Fosroc Renderoc HB45
Fibre-reinforced, polymer-modified high-build repair mortar (BS EN 1504-3 Class R4) for hand or wet-spray reinstatement of columns, beams and soffits.
What is it?
A single-component, fibre-reinforced, polymer-modified cementitious repair mortar of medium density, supplied as a pre-bagged dry blend that needs only clean site water. It conforms to BS EN 1504-3 Class R4 — the highest structural class for concrete reinstatement.
Where is it used?
Patch and full-depth repair of distressed reinforced concrete — columns, beams, soffits, ceilings, parapets, water tanks, bridge and flyover members, jetties, car parks, and any RC element suffering carbonation, chloride attack or rebar corrosion across Delhi NCR and Pan-India.
Why use it?
It builds thick in a single pass (up to 80 mm vertical, 70 mm overhead) without formwork, resists slump on overhead work thanks to its fibre reinforcement, and gives low permeability to water, chlorides and carbon dioxide so the repaired section is durably protected against re-corrosion.
How is it applied?
Saturate the prepared substrate, prime exposed steel and the concrete with the appropriate Fosroc primer, then trowel-apply (or wet-spray) HB45 mixed with roughly 3.5 litres of clean water per 25 kg bag, finishing in 10 mm minimum lifts and curing with Concure.
About Fosroc Renderoc HB45
Fosroc Renderoc HB45 is a high-performance concrete reinstatement mortar engineered for the structural repair of reinforced concrete that has lost section through carbonation, chloride ingress or reinforcement corrosion. It belongs to the well-established Renderoc family of hand- and spray-applied repair mortars and is positioned as the medium-density, high-build option in that range. The product arrives as a ready-to-use blend of Portland cement, graded aggregates, lightweight fillers, reinforcing fibres and chemical additives; the contractor simply adds clean water on site to produce a cohesive, thixotropic mortar. Because the formulation is polymer-modified and fibre-reinforced, it holds its shape on vertical and overhead faces and can be built up far thicker in a single application than a conventional sand-cement render, which is exactly what columns, beams and soffit repairs demand. For Indian projects — high-rise structures, water-retaining tanks, flyovers, industrial sheds and coastal RCC — HB45 sits in the sweet spot between lightweight overhead mortars and dense, heavy structural mortars, giving genuine structural strength without the dead weight or the slump problems that make overhead reinstatement so difficult. It is the kind of product a repair consultant specifies when the brief is a durable, code-compliant (BS EN 1504-3 Class R4) reinstatement that an applicator crew can place by trowel or wet-spray on site.
The technical insight
The defining feature of Renderoc HB45 is its medium fresh wet density combined with R4 structural strength. Most repair mortars force a trade-off: dense mortars are strong but heavy and prone to slumping or de-bonding when worked overhead, while lightweight mortars place easily overhead but rarely reach R4 strength. HB45 uses lightweight fillers and polymer modification to lower the wet density while reinforcing fibres provide green strength and crack control, so the mortar resists sag at lifts up to 70 mm overhead and 80 mm vertical yet still develops Class R4 compressive strength (>45 MPa), about 50 MPa at 28 days with roughly 20 MPa already at one day. Polymer modification is what drives the durability story — it cuts permeability to water, carbon dioxide and chloride ions, so the cured matrix shields the embedded steel from the very mechanisms (carbonation and chloride-induced corrosion) that caused the original damage. The mortar also contains no added chloride and incorporates shrinkage compensation for long-term dimensional stability, which matters when bonding fresh mortar to a rigid, aged concrete parent. In short, the chemistry is tuned so a single material can be placed thickly, overhead, by hand, and still behave as a structural, low-permeability protective layer.
Where it is used
- Reinstatement of carbonation- or chloride-damaged reinforced concrete columns and beams
- Soffit, ceiling and underside-of-slab repairs where overhead build and low slump are critical
- Repair of water-retaining structures such as tanks, sumps and treatment plant RCC
- Bridge, flyover and elevated-corridor pier, pier-cap and girder rehabilitation
- Marine and coastal structures — jetties, sea-facing facades and chloride-exposed RCC
- Multi-storey and basement car park decks, beams and columns
- Industrial plant structures, cooling towers and chimneys exposed to aggressive atmospheres
- Facade and parapet RCC restoration on commercial and residential high-rise buildings
Key advantages
- BS EN 1504-3 Class R4 structural performance with high early and 28-day compressive strength
- High-build in a single pass — up to 80 mm vertical and 70 mm overhead without formwork
- Fibre reinforcement resists slumping and controls plastic/shrinkage cracking on overhead work
- Medium density makes overhead and soffit placement far easier than dense structural mortars
- Low permeability to water, CO2 and chlorides protects reinstated steel against re-corrosion
- Single-component, pre-bagged — only clean water added on site, ensuring consistent site mixes
- Applies by trowel or wet-spray, suiting both small patch repairs and large-area mechanised work
- Contains no added chloride and offers shrinkage-compensated, dimensionally stable repairs
Limitations & considerations
- Minimum applied thickness of 10 mm — not suited to thin skim or feather-edge finishing (use a fairing coat such as Renderoc FC for that)
- Cementitious system; not a structural-strength solution for chemically aggressive (strong acid) exposure without additional protective coatings
- Requires correct surface preparation, rebar priming and bonding/curing regime — performance depends heavily on workmanship
- Wet-spray application needs suitable equipment and a trained crew
- Mixed mortar has a limited working time and must be placed promptly, especially in hot Indian site conditions
- Over-watering to ease placement reduces strength and increases shrinkage — water dosage must be controlled
- Not a free-flowing micro-concrete; for large-volume formed/poured pours a flowable repair micro-concrete is more appropriate
Selection & best practice
Treat HB45 as a system, not a standalone mortar. Break out unsound concrete to a square edge at least 10 mm deep, expose corroded reinforcement fully around its circumference, and grit/abrasive-blast the steel to bright metal. Apply a Fosroc zinc-rich or epoxy reinforcement primer (e.g. Nitoprime Zincrich / Galvafroid) and a cementitious bonding aid to the saturated-surface-dry substrate, then place HB45 wet-on-wet within the primer’s overcoat window. Pre-soak the substrate to a saturated-surface-dry (no standing water) state, mix each 25 kg bag with the recommended clean water (around 3.5 litres) using a forced-action or slow-speed drill mixer to a uniform consistency, and build in controlled lifts of 10 mm minimum up to the overhead/vertical maxima. Compact each layer well against the substrate to avoid voids, then cure immediately and thoroughly with Fosroc Concure curing membrane or wet hessian — critical in Delhi NCR summer heat to prevent plastic shrinkage cracking. Always confirm the live India Technical Data Sheet from Fosroc for the project-specific mix water, temperature limits and overcoat times before specifying.
