Sub-Surface Cracks?

[sgailey]

Hello everybody!

I had a customer come in today who was asking about an old repair (star fracture) done by another tech. He claimed that there were three legs coming out of the repair and that they were slowly growing larger.

I took a look at the culprits; the biggest one was no longer than a 1/4 in, they were thin and shiny with no dark spots. Near the ends of the cracks, there were splotchy-looking 'daisy petals'. Upon close examination, it was almost as if they were beneath the surface. Just to be sure, I felt above them with a probe, but couldn't feel any fracture on the glass. Applying pressure with the probe yielding no movement or flexing, either.

My friend insisted I try to repair them. So, promising nothing, I drilled a hole about a 1/8 inch downwind of the crack's tip, then tapped it with a probe. The crack refused to budge.

Now I've encountered these before on fresh dings, and they wouldn't appear to fill during the pressure cycles, yet the daisy petals would show up after curing was complete.

Naturally, I want to be able to tell my friend that there is nothing wrong and that these cracks are insignificant--- I'm dying to know more about these beforehand. Perhaps some of you have encountered this type of crack before?

1.) Are these cracks residing in the lamination layer?

2.) Is there danger of losing the windshield to these cracks?

3.) What is the best way to approach a repair that involves sub-surface cracks?

4.) Can I stop these cracks once the parent ding has been repaired?

Any advice you guys could give would be much appreciated.

Thanks!

[toab]

Trying to push resin by somebody elses repair sounds like a tricky proposition to me based on the fact that you said that there is a daisy around the repair meaning that somebody has pushed some resin pretty hard the first time right into the laminate but maybe some of the veterans on here would take a "crack' at it.(no pun intended).Looks like not much money in this one and a possibly badly educated customer thinking all repairs are 100% clarity.

[screenman]

These cracks sound to me like the inner legs on a combination break. These might have held tight onto any moisture content when the original repair was done.The daisy effect will quite likely be either over pressure or the original shape of the outside circumference of the damage, if it had been in a while before repairing.

These legs are unlikely to cuase any problems, but I would suugest to your friend that he calls you should one start to travel outside of the ring.

Most damage to windscreens is subsurface that is the nature of which glass breaks. Note I say most we all no of some surface craks and indeed most long cracks are to the surface.

If you look at the way glass breaks, the entrance hole will almost certainly be smaller than the exit hole. A nice bullseye is a perfect example of this.

It is very unlikey that the PVB will split or break. For any of you that have not handled this material I suggest you get some and try to tear it.

I hope that has answered your questions. By the way would you please tell us where you were trained I atrying to build up a picture of what other schools offer.

[sgailey]

Thanks, Toab and screenman for your quick replies!

I hope that has answered your questions. By the way would you please tell us where you were trained I am trying to build up a picture of what other schools offer.

There's one more question that comes to mind:

When there is a splotchy area around these 'inner cracks', are they considered filled?

Here is an illustration depicting the break as best I remember it:



BTW I was trained in Eugene, OR by Matt Larson. The training was complimentary of DeltaKits.

[screenman]

I would suggest the splochy area is where there was moisture that had not been dried out before the original repair took place. This moisture has since disappeared and normaly leaves a air space that when looked at from certain angles resembles the lights of a prism. When training we always start with wet repairs and we get the tech to do one without drying out, just to show them how they look.

I hope you have a practise screen and are carrying out wet repairs as part of your ongoing self training. This will hlep you enormously to become a good tech.