Tanking a wall is a critical process in construction and renovation that focuses on making a surface completely waterproof. This procedure is essential in areas prone to moisture, such as bathrooms, kitchens, and basements, to prevent water damage, mold growth, and structural decay. The term "tanking" refers to the application of a specialized membrane that creates a barrier against liquid penetration.
Understanding the Purpose of Tanking
The primary goal of tanking a wall is to protect the substrate from water ingress that can compromise its integrity. Unlike standard paint or plaster, a tanked surface prevents moisture from seeping through capillary action or under pressure. This is particularly important in environments where constant exposure to water is inevitable, ensuring the longevity of the internal structure and finishes.
The Science Behind Moisture Control
Water movement through porous materials like concrete or brick is a significant challenge in construction. Tanking materials are designed to block the pathways that allow water to travel. By creating a monolithic, impermeable layer, these systems redirect water to designated drainage points or waterproof membranes, effectively managing hydrostatic pressure without allowing the liquid to enter the living space.
Common Methods and Materials
Professionals utilize various techniques to achieve a tanked wall, depending on the substrate and the severity of water pressure. The choice of method dictates the longevity and reliability of the waterproofing solution.
Application of Cementitious Waterproofs
Cementitious coatings are a popular choice for internal tanking due to their ease of application and breathability. These are polymer-modified blends that are mixed with water and applied directly to the wall. Once cured, they form a flexible, crystalline structure that blocks water while allowing minimal vapor transmission, which helps prevent salt formation on the surface.
- Easy to apply with a brush or trowel.
- Gains strength through carbonation.
- Suitable for concrete and brick substrates.
Membrane and Sheet Systems
For high-risk areas, such as below ground or in shower rooms, sheet-applied membranes are often the superior choice. These come in rolls of asphalt, modified bitumen, or plastic sheets that are mechanically fixed or torch-applied to the wall. This method provides a high level of resistance to water pressure and is less susceptible to damage from minor substrate movement.
| Material Type | Best Use Case | Key Advantage |
|---|---|---|
| Cementitious | Internal walls & wet rooms | Breathable and flexible |
| Bituminous Membrane | External foundations | High puncture resistance |
| Liquid Membrane | Complex geometries | Seals corners and joints |
Surface Preparation is Key
Regardless of the method chosen, the success of tanking hinges entirely on surface preparation. A wall must be structurally sound, clean, and free of dust, grease, or loose particles. Cracks and holes need to be repaired with a suitable filler, and corners should be radiused to ensure the membrane does not thin out at these critical points. A well-prepared surface ensures maximum adhesion and prevents delamination.
Addressing Structural Movement
Walls naturally expand and contract due to temperature and humidity. If tanking is applied rigidly without accommodating this movement, it can crack and fail. Professional installers will often incorporate movement joints or use flexible waterproofing materials at corners and around penetrations. This allows the substrate to move independently of the waterproof layer, maintaining the integrity of the seal over time.
The Installation Process
The actual application of a tanked system is a multi-layered process that requires precision. It is not merely painting on a coat of paint; it is a structural application of defense against water.
- Priming: A primer is applied to improve the adhesion of the subsequent layers.
- Sealing Joints: All corners, edges, and penetrations are sealed with a flexible jointing compound.
- Primary Layer: The main tanking membrane is applied in a cross-hatch pattern to ensure full coverage.
- Protection: A protective plasterboard or render is applied over the membrane to protect it during construction and provide a finished surface.
Verification and Testing
After the tanking work is complete, it is vital to verify that the system is functioning correctly. A hydrostatic pressure test, often called a "tank test," involves filling the room with water to a specific level and marking it. After 24 to 48 hours, the water level is checked to see if it has dropped, indicating a leak. This practical test provides absolute certainty that the wall is performing as intended before finishes are applied.
