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For expansion joints in precast and tilt-up panels, brickwork, concrete, and fibre cement sheet, Seal 'N' Flex One P390 Polyurethane Sealant 300ml provides a Class-A joint seal that accommodates high-movement thermal cycles. It cures to a tough, flexible barrier that handles constant contraction and expansion without adhesive failure or pulling away from the joint faces.
Seal 'N' Flex One P390 is a low-modulus, moisture-curing polyurethane sealant formulated to handle cyclic joint movement of ±50% (100% total movement) of the original installed joint width. Because it is low modulus, the cured sealant exerts minimal stress on the bond line when the joint expands, preventing cohesive or adhesive failure in porous substrates like insitu concrete, mortar, and brickwork. The smooth, non-sag thixotropic paste holds its shape during application in vertical joints and can be tooled to a concave finish. It is acoustic rated to AS 2253 / 1276 and carries AS4020 approval for potable water contact.
Suitable for sealing joints in:
Surfaces must be completely clean, dry, and free of laitance, oil, dust, grease, frost, water, old sealants, and curing agents. Dust and loose particles must be vacuum cleaned.
Seal 'N' Flex One P390 adheres without primer to standard concrete, mortar, and bare Aluminium. However, a Pre-tested Adhesion to Substrate (P.A.T.S.) test is recommended prior to application. Substrate primers must be used for high-stress joints, extreme weather exposure, or highly porous surfaces:
Seal 'N' Flex One P390 can be painted after a minimum of 7 days. Coatings containing solvents, such as enamels or oil-based paints, may react with the sealant surface and create a tacky finish. Surface coatings may discolour in direct contact with the cured sealant, and cyclical joint movement may cause the paint film to crack or craze. Field testing is recommended to verify coating compatibility.
Yes, this sealant is approved to AS4020 for use in contact with potable water. This makes it suitable for sealing joints in tanks or other structures that will hold drinking water.
No, Bostik Seal N Flex One P390 is not recommended for use in trafficable joints. Selecting a product specifically designed for pedestrian or vehicle traffic loads will prevent premature failure.
Joints must be at least 5 mm wide and 6 mm deep. The maximum allowable joint width is 50 mm. Maintaining these dimensions is critical for the sealant to perform to its ±50% movement rating.
Yes, the sealant can be painted after a minimum of 7 days cure. Conduct a field test for compatibility, as solvent-based coatings may cause tackiness, and cyclical movement can cause cracking in the paint layer.
| Application | Key benefit | Primary trades |
|---|---|---|
| Expansion joints in concrete & masonry | Accommodates ±50% joint movement, preventing cracking and bond failure. Maintains integrity in construction and precast panels. | Concreters, commercial builders, precast installers |
| Perimeter sealing for aluminium windows | Forms a durable, flexible seal to withstand building movement without compromising the window system. | Window installers, façade contractors |
| Sealing plasterboard & fibre cement sheets | Acoustic rated to AS 2253 / 1276. Prevents sound transmission through joints and provides a durable, paintable finish. | Plasterers, acoustic installers, dryliners |
| Sealing joints in potable water structures | AS4020 certified for drinking water contact, ensuring health and safety compliance for water storage and supply systems. | Plumbers, water infrastructure contractors |
| Sealing GRC and fibreglass panels | Low modulus and high elongation (>900%) handle the dynamic movement often found in specialty panel systems. | Façade specialists, panel installers |
Signal word: Warning
Wear safety glasses with side shields, lightweight protective clothing, long-sleeved clothing, and impervious gloves (nitrile rubber recommended). Use appropriate respiratory protection, such as a respirator conforming to EN 140 with Type A/P2 filter or better, for organic gases and vapours.
Use only outdoors or in a well-ventilated area. Ensure adequate ventilation and consider showers and eyewash stations.
Keep containers tightly closed in a dry, cool, and well-ventilated place between 5°C and 30°C. Protect from moisture, oxidizing agents, and acids. Shelf life is 12 months in original unopened containers. Dispose of waste and empty containers in accordance with local regulations; do not dispose down drains or into waterways.
Proper surface preparation and primer selection prevent bond failure, ensuring the sealant performs as specified for cyclic movement.
Surface prep: Clean and dry surfaces. Remove laitance, oil, dust, grease, and any curing agents. Vacuum loose particles.
Primer: Not required for standard concrete or mortar that is clean, dry, and uncontaminated. For high-stress joints, extreme weather exposure, or overly porous surfaces, a primer is required. For periodically immersed or submerged applications, use Bostik N49 Primer.
Surface prep: Clean and dry. Remove any protective coating (wax or plastic) from composite panels before application.
Primer: Not required for bare aluminium. Always conduct a Pre-tested Adhesion to Substrate (P.A.T.S.) test beforehand.
Surface prep: Surfaces must be clean, dry, and free of contaminants. Absorbent surfaces that soak up water require careful priming.
Primer: Required for maximum performance, especially in periodically immersed or submerged applications. Use Bostik N49 Primer. Vertical expansion joints in masonry or concrete may not require priming if clean and dry.
Surface prep: Clean and dry surfaces where water beads as a droplet. Includes u-PVC, brass, copper, and stainless steel.
Primer: Required. Use Bostik N40 Primer, applied with the two-cloth method. Conduct P.A.T.S. to confirm adhesion.
| Property | Value |
|---|---|
| Product Type | One Component Polyurethane Sealant |
| Modulus | Low |
| Joint Movement Capability | ±50% |
| Shore A Hardness | 30 |
| Tensile Strength | > 1.3 N/mm² |
| Elongation at Break | > 900% |
| Application Temperature | 5 to 35°C |
| Service Temperature | -40 to 75°C |
| Tack Free Time | 6-12 hours |
| Cure Rate | 2 mm/24 hours (on porous substrates) |
| Full Cure Time | 7 days (on porous substrates), 14 days (joints >20mm wide) |
| Maximum Joint Width | 50 mm |
| Minimum Joint Depth | 6 mm |
| Specific Gravity | 1.25 g/ml |
| VOC Content | 74 g/L (TDS), 64 g/L (SDS) |
| Cure Method | Moisture curing |
| Shelf Life | 12 months |
Here are some common examples on where Bostik Seal 'N' Flex One P390 Polyurethane Sealant 300ml used by our customers.
