Fosroc Renderoc LA55
Single-component, low-alkali, free-flowing micro-concrete for large-volume structural concrete reinstatement by form-and-pour — EN 1504-3 Class R4.
What is it?
A pre-bagged, single-component, low-alkali micro-concrete reinstatement mortar based on Portland cement and graded aggregates (max 5 mm). It needs only on-site addition of clean water to produce a free-flowing, shrinkage-compensated micro-concrete for form-and-pour repairs.
Where is it used?
Structural repair of reinforced concrete elements — bridge piers and crossheads, columns, beams, jetty and marine structures, water-retaining tanks, soffits and large spalled sections where access is restricted or reinforcement is congested.
Why use it?
Its self-compacting flow fills congested, deep and restricted repairs without vibration; low alkali content reduces ASR risk; very low permeability protects against chloride and CO2 ingress; and it bonds to the substrate without an independent bonding primer.
How is it applied?
Saturate the prepared substrate to SSD, fix formwork, mix the powder with clean water, then pour or pump into the form in lifts of 50–200 mm. Strike the formwork and cure immediately with water plus a curing membrane such as Fosroc Concure.
About Fosroc Renderoc LA55
Fosroc Renderoc LA55 is a high-performance, free-flowing, low-alkali micro-concrete developed for the reinstatement of large structural sections of reinforced concrete. It belongs to Fosroc’s well-established Renderoc range of concrete repair mortars and is positioned as the “form-and-pour” solution for situations where hand- or trowel-applied mortars are impractical — deep repairs, congested reinforcement, restricted access, or soffit and full-perimeter column work.
The product is supplied as a ready-to-use blend of dry powders — Portland cement, carefully graded aggregates and performance additives — requiring only the controlled site addition of clean water. Once mixed, it produces a highly fluid, self-compacting micro-concrete that flows into and around reinforcement, displacing entrapped air and eliminating honeycombing without the need for poker or external vibration. The maximum aggregate size is 5 mm, and a unique dual-expansion system controls both plastic-state and long-term drying shrinkage, which is critical for achieving a durable, well-bonded repair across large areas.
For Indian contractors and consultants, the defining attributes are its low alkali content (which minimises the risk of alkali-silica reaction in aggressive or marine environments), its very low permeability to chloride and carbon dioxide, and its compliance with BS EN 1504-3 as a Class R4 structural repair mortar — the highest performance class in that standard. Because it bonds to sound, prepared concrete without an independent bonding primer, site application is simplified and a common source of debonding is removed. Renderoc LA55 is alkaline in nature and therefore continues to protect embedded steel reinforcement, and its electrical resistivity makes it compatible with electro-chemical rehabilitation techniques such as impressed-current cathodic protection and galvanic anode systems.
The technical insight
Renderoc LA55 is engineered around fluidity, shrinkage control and durability rather than thixotropy. Unlike trowel-grade Renderoc mortars (which are designed to stay put on vertical and overhead surfaces), LA55 is intentionally free-flowing so it can be placed by gravity pour or pump into closed formwork. This is why placement thickness is governed by the form rather than by sag — sections are typically 50–200 mm thick, with greater depths achievable depending on repair geometry, steel congestion and pour configuration. To avoid restrained-shrinkage cracking in long pours, Fosroc specifies a length-to-minimum-thickness ratio of no more than 20:1, reduced further in hot, drying conditions or for very small sections. The dual-expansion (shrinkage-compensating) system offsets plastic settlement and long-term drying movement so the cast micro-concrete remains in intimate contact with the parent concrete. Strength development is engineered for early formwork turnaround: the specification clause calls for a minimum 3-day compressive strength of 30 MPa and a 28-day strength of 60 MPa at 20°C, with an elastic modulus in compression exceeding 20 GPa per the EN 1504-3 declared performance — close to that of typical structural concrete, which keeps load-sharing between repair and substrate compatible. Because curing is the single biggest field variable for shrinkage-compensated micro-concretes, the TDS is emphatic that exposed faces must be soaked with clean water immediately after striking the formwork and then sealed with a curing membrane such as Fosroc Concure.
