BIOKIL 8mm Cavity Drain Membrane – Waterproof Tanking Membrane (2m x 20m, 2.4m x 20m)

The Biokil 8mm Cavity Drain Membrane is a highly durable, studded waterproof membrane designed to protect walls and floors from water ingress in below-ground and damp environments. Its high-profile stud design creates an effective drainage cavity, allowing moisture to be controlled and safely managed as part of a Type C waterproofing system in accordance with BS8102:2009.

Suitable for basements, cellars, and underground structures, this membrane delivers a Grade 3 habitable environment when installed as part of a complete waterproofing system. It is resistant to water, water vapour, ground salts, and contaminants, making it ideal for long-term damp-proofing and waterproofing projects.

Key Features & Benefits

• 8mm studded cavity design – creates an effective drainage void
• Type C waterproofing system – compliant with BS8102:2009
• Grade 3 environment capability – suitable for habitable spaces
• Waterproof and vapour resistant – protects against moisture and humidity
• Salt inhibiting – prevents contamination from masonry salts
• Root and contaminant resistant – suitable for aggressive environments
• Quick installation – minimal preparation required
• No drying time – redecorate immediately after installation
• Durable HDPE construction – long-lasting and robust
• Wide temperature tolerance – performs from -50°C to +80°C

Typical Applications

• Basement and cellar waterproofing
• Below-ground structures
• Walls and floors in damp environments
• Vaults and tunnels
• New build and refurbishment projects

How the System Works

The studded membrane creates a cavity between the substrate and internal finish, allowing water to pass behind the membrane and be directed into a drainage system. This prevents moisture from reaching internal finishes and ensures a dry, usable internal space.

This cavity drain approach is preferred over traditional tanking systems, as it manages water rather than resisting it, reducing long-term failure risk.

Installation Overview

• Apply membrane with studs facing the wall or floor
• Apply Biokil Lime Inhibitor to concrete surfaces before installation
• Drill through studs and fix using Biokil Brick Plugs (with seals for below ground)
• Fixings should be spaced at maximum 600mm centres
• Seal flanges using Biokil Sealing/Joining Tape
• Ensure correct overlap and positioning of sheets to prevent water ingress

Surface Preparation

Ensure all surfaces are sound, clean, and level prior to installation. Remove any loose plaster, render, or screed and repair using a suitable sand-cement mix with additive.

Where mould or fungal growth is present, treat with a suitable masonry biocide before installation. For above-ground applications, it is recommended to address moisture at source using a damp proof course such as Biokil BioDry ProCream.

Finishing Options

Stud Wall System: Install battens (minimum 25 x 38mm) aligned with fixing plugs and secure plasterboard to create a dry lining system without puncturing the membrane.

Dot and Dab Dry Lining: Apply bonding plaster dabs (minimum 8mm thick) covering at least 50% of the membrane surface. Plasterboard can then be fixed directly.

Floor Installation: Overlay with insulation and install tongue-and-groove flooring, leaving a 10mm expansion gap. Alternatively, apply a 65mm sand and cement screed.

Aftercare & Ventilation

The membrane creates a dry and habitable environment, but effective condensation control is essential, particularly in basements and high-moisture areas.

Mechanical ventilation systems are recommended to ensure airflow and prevent moisture build-up.

Technical Specifications

Available Sizes

• 2m x 20m – 40m² coverage
• 2.4m x 20m – 48m² coverage

Why Choose Biokil 8mm Membrane?

This high-performance membrane provides a robust and reliable waterproofing solution for demanding environments. Its deeper stud profile improves drainage capacity compared to lower-profile membranes, making it ideal for areas with higher moisture levels or water ingress risk.

Whether you're converting a basement or protecting a structure from damp, the Biokil 8mm Membrane offers a proven, professional-grade system designed for long-term performance.