BIOKIL Geotextile Membrane – Twin Layered Cavity Drain Waterproof Membrane (2m x 20m)

The Biokil Geotextile Membrane is a high-performance twin-layered cavity drain membrane designed to manage water and relieve hydrostatic pressure in below-ground and external waterproofing applications. Combining an 8mm studded HDPE membrane with a nonwoven geotextile filtration layer, this advanced system directs water safely towards drainage channels while protecting waterproof coatings from surrounding soil and groundwater.

The geotextile layer is manufactured from UV-stabilised, high-tenacity virgin polypropylene fibres that are mechanically entangled and thermally treated to provide exceptional durability, filtration performance, and resistance to abrasion. The system is ideal for retaining walls, external tanking, podium decks, green roofs, and civil engineering waterproofing projects.

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Key Features & Benefits

• Twin-layer waterproofing system – combines drainage and protection in one membrane
• 8mm studded HDPE core – creates an effective drainage cavity
• Integrated geotextile filtration layer – prevents silting and maintains drainage performance
• Relieves hydrostatic pressure – directs water towards land drains
• High drainage capacity – suitable for demanding waterproofing environments
• Ideal Radon barrier – helps reduce radon ingress
• High compressive strength – withstands stress and movement in backfill areas
• Allows back-filling with excavated earth – suitable for external applications
• Thermal insulation benefits – improves protection of waterproof coatings
• Rugged and durable construction – long-lasting waterproofing performance

Typical Applications

• Retaining walls
• External tanking systems
• Green roof systems
• Podium decks
• Below-ground waterproofing
• Hydrostatic pressure relief systems
• Protection of external waterproof coatings

How the System Works

The studded HDPE membrane creates a drainage cavity that channels water towards perimeter drainage systems, helping reduce hydrostatic pressure against the structure.

The bonded geotextile layer acts as a filtration barrier, preventing surrounding soil particles and debris from clogging the drainage cavity while maintaining water flow. This creates a combined drainage and protection system that improves long-term waterproofing performance. :contentReference[oaicite:0]{index=0}

Installation Overview

• Install membrane externally with the geotextile layer facing outward
• Apply vertically or horizontally as required
• Seal all overlaps using Biokil Corner Strip Tape
• Extend membrane to the level of the drainage channels
• Ensure drainage channels are encapsulated in granular infill below floor level
• Secure tightly around internal and external corners

Surface Preparation

Before installation, assess the soil composition and groundwater conditions to ensure suitability for the project. Consultation with a Geotechnical Engineer is recommended where hydrostatic pressure or complex site conditions exist.

All surfaces should be clean, stable, and free from sharp protrusions. Where necessary, form smooth transitions at wall-to-floor junctions using a suitable mortar fillet to allow seamless membrane installation.

Drainage & Finishing

Drainage pipes should be installed to carry water safely away from the structure either passively via natural falls or actively using sump and pump systems. Drainage systems should include jetting access points to allow future maintenance and cleaning.

When back-filling, care should be taken to avoid damaging the membrane or stressing fixing points. Proper installation ensures long-term waterproofing performance and drainage efficiency.

Condensation Control & Ventilation

While the membrane helps create a dry and protected environment, effective condensation control remains important in enclosed or moisture-prone spaces.

Mechanical ventilation systems are recommended where natural airflow is limited, particularly in basements and below-ground structures.

Technical Specifications

Feature	Specification	Test Standard
Material	HDPE & Geotextile Fabric	-
Total Unit Weight	0.61kg/m²	-
Sheet Thickness	0.97mm	EN 149-2
Stud Height	7mm	-
Colour	Black	-
Water Tightness	Pass	EN 1928
Compressive Strength	180kN	BS EN ISO 25619-2
Tensile Strength (MD/CD)	416N / 488N	BS 12311-2
CBR Puncture Resistance	1.27kN	EN ISO 12236
Permeability (H50)	79l/m²/s	EN ISO 11058
Reaction to Fire	Class F	BS EN 13501-1
Working Temperature	-50°C to +80°C	-
Life Expectancy	Lifetime of structure	-

Available Size

• 2m x 20m – 40m² coverage

Why Choose Biokil Geotextile Membrane?

This advanced twin-layer membrane combines waterproofing, drainage, filtration, and protection in a single system, making it ideal for challenging external waterproofing and civil engineering applications.

Its high drainage capacity, filtration performance, and durability provide long-term protection against hydrostatic pressure and water ingress while protecting the structure and waterproof coatings from surrounding soil conditions.