About Fosroc Proofex Torchseal 3S*, 4S* & 5S*

Fosroc Proofex Torchseal 3S, 4S and 5S are factory-made torch-applied waterproofing membranes built around a single, proven idea: take a heavily modified bitumen compound, carry it on a strong rot-proof reinforcement, and fuse it to the structure with controlled heat so the finished system behaves as one continuous tanked skin. All three grades share the same DNA – premium-grade heavily modified bitumen reinforced with a non-woven polyester fabric core weighing 180 g/m2. That polyester carrier is the engine of the product: it gives the sheet its mechanical strength, allows useful elongation so the membrane can accommodate movement and minor settlement, and provides high resistance to piercing during backfilling, reinforcement placement and follow-on trades.\n\nThe three designations refer to membrane build, with the numeral following Fosroc’s nominal-thickness convention seen across the Torchseal family (the sibling Proofex Torchseal 3P and 4P are the 3mm and 4mm APP-based grades). In practice, specifiers move up the range – 3S to 4S to 5S – as the waterproofing duty becomes more demanding: deeper basements, higher hydrostatic head, heavier backfill, longer design life, or sites with aggressive ground water. The membranes are supplied with different top-surface finishes depending on whether the sheet is the lower (sacrificial/underlay) layer or the exposed cap in a two-ply system, with slated/mineral and aluminium-faced options available within the wider Torchseal range.\n\nThe \”why torch-applied\” question matters in the Indian market, where liquid coatings and self-adhesive sheets compete hard. A torch-fused membrane gives the applicator a positive, visible bond – the bitumen flows and a small bead of molten compound appears at the lap – which is hard to fake and easy to inspect. There are no curing times to wait out as with cementitious or PU liquid systems, and the membrane thickness is guaranteed by the factory rather than dependent on site coats. For below-ground tanking against aggressive groundwater – a common condition near coastal cities, high-water-table plots in the NCR and reclaimed land – the chemical resistance and continuous bitumen mass of Proofex Torchseal make it a long-standing, conservative choice that consulting engineers are comfortable specifying.\n\nAs an authorised Fosroc distributor serving Delhi NCR and pan-India, Space Arc Engineering supplies the Proofex Torchseal grades together with the matching Fosroc primer, protection boards and detailing products so the whole tanking system comes from one accountable source.

The technical insight

The performance of any torch-applied membrane is governed by two things working together: the modified-bitumen compound and the reinforcement. In Proofex Torchseal, the bitumen is heavily polymer-modified, which widens the service-temperature window – it stays flexible enough to handle cold-weather laps and stays dimensionally stable on hot Indian roof decks where unmodified bitumen would flow. The 180 g/m2 non-woven polyester core is deliberately chosen over glass-fibre carriers used in cheaper felts: polyester elongates before it fails, so the sheet can bridge shrinkage cracks and tolerate substrate movement instead of tearing at a stress point. That same elongation, combined with the mass of the compound, is what gives the high puncture and piercing resistance that makes the membrane survive backfilling and screeding. The torch process itself is the third variable – the heat must fully reactivate the underface so the bitumen wets the primed substrate and the overlap fuses into a homogeneous seam; under-torching leaves a cold lap (the classic failure path), while over-torching scorches the compound and embrittles it.

Where it is used

• Below-grade tanking of basements, lift pits and foundation rafts
• Waterproofing of retaining walls and earth-retaining structures
• Water-retaining structures and tunnels
• Podium decks and car-park decks (with protection and wearing course)
• Concrete and timber roof slabs as a two-ply torch-on system
• Sites with aggressive ground water requiring chemical-resistant tanking
• Buried structures requiring puncture resistance under heavy backfill
• Bridge decks and civil-works substructures

Key advantages

• High-strength 180 g/m2 polyester reinforcement gives excellent resistance to puncture, piercing and stress during backfill and follow-on trades
• Heavily modified bitumen provides good flexibility and elongation to accommodate substrate movement and shrinkage cracking
• Fully bonded by torch fusion – laps and seams melt into a homogeneous, easily inspected joint with a visible bitumen bead
• Factory-controlled membrane thickness removes the site-coat variability of liquid-applied systems
• Chemical resistance suits tanking against aggressive ground water
• No curing or drying wait time – structure can progress quickly after sealing
• Rot-proof carrier means the reinforcement will not degrade in damp buried conditions
• Forms readily to contours, upstands and detailing

Limitations & considerations

• Requires an open LPG flame and trained applicators – a hot-works permit, fire watch and combustible-free zone are mandatory, especially on occupied or roof sites
• Cannot be torch-applied directly over green, damp or contaminated concrete; the substrate must be sound, dry, primed and properly cured
• Quality is highly applicator-dependent – cold laps from under-torching or embrittlement from over-torching are the common failure modes
• Bitumen is not UV-stable; exposed applications need a mineral/aluminium cap sheet, screed, protection board or wearing course
• Not suited to confined, poorly-ventilated spaces or near flammable insulation/membranes where open flame is unsafe
• Detailing at penetrations, drains and upstands is labour-intensive and must be executed correctly to avoid leak paths
• Published numeric engineering values (softening point, tensile, elongation) should be confirmed against the current country-specific Fosroc datasheet before specification

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Proofex Torchseal 3S*, 4S* & 5S*

Within the Fosroc range, Proofex Torchseal 3S/4S/5S are the heavily modified-bitumen, torch-applied membranes positioned for robust below-grade tanking and roofing; the sibling Proofex Torchseal 3P/4P are the APP-based grades, while Fosroc’s self-adhesive (Proofex Engage / Proofex GP) and liquid systems (Brushbond, Nitoproof, Polyurea) suit flame-free or seamless-detailing situations. Choose Torchseal when you want a factory-thickness, fully-bonded, inspectable membrane and have trained applicators and a hot-works-permissible site. Against the wider Indian market, it competes with Sika’s torch-on bituminous membranes (e.g. Sika BituSeal), MBS/STP Lymtech APP and SBS torch-grade membranes (Indian membrane majors), and is an alternative to Dr. Fixit’s largely liquid-applied basement and roof systems. Honestly, where a project cannot accommodate open flame, prefers a cold-applied installation, or needs a fully seamless monolithic finish around complex detailing, a self-adhesive sheet or a PU/polyurea liquid membrane may be the better fit – torch-on’s advantages are bonded strength, guaranteed thickness and proven long-term tanking, not flame-free convenience.

Related Waterproofing products

View all Waterproofing products →