I'm in the middle of sorting rust on both back arches. I work as a car detailer so I've used lots of different thing for rust prevention/protection. I'm using hammerite on the Micra, sanded back to metal then a couple coats of rust of rust protector. Once that was done sanded back using 80 then 240 then 400 grit sand paper for a smooth finish! But if there are still bumps and imperfections you can use a filler paste to fill then sand back for a smooth finish. Now just need to sort more rust areas then sand and prone ready for a full respray!
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