Fosroc Conbextra UHS
An ultra high strength, plastic-shrinkage-compensated cementitious precision grout built for the most heavily loaded machine bases, bridge bearings and precast connections.
What is it?
A single-part, factory-blended cementitious precision grout from Fosroc’s Conbextra range, engineered for ultra high early and ultimate strength. It arrives as a dry powder and needs only clean water on site to produce a free-flowing, non-shrink grout complying with ASTM C 1107 Type A.
Where is it used?
Under heavy rotating and reciprocating equipment, turbine and compressor bases, bridge bearing pedestals, crane rails and precast connections where bearing stresses and dynamic loads are high.
Why use it?
Its very low water demand delivers rapid strength gain and dense, high-strength hardened grout, while controlled expansion keeps the void completely filled so the full base plate stays in contact with the foundation.
How is it applied?
Mix one 25 kg bag with the specified quantity of clean water to a flowable consistency, then pour continuously from one side into a pre-formed, dampened, leak-tight formwork so the grout advances across the gap without trapping air.
About Fosroc Conbextra UHS
Conbextra UHS sits at the top of Fosroc’s cementitious grout ladder. Where the general-purpose Conbextra GP1 and GP2 grades cover routine static and dynamic machine bases, UHS is specified when the bearing stress, the dynamic loading, or the OEM’s strength clause pushes a standard grout to its limit. It is a plastic-shrinkage-compensated, high-flow, high early and ultimate strength grout that complies with ASTM C 1107 Type A, supplied as a ready-to-use 25 kg bag that needs only clean water on site. That single-pack format removes the site batching errors that quietly undermine grout performance, because the cement, graded fillers and expansion chemistry are already proportioned at the factory.
The value of the product shows up in the details that matter to a commissioning engineer. A very low water-to-powder ratio of around 0.13 is what drives both the rapid early strength and the dense, durable hardened matrix, so equipment can often be brought back into service quickly. The expansion system is non-metallic, so there is no iron to rust and stain the base or the anchor bolts, and the grout is chloride free, which protects embedded steel and machined surfaces. Free-flow behaviour without segregation or bleeding means the grout travels under the full footprint of a base plate and hardens into continuous, void-free contact, which is precisely what a high-load foundation needs to transfer load evenly.
The technical insight
The engineering logic behind Conbextra UHS is the trade-off between water and strength. Cementitious grouts gain strength as the water-to-cement ratio falls, but less water normally means a stiff, unworkable mix that will not flow under a base plate. Fosroc resolves this with graded fillers and flow-modifying chemistry that keep the mix mobile at a water-to-powder ratio near 0.13, far below a site-batched mortar. That low water content produces a tight capillary structure with high early and ultimate compressive strength and low permeability. The second half of the mechanism is controlled expansion in the plastic state: as the grout stiffens it develops a slight positive expansion rather than the drying shrinkage of ordinary mortar, so it stays hard up against the underside of the plate. The expansion is generated without any metallic iron and without releasing hydrogen gas, which means no corrosion staining and no risk of gas voids. The net result is a grout that stays fully in contact and carries concentrated, cyclic loads without cracking, spalling or pulling away from the interface.