Where it is used
- Form-and-pour reinstatement of spalled or delaminated reinforced concrete columns, beams and crossheads
- Repair of bridge substructures, piers, abutments and parapets affected by carbonation or chloride attack
- Marine and coastal structures — jetties, sea walls and splash-zone elements requiring chloride resistance
- Repairs to concrete affected by alkali-silica reaction (ASR), where low-alkali chemistry is required
- Large-volume soffit and deep-section repairs where access is restricted or reinforcement is congested
- Water-retaining and water-conveying structures (LA55 variants are potable-water approved to AS/NZS 4020 in some markets)
- Substrate for electro-chemical rehabilitation — impressed-current cathodic protection, realkalisation/desalination and galvanic anode systems
Key advantages
- Free-flowing, self-compacting placement fills deep and congested repairs without vibration
- Low alkali content minimises the risk of alkali-silica reaction (ASR)
- Very low permeability gives excellent resistance to chloride and carbon dioxide ingress
- Bonds to sound prepared concrete without an independent bonding primer
- Dual-expansion system controls plastic and long-term drying shrinkage
- Single-component, pre-bagged blend — only clean water is added on site, reducing batching variability
- High early strength (3-day compressive strength not less than 30 MPa) allows fast formwork turnaround
- Meets BS EN 1504-3 Class R4, the highest structural repair class
- Suitable for electro-chemical repair methods and compatible with cathodic protection / galvanic anodes
- Contains no chloride admixtures; remains alkaline to protect embedded reinforcement
Limitations & considerations
- Requires formwork — it is a pour/pump system, not a trowel-applied mortar for vertical or overhead patching
- Minimum practical section is around 50 mm; thin feather-edge or shallow patch repairs need a trowel-grade Renderoc instead
- Long, narrow pours must respect a length-to-minimum-thickness ratio of about 20:1 to avoid shrinkage cracking
- Strictly water-cementitious — strength and durability depend on accurate water addition; over-watering reduces strength
- Mandatory immediate curing (water soak plus curing membrane) after striking formwork; poor curing causes shrinkage and surface defects
- Substrate must be sound, clean, mechanically prepared and pre-saturated to SSD before placement
- Cementitious cure means strength gain and working life are temperature-dependent; hot Indian site conditions reduce handling time
- Larger maximum aggregate (5 mm) and minimum depths make it unsuitable for fine cosmetic or fairing applications
Selection & best practice
Break out to sound concrete and expose corroded reinforcement fully around its circumference; clean the steel to bright metal (abrasive blasting is preferred) and treat it with Fosroc Nitozinc/Nitoprime Zincrich where specified. Mechanically prepare the substrate to a roughened, open profile, remove dust and laitance, and pre-soak it to a saturated-surface-dry (SSD) condition. Erect rigid, grout-tight, well-braced formwork with a pouring hopper and adequate head, leaving air-relief points so the micro-concrete can displace air. Add only the manufacturer’s specified quantity of clean water and mix mechanically to a uniform, lump-free, free-flowing consistency; place continuously in lifts to avoid cold joints. Strike formwork only once the micro-concrete has gained adequate strength, then cure immediately — soak exposed faces with clean water and apply a Fosroc Concure curing membrane, extending curing in hot or windy weather. Always work to the project-specific Fosroc TDS and method statement for batch water content, pour limits and ambient-temperature constraints.
