Did you have a drainage?
At our place, rising water is supposed to be prevented by a drainage system.
I found this article from the Verband Privater Bauherren, which clearly speaks out against black tanks and clearly in favor of white tanks.
Verband Privater Bauherren advises: White tank always the first choice
BERLIN. "White tanks are no longer more expensive than black ones today. They should therefore long have been the standard," demands Dipl.-Ing. Klaus-Dieter Hammes, building expert at the Verband Privater Bauherren (Verband Privater Bauherren) and head of the Verband Privater Bauherren office in Aachen. "But the opposite is true. Many building owners still get a conventional basement beneath their house and struggle for decades with pressing groundwater. Some turnkey providers apparently are not willing to adapt to the state of the art."
Building professionals distinguish between so-called white and black tanks in basement construction. Black tanks are basements with a concrete floor slab and masonry exterior walls, which are protected against moisture from the outside before backfilling by a black bitumen coating or a welding membrane. The construction owes its name to the tar-colored surface coating, which usually only lasts about 30 years. White tanks are all-around closed constructions, where all parts consist of high-quality, watertight concrete. Experts also refer to the material as WU concrete. Its service life is between 60 and 80 years.
"White tanks are indispensable where water presses against the basement walls or floor slab from below or from the side, and that is almost always the case," building engineer Hammes knows from experience. One cause is the rising groundwater level – because less drinking water is extracted now than a few years ago. In addition, in many places the drainage, which is supposed to divert rainwater away from the house, may no longer be connected to the sewer system. The water not discharged then also presses as rising seepage water against the basement walls.
White tanks are so-called monolithic structures. They combine structural support and waterproofing in one. Because they are made in one piece, they are also relatively easy to construct. At least theoretically. "In fact, very few companies can build a white tank," criticizes building expert Hammes. For planning the white tank, the subsoil must first be carefully examined. This is impossible without a soil survey. It provides the data that planners need to precisely calculate the components and their reinforcement.
According to the Verband Privater Bauherren experience, implementation is also problematic. "The same mistakes are always made, especially when pouring the concrete," observes the engineer. To ensure the steel reinforcements are in the correct place in the concrete, they must be fixed with spacers before concreting. Only certain small parts made of plastic or cement-bound spacers are allowed for this purpose. "Many turnkey providers, however, use whatever they happen to have lying around in the yard. This is not permitted and leads to damage to the structure." Such negligence is only discovered if the construction site is regularly inspected by an independent expert.
Another problem is the correct composition of the concrete. To make it watertight, aggregate additives must be worked in. "This is also often done incorrectly. The aggregate additives are under-dosed and used incorrectly," observes Klaus-Dieter Hammes. The result is inferior concrete that cannot withstand pressure water. There are also failures in the necessary after-treatment of the WU concrete. Construction companies pour the concrete but then do not vibrate it afterwards, although correct compaction is naturally a prerequisite for impermeability. Often the covering of the concrete during setting is also omitted. "But this is necessary, as the concrete develops enormous temperatures during the one- to two-day drying phase, the so-called hydration, due to its chemical composition. If not worked on carefully, this leads to stresses and cracks." Verband Privater Bauherren consultants observe this again and again as well.
"Although there have been technical guidelines for building watertight basements for years, most turnkey providers still do not master the technique," criticizes building expert Hammes. "Building owners should therefore better not rely on luck but commission the independent expert with regular inspections of their construction site so that they actually get a watertight basement afterward."
Source: Verband Privater Bauherren
However, I think mainly two criteria are given as reasons for this:
- an increasingly rising groundwater level
- drainage systems often may not be connected to the sewer system
I would spontaneously claim that the first does not affect me because of the hillside location.
I do not yet know about the latter, but I imagine that this would not be a problem anyway because the drainage is supposed to divert water sideways away from the house as long as it is not connected to the sewer.
From there, the water can find its way downhill again; there is no house in the way anymore.
I do not know the association but would rate it as reputable.
The mentioned conversation is on Saturday.
Upon request, the architect roughly explained the problem to me again.
Since we are using facing bricks, a bearing surface for the facing bricks is needed.
Because concrete walls would be rather narrow and could barely support the basement ceiling, the facing bricks would have to rest on the basement ceiling; however, then the basement ceiling would represent a thermal bridge.
With masonry bricks, the wall can be made thicker and the facing bricks can rest directly on one part of the masonry bricks and the basement ceiling could be supported on the other part.
I cannot judge whether that makes sense.