Can you comment on the practice of applying iron phosphate (Bonderite 1030) over galvanized steel (G90) and then coating w/ TGIC Polyester powder 2mils thick. Specifically, what would the Q-panels look like after 1,000 hours salt spray with regard to adhesion, creep from scribe mark, corrosion.
Normally a zinc phosphate, not an iron phosphate, would be applied over a G90 substrate to achieve 1000 hours of salt spray resistance. Iron phosphate probably won’t provide as high a salt spray resistance (i.e. 650+ hours). The TGIC powder would provide excellent weatherability for outdoor applications but won’t effect the salt spray resistance on a scribed panel.
If, in fact you are using this substrate, pretreatment, and powder combination, then you would probably have more than 1/8 inch creepage and possibly some loss of adhesion after 1000 hours of salt spray exposure. Be aware that zinc phosphate has some waste water pollution considerations that are very different than iron phosphate. However, if 1000 hours of salt spray resistance is a requirement for your product, then you have little choice.