[General Lee]

You should clay your whole car if it needs it. One good way to tell if every area needs it is, place a plastic sandwich bag over your hand. Then run your hand over you ALREADY WASHED car surface. You will be able to feel the roughness and the grittiness on the paints surface if there are contaminants.

The key to avoid inducing new scratches is clay a small section and then *knead* your clay bar to create a fresh clay surface. Do not do your whole car without kneading your clay. By doing this the contaminants get embedded in the clay and it helps them stay clear of your finish. Once you are unable to obtain a fresh surface free of debris by kneading your clay, you should replace it. A lot of people break off pieces of clay and that seems to extend the life of the bar.