I use Ospho in a spray bottle, scuff with a scuff pad, then wipe with a paper towel. When I am ready to prime, I scuff with a scuff pad, then wipe with Wax and Grease remover. I have never had any problems.
The one caveat is that you can only apply phospohric acid once. Thus you have to be sure that the primer you are using doesn't also contain the acid. That means no etch primer and no hybrid epoxies that contain acid. I use Kirker Enduro that doesn't. I believe Valspar/House of Kolor is one that does contain acid. It is best to look at the manufacturers data sheets for the primer you are using to ensure that metal etched with phosphoric acid is a suitable substrate for the primer.
I hope this is helpful.
Regards,
Steve
New Orleans
