Fosroc Renderoc DSR
A rapid-setting, low-rebound, polymer-modified dry-spray (gunite-process) repair mortar for large-area concrete rehabilitation on bridges, tunnels, marine and infrastructure works — BS EN 1504-3 Class R4.
What is it?
A single-component, polymer-modified and fibre-reinforced, rapid-setting cementitious dry spray repair mortar based on Portland cement, graded aggregates, silica fume, chemical additives and polymer modifiers, conforming to BS EN 1504-3 Class R4 (the highest structural repair class).
Where is it used?
Large-area and isolated structural concrete repairs on bridges, tunnels, culverts, marine structures, dams, water-retaining structures, beams, columns, soffits and panels — typically where cover to reinforcement has spalled or where wide-scale overlay is needed to increase cover.
Why use it?
Its dry-spray (gunte/shotcrete-style) delivery covers large areas fast with low rebound and minimal wastage, builds up to 200mm vertically and 140mm overhead in a single layer, gains strength rapidly (7-10 MPa at 3 hours, 15 MPa at 1 day) and can be applied from 3°C, making it ideal for night possessions and fast-turnaround infrastructure works.
How is it applied?
Supplied as a ready-to-use dry powder, fed straight from the bag into a dry-spray machine hopper; water is added at the nozzle by the nozzleman onto a pre-soaked, prepared substrate, then finished as required and cured immediately with a Fosroc curing membrane or wet hessian/polythene.
About Fosroc Renderoc DSR
Fosroc Renderoc DSR is a high-performance concrete repair mortar engineered specifically for the dry-spray (gunite) application process rather than hand-applied patching. It belongs to Fosroc’s well-established Renderoc family of repair mortars and is positioned as the dry-spray, rapid-setting option for large-volume concrete reinstatement. The “DSR” denotes Dry Spray, Rapid — a formulation tuned for projects where surface area is large, downtime must be minimal, and a contractor needs to reinstate substantial cover thickness quickly.
The material is a ready-to-use blend of dry powders based on Portland cements, graded aggregates, silica fume, chemical additives, polymer modifiers and reinforcing fibres. The silica fume densifies the matrix and lowers permeability, the polymer modifiers improve bond and handling, and the fibres reduce plastic and drying shrinkage cracking. Crucially, the blend is designed for a low water demand: because water is metered in only at the spray nozzle, the in-place water/cement ratio stays low, which drives both rapid early strength and long-term durability.
For Indian contractors, consultants and infrastructure owners, the appeal of Renderoc DSR is its combination of throughput and structural credentials. It conforms to BS EN 1504-3 Class R4 — the top structural repair classification — and also satisfies the relevant UK Highways spray-applied concrete repair clauses, giving specifiers a recognised performance benchmark when no equivalent IS code-rated dry-spray product is named in a tender. It is most relevant to bridge rehabilitation, tunnel linings, culverts, marine and coastal structures, water-retaining structures and any project involving spalled or carbonated/chloride-attacked concrete over wide areas.
Space Arc Engineering, as an authorised Fosroc distributor and applicator across Delhi NCR and Pan-India, supplies Renderoc DSR alongside the full associated repair system (reinforcement primer, bonding aid and curing membranes) and can advise on substrate preparation, dry-spray rig selection and the wider BS EN 1504 repair strategy for a given structure.
The technical insight
The defining technical feature of Renderoc DSR is the dry-spray delivery: dry powder and compressed air are conveyed through a hose and hydrated only at the nozzle. This single-pass build of up to 200mm vertical / 140mm overhead is roughly a third more than typical 150mm dry-spray products, which directly reduces the number of layers (and therefore time) on deep repairs. The trade-off is that placement quality depends heavily on nozzleman skill — too little water raises rebound and dust, too much causes slump and sag. Strength development is the second key insight: tested results give 7-10 MPa at 3 hours, 15 MPa at 1 day, 40 MPa at 7 days and 50 MPa at 28 days, comfortably exceeding the Class R4 requirement of greater than 45 MPa, while drying shrinkage stays below 300 microstrain at 7 days. The low capillary absorption (0.1 kg/m²·h^-0.5 against a less-than-0.5 limit) and dense silica-fume matrix give it strong resistance to carbonation and chloride ingress, which is why it suits aggressive marine and de-icing-salt environments. Because it is rapid-setting (initial set under 10 minutes at 20°C), batching discipline and immediate curing are non-negotiable — there is little working time, and uncured surfaces are vulnerable to scour from rain or moving water.
