I have exterior steel railings that have factory seal and paint. They started rusting, due to nicks in the paint, from show shovels, kids, etc. In summer 2009, I completely stripped one of the railings, using a grinder. I did a very thorough job of removing rust, and then carefully applied Rustoleum primer and sealer paint.
The following spring, rust already spread across parts of the same railing! I live in Utah, where we have relatively low humidity (~65-70%), so I don't think the time between stripping and sealing would have been an issue.
Please provide tips on how to properly seal the remaining railings?