About Fosroc Proofex Anti Lime Coating

Fosroc Proofex Anti Lime Coating is a specialist surface treatment used inside drained-cavity (Type C) basement waterproofing systems. It is not a membrane in its own right and it is not a tanking slurry. Instead it is a water-based blend of high-performance silicates and wetting agents that is painted or sprayed directly onto the exposed face of the structural concrete before the cavity drainage membrane is installed. Its single job is to deal with free lime. New and damp concrete contains soluble calcium hydroxide (free lime) that water can dissolve and carry to the surface. In a conventional structure this shows up as harmless white efflorescence. But behind a Type C system such as Fosroc Proofex Cavitydrain, that lime-laden water travels through the air-gap cavity, into the perimeter drainage channels and on to the sump and pump. As the water evaporates or the pH shifts, the lime re-crystallises as hard scale that progressively blocks the dimpled membrane voids, silts up the channels and can seize the pump. The result is a drainage system that slowly stops draining, which is the one failure mode a Type C design cannot tolerate. Proofex Anti Lime Coating addresses this at source. When it contacts the concrete, the silicates react with the free lime to form insoluble calcium silicate compounds, in effect consuming the lime and sealing the pore structure at the surface so far less lime is available to migrate into the cavity over the life of the building. For contractors, consultants and waterproofing designers in India working on basements, metro structures, water-retaining tanks and deep substructures, it is a low-cost insurance step that protects a much more expensive drainage installation from long-term maintenance problems.

The technical insight

The chemistry is a pozzolanic-style silicate reaction rather than a film-forming paint. The reactive silicates combine with mobile calcium hydroxide (free lime) in the concrete to precipitate stable, insoluble calcium-silicate-hydrate type compounds within the near-surface pore network. This does two things at once: it densifies and seals the top layer of concrete, and it removes the soluble lime that would otherwise leach out. Because the product is water-based with a low solids content (roughly 8-10% by volume), most of what is applied is carrier water that penetrates and then evaporates, leaving the reactive fraction in the pores. A practical consequence engineers should brief site teams on is appearance: immediately after drying the treated surface can look patchy and uneven, because the reaction and the release of trapped water continue for weeks to months. This is normal and not a coating failure. The same silicate chemistry that seals the surface also slightly improves abrasion resistance and acid resistance of the treated face, but Proofex Anti Lime Coating should never be specified for those secondary benefits alone or as a standalone waterproofing layer.

Where it is used

• Pre-treatment of structural concrete before installing Fosroc Proofex Cavitydrain Type C drained-cavity membranes in basements
• Lining of lift pits, plant rooms and deep substructures where a cavity drain system manages water ingress
• Tunnels, metro stations and underground utility structures using internally drained waterproofing protection
• Reducing efflorescence and lime scale on fair-faced or exposed concrete that will sit behind a maintained drainage cavity
• Treatment of concrete water tanks, sumps and channels where lime leaching could foul downstream pumps and pipework
• Surface densification of green or damp concrete soffits and walls within a Type C system installation sequence

Key advantages

• Cuts free-lime leaching at source, protecting drainage cavities, channels and pumps from lime-scale blockage
• Water-based and low-VOC, making it suitable for enclosed basement and tunnel environments with limited ventilation
• Single-coat application by brush or spray keeps labour and programme impact minimal
• Reacts chemically into the concrete pore structure rather than sitting as a peelable film, so it cannot delaminate
• Improves surface abrasion and acid resistance of the treated concrete as a secondary benefit
• Integrates directly into the Fosroc Proofex Cavitydrain Type C system as a documented ancillary, giving single-source accountability
• Reasonable coverage of 2-4 m2/kg makes it economical insurance for a high-value drainage installation

Limitations & considerations

• Not a waterproofing membrane on its own; it does not resist hydrostatic pressure and must be used as part of a complete Type C system
• Will damage or pit glass, aluminium and painted surfaces on contact, so adjacent finishes must be masked and protected
• Treated surface often looks patchy and uneven for weeks to months while the reaction completes, which can alarm clients if not explained
• Effectiveness depends on adequate free lime and a clean, sound, absorbent substrate; sealed, very dense or contaminated concrete reacts less
• Limited application window (apply within roughly 5C to 35C, not on surfaces at 5C and falling); not suited to freezing or very hot site conditions
• Porous or high-lime concrete may need a second application, so coverage should be confirmed on a trial area
• Does not bridge cracks or replace joint sealing, crack injection or the cavity membrane itself

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Proofex Anti Lime Coating

Proofex Anti Lime Coating sits in a narrow but important niche: it is a system component for Type C drained-cavity waterproofing, not a general-purpose waterproofing product, so it should be specified alongside rather than instead of a membrane. Within the Fosroc range it pairs directly with Proofex Cavitydrain 80, 200, PB and PM20 drainage membranes and their channels, sumps and pumps, and complements pre-applied and post-applied membranes such as Proofex Engage and Proofex 3000 used for Type A and Type B protection. There is no exact like-for-like consumer alternative to this lime-reaction sealer from most Indian competitors, because it is engineered specifically for the Fosroc Cavitydrain system. The closest functional comparisons sit in two adjacent categories. For cavity drain systems themselves, specifiers may also consider Newton, Delta or Triton cavity membranes, which manage lime leaching primarily through filtration, regular flushing and maintenance access rather than a chemical surface treatment. For silicate-based concrete densifiers and pore sealers that reduce efflorescence and dusting, products from Sika (lithium and sodium silicate hardeners), MBS, Dr. Fixit and STP offer broadly similar surface chemistry, though they are sold as floor hardeners or waterproofing admixtures rather than as a dedicated anti-lime pre-treatment for drained cavities. The honest position is that if a project uses Fosroc Proofex Cavitydrain, this coating is the correct, manufacturer-matched way to protect that investment from lime fouling; if a different cavity system or a different waterproofing strategy is chosen, the lime-management approach should follow that manufacturer’s recommendations instead.

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