Fosroc Conbextra HT
A free-flow, chloride-free cementitious precision grout engineered to hold strength at service temperatures up to 400°C — the Fosroc answer for foundries, furnaces and hot-works baseplates.
What is it?
A high-strength, temperature-resistant cementitious precision grout from Fosroc — a pre-bagged blend of cements, graded aggregates and additives that develops controlled expansion in both the gaseous (plastic) and hardened states.
Where is it used?
Free-flow grouting of machine baseplates, columns and equipment seated in hot environments — foundries, steel and forging plants, furnace and kiln surrounds, hot-works zones and process areas where service temperatures approach 400°C.
Why use it?
Ordinary GP grouts lose integrity near sustained heat. Conbextra HT keeps high ultimate strength, low permeability and dimensional stability at elevated temperature, while rapid early strength shortens plant shutdowns.
How is it applied?
Site-mixed with a controlled, low quantity of clean water to a free-flowing consistency, then poured or pumped continuously into the gap under a baseplate with proper venting, head and curing.
About Fosroc Conbextra HT
Fosroc Conbextra HT sits in the high-performance end of the Conbextra cementitious grout family, distinguished by one job most precision grouts cannot do: holding structural performance where the steelwork above it runs hot. Where Conbextra GP or HF are specified for ambient machine bases and structural supports, Conbextra HT is formulated for plant that operates at sustained elevated temperatures, with a service temperature rated up to 400°C. That makes it the natural choice beneath foundry equipment, forging hammers, furnace and kiln-area baseplates, and the broad category Fosroc itself labels “hot works.”
The product is supplied as a ready-to-use dry powder — a factory-controlled blend of cements, graded aggregates and chemical additives. On site, only a measured quantity of clean water is added to produce a free-flowing grout that can be poured or pumped into the void beneath a baseplate. Two design features matter to the engineer. First, the dual-action controlled expansion: the system expands in the plastic (gaseous) state to compensate for early settlement and again in the hardened state, which keeps the grout in positive contact with the underside of the plate and maximises effective bearing area. Second, the deliberately low water demand, which is what delivers the high early strength, low permeability and long-term durability that let the grout survive thermal cycling rather than crack and ravel under it.
For an Indian project team, Conbextra HT answers a specific and recurring problem. Steel plants, foundries, ferrous and non-ferrous casting units, cement kilns, glass works and heavy forging shops all bed equipment that radiates or conducts significant heat into its foundation. Bedding that equipment on a standard non-shrink grout invites loss of strength, micro-cracking and eventual loosening of holding-down bolts. Conbextra HT is the off-the-shelf, Fosroc-backed specification that removes that risk — and as an authorised Fosroc distributor and applicator, Space Arc Engineering supplies it with the technical back-up to get the mix, gap design and curing right the first time.
The technical insight
The engineering value of Conbextra HT is not raw strength — many grouts hit 50–60 N/mm² at 28 days — it is strength retention under heat combined with dimensional stability. Three properties carry that. (1) The aggregate grading and cement blend are selected so the hardened matrix resists the loss of integrity that ordinary Portland-cement grouts suffer when held near 400°C; the graded fillers also minimise segregation and bleeding across a range of placement consistencies. (2) The non-metallic, chloride-free, hydrogen-free gaseous expansion compensates for plastic settlement, while a secondary hardened-state expansion holds the grout tight against the baseplate — together they preserve a high effective bearing area, which is what actually transmits load. Iron-free, chloride-free chemistry also means no staining, no corrosion driver at the steel interface and no expansive rust over time. (3) Low water demand drives both high early strength (rapid return-to-service) and low permeability (durability under thermal and chemical exposure). The practical caveat: 400°C is a service rating for the cured grout in place, not a guarantee against thermal shock or unlimited cyclic exposure — gap geometry, pour continuity and a proper damp/cure regime are what convert the data-sheet number into field performance.
