Water is the obvious answer. Leaking from the exterior, compromising the structure.
Has any water got into the basement under this area?
How long has it been bowed?
How old is the bath? Old mud jobs can have the tile let go of the substrate but continue to be connected to one another and prutrude from the wall.
If you push the bulge, does it move?
Has any water got into the basement under this area?
How long has it been bowed?
How old is the bath? Old mud jobs can have the tile let go of the substrate but continue to be connected to one another and prutrude from the wall.
If you push the bulge, does it move?