About Fosroc Supercast SW

Supercast SW is Fosroc’s hydrophilic waterstop system, engineered to waterproof the construction joints that form every time fresh concrete is cast against a previously set pour. Unlike a conventional PVC waterstop that has to be positioned centrally within the section and cast into both halves, Supercast SW is a compact strip that is simply bonded onto the face of the first pour. When the joint later comes into contact with water, the strip swells and presses tightly against the surrounding concrete, closing the tiny gap at the pour interface where seepage normally begins. This makes it a practical answer for the crowded, over-reinforced sections common in Indian basement rafts, retaining walls and water-retaining tanks, where threading a full dumbbell profile through the rebar is awkward or impossible.

The range is offered in more than one profile to suit the water pressure and joint width on site. Supercast SW10, the smaller 5 mm x 20 mm strip, can increase in volume by up to 300% and resists a hydraulic head of up to 60 metres, while the 10 mm x 20 mm SW20 profile expands by up to 200% and carries BBA approval. Both are supplied in continuous coils and are installed with Supercast SW Adhesive or the gun-grade SWX paste. For contractors and consultants across Delhi NCR and the rest of India, it is a genuinely quick-to-fit, low-fuss way of building watertightness into a joint that would otherwise be a long-term leakage risk.

The technical insight

The swelling action comes from hydrophilic groups that are built into the polymer itself, not a coating or filler that can wash out. When water reaches the strip these groups draw it in and the material expands, generating positive pressure against both concrete faces of the joint. Because the pressure acts outward across the whole interface, it closes the capillary path that water would otherwise track along. Two design details make it reliable on real sites: the swelling is chemically bound to the polymer, so repeated wet and dry cycles do not leach it out or reduce performance over the life of the structure; and the swell is deliberately delayed, so a strip that gets rained on before the second pour will not pre-expand and lose its grip once the concrete is placed. The material is also tolerant of dissolved salts in the concrete and in groundwater, which matters for coastal and high-water-table sites where chloride and sulphate levels are high.

Where it is used

• Kickers and construction joints in basement rafts and retaining walls
• Water-retaining structures such as RCC tanks, reservoirs and STP/ETP chambers
• Tunnels, cut-and-cover sections and underground metro or railway works
• Podium slabs and terrace-level construction joints over occupied space
• Swimming pools, water features and wet wells
• Pile cap to raft and raft to wall junctions in congested reinforcement
• Sealing around pipe penetrations and small service entries through concrete
• Joints where a full-section PVC dumbbell cannot be threaded through the rebar

Key advantages

• Swells on contact with water to seal the joint from within, without needing a full-depth cast-in profile
• Ideal for heavily reinforced sections where a PVC waterstop is hard to position
• Delayed swell action prevents premature expansion if the strip is wetted before the second pour
• Hydrophilic groups are bound into the polymer, so performance survives repeated wet/dry cycling
• Re-seals itself if the joint is re-wetted after an initial dry period
• SW10 resists a hydraulic head of up to 60 m; range independently tested to high pressures
• Tolerant of salts in concrete and groundwater, suiting coastal and high-water-table sites
• Quick to install by simple adhesive bonding, saving time on congested reinforcement

Limitations & considerations

• Intended for non-moving construction joints only, not for expansion or movement joints that flex
• The joint face must be sound, clean and reasonably flat for the adhesive bond to hold
• Must not be allowed to pre-swell from standing water or heavy rain before the concrete is cast against it
• Correct profile must be matched to the expected water head; an undersized strip will not seal high pressures
• Depends on the concrete on both sides being dense and well compacted around the strip
• Cannot bridge cracks or honeycombing in the parent concrete; those need separate repair

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Supercast SW

Supercast SW is the swellable-strip choice for non-moving construction joints; where a joint will actually move or open, specify a flexible profile from the same family, Fosroc Supercast PVC (Hydrofoil, Watafoil, XHD and Rearguard dumbbell and centre-bulb sections). Pair the strip with Supercast SW Adhesive or Supercast SWX paste for fixing and for tying into a PVC waterstop network. For the wider joint, cast against it with a quality Fosroc concrete admixture such as the Conplast range, and for surface-applied basement or tank waterproofing over the finished structure, we also supply Fosroc Brushbond and, from our other brands, Dr. Fixit and Sika crystalline and membrane systems. Our engineers can help you match the right waterstop and complementary products to the water head and joint type on your project.

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