Fosroc Supercast Synkoflex (FR)
Fuel-resistant, non-swelling preformed plastic adhesive waterstop for watertight construction joints in concrete structures — including bund walls, thin-section walls and fuel-contact environments.
What is it?
A fuel-resistant, non-swelling preformed plastic adhesive waterstop strip (12mm x 30mm section) that seals construction (day-work) joints in concrete by fusing with the fresh pour. It is the FR — fuel-resistant — grade of the Supercast Synkoflex range, distinct from swellable bentonite-type waterstops.
Where is it used?
Construction joints in water-retaining and below-ground concrete structures — particularly bund walls, fuel/chemical containment, tank farms, basements, pump pits and thin-section walls where a swelling waterstop is unsuitable or hydrocarbon exposure is expected.
Why use it?
It bonds to fresh concrete without swelling, resists fuels and chemicals, tolerates rainwater and long delays before the second pour, and adapts to complex joint geometry — giving reliable watertightness against a hydrostatic head of up to 30m.
How is it applied?
Pressed onto a clean, freshly poured or trowelled concrete surface; on existing/hardened concrete it is bonded over a 75mm-wide strip of Supastik E10 Adhesive. Strips are side-lapped/overlapped by 25mm, then the next concrete lift is cast over it with a minimum of 50mm cover.
About Fosroc Supercast Synkoflex (FR)
Fosroc Supercast Synkoflex (FR) is the fuel-resistant grade of Fosroc’s preformed adhesive waterstop system, engineered to deliver watertight integrity across construction (day-work) joints in concrete structures. Unlike the hydrophilic, bentonite-based waterstops it is often compared with, Synkoflex FR is a non-swelling preformed plastic mastic strip. It works by physically and adhesively fusing with the concrete on both sides of the joint, forming a continuous, impermeable barrier through which water cannot track. The “FR” suffix denotes its formulation for resistance to fuels and a range of chemicals, which is why it is specified for containment and hydrocarbon-contact applications where a standard swelling waterstop would be the wrong choice. Supplied as a flexible rectangular strip of nominal section 12mm x 30mm in 5-metre lengths, it is hand-applied rather than cast-in like rigid PVC or rubber waterstops, making it fast to install and highly adaptable around penetrations, kickers and irregular joint profiles. For the Indian market — where basement rafts, water tanks, STP/ETP structures, bunds and fuel-storage facilities are routinely built in phased pours — it offers contractors a practical, forgiving joint-sealing method that does not demand the precise formwork detailing of cast-in waterstops. Space Arc Engineering supplies Supercast Synkoflex (FR) along with its companion Supastik E10 Adhesive and the matching Supercast PVC waterstop range, and provides application support to consultants and applicators across Delhi NCR and Pan-India.
The technical insight
The defining technical point about Synkoflex FR is that it is NON-swelling. Many engineers assume any “Synkoflex”-type joint strip is a hydrophilic (water-swelling) waterstop, but the FR grade seals purely by adhesion and fusion with concrete, not by expanding on contact with water. This matters because swelling waterstops can over-expand in permanently saturated or cyclically wetted conditions, and they perform poorly against hydrocarbons — exactly the scenario in fuel bunds. The non-swelling, fuel-resistant chemistry is therefore a deliberate engineering choice, not a limitation. A second key insight is the rainwater tolerance: because the strip is unaffected by rainwater, the first pour can be left exposed for prolonged periods before the closing pour without compromising the bond — valuable on Indian sites where monsoon delays between lifts are common. The product is rated to resist a hydrostatic head of up to 30m. Critically, Synkoflex FR is a construction-joint product only — it CANNOT accommodate the cyclic movement of an expansion joint and must not be used as one. For movement joints, Fosroc’s cast-in Supercast PVC waterstops (to which Synkoflex FR can be neatly joined) or a gun-grade movement sealant such as Nitoseal or Thioflex is the correct selection.
