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Volume 8, Issue 1        January/February 2006

Side Lites
   Guest Opinion

Repair Science
by Michael Curl

Different techniques are used to perform windshield repair. I have done a great deal of research into the science of what happens when a windshield repair is done. 

Using a vacuum to help in the filling process greatly quickens the repair damage process. In cases where the vacuum is placed over the resin, some of the resin is pulled into the damage instantly but all the air is not pulled out. This causes resin and air to change places in a very tight area, especially in star breaks, which mainly consist of small tunnels in the glass. The air left in these tunnels has to slip past resin in a very tight area. This takes a long time. Time is money to the field technician, so a method to perform repairs in a timely manner and show good quality results is needed to be profitable.

In terms of the appearance of the repair, I have heard it said that some blemishes are okay to leave in the repaired area, but I disagree. When people call for a repair, they are, of course, trying to save money on a windshield replacement. These people want to get a repair that will prevent the additional cracking of the windshield, but they also want a repair that is as undetectable as possible. A repair does not look good if either air or moisture is left behind in the damage because air has a different refractive index than glass. Any air left in the damage shows up, even a trace of it. 

Many people donít realize that because of its incomplete chemical makeup, glass actually attracts moisture. It is hard for the average person to believe there is moisture in the windshield damage even if it hasnít rained in weeks, but moisture is always present in some form. Using a moisture evaporator is better than not using one, but all the moisture still cannot be removed this way. A strong vacuum without resin over the glass is the best method to remove this remaining moisture. Most people forget that the damage to a windshield is filled with pressurized air. We donít feel this pressure because we are used to it. In windshield repair, the damage is merely a space filled with air with from 14.7 to 9 pounds per square inch of pressure, depending on the altitude of the repair site. 

Michael Curl is president of Glass Pro Systems, Rockford, Ill.

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