Fosroc Conbextra DK
High-flow, chloride-free, non-shrink cementitious grout with controlled expansion in both the plastic and hardened state for precision bedding of machine foundations, baseplates and anchors.
What is it?
A factory-blended, ready-to-use cementitious grout from Fosroc’s Conbextra family that mixes with water to a high-flow, pumpable consistency and develops controlled expansion to stay non-shrink during placement and cure.
Where is it used?
Precision under-bedding of machine foundations, turbine and crane-rail soleplates, columns, structural baseplates, plus filling joints between concrete elements and anchoring/casting-in of bolts and starter bars.
Why use it?
It eliminates voids and shrinkage gaps under load-bearing plant, transmits dynamic loads fully into the foundation, resists chloride-free so it is reinforcement-friendly, and is classified to EN 1504-3 Class R4 for structural concrete repair.
How is it applied?
Gauge with a measured quantity of clean water in a forced-action mixer, pour or pump continuously from one side into a leak-tight, pre-soaked formwork box across gap thicknesses of 10 to 120 mm, then cure the exposed grout.
About Fosroc Conbextra DK
Fosroc Conbextra DK belongs to the long-established Conbextra range of cementitious grouts that contractors across India have relied on for plant installation and structural repair. It is supplied as a single-component, pre-blended dry powder comprising graded fillers, Portland cement and chemical additives; on site only clean water is added, which removes the batching errors that come with site-blended sand-cement grouts. Once mixed it flows readily under and around congested baseplates and reinforcement, then sets and hardens with a controlled, positive expansion that compensates for the natural settlement and plastic shrinkage of a normal cement matrix. The result is full, gap-free contact between the steel plate and the concrete foundation, so static and dynamic loads from the equipment are transmitted uniformly rather than concentrating on high spots. Conbextra DK is the designation used for the European/Denmark market within Fosroc’s global Conbextra system; its Indian-market counterparts in the same general-purpose, non-shrink, EN 1504-3 R4 cementitious grout class are Conbextra GP, Conbextra GP2 and Conbextra HF, which Space Arc Engineering stocks and supplies as authorised Fosroc distributor. Because it is chloride-free it can be used in direct contact with embedded steel and reinforcement without risk of corrosion, making it suitable for both new construction and remedial concrete repair. The product is classified to BS EN 1504-3 Class R4 (the highest structural repair class) under test methods 3.2, 4.4, 7.1 and 7.2, which confirms its compressive strength, bond, carbonation resistance and thermal-compatibility credentials for load-bearing structural use.
The technical insight
The defining feature of Conbextra DK is dual-stage controlled expansion. A conventional cement grout loses volume twice: as bleed water rises in the plastic state, and again through drying and chemical shrinkage as it hardens. Either mechanism leaves a thin void at the most critical plane, the underside of the baseplate, exactly where uniform bearing is needed. Conbextra DK incorporates an expansion system that generates a slight positive volume change while the grout is still plastic and a further restrained expansion as it cures, so the grout column remains in compression against the plate rather than pulling away. This is what lets it bed plant subject to vibration and impact. The second technical lever is rheology: the grout is engineered to remain high-flow and self-levelling at a fixed water addition, so it can be poured or pumped continuously across thick 10-120 mm gaps without segregation or the need for tamping. Two practical consequences follow from the chemistry. First, water dosage is the single most important variable a site team controls; over-watering to gain easier flow directly reduces strength and can promote bleed, so the manufacturer’s gauging quantity must be measured, not judged by eye. Second, because expansion is partly gas- or mineral-driven, it must be restrained by formwork and by completing the pour before the reaction peaks, which is why continuous single-direction placement matters.
Where it is used
- Precision grouting beneath machine and equipment foundations subject to static and dynamic loading
- Bedding of structural steel baseplates, stanchion bases and column kicker plates
- Under-grouting of crane rails, gantry soleplates and turbine/generator soleplates
- Filling joints and gaps between precast and in-situ concrete elements
- Anchoring and casting-in of holding-down bolts, dowels and starter bars into pockets
- Free-flow void filling and structural concrete repair classified to EN 1504-3 R4
- Grouting of bearing plates for bridges, beams and heavy structural connections
- Pumped grouting of confined or congested cavities where hand placement is impractical
Key advantages
- Ready-to-use pre-blended powder, gauged with water only, giving consistent on-site quality and eliminating sand-cement batching errors
- Controlled expansion in both the plastic and hardened stages ensures genuinely non-shrink, gap-free bedding under baseplates
- High-flow, self-levelling consistency fills congested and confined cavities without tamping or rodding
- Pumpable, allowing continuous placement into deep or inaccessible voids
- Chloride-free formulation is safe in contact with reinforcement and prestressing steel
- Wide single-product gap range of 10 to 120 mm covers most plant-bedding and baseplate jobs
- Classified to BS EN 1504-3 Class R4, the top structural repair class, for documented load-bearing performance
- High early and ultimate strength supports rapid commissioning of grouted equipment
