you can but i. abrade the surface with sand paper or a knife to get the top shinny coat off to dull JB up so you will get better hook up on the new top coat . JB weld i used it many times on intake ports like the roofs on the old 862 bow tie heads and port blending were time and welding with a tig is not in the plans. to get the best hookup on the surface clean with thinner then wire wheel if needed . i used a spring loaded punch and prick punch were i going to putty .this helps hook up the putty . a small shop pocket steel ruler works for tooling it and some lacquer thinner to keep ruller clean and from sticking by damping it or a finger works good to if you keep it damp with thinner . there not much sanding if you take your time ,but some may worry about damping you finger in thinner i am past that .there other stuff like A&B putty and spalsh zone but the JB work s good for most stuff