Fosroc Renderoc DS
Polymer-modified, fibre-reinforced dry-spray mortar for fast, large-area structural concrete repair — EN 1504-3 Class R4.
What is it?
A single-component, polymer-modified and fibre-reinforced cementitious repair mortar formulated for the dry-spray (dry-process gunite) technique, classified EN 1504-3 Class R4.
Where is it used?
Large-area and awkward-access concrete repairs on bridges, tunnels, jetties, chimneys, cooling towers, culverts, retaining walls and building facades.
Why use it?
Machine spraying restores big surface areas quickly with minimal rebound, high early strength (20 MPa at 1 day) and low permeability that shields reinforcement from chlorides and CO2.
How is it applied?
Fed dry into a spray gun where water is added at the nozzle, then built up in passes onto a prepared, primed substrate and finished by hand or float.
About Fosroc Renderoc DS
Renderoc DS is Fosroc’s answer to the concrete repair problem that hand-trowelling cannot solve economically: large, continuous areas of deteriorated cover concrete spread across piers, soffits, tunnel linings and sea-facing walls. Instead of packing mortar patch by patch, the material is delivered as a ready-blended dry powder that is conveyed through a hose and hydrated at the nozzle, letting a two-person crew reinstate square metres of section in a fraction of the time. It is polymer-modified for adhesion and impermeability and fibre-reinforced to control plastic cracking, and it carries an EN 1504-3 Class R4 rating — the highest structural-repair class in the standard.
For Indian engineers and applicators, the appeal is throughput without compromising durability. Renderoc DS builds up to 150 mm on vertical faces and 90 mm overhead in a single application, develops roughly 20 MPa at one day and 60 MPa at 28 days, and forms a dense, low-permeability matrix that restricts the ingress of waterborne chlorides, oxygen and acid gases. That combination makes it a genuine gunite-grade repair system rather than a cosmetic render, suited to coastal, industrial and infrastructure structures where both speed and long-term protection of the steel matter.
The technical insight
The performance of Renderoc DS comes from how the dry-spray process compacts the mix. Because water is introduced only at the nozzle, the mortar strikes the substrate at high velocity and consolidates on impact, producing a denser, lower-water-cement-ratio layer than most hand-applied mortars can achieve. That density is what drives the early strength and the low permeability. Polymer modification bridges the cement matrix to the existing concrete for a strong monolithic bond, while the fibre content resists shrinkage micro-cracking as the section cures. The net result is a repair that is impermeable enough to slow carbonation and chloride diffusion, keeping the passivating environment around the reinforcement intact so the underlying corrosion cause is not simply buried and left to continue.
Where it is used
- Large-area reinstatement of spalled cover concrete on bridge piers, abutments and soffits
- Repair and overlay of tunnel and culvert linings
- Rehabilitation of marine and coastal structures such as jetties, sea walls and splash-zone elements
- Resurfacing of cooling towers, chimneys and other tall or awkward-access RCC structures
- Reprofiling of retaining walls and large facade panels on commercial buildings
- Wide-scale overlays applied to increase cover to reinforcement on carbonated concrete
- Repair of industrial structures and water-retaining RCC where low permeability is required
- High-output patch and area repair on car park decks and elevated slabs
Key advantages
- EN 1504-3 Class R4 — the highest structural repair classification in the standard
- Very high output: covers large areas far faster than hand-applied mortars
- High early strength of around 20 MPa at 1 day speeds up return to service
- Low rebound compared with conventional dry-spray products, reducing material waste
- Fibre reinforcement controls plastic shrinkage and micro-cracking
- Dense, low-permeability matrix resists chloride, oxygen and CO2 ingress
- Single-component powder — only clean water is added, simplifying site logistics
- Can be applied down to 3 C substrate temperature, extending the working window
Limitations & considerations
- Requires dry-spray (gunite) plant and a trained nozzle operator — not a hand-trowel product, so it is uneconomical for small isolated patches
- Rebound and overspray demand containment and add to material consumption on complex geometry
- Substrate must be correctly prepared, saturated surface-dry and, where specified, primed and the reinforcement treated before spraying
- Dry-process spraying generates dust, so respiratory protection and site controls are essential
- As a cementitious system it needs proper curing to develop strength and resist early cracking
- It reinstates section and protects steel but does not by itself correct the original corrosion driver if chlorides remain in the surrounding concrete
Selection & best practice
Break out all defective concrete to sound material and cut back to expose the full circumference of corroded steel. Clean the reinforcement to bright metal and apply a Fosroc zinc-rich primer such as Nitoprime Zincrich where called for. Bring the substrate to a saturated surface-dry condition and prime as specified before spraying. Feed the dry powder through the gun and hydrate at the nozzle, building the section up in controlled passes within the 10 mm minimum and the 150 mm vertical / 90 mm overhead single-pass limits; greater depths are reached by successive layers once each has stiffened. Keep substrate and ambient temperatures between 3 C (and rising) and about 35 C. Finish by float or trowel to the required profile and cure thoroughly — with an approved curing membrane such as Concure or by other suitable means — to protect the fresh mortar from rapid drying.
Specifications
| Product type | Polymer-modified, fibre-reinforced dry-spray cementitious repair mortar |
| EN 1504-3 classification | Class R4 (structural repair) |
| Compressive strength (1 day) | approx. 20 MPa |
| Compressive strength (7 days) | approx. 45 MPa |
| Compressive strength (28 days) | approx. 60 MPa |
| Application thickness | 10 mm min; up to 150 mm vertical / 90 mm overhead per single application |
| Application temperature | 3 C (and rising) to approx. 35 C |
| Pack size | 25 kg bags |
| Yield | approx. 12.5 litres per 25 kg bag |
Industry use cases
Bridges & Infrastructure
Reinstating large spalled zones on piers, abutments and soffits at high output, restoring section and cover on ageing highway structures.
Marine & Coastal
Repairing chloride-attacked sea walls, jetties and splash-zone concrete with a dense, low-permeability layer that helps re-protect the reinforcement.
Tunnels & Culverts
Spraying continuous overlays to linings and invert walls where continuous large-area coverage is faster and more uniform than hand repair.
Industrial Structures
Resurfacing cooling towers, chimneys and tall RCC elements where dry-spray reaches awkward, high-access faces efficiently.
Water-Retaining RCC
Reprofiling large areas of tanks and channels where low permeability and Class R4 strength are needed across broad surfaces.
Frequently asked questions
Is Renderoc DS a hand-applied mortar or a sprayed product?
How thick can it be applied in one pass?
What strength does it reach?
Does it protect the reinforcement from further corrosion?
In what pack size is it supplied and what is the yield?
What surface preparation does it need?
When should I choose Renderoc DS over other Fosroc repair mortars?
How we position Fosroc Renderoc DS
Renderoc DS sits at the high-output end of the Fosroc concrete-repair range and is best paired with the supporting products in that system: Nitoprime Zincrich for reinforcement priming, and a curing membrane from the Concure range to protect the fresh mortar. Where the repair is small, isolated, or spray plant cannot be mobilised, the hand-applied and equally structural Fosroc Renderoc S (Class R4) is the natural alternative, while the lightweight Renderoc HB range suits vertical and overhead patch repairs without formwork. For free-flowing reinstatement into congested formwork, Renderoc RG micro-concrete is the complementary choice. Across our other brands, Space Arc can also advise on Dr. Fixit and MC-Bauchemie repair systems where a project specification calls for them.
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