Fosroc Conbextra HR
A refractory-grade, shrinkage-compensated cementitious grout that keeps machinery bases seated and load-bearing through repeated heat cycles up to 500C.
What is it?
A single-component, ready-to-use dry powder grout based on Portland cement, graded fillers and expansion additives, engineered to stay dimensionally stable and load-bearing at elevated service temperatures up to 500C.
Where is it used?
Under boiler, kiln, furnace, hot fan and turbine base plates, and any equipment where the substrate runs hotter than ordinary grouts can tolerate.
Why use it?
Standard grouts crack, spall or lose contact when heated. Conbextra HR is formulated so the bedding under hot equipment stays intact, keeping the base fully supported after thermal cycling.
How is it applied?
Mixed with a controlled amount of clean water to a free-flowing consistency, then poured into the gap between base plate and foundation, wet-cured, and heated up gradually per the commissioning schedule.
About Fosroc Conbextra HR
Conbextra HR is Fosroc’s answer to a problem every plant engineer eventually meets: how to grout equipment that gets hot and stays hot. Ordinary cementitious grouts are formulated and tested at ambient conditions. Put them under a boiler saddle or a kiln support that runs at a few hundred degrees and the bedding begins to break down, micro-cracks open, and the positive contact that transfers load into the foundation is lost. Conbextra HR is built around refractory-grade binders and a graded filler system that resist this thermal breakdown, so the grout carries on doing its job in the temperature range where the equipment actually operates.
Supplied as a factory pre-blended dry powder in 25 kg bags, it needs nothing on site but clean water and disciplined mixing. The addition of a controlled amount of water gives a free-flowing grout that fills the base-plate gap and self-levels around anchor bolts, while the built-in expansion system compensates for plastic shrinkage so the hardened grout stays in firm contact with both the plate and the foundation. It is also iron-free, so there is no risk of rust staining bleeding through the pour. For Delhi-NCR and pan-India process plants, cement works, power stations and steel mills, it is a specialist grout that removes a genuine failure mode from hot-running equipment.
The technical insight
The reason a normal grout fails under heat is thermal incompatibility. Conventional cementitious grouts rely on hydrated cement phases and fillers that were never intended to see sustained high temperatures; as the mass heats, differential expansion and progressive dehydration of the binder generate internal stress, and the grout micro-cracks and loses strength at exactly the load path that matters. Conbextra HR is engineered around refractory-grade cementitious binders and a carefully graded aggregate skeleton whose thermal movement is far better matched, so the grout retains its integrity through repeated heat-up and cool-down cycles. The controlled-expansion additive does the second half of the work: while the grout is still plastic it expands slightly, compensating for the natural settlement and shrinkage of cement, which guarantees that once cured the grout bears hard against the underside of the base plate rather than leaving a gap. The net effect is a bedding that stays in full contact and keeps transferring machine loads into the foundation even after the equipment has been through many thermal cycles.
Where it is used
- Grouting boiler base plates and support saddles that run at sustained high temperature
- Bedding kiln, rotary dryer and calciner support frames in cement and mineral plants
- Grouting hot induced-draft and forced-draft fan and blower foundations
- Structural support grouting for furnaces, incinerators and heat-treatment equipment
- Base grouting of hot-gas compressors, turbines and process rotating equipment
- Anchoring holding-down bolts on machinery where the substrate exceeds normal grout limits
- Repair and re-grouting of previously failed high-temperature equipment bases
- Precision alignment grouting of hot process equipment requiring full load transfer
Key advantages
- Retains strength and integrity at service temperatures up to 500C, well beyond ordinary grouts
- Shrinkage-compensated so the hardened grout stays in positive contact with the base plate
- Free-flowing when mixed, filling tight gaps and self-levelling around anchor bolts
- High early and ultimate strength for fast return to service and full load transfer
- Iron-free formulation avoids rust staining of the pour and adjacent concrete
- Factory pre-blended single component means only clean water is added on site
- Ready-to-use dry powder gives consistent, repeatable results with no site batching of aggregates
