Fosroc Renderoc HB45
A high-strength, fibre-reinforced reinstatement mortar that rebuilds columns, beams and soffits in thick single passes without formwork, certified to BS EN 1504-3 Class R4.
What is it?
A one-component, polymer-modified, fibre-reinforced cementitious repair mortar supplied as a pre-bagged dry blend that needs only clean water on site. It carries a BS EN 1504-3 Class R4 classification and reaches 50 MPa at 28 days.
Where is it used?
Structural patch repair and reprofiling of reinforced concrete columns, beams, soffits, bridge and car-park elements where higher strength and low permeability matter.
Why use it?
It builds up to 80 mm on verticals and 70 mm overhead in a single application without formwork, cutting the number of layers and, in many cases, removing the need for shuttering altogether.
How is it applied?
Prepare and prime the substrate, prime exposed steel with Nitoprime Zincrich Plus, mix one 25 kg bag with roughly 3.25 litres of water, then hand-trowel or wet-spray onto a Renderoc Primer coat and cure with Nitobond AR.
About Fosroc Renderoc HB45
Renderoc HB45 is Fosroc’s workhorse high-build repair mortar for situations where a repair has to be strong, thick and vertical or overhead at the same time. It arrives as a ready-blended powder of Portland cement, graded aggregates, lightweight fillers, fibres and chemical additives; site crews add only clean water. The formulation is deliberately low in water demand, which is what lets it develop a 28-day compressive strength of 50 MPa while still troweling and spraying cleanly. Because it is one component and factory-bagged, the batch-to-batch variation that plagues site-mixed sand-cement renders is taken out of the equation, and there are no chloride admixtures to threaten the reinforcement it is meant to protect.
For engineers and applicators in Delhi NCR and across India, the appeal is practical. Corroded columns, spalled beam sof
fits, delaminated slab undersides and carbonation-damaged facades can be rebuilt in far fewer passes than a standard mortar allows, and often with no shuttering at all. The mortar’s polymer modification gives it very low permeability to water, carbon dioxide and chlorides, so the completed repair does more than fill a void, it re-establishes the cover concrete’s protective role. Space Arc Engineering supplies Renderoc HB45 as an authorised Fosroc distributor and applicator, with site guidance on preparation, priming and curing so the datasheet numbers actually translate into durable repairs on the structure.
The technical insight
The reason HB45 can be laid thick on a vertical or overhead face without slumping comes down to its rheology and its shrinkage-compensation system working together. The graded aggregates, lightweight fillers and fibres give the wet mortar enough internal cohesion and green strength to stay in place at 70 to 80 mm, while the low water:powder ratio (nominally 0.13) keeps the paste dense so strength gain is not sacrificed for buildability. As it cures, the built-in shrinkage-compensation chemistry offsets the drying shrinkage that would otherwise pull a thick section away from the parent concrete, holding drying shrinkage below 300 microstrain at 7 days and preserving the bond. That bond is not left to chance either: exposed steel is first primed with Nitoprime Zincrich Plus for cathodic protection, and the concrete face receives a Renderoc Primer scrub coat, so the mortar keys into a saturated, prepared substrate. The result is a repair that behaves monolithically with the structure, resists the ingress that caused the original corrosion, and achieves a pull-off bond above 2.0 MPa.
