Fosroc Nitocote SN522 WB
Single-component, water-based silane-siloxane impregnating water repellent that penetrates porous masonry to cut water and chloride ingress while letting the structure breathe.
What is it?
A single-component, water-based (WB) silane-siloxane penetrating water repellent. It soaks into porous mineral substrates and reacts in situ to line the pore walls with a hydrophobic, breathable barrier rather than forming a surface film.
Where is it used?
Exterior facades and exposed concrete: RCC structures, fair-faced and precast concrete, brickwork, cement render, plaster, fly-ash and AAC blockwork, and natural or cast stone – typically on elevations, parapets, chajjas, bridges and coastal structures.
Why use it?
It dramatically reduces absorption of rainwater and dissolved chlorides/salts (the main drivers of reinforcement corrosion, efflorescence and freeze-thaw damage) without trapping vapour, and the water-based chemistry means low odour and far lower flammability than solvent-based silicones.
How is it applied?
Applied to clean, sound, essentially dry substrate by brush, roller or low-pressure spray as a flood coat, usually in two saturating passes wet-on-wet, working from the bottom up so runs are re-absorbed.
About Fosroc Nitocote SN522 WB
Fosroc Nitocote SN522 WB is the water-based member of Fosroc’s Nitocote SN522 family of penetrating water repellents. Where the long-established Nitocote SN522 is a colourless, solvent-borne silicone resin solution, the “WB” version delivers the same impregnating, breathable protection from a water-based silane-siloxane formulation – eliminating the solvent odour and the low flash point that make solvent products awkward to use on occupied buildings or in enclosed areas. It is supplied ready to use as a single component, so there is no mixing, induction time or pot life to manage on site, which suits the fast pace of Indian facade and infrastructure work. Functionally, SN522 WB is an impregnation treatment, not a coating in the film-forming sense. It is drawn into the capillary pore network of the substrate, where the active silane-siloxane reacts with moisture and the mineral surface to bond a water-repellent lining onto the pore walls. The result is a substrate that sheds liquid water and the chlorides and sulphates carried with it, yet remains fully vapour-open so any moisture already inside can still dry out. Because it leaves no continuous film on the surface, it is colourless and non-staining, preserving the natural appearance and texture of fair-faced concrete, exposed brick and stone – an important point for architects who do not want a visible “wet look” or sheen. For Indian conditions – monsoon-driven rain, high humidity, urban pollution and aggressive coastal/marine chloride exposure – this profile is valuable. By keeping bulk water and chloride out of the cover concrete, SN522 WB slows the onset of carbonation-assisted and chloride-induced rebar corrosion, reduces efflorescence on brickwork, limits dirt pick-up and biological growth, and improves the structure’s self-cleaning behaviour under rain. It is equally effective on new construction as a preventative measure and on existing/ageing surfaces as part of a durability upgrade. Space Arc Engineering, as an authorised Fosroc distributor and applicator across Delhi NCR and Pan-India, supplies SN522 WB alongside specification support, substrate assessment and trained application for facade-protection and concrete-durability projects.
The technical insight
The performance of any silane-siloxane impregnation is governed by depth of penetration and the integrity of the in-pore reaction, not by film thickness – so there is no DFT to measure. Penetration depends almost entirely on substrate dryness and porosity: the drier and more open the pores, the deeper the active reaches before it reacts with ambient moisture. This is why surface preparation and a genuinely dry (or only slightly damp) substrate matter far more than they do for film-forming coatings, and why the documented coverage of 4.5-9 m2 per litre is a wide band – dense, smooth render sits near the high end while open brickwork or porous block demands the low end and a heavier flood coat. The legacy Nitocote SN522 is classified to BS 6744 (silicone-based water repellents), achieving Class A on predominantly siliceous substrates (concrete, cement render, most brick/stone) and Class B on calcareous substrates (sandstone, limestone, calcium silicate) – a useful indicator of the chemistry’s substrate breadth. The practical implication is that SN522 WB protects against capillary and rain-driven water ingress but is not a tanking or waterproofing membrane: it does not resist standing water under hydrostatic pressure and must not be specified for water-retaining or below-grade applications. It is a durability and weather-protection layer that complements, rather than replaces, membranes and crack-bridging coatings.
