The invention relates to a coating system comprising I) a primer coating composition comprising a binder component PA that contains primary amine functionality blocked with a ketone or aldehyde, a binder component PB that contains acetoacetate or acetoacetamide functional groups and II) a RMA crosslinkable coating composition a component A with at least two acidic protons C—H in activated methylene or methine groups, a component B with at least two activated unsaturated C═C groups and a base crosslinking catalyst C. The invention also relates to the use of the specified primer coating composition for improving adhesion of a RMA crosslinkable coating composition, in particular to metal substrates, to a method for coating a substrate and to coated substrates coated with the coating system of the invention.