Now comes the messy part! After the entire car was given a light guidecoat from a rattle can, I sanded the primer wet using 400-grit wet and dry paper on a rubber block. Do not use soap in the water at this stage, just plain water, and ensure the bucket, water, and sponge are totally clean and free of debris. Note I masked the joint between the fenders and sail panels to prevent buildup of the primer/water solution in the joint. You may be wondering why my fingers are covered in tape too. Wet-sand a whole car without doing this and your fingerprints will disappear from the constant friction between sandpaper and skin. Go further and blood will seep from your thin-skinned fingertips for a couple of days. Not fun!