Brickwork is naturally porous and has a tendency to absorb water. This is one reason why cavity walls are now considered standard in most new build properties; this cavity between the inner and outer facings helps to prevent water wicking into the interior of the property and so serves as a useful source of damp proofing.
However rooms built underground – namely cellars and basements – have additional problems. This is because the porous brickwork can absorb moisture from the surrounding earth. In areas with poor drainage or a high water table this can be particularly problematic, causing basements and cellars to remain permanently damp. This dampness of course can not only damage the contents of these rooms but can even impact the overall structure of the room over time.
For this reason, many houses with basements benefit from some form of waterproofing to help keep the moisture outside and to create a more liveable internal environment. In the case of basement waterproofing the most important element is ensuring that the entire basement is suitably waterproofed. This means that a waterproof coating is applied to both the walls and the floor, paying particular attention to where the two join, which is the most common source of water ingress.
In essence then, waterproofing a basement involves the application of some kind of non-porous material; a waterproof coat if you will. This process of creating a waterproof “jacket” for your cellar is known as “tanking”. Think of it as creating a waterproof “fish tank” in your cellar through which water cannot travel.
Different Types of Tanking
Over the years a number of different forms of tanking have evolved, and each has its own particular strengths and weaknesses. For this reason different solutions may be used in different situations, depending on cost and effectiveness given your own unique property.
One of the most common types of tanking involves the application of a waterproof coating to the inside of the cellar. In this way, while water is still able to permeate into the brickwork of the cellar, it is unable to actually enter the basement proper as this is protected inside a waterproof “envelope”. In many cases this is the cheapest and easiest solution as it requires minimal structural work.
An alternative form of tanking involves the creation of a new “cavity wall” whereby a false wall is created inside the basement using waterproof board. The wall is deliberately built slightly smaller than the brick wall, creating a “cavity” between the two. This cavity can then help to keep water out of the basement.
It should be mentioned here that the cavity wall solution may require the use of artificial drainage in places where floods are possible. In such cases a pump is often used, so that water that sits between the two layers of the wall can be effectively removed.
Lastly, in some instances it may be necessary to carry out external tanking whereby the waterproof membrane is placed outside the basement wall. Clearly this can be a rather more involved method as it can involve a lot of digging in order to access the brickwork for treatment.
One of the most important factors that is taken into consideration when choosing the most suitable type of tanking is the state of the existing brickwork. For tanking to be effective, generally you will need a good level of workmanship. This is for two main reasons. Firstly, if a waterproof membrane is to be added to the surface of the wall then it is important that the brickwork is in good enough condition to take the treatment. There is little point waterproofing a cellar if the plaster starts to peel off soon afterwards.
The second reason is that when a basement has been waterproofed, water will normally build up around it. This is because the water has nowhere to go (when it would normally permeate through the brickwork) and so it just stops, sitting against the waterproof surface. In enough volumes, this stationary body of water starts to exert pressure on the brickwork.
If the brickwork I not up to standard, it will thus struggle to hold back the water pressure as it builds which can lead to structural failures. In many cases then the full and detailed survey of the brickwork in place will be necessary, followed by remedial work in terms of repointing and replastering as necessary to ensure that the cellar walls and floor are suitable before the waterproofing is commenced.