Fosroc Nitofill UR63
A two-part, water-reactive polyurethane resin injected under pressure to stop active water leaks through cracks in concrete and masonry.
What is it?
A two-part, solvent-free, low-viscosity polyurethane injection resin that reacts with water to form a tough, slightly flexible closed-cell seal inside cracks.
Where is it used?
Wet or actively leaking cracks and joints in basements, water tanks, tunnels, lift pits, retaining walls and other below-ground or water-retaining concrete structures.
Why use it?
It cures in the presence of water and even flowing seepage, so it seals live leaks that rigid epoxy resins cannot handle, while staying flexible enough to accommodate minor crack movement.
How is it applied?
Pumped through injection packers drilled at roughly 45 degrees along the crack, using a resin-injection pump at a pressure of at least 0.4 N/mm2 (4 bar).
About Fosroc Nitofill UR63
Nitofill UR63 is Fosroc’s water-reactive polyurethane injection resin, made for one of the most stubborn problems on any site: a crack that is already leaking. It arrives as a two-part, solvent-free liquid with a very low viscosity, so once the base and hardener are combined the resin flows readily into fine cracks and hairline paths that coarser materials would bridge over. What sets it apart is its chemistry. On contact with water it reacts and expands, driving itself deep into the wet crack and curing into a tough, slightly flexible closed-cell mass that grips the crack walls and shuts off the flow. Because it needs moisture to cure, damp or running conditions that would defeat an epoxy actually work in its favour.
For engineers and applicators across Delhi NCR and the rest of India, that makes UR63 a practical answer to below-ground and water-retaining leak problems where you cannot dry the substrate first. It is used to seal seepage through construction joints, cold joints and structural cracks in basements, tanks, tunnels, lift pits and retaining walls. The cured resin is not fully rigid; it retains enough flexibility to tolerate the small movements these structures experience, so the seal is less likely to be re-cracked by thermal or settlement cycles. Space Arc Engineering supplies genuine Fosroc Nitofill UR63 with the technical and applicator support needed to specify, inject and verify the repair correctly.
The technical insight
The resin works because polyurethane prepolymers react with water rather than being harmed by it. When the mixed resin meets moisture in the crack, the reaction generates gas that makes the material foam and expand — Fosroc quotes a free expansion of around 800% — so it pushes forward against the water pressure and fills the void instead of being washed out. As the reaction completes, it sets into a closed-cell polyurethane with good adhesion to concrete and masonry. The low mixed viscosity (base around 105 mPa·s and hardener around 8 mPa·s at 25°C) is what lets it travel into fine cracks before it gels, and the injection is done under pressure — at least 0.4 N/mm2 (4 bar) — so the resin is actively forced through the full depth of the section rather than merely coating the surface. The end result is a flexible, water-tight seal that both stops the present leak and remains slightly elastic against future movement.
Where it is used
- Sealing active water leaks through cracks in basement and diaphragm walls
- Stopping seepage at construction joints and cold joints in below-ground structures
- Waterproofing crack and joint leaks in water tanks and reservoirs
- Sealing water ingress in tunnels, subways and underground car parks
- Leak sealing in lift pits, sumps and machine foundations
- Crack injection in retaining walls and other earth-retaining concrete
- Emergency sealing of live seepage during construction before final finishing
- Repairing damp, moving cracks where a flexible seal is required rather than a rigid one
Key advantages
- Cures in the presence of water, so it seals cracks that are damp or actively leaking
- Expands on reaction (about 800% free expansion) to drive itself into wet cracks and resist water pressure
- Very low mixed viscosity penetrates fine and hairline cracks
- Cured seal stays slightly flexible and tolerates minor crack movement
- Good adhesion to concrete and masonry surfaces
- Solvent-free formulation
- Well suited to Indian below-ground and water-retaining structures
- Backed by Fosroc technical data and Space Arc applicator support
Limitations & considerations
- It is a leak-sealing resin, not a structural crack-bonding resin — where rigid load transfer is needed, a low-viscosity epoxy such as Nitofill LV is the correct choice
- Best results depend on correct packer spacing, drilling angle and injection pressure, so trained applicators are strongly recommended
- On structures subject to continuing significant movement, a secondary waterproofing system may still be required
- Once cured the resin can only be removed mechanically
- Uncured resin must be cleaned from equipment promptly using a proprietary polyurethane cleaner
- Shelf life is limited (around 6 months), so stock should be rotated and used fresh
Selection & best practice
Map the crack and drill injection ports (packers) on alternate sides at roughly 45 degrees so each hole intersects the crack within the section; typical packer spacing is in the range of 200-500 mm depending on crack width and wall thickness. Make sure contact surfaces at the packers are free of oil, grease and loose material, and seal the crack face where necessary so the resin builds pressure inside rather than bleeding out. Mix the base and hardener in the supplied proportions and inject with a resin-injection pump at a pressure of at least 0.4 N/mm2 (4 bar), working from the lowest packer upward and moving on once resin appears at the next port. Because UR63 reacts with water, a little pre-wetting of a very dry crack can help initiate the reaction. Clean all equipment immediately after use — and during breaks — with a proprietary polyurethane cleaner, as cured resin can only be removed mechanically. Always work to the current Fosroc data sheet and observe the recommended PPE.
Specifications
| Product type | Two-part, solvent-free, water-reactive polyurethane injection resin |
| Cured form | Tough, slightly flexible closed-cell seal |
| Base viscosity | 105 mPa·s at 25°C |
| Hardener viscosity | 8 mPa·s at 25°C |
| Base density | 1.08 kg/l |
| Hardener density | 0.947 kg/l |
| Free expansion | Approx. 800% |
| Injection pressure | At least 0.4 N/mm² (4 bar) |
| Shelf life | 6 months from manufacture in unopened containers |
Industry use cases
Basements & underground structures
Sealing live seepage through wall cracks, construction joints and cold joints in basement retaining walls and underground car parks.
Water-retaining structures
Stopping leaks through cracks and joints in water tanks, reservoirs and treatment structures where the substrate cannot be dried out.
Tunnels & infrastructure
Injecting active water ingress in tunnel linings, subways and metro civil works under hydrostatic pressure.
Building services pits
Sealing seepage in lift pits, sumps and machine foundations where standing or running water is present.
Repair & rehabilitation contractors
An emergency and remedial tool for sealing leaking cracks on existing concrete before applying finishes or secondary waterproofing.
Frequently asked questions
Can Nitofill UR63 seal a crack that is actively leaking water?
Is UR63 a structural repair for cracks?
How is it injected?
Does the cured resin stay flexible?
How do I clean tools after use?
Do you supply and apply UR63 in Delhi NCR?
How we position Fosroc Nitofill UR63
Within the Fosroc injection range, Nitofill UR63 is the water-reactive PU grade for wet and actively leaking cracks. Where a crack is dry and static and the goal is a rigid structural bond that restores load transfer, specify the low-viscosity epoxy Nitofill LV instead, or Nitofill EPLV for damp-tolerant epoxy injection. Pair UR63 with a surface crack sealant and, on moving or high-risk structures, a secondary waterproofing membrane. Space Arc also carries complementary systems from other brands we distribute — including crystalline and cementitious waterproofing coatings and polyurethane/PU injection resins across the Dr. Fixit, Sika and MC-Bauchemie ranges — so the full leak-sealing and waterproofing package can be specified from one source.
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