Rags and sponges used in driveway washing inevitably pick up particles of grit and can scratch your vehicle’s surface. In addition, garden hoses do not have enough water pressure to remove all the soap film, leaving a damaging film behind. The University of Texas proved that a single home hand-wash can leave scratches in your finish as deep as 1/10 of the paints total thickness. In fact, these studies have shown that the home hand-wash is one of the easiest ways to damage a car’s factory paint job. UV rays.