A thermally cured silicon coating on a plastic, in particular a thermoplastic, can be adhesively bonded without use of an adhesive primer. Such thermally cured silicon coatings are produced by a process including: application of a silicon composition to the surfaces of a plastic or to the surface of a plastic treated with a plastic primer; air drying of the silicon composition to form a silicone film; baking at a temperature in the range from 80° C. to 200° C.; and application of a bonding agent composition to the silicone film during baking or during the phase of cooling to ambient temperature after baking.