Fosroc Proofex Waterproof Render
Single-component, polymer-modified cementitious tanking render for internal (Type A) waterproofing of below-ground structures, applied in just two coats.
What is it?
A factory pre-bagged, polymer-modified cementitious render that needs only clean water on site. It bonds tightly to concrete and masonry to form a continuous internal waterproof barrier (a tanking system) against ground water.
Where is it used?
Internal faces of below-ground structures such as basements, lift-pits, cellars, retaining walls, water tanks and tunnels where negative-side (Type A) waterproofing is specified.
Why use it?
It cures to an extremely low-permeability skin that resists both positive and negative hydrostatic pressure (5 bar for 3 days), needs only two coats instead of three, and removes the variability of site-batched cement slurries.
How is it applied?
Mechanically prepare and saturate the substrate, mix the powder with clean water to a consistent render, then apply two coats by brush, trowel or spray, allowing the first coat to set before overcoating, and moist-cure.
About Fosroc Proofex Waterproof Render
Fosroc Proofex Waterproof Render is a ready-to-use blend of dry powders that requires only the site addition of clean water to produce a highly consistent cementitious render. It is built on a blend of cements, graded aggregates, special fillers and chemical additives, with polymer modification that gives the cured layer extremely low permeability to water, carbon dioxide and chlorides. The product is supplied as a single component, pre-bagged formulation so that the inconsistency of hand-batched, site-mixed cement-and-waterproofer slurries is taken out of the equation. It contains no chloride admixtures, which makes it safe to use against reinforced concrete.
In Indian construction terms this is a “tanking render” or “negative-side waterproofing plaster” used to line the inside face of below-ground concrete and masonry. Most basements, lift-pits and underground tanks in Delhi NCR and across the country sit in soils with a seasonal water table that rises sharply during the monsoon, generating hydrostatic pressure against the structure. Where the external (positive-side) membrane cannot be accessed or has failed, an internal cementitious render is the practical remedy. Proofex Waterproof Render is engineered for exactly this duty: it is a Type A (barrier) protection system under BS 8102:2022, the British standard widely referenced by Indian consultants for the protection of below-ground structures.
For Space Arc Engineering customers, the product is positioned as the modern, faster-to-apply member of the Fosroc Proofex tanking family. Where many traditional renders require three coats, Proofex Waterproof Render is formulated to deliver a watertight system in two coats, which compresses the programme on basement and lift-pit jobs where access and curing time are always tight. It is fully compatible with other Fosroc Renderoc repair mortars and Dekguard protective coatings, so a single specification can cover concrete repair, tanking and surface protection from one manufacturer’s system.
The technical insight
The waterproofing mechanism here is densification plus polymer film formation, not a chemical crystalline reaction. The graded aggregate and special-filler skeleton produces a tightly packed matrix with minimal capillary voids, while the redispersible polymer modifies the cement paste so that pores are partially blocked and bond is improved at the substrate interface. The result is a low-permeability skin that resists water ingress under pressure from the positive (water) side and, critically for negative-side use, resists being pushed off the substrate from behind (negative hydrostatic pressure). Fosroc states resistance to positive and negative pressure of 5 bar for 3 days, which corresponds to roughly a 50 m head of water, comfortably covering the depth of most Indian basements and lift-pits. Because adhesion governs negative-side performance, substrate preparation is the make-or-break step: the concrete or masonry must be sound, free of laitance, oil and loose material, and pre-saturated to a saturated-surface-dry (SSD) condition so the render does not dry out prematurely. The product is classed R2 under BS EN 998-1 (the European standard for repair mortars) and is suitable for BS EN 1504 repair method 3.1, meaning it is compatible with the host concrete in stiffness and thermal movement and will not introduce damaging stress at the bond line. Its stated substrate window of 20-45 MPa concrete covers ordinary structural grades from M20 upward.
