About Fosroc Nitofill PU27R

Fosroc Nitofill PU27R is a two-component, high-strength hydrophobic polyurethane (PU) injection grout developed for one of the hardest problems on any waterproofing job — sealing a crack or joint that is actively leaking water under pressure. It belongs to Fosroc’s Nitofill family of injection resins, the same range that includes the flexible PU crack-injection resin Nitofill UR63, the single-component foaming resin Nitofill PU 1F and the low-viscosity epoxy Nitofill LV. Within that family, PU27R is the workhorse for water-reactive, expansive, structural sealing.

Chemically it is a polyol-and-isocyanate system supplied as two parts that are combined at the point of injection. The formulation is phthalate-free, tin-free and solvent-free, which makes it cleaner and safer to handle on confined-space sites such as tunnels, shafts and lift pits than older solvented PU grouts. Its defining characteristic is that it is hydrophobic and water-reactive: instead of being displaced by flowing water, it reacts with that water, foams and expands in volume to physically fill the crack or void, then cures to a tough, rigid mass with high compressive strength and high bond strength to the surrounding substrate.

That behaviour is what separates PU27R from a joint sealant. A gun-grade or pourable sealant (Fosroc Nitoseal, Thioflex, Colpor) is applied into a dry, accessible joint to accommodate movement at the surface. PU27R is pressure-injected into the body of the structure, through drilled ports, to chase down and choke off a leak path you often cannot even see. It is a curtain-and-crack injection material first and a ground-consolidation grout second, not a movement-accommodating sealant.

For Space Arc Engineering’s contractors in Delhi NCR and across India, PU27R is specified where water is already coming through — leaking basement raft cracks, construction joints in water-retaining structures, segmental tunnel-lining joints, leaking rock fissures and soft, water-bearing ground that needs both waterproofing and strengthening. Because the cured product is rigid and strong, it also stabilises and consolidates the surrounding concrete, masonry or ground as part of the same operation. All technical values for a specific project should be confirmed against the current region-specific Technical Data Sheet, available from Fosroc on country selection.

The technical insight

The engineering logic of Nitofill PU27R sits in three properties working together. First, low enough viscosity for good flow and penetration, so the injected resin travels into fine cracks and tight rock fissures before it sets rather than bridging only the mouth of the crack. Second, water reactivity with foaming and volume expansion: the moment the resin contacts water in the crack, the reaction kicks off and the material expands to fill the available space and push back against the water, which is why it works on live, flowing leaks where a non-reactive resin would simply be washed away. Third, it cures hard. Unlike a flexible PU such as Nitofill UR63 — which stays slightly elastic to absorb differential movement — PU27R develops high compressive strength and high bond strength, so it not only seals the leak but contributes structurally, consolidating fractured concrete, masonry or loose ground into a coherent, load-bearing mass. The trade-off is movement: a rigid, foamed grout is a sealing and consolidation product, not a joint that flexes, so designers pair it with a flexible injection resin where ongoing movement is expected. Reaction speed and expansion are influenced by the volume of water present and by temperature, which is why packer spacing, injection pressure and pump rate are set on site in response to the actual water flow rather than from a fixed recipe.

Where it is used

• Sealing active, flowing water leaks through cracks, joints and cavities in concrete and masonry
• Crack and void injection in basement rafts, retaining walls and below-grade structures
• Construction-joint and segment-joint sealing in tunnels, shafts and culverts
• Waterproofing of water-bearing soft ground, rock and fissured rock by curtain injection
• Ground consolidation and stabilisation of loose or fractured strata ahead of excavation
• Stabilisation and underpinning of settled or cracked concrete slabs
• Leak sealing in water tanks, sumps, lift pits and STP/ETP structures
• Stopping ingress in dam galleries, hydro works and water-retaining infrastructure

Key advantages

• Water-reactive: foams and expands on contact with water, so it seals live, flowing leaks that conventional grouts cannot hold
• High compressive and bond strength — seals and structurally consolidates the substrate in one operation
• Good flow and penetration into fine cracks, joints and tight rock fissures
• Hydrophobic chemistry resists wash-out during cure under hydrostatic pressure
• Phthalate-free, tin-free and solvent-free — cleaner and safer for confined-space and below-grade work
• Two-component control allows reaction to be tuned to the water flow encountered on site
• Works on wet substrates, which is exactly where water-stopping is needed
• Versatile across waterproofing and ground-consolidation applications

Limitations & considerations

• Not a joint sealant — it is rigid when cured and does not accommodate ongoing joint movement; use a flexible PU (e.g. Nitofill UR63) or a movement-accommodating sealant where cyclic movement is expected
• Requires specialist injection equipment — packers and a suitable injection pump — and trained operators, not a hand-applied product
• Reaction and expansion depend on the presence of water and on temperature, so behaviour varies with site conditions and needs on-site control
• As a two-component PU it has a limited working/gel time once mixed and demands disciplined pump and mixing-ratio control
• Isocyanate-based — appropriate PPE, ventilation and handling precautions are essential, especially in confined spaces
• Numeric performance values (viscosity, density, mix ratio, strengths, pack sizes) must be confirmed against the current region-specific Fosroc TDS before specification

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Nitofill PU27R

Within the Fosroc range, Nitofill PU27R is the hydrophobic, foaming, high-strength member of the Nitofill injection family — chosen when water is actively flowing and the structure needs both sealing and consolidation. Its closest siblings are Nitofill UR63 (a flexible PU resin for crack injection where movement must be accommodated) and Nitofill PU 1F (a single-component elastic foaming water-stopper); Nitofill LV is the low-viscosity epoxy alternative for structurally bonding dry, non-leaking cracks. It is important not to confuse PU27R with Fosroc’s true joint sealants — Nitoseal (polyurethane and silicone sealants), Thioflex (polysulphide) and Colpor (pourable joint sealant) — which seal accessible movement joints at the surface and accommodate cyclic movement, a job PU27R is not designed for. Among competing injection systems, credible alternatives that consultants in India will recognise include Sika’s polyurethane injection resins (the Sika Injection / SikaFix PU range), MBCC/Master Builders Solutions MasterInject and MasterSeal injection grouts, and STP (Krishna Conchem / Zentrifix-type) PU injection products. Specifying PU27R should be a deliberate choice for water-reactive, rigid, consolidating crack and curtain injection — and where ongoing joint movement is the real issue, the correct answer is a flexible injection resin or a movement-accommodating sealant instead. Space Arc Engineering supplies Nitofill PU27R as an authorised Fosroc distributor and can provide the application as a Fosroc applicator across Delhi NCR and Pan-India; verified technical values should always be drawn from the current region-specific Fosroc TDS.

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