Fosroc Brushbond K1
Two-component, acrylic polymer modified cementitious waterproof coating — brush, roller or spray applied for water tanks, terraces, basements and concrete protection.
What is it?
A two-component, acrylic polymer modified cementitious waterproof coating from the Fosroc Brushbond family — a powder (cement/graded aggregate blend) plus an acrylic polymer liquid that cure to a seamless, flexible, water-tight membrane bonded directly to the substrate.
Where is it used?
Water-retaining and water-excluding structures across India: RCC water tanks and reservoirs, sumps, terraces and roof slabs, wet areas (toilets, balconies), basement retaining walls, swimming pool shells and as an anti-carbonation protective coating on exposed concrete.
Why use it?
It waterproofs and protects in one product — bonding to damp or dry concrete and masonry, bridging fine shrinkage cracks, resisting carbonation and chloride ingress, while remaining non-toxic for potable water contact and breathable so trapped vapour can escape.
How is it applied?
Gauge the powder into the liquid, mix 2-4 minutes to a lump-free brushable slurry, then apply in two coats by stiff brush, roller, spray or trowel to a nominal 1 mm total dry film, with the second coat laid once the first is touch-dry.
About Fosroc Brushbond K1
Fosroc Brushbond K1 is part of Fosroc’s long-established Brushbond range of acrylic polymer modified cementitious coatings — the same family that Indian contractors have specified for decades on water tanks, terraces and basements. Supplied as a ready-to-use kit, it pairs a pre-batched cementitious powder with a measured acrylic polymer emulsion. When the two are blended on site (K1 requiring only the kit components, with clean water added where consistency adjustment is needed for spray work), they react into a flexible, seamless coating that bonds tenaciously to the structure rather than sitting on top of it like a loose sheet membrane.
The “K1” designation places it in Fosroc’s kit-based Brushbond line-up alongside variants such as Brushbond RFX, Brushbond UltraFlex and Brushbond Crystal. What unites them is the polymer-modified cementitious chemistry: the cement fraction hydrates and bonds into the concrete pore structure, while the acrylic polymer imparts flexibility, adhesion and reduced permeability that plain cementitious renders cannot match. The result is a positive-side or negative-side waterproofing layer that behaves as a monolithic, jointless skin — a meaningful advantage on the complex geometries (tank corners, pipe penetrations, construction joints) where sheet membranes are slow to dress and prone to failure.
For Indian site conditions, Brushbond K1 has three practical strengths. First, it can be applied to damp (but not running-wet) substrates, which suits freshly cured tanks and monsoon-season terrace work where bone-dry surfaces are rarely available. Second, it is non-toxic once cured, making it suitable for potable water tanks and reservoirs. Third, it is breathable — it transmits water vapour from within the structure outward, so it will not blister or delaminate the way impermeable barriers can when vapour pressure builds behind them. Because it is brush, roller and spray applicable, it is equally at home on small domestic sumps and on large reservoir or treatment-plant areas where spray application speeds up output.
As an authorised Fosroc distributor and applicator serving Delhi NCR and Pan-India, Space Arc Engineering supplies genuine Brushbond K1 with batch traceability and can advise on the correct Brushbond variant, primer, fillet and detailing system for your specific structure.
The technical insight
The performance of Brushbond K1 comes from the interaction of two phases. The acrylic polymer emulsion forms a continuous, flexible film as it coalesces, while the cementitious powder hydrates and chemically integrates with the concrete substrate. This dual mechanism is why the coating both bridges fine cracks (the polymer film stretches) and resists hydrostatic pressure from the positive side (the cement bond and dense matrix). Independent test data on the Brushbond two-component acrylic system records tensile strength of more than 1 N/mm² (ASTM D638), pull-off bond strength to concrete of more than 1 N/mm² (ASTM D4541), and moisture-vapour transmission greater than 300 g/m²/day (ASTM E96) — confirming the breathability that lets vapour escape rather than build up behind the film. Tested against accelerated carbonation per NT Build 372, the coated concrete shows effectively 0 mm of carbonation depth, demonstrating its value as an anti-carbonation barrier on exposed RCC, not merely a water stopper. The product is mixed by adding powder gradually to the liquid and blending for 2 to 4 minutes to a homogeneous, lump-free slurry; pot life is approximately 80 minutes at 25°C, shortening to about 50 minutes at 35°C, so on hot Indian sites material should be mixed in workable batches. It is applied in two coats to build the nominal 1 mm dry film, the second coat following as soon as the first reaches touch-dry, with application restricted to substrate and ambient temperatures above 5°C and below 45°C.
