Fosroc Renderoc HS
Chloride-free, high-strength cementitious repair mortar for sprayed and hand-applied structural concrete and masonry rehabilitation.
What is it?
A single-component, chloride-free cementitious repair mortar supplied as a ready-to-use dry powder blend that needs only clean water to mix. It is engineered for high-strength structural repair of concrete and masonry and can be applied by trowel or by wet/dry spray.
Where is it used?
Used to reinstate spalled and delaminated concrete on buildings, bridges, flyovers, water-retaining structures, industrial floors, marine and coastal works, RCC columns, beams, soffits and facades across India.
Why use it?
It restores section and cover concrete with high early and ultimate strength, contains no chlorides or metallic aggregate, and offers extremely low permeability for durable protection of embedded reinforcement against carbonation and chloride attack.
How is it applied?
The substrate is broken out, reinforcement de-rusted and primed, then the mortar is mixed with the specified clean water, applied by trowel up to 50mm per layer (greater thicknesses by spray), compacted, finished and cured.
About Fosroc Renderoc HS
Fosroc Renderoc HS is a high-strength concrete repair mortar that sits in the upper tier of Fosroc’s Renderoc repair range. It arrives on site as a factory-blended bag of dry powders, so the only thing a crew adds is clean, potable water in the dosage stated on the bag. That single-component format removes the site batching errors that plague gauged sand-cement plaster and is a big reason consultants specify it for load-bearing repairs rather than cosmetic patching.
Chemically, Renderoc HS is a cementitious mortar built on selected cements, graded aggregates and performance additives. Crucially, it carries no added chloride and no metallic aggregate, which matters when the repair surrounds steel reinforcement that has already corroded once. It hardens to a dense, low-permeability matrix that both rebuilds the lost concrete section and re-establishes the protective alkaline cover (the “covercrete”) around the rebar.
The product is dual-purpose in how it goes on. For routine patch and reinstatement work it is trowel-applied, building up to 50mm in a single pass by hand. For larger areas, soffits and overhead sections, the same material is spray-applied (wet or dry process), where greater build thicknesses become achievable and rebound losses stay low to save material. This flexibility lets a contractor run hand and machine application from one product on the same project, which simplifies procurement and training.
In India, Renderoc HS is a workhorse for concrete rehabilitation of ageing RCC infrastructure: car parks, bridges, water tanks, chimneys, jetties and industrial buildings exposed to carbonation, chlorides and aggressive environments. It is normally specified as part of a system alongside a Fosroc anti-corrosion primer (Nitoprime Zincrich) and, where needed, an epoxy bonding aid (Nitobond EP) and a curing or protective coating, rather than as a standalone product.
The technical insight
The defining engineering value of Renderoc HS is its combination of high compressive strength with extremely low permeability. Independent and supplier datasheets quote roughly 50 N/mm2 at 7 days rising to about 70 N/mm2 at 28 days for the base HS grade, which comfortably exceeds the strength of most host concrete it repairs and lets the patch carry structural load. The dense, low-permeability matrix is what gives the durability claim teeth: by resisting the ingress of water, oxygen and chloride ions, it slows the re-corrosion of reinforcement that often dooms cheaper repairs within a few years.
A practical detail engineers should respect is the fixed water demand and the “whole bag only” rule. The mortar is designed around one water-to-powder dosage; adding extra water to improve workability, or using part bags, raises permeability and shrinkage and undermines the very properties the product is bought for. For repairs where drying-shrinkage cracking is the dominant risk, or where larger pours and longer working times are needed, Fosroc offers the upgraded Renderoc HSXtra, which adds polymer modification and Dimensional Stability Technology and reaches higher compressive strengths (around 60 N/mm2 at 7 days and 80 N/mm2 at 28 days). Renderoc HS remains the proven, cost-effective choice where its strength and permeability envelope is sufficient.
