Fosroc Renderoc M
A medium-aggregate, polymer-modified cementitious mortar for hand-applied concrete reinstatement in 15-50 mm sections, on columns, beams, soffits and facades.
What is it?
A single-component, polymer-modified cementitious repair mortar carrying a medium-graded aggregate (roughly 4-6 mm), site-mixed with water alone to a trowellable consistency.
Where is it used?
Patch and section repair of damaged reinforced concrete: columns, beams, slab soffits, bridge elements, car-park decks and building facades across Delhi NCR and pan-India projects.
Why use it?
It rebuilds lost concrete cover in a controlled, factory-blended package, cuts down site batching error, and bonds to sound prepared substrate while resisting the shrinkage cracking that plagues plain sand-cement patching.
How is it applied?
Prepare and saturate the substrate, prime the exposed steel and concrete, then hand-trowel the mixed mortar in 15-50 mm lifts and cure the finished repair.
About Fosroc Renderoc M
Fosroc Renderoc M sits in the middle of the Renderoc concrete-repair range, and that positioning tells you exactly where it earns its keep. It is a factory pre-blended powder, made from cement, graded medium aggregate up to around 4-6 mm and performance additives, that you gauge with clean water on site to a stiff, trowellable mortar. Because the aggregate is coarser than a fairing coat but finer than a heavy hand-placed reinstatement mix, it fills the everyday repair volumes that most jobs actually present: spalled cover over corroded rebar, honeycombed pours, and the mechanical damage that shows up on columns, beams and soffits once formwork comes off. For a distributor’s technical desk in Delhi NCR, it is one of the products contractors reach for when a defect is too deep for a skim but does not warrant a full structural-grade R4 system.
The polymer modification is the reason it behaves so differently from a hand-batched sand-cement patch. Polymers improve the fresh mortar’s cohesion and its grip on the parent concrete, and they help the hardened repair resist the drying shrinkage that otherwise opens a debonding crack around the patch perimeter within weeks. Applied in lifts of 15-50 mm and typically primed with a Nitobond bonding aid, Renderoc M develops a medium-strength matrix — the page cites a 28-day compressive strength above 35 MPa and bond strength above 1.5 MPa — that is well matched to the general-purpose reinforced concrete it is meant to restore. It is deliberately a repair mortar, not a waterproofing membrane, so below-grade tanking still needs a dedicated system layered over it.
The technical insight
Durable concrete repair is a compatibility problem before it is a strength problem. When you patch old concrete with fresh mortar, the new material shrinks as it cures while the surrounding concrete does not; if that shrinkage is unrestrained and the bond is weak, the interface simply lets go and the repair delaminates. Renderoc M tackles both halves of that equation. The dispersed polymer film raises adhesion to the prepared, saturated-surface-dry substrate so the interface can carry stress instead of failing at it, and it densifies the cement matrix to reduce the free shrinkage that drives cracking in the first place. The medium graded aggregate does its own structural work: a well-distributed skeleton of 4-6 mm particles lets the mortar be built out to 50 mm in a lift without slumping off a vertical or overhead face, and it limits paste content so the section stays dimensionally stable as it hardens. Priming with Nitobond EP or Nitobond SBR reinforces the bond line and, on corrosion repairs, protects the cleaned steel. The net result is a patch that behaves monolithically with the parent element rather than as a stressed inclusion waiting to pop.
