How can I prevent water ingress in the cellar?
How can I prevent water ingress in the basement?
The outer wall of the basement must fulfil special requirements due to its predominantly underground location.
As part of the building envelope, in addition to thermal insulation and statics, particular attention must be paid to sealing the basement against moisture, as depending on the geological conditions, high water pressure can sometimes occur due to the surrounding soil.
The cellar shell can be imagined as a large tub in which water must not penetrate at any point. Two sealing methods have become established: the black and the white tank.
With the black tank, the cellar wall is divided into a load-bearing and a sealing level. The supporting structure made of reinforced concrete is protected from the outside by an additional seal, which usually consists of a bitumen or plastic seal. The thickness and number of sealing layers is specified in Önorm B 3692 according to the respective load case. The application of the waterproofing is heavily dependent on the weather, which can lead to delays in the construction process when installing the black tank.
In the case of the white tank, the static structure made of reinforced concrete is also the sealing layer. The concrete must therefore have a high resistance to water penetration. The wall should therefore be at least 30cm thick and have a thicker reinforcement than usual to prevent even the smallest cracks. The joints between different concrete components, such as transitions from ceilings to walls, must be protected against water ingress with an additional sealing tape.
A mixture of the first two variants is the brown tank. It is named after bentonite, a naturally occurring, highly swellable brown clay that is applied to the ground in the form of sealing sheets on the outer wall of the basement made of waterproof concrete. As the contact pressure from the outside plays an important role in waterproofing, the brown tank is used exclusively for underground components. The material has a swelling effect, which ensures greater protection against water penetration compared to the white tank.
If carried out carefully, the white tank is more economical than the black tank due to its reduced number of work steps. The brown tank has the advantage that no additional construction work is required to produce the watertight concrete components, as small cracks are sealed by the bentonite that is pressed on from the outside and swells.
Compared to the white tank, there is therefore no need for additional reinforcement or larger component dimensions.
In addition to the basement waterproofing, there are measures that reduce the water pressure on the waterproofing. Drainage trenches around the basement or under the basement ceiling ensure faster drainage of rainwater or groundwater and thus relieve the pressure on the building components.
As it is rarely possible to avoid building services such as rainwater or sewer pipes penetrating the basement envelope, attention must be paid to these weak points and appropriate sealing elements must be used professionally.
Efficient planning minimises these points.
