Fosroc Conbextra STD
A standard-grade, non-shrink cementitious precision grout for base plates, anchor pockets and equipment beds where a clean, economical fill in 10-100 mm gaps is what the job actually calls for.
What is it?
A single-component, factory pre-blended non-shrink cementitious grout that needs only clean water on site. Standard grade, chloride-free, with no metallic iron content.
Where is it used?
Structural steel base plates, precast column pockets, anchor-bolt fixing, machine and equipment bases, and general void filling in gaps of 10 to 100 mm.
Why use it?
Positive plastic-phase expansion removes settlement voids so the grout stays in full bearing contact, at a price point suited to routine, non-critical grouting.
How is it applied?
Gauge with measured clean water, mix to a flowable or trowelable consistency, then pour or pump continuously from one side of a pre-soaked, formed pocket.
About Fosroc Conbextra STD
Conbextra STD is Fosroc’s standard-grade member of the Conbextra family of non-shrink precision grouts. It arrives as a ready-blended dry powder in 25 kg bags: a special cement, graded fillers, flow-control agents and an expansive additive, all proportioned at the factory so the site team only has to add a measured quantity of clean water. That single step matters more than it sounds. On a busy site, the biggest source of grout failure is inconsistent hand-batching of cement, sand and additives; a pre-packaged system takes that variability out and gives every pour the same characteristics from the first bag to the last.
Where it sits in the range is worth being honest about. Conbextra STD is built for routine, non-critical grouting where the loads are moderate and the priority is a sound, void-free fill at a sensible cost, rather than the high early strengths a dynamic machine foundation would demand. It delivers a compressive strength greater than 35 MPa at 28 days and a flow above 125 mm measured to ASTM C940, which comfortably covers base plates, column pockets and equipment beds on general construction and precast work. When a specifier needs 60-plus MPa or rapid strike, the family scales up to Conbextra GP2 and GP3. Understanding that hierarchy is how you spec the right grade instead of over- or under-paying for the wrong one.
The technical insight
The whole point of a precision grout is that it must not shrink away from the surfaces it is meant to bear against. Ordinary cementitious mixes lose volume as they set and as bleed water rises, leaving a thin gap under a base plate exactly where full contact is most needed. Conbextra STD counters this with a gas-releasing expansion system that works during the plastic phase: a controlled chemical reaction generates fine gas bubbles that gently expand the mix while it is still fluid and workable, offsetting settlement and driving the grout into intimate contact with both the substrate and the underside of the plate. Because the expansion happens before the grout stiffens, it does not disrupt the hardened matrix or leave the material under uncontrolled internal stress. The graded fillers and flow-control agents let the mix stay cohesive and free of segregation even as it flows across the bearing area, so the load path that eventually forms is continuous rather than pockmarked with air. Chloride-free chemistry and the absence of any metallic iron content mean there is nothing in the mix that will rust and stain, or set up a corrosion cell against embedded steel and anchor bolts.
