Fosroc Proofex Torchseal 4SI
4mm slated-finish, torch-applied polymer-modified bituminous membrane for roofs, basement tankings, podium decks and buried structures.
What is it?
A 4mm thick, slated (mineral) finish torch-applied waterproofing membrane made from polymer-modified bitumen reinforced with a non-woven polyester carrier, supplied in rolls.
Where is it used?
Concrete roof and floor slabs, deep basement tankings, car park and podium deck slabs, retaining walls, tunnels and subways across building and infrastructure projects in India.
Why use it?
Heat-fused application gives a fully bonded, monolithic, seamless barrier; the polyester core resists puncture and stress while the slate finish adds surface protection and grip.
How is it applied?
The primed concrete substrate is heated with a propane torch as the roll is unrolled, melting the underside so the membrane fuses to the deck; side laps overlap at least 10 cm and end laps 15 cm.
About Fosroc Proofex Torchseal 4SI
Fosroc Proofex Torchseal 4SI is part of Fosroc’s Proofex Torchseal range of torch-applied (heat-welded) bituminous waterproofing membranes. As the official Fosroc datasheet describes it, the 4SI is a “4mm Slated Finish Torch applied waterproofing membrane” — a factory-made sheet of polymer-modified bitumen reinforced with a non-woven polyester fabric core and finished on the upper face with fine mineral slate granules. In the Proofex Torchseal naming, the number (4) denotes nominal thickness in millimetres and the letter family (S) denotes the slated/mineral finish, distinguishing it from the plain-finish “P” grades. It is delivered as pre-formed rolls that are bonded to the structure on site by flame heating, producing a continuous, fully adhered waterproof skin without curing time or wet trades. For Indian projects — where monsoon loading, high roof-deck temperatures and aggressive ground water are routine — this kind of reinforced, fully-bonded membrane is a workhorse system for both above- and below-grade waterproofing. Space Arc Engineering supplies Proofex Torchseal 4SI as an authorised Fosroc distributor serving Delhi NCR and Pan-India, alongside the matching Proofex Torchseal Primer and ancillary detailing products needed for a complete, warrantable installation. Because the membrane is torch-bonded rather than loose-laid, it is well suited to surfaces with falls, upstands and complex geometry, and the reinforcement gives it the mechanical robustness to survive follow-on trades and protective screeds.
The technical insight
The performance of a torch-applied membrane comes from three things working together: the bituminous compound, the reinforcement carrier, and the quality of the heat-fused bond. In the Proofex Torchseal family the compound is a polymer-modified bitumen — modification widens the service-temperature window so the sheet stays flexible in cold conditions and resists flow/sag at high deck temperatures, both of which matter on Indian roofs that can swing from winter nights to 60-plus degree C surface temperatures in summer. The reinforcing core is a non-woven polyester fleece; polyester is chosen over glass because it combines high tensile strength with significant elongation, letting the membrane bridge minor cracks and accommodate substrate movement without tearing, while remaining rot-proof and puncture-resistant. The slate (mineral) top finish is the practical differentiator of the “S” grade: the granular surface improves UV durability where the membrane may be temporarily exposed, reduces surface tackiness and adds slip resistance for installers, whereas plain “P/I” grades are intended to be screeded or boarded over. The torch-and-roll method fuses the underside of the sheet directly to a primed substrate, so the bond is continuous rather than spot-fixed — this is what makes the system genuinely monolithic and resistant to lateral water tracking, provided laps are properly heat-welded. Note that exact mechanical figures (softening point, tensile strength, elongation, low-temperature flexibility) for the 4SI grade are published in Fosroc’s region-specific datasheet and should be read off the current India datasheet for any specification, since values differ between the slated, plain and SBS-reinforced variants in the range.
