Ask the Doctor
by Walt Gorman
Q: Would you discuss the use of heat in the repair process? I have had a few bad experiences with customers when their windshields cracked out while I was heating the windshield during a repair. I cannot understand why it works fine sometimes and other times it is a disaster.
A. First, you have to understand that glass, like many other materials, expands when heated. If you apply too much heat too quickly to a small area where it already has a break, the expansion will almost surely cause the crack to run.
If you are using the heat to make the resin run into the end of a tight leg remember that the crack will close up and appear to be filled, but when it cools down it will open up again. If you have your resin under pressure, the reopening will tend to suck it into the tip of the leg. Apply a small amount of heat, moving the flame or other heat source, in a circular path, quickly, around the break a few times until you see the leg(s) close. Wait until it is cool to the touch.
In summer the whole windshield is hot, so do not try to cool just the small area on which you are working. (We will discuss that in the spring.)
Q: I ran into a problem recently and would like to know how you would have handled it. I had to repair a fairly large star break on a very expensive luxury car and one leg was not connected to the pit. I did not want to drill another hole, but I had no choice.
A. A disconnected star can be joined to the pit by inserting a sewing machine needle from the pit in the direction of the unjoined leg at a 45-degree angle and tapping it gently with a screw driver handle. It is important to get the proper angle or you could either take a chip out of the glass or pierce the laminate. Rememberóthe proper angle and light taps. You would be wise to practice this technique and perfect it before using it on a customerís windshield.
Walt Gorman is the owner and founder of A-1 Windshield Doctor in Seekonk, Mass. He has 15 years experience in windshield repair and runs a training school for technicians. E-mail your questions to firstname.lastname@example.org.
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