Where it is used
- Reinstatement of spalled and delaminated structural concrete on beams, columns, slabs and soffits
- Vertical and overhead repairs to restore concrete cover (covercrete) over corroded reinforcement
- Repair of honeycombed and poorly compacted concrete and form-tie pockets
- Rehabilitation of bridges, flyovers, jetties, water tanks and other RCC infrastructure
- Sprayed (wet/dry gunite-type) repairs to large areas and difficult-access soffits
- Repairs to industrial floors, parking structures and facades exposed to carbonation and chlorides
- Marine and coastal concrete repair where dense, low-permeability mortar is required
Key advantages
- High strength gain – around 50 N/mm2 at 7 days and 70 N/mm2 at 28 days, suitable for load-bearing structural repair
- Chloride-free and contains no metallic aggregate, so it will not introduce corrosion-promoting salts around reinforcement
- Extremely low permeability gives strong resistance to water, carbonation and chloride attack and protects embedded steel
- Single-component, ready-to-use dry powder – only clean water is added, minimising site batching errors
- Versatile application – trowel-applied up to 50mm per layer by hand, or wet/dry spray-applied for greater thicknesses
- Low rebound when dry-spray applied, reducing material wastage and overall cost on large areas
- Part of a complete Fosroc repair system with compatible primers, bonding agents and protective coatings
Limitations & considerations
- Should not be applied when ambient temperature is below 5 C and falling without special precautions
- Part bags must not be used and no additional water should be added beyond the specified dosage, or performance is compromised
- Not formulated as a shrinkage-controlled mortar – for high shrinkage-crack risk or large pours, Renderoc HSXtra is preferred
- Should not be exposed to running water during application or before final set
- Requires correct surface preparation – breaking out to sound concrete, reinforcement de-rusting and priming – to perform as specified
- Proper wet/membrane curing is essential in hot, dry Indian conditions to develop strength and avoid plastic and drying cracking
- Cementitious mortar releases alkalis when wet; PPE (gloves, eye and respiratory protection) is required during handling
Selection & best practice
Specify Renderoc HS as part of a full repair system rather than as a stand-alone patch. Break out the defective concrete back to a sound, square-edged substrate, expose corroded reinforcement fully around its circumference, grit-blast or wire-brush the steel to bright metal and apply a Fosroc anti-corrosion primer such as Nitoprime Zincrich. Saturate the substrate to a saturated-surface-dry condition (or use a Nitobond EP epoxy bond coat where enhanced bond, a moisture barrier or extended working time is needed). Mix a complete bag with only the clean water dosage stated on the packaging – never part-mix and never over-water. Apply in compacted layers up to the recommended single-layer thickness, finish to the required profile, and cure thoroughly with a curing membrane or wet hessian, which is critical in Indian summer conditions. Overcoat with a protective anti-carbonation coating where long-term durability is required.
Specifications
| Product type | Single-component cementitious high-strength repair mortar |
| Form | Ready-to-use blend of dry powders (add clean water only) |
| Compressive strength | Approx. 50 N/mm2 at 7 days; 70 N/mm2 at 28 days |
| Chloride content | Chloride-free |
| Aggregate | Contains no metallic aggregate |
| Permeability | Extremely low permeability |
| Application method | Trowel (hand) or wet/dry spray |
| Maximum thickness, hand application | Up to 50 mm per layer in one application |
| Greater thickness | Achievable when spray-applied |
| Substrates | Structural concrete and masonry |
| Recommended bonding agent | Nitobond EP (where required) |
| Anti-corrosion primer | Nitoprime Zincrich |
| Pack size | 25 kg bag |
| Minimum application temperature | Not below 5 C and falling |
Industry use cases
Bridges & Flyovers
Reinstating spalled cover concrete on girders, piers and soffits of ageing RCC bridges and elevated corridors, where high strength and low permeability protect reinforcement from chloride and carbonation-driven corrosion.
Water-Retaining Structures
Repairing water tanks, sumps, STPs and reservoirs with a dense, chloride-free mortar that resists water ingress; combined with Nitobond EP where the substrate stays permanently damp.
Marine & Coastal Works
Restoring jetties, seawalls and coastal RCC exposed to chloride-laden environments, where the low-permeability matrix is essential to slow re-corrosion of steel.
Industrial & Commercial Buildings
Patch repair of columns, beams, parking decks and facades suffering carbonation-induced spalling, using spray application for fast coverage of large or overhead areas.
Infrastructure Rehabilitation
Structural repair of chimneys, cooling towers, silos and process structures where the repair mortar must carry load and match the durability of high-grade host concrete.
Frequently asked questions
What is Fosroc Renderoc HS used for?
What compressive strength does Renderoc HS achieve?
Can Renderoc HS be spray-applied?
How much water do I add to Renderoc HS?
What is the difference between Renderoc HS and Renderoc HSXtra?
Do I need a primer or bonding agent with Renderoc HS?
Is Renderoc HS suitable for the Indian climate?
How we position Fosroc Renderoc HS
Within Fosroc’s Renderoc concrete repair family, Renderoc HS is the high-strength structural workhorse, positioned above lighter hand-placed mortars like Renderoc S and the general-purpose Renderoc GP/HB grades, and just below the premium shrinkage-controlled Renderoc HSXtra. It is almost always specified as part of a system: pair it with Nitoprime Zincrich anti-corrosion primer on cleaned reinforcement, Nitobond EP epoxy bonding agent on damp or critical substrates, Renderoc RG free-flow grout or a microconcrete for confined high-volume repairs, and a Dekguard or anti-carbonation coating for long-term protection. Where drying-shrinkage cracking or large pour sizes govern, step up to Renderoc HSXtra. Against the wider market, credible alternatives in the same high-strength repair-mortar class include Sika MonoTop and SikaRep, MBS (MYK Schomburg) repair mortars, Dr. Fixit Krend / structural repair mortars from Pidilite, and STP (Shalimar) repair systems; specifiers usually choose between them on the basis of strength grade, shrinkage control, approved-applicator support and project-specific durability requirements. As an authorised Fosroc distributor and applicator serving Delhi NCR and Pan-India, Space Arc Engineering supplies Renderoc HS with the matching primers, bonding agents and protective coatings, plus method-statement and on-site application support.
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