Longhorn, I have used POR15 several times on gas tanks, and chassic's and have had great results. A year ago I blasted my fame with medium sand with my pressurized sandblaster and then put the POR15 straight onto it. It looks really nice..... later I had to grind some off to attach a power steering bracket and that stuff is tough! It still looks good to day.
I don't know what happened and I"m only suggesting what MIGHT have happened. Did the frame get moisture on it before doing the stuff?? (...of coarse the POR is suppose to stop rust)
After the first coat did you wait the recommended time before putting on the second coat? The second coat is suppose to be put on while the first coat still has a little tack/grap to it. If it dries it will have a gloss slick finish and nothing for the top coat to hold onto.
Did you thin the POR?? For the rust to come through you'd think the coverage was not that good??
Bottom line is I really don't know. I have used it sucessfully and I might add that the last frame I did I only put on one good ooat and it is holding up well.
Let us know if you find out anything else. I'm curious.
