Fosroc Proofex Torchseal 4PI Standard
4mm plain-finish, APP-modified bituminous torch-on membrane reinforced with non-woven polyester for terraces, basements, podiums and below-grade structures.
What is it?
A 4 mm thick, plain-finish (the ‘PI’ in the name), torch-applied waterproofing membrane made from APP (atactic polypropylene) modified bitumen and reinforced with a non-woven polyester carrier. The ‘Standard’ grade is Fosroc’s general-purpose APP membrane for everyday building waterproofing.
Where is it used?
Concrete roof and floor slabs, terraces and podiums, deep basement tankings, car-park deck slabs, concrete retaining structures, and tunnels/subways across residential, commercial and light-industrial projects in India.
Why use it?
It delivers a fully bonded, monolithic, seam-welded waterproof layer with high puncture and tensile resistance from the polyester core, good UV/weather durability, and the proven track record of the Fosroc Proofex brand at a cost-effective price point.
How is it applied?
The substrate is float-finished, dried and primed with Proofex Torchseal Primer (0.2-0.8 L/m2); the membrane is then heat-bonded with a propane torch, melting the underside so it fuses to the deck, with 100 mm side laps and 150 mm end laps.
About Fosroc Proofex Torchseal 4PI Standard
Fosroc Proofex Torchseal 4PI Standard is a torch-applied, polymer-modified bituminous waterproofing membrane that sits in the heart of Fosroc’s well-known Proofex Torchseal range. It is built around two components working together: a waterproofing compound of bitumen heavily modified with APP (atactic polypropylene), and a strong non-woven polyester fabric carrier embedded at the centre of the sheet. The APP modification gives the bitumen a higher softening point and better resistance to flow at elevated temperatures, which matters enormously on Indian terraces and exposed roofs where surface temperatures routinely cross 60-70 degrees C in peak summer. The polyester reinforcement, in turn, carries the mechanical load – it resists puncture during installation and over-blinding, accommodates substrate movement, and stops the sheet from tearing under stress.
The product name itself is a useful shorthand. The “4” refers to the nominal 4 mm sheet thickness, and the “PI” denotes a Plain (mineral-free) upper Isofinish – in other words a smooth top surface rather than a slate-granule (“SI”) finish. Plain-finish sheets like the 4PI are intended to be covered: with screed, tiles, a protection board, or a separate UV-protective top coat, since exposed bitumen degrades under sustained sunlight. The “Standard” suffix distinguishes this everyday grade from heavier-duty or specially reinforced variants in the same family.
For Space Arc Engineering’s customers across Delhi NCR and pan-India, the 4PI Standard is the workhorse of the torch-on category. It is the membrane specified when a project wants a fully bonded, fully welded waterproofing layer that behaves as one continuous sheet rather than a cold-applied liquid or a loose-laid sheet. Because every overlap is heat-fused, there are no cold joints to fail, and the bond to the primed deck is intimate and continuous. It is supplied in 10 m long by 1 m wide rolls, coloured black, with a 12-month shelf life when stored cool, dry, vertical and away from direct heat.
The technical insight
The defining technical choice in this product is APP rather than SBS modification. APP (atactic polypropylene) raises the bitumen’s softening point and gives the membrane “plastomeric” behaviour – excellent heat stability and resistance to flow on hot roofs, plus good UV and ageing resistance. The trade-off versus SBS (“elastomeric”) membranes is reduced low-temperature flexibility and less elastic recovery, which is rarely a constraint in the hot, freeze-free plains of most of India but does matter in high-altitude or cold-climate projects. The non-woven polyester carrier (Fosroc’s wider 3P/4P range uses a 180 g/m2 polyester fabric) is the second key element: polyester offers higher elongation and puncture resistance than glass-fibre carriers, so the sheet tolerates structural movement and rough decks. The application physics are equally important – torch heat must melt only the thin underside polymer film so it wets and bonds to the primed substrate; over-heating burns the bitumen and destroys the membrane, while under-heating leaves voids and unbonded laps that become leak paths.
