DK
I have Z2 on my chrome wheels, without Z1, as most recommended that. The theory I hear is that the Z1 is not needed, because the Z1's purpose is to bond to the paint, as sort of a "primer."
But, I also hear that Z1 is a bit of a curing agent. If so, then it might make sense to always apply Z1, first, even to chrome.
Do you have any info? Or, a speculation?