Scrap off the old surface to remove dust, grease, paint, etc.
Make the putty mix with water according to the manufacturer’s instructions.
Apply the first coat of putty from bottom to top using a spatula or blade.
Let it dry out and sand the surface lightly to remove loose particles.
Apply the final coat and leave it to dry for a minimum of 6 to 8 hours. Smoothen out by rubbing or gentle sanding.