Fosroc Supercast Steel WS
Active-coated galvanised steel-plate waterstop for non-movement construction joints in basements, tunnels, retaining walls and water-retaining structures.
What is it?
A galvanised steel-plate waterstop coated on both faces with a special active material that chemically reacts with the surrounding wet concrete to form a tenacious, watertight bond across non-movement construction joints.
Where is it used?
Cast into construction (day-work) joints of below-grade and water-retaining reinforced concrete: basement rafts and walls, tunnels and subways, retaining walls, foundations, slabs, and bund/spillage containment structures.
Why use it?
It acts as both an active and a passive barrier, resists hydrostatic pressure up to roughly 5 bar (about 50 m head), clips together without welding or special intersections, and unlike hydrophilic strips its coating is not triggered by rain or site humidity, so there is no protective tape to remove.
How is it applied?
The plate is fixed centrally at the joint into the first concrete pour, adjacent lengths are clip-jointed and bent on site to follow the joint, then the second pour is cast against the exposed half so the active coating bonds to the fresh concrete.
About Fosroc Supercast Steel WS
Fosroc Supercast Steel WS is the steel-plate member of Fosroc’s Supercast waterstop family, engineered to seal non-movement construction joints in in-situ reinforced concrete. Each length is a galvanised steel core plate coated on both sides with a proprietary active material. When the second concrete pour is placed against the exposed face, the coating reacts with the alkaline, water-bearing fresh concrete and develops a tenacious chemical and physical bond to the cement matrix. The result is a continuous, two-sided seal that both physically interrupts any water path along the joint (passive action) and chemically locks itself to the concrete on either side (active action). Critically for site conditions in India, the active coating is formulated so that it does not react with rainwater or atmospheric humidity, meaning the strip can sit exposed between pours without being prematurely “spent” and without any protective release tape that must be stripped off before concreting. The product is BBA certified and is recognised as suitable for waterproofing basements to grades 1, 2 and 3 as defined in BS 8102:2009, the British Standard for protection of below-ground structures against water. Space Arc Engineering, as an authorised Fosroc distributor and applicator covering Delhi NCR and Pan-India, supplies Supercast Steel WS alongside the wider Fosroc joint-treatment, waterproofing and grouting range, with technical support on joint detailing and specification.
The technical insight
It is important for specifiers to classify Supercast Steel WS correctly: it is a coated-steel construction-joint waterstop, NOT an elastomeric sealant and NOT a movement-joint product. It has no movement accommodation factor and must not be used where the joint is designed to expand, contract or shear. For genuine movement and expansion joints, an external PVC waterstop (such as the Fosroc Supercast PVC range) or a gun/pour-grade elastomeric sealant is required, and Supercast Steel WS is in fact designed to be compatible with Supercast PVC waterstops where a run of construction joints meets an expansion joint. Its sealing mechanism is fundamentally different from the hydrophilic Supercast SW swellable strips: those rely on controlled crystalline/elastomeric swelling under water contact to exert sealing pressure, whereas Steel WS relies on a rigid steel barrier plus a chemically bonding coating cured by the concrete itself. This rigidity is an advantage in resisting hydrostatic head (rated around 5 bar) and in eliminating the swell-displacement and dry-out concerns of hydrophilic strips, but it also means the plate cannot tolerate joint movement. Because the steel is galvanised and the coating bonds intimately to the concrete, the system delivers good durability when fully encapsulated with adequate concrete cover and proper compaction around the plate.
Where it is used
- Construction (day-work) joints in basement rafts, walls and slabs
- Tunnels, subways and other below-grade cut-and-cover structures
- Earth-retaining and retaining walls subject to ground-water
- Foundations, pile caps, ground slabs and water-retaining tanks
- Bunds and fuel/chemical spillage-containment structures
- Junctions where construction-joint runs meet PVC expansion-joint waterstops
- Waterproofing of basements to BS 8102 grades 1, 2 and 3
Key advantages
- Dual action: forms both an active (chemically bonding) and a passive (physical) barrier to water across the joint
- Resists hydrostatic pressure of approximately 5 bar (around 50 m water head)
- Simple clip-jointing arrangement: no on-site welding, solvent welding or heat fusion required
- Active coating is unaffected by rainwater and atmospheric moisture, so there is no protective tape to remove and no risk of premature activation between pours
- Can be laid directly into fresh / first-pour concrete and bent on site to follow the joint line, with no purpose-made intersection pieces needed
- Compatible with Fosroc Supercast PVC waterstops where construction joints meet expansion joints
- BBA certified and suitable for BS 8102:2009 basement grades 1, 2 and 3
- Galvanised steel core provides a robust, rigid barrier that is not displaced by water flow, unlike some swellable strips
Limitations & considerations
- Strictly for non-movement construction joints only; it has no movement accommodation factor and must not be used in expansion, contraction or seismic movement joints
- Not a sealant: it cannot bridge a visible surface gap or be gun-applied like Nitoseal or Thioflex products
- Sealing depends on the second-pour concrete being well compacted around the plate; honeycombing or voids around the strip can create leakage paths
- Correct central positioning and adequate concrete cover on both faces are essential; poor fixing or insufficient cover compromises performance
- Performance assumes sound, durable structural concrete; it does not waterproof cracked or porous concrete away from the joint
- As a rigid steel plate it suits straight and gently curved joints; tight three-dimensional details still require careful planning even though no special intersection pieces are used
- Galvanised steel can be vulnerable in highly aggressive or chloride-laden ground if not fully encapsulated in good-quality concrete
Selection & best practice
Use Supercast Steel WS only on non-movement construction joints; for any joint expected to move, switch to a PVC waterstop or an elastomeric sealant. Position the plate centrally across the joint so that roughly half its width is embedded in each pour, and fix it securely (typically tied to the reinforcement) so it cannot be displaced or tilted during concreting. Maintain adequate concrete cover to both faces and ensure the concrete is thoroughly compacted around the plate to avoid honeycombing and voids that would otherwise form a leakage path. Join successive lengths using the manufacturer’s clip arrangement and bend the strip on site to follow changes in direction; transitions to expansion joints should be made to the matching Fosroc Supercast PVC waterstop. Keep the exposed coated face clean and free of release agents, oil, laitance or debris before the second pour, and place that pour while detailing follows Fosroc’s installation guidance and the project waterproofing design (for example a BS 8102 grade-appropriate strategy). Confirm current dimensions, pack sizes and exact clip/overlap details against the live Fosroc datasheet for the supplied batch, and involve Space Arc’s technical team at the joint-detailing stage.
