Be aware that some epoxy primers or enamels etc can react to the Ospho. I apply a second set coat and let it sit some but NOT begin to dry and neutralize with water. You cold treat metal with the Ospho and prime and paint and a reaction could occur months later. I like the stuff but beware. There are products that "coat" the rust making it turn into supposed not rust but something???? If I can not grind something and it be steel I don't ant to put paint on it!!!!