Fosroc Conbextra HES
A rapid-setting, non-shrink precision grout that reaches around 25 MPa in just two hours, letting plant return to service the same shift instead of waiting a day or more.
What is it?
A high-early-strength, chloride-free, non-shrink cementitious precision grout supplied as a ready-to-use dry powder that only needs clean water on site.
Where is it used?
Under machine base plates, crane rails, turbine and compressor foundations, bridge bearings and anchor pockets where a fast return to service is the deciding factor.
Why use it?
It develops usable compressive strength within hours rather than the usual 24-48, compressing downtime on shutdowns, breakdowns and tight commissioning windows.
How is it applied?
Poured or pumped at a flowable or plastic consistency into pre-soaked, formed gaps of 15 to 150 mm, from one side to keep a continuous grout front and avoid air entrapment.
About Fosroc Conbextra HES
Conbextra HES is Fosroc’s rapid-strength member of the Conbextra precision-grout family, built for one job above all others: getting equipment back under load fast. It is a factory-blended powder of cements, graded aggregates and performance additives that you gauge with a measured amount of clean water on site. That controlled, low water demand is the whole point of the formulation, because it is what buys the early strength and the long-term durability without resorting to chlorides or metallic fillers that can stain or corrode.
For engineers and maintenance teams across Indian industry, the value shows up on the programme rather than on the datasheet alone. A conventional cementitious grout may hold up a machine handover by a day or two while it cures. Conbextra HES reaches roughly 25 MPa within two hours at a flowable consistency and around 30 MPa at a stiffer plastic mix, so a base plate grouted in the morning can often carry static load and be commissioned the same shift. On a plant shutdown, an emergency motor replacement or a fast-track project running against a fixed commissioning date, that saved time is the difference between meeting the window and slipping it.
The technical insight
The behaviour that matters here is the balance between speed and stability. Ordinary cement grouts trade one against the other: accelerate the set and you usually invite shrinkage, cracking and lost contact under the plate. Conbextra HES manages both through a rapid-hardening cement system paired with a controlled-expansion mechanism that generates a slight positive volume change (Class C) as the grout stiffens and hardens. That gentle expansion counters plastic and drying shrinkage, so the grout stays in intimate contact with both the foundation and the underside of the base plate, maintaining full bearing area for the bolt loads to transfer through. The graded aggregate, capped at 5 mm, is engineered to resist segregation and bleed across a wide consistency range, which is why the same bag can be poured thin and flowable or placed stiffer and plastic without the mix falling apart. Low permeability in the hardened state and the absence of chlorides round it out, giving a dense, durable, non-staining grout that protects embedded steel rather than attacking it.
Where it is used
- Grouting machinery and equipment base plates where the plant must be returned to service within hours
- Compressor, pump, motor and turbine foundations on plant shutdowns with fixed restart deadlines
- Emergency and breakdown repair grouting of machine plinths and bedplates
- Anchor-bolt and holding-down-bolt pockets requiring rapid structural loading
- Bridge bearing plates and precast connections where early load transfer is needed
- Crane rail and rolling-stock base grouting on tight maintenance windows
- Fast-track commissioning of structural steel column base plates
- Underplate grouting in gaps from 15 mm up to 150 mm in a single pour
Key advantages
- High early strength of about 25 MPa at 2 hours (flowable), enabling same-shift loading and commissioning
- Non-shrink with controlled positive expansion per ASTM C1107, keeping full plate-to-foundation contact
- Chloride-free and free of metallic fillers, so it will not stain or promote corrosion of embedded steel
- Strength continues to develop well even at lower ambient temperatures
- Excellent initial flow and flow retention for reliable filling under large base plates
- Single-component powder, water-only on site, removing on-site batching variation
- Handles a wide consistency range, from pumpable flowable to placed plastic
- Low permeability and high ultimate strength for long-term durability of the hardened grout
Limitations & considerations
- Short working window – place within about 10 minutes of mixing and expect an initial set near 30 minutes, so pours must be planned and continuous
