I have a 100 year old house with what I can assume is limestone basement walls. Every month or so, I have to vacuum the floors around the edges b/c the walls crumble, leaving a fine sand on the floor. When I try to brush the walls, it seems like it will never end. Some area are really bad and you can see actual stones and some areas are fine and completely flat. Is there any type of product I can put on the walls to even them out and end the crumbling?