Fosroc Brushbond UltraFlex
Two-component polymer-modified elastomeric membrane that stretches beyond 150%, bridges 1.0 mm cracks and shows nil permeability under negative pressure — built for Indian roofs, tanks and wet areas.
What is it?
A two-component elastomeric waterproofing membrane: a cementitious powder of selected cements and graded aggregates, mixed on site with a liquid polymer into a brushable coating.
Where is it used?
Roofs and terraces, bathrooms and wet areas, overhead and underground water tanks, reservoirs, swimming pools and precast joints on concrete or masonry.
Why use it?
Elongation above 150% and 1.0 mm crack bridging keep the film intact as hairline cracks move, and it passes USFDA CFR 175-300 migration testing for potable water contact.
How is it applied?
Mix liquid and powder with a slow-speed drill for 4-5 minutes, then apply two 500-micron coats by stiff brush, roller, trowel or approved airless spray.
About Fosroc Brushbond UltraFlex
Brushbond UltraFlex is Fosroc’s high-flexibility grade in the Brushbond family — a two-pack, polymer-modified elastomeric membrane supplied as a ready-to-mix 25 kg kit of 15 kg powder and 10 kg liquid polymer. Once blended, it brushes on like a heavy paint and cures into a seamless, tough elastic film that stays watertight even when the substrate develops hairline movement. The membrane records elongation above 150% and tensile strength over 1.50 N/mm² to ASTM D412, with nil water permeability under negative pressure to EN 12390 Part 8 — meaning it resists water pushing from behind the coating, not just from above.
Space Arc Engineering supplies genuine Fosroc material with current-batch documentation across Delhi NCR and pan-India, and can deploy trained applicator crews where site execution matters as much as material selection. For consultants, we back every enquiry with the official TDS, method statement support and coverage estimation, so the product specified is the product that actually goes on the slab.
The technical insight
The membrane works by film formation within a cementitious matrix. As the mix cures, polymer particles in the liquid component coalesce around the hydrating cement and graded aggregates, producing a continuous elastic network reinforced by a hard mineral skeleton — the cement gives adhesion (over 1.0 N/mm² to ASTM D4541) and alkalinity-compatibility with concrete, while the polymer gives the stretch. This dual structure is why UltraFlex bridges cracks up to 1.0 mm (ASTM C1305) where plain cementitious slurries simply crack with the substrate. Usefully, the film is still breathable — water vapour transmission of roughly 20.81 g/m²·hr to ISO 7783 lets trapped construction moisture escape instead of blistering the coating, while liquid water is blocked in both directions.
Where it is used
- Roof and terrace waterproofing over concrete and masonry
- Bathrooms, toilets and sunken wet areas before tiling
- Overhead and underground water storage tanks, including potable supply
- Swimming pools and reservoirs, finished with protective plaster or tile
- Balcony slabs, chajjas and parapet junctions
- Precast element joints requiring a tough, watertight elastomeric seal
- Internal wet rooms, utility and plant areas
Key advantages
- True elastomeric behaviour: over 150% elongation with 1.0 mm crack bridging
- Bonds to damp substrates with no primer, saving prep time in monsoon-season programmes
- Nil permeability under negative (back) pressure to EN 12390-8 — handles water pushing from behind
- Passes USFDA CFR 175-300 migration test, so it is suitable for potable water tanks
- Low-VOC and non-flammable — safer for enclosed tank and basement application
- Factory pre-batched two-pack kit eliminates site gauging errors and batch variation
- Accepts light foot traffic in about 6 hours; apply by brush, roller, trowel or spray
Limitations & considerations
- Not a wearing surface — anything beyond light foot traffic needs a protective screed or tile finish
- Water-retaining structures such as pools and tanks require a plaster or tile protection layer over the membrane
- Pot life is only about 1 hour at 27°C and shortens in hot weather — mix strictly to consumption
- Suits damp substrates, not wet ones: no standing water, and no application during rain
- Bridges movement up to 1.0 mm only; structural cracks and spalls must be repaired first (Renderoc system)
- Practical coverage falls below the theoretical 16 m² per pack on rough or porous substrates
Selection & best practice
Start with the substrate: remove oil, grease, laitance and loose matter, and cut back spalled or disintegrated concrete to sound material, reinstating with Renderoc repair mortars. Pre-dampen the surface — damp, never ponded. Pour the full liquid component into the mixing drum first, then add powder gradually while mixing 4-5 minutes with a slow-speed drill (350-450 rpm) and Fosroc MR3 paddle until lump-free. Apply with a stiff 120-200 mm brush in two coats of 500 microns each for a 1 mm system, allowing the first coat to dry (typically 4-6 hours at 27°C) before recoating; water-retaining structures need additional coats plus a plaster or tile protection layer. For potable tanks, allow full cure — about 7 days — and rinse before filling. Wash tools immediately; cured material only comes off mechanically.
Specifications
| Supply | 25 kg kit (15 kg powder + 10 kg liquid) |
| Coverage | Approx. 16 m² per 25 kg pack at 1.0 mm thickness |
| Pot life at 27°C | Approx. 1 hour |
| Tensile strength (ASTM D412) | > 1.50 N/mm² |
| Elongation at break (ASTM D412) | > 150% |
| Adhesion to substrate (ASTM D4541) | > 1.0 N/mm² |
| Crack bridging (ASTM C1305) | 1.0 mm |
| Water permeability, negative pressure (EN 12390-8) | Nil |
| Foot traffic | 6 ± 1 hours |
Industry use cases
Residential & Group Housing
Terrace slabs, sunken bathroom portions and balcony junctions in apartment projects, where hairline slab movement defeats rigid slurry coatings.
Water Infrastructure
Municipal overhead and underground tanks and treatment-plant reservoirs — CFR 175-300 migration compliance covers potable contact after full cure.
Hospitality & Commercial
Swimming pools, spas and podium wet areas in hotels and clubhouses, coated before the plaster or tile finish goes on.
Precast & Industrial
Sealing precast element joints and plant-room wet areas where a tough, elastic, foot-trafficable membrane is required quickly.
Basements & Retaining Structures
Negative-side damp-proofing duty where nil permeability under back pressure (EN 12390-8) is the governing requirement.
Frequently asked questions
What area does one 25 kg pack cover?
Is it safe for drinking-water tanks?
Can it be applied during the monsoon or on damp concrete?
Does it need a primer?
Can I tile directly over it, or leave it exposed?
How is it different from standard Brushbond?
How we position Fosroc Brushbond UltraFlex
Within the Fosroc family, specify standard Brushbond for economical damp-proofing on stable substrates, Brushbond FLXIII where an established acrylic-flexible system is already in the BOQ, Nitoproof liquid PU membranes for exposed roofs demanding higher movement and UV endurance, and Renderoc mortars for pre-coating concrete repair. Among our other brands, Dr. Fixit Pidifin 2K is the closest acrylic-cementitious equivalent where the client standardises on Pidilite. Space Arc supplies and applies all of these, so selection can follow the structure, not the stockist.
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