Where it is used
- Grouting base plates of turbines, compressors and boiler feed pumps carrying high static and dynamic loads
- Foundations for heavy reciprocating and rotating equipment in refineries, cement plants and power stations
- Bridge bearing pedestals and seats subjected to concentrated bearing pressure
- Precast concrete connections and joints requiring high early strength before onward loading
- Crane rails, rail bearing plates and gantry supports under repeated dynamic loading
- Anchoring of holding-down bolts, masts and heavily loaded fixings
- Structural connections where OEM specifications demand ultra high strength grout
- Re-grouting and machinery re-alignment work where fast strength gain reduces plant downtime
Key advantages
- Ultra high early and ultimate strength from a very low water demand, complying with ASTM C 1107 Type A
- Plastic-shrinkage-compensated, so the grout keeps full contact under the base plate
- Free-flowing without segregation or bleeding, filling the gap completely without external aids
- Chloride free, protecting anchor bolts, embedded steel and machined surfaces from corrosion
- Non-metallic expansion system with no iron staining and no hydrogen gas generation
- Factory pre-blended single pack that removes on-site batching variation
- Micro-cellular hardened structure with good frost, fire and oil resistance
- Pourable and pumpable, suiting deep or congested foundations
Limitations & considerations
- It is a cementitious grout, so for aggressive chemical exposure, very thin sections or the highest impact duty an epoxy grout such as Conbextra EP series is more appropriate
- Strength and flow depend heavily on using the exact specified water quantity; excess water sharply reduces performance
- Single-pour gap thickness is limited, so very deep pours may need the grout to be extended with graded aggregate per Fosroc guidance
- Working life shortens in hot Indian ambient conditions, leaving less time to place each mix
- Formwork must be leak-tight and the substrate saturated surface dry, or flow and bond suffer
- Full design strength develops over the standard cure period, so early loading must respect the specified early-age values
Selection & best practice
Success with Conbextra UHS is mostly about preparation and discipline. Roughen and clean the concrete foundation, remove laitance and oil, and keep it saturated surface dry, with anchor pockets pre-filled first. Build rigid, leak-tight formwork with a pour side and a head box, allowing generous clearance on the pour side and a tight gap on the far side so the grout self-vents as it advances. Add powder to the pre-measured clean water, not the reverse, and mix mechanically with a slow-speed drill and paddle for two to three minutes to a uniform, lump-free flow. Pour continuously from one side only and never from opposite sides, keeping a constant head so air is pushed ahead of the grout rather than trapped under the plate. Place the full mixed quantity within the working life, which is shorter in hot weather, and never re-temper stiffening grout with extra water. Once placed, cure the exposed shoulders immediately with wet hessian or a Fosroc curing membrane to protect early strength. On site in Delhi NCR our team can advise on water dosage, pour rate and cure for the actual ambient conditions.
Specifications
| Product type | Ultra high strength, non-shrink cementitious precision grout |
| Standard compliance | ASTM C 1107 Type A |
| Shrinkage compensation | Plastic shrinkage compensated (controlled expansion) |
| Consistency | Free-flowing (flowable); pourable and pumpable |
| Water/powder ratio | Approx. 0.13 at flowable consistency |
| Yield | Approx. 12 litres per 25 kg bag at flowable consistency |
| Pack size | 25 kg bag |
| Chloride content | Chloride free |
| Expansion system | Non-metallic, hydrogen free |
Industry use cases
Power & Turbines
Grouting turbine-generator sets, boiler feed pumps and large compressor bases where high dynamic loads and OEM strength clauses rule out a standard grout.
Oil, Gas & Refineries
Precision grouting of heavy reciprocating compressor and pump foundations where chloride-free, corrosion-safe, high-strength support is essential.
Bridges & Infrastructure
Bedding bridge bearings and pedestals under concentrated bearing pressure, with controlled expansion keeping full contact under the bearing plate.
Precast & Industrial Construction
High-early-strength grouting of precast connections, crane rails and machine bases so structures and equipment can be loaded sooner.
Frequently asked questions
How is Conbextra UHS different from Conbextra GP2?
How much water do I add per 25 kg bag?
Is it suitable for deep pours?
Will it corrode my anchor bolts or machined surfaces?
Cementitious UHS or an epoxy grout for my application?
Do you supply Conbextra UHS across India?
How we position Fosroc Conbextra UHS
Conbextra UHS is the top of the Fosroc cementitious grout ladder for heavily loaded foundations. For routine static and dynamic machine bases the standard Fosroc Conbextra GP2 is the more economical choice, while Conbextra HF suits ultra-fluid, congested pours and Conbextra HR is used where the foundation is exposed to heat. Where the exposure is chemically aggressive or the section is very thin, step across to a Fosroc epoxy grout in the Conbextra EP range. Anchoring of individual bolts and bars is better served by a Fosroc Lokfix resin anchor than by a flowable grout. Beyond the Fosroc family, we also supply comparable high-strength grouts from Sika, MC-Bauchemie and Master Builders Solutions, so we can match the specification a consultant or OEM has already written rather than pushing a single brand.
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