About Fosroc Nitoprime 25

Nitoprime 25 is the primer Fosroc specifies to sit between prepared concrete and its resin flooring range. It is a two-component product: a modified epoxy base and a hardener that are combined on site. What sets it apart from a plain sealer is its penetration. The formulation is deliberately mobile so that once brushed or rolled onto an open concrete surface it is drawn down into the pores rather than sitting as a skin on top. That anchoring is what gives a Nitoflor topping or a Nitocote coating something mechanical to hold onto, and it is why a properly primed slab resists the delamination that plagues coatings laid straight onto bare, dusty concrete.

Because it carries solvent, the product also handles a problem Indian sites see constantly, substrates that are not bone dry. Nitoprime 25 can be applied even on damp surfaces, and on porous concrete it is absorbed so fast that light-coloured dry patches appear almost immediately. Those patches are a signal, not a defect: they mark thirsty areas that need a second priming pass to seal air release and stop pinholes forming in the finished floor. Used this way it becomes a reliable, forgiving first coat for the whole Fosroc resin system rather than a cosmetic step that gets rushed.

The technical insight

The mechanism is mechanical keying plus outgassing control. Concrete is porous, and any air trapped in those pores will try to escape upward as an epoxy topping cures over it, blowing bubbles and pinholes into an otherwise perfect floor. Nitoprime 25 is engineered with low viscosity and high wetting-out characteristics so it flows into the capillary structure of the slab, displaces surface dust at the interface, and forms a continuous bonded layer once the epoxy cures. On highly porous concrete a single coat is often swallowed whole, which is why Fosroc calls for a second coat over the dry patches: the first coat seals the deepest voids and the second builds the continuous film the topping actually bonds to. The result is a monolithic build-up, primer locked into the concrete, topping locked into the primer, with no weak plane in between.

Where it is used

• Priming concrete before Nitoflor SL2000 and SL4000 self-levelling epoxy floor toppings
• Priming ahead of Nitoflor TS and TF trowel-applied and broadcast floor systems
• Sealing and keying substrates before Nitocote protective and chemical-resistant coatings
• Bonding coat under Nitomortar epoxy repair and reinstatement mortars
• Floor preparation in food processing, dairy and beverage plants where hygienic resin floors are used
• Substrate priming in pharmaceutical, warehouse and light-industrial manufacturing units
• Priming car park decks, workshop and factory floors before resin overlays
• Dealing with marginally damp slabs where a fully solvent-free primer would struggle to wet out

Key advantages

• Penetrates concrete pores rather than sitting on top, giving a genuine mechanical key
• Can be applied even on damp surfaces, a real advantage in humid and monsoon conditions
• Long open time and high wetting-out, so it flows and bonds before it starts to set
• Improves the adhesion of epoxy floor toppings and repair mortars to the substrate
• Simple brush or roller application with no specialist plant needed on smaller areas
• Works across the full Nitoflor, Nitocote and Nitomortar range as a single common primer
• Generous coverage of 5.5 to 6.5 m2 per litre keeps material cost per square metre low
• Twelve-month shelf life in unopened packs makes it easy to hold as site stock

Limitations & considerations

• It is solvent-containing and flammable, with a flash point of 25 C, so naked flames, sparks and smoking must be kept away and adequate ventilation is essential
• Solvent vapour means enclosed areas need forced ventilation or breathing apparatus, unlike a fully solvent-free primer
• Short working window once mixed, roughly 90 minutes at 20 C falling to about 30 minutes at 30 C, so only mix what can be used
• New concrete must be at least 28 days old or below 5% moisture before priming, which can hold up fast-track programmes
• Overcoating timing is system-specific, overnight drying for Nitoflor SL, but tacky-stage for Nitoflor TF, Nitomortar and Nitocote, so the topping datasheet must be checked
• Rising damp or a missing DPM will still cause failure; the primer tolerates surface dampness, not hydrostatic pressure from below

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Nitoprime 25

Nitoprime 25 is the workhorse solvent-containing primer within the Fosroc flooring family and is meant to be bought alongside the topping it serves, whether that is a Nitoflor SL self-levelling epoxy, a Nitoflor TF broadcast system, a Nitocote protective coating or a Nitomortar repair mortar. Site teams should also keep Nitoflor Sol on hand for cleaning tools before the primer sets, and Reebaklens where small areas are etched rather than mechanically prepared. Where a project cannot tolerate solvent odour, in an occupied building, a food line or a poorly ventilated basement, the solvent-free Fosroc Nitoprime 31 is the sister product to specify instead. For steel rather than concrete, priming falls to Fosroc’s Nitozinc or Nitoprime Zincrich range. Space Arc supplies the full Fosroc line and, where a client standardises on another brand, equivalent flooring primers from Sika, MC-Bauchemie and Master Builders Solutions.

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