Causes rust spots can generally be divided into two: the first cause of rust from the iron contained in copies of the stone itself. In general, the number of each stone itself contains elements of iron, when the rain of iron and stone were exposed in the future, will gradually form a rust, more difficult to remove this rust, have to spend a longer time to process, use of herbicides / macular scavengers can effectively remove rust and do not hurt the stone, to avoid the use of industrial or other corrosive acid hydrogen peroxide, or self-defeating. The most important thing is how to prevent rust regeneration, the most effective way is for rust protection immediately after treatment to prevent further infiltration of water inside the stone, remove the rust regeneration. The second rust is an exotic, such as processing of grit or residue of iron construction, decoration of the metal components, etc., that rust easily removed by using the same cleaning agent also with the former. Generally stone to completely clear the produce rusty after quite easy. So off than stone installation before the protective treatment after completion of treatment for better protection, because after the completion of the external walls have a considerable height, the construction is not easy, and stone installation process may also have exposure to acid rain, so the protection is done before construction the best, but also can rust stain.