Fosroc Renderoc DS40
A low-rebound, fibre-reinforced dry-spray repair mortar for large-volume structural reinstatement, conforming to BS EN 1504-3 Class R4.
What is it?
A single-component, polymer-modified, fibre-reinforced cementitious mortar supplied as a dry powder blend and applied by the dry-spray (gunite) process to rebuild damaged concrete.
Where is it used?
Large-area and hard-to-reach repairs on bridges, tunnels, culverts, marine structures, retaining walls, silos and building frames where hand-applied mortars are impractical.
Why use it?
It reinstates concrete to a true structural R4 grade (60 MPa at 28 days) at high productivity, with low rebound and excellent bond, making it economical over big surfaces.
How is it applied?
Emptied dry into the spray-machine hopper and gunned onto a saturated, prepared substrate, with water metered by the nozzleman at the nozzle rather than pre-batched.
About Fosroc Renderoc DS40
Renderoc DS40 sits in Fosroc’s Renderoc DS dry-spray family, the answer to a problem every rehabilitation contractor knows well: when the area to be repaired runs into tens of square metres, hand-packing mortar trowel by trowel is slow, inconsistent and expensive. Renderoc DS40 is instead pneumatically sprayed. It arrives as a ready-blended dry powder based on Portland cement, graded aggregates, silica fume, polymer modifiers and reinforcing fibres, and it is fed straight into a dry-spray machine where the nozzleman adds only the water the mix needs at the point of placement. The result is a dense, well-compacted mortar built up in a fraction of the time a manual repair would take, with a hardened strength that genuinely matches or exceeds the parent concrete.
For Indian projects, that combination is what makes it useful on real infrastructure: metro and rail tunnels, dam faces and spillways, sea-facing jetties and culverts, deep beams, columns and the underside of bridge decks. It carries a Class R4 rating under BS EN 1504-3, the highest structural repair class, and complies with Highways England specification clauses for spray-applied repair. It is also suitable for use alongside cathodic protection systems, which matters on chloride-contaminated coastal and marine structures. Space Arc supplies Renderoc DS40 and, as an authorised applicator, can put trained nozzle crews on site across Delhi NCR and Pan-India so the sprayed finish actually delivers the lab-tested numbers.
The technical insight
The performance of a dry-spray repair is decided in the last few centimetres before the wall. In the dry process the powder travels through the hose dry and water is introduced only at the nozzle, so the mix hits the substrate at high velocity with a low, tightly controlled water content. That low water-cement ratio is the whole point: less mixing water means fewer capillary voids, higher strength gain and better long-term durability than a wetter, hand-applied patch of the same mortar could reach. The silica fume packs the microstructure denser still, which is why the cured mortar shows low capillary absorption (0.41 kg/m2.h-0.5) and high resistance to carbon dioxide and chloride ingress, protecting the reinforcement it covers. The high-velocity impact also compacts the material against the concrete and around exposed bars, giving the pull-off bond of 2.7 MPa that lets the repair behave monolithically with the parent structure. The trade-off inherent to the method is rebound and dust when the nozzleman runs the mix too dry, or slump and sag when it is too wet, so getting the water right at the nozzle is what separates a sound R4 repair from a weak one.
