How does rust move?

I have a question about rust. On my 1990 I'm working on restoring, I'm going to be eliminating all the rust on the floorpans both top and bottom and framerail. I'm then going to coat it all with Herculiner. I know that rust that starts on one side can eat through to the other side of a metal. Here's my question. If I prep and paint (with bedliner) a certain area, but don't get to the area around it for a bit...can rust creep underneath what I get laid down? Keep in mind this thing just sits outside in my driveway right now with no drivetrain, so its not like other Jeeps being driven around in this situation. I have seen how fast the stuff moves and just don't want work to be in vein. If any of you guys are rust experts or have dealt with this before, let me know please.
Thanks,
Collin

Rust starts with standing water, then the texturing captures more water which causes more rust. You can cover rust and any moisture that was trapped underneath will continue to oxidize the metal. You need to either remove the rust, fully and completely encapsulate it, and remove any moisture.

ehall said:

Rust starts with standing water, then the texturing captures more water which causes more rust. You can cover rust and any moisture that was trapped underneath will continue to oxidize the metal. You need to either remove the rust, fully and completely encapsulate it, and remove any moisture.

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Okay but if I say paint an area that I am positive is free of rust, can rust from a surrounding area still creep underneath it?

If the other rust is holding water, yeah

You gotta kill rust. The only sure fire way is to cut out the rusty panel. The next best thing is to sandblast off as much rust as possible and treat the remainder with tannic acid rust converter (the kind that turns the rust black) or phosphoric acid which dissolves the rust and coats the steel with a passive protective layer of iron phosphate. I'm not sure which approach is better, I'll let you know when I move back to Vermont someday. Then seal it up with some sort of coating, I've heard great things about moisture cured urethanes like POR15, etc.

I pasted a bunch of links in this thread, you might find it useful.
http://www.naxja.org/forum/showthread.php?t=908754

n1ywb said:

You gotta kill rust. The only sure fire way is to cut out the rusty panel. The next best thing is to sandblast off as much rust as possible and treat the remainder with tannic acid rust converter (the kind that turns the rust black) or phosphoric acid which dissolves the rust and coats the steel with a passive protective layer of iron phosphate. I'm not sure which approach is better, I'll let you know when I move back to Vermont someday. Then seal it up with some sort of coating, I've heard great things about moisture cured urethanes like POR15, etc.

I pasted a bunch of links in this thread, you might find it useful.
http://www.naxja.org/forum/showthread.php?t=908754

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This and the links you posted are very good information. I've known the basics of rust (either cut it out or sand it down) for years, but knowing that I actually have to kill it and then etch it is very helpful. I bought a Por-15 Mix Pack with Marine Clean and Metal Ready about a year ago and just haven't gotten around to doing much with it yet. I know water got in one of my cans and infected it so I had to throw that one out. I need to get going on this project again before winter, that's why I posted this, hoping I could gather some info to get me reinspired. Thanks again for the help.
-Collin

The metal ready has tannic acid, you can tell from the pics on the por15 website, it turns the rusty areas black. I don't know if it has phosphoric acid. You can use phosphoric acid to etch but rinse it off before it dries and then use tannic acid. I dont' know if tannic acid would be effective after the acid dries, and I don't think acid would be effective over tannic treaded rust.

Another option is zinc primer, although it's probably not the best choice for already rusty metal afaik. It has to be in direct contact with the steel to be effective, which it can't be if it's been tannicized or phosphorized.

Nevermind, according to the Metal Ready MSDS it consists of [FONT=Verdana, Helvetica]Phosphoric Acid, [/FONT][FONT=Verdana, Helvetica]Zinc Phosphate, and [/FONT][FONT=Verdana, Helvetica]Octylphenoxy Polyethanol Ethanol Triphenol Methane. You can buy something similar or identical at home depot. you can get tannic acid rust converters there too of course...
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How does rust move???------

3 mexicans and a rented Penske truck

_MURDERED OUT_ said:

How does rust move???------

3 mexicans and a rented Penske truck

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WHAT IS THAT SUPPOSE MEAN?? Dumb ass...

Elias