Fosroc Proofex Alkorplan 35041
Loose-laid, hot-air-welded flexible PVC membrane for tunnels, basements and podiums — with a dual-colour signal layer for fast on-site damage detection.
What is it?
A flexible, loose-laid PVC (polyvinyl chloride) synthetic sheet membrane, hot-air welded at the laps, used as a primary tamper-proof waterproofing barrier for below-ground and buried structures. Formerly marketed by Fosroc as Proofex PGP.
Where is it used?
Tunnel and metro linings, deep basements and retaining walls, podium decks and covered/buried roofs, and water-retaining civil structures — typically as a sheet-membrane system behind the structural concrete.
Why use it?
It is cold-applied (no torch, no flame), fast to lay over large areas, highly puncture- and tear-resistant, and its welded seams give a fully continuous, monolithic waterproof envelope. The two-tone light-grey/black construction lets installers instantly spot mechanical damage before concreting.
How is it applied?
Rolls are loose-laid over a prepared substrate (usually with a geotextile fleece protection/separating layer), overlapped to give a minimum 50 mm weld and joined by hand or automatic hot-air welding equipment; PVC fitter discs and flanges anchor the sheet and form injectable compartments.
About Fosroc Proofex Alkorplan 35041
Fosroc Proofex Alkorplan 35041 is a flexible PVC synthetic waterproofing membrane engineered for the most demanding below-ground and buried-structure applications — principally tunnels, deep basements, podium decks and covered roofs. It is the current name for the product Fosroc previously supplied as Proofex PGP, and the two share the same construction and performance data. Rather than being bonded to the substrate, the sheet is laid loose over a fleece protection layer and the individual sheets are fused together with hot-air-welded laps, producing a single continuous, flexible waterproof envelope that is independent of the concrete behind it.
The membrane is manufactured in two contrasting colours: light grey on the upper (exposed) face and black on the underside. This is not cosmetic — it is a deliberate signal layer. Any cut, puncture, scuff or weld defect that exposes the black underside is immediately visible against the grey surface, so site supervisors and Fosroc-approved applicators can find and repair damage before the protective concrete or backfill goes on. For a buried membrane that becomes effectively un-inspectable once the structure is complete, that built-in quality check is one of the system’s biggest practical advantages.
Because the system is cold-applied and welded rather than torched or solvent-bonded, it can be installed quickly and safely on confined tunnel and basement sites where naked flames are undesirable. It is supplied in a range of thicknesses to suit the hydrostatic head and mechanical risk of each project, and integrates with a family of Fosroc PVC accessories — fitter discs, flanges and Supercast waterstops — to build compartmentalised, re-injectable waterproofing zones. For Indian contractors and consultants, Space Arc Engineering supplies Proofex Alkorplan 35041 as part of a complete tunnelling and basement waterproofing package, with technical and applicator support across Delhi NCR and Pan-India.
The technical insight
The defining feature is the compartment (or “control”) system this membrane enables. By welding Proofex PGP Flanges (182 mm diameter PVC flanges with a connector pipe) into the membrane and combining them with Supercast Rearguard waterstops and Supercast Predimax injection-hose waterstops, the lined surface is divided into discrete sealed compartments. If water ever finds a path behind the membrane, leakage is confined to a single compartment and can be re-sealed by injecting resin through the pre-installed hoses — without demolishing the structure. This “post-installation injectability” is what distinguishes a true tunnelling-grade PVC system from a simple sheet membrane, and it is why Proofex Alkorplan 35041 is specified on metro, road-tunnel and deep-basement projects rather than only on flat roofs. The welded lap (minimum 50 mm, hand or machine hot-air) routinely tests stronger than the parent sheet, with lap-joint strength quoted at greater than 1000 N/50 mm — joints typically fail in the sheet, not the weld.
Where it is used
- Tunnel and underground metro waterproofing (loose-laid behind the secondary lining, with a geotextile protection layer)
- Deep basement and retaining-wall tanking against hydrostatic groundwater
- Podium decks and covered / buried roof slabs
- Water-retaining and water-excluding civil engineering structures
- Compartmentalised, re-injectable waterproofing systems on critical infrastructure
- Cut-and-cover structures and box culverts requiring a flexible loose-laid membrane
Key advantages
- Cold-applied and welded — no torch, flame or solvent adhesives, so it is safe in confined tunnel and basement environments
- Dual-colour signal layer (light grey over black) reveals mechanical damage instantly for inspection before concreting
- Hot-air-welded seams give lap strength >1000 N/50 mm — a continuous, monolithic waterproof envelope
- High puncture resistance (up to >3 kN at 3.0 mm to EN 12236) suited to rough backfill and shotcrete substrates
- Highly flexible with cold flexibility passing at below -3 degC (EN 495-5), accommodating substrate movement
- Loose-laid system is independent of substrate cracking and decoupled from concrete movement
- Enables re-injectable compartment systems using Fosroc flanges and Supercast waterstops
- Root resistant (EN TS14416, no penetration) and non-flammable; available in four thicknesses for varied head and risk
Limitations & considerations
- Not for permanent exposure — heat, direct sunlight or UV cause colour change and can alter physical properties, so it must be covered/buried
- PVC membranes can be incompatible with bitumen, tar, certain insulation foams and some oils; check compatibility of adjacent materials
- Requires skilled, Fosroc-approved applicators and calibrated hot-air welding equipment plus weld-testing — it is not a DIY product
- Substrate must be free of cavities, projecting nibs and running water; a geotextile protection/separating layer is generally needed
- As a loose-laid system, lateral water tracking behind the sheet is a risk unless properly compartmentalised with waterstops/flanges
- Hot-air welding quality is temperature- and operator-sensitive; poor welds are the main failure mode and must be probe-tested
Selection & best practice
Specify the membrane thickness to the project’s hydrostatic head and mechanical risk (heavier 2.0-3.0 mm grades for tunnels and high-head basements; 1.2-1.5 mm for lighter podium/roof duty). Always lay it loose over a continuous geotextile fleece protection/separating layer (e.g. Fosroc Geotextile SNW), never directly on rough shotcrete. Ensure the substrate is free of running water, cavities and projecting nibs before laying. Achieve a minimum 50 mm hot-air weld at every lap and probe-test or vacuum-test all seams. On tunnels and critical structures, build a compartment system using Proofex PGP Flanges with Supercast Rearguard and Predimax injection-hose waterstops so any future leak can be resin-injected rather than excavated. Use Proofex PGP Fitters (80 mm PVC ribbed discs) to fix the sheet on vertical faces. Store rolls horizontally, no more than one pallet high, in a cool dry place out of sunlight, and cover or concrete the membrane promptly to avoid UV exposure.
