VOLUME 6 -
by Walt Gorman
Editors note: In a departure from his normal question-and-answer column, Walt Gorman looks at the issue of water and how it impacts the repair process.
H2Ois its name and life is its game. More than half of the earth’s surface is water and more than half the human body is composed of water. So water is almost everywhere we want it. Unfortunately, it is also in almost as many places as we do not want it, including the breaks in the windshields we are struggling to repair.
Water in and on a windshield can come from direct impact (rain, snow, car wash, etc.) and from condensation where the temperature of the glass drops below the dew point of the moist air surrounding it. This causes the glass to fog.
Water, Water, Everywhere
Whatever the source, water in and on a glass repair site can ruin your repair for two reasons, one mechanical and one chemical.
For a repair resin to bond to a glass surface, the resin and the glass must be in total contact. If a film of water keeps the glass and the resin apart there will be no bond. Since the surface of a glass break is as full of hills and hollows as a mountain range, it is easy for a film of water to be trapped in that tough surface.
A chemical problem comes from the fact that most glass repair resins contain one or more chemicals that absorb water from the air or from the surface of the glass. Absorp-tion may dilute the resin and lower its strength or even prevent the resin from curing at all. (This is why resin used on a windshield should never be returned to the bottle where it may poison the whole container, and why it should be capped when it is not being used to load an injector.)
So how to get rid of water? There are no foolproof methods, but there are a couple of tricks that sometimes work, and both are based on speeding up the rate of evaporation of the water in the repair site.
High and Dry
If the surface of the glass is covered with water, put off the repair because there is little chance water can be removed. If the surface is dry, sometimes an injection of alcohol may help clean out any water lurking in the site.
Use isopropyl (rubbing) alcohol but remember alcohol has a lower boiling point than water, so it evaporates faster. When mixed with water, the mixture will have a lower boiling point than water alone, so the mixture will evaporate more quickly than water does by itself.
First, check with your injector manufacturer to see if the injector assembly will be damaged by alcohol. If not, inject a small amount of alcohol (just a few drops) into the entire length of the break.
Keep in mind that a film of alcohol is as bad as a film of water and that the entire alcohol and water mixture must be removed from the repair site before any resin is introduced.
With or without alcohol, heat removes water since it speeds evaporation. A small hair dryer is a good source. Do not use an industrial heat gun as it will damage plastics.
Keep the gun moving to minimize hot spots. Heat the entire length of the repair just to the point that the glass becomes uncomfortable to the touch. Since some resins will boil and vaporize at temperatures the hair dryer can produce, let the glass cool to room temperature before injecting the resin.
Given the wide variation in the composition of the windshield plastic interlayer and the fact that plastic and glass both age unpredictably, be very cautious with both alcohol and heat. This is particularly true if you are working near any aftermarket glass treatment that might not like alcohol or heat. Do not forget that even a drop of alcohol may ruin an expensive paint job.
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..