I've had great luck with it patching rusty floors. POR-15 combined with fiberglass has made some very strong and very long-lasting patches for me since the '80s. I have had it peel off when I tried it over clean metal and had it fail on a master cylinder.

No such thing as a chemical cure for a mechanical problem.
If you have rust, cut it out and replace the metal.

Trash!

This opinion is after brushing it on, spraying it on and following their instructions.

Snake oil!

Use a good epoxy primer like PPG DP90LF.

Honestly, Rustolem out of a rattlecan holds up 10x better than POR-15!

I want my $@#! money back!

?????????
Yes the best solution is the elimination of any cancer.
However the problem is chemical. Rust is a chemical reaction. In particular its the formation of certain iron oxides and iron hydroxides. Chemically or electrochemically, they are reversible. However the steel will never be the same again. The hydroxides are a major problem - the flakey rusts that form tiny pockets where moisture is retained. These are a key part of the rusts that grow and grow.

Its the tiny pockets and the dust that will cause a film forming polymer to fail even if it seals out new moisture. However, if there is a good surface to adhere to, a rust converter or rusty metal primer has a good chance of working when topped with a non-permeable coating.

This stuff is evil.
I have worked on cars with this crap slathered on and it sucks. Try to sand or feather edge this crap....Not good.

Agreed, I over simplified the response.
I get Oxidization is a chemical process.
My meaning was the only proper cure is the physical act of replacing the damaged metal.

I've used POR-15 for years and never had a failure. Including an entire 1953 Chevy pickup frame which has been on the road for 15 years now and the frame still looks perfect. The trick is to follow their directions and use their cleaners and prep spray. If you do that it will work....at least it does for me.

You have been very fortunate!

Following their directions and using the entire "treatment process" to the "T" still resulted in many failures, on several different levels. When it works, it was great, but when it failed, it failed miserably. The problem was you never could be sure which outcome you were going to get until the party was over. For what the stuff costs, it should work the perfectly every time, and that wasn't the results me and many others have gotten. Gene

I'm one that had bad results. Followed the directs to a 'T' since it was so dang expensive and, if anything, the rusting process seemed to speed up under the treated area. Where I had pitted metal when I applied it, a few years later, there was a gaping hole.

This was on a trunk pan, out of the weather, and not even getting wet from the underside as it was above the gas tank.

I have a pair of fenders in storage I need to pull out and take pics of. One fender I painted with just plain ol' Rustoleum the other POR15........20 yrs later, guess which one shows rust. Neither fender has been on a car since painting, always stored inside out of the weather.

Straight up crap.

I'd like to believe the formulation has improved in the 20 yrs since I last used it, but, I know it hasn't.

It's very sensitive to humidity too... I use similar products, but never por-15 anymore. Only por-15 ever peeled off for me.

another band aid that might stick for a while
but it does nothing to heal the wound...

Same here. I dumped a bunch of money into it including all their prep products and followed all their instructions. I still have a gallon of their metal prep product in my garage.

Seems like a lot of people have not had luck with this stuff glad I ask before purchasing it. Rattle rust oleum seems to just as Good ,lots of good response here .....Thaxs fellas

I went with Chassis Saver. It's tough as nails.