In general, the products of the Procrom line adhere directly to the metal, as long as the surface is properly prepared.
WARNING: Check if the paint is suitable for your substrate, check the container label or this FAQ section. Not all enamels adhere the same to all metals. For example, for aluminum, PREMIUM enamel is applied without a primer, while SMOOTH enamel requires a MULTIPRIMER primer coat. For steel, both are applied directly.