Frequently Asked Questions

What is the practical difference between Fosroc Concure WB (water-based) and Concure HC (solvent-borne) and when should each be specified on a construction project in India?

Fosroc Concure WB (water-based acrylic) and Concure HC (solvent-borne white-pigmented resin) are both concrete curing compounds that form a moisture-retaining film on freshly placed concrete — they serve the same fundamental purpose of preventing rapid moisture loss from concrete during the early curing period, but they have meaningfully different performance levels, application environments, and cost profiles that govern their appropriate use on Indian construction projects. Concure WB (water-based): water retention efficiency — meets ASTM C309 Type 1 minimum (85 per cent), adequate for most building and infrastructure concrete curing; safety — non-flammable, low-VOC water-based product, safe for application in enclosed and confined spaces (basements, underground car parks, tunnel linings, interior slabs); pigmentation — white, providing visible coverage confirmation without solvent health and safety concerns; removal — more easily removed by light abrasive preparation before subsequent coatings; applications — repair mortars, interior slabs, basement walls, precast elements, floor screeds, any enclosed environment. Concure HC (solvent-borne): water retention efficiency — meets ASTM C309 Type 1-D (pigmented, solvent-borne) requirements, typically 90 to 95 per cent water retention, the highest efficiency available; heat reflection — white pigment reflects solar radiation, reducing concrete surface temperature and thermal gradient cracking on slabs exposed to direct sunlight; regulatory approval — approved for highway and airport concrete in India; applications — outdoor road concrete, highway slabs, airport runways, bridge decks, large exposed industrial pavement slabs where maximum curing efficiency and solar heat reflection are required. The decision rule for Indian projects: for all interior, enclosed, and basement concrete, and for repair mortar curing, specify Concure WB; for outdoor road, runway, bridge deck, and large industrial pavement slabs with direct sun exposure, specify Concure HC.

Can Fosroc Concure WB be used to cure freshly placed Renderoc repair mortars and is a dedicated repair mortar curing compound necessary or can wet hessian curing be used instead?

Yes — Fosroc Concure WB is specifically recommended by Fosroc for curing Renderoc repair mortars after placement and finishing, and it is the preferred curing method for repair mortars in most site conditions. The requirement for curing repair mortars is often underestimated on Indian construction sites, where the repair mortar is placed and finished and then left uncovered and exposed to sun, wind, and low humidity — the same adverse site conditions that cause plastic shrinkage cracking and early strength deficiency in concrete are even more severe for the smaller-mass, thin-section repair mortars that lose moisture much more rapidly than mass concrete due to their high surface-to-volume ratio. The alternative curing methods for repair mortars are: wet hessian (burlap) curing — keep hessian wet and in contact with the mortar surface for 3 to 7 days; this is effective when the hessian can be kept continuously wet (difficult on vertical and overhead repairs where the hessian falls away from the repair surface) and when labour is available for the multiple-day maintenance of wet hessian; curing membrane (Concure WB) — spray Concure WB onto the finished repair surface immediately after the mortar has been finished and the surface bleed water has disappeared; one coat of Concure WB is sufficient for horizontal repairs, two coats (applied at right angles) are recommended for vertical repairs exposed to direct sun or wind. Concure WB is preferred over wet hessian for overhead and vertical repair curing (gravity prevents hessian from remaining in contact), for large-area horizontal repairs where labour cost of maintaining wet hessian is high, for exposed repairs subject to wind-drying where hessian dries rapidly between wetting, and for high-security or occupied building repair where wet dripping hessian creates slip and safety hazards. After the 3 to 7 day curing period, Concure WB film is left on the repair surface and is removed only when a subsequent coating, waterproof membrane, or additional repair layer is to be applied — at that stage, light wire brushing, abrasive blasting, or grinding is used to remove the acrylic curing film before the bonding primer or next layer is applied.

What is the coverage rate of Concure WB and how many litres are needed to cure the Renderoc repair mortar on a concrete bridge beam repair project involving 150 square metres of repair area?

The coverage rate of Fosroc Concure WB is approximately 4 to 6 square metres per litre at the recommended application rate of one coat — this coverage rate provides the film weight per unit area needed to form a continuous moisture-retaining acrylic film over the concrete or mortar surface, assuming uniform spray application with no missed areas. The coverage rate varies slightly with the texture and porosity of the mortar surface — freshly trowelled smooth mortar surfaces (Renderoc S, Renderoc FC after steel float finish) have lower absorption and allow coverage at the higher end of the range (5 to 6 square metres per litre); coarser-textured mortar surfaces (Renderoc HB40, Renderoc Microconcrete with textured surface) absorb slightly more compound into the open surface texture and yield coverage at the lower end of the range (4 to 4.5 square metres per litre). For the bridge beam repair project of 150 square metres of repair area: at 5 square metres per litre coverage (one coat), the required Concure WB volume is 150 divided by 5 equals 30 litres; for two-coat application (recommended for vertical and overhead bridge soffit repair exposed to sun and wind), double the volume to 60 litres; adding a 10 per cent contingency for wastage, overspray, and additional coverage in corners and edges, the purchase quantity should be 33 litres (one coat) or 66 litres (two coats). Concure WB is typically supplied in 5-litre and 20-litre containers. For the 150 square metre bridge repair example at two coats: 3 x 20-litre containers plus 1 x 5-litre container equals 65 litres (slightly under the 66-litre calculation) — order 4 x 20-litre containers (80 litres) to ensure adequate stock for the project without running short during application. Contact Space Arc Engineering, Authorized Fosroc Distributor for Delhi NCR, for current Concure WB pricing and availability for your bridge repair project.