Sika Injection-201 IN
A very low-viscosity, solvent-free polyurethane injection resin that flows into fine cracks and cures to a permanently flexible watertight seal.
What is it?
A two-part, water-reactive, solvent-free polyurethane injection resin. Mixed A+B has a viscosity of only ~250-600 mPa.s, so it penetrates cracks wider than 0.2 mm and cures to a permanently elastic, non-shrink seal.
Where is it used?
Dry, damp or water-bearing cracks and joints in concrete, brickwork and natural stone – basements, tunnels, water tanks, reservoirs, retaining walls and construction joints, including single-injection of the Sika Fuko hose system.
Why use it?
It stays flexible after curing so it accommodates limited structural movement without cracking, shows no shrinkage in later dry conditions, and is chemically inert and safe for use in groundwater protection zones.
How is it applied?
Mix Part A to Part B at 2:1 by volume for at least 2 minutes, then inject through a single or two-component pump within the pot life, working between +5 C and +35 C.
About Sika Injection-201 IN
Sika Injection-201 IN is a specialist crack-repair resin designed for one job that many products struggle with: making a damp or actively leaking crack permanently watertight without losing flexibility. It is a solvent-free, two-component polyurethane supplied as a translucent Part A and a dark-brown Part B in a combined 16 kg unit. Because the mixed resin is so thin – viscosity is only around 250 to 600 mPa.s at +30 C – it wicks deep into hairline cracks above roughly 0.2 mm that thicker epoxy or cementitious systems cannot reach, then reacts with the moisture already present to build a closed, uniform pore structure.
For engineers and applicators in India, the appeal is durability under real-site conditions. Once cured, the resin is inert, chemically resistant and does not shrink back in dry weather, so the seal it forms keeps its watertight grip through wetting and drying cycles. Crucially it stays elastic, absorbing the small movements that concrete and masonry undergo with thermal and structural loading – the kind of movement that would open a brittle repair straight back up. This is a professional-use material: Sika restricts it to experienced injection specialists, and correct pump selection and crack preparation matter as much as the resin itself.
The technical insight
The resin works by moisture-triggered polymerisation. Polyurethane prepolymers in the mixed system react with the water sitting inside a damp or water-bearing crack, and instead of simply hardening they build a uniform, closed and therefore watertight pore structure that remains elastic. That is the key difference from a foaming water-stopper: Injection-201 IN is a low-viscosity sealer, not an aggressive expander, so it is chosen to travel into fine cracks and cure to a flexible seal rather than to violently block a torrent. Where a crack is under real hydrostatic pressure with running water, Sika’s own guidance is to knock the flow down first with a fast-foaming resin such as Sika Injection-101h or a cementitious grout with a non-shrink additive, then use Injection-201 IN as the permanent flexible seal behind it. The controlled gel time – roughly 70 to 90 minutes for the mixed system at +20 C – gives the applicator working time to pump the resin fully into the crack network before it sets.
