The other day I had a client call me to come out to look at a long vertical crack on her windshield. She explained to me that the day before she had driven her vehicle through one of those drive through car washes and when she entered the wash there was no damage to her windshield, but when she exited the other end she noticed a 12 inch break on windscreen, and that something in the car wash had to have been responsible for the damage. I said let’s inspect the damage. After looking at the crack, it was obvious what had caused the damage. There was a small star break down in the black shaded area about an inch from the edge. I explained to my customer that 98% of the time there is hidden damage in the black area around windshield and most people never see it, and that the outer 3 inches is the weakest part of a windshield. The main reason for the damage to spread when you are having your car washed is that glass does not do well when there is hidden damage ( already a weak spot ) and there is a quick temperature change between hot glass and cool water or visa versa.