Fosroc Conbextra TS
High-flow, non-shrink cementitious grout engineered for large gap thicknesses of 75 to 500 mm in a single pour, conforming to BS EN 1504-3 Class R4.
What is it?
A ready-to-use, aggregate-filled cementitious grout that flows freely into wide voids and sets without shrinkage, developing structural strength above 60 MPa at 28 days.
Where is it used?
Under heavily loaded stanchion and machine baseplates with large gaps, joints between precast panels, and filling of box sections and deep pockets.
Why use it?
It handles thick sections up to 500 mm in one continuous pour without segregation, bleed or the thermal cracking that plagues deep cementitious placements.
How is it applied?
Mix a 25 kg bag with 3.3 litres of clean water for five minutes, then pour or pump into pre-soaked, leak-proof formwork within 20 minutes.
About Fosroc Conbextra TS
Conbextra TS is Fosroc’s answer to a problem that trips up a lot of site teams: how do you grout a large gap, sometimes as deep as half a metre, in one shot without the mix separating, bleeding water to the top, or cracking as it heats up? Most general-purpose grouts are designed for thin bedding layers of 10 to 75 mm and simply cannot cope with the volume and heat of a thick section. Conbextra TS is formulated specifically for that gap band, 75 to 500 mm, and pours as a genuinely fluid grout that self-levels into the void and flows around anchor bolts and baseplate stiffeners without help. It arrives as a single-component dry powder in 25 kg bags, so the only thing added on site is a measured quantity of clean water, which keeps the mix consistent from bag to bag and from crew to crew.
Underneath the convenience is a carefully graded blend of Portland cements, selected aggregates, fillers and chemical additives. That filler grading is the clever part: it packs the mix densely enough to resist segregation and bleed while keeping the water demand low, which is why the grout reaches high early strength and holds up over decades. The product carries a BS EN 1504-3 Class R4 classification, the top structural repair band, and is chloride free, so there is no risk of the grout contributing to reinforcement corrosion. For Indian projects, that combination of large-gap capability, verified strength and a clean chemistry makes it a dependable choice for structural steel bases, precast connections and heavy plant foundations. Space Arc supplies it across Delhi NCR and Pan-India as an authorised Fosroc distributor and applicator.
The technical insight
The engineering challenge with any deep grout pour is heat. As cement hydrates it releases energy, and in a section thicker than about 100 mm that heat cannot escape fast enough, so the core gets hot, expands, and then cracks as it cools and contracts against the cooler outer skin. Conbextra TS is graded to tackle this on two fronts. First, the selected aggregate and graded filler content displaces a portion of the reactive cement, which lowers the total heat generated per unit volume and flattens the exotherm. Second, the low water requirement, a water-to-powder ratio of just 0.132, means the mix is not carrying excess water that would otherwise bleed to the surface and leave voids or a weak laitance layer at the plate interface. Non-shrink performance comes from a gaseous expansion system that produces a controlled volumetric expansion of up to 1 percent while the grout is still plastic. That slight expansion keeps the grout in firm, gap-free contact with both the substrate and the underside of the baseplate as it stiffens, ensuring the load path is fully bedded rather than resting on high spots. The result is a dense, low-permeability grout that transfers load uniformly and resists the freeze-thaw and carbonation exposure a structural bedding material will see over its service life.
