Fosroc Conbextra HF Plus
A non-shrink, dual-expansion cementitious precision grout engineered for free-flow placement under machine baseplates, anchor bolts and structural bearings.
What is it?
A pre-bagged, single-component cementitious precision grout that mixes with clean water to a free-flowing, non-shrink slurry. It uses a non-metallic dual-expansion system to compensate for shrinkage in both the plastic and hardened states.
Where is it used?
Under turbine, generator, compressor and press baseplates; bridge and structural bearings; crane rails; anchor bolts and starter bars; column bases; and joints between precast elements.
Why use it?
It delivers high early and ultimate strength (around 30 MPa at 1 day, ~80 MPa at 28 days), low permeability and positive expansion without bleed, giving full effective bearing contact under load-bearing plant.
How is it applied?
Pre-soak and clean the substrate, mix one 25 kg bag with 4.0-4.5 litres of clean water for 5 minutes, then pour continuously from one side into leakproof formwork for gaps of 10-150 mm; cure exposed faces.
About Fosroc Conbextra HF Plus
Fosroc Conbextra HF Plus is a non-shrink, high-strength, highly fluid cementitious precision grout supplied as a ready-to-use pre-bagged dry powder. It is a factory blend of Portland cements, carefully graded fillers and chemical additives; the only site addition is a controlled quantity of clean water. On mixing it produces a free-flowing grout that can fill gap thicknesses from 10 mm to 150 mm, with the low water demand (a water-to-powder ratio of around 0.16) driving the high early strength and long-term durability that heavy industrial plant demands. The “HF” denotes high flow, and the “Plus” formulation pairs that flow with rapid strength gain so equipment can be commissioned sooner. For consultants, structural engineers and EPC contractors in India, the practical attraction of Conbextra HF Plus is the combination of three properties that rarely coexist: genuine fluidity for long flow distances under low head, a controlled dual-expansion mechanism that guarantees positive contact with the underside of a baseplate, and a strength profile that reaches roughly 80 N/mm2 by 28 days. The expansion is non-metallic, so there are no embedded iron particles to rust and stain, and it is hydrogen-free and chloride-free, which makes the cured grout suitable for use in contact with potable water and acceptable in reinforced and prestressed environments. Because it is a cement-based system rather than an epoxy, it shares the thermal expansion characteristics of the surrounding concrete and handles thick sections without the exotherm risk of resin grouts, making it the workhorse choice for the majority of structural and mechanical grouting on Indian sites where pour depths and ambient temperatures vary widely.
The technical insight
The defining engineering feature is the dual non-metallic expansion system. Conventional cement grouts shrink as they hydrate, which can leave a hollow zone directly beneath a baseplate exactly where bearing is most critical. Conbextra HF Plus counters this in two phases: a gaseous, hydrogen-free expansion (a volumetric expansion of up to roughly 2 percent) acts while the grout is still plastic to keep it firmly against the underside of the plate, and a separate hardened-state mechanism compensates for drying shrinkage in the set grout. Crucially, the gaseous phase is time-limited, which is why the datasheet instructs placement within about 15 minutes of mixing at 25 degrees C so the expansion occurs while the grout is captive under the plate rather than after it has been poured. The graded filler package is engineered so the mix does not segregate or bleed (ASTM C940 bleed result is Nil) across a range of consistencies, meaning the dense, high-strength matrix you design for is actually what cures in place rather than a weak, water-rich top layer. Flow exceeds 150 percent on the ASTM C1437 flow-table test, and the published flow charts show the grout travelling up to 3,000 mm at a 250 mm head for a 50 mm gap depth, which lets a single pour point feed a large baseplate. With a modulus of elasticity above 22,000 MPa and very low chloride permeability (ASTM C1202), the cured grout behaves as a stiff, durable, low-permeability extension of the foundation.
Where it is used
- Precision grouting beneath gas and steam turbine, generator, compressor and large pump baseplates
- Bedding of bridge bearings, pot bearings and structural support bearings
- Grouting of crane rails and rail soleplates subject to dynamic load
- Anchoring of holding-down bolts, anchor rods, dowels and reinforcing starter bars in pockets and drilled holes
- Filling joints and connections between precast concrete panels and segments
- Grouting under heavy reciprocating and rotating plant such as presses, mills and engine beds
- Pumped grouting of large or congested voids where pour access is restricted
- Column base and stanchion baseplate grouting in industrial and structural steel frames
Key advantages
- Non-shrink with a dual non-metallic expansion system that compensates for shrinkage in both the plastic and hardened states for full effective bearing
- High early strength (around 30 N/mm2 at 1 day) allows rapid installation and early commissioning of plant
- High ultimate strength of approximately 80 N/mm2 at 28 days with low permeability for long-term durability
- Excellent initial flow and flow retention for long flow distances under modest grout head
- No bleed or segregation across a wide range of consistencies, giving a uniform dense matrix
- Chloride-free and hydrogen-free gaseous expansion, safe around reinforcement and acceptable for potable-water contact
- Meets or exceeds ASTM C1107 and is supported by recognised ASTM and BS test methods
- Suitable for both pouring and pumping, and for gap thicknesses up to 150 mm
Limitations & considerations
- Cement-based, so it should not be placed in unrestrained situations such as open plinths; failure to restrain can cause cracking (bolt pockets are acceptable)
- Maximum single-pour thickness is about 125 mm; deeper sections need staged pours or consultation with Fosroc
- Working life is short once mixed; place within roughly 15 minutes at 25 degrees C to capture the plastic-state expansion
- Performance depends on disciplined substrate preparation and pre-soaking for at least 2 hours, with free water removed before pouring
- Not an epoxy grout; for aggressive chemical exposure, very high dynamic fatigue or thin-section vibration-critical machinery, an epoxy grout such as Conbextra EP series may be more appropriate
- Requires accurate water measurement (4.0-4.5 L per 25 kg bag); over-watering reduces strength and can induce bleed
- High-temperature placement above 35 degrees C needs cooled water and material plus continuous working to manage flow and set
Selection & best practice
Treat substrate preparation and water control as the two decisive variables. Cut back any laitance or defective concrete to a sound base, blow bolt holes and pockets clean, then flood the cleaned area with fresh water for at least 2 hours and remove all standing water immediately before grouting. Build leakproof formwork using foam strip or mastic, keeping the unrestrained surface to a minimum (a gap of no more than 75 mm on the pouring side and 25 mm on the opposite side). Measure exactly 4.0 litres of clean water per 25 kg bag for flowable consistency (4.5 litres for fluid), add the powder to the water, and mix mechanically for a full 5 minutes; for batches up to 60 kg use a slow-speed drill with a Fosroc MR3 paddle, and a high-shear vane mixer for larger volumes, never a colloidal impeller. Pour continuously from one side only across the shortest travel to expel air and surplus water, maintain a constant grout head, and place within about 15 minutes of mixing. Cure all exposed faces promptly with Concure curing membrane or continuous wet hessian. In summer Indian conditions above 35 degrees C, shade the materials, keep mixing water below 20 degrees C, and stage labour so the pour is continuous.
