I can't imagine why you'd spray varnish on it. That's for wood. You can spray a clear coat over it to protect it. If you don't want it shiny, they do make flat clear coats.

 

yeah clear coat sorry, thinking in French and then writing in English, in French it's the same word...

 

Sorry man... I didn't realize you were working with another language. I used to sell automotive paint and ran into plenty of people who really did use the wrong products on things.

 

no harm done ;-)