Proper windshield installation, a profitable part of the collision repair process, ensures that replacement glass does not leak and provides structural integrity
Proper windshield installation is an often overlooked part of the collision repair process. Today's unibody vehicles incorporate the windshield, and other fixed glass, as a structural element. This is an important fact to consider during repair.Using a structural adhesive, automakers bond the glass to the body, thereby increasing the strength of the vehicle. Automotive glass also helps keep passengers inside the vehicle and keeps air bags from protruding from the cab during a collision.
How a windshield performs during an accident is governed by Motor Vehicle Safety Standards (MVSS) No. 212 for windshield retention and MVSS No. 216, a roof crush test. Some OEMs may have more stringent standards and recommendations for replacement procedures because of design characteristics of their vehicles.
The introduction of top-loading passenger side air bags has placed added importance on the proper installation of replacement auto glass. When the occupant rushes forward into the air bag, this applies pressure to both the bag and the windshield, breaking the glass. If the windshield is improperly installed, the pressure of the occupant striking the bag could eject the windshield causing the air bag system to fail. Serious injury to the passenger could result.
Most OEMs use urethane adhesive systems for installing their flush mounted and encapsulated windshields. Urethane provides the strength necessary to meet both MVSS No. 212 and No. 216. Other types of adhesive and adhesive tapes may not provide the level of strength necessary to hold the glass in place during a collision.
Installation Procedures
First, remove any molding from around the glass. Remove the windshield wipers and the cowl panel if necessary. Then, remove the damaged glass from the vehicle. Several tools are available for this use: Cold and hot knives; piano wire; or a power-tool with a reciprocation knife blade. Whatever tool you use, be careful not to damage the car body around the glass. Masking tape placed around the glass will help to prevent nicks and chips. Always make sure you follow proper safety precautions.Short Cut-Out
At this point, you must figure out if the old urethane will provide a good base for the new windshield. If the urethane is in good shape, a partial cut-out repair may be performed. In this repair, the original urethane is trimmed evenly around the pinchweld. This will provide a base for the new adhesive.Check with both the adhesive manufacturer's and vehicle manufacturer's recommendations regarding short cut-out or full cut-out methods. Increasingly, manufacturers suggest full cut-out installation to guarantee the integrity of the repair work.
Next, repair any paint damage to the pinchweld. Be careful not to allow paint or other materials to contaminate the OEM urethane. Once the paint is dry, you can test-fit the windshield.
Set the windshield in place. Check to make sure that the window is flush with the car body. If it is not, trim the old urethane until the windshield sits flush. Next, mark the windshield in position using masking tape. Apply the tape across the glass and body in several spots. This will help you guide the glass into position during windshield installation.
Full Cut-Out
If the body repair work you are doing requires you to remove the old urethane, a full cutout repair is necessary. This method is also necessary if the glass was previously replaced and butyl tape was used during the replacement installation.First, remove the glass and moldings as outlined above. Then, remove all of the old urethane from the pinchweld and be careful not to damage the vehicle. Clean the area with wax and grease remover. Repair any damage caused by the glass removed, and perform any body repair as necessary.
Apply a urethane bonding primer to the pinchweld. It is important to use a primer recommended by your urethane manufacturer. Like auto refinish materials, adhesive systems are designed to be used with compatible products.
Test-fit the new windshield and mark it with masking tape for alignment. To get the windshield flush, install the original spacer blocks used by the vehicle manufacturer.
Glass Installation
Clean the new windshield to ensure that it is free from contamination. Apply glass prep to the outer edges of the windshield following manufacturer directions to ensure a good bond. After cleaning, take care not to touch the windshield near the area to be bonded. Fingerprints and other dirt will affect the adhesion and strength of the bond. Apply black urethane glass primer to the outer edge to enhance adhesion and provide ultraviolet protection for the urethane.Apply a continuous bead of urethane adhesive directly to the pinchweld of the vehicle. With a helper, install the glass in the windshield opening. Use the masking tape marks as a guide.
With the windshield in place, firmly press down on the glass to set it into the adhesive. Be careful to avoid excessive pressure that could cause too much adhesive to squeeze out. Apply tape to hold the glass in place during the curing process.
Water test the installation immediately. Avoid directing a hard stream of water directly at the adhesive. If water leaks are found, apply additional adhesive to the areas using a disposable brush or flat bladed paddle. Urethane is a moisture-curing material. Water applied during the water test helps speed the curing process.
Finally, reinstall the moldings, trim and windshield wipers. Check the adhesive manufacturer's recommendations for cure times. Most adhesives will provide green, or holding strength, within a few hours. Complete cure can take as long as 24 hours. While this may not be a problem for the average collision repair, if the vehicle just requires glass replacement this fact must be considered and explained to the customer.
