Just to clarify a couple points, Len's test included use of Rass-O-Nil, a rust converter that he strongly advocates/uses. Neither POR nor ZR are converters, that is, neither changes the structure of the rusty metal or, for that matter, the white metal blasted surface they might be applied to. In ZR's case, ZR IS the primer AND the topcoat (unless you top it with something else for esthetic reasons) and this can be done without jumping through another process/product.
In our experience, there is no need to use the Rass prior to coating with ZR, in fact and again based on our observations, 9 times out of ten, it tends to interfere with the job ZR is designed to and actually does, ALL BY ITSELF. There are others who swear by Rass and we'd be the last to pour cold water on their experience and advocacy. Forgive me, but "it's whatever floats your boat" -ouch - no pun intended.
HTH
WK Irish
