From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Windshield cracks
Date: Mon, 05 Mar 2001 17:08:05 -0500

Dave Krajcar wrote:

> Hi everyone:
>
> I'm wondering if any of you have experience with front windshield cracks.
> My class A Bounder developed a 8 inch crack from the bottom up.  I'm
> wondering if it can be repaired or does the whole windshield need to be
> replaced?  Have any of you had them repaired and do the repairs last?  Seems
> like a real waste to just replace such a large windshield for a small crack.
> Should I be worried that it might get bigger and cause some other problem?
>
> thanks!
>
> -Dave

There are companies that can impregnate the crack with optical epoxy
that will make it disappear for a few years until the epoxy
yellows.  Check your yellow pages.

The more pressing requirement is to stop the crack from spreading.
It WILL spread!  Probably during the first really cold weather.  I
have a brandy new $400 windshield in my 68 Fury compliments of a
stone bruise and a frosty night!

The only way to stop the crack from spreading is to relieve the
stress on the crack by drilling it.  I use a tiny half millimeter
diamond drill in a dremel tool to do the drilling.  Simply find the
end of the crack (hard to do sometimes - look obliquely across it in
strong light) and drill it. Normally the crack will be only in the
outside layer of glass so you only have to drill down to the safety
laminate.  Once the hole is drilled and dried, fill it with either
optical epoxy or clear RTV.  The idea is to keep water out so it
won't freeze and crack again or cause the glass to delaminate.  I
got my diamond drill from an outfit called Truebite in NY.  I think
they have a web site now.  Of course, diamond bits are available
from all sorts of places these days.  The one I use is designed to
drill post holes in glass ear rings.  It must be used wet.  The
diamond dust comes off instantly if allowed to run dry.

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Glass Chip:  Do we have an authority on glass?
Date: Tue, 29 May 2007 23:26:58 -0400
Message-ID: <kvqp5316oa0iojr8jaokbgr34gojkdqd4u@4ax.com>

I'm not a car windshield specialist but I DO have a lot of experience with glass.

The concern is whether there are micro-fissures and/or stress risers in the glass
wound that will allow cracks to form when the weather changes.  It is very hard to
tell by looking, even with a microscope.

The procedure I use is fairly standard for all sorts of glass wounds.  Basically,
grind out the damaged part, polish the work area and optionally, fill the wound with
optical cement of the same refractive index.  That's what the Permatex kit is that
Sandy mentioned, though there are much stronger adhesives available if one has a UV
lamp to cure it with.

The basic drill (heh!) is to grind out the damage with a tiny diamond burr mounted in
an industrial version of a dental drill.  A dremel tool will work but much slower.  I
grind the damage into a smooth hemisphere.  Then starting with carborundum or diamond
dust and working up to cerium oxide on hard felt tips, polish the work area back to
the original finish.  What results is a tiny concave lens.  If that's in your line of
vision then fill it with optical cement.  Otherwise leave it be.

Diamond burrs last almost forever if used wet and mere milliseconds dry.  My drill
sprays a jet of mist but I try to arrange a garden hose to trickle water down across
the work area.  You can do the same with a dremel tool.

If there are cracks developing then the procedure to relieve the stress is to drill
into the end of the crack with a tiny diamond bit, then fill the hole with optical
cement.  The much larger radius of a hole of even a few thousands diameter spreads
out the stress that remains.  I get my 1/8" shank (standard Dremel) micro diamond
glass drills from a jewler's supply.  The smallest I have is 0.015" and I think they
have smaller.

The kit that Sandy mentioned works well IFF there is little residual stress and no
stress risers.  If micro-cracks are present then they'll probably run despite the
adhesive.  The adhesive is actually more effective once cracks have formed because it
can wick into the crack and bond the sides together.

If it's a very minor wound with little penetration then I'd leave it alone.  If not
then I'd grind it out (or have it done) to be sure.

John


On Tue, 29 May 2007 10:08:09 -0400, "Steve Wolf" <news@w8iz.com> wrote:

>I have the tiniest of chips in my motorhome windshield.  There are no
>cracks.  It is simply a tiny chip.  I called around and the local companies
>don't do anything until there is a crack radiating out from the chip.  My
>last motorhome had a chip that eventually resulted in a crack.  It did that
>when it was 70 inside and minus 5 outside.
>
>I am looking for information from someone who actually took action on a tiny
>chip.  What did you do?  Alternatively, I am looking for someone who is
>fluent is the technicalities of automobile glass who can confirm that a tiny
>chip isn't something that calls for action.
>
>I know about kits that are available and am not seeking that type of
>information.  I'm more interested in if we have a good glass guy or girl
>here who has enough hands-on experience to speak authoritatively on the
>subject of large motorhome windows subject to significant temperature
>differentials.
>
>Thanks,
>Steve
>www.wolfswords.com under the motorhome link
>

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Glass Chip:  Do we have an authority on glass?
Date: Wed, 30 May 2007 15:21:46 -0400
Message-ID: <hhjr53dhpin4rihbnl0jvbp03nus0d1a3n@4ax.com>

On Wed, 30 May 2007 04:37:44 GMT, Al Balmer <albalmer@att.net> wrote:

>On Tue, 29 May 2007 23:26:58 -0400, Neon John <no@never.com> wrote:
>
>>The procedure I use is fairly standard for all sorts of glass wounds.  Basically,
>>grind out the damaged part, polish the work area and optionally, fill the wound with
>>optical cement of the same refractive index.  That's what the Permatex kit is that
>>Sandy mentioned, though there are much stronger adhesives available if one has a UV
>>lamp to cure it with.
>
>Heh. Here in Phoenix, we don't need no stinkin' UV lamp. Just back it
>out of the garage for a few minutes.

Actually you do.  Most UV cured optical cements are designed to cure only using the
very short 235nm UV mercury emission.  This is so precisely so that stray sunlight or
fluorescent light won't trigger premature curing.  There are a few varieties designed
to cure under black lights that will cure in sunlight but they're mainly marketed to
the hobby market.

Don't feel bad.  I had the same notion too.  Too bad it didn't work.  A germicidal
lamp does a bang-up job of curing, however.

John