Auto Glass Installation


Here are the steps to installing a windshield and a description of steps sometimes skipped or incorrectly performed by a disreputable installer. Any skipped steps that lead to a failure of the urethane to bond to the glass or vehicle can result in the passenger air bag deploying incorrectly during a collision. In the case of a vehicle roll over, an incorrect installation may result in the windshield not supporting the roof.

  • The first step is to determine you have the correct windshield for the vehicle, and it isn’t defective. Next, remove the windshield wipers and cowl. The cowl is the cover on the bottom of the glass that is partially underneath the hood. Its main purpose is to hide and protect the bottom edge of the glass. Not removing the cowl is a typical example of how an improper windshield installation is performed. To save time the cowl is not removed. I will explain during the installation procedure how this affects the final result.
  • Remove and discard the top and side moldings. The moldings are to protect the edges of the glass which is the most vulnerable part. Some of the newer vehicles do not have moldings or the molding is part of the glass, which is known as encapsulated. When an old molding is removed it is often damaged, because it is either stretched or torn, and a new molding should be used. Reusing the damaged molding by gluing it to the new windshield is a common practice, but the customer may be charged for a new one.
  • Tape the painted surface of the vehicle next to the windshield to protect it from tool scratches during removal. If this step is skipped, the paint may be scratched, leading to rust and an eventual failure of the urethane bond.
  • The dashboard should be covered to protect it from damage. Skipping this step may result in a scratched dashboard.
  • The windshield is removed using a variety of methods determined by the installer. The main goal should be to remove the glass without damaging the vehicle’s paint or pinch weld. A major problem with an improper installation is that the paint surface may be compromised by scratches, which can cause rust if not treated properly and result in the failure of the urethane bond.
  • The pinch weld area is cleaned and the urethane is removed leaving a 1/16” base to bond the new urethane to. This is called the “full-cut method” and is the only installation method recommended by car manufacturers. The “close-cut method,” which leaves the majority of urethane, is used to save on the amount of urethane used in the installation. This method can compromise the safety of your vehicle by causing a failure of the urethane bond.
  • Primer is applied to the glass, if required by the type of urethane used and also to any area of the pinch weld that has been scratched. Skipping this step can cause the surface of the pinch weld to eventually rust, resulting in a water leak, and possibly failure of the urethane bond. 
  • After cutting a V-shape in the nozzle, the urethane is applied around the perimeter of the pinch weld and the windshield is set into it.  The V-shape is important for creating a complete, uniform seal.  Secondly, the installer who didn’t remove the cowl in the first step must use a procedure known as “cowl jumping,” in which the windshield is slid past the cowl onto the urethane. This causes the urethane to be smeared along the bottom of the glass and creates a defective seal.

For more information about auto glass and to see a video about the dangers of an improperly installed windshield visit the Auto Glass Safety Council website,


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