Been a lot of articles in FSM on this. Any smooth finish putty can be used, the trick is to do a small area at a time and let it dry. If you try to do a large area, the putty will dry before you can finish it and it will crumble. I will confess that I find Zimmerit tedious. Anyway, have research material to determine the right pattern, since different vehicles used different patterns. Experiment on scrap plastic with different putties and tools. Spread the putty thin, and try anything from a straight pin in a pin vise, an X-Acto blade, the back of a blade, a serrated metal glue spreader from a shoe repair kit or a vinyl repair kit, an aftermarket spreader, or whatever works best for you.