My shower had 2 towel bar anchors mounted on the shower wall when I moved in.

Eventually, one of the anchors has broken and taken the plaster it was mounted to with it. This has left a 2 in. hole in the wall surrounded by tile and no exposed surface to fix any replacement wall to without tearing out additional tile.

I don't care about replacing the anchor (I hated it), but I need to figure out how to fill the hole permanently before the moisture sets into the wall cavity.

Any suggestions?