Fosroc Conbextra EP75
Solvent-free epoxy grout that reaches 80 N/mm² in 24 hours — specified under turbines, compressor frames and crane rails where downtime costs more than material.
What is it?
A three-component, solvent-free epoxy resin grout — base, hardener and graded aggregate — supplied pre-proportioned for whole-pack mixing on site.
Where is it used?
Under machine base plates, turbine and compressor foundations, crane and transporter rails, and high-strength structural infill in gaps of 10 mm to 75 mm.
Why use it?
100 N/mm² compressive strength by day 7 with 80 N/mm² inside 24 hours, non-shrink bearing contact and chemical resistance under dynamic loads.
How is it applied?
Power-mix base and hardener, blend in the aggregate, then pour from one side under a hydrostatic head into leak-proof formwork within the 75-minute pot life.
About Fosroc Conbextra EP75
Conbextra EP75 is Fosroc’s heavy-duty epoxy grouting system for situations where cementitious grout stops being good enough: base plates under turbines and reciprocating compressors, crane rails taking impact loads, and machine foundations in refineries and electroplating shops where spilled chemicals would attack a cement matrix. It arrives as three pre-weighed components — resin base, hardener and specially graded aggregate — that mix on site into a free-flowing, self-compacting grout. It fills gaps from 10 mm to 75 mm without vibration and cures with no shrinkage, locking the plate to its foundation in full contact.
Space Arc Engineering stocks and applies EP75 across Delhi NCR and supplies Pan-India against project schedules. The number that usually decides the specification is early strength: 80 N/mm² compressive within 24 hours means a machine can be aligned, grouted and returned to service inside a single shutdown window, rather than waiting the days a cementitious grout needs to carry comparable load. Flexural strength of 30 N/mm² and tensile strength of 14 N/mm² at 7 days provide the fatigue margin that dynamic equipment demands.
The technical insight
An epoxy grout cures by chemical cross-linking between resin and hardener, not by cement hydration, and most of EP75’s behaviour follows from that. With no mix water there is no bleed, no plastic shrinkage and no capillary porosity — the hardened grout stays in intimate contact with the underside of the plate, which is what preserves machinery alignment under vibration. The cross-linked matrix also carries tension and flexure in a way cement paste cannot, which is why its 7-day flexural figure of 30 N/mm² is roughly three times what a good cementitious grout achieves, and why the material resists creep under sustained loading. The graded aggregate is not just economy: it moderates exotherm in thick pours and pulls the coefficient of thermal expansion down to 3.2 x 10^-5, so the grout moves less against steel and concrete through thermal cycles.
Where it is used
- Base plate grouting under turbines, generators and reciprocating compressors subject to dynamic loads
- Under-plate grouting to heavy structural elements and stanchion bases
- Machine foundations in steelworks, refineries, chemical plants and electroplating shops
- Crane rail and transporter rail grouting in ports and heavy industry
- High-strength structural infill between steel and precast elements
- Bearing plate grouting on bridge and rail infrastructure
- Holding-down bolt pockets where early strength and vibration resistance are needed
Key advantages
- Reaches 80 N/mm² compressive strength in 24 hours, so machinery can be aligned and re-commissioned within short shutdowns
- Free-flowing and self-compacting — travels up to 3,500 mm under a 100 mm head in a 70 mm gap, no vibration needed
- Non-shrink cure maintains full surface-to-surface bearing beneath base plates, protecting alignment
- Withstands repetitive dynamic and impact loading from turbines, compressors and reciprocating machinery
- Good general chemical resistance for refinery, chemical-plant and electroplating environments
- Three pre-proportioned components mixed as full packs — no site batching judgement, repeatable results
- 30 N/mm² flexural and 14 N/mm² tensile strength at 7 days give a fatigue margin cementitious grouts cannot match
