Fosroc Conbextra GP2N
Free-flow, non-shrink cementitious precision grout for machine bases and structural bearing plates carrying static and dynamic loads.
What is it?
A single-component cementitious precision grout from Fosroc, factory-blended from Portland cement, graded fillers and expansion additives. Mixed with water, it produces a free-flowing, non-shrink, chloride-free grout.
Where is it used?
Under base plates of turbines, compressors and boiler feed pumps, stanchion and column bases, crane rails, and for anchoring bolts, masts and fixings — in gaps up to 100 mm per pour.
Why use it?
Its gaseous expansion system compensates for plastic shrinkage, so the hardened grout stays in full contact with the plate. Strengths reach 78 N/mm² at 28 days without chlorides or metallic iron.
How is it applied?
Presoak the substrate, set leakproof formwork, machine-mix with 4.5-4.8 litres of water per 30 kg bag for 5 minutes, and pour continuously from one side within 20 minutes of mixing.
About Fosroc Conbextra GP2N
Conbextra GP2N is the mid-range workhorse of Fosroc’s Conbextra GP precision grouting family, specified wherever a baseplate or anchor must transfer static and dynamic loads into the foundation without any loss of bearing. It arrives on site as a ready-to-use dry powder; adding a controlled quantity of clean water produces a free-flowing grout that can be poured or pumped into gaps and placed up to 100 mm thick in a single operation. Because the blend is factory-controlled, every bag delivers the same flow and strength — eliminating the batching variations that plague site-mixed cement-sand grouts.
For Indian plant and infrastructure work, GP2N hits a practical sweet spot: pourable-consistency strengths of 27 N/mm² at just one day allow early alignment checks and fast recommissioning, while 28-day strengths of 65-78 N/mm² comfortably satisfy the typical specification clause of 60 N/mm². Space Arc Engineering stocks Conbextra GP2N across Delhi NCR with pan-India despatch, and our applicator teams handle presoaking, formwork and pumped placement for large pours.
The technical insight
Ordinary cement grout shrinks as it sets, pulling away from the underside of the plate and leaving hard-point contact that hammers foundations under dynamic load. GP2N counters this with a gaseous expansion system: additives in the powder generate a controlled 0-4% unrestrained expansion while the grout is still plastic, starting about 20 minutes after mixing and finishing by 120 minutes. Confined under a baseplate, that expansion presses the grout against the steel before set, locking in full bearing contact. Equally important is the low water demand — a water-powder ratio of just 0.15 (pourable) to 0.16 (flowable) — which drives high early strength and a dense, durable matrix without chloride accelerators. The timing matters: place the grout within roughly 20 minutes of mixing at 30°C, or the expansion is spent in the bucket instead of under the plate.
Where it is used
- Precision grouting of turbine, compressor and boiler feed pump base plates
- Stanchion and column base plate grouting on steel structures
- Crane rail and bearing plate grouting subject to dynamic loads
- Anchoring bolts, masts, fence posts and a wide range of fixings
- Filling bolt pockets and voids ahead of underplate grouting
- Grouting precast concrete connections and structural joints
- Thick-section pours beyond 100 mm when extended with 50-100% of 10 mm aggregate
- Pumped grouting of large-volume machine foundations using diaphragm pumps
Key advantages
- Gaseous expansion compensates for shrinkage and settlement in the plastic state, maintaining full bearing contact
- High early strength without chlorides — 24-27 N/mm² at one day permits rapid recommissioning
- High ultimate strength: up to 78 N/mm² at 28 days (pourable consistency) for durable, heavily loaded bases
- Free-flow ensures a high level of contact even under large plates with limited access
- Pre-packed, factory-blended powder removes on-site batching variation
- No metallic iron content, so no rust staining on exposed grout shoulders
- One bag covers two consistencies — pourable or flowable — by adjusting water within the stated limits
- Can be poured or pumped, making it practical for both small pads and large continuous pours
