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Last year, I had a big stone chip with growing rust. I thoroughly sanded it, applied primer, and painted it. It wasn't meant to look good as I just wanted to prevent the rust expansion.
However, after a year, the rust bubbled up again as shown below:
How can I eliminate the persistent rust? Should I use either of the following products before painting:
I'm not sure if they are good with car body paint or which one is better.
So I've thought about this question for a long time now and finally decided to answer.
If you really want to keep the rust at bay, then you are definitely going to need to apply a product designed to do so before applying any cover-up paint. I believe that a rust converter product is the best option. Take a look at products like Corroseal Rust Converter Primer when shopping for a good rust converter. The Corroseal one has very high ratings and plenty of success stories.
First, sand the paint back down to the rust. Then, use a wire wheel (alternatively, you could use a stripping disk which is also very effective at removing surface rust) to remove as much rust as you possibly can. This probably won't get all of the rust, but that doesn't matter since you'll then use a rust converter product.
Find a hearty rust converter that is a rust converter primer as this will add just one more layer of protection once applied. The Corroseal product I mentioned before converts the rust and then changes to a black primer color. From there, lightly sand the black primer and apply a good primer sealer on top of it.
Provided that you spray your primer sealer evenly and it looks good when dry, you don't need to sand it before then applying your car paint on top of that. It's recommended that you paint over a primer sealer within 1-2 hours time of it being applied. However, if you miss your time window, lightly sand the primer sealer with 600 grit wet sandpaper. From there you should be able to spray your automotive paint over the primer as you did before.
Be aware though this is not a lifetime guarantee that the rust won't come back in this spot. Once rust has seated itself into metal, it usually takes a patch panel to really ensure that it will stay away. However, if you properly follow the steps on each of the products mentioned, you should be able to apply a decent paint job that will keep the rust at bay for quite some time. Best of luck with your endeavors.