- 12-month shelf life when stored below 35°C suits project stores and staged procurement
Limitations & considerations
- Grout shoulders must be restrained; placed against unconfined plinth edges the grout can crack — detail formwork accordingly
- Pot life of 75 minutes at 23°C shortens sharply in heat; above 35°C ambient you need cooled storage, shaded equipment and a fully manned pour
- Single-pour design range is 10-75 mm gaps — thinner gaps call for a low-viscosity epoxy such as Conbextra EP10, deeper sections need staged placement
- Costs several times more than cementitious grout, so it is poor value on static, lightly loaded bases
- Epoxy resins can sensitise skin — gloves, eye protection and ventilation are mandatory; Nitoprime 25 and Fosroc Solvent 102 are flammable (flash points 39°C and 33°C)
- All contact surfaces must be dry at placement; damp or oil-contaminated foundations compromise bond
Selection & best practice
Preparation decides the outcome. Cut back weak or laitance-affected concrete to sound material, blow bolt pockets clean and make sure every surface is dry at the time of pouring. If steel plates will sit exposed before grouting, blast-clean the underside to SA 2½ and coat with Nitoprime 25 (4.0-5.0 m²/litre) to prevent rust and secure bond. Build leak-proof formwork — EP75 is a free-flow grout and will find any gap — keeping the pour-side clearance within 150 mm and the remaining sides within 50 mm, with relief holes to vent trapped air. Mix the full hardener pack into the base with a slow-speed drill until homogeneous, then add all the aggregate and mix about two minutes to a uniform colour. Pour from one side only under a constant hydrostatic head (use a header hopper) so the grout advances as a single front, and complete placement inside the 75-minute pot life at 23°C — quicker in summer. Clean tools immediately with Fosroc Solvent 102.
Specifications
| Compressive strength (ASTM C349) | 80 N/mm² at 1 day; 95 N/mm² at 3 days; 100 N/mm² at 7 days |
| Flexural strength (ASTM C348) | 30 N/mm² at 7 days |
| Tensile strength (ASTM C881) | 14 N/mm² at 7 days |
| Pot life | 75 minutes at 23°C |
| Gap width range | 10 mm to 75 mm in a single pour |
| Maximum flow distance (100 mm head, 20°C) | 2,000 mm at 35 mm gap; 3,500 mm at 70 mm gap |
| Coefficient of thermal expansion (ASTM C531) | 3.2 x 10^-5 |
| Pack sizes | 8-litre and 15-litre three-component packs |
| Shelf life | 12 months stored below 35°C |
Industry use cases
Power & Energy
Turbine soleplates and generator frames, where non-shrink contact preserves shaft alignment and 24-hour strength keeps outage schedules intact.
Oil, Gas & Petrochemical
Reciprocating compressor and pump bases in refineries, where the grout must shrug off oil and chemical spillage as well as constant vibration.
Steel & Heavy Industry
Mill stand bases, crane rails and transporter rails carrying the repetitive impact loading that fatigues cementitious grouts.
Rail & Metro Infrastructure
Bearing plates and rail-support grouting on track and depot works, where high early strength shortens possession times.
Precision Engineering
Machine-tool beds and measuring-equipment foundations, where creep under sustained load would surface as lost accuracy.
Frequently asked questions
How quickly can machinery be re-commissioned after grouting?
What gap thicknesses can it be poured in?
How do we handle it in Indian summer temperatures?
Is a primer required before grouting?
When does epoxy grout justify its cost over cementitious?
What pack sizes are available and how do we estimate quantity?
How we position Fosroc Conbextra EP75
EP75 sits at the top of the Conbextra grout family we stock. For gaps under 10 mm — shim pockets and precision beds — Conbextra EP10 is the low-viscosity partner; for everyday static base plates and column bases, cementitious Conbextra GP2 delivers non-shrink performance at a fraction of the cost, with Conbextra HF where higher flow is needed. Nitoprime 25 is the standard companion primer for steel plates. Where a project has standardised on another system house, we also supply comparable epoxy grouts from Sika’s Sikadur range — we will quote whichever genuinely meets the specification.
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