Specifications
| Product type | Single-component, fibre-reinforced, polymer-modified cementitious repair mortar (medium density) |
| Standard / Classification | BS EN 1504-3, Class R4 (structural) |
| Repair methods (BS EN 1504-3) | 3.1, 3.3, 4.4, 7.1, 7.2 |
| Compressive strength | ~20 MPa @ 1 day; ~50 MPa @ 28 days (R4 = >45 MPa) |
| Flexural strength | 7.5 MPa @ 28 days |
| Tensile strength | 2.1 MPa @ 28 days |
| Minimum applied thickness | 10 mm |
| Maximum build (overhead) | Up to 70 mm in a single application |
| Maximum build (vertical) | Up to 80 mm in a single application |
| Mixing water | Approx. 3.5 litres clean water per 25 kg bag |
| Yield | Approx. 14 litres per 25 kg bag |
| Coverage | Approx. 1.4 m² at 10 mm thickness per 25 kg bag |
| Chloride content | Contains no added chloride; low chloride ion content |
| Application method | Hand (trowel) or wet-spray, without formwork |
| Curing | Cure with Fosroc Concure membrane or wet hessian |
| Pack size | 25 kg bag |
Industry use cases
High-rise & commercial buildings
Reinstating carbonation-damaged columns, beams and slab soffits in ageing towers and basements, where overhead build without formwork and a durable, low-permeability finish are essential.
Bridges, flyovers & infrastructure
Structural repair of pier caps, girders and soffits on elevated corridors and bridges exposed to traffic loading and atmospheric carbonation, restoring R4 section strength.
Water & wastewater structures
Repairing RCC in tanks, sumps and treatment-plant elements where low permeability resists water and chloride ingress and protects reinstated reinforcement.
Marine & coastal RCC
Rehabilitating jetties, sea-facing facades and chloride-attacked concrete in coastal projects, combining structural strength with a corrosion-protective, low-chloride matrix.
Industrial & power plants
Restoring beams, columns and overhead members in factories, cooling towers and chimneys subject to aggressive atmospheres, using wet-spray for fast large-area output.
Frequently asked questions
What type of product is Fosroc Renderoc HB45?
How thick can Renderoc HB45 be applied in one pass?
What is the coverage and yield per 25 kg bag?
How much water do I add per bag?
Does Renderoc HB45 need a primer and curing?
How is HB45 different from Renderoc HB and other Renderoc mortars?
How we position Fosroc Renderoc HB45
Within Space Arc Engineering’s Fosroc concrete repair and rehabilitation portfolio, Renderoc HB45 is the go-to high-build structural mortar for vertical and overhead reinstatement — columns, beams and soffits — where R4 strength is needed but dead weight and slump must be kept down. It is best specified as part of a system: pair it with a Fosroc rebar primer such as Nitoprime Zincrich or Galvafroid for steel protection, a cementitious bonding aid for adhesion, Renderoc FC for thin fairing/levelling coats, and Concure for curing; where a flowable, formed pour is required instead of a hand-applied patch, a Renderoc micro-concrete is the better fit, and Renderoc HB serves as a closely related high-build alternative in the same range. Compared with competing systems on the Indian market, HB45 sits against Sika MonoTop and SikaRep repair mortars, MBS (MYK) structural repair mortars, Dr. Fixit Krishna/Pidicrete repair mortars, and STP/Choksey repair products. Many of these offer comparable R3/R4 mortars, so the decision usually turns on the specified standard, local availability, applicator familiarity and the strength of the surrounding system (primers, bonding aids and protective coatings). For projects in Delhi NCR and Pan-India that already lean on Fosroc’s Renderoc, Nitoprime, Nitobond and Dekguard ecosystem, HB45 is a natural, fully compatible choice. As always, specification should be confirmed against the current Fosroc India Technical Data Sheet for project-specific values.
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