Fosroc Renderoc HB
Lightweight, polymer-modified high-build repair mortar engineered for vertical and overhead concrete repairs – applied up to 80 mm thick without formwork.
What is it?
A single-component, lightweight, polymer-modified cementitious repair mortar (Class R2 to EN 1504-3) that needs only the site addition of clean water. Its low fresh wet density lets it be built up in thick sections on vertical and overhead surfaces.
Where is it used?
Patch repair and reprofiling of spalled or carbonated reinforced concrete – columns, beams, soffits, facades, balconies, water tanks, bridges and industrial structures – across Delhi NCR and Pan-India repair and rehabilitation projects.
Why use it?
It allows extra-high build (up to 80 mm vertical / 50 mm overhead by hand, far more by wet spray) in fewer passes, reduces or eliminates formwork, is alkaline to re-passivate steel, and offers very low permeability to chlorides and carbon dioxide for durable repairs.
How is it applied?
Cut back and clean the substrate, prime exposed steel with Nitoprime Zincrich and the substrate with Nitobond HAR, then mix one 20 kg bag with 3.45-3.60 litres of water and apply by gloved hand, trowel or wet spray; cure immediately with Nitobond AR or Concure A99.
About Fosroc Renderoc HB
Fosroc Renderoc HB is a ready-to-use, pre-bagged concrete repair mortar that arrives as a blend of dry powders requiring only clean water on site. It is formulated from Portland cement, graded aggregates, lightweight fillers and chemical additives, and is polymer modified to give good handling while keeping water demand low. The “HB” denotes “high build” – the deliberately lightweight, low fresh wet density (around 1400 kg/m3) is what allows the mortar to be placed in thick sections on vertical faces and overhead soffits without slumping and, in most cases, without formwork. For construction-chemicals buyers in India, Renderoc HB sits in the workhorse middle of the Fosroc Renderoc repair range: heavier-duty than a thin skim, but lighter and more economical than the high-strength structural grades. It is the product a contractor reaches for when a column, beam or soffit has spalled, the cover concrete has carbonated or chloride-contaminated, and the reinforcement needs to be re-encased in a protective, alkaline mortar that bonds tightly and resists further carbon dioxide and chloride ingress. Because it is supplied pre-bagged, site-batching variation is removed – the only variable the applicator controls is the measured water addition, which keeps quality consistent from bag to bag across a large rehabilitation contract.
The technical insight
Renderoc HB is classified R2 to BS EN 1504-3 and is suited to repair methods 3.1, 3.3, 7.1 and 7.2, making it appropriate for non-structural and medium-strength reinstatement rather than load-bearing structural concrete (for which Fosroc’s R4 grades or micro-concretes are specified). The published properties, obtained at a water:powder ratio of 0.18 and 20 degrees C, give compressive strength of roughly 10 MPa at 1 day, 12 MPa at 3 days, 20 MPa at 7 days and 28 MPa at 28 days, with 28-day flexural strength of 3.9 MPa and tensile strength of 2.2 MPa. The mortar is shrinkage compensated and alkaline, so it both restores the concrete profile and re-establishes the passivating environment around embedded steel. Its hardened matrix is engineered for extremely low permeability to carbon dioxide and chlorides, which is the durability mechanism that slows re-corrosion – the original cause of most spalling. Two practical limits define correct use: the minimum applied thickness is 10 mm (it is not a feather-edge skim and not a broad-scale render), and because it is lightweight it must not be used in trafficked or abraded areas.
Where it is used
- Reinstatement of spalled, carbonated or chloride-affected reinforced concrete columns, beams and soffits
- Vertical and overhead patch repairs where formwork is impractical or uneconomical
- Reprofiling of concrete facades, parapets, chajjas and balcony edges in buildings
- Repair of water-retaining structures, RCC tanks and sumps where low permeability is required
- High-build reinstatement of bridge piers, abutments and sub-structures by hand or wet spray
- Large-area concrete rehabilitation applied efficiently by the wet-spray (gunite-style) process
- Encasement and protection of exposed reinforcement after grit-blasting and priming
Key advantages
- Lightweight formulation enables extra-high build, cutting the number of applications and saving time and cost
- Reduces or eliminates the need for formwork on vertical and overhead repairs
- Can be wet-sprayed for fast, very high-build placement with enhanced bond and density
- Extremely low permeability to carbon dioxide and chlorides for durable, corrosion-resisting repairs
- Alkaline and shrinkage-compensated – re-passivates steel and maintains long-term dimensional stability
- Pre-bagged single component; only measured clean water is added on site, removing batching variation
- Contains no chloride admixtures and offers excellent bond to prepared concrete substrates
- Long 36-month shelf life in sealed bags eases procurement and stock planning
Limitations & considerations
- Class R2 / medium strength – not a structural-grade repair; use higher Renderoc grades or micro-concrete for load-bearing reinstatement
- Minimum applied thickness is 10 mm; it cannot be feather-edged and is not a thin skim coat
- Not designed as a broad-scale building render or plaster
- Being lightweight, it must not be used in areas subjected to traffic or abrasion
- Should not be applied below 5 degrees C and falling, or exposed to moving water or heavy rain before final set
- Requires correct priming (Nitoprime Zincrich on steel, Nitobond HAR on substrate) and immediate curing to perform as specified
- Performs best within its design strength band – where below 30 MPa with high build is needed, the HB25 variant is preferred
Selection & best practice
Treat preparation and curing as non-negotiable. Saw-cut the repair perimeter to at least 10 mm to give a square edge (never feather-edge), break out all unsound concrete, and grit-blast exposed steel – paying attention to the back of the bars – removing all corrosion and chloride deposits. Prime reinforcement with one full, unbroken coat of Nitoprime Zincrich and prime the soaked, surface-dry substrate with Nitobond HAR, applying the mortar while the primer is still tacky (re-prime if it dries). Mix one full 20 kg bag with 3.45-3.60 litres of clean water in a forced-action mixer for 3-5 minutes, always adding powder to water, and respect the 3.6-litre maximum. Build vertical work up to 80 mm and overhead up to 50 mm per pass by hand; for thicker or large areas use the wet-spray process. Finish, then cure immediately and continuously with Nitobond AR or Concure A99 (and polythene in fast-drying conditions). In Indian summer conditions above 35 degrees C, shade the material and use cool mixing water; finally protect the wider structure with a Dekguard anti-carbonation coating to bring it to the same durability standard as the repair.
