Fosroc Renderoc S2
A two-component, polymer-modified structural repair mortar for localised patch reinstatement of spalled and corrosion-damaged concrete, reaching 45 N/mm2 at 28 days.
What is it?
A factory pre-packed, two-component (grey powder plus liquid polymer) cementitious patch repair mortar that is shrinkage-compensated and alkaline, so it re-passivates and protects embedded reinforcement.
Where is it used?
Small, localised repairs to spalled or delaminated columns, beams, slab soffits and facades where a high-strength structural reinstatement is needed.
Why use it?
It delivers 45 N/mm2 compressive and 8 N/mm2 flexural strength at 28 days with very low permeability, guarding the repair against chlorides and carbon dioxide.
How is it applied?
Prime the steel with Nitozinc Primer and the substrate with Nitobond AR, then hand or trowel apply 5-15 mm per pass on vertical faces (up to 100 mm horizontal), and cure.
About Fosroc Renderoc S2
Renderoc S2 is Fosroc’s answer to the everyday problem every repair contractor in India faces: a column corner has blown, a beam soffit is spalling over rusted stirrups, or a chloride-attacked patch on a facade needs to be cut out and reinstated to full structural performance. It arrives as a two-part system, a 25 kg bag of graded cement-and-filler powder together with a 0.25 kg liquid polymer, so all the batching is done in the factory. On site the crew adds only clean water, which removes the guesswork and inconsistency that plague hand-mixed sand-cement patches. The polymer modification gives the mix good workability at a very low water demand (a water:powder ratio of just 0.13), and that low water content is exactly what drives the fast strength gain, the dense low-permeability matrix and the long-term durability of the finished repair.
Because the mortar is alkaline it restores the protective chemical environment around exposed steel, and its shrinkage-compensated formulation means the patch stays bonded rather than pulling away at the edges as it cures. Test data backs this up: after 24 hours’ immersion water absorption is only 0.45 percent, chloride ion diffusion registers nil, and accelerated carbonation depth is nil at four hours, so the repaired zone becomes one of the most durable parts of the element. Renderoc S2 is deliberately a patch-repair product for small, defined pockets rather than a large-area render, which keeps expectations honest and results predictable. As an authorised Fosroc distributor and applicator serving Delhi NCR and clients across India, Space Arc supplies genuine batch-traceable material along with the matching primers and curing compound so the whole repair system performs as designed.
The technical insight
The performance of Renderoc S2 comes from managing water, not adding it. The liquid polymer is always dispersed into the gauging water first and mixed for two minutes before the powder goes in, so the polymer is evenly distributed through every particle of the matrix. This lets the mortar reach a workable, trowellable consistency at only 3.25 to 3.5 litres of water per 25 kg bag. A low water content means fewer capillary voids as the paste hydrates, which is what produces the dense, impermeable microstructure that stops chlorides, oxygen and CO2 from reaching the reinforcement. The polymer film that forms within the pores also improves the bond to the parent concrete and gives the patch enough tensile flexibility to absorb thermal movement, helped by a coefficient of thermal expansion of 7 to 12 x 10-6 per degree C that is closely matched to structural concrete. Shrinkage compensation counteracts the natural drying contraction that would otherwise crack a rigid patch or debond it at the arris. The result is a repair that behaves monolithically with the substrate rather than as a stiff plug sitting inside it.
