About Fosroc Supercast SWX

Fosroc Supercast SWX is the gun-applied member of the Supercast SW family of swellable waterstops, supplied as a grey, ready-to-use elastomeric paste in a cartridge and applied exactly like a conventional sealant. Its function, however, is fundamentally different from a movement-accommodating joint sealant. SWX is a hydrophilic waterstop: hydrophilic groups bonded into its polymer backbone draw in water and cause the material to swell by up to 200% of its volume. That controlled expansion develops a positive pressure against the two concrete faces of a joint and physically blocks the passage of water through it. Because the hydrophilic groups are an intrinsic part of the polymer rather than a soluble additive, the swelling action survives repeated wet/dry cycling without significant loss of performance, which is what distinguishes a good hydrophilic product from cheaper bentonite-based strips that can wash out over time.\n\nIn Indian practice SWX plays three connected roles on a basement or water-retaining structure. First, it is a swellable adhesive for bonding Supercast SW formed strip (SW10 / SW20) to the concrete arris of a construction joint, where it also fills surface undulations and blow-holes beneath the strip. Second, it is a problem-solver in difficult-access detailing — around pipe and cable-duct entries, H-beams and other penetrations, between rough slurry walls and slabs, and around precast segments and manhole rings, where shuttering a conventional waterstop would be uneconomic or impossible. Third, it acts as the connector that links Supercast SW (used on construction joints) into a conventional Supercast PVC waterstop network (used on expansion joints), so a single integrated waterproofing line can run continuously around a structure even though it changes waterstop type at each joint.\n\nFor specifiers, consultants and waterproofing contractors across Delhi NCR and Pan-India, SWX is best understood as a construction-joint waterstop in a tube, not a sealant for visible building joints. Used within its envelope it is fast, forgiving on damp substrates and highly adaptable to complex geometry; used outside it (on expansion joints, free-standing walls or as a general building sealant) it will disappoint. Space Arc Engineering, as an authorised Fosroc distributor and applicator, supplies SWX alongside the full Supercast SW and PVC waterstop range and the Nitoseal, Thioflex and Colpor movement sealants that complete a correctly detailed waterproofing scheme.

The technical insight

The defining number for design is the swell mechanism, not a movement accommodation factor — SWX is a non-movement waterstop, so MAF is effectively zero and the product must never be specified on a joint that flexes. Fosroc’s datasheet records a volumetric swell ratio of 200%, a Shore A hardness of around 30, a tack-free time of approximately 1 hour at 20°C/50% RH and a cure rate of 3 mm in 24 hours. The single most important detailing rule is concrete cover: the swelling pressure must be confined to work, so the India TDS calls for a minimum of 70 mm cover over the bead (the wider Supercast SW range data uses 75 mm for SW10 and 80 mm for SW20 strip). Too little cover and the expanding paste can crack or spall thin sections instead of sealing. The bead must be continuous and at least 15 mm in diameter as a standalone seal, or a minimum 12 mm diameter when used to bond SW strip to rough concrete. SWX tolerates damp concrete but not running or standing water, and it must be protected from heavy rain while curing because premature wetting triggers swelling before the surrounding concrete is in place — the same reason large pours that risk direct contact with the seal are held for 8 hours.

Where it is used

• Construction (non-movement) joints in in-situ reinforced concrete water-retaining and below-ground structures
• Bonding Supercast SW10 / SW20 swellable strip to concrete joint faces, including filling undulations and blow-holes beneath the strip
• Sealing around pipe entries, cable ducts and H-beams or other penetrations through concrete structures
• Sealing joints in precast manhole covers, chamber rings and tunnel/shaft segments
• Sealing rough interfaces such as secant or diaphragm slurry walls to floor slabs and kicker joints
• Linking Supercast SW (construction joints) into Supercast PVC waterstop networks (expansion joints) for a continuous system
• A belt-and-braces secondary seal gunned alongside conventional rubber or PVC waterstops prior to the concrete pour
• Emergency and remedial sealing where hand-placed concrete cover is needed within ~2 hours

Key advantages

• Applied like a sealant from a standard cartridge gun — no shuttering, grooves or specialist plant required for awkward details
• Swells up to 200% by volume on contact with water to form a self-energising compression seal across the joint
• Bonds to damp and uneven concrete and plugs surface inequalities, giving a reliable seal on rough substrates
• Hydrophilic groups are bound into the polymer, so swelling performance is retained through repeated wet/dry cycling and is tolerant of salts in concrete and groundwater
• Fast curing — allows hand-placed concrete cover in about 2 hours and large pours after 8 hours, supporting tight programmes
• Integrates Supercast SW and Supercast PVC waterstops into one continuous waterproofing network
• Highly adaptable to complex joint shapes and penetrations where a formed waterstop cannot easily be fitted
• Backed by Fosroc’s BS EN ISO 9001 quality scheme and full technical/CAD support through Space Arc as authorised distributor

Limitations & considerations

• Not a movement joint sealant — must not be used on expansion joints or joints subject to significant or repetitive movement
• Requires a minimum of 70 mm concrete cover over the bead to safely confine swelling pressure; thin sections risk cracking
• Cannot be applied over running or standing water, and must be protected from heavy rainfall while curing to prevent premature expansion
• Concrete must not be poured directly onto the seal; care during placement is essential (hence the 8-hour wait for large pours)
• Not suitable as a general-purpose building or facade sealant
• Must not be used where swelling is unrestrained or on free-standing / bund / dwarf walls, where swell pressure could lift the wall — refer to Fosroc for an alternative
• Relatively short shelf life of 9 months in unopened cartridges; stock should be rotated
• May cause skin sensitisation — gloves and eye/face protection required, use in well-ventilated areas

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Supercast SWX

Within Fosroc’s joint-treatment portfolio, Supercast SWX sits firmly on the waterstop side, not the sealant side. It is the gun-applied partner to Supercast SW10/SW20 swellable strip and Supercast SW Adhesive, and the connector that ties those construction-joint products into the Supercast PVC waterstop range used on expansion joints. It should not be confused with Fosroc’s movement-accommodating sealants — Nitoseal (polyurethane/MS-polymer gun-grade sealants), Thioflex 600 (polysulphide) and Colpor 200PF (pouring-grade sealant for trafficked floor and pavement joints) — which are the correct choice wherever a joint actually moves; a well-detailed water-retaining structure typically uses SWX/SW on its construction joints and a Nitoseal/Thioflex/Colpor sealant over the waterstop on its expansion joints. Among competing brands, the closest hydrophilic-swellable equivalents are Sika’s Sikaswell-S/Sikaswell-A swellable sealants and profiles, Master Builders Solutions (formerly BASF) MasterSeal swellable/hydrophilic waterstops, and locally STP (Shalimar Tar Products) and similar Indian manufacturers’ swellable waterstop pastes. SWX competes on its proven wet/dry-cycling durability, ease of application to damp rough concrete and seamless integration with the established Supercast PVC system. Space Arc Engineering supplies and applies the complete Fosroc Supercast and sealant range across Delhi NCR and Pan-India and can advise on the right combination of swellable waterstop and movement sealant for a given joint.

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