About Fosroc Proofex Cavitydrain

Fosroc Proofex Cavitydrain is a cavity-drainage (Type C) waterproofing membrane built around a sheet of profiled high-density polyethylene (HDPE) embossed with a regular pattern of studs, or dimples. When the membrane is fixed against the inner face of a basement wall or laid beneath a floor screed, those studs hold the sheet a fixed distance off the structure, creating a continuous, permanent air gap. The principle is fundamentally different from a barrier coating or a bonded sheet: instead of trying to hold back ground water under hydrostatic pressure, Proofex Cavitydrain accepts that some water may pass through the structural concrete and gives that water a controlled, depressurised path to travel. Any seepage runs down the void behind the membrane, is collected in perimeter drainage channels, and is led to a sump from where a pump discharges it clear of the building.

The system is offered in two principal grades. Proofex Cavitydrain 80 carries a 6.5 mm stud and is the economical choice for vertical surfaces — typically the internal face of basement walls. Proofex Cavitydrain 200 carries a deeper 20 mm stud, a much higher flow capacity and a higher compressive rating, making it suitable for both vertical walls and horizontal floor-slab applications where greater drainage volume or load transfer is needed. Around these two membranes sits a complete kit of proprietary accessories — sealed fixing plugs, butyl sealing tape and rope, overtape, corner strip, perimeter drainage channel with connectors, corners, T-pieces, jetting eyes and universal outlets — so that the whole drained-cavity envelope can be detailed as a single, coordinated system rather than an assembly of incompatible parts. The HDPE is chemically inert and resistant to most acids, alkalis, oils and fuels, and is rot-proof, so the cavity does not degrade over the life of the structure.

For Indian basements, deep car parks, metro stations and high-water-table sites, this management approach is increasingly specified because it remains serviceable: the cavity, channels and sump can be inspected, jetted and maintained, and the system can be designed to a defined grade of internal environment to BS 8102 either on its own or alongside Type A (barrier) or Type B (integral) waterproofing.

The technical insight

The defining numbers are the stud height and the flow rate, because together they set how much water the cavity can carry away before it backs up. Proofex Cavitydrain 80, on a 0.5 mm HDPE sheet with a 6.5 mm stud, drains roughly 1.65 L/s per metre width vertically and 0.30 L/s per metre horizontally at 20 kPa, with a compressive strength of about 200 kPa to ISO 25619-2. Proofex Cavitydrain 200, on a 1 mm sheet with a 20 mm stud, lifts that to about 10 L/s.m vertical and 2.50 L/s.m horizontal at 20 kPa, with a higher compressive capacity — which is why it is the grade chosen under floor slabs and where heavy load transfer or high inflow is expected. Crucially, Type C is a water-management strategy, not a sealing one: the membrane itself is not bonded waterproofing, so the design must guarantee that collected water actually reaches the sump and that the pump (ideally with a standby pump and high-level alarm) reliably discharges it. The membrane conforms to EN 13967 and is third-party assessed under a BBA Agrément certificate; correct detailing to BS 8102 and a maintainable drainage and pumping arrangement are what make the installation perform.

Where it is used

• BS 8102 Type C (drained cavity) waterproofing of basement walls and floor slabs
• Deep basement car parks, plant rooms and storage areas below the water table
• Lift pits, escalator pits and tank rooms requiring a dry, serviceable internal face
• Retaining walls and earth-retaining structures where seepage must be managed
• Metro stations, underpasses, tunnels and other infrastructure below ground
• Refurbishment and remediation of leaking existing basements where re-tanking is impractical
• Combined systems used with Type A barrier or Type B integral waterproofing to upgrade the grade of environment

Key advantages

• Manages rather than resists water, so it is not defeated by pinholes, hairline cracks or local barrier failures in the structure
• Fully serviceable and maintainable — cavity, channels and sump can be inspected and jetted over the building’s life
• Inert HDPE resists most acids, alkalis, oils and fuels and is rot-proof for long-term durability
• Two grades (6.5 mm and 20 mm studs) cover walls and floors with different flow and load requirements
• Complete proprietary accessory range (sealed plugs, tapes, channels, outlets, sump and pump) for coordinated detailing
• Conforms to EN 13967 with BBA third-party assessment, supporting BS 8102 specification
• Dry, finished internal face can be lined or screeded directly, reclaiming basement space
• Suited to remedial use where bonded re-tanking of a wet basement is impractical

Limitations & considerations

• Type C is a drained, not sealed, system — performance depends entirely on a reliable, maintainable drainage and pumping arrangement
• Requires a sump and pump (ideally with standby pump and high-level alarm and battery back-up); a power or pump failure can flood the cavity
• Not a structural waterproofing barrier on its own; the concrete and drainage design carry the duty
• Channels and sumps can silt up or block, so periodic inspection and jetting are essential
• Penetrations, service entries and construction joints must be sealed carefully or they become leak paths into the dry side
• Membrane is mechanically fixed, so substrate condition and competent fixing of sealed plugs are critical
• Not intended for positive-side external tanking; it is an internally applied management system

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Proofex Cavitydrain

Proofex Cavitydrain is Fosroc’s Type C (drained cavity) answer within a broader basement-waterproofing toolkit, and it is best specified alongside Fosroc’s barrier and integral systems rather than in isolation. For Type A barrier protection, Fosroc Proofex membranes and the Brushbond range of cementitious/acrylic coatings are common companions; for Type B integral protection, water-resisting admixtures such as Conplast and Auracon-type integral waterproofers densify the concrete itself; movement and construction joints are typically sealed with Fosroc waterstops, Nitoseal sealants and Renderoc/Conbextra repair and grouting products — so a single specifier can combine A, B and C to reach the required grade of environment. Among competing cavity-drainage and membrane systems, credible alternatives an Indian consultant may evaluate include Sika (Sikaplan and cavity-drainage membranes), STP Limited (a large Indian below-ground waterproofing specialist), Dr. Fixit (Pidilite) for crystalline and membrane systems, and MBS / regional HDPE dimple-sheet suppliers. Proofex Cavitydrain’s strengths are its two purpose-matched grades, its complete sealed-accessory and drainage range, and BBA/EN 13967 third-party backing; the trade-off, common to all Type C systems, is dependence on a maintained sump and pump. As an authorised Fosroc distributor and applicator, Space Arc Engineering positions Proofex Cavitydrain as the serviceable, maintainable choice for deep basements and remediation work, supplied with design support and certified installation across Delhi NCR and Pan-India.

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