##### July/August 2001

pros who know

Lazy, Hazy, Crazy Days of Summer Upon Us
by Dave Shores

With the trees budding and the dandelions blooming, we are all beginning to encounter some old problems that we haven’t faced since last year at this time. No, I am not talking about allergies, which I know a lot of us face this time of the year. I am, in fact, talking about doing windshield repair in hot weather. Both have a tendency to bring tears to your eyes if things aren’t going right.

As the temperature rises, so does the risk of breaks running or spreading while we are working on them. Let’s discuss some of the reasons why this happens.

Thermal stress and glass breakage are created when a piece of glass is warmer at the center than the edge. The expansion of the central zone places a tensile stress on the glass edge. Based upon the coefficient of thermal expansion for soda-lime glass, a one-degree Fahrenheit temperature gradient creates 50-pounds-per-square-inch mechanical stress in the glass edge. When the stress exceeds the strength of the glass edge, a thermal fracture will occur. Remember that a windshield with a break in it is weakened greatly already. Because of that, the thermal stress is going to allow the break to spread more quickly than it normally would.

This stress can be compounded when the windows are all rolled up, allowing pressure to build up inside of the vehicle as the temperature increases. This pressure is pushing out on the windshield and can also cause the break to run.

What does all this mean to windshield repair technicians? Don’t work on hot windshields!
I know what you’re thinking: “Here I am in Texas and it is over 100 degrees Fahrenheit and I have bills to pay.”

Well, there are some solutions. First, get the windows down so that air can circulate through the car. Try to move the car inside or into some shade. Both of these techniques will allow the windshield to cool down. Try to get the windshield to the point that it feels cool to the touch. Keep in mind that our body temperature is 98.6 degrees Fahrenheit.

Next we want to use a resin that is thicker than the ones we have been using in the cooler temperatures because the laminate is much softer in hotter weather. The softer the laminate, the easier it is to “flower” the break, or cause the resin to flow between the laminate and the outer layer of glass. It looks just like one might envision: a flower petal appearance around the outside perimeter of the break. This is not something the customer wants to see in his windshield. Incidentally, you can also cause flowering by using too much pressure while injecting resin into the break.

If you slow down and make sure that you do things right on these hot summer days, your work will go a lot smoother and you will give your customers a repair with which they are most satisfied. I hope that you enjoy the summer.

Dave Shores is vice president of Glas-Weld Systems of Bend, Ore., and serves on the board of directors of the National Windshield Repair Association.

AGRR