Tanking Slurry & Membranes

Tanking is the process of applying a waterproof barrier directly to a substrate to prevent water and moisture from passing through. Unlike cavity drain systems, which manage water by allowing it to enter and directing it to drainage, tanking products resist water at the surface, forming a continuous barrier that keeps the structure dry. Correctly specified and applied, a tanking system provides Type A barrier waterproofing as classified under BS 8102:2009, making it the appropriate choice for basements, cellars, retaining walls and wet rooms where a sealed surface is required. The range at Construction Supplies UK includes cementitious tanking slurries, liquid-applied coatings, epoxy barrier systems, bituminous waterproofing compounds and dual-function membranes offering both waterproofing and ground gas resistance, covering the full spread of tanking applications in professional construction and refurbishment work.

Cementitious Tanking Slurry

Cementitious tanking slurry is a powder-based waterproofing compound mixed with water on site to produce a thick paste that is applied to concrete or masonry by brush. As it cures, it undergoes a crystallisation process that penetrates the capillary pores of the substrate and blocks moisture pathways, forming a rigid, alkaline waterproof coating that bonds directly into the masonry rather than sitting as a surface film. It is the most widely used tanking product for below-ground masonry and concrete, providing reliable waterproofing performance on basement walls, cellar floors and retaining walls in both new construction and refurbishment. 

The range includes RIW Cementseal, a two-component polymer-modified cementitious coating that resists both positive and negative water pressures, and RIW Cementflex, the flexible variant incorporating elastomeric polymers to accommodate minor substrate movement. RIW Granules can be added to cementitious mixes to further improve waterproofing performance. The Natural Cement range provides an alternative specification route, with Natcem 35 and Natcem Tank offering natural hydraulic cement-based tanking compounds, and Natcem Waterstop providing a rapid-setting solution for stopping active water ingress before the main tanking system is applied.

Tanking slurry is applied in a minimum of two full coats, with the substrate dampened prior to application to prevent premature drying and to initiate the crystallisation process. The first coat is worked vigorously into the surface with a stiff brush, covering both vertical and horizontal strokes. A second coat is applied once the first is touch-dry, within 24 hours depending on site conditions. The coved junction between wall and floor is a critical detail: a fillet of cementitious mortar at this junction prevents stress concentrations at the right-angle joint and ensures continuity of the waterproof barrier.

Liquid-Applied Waterproof Coatings

Liquid-applied tanking products are brush, roller or spray-applied systems that cure to form a continuous waterproof film over the substrate. Rather than relying on crystallisation within the masonry, these coatings form a surface membrane that bridges minor surface irregularities and, in the case of flexible formulations, accommodates a degree of structural movement. They are suited to a wide range of substrates and applications, from below-ground concrete structures to retaining walls and specialist installations where chemical resistance or gas-proofing is also required.

RIW LAC is a liquid-applied bituminous coating for below-ground waterproofing of concrete and masonry. RIW Hydrocoat is a water-based, brush-applied waterproof coating for internal and external applications on concrete, brick and blockwork. RIW Toughseal is a solvent-free epoxy water and vapour barrier coating, specified for demanding applications where high waterproofing performance, chemical resistance or vapour control is required. GCP Betec 350 and GCP Betec Flex are bituminous waterproofing coatings for structural and below-ground use, with Betec Flex offering greater flexibility for substrates where movement is a consideration.

RIW Structureseal is a bentonite geocomposite pre-applied tanking system for use under slabs and against retaining walls in new construction. It is installed before the concrete pour, with the bentonite layer expanding on contact with moisture to form a dense, continuous waterproof barrier against the structure. The Visqueen Liquid Gas Membrane is a dual-function liquid-applied product providing both waterproofing and ground gas resistance in a single applied layer, covering radon, methane, carbon dioxide and VOCs where both moisture and gas management are required within the same barrier.

