About MC-Bauchemie Compliform 25

When concrete is broken out for repair, the reinforcement that gets exposed is rarely in pristine condition. It may be pitted from chloride attack or depassivated by carbonation, and the moment it sees oxygen and moisture it starts corroding again. Compliform 25 is MC-Bauchemie’s response to that problem — a two-component, zinc-rich epoxy primer engineered specifically for freshly cleaned rebar rather than for general steelwork. It combines a high loading of metallic zinc dust, more than 80% by mass in the cured film, with an epoxy binder that anchors the coating to the bar and provides chemical resistance in the alkaline patch environment.

What sets it apart from an ordinary epoxy touch-up is the mechanism. The zinc is not there to look protective; it is there to be consumed. Because zinc is more electrochemically active than steel, it becomes the anode and sacrifices itself, keeping the underlying reinforcement cathodic and therefore protected. That behaviour is recognised under EN 1504-7, the European standard for reinforcement corrosion protection by coating, which is the framework specifiers reach for when a repair has to last. For engineers, contractors, and consultants working on structures in Delhi NCR and across India — where humidity, de-icing salts on flyovers, and coastal exposure all accelerate rebar decay — that combination of galvanic action and a documented standard is the reason this primer earns a line in the specification.

The technical insight

The value of Compliform 25 lives in electrochemistry, not film formation. In a repaired member, the newly patched zone and the surrounding old, chloride-laden concrete sit at different electrical potentials. That difference drives a macro-cell in which the steel just outside the patch can start corroding aggressively — the well-documented incipient-anode or “ring-anode” effect that causes fresh repairs to fail at their edges within a few years. A passive barrier coating does nothing to stop this; it only works while it is perfectly intact, and the first pinhole or scratch becomes a concentration point for attack. Zinc-rich priming works differently. With over 80% zinc in the dry film, the coating is electrically continuous with the steel, so the zinc particles form a sacrificial anode bonded directly to the bar. They corrode preferentially, holding the reinforcement at a cathodic potential and throwing protection across small breaks in the film — a level of forgiveness a barrier coat can never offer. Building the film to 75-150 microns per coat over two coats, for a total of 150-300 microns, provides enough zinc reservoir to sustain that galvanic action through the service life of the repair, while the epoxy binder keeps the zinc adhered and chemically stable until the repair mortar is placed over it.

Where it is used

• Priming chloride-decontaminated reinforcement in bridge and flyover deck repairs before patch reinstatement
• Protecting carbonation-depassivated rebar exposed during building and facade concrete repairs
• Suppressing the incipient-anode effect at the perimeter of partial and section repairs
• Coating reinforcement in marine, coastal, and splash-zone structures subject to high chloride loads
• Safeguarding rebar that must stay exposed for an extended period before mortar is applied
• Repair of infrastructure elements — columns, beams, soffits — in aggressive, high-chloride service environments
• Localised anti-corrosion priming during industrial and water-retaining structure rehabilitation
• Spot treatment of corroded bar in car park and podium slab breakout areas

Key advantages

• Active galvanic protection — zinc corrodes sacrificially to keep the steel cathodic, rather than merely acting as a passive barrier
• Tolerant of minor film defects: protection carries across small pinholes and scratches instead of failing at them
• Directly targets the incipient-anode effect that causes ordinary patch repairs to fail at their edges
• High zinc loading of more than 80% by mass in the dry film for a substantial sacrificial reservoir
• Conforms to EN 1504-7, giving specifiers a recognised standard to cite in repair documentation
• Two-component epoxy chemistry adheres firmly to prepared steel and resists the alkaline repair environment
• Simple brush application suits congested reinforcement and awkward site geometry
• Compatible with cementitious and epoxy repair mortars overcoated on top as part of an EN 1504 repair system

Limitations & considerations

• Performance depends heavily on surface preparation — steel must be cleaned to St 3 or Sa 2; oil, rust scale, or loose material will compromise adhesion and galvanic contact
• It is a rebar primer, not a repair mortar; it must be overcoated with an appropriate patching material to complete the system
• As a two-component product it requires correct mixing ratio and has a limited working time once combined — the manufacturer’s data sheet governs pot life
• The specified 150-300 micron total DFT across two coats must be achieved; under-application reduces the zinc reservoir and the duration of protection
• The 4-hour minimum between coats has to be respected on site, which affects sequencing on fast-track repairs
• As a sacrificial system the zinc is consumed over time; it is not a permanent inert coating and its life is finite relative to exposure severity

Selection & best practice

Specifications

Industry use cases

How we position MC-Bauchemie Compliform 25

Compliform 25 sits in MC-Bauchemie’s concrete repair and protection line as the dedicated active-protection primer for exposed reinforcement, and it is best specified as one step in a full EN 1504 sequence — pair it with an MC-Bauchemie cementitious or epoxy repair mortar overcoated on top, and, where the whole face needs long-term defence, an MC-Bauchemie surface protection or anti-carbonation coating once the repair has cured. Where a project is standardised on a single supplier’s repair system, we also stock directly comparable zinc-rich primers from our other brands — Fosroc’s Nitozinc Primer being the closest like-for-like — alongside Sika and Dr. Fixit rebar-protection options, so the primer can be matched to whichever repair mortar and protective coating family the specification already calls for. Our team can align the primer, mortar, and topcoat into one compatible system rather than mixing brands across a single repair.

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