Frequently Asked Questions

What is the correct application procedure for Nitoprime 25 on a concrete floor before Nitoflor floor coating?

The Nitoprime 25 application procedure on a prepared concrete floor involves the following sequence of steps. First, confirm the concrete substrate has been prepared to the correct standard: shot blasting or grinding to remove laitance, contamination, and weak surface concrete; vacuum cleaning to remove all grit and dust; and moisture content check to confirm the concrete is below the maximum moisture content for epoxy primer application (typically 75 per cent relative humidity measured by hygrometer probe — very wet concrete may require a moisture-tolerant primer or extended drying before standard epoxy primer). Second, mix the Nitoprime 25 components (Part A epoxy and Part B amine hardener) in the correct ratio specified on the packaging, using a low-speed mechanical mixer for 3 to 5 minutes until the components are thoroughly blended. Third, pour the mixed Nitoprime 25 onto the concrete floor in a pool and spread with a short-pile roller, squeegee, or brush to cover the surface at the specified coverage rate of 5 to 8 square metres per litre. For very porous concrete, the coverage rate will be lower as the primer is absorbed readily — the primer should be applied liberally enough to wet the surface thoroughly and to penetrate into the pores. Fourth, spread any pooled primer that has not been absorbed within 10 to 15 minutes using the roller to prevent runs and puddles that would form a thick film which may crack on curing. Fifth, allow the primer to dry to a tacky condition (the recoat window of 2 to 8 hours at 25 degrees Celsius) before applying the Nitoflor floor coating — the floor coating must be applied while the primer is still tacky to achieve intercoat adhesion.

Can Nitoprime 25 be applied to a concrete floor that is still within the first 28 days of curing and has high residual moisture?

Applying Nitoprime 25 to concrete that is still within the first 28 days of curing and has high residual moisture content is a critical risk factor for floor coating adhesion failure. Standard epoxy primers, including Nitoprime 25, are not formulated for application to very wet concrete — they require the concrete to be at or below 75 per cent relative humidity (measured at 25 mm depth using an in-situ hygrometer or probe following BS 8203 procedure) before application. Concrete within the first 28 days of placing typically has a relative humidity at 25 mm depth of 85 to 95 per cent or higher — well above the threshold for epoxy primer adhesion. If Nitoprime 25 is applied to concrete with high residual moisture: the moisture in the concrete generates vapour pressure when the temperature rises during the day, driving moisture vapour upward through the concrete and building pressure under the primer film — this bubbles and delaminates the primer and, subsequently, the floor coating. For new concrete floors that must be coated before the 28-day drying threshold is reached (fast-track construction schedule), there are two options: specify a moisture-tolerant epoxy primer grade (ask Fosroc for the moisture-tolerant primer appropriate for Nitoflor floor coating systems) that is tested for application up to 80 to 85 per cent relative humidity; or delay the coating until the concrete has dried to below 75 per cent RH, monitoring with in-situ humidity probes at weekly intervals.

Is Nitoprime 25 the same as Nitoprime 30 and what are the differences between primer grades in the Nitoprime range?

Nitoprime 25 and Nitoprime 30 are two different grades within the Fosroc Nitoprime epoxy primer range, differing primarily in viscosity and the specific use context. Nitoprime 25 is the lower-viscosity (thinner) grade, with a viscosity of approximately 25 centipoise (or the equivalent in the Fosroc designation system) — it is specifically formulated for penetrating primer applications where the goal is deep penetration into the concrete pore structure before a Nitoflor floor coating. Nitoprime 30 is a slightly higher-viscosity grade (approximately 30 centipoise equivalent) that provides a somewhat thicker primer film and is appropriate for substrates where a balance between penetration and film build is needed — for example, on concrete surfaces that are very smooth or have been over-ground to a dense, low-porosity state where very deep penetration is less important. Both primers are two-component solvent-free epoxy systems, compatible with the Nitoflor floor coating range, and have essentially the same chemical resistance and bond performance characteristics after curing. The choice between Nitoprime 25 and Nitoprime 30 for a specific project is typically made on the basis of the concrete surface porosity assessment during preparation: for normal to high-porosity prepared concrete (most industrial and commercial concrete floors), Nitoprime 25 is the standard specification; for very smooth, dense, low-porosity concrete (very high-strength concrete, very smooth factory-cast precast panels), Nitoprime 30 or a filled primer that provides some physical interlock on a very smooth surface may be preferred. Confirm the correct primer grade with Fosroc or Space Arc Engineering technical support based on the floor specification.