Fosroc Nitofill PU 23R
Two-component, water-reactive polyurethane injection resin for sealing leaking cracks, construction joints and diaphragm walls in concrete structures.
What is it?
A two-component, solvent-free, low-viscosity polyurethane injection resin from Fosroc that reacts on contact with water to expand and cure into a rigid foam, permanently sealing cracks and active water paths in concrete. It is an injection grout, not a gun- or pouring-grade joint sealant.
Where is it used?
Injected into leaking cracks, cold joints, construction joints and honeycombed concrete in basements, water tanks, tunnels, lift pits, diaphragm walls, retaining walls and below-grade structures across India.
Why use it?
It stops active water ingress even against flowing water and low hydrostatic pressure, bonds to damp concrete, mortar, brick and steel, and is non-flammable and solvent-free, making it suitable for confined and occupied structures.
How is it applied?
Drilled injection ports (packers) are set across the crack, the two components are metered and injected under pressure with a single- or twin-line pump; on meeting water the resin foams, expands and cures to seal the void.
About Fosroc Nitofill PU 23R
Fosroc Nitofill PU 23R is a member of Fosroc’s Nitofill polyurethane injection-resin range and is catalogued by Fosroc under injection grouts rather than joint sealants. It is a two-component, solvent-free polyurethane system supplied as a base resin and an accelerator/hardener that are combined at the point of use. The product is engineered for the remedial waterproofing of cracked and leaking concrete: it is a low-viscosity liquid that penetrates fine cracks and, on contact with water, reacts rapidly to expand into a tough, closed rigid foam that fills the void and arrests water flow. Importantly for Indian site conditions, the reaction proceeds even where water is moving, so it can be used to chase down live leaks rather than only treating dry, dormant cracks.
For Space Arc Engineering’s contractors and consultants it is worth being precise about what this product is and is not. Despite the “PU” name, Nitofill PU 23R is not an elastomeric movement-accommodating joint sealant in the family of Fosroc Nitoseal, Thioflex or Colpor. Those are gun-grade or pouring-grade sealants that flex over a designed joint with a backer rod and primer. Nitofill PU 23R, by contrast, is a pressure-injected grouting resin whose job is to seal a water path and bond the crack faces, not to flex repeatedly across a moving joint. Specifying it correctly — as a crack-injection / water-stopping resin within a remedial-waterproofing scope — avoids the common mistake of treating it as a joint-sealing caulk. The “R” suffix in the Fosroc catalogue denotes the resin/reactive variant within the PU23 family; the system is paired with an accelerator that allows the reaction rate to be tuned to the inflow conditions on site.
The technical insight
The defining behaviour of Nitofill PU 23R is its water-triggered, gas-generating cure. The polyurethane prepolymer reacts with water (the leak itself acts as the catalyst), liberating CO2 and foaming as it cures into a rigid cellular solid. This is why it works against active ingress: the resin chases the water back into the crack and expands to fill it, rather than being washed out before it sets. The accelerator component lets the applicator shorten the reaction/foaming time where the inflow is heavy, or extend it for deeper penetration into hairline cracks where a slower, more fluid front is wanted. Because the cured product is a rigid foam, it is best understood as a structural-seal/water-cutoff resin rather than a flexible one — for cracks that will continue to move, a flexible PU resin (e.g. Fosroc Nitofill UR-type) or a properly designed flexible joint sealant is the correct choice. Low viscosity is the second key property: it governs how fine a crack the resin can enter and how far it travels from each port, which in turn drives packer spacing and the achievable seal. Specifiers should always confirm the current edition of the Fosroc technical data sheet for exact mix ratio, viscosity, foaming/expansion factor, gel and cure times and temperature limits before writing a method statement.
