About Fosroc Nitoseal PU

Nitoseal PU is Fosroc’s single-component polyurethane building sealant, formulated for the joints that never sit still. Concrete slabs expand and contract with temperature, precast panels drift, and window frames work loose against their reveals; a rigid pointing mortar simply cracks under that cyclic loading. Nitoseal PU stays elastic instead, stretching and compressing with the joint through thousands of thermal cycles while keeping water, dust and draughts out. It cures by reacting with moisture in the air, so there is no two-part measuring and no pot-life to race against on site: an applicator loads the cartridge, guns a clean bead, tools it, and moves on.

The chemistry is a low-modulus polyurethane, which matters more than it sounds. Low modulus means the cured rubber is soft enough to flex without pulling itself off the joint faces, so the stress stays inside the sealant rather than at the bond line where failures start. Fosroc rates it to ISO 11600 Type F 25LM and a movement accommodation factor of 25%, and it bonds to concrete, masonry, timber and metal. On porous substrates it is often used without primer; on dense or non-porous faces a Fosroc primer is specified to lock down adhesion. For Space Arc’s clients across Delhi NCR and Pan-India, that combination of movement capability, single-part convenience and broad substrate range makes it a dependable default for perimeter and movement-joint sealing.

The technical insight

The whole point of an elastomeric joint sealant is that the joint face moves and the sealant must follow it without letting go. Two numbers govern whether it survives: modulus and movement accommodation factor (MAF). Modulus is how hard the cured sealant resists being stretched. Nitoseal PU is a low-modulus polyurethane (Shore A around 25), so as the joint opens in winter the sealant elongates under low internal stress and passes very little of that stress to the adhesive bond at the concrete face. High-modulus sealants, by contrast, develop large peel forces at the bond line and are the ones you see torn away from one edge. MAF is the total movement, as a percentage of joint width, that the product can cycle through indefinitely; at 25% (ISO 11600 F 25LM) a correctly sized 20 mm joint handles about 5 mm of combined open-and-close movement. This is also why joint geometry is not optional: the bead must be backed by a bond-breaker rod so the sealant bonds to only two faces and is free to deform, and the width-to-depth ratio must be right so the section can actually stretch. Moisture curing does the rest, the polyurethane reacting with airborne humidity from the surface inward, which is why very deep beads and non-porous joints cure more slowly and why a backing rod that limits depth also helps the cure.

Where it is used

• Expansion and movement joints in concrete floors, pavements and podium decks
• Perimeter sealing of aluminium and uPVC window and door frames against reveals
• Vertical movement joints in brick, block and stone masonry facades
• Joints between precast concrete panels and cladding units
• Construction and control joints in walls, slabs and retaining structures
• Weather-sealing around parapets, copings and service penetrations
• Resealing of aged or failed joints during building maintenance and refurbishment
• General building-envelope gap sealing where flexible, watertight joints are required

Key advantages

• Single-component and gun-ready: no mixing, no pot-life, less site wastage
• Low-modulus elastomer accepts 25% total joint movement (ISO 11600 F 25LM) without cracking or debonding
• Cures on atmospheric moisture to a tough, permanently elastic rubber
• Bonds to concrete, masonry, timber and metal; primerless on many porous substrates
• Overpaintable with most decorative coatings once tack-free
• Wide service range roughly -40 C to +70 C once fully cured, suiting Indian climate extremes
• Neutral-cure chemistry is low-odour and non-corrosive to most substrates
• Available in a range of colours to match architectural finishes

Limitations & considerations

• Not intended for continuous water immersion or permanently submerged joints
• Single-component PU has more limited long-term UV and colour stability than polysulfide or MS-polymer sealants; some surface chalking is possible on exposed elevations
• Cure is moisture-dependent, so deep or non-porous joints cure slowly from the surface inward
• Non-porous and dense substrates require the correct Fosroc primer for reliable adhesion
• Not a structural adhesive or a trafficable flooring compound; it seals joints, it does not carry loads
• Joints must be correctly designed with a bond-breaker backing rod and proper width-to-depth ratio, or movement capacity is lost

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Nitoseal PU

Within the Fosroc range, Nitoseal PU is the everyday single-component workhorse for building-envelope movement and perimeter joints. Where a specifier needs the exact factory grade and datasheet, the direct match is Nitoseal PU40, the flagship one-part low-modulus PU building sealant. For dynamic joints demanding higher durability and wider bite, Nitoseal PU50 extends the joint range, while Nitoseal PU400 is the medium-modulus PU used where the seal must also act as a high-strength, abrasion-resistant adhesive. For below-ground, trafficked or fuel-resistant joints, step up to the two-part, pitch-modified Nitoseal PU220. Where superior UV and colour stability is the priority on exposed elevations, Fosroc’s MS-polymer Nitoseal MS600 is the better choice, and for reciprocating or highly durable joints Thioflex 600 polysulfide remains the traditional alternative. Across our other brands, Space Arc can also supply equivalent PU and hybrid sealants from Sika and MC-Bauchemie where a project standard calls for them. Correct joint sealing is only as good as the joint prep, so we typically pair the sealant with the right backing rod, primer and, for structural or expansion-joint details, a compatible Fosroc joint system.

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