ideally yes if you want it done properly depends also where it is flaking if you want to spray only a small section . But i would say the paint peeling is a sign it has had a bad spray job on it done . To remedy that and stop it coming back you should sand down where all the peeling is and primer that but spray the whole bumper. use a scotchbrite pad to take shine off whole bumper before painting again . the paint will be peeling because it has not been properly prepared for spraying 1st time, i.e. rubbing previous shine from laquer before paint job