Fosroc Renderoc MB50
High-performance, polymer-modified medium-build reinstatement mortar for structural concrete repairs to columns, beams and soffits — reaching 50 N/mm2 at 28 days with extremely low permeability.
What is it?
A single-component, pre-bagged, acrylic polymer-modified cementitious repair mortar engineered for medium-build reinstatement of reinforced concrete where high compressive strength (50 N/mm2 at 28 days) and low permeability matter.
Where is it used?
Repair of reinforced concrete columns and beams, soffits and overhead sections, and small localised patch repairs — on bridges, flyovers, industrial structures, water-retaining structures and high-rise buildings across India.
Why use it?
It rebuilds the original cross-section and protects embedded steel: low permeability resists chloride, CO2 and acid-gas ingress, controlled aggregate reactivity and <3 kg/m3 alkali content guard against ASR, and built-in shrinkage compensation keeps the repair dimensionally stable.
How is it applied?
Mixed with 3.60-3.80 litres clean water per 25 kg bag in a forced-action mixer, then hand- or trowel-applied over a Nitoprime Zincrich Plus steel primer and a Nitobond HAR bonding bridge — up to 25 mm per layer vertically, 15 mm overhead, 10 mm minimum.
About Fosroc Renderoc MB50
Fosroc Renderoc MB50 is a high-performance, medium-build concrete reinstatement mortar from Fosroc’s well-established Renderoc family of repair products. It is supplied as a ready-to-use blend of dry powders that needs only the site addition of clean water, removing the inconsistency that comes with site-batched repair mixes. The result is a medium-weight mortar with good handling characteristics, a deliberately low water demand, and the strength and durability profile required for structural concrete repair.
The product sits in a clear position within the Renderoc range. Where a repair calls for genuinely high compressive strength alongside low permeability, Renderoc MB50 is the choice — it develops 32 N/mm2 by 3 days and reaches 50 N/mm2 at 28 days. By contrast, the high-build Renderoc HB40 and Renderoc HB25 are intended where compatibility with lower-strength parent concrete and thicker single-pass builds are the priority. Fosroc’s own guidance is explicit: where strengths below 30 N/mm2 or higher builds are needed, Renderoc HB25 should be used instead.
What distinguishes MB50 technically is its acrylic polymer-modification, which gives the cured mortar extremely low permeability. This matters enormously in the Indian context, where the underlying cause of most concrete distress is the corrosion of reinforcement driven by carbonation or chloride ingress — whether from coastal humidity, de-icing salts on northern highway structures, or contaminated aggregates and groundwater. A dense, impermeable repair mortar slows the re-entry of the very agents that caused the original damage, extending the working life of the repair rather than simply cosmetically patching it.
For Space Arc Engineering’s customers across Delhi NCR and Pan-India, Renderoc MB50 is typically specified on bridge and flyover rehabilitation, multi-storey car parks, industrial frames, sewage and water-treatment works, and ageing RCC buildings where columns, beams and undersides of slabs have spalled and exposed corroded steel. It is part of a complete repair system — used with Nitoprime Zincrich Plus for reinforcement priming, Nitobond HAR as a bonding bridge, Nitobond AR as a curing membrane, and the Dekguard anti-carbonation coating range for long-term protection. It is also compatible with Galvashield XP sacrificial anodes for galvanic corrosion control, making it suitable for durability-led repair specifications.
The technical insight
Renderoc MB50 is intentionally formulated at a low water-to-powder ratio of 0.15 (about 3.60-3.80 litres per 25 kg bag), and this single fact drives most of its performance. Lower water content means a denser cement matrix with fewer capillary pores, which is why the mortar achieves both high strength (50 N/mm2 at 28 days) and the extremely low permeability the polymer modification is designed to deliver. The trade-off is that mixing discipline is critical: the datasheet warns that, like other one-pack repair mortars, MB50 can feel workable even when under-mixed or over-watered, yet under-mixing or excess water silently destroys strength and durability. A forced-action mixer is mandatory, free-fall mixers are prohibited, and part-bag mixing is not allowed. Durability is engineered in three ways beyond density: an exceptional shrinkage-compensation system (drying shrinkage held below 300 microstrain at 7 days) to keep the repair dimensionally stable and bonded; aggregate reactivity controlled to DTp Clause 1704.6 with equivalent sodium oxide below 3 kg/m3 to resist alkali-silica reaction; and a chloride-free formulation so the repair never introduces new corrosion risk to the steel it surrounds. Its coefficient of thermal expansion of 11.3 x 10^-6 per degC is close to that of normal-weight concrete, which limits differential stress between repair and substrate during India’s wide seasonal temperature swings.
