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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.
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.
This sealant adheres to masonry, brick, stone, porcelain, timber, plastics, painted surfaces, rubber, fibreglass, powder coat, concrete, wood, and waterproof membranes. Typical installations include:
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.
While adhesion is typically achieved without a primer, high-stress joints or critical applications require specific preparation:
Yes. Megaprene 40GG is designed for movement and expansion joints with ±25% joint movement capability. It remains permanently flexible and is suited to concrete panels, pavement joints, façade joints, and cladding systems where thermal and structural movement occur.
Yes, Megaprene 40GG is paintable with acrylic, oil, and rubber-based paints. Adhesion testing is recommended before full application because non-flexible paint systems may crack when the joint moves.
Yes, once cured it is suitable for below-waterline applications. The sealant must be fully cured before exposure to water and should not be used for aquarium installations or high-chlorine pool environments.
Megaprene 40GG adheres to common construction materials including concrete, masonry, timber, aluminium, painted surfaces, powder coat, fibreglass, and waterproof membranes. Adhesion testing is still recommended before large-scale application.
No. Megaprene 40GG is not recommended for bituminous substrates, EPDM rubber, or surfaces that may leach oils or plasticisers. These materials can cause adhesion failure and long-term sealant degradation.
| Application | Key benefit | Primary trades |
|---|---|---|
| Expansion joints in precast and tilt-up panels | Accommodates ±25% joint movement while maintaining a waterproof flexible seal | Commercial builders, precast installers |
| Window perimeter sealing | Creates durable weather-resistant joints around façade openings | Glaziers, façade contractors |
| Curtain wall sealing | Maintains long-term elasticity across moving façade connections | Façade installers, aluminium fabricators |
| Metal cladding and lap joints | Strong adhesion to common construction metals including powder coat | Cladding installers, sheet metal trades |
| Pavement joints, car parks, and driveways | Flexible polyurethane seal resists intermittent fuel and oil exposure | Civil contractors, concrete trades |
| General construction sealing and bonding | Single-component application simplifies on-site sealing and adhesive work | Builders, maintenance contractors |
| Marine and vehicular manufacturing | Permanently elastic seal absorbs vibration and material movement | Marine fabricators, transport manufacturers |
Start with a clean, dry, structurally sound surface. Remove dust, grease, curing compounds, release agents and any contamination that can compromise adhesion.
Allow concrete to cure for at least 28 days. Prime critical porous surfaces with Everflex Supaprime where required.
Use a fine abrasive pad where suitable, then clean using the two-wipe process and prepare with Adheseal 50A Surface Prep for critical applications.
Correct joint geometry is what lets the sealant move properly and stay bonded under load.
Aim for a 2:1 width-to-depth ratio where possible. Internal joints should be minimum 5mm wide and deep, and external joints minimum 12mm.
For joints deeper than 10mm, use open cell backing rod about 25% larger than the joint width. Where backer rod cannot fit, use bond breaker tape to stop three-sided adhesion.
For sealing work, cut the nozzle at a 45-degree angle to suit the bead size, load the sausage and gun the sealant by pushing it ahead of the nozzle.
Keep the nozzle in contact with both sides of the joint and maintain a steady continuous bead so the sealant is pressed firmly into place.
Fill the joint completely and avoid trapping air, as entrapped air can form bubbles in the cured sealant.
For adhesive use, cut the nozzle to form a triangular bead and compress the joined surfaces evenly.
Cut the nozzle at 90 degrees to bead width, then cut a wedge twice the bead height. Apply a steady triangular bead and compress surfaces to no less than 2mm.
Tool with a moistened spatula for a smooth finish. Clean wet excess with Xylene. If cured residue remains, soften with solvent and scrape carefully.
DANGER. Wear nitrile gloves, apron, safety glasses, and respirator protection where inhalation risk exists.
Use with adequate ventilation. Where inhalation risk exists, wear an organic vapour or particulate respirator meeting AS/NZS 1715 and AS/NZS 1716 requirements.
Correct substrate preparation improves long-term adhesion performance and reduces the risk of joint failure, bubbling, or delamination.
Surface prep: Allow concrete to cure for at least 28 days. Remove dust, loose material, curing compounds, grease, oils, and surface contamination before sealing.
Primer: Required. Use Everflex Supaprime on porous concrete, render, mortar, and brick substrates for improved adhesion performance.
Surface prep: Lightly abrade with a fine abrasive pad and clean using the two-wipe method with Adheseal 50A Surface Prep.
Primer: Optional. Priming improves adhesion performance on critical or highly stressed joints.
| Property | Value |
|---|---|
| Type Of Product | Polyurethane |
| Curing System | Moisture |
| Cure Time | 3mm per 24 hours |
| Density | Black 1.15, Others 1.16±0.02 |
| Shore A Hardness | 25 after 14 days |
| Joint Movement Capability | +/-25% |
| Tear Strength | 6.5N/mm |
| Elongation At Break | >400% |
| Modulus Elongation | 0.4 MPa @ 100% |
| Application Temperature | +5°C to +35°C |
| Service Temperature | -40°C to +80°C |
| Working Time | 25 minutes @ 23°C & 50% RH |
| Skinning Time | 60 minutes @ 23°C & 50% RH |
| VOC | <1.5g/L |
| Shelf Life | 18 months in original packaging |
| Storage | Cool dry between 10°C and 35°C |
| UV Resistance | 500h Good |
| Chemical Resistance | Excellent for water, detergent solutions, moderately diluted acids and alkalis, petrol and oil for short periods |
| Sealant Classification | ISO 11600 Type F Class 25 LM |
| AS1530.3 Test | Ignitability Index 0, Spread of Flame Index 0, Heat Evolved Index 0, Smoke Developed Index 0-1 |
| Colours | Black, Grey |
| Packaging | 600ml foil sausages |
Here are some common examples on where Adheseal Megaprene 40GG Polyurethane Sealant used by our customers.
