Frequently Asked Questions

What substrate moisture content is acceptable for applying MC-DUR 1150 epoxy floor coating to a concrete slab in a new Ghaziabad factory construction, and what are the consequences of applying epoxy over concrete with excessive moisture?

Moisture in the concrete substrate is the most common cause of epoxy floor coating failure on new construction in India, and it is a problem that is particularly acute in Ghaziabad and Delhi NCR construction projects for two reasons. First, new construction schedules in Indian real estate and industrial projects are typically compressed, with pressure from developers and contractors to apply floor coatings as early as possible after concrete slab placement — often within 4 to 8 weeks of the slab being poured, well before the concrete has dried to a moisture level compatible with epoxy application. Second, Indian concrete slabs are often poured at water-cement ratios above the design specification due to site practices (addition of water at the truck drum on site to improve workability), meaning the slab contains more evaporable water at the time of pour than a properly batched slab, and takes longer to dry. The critical moisture threshold for applying a solvent-free epoxy floor coating such as MC-DUR 1150 is a substrate moisture content of less than 4 to 5 percent by weight (measured using an electronic concrete moisture meter — the reading must be taken at 20 mm depth, not just the surface, as the surface can appear dry while the body of the slab is still wet). When the moisture content exceeds this threshold, evaporation of moisture vapour from the slab creates a vapour pressure at the concrete-epoxy interface that exceeds the bond strength of the epoxy to the concrete surface, causing the epoxy to lift, blister, and delaminate within days to weeks of application. The blisters are typically 50 to 300 mm diameter domes on the epoxy surface, filled with either water vapour or liquid water, and once a blister forms the entire surrounding epoxy is destabilised and progressive delamination follows. Remediation requires complete removal of the debonded epoxy by grinding, which wastes all the material and labour cost of the initial application, plus the additional cost of remediation and re-application. For a concrete slab in a new factory in Ghaziabad poured in OPC concrete in the monsoon season (July to September), the following drying programme should be expected before epoxy application. A 150 mm thick slab poured at the correct water-cement ratio (0.45 to 0.50) and properly cured will take a minimum of 60 to 90 days to dry to less than 4 percent moisture content in hot, dry conditions (November to February in Delhi NCR). In cooler or humid conditions, or if the slab was poured at a higher water-cement ratio, this period extends to 90 to 120 days. The moisture content must be verified by measurement (not assumed from the age of the slab) using a calibrated electronic moisture meter at multiple points across the floor area, including the centre of large bays (which dry more slowly than the perimeter). If the schedule does not allow drying to less than 4 to 5 percent moisture before epoxy is required, two options are available. First, MC-Bauchemie MC-Dur 1225 moisture-tolerant epoxy primer can be applied as a base coat over concrete with moisture up to 7 to 8 percent (check current TDS for exact tolerance limit) — this provides a vapour barrier layer that prevents moisture vapour from reaching the epoxy topcoat. This approach adds one priming stage but allows epoxy application several weeks earlier than waiting for full drying. Second, a moisture-tolerant polyurethane floor coating (instead of epoxy) can be specified for the final surface — polyurethane systems have higher water vapour permeability and are less susceptible to moisture blister formation, at a modest compromise in chemical resistance versus epoxy. For food and pharmaceutical facilities where epoxy is mandatory for GMP compliance and chemical resistance, the moisture primer approach is the standard recommendation. Space Arc Engineering can advise on moisture measurement, primer selection, and application scheduling for specific new construction projects in Ghaziabad and Delhi NCR.