Automobile windshields are comprised of three layers. The outer-most layer is made of UV plate glass. The middle layer, made of polyvinyl butyral (or PVB) is a resin usually used for applications that require strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. The inside layer is also made of UV plate glass. These three layers are laminated together to create a strong, yet somewhat flexible, windshield.
When a rock hits the windshield, it hits with a force, great enough to cause the two top layers to separate, leaving a gap which looks like the familiar bull’s eye rock chip, or star-like chip. The damage usually includes a small hole where the rock actually hit the glass.
The three factors that most effect what happens next are:
- Heat (or any extreme weather, cold or hot)
Once the windshield is damaged, it is no longer structurally secure, regardless of how small the rock chip is. Vehicle owners are often lulled into thinking that the chip is small enough so that it won’t like grow in size or crack further. This couldn’t be less accurate. It is not a questions of will the rock chip spread? It is a matter of when. It is wise to have the rock chip repaired asap regardless of the size of the damage.
Heat (also extreme cold) is the next enemy. All glass, including auto windshields, expand with heat and contract in cold weather. The rock chip you are seeing is almost always accompanied by small, not always visible, cracks and micro cracks. If the windshield expands with heat or contracts in cold weather, it will send one of the cracks clear across the windshield.
Last, moisture (water). The rock has left an opened hole in the windshield. Moisture can easily collect in the damaged area leaving a darkened ring inside the rock chip which is very hard to remove. Technicians can use a drying tool to help dry out some of the moisture, but using a drying tool on a structurally damaged windshield can cause it to crack further.
All three problems can be minimized so that the odds of a successful repair are in your favor. As soon as you have rock chip damage:
- Cover the rock chip with a small piece of clear packing tape to keep dirt, debris and moisture out.
- Call for a repair appointment asap. Waiting can mean the difference between a simple rock chip repair, or having to replace your windshield.
- Do not allow your windshield to heat up in the warm weather or get too cold in colder weather before you have it repaired. In the warmer months, run your car air conditioner on medium and defrost when you are driving to your repair appointment. The windshield has to be between 60-80 degrees to work on, (ideally, 70 degrees).