Remove dirt, debris and stains that might inhibit the bond between the vinyl surface and the Sculpey clay. Dampen a clean cloth with rubbing alcohol, which serves as an effective solvent.
Wipe the vinyl surface with the damp cloth until it's clean. Dry the vinyl with another cloth.
Sand the surface lightly with 120-grit sandpaper. Smooth out any blemishes in the vinyl and rough it up to create a surface more conducive to bonding.
Dust the vinyl surface with a dry cloth to remove dust from sanding. Wipe the vinyl again with rubbing alcohol to ensure it's clean before drying it with another cloth.
Apply the Sculpey compound as instructed by the manufacturer's directions.