Where it is used
- Waterproofing of RCC underground and overhead water tanks, sumps and reservoirs
- Lining of potable water storage tanks (non-toxic once cured)
- Roof slab, terrace and chajja waterproofing
- Wet-area waterproofing in toilets, bathrooms and balconies
- Basement and retaining-wall waterproofing (positive and negative side)
- Swimming pool shell waterproofing prior to tiling
- Anti-carbonation protective coating on atmospherically exposed concrete columns, beams and facades
- Protection of concrete against chloride-ion, acid-gas and oxygen ingress in marine and aggressive environments
- Re-facing and reprofiling of weathered concrete and masonry surfaces
- Sewage and effluent treatment plant structures requiring a tough, water-resistant skin
Key advantages
- Seamless, jointless membrane that dresses easily around corners, penetrations and complex tank details where sheet membranes struggle
- Bonds tenaciously to concrete and masonry — no separate adhesive layer and no risk of water tracking under the membrane
- Can be applied to damp (not running-wet) substrates, suiting freshly cured structures and monsoon-season work
- Non-toxic when cured — suitable for potable water tanks and reservoirs
- Breathable: transmits internal water vapour (>300 g/m²/day) so the film resists blistering and delamination
- Flexible acrylic film bridges fine shrinkage and thermal cracks in the substrate
- Provides anti-carbonation and chloride-resistance protection to the reinforced concrete, extending structure life
- Versatile application by stiff brush, roller, spray or trowel to suit area size and required texture
- Supplied as a pre-batched ready-to-mix kit, reducing on-site gauging error
- Withstands light pedestrian traffic once fully cured
Limitations & considerations
- Not a structural crack-bridging system — accommodates fine shrinkage cracks only; live, moving or wide cracks need a dedicated elastomeric system such as Brushbond RFX/UltraFlex or a joint sealant
- Rigid-to-semi-flexible cementitious film; on substrates with significant ongoing movement a higher-elongation membrane is preferred
- Pot life is short in heat (about 50 minutes at 35°C) — mix in small workable batches on hot days
- Application is temperature-limited: substrate/ambient must be above 5°C and below 45°C
- Requires sound, clean, laitance-free substrate preparation and proper fillets at wall-floor junctions; performance depends heavily on workmanship
- As a thin protective/waterproof coating it is not a wearing screed and needs a screed or tile finish where heavy traffic or point loading occurs
- Cannot be applied over running water or active leaks without prior plugging (use a Renderoc plug mortar first)
- Confirm potable-water and current TDS approvals for the specific batch and country with Fosroc before specifying for drinking-water contact
Selection & best practice
Prepare the substrate first: remove laitance, oil and loose material, fill blowholes and form a 25 mm cementitious fillet at all wall-to-floor junctions and around penetrations. Pre-saturate the concrete to a damp, surface-dry condition (no standing water). Add the powder gradually to the liquid and mix mechanically for 2-4 minutes to a lump-free slurry; only mix what can be used within the pot life (about 80 min at 25°C, 50 min at 35°C). Apply two coats by stiff brush or roller, laying the second coat at right angles to the first once it is touch-dry, to build a continuous nominal 1 mm film with no pinholes. Reinforce stress points (corners, joints, pipe collars) with a scrim/fibre layer where the structure warrants. Keep application within 5-45°C, protect fresh coating from rain and direct sun, and water-cure as advised before filling a tank or applying tile/screed finishes. Always work to the current Fosroc TDS for the exact pack and confirm coverage on a site trial.
