Waterproofing Swimming Pools
The walls and the ground of a swimming pool are subject to constant water pressure. For enjoying the swimming pool it is important to have a permanent waterproofing.
For waterproof structures made of concrete we have in the German language two expressions that have no real equivalent in English: The "Weisse Wanne" (white tub) and the "Schwarze Wanne" (black tub). Both expressions are mainly used for concrete basements, which are exposed to ground water. White and Black tubs can also be used for swimming pools.
A white tub describes an impermeable structure. The concrete used in itself is impermeable. Water penetrates from one side into the capillary layer. The concrete wall’s core remains free of liquid. On the dry side of the wall the water diffuses through the white tub’s diffusion layer. A ventilated dry side will pass humidity. On the dry side of the wall water is present only in small quantities in gaseous aggregate.
Cement should be the equivalent of German Festigkeitsklasse c35/45 or c40/50.
It must be mentioned that a structure will not become a white tub just by using impermeable concrete. The joints between concrete sections, the way the concrete is compacted and alignment of reinforcing rods are also an element of a white tub. Building companies are not recommended to offer white tubs if they do not have the right experience and knowledge as it is a specialist's task.
This describes a system that is impermeable just like a white tub. However the concrete walls are not impermeable. The system is waterproofed by a water resistant layer. This layer is applied on the water side of the wall, e.g. inside the swimming pool. Examples for black tubs are tiled swimming pools, whereas the tiles are glued onto a water resistant layer. This layer forms a rubbery coating on the concrete. An other example for a black tub is a pool using vinyl liner. This is a foil that will be attached to the wall and will hold the water similar to a plastic bag.
While basements in Germany are nowadays mostly built as white tubs, white tubs are less popular for swimming pools. One reason could be the access to the water resistant layer. While the water resistant layer on basement walls would be on the outside of the building this layer will eventually be buried inside the ground. It is therefore difficult to access for repair or checks. In a pool the water resistant layer is easily accessible when the water is pumped out of the tank.
There should not be many worries with free standing pools in the open air. Pools, that are inside the house and even not on the lowest floor should be planned carefully. A combination of a white and a black wall could be taken into account. This adds an impermeable concrete wall as a measure of safety to the water resistant coating.