Fosroc Renderoc Spray HBL
A lightweight, polymer-modified cementitious mortar built for wet-spray reinstatement of large vertical and overhead concrete surfaces, without formwork.
What is it?
A single-component, lightweight, polymer-modified cementitious repair mortar based on Portland cement, graded aggregates and lightweight fillers, engineered for wet-spray application onto reinforced concrete. It corresponds to the Renderoc HB family and meets Class R2 of BS EN 1504-3.
Where is it used?
Large-area rehabilitation of vertical and overhead RC surfaces: bridge and flyover soffits, beam and column faces, car-park decks, tunnel linings, water-retaining structures and building frames across Delhi NCR and pan-India.
Why use it?
Its low fresh wet density (around 1,400-1,430 kg/m3) lets applicators build far thicker layers overhead and vertically than trowel mortars, while wet spraying places material several times faster than hand application and yields a denser, better-bonded repair.
How is it applied?
Prepared substrate is primed, then the mortar is pumped through a wet-spray machine and gunned onto the surface in passes of 10 mm and above, cut back to profile with a steel float, finished and cured. Exposed rebar is primed with Nitoprime Zincrich beforehand.
About Fosroc Renderoc Spray HBL
Renderoc Spray HBL is the spray-applied, high-build member of Fosroc’s Renderoc HB lightweight repair range. It arrives as a pre-bagged blend of dry powders that needs only clean water added at the machine, which removes the site-batching guesswork that plagues field-mixed mortars. The formulation combines Portland cement, graded aggregates, lightweight fillers, polymer modifiers and a shrinkage-compensation system. That polymer modification is what gives the cured mortar its very low permeability to water, carbon dioxide and chloride ions, so a repair does more than fill a hole; it re-establishes the protective cover that failed in the first place. Because the material is alkaline, it also re-passivates the steel it encases.
Where the product earns its place is on the parts of a structure that are hardest to repair: soffits, beam undersides and tall column faces. A conventional dense mortar slumps off an overhead surface once you exceed a modest thickness. The lightweight matrix here resists that, so applicators achieve extra build in fewer passes and generally without formwork. Deployed through a wet-spray rig, it lets a small crew reinstate square metres of carbonated or chloride-damaged concrete at a pace hand-trowelling cannot match, with the added benefit that the sprayed, compacted mortar is denser and bonds more tightly to the parent concrete than a hand-placed equivalent.
The technical insight
The engineering logic sits on two levers working together: density and placement energy. Lightweight fillers pull the fresh wet density down to roughly 1,400-1,430 kg/m3, well below a standard sand-cement mortar. Lower self-weight means gravity has less to pull down before the fresh mortar’s cohesion and the tacky primer bond can hold it, which is precisely why overhead and vertical build thicknesses can be pushed so much higher without sagging. The polymer component minimises water demand (the mix runs at a water:powder ratio around 0.18), and a low water content is the single biggest driver of a dense, low-porosity, durable matrix once cured. Wet spraying then adds kinetic compaction: the mortar strikes the substrate at velocity, driving out entrapped air and pressing paste into the surface profile and around reinforcement. The result is a repair that is more homogeneous and better keyed to the parent concrete than a hand-placed layer, with an oxygen-, chloride- and acid-gas-resistant skin that slows the electrochemical corrosion cycle rather than just masking it.