Where it is used
- Internal waterproofing (tanking) of basements and multi-level basement car parks
- Lining of lift-pits and machine pits where standing water collects
- Negative-side waterproofing of underground water tanks, sumps and STP chambers
- Cellars, storage vaults and below-ground archive rooms
- Tunnels, subways and underpass walls
- Retaining walls and earth-retaining structures subject to seasonal ground water
- Refurbishment of leaking basements where external membranes cannot be re-accessed
- Concrete repair to BS EN 1504 method 3.1 in combination with the Fosroc Renderoc range
Key advantages
- Watertight system in only two coats, reducing labour and shortening the programme versus typical three-coat renders
- Resists both positive and negative hydrostatic pressure (5 bar for 3 days), suited to high-water-table sites
- Polymer modification gives extremely low permeability to water, carbon dioxide and chlorides
- Single-component, pre-bagged powder removes site-batching variability and the risk of wrong dosing
- Contains no chloride admixtures, so it is safe against reinforced concrete
- Conforms to BS 8102:2022 Type A and BS EN 998-1 Class R2, supporting specification-led projects
- Excellent bond to both concrete and masonry substrates
- Fully compatible with other Fosroc Renderoc mortars and Dekguard coatings for a single-source system
- 12-month shelf life gives flexibility on procurement and storage
Limitations & considerations
- It is an internal, negative-side (Type A barrier) system; it is not a substitute for external positive-side waterproofing where that can be specified
- Performance depends heavily on substrate preparation and pre-wetting; poor surface prep is the most common cause of failure
- Active running leaks and moving cracks must first be plugged with a fast-setting plugging compound and structurally treated before rendering
- As a cementitious render it needs proper moist curing; on hot, dry NCR sites premature drying can craze the surface
- It manages water through the structure rather than the source, so it should be part of a designed system, not a sole remedy on severely defective concrete
- Not designed as a wearing surface or for chemical-tank linings without a suitable topcoat
- Stated 5 bar/3 day pressure rating should be checked against very deep structures with permanently high heads
Selection & best practice
Treat substrate preparation as the load-bearing part of the job. Hack off all unsound plaster, remove laitable and loose material by mechanical means to expose a sound, slightly roughened concrete or masonry surface, and rake out mortar joints. Plug any active leaks with a rapid plugging compound and address structural cracks separately before tanking. Pre-soak the prepared surface and bring it to a saturated-surface-dry (SSD) condition, with no standing water, immediately before application. Mix only with clean water at the dosage on the bag, using a slow-speed paddle, and never re-temper material that has started to stiffen. Apply two coats, allowing the first to set before the second so the layers key together, and form coves at all wall-to-floor junctions. Continuously moist-cure the finished render and protect it from direct sun and drying winds, which is essential in Delhi NCR summers. Always work to the current Fosroc Technical Data Sheet for mixing ratio, coat thickness, coverage and curing times, and request a project-specific method statement from Space Arc Engineering for high-pressure or deep-basement applications.
Specifications
| Product type | Polymer-modified, pre-bagged cementitious waterproof render (tanking system) |
| Composition | Blend of cements, graded aggregates, special fillers and chemical additives |
| Components | Single component (powder); add clean water on site |
| Waterproofing classification | BS 8102:2022 Type A (barrier) protection |
| Mortar class | BS EN 998-1 Class R2 |
| Concrete repair method | Suitable for BS EN 1504 repair method 3.1 |
| Hydrostatic pressure resistance | Positive and negative pressure, 5 bar for 3 days |
| Number of coats | 2 coats |
| Permeability | Extremely low to water, carbon dioxide and chlorides |
| Substrate compatibility | Structural and non-structural concrete, 20-45 MPa compressive strength |
| Chloride content | Contains no chloride admixtures |
| Substrate bond | Excellent bond to concrete and masonry |
| System compatibility | Compatible with Fosroc Renderoc mortars and Dekguard coatings |
| Shelf life | 12 months (in original sealed packaging, correctly stored) |
Industry use cases
Residential and commercial basements
Negative-side tanking of basement walls and floors in NCR apartment and office projects where a high monsoon water table loads the structure and external membranes are inaccessible after backfill.
Real estate and high-rise
Waterproofing of lift-pits and machine pits in towers, where standing water and humidity would otherwise corrode pit ironmongery and lift equipment.
Water and sanitation infrastructure
Internal lining of underground water tanks, sumps and STP chambers to keep stored water in and ground water out, using a chloride-free, reinforcement-safe render.
Transport and tunnelling
Tanking of metro entrances, subways, underpasses and tunnel walls subject to ground-water seepage under pressure.
Repair and refurbishment
Remediation of existing leaking basements and cellars, combined with Fosroc Renderoc repair mortars to make good spalled concrete to BS EN 1504 before tanking.
Frequently asked questions
What exactly is Fosroc Proofex Waterproof Render used for?
How many coats are required and why does that matter?
How much water pressure can it resist?
Is it safe to apply over reinforced concrete?
Does it replace external waterproofing?
What surface preparation does it need?
Can I get it in Delhi NCR and across India?
How we position Fosroc Proofex Waterproof Render
Within the Fosroc tanking range, Proofex Waterproof Render is the faster, modern alternative to traditional three-coat renders, and it sits alongside the wider Proofex family (such as Proofex 3000/3000MR sheet membranes and Proofex Engage pre-applied membranes) which handle external positive-side waterproofing. For concrete repair before tanking it pairs with Fosroc Renderoc mortars, and for above-ground surface protection with Dekguard coatings, giving a single-manufacturer specification. Compared with crystalline and acrylic-cementitious systems from other brands, it is closest in function to Sika’s tanking renders and SikaTop products, Dr. Fixit’s negative-side waterproofing plasters and LW/crystalline range, MBCC/Master Builders Solutions cementitious coatings (MasterSeal), and STP (Shalimar) coatings; the practical differentiators are its two-coat application, no-chloride formulation, BS 8102:2022 Type A compliance and stated 5 bar positive/negative pressure resistance. Space Arc Engineering recommends selecting between these on the basis of pressure head, substrate condition and whether positive- or negative-side treatment is required, and can advise the correct Fosroc system or equivalent for a given basement, pit or tank.
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