I was told that by the tech guy at Southern Polyurethanes. I have also read where if the epoxy primer has some acid , that can trigger a reaction. I have used the Ospho many times without neutralizing it, but it died at least 24 hours. I have also read where if not neutralized a reaction could occur months later?? I did apply some Rusteloem over bare rusty pitted metal I had snaded best i could cleaned with the Ospho and it did have a wrinkle in a couple of spots, but I was stuck great. Several years later, no problem, and I could hardly DA it off at all. I did it as an experiment.