Frequently Asked Questions

What is the application procedure for Fosroc Nitoflor Roc dry-shake floor hardener on a freshly placed concrete slab and what is the critical timing for each step?

The application of Fosroc Nitoflor Roc dry-shake floor hardener to a freshly placed concrete floor slab requires precise timing at each step — the dry-shake must be applied at exactly the right concrete surface condition to achieve the correct blending of the hardener into the surface concrete without sinking into a wet surface or being unable to blend into a prematurely set surface. The complete application procedure and timing is: concrete placement and strike-off — place, distribute, and strike off the concrete to the level required using a vibrating screed or rod strike-off, ensuring adequate compaction across the full slab area; surface bleeding — after strike-off, allow the concrete to bleed (the natural rise of excess mix water to the concrete surface); this period can last from 20 minutes to 2 hours depending on the mix design, ambient temperature, wind speed, and concrete slump; do not begin Nitoflor Roc application while a surface sheen of bleed water is visible — applying dry-shake to a wet bleeding concrete surface causes the material to absorb the excess water, creating a water-cement ratio at the surface that may be equal to or higher than the plain concrete surface, negating the hardening benefit; first application (approximately 2/3 of total specified application rate) — when the concrete surface shows the first signs of stiffening (the first footprint from a boot begins to leave a surface impression but does not sink deeply into the concrete), broadcast the first Nitoflor Roc application evenly by hand or mechanical spreader at approximately 2/3 of the total specified rate; allow the concrete bleed water to be absorbed by the dry-shake material for 3 to 5 minutes until the surface begins to darken from the water absorption; machine-float (or hand-float for smaller areas) the surface to blend the Nitoflor Roc into the concrete surface — apply enough passes to work the material fully into the concrete surface until a uniform colour is achieved; second application (remaining 1/3 of total rate) — apply the remaining Nitoflor Roc at right angles to the first application direction, allow water absorption for 3 to 5 minutes, and machine-float again; final trowelling — when the concrete has stiffened to the required firmness, apply finish trowelling (hand or power trowel) in multiple passes as normal for a power-trowelled concrete floor, with progressively tighter and denser trowel passes as the surface stiffens.

What is the difference between the mineral aggregate grade and the metallic iron aggregate grade of Nitoflor Roc and when should the more expensive metallic grade be specified?

Fosroc Nitoflor Roc is available in two principal aggregate grades that serve different floor traffic and service conditions — the mineral quartz or silicon carbide aggregate grade for standard industrial floors, and the metallic iron aggregate grade for the most demanding heavy-duty and ultra-high-abrasion floor applications. The differences between the two grades are: mineral aggregate grade (quartz or silicon carbide hardener): the hardening aggregate is high-purity quartz (silica, Mohs hardness 7) or silicon carbide (Mohs hardness 9 to 9.5 — approaching diamond); surface hardness — Mohs hardness 7 to 9.5 depending on the specific mineral used; abrasion resistance — substantially better than plain concrete (which is Mohs 4 to 6 at the surface); colour — typically available in light grey or buff matching the concrete colour; application rate — 3 to 5 kg/m² for standard industrial floor applications; cost — moderate (lower than metallic grade). Metallic iron aggregate grade: the hardening aggregate is specially processed metallic iron or ferrous aggregate with very high density and hardness; surface hardness — high, based on metallic aggregate hardness; abrasion resistance — maximum available for a dry-shake floor hardener — typically 3 to 5 times the abrasion resistance of the mineral grade and 4 to 8 times the abrasion resistance of plain concrete; colour — dark grey to black (the metallic iron pigments the concrete surface dark); application rate — 5 to 7 kg/m² for heavy-duty applications; cost — significantly higher than mineral grade (50 to 100 per cent premium for the metallic aggregate). The metallic grade is specified over the mineral grade for: floors with constant steel-wheeled forklift or trolley traffic at heavy loads (steel wheels are the most abrasive traffic type on floor surfaces); steel processing, fabrication, and storage floors where steel sections are dragged or pushed across the floor; aircraft hangar floors subject to aircraft tractor steel wheels and FOD (foreign object debris) from the floor — metallic floors are widely used in Indian Air Force and commercial airline maintenance hangars. For standard forklift warehouse and logistics park floors in India (rubber-tyred forklifts at 3 to 5 tonne capacity), the mineral quartz or silicon carbide grade is adequate and more economical.

How should a Nitoflor Roc floor surface be cured after completion of power trowelling and what happens to the floor hardener surface quality if curing is inadequate?

Curing of a concrete floor with Nitoflor Roc dry-shake hardener is critical and is frequently underestimated on Indian construction sites — the investment in a dry-shake hardener to upgrade the floor surface quality is largely wasted if the cured surface is not properly cured during the first 7 days, because the high-strength hardener surface zone at the top of the slab is the thinnest and most vulnerable to moisture loss. The surface hardener zone (the top 2 to 5 mm of the concrete incorporating the Nitoflor Roc material) has a lower water-cement ratio and higher cement content than the parent concrete below it — this is precisely the chemistry that makes it harder — but the low w/c also means it requires thorough curing to achieve the full degree of hydration and therefore the full strength and hardness potential. If the Nitoflor Roc surface is not adequately cured and is allowed to dry rapidly after power trowelling (common in Indian hot-dry conditions in summer, and in buildings with strong through-draughts), the following defects can occur: dusting — if the hardener surface zone dries too rapidly before the cement has hydrated adequately, the surface remains porous and weak, with a higher risk of the surface deteriorating to a dusting floor — precisely the defect the hardener was intended to prevent; surface map cracking — rapid drying shrinkage of the thin hardener surface zone can produce a fine map cracking pattern (plastic shrinkage cracking) on the floor surface in the first 24 to 48 hours after power trowelling; colour mottle — uneven drying due to wind, sun patches, and air movement creates uneven curing and uneven colour and texture in the hardened surface. The correct curing method for a Nitoflor Roc floor is to apply a curing compound (Fosroc Concure WB — water-based acrylic curing compound) to the power-trowelled floor surface immediately after the final trowelling pass — spray Concure WB uniformly across the floor surface and allow it to dry to a thin acrylic film; this seals the surface and retains 85 to 90 per cent of the concrete moisture for the first 7 days, providing the curing condition required for maximum hardener hydration. Alternatively, cover the trowelled floor with polythene sheet laid flat on the surface (no gaps, overlapping joints sealed with tape) for 7 days — equally effective but more labour-intensive. Do not use wet hessian directly on a freshly trowelled Nitoflor Roc surface — the hessian marks and scratches the soft fresh surface during the first 24 hours.