Moisture causes windshield delamination?

[VetteMed]

I stopped in at a NAPA auto parts store today, to pick up a few odds & ends. A customer starts talking to me about the ZR-1, mentions that he has an '80 C3, etc. He says "looks like your windshield is about done", and then proceeds to tell me to beware of intermittent electrical problems, due to moisture getting into the fuse panel on the passenger side. He claims that the windshield delamination occurs due to moisture.

When I mentioned that some ZR-1s have had delamination since they left the dealer, it seems, he replied that he was a GM Master Tech. I asked if he was also LT5 certified, he seemed a bit insulted and reiterated that he was a GM Master Tech (I guess being a master tech means you've taken every course GM offers)?

He also claims to have built up several LT5s.

Obviously I've got no way to know if he's totally FOS or if there's any validity to his claim about the moisture. Just thought it was a bit interesting and entertaining.

[ZZZZZR1]

Lots of mysteries with windshields but:

The last ZR-1 built has less than 20 miles, outdoors for a few hours and no moisture

That car has some of the worst delamination of any Z

Then again I've seen some every day drivers (with 100k plus), stored outdoors and NO delamination

Go figure!



David

[VetteMed]

David, that's always been my impression as well. This guy was pretty convinced otherwise. (shrug)

-Andrew

[Kevin]

my working theory, based off the fact that the carlisle sticker I had on the window for awhile caused delam and the inspection sticker doesn't, is that the windshield needs sunlight/uv rays to not delam.

[VetteMed]

Kevin, that's interesting... I'm sure there's a glass engineer somewhere who knows for sure, why it happened to these windshields. Interestingly, I've never seen delamination in other vehicles with the solar windshields (some of the GM minivans, fullsize B-body cars, etc).

[LGAFF]

My understanding is that moisture can be a factor, but really the issue is that its a mutlilayer glass and a mutlitude of things can cause its failure. Poor adhesion products, micro air pockets.....all of which could be impacted by moisture or simple contaction/expansion due to heat.....look at some cars stored outside, such as 90 702, bad delam....on the other had there is a 91 up here with a few hundred miles and the windshiled is fogged, its bad construction and failure of the adhesion materials....

[LGAFF]

Laminators are constantly being challenged to reduce or eliminate visual defects in laminated glass structures. Some defects can be directly attributed to glass quality but many are considered to be associated with the laminating process andmore specifically with the commonly used polyvinylbutyral (PVB) interlayer. Defects can look like bubbles or pockets of air with elongated worm-like or dendritic shapes. Elongated worm-like and dendritic defects are often referred to as delamination. Some defects are visible immediately after autoclaving, but others develop hours or days after lamination. Laminators who use vacuum for de-airing tend to experience higher defect rates in warm weather.

Traditionally, delamination is viewed as the result of adhesive bond failure between the glass and the PVB interlayer. That is, the adhesive forces cannot withstand the stresses that are due to mismatches in the glass as well as gaps andpinches. A typical explanation for defects that are near a laminate's edge, is that the PVB absorbs moisture from the environment, which lowers the adhesion level leading to defect formation. Therefore, it is rationalized that during warm and humidseasons, moisture is absorbed at a higher rate, and hence causes more defects.

In the laminating industry there is general agreement that gaps and pinches do lead to defects. In fact gaps of approximately 0.1 mm in height over a distance of 5 cm are suspects for causing defects. The load required to achieve a 0.1 mm gapor pinch can be calculated from mechanical considerations, and it is a surprisingly low, 1.0 N/cm for 2.1-mm thick glass. For this reason, adhesive forces cannot explain the formation of most defects.

If the adhesion level is primarily responsible for defects, then higher adhesion levels should be able to overcome more stress, and hence, would accommodate larger gaps and pinches without causing a defect. However, our findings have shown thisnot to be true.

With respect to moisture absorption, the adhesive interlayer absorbs moisture from the environment until equilibrium is reached. The equilibrium level depends on the relative humidity and may differ for different interlayers. The mechanism formoisture absorption is diffusion, which means that the concentration of the diffusant is highest at the phase boundary (i.e., at the laminate's edge). A typical moisture profile of a PVB laminate exposed to 95% relative humidity at 40.degree. C. forone week shows that only interlayer within 3-4 mm from the edge has moisture higher than 1.5%, and the moisture level hardly changes about 8 mm in from the edge. Most of the observed defects occur about 3-12 mm away from the edge and some extendslightly farther inwards. Very few defects are open to the edge where the moisture level is highest and where one would expect to have the lowest level of adhesion.

It is possible to adjust the adhesivity of the PVB interlayer so that even when laminated at high moisture, the final adhesion is suitable for use in automobile windshields. However, laminates made this way would fail if they are installed intoautomobiles which are driven in or exposed to high ambient temperatures. Bubbles form readily at temperatures less than 100.degree. C. in laminates where the PVB interlayer has been equilibrated prior to lamination to a relative humidity higher than50%. These laminates most likely would not pass the bake test or the boil test required by national and international standards (e.g., ANSI Z26, JIS R-3212, EC R-43, and others).

Another reason moisture intrusion does not explain many of the defects is that even in the absence of high moisture, adhesion at 30.degree. C. is only a fraction of what it is at room temperature. Increasing the adhesion between the glass andthe adhesive interlayer at room temperature, therefore, would not help to eliminate defects which tend to occur at higher temperatures. Further, correlation between data from tests run at temperatures well below room temperature, such as the pummeltest, and delaminations is at least questionable.

We have found that the presence of air plays a most significant role in defect formation in laminated glass. De-airing and edge seal must be as complete as possible in pre-pressed laminates before autoclaving in order to avoid defects. However,optimizing de-airing alone does not appear to solve the delamination problem completely.

The typical approach in attempting to solve delamination problems has been to include various additives in the adhesive sheet to increase the strength of the adhesive bond between the sheet and the glass plate. While such approaches have beensuccessful in changing the adhesive level, and to some extent reducing delaminations, increasing adhesion upsets the delicate balance of properties which make laminated products so desirable in automotive and other fenestration applications. It is wellknown that an adhesion level that is too high can render the laminate monolithic and unable to absorb an impact, or if the adhesion is too low, glass shards fly from the structure on impact. In each instance, changing the adhesion level renders thelaminate unacceptable.

[GOLDCYLON]

Well at least he knew where the fuse panel was. Who really knows

[mike100]

I had detailed my 91 real well recently and it was looking great except for the windshield delam.

For about 3 bills, one could really freshen up the appearance on these cars. I'm honestly considering it. It would also free up my radar detector options.

[VetteMed]

Originally Posted by mike100

I had detailed my 91 real well recently and it was looking great except for the windshield delam.

For about 3 bills, one could really freshen up the appearance on these cars. I'm honestly considering it. It would also free up my radar detector options.

Yep, I'm having that very thing done within the next week or two. My gripe isn't even the delam, it's the pitting and chipping that 21 years and lots of miles brings with it. It's downright dangerous at certain times of day.