About Fosroc Renderoc S

Fosroc Renderoc S is a high-performance concrete reinstatement mortar engineered for the structural repair of reinforced concrete where low permeability, high compressive strength and abrasion resistance are required together. Supplied as a ready-to-use blend of dry powders needing only the site addition of clean water, it conforms to BS EN 1504-3 Class R4, the most demanding category for cementitious concrete repair. In Indian conditions — where chloride-laden coastal air, carbonation in polluted urban centres, monsoon wetting-and-drying cycles and heavy traffic loading all attack ageing concrete — Renderoc S is positioned as a workhorse for large-area reinstatement as well as localised patch repairs.\n\nThe product is built on Portland cement, carefully graded aggregates and chemical additives, with the polymer modification doing the heavy lifting on durability: it gives the cured mortar extremely low permeability to water, carbon dioxide and chloride ions, the three principal drivers of reinforcement corrosion in Indian structures. A built-in shrinkage-compensation system delivers long-term dimensional stability so the repair stays bonded and crack-free over years of service. Because it is one-component and factory pre-bagged, it eliminates the site-batching inconsistency that plagues hand-mixed sand-cement repairs on Indian sites.\n\nRenderoc S is specifically designed for vertical and horizontal surfaces. By hand or trowel it builds up to 10 mm in vertical locations and up to 100 mm horizontally in a single application; greater vertical thicknesses are achieved by wet-spray, which also speeds up large-area work on facades, soffits and substructures. For horizontal trafficked locations, individual bays should not exceed 4 m to control shrinkage stresses. It is one part of the Fosroc Systematic Approach to concrete repair, which pairs the mortar with reinforcement priming (Nitoprime Zincrich Plus), bonding aids (Nitobond AR / Nitobond EP) and protective anti-carbonation coatings (Dekguard range). Where compatibility with weaker parent concrete or higher vertical build is needed, Fosroc directs users to Renderoc HB30 or HB45 instead — an honest scoping that Space Arc Engineering reinforces during specification.\n\nAs an authorised Fosroc distributor serving Delhi NCR and Pan-India, Space Arc Engineering supplies genuine, batch-traceable Renderoc S in 25 kg bags with technical data sheets, MSDS and on-site application guidance, helping contractors and consultants specify the correct Renderoc grade for each repair scenario rather than a one-size-fits-all approach.

The technical insight

Renderoc S is classified R4 to EN 1504-3, which requires compressive strength above 45 MPa, adhesive bond above 2.0 MPa and elastic modulus above 20 GPa — and the cured mortar clears all three comfortably (55 MPa, ~2.1 MPa pull-off bond, ~37 GPa modulus). The high elastic modulus is the technically important point: it makes Renderoc S relatively stiff and best suited to repairing structurally sound, higher-strength parent concrete (30-60 MPa). Used over weaker, more flexible substrates, the stiffness mismatch can concentrate stress at the bond line, which is precisely why Fosroc steers low-strength-concrete repairs toward Renderoc HB30. The other defining property is permeability: built around a 0.11 water:powder ratio and a polymer matrix, the hardened mortar is effectively impermeable to acid gases, waterborne chlorides and oxygen, while chloride ion content stays below 0.05% — so the repair itself never re-initiates rebar corrosion. Shrinkage stays under 300 microstrain at 7 days, and the A2-s1,d0 (non-combustible) fire rating allows unrestricted use in enclosed structures, basements and tunnels.

Where it is used

• Reinstatement of spalled and delaminated reinforced concrete on bridges, flyovers and elevated road structures
• Large-area and localised patch repair of car park decks, ramps and industrial floors needing abrasion resistance
• Repair of marine and coastal RC structures (jetties, sea walls, splash zones) exposed to chloride attack
• Reinstatement of water-retaining and water-handling structures — tanks, reservoirs, treatment plants
• Repair of carbonation- and pollution-damaged concrete facades, columns and beams in urban buildings
• Substructure and basement repairs where low permeability and non-combustibility are required
• Wet-spray reinstatement of large vertical surfaces and soffits in tunnels and infrastructure works

Key advantages

• Conforms to BS EN 1504-3 Class R4 — the highest structural concrete-repair classification
• High compressive strength (~55 MPa at 28 days) with high abrasion resistance for trafficked surfaces
• Polymer modification gives extremely low permeability to water, CO2 and chlorides, protecting embedded steel
• Built-in shrinkage compensation for long-term dimensional stability and crack-free repairs
• High single-pass build — up to 100 mm horizontal and 10 mm vertical (more by wet-spray)
• One-component, pre-bagged formulation removes site-batching variation; only clean water is added
• Contains no chloride admixtures and carries an A2-s1,d0 non-combustible fire rating
• Can be applied efficiently over large areas by wet-spray, hand or trowel

Limitations & considerations

• Stiff, high-modulus mortar — best matched to sound 30-60 MPa parent concrete; for weaker substrates Fosroc recommends Renderoc HB30 instead
• Limited vertical hand-applied build (max 10 mm); higher vertical/overhead build needs wet-spray or Renderoc HB30/HB45
• Horizontal trafficked bays must not exceed 4 m to control shrinkage stresses
• Requires a forced-action mixer; free-fall mixers and part-bag mixing are prohibited, so disciplined site practice is essential
• Performance is highly sensitive to water dosage (2.5-3.0 L max per bag) and mixing time — over-watering or under-mixing sharply reduces strength
• Demands full surface preparation plus reinforcement and substrate priming (Nitoprime Zincrich Plus, Nitobond AR/EP) for the system to perform
• Minimum application thickness of 5 mm — not suitable as a thin skim or fairing coat (use Renderoc FC for that)
• 12-month shelf life and must be kept dry in unopened bags; humid Indian monsoon storage can shorten usable life

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Renderoc S

Within the Fosroc concrete-repair range, Renderoc S is the high-strength, low-permeability workhorse for sound, higher-grade concrete and large horizontal or wet-spray repairs; it sits alongside Renderoc HB30/HB45 (chosen for high vertical/overhead build and weaker substrates), Renderoc GP (general-purpose patching), and Renderoc FC (thin fairing/levelling coat), and is typically paired with Nitoprime Zincrich Plus, Nitobond AR/EP and a Dekguard protective coating. Against competitor systems, it competes directly with Sika MonoTop R4-class mortars (e.g. MonoTop-412), MBS/MC-Bauchemie Nafufill repair mortars, Dr. Fixit Krack-X/Pidicrete repair systems, and STP (Sika-owned) structural repair mortars. Honest positioning: specifiers should select on EN 1504-3 class, substrate strength and modulus compatibility, and required build thickness rather than brand alone — for weak or highly flexible substrates a lower-modulus mortar may bond more reliably than Renderoc S. Space Arc Engineering’s value is supplying genuine Fosroc material with the matched primer/coating system and India-specific technical guidance, so the full repair system performs as designed rather than a single component bought in isolation.

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