When wash a driveway we first apply a mildew killer, 2nd followed by surface cleaning, 3rd then rise, and lastly 4th we apply alcide with a brighten. Although these are diffent chemicals try to looking at this way. A washing machine has two or three holders for soap, bleach, and softer. If you use nothing your clothes wil lbe little cleaner after you wash them with just water than before. You use soap it’s even better, bleach and wow it looks like new. That is what we aim for. But are chemicals will keep your drive way cleaner for a much longer time, than just a pressure washing alone.