MC-Bauchemie MC-Injekt 2133 flex
A one-component, water-reactive PU resin that foams the instant it touches water, sealing running leaks in cracks from 0.3 mm even while water is actively flowing.
What is it?
A single-component, hydrophobic MDI-polyurethane injection resin that stays liquid indefinitely until it meets water, then reacts into a closed-cell, flexible foam.
Where is it used?
Water-bearing cracks and joints of 0.3-5 mm in concrete, masonry and rock; building-pit closures; tunnel and metro linings; and membrane-to-structure contact zones.
Why use it?
It needs no mixing, has unlimited pot life before contact with water, and starts foaming in as little as 30 seconds – stopping active flow on the spot.
How is it applied?
Injected neat through packers with a one-component PU injection pump; dry substrates are pre-wetted first, and equipment is flushed with MC-Verdünnung PU, never water.
About MC-Bauchemie MC-Injekt 2133 flex
MC-Injekt 2133 flex is a one-component, MDI-based polyurethane resin built around a simple idea: let the leak trigger its own seal. Hydrophobic in its raw state, it glides along the water film into the crack instead of washing away in wet ground, and only reacts once it actually meets water. Foaming begins within about 30 seconds, expands to roughly ten times its liquid volume, and cures into a closed-cell foam. Because the cells are closed rather than interconnected, the cured foam itself blocks further water passage.
On Indian sites this makes it the practical first move on genuinely active leaks – basement seepage, a weeping tunnel joint, or a diaphragm-wall panel running water mid-excavation – where a rigid epoxy or cementitious grout would get washed out before it cures. Space Arc positions it as the fast-reacting, flexible half of MC-Bauchemie’s two-stage injection system: 2133 flex stops the water, and where the crack moves or needs a permanent pressure-rated seal, it is typically followed by structural post-injection with MC-Injekt 2300 top or 2300 flow. It ships as a ready one-component 10-litre pack.
The technical insight
The figure worth reading twice is the viscosity split: about 800 mPa·s neat, dropping to roughly 260 mPa·s once it is reacting with water – low enough to still reach a 0.3 mm hairline crack before it gels. The elongation numbers explain the “flex” name: 66% free elongation and 21-39% elongation tested inside a simulated crack (DIN 12618-2), well beyond what a rigid grout tolerates under movement. Read the adhesive tensile strength – about 0.15 N/mm² on damp concrete – as a caution, not a headline: this is a sealing bond, not a structural one, which is exactly why permanent, load-bearing repairs are left to epoxy systems or a follow-up structural injection.
Where it is used
- Durable sealing injection of water-bearing cracks and voids, roughly 0.3-5 mm
- Sheet-pile and diaphragm-wall building-pit closures against groundwater ingress
- Tunnel and metro box linings – sealing segment and construction joints
- Consolidation grouting of water-bearing rock and subsoil in mining and hydropower works
- Flexible filling and sealing of voids under dry or water-bearing conditions
- Sealing voids and cracks in masonry, including heritage structures
- Large-scale sealing of waterproofing membrane-to-structure contact zones
Key advantages
- Foams within 30-180 seconds of touching water, shutting off active flowing leaks fast
- One-component system – no mixing ratios, no pot-life pressure before it meets water
- Closed-cell structure blocks water after cure, unlike open-cell foams that can wick moisture
- High elongation (66% free, 21-39% in-crack) lets the seal move with the structure
- Reacted viscosity of about 260 mPa·s still reaches hairline 0.3 mm cracks
- Phthalate-free, documented harmless to groundwater – suits potable-water-adjacent and monitored-discharge sites
- Wide +6°C to +35°C working range suits most Indian site conditions year-round
Limitations & considerations
- Not marketed as a stand-alone permanent seal against sustained pressurised water – pair with MC-Injekt 2300 top or flow for that
- Needs a dedicated one-component PU pump and a trained crew, not a DIY product
- Reaction depends on moisture, so dry cracks must be pre-wetted before injection
- Below +6°C the reaction slows sharply, limiting cold-weather or high-altitude use
- Seals rather than structurally bonds – not a substitute for epoxy where load transfer is needed
Selection & best practice
Treat 2133 flex as the leak-stopping first stage, not the final word. Pre-wet dry substrates to confirm injectivity and trigger the reaction, set packers with a weir opening of at least 1.5 mm, and plan the hole pattern to an injection concept per DIN EN 12715 rather than drilling by instinct. Keep material and substrate temperature above +6°C throughout. Flush the pump and hose with MC-Verdünnung PU – never water – the moment work pauses. Where the crack carries sustained hydrostatic pressure or needs a structural repair, follow up with MC-Injekt 2300 top or 2300 flow once the active flow has stopped.
Specifications
| Chemistry | One-component, hydrophobic PU (MDI-based) elastomer resin |
| Density | approx. 1.03 kg/dm³ (DIN 53479) |
| Viscosity (neat) | approx. 800 mPa·s (DIN EN ISO 3219) |
| Injection viscosity with water | approx. 260 mPa·s (DIN EN ISO 3219) |
| Free elongation | 66% (DIN 53455) |
| Elongation in crack | 21-39% (DIN 12618-2) |
| Adhesive tensile strength | approx. 0.15 N/mm² on dry/damp concrete (DIN EN 12618-1) |
| Volume increase / foaming time | approx. 1000% (free foaming); starts/ends in 30/180 seconds |
| Application temperature / pack size | +6°C to +35°C; 10 litre pack |
Industry use cases
Metro & underground transit
Sealing diaphragm-wall and station-box construction joints against groundwater during excavation
Basements & lift pits
Stopping active seepage before applying a permanent waterproofing system
Tunnels & hydropower
Sealing segment joints and water-bearing rock fissures in tunnel drives and dam galleries
Building-pit dewatering
Closing leaks in sheet-pile or secant-pile cofferdams so excavation can proceed
Masonry & heritage repair
Flexibly filling voids and cracks where rigid cementitious grout would crack under movement
Frequently asked questions
Is MC-Injekt 2133 flex a permanent waterproofing fix on its own?
Can it be injected while water is actively running out of the crack?
What crack widths does it actually work in?
How is it different from an epoxy crack-injection resin?
What equipment and skill level does application need?
What is the shelf life and how should it be stored on site?
How we position MC-Bauchemie MC-Injekt 2133 flex
2133 flex is the fast-reacting, flexible half of MC-Bauchemie’s structural injection system. Pair it with MC-Injekt 2300 top or 2300 flow when a stopped leak needs to become a permanent, pressure-rated structural seal, and with MC-Injektionspacker DS14 packers and an MC-I series pump for the injection itself. Where a specification calls for a Fosroc-branded chain instead, Nitofill PU 1F covers the same single-component, water-reactive foam duty for live leaks. Space Arc can supply and apply either system as part of one injection-grouting scope.
Fosroc Nitofill PU 1F — A specifier already running a Fosroc-branded waterproofing chain, or working to a spec that names Fosroc explicitly, would choose Nitofill PU 1F for the same single-component, water-reactive PU foam duty on live, flowing leaks.
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