Where it is used
- Permanent watertight sealing of dry, damp or water-bearing cracks in concrete, brickwork and natural stone
- Sealing construction joints and cold joints where limited movement must be accommodated
- Single-injection of the Sika Fuko hose system in new construction joints (non re-injectable)
- Basement and below-grade structure waterproofing repair
- Tunnel and underground structure crack sealing
- Water-retaining structures such as tanks and reservoirs
- Retaining walls and bridge structures subject to water ingress
- Permanent flexible seal behind a preliminary foam or cementitious injection where hydrostatic pressure is present
Key advantages
- Permanently elastic – absorbs limited structural and thermal movement without re-cracking
- Very low viscosity (~250-600 mPa.s) penetrates fine cracks wider than 0.2 mm
- No shrinkage in subsequent dry conditions, so the seal stays tight through wet-dry cycles
- Cured resin is inert and chemically resistant for long service life
- Solvent-free and environmentally friendly – usable in groundwater protection zones
- Reacts with moisture already in the crack, so the substrate need not be fully dry
- Supplied pre-portioned as a 16 kg A+B unit at the correct 2:1 mixing ratio
- Controlled ~70-90 minute gel time gives adequate working and pumping window
Limitations & considerations
- For experienced professional injection applicators only – not a DIY or general-purpose product
- Cannot stop strong running water on its own; heavy flow under hydrostatic pressure must first be reduced with Sika Injection-101h or a cementitious grout
- When used with the Sika Fuko hose system it is single-injection only and non re-injectable
- Application is limited to a substrate and ambient temperature window of +5 C to +35 C
- Requires a suitable single- or two-component injection pump and clean, dust-free crack surfaces
- Uncured resin cleans off tools only with Xylene; once hardened it can be removed only mechanically
Selection & best practice
Start by cleaning the crack thoroughly – surfaces of cavities and cracks must be free of loose particles, dust, oil and any bond-breaking substances, with dirt blown out by compressed air. Empty Parts A and B into a mixing vessel at the supplied 2:1 ratio by volume and mix slowly and thoroughly for at least 2 minutes at no more than 250 rpm until homogeneous. Pour into the pump feed container, stir briefly and inject within the pot life using a pump rated for the product. Keep both substrate and ambient temperature between +5 C and +35 C. If the crack is carrying water under pressure, first inject Sika Injection-101h or a cementitious grout to cut the flow, then follow with Injection-201 IN as the permanent flexible seal. Clean tools with Xylene before the resin cures, and always read the current Safety Data Sheet before handling.
Specifications
| Chemical base | Solvent-free, water-reactive 2-part polyurethane resin (liquid) |
| Mixing ratio | 2 : 1 parts by volume (Part A : Part B) |
| Colour | Part A translucent; Part B dark brown |
| Viscosity (mixed, +30 C) | ~250-600 mPa.s (cps) |
| Density | Part A ~1.04 kg/L; Part B ~1.22 kg/L |
| Gel time (mixed, +20 C) | ~70-90 minutes |
| Application / substrate temperature | +5 C min. to +35 C max. |
| Packaging | 16 kg unit (Part A + Part B) |
| Shelf life / storage | 12 months; store dry, sealed, +10 C to +35 C |
Industry use cases
Basements & below-grade
Permanently sealing damp or leaking wall and slab cracks in basements and podiums where the substrate cannot be fully dried before repair.
Tunnels & metro
Injecting fine cracks and construction joints in tunnel linings and underground structures to stop seepage while allowing limited movement.
Water-retaining structures
Sealing cracks and joints in tanks, reservoirs and treatment works with a chemically resistant, non-shrink flexible seal.
Bridges & retaining walls
Restoring watertightness to cracked concrete in bridge decks, abutments and retaining walls subject to thermal cycling.
New construction joints
Single-injection of the Sika Fuko hose system to waterproof planned construction joints in fresh concrete work.
Frequently asked questions
Is Sika Injection-201 IN an acrylic gel or a polyurethane resin?
Can it be injected into cracks that are actively leaking water?
How fine a crack can it penetrate?
What is the mixing ratio and working time?
What pack size does it come in and how long does it store?
Does the seal stay flexible or does it become brittle over time?
How we position Sika Injection-201 IN
Within the Sika injection family, pair Injection-201 IN with Sika Injection-101h, the fast-foaming polyurethane used to knock down heavy water flow before the permanent flexible seal goes in, and specify it alongside the Sika Fuko hose system for waterproofing planned construction joints. For rigid, structural (force-transmitting) crack bonding on dormant cracks, a Sikadur epoxy injection resin is the correct choice instead. From our other brand lines, we can supply comparable water-reactive PU injection resins from Fosroc and MC-Bauchemie, plus surface waterproofing systems from Dr. Fixit and STP where the repair extends beyond crack injection to full membrane or coating works.
Fosroc Nitofill UR63 — Choose the Fosroc option when the priority is stopping active, running-water leaks – Nitofill UR63 is a water-reactive foaming PU that expands to block flow, complementing 201 IN’s role as a low-viscosity flexible sealer.
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