STP ShaliGrout PU 2K 20
A hydrophobic, water-reactive polyurethane injection grout that foams on contact with water to shut down active leaks in cracks, joints and pipes fast.
What is it?
A single-component, solvent- and phthalate-free hydrophobic polyurethane grout (with Catalyst D) that reacts with water to form a stiff, closed-cell foam.
Where is it used?
Actively leaking cracks, construction and expansion joints, and sewer pipes in basements, tunnels, retaining walls, water tanks and treatment plants.
Why use it?
It reacts only with water, so it chases the leak path and expands 2800-3000% to physically block flowing water under hydrostatic pressure.
How is it applied?
Pressure-injected through packers drilled at 45 degrees across the crack, after blending resin with water and Catalyst D to set the gel time.
About STP ShaliGrout PU 2K 20
STP ShaliGrout PU 2K 20 is the product you reach for when water is already coming through a crack and a rigid resin simply will not hold. It is a hydrophobic, water-reactive polyurethane that stays inert in the drum and only kicks off once it meets moisture inside the structure. On contact with water it foams aggressively, expanding roughly 28 to 30 times its liquid volume into a tough, closed-cell polyurethane that grips the crack walls and stops the flow. Because it is solvent-free and phthalate-free, it is comfortable to use in the enclosed, poorly ventilated spaces where leaks usually live: lift pits, basement rafts, tunnel linings and wet joints.
For engineers used to two-part PU resins, the working logic here is a little different. ShaliGrout PU 2K 20 ships as a single resin component plus a separate Catalyst D, and you dial in the reaction speed by how much catalyst you add. A small dose gives you close to two minutes of working time for hairline cracks; a heavy dose slams the gel time down to around 25 seconds so you can knock back a gushing leak before it washes the resin out. That control is what makes it a genuine site tool rather than a lab product, and it is why applicators treat PU 2K 20 as their first-response water stop before permanent sealing.
The technical insight
The chemistry is deliberately water-triggered. The resin is a hydrophobic polyurethane pre-polymer whose isocyanate groups react with water; that reaction releases carbon dioxide, which is what blows the resin into a foam that expands 2800-3000% and drives itself into every branch of the crack. Because the trigger is the leaking water itself, the grout naturally travels toward the wettest zone, the exact path you are trying to seal. Catalyst D governs the kinetics: at 2% you see a cream time of 25-30 seconds and a gel time of 100-110 seconds, while at 20-30% cream time collapses to 5-10 seconds and gel time to 20-35 seconds. The very low mixed viscosity of 20-65 mPa.s lets the resin penetrate fine cracks before it foams, and the cured foam is elastic enough (5-16% elongation to ASTM D 638) to tolerate minor movement and high hydrostatic pressure without cracking off the substrate. Being hydrophobic, the cured foam does not re-absorb water and re-swell, so the seal stays dimensionally stable rather than shrinking back when the structure later dries out.
Where it is used
- Rapid, temporary water-stopping of actively leaking cracks in concrete structures
- Sealing leaking construction and expansion joints under hydrostatic pressure
- Curtain and crack injection in tunnels, metro and railway underground works
- Stopping seepage in basement rafts, retaining walls and lift pits
- Arresting leaks in large- and small-bore sewer and drainage pipes
- Sealing water-leaking joints in water-retaining structures and treatment plants
- First-response leak control ahead of permanent elastic sealing with ShaliGrout PU 2K
- Foundation and substructure crack injection against pressurised groundwater
Key advantages
- Reacts only with water, so it follows and blocks the active leak path
- Massive 2800-3000% free foam expansion fills cracks and voids fully
- Gel time tuned on site from about 25 to 110 seconds via Catalyst D dosage
- Very low 20-65 mPa.s viscosity penetrates fine cracks before foaming
- Solvent- and phthalate-free, so it is workable in confined, unventilated spaces
- Suitable for contact with potable water and reacts with sea and mineral water too
- Good adhesion to damp substrates and resistance to high hydrostatic pressure
- Works with both electric and pneumatic injection pumps
Limitations & considerations
- It is a water-stop, not a structural or permanent elastic seal; follow up with ShaliGrout PU 2K for a durable flexible joint
- Gel time depends entirely on correct catalyst dosing, so a trial mix per site condition is essential
- Needs injection packers, a pump and trained applicators, not a hand-applied or cartridge product
- Sensitive to moisture in the drum: an opened pack must be used immediately and purged with nitrogen if part-used
- Reaction speed and foam behaviour shift with temperature, so hot or cold sites need dosage adjustment
- Cured foam can only be removed mechanically once set, so tools must be cleaned before the resin gels
Selection & best practice
Start by drilling injection ports at a 45-degree angle to intersect the crack about 100 mm (4 inches) below the surface, staggering holes on alternate sides roughly 200 mm (8 inches) apart. Decide your gel time first: refer to the catalyst table and choose the Catalyst D percentage for your leak severity, then blend 100 g of resin with about 20 g of water and the chosen catalyst, mixing for around half a minute to a homogeneous state. Keep the pump reservoir covered so ambient moisture does not pre-react the resin. Inject at a minimum of 4 bar, working packers sequentially and, on vertical cracks, starting from the lowest packer upward. For heavy flows, catalyse hard for a very short gel time to knock the water back first, then re-inject. On fine cracks, re-inject until clean resin (not foam) emerges at the face, trim excess with a sharp knife once foaming stops, and clean all tools before the resin sets.
