Scratches are usually shallow and affect just the outer layer of your windscreen. They are often caused by windscreen wiper... moreScratches are usually shallow and affect just the outer layer of your windscreen. They are often caused by windscreen wiper blades that have not been replaced in a while. If you fail to replace your windshield wiper blade, the rubber on them wears off, leaving the metal in the wiper exposed. The metal will cause a scratch that will deepen with time.