Fosroc Renderoc 65
A high-build, polymer-modified cementitious mortar that rebuilds deep concrete section loss on vertical and overhead faces in fewer passes and without formwork.
What is it?
A polymer-modified, coarse-graded cementitious repair mortar formulated to be placed in thick single coats on vertical and overhead concrete without slumping or the need for shuttering.
Where is it used?
Deep spalls and heavy section loss on bridge piers, columns, pile caps, beam soffits, retaining walls and abutments where the repair depth runs well beyond a normal patching mortar.
Why use it?
It lets a crew rebuild lost cover in far fewer lifts, resists water and chloride ingress, and shrinks less than plain sand-cement, so the finished repair stays bonded and durable.
How is it applied?
Hand-trowelled onto a saw-cut, mechanically prepared substrate that has been primed with a bonding coat, built up in controlled layers and then moist-cured.
About Fosroc Renderoc 65
Renderoc 65 belongs to Fosroc’s Renderoc family of concrete repair mortars, and its role on site is straightforward: it is the material you reach for when the damage is deep. Ordinary patch repair mortars are designed for shallow reinstatement of a few millimetres to a couple of centimetres. Renderoc 65 is engineered for the opposite situation, where corroded reinforcement, mechanical damage or long-term deterioration has left a genuine void to fill. The number in its name reflects what matters most in that scenario, its ability to be laid up to 65 mm thick in a single coat on a vertical or overhead surface and stay exactly where the trowel leaves it. That build capability, combined with a polymer-modified binder and a coarser aggregate grading, is what separates it from the thinner fairing and general-purpose grades in the same range.
For engineers and contractors working across Delhi NCR and the rest of India, the appeal is practical. Deep repairs done in many thin passes are slow, and every cold joint is a potential weakness. A mortar that reinstates 40 mm or more of lost section in one controlled operation shortens the programme and reduces the number of interfaces in the finished repair. Space Arc Engineering supplies Renderoc 65 as an authorised Fosroc distributor and applicator, which means the material arrives with the right companion primers and with guidance on where it fits against the lighter Renderoc grades. The result is a repair system rather than a single bag of mortar, matched to the actual depth and orientation of the defect in front of you.
The technical insight
The behaviour that makes a high-build mortar useful is the combination of thixotropy and internal cohesion. Renderoc 65 is polymer-modified, and that polymer does two jobs at once: it improves adhesion to the prepared concrete and it holds a freshly placed thick section together so it does not sag under its own weight before the cement sets. The coarser aggregate grading gives the mix body and reduces the paste fraction, which in turn keeps drying shrinkage lower than a fine sand-cement render placed at the same thickness. Lower shrinkage matters because a deep repair that shrinks hard will try to peel away from its bond line; controlling it is what keeps the patch attached over years, not months. The dense, low-permeability matrix then slows the movement of water and chloride ions into the repair, which protects the very reinforcement the repair was carried out to save. None of this works without the bonding primer, though. The primer is the mechanical and chemical link between old, carbonated or contaminated concrete and the new mortar, and skipping it is the fastest way to turn a sound-looking repair into a drummy one.
