The number one obstacle a windshield repair technician finds when treating a rock chip is, water – moisture, to be more exact. Water and the resin used in the repair process simply do not mix. There are three layers that comprise a windshield. The two outer layers are UV glass and the middle layer is made of Polyvinyl butyral (or PVB) a resin usually used for applications that require strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. It is prepared from polyvinyl alcohol by reaction with butyraldehyde. The major application is laminated safety glass for automobile windshields The three layers are laminated together to form a windshield. When an object hits your windshield, it hits the force of the moving object, and also the force of the speed of your vehicle. It instantly causes the laminate from the top layer of the windshield and the PVB layer to split and crack. The result is the typical bulls eye rock chip or star-like crack. It also leave a small open hole from the outer layer, leading into the the PVB layer. Most often, the rock, or other flying object causes the surface glass of the windshield to propel inward. So in addition to the initial damage, small chards of glass are also in the damaged area. Left untreated, the open hole in the windshield allows dirt, debris, and moisture to collect inside the windshield. Water or moisture show up as a dark, almost black looking shadow. A slight rainbow effect may also be present. The windshield repair technician can use a drying tool to dry out some of the moisture, but it is not 100% effective. The combination of repair resin and moisture left in the damaged area leaves a cloudy, sometimes patchy, result. Car owners can help prevent dirt and debris, water and moisture, from getting into the windshield by simply placing a small piece of clear packing tape (the kind you use to ship a package) directly over the rock chip on the outside of the windshield. The sooner the rock chip is repaired, the better it will look cosmetically once completed. -Its a simple “trick” but it is so effective.