ᐅ Rising Damp in the Foundation Base

Hello, I have the following problem:

On the east side of our house, the terrace was built raised and is one meter (3.3 feet) higher than the garden. Accordingly, one meter (3.3 feet) of gravel was filled in there. Now, over a length of three meters (9.8 feet), the base of the wall is somewhat damp. To be specific, two years after the house was completed, there are slight efflorescence deposits forming on the plaster, and the plaster is chalking.

The terrace slopes down towards the garden, and since the roof has an overhang, rain usually does not reach closer than half a meter (1.6 feet) to the house wall. So, I suspect that the moisture is rising from below. The efflorescence appears just slightly above the terrace level. A dimpled membrane was installed on the wall in the ground, and between the wall and the paving, there is a 20cm (8 inches) wide and deep gravel strip. In this area, there is no basement, only a deep strip foundation. My suspicion is that the dimpled membrane does not seal properly at the bottom, and moisture seeps through the gravel up to the base of the wall and then rises.

Now, I do not want to have the terrace torn up and the gravel excavated to a depth of one meter (3.3 feet), which would also damage my garden.

My plan is therefore: remove the gravel bed so that it is about 10cm (4 inches) below the terrace level. Use an angle grinder to cut a horizontal groove in the plaster until reaching the insulation boards (Styrodur). Then fill the groove with bitumen to prevent moisture from rising further. Refill the gravel bed—so the bitumen is no longer visible—and then repaint the base of the wall. I know this sounds rather daring, but would this work?

Two years after completion? Contact your tradespeople, developer, or main contractor.

That’s exactly the point. I have spoken with both the landscaper and the plasterer. The plasterer believes that the landscaper must have damaged the dimpled membrane, while the landscaper says the plasterer didn’t properly connect the dimpled membrane. After a lot of back and forth, both would be willing to step in, tear up the terrace, excavate the gravel a meter (3 feet) deep, and repair it at the bottom. The problem is that a mini excavator can no longer reach that area, and there is no space to store all the materials. There are beds everywhere there, which would be damaged. That’s why I prefer my own idea, which would mean about 1.5 days of work for me and, apart from some facade paint and bitumen sealing compound, would cost nothing.

If this option made sense, the contractors responsible for warranty would have suggested it! They wouldn’t propose such a costly solution for themselves without good reason.