Where it is used
- Reinstating deep spalls on bridge piers and columns where section loss exceeds roughly 40 mm
- Rebuilding pile caps and beam soffits that have lost significant cover to reinforcement
- Repairing retaining walls and abutments at depths beyond the reach of standard patch mortars
- Restoring large delaminated or spalled areas on vertical concrete faces
- Building up multi-layer repairs where the total depth is made up in controlled lifts
- Overhead soffit reinstatement where the mortar must resist slumping without shuttering
- Reprofiling corroded RC members after the steel has been cleaned and primed
- Structural cover replacement on industrial and infrastructure concrete in coastal or aggressive environments
Key advantages
- Places up to 65 mm in a single coat on vertical and overhead surfaces, cutting the number of lifts on deep repairs
- Holds its shape without sagging, so formwork is generally not required
- Polymer modification gives strong adhesion to properly prepared and primed concrete
- Coarse-graded formulation reduces drying shrinkage compared with plain sand-cement mortar
- Dense matrix resists water penetration and chloride ingress, protecting embedded steel
- Compatible with common non-structural concrete substrates in the everyday strength range
- Fewer cold joints in a deep repair means fewer potential weak planes
- Supplied with matched Fosroc bonding primers and application guidance through Space Arc
Limitations & considerations
- A bonding primer such as Nitobond SBR or Nitobond EP is essential; the mortar should not be applied to bare, unprimed concrete
- It is a repair mortar, not a structural replacement for concrete, and does not restore lost load capacity on its own
- Substrate must be saw-cut to a firm edge, mechanically broken out to sound concrete and thoroughly prepared before placing
- Corroded reinforcement has to be exposed, cleaned and treated before the mortar goes on, or the corrosion will continue behind the repair
- Requires proper moist curing; allowing the surface to dry out too early risks shrinkage cracking and loss of strength
- Very deep or heavily loaded repairs may call for a different Renderoc grade or a formwork-and-pour micro-concrete approach
Selection & best practice
Start by cutting a clean, square edge around the repair area rather than feathering the mortar out to nothing, then break out all loose, cracked or contaminated concrete back to a sound, roughened substrate. Expose any corroded reinforcement fully, clean it, and treat it before you go further. Dampen the prepared concrete to a saturated surface-dry condition and apply the bonding primer, Nitobond SBR or Nitobond EP depending on the exposure, then place the mortar while the primer is still tacky and working. On deep sections, build up in controlled layers, scratch-key intermediate surfaces, and take care to compact the mortar well against the substrate and around the steel so no voids are left behind. Finish to the required profile, then protect and moist-cure the repair for the specified period, keeping it damp and out of direct drying wind and sun. Where the repair will be exposed to weather or an aggressive environment, follow up with a Fosroc protective coating so the whole element ages evenly.
Specifications
| Product type | High-build, polymer-modified cementitious repair mortar |
| Maximum single-coat thickness | Up to 65 mm (vertical and overhead) |
| Compressive strength (28 days) | Greater than 40 MPa |
| Bond strength (with primer) | Greater than 1.5 MPa |
| Chloride permeability | Low |
| Application method | Hand trowel |
| Recommended primer | Nitobond SBR or Nitobond EP |
| Minimum curing | 3 days moist curing (overcoat after 7-14 days per system) |
Industry use cases
Bridges & Infrastructure
Reinstating deep spalls on piers, pile caps and beam soffits where chloride-driven corrosion has stripped cover from the reinforcement.
Water-Retaining Structures
Rebuilding damaged sections of retaining walls and abutments that sit in wet or aggressive ground conditions.
Industrial Concrete
Restoring lost section on columns and structural members in plants and warehouses exposed to moisture and mechanical damage.
Marine & Coastal
Deep repair of RC elements in coastal Indian environments where the dense, low-permeability matrix helps resist ongoing chloride attack.
Building Rehabilitation
Cover replacement and reprofiling on ageing concrete frames during structural repair and life-extension programmes.
Frequently asked questions
What does the 65 in Renderoc 65 mean?
Do I really need a primer, or can I trowel it straight onto the concrete?
How deep a repair can it handle in one go?
How is it different from Renderoc HB?
Does it stop the reinforcement from corroding again?
How long before the repair can be overcoated or put back into service?
How we position Fosroc Renderoc 65
Renderoc 65 sits in the deep-repair slot of the Fosroc Renderoc range. For lighter, extra-high-build work placed by wet spray, Renderoc HB is the natural sibling; for thin fairing coats and blowhole filling ahead of a coating, Renderoc FC or a general-purpose grade like Renderoc GP is more appropriate; and where a defect is best filled by pouring into formwork, a flowable Renderoc micro-concrete is the right call. It is always used with a Fosroc bonding primer, Nitobond SBR for general work or Nitobond EP where a tougher epoxy bond line is wanted, and repairs in exposed or aggressive settings are best finished with a Fosroc protective coating such as Dekguard or a Nitocote system. Space Arc Engineering also stocks equivalent concrete-repair mortars from Sika, Dr. Fixit and MC-Bauchemie, so if a project specification calls for a particular brand we can match the Renderoc 65 role across those ranges.
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