Limitations & considerations
- Maximum 100 mm thickness per pour; deeper sections need extension with 10 mm aggregate or a micro-concrete such as Renderoc LA Xtra
- Expansion completes by about 120 minutes — grout must be placed within roughly 20 minutes of mixing at 30°C, and retempering is not permitted
- Below 10°C strength gain slows considerably: warm water (30-40°C) is recommended and formwork must stay in place at least 36 hours
- Above 40°C ambient, mixing water must be cooled below 20°C — a real constraint for North Indian summer pours
- Unrestrained surface area must be minimised (max 150 mm gap on the pouring side, 50 mm opposite), so formwork detailing cannot be improvised
- Shelf life is 6 months in sealed bags and drops in hot, humid storage
Selection & best practice
Preparation decides the result. Cut back defective or laitence-affected concrete to a sound base, and blow bolt holes and pockets clean. Saturate the substrate with fresh water several hours before grouting, then remove all free water — especially from pockets — immediately before the pour. Formwork must be genuinely leakproof (foam strip or mastic under the boards) and sized to the 150 mm/50 mm gap rule; grease any levelling shims that will be removed later. Measure the water first — 4.5 litres per 30 kg bag for pourable, 4.8 for flowable — then add the full bag and machine-mix for 5 minutes with a slow-speed drill and paddle (400-500 rpm) for batches up to 50 kg, or a heavy-duty mixer beyond that. Grout bolt pockets before the underplate pour. Pour from one side only, across the shortest travel distance, keeping a continuous grout head so air and presoak water are pushed out ahead of the front. Cure exposed shoulders with Concure WB, water or wet hessian.
Specifications
| Compressive strength, 28 days (BS 1881-116) | 65 N/mm² flowable / 78 N/mm² pourable |
| Compressive strength, 1 day | 24 N/mm² flowable / 27 N/mm² pourable |
| Flexural strength, 28 days (BS 4551) | 10.0 N/mm² (W/P 0.16) |
| Tensile strength, 28 days | 3.5 N/mm² (W/P 0.16) |
| Unrestrained plastic expansion | 0-4%; starts ~20 min, complete by ~120 min after mixing |
| Water addition per 30 kg bag | 4.5 L pourable / 4.8 L flowable |
| Fresh wet density | Approx. 2200-2300 kg/m³ |
| Yield per 30 kg bag | 15.6 L pourable / 15.8 L flowable |
| Packaging & shelf life | 30 kg bags (25 kg on request); 6 months in dry, sealed storage |
Industry use cases
Power & Energy
Grouting turbine, generator and boiler feed pump base plates where full bearing contact under vibration is non-negotiable and one-day strength allows early alignment.
Heavy Manufacturing
Compressor skids, machine beds and press foundations — the 0-4% plastic expansion keeps grout tight to the frame under repeated dynamic loading.
Steel Structures & PEB
Stanchion base plates and anchor bolt grouting on warehouses, mills and process structures, with pourable consistency for narrow shuttered gaps.
Infrastructure & Metro
Bearing plates, crane rails and precast connection joints where a chloride-free, non-staining grout is called for in the specification.
Cement & Process Plants
Large-volume pumped pours under mills and kilns drives, extended with 10 mm aggregate for sections deeper than 100 mm.
Frequently asked questions
What is the difference between Conbextra GP1 and GP2N?
How much water do I add per bag?
How many bags do I need per cubic metre of grout?
Can Conbextra GP2N be poured deeper than 100 mm?
How soon can machinery be re-installed or loaded?
Does the grout need curing?
How we position Fosroc Conbextra GP2N
Within the Fosroc family, GP2N sits between Conbextra GP1 — the economical choice for moderately loaded column bases with gaps up to about 50 mm — and Conbextra GP3, specified when even higher performance or rapid strength gain drives the programme. For voids deeper than 100 mm, Renderoc LA Xtra micro-concrete is the cleaner solution, and Concure WB completes the system as the curing membrane. Where grout is exposed to oils, chemicals or severe dynamic loading, ask us about Fosroc’s Conbextra EP epoxy range instead. Space Arc supplies all of these ex-stock with applicator support across Delhi NCR and pan-India.
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