[ChrisHamilton]

If you do use Ospho, make sure you neutralize it before applying epoxy. Otherwise the epoxy wont adhere.

To neutralize you would simply re-wet the treated area with Ospho, keep it wet with Ospho for 10-15 minutes, taking care not to let it dry. You can use a wire brush or scotchbrite pad to help remove some of the crud while doing this. After the 10-15 minutes simply rinse with water thoroughly and quickly dry. It is now neutralized.

Same procedure would apply to any phosphoric acid based product. Epoxy and acid films don't work well together. Often if epoxy is applied over a phos. acid treatment that hasn't been neutralized properly it will simply peel/tear off after the epoxy sets up.

If one is ever in doubt always defer to what the manufacturer of the paint product going over an acid treatment says rather than what the acid treatment manufacturer says. Very important.