- Withstands thermal cycling and thermal gradients without losing bearing contact
Limitations & considerations
- It is a specialist high-temperature grout; for ambient equipment a standard grout such as Conbextra GP is more economical
- Maximum pourable placement depth is limited per lift, so very deep gaps must be filled in stages or aggregate-extended per Fosroc guidance
- Water addition must be controlled precisely, over-watering reduces strength and can cause bleeding
- Requires disciplined wet curing and a gradual, controlled heat-up before the equipment reaches full operating temperature
- Not a refractory castable or a fire-protection lining, it is a load-bearing grout rated for hot service, not for direct flame or lining duty
- Performance depends on a clean, saturated-surface-dry, properly prepared foundation and base plate
Selection & best practice
Success with Conbextra HR is mostly about preparation and heat-up discipline. Chip back the foundation to a sound, roughened surface, remove all oil, dust and laitance, and saturate the concrete so it is saturated-surface-dry (damp but with no free water) before pouring. Clean the underside of the base plate and check that vent holes are provided so air can escape as the grout rises. Mix only with clean water in the specified quantity using a forced-action mixer to a free-flowing but not watery consistency; do not re-temper with extra water. Pour continuously from one side so the grout advances across the gap and pushes air ahead of it, avoiding trapped voids, and keep a head of grout in the hopper or dam to maintain flow. Once placed, keep the exposed grout continuously wet-cured for the recommended period, then allow the specified full-cure time before commissioning. Critically, bring the equipment up to temperature slowly following the plant warm-up protocol so thermal expansion is controlled rather than shocking freshly matured grout. For gaps outside the recommended pourable range or very large pours, follow Fosroc’s guidance on lift thickness and any approved aggregate extension.
Specifications
| Product type | Heat-resistant, non-shrink cementitious precision grout |
| Composition | Portland cement, graded fillers and controlled-expansion chemical additives (iron-free) |
| Maximum service temperature | Up to 500C (per Fosroc technical data) |
| Compressive strength | Approx. 30 N/mm2 at 2 hours, 70 N/mm2 at 1 day, 100 N/mm2 at 28 days (per Fosroc technical data) |
| Fresh (wet) density | Approx. 2.3 kg/litre |
| Consistency | Free-flowing / pourable when mixed with clean water |
| Volume change | Shrinkage compensated (non-shrink), controlled expansion in plastic state |
| Typical application gap | 10 mm to 75 mm |
| Pack size | 25 kg bag, supplied as ready-to-use dry powder |
Industry use cases
Power & Boilers
Grouting boiler saddles, economiser supports and hot fan foundations where sustained heat rules out an ordinary grout.
Cement & Minerals
Bedding kiln, calciner and rotary dryer support frames that operate under continuous elevated temperature.
Steel & Metals
Base grouting for furnaces, reheat equipment and hot rotating machinery in steel and non-ferrous plants.
Petrochemical & Process
Grouting hot-gas compressor, turbine and process pump bases where substrate temperatures exceed normal grout limits.
Plant Maintenance & Revamp
Re-grouting equipment whose original bedding has cracked or spalled from heat, restoring full load transfer.
Frequently asked questions
What temperature can Conbextra HR actually withstand?
How is it different from ordinary Conbextra GP grout?
Is it a single-component product or does it need site mixing of aggregate?
What gap thickness can it be poured into?
Does it stain the concrete or the base plate?
How soon can the equipment be heated up after grouting?
How we position Fosroc Conbextra HR
Conbextra HR sits at the high-temperature end of the Fosroc Conbextra grout family. Where equipment runs at ambient temperature, Conbextra GP is the standard, more economical non-shrink grout for the same base-plate and anchor-bolt duty; where large voids or pre-packed aggregate masses must be filled, Conbextra HF is the high-flow option. For very high early strength and heavy dynamic machine loads at normal temperatures, Conbextra HF or the epoxy-based Conbextra EP range are worth specifying instead. As an authorised Fosroc distributor and applicator across Delhi-NCR and pan-India, Space Arc can also match Conbextra HR against equivalent high-temperature grouts from MC-Bauchemie and Sika where a project or approved-vendor list requires it, and supply the associated Fosroc anchor-bolt and repair products for a complete equipment-foundation package.
Related Grouts & Anchors products
Source Fosroc Conbextra HR for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.