Frequently Asked Questions

For an underground drinking water sump in a residential apartment complex in Ghaziabad, should the structural engineer specify MC-Crete 810 integral waterproofing admixture in the concrete mix, a surface-applied crystalline coating like MC-Nafuplan on the inside face, or both systems together, and what does IS 3370 say about water retaining concrete?

The specification of waterproofing treatment for an underground drinking water sump serving a residential apartment complex in Ghaziabad is governed primarily by IS 3370:2021 (Code of Practice for Concrete Structures for Storage of Liquids), which is the principal Indian standard for the design and construction of water-retaining concrete structures. IS 3370 requires that concrete used for liquid-retaining structures be of adequate impermeability to prevent leakage through the concrete walls and floor, and prescribes minimum concrete grades (M30 and above for reinforced concrete water tanks), maximum permissible crack widths (0.1 mm for structures in aggressive environments, 0.2 mm for normal exposure), and minimum cover to reinforcement. IS 3370 does not specifically mandate the use of waterproofing admixtures, but it does specify that the concrete mix must achieve a maximum water penetration depth of 30 mm in the DIN 1048 pressure permeability test, or equivalent impermeability demonstrated by another recognised test. For a Ghaziabad underground sump, the recommended approach is a three-layer strategy. First, specify MC-Crete 810 at the recommended dosage (0.8 to 1.0 percent by mass of cement) in the RCC concrete mix for the sump walls and raft slab. The admixture reduces the inherent capillary porosity of the concrete throughout the entire cross-section, reducing the base permeability of the concrete to levels that approach or meet the IS 3370 permeability requirement without any additional surface treatment. This integral waterproofing provides protection that cannot be damaged by construction activity (like membrane puncture) and is permanently embedded in the structural element. Second, seal all construction joints, day joints, kicker joints, and wall-slab junctions with a swelling hydrophilic rubber waterstop (PVC waterstop centrally positioned in each joint) and/or by injection hose installation at each joint to allow post-construction grouting if leakage is detected through the joint. These joints are the primary path for water ingress in what is otherwise a well-designed concrete sump, and their treatment is more critical than the concrete permeability specification. Third, apply MC-Nafuplan crystalline waterproofing coating to the interior concrete surfaces of the sump (walls and floor) after curing of the concrete structure. The crystalline coating provides an additional layer of protection by treating the surface pores and any hairline cracks in the concrete with insoluble crystals that block water flow paths, and provides a degree of self-healing for cracks that form after the coating is applied. For a potable water sump, the crystalline coating must be certified as non-toxic and safe for contact with drinking water — both MC-Nafuplan and MC-Protect 2K have appropriate certifications. This three-layer approach (MC-Crete 810 integral admixture in the concrete + waterstops at all joints + MC-Nafuplan crystalline surface coating) provides the most comprehensive and reliable waterproofing strategy for a Ghaziabad underground sump, addressing the three main leak paths: concrete matrix permeability (addressed by MC-Crete 810), construction joints (addressed by waterstops), and surface microcracking (addressed by MC-Nafuplan). For sumps with straightforward rectangular geometry, good quality concrete (M30 or above), and properly treated joints, MC-Crete 810 alone may provide adequate watertightness and the surface coating may not be strictly necessary — but the additional cost of MC-Nafuplan surface treatment is modest (typically 3 to 5 percent of the total concrete cost) and the insurance value against leakage in a potable water sump that serves a residential building justifies the combined approach. Space Arc Engineering provides complete underground water sump waterproofing specification support, product supply, and applicator guidance for residential and commercial projects across Delhi NCR, Ghaziabad, Noida, and Uttar Pradesh.