What Does Tanking a Wall Mean? A Complete Guide

To understand what is meant by tanking a wall, it is essential to look beyond the literal act of applying a waterproof coating. In the construction and renovation industries, tanking specifically refers to the process of creating a continuous, impermeable barrier against groundwater and moisture. This critical procedure is most commonly associated with below-ground structures such as basements, cellars, and underground parking garages, where hydrostatic pressure from the surrounding soil can force water through concrete walls and floors.

The Science Behind Tanking

Unlike surface treatments that merely shed water, tanking addresses the fundamental physics of water movement through porous materials. Concrete, despite its density, is inherently porous, containing a network of microscopic capillaries that allow water to wick through via capillary action. Tanking counteracts this by applying a dense membrane that disrupts these capillary paths. The goal is to maintain the internal dryness of a structure regardless of the external water table, effectively turning a vulnerable foundation into a sealed vessel capable of withstanding significant pressure.

Methods of Tanking Application

The methodology of tanking varies depending on the substrate and the environment, but the core principle remains the same: to exclude water. Professionals typically employ one of several proven systems, each with specific advantages for different substrates and aesthetic requirements.

• Membrane Tanking: This involves applying a sheet membrane or liquid-applied membrane that adheres to the wall, creating a seamless barrier.
• Cementitious Tanking: A cement-based slurry is brushed or sprayed directly onto the wall, forming a crystallizing barrier that blocks water pores within the substrate itself.
• Bituminous Tanking: Traditionally used in road construction, bitumen sprays or sheets are applied to provide a highly flexible and durable waterproof layer.

Why Tanking is Non-Negotiable

Skipping the tanking process or performing it inadequately can lead to severe structural and aesthetic consequences. Moisture ingress is not just a cosmetic issue; it is a silent destroyer of a building's integrity. Continuous dampness within a wall promotes the growth of mold and mildew, which can degrade internal finishes and pose health risks to occupants. Furthermore, the salts carried by water can cause efflorescence, where crystalline deposits crumble the mortar and brick, leading to spalling and the eventual weakening of the structural lattice.

Tanking vs. Damp Proofing

It is a common misconception that tanking and damp proofing are interchangeable terms. While both aim to manage moisture, they operate at different levels of defense. A standard damp proof course (DPC) is designed to stop rising damp—capillary moisture traveling up from the ground through a masonry wall. Tanking, however, is a more aggressive solution intended to manage high water pressure and standing water. It is a preventative measure for areas subjected to driving rain, groundwater, or constant hydrostatic pressure, rather than just the gentle wick of moisture from the soil.

The Process of Tanking a Wall

The successful execution of tanking requires a systematic approach. It begins with the meticulous preparation of the substrate. The wall surface must be stable, clean, and free from any dust, grease, or loose particles. Cracks and joints are repaired with a suitable filler to ensure continuity. The choice of tanking membrane dictates the installation process; some require a primer application, while others rely on mechanical fastening or specific mixing ratios for cementitious blends. Attention to detail at the junctions, corners, and where the wall meets the floor slab is crucial, as these are the most vulnerable points where leaks commonly initiate.

Material Selection and Compatibility

Selecting the correct tanking material is arguably the most critical decision in the process. The product must be compatible with the substrate—whether it is brick, concrete, or blockwork—and capable of handling the specific environmental conditions it will face. For instance, a membrane used in a high-traffic area or a location prone to minor abrasion must exhibit enhanced durability. Furthermore, the final finish must be considered; tanking membranes can be plastered over with cementitious finishes or tiled directly, provided the membrane is specifically designed to accept such applications.

Common Failures and Misconceptions

Even with a robust tanking system installed, failures can occur if the building movement is not accounted for. Structures naturally settle and flex over time, and a rigid tanking membrane may crack if the substrate moves. This is why modern tanking solutions often incorporate flexibility or are designed to accommodate slight movements. Another prevalent myth is that tanking is only necessary for below-ground areas. In reality, any structure exposed to significant moisture, such as shower rooms or areas with poor external drainage, can benefit from a form of tanking to protect the walls and ensure a long-lasting, dry interior.