Specifications
| Chemistry | Single-component hydrophobic, water-reactive polyurethane with Catalyst D |
| Mixed viscosity | 20-65 mPa.s at 25 C |
| Free foam expansion | 2800-3000% |
| Elongation at break | 5-16% (ASTM D 638) |
| Mixing recipe | 100 g resin : 20 g water : Catalyst D as required |
| Gel time | About 25-110 seconds, depending on catalyst dosage (2-30%) |
| Cream time | 5-30 seconds, depending on catalyst dosage |
| Recommended temperature range | 5 C to 45 C |
| Minimum injection pressure | 4 bar |
| Pack size | 5.5 kg (5 kg Part A + 0.5 kg Catalyst D) |
| Shelf life | 12 months unopened, stored at 5 C to 35 C |
Industry use cases
Metro & Tunnels
Curtain and crack injection to stop active ingress through segment joints and tunnel linings, where fast catalysed gel times cut water flow quickly in confined, unventilated bores.
Basements & Lift Pits
First-response leak sealing in rafts, retaining walls and pits under hydrostatic head, ahead of a permanent elastic seal, without solvent fumes in enclosed spaces.
Water & Sewage Infrastructure
Sealing leaking joints in water-retaining tanks and treatment plants, and arresting leaks in large- and small-bore sewer pipes, with potable-water contact suitability.
Dams & Water-Retaining Structures
Blocking pressurised leaks through cracks and joints, using heavy catalyst dosing to achieve very short gel times against high-flow seepage.
Foundations & Substructures
Injection against pressurised groundwater in foundation and substructure concrete, where low viscosity lets the resin reach fine cracks before it foams.
Frequently asked questions
Is ShaliGrout PU 2K 20 a permanent crack seal?
How do I control the reaction speed on site?
Can it be used where water is actively flowing?
Is it safe near drinking water?
What equipment and pressure are needed?
How is it packed and how long does it store?
How we position STP ShaliGrout PU 2K 20
Within the STP ShaliGrout family, PU 2K 20 is the water-stop specialist and is meant to be paired, not confused, with its siblings. Use PU 2K 20 to kill the active leak, then inject STP ShaliGrout PU 2K, the low-viscosity two-component elastic resin, to form the permanent flexible seal in the same crack. For non-ionic acrylic-style grouting, ShaliGrout PU F is the family option, while ShaliGrout PU 2K FS covers fast-set two-component water-stopping. Where a client specifies Fosroc, Space Arc supplies the direct equivalent from that range, and for hydrophilic (swelling) chemistry or epoxy structural injection we can cross-reference Sika, MC-Bauchemie and Dr. Fixit systems from our wider portfolio so the specifier gets the right water-stop for the flow, movement and durability the job actually demands.
Fosroc Nitofill PU 11R — Choose the Fosroc option when the project or consultant has standardised on the Fosroc system; Nitofill PU 11R is a comparable water-reactive PU that foams to seal actively leaking cracks and joints under hydrostatic pressure.
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