Limitations & considerations
- Gap thickness governs the product: sections below 10 mm need a free-flow/epoxy alternative and sections above 120 mm need a thick-section grout such as Conbextra TS or aggregate extension
- Strictly water-sensitive; exceeding the specified gauging water sharply reduces strength and can cause bleed and segregation
- Requires leak-tight, pre-soaked formwork and continuous single-direction pouring to develop full expansion and avoid cold joints
- As a cementitious grout it is not a chemical-resistant bedding material; aggressive acid or solvent exposure calls for an epoxy grout like Conbextra EP/EPR
- Exposed grout must be cured promptly (wet hessian, ponding or curing membrane) to prevent surface drying cracks
- Placing temperature should be controlled; very hot or cold conditions alter flow time and expansion and need hot/cold-weather precautions
- Not intended as a high-build patch repair mortar on vertical or overhead faces — it is a flowable grout
- DK is the European market designation; for India-supplied projects the equivalent Conbextra GP/GP2/HF grades are normally specified
Selection & best practice
Establish the gap depth first and confirm it sits within the 10-120 mm range before selecting Conbextra DK; for shallower or deeper sections move to the correct family member. Build rigid, leak-tight formwork with a generous head box on the pour side and a 100 mm clearance on the far side to let air and grout escape, and pre-soak the concrete substrate so it is saturated surface-dry, removing all standing water, oil, laitance and debris. Mix only with the manufacturer’s measured water quantity in a forced-action or paddle mixer — never over-water to improve flow. Pour or pump continuously from one side only so the advancing front pushes air ahead of it, keeping a constant head until grout rises uniformly on the far face. Place the full bay in one operation to avoid cold joints, then cure the exposed surfaces immediately with wet hessian, ponding or a curing membrane and protect from hot sun, wind or frost. Allow the specified strength gain before loading or commissioning the equipment.
Specifications
| Product type | Single-component, pre-blended cementitious non-shrink grout (water-gauged) |
| Expansion system | Controlled positive expansion in both plastic and hardened states |
| Consistency | High-flow, self-levelling, pumpable |
| Gap / section thickness | 10 to 120 mm in a single pour |
| Chloride content | Chloride-free |
| Standard classification | BS EN 1504-3 Class R4 (methods 3.2, 4.4, 7.1, 7.2) |
| Typical compressive strength (R4 grout family ref.) | approx. 15 MPa at 1 day, 45 MPa at 7 days, 60-65 MPa at 28 days |
| Typical fresh wet density (R4 grout family ref.) | approx. 2,100-2,150 kg/m3 |
| Primary uses | Machine foundations, baseplates, crane rails, joints, bolt anchoring, structural repair |
| Mixing | Add measured clean water only; forced-action mixer recommended |
| Curing | Wet cure exposed surfaces (hessian / ponding / membrane) |
| Market designation | European/Denmark designation; India equivalents: Conbextra GP / GP2 / HF |
Industry use cases
Power & Heavy Engineering
Bedding turbine, generator and compressor soleplates and pump bases where vibration demands void-free, non-shrink contact for full dynamic load transfer.
Manufacturing & Process Plants
Grouting under press, mill, conveyor and rotating-machinery baseplates so holding-down bolts and frames bear evenly on the foundation.
Infrastructure & Bridges
Under-grouting bearing plates, soleplates and connection joints between precast and in-situ elements in bridge and viaduct works.
Material Handling & Logistics
Setting crane rails, gantry beams and rail soleplates where accurate level and continuous support along the rail are critical.
Structural Steel Construction
Bedding column and stanchion baseplates after steel erection, transferring building loads from the steel grillage into the RCC foundation.
Repair & Rehabilitation
EN 1504-3 R4 structural repair and pocket-filling for anchoring dowels, starter bars and holding-down bolts in remedial works.
Frequently asked questions
Is Fosroc Conbextra DK a cementitious or an epoxy grout?
What gap thickness can Conbextra DK be poured at?
How does it stay non-shrink?
What standard does Conbextra DK meet?
Is Conbextra DK available in India, and what is the equivalent?
How important is the water dosage?
How long before grouted equipment can be loaded?
How we position Fosroc Conbextra DK
Within Fosroc’s Conbextra system, Conbextra DK sits as the European/Denmark designation for a general-purpose, non-shrink cementitious grout in the EN 1504-3 R4 class. For Indian projects the natural cross-references are Conbextra GP and GP2 (10-75 mm general grouting), Conbextra HF (high-flow to 100 mm) and, for deeper pours beyond its 120 mm ceiling, the aggregate-filled Conbextra TS; where chemical resistance or very high precision is needed the epoxy Conbextra EP/EPR range takes over. As a specifier you would reach for a cementitious grade like this for the vast majority of plant-bedding and baseplate work, and step up to epoxy only for aggressive-exposure or thin-section, high-load duties. Against the wider Indian market it competes with Sika’s SikaGrout range, MBS Grout/MasterFlow (MBCC/Master Builders), Dr. Fixit Pidicrete and STP’s grout offerings, all of which carry comparable non-shrink cementitious grades. Space Arc Engineering recommends matching the grout to the gap depth, the load type (static versus dynamic) and the exposure, and as an authorised Fosroc distributor and applicator across Delhi NCR and pan-India we can confirm the correct Conbextra grade, supply it and, where required, undertake the grouting on site to specification.
Related Grouts & Anchors products
Source Fosroc Conbextra DK for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.