About Fosroc Nitocote CM665

Fosroc Nitocote CM665 is a flexible, polymer-modified cementitious waterproofing coating from the global Fosroc range, designed for the protection and waterproofing of concrete and masonry in both water-retaining and water-excluding structures. It is supplied as a two-component system: a graded cementitious powder and a co-ordinated acrylic polymer liquid. When the two are blended on site, the polymer reacts with and modifies the cement matrix to produce a tough yet elastic film that bonds tenaciously to the substrate and moves with minor structural movement instead of cracking and debonding the way an unmodified cement slurry would.

What sets CM665 apart within the Nitocote cementitious family is its grey colour and its ability to resist water pressure from either direction. Because it is grey rather than black, it can be left exposed as a final, presentable layer on tank interiors, basement walls and similar surfaces, avoiding the messy, tar-like finish associated with bituminous coatings. Its capacity to hold back negative (rear-face) hydrostatic pressure is especially valuable in Indian basement, lift-pit and below-grade work, where ingress is often tackled from the dry, internal face because the external water-side face is buried and inaccessible.

For Indian contractors, consultants and architects, CM665 fills the gap between thin decorative cementitious slurries and heavier elastomeric membranes. It cures fast, is non-toxic once set, and—being part of an internationally specified system—is routinely accepted by consultants and clients who want a recognised brand on water tanks, STPs/WTPs, basements and podium decks. Space Arc Engineering supplies and applies the Fosroc Nitocote range across Delhi NCR and Pan-India.

The technical insight

The performance of Nitocote CM665 comes from polymer modification of a cement matrix. On its own, a cement-sand slurry is rigid and brittle: it waterproofs by pore-blocking but fails the moment the substrate flexes or a shrinkage crack opens. By replacing part of the gauging water with an acrylic polymer emulsion, CM665 builds a continuous polymer film through and over the hardened cement. This film does three things that plain cement cannot: it adds tensile elongation so the coating bridges fine surface cracks, it dramatically improves adhesion to a sound substrate, and it lowers permeability so the film resists water under pressure.

The resistance to negative pressure is the technically demanding part. Under positive pressure, water pushes the membrane against the wall and adhesion is assisted; under negative pressure, water pushes the membrane away from the wall, so the coating must develop genuine tensile bond strength into the substrate to stay attached. Polymer-modified cementitious systems achieve this because the cement fraction grows crystals into the substrate pores while the polymer ties the film together—an inherent advantage over surface-laid sheet or liquid membranes that rely only on a glue line.

Two application details govern the result in practice. First, the substrate must be saturated surface-dry (SSD)—damp but with no standing water—so the thirsty concrete does not pull water out of the film before the cement hydrates. Second, the specified two-coat, cross-direction technique exists to eliminate pinholes: the second coat covers the inevitable micro-defects left by the first. Skimping on either coat or on damp curing is the most common cause of field underperformance.

Where it is used

• Internal and external waterproofing of RCC and masonry water tanks and overhead/underground reservoirs
• Basements, lift pits, sumps and retaining walls, including negative-side (internal) treatment of below-grade structures
• Sewage and water treatment plant (STP/WTP) structures, channels and wet wells
• Terraces, podium decks, planter boxes and balconies under screed or tiles
• Bathrooms, toilets, kitchens and other wet areas before tiling
• Swimming pools, fountains and decorative water features
• Protection of concrete against water and waterborne aggressive ions in foundations and substructures
• Waterproofing of shrinkage-cracked concrete surfaces as a protective overlay

Key advantages

• Resists both positive (water-side) and negative (rear-face) hydrostatic pressure, allowing internal treatment where the external face is inaccessible
• Flexible polymer-modified film bridges surface shrinkage cracks instead of cracking with the substrate
• Grey finish can be left exposed as a final layer—cleaner and more presentable than black bituminous coatings
• Bonds directly to sound concrete and masonry without a separate primer, saving a coat and material
• Excellent adhesion to damp (SSD) substrates—suits Indian site conditions where surfaces are rarely bone-dry
• Non-toxic and odourless when cured, with potable-water-grade versions in the same family for drinking-water tanks
• Brush, broom or trowel applied with simple tools and water clean-up before set
• Vapour-permeable cementitious system that lets the slab breathe rather than trapping moisture

Limitations & considerations

• A coating, not a tanking membrane—needs sound, structurally stable concrete; it will not bridge live, moving or structural cracks or expansion joints
• Surface preparation is critical: laitance, oil, curing compounds and loose material must be removed and the substrate brought to saturated surface-dry before application
• Two-component product with a limited pot life once mixed—only mix what can be used within the working time, and do not retemper with water
• Requires damp/water curing after application; in hot, dry or windy Delhi-NCR conditions, rapid drying can compromise the film
• Not a decorative topcoat in the architectural sense—colour is limited to grey and it is not UV-engineered like an anti-carbonation acrylic such as Nitocote Wallguard
• Should not be applied over standing water, during rain, or when ambient/substrate temperatures are below the manufacturer’s minimum
• Movement joints and construction-joint detailing must be handled separately with appropriate sealants and tapes

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Nitocote CM665

Within Fosroc’s own range, Nitocote CM665 sits between the thinner Nitocote CM650 cementitious coating and the potable-water-approved Nitocote CM660, and alongside the heavier-duty and decorative options. Where a project needs UV-stable, anti-carbonation protection on exposed external facades, Nitocote Wallguard or an elastomeric acrylic is the better fit; where drinking-water certification is the priority, CM660 or the relevant potable-grade variant should be specified; and on cracked or repaired concrete, CM665 is typically used as the waterproofing layer on top of Fosroc’s Renderoc repair mortars and Nitobond polymer bonding aids. Against competitor systems available in India, CM665 competes most directly with two-component acrylic-cementitious coatings such as Sika’s SikaTop Seal-107/Sika MonoTop range, MBCC/Master Builders Solutions (formerly BASF) MasterSeal cementitious coatings, Dr. Fixit’s Pidicrete/Roofseal flexible cementitious products, and STP Limited’s cementitious crystalline and polymer-modified coatings. All occupy the same flexible-cementitious niche; selection usually comes down to specified film thickness, certified pressure and crack-bridging data, potable-water approvals, and—on Indian sites—local availability, applicator familiarity and the assurance of a recognised brand backed by an authorised distributor-applicator. Space Arc Engineering supplies and applies the genuine Fosroc Nitocote system across Delhi NCR and Pan-India and can advise on the correct Nitocote variant for tanks, basements, podiums and treatment plants.

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