Tiny Chip to 3" Crack...Grrr

[blemon56]

Attempted to fix a tiny windshield chip today in Orlando area. The chip filled right away... one vacuum cycle and back... went to get my pit resin and came back to a three inch crack with the repaired chip in the middle. Moderate temperature, light misty rain, no sunshine, and I wasn't in a hurry! This happened to me once before on a complicated combination chip. What causes these fluke cracks? Do others see this from time to time? Am I just venting? Grrr

[Auto Glass Rescue]

Do you inspect the damage and flex the glass before you started the repair? The crack might have been there the whole time and was not visible when you started the repair...

[GlassStarz]

I find head pressure is often the cause.

[blemon56]

Definitely no visible crack before I started. Inspected it from both inside and out. The chip was barely visible with 2 star legs all within about an eighth inch.

Head pressure? I turn the injector nozzle about 3/4 turn after it makes contact, then the bridge adjusters About one full turn each, but in 1/4 turn increments. A small resin drip seeped out of the injector seal during the process.

I sometimes put a little pressure on the plunger if the chip won't fill, but this one filled right away. I was really surprised to see the crack.

[GlassStarz]

Often the glass temp is at fault as well. Real hot or cold glass is more fragile you get a feel after awhile as to which ones to take extra care with.

[Auto Glass Rescue]

Definitely no visible crack before I started. Inspected it from both inside and out. The chip was barely visible with 2 star legs all within about an eighth inch.

Head pressure? I turn the injector nozzle about 3/4 turn after it makes contact, then the bridge adjusters About one full turn each, but in 1/4 turn increments. A small resin drip seeped out of the injector seal during the process.

I sometimes put a little pressure on the plunger if the chip won't fill, but this one filled right away. I was really surprised to see the crack.

But did you probe/flex the damaged area? Some cracks will not show until they are flexed.

[blemon56]

I probed and flexed, but not to any great extent. This was a very small chip. I could only see the two star legs from inside the car. I initially thought the chip wasn't even connected to the legs, and I would need to drill, but the legs filled as soon as I released the injector plunger. I even removed the mirror to assure it filled. The two cracks, though they look like one long one, appeared while I walked over to my box to prepare for the next step.

Maybe I should have probed a bit more. Do you normally flex a chip from all angles before you start the repair? I will probe and flex when a star or combination chip has longer legs.

[GlassStarz]

It rally dos sound like head pressure got to you. Just tight enough to ensure a seal no more is what you are looking form. Often it will leak a little and rather than back up and start again its easier to just tighten it down doing it this way you are giving more pressure from the head esentialy overflexing and prone to a run. Lose seal back it of and start again is the rule.

[Glasseye]

Another possibility is stressed glass. During the manufacture of the windshield, the glass may have cooled too quickly at the end of the process. This might cause stress inside the glass which could affect the repair. Less of a problem nowadays with improvements in manufacture but I have experienced this problem before. Impossible to detect, I always watch carefully at the start of the process for crack creep.

[blemon56]

Talked with Korey today at the Florida Mobile Tech Expo... Sometimes Chips just run! I'm moving on. Thanks to all who responded. The lesson here is that even the tiny chips can be huge!