Adheseal Hi-Flex Construction Plus MS Polymer Sealant

For expansion joints, perimeter window fixing, and cladding joints where high movement capability is required, Adheseal Hi-Flex Construction Plus MS Polymer Sealant provides a neutral-cure, low-modulus elastomeric seal that accommodates up to 50% joint movement. Based on hybrid MS polymer technology, this single-component sealant complies with ASTM C920-CLASS 50 and ASTM C1248, maintaining permanent flexibility without bleeding or staining adjacent substrates.

What it does

Hi-Flex Construction Plus MS Polymer Sealant cures by reacting with atmospheric humidity to form a durable, elastic joint. Because it contains no isocyanates, solvents, or acids, it is non-corrosive to sensitive metals like galvanized steel, zinc-coated steel, and concrete. It is formulated to inhibit mould and biological growth, making it suitable for hot and humid service environments. The cured sealant can be painted with acrylic, oil, and rubber-based paints, though non-flexible paints may crack under movement.

Numbers that matter

• ±50% movement capability (ASTM C719): High joint movement accommodation to prevent adhesive or cohesive failure in moving facade joints and window frames.
• 1100% elongation at break (ASTM D412): Extreme elasticity allows the cured seal to stretch repeatedly without tearing.
• 3mm per 24 hours cure rate: Cures from the surface inward under standard atmospheric conditions (25°C and 50% relative humidity).
• -40°C to 100°C service temperature: Maintains its physical properties and elastomeric performance under extreme environmental exposure.
• 25 Shore A hardness (ASTM D2240): A low-modulus rating that ensures the seal remains soft and flexible enough to minimise stress on the bond line.

Where to use it

This sealant is compatible with most common building materials, including concrete, masonry, brick, timber, metals (excluding lead and copper), plastics, stone, porcelain, fibreglass, powder coat, and waterproof membranes. Suitable applications include:

• Perimeter window sealing and fenestration details
• Expansion joints in precast and tilt-up panels
• Curtain walls and external facade cladding joints
• Seam sealing, bolted lap joints, and mechanical fixing joints
• Acoustic ceiling tiles and lightweight component bonding
• Automotive and marine manufacturing assembly

Limitations

• Water immersion: Do not use for long-term water immersion, aquariums, or internal swimming pools with high chlorine exposure.
• Confined spaces: Do not use in totally confined spaces; the sealant requires atmospheric humidity to cure.
• Stone substrates: Do not use on stone without completing a stain-testing program (Adheseal S100 is recommended for marble and granite).
• Metal restrictions: Do not use on lead or copper; the sealant may discolour copper and brass.
• Incompatible compounds: Do not use on bituminous surfaces, natural rubber, EPDM rubber, or in contact with compounds that leach oils, plasticisers, or solvents.
• Mirrors: Not suitable for adhering mirrors (use Hi-Power or MS609 instead).
• Structural glazing: Do not use for structural glazing (use N-80 or N-60 glazing silicone).
• Substrate moisture: Do not apply when moisture-vapour transmission is emanating from the substrate, as air entrapment can cause bubbling.
• Chemical exposure: Do not expose the sealant to cleaning agents, solvents, or alcohol during its curing phase.

Installation and joint design

All surfaces must be clean, dry, structurally sound, and free of oils, grease, curing compounds, or release agents. Concrete must cure for at least 28 days before application. For non-porous substrates like aluminium, stainless steel, PVC, galvanized steel, and glazed tiles, clean and pre-treat with Adheseal 50A surface prep, then apply sealant between 30 minutes and 2 hours after priming. For porous substrates like concrete and brick, prime with Everflex Supaprime and apply sealant within the same 30-minute to 2-hour window.

Design joints to a 2:1 width-to-depth ratio. Internal joints must be a minimum of 5mm wide and 5mm deep; external joints must be a minimum of 12mm wide. For joints deeper than 10mm, use an open-cell foam backer rod (such as Adhefoam) sized 25% larger than the joint width to control depth and prevent three-sided adhesion.

Apply when temperatures are between 5°C and 40°C. For adhesive bonding, apply a triangular bead by holding the nozzle flat at a 90-degree angle, then compress the surfaces together to a minimum thickness of 2mm. Tool wet sealant with a moistened spatula within 5 minutes, before the 10-minute skin time. Wet sealant and tools can be cleaned with Xylene; cured material must be removed mechanically.