Where it is used
- Waterproofing concrete roof and floor slabs (terraces, podiums)
- Deep basement tanking and below-grade concrete structures
- Car-park deck slabs and intermediate suspended decks
- Concrete retaining structures and water-retaining walls (external face)
- Tunnels, subways and underground box structures
- Sandwiched waterproofing under screed, tiles or protection board on residential and commercial buildings
Key advantages
- Fully bonded, seam-welded membrane forms one continuous monolithic waterproof layer with no cold joints
- High-strength non-woven polyester reinforcement gives excellent puncture and tensile/stress resistance
- APP modification provides high softening point and good flow resistance on hot Indian roofs
- Factory-controlled, uniform 4 mm thickness removes the dry-film-thickness uncertainty of liquid systems
- Readily formed to contours, upstands, drains and detailing
- Trafficable and immediately watertight once cooled – no long curing wait
- Proven Fosroc Proofex brand with wide distributor and applicator support in India
Limitations & considerations
- Plain finish is not UV-stable for permanent exposure – must be covered with screed, tiles, protection board or a UV top coat
- Requires skilled torch applicators and open-flame (LPG) work, with associated fire-safety controls; not a DIY product
- APP membranes are less flexible at low temperatures than SBS grades – less suited to very cold or high-altitude regions
- Substrate must be sound, float-finished, dry and properly primed; poor surface prep causes blistering and debonding
- Detailing at penetrations, drains and upstands is labour-intensive and quality depends heavily on workmanship
- Overheating during torching can scorch the bitumen and ruin the membrane locally
Selection & best practice
Always prime the float-finished, fully dry concrete with Proofex Torchseal Primer and let it become tack-free before torching; re-prime any area left exposed for more than 24 hours. Maintain a minimum 100 mm overlap on side laps and 150 mm on end laps, and stagger end laps between courses so four layers never meet at one point. Torch only enough to melt the underside film and produce a small, continuous bead of molten bitumen ahead of the roll – this bead is the visual proof of a sound bond. Pay particular attention to upstands, drains, pipe penetrations and corners, using cut pieces and extra reinforcement at these details. Because the 4PI is a plain-finish sheet, protect it immediately with a screed, protection board or tiles, or apply a UV-resistant top coat where it remains exposed. Carry out a flood test (24-48 hours of ponded water) on horizontal areas before covering, and never torch over damp substrates or in unsafe fire conditions.
Specifications
| Product type | Torch-applied polymer-modified bituminous waterproofing membrane |
| Polymer modification | APP (atactic polypropylene) modified bitumen |
| Reinforcement / carrier | Non-woven polyester fabric (Proofex 3P/4P range uses 180 g/m2 polyester) |
| Nominal thickness | 4 mm |
| Surface finish | Plain finish (PI) – mineral-free, to be overlaid |
| Roll size | 10 m long x 1 m wide |
| Colour | Black |
| Application method | Propane/LPG torch heat-bonding to primed substrate |
| Recommended primer | Proofex Torchseal Primer (coverage 0.2-0.8 L/m2) |
| Side lap / end lap | 100 mm (side) / 150 mm (end), minimum |
| Shelf life | 12 months in cool, dry, original packing |
| Storage | Below 30 degrees C, rolls stored vertically, away from heat and sunlight |
Industry use cases
Residential & commercial buildings
Terrace and podium waterproofing sandwiched under screed and tiles, and wet-area/sunken-slab protection in apartments, offices and hotels.
Basements & below-grade
Deep basement tanking and external waterproofing of retaining walls and rafts for high-rise and mixed-use developments in Delhi NCR.
Infrastructure & transport
Car-park deck slabs, tunnels, subways and underground box structures where a robust, puncture-resistant bonded membrane is required.
Industrial & water-retaining
Roof slabs of warehouses and light-industrial sheds, and the external face of concrete water-retaining structures.
Frequently asked questions
Is Proofex Torchseal 4PI Standard an APP or SBS membrane?
What does ‘4PI’ mean in the product name?
Can the 4PI Standard be left exposed to sunlight?
What primer and overlaps are required for installation?
How is it supplied and what is the shelf life?
How does it compare with liquid-applied waterproofing?
How we position Fosroc Proofex Torchseal 4PI Standard
Within Fosroc’s own range, the 4PI Standard is the everyday 4 mm plain-finish APP membrane; step up to a slate-finished grade (e.g. Proofex Torchseal SI variants) where limited UV exposure is needed, or to SBS-based Torchseal grades for better low-temperature flexibility. For below-grade work it pairs naturally with Fosroc Proofex Engage or Nitoproof liquid systems at complex details, and Proofex Torchseal Primer is the mandatory companion product. Against the wider market, it competes with Sika’s torch-on APP/SBS membranes (Sika BituSeal / Sikaplan), STP’s bituminous torch membranes, IWL/other APP membranes, and on the liquid side with Dr. Fixit (Pidilite) and MBS/MYK acrylic and PU coatings. Honest positioning: a torch-on sheet like 4PI is the right call when you want a thick, fully bonded, puncture-resistant membrane under screed or in a basement; a liquid system (Dr. Fixit, MBS, Nitoproof) is often better for intricate detailing, thin profiles, or where open flame is unacceptable. Space Arc Engineering, as an authorised Fosroc distributor, supplies 4PI Standard with the correct primer and detailing accessories and can advise on the APP-vs-SBS and torch-vs-liquid choice for a given project.
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