Where it is used
- Penetrating water repellent for exposed RCC, fair-faced and precast concrete facades
- Water and chloride-ingress protection on coastal, marine and bridge structures
- Impregnation of brickwork and blockwork to reduce efflorescence and rain penetration
- Self-cleaning, anti-staining treatment for architectural exposed brick, stone and cement render
- Durability upgrade for ageing concrete to slow chloride- and carbonation-related reinforcement corrosion
- Protection of natural or cast stone (sandstone, limestone) cladding and heritage masonry
- Pre-paint moisture control on porous external surfaces (applied before, not under, water-based paints)
Key advantages
- Water-based: low odour and far lower flammability than solvent-borne silicone repellents, better for occupied or enclosed sites
- Penetrates and reacts within the substrate to bond a water-repellent lining rather than a peelable surface film
- Breathable – allows trapped water vapour to escape, so it does not blister or cause moisture build-up
- Reduces ingress of water and water-borne chlorides/salts, improving concrete durability and limiting rebar corrosion
- Colourless and non-staining – preserves the natural colour and texture of concrete, brick and stone
- Single component and ready to use – no mixing, no pot life, fast site application by brush, roller or spray
- Minimises efflorescence on brickwork and improves rain-driven self-cleaning of facades
- Effective on both new and existing/old surfaces
Limitations & considerations
- Not a waterproofing membrane – will not resist standing water or hydrostatic pressure; unsuitable for tanking, water tanks or below-grade use
- Performance depends heavily on a dry, sound, porous substrate; cracks, defects and joints must be repaired separately beforehand
- Penetrating treatment – cannot bridge cracks or accommodate structural movement
- Substrate must be free of oil, grease, laitance, moss/algae and loose material or penetration is compromised
- Water-based cement or emulsion paints should not be applied over treated surfaces (apply such finishes before treatment)
- Effectiveness diminishes on very dense, low-porosity or pre-sealed surfaces that resist absorption
- Not a decorative or pigmented coating – provides no colour, opacity or UV-stable film build
- Coverage varies widely (4.5-9 m2/litre) with porosity, so site trials are needed to confirm consumption
Selection & best practice
Always start with a representative trial patch to confirm absorption, coverage and the absence of any colour change before treating the full elevation. Ensure the substrate is sound, cured and essentially dry – allow new concrete/render to cure fully and let surfaces dry for several rain-free days; clean off oil, grease, laitance, dust and any moss or algae (Fosroc recommends cleaning aids such as Reebaklens). Rake out and re-point defective brick joints and repair cracks/spalls with the appropriate Fosroc Renderoc or Nitomortar repair system first, since the impregnation seals but does not heal defects. Apply by flood-coating with brush, roller or low-pressure spray in two wet-on-wet passes, working bottom-up so runs are re-absorbed, and saturate porous surfaces generously. Protect adjacent glass, aluminium, paintwork and planting from over-spray, and do not apply in rain or onto a wet substrate. Where a painted or pigmented finish is wanted, apply that decorative system before SN522 WB – not over it. Keep containers resealed between uses, observe the shelf-life, and verify the current product Technical Data Sheet and Safety Data Sheet from Fosroc for the exact grade supplied, as regional formulations and figures can differ.
Specifications
| Product type | Single-component, water-based silane-siloxane penetrating water repellent (impregnation) |
| Form / appearance | Liquid, colourless / non-staining after application |
| Components | One component – ready to use, no mixing |
| Coverage | 4.5-9 m2 per litre on brickwork and smooth cement renderings (varies with substrate porosity) |
| Number of coats | Flood coat; porous surfaces saturated by two wet-on-wet coats |
| Application method | Brush, roller or low-pressure spray |
| Suitable substrates | Concrete, fair-faced/precast concrete, brickwork, cement render, blockwork, natural & cast stone |
| Standards (family) | Nitocote SN522 complies with BS 6744 – Class A (siliceous substrates) & Class B (calcareous substrates) |
| Water vapour | Breathable – permits water vapour transmission / drying of substrate |
| Function limit | Resists rain and capillary water; not effective under hydrostatic pressure |
| Cleaning of tools | Clean equipment immediately after use (water for the WB grade) |
| Pack sizes (SN522 range, India) | 1, 5 and 20 litre containers |
Industry use cases
Coastal & marine structures
Impregnating exposed concrete on seafront buildings, jetties and structures in cities like Mumbai, Chennai and Visakhapatnam to cut chloride-laden rain ingress and slow reinforcement corrosion.
High-rise & commercial facades
Treating fair-faced concrete and exposed-brick elevations on towers and IT parks across Delhi NCR to reduce rain penetration, dirt staining and efflorescence while keeping the natural finish.
Infrastructure & bridges
Applying a breathable water/chloride repellent to bridge piers, decks soffits and RCC sub-structures as a durability measure against monsoon exposure and de-icing/road salts.
Heritage & stone masonry
Protecting sandstone, limestone and historic brickwork with a colourless, vapour-open treatment that reduces water uptake and salt-driven decay without altering appearance.
Industrial & institutional buildings
Weatherproofing render and blockwork on factories, warehouses and campuses where low-odour water-based application is preferred over solvent silicones near occupied areas.
Frequently asked questions
Is Fosroc Nitocote SN522 WB a waterproofing coating?
What is the coverage rate of SN522 WB?
How is SN522 WB different from the standard Nitocote SN522?
Will it change the colour or appearance of my facade?
Can I paint over a surface treated with SN522 WB?
What substrates and preparation does it need?
How we position Fosroc Nitocote SN522 WB
Within Fosroc’s protective-coatings portfolio, Nitocote SN522 WB occupies the “penetrating impregnation” niche – it is the breathable, colourless water/chloride repellent you reach for when the goal is durability and weather protection without changing a facade’s appearance. It complements rather than competes with Fosroc’s film-forming and decorative systems: where an anti-carbonation, pigmented and crack-bridging coating is required, the Dekguard range (e.g. Dekguard S / Dekguard E) is the right specification, while elastomeric waterproof coatings such as Brushbond and membranes like Nitoproof handle positive-side waterproofing and movement accommodation. On Indian sites, SN522 WB is frequently specified together with Renderoc repair mortars and Nitobond bonding aids as part of a complete concrete-repair-and-protect sequence. Among credible alternatives, Sika offers Sikagard penetrating water repellents (silane/siloxane creams and liquids) and Sikagard anti-carbonation coatings; MBCC/Master Builders Solutions (formerly BASF) supplies the MasterProtect silane/siloxane impregnation and coating line; Dr. Fixit (Pidilite) markets water repellents and silicone-based facade products widely available in India; and STP Limited offers comparable masonry water-repellent treatments. For pure hydrophobic impregnation with a vapour-open, invisible finish, SN522 WB is well placed; for projects needing colour, opacity, proven anti-carbonation classification or crack-bridging, a Dekguard-type or competitor coating is the more appropriate choice. Space Arc Engineering can advise on the right system per substrate and exposure and supply it across Delhi NCR and Pan-India.
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