Wet Room Tanking

Tanking is also the established method for waterproofing wet rooms and shower enclosures before tiling. In this application, a liquid-applied tanking membrane is brushed or rolled onto wall and floor backgrounds to create a fully sealed surface, preventing water from tracking behind tiles and into the substrate below. Wet room tanking is a standard requirement ahead of tiling in any area subject to direct water contact, and the correct specification of the tanking membrane and associated jointing tape is essential to the long-term performance of the installation.

The Everbuild Aquaseal Wet Room System and Aquaseal Waterproof Tanking Membrane are the wet room tanking products in the CSUK range. These purpose-formulated Sika Everbuild products are applied to tile backer boards and other suitable backgrounds to form a flexible, continuous waterproof barrier prior to tiling. Waterproof jointing tape is embedded into the wet membrane at all internal corners, junctions and pipe penetrations to ensure the barrier is maintained at the most vulnerable points of the installation.

Applying Tanking Products

Correct preparation is the single most important factor in the performance of any tanking system. All surfaces must be structurally sound, clean and free from loose material, paint, plaster, efflorescence and any previous coating that would impair adhesion. Defective joints, cracks and voids should be cut back and repaired with a suitable cementitious repair mortar before tanking begins. Where active water ingress is present at the time of application, a rapid-setting waterstop compound such as Natcem Waterstop should be used to arrest the leak before the main tanking product is applied.

For cementitious tanking slurry, the substrate must be thoroughly dampened with clean water immediately before application. This prevents the masonry from drawing moisture out of the slurry too quickly, which would impair crystallisation and reduce the effectiveness of the coating. For liquid-applied systems, a primer may be required on porous or horizontal surfaces depending on the specific product being used. Jointing tape should be applied at all internal angles and pipe penetrations in both cementitious and liquid membrane systems, embedded into the first wet coat before the full application is completed.

Application rates, mixing ratios, overcoating times and curing requirements vary between products. Always refer to the manufacturer's technical data sheet for the product being used, and ensure site conditions, particularly temperature and humidity, are within the specified range before beginning work.

Choosing the Right Tanking Product

The appropriate tanking product depends on the substrate, the application, the degree of water exposure and whether the structure needs to accommodate movement.
Cementitious tanking slurry is the standard specification for masonry and concrete basement and cellar walls where the substrate is sound and movement is not anticipated. It bonds into the masonry, performs well under both positive and negative water pressure, and can be plastered or rendered over once fully cured. Flexible cementitious systems such as RIW Cementflex provide crack-bridging capability for substrates where minor movement is expected. Where the highest waterproofing performance is required, or where chemical or vapour resistance is also a factor, an epoxy-based system such as RIW Toughseal is the appropriate specification.

For new below-ground construction where a pre-applied system is preferred, RIW Structureseal provides a bentonite geocomposite solution installed prior to the concrete pour. Where both waterproofing and ground gas resistance are required in a single product, the Visqueen Liquid Gas Membrane covers both functions. For wet room and shower applications, the Aquaseal system provides a purpose-formulated tanking membrane suited to tiled backgrounds.

All products in this range are suitable for applications where no hydrostatic water pressure is expected. Where groundwater pressure is present, a Type A structural waterproofing membrane system designed to resist hydrostatic head is required. See our Waterproofing Membranes range for these applications.

Why Choose Construction Supplies UK for Tanking Slurry and Membranes?

Tanking products for every application: From cementitious tanking slurry for basements and retaining walls to liquid-applied coatings, epoxy barriers and wet room tanking systems, we stock products covering the full range of tanking applications.

Trusted industry brands: Shop leading manufacturers including RIW, GCP, Natural Cement, Sika and Visqueen.

Competitive trade prices: Tanking slurry and membranes at competitive trade prices with no minimum order value.

Fast UK-wide delivery: Reliable nationwide delivery with free shipping on orders over £300.

Expert support when you need it: Our team can help you choose the right tanking product for your project. Contact us at sales@constructionsuppliesuk.co.uk or call 03300 55 32 02.