Jetta

[mobilesmartrepairsys]

I had a similar scenario on a Honda Jazz during the (summer) last year, I was presented with a starbreak, having started the pressure cycle I had a crack out, I drilled the glass, created the bullseye to catch the crack and it cracked out. At this point I STOPPED to think what was/could be causing this, as I was working outside the screen was in direct sunlight and the glass was reasonably hot to the touch, inside the car was very humid.
As I had never experianced this before I thought it must be temperature related, as I was unable to get the car out of the sun I started the engine, cranked up the air-con and directed the air at the windscreen. I left the air-can on for a good 10 minutes until the inside of the car had cooled down, there was a noticable change in the outside temperature of the glass so I started the repair again, drilled the glass, created the bullseye, injected the resin - jobs-a-good-en!

It is fair to say that when the glass is hot it expands, when you intentionally apply pressure to a weak point in a hot windscreen there is a good chance the damage will become even more unstable and worsten when pressure is applied.

My answer is, get the vehicle out of the sun or crank up the air-con to cool the glass down before attempting the repair. Secondly the same applies if the glass is really cold, but I have found the damage is harder to fill which I believe is down to shrinkage in the glass due to low temperature, if this is the case put the heater on in the car to raise the temperature of the screen (caution, severe changes in temperature of the screen can result in further damage)

[screenman]

Shrinkage in the glass will actually make the damage open up more, heat will expand the glass making the damage shut more. The cooler temperatures will make your resin very slightly thicker. Last but not least in the winter there is far more moisture about, also people are far less likely to reach for a UV shield, 2 reasons why breaks can be harder to fill n winter.