About Fosroc Conbextra Rock Grout

Fosroc Conbextra Rock Grout sits within the well-known Conbextra family of cementitious grouts, but it is purpose-built for one job that the everyday GP-series grouts handle poorly: filling wide gaps and thick sections in a single, uninterrupted pour. Where Conbextra GP, GP2 or HF are designed for the typical 10-100 mm baseplate clearance and are usually placed in thinner lifts, Rock Grout is blended specifically to remain stable and non-segregating across a gap range of roughly 20 to 76 mm.

The product is supplied as a factory pre-blended dry powder — a balanced mix of inorganic cements, graded hard-wearing aggregates, a plasticiser and set-and-expansion modifying additives. The contractor simply adds clean water on site and mechanically mixes to the required consistency; no separate aggregate, accelerator or expansion agent has to be batched in the field. The graded aggregate is what gives the grout its body and lets it be poured in thick sections without the segregation, bleed and plastic settlement you would see if a fine precision grout were placed at the same depth.

Three characteristics define its behaviour. First, it is non-shrink: built-in controlled expansion compensates for the plastic and drying shrinkage that would otherwise open a gap between the grout and the substrate or embedded steel, preserving full contact bearing. Second, it develops high early strength, so anchors, dowels and baseplates can be loaded or commissioned sooner. Third, it is chloride-free (it contains no added calcium chloride), which matters wherever the grout surrounds reinforcement, rock bolts, dowels or other embedded steel that must be protected from chloride-induced corrosion.

One point of transparency for Indian buyers: Conbextra Rock Grout is a regionally produced and marketed product — Fosroc lists it with Jordan and Saudi Arabia datasheets, formulated to suit Middle East conditions. It is not the default catalogue grout that Fosroc India stocks for general precision grouting (that role is filled by Conbextra GP, GP2, GP3, HF and the EP epoxy range). Space Arc Engineering can advise whether Rock Grout itself, or an equivalent wide-gap solution from the India range, is the correct specification for your project and can source it on a project basis.

The technical insight

The engineering value of Rock Grout is in its aggregate grading and expansion system rather than in any single headline strength number. A standard precision grout placed at 60-70 mm depth tends to bleed and settle, leaving a weak, low-density layer at the top of the pour and incomplete contact under the plate. Rock Grout’s coarser, hard-wearing graded aggregate increases the mix’s internal stability so it can be cast at these depths in one lift while still flowing into the void. The modifying additives control both the rate of set and a measured expansion while the grout is still plastic, which counteracts settlement and locks the hardened grout against the substrate and embedded steel. Because the powder is pre-blended, the water/powder ratio is the single most important field control: too much water raises flow but reduces density, strength and expansion and increases bleed, so the regional Technical Data Sheet’s stated water addition per bag must be followed and not exceeded. As a cementitious grout it cures by hydration, so like all Conbextra cementitious grouts it depends on proper curing and is sensitive to placement temperature and gap geometry.

Where it is used

• Anchoring rock bolts, dowels and anchor bars into rock and rock sockets
• Filling wide gaps (approx. 20-76 mm) beneath machine baseplates and structural steel baseplates
• Grouting deep pockets, sockets and recesses for columns, crash barriers and balustrades
• Bedding and infilling around heavy stanchions and equipment requiring a thick grout section
• Foundation underpinning and filling of structural voids where a single thick pour is needed
• Fixing of starter bars, tie-bars and holding-down bolts in oversized holes or wide annular gaps
• General non-shrink grouting where the clearance is too large for a standard precision grout in one operation

Key advantages

• Bridges wide gaps of approximately 20 to 76 mm in a single pour, avoiding multiple thin lifts
• Non-shrink with controlled expansion, maintaining full contact bearing under plates and around steel
• High early strength allows earlier loading, bolt tightening and commissioning
• Chloride-free (no added calcium chloride), protecting embedded reinforcement, dowels and rock bolts
• Supplied pre-blended — only clean water is added on site, reducing batching error and labour
• Graded hard-wearing aggregate gives a stable, non-segregating mix at thick section depths
• Good flowability for placement into deep pockets and around congested embedded steel
• Consistent factory-controlled quality from a globally recognised Conbextra grout range

Limitations & considerations

• A regional Fosroc product (Middle East datasheets); not the default India-catalogue grout — confirm availability and lead time for Indian projects
• Designed for a defined gap window (~20-76 mm); for gaps below ~20 mm use a precision grout such as Conbextra GP2, and for very large pours consult Fosroc for an aggregate-extended solution
• Cementitious system — not suitable where high chemical resistance or dynamic/vibration-fatigue resistance is required; those duties need an epoxy grout (Conbextra EP series)
• Performance is sensitive to the water/powder ratio; over-watering reduces strength, density and expansion and causes bleed
• Requires proper curing and is affected by ambient and substrate temperature; hot- or cold-weather placement needs precautions
• Substrate must be sound, clean, roughened and pre-saturated (saturated surface-dry) for the bond and expansion to develop correctly
• Exact numeric specifications (strength, density, yield) must be read from the current regional Technical Data Sheet for the country of supply before specification

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Conbextra Rock Grout

Within Fosroc’s grout portfolio, Conbextra Rock Grout occupies the wide-gap and rock-anchoring niche that the mainstream Conbextra GP, GP2 and GP3 precision grouts and the high-flow Conbextra HF are not optimised for, while remaining a cementitious system — distinct from the Conbextra EP epoxy grouts (EP10/EP75/EP300) used where chemical resistance and dynamic load resistance dominate. For rock-bolt and bar anchoring specifically, it also overlaps in intent with Fosroc’s polyester resin anchoring grout Lokfix, though Lokfix is a chemical-anchor system rather than a pourable cementitious grout. Because Rock Grout is a Middle East regional product, Indian specifiers will most often pair the same project requirement with a stocked India equivalent — Conbextra GP2 or GP3 for narrower precision gaps and an aggregate-extended GP for larger pours — and Space Arc can advise which route is appropriate. Among comparable wide-section, non-shrink and anchoring grouts available in the Indian market, credible alternatives include Sika’s SikaGrout range and Sika anchoring grouts, MBS (MYK) cementitious grouts, Dr. Fixit’s Pidigrout / non-shrink grout line, and STP’s grouting products. As an authorised Fosroc distributor and applicator in Delhi NCR and Pan-India, Space Arc Engineering’s recommendation is to confirm the exact gap size, embedment and load case against the current regional Technical Data Sheet before specifying, so the chosen grout — Rock Grout or an equivalent — genuinely matches the wide-gap or anchoring duty rather than being over- or under-specified.

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