Fosroc Ferroseal
A single-component cementitious coating that re-passivates exposed reinforcement steel and shields it against moisture and oxygen before patch repair.
What is it?
A single-component, brush-applied cementitious coating that restores alkalinity around corroded rebar and forms a protective barrier before repair mortar is placed.
Where is it used?
Concrete repair on buildings, bridges, car parks, water-retaining and industrial structures wherever reinforcement has been exposed or has begun to corrode.
Why use it?
It stops fresh corrosion at the steel and gives the following Renderoc repair a clean, well-bonded, protected substrate — extending the life of the patch.
How is it applied?
Clean the steel to Sa 2.5 or St 3, mix Ferroseal with clean water to a brushable slurry, and apply two coats by brush to roughly 1 mm total dry film, letting the first coat firm up before the second.
About Fosroc Ferroseal
When concrete cracks, carbonates or takes in chlorides, the steel inside loses the alkaline film that normally keeps it from rusting. Once that passive layer breaks down, corrosion spreads under the surface and pushes the cover concrete apart. Fosroc Ferroseal is made for exactly this moment in a repair. It is a single-component cementitious coating that you brush directly onto the cleaned reinforcement, re-establishing a high-alkalinity environment right at the bar and cutting off the oxygen and moisture that feed the corrosion cell. In practice it is the step between breaking out damaged concrete and reinstating the section with a repair mortar.
For engineers and applicators working across Delhi NCR and pan-India, Ferroseal is valued because it is straightforward on site and predictable in performance. There is no resin mixing, no induction time and no two-part ratios to get wrong — just add clean water and brush it on. It is formulated to work as part of the Fosroc Renderoc concrete repair system, so the coating, the repair mortar and the curing regime are designed to behave as one. That system compatibility matters: a rebar primer that bonds poorly or reacts badly with the overlying mortar can quietly undermine an otherwise sound repair. Ferroseal is engineered to avoid that, giving contractors a dependable first line of defence on structural rehabilitation jobs.
The technical insight
Steel embedded in sound concrete is protected by a passive oxide film that forms because the surrounding cement paste is strongly alkaline, around pH 12 to 13. Carbonation and chloride ingress destroy that chemistry — carbonation drops the pH, chlorides break the film locally — and corrosion begins. Ferroseal works on two fronts. Being cement-based, it reinstates a high-pH skin directly against the bar, chemically re-passivating the steel the way fresh concrete cover would. At the same time the cured film acts as a physical barrier, restricting the oxygen and water that any electrochemical corrosion cell needs to keep running. Because it shares a cementitious chemistry with the repair mortar placed over it, the two develop an integrated bond rather than sitting as dissimilar layers, which is why it is specified as the reinforcement primer within the Renderoc repair sequence.
Where it is used
- Priming exposed reinforcement in carbonated concrete repairs to buildings, bridges and car parks
- Protecting rebar in chloride-contaminated concrete, including coastal and marine-influenced structures
- Reinforcement protection in water-retaining and effluent treatment structures under repair
- Preparing cleaned steel ahead of Fosroc Renderoc repair mortar application
- Coating partially corroded bars exposed during break-out and phased demolition works
- Anti-corrosion priming in aggressive industrial and chemical-exposure environments
- Localised patch repairs where cover has spalled and bars are visible
- Reinstatement of durability on structures being rehabilitated for extended service life
Key advantages
- Single component — no resin ratios or induction time; only clean water is added on site
- Re-passivates the steel chemically while also forming a physical moisture and oxygen barrier
- Brush-applied, so it reaches congested reinforcement and awkward corners easily
- Purpose-matched to the Fosroc Renderoc repair mortar system for reliable integrated bonding
- Cementitious base is compatible with damp concrete conditions typical of Indian repair sites
- Low technical risk for site crews — hard to get the mix badly wrong
- Helps extend the service life of the repair patch by arresting active corrosion early
- Backed by Fosroc India support and Space Arc technical guidance across pan-India projects
Limitations & considerations
- Not a structural repair material — it protects steel but does not reinstate section; a repair mortar such as Renderoc is still required
- Performance depends heavily on surface preparation; inadequate cleaning of the rust and scale will compromise it
- Being cementitious, it is a barrier and passivating primer, not an ‘active’ galvanic system like a zinc-rich primer
- The overcoat window is limited, so the repair mortar should follow within the recommended time after priming
- Not a standalone corrosion cure for heavily section-loss bars, which may need supplementary reinforcement
- Correct dry film thickness must be achieved by two coats; a single thin coat will under-protect the steel
Selection & best practice
Start by exposing the full circumference of any corroded bar and breaking back to sound concrete around it. Clean the steel to Sa 2.5 by grit blasting where possible, or St 3 by mechanical wire brushing as a minimum, removing all loose rust, scale and contamination. Mix Ferroseal with clean water to a smooth, brushable slurry, then work the first coat well into the surface of the bar including the underside. Allow that coat to dry to a firm touch, then apply a second coat to build up to roughly 1 mm total dry film. Reinstate with the repair mortar within the recommended overcoat window — generally within about four hours in normal conditions, or sooner in high humidity — so the two layers bond as a system. On hot or windy days, protect the freshly coated steel from rapid drying, and never leave primed bars exposed to rain or fresh contamination before the mortar goes on.
Specifications
| Product type | Single-component cementitious passivating and protective coating |
| Base chemistry | Cement, fine fillers and corrosion-inhibiting compounds |
| Application method | Brush applied (mix with clean water only) |
| Number of coats | Two coats, second applied once first is firm to touch |
| Dry film thickness | Minimum 1.0 mm on the steel surface |
| Coverage | Approximately 1.5–2.0 kg/m² at 1 mm DFT |
| Steel preparation | Sa 2.5 (grit blast) preferred, or St 3 (mechanical) minimum |
| System compatibility | Formulated for use with the Fosroc Renderoc repair mortar range |
Industry use cases
Bridges & Highways
Priming exposed rebar in carbonated pier caps, soffits and deck edges before Renderoc reinstatement, arresting corrosion that would otherwise re-spall the repair.
Buildings & Facades
Treating corroded reinforcement in spalled columns, beams and balcony edges during structural rehabilitation of ageing RCC buildings.
Water & Wastewater
Protecting steel in repaired tanks, channels and treatment structures where constant moisture accelerates corrosion of exposed bars.
Industrial Structures
Anti-corrosion priming of reinforcement in plants and warehouses exposed to chemical fumes, chlorides or aggressive process environments.
Car Parks & Podiums
Reinstating durability on chloride-affected decks and ramps where de-icing salts or vehicle contamination have depassivated the steel.
Frequently asked questions
What exactly does Fosroc Ferroseal do?
Is Ferroseal the same as a zinc-rich primer?
How many coats are needed and how thick should it be?
How do I prepare the steel before coating?
Can I apply the repair mortar straight after Ferroseal?
Does Space Arc supply Ferroseal across India?
How we position Fosroc Ferroseal
Ferroseal is one step in a complete concrete repair system rather than a standalone product, so it is almost always specified alongside the Fosroc Renderoc repair mortars that reinstate the concrete section over the primed steel, with a Fosroc curing membrane such as Concure to finish. Where a specification calls for an active, sacrificial rebar primer instead of a cementitious passivating coating, the natural Fosroc counterpart is Nitoprime Zincrich. Across our wider brand shelf, teams standardising on other systems may look at equivalent reinforcement primers and repair mortars from Sika, Dr. Fixit or MC-Bauchemie, and our technical team can help match the primer to the specified repair mortar so the two are always compatible.
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