Where it is used
- Grouting structural steel column and stanchion base plates
- Filling precast column-to-column connection joints and pockets
- Bedding anchor bolts and holding-down assemblies in formed recesses
- Grouting standard machinery and equipment bases under static and moderate loads
- General void filling and gap grouting in structural concrete from 10 to 100 mm
- Filling lifting-socket and cast-in recesses in precast elements
- Making good pockets and blockouts around precast connections
- Beddings for bearing plates and support brackets in building frames
Key advantages
- Non-shrink: plastic-phase gas expansion offsets settlement and keeps full bearing contact
- Factory pre-blended, so every bag mixes to the same consistency and strength
- Single component: only clean water is added, with no site batching of sand or additives
- Chloride-free and free of metallic iron, so no rust staining or corrosion risk to steel
- Placeable by gravity pour or pump, and adjustable between flowable and trowelable consistency
- Handles a wide 10-100 mm gap range in a single operation
- Economical standard grade for routine, non-critical grouting
- Twelve-month shelf life in sealed, dry storage for reliable site stocking
Limitations & considerations
- Standard grade only: for high early strength or dynamic machine foundations, step up to Conbextra GP2 or GP3
- Single-lift placement is limited to roughly 100 mm; deeper pockets need extension with graded aggregate or successive lifts per the datasheet
- Cementitious and water-sensitive, so it must be protected from rain during the initial set
- Substrate must be saturated surface-dry with all standing water removed, or bond and expansion suffer
- Working time is finite once gauged; mix only what can be placed continuously and use opened bags the same working day
- Not a free-flowing epoxy grout, so it is unsuited to chemically aggressive or heavy vibration duty
Selection & best practice
Success with Conbextra STD is mostly about preparation and discipline. Clean the concrete substrate back to a sound, roughened surface, then keep it saturated for several hours and blow off any free-standing water so the base is damp but not flooded. Box the pocket with a leak-tight, grout-tight formwork that leaves a head box or hopper on one side and adequate air relief on the far side. Gauge only measured clean water into the mix, add the powder and mix mechanically to a smooth, lump-free grout at the consistency the gap demands. Always pour or pump continuously from a single side so the advancing front pushes air ahead of it and never traps a void; do not vibrate a flowable grout, as it can encourage segregation. Place the whole pocket in one operation wherever the depth allows, cure the exposed surfaces against early moisture loss, and protect fresh work from rain and direct sun until it has gained strength. For gaps beyond about 100 mm, extend the grout with well-graded aggregate strictly as the product datasheet specifies.
Specifications
| Product type | Standard-grade non-shrink cementitious precision grout |
| Expansion system | Gas-releasing, acting in the plastic phase |
| Compressive strength (28 days) | > 35 MPa |
| Flow (ASTM C940) | > 125 mm |
| Application gap range | 10-100 mm in a single lift |
| Chemistry | Chloride-free; no metallic iron content |
| Mixing | Single component; clean water added on site |
| Pack size | 25 kg bag |
| Shelf life | 12 months in sealed, dry storage |
Industry use cases
Structural Steel Fabrication
Grouting column and stanchion base plates on warehouse, factory and multi-storey steel frames where loads are static and a clean, void-free fill is enough.
Precast Concrete
Filling column connection pockets, cast-in recesses and lifting sockets during precast erection, where consistent bag-to-bag behaviour keeps the sequence moving.
General Building & Infrastructure
Bedding anchor bolts, holding-down assemblies and bearing plates, plus routine void and gap filling in structural concrete.
Plant & Equipment Installation
Grouting standard machine and equipment bases under static to moderate loads, where high early strength is not the governing requirement.
Frequently asked questions
What is the difference between Conbextra STD and Conbextra GP2?
How thick a gap can Conbextra STD fill in one pour?
Does it contain chloride or any iron that could rust?
How is it mixed and placed on site?
What pack size does it come in and how long does it store?
Is Conbextra STD suitable for a dynamic machine foundation?
How we position Fosroc Conbextra STD
Conbextra STD is the entry point into Fosroc’s Conbextra grout family and should be specified where the duty is routine. When the design calls for higher strength or a dynamic load path, move up to Conbextra GP2 (around 65 N/mm2 at 28 days) or Conbextra GP3 for rapid early strength; for chemically aggressive or high-vibration duty, an epoxy grout is the correct family instead. It pairs naturally on site with Fosroc’s anchoring and repair range, including Lokfix resin anchor grouts for post-fixed bolts and the Renderoc concrete repair mortars for making good surrounding substrate before grouting. Across our other brands, comparable cementitious grouts include Sika’s SikaGrout series and MC-Bauchemie’s Emcekrete range, and Dr. Fixit or STP products cover the associated waterproofing and joint treatment; we can help you match grade to load across any of these. As an authorised Fosroc distributor and applicator serving Delhi NCR and Pan-India, Space Arc supplies genuine, batch-traceable material with technical support on grade selection, pocket design and placement.
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