Where it is used
- Structural repair of reinforced concrete columns and beams where high compressive strength is required
- Soffit and overhead reinstatement on slab undersides, beam soffits and similar locations (up to 15 mm per layer without formwork)
- Vertical concrete repairs built up to 25 mm per layer in a single application
- Small, localised patch repairs to spalled or carbonation-damaged concrete
- Reinstatement of cover concrete over corroded reinforcement on bridges, flyovers and elevated structures
- Rehabilitation of industrial RCC frames, columns and beams in plants and warehouses
- Repair of water-retaining and sewage/effluent structures where low permeability resists aggressive water-borne chlorides and acid gases
- Concrete repair as part of a Galvashield XP galvanic anode corrosion-control system
Key advantages
- Reaches high compressive strength — 32 N/mm2 at 3 days, 41 N/mm2 at 7 days and 50 N/mm2 at 28 days — allowing medium-build repairs without sacrificing structural performance
- Acrylic polymer-modification gives extremely low permeability, severely retarding chloride, CO2, acid-gas and oxygen ingress that drive rebar corrosion
- Suitable for vertical (up to 25 mm) and overhead/soffit (up to 15 mm) repairs in a single application without formwork
- Exceptional shrinkage compensation (drying shrinkage <300 microstrain at 7 days) for long-term dimensional stability and durable bond
- Single-component, pre-bagged formulation eliminates site-batching variation — only clean water is added
- Chloride-free with controlled aggregate reactivity and equivalent sodium oxide <3 kg/m3, guarding against ASR and new corrosion risk
- Coefficient of thermal expansion (11.3 x 10^-6/degC) close to host concrete, minimising thermal-differential stress
- Galvashield XP compatible and integrates into a full Fosroc repair-and-protect system (Nitoprime, Nitobond, Dekguard)
Limitations & considerations
- Not suitable for areas subjected to traffic or trafficked surfaces — Renderoc S should be specified for those locations
- Minimum applied thickness is 10 mm; thin feather-edges must be avoided by saw-cutting square edges
- Single-layer build limited to 25 mm (vertical) and 15 mm (overhead) — thicker repairs require multiple layers with re-priming
- Performance is highly sensitive to correct mixing: a forced-action mixer is essential, free-fall mixers are prohibited and part bags must never be mixed
- Where strengths below 30 N/mm2 or higher builds are required, Renderoc HB25 is the correct product rather than MB50
- Should not be applied below 5 degC and falling, nor exposed to moving water during application; heavy rainfall before final set can cause surface scour
- Requires a complete priming and curing system (Nitoprime Zincrich Plus, Nitobond HAR/AR) — it is not a standalone single-step patch material
- Shelf life of 12 months can drop below 6 months if stored in high temperature/humidity, a real concern in many Indian site conditions
Selection & best practice
Treat MB50 as a system, not a single product. Saw-cut the repair perimeter to at least 10 mm to give square edges and break out the full area to a minimum 10 mm depth — never feather-edge. Expose all corroded steel fully, abrasive-blast it to bright metal (paying attention to the back of bars), and where chloride-induced corrosion is present, high-pressure wash with clean water immediately after blasting. Prime the steel with a full, unbroken coat of Nitoprime Zincrich Plus and allow it to dry. Bring the substrate to a saturated surface-dry condition, then scrub in one coat of Nitobond HAR and apply MB50 while the primer is still tacky. Place 3.60-3.80 litres of clean water in a forced-action mixer first, add one full 25 kg bag, and mix 3-5 minutes until homogeneous — always powder into water, never the reverse. Compact firmly around reinforcement; build vertical sections up to 25 mm and overhead up to 15 mm per pass, comb-scratch and cure intermediate layers with Nitobond AR before re-priming. Cure immediately with Nitobond AR sprayed as a continuous film, curing 0.5 m2 at a time as trowelling progresses. In Indian summer above 35 degC, store bags in shade and use cool mixing water; below 5 degC, use warm water (up to 30 degC) and protect from freezing. Finally, overcoat with the Dekguard anti-carbonation range to limit future chloride and CO2 advance.
