It’s a problem we come across all too often. A cowboy builder slaps a thick coat of concrete render on and a few years later the house owner wonders why they have damp coming through the walls.
What’s happening is that thick render has pulled away slightly from the wall slightly as it dries. Water then gets in behind the render and has nowhere to go but into the house.
Once the old render is removed and the joints in the stonework are raked out, a proper re-rendering can be done. It’s one of those jobs you either do properly or not at all.