Does windshield rock chip repair prevent crack propagation?

Got a nasty rock chip in my windshield. Three impact divots connected
by a crack about 1.5" long. Short star pattern at each impact.
It's well out of the normal field of view, but I'm very concerned about
the crack propagating.
Googling informs me that the rock chip repair people are good at filling
in holes, but there's a lot of hemming and hawing about whether they
can keep a crack from propagating.
I hate to blow $60 on a chip repair and have to replace the windshield
next month anyway.

Any chance that a vacuum pump and superglue will help? The kits you buy
at the auto store show examples of fixes other than cracks.
Doesn't have to be pretty, just not crack more.

Direct personal experience?
Thanks, mike
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On Mon, 07 Mar 2005 12:32:46 -0800, mike > wrote:

>Got a nasty rock chip in my windshield. Three impact divots connected
>by a crack about 1.5" long. Short star pattern at each impact.
>It's well out of the normal field of view, but I'm very concerned about
>the crack propagating.
>Googling informs me that the rock chip repair people are good at filling
>in holes, but there's a lot of hemming and hawing about whether they
>can keep a crack from propagating.
>I hate to blow $60 on a chip repair and have to replace the windshield
>next month anyway.
>
>Any chance that a vacuum pump and superglue will help? The kits you buy
>at the auto store show examples of fixes other than cracks.
>Doesn't have to be pretty, just not crack more.
>
>Direct personal experience?
>Thanks, mike
>--

A =small= circular hole drilled at each end of the crack will keep it
from propagating. Holes completely through the glass. Fill in with
any transparent gunk of your choice, so long as it doesn't drip out
while drying/curing.

Lg

The fix keeps water out of the fracture. Water can freeze and
expand in there and spread the damage. The patching can't restore the
strength of the glass, so any more stressing (cold water on a hot
windshield) will make the crack take off.

Dan

On 7 Mar 2005 15:06:20 -0800, wrote:

> The fix keeps water out of the fracture. Water can freeze and
>expand in there and spread the damage. The patching can't restore the
>strength of the glass, so any more stressing (cold water on a hot
>windshield) will make the crack take off.
>
> Dan

You can stop the crack by drilling holes at the exact ends of the
crack. They don't have to be large, just enough to mitigate the
fracture line.

Lg

>You can stop the crack by drilling holes at the exact ends of the
>crack

I've NEVER seen that done to glass. Common practice with
acrylic aircraft windshields, though. The auto windshield is two layers
of glass, and it's the outer one that usually cracks. Trying to
stopdrill it is probably futile.

Dan

On 7 Mar 2005 16:33:43 -0800, wrote:

>>You can stop the crack by drilling holes at the exact ends of the
>>crack
>
> I've NEVER seen that done to glass. Common practice with
>acrylic aircraft windshields, though. The auto windshield is two layers
>of glass, and it's the outer one that usually cracks. Trying to
>stopdrill it is probably futile.
>
> Dan

What does OP have to lose by doing the little experiment? Not much.
If he doesn't act now, you know it is only going to get worse.

Lg

"Lawrence Glickman" > wrote in message
...

> What does OP have to lose by doing the little experiment? Not much.
> If he doesn't act now, you know it is only going to get worse.
>
> Lg

It is a common practice in preventing propagation of cracks in
metals...referred to as removal of stress raisers.

That is why you grind away sharp casting seams when prepping an engine for
high performance operation. You remove the stress raiser before a crack can
form.

It would doubtlessly be effective in glass if it could be applied easily and
consistently.

As far as I know, it isn't done often in automotive glass.

Actually, he can probably make it much worse if he doesn't "do the
drill" right. As I'm sure would happen if I tried that... HA HA.

I'd go ahead and either try the chip kit from the local auto store or
have a glass place give an opinion on what they think. They are the
experts. My local guys have always been very straightforward with me
on cheap ways to fix the glass and avoid giving them any money.

On 7 Mar 2005 17:27:01 -0800, wrote:

>Actually, he can probably make it much worse if he doesn't "do the
>drill" right. As I'm sure would happen if I tried that... HA HA.
>
>I'd go ahead and either try the chip kit from the local auto store or
>have a glass place give an opinion on what they think. They are the
>experts. My local guys have always been very straightforward with me
>on cheap ways to fix the glass and avoid giving them any money.

OK, OP has always had, and has now, the opportunity to take the
vehicle to a glass shop. I suspect he would end up with an entirely
new windshield however.

I have drilled glass and glazed ceramics many many times. The thing
about auto glass is it is pre-stressed so it doesn't break into shards
but rather billions of tiny bits. This can be seen if you park your
car in the sun and wear polarized sunglasses.

A wrong move with the bit, and kablammo, the entire windshield will
disintegrate in a second or less, into a kazillion bits that will take
a week to clean up. So there IS some *risk* involved.

However, I have as I said, drilled glass and glazed ceramics many many
times without fracturing anything, just not AUTOMOBILE glass, a.k.a.
"safety glass." So it would be an experiment with one of 2 possible
outcomes:

a) CATASTROPHIC FAILURE
or
b) success

I can't give "odds" on which it would be ;-) But were it my vehicle,
I would be thinking about it.

Lg

"Lawrence Glickman" > wrote in message
...
> I have drilled glass and glazed ceramics many many times. The thing
> about auto glass is it is pre-stressed so it doesn't break into shards
> but rather billions of tiny bits. This can be seen if you park your
> car in the sun and wear polarized sunglasses.
>
> A wrong move with the bit, and kablammo, the entire windshield will
> disintegrate in a second or less, into a kazillion bits that will take
> a week to clean up. So there IS some *risk* involved.

What you say is true of auto glass other than the windshield. A side window
will break into tiny pieces if it is broken but a windshield is designed to
stay together as much as possible for obvious reasons.
Bob