Once the glass is cracked...IT CAN BE REPAIRED.
The disturbing noise all of us have heard while driving carefree. The little crack break we later spotted on the windshield of our car, is waiting for the right conditions [temperature variations, vibrations, pressure, etc.] to grow into a long crack across the entire windshield.
A large percentage of the replaced windshields could have been repaired in the early stage of breaking. This arises from surveys in the USA and Europe. This is because most of the breakages are caused by stones hurled by other vehicles onto the windshield of our car.
The stone usually causes a small star or eye shaped break of 5-30 mm in diameter. Cracking is most of the times limited to only the outside of the windshield glass, which is known to comprise of two glass panels with one PVB film between them. At this stage and before the lines get extended, it is possible to perform a repair.
This technology started from the US in 1971. 3M [Minnesota Mining and Manufacturing] company developed an apparatus which injects adhesive-like resin in the crack aided by ultrasounds. In the first stage of this technology, the device was bulky and its use was very costly.
However, by the mid-1980s, many companies in the US and then in Europe developed devices and materials which were more efficient and with a lower repair implementation cost.
Through the simultaneous use of vacuum and pressure, a transparent resin is injected into the rupture, following air removal. This special resin, with its highly adhesive properties, fills the crack and since it is transparent or of the same color with the glass, eliminates the break at a rate about 80%. The percentage of visible success depends on the time between damage and repair. Then, using ultraviolet light there is structural restoration of the glass through curing of the resin.