Where it is used
- Reinstating spalled concrete on columns, beams and slab soffits after corrosion damage
- Rebuilding blown or damaged column corners and slab edges to a square profile
- Localised patch repair of chloride-attacked or carbonation-affected facades and balconies
- Repairing honeycombed or poorly compacted pockets exposed during striking of shuttering
- Restoring cover to exposed reinforcement in car parks, bridges and water-side structures
- Making good after cutting out defective concrete around embedded fixings or conduits
- Structural patch repairs where high early and 28-day strength is specified
- Small-area reinstatement ahead of applying a Dekguard anti-carbonation protective coating
Key advantages
- Reaches 45 N/mm2 compressive and 8 N/mm2 flexural strength at 28 days, with 12 N/mm2 already at 1 day
- Two-component factory pre-pack means no site batching and repeatable, consistent mixes
- Very low permeability shields embedded steel from chlorides, oxygen and carbon dioxide
- Alkaline chemistry re-passivates reinforcement and contains no chlorides itself
- Shrinkage-compensated so the patch stays bonded without edge cracking or debonding
- Thermal expansion matched to concrete (7-12 x 10-6/degC) for compatible long-term behaviour
- Good hand and trowel workability at a low 0.13 water:powder ratio
- Backs onto a complete Fosroc system of primers, bonding aids and protective coatings
Limitations & considerations
- Strictly a localised patch-repair mortar, not to be used as a render over large continuous areas
- Vertical application is limited to 5-15 mm per pass; thicker vertical sections need formwork
- Minimum applied thickness is 5 mm, so it is unsuitable for very thin skim or feather edges
- Requires the correct primers (Nitozinc on steel, Nitobond AR on the substrate) to perform as specified
- Must not be applied when temperature is 5 degC and falling, or exposed to moving water or heavy rain during application
- Cement-based and must be properly cured; short shelf life of about 6 months in dry storage
Selection & best practice
Success with Renderoc S2 is decided before any mortar is mixed. Saw-cut the repair perimeter to at least 10 mm to give a square edge and avoid feather edging, then break out the full area to a minimum 10 mm depth. Grit-blast exposed steel back to bright metal, paying attention to the back of the bars, and where chlorides are present high-pressure wash immediately afterwards to flush corrosion products from the pits. Apply one full coat of Nitozinc Primer to the cleaned steel and let it dry. Soak the concrete substrate, remove excess water, then scrub in one coat of Nitobond AR and apply the mortar while the primer is still tacky; use Nitobond EP instead where the substrate stays permanently damp or a barrier is needed. Always add the polymer to the water first, mix two minutes, then add powder and mix three minutes in a forced-action or slow-speed paddle mixer, never a free-fall drum, keeping water at or below 3.5 litres per bag. Compact firmly around the reinforcement, finish with a wood or plastic float without overworking, and cure continuously with Concure WB or taped polythene, working in 0.5 m sections as you go. In cold weather down to 5 degC use warm water up to 30 degC; above 35 degC store the material in shade and mix with cool water.
Specifications
| Product type | Two-component, polymer-modified, shrinkage-compensated structural repair mortar |
| Compressive strength | 12 N/mm2 at 1 day, 45 N/mm2 at 28 days |
| Flexural strength | 8 N/mm2 at 28 days |
| Water absorption (24 hr immersion) | 0.45 % |
| Application thickness | 5-15 mm per pass vertical; up to 100 mm horizontal; 5 mm minimum |
| Water : powder ratio | 0.13 (3.25-3.5 litres water per 25 kg bag, 3.5 L max) |
| Yield | Approx 13.5 litres per 25 kg bag (1.30 m2 at 10 mm) |
| Setting time | Initial set 3 hr 15 min; final set 4 hr 30 min |
| Packaging | Part A 25 kg powder + Part B 0.25 kg liquid polymer |
Industry use cases
Bridges & Infrastructure
Reinstating cover and repairing spalled soffits and edges on RCC bridge elements exposed to de-icing salts and traffic, where a durable, low-permeability patch is essential.
Commercial & High-Rise Buildings
Structural patch repairs to corrosion-damaged columns and beams during facade rehabilitation, delivered as a clean two-part pack that avoids messy site batching on occupied premises.
Marine & Water-Retaining Structures
Localised reinstatement of chloride-attacked concrete on jetties, tanks and coastal structures where nil chloride diffusion and low permeability protect the reinforcement.
Car Parks & Podiums
Repairing delaminated slab soffits and column bases affected by leaching and carbonation, with high early strength to shorten the time bays are out of service.
Industrial Plants
Making good honeycombing, corrosion pockets and impact damage on structural frames, ready to receive a Dekguard protective coating for long-term chemical resistance.
Frequently asked questions
Is Renderoc S2 spray applied or hand applied?
How thick can I apply Renderoc S2 in one pass?
How much water do I add and does it come with the polymer?
What strength does Renderoc S2 achieve?
Which primers do I need with Renderoc S2?
What is the coverage per bag?
How we position Fosroc Renderoc S2
Renderoc S2 sits at the small-patch, high-strength end of Fosroc’s concrete repair range. It works as a system with Nitozinc Primer for steel, Nitobond AR or Nitobond EP as the bonding coat, Concure WB curing compound, and a Dekguard anti-carbonation coating to protect the surrounding concrete. Where a job needs thicker vertical or overhead build-up without formwork, step up to Renderoc HB or Renderoc HB40; for free-flowing full-depth section reinstatement a micro-concrete such as Renderoc RG(S) is more appropriate. From our wider portfolio, pair the repair with Fosroc Nitomortar or Nitobond epoxy systems for bonding, and if the client is standardised on another brand we also supply equivalent concrete-repair mortars from Sika (Sika MonoTop range), MC-Bauchemie and Dr. Fixit. Space Arc can advise on the right grade and quantities for your specific element and exposure condition.
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