degree angle, matching the joint width. Apply the sealant in a steady motion, maintaining consistent pressure. For deeper joints, use backer rods where appropriate to achieve the correct joint dimensions.
Work in sections, smoothing the sealant with a wet, round ended tool. This creates a professional finish and ensures proper contact with both sides of the joint.
A quality expansion joint sealant helps protect your building from structural damage by allowing controlled movement between different construction materials. These specialised sealants work by expanding and contracting with your building's natural movement while maintaining a weatherproof barrier.
When properly installed, expansion joint sealants prevent water infiltration and-, debris accumulation. The sealant creates a flexible bond that moves with temperature changes and building shifts without cracking or separating.
For maximum effectiveness, choose a sealant that matches your specific application needs. Consider factors like joint width, expected movement range, and exposure to environmental conditions when selecting the right product for your project.