- Not for use above roughly 35 C ambient, where premature stiffening makes handling and placement very difficult
- Below about 15 C the mix should be kept flowable, warm gauging water used and formwork left in place at least 24 hours
- Pours deeper than 150 mm need bulking with Conbextra Grout Aggregate or a switch to a deep-pour grout to manage heat build-up
- Formwork must be genuinely leakproof and the gap pre-soaked, or a free-flowing grout will leak and lose contact
- Partially set or stiffened grout must be discarded, never re-tempered with extra water
Selection & best practice
Success with Conbextra HES is mostly about preparation and pace, because its speed leaves little room to improvise. Cut back any laitance or defective concrete to a sound, roughened base, blow bolt holes clean, and pre-soak the formed area with clean water for at least two hours before grouting, draining off free water immediately before the pour. Build leakproof formwork, keeping the unrestrained surface small – no more than 150 mm on the pouring side, 50 mm on the far side, and no gap at the flanks. Measure the water accurately (a lower water addition gives the quoted strengths), add the powder to the water, and mix with a forced-action mixer for three to five minutes to a smooth, even consistency; never a colloidal impeller. Have enough mixed grout and labour ready to pour continuously from one side across the shortest travel, maintaining a constant grout head so a single front pushes air and surplus water ahead of it. Cure exposed surfaces promptly with a Concure curing membrane or wet hessian. In hot weather stage the work for early morning; in cold weather use warm gauging water and keep the forms on longer.
Specifications
| Product type | High-early-strength, non-shrink cementitious precision grout (powder, water-only) |
| Compressive strength (flowable) | Approx. 25 MPa at 2 hours; developing to around 50 MPa at 28 days |
| Compressive strength (plastic) | Approx. 30 MPa at 2 hours; up to around 58 MPa at 28 days |
| Expansion / shrinkage | Controlled positive expansion (Class C); non-shrink to ASTM C1107:2020 |
| Section thickness | 15 mm to 150 mm in a single pour |
| Setting time | Initial approx. 30 minutes; final approx. 45 minutes (ASTM C953) |
| Working time | Place within about 10 minutes of mixing |
| Maximum aggregate size | 5.0 mm |
| Chloride content | Chloride-free; no metallic ion content |
| Temperature range | Do not use above ~35 C; use warm water and extended formwork below ~15 C |
| Shelf life | 18 months in original unopened bags, stored dry |
Industry use cases
Heavy manufacturing & process plants
Re-grouting compressors, pumps and drive motors during a shutdown so lines restart within the same maintenance window instead of losing an extra day to curing.
Power generation
Turbine, generator and auxiliary base-plate grouting where every hour of outage carries a cost and early load transfer keeps the outage plan on track.
Infrastructure & bridges
Bearing plates and precast connections that must accept load quickly on projects with fixed possession or commissioning dates.
EPC & fast-track construction
Structural column base plates and equipment skids grouted late in the programme, where same-shift strength keeps mechanical completion on schedule.
Emergency & breakdown maintenance
Unplanned motor or gearbox replacements where a rapid grout is the only way to return critical equipment to service within hours.
Frequently asked questions
How quickly can we load equipment after grouting with Conbextra HES?
What gap thickness can it fill in one pour?
How is it different from standard Conbextra GP2?
Can we use it in Indian summer conditions?
How much water do we add, and does it affect strength?
Is it safe for reinforced and embedded steel?
How we position Fosroc Conbextra HES
Reach for Conbextra HES when time is the constraint – a shutdown, a breakdown or a fixed commissioning date. When rapid strength is not the driver, Fosroc Conbextra GP2 is the more economical everyday precision grout for machine foundations and base plates, and Conbextra EP 150 is the epoxy option for deep gaps under heavy dynamic or chemically aggressive duty. For pours beyond 150 mm, bulk out with Conbextra Grout Aggregate or specify a deep-pour grout. Across our other brands, Space Arc can offer comparable rapid and non-shrink grouts from MC-Bauchemie (Emcekrete) and Sika (SikaGrout) where a specifier prefers an alternative source. As Fosroc’s authorised distributor and applicator across Delhi NCR and Pan-India, we can advise on the right grade, dosage and site method for your loading and programme requirements.
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