Sika UCS h
A chloride-free powder stabiliser that stops cement paste washing out of concrete and grout placed under water, so tremie and submerged pours hold their strength.
What is it?
A white powder admixture based on alkali-resistant stabilisers that gives cementitious mixes an anti-washout, anti-bleed, thixotropic character for placement under water.
Where is it used?
Marine and port structures, bridge piers, jetties, offshore foundations, tremie and submerged pours, and grout or cement injection in water-bearing ground.
Why use it?
It keeps the cement paste bound to the aggregate during placement, so far less binder is lost to the surrounding water and the hardened concrete reaches its intended strength.
How is it applied?
Added at the batching plant with the aggregate or cement at 1.0-3.0% by weight of binder for concrete, then wet-mixed for at least 90 seconds before placing.
About Sika UCS h
Placing concrete or grout under water is one of the harder problems a site team faces. The moment fresh mix meets water, the cement paste and fines start to disperse, leaving a weak, segregated, honeycombed mass that never develops the strength the design assumed. Sika UCS h is engineered to stop that from happening. It is a white powder admixture built around alkali-resistant stabilisers that thicken the mix water into a cohesive, thixotropic gel, holding the binder and fine particles in place while the concrete descends through water and settles into position.
For engineers working on ports, bridge foundations, jetties and offshore works across India, the appeal is practical. The product is chloride-free, so it does not introduce a corrosion risk to embedded steel, and once it is locked into the hardened cement matrix it is ecologically harmless. It is supplied as a dry powder in 15 kg bags that can be dosed straight into the batching plant, which keeps the workflow familiar for ready-mix and site batching crews. Used correctly, it turns a high-risk underwater pour into a controlled, repeatable operation.
The technical insight
The mechanism is rheological rather than chemical hardening. The alkali-resistant stabiliser hydrates in the mix water and raises its viscosity, forming a shear-thinning, thixotropic phase around the cement grains and fines. Because the water phase is now cohesive rather than free, it resists being stripped away as the concrete passes through the surrounding water column. At rest the mix stays stiff and holds its shape; under the shear of mixing, pumping or tremie flow it thins enough to place, then recovers its body once movement stops. That balance is what lets the paste stay welded to the aggregate instead of bleeding out, and it is also why wet mixing for at least 90 seconds matters, as the stabiliser needs that time to fully develop before placement. Because it works by controlling cohesion, not by accelerating set, it does not compromise the reinforcement or the long-term chemistry of the matrix.
Where it is used
- Underwater concreting for marine and port structures such as quay walls and berths
- Tremie-placed and pump-placed submerged foundation pours
- Grout and cement injection in water-bearing ground conditions
- Bridge pier and pile-cap concreting below the waterline
- Jetty, wharf and offshore platform foundation works
- Anti-bleed stabilisation of cementitious mixes where segregation is a risk
- Cofferdam and caisson infill concrete placed under standing water
Key advantages
- Sharply reduces wash-out of cement paste and fines during underwater placement
- Strengthens the bond between cement paste and aggregate for sounder hardened concrete
- Chloride-free formulation that does not attack embedded reinforcement
- Improves cohesion and gives a controllable thixotropic, anti-bleed mix
- Ecologically harmless once bound into the cement matrix
- Supplied as an easy-to-dose dry powder that fits standard batching workflows
- Suitable for both structural concrete and injection grouts with a single product
Limitations & considerations
- A stabiliser only, it provides no plasticising effect, so a separate superplasticiser is usually needed to keep workability where high cohesion is introduced
- Requires a wet mixing time of at least 90 seconds, which longer or underpowered mixers must accommodate
- Dosage must be trialled and controlled, as overdosing stiffens the mix and complicates placement
- Performance depends on correct dispersion, so it should be added at the batching plant rather than hand-dosed on site
- Being a dry powder it must be kept in sealed bags and protected from moisture, sunlight and frost before use
Selection & best practice
Add Sika UCS h at the batching plant together with the aggregate or cement so it disperses evenly, rather than dosing it late into a loaded mixer. Start at the lower end of the 1.0-3.0% by weight of binder range for concrete and adjust upward through trial mixes until wash-out is acceptable without the mix becoming unplaceable; for grout and cement injection work within 0.2-1% by weight of cement. Always run a wet mixing time of at least 90 seconds so the stabiliser fully develops. Because the admixture increases cohesion, pair it with a compatible Sika superplasticiser to recover workability instead of adding extra water, which would defeat the purpose. Place through a tremie or pump with a continuous, controlled flow, keep the discharge embedded in the fresh concrete, and store unopened bags dry between +5 and +40 degrees C, protected from sunlight and frost, using stock within its shelf life.
Specifications
| Product type | Anti-washout / anti-bleed stabiliser admixture for underwater concrete and grout |
| Chemical base | Alkali-resistant stabiliser, chloride-free |
| Appearance | White powder |
| Density | Approx. 0.8 kg/l at 25 degrees C |
| Dosage (concrete) | 1.0 – 3.0% by weight of cement / binder |
| Dosage (grout / injection) | 0.2 – 1% by weight of cement |
| Wet mixing time | At least 90 seconds |
| Packaging | 15 kg bags |
| Storage | Store dry between +5 and +40 degrees C, protected from sunlight and frost |
Industry use cases
Ports & Marine
Concreting quay walls, berths and breakwater elements below the tide line where paste loss would otherwise leave weak, porous surfaces.
Bridges & Infrastructure
Placing pier bases, pile caps and foundation concrete under standing or flowing water using tremie or pump methods.
Offshore & Hydraulic
Foundation and platform works in submerged conditions where reliable underwater strength gain is critical.
Ground Engineering
Cement and grout injection in water-bearing strata, where the stabiliser prevents dilution and wash-out of the binder.
Repair & Rehabilitation
Underwater patching and infill of cofferdams, caissons and submerged structures without dewatering the pour.
Frequently asked questions
What does Sika UCS h actually do to the concrete?
How much do I dose?
Does it corrode the reinforcement?
Does it make the concrete workable enough to place?
How is it added on site?
How is it supplied and stored?
How we position Sika UCS h
Sika UCS h sits within Sika’s underwater and specialty admixture range and is best specified alongside a Sika superplasticiser such as the Sikament or SikaPlast lines, which restore the workability lost to its high cohesion. On projects that also need general waterproofing or set control, it pairs naturally with the wider Sika ViscoCrete admixture family. Where a client is standardising on a single brand for their concrete package, our Fosroc equivalent, Conplast UW, delivers the same anti-washout function, and we also stock comparable specialty admixtures from MC-Bauchemie and Master Builders Solutions so the specification can be matched to the approved vendor list rather than forced to one supplier.
Fosroc Conplast UW — Choose Conplast UW when the project is standardised on Fosroc or wants an anti-washout admixture that also carries built-in plasticising agents to hold workability in one product.
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