I had a tube puncture from a rust spire. Sharp little bugger, that. Very odd trying to ride with the rear tire going 2 inches alternately left or right.
Anyway, did the wire brush/sanding, and even steel file thing to reduce the brown and bring out the shiny steel. Then I used Zinc Chromate primer to paint the inside of the rim. The paint carrier does a fair job of sealing the surface. And, the zinc is sacrificial, in that it will give up to the corrosive assault before the steel gets involved. Does a fair job of deterring any rust sites you may have missed, too. Also, any nicks in the surface paint membrane rust at a slower rate due to the surrounding zinc.
I've changed the tire twice on this rim, now. No new rust has been found on the rim in the 15 years since this treatment.
Beware that some paint companies use zinc chromate as a color designator without actually putting zinc in the formula. The chromate is there to bond well with aluminum. However, it bonds nicely to steel, as well. Aircraft supply shops have the real deal, if you have difficulty getting it in your area. Some locales restrict offerings to the public as breathing in the zinc is not wise. Either spray or brush application works well. I had a spray can, handy at the time.
Despite it's clever marketing name, Rustoleum, while a good coating membrane, doesn't do a thing to convert rust. And, rusty surfaces so painted, continue to rust from under the coating anyway. Zinc phosphate would be the preferred treatment to the steel before covering it with a paint membrane like Rustoleum.
I find the single zinc chromate application (either green or yellow) a speedy way to deal with such hidden areas. Prepare, paint and use next day.
Cheers,