Where it is used
- Spray-applied repair of spalled and delaminated concrete on highway and railway bridges, piers and abutments
- Tunnel lining repair and re-profiling, including invert and soffit reinstatement
- Repair and lining of culverts, channels and other buried/water-conveyance structures
- Marine and coastal structure rehabilitation — jetties, sea walls, splash-zone and tidal-zone elements
- Increasing cover to reinforcement via wide-scale overlay where existing cover is inadequate
- Large-area reinstatement of beams, columns, soffits, retaining walls and panels in industrial and commercial structures
- Fast-turnaround possession works where structures must be returned to service quickly (rail/road)
- Rehabilitation of carbonated or chloride-contaminated concrete as part of a BS EN 1504 repair strategy
Key advantages
- BS EN 1504-3 Class R4 — the highest structural repair classification; also meets UK Highways spray-applied repair clauses (5703/5704/5717/1704.5)
- High single-pass build: up to 200mm vertically and 140mm overhead, reducing layers and programme time on deep repairs
- Rapid early strength (7-10 MPa at 3 hrs, 15 MPa at 1 day) ideal for night possessions and quick return to service
- Low rebound and low dust compared with conventional dry-spray mortars, cutting material wastage and clean-up
- Dense, low-permeability silica-fume matrix gives high resistance to carbonation, chloride ingress and freeze-thaw (verified pull-off 2.7 MPa, freeze-thaw 2.3 MPa)
- Can be applied from 3°C and rising, extending the working window in cooler conditions
- Single-component, ready-to-use dry powder — no on-site blending of separate components, simple logistics
- Fibre reinforcement plus low drying shrinkage (<300 microstrain at 7 days) reduces cracking risk
- Non-combustible (Reaction to fire Class A1)
Limitations & considerations
- Requires specialised dry-spray (gunite/shotcrete) equipment and a skilled nozzleman — not a hand-applied patch repair; placement quality depends on operator control of water at the nozzle
- Rapid set (initial set under 10 minutes at 20°C) leaves very little working time; immediate curing is essential
- Must not be applied when temperature is 3°C and falling; needs frost protection in cold conditions
- Should not be exposed to moving water during application, and heavy rainfall before final set can cause surface scour
- Performance benchmarks are BS EN / UK Highways based; not certified to a specific Indian (IS) code, so specifiers must accept EN equivalence
- Generates dust and rebound if water dosing is incorrect — dust-control and PPE measures are required (refer HSE CIS36 / equivalent)
- Requires a full system (reinforcement primer, bonding aid, curing membrane) for durable results, not the mortar alone
- 12-month shelf life and sensitivity to high heat/humidity storage demand careful stock management in Indian conditions
Selection & best practice
Treat Renderoc DSR as a system, not a single product. Prepare the substrate thoroughly — remove all unsound, contaminated or laitance-bearing concrete, cut back the repair perimeter at least 10mm to allow the patch to be ‘toed-in’, and expose and clean corroded steel to a bright condition (abrasive blast or hydrodemolition). Prime exposed reinforcement with Nitoprime Zincrich Plus and allow it to dry, then thoroughly pre-soak the concrete substrate to a saturated surface-dry condition before spraying. Use a competent nozzleman to control water addition at the nozzle: aim for a mix that builds without slumping while keeping rebound and dust low. For depths beyond a single pass, jet the hardened first layer with maximum water/air to remove laitance, leave no standing water, and use Nitobond AR as the curing/bond membrane between layers. Cure immediately after finishing using Concure WB, Fosroc Cure B, wet hessian or polythene — and protect from freezing, heavy rain and moving water until set. Always work to the latest Fosroc datasheet and, for critical structures, involve Fosroc/Space Arc technical services in the repair specification.
