Reasonably good results can be obtained if one of the following is used, but note that chrome is not an “”approved”” substrate:
Good – Grill – Sand the surface as well as possible, apply two coats of RAPTOR Adhesion Promoter (UP5024), allow to dry then apply RAPTOR.
Best – Bumper and Grill – Sand the surface as well as possible, apply epoxy primer (following primers guidelines), then apply RAPTOR.
Another option could be to sand and apply 2 coats of RAPTOR Acid Etch Primer (UP5023) and then apply RAPTOR. Note that this has not been fully tested, so test in an inconspicuous spot first.