Where it is used
- Reinstating spalled and delaminated cover concrete over corroded reinforcement on columns and beams
- Patch repair of honeycombed, segregated or under-vibrated pours after formwork strip
- Repairing slab soffits and beam undersides where hand-applied vertical and overhead build-up is needed
- Bridge pier, abutment and deck-edge concrete repair on infrastructure works
- Concrete rehabilitation in multi-storey and basement car-park structures
- Making good building facades and external RCC walls damaged by weathering or impact
- General reinstatement across industrial sheds, plants and utility structures
- Medium-depth repairs (15-50 mm per layer) that are too deep for a fairing coat but do not require a structural R4 mortar
Key advantages
- Factory pre-blended single-component powder — gauge with water only, so site batching variation is largely removed
- Medium graded aggregate builds 15-50 mm in a single lift without slumping on vertical or overhead faces
- Polymer modification gives strong adhesion to prepared substrate and reduces drying-shrinkage cracking at the patch edge
- Balanced medium strength (28-day compressive strength above 35 MPa) well matched to general reinforced concrete
- Bond strength above 1.5 MPa supports genuinely monolithic repairs when correctly primed
- Trowellable, cohesive consistency suits hand application without specialist spray plant
- Backed by the wider Fosroc repair system — Nitobond primers and Renderoc grades — for a complete, compatible specification
- Cost-sensible middle option between a thin fairing mortar and a premium structural reinstatement system
Limitations & considerations
- Not a waterproofing product — below-grade or water-retaining structures still need a dedicated tanking or membrane system over the repair
- Requires a bonding primer (Nitobond EP or SBR) and correct substrate saturation; skipping this undermines the bond it depends on
- Medium strength grade is not intended for high-strength (R4-class) structural reinstatement — step up to a higher Renderoc grade where a certified structural mortar is specified
- Per-lift thickness is bounded (about 15-50 mm); very deep or very thin repairs need a different product or built-up layers
- Performance is sensitive to workmanship — substrate preparation, mixing water and curing must follow the datasheet or strength and durability suffer
- As a cementitious repair it should not be relied on where significant chemical or acid attack is expected without a suitable protective coating
Selection & best practice
Start with honest substrate preparation. Break out all loose, cracked and carbonated concrete back to a sound, mechanically roughened surface, cut back at least to a square edge (avoid feather-edging), and expose corroded steel fully around its circumference. Clean the reinforcement to bright metal, then apply the specified primer to the steel and the concrete. Bring the substrate to a saturated surface-dry condition — damp but with no standing water — before priming and placing. Mix only with clean water at the recommended ratio using a forced-action or slow-speed drill mixer to a uniform, lump-free mortar, and place it wet-on-wet onto the still-tacky bonding primer. Build the section in 15-50 mm lifts, compacting each firmly against the substrate and scratch-keying between layers where multiple lifts are needed. Finish to line, then cure diligently — Nitobond AR curing membrane or wet hessian and polythene — because a polymer-modified repair loses its shrinkage advantage if it is allowed to dry out too fast. Avoid application in the peak of Indian summer heat without protecting the work from direct sun and drying wind.
Specifications
| Product type | Single-component, polymer-modified cementitious repair mortar |
| Aggregate grading | Medium aggregate, up to approximately 4-6 mm |
| Mixing | Add clean water only, on site |
| Application thickness | 15-50 mm per layer |
| Compressive strength (28-day, typical) | Greater than 35 MPa |
| Bond strength (typical) | Greater than 1.5 MPa |
| Recommended primer | Nitobond EP or Nitobond SBR |
| Application method | Hand / trowel applied, including vertical and overhead |
| Substrate condition | Mechanically prepared, saturated surface-dry |
Industry use cases
Bridges & Infrastructure
Reinstating spalled cover on piers, abutments and deck edges where medium-depth patch repair restores the section without a full R4 structural mortar.
Car Parks & Commercial RCC
Repairing corrosion-driven spalling on columns, beams and soffits in multi-storey and basement car parks, primed and built out in controlled lifts.
Building Facades & Elevations
Making good weather-damaged and impact-damaged external RCC on facades and parapets, with a trowellable mortar that holds on vertical faces.
Industrial Structures
General concrete reinstatement across plants, sheds and utility structures where a dependable medium-grade repair mortar keeps assets in service.
Post-Construction Snagging
Correcting honeycombing and mechanical damage revealed after formwork strip, giving a durable, factory-consistent patch instead of a hand-batched mix.
Frequently asked questions
Is Renderoc M a structural repair mortar?
Do I need a primer with Renderoc M?
How thick can I apply it in one pass?
Can I use Renderoc M to waterproof a basement or water tank?
What surface preparation does it need?
Does Space Arc supply Renderoc M across India and offer technical support?
How we position Fosroc Renderoc M
Renderoc M is the sensible middle of the Fosroc concrete-repair range, and it works best as part of a complete system rather than in isolation. Pair it with a Nitobond primer — Nitobond EP or Nitobond SBR for bonding and steel protection, and Nitobond AR as a curing aid — to get the bond and shrinkage performance the mortar is designed for. Where the repair is shallow, a lighter fairing or general-purpose Renderoc grade is more economical; where the specification calls for a certified high-strength structural reinstatement, move up within the same family. On corrosion repairs, a Fosroc zinc-rich or migratory corrosion-inhibitor treatment on the exposed steel complements the mortar. From our wider portfolio, Space Arc can layer a Dr. Fixit or Fosroc protective anti-carbonation coating over the finished repair, and specify an appropriate crack-injection or sealant solution from Fosroc or Sika where the underlying defect involves active cracking or joints.
Related Concrete Repair products
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