About 2 years ago now, I had the gas tank out during my six conversion and touched up some patches of surface rust on the painted metal surrounding the tank with POR-15. (I used their clear stuff 'cause I wanted to keep an eye on some of my welds elsewhere in the car.) Got in there with a wire wheel first to remove the loose rust, but following the mfr's advice:

"Surface preparation:
Rusted surfaces are best; seasoned metal and sandblasted surfaces are also good. "

So I didn't grind all the way down to shiny metal.

OK, 2 yrs later, tank is out again (chasing down a persistent fumes issue). One glance at the POR'd areas and I see NEW rust "spiders" (throught the clear POR) growing out from the original area. Nothing major, no "bubbles", but stuff that clearly wasn't there when I painted it.

WTF???

Maybe this is what happened:

http://www.por15.com/faqs/faqmoist.html

i used metal ready first, the put por-15 over it ...
the metal-ready is supposed to change the rust chemically into, hum, something else ?

Andy

"Iron Oxide" But some of the acid preps require a wash down that most people omit.

does the metal ready turn the rust black?

kevin

Rust never sleeps

I haven't visited the POR-15 website in quite a while, except to order. This "scenario" wasn't on there when I researched the stuff a few years ago.

The story they listed didn't mention at all the use of Metal-Ready/Prep, whatever.

I'm not sure that it's an issue if you do all the prep steps.

-Rusty

Thanks for pointing out that FAQ response, didn't see it when I went through the site in detail 2 yrs ago. I did use Metal Ready on the area, but the residual moisture thing is quite possible. But for chrissakes, steel is used to HOLD water (and gases, etc), HOW POROUS IS IT??? I didn't know I had to bake the car first <_< . What do car manufacturers do when they start out with ALL bare metal?

So the question now is, does the rusting peter out after awhile (ie after all the "O" in the H2O is converted to FeOx)? I took a pic of the area, and I'm sure I'll be pulling the tank next year for some damn reason or other...

Yep.

I have pushed and pushed POR15 and it came back to bite me. I put it on a stock battery tray that was solid... 2 years later... rust.. just like before. It was the first time I had used the POR.

B

No, it turns white...

So what should I use, if not POR15?

Use POR 15, just not that clear shit. If you want the bare metal look, use Metal Mask.