Windshield Repair Forum

Fact: Warming windshield repair resin will effectively lower the viscosity, thereby allowing it to flow into tight spaces more easily. A Viscometer is used to measure the resistance of the liquid as it flows through a constricted space. For information on how a Viscometer works or how heat lowers the viscosity of a liquid all you have to do is google it. To prove it for yourself buy a Viscometer and start testing. Hope this helps 14UPONDER.

Fact: Heat heating glass will cause it to expand. Heating glass unevenly can cause it to crack. Heating glass to quickly or from one side only causes uneven heating.

As someone who has lived in an area where the ambient temperature is frequently below freezing in the winter, I can tell you there are times when warming the glass and the resin will help you to do better repairs. Having also lived in a climate where temperatures were sometimes over 100 degrees Fahrenheit in the summer I can tell you there are times whey cooling the windshield provides a benefit, although the latter has more to do with minimizing the chance of flowering and crack-outs than with resin flow.

I assume all those who believe that heat should never be used cool every windshield to...what...40 degrees Fahrenheit? If warm is bad cold has to be good right? I know, that is totally ridiculous, but I'm trying to make a point here. I think if you say the glass should never be warmed, you have to also say that you cannot do successful repairs on warm glass, and I know every single one of you do repairs on warm glass. In fact I've yet to meet a technician that preferred doing repairs on 40 degree glass than on 70 degree glass. 70 degrees is on the low end of my personal preference, but how warm the glass should be is somewhat dependent on the equipment and resins used and largely a preference based on experience. We have a recommended temperature range that we suggest to Delta Kits users based on well over 25 years of testing, but that does not mean an experienced windshield repair technician cannot successfully complete repairs below or above that temperature range.

With that in mind I hope we can agree that the debate is really about the optimal temperature and how to control it. Whenever possible I believe it is best to slowly warm or cool the entire windshield from both sides until the desired temperature is achieved. It's also extremely important that your resin temperature is close to the temperature of the glass. Again, this is not so much for controlling the flow, but to minimize the chance of crack-outs.

Practically speaking it is not always possible to warm the entire windshield, but I'm a firm believer that the larger the area the better. I agree with the "no-heat" advocates that too much heat is often worse than no heat at all and heating from the inside produces different results than heating from the outside or both sides. If you get the glass too hot it will expand, temporarily closing the cracks. This can make it difficult to get resin into the cracks and often gives the false impression that a crack has been properly filled. If you do "overheat" the glass, such as when drying out moisture, you must allow it to cool before before curing to be sure the cracks are completely filled. Depending on the ambient temperature cooling can take a significant amount of time so a heat exchanger may be used to speed up the process.

I find that using a hair dryer to blow warm air across the outside of the glass to be an efficient and safe way to regulate the temperature during the repair process but depending on the climate using the defrosters from the inside in conjunction with a hair dryer or hair dryers on both sides of the glass works better yet. There are a number of other ways to warm the glass that are also acceptable in my opinion. My least favorite is to use an open flame from the inside of the glass, however if no other means are available even a cigarette lighter may be used to warm the glass from the inside. In fact, we do use that method in our training classes as we seldom require heat and hair dryers are not practical in large groups; too loud and too many cords for a confined space. I apologize if we have ever given trainees the impression that using a lighter or heating from the inside is our preferred method, as that is simply not the case.

I have a great deal of experience, am quite capable of completing excellent repairs and my failure rate is extremely low. I also have several thousand customers who's experience I draw from and the majority agree that warming the glass is an acceptable practice if done properly. If you live in a climate where adjusting the temperature of the glass is "never" necessary, more power to you, but for most professional windshield repair technicians, warming and cooling the glass are essential skills.

I know we'll never all agree on this but as long as your repairs are good and your failure rate is low I have no beef with those who have varying opinions. It's when your repair quality is unsatisfactory or if you are having problems with crack-outs that you have to start thinking about alternative methods. Until then I recommend following the recommendations supplied by the manufacturer of the equipment you use. Hopefully they are the experts who know how to get the most of of their products.

screenman wrote:Puka, Delta and I have often not quite been eye to eye on all our techniques.