Specifications
| Material / chemistry | Flexible PVC (polyvinyl chloride) synthetic sheet membrane, loose-laid |
| Thickness options (EN 1849-2) | 1.2 mm, 1.5 mm, 2.0 mm and 3.0 mm |
| Standard colours | Upper layer light grey / underside black (signal layer for damage detection) |
| Tensile strength (ASTM D412 & EN 12311-2) | Longitudinal 16.5 N/mm2; Transversal 15 N/mm2 |
| Elongation at break (ASTM D412 & EN 12311-2) | >300% longitudinal and transversal |
| Puncture resistance (EN 12236) | 3.0 mm: >3 kN; 2.0 mm: 2.9 kN; 1.5 mm: 2.6 kN; 1.2 mm: 1.2 kN |
| Tear resistance (EN 12310-1) | 3.0 mm: >1000 N; 2.0 mm: >460 N; 1.5 mm: >340 N; 1.2 mm: >220 N |
| Water impermeability (EN 1928) | Pass test |
| Water vapour transmission (ASTM 96) | Nil |
| Lap joint strength (EN 12317 & UEAtc) | >1000 N/50 mm (broken out joint) |
| Cold flexibility (EN 495-5) | Pass at below -3 degC |
| Root resistance (EN TS14416) | Pass — no penetration |
| Minimum weld overlap | 50 mm, hand or automatic hot-air welded |
| Roll size / supply | 2.10 m wide x 25 m long rolls (all thicknesses) |
| Accessories | Proofex PGP Fitters (80 mm PVC ribbed discs); Proofex PGP Flanges (182 mm PVC flange with connector pipe) |
| Fire | Non-flammable (membrane, fitters and flanges) |
| Former name | Fosroc Proofex PGP |
Industry use cases
Metro & Road Tunnels
Loose-laid behind the secondary/cast-in-situ lining over a geotextile layer, with welded compartments and injection hoses so any future ingress is isolated and resin-injected rather than re-excavated.
Deep Basements & Metro Stations
Full tanking of multi-level basements and station boxes against high groundwater heads, using 2.0-3.0 mm grades for puncture resistance against shotcrete and backfill.
Podium Decks & Buried Roofs
Continuous welded membrane under landscaped podiums, plaza decks and covered roof slabs where the membrane is permanently protected from UV.
Water & Civil Infrastructure
Water-retaining and water-excluding structures such as cut-and-cover boxes and culverts where a flexible, movement-tolerant loose-laid barrier is required.
High-Value Commercial & Institutional Builds
Hospitals, data centres and premium commercial towers in Delhi NCR where a tamper-proof, inspectable, re-injectable basement waterproofing system is specified for long design life.
Frequently asked questions
Is Proofex Alkorplan 35041 the same as Proofex PGP?
What thicknesses are available and which should I specify?
Why is the membrane grey on one side and black on the other?
How are the sheets joined and how reliable are the seams?
Can leaks be repaired after the structure is built?
Does Space Arc Engineering supply Proofex Alkorplan 35041 in India?
How we position Fosroc Proofex Alkorplan 35041
Within the Fosroc range, Proofex Alkorplan 35041 is the loose-laid, hot-air-welded PVC sheet-membrane solution for tunnels, deep basements and podiums, and it is designed to work as a system with Fosroc Geotextile SNW (protection/separating layer), the Supercast range of PVC and hydrophilic waterstops (Supercast Rearguard, Supercast Predimax injection hose), and Proofex PGP Fitters and Flanges. It sits alongside Fosroc’s bonded membrane options such as Proofex 3000 and the Proofex Engage pre-applied range — where a project needs a fully bonded HDPE-type membrane that resists lateral water migration, those products are the comparison point; where a flexible, inspectable, re-injectable loose-laid PVC envelope is preferred, Alkorplan 35041 is the fit. Against the wider Indian market, the closest credible alternatives are Sika’s loose-laid PVC tunnel membranes (Sikaplan WT range), the Renolit Alkorplan equivalents from other distributors, BASF/MBCC (formerly MBS) waterproofing membrane systems, and pre-applied HDPE membranes such as those from STP Limited. Brands like Dr. Fixit (Pidilite) are strong in liquid-applied and crystalline basement waterproofing but are not the natural like-for-like for a welded PVC tunnel-lining membrane. The honest positioning is that Proofex Alkorplan 35041 is a specialist, applicator-installed tunnelling/basement membrane: it is at its best on infrastructure and high-value structures where its compartment/injection capability and signal-layer inspectability justify the skilled installation it demands — not on small residential jobs where a liquid-applied or self-adhesive product would be simpler and more cost-effective.
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