Expert
Posts: 5870
       Location: western PA | You can apply the new product over the old if it is well cleaned with soap and water. Car soap works well. You will want to use a soap the rinses clean, and leaves no residue. Scrub it well with a push broom or roofing brush. Flush it well after its application. Let the coating completely dry before applying the new. You probably won't need a fourth coating |