Fosroc Renderoc HB2
Lightweight, polymer-modified high-build repair mortar engineered for vertical and overhead concrete reinstatement without formwork.
What is it?
A single-component, factory pre-blended, polymer-modified cementitious repair mortar with a lightweight aggregate formulation, designed for high-build patching where low permeability matters more than raw compressive strength.
Where is it used?
Vertical faces and overhead soffits of reinforced concrete: columns, beams, slab undersides, cantilevers and exposed-aggregate ceilings in bridges, buildings and infrastructure.
Why use it?
Its lightweight body resists sagging, so contractors can build up sound cover in thick sections by hand or wet spray while gaining excellent resistance to chloride ingress and carbon-dioxide diffusion.
How is it applied?
Applied by gloved hand or trowel onto a primed substrate, 10-40 mm per lift vertically and up to 25 mm overhead; mixed on site by adding clean water to the powder.
About Fosroc Renderoc HB2
Renderoc HB2 belongs to Fosroc’s Renderoc HB family of high-build concrete reinstatement mortars, sitting between the general-purpose HB25 and the higher-strength HB40. It arrives as a ready-to-use blend of Portland cements, graded sands, lightweight fillers and chemical additives; the applicator only adds clean water on site, which removes the batching variation that plagues hand-mixed mortars. The formulation deliberately keeps water demand low, so early strength gain and long-term durability are protected without the density that would make an overhead repair slump off the soffit.
What sets HB2 apart is where it is meant to work rather than how strong it is. Fosroc engineered it for the reinstatement of large areas of reinforced concrete where low permeability and high-build behaviour are the priorities and very high compressive strength is not the deciding factor. It is shrinkage compensated, contains no chloride admixtures, and offers excellent resistance to the acidic gases and waterborne chlorides that drive reinforcement corrosion. For engineers and consultants across Delhi NCR and the rest of India, that makes it a dependable patch-repair choice for corrosion-damaged, spalled or carbonated concrete on facades, bridge elements and building frames where cover has been lost.
The technical insight
The mortar’s usefulness comes from a balance of density and chemistry. Lightweight fillers lower the wet density enough that a freshly placed layer holds its shape against gravity on a vertical face or an inverted soffit, which is why thick lifts can be built without formwork and with fewer cold joints. At the same time, polymer modification tightens the cured matrix so it becomes a genuine barrier: capillary porosity is reduced and the cured mortar strongly retards the passage of water, carbon dioxide and chloride ions. That barrier is the real repair mechanism. Corrosion of embedded steel is an electrochemical process fed by moisture, oxygen and chlorides reaching the bar; by restoring alkaline, low-permeability cover and priming the exposed steel with a zinc-rich primer, HB2 re-establishes both the physical and chemical protection the original concrete has lost. Shrinkage compensation keeps the new material dimensionally stable as it cures, so the bond line to the parent concrete stays intact rather than debonding as a shrinking patch would.
Where it is used
- Reinstatement of spalled or corrosion-damaged cover on reinforced concrete columns and beams
- Overhead soffit and slab-underside repair on bridges, flyovers and parking structures
- Vertical wall and facade patch repair where cover concrete has carbonated
- Repair of exposed-aggregate ceilings and roof beams
- Localised patch repair around exposed and cleaned reinforcement steel
- Reprofiling of cantilevers, chajjas and projecting elements without formwork
- High-build reinstatement of large repair areas by hand or wet-spray application
- Restoration of low-permeability cover on marine and coastal concrete exposed to chlorides
Key advantages
- Lightweight body resists sagging, allowing genuine high-build in vertical and overhead work
- Frequently eliminates the need for formwork, speeding up thick-section repairs
- Extremely low permeability to water, carbon dioxide and chloride ions
- Shrinkage compensated for long-term dimensional stability and a durable bond
- Single-component, pre-bagged supply removes site-batching variation
- Contains no chloride admixtures, protecting embedded reinforcement
- Only clean water is added on site, keeping mixing simple and consistent
- Can be placed by hand, trowel or wet spray to suit the scale of the job
Limitations & considerations