Specifications
| Product type | Single-component, free-flowing, low-alkali micro-concrete reinstatement mortar |
| Base chemistry | Portland cement, graded aggregates and additives (just add clean water) |
| Maximum aggregate size | 5 mm |
| Standard / classification | BS EN 1504-3, Class R4 (structural repair); repair methods 3, 4 and 7 |
| Compressive strength — 3 day | Not less than 30 MPa (at 20°C) |
| Compressive strength — 28 day | 60 MPa (at 20°C) |
| Elastic modulus in compression | >20 GPa (EN 1504-3 declared value) |
| Application thickness | 50–200 mm per lift (greater achievable subject to geometry; some markets cite 25–200 mm) |
| Length : minimum-thickness ratio | Not more than 20:1 (reduce in hot/drying conditions) |
| Approx. yield | ~12.0 litres per 25 kg bag |
| Placement method | Pour or pump into formwork; self-compacting (no vibration required) |
| Chloride admixtures | None (contains no added chlorides) |
| Permeability | Very low — resists chloride and CO2 ingress |
| Bonding primer | Not required on sound prepared concrete; bonds directly |
| Electrical resistivity | <15,000 Ω·cm @ 28 days (suitable for incipient-anode / electro-chemical repair) |
| Curing | Immediate water soak + curing membrane (e.g. Fosroc Concure) after striking formwork |
| Pack size | 25 kg bag (regional 20 kg packs also marketed) |
Industry use cases
Bridges & highway structures
Reinstating spalled bridge piers, crossheads and abutments suffering carbonation- or chloride-induced corrosion, where deep form-and-pour sections and fast strength gain enable quicker reopening to traffic.
Ports, jetties & marine works
Repairing splash-zone and tidal-zone reinforced concrete where low permeability and chloride resistance are essential, and where LA55 can be combined with cathodic protection for long-term durability.
Water & wastewater infrastructure
Rehabilitating water-retaining tanks, sumps and treatment structures; low-alkali, low-permeability micro-concrete suits aggressive and submerged exposure (potable-approved variants where required).
Industrial & power plants
Restoring load-bearing columns, beams and foundations in cement, fertiliser, power and process plants where ASR or chemical attack has degraded structural concrete.
High-rise & commercial buildings
Structural reinstatement of congested RCC columns and beams during retrofit and seismic strengthening, where free-flowing placement reaches areas trowel mortars cannot.
Frequently asked questions
Is Fosroc Renderoc LA55 a real product, and which standard does it meet?
How is Renderoc LA55 different from trowel-applied Renderoc mortars?
What thickness can be applied in one pour, and is reinforcement an issue?
Does Renderoc LA55 need a bonding primer or rebar treatment?
How important is curing, and what should be used?
Can Space Arc supply Renderoc LA55 and provide site support in India?
How we position Fosroc Renderoc LA55
Renderoc LA55 is the form-and-pour member of Fosroc’s Renderoc concrete-repair family, complementing the trowel-applied grades (such as Renderoc HB / S used for hand-placed vertical and overhead patching) and pairing naturally with companion Fosroc products — Nitozinc Primer for reinforcement protection, Nitobond for bonding, and Concure for curing — to deliver a complete EN 1504-compliant repair system. Within that family its niche is clear: deep, large-volume, congested or restricted-access structural repairs that need a fluid, low-alkali, low-permeability micro-concrete rather than a hand-applied mortar. Credible alternatives that consultants in India may also specify include Sika’s MonoTop micro-concrete repair range (e.g. MonoTop / SikaGrout micro-concretes), MBS (MYK / MBCC-derived) repair micro-concretes, Dr. Fixit (Pidilite) Krishna/structural repair micro-concretes, and STP repair systems — each offered as EN 1504-3 class repair products. Renderoc LA55’s particular strengths in a like-for-like comparison are its low-alkali (ASR-resistant) chemistry, primer-free bonding, dual-expansion shrinkage control and proven compatibility with electro-chemical rehabilitation, which make it a strong choice for marine, bridge and water-retaining structures. As an authorised Fosroc distributor and applicator across Delhi NCR and Pan-India, Space Arc Engineering can advise on the right Renderoc grade for each repair situation and supply the full supporting system.
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