Where it is used
- Sealing active and dormant cracks in below-grade concrete (basements, lift pits, sumps)
- Stopping leaks at construction joints and cold joints in water-retaining structures
- Remedial waterproofing of water tanks, STP/ETP tanks and reservoirs
- Cutting off water ingress in tunnels, shafts, metro and underground works
- Treating leaking diaphragm walls, retaining walls and secant pile walls
- Filling and sealing honeycombed or segregated concrete pockets
- Curtain/contact grouting behind tunnel linings and against rock faces
- Ground and soil consolidation in wet conditions ahead of excavation
Key advantages
- Reacts and seals even against flowing water and low hydrostatic pressure
- Low viscosity allows penetration of fine cracks for a thorough seal
- Two-component system with adjustable reaction rate via the accelerator
- Cures to a tough, rigid closed-cell foam that resists water re-entry
- Good adhesion to concrete, mortar, brick and steel, including damp substrates
- Solvent-free and non-flammable, suitable for confined and occupied spaces
- Expands on cure to fill voids and irregular crack geometry
- Backed by Fosroc technical support and Space Arc applicator expertise in India
Limitations & considerations
- Not a movement-accommodating joint sealant — do not specify it in place of Nitoseal, Thioflex or Colpor for flexible joints
- Cured rigid foam offers limited flexibility, so it is unsuitable for cracks that will keep moving significantly
- Requires specialist injection equipment (packers/ports and a pressure pump) and trained applicators
- Performance depends on correct packer spacing, injection pressure and accelerator dosing for the inflow rate
- Fosroc does not publish full numeric properties on the summary product page, so the current TDS must be confirmed before specification
- Being water-reactive, the resin and accelerator must be kept sealed and protected from moisture before use
- Surface and ambient temperature affect reaction and cure times and must be checked against the TDS
- Not a substitute for sound structural repair where cracking is caused by ongoing structural movement or load
Selection & best practice
Treat Nitofill PU 23R as a remedial crack-injection / water-stopping system, not a joint caulk. Begin with a survey to establish whether the crack is dormant or live and whether movement will continue — if it will, choose a flexible resin or a designed flexible joint instead. Clean the crack line, then drill injection ports (packers) at an angle that intersects the crack, spacing them at roughly the structure thickness and staggering either side; closer spacing is used for finer cracks and higher pressures. Flush the crack with water to wet the substrate and locate the flow path, then inject the metered two-component resin from the lowest port upward (for vertical cracks) using a single- or twin-line pump, moving to the next port as resin appears. Dose the accelerator to suit the inflow — faster for heavy flows, slower for deep penetration of hairline cracks. Allow the foam to expand and cure, re-inject where needed, then remove packers and make good the surface. Always work to the current Fosroc TDS for mix ratio, pressures and temperature limits, and use trained applicators — Space Arc Engineering can supply both the material and the application crew.
Specifications
| Brand | Fosroc |
| Product | Nitofill PU 23R |
| Fosroc category | Injection grout / crack-injection resin |
| Chemistry | Two-component polyurethane resin |
| Components | Base resin + accelerator/hardener (mixed on site) |
| Reaction trigger | Reacts with water; expands to rigid foam |
| Viscosity | Low viscosity (penetrates fine cracks) — confirm value on current TDS |
| Cured form | Rigid closed-cell polyurethane foam |
| Application method | Pressure injection via packers/ports |
| Solvent / flammability | Solvent-free; non-flammable |
| Substrate adhesion | Concrete, mortar, brick, metal (incl. damp surfaces) |
| Primary use | Sealing leaking cracks, joints, diaphragm walls; ground consolidation |
| Not suitable as | Flexible movement-accommodating joint sealant |
| Mix ratio / cure times / expansion | Refer to current Fosroc technical data sheet |
Industry use cases
Metro & tunnelling
Cutting off active water ingress through segment joints, cracks and rock faces in metro tunnels, shafts and underground stations where leaks must be stopped against pressure.
Water & wastewater
Remedial sealing of cracks and construction joints in water tanks, reservoirs, STP/ETP structures and sumps to restore watertightness.
Basements & high-rise substructure
Stopping leaks in basement walls, rafts, lift pits and retaining walls of commercial and residential towers across Delhi NCR.
Infrastructure & deep excavation
Sealing leaking diaphragm walls, secant piles and consolidating wet ground ahead of or during deep excavation works.
Industrial & power
Arresting seepage through cracked concrete in plant rooms, cable tunnels, cooling-water structures and below-grade industrial slabs.
Frequently asked questions
Is Fosroc Nitofill PU 23R a joint sealant?
How does it stop a leak that is actively flowing?
Is it flexible enough for a moving crack or expansion joint?
What does the ‘R’ in PU 23R mean?
Can it be applied to damp or wet concrete?
Where can I buy Nitofill PU 23R and get it applied in India?
How we position Fosroc Nitofill PU 23R
Within Fosroc’s range, Nitofill PU 23R sits in the crack-injection / water-stopping resin family alongside products such as Nitofill UR (flexible PU injection resin), Nitofill LV and Nitofill TH (epoxy injection resins) and the Nitofill WS water-stopping resins — it should not be confused with Fosroc’s flexible joint sealants Nitoseal (polyurethane/silyl), Thioflex (polysulphide) or Colpor (pavement-grade), which are the correct choice for designed movement joints. Choose Nitofill PU 23R when the goal is to inject and seal a leaking crack or joint against water; choose a Nitoseal/Thioflex/Colpor sealant when the goal is to seal and flex across a movement joint. Credible alternatives in the injection-resin space include Sika’s Sikadur and SikaFix PU injection systems, MBCC/Master Builders Solutions MasterInject and MasterSeal injection resins, and STP/other local PU grouting resins; for flexible joint sealing the comparable products are Sika Sikaflex, MasterSeal joint sealants and equivalent polyurethane/polysulphide ranges. Space Arc Engineering can advise on the correct selection, supply genuine Fosroc material and carry out the injection works.
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