Where it is used
- Spray reinstatement of spalled and delaminated bridge and flyover soffits
- Rehabilitation of car-park and podium deck undersides and beams
- Repair of tall RC column faces and shear walls without formwork
- Tunnel-lining and underpass concrete restoration over large areas
- Restoration of carbonation-damaged building frames and facades
- Reprofiling of chloride-contaminated marine and coastal structures
- Large-volume patch repair around densely reinforced zones
- Re-establishing durable cover to corroding embedded steel
Key advantages
- Lightweight matrix (around 1,400-1,430 kg/m3) enables high overhead and vertical build with reduced slump risk
- Wet-spray placement covers large areas far faster than hand-trowelling, cutting labour on major projects
- Pre-bagged single component removes site-batching variation; only clean water is added
- Very low permeability to water, CO2 and chlorides protects embedded reinforcement long term
- Meets Class R2 of BS EN 1504-3 for non-structural concrete repair (methods 3.1, 3.3, 7.1, 7.2)
- Shrinkage-compensated for long-term dimensional stability and fewer cold joints
- Frequently eliminates the need for formwork, saving time and access cost
- Contains no chloride admixtures and carries a Class A2 non-combustible fire rating
Limitations & considerations
- Not designed for horizontal trafficked surfaces; its lightweight nature makes it unsuitable where wheel or foot abrasion is expected (use a trafficable repair mortar instead)
- Medium-strength product (around 22-28 MPa at 28 days); where high compressive strength is the priority, a structural Class R4 mortar is required
- Should not be applied below 5 C on a falling temperature, nor exposed to moving water or heavy rainfall before final set
- Wet spraying needs suitable pumping/spraying plant and a trained operator, so it is not economic for isolated small patches
- Powdered cementitious product carries standard alkaline-dust handling precautions during mixing and spraying
Selection & best practice
Success is decided at the substrate. Saw-cut the repair perimeter to at least 10 mm to form a square edge and avoid feather-edging, then break out all unsound, carbonated or chloride-contaminated concrete. Expose corroded reinforcement fully, grit-blast it to a bright finish paying attention to the back of the bars, and where chloride corrosion is present, high-pressure wash immediately after blasting. Prime cleaned steel with one full coat of Nitoprime Zincrich and let it dry. For hand build-up, prime the saturated-surface-dry substrate with Nitobond HAR (or Nitobond EP where the repair will stay wet or immersed); for wet spraying, a bonding primer is generally not required. Maintain a minimum applied thickness of 10 mm, build overhead and vertical faces in controlled passes, cut back sprayed mortar to profile with a steel float, and cure immediately with Nitobond AR or a curing membrane. Overcoat the wider structure with a Dekguard anti-carbonation coating to bring surrounding concrete up to the same protective standard as the repair.
Specifications
| Standard compliance | BS EN 1504-3 Class R2; repair methods 3.1, 3.3, 7.1, 7.2 |
| Compressive strength | 10 MPa @ 1 day; 20 MPa @ 7 days; approx. 22-28 MPa @ 28 days |
| Flexural / tensile strength | 3.9 MPa flexural; 2.2 MPa tensile @ 28 days |
| Bond strength (pull-off) | 1.9 MPa (EN 1542; requirement >0.8 MPa) |
| Fresh wet density | Approx. 1,400-1,430 kg/m3 (lightweight) |
| Chloride ion content | 0.02% (requirement <0.05%) |
| Applied thickness | Minimum 10 mm; wet-spray build up to ~175-250 mm vertical / 150-200 mm overhead |
| Water demand / setting | Water:powder ~0.18 (approx. 3.1-3.6 L per bag); initial set ~3.5 h, final ~5.5 h |
| Pack size / yield | 18 kg / 20 kg bags; approx. 14.5-16.6 L yield (~1.5-1.6 m2 at 10 mm thick) |
Industry use cases
Bridges & Highways
Spray reinstatement of spalled girder soffits and pier caps on ageing flyovers, restoring cover to corroding rebar over large areas with minimal traffic disruption.
Car Parks & Podiums
Rehabilitating chloride- and carbonation-damaged deck undersides, beams and columns where lightweight high build avoids formwork on overhead faces.
Tunnels & Metro
Restoring degraded tunnel-lining and underpass concrete across long stretches, where spray speed keeps possession windows short.
Coastal & Marine
Reprofiling salt-attacked columns, retaining walls and jetty structures, using the mortar’s low chloride permeability to slow further corrosion.
Commercial & Industrial Buildings
Large-scale facade and frame repair on carbonation-affected RC structures, reinstating durable cover before an anti-carbonation coating is applied.
Frequently asked questions
Is Renderoc Spray HBL a structural repair mortar?
Why is it lightweight, and what does that gain me?
Can it be hand-applied, or only sprayed?
What surface preparation and priming does it need?
Can I use it on a car-park floor or ramp?
How much do I need, and what pack size does it come in?
How we position Fosroc Renderoc Spray HBL
Renderoc Spray HBL sits at the lightweight, large-area end of Fosroc’s concrete repair range. Within the same Fosroc family, pair it with Nitoprime Zincrich for rebar priming, Nitobond HAR or Nitobond EP for substrate bonding, Nitobond AR for curing, and the Dekguard anti-carbonation coatings to protect the wider structure after repair. When a project needs higher structural strength or fibre reinforcement rather than lightweight build, step up to Renderoc HB45; for horizontal trafficked repairs the lightweight grade is unsuitable and a denser flowable or free-flow micro-concrete should be used instead. Across our other brands, comparable spray and hand-applied polymer-modified repair mortars are available from Sika (Sika MonoTop range), MC-Bauchemie (Nafufill/Zentrifix) and Dr. Fixit, which our team can cross-reference on specification, availability and lead time.
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