About Fosroc Supercast SW10

Fosroc Supercast SW10 is a hydrophilic swellable waterstop designed to give a positive, self-sealing barrier against water passing through non-movement joints in cast in-situ concrete. It is a solid, preformed rectangular elastomeric strip measuring 5mm x 20mm, supplied in convenient 15-metre coils and black in colour. Unlike traditional centre-bulb PVC waterstops that physically span a joint and rely on being cast across the pour line, Supercast SW10 works on a different principle: the polymer contains hydrophilic groups that absorb water and cause the strip to swell. As it swells against the confined faces of a hardened concrete joint, it develops a positive contact pressure that closes off the seepage path. Critically, the hydrophilic groups are an intimate part of the polymer structure and are not leached out by repeated or prolonged wetting, so the seal is durable rather than a one-time reaction. The product is bentonite-free and contains no rubber or sodium-bentonite inclusions, which is an important distinction in Indian water-retaining and basement work where sodium-bentonite tapes can over-swell, lose strength on dry-out, and fail under wet/dry cycling. Supercast SW10 is the smaller-section member of the Fosroc Supercast SW family, sitting alongside the larger 10mm x 20mm Supercast SW20 (red), the gun-applied Supercast SWX swellable paste, and Supercast SW Adhesive. It is WRAS-approved and suitable for contact with potable water, making it appropriate for drinking-water tanks, treatment plants and reservoirs. Space Arc Engineering supplies and applies the full Fosroc Supercast range across Delhi NCR and Pan-India, with technical detailing support for basements, STPs/WTPs and water-retaining structures.

The technical insight

The behaviour that matters most on site is the delayed-swell action. Supercast SW10 does not begin swelling significantly the instant it gets wet; the onset is deliberately retarded so the strip is not pre-swollen by rain, groundwater splash or fresh-concrete water before the second pour is placed and cured. Swelling in fresh (highly alkaline, low free-water) concrete is minimal, which is exactly what you want — premature expansion against an unconfined edge wastes the swell capacity and can spall thin cover. The strip needs to be confined to perform: as it tries to expand within a hardened joint that has at least 75mm of concrete cover, the restraint converts the swell into compressive sealing pressure rather than free volume change. This is why concrete cover and edge distance are non-negotiable, not a nicety. The unrestrained volumetric expansion is rated up to 200% and the SW10 grade resists a hydrostatic head of up to 60 metres; the larger SW20 (100m head) is specified where contact area and risk are higher, such as Grade 3 watertight basements. Because the strip is a solid hydrophilic elastomer (100% solids, no solvent), there is no cure shrinkage and no volatile loss. Application temperature is -5C to 50C and the cured seal serves from -30C to 70C, comfortably covering Indian climatic extremes. The single biggest field failure mode is incorrect substrate or fixing — the strip must be continuously bonded to a sound, clean surface with no gaps that water can track behind.

Where it is used

• Sealing horizontal and vertical construction joints (day-work joints) in water-retaining and below-grade concrete
• Kicker joints and base-to-wall junctions in basements, tanks and reservoirs
• Pile caps and joints between piles and the capping beam in secant-piled and diaphragm-walled basements
• Joints cast against existing or old hardened concrete where a through-wall PVC waterstop cannot be installed
• Pipe and service entry detailing through concrete walls and slabs
• Sewage and effluent treatment plant (STP/ETP) tanks, sumps and channels
• Potable-water structures — clear-water tanks, WTP basins and underground reservoirs (WRAS approved)
• Lift pits, basement raft-to-wall joints and metro/tunnel cut-and-cover construction joints
• Linking into Supercast PVC waterstop networks (via Supercast SWX) so PVC handles movement joints and SW10 handles construction joints

Key advantages

• Seals construction joints without the complex shuttering and pour-blocking that centre-bulb PVC waterstops require
• Bentonite-free and rubber-free — avoids the over-swell, strength-loss and wet/dry degradation associated with sodium-bentonite tapes
• Swelling properties are unaffected by long-term wet/dry cycling and are tolerant of salts in concrete and groundwater
• Delayed-swell action gives genuine on-site tolerance, reducing the risk of pre-swell before the second pour
• WRAS approved and suitable for contact with potable water
• Solid 100% solids elastomer — no cure shrinkage, no solvent loss, dimensionally stable
• Highly adaptable to complex joint shapes, pipe penetrations and tight detailing
• Can be installed by adhesive bonding to damp substrates (using Supercast SWX / SW Adhesive) or cast directly into the joint
• Integrates with Supercast PVC networks for a single continuous waterproofing system
• Compact 5mm x 20mm section and 15m coils are easy to handle and fix on congested reinforcement

Limitations & considerations

• For non-movement (construction) joints only — it is not a movement-accommodating sealant and must not be used in isolation across expansion or contraction joints; pair with Supercast PVC for movement joints
• Requires a minimum of 75mm concrete cover over the strip to safely contain swelling pressure; thin sections risk spalling
• Performance depends entirely on correct fixing — must be continuously and fully bonded to a clean, sound substrate with no voids behind it
• Must be protected from prolonged ponding, heavy rain or standing water before the confining concrete is cast, or it will pre-swell and waste capacity
• Not a surface sealant or a crack-injection product — it works only when embedded and confined within a joint
• Hydrostatic head limited to 60 metres for the SW10 section; use SW20 where head, contact area or basement grade demands more
• Concrete joint faces must be free of laitance, dust, oil, curing compound and loose material before fixing
• Not a substitute for sound concrete mix design, compaction and overall waterproofing detailing

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Supercast SW10

Within the Fosroc joint-sealing range, Supercast SW10 occupies the swellable-waterstop slot for non-movement construction joints — a different job from Fosroc’s gun-grade movement-joint sealants. For true expansion and movement joints you would specify a polyurethane sealant such as Fosroc Nitoseal (e.g. Nitoseal MS or PU grades), a polysulphide such as Thioflex 600, or for trafficked horizontal joints the pourable Colpor 200PF; SW10 complements rather than competes with these by handling the day-work joints those sealants are not designed for. Against PVC waterstops, SW10 is chosen where complex shuttering, pile caps or casting-against-existing-concrete make a centre-bulb PVC strip impractical, and the two systems are routinely combined via Supercast SWX. Credible alternatives in the swellable-waterstop category include Sika’s hydrophilic profiles (such as SikaSwell), BASF/MBCC MasterSeal swellable waterstop ranges, and Indian-market options from STP Limited and similar manufacturers — these are broadly comparable in principle, so selection usually comes down to head/cover requirements, potable-water approval, bentonite-free chemistry and a single accountable supply-and-apply source. As an authorised Fosroc distributor and applicator, Space Arc Engineering positions Supercast SW10 where a verified WRAS-approved, bentonite-free strip with documented 200% swell and 60m head performance is needed for basement and water-retaining construction joints across Delhi NCR and Pan-India.

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