- Not intended where high compressive strength is the governing requirement; use Renderoc HB40 or a higher-strength grade instead
- Lightweight formulation is not suited to floors, decks or areas subjected to traffic or abrasion
- Requires the correct primer regime (steel and substrate) to develop full bond and protection
- Minimum applied thickness is 10 mm; feather-edging should be avoided by saw-cutting square edges
- Being cement based, it must not be applied below 5 C and falling, and must be cured immediately
- Not designed for use as a broad-scale building render over large plain areas
Selection & best practice
Success with HB2 is mostly about preparation and priming. Saw-cut the repair perimeter at least 10 mm deep to give a square edge and avoid feather-edging, then break out all unsound concrete and expose corroded steel fully, cleaning it back to a bright condition, including behind the bars. Prime exposed reinforcement with Nitoprime Zincrich and let it dry, then soak the substrate, remove standing water and scrub in Nitobond HAR (or Nitobond EP where the repair will stay wet or immersed). Mix by adding one full bag to the pre-measured clean water in a forced-action mixer and blend to a homogeneous mortar; never use a free-fall mixer or mix part bags off-ratio. Place onto the tacky primer, compact well around the steel, and keep single lifts within the vertical and overhead limits, building up in scratch-keyed layers for deeper sections. If any sagging appears, take the material off and reapply thinner on a freshly primed surface. Finish once the mortar has stiffened, then cure immediately with Nitobond AR or Concure A99, protecting the repair from fast drying, heavy rain before set, and frost.
Specifications
| Product type | Single-component, polymer-modified, lightweight cementitious high-build repair mortar |
| Composition | Preblended Portland cements, graded sands, lightweight fillers and chemical additives; no chloride admixtures |
| Application thickness (vertical) | 10 mm to 40 mm per lift by hand/trowel |
| Application thickness (overhead) | Up to 25 mm per lift by hand/trowel |
| Minimum applied thickness | 10 mm |
| Mixing | Site addition of clean water only; powder added to water in a forced-action mixer |
| Reinforcement primer | Nitoprime Zincrich (zinc-rich) |
| Substrate primer / bonding aid | Nitobond HAR; Nitobond EP for permanently wet or immersed repairs |
| Curing | Nitobond AR or Concure A99 curing membrane |
Industry use cases
Bridges & Highways
Reinstating spalled cover on beam soffits, pier caps and deck undersides where chloride-driven corrosion has exposed steel and formwork is impractical overhead.
Commercial & Residential Buildings
Repairing carbonated, corrosion-damaged columns, beams and chajjas on facades and balconies, restoring low-permeability cover on vertical elements.
Marine & Coastal Structures
Patch-repairing concrete exposed to salt-laden air and splash zones, where the mortar’s chloride and CO2 resistance slows further reinforcement corrosion.
Water & Industrial Structures
Reprofiling walls and soffits of tanks, channels and plant structures where a dense, low-permeability barrier over the reinforcement is the priority.
Parking & Multi-storey Structures
Overhead and vertical repair of slab undersides and columns in car parks affected by de-icing salts and moisture ingress.
Frequently asked questions
Is Renderoc HB2 a structural, high-strength repair mortar?
How thick can I build HB2 in a single pass?
Do I need a primer, or can I apply it straight onto the concrete?
How is it mixed and can I use part bags?
Will it sag when applied overhead?
Can it be used on floors or trafficked areas?
How we position Fosroc Renderoc HB2
Renderoc HB2 sits in the middle of Fosroc’s Renderoc HB high-build family. Choose it when low permeability and easy vertical or overhead build are the priority; step up to Renderoc HB40 when the design calls for compatibility with higher-strength concrete, or to Renderoc S2 for shrinkage-compensated structural reinstatement in columns, beams and slabs. Every HB2 repair also depends on the supporting Fosroc system Space Arc stocks: Nitoprime Zincrich to protect exposed steel, Nitobond HAR or the epoxy Nitobond EP as the bonding primer, and Nitobond AR or Concure A99 for curing; a Dekguard anti-carbonation coating is worth specifying over the surrounding concrete to bring it up to the same protective standard. Where a client needs a free-flowing micro-concrete for deep, formed sections rather than a hand-applied patch, Renderoc RG or a Conbextra grout from the same Fosroc range is the better fit, and Space Arc can advise across all of these as an authorised Fosroc distributor and applicator.
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