How to get rid of moisture in legs of star break?

[BrightFastWSR]

Brent, have you ever measured the heated area by a Drystar right away after heating about 20 seconds ? What was the temperature you measured? Thank you.

[BrightFastWSR]

I have gotten a hot air gun(or heat gun which can blow hot air with temperature around 572F) in my hand.

I have tested it can heat the windshield surface temperature over 212F(boiling point of water) in 45 seconds. Should I heat the windshield over 212F to make sure that moiture out of the breaks? Will this temperature be harmful to the middle plastic layer? Since drystar make the moiture inside the break boiling, I think it must be heated over 212F. Thank you.

[Brent Deines]

Brent, have you ever measured the heated area by a Drystar right away after heating about 20 seconds ? What was the temperature you measured? Thank you.

Yes I have measured the heated glass but I can't really give you the answer you are looking for due to the number of variables involved. Here are a few...

1) Temperature of the glass prior to applying the moisture evaporator. We did a test this morning starting with a glass temperature of approximately 76 degrees and after the moisture evaporator was applied for 20 seconds we got an average glass temperature reading of 140 degrees. We did the same test but this time preheated the glass to 125 degrees, then applied the moisture evaporator for 20 seconds. This time we got an average glass temperature reading of 197 degrees. Never did the glass temperature reach 212 degrees, but the water did begin to bubble in 10-12 seconds and was gone in 16-17 seconds. The interesting thing to note here is that heating the glass to 140 degrees with a hair dryer did not remove the water from the break but heating the glass to 140 degrees with a moisture evaporator did! I'm sure there is a good explanation for that but I have to admit I don't know what it is.

2) It is very difficult to get an accurate reading of the glass temperature of glass using an infrared thermometer. An inexpensive infrared thermometer is fine for finding an acceptable temperature range, but readings are not consistent enough for serious glass temperature testing, especially at hotter temperatures. In our testing we used an inexpensive model (under $50) and a mid-range model (under $150). They were close at lower temperatures but over 200 degrees the variance became increasingly significant. Even the better model failed to produce consistent results in repeated tests.

3) I have two technicians do the testing and while their results were similar, they were not identical. I would guess no two people will get the same results with these unsophisticated testing methods.

4) We tested several different moisture evaporators and each one performed slightly differently. We tried to measure the heating elements with the infrared thermometers but the results were extremely inconsistent. We did however get consistent temperature readings far in excess of 212 degrees with both thermometers. Again, I just don't think an infrared thermometer is well suited for this purpose and we do not have another way of testing the actual temperature of the heating elements at this time, but in every test the water began to bubble and then disappeared within the recommended 20 seconds. Perhaps it is the heating element in proximity to the moisture in the break that is the most important factor in the successful removal of moisture.

A heat gun most certainly produces enough heat to get the water in a break to boil, as does a torch. We don't recommend a heat gun because there are even more variables that come into play. There's just no way for us to tell a technician what heat setting to use, how far from the glass to hold it, or how long to leave it on the glass. The same is true for torches, plus using an open flame brings up additional safety issues. That's not to say you cannot use these tools to remove moisture, but just that I believe the moisture evaporator is a safer option.

We did have one very unexpected result in our testing today. We wanted to see how hot we could get the glass with our blow dryer and if we could actually dry out the break with it. In my previous tests it took so long that I finally gave up without ever getting all the water out, but today we used a very powerful blow dryer and placed it directly on the glass over the break to see what would happen. The glass temperature reached 170 degrees and although the water never bubbled, after 8 minutes it did evaporate. So I have to retract my previous comments about it taking all day to remove moisture with a blow dryer. Given the choice of 20 seconds vs 8 minutes to dry out the break I would still opt for the moisture evaporator, but depending on the model used it is obviously possible to dry out a break using a blow dryer (without taking all day). My apologies to those I have told it could not be done. Still learning!!!

One other unexpected result from our testing today was that the glass did not crack during any of our moisture evaporator tests. The combination break that we dried out using the blow dryer also did not crack out, but a nearby star break did crack out before we could get the moisture out using the blow dryer. The glass cooled much faster after using the moisture evaporator than it did after using the blow dryer because the blow dryer heated a far larger area of the glass. Also worth noting, was that the inside of the glass got hotter using the blow dryer than it did with the moisture evaporator. One or both of these factors may have contributed to the star break crack out but that is only an assumption. We would need much more testing to verify.

All temperatures readings were measured in Fahrenheit.

[screenman]

I have found a surface break far more likely to run than a subsurface one, even a very small one. This is one of many reasons I check and inspect every repair before starting work.

[CV Windshield Repair]

Brent did you conduct these test on a windshield that was on the vehicle or on a stand? I understand that a windshield that is glued to the vehicle is under far more stress than a windshield that is sitting on a windshield stand.

[Brent Deines]

Today's tests were performed on a stand. I agree that there can be more stress on a windshield that is installed in a vehicle, especially one that has been previously replaced.

In our real world experience we have had some cracks grow a bit while heating with the moisture evaporator as well as when warming with the hair dryer, but have yet to have a crack out caused from the use of either one. I'm sure it will happen some day but we are very careful about how we warm and cool the windshield prior to performing a repair so I certainly don't expect it to happen very often.

[t4k]

I agree that there can be more stress on a windshield that is installed in a vehicle, especially one that has been previously replaced.

In another thread everyone agreed there was no difference between a replaced windshield's stress or it's ability to crack out over that of the OEM glass. Here you are saying the opposite. Am I missing something here?

[Brent Deines]

In the other thread I agreed that I don't notice any difference in the repairability (I know, not a real word) between and OEM and an aftermarket windshield. I do however know for a fact that many windshields are installed incorrectly which can sometimes put stress on the glass that you don't typically find in a factory installed windshield. In fact, I was recently told that in Europe a news channel ran an expose about a large replacement company purposely putting a small rock between the glass and the pinch weld when they replaced the glass so that the glass would have a greater chance of cracking under normal driving conditions. I cannot verify the validity of this claim but according to my source it was a major news story in at least one country. But I digress.

If the bead of urethane is laid too high, too low, or unevenly, stress points are created. If the edge of the glass is chipped a tiny crack may already be present at the time of installation. If the glass is placed too close to the edge of the car body and a molding is forced between the two it can cause stress or even a crack. Long story short, there are many variables in an the process of installing an aftermarket windshield that can cause the glass to be more likely to crack when a repair is attempted.

However, I stand by my previous posts stating that I don't treat an aftermarket installed windshield any differently than I do a factory installed windshield. I'm careful with all of them! In this thread I was simply trying to acknowledge the fact that there "could" be more stress on an installed windshield than there is in a windshield that has not yet been installed, which could cause it to react differently when we ran out tests on the moisture evaporator. Sorry I didn't explain myself better.

[t4k]

I approach the repair the same too but I do check to see if it is a replacement or the OEM because of the exact reasons you just stated. The replacement glass is not and can not be installed with the same precision that the OEM glass is thus causing a degree of extra stress.

[Glasseye]

The assumption that OEM glass is always installed precisely is incorrect. A few years ago, the company I worked for then, were asked by a major car manufacturer to do remove and refits on a specific vehicle, numbering a 100 plus. On inspection of the windscreens that were removed at my branch, we found that only 90% of the PU bead had adhered to the pinchweld and the bead bed width on the rest of the screen was only about 1/16" in places. Most major car manufacturing systems use robotics for most, if not all, of the direct glass installations, these can have quality control issues, just like any other automated system.