When your project demands a sealant that performs across diverse conditions – handling significant movement, resisting intermittent fuel spills, and delivering durable performance across demanding environments. It seals critical expansion joints in high-traffic zones like car parks and industrial floors. It ensures flexible, durable connections for marine builds, vehicular manufacturing, and architectural panels. Get a resilient, elastic seal where performance matters most.

Why this product exists

We engineered Megaprene 40GG to meet the need for a high-elasticity, single-component polyurethane sealant capable of performing in demanding construction and industrial environments. This sealant provides durable, elastic seals for movement and connection joints where chemical resistance, including intermittent fuel spills, and specific environmental certifications are critical. Unlike higher-modulus structural bonding polyurethanes, Megaprene 40GG is specifically formulated for low-modulus, high-movement sealing, ensuring the joint itself, not the bond, takes the stress.

The numbers that matter

Its joint movement capability of ±25% (ASTM C 719) means a 10mm joint can expand or contract by 2.5mm without failure, accommodating substantial building movement and reducing the risk of joint breakdown. A low modulus of 0.4 MPa @ 100% elongation ensures the sealant stretches easily, placing less stress on the bond line and adjacent substrates. This protects your work from adhesive failure, even under constant flex. Rated for intermittent fuel spills, this sealant provides critical durability for pavement joints, industrial floors, and infrastructure projects exposed to demanding service conditions.

What it's like to use

Prepare surfaces thoroughly: they must be structurally sound, dry, clean, and free of contaminants. For impervious substrates, use a two-wipe process with Adheseal Xylene Solvent. For optimal adhesion in critical applications, pre-treat non-porous surfaces with Adheseal 50A Surface Prep. For porous substrates like concrete, prime with Everflex Supaprime Sealant Primer. Ensure a 2:1 width-to-depth ratio for joints. Control sealant depth and prevent three-sided adhesion with a compatible Adheseal backer rod or bond-breaker tape. Apply between 5°C and 40°C. Tool the sealant with a moistened spatula within the 60-minute skinning time to achieve a smooth, professional finish. Clean wet spills and tools with Adheseal Xylene Solvent. For skin, use Adheseal Hand Wipes.

Where this product excels

  • Civil Construction: Use on pavement joints in car parks and driveways where you need a flexible seal resistant to intermittent fuel spills and heavy traffic. It maintains joint integrity against weathering and mechanical stress.
  • Glazing & Façade: Apply for perimeter sealing of windows and curtain wall joints. Its high elasticity and UV stability provide a weatherproof, durable seal that handles building movement without cracking or degradation.
  • Marine & Vehicular Manufacturing: Ideal for creating elastic seals in fibreglass and mixed-substrate assemblies. Its 'below waterline' suitability (once cured) and compatibility with diverse materials ensure reliable, long-lasting bonded joints in demanding transport applications.
  • Precast & Masonry: Perfect for expansion joints in precast and tilt-up panels. It accommodates the significant movement these large elements experience, preventing structural joint failure and reducing costly callbacks.

How it fits in a real system

Megaprene 40GG typically functions as the final sealing component in multi-stage construction joint systems. Its position requires careful surface preparation and often priming to establish an optimal bond. Following substrate cleaning and any necessary roughening, apply the appropriate Adheseal primer (e.g., Everflex Supaprime Sealant Primer for porous surfaces, Adheseal 50A Surface Prep for non-porous). Once the primer has flashed off, install a compatible backer rod to control joint depth and ensure two-sided adhesion. Then, apply Megaprene 40GG, tooling it off to create a smooth, continuous, and durable seal. This sequence ensures maximum performance and longevity for the joint.

Choose this when

  • When your joint needs to accommodate significant movement up to ±25%, such as in expansion or connection joints.
  • When you require a seal that can withstand intermittent fuel spills, critical for car parks, garages, or industrial settings.
  • When you need a durable, flexible sealant for vehicular or marine manufacturing that adheres to fibreglass and mixed substrates.

Don't use this when

  • Not for: Structural glazing applications. For that, consider a dedicated structural glazing silicone like Dowsil 795 Silicone Sealant.
  • Not for: Totally confined spaces, as this sealant requires atmospheric humidity to cure properly.
  • Not for: Internal swimming pool applications, especially with high chlorine levels (maximum 5 ppm chlorine exposure).
  • Not for: Direct contact with bituminous, natural rubber, EPDM rubber surfaces, or any compounds that may leach oils or plasticisers.
  • Not for: Critical natural stone applications without first conducting a stain testing program. For sensitive stone, test with Adheseal S100 Sanitary Silicone Sealant.

Megaprene 40GG meets rigorous performance and safety standards, providing confidence in its application. It complies with ASTM C-920 & SNJF Class 1 Elastomeric for sealant performance and is classified as Type F Class 25 LM (ISO 11600), affirming its suitability for low modulus, high movement applications. It has been tested beyond ASTM C793-05 for UV and weathering, showing no chalking or cracks, and features AS1530.3 Low Ignitability with an Ignitability Index of 0.