Fosroc Conbextra GP1
Non-shrink, free-flow cementitious grout for base plates, stanchions and machinery foundations — 45 N/mm² at 28 days from a single water-mixed bag.
What is it?
A factory-blended, single-component cementitious grout that needs only clean water — 3.75 litres per 25 kg bag — to produce a free-flowing, non-shrink mix with controlled 1–4% expansion in the plastic stage.
Where is it used?
Under machine base plates, stanchion and column bases, crane and transporter rails, pump sets and steel rolling mill beds — wherever static loads must transfer cleanly from steel into the foundation.
Why use it?
It expands while still plastic, locking into full contact with the plate underside instead of settling away from it. Chloride-free and iron-free, so anchor bolts and machine parts stay protected from corrosion and staining.
How is it applied?
Saturate the prepared substrate, mix a full bag with accurately measured water for 5 minutes using a high-shear mixer, then pour continuously from one side within 20 minutes of mixing, keeping the grout head topped up.
About Fosroc Conbextra GP1
Conbextra GP1 is the general-purpose member of Fosroc’s Conbextra grout family and one of the most widely specified non-shrink grouts on Indian industrial and infrastructure sites. It arrives as a ready-to-use dry powder in 25 kg HDPE-lined bags — a blend of specially processed cement, pre-graded fillers and additives engineered to keep the water demand down to a 0.15 water-powder ratio. That low water content is what drives its strength curve: around 10 N/mm² within a day and 45 N/mm² at 28 days at flowable consistency, while the free-flow character fills bolt pockets and underplate voids without rodding, poking or chaining.
Because every bag is batched under factory control, site performance is repeatable — no sand-quality disputes, no blending variation between pours. Space Arc Engineering supplies genuine Fosroc stock across Delhi NCR and pan-India, and where a project needs placement as well as material, our applicator teams take on the grouting works — from single pump plinths to full mill-bed programmes.
The technical insight
Ordinary site-mixed cement grout bleeds and settles as it stiffens, leaving a thin gap under the base plate that concentrates load onto a few high spots. Conbextra GP1 counters this with a controlled expansion system that works while the grout is still plastic: expansion begins roughly 20 minutes after mixing and finishes by about 150 minutes, generating 1–4% unrestrained growth against a restraining pressure of only about 0.004 N/mm². Confined under a plate, the grout swells gently into the void and then hardens in that position, preserving the effective bearing area the designer assumed. The cured material has a micro-cellular structure with good frost, fire and oil resistance and a Young’s modulus of 24 kN/mm², giving stable, long-term load transfer under static duty.
Where it is used
- Grouting machine and equipment base plates carrying static loads
- Stanchion, column and tower base grouting during structural steel erection
- Crane and transporter rail beds in ports, workshops and heavy engineering bays
- Anchor bolt, holding-down bolt and fixing-pocket grouting
- Pump sets and standing equipment bed plates
- Steel rolling mill beds
- Underplate void filling up to 100 mm in a single pour, with aggregate extension for deeper sections
Key advantages
- Controlled 1–4% plastic-stage expansion keeps the cured grout in full contact with the plate — no shrinkage gap
- Genuine free flow: travels 1–2 m across a 50 mm gap under a modest grout head, filling voids without vibration
- Fast, useful strength gain — about 10 N/mm² in 1 day and 45 N/mm² at 28 days at flowable consistency
- Chloride-free and iron-free, so anchor bolts and machine parts in contact face no corrosion or rust staining
- Single-component and water-only mixing eliminates site batching errors
- Pumpable with a heavy-duty diaphragm pump for large-volume pours
- Can be extended 50–100% by weight with clean 10 mm aggregate for thick sections, controlling heat build-up
Limitations & considerations
- Must be placed within about 20 minutes of mixing at 30°C to capture the expansion phase — late placement forfeits the non-shrink benefit
- Exposed grout edges wider than 50 mm need restraint, otherwise unrestrained expansion can crack the shoulder
- It is a general-purpose grade: dynamic or vibrating machinery, heavier loads and precision seating call for Conbextra GP2 or an epoxy grout instead
- Flow design matters — minimum unrestricted flow width is 300 mm and long travel distances need adequate head, not guesswork
- Shelf life is 6 months in dry storage, and exposed surfaces must be cured with water, wet hessian or a curing membrane
Selection & best practice
Preparation decides the outcome. Cut back laitance and defective concrete to a sound base, blow bolt holes and pockets clean, then saturate the substrate with clean water several hours before grouting — removing every trace of free water just before the pour. Build leak-proof formwork and keep the gap between formwork and plate edge within 150 mm on the pouring side and 50 mm opposite. Mix one full 25 kg bag with an accurately measured 3.75 litres of water for a full 5 minutes using a slow-speed drill and high-shear paddle (never a colloidal impeller); larger volumes need a high-shear vane mixer and enough labour to keep batches continuous. Grout bolt pockets first, then pour from one side only across the shortest travel distance, maintaining the grout head so a single front sweeps the void without trapping air. Cure exposed shoulders promptly, and clean tools with water before the grout sets.
Specifications
| Form / composition | Single-component cementitious powder (processed cement, pre-graded fillers, additives) |
| Compressive strength (ASTM C 109, flowable, W/P 0.15) | 10 / 27 / 35 / 45 N/mm² at 1 / 3 / 7 / 28 days |
| Water addition (flowable consistency) | 3.75 litres per 25 kg bag (water-powder ratio 0.15) |
| Yield | 12.5 litres per 25 kg bag |
| Fresh wet density | Approx. 2,200 kg/m³ at flowable consistency |
| Unrestrained expansion | 1–4%; starts ~20 minutes, completes ~150 minutes after mixing |
| Young’s modulus | 24 kN/mm² |
| Section thickness | Up to 100 mm in a single pour; extend with 10 mm aggregate (50–100% by weight) beyond |
| Packaging / shelf life | 25 kg HDPE-lined bag; 6 months in dry, enclosed storage |
Industry use cases
Manufacturing & heavy engineering
Bedding machine tools, presses and pump sets so operational loads transfer evenly into the foundation without hard spots or rocking plates.
Steel & metals plants
Grouting rolling mill beds and mill stand base plates, where free flow must carry the grout across long, narrow underplate voids in one continuous front.
Power & process plants
Setting stanchion bases, static equipment skids and holding-down bolts during structural steel erection, with day-one strength supporting tight sequencing.
Ports & material handling
Crane rail and transporter rail grouting, where continuous void-free support prevents rail rock and edge crushing under wheel loads.
Commercial & precast construction
Column base plates, fixing pockets and precast connection grouting on institutional and industrial buildings.
Frequently asked questions
How much water goes into one 25 kg bag?
When can the equipment be loaded?
What is the maximum thickness in one pour?
How many bags do I need?
Conbextra GP1 or GP2 — which should I order?
Does the grout need vibration or compaction?
How we position Fosroc Conbextra GP1
Conbextra GP1 is the workhorse of the Fosroc grout range — the default order for static base plate and bolt-pocket grouting on Indian sites. When the duty exceeds its envelope, the same family covers you: Conbextra GP2 for higher-strength grouting, and Fosroc’s epoxy grout line where vibrating machinery or chemical exposure rules out a cementitious system. Anchor installations pair naturally with Fosroc Lokfix resin anchor grouts, and foundation repairs around grouting works with the Renderoc mortar family. Where a project document specifies another manufacturer, Space Arc also supplies comparable non-shrink grouts from our Sika and MC-Bauchemie ranges, so the material delivered always matches the specification you tendered against.
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