Building & Roofing Sealants

What are Building & Roofing Sealants?

Building and Roofing Sealants are specialist compounds designed to accommodate structural movement while maintaining a robust barrier against water, air, and pollutants. 

Unlike rigid fillers or mortars, their defining characteristic is elasticity, allowing them to expand and contract with the building's components as they react to thermal and environmental changes. 
 
These sealants are capable of adhering to multiple, often dissimilar, substrates (e.g., uPVC to brick, metal to concrete) and cure via a chemical reaction - typically with atmospheric moisture - to form a resilient, solid rubber-like seal. 

Their performance is essential for preventing leaks, improving airtightness, and absorbing stresses between different parts of a building.

Exterior Sealant Benefits

• Weather and UV Resistance: Features advanced polymers that are inherently resistant to degradation from UV radiation, ozone, and extreme temperatures. This prevents the cured sealant from hardening, cracking, or discolouring over its service life.
• Flexibility (Movement Accommodation): This is the most critical mechanical property.
  • Modulus: This defines the sealant's stiffness. Low Modulus sealants are soft and highly flexible, requiring little force to stretch. They are the standard for joints with significant movement, such as building expansion joints and the perimeter seals around window and door frames, as specified in BS EN 15651-1 (Type F).
  • Movement Accommodation Factor (MAF): Shown as a percentage (e.g., ±25%), this quantifies how much a sealant can stretch and compress from its original width. A higher MAF is essential for joints with a large degree of thermal expansion and contraction.
• Adhesion: Forms a tenacious, long-lasting bond to various construction materials without the need for complex surface treatments. The sealant's chemical base (e.g., neutral cure silicone, hybrid polymer) determines its adhesion profile.

Low Modulus Neutral Cure Silicones

This is the benchmark technology for professional facade and perimeter sealing. The "neutral cure" mechanism is non-corrosive, making it safe for use on sensitive metals and compatible with most plastics and alkaline substrates like concrete and mortar. 

Its low modulus provides the high flexibility required to handle the differential movement between a window frame and the surrounding wall structure.

• Primary Application: Perimeter sealing of exterior window and door frames; sealing movement and expansion joints.
• Key Product Example: Everbuild Silicone 825 is a low modulus, neutral cure sealant specified for these purposes.

Specialist Neutral Cure Silicones

Within the neutral cure family, some products are formulated for specific, challenging substrates. For roofing applications, sealing around lead flashing, rooflights, and gutters requires a specialist sealant that offers exceptional adhesion to metals without causing corrosion or lifting.

• Primary Application: Weather-sealing lead flashing, gutters, and other metal roofline components.
• Key Product Example: Everbuild Everflex Lead Mate Sealant.

Advanced Hybrid Polymers (SM Polymers)

Hybrid polymers merge the durability and strength of polyurethanes with the flexibility and weather resistance of silicones. This creates an extremely versatile high-performance sealant and adhesive. 

They offer excellent movement accommodation and can bond to almost any material, often without a primer. Their ability to be applied in damp conditions makes them a powerful tool for remedial and roofing work.

• Primary Application: High-strength sealing and bonding in demanding construction scenarios; sealing joints with very high movement.

Acrylic Mastic Sealants

Acrylic sealants are a solvent-based or water-based compound typically used for general-purpose gap-filling where movement is minimal. 

Their main advantage for exterior use is that they are over-paintable, allowing for a seamless decorative finish around frames. However, they generally have lower flexibility and weather resistance than silicones or polymers. This makes them unsuitable for dynamic joints or areas with high weather exposure.

• Primary Application: Simple, low-movement exterior gaps that require painting.
• Key Product Example: Everbuild Window & Door External Frame Sealant.

Polyurethane (PU) Foam Adhesives

While not a finishing sealant for joints, PU foam is a crucial product in the "sealing" process during installation. 

It is an expanding foam used to fill, seal, and insulate the larger, irregular gaps between a component (like a window frame) and the structural opening. It provides thermal and acoustic insulation before the final, neat weather seal is applied with a silicone or polymer sealant.

• Primary Application: Insulating, fixing, and filling large installation gaps.

Application & Joint Design

• Standards: For facade joints, specify products conforming to BS EN 15651-1 (Type F). The classification will also indicate suitability for exterior/interior use (EXT-INT) and cold climates (CC).
• Joint Design: For optimal movement, the sealant depth should be approximately half the joint width. To prevent three-sided adhesion (which severely restricts movement), a backer rod or bond breaker tape must be installed in the base of the joint. This ensures the sealant only adheres to the two opposing sides, allowing it to stretch freely.
• Surface Preparation: All substrates must be structurally sound, clean, and completely dry. Any dust, laitance from concrete, or oils will cause adhesive failure. A non-residual solvent should be used to clean non-porous surfaces. Some substrates may require a specific primer to ensure a lasting bond; always consult the product's technical data sheet.
• Tooling: Tooling the sealant immediately after application is critical. It creates a neat finish and, more importantly, ensures full contact and adhesion between the sealant and the substrate walls of the joint.