Where it is used
- Reinstating spalled or carbonation-damaged reinforced concrete columns and beams
- Repairing slab soffits and beam soffits where a medium wet density is needed for overhead work
- Rebuilding cover concrete over corroded reinforcement in bridges and flyover elements
- Facade and structural frame repairs on buildings where low permeability is specified
- Car-park deck soffit, downstand and column repairs
- Wet-spray reinstatement of large repair areas where hand-trowelling would be uneconomic
- Deep pocket filling around exposed reinforcement in a single pass where the configuration allows
- Repairs demanding higher compressive strength and durability than a general-purpose mortar offers
Key advantages
- High-build capability up to 80 mm vertical and 70 mm overhead in one application, so fewer layers are needed
- Frequently removes the need for formwork, saving time and shuttering cost on columns and soffits
- Reaches R4-grade strength (50 MPa at 28 days, 20 MPa at 1 day) for structural repairs
- Polymer modification gives very low permeability to water, carbon dioxide and chlorides
- Shrinkage-compensation system holds drying shrinkage below 300 microstrain at 7 days for dimensional stability
- One-component, pre-bagged formulation eliminates site-batching variation
- Contains no chloride admixtures, protecting embedded steel
- Can be placed by hand trowel or wet spray, giving flexibility across job sizes
Limitations & considerations
- Not suitable for surfaces subjected to traffic or wheel loads; Renderoc S should be specified instead
- Minimum applied thickness is 10 mm, so it is not a skim or fairing coat; use a Renderoc fairing product for thin work
- Should not be used below 3 C and falling, and needs winter-working precautions in cold conditions
- Where compatibility with lower-strength parent concrete is required, the lower-modulus Renderoc HB30 is the correct choice
- Must not be exposed to moving water during application, and heavy rain before final set can cause surface scour
- Part-bag mixing and free-fall mixers are prohibited, which demands disciplined site batching
Selection & best practice
Success with HB45 is decided at the preparation stage. Break out to a square-edged perimeter at least 10 mm deep, avoiding feather edges, and clean the concrete back to a sound, laitance-free surface. Expose corroded steel fully, clean it to bright metal front and back, then apply a full coat of Nitoprime Zincrich Plus and let it dry. Bring the concrete to a saturated-surface-dry condition and scrub in Renderoc Primer (3 parts A to 1 part B by volume) immediately before placing the mortar. Mix one full 25 kg bag into 3.0 to 3.5 litres of clean water (typically 3.25) in a forced-action mixer for 3 to 5 minutes, always adding powder to water and never mixing part bags. Trowel or spray onto the primed, still-tacky surface, compacting well around reinforcement; if it sags, remove it and reapply at reduced thickness. Cure immediately with a continuous film of Nitobond AR, curing in roughly 0.5 m2 sections as you go, and use polythene or damp hessian backup in fast-drying Indian summer conditions. In cold weather use warm mixing water up to 30 C; in heat above 35 C store in shade and mix with cool water.
Specifications
| Standard / Classification | BS EN 1504-3 Class R4 (repair methods 3.1, 3.3, 4.4, 7.1, 7.2) |
| Compressive strength (EN 12190) | 20 MPa at 1 day, 50 MPa at 28 days |
| Flexural strength (BS 6319) | 7.5 MPa at 28 days |
| Tensile strength (BS 6319) | 4.0 MPa at 28 days |
| Bond strength, pull-off (EN 1542) | 2.1 MPa |
| Build thickness (single pass) | 10 mm minimum; up to 70 mm overhead; up to 80 mm vertical |
| Fresh wet density | Nominally 2000 kg/m3 |
| Water content per bag | 3.0 to 3.5 litres (typically 3.25) per 25 kg bag |
| Pack size / yield | 25 kg bag; approx. 14 litres, about 1.4 m2 at 10 mm |
Industry use cases
Bridges & Infrastructure
Reinstating spalled beam and slab soffits and corroded piers on highway and flyover structures, meeting Highways Works repair-mortar clauses for structural durability.
Commercial & High-Rise Buildings
Rebuilding carbonation-damaged columns and beam soffits on RCC frames where low permeability and R4 strength are specified to restore design life.
Car Parks & Podiums
Repairing soffits, downstands and columns overhead without formwork, keeping headroom clear and turnaround times short.
Industrial Structures
Restoring cover to corroded reinforcement on plant frames, silos and support structures in aggressive, chloride-laden environments.
Water & Marine-Adjacent Assets
Reprofiling reinforced concrete exposed to chloride ingress, using the mortar’s impermeability to acid gases and chlorides to slow re-corrosion.
Frequently asked questions
What is the difference between Renderoc HB45 and HB30?
How thick can Renderoc HB45 be applied in one pass?
Does it need a bonding primer?
How much water and how big is a bag?
What coverage should I expect per bag?
Can it be used on trafficked floors or slabs?
How we position Fosroc Renderoc HB45
Renderoc HB45 sits at the high-strength end of Fosroc’s hand- and spray-applied repair range, above the R3 Renderoc HB30 and the general-purpose Renderoc GP. Specify HB45 when the parent concrete is strong and the repair is structural; step down to HB30 when compatibility with lower-strength concrete matters. It works as a system with Nitoprime Zincrich Plus (steel primer), Renderoc Primer (bonding coat), Nitobond AR (curing membrane) and the Dekguard range of anti-carbonation coatings for whole-structure protection; for trafficked or flowable-repair situations, pair the enquiry with Renderoc S or a Renderoc RG grout instead. Space Arc also stocks equivalent repair systems from Sika (Sika MonoTop), Dr. Fixit and MC-Bauchemie, so we can match the specification, budget and site conditions rather than push a single brand.
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