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How to Determine if it Can Be Repaired

According to the National Windshield Repair Association (NWRA), the location of the damage or crack and the actual size of the damage or crack are both important in the decision to recommend repair.

Also known as the critical area or primary vision area, the acute area is the area of the windshield in the driver's direct line of sight. According to the NWRA Recommended Practice, the acute area is "an area approximately 8.5 inches (21.59 cm) high by 11 inches (27.94 cm) wide directly in front of the driver and beginning just above the steering wheel." (See Fig. 1.)

In the acute area of the windshield, NWRA recommends repair "if the damage can be completely covered by a 25-cent U.S. coin (.95 inch diameter circle; 24.13 mm), if the finished pit will be less than 3/16 of an inch (4.76 mm), and there will be minimal cosmetic blemishes remaining in the damaged area after the repair is completed."
You must be able to identify the type of break. Table 1 illustrates the types of breaks that you will encounter.

Cracks
The types of cracks you will encounter are:
  • Short crack. A crack on the windshield of 6 inches (15.24 cm) or less.
  • Long crack. A crack on the windshield of more than 6 inches (15.24 cm).
  • Horizontal crack. The most common crack.
  • Vertical crack. The tightest crack.
  • L-Shaped crack. The second most common crack.
  • Edge crack. Any crack on the windshield that extends to an edge.
  • Floating crack. Any crack on the windshield that does not extend to an edge.
  • Stress crack. Any crack extending from an edge without an impact point.
  • Cracks Off a Star or Bullseye. The most difficult to repair; the crack expander works for this.
Repair Guidelines
Neither the National Glass Association (NGA) nor NWRA recommends windshield repair under the following circumstances (i.e., do not repair if these conditions exist):
  • Damage penetrates both layers of laminated glass simultaneously.
  • Damage with three or more extended long cracks.
  • Damage or crack contaminated by chemicals which inhibit repair.
  • Damage or crack on the inside layer of glass.
  • Damage or crack that is visibly dirty.
  • Damage or crack in a heated wiper rest area.
  • Damage or crack in a fully-heated windshield.
  • Damage with pit size larger than 3/8 of an inch (9.525 mm).
  • Damage with pit depth of the laminate.
  • Cracks that run through the acute area of the windshield.
  • Edge cracks that intersect more than once with an edge.
  • Stress cracks.
  • Bullet-resistant windshields.
  • Glass on commercial aircraft; i.e., airplanes with pressurized cabins.
The older a break is, the harder it is to repair. The longer a break goes without being repaired, the more likely it is to be contaminated by windshield cleansing agents, wax from car washings, windshield water repellent, and other substances.

Source: This material has been adapted from the Auto Glass Repair Technician Reference Manual, an NGA and NWRA recommended reference to prepare the auto glass repair technician for the Auto Glass Repair Technician Certification examination.