Frequently Asked Questions

When exactly should Concure HC be applied to freshly placed road concrete and what happens if it is applied too early or too late?

The timing of Concure HC application is critical — application too early or too late both produce inadequate curing and potential concrete surface defects. The correct application window is after the bleed water has evaporated from the concrete surface and after the surface has been finished (floating, texturing, and any surface treatment), but before the concrete begins to take its initial set and lose its surface moisture. The specific indicator on site is the disappearance of the surface sheen — freshly placed concrete initially has a wet, shiny surface from the bleed water sitting on top; as the bleed water evaporates, the surface sheen disappears and the surface appears matte and slightly dry to the touch. This is the correct moment for Concure HC application. If Concure HC is applied while bleed water is still present on the surface (too early — while the surface is still shiny), the curing compound is diluted by the bleed water and cannot form a continuous, effective resin film — the diluted compound produces a weak, patchy curing membrane with poor water retention efficiency. Additionally, bleed water sitting under the applied compound can displace the resin film from the concrete surface. If Concure HC is applied too late (after the concrete has begun to set and the surface has dried and begun to crack), the compound may be unable to seal the partially dried surface effectively, and the critical early curing period (the first 4 to 6 hours when evaporation rate from hot concrete is highest) has already been lost. In Indian summer conditions (35 to 40 degree ambient temperature, low humidity, and wind), the bleed water can evaporate within 20 to 40 minutes of placing — the Concure HC application crew must be ready at the pour front to apply the compound immediately as each slab panel finishes bleeding.

Does a cured concrete surface treated with Concure HC need to be removed before applying a floor coating or waterproofing membrane and how is the curing compound removed?

Yes — Concure HC and virtually all resin-based curing compounds must be removed from a concrete surface before applying any adhesive bonding agent, floor coating, waterproof coating, or repair mortar that requires adhesion to the concrete. This is one of the most important and most frequently overlooked requirements in construction in India. A curing compound forms a resin film on the concrete surface that is specifically designed to be impermeable (to retain concrete moisture) — this impermeable resin film also prevents adhesion of any subsequently applied material to the concrete below. If a concrete floor slab is cured with Concure HC and then a floor coating (Nitoflor Epoxy SL, Nitoflor FC130, or any other epoxy or PU floor system) is applied over the curing compound without removing it, the floor coating bonds to the curing compound resin rather than to the concrete — and when the floor coating is subjected to wheel traffic, impact, and thermal cycling, the floor coating will delaminate from the concrete (pulling the curing compound with it) because the bond between the coating and the curing compound is much weaker than the required concrete-to-coating bond. Similarly, waterproofing membranes applied over a concrete surface that retains curing compound will delaminate under water pressure. Concure HC (and similar resin-based curing compounds) is removed by: mechanical abrasive blasting (shot blasting) — the preferred and most complete removal method for floor areas; diamond grinding — also effective and commonly used for floor preparation; or high-pressure hydro-jetting at sufficient pressure to remove the surface resin film. Chemical solvent removal is not recommended as the penetrating solvent partially dissolves the compound into the concrete surface pores rather than removing it. All surface preparation for floor coatings must include verification that curing compound has been removed — the standard test is a water drop test: water dropped on the prepared surface should be absorbed by the concrete within 30 seconds; if it beads and stands on the surface, curing compound residue remains and further preparation is required.

Can Concure HC be used as a curing membrane for repair mortars (Renderoc, Patchroc) after application and is there a Fosroc curing compound specifically for repair mortars?

Yes — curing compound application to repair mortars after placement is an important part of the repair mortar curing procedure, particularly for overhead and vertical repairs where wet hessian curing is impractical, and for large-area repair patches where maintaining continuous wet curing over many separate patches would require a large labour force and continuous monitoring. However, the selection of curing compound for repair mortars must be made with care — Concure HC is a high-performance road and slab curing compound designed for mass concrete and pavement curing, and while it can be used over repair mortars, the coverage rate, adhesion to the mortar surface, and compatibility with subsequent finishes must be confirmed. For repair mortar curing, a dedicated low-film-thickness, non-wax curing compound (such as Fosroc Concure WB — the water-based acrylic curing compound also in the Fosroc range) may be more appropriate than the solvent-borne Concure HC, because: water-based curing compounds are easier to apply by brush or roller to small repair areas without the overspray and solvent exposure issues of a solvent-borne spray compound; water-based compounds generally have lower film build and are more easily removed or degraded before subsequent coatings; and the water-based chemistry is non-flammable, which is an important site safety consideration when applying solvent-borne products in enclosed basement and below-grade repair environments. For curing repair mortars in an exposed outdoor environment (bridge soffit repair, facade repair) where larger areas are being repaired and spray application is practical, Concure HC can be used on the repair mortar surface after the mortar has been trowelled to the required finish — apply one coat of Concure HC and maintain for 3 days minimum before recoating with subsequent repair layers or protective coatings.