UltraTech Seal & Dry Flex
A two-component, styrene-acrylic cementitious coating built to bridge hairline cracks and stop water ingress on terraces, roofs, tanks and balconies.
What is it?
A factory-proportioned, two-part flexible waterproofing coating — cementitious powder blended on site with a styrene-acrylic polymer liquid — brushed on in two coats to form a seamless, crack-accommodating membrane.
Where is it used?
Exposed terraces and sloping roofs, RCC water tanks and sumps, balconies and wet-area upturns, domes and curved surfaces, and retrofit waterproofing on occupied structures up to roughly 10,000 sq ft per project.
Why use it?
It stretches with the substrate rather than cracking alongside it, giving positive-side protection on decks that see daily thermal movement, monsoon ponding and foot traffic.
How is it applied?
Mix roughly 2 parts powder to 1 part liquid by weight into a lump-free slurry, then brush-apply two coats — the second run perpendicular to the first — onto a clean, saturated-surface-dry substrate, leaving a minimum 8-hour gap between coats.
About UltraTech Seal & Dry Flex
Seal & Dry Flex sits in UltraTech’s waterproofing range as the flexible, brush-applied option for engineers who need more give than a rigid cementitious slurry offers, without moving up to a fully elastomeric membrane. It pairs cementitious powder with a styrene-acrylic polymer liquid supplied as a factory-matched kit, so the mix ratio stays consistent across labour teams instead of depending on how generously a mason eyeballs the water. Cured, the film stretches beyond 50% of its length under load — enough to ride out the hairline movement that opens up around parapet junctions, pipe sleeves and construction joints on an Indian terrace through a monsoon-to-summer cycle. Being a positive-side system, it sits atop the slab facing the weather rather than inside a tank wall fighting pressure from behind, and UltraTech scopes it for jobs under roughly 10,000 sq ft — the bracket covering most residential and mid-size commercial roofs Space Arc quotes across Delhi NCR.
The technical insight
The polymer does the structural work. Styrene-acrylic latex particles coalesce as the slurry dries, knitting a continuous, flexible film around the cement hydration products instead of leaving a rigid, brittle matrix the way an unmodified slurry would. That film is what lets the coating absorb over 50% elongation at a tensile pull of 50 kg/sq.cm without splitting, and what closes its pore structure enough to resist water penetration once cured. Two coats, brushed at right angles to each other, matter more than they sound: the crossed strokes even out pinholes and thin patches a single pass tends to leave along masonry high points, so the finished film reaches a workable 1.2–1.5 mm dry thickness with reasonably even coverage.
Where it is used
- Positive-side waterproofing of exposed terraces and sloping RCC roofs
- RCC overhead and underground water tanks, sumps and water-retaining structures
- Balconies, sit-outs and wet-area upturns at parapets and door thresholds
- Domes, chajjas and other curved or non-planar concrete surfaces
- Retrofit and renovation waterproofing on occupied buildings under roughly 10,000 sq ft
- Bridging hairline cracks and construction joints subject to thermal movement
Key advantages
- Flexible film with over 50% elongation absorbs substrate movement instead of cracking with it
- Factory-proportioned powder-and-liquid kit keeps the mix ratio consistent across labour teams
- Brush application needs no specialised spray equipment, so smaller crews mobilise fast
- Strong mechanical bond to concrete and masonry without a separate bonding coat
- Two-coat, cross-brushed method self-corrects for pinholes and uneven substrate texture
Limitations & considerations
- Positive-side only — not rated to resist water pressure from the reverse, negative face
- Scoped by UltraTech for areas under roughly 10,000 sq ft; larger decks typically call for Hi-Flex or a membrane system
- Needs a saturated-surface-dry substrate and a minimum 8-hour gap between coats, so it is weather- and schedule-sensitive during monsoon work
- Elongation tops out around 50%, lower than fully elastomeric or Hi-Flex-grade coatings, so it is not the first choice on decks with wide, active joints
- Being cementitious, it still needs sound concrete beneath it — it is not a repair mortar for spalled or honeycombed sections
Selection & best practice
Treat surface preparation as half the job: wire-brush and jet-wash the slab to bare, sound concrete, then pre-wet it so the substrate is saturated but shows no standing water when the first coat goes on — a bone-dry or puddled deck is the commonest cause of debonding on site. Mix only what the crew can apply within the working window, keep the second coat strictly perpendicular to the first, and respect the minimum 8-hour recoat gap even under schedule pressure. On terraces that will carry tiles or screed afterward, protect the cured film until the topping goes down.
Specifications
| Product type | Two-component, cement-based, styrene-acrylic polymer modified flexible waterproof coating |
| Mix ratio | Approx. 2 parts powder : 1 part liquid, by weight |
| Coverage | 12–14 sq.ft per kg at 1.2–1.5 mm DFT, over 2 coats |
| Elongation | >50% at 50 kg/sq.cm tensile force |
| Number of coats | 2 coats; second coat applied perpendicular to the first |
| Recoat interval | Minimum 8 hours between coats under normal conditions |
| Pack size | 15 kg factory-proportioned kit (powder + liquid) |
| Recommended project area | Positive-side jobs under roughly 10,000 sq ft |
| Application tool | Stiff nylon brush |
| Substrate condition | Saturated surface dry (SSD), no standing water |
| Storage | Cool, dry, shaded storage; refer to TDS for shelf life |
Industry use cases
Residential terraces and sloped roofs
Positive-side film that flexes with seasonal thermal movement across Delhi NCR’s hot summers and monsoon cycles.
RCC water tanks and sumps
Brush-applied lining for overhead and underground tanks where a seamless, crack-bridging coat beats a rigid slurry.
Balconies and wet areas
Upturns at parapets, door thresholds and pipe sleeves where movement-prone junctions need a coating that will not split.
Renovation and retrofit work
Occupied buildings under roughly 10,000 sq ft where brush application avoids spray-membrane mobilisation costs.
Domes and curved surfaces
Non-planar concrete geometry where a flexible film conforms more evenly than a rigid coating.
Frequently asked questions
Can Seal & Dry Flex go on the negative, inside face of a water tank?
How much material does a typical terrace need?
What is the difference between Flex and Hi-Flex?
Does the surface need a primer first?
Can tiles go directly over the cured coating?
How we position UltraTech Seal & Dry Flex
Within UltraTech’s own range, Seal & Dry Flex is the mid-tier brush-applied option — more flexible than a plain cementitious slurry like ILW+, but scoped for smaller decks and lower elongation than Hi-Flex. Space Arc typically specifies it for terraces, balconies and tanks under 10,000 sq ft where budget and brush-crew mobilisation matter more than maximum crack-bridging capacity; wider active joints or larger areas are usually better served by stepping up within the range or to a fully elastomeric membrane.
Fosroc Brushbond UltraFlex — Specifiers who need a wider crack-bridging tolerance often step up to Brushbond UltraFlex, rated for over 150% elongation and up to 1.0 mm crack width against Flex’s ~50% and hairline range, on exposed decks with more active joint movement.
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