Wall tanking is a specialised waterproofing process applied to the internal surfaces of a basement or underground structure to prevent groundwater and soil moisture from penetrating the walls. Unlike surface coatings that sit on top of the substrate, this method often involves installing a bonded or drained membrane system that manages water ingress and protects the internal environment.
Understanding the Mechanics of Wall Tanking
The core principle of wall tanking revolves around creating a continuous, waterproof barrier between the damp earth and the interior living space. This barrier is designed to resist hydrostatic pressure, which is the force exerted by groundwater pushing against the foundation walls. When implemented correctly, the system channels any incidental moisture towards designated drainage points, preventing it from seeping through porous concrete or masonry.
Types of Tanking Systems: Cementitious vs. Membrane
There are generally two primary categories of tanking materials used for walls. Cementitious tanking involves applying a cement-based slurry that cures to form a rigid, monolithic layer, ideal for situations where minor substrate movement is expected. Alternatively, polymer-modified membranes offer more flexibility, accommodating slight shifts in the structure without compromising the seal, which is often a superior choice for dynamic soil conditions.
The Application Process and Best Practices
Professional wall tanking is not a simple brush-on solution; it requires meticulous surface preparation. The substrate must be structurally sound, free of dust, oil, and loose particles, and any defects like cracks or voids need to be repaired with a suitable filler. Adhesion is key, and the surface is often dampened before the first coat is applied to ensure a strong bond.
- Assessment of the existing wall substrate for structural integrity.
- Crack sealing and repair of any defects to create a smooth base.
- Application of a primer to enhance adhesion between the wall and the tanking layer.
- Layering the tanking membrane with careful attention to overlaps and corners.
- Ensuring termination at a secure point, often into a wall slab or vertical cut-off.
Drainage Integration: The Final Layer of Defence
Modern waterproofing standards, such as those outlined in British Standards BS 8102, emphasise that tanking should be integrated with a cavity drain membrane system. This approach involves a physical gap between the tanked wall and the earth, allowing water that enters the structure to be collected and diverted to a sump pump or drain. This mitigates the pressure on the tanked surface and provides a secondary line of defence.
Addressing Sulphate Attack and Chemical Exposure
In specific environments, such as areas with high clay content or former mining sites, the ground may contain sulphates that can attack standard cementitious materials. In these instances, a specialised tanking system resistant to chemical and sulphate attack is necessary. Selecting the correct product for the specific soil chemistry is critical to the long-term success of the project.
Common Misconceptions and Limitations
It is important to understand that no tanking system is entirely immune to failure if subjected to extreme pressure or poor installation. The term "tanking" does not imply that the wall is indestructible; rather, it means the system is designed to manage water effectively. Furthermore, ventilation is still required to prevent condensation on cold interior surfaces, which tanking does not address.
For optimal results, wall tanking should always be specified and installed by experienced professionals who understand the interplay between waterproofing, drainage, and substrate preparation. When done right, it transforms a vulnerable basement into a dry, usable space that is protected from the damaging forces of groundwater.
