The area under the shower door in my 1940's house is not tiled. The inside of the shower isn't tiled, either, and this hasn't been a problem until now. Recently I noticed bubbling in the plaster, or whatever material it is, under the shower door. When I rubbed it, the paint fell away, and a sizable area of the wall (about 3" by 4") crumbled to the floor. What patching material should I use to fix the hole?
I'd never seen an untiled shower --or at least one with a fiberglass surround-- but then this old house is full of quirks. Your advice is greatly appreciated!