Where it is used
- Large-area concrete reinstatement on bridge soffits, piers and deck undersides
- Tunnel and metro lining repair, and culvert refurbishment
- Dam faces, spillways and other water-retaining civil structures
- Marine and coastal repairs on jetties, sea walls and chloride-attacked concrete
- Repairs to beams, columns and panels in building and industrial frames
- Wide-scale overlay to increase cover to reinforcement over deteriorated surfaces
- Silo, bunker and retaining-wall repair where access favours spraying over hand application
- Structural repairs run in conjunction with impressed-current cathodic protection systems
Key advantages
- True structural R4 grade under BS EN 1504-3, reaching 60 MPa compressive strength at 28 days
- Low rebound and high placement rates make large repairs fast and material-efficient
- Excellent bond to prepared concrete (2.7 MPa pull-off) for monolithic, load-bearing repair
- Builds up to 150 mm vertically and 90 mm overhead in a single pass, cutting the number of layers
- Silica-fume density gives low chloride diffusion and strong carbonation resistance for durable cover
- Fibre reinforcement and controlled alkali level reduce cracking and alkali-silica reaction risk
- Application possible down to 3 degrees C static or rising, extending the winter working window
- Non-combustible (Reaction to Fire Class A1) and compatible with cathodic protection systems
Limitations & considerations
- Needs specialist dry-spray plant, an air compressor and a trained nozzleman, so it is not a hand-patch product for small jobs
- Rebounded material must be removed and discarded, not re-sprayed, which adds to wastage on tight sites
- Must not be applied below 3 degrees C falling, and must be protected from moving water and heavy rain before final set
- Substrate must be thoroughly prepared and pre-soaked, and exposed steel primed, or bond and compaction suffer
- Single-pass build is capped at 150 mm vertical and 90 mm overhead; greater depths need jetted, multi-layer application
Selection & best practice
Success starts with preparation, not spraying. Cut back the perimeter of the repair to at least 10 mm so the patch can be toed-in flush, and remove all unsound concrete, laitance, oil and contamination. Fully expose corroded steel, clean it back to bright metal front and back, and prime it with Nitoprime Zincrich Plus, letting it dry before spraying. Soak the prepared concrete thoroughly and let surplus water drain so the surface is saturated but not standing wet. During application the nozzleman controls water at the nozzle: too little raises rebound and dust, too much causes slump, and any sagging means the material should be removed and re-sprayed thinner. For depths beyond a single pass, jet the hardened surface with maximum water and air pressure to remove laitance, apply Nitobond AR as the curing membrane between layers, and place the next pass with no free water on the face. Finish as-sprayed for a textured look, or strike off and close with a steel float, then cure immediately with Concure WB, Fosroc Cure B, wet hessian or polythene. Where the repair will be overcoated, use Nitobond AR in place of the standard curing compound.
Specifications
| Standard / repair class | BS EN 1504-3 Class R4 (structural) |
| Compressive strength (EN 12190) | 20 MPa @ 1 day, 45 MPa @ 7 days, 60 MPa @ 28 days |
| Bond strength (pull-off, EN 1542) | 2.7 MPa |
| Chloride ion content | 0.02% |
| Elastic modulus | 28.6 GPa at 28 days |
| Setting time | Initial set 3.5 hours; final set 5.0 hours |
| Single-pass build thickness | Min 10 mm; up to 150 mm vertical, 90 mm overhead |
| Fresh wet density | Nominally 2200 kg/m3 |
| Pack size / yield | 25 kg bag (also 500 & 1000 kg sacks); approx. 12.5 litres per 25 kg bag |
Industry use cases
Bridges & Highways
Reinstating spalled soffits, piers and deck undersides over large areas, meeting Highways specification clauses for spray-applied repair without hand-patching every square metre.
Tunnels & Metro
Repairing and re-profiling tunnel and culvert linings by gunite, where confined access and long stretches make the dry-spray process far quicker than manual mortars.
Dams & Water Structures
Rebuilding eroded dam faces, spillways and channels with a dense, low-permeability R4 mortar that resists continued water and chemical attack.
Marine & Coastal
Restoring chloride-damaged jetties, sea walls and splash-zone concrete, with low chloride diffusion and compatibility with cathodic protection to protect reinforcement.
Industrial & Buildings
Repairing silos, bunkers, retaining walls, beams and columns, or overlaying deteriorated faces to restore cover to the reinforcement across wide surfaces.
Frequently asked questions
What is the difference between Renderoc DS40 and hand-applied Renderoc mortars like HB40?
What compressive strength does Renderoc DS40 reach?
How thick can it be built in one application?
Do I need special equipment and a trained crew?
Can it be used on marine and chloride-contaminated structures?
What is the coverage and pack size?
How we position Fosroc Renderoc DS40
Renderoc DS40 is the large-volume, spray-applied member of Fosroc’s concrete repair range. For smaller isolated or overhead patch repairs done by hand, specify Renderoc HB40; for pourable or flowable reinstatement into formwork, look at the Renderoc micro-concrete grades. The system products belong with it too: prime exposed reinforcement with Nitoprime Zincrich Plus, use Nitobond AR as the inter-layer and pre-overcoat bonding aid, and cure with Concure WB or Fosroc Cure B. Where a project standardises on other brands in our portfolio, comparable dry-spray and repair mortars are available from Sika, MC-Bauchemie and Master Builders Solutions; our technical team can match the R4 specification across brands so you are not locked to a single supplier on tender.
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