Where it is used
- Sealing horizontal and vertical construction (day-work) joints in water-retaining concrete structures
- Bund walls and secondary containment around fuel and chemical storage tanks
- Thin-section reinforced concrete walls where cast-in PVC/rubber waterstops are impractical
- Basement rafts, retaining walls and below-ground structures subject to ground-water pressure
- Water and effluent tanks, STP/ETP and treatment-plant structures
- Pump pits, lift pits, sumps and service trenches
- Joints where the second concrete pour is delayed (e.g. to fix reinforcement) or exposed to rain before casting
- Tying into and continuing a Supercast PVC waterstop line at the junction of construction and expansion joints
Key advantages
- Fuel-resistant and chemical-resistant — suitable for hydrocarbon-contact containment where swelling waterstops fail
- Non-swelling: seals by adhesion/fusion with concrete, avoiding over-expansion problems in saturated conditions
- Can be applied directly to freshly poured concrete, fusing with the pour
- Unaffected by rainwater, allowing long delays between first and closing pours
- Adaptable to complex joint shapes, penetrations and irregular profiles without special formwork
- Fast, low-skill hand application — no need to cast-in or split formwork as with rigid waterstops
- Joins readily to Fosroc Supercast PVC waterstops at expansion-joint transitions
- Withstands a hydrostatic head of up to 30m
- Cost-effective installation compared with cast-in waterstop systems
Limitations & considerations
- NOT a movement/expansion-joint product — cannot accommodate cyclic joint movement and must not be used in expansion joints
- Construction-joint sealing only; it is a waterstop, not a gun-grade or pouring-grade elastomeric sealant
- Requires a minimum of 50mm concrete cover over the strip; should not be installed at less cover
- Application onto existing/hardened concrete needs the correct primer/adhesive (Supastik E10 Adhesive) and a clean, dry, debris-free surface
- Strips must be correctly side-lapped/overlapped (25mm) to maintain continuity — poor lapping creates leak paths
- Performance depends on good concrete compaction around the strip; honeycombing at the joint compromises the seal
- Limited to its supplied 12mm x 30mm section and 5m strip length; not a poured or trowel-grade material for wide gaps
- Not a substitute for surface waterproofing membranes — it treats the joint, not the slab/wall face
Selection & best practice
Confirm the joint is a construction (day-work) joint, not an expansion joint — Synkoflex FR is for the former only. Ensure the substrate is clean, sound and debris-free; on fresh concrete press the strip firmly into the surface so it fuses, and on existing/hardened concrete first trowel a 75mm-wide band of Supastik E10 Adhesive and bond the strip onto it. Position the strip so it will sit centrally in the joint with no less than 50mm of concrete cover on all sides. Maintain continuity by side-lapping or overlapping consecutive strips by at least 25mm, and form neat, fully-bonded laps at corners and around penetrations. Where the construction-joint line meets an expansion joint, transition into and join with a cast-in Supercast PVC waterstop rather than relying on Synkoflex FR across the moving joint. Protect the placed strip from damage and contamination before the closing pour, and ensure the second lift is well compacted around it to avoid honeycombing. Always follow the current Fosroc datasheet for the specific structure, hydrostatic conditions and exposure.
Specifications
| Product type | Fuel-resistant, non-swelling preformed plastic adhesive waterstop |
| Form | Rectangular-section flexible waterstop strip |
| Nominal section | 12mm x 30mm |
| Strip / roll length | 5 m |
| Colour | Blue |
| Relative density | approx. 1.60 |
| Hydrostatic head resistance | Up to 30 m |
| Minimum concrete cover | 50 mm (must not be installed at less) |
| Side lap / overlap of strips | 25 mm |
| Primer/adhesive for existing concrete | Supastik E10 Adhesive, applied 75mm wide |
| Application to fresh concrete | Direct — fuses with the pour, no primer required |
| Fuel / chemical resistance | Resistant to fuels and a range of chemicals |
| Rainwater tolerance | Unaffected by rainwater; tolerates prolonged delays before closing pour |
| Joint suitability | Construction (day-work) joints only — not for expansion joints |
| Compatibility | Joins to Fosroc Supercast PVC waterstops |
| Pack / supply | 5 m strips, typically 6 strips (30 m) per box |
Industry use cases
Fuel & chemical storage / tank farms
Sealing construction joints in concrete bund walls and secondary containment where stored hydrocarbons rule out swelling waterstops; the fuel-resistant chemistry maintains the seal under spill and immersion conditions.
Water & wastewater infrastructure
Watertight construction joints in clear-water tanks, sumps, STP/ETP and treatment structures, holding against ground-water and contained-water pressure up to 30m head.
Basements & below-ground (commercial / residential)
Joint treatment in basement rafts, retaining walls and lift/pump pits cast in phased pours, where rainwater tolerance suits monsoon-affected Indian sites.
Industrial & process plants
Thin-section walls, trenches and bunds in factories and process facilities where cast-in waterstops are impractical and chemical resistance at the joint is required.
Infrastructure & utilities
Construction joints in box culverts, service reservoirs and underground utility structures, with neat transitions into Supercast PVC waterstops at expansion joints.
Frequently asked questions
Is Fosroc Supercast Synkoflex (FR) a swelling (hydrophilic) waterstop?
What does the ‘FR’ stand for?
Can it be used in expansion joints?
Does it need a primer?
How much concrete cover is required over the strip?
What hydrostatic pressure can it resist, and what are the strip dimensions?
How we position Fosroc Supercast Synkoflex (FR)
Within the Fosroc Supercast range, Synkoflex (FR) is the fuel-resistant, non-swelling adhesive waterstop for construction joints — sitting alongside the standard 25mm x 25mm Supercast Synkoflex and the cast-in Supercast PVC waterstops used for expansion/movement joints. The two are complementary on the same structure: Synkoflex FR seals the day-work joints and ties into a PVC waterstop where it meets a moving joint. It is not a gun-grade or pouring-grade elastomeric sealant, so for sealing visible movement joints, floor saw-cuts and facade gaps the correct Fosroc products are the polysulphide Thioflex 600 (pouring and gun grades), the polyurethane Nitoseal range, or Colpor 200PF for trafficked pavement/floor joints. Among credible alternatives, comparable construction-joint and movement-joint sealing systems include Sika’s SikaSwell/Sikadur and Sikaflex sealants, MBCC/Master Builders Solutions MasterSeal and MasterFlex lines, and STP (Shalimar Tar Products) hydrophilic and PVC waterstops widely used in India. Selection should be driven by joint type (construction vs expansion), exposure (water vs fuel/chemical), and movement accommodation: choose Synkoflex FR specifically when you need a fast, adaptable, fuel-resistant seal across a non-moving construction joint rather than a movement-accommodating elastomeric sealant.
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