Where it is used
- Bedding of foundry and casting-shop equipment baseplates exposed to radiant and conducted heat
- Grouting under furnace, kiln and heat-treatment plant where service temperatures approach 400°C
- Hot-works and forging-shop machinery foundations subject to thermal cycling
- High-strength free-flow grouting of columns, stanchions and machine bases in hot process areas of steel and metallurgical plants
- Re-grouting and repair of heat-affected baseplate beddings where standard grout has degraded
- Anchoring and bedding of holding-down bolts and pockets in elevated-temperature zones
Key advantages
- Rated for service temperatures up to 400°C, where general-purpose cementitious grouts lose integrity
- Rapid early strength gain enables fast installation and return to operation with minimum plant shutdown
- Excellent initial flow and flow retention for continuous, void-free placement under large baseplates
- High ultimate strength and low permeability for durable, long-life performance in harsh plant environments
- Controlled dual expansion in the plastic (gaseous) and hardened states maintains contact and high effective bearing area
- Chloride-free and iron-free chemistry — no corrosion driver or staining at the steel interface
- Supplied as a pre-bagged, factory-controlled powder needing only addition of clean water on site
Limitations & considerations
- Specialised high-temperature product — overkill (and cost-inefficient) for ordinary ambient machine bases where Conbextra GP/GP2 or HF are the correct choice
- The 400°C rating is a service temperature for the cured grout in position, not a tolerance to thermal shock or unlimited rapid cycling
- Cementitious system: not designed for dynamic/vibrating or chemically aggressive duty where an epoxy grout such as Conbextra EP range or Conbextra EPHT is specified
- Performance depends on low, accurately measured water content — over-watering reduces strength, increases bleed and permeability
- Requires correct gap design, venting, continuous pour and proper damp curing; poor placement causes voids and bond loss at the heated interface
- Project-specific values (compressive strength at age, yield, water demand) must be confirmed against the current Fosroc TDS for the supplied grade and region
Selection & best practice
Treat Conbextra HT as a system, not just a bag of powder. Confirm the actual service temperature, gap thickness and baseplate size against the current Fosroc Technical Data Sheet before ordering, and use only the manufacturer’s specified water quantity — measure it, do not judge it by eye, because excess water is the single biggest cause of lost strength and increased permeability in a heat-exposed grout. Mix mechanically to a uniform free-flowing consistency, place from one side in a continuous pour with adequate hydrostatic head and air venting so no air is trapped beneath the plate, and never trowel-pack a heated baseplate. Provide a strong grout shoulder, then cure under damp hessian/polythene or curing compound to control early moisture loss; for hot-works areas, let the grout reach adequate maturity before the plant is brought up to operating temperature so the matrix is not thermally loaded green. As an authorised Fosroc distributor and applicator, Space Arc Engineering can advise on gap design, batch sizing, pour sequencing and curing for your specific foundry or hot-works application across Delhi NCR and Pan-India.
Specifications
| Product type | High-strength, temperature-resistant cementitious precision grout |
| Composition | Blend of cements, graded aggregates and additives (pre-bagged dry powder) |
| Service temperature | Up to 400°C (cured grout in position) |
| Expansion system | Controlled dual expansion — gaseous (plastic) and hardened state; non-metallic, hydrogen-free |
| Chloride content | Chloride-free (and iron-free) |
| Consistency | Free-flow (pourable / pumpable) after site addition of clean water |
| Mixing | Site-mixed with a controlled, low quantity of clean water |
| Key performance | Rapid early strength; high ultimate strength; low permeability; excellent flow retention |
| Application | Free-flow grouting under baseplates / machine bases in hot-works and foundry environments |
| Form / supply | Ready-to-use pre-bagged powder (confirm pack size and yield against current Fosroc TDS) |
| Manufacturer | Fosroc (Conbextra grout range) |
Industry use cases
Foundries & metal casting
Bedding of moulding, casting and ladle-handling equipment baseplates that radiate heat into the foundation, where standard grout would soften and crack.
Steel & forging plants
Grouting of forging hammers, rolling-line and heat-treatment equipment bases subject to sustained elevated temperatures and thermal cycling.
Cement, glass & refractory works
Baseplate bedding around kilns, furnaces and hot process lines where service temperatures climb well above what ambient grouts tolerate.
Power & heavy industry
Grouting of hot-side auxiliary plant and equipment in thermal generation and process industries requiring rapid return to service after shutdown.
Plant maintenance & repair
Re-grouting of heat-degraded baseplate beddings during shutdowns, restoring full bearing contact and holding-down bolt integrity quickly.
Frequently asked questions
What exactly is Fosroc Conbextra HT?
How hot can Conbextra HT actually withstand?
How is Conbextra HT different from Conbextra GP or HF?
Is it a cementitious or an epoxy grout?
How much water do I add, and what is the yield per bag?
Can Space Arc Engineering supply and apply Conbextra HT in India?
How we position Fosroc Conbextra HT
Within the Fosroc grout portfolio, Conbextra HT is the niche, high-value specialist: where Conbextra GP / GP2 cover general-purpose machine bases and HF covers high-flow precision grouting with dual shrinkage compensation, HT is the one specified when the steelwork above runs hot. For dynamic, vibrating or chemically aggressive duty — bridge bearings, rail bedding, vibrating machinery — the team would step across to Fosroc’s epoxy grouts (the Conbextra EP range, or Conbextra EPHT where elevated-temperature epoxy performance is needed), and for resin anchoring of bolts and bars to Fosroc Lokfix. Among competing brands available in India, credible high-temperature and precision-grout alternatives include Sika (SikaGrout high-strength non-shrink grouts and Sikadur epoxy grouts for hot/chemical duty), MBCC/Master Builders Solutions (MasterFlow non-shrink and epoxy grout range), and STP/Pidilite-Dr. Fixit cementitious grouts for general bedding — though genuinely heat-rated, foundry-grade cementitious options are a narrow field, which is precisely where Conbextra HT earns its place. Space Arc Engineering positions Conbextra HT not as a commodity grout but as a problem-solver for foundries, forging shops and furnace areas, backed by authorised Fosroc supply and applicator-level site support across Delhi NCR and Pan-India. Project teams should always confirm grade-specific performance values against the latest Fosroc TDS before specification.
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