ᐅ Laying Drainage Pipes on Clay Soil?

Because we have mold developing in our basement despite ventilation, and the walls are occasionally damp, the sand used above the drainage system was tested. Only in parts, at two test boreholes, was non-permeable clay found; otherwise, the sand is permeable. What puzzles me is that, according to the layering report, the drainage was installed directly on the existing natural clay soil. The geotextile membrane was laid directly on it, and only a small amount of gravel was placed around the pipe—is this correct? So far, the drainage has not carried water in the three years since installation, which is also clearly visible in the sump pit at the pipes. How can the drainage system be tested?

Hello,

Krolock schrieb:
Because mold forms in our basement despite ventilation and the walls are occasionally damp, the sands installed above the drainage were checked. ...

What sustainable purpose does that serve, since water is known to flow “downhill” voluntarily!
If walls become damp, there are basically two possible causes:
1. Internal moisture from room usage, condensation on the walls due to insufficient ventilation.
2. External moisture penetration due to inadequate vertical damp proofing.

Regarding point 2, there are usually two scenarios: water under pressure and water without pressure.
Depending on the situation, the necessary vertical damp proof courses are planned and executed accordingly!

Opinions on drainage systems may certainly vary.
For example:
The surrounding native soil contains a significant amount of clay, so it has low permeability for surface water.
At the construction site, a drainage system with a permeable gravel layer is installed around the building. This acts as a welcome “sink” for surface water. As a result, the rising walls are significantly stressed.

Best regards.

A drainage system should also be cleaned regularly (flushed through), otherwise it can become blocked and will no longer be effective. Do you also have enough slope for the drainage?

The planning and installation of a drainage system must comply with the standards of DIN 4095 from 1990:06. The drainage pipe is installed within a filter layer, which serves two purposes: first, to prevent both incoming water and any transported solid particles from being washed away together, allowing only the water to be drained; second, to ensure that the drainage pipe does not become clogged during operation.

Whether a drainage system is functioning can be easily checked by flooding the backfilled excavation with a garden hose over an extended period and then verifying if water is actually being discharged.

However, one important point is that the drainage system is not responsible for the building’s waterproofing. That is the task of the waterproofing layer.

If moisture occurs in the basement only temporarily and not continuously, this could indicate a dew point issue rather than a defective waterproofing. This would also be supported by the lack of water loading in the drainage system.

Such moisture problems usually arise in spring or summer and rarely in winter.