Limescale must be removed. To do so, a cleaner from the kit can be used. If the cleaner does not completely remove the limescale, the remains should be cleaned by using sandpaper.
Rust must be removed. Use sandpaper and cleaner from the kit.
Silicone must be removed completely. If the material is applied on a surface where silicone is not removed, the material may peel off.
If your bathtub was covered with paint it is necessary to remove the old paint. Paint which peels off from bathtub should be removed in order for the new layer to have a good adhesion and does not peel off in the future. To remove the old paint heat it then take off old paint by spatula.