Specifications
| Product type | Lightweight, polymer-modified, single-component cementitious high-build repair mortar |
| Standard / classification | Class R2 to BS EN 1504-3 (repair methods 3.1, 3.3, 7.1, 7.2) |
| Compressive strength | approx. 10 MPa @ 1 day, 12 MPa @ 3 days, 20 MPa @ 7 days, 28 MPa @ 28 days |
| Flexural strength (28 days) | 3.9 MPa |
| Tensile strength (28 days) | 2.2 MPa |
| Fresh wet density | approx. 1400 kg/m3 (lightweight) |
| Setting time | Initial set approx. 2 hours; final set approx. 5 hours |
| Mixing water | 3.45 – 3.60 litres per 20 kg bag (water:powder ratio approx. 0.18; max 3.6 L/bag) |
| Yield | approx. 16.1 – 16.6 litres per 20 kg bag (about 1.6 m2 at 10 mm thickness) |
| Build thickness (hand/trowel) | Up to 80 mm vertical, up to 50 mm overhead per layer; minimum 10 mm |
| Build thickness (wet spray) | Substantially higher – typically 70-150 mm vertical and 70-100 mm overhead |
| Application temperature | 5 degrees C (rising/static) to 35 degrees C; use warm water in cold, cool water above 35 degrees C |
| Reinforcement primer | Nitoprime Zincrich |
| Substrate primer | Nitobond HAR (Nitobond EP where immersed/permanently wet) |
| Curing | Nitobond AR or Concure A99 applied immediately as a continuous film |
| Pack size | 20 kg bag (code FC306095-20KG) |
| Shelf life | 36 months in original, unopened bags in cool, dry conditions |
Industry use cases
Commercial & residential buildings
Reinstating spalled RCC columns, beams, soffits and chajjas in ageing high-rises and apartments where carbonation has reached the reinforcement, with overhead work done without formwork.
Water & wastewater
Repairing RCC water tanks, sumps and treatment structures, taking advantage of the mortar’s low permeability and chloride resistance (with Nitobond EP priming for permanently wet zones).
Bridges & infrastructure
High-build reinstatement of bridge piers, abutments and sub-structures, applied by wet spray for fast placement over large repair areas.
Industrial plants
Reprofiling damaged concrete frames, walls and structural elements in factories and warehouses where medium-strength, durable, non-trafficked repairs are required.
Facade & heritage rehabilitation
Restoring the profile of weathered concrete facades, parapets and balcony edges, then over-coating the wider structure with Dekguard anti-carbonation systems.
Frequently asked questions
Is Fosroc Renderoc HB a structural repair mortar?
How thick can Renderoc HB be applied in one pass?
What primers does Renderoc HB need?
How much water and how much area does a 20 kg bag give?
Does Renderoc HB need curing, and how is it cured?
Where can I buy Fosroc Renderoc HB in Delhi NCR or Pan-India?
How we position Fosroc Renderoc HB
Within the Fosroc system, Renderoc HB is the lightweight, high-build vertical-and-overhead repair grade. It pairs naturally with Nitoprime Zincrich (rebar primer), Nitobond HAR and Nitobond EP (substrate primers / bonding aids), Nitobond AR or Concure A99 (curing membranes) and the Dekguard anti-carbonation coatings that protect the surrounding structure. Choose between Renderoc grades by duty: where below-30 MPa strength with high build is acceptable, Renderoc HB25 is the economical option; for higher-strength patch repair stay with Renderoc HB; for flowable, formwork-placed structural reinstatement specify a micro-concrete such as Renderoc RG. Among competing brands available in India, credible alternatives include Sika MonoTop (e.g. MonoTop-412 / -612) and Sika’s polymer-modified repair mortars, MBS (MYK Schomburg) repair systems, Dr. Fixit Pidicrete / repair mortars from Pidilite for building-segment work, and STP (Sika-owned legacy) repair products. Renderoc HB’s particular strengths in this field are its genuinely lightweight high-build behaviour – allowing thick overhead placement without formwork – its EN 1504-3 R2 classification, and the completeness of the surrounding Fosroc repair-and-protect ecosystem, which makes it a dependable specification for medium-strength concrete rehabilitation in the Indian market.
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