About Fosroc Nitocote CM660

Fosroc Nitocote CM660 is a flexible, polymer-modified cementitious waterproof coating supplied as a two-component pre-packaged system: a graded cement/aggregate powder and an acrylic-polymer liquid that are blended on site. When the two are combined and cured, the powder hydrates while the polymer forms a continuous flexible film through the matrix, producing a tough but elastic membrane that bonds tenaciously to concrete, render and masonry. Unlike a rigid cementitious slurry, CM660 retains enough elasticity to accommodate minor movement and to bridge the fine shrinkage cracks that inevitably form in concrete water structures.

The product is grey, which lets it serve as a finished surface in tanks and on roofs without the staining and re-coating issues associated with black bituminous products. A defining feature is its tolerance of water pressure from both directions: the cured coating is designed to resist positive hydrostatic pressure (water pushing against the coating from the wet face) as well as negative pressure (water trying to push the coating off the substrate from behind), which is what makes it suitable for basements and below-ground structures where the membrane must work on the inner, dry face. Because Nitocote CM660 carries approvals for use in public/potable water supply, it is widely specified for drinking-water reservoirs and domestic tanks where many bituminous or solvent-borne systems cannot be used.

For Indian projects, Space Arc Engineering positions CM660 as a robust tanking and water-retaining-structure coating that pairs well with the rest of the Fosroc waterproofing and concrete-repair range, giving consultants a single warranted system from substrate repair through to the finished waterproof layer.

The technical insight

The performance of Nitocote CM660 comes from the interaction of two chemistries working at once. The cementitious fraction provides compressive strength, alkalinity and a strong chemical/mechanical bond to the concrete substrate, while the acrylic polymer modifies the hydrated cement matrix – reducing permeability, increasing tensile and flexural capacity, and introducing the elasticity that lets the film flex rather than crack. This polymer modification is why the coating can bridge cracks up to roughly 0.8 mm wide that develop after curing, provided a continuous coat of about 2 mm has been built up; a plain cement slurry of the same thickness would simply fracture over the same crack.

The dual positive/negative pressure rating (7 bar positive, 3 bar negative when tested to DIN 1048) is the spec that matters most to engineers. Positive-side resistance is comparatively easy to achieve; resisting negative pressure is harder because the coating must maintain adhesion under water trying to delaminate it – so the 3 bar negative figure (roughly a 30 m head) signals genuine adhesion strength, not just film density. To realise these values the substrate must be sound, clean and brought to a saturated-surface-dry (SSD) condition before application: the polymer film needs intimate contact with damp – not flooded, not dust-covered – concrete to develop its bond. Because no separate primer is required, surface preparation and SSD wetting effectively replace priming, and getting that step right is the single biggest determinant of long-term performance.

Where it is used

• Internal lining of potable-water tanks, overhead and underground reservoirs, and domestic/commercial water sumps
• Waterproofing of swimming pools, water features and decorative ponds
• Tanking of basements, lift pits, retaining walls and below-ground structures on both positive (water) and negative (dry) faces
• Waterproofing of canals, culverts, channels and other hydraulic water-conveyance structures
• Sewage treatment plant (STP) and water treatment plant (WTP) tanks and channels
• Waterproofing of terraces, flat roofs, balconies, chajjas and wet areas such as bathrooms and kitchens
• Refurbishment and re-waterproofing of existing leaking concrete and masonry structures

Key advantages

• Resists high positive (7 bar) and negative (3 bar) hydrostatic pressure, suiting it to both water-retaining and below-ground water-excluding structures
• Flexible, polymer-modified film bridges fine shrinkage cracks up to ~0.8 mm at 2 mm thickness
• Approved for contact with potable/drinking water, so it can line water-supply tanks and reservoirs
• Bonds tenaciously to concrete and masonry without a separate primer, simplifying application
• Grey colour can be left as the finished surface – no staining or bleed associated with bituminous coatings
• Pre-packaged two-component system gives consistent on-site mixing and reliable, repeatable performance
• Breathable, water-based and low-odour, allowing application in enclosed tanks and internal wet areas
• Can be applied to slightly damp substrates and over the wet face, reducing downtime on refurbishment work

Limitations & considerations

• It is a thin flexible coating, not a structural repair – active, moving or structural cracks must be treated separately before coating
• Crack-bridging is limited to fine cracks (~0.8 mm); it will not span large or live joints, which need a dedicated joint/sealant detail
• Substrate must be sound, clean and brought to saturated-surface-dry condition; honeycombing, laitance and contamination must be made good first
• Not formulated as a chemical-resistance lining for aggressive acids, solvents or fuels – specialised epoxy or PU linings are required for such exposure
• Not a decorative wear coat or a trafficable deck system on its own; needs protection/screed where foot or vehicle traffic occurs
• Performance depends heavily on workmanship – correct mixing ratio, two-coat build and adequate cured thickness are essential to reach rated pressures
• Application and curing are temperature-sensitive; very hot, freezing or rapidly drying conditions require protection and curing precautions

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Nitocote CM660

Within the Fosroc range, Nitocote CM660 sits at the higher-performance end of the cementitious waterproofing family, above the general-purpose Nitocote CM210 elastomeric coating and alongside the CM662 variant, and it works hand-in-hand with Fosroc Renderoc repair mortars and Nitobond bonding agents for substrate make-good before coating; where deck-level traffic or chemical exposure is involved it is typically over-coated or substituted with a Fosroc epoxy/PU system such as the Nitocote or Nitoflor lines. For Indian specifiers comparing brands, credible flexible polymer-modified cementitious alternatives include Sika (SikaTop Seal / Sikalastic), MBS (Build-Aid / Powerflex crystalline and acrylic-cementitious coatings), Dr. Fixit (Pidicrete URP and the Dr. Fixit cementitious waterproofing slurries) and STP (Polyalk and related cementitious systems). The honest positioning is that CM660 is a strong, well-documented choice specifically where high negative-side pressure resistance and verified potable-water approval are needed; for purely positive-side terrace waterproofing or budget-driven repairs, a Dr. Fixit or Sika cementitious slurry may be more cost-effective, so Space Arc Engineering recommends selecting on the basis of pressure head, crack-bridging demand, potable-water certification and the warranty package rather than brand alone.

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