It is simply MUCH, MUCH safer to wash the car with just a bit of carwash. If you were just going to quick detail your car for the enjoyment of it and just wanted it to LOOK CLEAN before using it, then sure just quick detail. HOWEVER, if you want to apply a polish, glaze, wax, etc, then think it over. You are going to be using an applicator to spread out some Klasse SG. Are you absolutely sure, that there is not going to be any debris, dust, etc.. All this will easily scratch your car as you're rubbing an applicator over the car. So be careful. Or, just wash the car. Laters