crack repair techniques

[desertstars]

I post this because there seems to be 180's concerning filling cracks. Some techniques I've read I have never tried, myself. Applying pit filler over the crack before starting the repair is one example. I'd be interested in any comments in regard to my technique.

(Problem)

A crack was filled with resin, the crack disappeared, but after curing it looked as if it had returned.

(One solution)

That crack most likely DID disappear before it was cured.

However, repair resin shrinks when it cures. So, during the curing process the contracting resin pulls back from the edges of cracks leaving those edges exposed.

Then, the light refracted from those exposed edges make it seem as though the crack was never filled.

The solution to the problem of cracks re-appearing is to OVERFILL the crack with repair resin.

Consequently, the normal shrinkage of the resin during UV cure will not expose the edges of the crack.

Over-filling a crack in a windshield with crack resin is simple.

Drag the injector on its suction cup along the crack, filling the crack with repair resin as usual and making sure you do NOT get ahead of the filling area. (A light path of lubricant will facilitate injector-slide.) Make sure that you maintain pressure on the resin and make sure that you refill the injector if and when necessary. When refilling, very s l o w l y unscrew the stem (in order to minimize vacuum) and then perform the refill. I use a miniature spout.) Go back to pressure and continue.

To keep resin from spilling from the crack, slide a strip of curing film along the crack BEHIND the injector as you are working.

When the crack is fully injected with resin, place an extra drop of resin every two inches or so under the curing tabs to overfill the crack. I cure cracks under slight pressure.

The curing tabs should lift just clear of the surface of the glass, floating on a small stream of overfilled resin. Do not press the curing tabs flat against the windshield.

That liquid resin stream is then UV cured solid as usual. (I cure cracks under slight pressure by leaving the equipment attached to the end of the crack.)

A good crack repair will have a ridge of cured resin along the length of the crack.

This ridge of cured resin along the crack is then scraped off by a vertically-held razor blade.

(The razor blade is held vertically to avoid the possibility of the edge of the blade snagging and popping out any repair resin that isn't completely cured.)

There is also an alternate technique for curing behind you as you proceed along the crack but my fingers are tired and I need to prepare my lawsuit against Jeff for carpel tunnel syndrome.

And, there's another three bucks down the drain.

[sydfloyd44]

Just a couple quick notes.

I am assuming you are curing the point under pressure. I have seen people cure the crack itself while still under pressure from the bridge and/or the spreader. I have found that this actually causes a distortion due to the glass being "offset" from pressure.



For several reasons, I haven't personally done a crack repair in well over a year. (5"+)



This company has requested no mention of their name or products in this forum

[desertstars]

Interesting observation and good input, sydfloyd.

"Curing the crack under pressure" is qualified. I cure under pressure but under MINIMUM pressure to just before pulling a vacuum and cetainly not enough to distort either the windshield or the laminate.

Allowing a vacuum or too much pressure defeats the purpose.

That same hump-back resin stream applies to when I decide to cure the filled crack behind me while I work on the unfilled crack in front.

I either back-cure or not depending on the angle of the UV rays and how much I think the repair process can be shielded.

Believe it or not, I even shield my repairs when working in someone's garage because I'm cautious of reflected UV.

(I live in Arizona.)

I didn't go into back-curing because it is dangerous to fill a crack if it isn't shielded properly and allows frontal cure because of reflected UV rays.

That eventuality would require another drill point in the crack.

My main point was that I prefer to leave the crack open in order for the resin flow to force out and/or absorb the air along the crack while I work along it rather than applying some type of resin to close the crack ahead of me.

I was interested in the physics and mechanical properties of that approach.

And, I agree with you. I turn down crack repair nowdays if they aren't dead straight and less than a few inches in spite of the fact that, in the past, I've successfully worked on two and three foot or more cracks many times.

It ain't worth the time; it ain't worth the effort.

I leave those jobs to the snipped suppliers referred to in your post.

In fact, I will give them a lead in that regard.

If I personally cannot save a windshield or prevent a replacement, I'm only happy to turn it over to someone who says they can and believes they will.

[Coitster]

I have to agree with DesertStar about 2 to 3 foot cracks taking a long time. In the time it takes me to fix one, I could of sold 2 or 3 chip repairs and made more money. Also the older the crack is, the more chance of dirt being in the crack, and you can't get that out. It also hampers the strenght of the repair.

I personaly limit my crack repair to about 1 foot and it must be very recent. No older then a month or so.
David
Coitster

[DaveC]

I must be lazy

I have a set price for simple cracks up to 5 inches. And then rely on my Miami upbringing (where you buy Cuban sandwiches by the inch) and charge an additional amount for each inch thereafter. I won't insurance bill on long cracks, so cash is King!!!!

[Nemat]

So is there anyway to get the resin out once it has hardened? I say this because, as some of you have mentioned, everything looked fine and the crack was less apparent until it cured and now the crack seems to have reappeared but the windshield is flush and smooth over the crack. I'd like to take the resin out and redo it and make sure the resin seeps deeper into the crack.

[Nomad]

I know of no way to get the resin out of the crack after it has cured.

Depending on the equipment you use, grease a path for the injector to slide. Drill a stop hole and tap, use slide hammer to tap on surface to break crack into hole if it doesn't go by itself. Drill another hole maybe an inch away from the end. Tap that hole to produce a half moon. Put injector on end hole and fill to the second hole if it will go that far, then go to second hole and inject there. It will usually go quite a way down the crack.

The injector puts down pressure on the glass, so attach a suction or vacuum cup opposite the injector and pull up with enough force to open the crack. You will be able to see air being pulled into the part that has already been filled. Maintain pressure on cup while filling. Slide injector along crack all the way, Might have to move cup along the crack if it is a long one. When done injecting move injector off crack and slowly release upward force on suction cup. Most times I will gently wipe resin from the crack line and look for gaps in resin. Use same technique to chase bubbles and gaps from cracks then leave it to cure. The crack will close a little when you release the up pressure on the cup. This will leave a bead of resin on the surface of the crack so if there is some shrinkage it will fill it. On a really long crack sometimes I only fill half of it and cure, then move to the other half, as manipulation of the injector and the cup will likely cause bubbles in the part already filled.

Running a bead of resin down the crack and covering with curing tape will likely improve things quite a bit. After you release the up pressure on the cup do not touch the glass as any pressure will open or close the crack drawing in air.

I can do quite long cracks as quickly as I can fill a bad chip. And get more money. Motorhomes have thicker glass and will not flex as easily or maybe at all. Sometimes they fill nicely, sometimes I have had to drill a series of holes to fill them. It helps to have a helper on motorhomes to push on the inside to flex the crack open. You should remember you are working on a 2 to 3,000 dollar windshield on one piece MH windshields, so a little extra time and effort will be much appreciated by the owner. Charge more for this as it is more difficult to do.