My house is concrete or cinder block (I don't know the difference) faced with brick and siding on a cement slab. It is all above ground and I have never had any water/moisture/leaking problems in the 29 years of its existence. We have never finished half of the lower level, but have used it for laundry and storage. The walls were painted white in 1978 and I have never painted again. However, there have over the years appeared random areas of a black, sugary erosion on one of the walls, which I have not addressed. There appears to be little holes that fill up with a sugary black residue, but the paint falls away and exposes more of the block around the initial "hole" which is about a quarter of an inch. They appear to have no pattern, no specific area, just anywhere on the wall from the top to the bottom. There are about 30 of them on a wall 8 feet high by 20 feet long. Is there a breakdown occurring in the blocks? What would cause this scattered erosion? How to stop it? Can I spackle and paint over it or apply quikcrete?

ThomasCKeat

Black is the color of bad mold that is also unheathly and yes it can along with moisture destroy cinder blocks. Get some professional help to see what this substance is quickly