Tanking walls refers to the specialized process of applying a waterproof membrane or protective coating to the interior or exterior surfaces of a basement or foundation wall. The primary objective is to prevent groundwater and soil moisture from seeping through the concrete, thereby protecting the interior of a building from dampness, mold, and potential structural damage. This critical defensive barrier acts as the first line of defense against the immense hydrostatic pressure exerted by the surrounding earth.
Understanding Hydrostatic Pressure
To appreciate the necessity of tanking walls, one must first understand the concept of hydrostatic pressure. Water in the soil surrounding a foundation seeks the path of least resistance, which is often through the porous concrete walls. As the water table rises, the pressure exerted on the wall increases significantly. Without a proper tanking system, this relentless force can overwhelm standard concrete, forcing moisture through capillary action or even creating cracks, leading to significant leaks and instability over time.
Tanking vs. Damp Proofing: Key Differences
While the terms are sometimes used interchangeably, tanking and damp proofing serve distinct purposes. Damp proofing is typically a thin barrier designed to slow down moisture vapor transmission, whereas tanking creates a continuous, monolithic seal that is waterproof. Tanking is a more robust solution specifically engineered to resist positive hydrostatic pressure, making it essential for environments prone to high water tables or frequent flooding.
Common Tanking Materials
- Cementitious Tanking Slurries: These are cement-based coatings that cure to form a flexible, crystalline barrier bonded directly to the substrate.
- Bituminous Membranes: Pre-formed sheets or liquid-applied bitumen that provide a durable, rubberized seal.
- Polyurethane Injections: Primarily used for cracks, this chemical grout is injected into voids to create a solid, impermeable block.
- Bentonite Clay Boards: Used externally, these boards swell upon contact with water to form a gel-like barrier that blocks moisture.
The Application Process
Effective tanking is not merely about applying a coat of paint; it requires meticulous surface preparation and a thorough understanding of the substrate. The wall surface must be structurally sound, free of dust, oil, and loose particles. Joints and cracks are primary entry points for water, so they must be treated with a suitable sealant or injected before the main tanking membrane is applied to ensure a continuous, unbroken seal.
Internal vs. External Tanking
External tanking involves applying the membrane to the exterior face of the wall before the soil is replaced, which is often the most effective method as it deals with water at the source. Internal tanking, applied to the inside of the basement, is typically a retrofit solution used when external access is impossible. While internal methods manage the water that enters the structure, they often require a drainage system, such as a French drain, to channel water away safely.
Why Tanking is a Critical Investment
Ignoring moisture issues can lead to a cascade of other problems, including efflorescence, spalling of concrete, and the growth of toxic mold, all of which degrade indoor air quality and devalue a property. Properly executed tanking walls provide long-term protection, preserving the structural integrity of the foundation and eliminating the need for costly repairs down the line. It is a proactive measure that safeguards the health of the building and its occupants.
Compliance and Standards
In modern construction, tanking walls are a non-negotiable requirement for below-ground structures. Building regulations, such as BS 8102 in the UK, provide comprehensive guidelines for the design and application of waterproofing systems. Adhering to these standards ensures that the tanking system is specified and installed correctly, offering a reliable warranty against future leaks and providing peace of mind for builders and homeowners alike.
