About Fosroc Supercast WCP

Fosroc Supercast WCP — short for Watertight Concrete Powder, and previously marketed as Conplast WP402 — is an integral water-resisting admixture rather than a surface coating or a joint sealant. It is supplied as a white, chloride-free powder based on a unique blend of fatty acid salts and hydrophobic materials, pre-weighed into water-soluble bags so that a measured dose can be dropped straight into the mixer without manual weighing or dust. When the bag dissolves, the actives disperse through the cement matrix and line the capillary pores with a water-repellent (hydrophobic) layer, while also helping to block and refine the pore structure. The net effect is concrete that resists the passage of water under both capillary action and hydrostatic pressure.

The product sits squarely within the “Type B — structurally integral protection” route described in BS 8102:2009, the British Standard for protection of below-ground structures against water ingress. In that approach the reinforced concrete element is itself the primary barrier, and an admixture like Supercast WCP is used to lower the permeability of that element. Because it is chloride-free, it is suitable for use in steel-reinforced and prestressed concrete without contributing to corrosion risk — a meaningful distinction from older calcium-chloride-bearing waterproofers. The grade carries third-party assurance: a British Board of Agrément (BBA) certificate, conformity with the water-resisting admixture requirements of EN 934-2 Table 9, and inclusion on the UK Drinking Water Inspectorate (DWI) list of products approved for contact with public water supply, which is why it is used in potable-water tanks and treatment structures.

For Indian projects, Supercast WCP is positioned as the “integral” leg of a complete Fosroc waterproofing system. It is rarely specified alone — it is combined with properly designed construction and movement joints sealed using swellable strip waterstops (Supercast SW20 with SWX adhesive sealant) or PVC waterstops, and frequently with an external Fosroc membrane or drained-cavity system where the water table or exposure is severe. Space Arc Engineering supplies and supports Supercast WCP, the associated waterstop range and the wider Fosroc system across Delhi NCR and Pan-India.

The technical insight

The mechanism is hydrophobic pore-blocking, not film-forming. The fatty-acid-salt actives react within the cement paste to deposit a water-repellent lining inside the capillary pore network, so water beads and is held back rather than wicking through. This simultaneously lowers porosity, reduces permeability and cuts the chloride/ion diffusion coefficient — which is why the same admixture is specified both for watertightness and for durability in aggressive (chloride/sulphate) exposure classes. Crucially, performance is conditional on a sound concrete mix: Fosroc’s guidance calls for a minimum cement content of about 350 kg/m³, a maximum free water/cement ratio of 0.45, and a workable consistency of class S2 or greater, all placed and compacted to give dense, crack-controlled concrete. The admixture reduces permeability of the matrix; it cannot bridge structural cracks, honeycombing or unsealed joints, so mix design, reinforcement detailing for crack-width control, and joint sealing carry equal weight. Over-dosing should be avoided — excess can act as an unintended plasticiser and may reduce early strength.

Where it is used

• Type B integral watertight concrete to BS 8102:2009 for basements, lift pits and underground car parks
• Water-retaining structures: clear-water tanks, reservoirs, sumps and sewage/effluent treatment tanks
• Water-excluding structures below the water table such as retaining walls, podium slabs and tunnels/cut-and-cover sections
• Potable-water structures where DWI approval for contact with drinking water is required
• Concrete exposed to aggressive XS/XD/XA exposure classes where reduced permeability improves durability
• Marine and coastal substructures where lower chloride diffusion protects embedded reinforcement
• Foundations and rafts in high-water-table or waterlogged ground across coastal and riverine Indian sites

Key advantages

• Chloride-free, so safe for reinforced and prestressed concrete with no added corrosion risk
• Pre-weighed water-soluble bags eliminate site weighing, reduce dust and give consistent dosing
• Builds water resistance into the full thickness of the concrete rather than a thin surface layer
• Reduces porosity, permeability and ion-diffusion coefficient in one admixture, aiding both watertightness and durability
• Third-party assured: BBA certificate, EN 934-2 Table 9 conformity and DWI potable-water approval
• No change to normal placing, compaction or curing procedures; dosed at the batching plant or truck mixer
• Integrates with the wider Fosroc system — swellable/PVC waterstops and external membranes — for a complete Type A+B solution

Limitations & considerations

• Not a sealant, coating or waterstop — it does not seal joints, cracks or penetrations and must be paired with waterstops and joint sealants
• Cannot bridge structural or shrinkage cracks; relies on good crack-width control and dense, well-compacted concrete
• Effective only if mix discipline is maintained (min ~350 kg/m³ cement, max 0.45 w/c, S2+ consistency); poor mixes undermine performance
• Over-dosing can cause an unintended plasticising effect and may reduce early strength
• Best treated as one part of a designed system; in high hydrostatic head or critical structures an external membrane/drained cavity is still advisable
• As a powder added at batching, it depends on accurate dispensing and thorough mixing for uniform dispersion
• Imported/specified UK-origin certifications (BBA, DWI) should be cross-checked against the relevant Indian project specification and IS provisions

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Supercast WCP

An important clarification: although our internal brief listed Supercast WCP under joint sealants, verification against Fosroc’s official sources shows it is an integral watertight concrete admixture (powder), not a sealant, coating or waterstop. We have written this page accurately on that basis. Within the Fosroc range, WCP is the “make the concrete itself watertight” component and works alongside — not instead of — the genuine joint products: Supercast SW20 swellable strip with Supercast SWX adhesive sealant, and the Supercast PVC waterstop range for movement and construction joints. Where a gun-applied movement-joint sealant is needed on the same project, that is the role of Fosroc’s Nitoseal (polyurethane/silicone), Thioflex 600 (polysulphide) or Colpor 200PF (for trafficked/expansion joints) — distinct products covered separately. As a watertight-concrete admixture, comparable offerings in the Indian market include Sika WT-200 P / Sika-1 (Sika), MasterLife and MasterSeal integral systems (Master Builders Solutions), and Dr. Fixit / Pidicrete-style integral waterproofers (Pidilite), as well as STP integral admixtures. Specifiers typically choose Supercast WCP when they want a chloride-free, BBA- and DWI-credentialed integral admixture that slots cleanly into a complete Fosroc Type B waterproofing system. Space Arc Engineering, as an authorised Fosroc distributor and applicator, supplies WCP together with the matching waterstops and membranes and advises on correct dosage and joint detailing for projects across Delhi NCR and Pan-India.

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