Damn sb, that's one of the best posts I've ever seen on salt-related rust! I'm reposting here for posterity:
I've been wanting to write this up for a while, may as well be now. I learned about rust when I owned a 1964 Triumph TR4. For as long as I owned the car, I was engaged in an epic life-or-death battle with rust. I learned a lot - mostly what doesn't work - as I experienced fun things like having a rear fender fall off while rounding a curve, and, even more fun, having the steering gearbox break free of the rotting frame, jamming the steering just as I entered a curve. Both I and the owner of the brand-new split rail fence I destroyed found that episode quite amusing.
Anyway, maybe this will help someone protect their truck:
There are two fairly effective ways to treat surface
rust. I say fairly effective because nothing will work 100% or last forever. But you can knock it back pretty well.
The first approach is to use a "rust dissolver". That's a phosphoric acid etching solution, sometimes with added ingredients. Naval Jelly and Ospho are probably the two most popular. You absolutely must cover the treated area with an impervious oxygen and moisture barrier, otherwise the rust will start up again quite soon, sometimes within hours.
The second is to use a "rust converter" which chemically reacts with iron oxide to produce a compound that inhibits further rust. By itself, a rust converter will last much longer than a rust dissolver by it
self, but ultimately a converter also needs an impervious topcoat for the longest lasting effect. Originally, rust converters were based on phosphoric acid, since it reacts with iron to produce iron phosphate, which provides the steel some protection from further rust. The best converters now use tannic acid, which reacts to produce iron tannate - a much more durable rust preventative than iron phosphate.
Most people who have treated rust with dissolvers or converters have found that they don't work for long on vehicles. The reason is salt. The salt ions actually chemically and electrically alter the steel to cause it to generate low voltage electricity that essentially does electro-plating in reverse: instead of depositing metal, the salt causes the metal to be electrically eroded. If steel has been in contact with road salt for an extended period, it is practically impossible to remove the chlorides from the steel, so even if you treat it with rust converter, the steel will still electrochemically corrode.
I actually did find a product that worked amazingly well on my old TR4 - for the surface rust. The problem was that by the time I found the product, most of the body and frame of my poor TR4 was shot through with rust, and when that happens, nuttin helps.
The product that worked quite well is "Fertan". It was developed for the British Navy, and it is used widely in the marine industry around the world. The reason Fertan works well is that it contains zinc. Zinc is electrically a more active "anode" than steel, and when in contact with steel it will sacrifice itself and protect the steel. Most ocean-going vessels have zinc clamped to the propeller shaft to protect the shaft and propeller from corrosion.
There's some info about Fertan here:
Fertan is great for the frame/suspension, especially if it's top-coated with one of the chassis paints listed in the post linked above.
BUT. The problem with Fertan is that it is somewhat "thick". It needs to be thick to provide a reservoir of zinc. For that reason, I'm not sure whether it would work for the inside of the wheel. I would worry that the surface would not be smooth enough to provide an air-tight seal for the tire.
So in your case, the rust dissolver/impervious topcoat approach might work better. Fortunately, there is a great dissolver that also contains zinc - and it probably would work well for those wheels. It's called "RustBlast" and it's made by KBS, a maker of coatings similar to (but I think better than) POR-15's product line. RustBlast is mainly phosphoric acid - it does dissolve rust like naval jelly or Ospho, but it also contains zinc phosphate that counteracts the chlorides that have infected the steel. It should be top-coated with KBS's "RustSeal" product or with POR-15. That provides a smooth, glossy, impervious finish that is very tough and also should provide a nice airtight seal for your tires.
Surface prep is everything, so you may want to sand the rusty areas smooth, clean and degrease the area with something like KBS's AquaKlean, then treat with RustBlast, and finish up with RustSeal. That's the best thing I can think of for those wheels.
Oh yeah. I lost that life-or-death struggle with rust on the old Truimph. I learned that once rust has gone deep, nothing can stop the metal from returning to Mother Earth. I gave what was left of the car to another TR4 owner to use as a parts car. Too bad - that car had more "soul" than any vehicle I've ever driven. __________________