Right here we go to try an simplify things a bit.

First could you answer this very simple question, what happens when glass is warmed up?

When and if you can answer that question I will explain the way that heat can restrict the flow of resin.

Yes, but you use heat to remove the moisture correct? So it's not that you are opposed to heating, but just that prior to curing, the glass has cooled to a point that cracks have not closed due to expansion. That I agree with.

Your last post is correct Brent, thank you.

Now what I would like to see is somebody with a little bit of time, warm a chip up without introducing resin and watch the legs close, take a temperature reading and allow to cool until the legs completely re-open and time this. I have done this often and have recently shown the test to the countries to assessors, much to their astonishment.

14u2ponder wrote:Thanks brent. Far be it for me to come onto a website forum and start trouble. I just couldn't understand what screenman was saying and I never take people's word for things.

I have always sorta believed that buying a medium viscosity resin and heating it to achieve a thinner product was what most repairmen were doing. I was surprised to learn that that wasn't the case. Like you I kept wondering things like, if heat is inherently bad WHY does it affect only the tip of the fingers of a break and not the area closer to the impact point.

It seems to me that the problem might be how can you keep the resin stable at the edge of the break long enough to allow curing without the sheer force of the windshield contracting back onto itself.

I use a low viscosity resin and rarely have a problem getting the resin into the end of even the tightest cracks.

Heat affects the end of the crack first because it is the tightest part of the crack, but if enough heat is used it will sometimes close the entire length of the crack temporarily. What I have a hard time getting my mind wrapped around is that if you spot heat a 50 degree windshield to 100 degrees it's very likely the glass expands and closes the crack, but if the windshield has been in the sun for an hour and is 100 degrees the same crack will often still be open. I've done some research on it and I'm convinced it has something to do with how the glass reacts to heating one side, or maybe having cold glass around it, vs heating all the way through, but I still don't understand it well enough to explain it to others. Water actually contracts as it is heated from a 0 degrees but at some point it begins to expand. Some metals have a similar reaction I'm told, especially when heated from one side, but I've not been able to confirm that happens with glass. All I know is a little heat often has a positive effect while too much heat has a very negative effect, at least in my experience.

screenman wrote:Your last post is correct Brent, thank you.

Now what I would like to see is somebody with a little bit of time, warm a chip up without introducing resin and watch the legs close, take a temperature reading and allow to cool until the legs completely re-open and time this. I have done this often and have recently shown the test to the countries to assessors, much to their astonishment.

In my experience it is not always a fixed amount of time or even a specific temperature. Applying the heat exchanger cools quicker but I've noticed it also opens cracks at a lower temperature, presumably due to the slight thermal shock of faster cooling. Flexing will sometimes do the same thing although I'm pretty cautions about flexing glass if it is too hot or too cold. Even after the glass has cooled to the ambient temperature the cracks still appear closed at times if I don't use the heat exchanger, but I find that when I inject resin at that point they open back up as the resin flows in. Have you experienced that?

Yes. If both sides of the crack expand the crack will become narrower. Glass really doesn't expand much, but even a little will close the tip of a crack. The wider the crack is (closer to the pit) the less you will notice it closing. Think of two marshmallows side by side with a slight gap between them. As they are heated they swell up, thereby closing the crack.

I know it's a poor analogy but it does provide a good visual doesn't it? It's also making me hungry...I'm off to lunch!

Mmmm! Toasted marshmallows, now you are talking

Man! This thread is really heatin' up ! sorry couldn't help myself
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I have a rubberband in the bottom of my kit for practice WS's. Since I purchased the Spring Hammer I dont use it. The spring hammer allows me to deelope my skills at drilling to the proper depth, without scratching the glass up, and then I pop a buseye and make the repair. I must have read into the post. It sounded like he was using the rubber band to create bullseyes for a repair. I dont leave anything for chance. I see techs doing odd things to glass in the field and on youtube. Some things I see actually work, that may be unusual for a seasoned tech.