Specifications
| Product type | Active-coated galvanised steel-plate waterstop for non-movement construction joints |
| Core material | Galvanised steel plate |
| Coating | Special active coating on both faces; reacts with wet concrete to form a tenacious watertight bond |
| Sealing action | Active (chemical bond to concrete) plus passive (physical barrier) |
| Joint type suitability | Non-movement construction (day-work) joints only |
| Movement accommodation | None (not a movement-joint product) |
| Hydrostatic resistance | Up to approximately 5 bar (about 50 m water head) |
| Reaction to rain / humidity | Active coating does not react with rainwater or atmospheric moisture; no protective tape to remove |
| Jointing method | Simple clip-jointing; bent on site to suit; no special intersections required |
| Compatibility | Compatible with Fosroc Supercast PVC waterstops at expansion joints |
| Certification | BBA certified |
| Standard | Suitable for BS 8102:2009 basement waterproofing grades 1, 2 and 3 |
| Typical applications | Basements, tunnels/subways, retaining walls, foundations, slabs, bunds/spillage containment |
| Dimensions / pack sizes | Confirm against current Fosroc datasheet for the supplied region/batch |
Industry use cases
Basement construction (commercial / residential)
Sealing wall-to-raft and wall-to-wall construction joints in deep basements and podiums, supporting a BS 8102 grade 1-3 waterproofing strategy in high water-table sites across Delhi NCR and coastal cities.
Tunnels, metros and subways
Watertight day-work joints in cut-and-cover tunnel boxes, station diaphragm/structural walls and pedestrian subways, where consistent hydrostatic resistance along long joint runs is critical.
Water and wastewater infrastructure
Construction joints in water-retaining tanks, treatment-plant structures, sumps and reservoirs that must remain watertight under sustained internal or external head.
Industrial bunds and containment
Joints in fuel, oil and chemical spillage-containment bunds where leakage through the joint must be prevented for environmental compliance.
Retaining walls and foundations
Earth-retaining walls, pile caps and foundation rafts where ground-water ingress through construction joints would otherwise threaten the structure and finishes.
Frequently asked questions
Is Fosroc Supercast Steel WS a sealant or a waterstop?
Can it be used in expansion or movement joints?
How much water pressure can it resist?
Does the coating get activated by rain on site before concreting?
How is it different from Fosroc Supercast SW swellable waterstops?
What standards and approvals does it carry?
What are the key installation points?
How we position Fosroc Supercast Steel WS
Within Fosroc’s joint-sealing portfolio, Supercast Steel WS sits firmly on the waterstop side rather than the sealant side, so it is best understood by what it is not: it is not a gun-grade or pour-grade elastomeric sealant like Fosroc Nitoseal (polyurethane/polysulphide sealants), Thioflex 600 (polysulphide) or Colpor 200PF (pourable PU for trafficked floor and pavement joints), all of which accommodate joint movement at a free surface. Steel WS instead waterproofs non-movement construction joints from within the concrete, competing in the same role as cast-in PVC waterstops, hydrophilic strips (Fosroc’s own Supercast SW range) and rival coated-steel and swellable systems such as Sika’s Sikadur-Combiflex and Sika Waterbar / hydrophilic profiles, MBS / Master Builders Solutions MasterSeal waterstops and hydrophilic strips, and STP’s waterstop offerings. The honest positioning is therefore complementary, not interchangeable: specify Supercast Steel WS for static day-work joints where you want a rigid, high-head, tape-free, weld-free barrier; pair it with a Supercast PVC waterstop at the expansion joints; and reach for a Nitoseal, Thioflex or Colpor sealant only where a surface movement joint actually needs to be sealed. Space Arc Engineering can supply the full Fosroc set and advise on which member of the system each joint condition calls for.
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