Adheseal Megaprene 40GG Polyurethane Sealant

For expansion and connection joints in tilt-up panels, pavement slabs, and window frames where high movement and weathering resistance are required, Adheseal Megaprene 40GG Polyurethane Sealant is a single-component, moisture-curing joint sealant that accommodates +/- 25% joint movement. It cures to form a tough, permanently elastic seal that resists dust, moisture, and biological growth, making it suitable for both internal and external structural applications.

What it does

Megaprene 40GG Polyurethane Sealant functions as both a joint sealant and a construction adhesive. It cures by reacting with atmospheric moisture at a rate of 3mm per 24 hours. The polyurethane chemistry provides a Shore A hardness of 25 after 14 days and an elongation to break of over 400% (tested to ISO 8339), allowing the joint to absorb thermal expansion and contraction without adhesive or cohesive failure. It has high chemical resistance, including resilience against short-term petrol and oil spills, and is suitable for below-waterline applications once fully cured.

Numbers that matter

• +/- 25% joint movement: Accommodates standard expansion and contraction cycles in precast concrete, pavements, and cladding joints without tearing.
• 0.4 MPa modulus: Low-modulus performance (tested to ISO 8339 at 100% elongation) ensuring minimal stress is transferred to the substrate bond line.
• AS1530.3 fire indices: Ignitability, Spread of Flame, and Heat Evolved indices of 0, with a Smoke Developed index of 0-1, providing documented fire performance.
• -40°C to +80°C service temperature: Sustains elasticity and adhesion under extreme environmental exposure after curing.

Where to use it

This sealant adheres to masonry, brick, stone, porcelain, timber, plastics, painted surfaces, rubber, fibreglass, powder coat, concrete, wood, and waterproof membranes. Typical installations include:

• Expansion joints in precast and tilt-up concrete panels.
• Pavement, driveway, and car park joints.
• Perimeter sealing of window frames, curtain walls, and metal cladding lap joints.
• Vehicular, marine, and aluminium fabrication sealing.
• Internal floor mouldings, skirting boards, and acoustic ceiling tiles.

Limitations

• Confined spaces: Do not use in totally confined spaces; the product requires atmospheric humidity to cure.
• Chlorine limits: Not suitable for internal swimming pools where chlorine levels exceed 5ppm.
• Substrate exclusions: Do not use on bituminous surfaces, natural rubber, EPDM rubber, or materials that leach oils, plasticisers, or solvents. Do not use for structural glazing or to adhere mirrors.
• Copper and brass: May cause discolouration on copper and brass surfaces.
• Stone substrates: Conduct a stain-testing program before using on any natural stone.
• Moisture vapor: Avoid application when moisture-vapour-transmission is actively emanating from the substrate, as this may cause bubbling.
• Chemical exposure: Do not expose the uncured sealant to cleaning agents, solvents, or alcohol during the curing window.

Installation and joint design

Joints should be designed to a 2:1 width-to-depth ratio. The minimum joint width and depth is 5mm for internal applications, and 12mm for external applications. For joints deeper than 10mm, install an open-cell backer rod (sized 25% larger than the joint width) or a bond-breaker tape to prevent three-sided adhesion.

Apply when temperatures are between +5°C and +40°C. New concrete must be fully cured for at least 28 days prior to application. Tooling must be completed before the skin forms (approximately 5 to 15 minutes depending on conditions) using a moistened spatula. Clean wet tools and excess sealant immediately with Xylene; cured material must be removed mechanically.

Priming requirements

While adhesion is typically achieved without a primer, high-stress joints or critical applications require specific preparation:

• Non-porous surfaces (Aluminium, stainless steel, PVC, glazed tiles): Lightly key the surface with a fine abrasive pad. Clean and pre-treat with Adheseal 50A surface prep. Allow between 30 minutes and 2 hours drying time before applying the sealant.
• Porous surfaces (Concrete, render, brick): Prime the joint faces using Everflex Supaprime. Allow a minimum of 30 minutes and a maximum of 2 hours drying time before applying the sealant. Avoid excessive primer application to prevent puddling at the base of the joint.