Specifications
| Product type | Single-component, acrylic polymer-modified cementitious medium-build reinstatement mortar |
| Compressive strength (BS 4551, dry cure) | 32 N/mm2 at 3 days; 41 N/mm2 at 7 days; 50 N/mm2 at 28 days |
| Flexural strength (BS 6319 Pt 3) | 8.2 N/mm2 at 28 days |
| Tensile strength (BS 6319 Pt 7) | 3.0 N/mm2 at 28 days |
| Drying shrinkage (20 degC / 55% RH) | < 300 microstrain at 7 days |
| Coefficient of thermal expansion | 11.3 x 10^-6 per degC |
| Setting time (BS 4551 Pt 14) | Initial set 3 hours; final set 5 hours |
| Fresh wet density | Approximately 1998 kg/m3 (consistency-dependent) |
| Water : powder ratio | 0.15 (3.60 to 3.80 litres clean water per 25 kg bag) |
| Applied thickness per layer | Up to 25 mm vertical; up to 15 mm overhead; minimum 10 mm |
| Coverage / yield | Approx. 14.3 litres per 25 kg bag (approx. 1.4 m2 at 10 mm thickness) |
| Equivalent sodium oxide content | Less than 3 kg/m3 |
| Chloride admixtures | None (chloride-free) |
| Standards compliance | DTp Specification BD27/86 Clause 6; aggregate reactivity to DTp Highways Works Clause 1704.6 (1998) |
| Application temperature | 5 degC static or rising minimum; above 35 degC use cool water / store in shade |
| Packaging | 25 kg bags |
| Shelf life | 12 months in dry, unopened storage (may reduce below 6 months in high heat/humidity) |
Industry use cases
Bridges & Highways
Reinstating cover concrete on bridge and flyover piers, beams and crossheads where chloride- or carbonation-induced corrosion has spalled the section, restoring 50 N/mm2 structural capacity with low-permeability protection for the exposed rebar.
Industrial & Manufacturing
Repairing RCC columns and beams in plants, warehouses and process buildings where high compressive strength is needed quickly (32 N/mm2 by 3 days) to limit downtime, while resisting aggressive plant environments.
Water & Wastewater
Patch and section repair of water-retaining tanks, sewage and effluent structures, exploiting MB50’s impermeability to water-borne chloride ions and acid gases that attack conventional repair mortars.
High-Rise & Commercial Buildings
Overhead soffit and beam repairs on ageing multi-storey RCC frames and car parks, where 15 mm overhead build without formwork and Galvashield XP anode compatibility support durability-led refurbishment.
Marine & Coastal Structures
Concrete repair on jetties, coastal buildings and infrastructure in high-chloride, high-humidity coastal belts of India, where low permeability is essential to slow re-corrosion of reinforcement.
Frequently asked questions
What compressive strength does Fosroc Renderoc MB50 achieve?
How thick can Renderoc MB50 be applied in one pass?
How much water and coverage do I get per 25 kg bag?
What is the difference between Renderoc MB50 and Renderoc HB25/HB40?
Does Renderoc MB50 protect reinforcement from corrosion?
Is Renderoc MB50 suitable for floors or trafficked areas?
How we position Fosroc Renderoc MB50
Within the Fosroc Renderoc range, MB50 occupies the high-strength, medium-build niche: choose it over the high-build Renderoc HB25/HB40 when 50 N/mm2 compressive strength and low permeability outrank thick single-pass build, and over Renderoc S when the location is a column, beam or soffit rather than a trafficked floor. It pairs naturally with Nitoprime Zincrich Plus, Nitobond HAR/AR and the Dekguard protective coatings to form a complete repair-and-protect system, and is Galvashield XP compatible for galvanic corrosion control. Among competitor systems available in India, it competes directly with Sika MonoTop polymer-modified repair mortars (e.g. MonoTop-615/R2 grade structural mortars), MBS (MYK/MBS) and BASF MasterEmaco repair-mortar lines, Pidilite Dr. Fixit Pidicrete/Krishna repair-grade mortars, and STP (Sika’s earlier STP-branded) repair products. Renderoc MB50’s differentiators are its documented BS-tested strength progression, controlled aggregate reactivity to DTp standards, and a mature, fully-specified ancillary system. Honest caveat: it is a UK-origin specification product, so for India projects buyers should confirm current local availability, batch certification and the appropriate equivalent grade with an authorised distributor like Space Arc Engineering, and verify suitability against IS 13620/EN 1504-3 class requirements where the specification demands a CE/EN-classified mortar.
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