Specifications
| Product type | Two-component, acrylic polymer modified cementitious waterproof coating (powder + acrylic liquid kit) |
| Components | Cementitious powder + acrylic polymer emulsion liquid (ready-to-mix kit) |
| Application method | Stiff brush, roller, spray or trowel |
| Number of coats | Two coats (second coat when first is touch-dry) |
| Nominal dry film thickness | ~1 mm total (built in two coats) |
| Mixing time | 2 to 4 minutes (powder added gradually to liquid, lump-free) |
| Pot life | ~80 minutes at 25°C; ~50 minutes at 35°C |
| Application temperature | Substrate/ambient above 5°C and below 45°C |
| Tensile strength | >1 N/mm² (ASTM D638) — Brushbond 2-component acrylic system |
| Bond / pull-off strength | >1 N/mm² (ASTM D4541) |
| Moisture vapour transmission | >300 g/m²/day (ASTM E96) — breathable |
| Carbonation resistance | 0 mm carbonation depth on coated concrete (accelerated test, NT Build 372) |
| Substrates | Concrete, RCC, cementitious renders and masonry (damp but not running-wet) |
| Potable water contact | Non-toxic once cured — suitable for potable water tanks (confirm current approval) |
| Shelf life / storage | Approx. 12 months unopened, stored cool and shaded per Fosroc TDS |
Industry use cases
Residential & Housing
Waterproofing of overhead and underground RCC water tanks, terrace slabs, sunken toilets and balconies in apartments and independent homes across Delhi NCR — bonded directly to damp concrete and safe for potable storage.
Commercial & Institutional
Basement retaining walls, lift pits, terraces and exposed concrete facades of offices, malls, hospitals and schools, where its anti-carbonation and breathable properties protect the RCC while keeping interiors dry.
Water & Wastewater Infrastructure
Lining of municipal reservoirs, clear-water sumps, STP and ETP tanks, where a seamless, non-toxic, chloride-resistant coating is needed on complex water-retaining geometry.
Hospitality & Recreation
Swimming pool shells, decorative water features and rooftop amenity decks in hotels and clubs, waterproofed before tiling or finishing.
Industrial & Marine
Protection of exposed concrete in industrial plants and coastal structures against acid gases, oxygen, water and chloride ingress that drive reinforcement corrosion and carbonation.
Frequently asked questions
Is Fosroc Brushbond K1 a real Fosroc product?
Can Brushbond K1 be used inside potable (drinking) water tanks?
How many coats are needed and what thickness should I achieve?
Can I apply Brushbond K1 on a damp surface during the monsoon?
How does Brushbond K1 differ from Brushbond RFX or UltraFlex?
What is the pot life and how does heat on site affect it?
How we position Fosroc Brushbond K1
Brushbond K1 sits in the middle of Fosroc’s acrylic-cementitious waterproofing ladder: it is the dependable, general-purpose two-coat brush/spray system for tanks, terraces, basements and concrete protection. Where the structure is subject to greater movement or wider crack-bridging is required, Space Arc typically steps clients up to Fosroc Brushbond RFX or Brushbond UltraFlex (higher flexibility/elongation), while Brushbond Crystal offers a crystalline capillary alternative for negative-side and self-healing performance. It is commonly specified alongside complementary Fosroc systems — Renderoc repair mortars for substrate reinstatement, Nitoproof liquid-applied membranes for high-build elastomeric needs, Conplast integral waterproofers for the concrete mix, and Supercast/Nitoseal sealants and waterstops for joints. Against the wider Indian market, credible alternatives in the two-component cementitious waterproofing class include Sika (Sika MonoTop / SikaTop Seal-107), MYK Laticrete / MBS, Dr. Fixit (LW+ and 2K cementitious coatings) and STP (Krystaline / cementitious slurries). Fosroc’s edge is its integrated repair-and-protect ecosystem, established consultant approvals and nationwide technical support — which, paired with Space Arc Engineering’s authorised supply and applicator services in Delhi NCR and Pan-India, makes Brushbond K1 a low-risk specification for water-retaining and protective waterproofing work.
Related Waterproofing products
Source Fosroc Brushbond K1 for your project
Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.