When an expansion joint must move with the building, perform in challenging conditions, and meet strict certifications, the right sealant is non-negotiable. Bostik Seal 'N' Flex One P390 provides this assurance. It is engineered for high-movement applications in concrete, masonry, and precast panels, ensuring seals remain intact where flexibility and compliance are paramount.

Why this product exists

Bostik Seal 'N' Flex One P390 is a low modulus, one-component polyurethane sealant formulated for the demands of Australian construction. It maintains a durable, flexible seal across an impressive ±50% joint movement. This capability prevents common joint failures, especially in dynamic structures like tilt-up panels or concrete slabs. With over 900% elongation at break, it provides a substantial safety margin, absorbing thermal shock and minor settlement that could compromise lesser sealants. This product was developed to deliver reliable performance where AS4020 potable water approval or acoustic rating is required for expansion and construction joints.

The numbers that matter

• Total Joint Movement: ±50%. This Class-A movement rating means a 20mm joint can expand and contract by 10mm without bond failure, making it suitable for significant structural movement.
• Elongation at Break: >900%. While rated for ±50% movement, its extreme elongation capacity provides exceptional resilience against unexpected stresses, minor substrate shifts, or temperature extremes, significantly reducing the risk of premature failure.
• Shore A Hardness: 30. This low modulus value indicates a soft, flexible sealant that readily accommodates joint movement, transferring minimal stress to bond lines and ensuring long-term adhesion.
• Cure Rate: 2mm per 24 hours. This allows for sufficient tooling time (6-12 hours tack-free) while ensuring a steady, predictable cure to full strength over 7 days (or 14 days for joints exceeding 20mm width). This controlled cure minimises the risk of cracking in the sealant film during early movement cycles.

What it's like to use

Bostik Seal 'N' Flex One P390 is supplied as a one-component system, requiring no mixing, simplifying on-site application. It can be applied in temperatures ranging from 5°C to 35°C using a standard caulking gun. For optimal performance, ensure all surfaces are clean and dry, free from contaminants. While the sealant offers good adhesion to many substrates without a primer, critical or high-performance applications, especially on porous surfaces or those subject to periodic immersion, benefit from Bostik N49 Primer. For non-porous plastics and metals, Bostik N40 Primer is recommended using a two-cloth method. Tooling should occur within the tack-free time to achieve a smooth, concave finish. Once cured (minimum 7 days), the sealant can be painted, though a field test for compatibility with solvent-based coatings is always recommended. Always use a compatible backer rod to control sealant depth and prevent three-sided adhesion.

Where this product excels

• Concrete and Masonry Expansion Joints: For sealing expansion joints in in-situ concrete, precast, tilt-up panels, brickwork, and blockwork, it handles significant cyclic movement (±50%) without cracking or bond failure.
• Potable Water Infrastructure: Certified to AS4020 for contact with drinking water, it is ideal for sealing joints in water storage tanks, reservoirs, and piping systems where water quality is critical.
• Acoustic Sealing: Acoustic rated to AS 2253 / 1276, it effectively reduces sound transmission through joints in plasterboard and fibre cement sheets, crucial for quiet commercial or residential spaces.
• Specialty Panel Systems: Its low modulus and high elongation make it well-suited for sealing joints in GRC, fibreglass, and other specialty panel systems, accommodating their dynamic movement.

Choose this when

• When you need ±50% movement capacity: Specify for expansion and construction joints in concrete, precast, or masonry where significant, ongoing movement is expected.
• When potable water contact is required: Use in applications where the sealant will be in contact with drinking water, such as water tanks or reservoirs, ensuring AS4020 compliance.
• When acoustic performance matters: Select for sealing plasterboard or fibre cement joints where sound transmission needs to be minimised and a certified acoustic rating is beneficial.
• When durability and flexibility are critical: Opt for this sealant in environments with temperature fluctuations or structural settling, leveraging its high elongation at break to maintain integrity.

Don't use this when

• Not for: Chlorinated water immersion, such as swimming pools or spas, as it is not formulated for these chemical environments.
• Not for: Glazing applications or on any material containing bitumen, which can lead to compatibility issues or staining.
• Not for: Applying to cement-based substrates within 28 days of initial pour or set, as uncured concrete can affect adhesion and cure.
• Not for: Trafficable joints, as its low Shore A hardness and modulus are not designed to withstand pedestrian or vehicular traffic.
• Not for: Extreme movement joints exceeding ±50%, as a dedicated high-movement sealant like Seal 'N' Flex One Plus P590 would be a more suitable choice.

Bostik Seal 'N' Flex One P390 vs. Seal 'N' Flex One Plus P590

Bostik Seal 'N' Flex One P390 is the go-to for expansion and construction joints requiring robust ±50% movement and specific certifications like AS4020 potable water approval and acoustic rating. It is a proven performer for standard high-movement applications on dry substrates. In contrast, for joints demanding extreme movement capacity, exceeding ±50% (up to +100%/-50%), or where application on damp or even wet concrete substrates is necessary, Seal 'N' Flex One Plus P590 offers a more advanced solution. The choice between them hinges on the precise movement profile and substrate conditions of the project.

Related products

• Bostik Seal ‘N’ Flex One Plus P590
• Bostik Fireban One