Specifications
| Product type | Polymer-modified, fibre-reinforced, rapid-setting, low-rebound dry spray repair mortar (single component) |
| Base composition | Portland cements, graded aggregates, silica fume, chemical additives, polymer modifiers |
| Standard compliance | BS EN 1504-3:2006 Class R4 (structural repair); UK Highways clauses 5703/5704/5717 & 1704.5 |
| Compressive strength (EN 12190) | 7-10 MPa @ 3 hrs; 15 MPa @ 1 day; 40 MPa @ 7 days; 50 MPa @ 28 days (R4 requirement >45 MPa) |
| Bond / pull-off strength (EN 1542) | 2.7 MPa (requirement >2.0 MPa) |
| Freeze-thaw with de-icing salt (EN 13687-1) | 2.3 MPa (requirement >2.0 MPa) |
| Elastic modulus (EN 13412) | 31.7 GPa @ 28 days (requirement >20 GPa) |
| Chloride ion content (EN 1015-17) | 0.01% (requirement <0.05%) |
| Capillary absorption (EN 13057) | 0.1 kg/m²·h^-0.5 (requirement <0.5) |
| Drying shrinkage (ASTM C596) | <300 microstrain @ 7 days (wet) |
| Initial setting time | <10 minutes @ 20°C |
| Fresh wet density | Nominally 2200 kg/m³ |
| Reaction to fire | Class A1 (non-combustible) |
| Build thickness | Min 10mm; up to 140mm overhead and up to 200mm vertical per layer (multiple layers for greater depth) |
| Application temperature | 3°C and rising minimum; store in shade above 35°C ambient |
| Coverage / yield | Approx. 12.5 litres per 25 kg bag (approx. 80 bags/m³, theoretical) |
| Pack sizes | 25 kg bags, 500 kg bags, 1000 kg sacks |
| Shelf life / storage | 12 months from manufacture in unopened bags, kept cool and dry |
| Associated products | Nitoprime Zincrich Plus (rebar primer); Nitobond AR (bond/cure for multi-layer); Concure WB / Fosroc Cure B (curing) |
Industry use cases
Bridges & highway structures
Spray reinstatement of spalled cover concrete on piers, abutments and soffits during night possessions, where 15 MPa at 1 day allows fast return to traffic and the R4 / UK Highways compliance satisfies infrastructure specifiers.
Tunnels & metro
Re-profiling and large-area lining repair where high single-pass build (up to 200mm vertical) minimises passes and the low-permeability matrix resists ingress in damp underground environments.
Marine & coastal
Rehabilitation of jetties, sea walls and splash-zone elements attacked by chlorides, leveraging low chloride-ion content, verified freeze-thaw/salt performance and low capillary absorption.
Water & wastewater / dams
Reinstatement of culverts, channels, spillways and water-retaining concrete over wide areas, using the dense silica-fume mortar to restore section and durability.
Industrial & commercial buildings
Large-area repair of carbonated or distressed beams, columns and panels, and overlay to increase cover to reinforcement as part of a planned BS EN 1504 rehabilitation.
Frequently asked questions
Is Fosroc Renderoc DSR a hand-applied repair mortar?
What strength does Renderoc DSR achieve and how fast?
How thick can Renderoc DSR be applied in one pass?
Does it meet Indian (IS) standards?
What primer and curing products are needed with it?
What pack sizes and shelf life does Renderoc DSR have?
How we position Fosroc Renderoc DSR
Within Fosroc’s own range, Renderoc DSR sits as the rapid-setting dry-spray option for large-volume structural repair, alongside the standard dry-spray grade Renderoc DS; for hand-applied work, Fosroc Renderoc HB (high-build) and Renderoc GP (general purpose) are the natural companions, while flowable reinstatement uses Renderoc RG and micro-concrete grades. A complete DSR repair also draws on Nitoprime Zincrich Plus (rebar primer), Nitobond AR (bonding/curing aid) and Concure WB / Fosroc Cure B (curing) — Space Arc supplies these as a single system. Against competitors, the most direct alternative for sprayed/repair mortars in India is Sika (Sika MonoTop and SikaCrete gunite/shotcrete systems), which offers comparable EN 1504-3 R4 performance and a strong technical-service footprint. MBS (MYK Arment / MYK Schomburg) and STP (Shalimar / STP) provide repair-mortar ranges that are competitive on price and availability for less specialised work, while Dr. Fixit (Pidilite) is strong in the waterproofing-led repair and general-contractor segment but is less commonly specified for high-throughput dry-spray structural rehabilitation. Renderoc DSR’s differentiators are its high single-pass build (200mm vertical), low rebound, rapid early strength and recognised UK Highways compliance — making it most compelling on infrastructure, marine and tunnel projects where programme speed and durability outweigh first cost. For routine small patch repairs or budget-driven jobs, a hand-applied mortar from Fosroc or a competitor may be the more economical choice.
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