3,Usually use the rust remover to process the rust spot. When process it, pay attention following:
(1),Try best not to use oxalic acid to clean the rusty spot, as oxalic acid is just simple to restore the rusty spot（Fe2+）, the iron ion which is Redox still not so steadily, very easy to react again with the air and oxygen in the air and become rusty spot again. In addition, because the flow of oxalic acid, it expand the rusty spot area.
(2),when choose the rust remover, must choose the good quality product, because good quality rust remover contain not only the acid, but also contain additive which could keep the iron ion to be steadily after Redox. Use this kind of rust remover, the stone processed will not have the rust spot again for very long time. On the contrary, some rust remover is only some simple acid mixing liquid, could not keep the iron ion to be steadily, so stone easily have the rust again.
(3),As the composition of the granite and marble are different, so they are different. The main composition of marble is calcium carbonate, to be alkalescence, while the granite main composition is silicon dioxide, to be acid. So when use the rust remover, must identify whether it is used for granite or used for marble. The rust remover for granite could not be used for marble.
(4),To process the rust on the surface level, just brush the rust remover on the surface then it will be ok. Sometimes, it also could adopt the surface polish to process it. While for deep level rusty, it will be more complicated. Need to have a certain quantity of rust remover and a certain of reaction time. Sometimes, it require repeat use of rust remover so to get ideal result.
(5),After using the rust remover, suggest to clean the stone again. After drying, use good quality stone protection material to process it. The purpose is to get rid of the residue completely after Redox, so to prevent the 2nd time of Oxidizing reaction.
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