I have a hole in the wall of my shower about 4 inches in diameter. I think there is fiberglass underneath. What is the best way to fix the wall and what kind of paint could I use to make it blend in with the rest of the tub?
You can actually repair it. Generally make it dry. Sand down the surface around the effected areas. If there is an actual hole try using plywood to fill the hole. Apply fibreglass (you can buy strips of it) and coat each piece entirely in epoxy resin. Let it cure and repeat until there is a correct thickness. You can then sand that down as well to make it smooth and flush with the rest of the structure. You can paint it over with an epoxy based paint that will stick and not peel.