Where it is used
- Waterproofing concrete roof and floor slabs
- Deep basement and below-grade tanking
- Car park and podium deck waterproofing
- Retaining walls and buried concrete structures
- Tunnels, subways and other civil infrastructure
- Foundations and rafts subject to ground water
Key advantages
- High-strength polyester reinforcement gives excellent resistance to puncture and applied stress
- Heat-fused, fully bonded application creates a continuous, seamless, monolithic barrier
- Easily torch applied and readily formed around contours, upstands and details
- Slated mineral finish adds UV durability and surface grip where temporarily exposed
- Polymer-modified compound stays flexible across a wide service-temperature range
- No curing time or wet mixing on site, allowing fast progress and immediate overlay once cooled
- Backed by Fosroc technical support and supplied with the matching Proofex Torchseal Primer
Limitations & considerations
- Requires skilled applicators with open-flame (propane torch) equipment, raising fire-safety and supervision needs on site
- Substrate must be sound, dry, float-finished, primed and free of laitance, frost and contamination before application
- Open-flame work is restricted or prohibited near combustible insulation, finishes and in confined or occupied spaces
- Lap quality is workmanship-dependent; poorly welded side/end laps are the common failure point
- Exposed membranes generally need protection (screed, board or paving) on trafficked or long-term-exposed decks
- Detailed mechanical property values are region/grade specific and must be confirmed against the current India datasheet, not assumed from sister grades
Selection & best practice
Prepare a sound, float-finished concrete substrate that is dry and free from frost, surface laitance and contamination, then apply Proofex Torchseal Primer and allow it to dry tack-free before laying; re-prime any surface left more than 24 hours. Lay rolls with the correct orientation, heating the underside with a propane torch so the bitumen just melts and flows, and roll into place with even pressure. Maintain a minimum 10 cm side lap and 15 cm end lap, fully heat-welding every lap and forming detailing at upstands, drains and corners. Always provide trained applicators, fire-watch and extinguishers for open-flame work, and protect the finished membrane with a screed, board or paving where it will be trafficked or permanently exposed. Confirm grade selection, primer coverage and current property values against the latest Fosroc India datasheet.
Specifications
| Product type | Torch-applied (heat-fused) polymer-modified bituminous waterproofing membrane |
| Nominal thickness | 4 mm |
| Top surface finish | Slated / mineral finish |
| Reinforcement carrier | Non-woven polyester fabric core |
| Application method | Propane gas torch, fully bonded to primed substrate |
| Primer | Proofex Torchseal Primer (applied to tack-free before laying) |
| Side lap / end lap | Minimum 10 cm (side) / 15 cm (end), heat-welded |
| Roll size (Torchseal range) | Typically 10 m long x 1 m wide |
| Primer coverage (range) | 0.2 – 0.8 litre/m² |
| Shelf life | 12 months in cool, dry, unopened storage (store horizontally) |
Industry use cases
Commercial buildings
Waterproofing exposed and protected roof slabs on offices, malls and mixed-use towers where a tough, reinforced membrane is needed under traffic and follow-on trades.
Residential and high-rise
Terrace and podium deck waterproofing on apartment projects, providing a fully bonded barrier that resists monsoon ponding and thermal stress.
Infrastructure
Tanking and protection of tunnels, subways, retaining structures and bridge decks against ground water and hydrostatic pressure.
Parking and podiums
Car park and podium deck slabs where puncture resistance and a continuous heat-welded barrier are essential before screeds and paving are laid.
Industrial and below-grade
Deep basement tankings, foundations and buried concrete in industrial facilities, including sites with aggressive ground water conditions.
Frequently asked questions
What is Fosroc Proofex Torchseal 4SI?
What does the 4SI naming mean?
Where can Proofex Torchseal 4SI be used?
What primer is required, and how is it applied?
Is it suitable for exposed roofs in the Indian climate?
How does it compare with liquid-applied waterproofing?
How we position Fosroc Proofex Torchseal 4SI
Proofex Torchseal 4SI sits in Fosroc’s reinforced torch-applied membrane line, where it is the 4mm slated-finish grade. Within the same Fosroc range, buyers commonly weigh it against the plain-finish 4PI (intended to be overlaid/protected), the 3S/4S/5S SBS-reinforced membranes, and the 3P/4P plain grades; for fire-sensitive or highly detailed areas Fosroc’s liquid-applied Brushbond systems or self-adhesive Proofex options can be specified instead of an open-flame membrane. Against the wider Indian market it competes with torch-applied and APP/SBS membranes from Sika (Sikaplan/SikaBit), STP Ltd (Sturdy/Insulayer torch membranes), MBS (Master Builders Solutions / former BASF MasterSeal membranes) and Dr. Fixit (Pidilite) torch-applied bituminous ranges. Honestly positioned, Proofex Torchseal 4SI is a dependable, well-supported reinforced membrane for projects already standardising on Fosroc; specifiers wanting to avoid hot works, or needing fully cold-applied detailing, should compare it with self-adhesive or liquid alternatives. Space Arc Engineering, as an authorised Fosroc distributor for Delhi NCR and Pan-India, can supply the membrane with the correct primer and detailing accessories and confirm current grade specifications.
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