I have a house whose back part is built into the surrounding mountain. The walls of the two back rooms are slightly humid. In addition, they are poorly ventilated.
In some spots, the plaster wall is coming off. Here is what we managed to remove with a spatula, applying no pressure:
This seems to be a pretty common sight around here. The locals tend to apply a waterproof coating to any walls that have this.
However, that method eventually leads to bubbles forming in the wall, and we're not sure whether it is the best way to go.
What should we do?