Specifications
| Product type | Non-shrink, high-strength, highly fluid cementitious precision grout |
| Composition | Blend of Portland cements, graded fillers and chemical additives (dual non-metallic expansion) |
| Gap / section thickness | 10 mm to 150 mm (up to 125 mm in a single pour) |
| Water : powder ratio | Approx. 0.16 |
| Mixing water per 25 kg bag | 4.0 L (flowable) / 4.5 L (fluid) at 20 degrees C |
| Compressive strength (BS 1881 Part 116) | 30 N/mm2 @ 1 day; 50 N/mm2 @ 3 days; 65 N/mm2 @ 7 days; 80 N/mm2 @ 28 days |
| Flow (ASTM C1437) | Greater than 150% |
| Bleed (ASTM C940) | Nil |
| Setting time (ASTM C191, 23 degrees C) | Initial 8-9 hours; Final 10-11 hours |
| Fresh wet density (BS 1881:107) | Approx. 2,200 kg/m3 |
| Modulus of elasticity (ASTM C469) | >22,000 MPa |
| Expansion | Up to ~1-2% (gaseous, hydrogen-free; ASTM C940) |
| Chloride permeability (ASTM C1202) | Very low |
| Standards compliance | Meets or exceeds ASTM C1107; suitable for contact with potable water |
| Chloride content | Chloride-free |
| Yield per 25 kg bag | ~13.15 L (flowable) / ~13.5 L (fluid) |
| Pack size | 25 kg bags |
| Shelf life | 12 months in sealed bags in dry storage |
Industry use cases
Power generation
Bedding gas and steam turbine, generator and condenser baseplates where positive non-shrink contact and high early strength let the EPC contractor advance commissioning schedules.
Bridges & infrastructure
Grouting bridge and pot bearings, pedestals and segment joints, using the long flow distance to fill bearing recesses fully from a single pour point.
Heavy manufacturing & cement plants
Grouting under presses, mills, crushers, kiln drives and reciprocating compressors where dynamic loads demand a dense, low-permeability, vibration-resistant bedding.
Industrial steel structures
Column base and stanchion baseplate grouting and anchor-bolt fixing in factory sheds, warehouses and process plants across Delhi NCR and Pan-India projects.
Precast & prefabrication
Filling joints and connections between precast panels, beams and segments, and grouting starter-bar and dowel pockets for moment continuity.
Water & utilities
Anchoring and base grouting for pumps and equipment in water treatment and reservoir works where the chloride-free, potable-water-safe formulation is required.
Frequently asked questions
Is Conbextra HF Plus a cementitious grout or an epoxy grout?
What gap thickness and strength can I expect?
How much water do I add per bag?
How is it different from standard Conbextra GP or Conbextra HF?
Does it contain chloride or metallic expansion agents?
Can it be pumped, and what are the standards it meets?
How we position Fosroc Conbextra HF Plus
Within the Fosroc grouting range, Conbextra HF Plus sits at the high-flow, high-early-strength end. It is a step up from the general-purpose Conbextra GP and GP2, and a close sibling of Conbextra HF, differentiated by its faster strength gain for earlier plant commissioning; where pour depths or heat exceed cementitious limits, or where chemical and fatigue resistance is critical, the epoxy Conbextra EP range is the natural alternative. It pairs well on site with related Fosroc systems such as Nitobond EP/SBR bonding agents, Conbextra EP for resin pockets, Renderoc repair mortars for substrate reinstatement, and Concure curing membranes. Against the wider Indian market, credible equivalents that consultants may cross-specify include Sika SikaGrout (e.g. SikaGrout-214/212) and MasterFlow from MBS/MasterBuilders Solutions in the premium non-shrink class, with Dr. Fixit Pidicrete and STP grout products positioned for general and value-grade work; Conbextra HF Plus competes on its proven dual-expansion mechanism, ASTM C1107 compliance and the strength-plus-flow balance. As an authorised Fosroc distributor and applicator serving Delhi NCR and Pan-India, Space Arc Engineering supplies genuine, batch-traceable Conbextra HF Plus with technical data sheets, method-statement support and on-site guidance.
Related Grouts & Anchors products
Source Fosroc Conbextra HF Plus for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.