Where it is used
- Bedding heavily loaded stanchion and column baseplates where the gap between steel and foundation is 75 mm or greater
- Grouting machine and heavy plant baseplates that require a thick, load-bearing bed
- Filling joints between precast concrete panels and segmental units
- Filling hollow box sections and deep structural voids in one continuous pour
- Grouting large anchor-bolt pockets and holding-down bolt assemblies
- Second-stage grouting over a first-stage bed of Conbextra GP or Lokfix in staged pours
- Deep bedding under crane rails and bridge bearings where fluid, self-levelling flow is needed
- Structural repair and reinstatement work classified to BS EN 1504-3 Class R4
Key advantages
- Handles large gap thicknesses of 75 to 500 mm in a single pour, avoiding staged lifts
- Non-shrink with controlled expansion up to 1 percent, keeping the baseplate fully bedded
- Free-flowing and self-levelling, so it fills around bolts and stiffeners without rodding
- Reaches high strength, above 40 MPa at 7 days and 60 MPa at 28 days
- Chloride free, so it poses no corrosion risk to embedded reinforcement or bolts
- Graded to resist segregation and bleed and to reduce exothermic heat in thick sections
- Can be either poured or pumped, suiting both small pockets and high-volume placements
- Single-component powder, add water only, giving consistent results across site crews
Limitations & considerations
- Not suitable for thin bedding below 75 mm; use Conbextra HF or Conbextra GP for those gaps
- Formwork must be genuinely leak-proof because the grout is very fluid and will find any gap
- The foundation must be pre-soaked with clean water for at least 2 hours and free surface water removed before pouring
- Placement window is short; the grout must be poured within 20 minutes of mixing to gain full expansion benefit
- In cold conditions below 10 degrees C the formwork must stay in place at least 36 hours and the grout protected from freezing for 48 hours
- Not supplied in waterproof packaging, so shelf life falls below 6 months in hot, humid storage
Selection & best practice
Success with Conbextra TS is mostly about preparation and continuity. Cut back any defective or laitance-covered concrete to a sound base, blow bolt holes and pockets clean of debris, then flood the cleaned foundation with fresh water for at least two hours before grouting and remove all standing water immediately before the pour. Build the formwork to be fully leak-proof, using foam rubber strip or Silicone Sealant 33HM at joints, and keep the pouring-side gap under 150 mm and the far side under 50 mm with no gap at the flanks. Mix each 25 kg bag with exactly 3.3 litres of clean water using a mechanical grout mixer or a paddle-fitted heavy-duty drill for at least five minutes to a smooth consistency; never use a colloidal impeller mixer. Pour from one side only, across the shortest travel distance, and keep a continuous grout head so a single unbroken front sweeps air and pre-soak water ahead of it. Have enough mixed grout and labour ready to place without interruption. Cure exposed surfaces immediately with Concure WB, ponded water or wet hessian. In heat above 35 degrees C mix with cool water and store the mix in shade; in cold below 5 degrees C use warm water at 30 to 40 degrees C.
Specifications
| Product type | High-flow, non-shrink, aggregate-filled cementitious grout |
| Standard compliance | BS EN 1504-3 Class R4 |
| Gap thickness range | 75 mm to 500 mm in a single pour |
| Compressive strength | 14 MPa @ 1 day, 42 MPa @ 7 days, 60 MPa @ 28 days |
| Flexural strength | 6.7 MPa @ 28 days |
| Water addition | 3.3 litres per 25 kg bag (w/p ratio 0.132) |
| Flow / consistency | 750 mm spread within 10 seconds |
| Chloride ion content | Less than 0.05% (0.02% typical) |
| Yield per bag | Approximately 12 litres (0.012 m3) per 25 kg bag |
Industry use cases
Structural Steel Fabrication
Bedding column and stanchion baseplates onto RCC foundations where erection tolerances leave gaps of 75 mm or more under the steel.
Heavy Industry and Power
Grouting large machine and turbine baseplates and equipment skids that demand a thick, uniformly load-bearing bed.
Precast and Infrastructure
Filling joints between precast panels and segments, and deep pockets in bridge and viaduct construction, in single continuous pours.
Ports and Material Handling
Deep bedding under crane rails, bearings and heavily loaded support frames where a fluid, self-levelling grout is essential.
Retrofit and Rehabilitation
Class R4 structural reinstatement of voided or degraded bearing zones during strengthening and repair projects.
Frequently asked questions
What gap thickness is Conbextra TS designed for?
How much water do I add per bag and what is the yield?
What compressive strength does it reach?
Is Conbextra TS chloride free?
Do I need to pre-soak the foundation before grouting?
Can it be pumped for large-volume pours?
How we position Fosroc Conbextra TS
Conbextra TS sits at the deep-section end of Fosroc’s Conbextra grout family. For gaps of 10 to 75 mm, Fosroc Conbextra GP is the general-purpose baseplate and anchor grout; where a very fluid, highly pumpable grout is needed for thinner sections or pre-packed aggregate work, Fosroc Conbextra HF is the right pick, and the TDS itself names it for sections thinner than 75 mm. On staged pours, Conbextra GP or Lokfix can form the first-stage bed with Conbextra TS placed as the second stage. For high early-strength epoxy anchoring of bolts and dowels, Fosroc’s Lokfix epoxy resin is the complementary product. Space Arc also supplies equivalent large-gap and precision grouts from Sika, MC-Bauchemie, Dr. Fixit and Master Builders Solutions, so where a specification calls for a particular brand or a rapid-strength or epoxy grout, we can match the requirement across our full range.
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Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.