Initially I want to ask about Ospho vs POR15.
I know Ospho is a rust converter and POR15 is a coating, but has anyone compared results between the two when cleaning and painting rust? Would you be able to use Ospho and then POR15 over it? Not sure if it would bond or not.
Ospho and POR-15 metal prep are pretty similar so I'd imagine you could use it before the POR-15, I'm sure someone here has experience with it. I'm a firm believer that you should hit bare metal (especially after cleaning up surface rust) with a product like Ospho before whatever etching primers or coatings you put on top.
Adam
Haven't tried Ospho yet, but I can say I've had better luck with POR-15 than with Rust Bullet, which hasn't impressed me much at all. It seems to work about as well as Rust-o-leum, which is cheap and you can get it anywhere.
My project car sits for long periods with bare metal that have been wiped with Ospho and it definitely does not rust. I have kinda been keeping track of how long the RR quarter panel (near the garage door) can go before it starts to show rust. It has been at least 6 months now. The instructions for Ospho say the metal is ready for paint coatings as soon as it is properly dry.
I used ospho on these MGA fenders then finished with the Eastwood version of por 15 rust encapsulator 
I've had good luck with grinding, wire wheeling rust away and then coating with POR-15. I didn't find much difference between using metal ready and not, assuming virgin, rough metal is underneath the POR-15. I paid for a body shop to sand blast and refinish some dog leg areas and the results were far worse and did not last anywhere near as long as my DIY attempts in other areas.
I've been doing ospho as a prep for all steel painted surfaces with very good results.
As a foundation layer for por15, it works much better than their metal ready product. The only gotcha after letting it sit overnight is neutralizing it by reapply opsho to wet the acid and washing it off with water. Otherwise, acid may be trapped under the new paint.
Interesting tips. If I want to stop things can I just use the Ospho you think or should I double down with both?
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