Windshield Repair Forum

In my short two plus decades in WSR I've used four techniques for repairing cracks up to 36 or so inches (although I've repaired cracks up to 63 inches long):

1. Injecting the resin under pressure with a bridge and injector, watching the resin travel as far as the pressure would allow (roughly four inches), drilling again, injecting again, etc, etc. Obviously not a recommended practice. I quit using that technique about 1988 or 89.
2. Drilling the tip, injecting resin, observing how far the resin traveled and then continuing on by running the dropper tip of the resin bottle along the crack. This is a very messy technique and wastes an enormous amount of resin (not that your resin supplier would complain). I learned to somewhat compensate for the wasted resin by catching the drips with a razor blade and feeding the resin to the crack by moving the blade. Overall, this technique demonstrates inconsistent results. In order for it to work you need a crack that's sufficiently surfaced along it's entire length so that the resin can wick into the damage by capillary action. Curves and "zig-zaggy" areas generally are too tight for capillary action to work although sometimes you get lucky.
3. Using a syringe rather than a droppper-tip bottle. With practice, you can use a lot less resin but as in example #2, you rely on the physical qualities of the crack to get it to properly fill. You could be proactive and set up a crack expander tool at potential trouble points, but there is no reliable way to tell if or where a crack will "tighten up".
4. Moving the bridge and injector along the crack from drilled tip to impact point or edge of glass and injecting resin under pressure. This is the most reliable technique that I've used and is the one I use almost exclusively. When I was working a lot more there were years when I was repairing well over three hundred cracks over six inches long. There are a lot of tips and tricks relative to using this technique that make it consistently successful and profitable. I spent two or three years of of trial and error and experimentation and a few hundred substandard long crack repairs before I was satisfied with the reliablility of the process. If anyone is really serious about repairing long cracks (more than 7 inches) I recommend this technique without reservation. However, you need a bridge that you can move smoothly, an acceptable lubricant for the cups and the correct lubrication technique (hint: it's not KY jelly, water, hand lotion or vaseline), an injector seal that allows you to achieve the needed pressure and for ease of execution a traditional screw-type injector, although some of the more recent injector designs might work as well with sufficient practice. The further you initially mount the suction cups from the tip of the crack, the less chance there is for the crack to spread. Mount the cups closer to the impact point or the edge of the glass and slide the bridge toward the drill hole at the tip before beginning the repair. Also, when mounting the bridge over the drilled tip prior to injection, do not line up the injector, cup (suction or vacuum) and the leveling bolt(s) on the same axis as the direction of travel, ie: in line with the crack. Mount the structure along the side of the crack. This lessens the potential for the crack to spread. And finally, whatever technique you choose ALWAYS start at the tip of the crack and work toward the impact point or the edge of the glass. Working from the impact point or glass edge toward the tip is less reliable, more frustrating, will normally require more "fix-up" steps (which costs you money and time), and does not inspire confidence.

Well I completely disagree with doctor ding on this one, but I have stated my opinion on this subject over and over on this forum. All you have to do is search if you want to know the technique I use and why I recommend it. I have tried all the techniques mentioned, using dozens of different types of equipment, but I get the best and most reliable results filling from the impact point out to the end, and by not sliding the injector.

I do agree with Doctor Ding that there are some simple tips and/or tricks that will help you regardless of the method used, and that practice is very important if you want to get the best possible results. I will also add that although some technicians claim that every long crack repair comes out perfect, I'm afraid I have my doubts about that.

There are many variables in long crack repair that can effect the outcome, one of the most common being the age of a crack and the age of the glass. If the glass is old and the crack has been left unrepaired for an extended period of time the PVB may begin to deteriorate due to excessive exposure to air and moisture.

As always, if you are using a Delta Kits system and are having problems with repairs, or have just started in the windshield repair business using a Delta Kits windshield repair system I highly recommend that you try our methods and talk to us before you try alternative methods, but if you are using a competitor's tool, by all means try their method before trying anything else. If you are having success with the method you use, stick with it regardless of the system you use.

Well, I guess Brent and I will just have to agree to disagree about technique because we could beat around this bush forever, but I will agree that not every repair comes out "perfect" and that the age of the glass and the age of the crack is an important criteria for performing a repair that will endure the test of time. As virtually all of my long crack repairs are performed for my fleet accounts, I rarely encounter a crack that is more than two weeks or so old. As a result, virtually all of the cracks I encounter are reasonably free of contamination and consequently the resin-to-glass bond is usually not adversely affected - which, of course materially affects the success rate in a positive context. Years ago I sweet talked a few car dealers into letting me repair cracks on used inventory with enough negative results that we agreed not to continue the exercise. Most of those cracks were obviously old and contaminated to the point that a significant portion of the length appeared gray or even black after resin injection. Because it's often difficult-to-impossible to identify contamination by normal visual inspection I would suggest that if you are not reasonably certain that the crack is less than two weeks old you drip a little resin into the crack about three or so inches in from the edge of the glass or if it's a floater type drip a little near the impact point and look for gray or black - the resin will remove the refraction and make any contamination more visible. If the crack looks gray or black after this experiment, pass on the job. Extremely old cracks will exhibit laminate-to-glass separation in the immediate area of the crack and extend along at least a portion of the cracks length. Those should be avoided as well.