when you repair long cracks should they be visible?

[specialeffects]

i hear you guys talking bout fixing cracks longer than 12", are these cracks visible after the repair, especially with cracks that have lots of curves, i'v been trying to get this done for a while now and am unsuccessful, the cracks never fill out all d way no matter how much holes i drill in it or how much i flex the glass, any advice? thanx

[puka pau]

Please describe in detail your basic crack repair technique. How do you prepare the crack prior to repair? What method do you use to inject resin into the crack? What is the approximate viscosity of your repair resin? Where and how frequently do you drill? What criteria do you use to determine where and when to drill? Do you use crack expanders/openers? What is the approximate temperature of the glass? What is the approximate age of the crack? Are you certain that the crack is free of contamination prior to repair? Describe what you see after repair that indicates to you that the crack is not properly filled.
There are several techs that post frequently on this board that are qualified to offer advice if you provide sufficient responses to these questions.

Cheers;

Puka Pau

[t4k]

Puka pau can you describe how you would repair a long crack under normal conditions?

[just chippen away]

Puka Pau, the number one question you failed to ask is what make and model is the car.... that will tell us the thickness of the glass they are working on. some glass is more fragile being thicker that others that are more thicker that also take and will take more flexing with the use of a crack jack or more. Thicker windshields need more jacked to flex the crack open that a thinner w/shield.
You also need to be sure the crack is 100% dried out. Resin and water to not mix.

To answer the Q on the table, If you have done your job right, you may see a silhouette of the lines from the crack like looking through bifocals. If you see black pockets, you still have air in the crack and it may not hold. The fresher the crack, the less visible the repair will be... It also depends on the resin you are using to fill the crack...

This is only touching the subject briefly, cracks are a master trade to me. they take time to learn most of the trade, ya learn as you go on them.

[puka pau]

In my experience I've found no significant additional difficulty in repairing truck or bus glass than auto glass and no significant difference between glass in various makes or models of autos. Actually, I've encountered more problems repairing long cracks in aftermarket glass than factory-installed glass primarily (I think) because of the quality of the installation.

I always drill about 1/16" out from the tip of the crack, pop a bullseye, set up a crack expander on the inside about two to three inches from the tip, inject resin at the tip (normally it will travel at least three-to-four inches and many times more than that) and then slide the bridge (and, if neccessary, the crack expander) along the crack to fill the remainder. I lube the area that the suction cups (not vaccuum cups) on both the bridge and the crack expander travel with a synthetic silicone-based lubricant that doesn't dry out like water-based lubricants. Proper lubrication is critical for a successful result. There are two main reasons that I always work from the tip to the edge and in one direction only: Normally, as you get closer to the edge, the crack gets wider and requires less pressure (either from the injector or the crack expander) to fill. It's always easier to reduce pressure than increase pressure when filling cracks. If you have to increase pressure on the crack expander somewhere in the middle of the crack you risk opening part of the filled portion (even if it's tabbed) which introduces air into the repair neccessitating a re-do; the second reason for injecting the resin in one direction is that if you start at the tip and then continue the repair from the edge working back toward the tip you risk trapping air at the bottom of the crack as the two beads of resin meet somewhere in the middle. This anomaly is defined by a razor-thin line of black or silver. It's possible to evacuate this air but it takes more time and effort. I address the damge that caused the crack by filling the crack up to the damage on each side, curing the resin in the crack and then setting up on the damage and filling it. That's the short story. In real life there are many variations on this theme which would just about fill a book. I've used other methods from time to time but after thousands of long crack repairs on a wide variety of vehicles I find this technique by far the most consistently reliable - for me, anyway.

I find it curious that anyone would suggest as a primary technique filling a long crack by drizzling resin over it; we weren't taught to fill stars or bullseyes by dripping resin on the pit - why in the world would we want to fill cracks that way?

Cheers;

Puka Pau

[just chippen away]

"I find it curious that anyone would suggest as a primary technique filling a long crack by drizzling resin over it; we weren't taught to fill stars or bullseyes by dripping resin on the pit - why in the world would we want to fill cracks that way?"

Did I miss something in the reading on this thread? Or is that just out of the blue talking?

I more less do the same in repairing cracks, I may use 3 - 8 crack jacks to eliminate to much flexing as I move my injector that will cause the air pockets.... I still say doing cracks is a master trade, you either have it or you do not.... I like the challenge of cracks.

[puka pau]

On January 3, 2011 Specialeffects (the same tech that launched this thread) started a thread titled "Can't Fix Long Crack". After receiving several responses he answered in part: "...I applied a few drops on the crack every 1/2" or so but that didn't seem to work..." It's possible that he arrived at this technique on his own, or he may have been taught this technique by someone, but it appears that we both agree that with a few exceptions dripping resin on the surface of a crack is an inappropriate technique. However, having said that, I will add that applying resin to the surface of a crack can be a useful approach in some well-defined situations. In the case of an edge crack that is, say, six or so inches long and does not display a normal sized star or bullseye somewhere in its length, an adequate approach would be to drill and fill the tip and apply resin to the top of the remaining length all the way to the edge if the remaining length is adequately surfaced. The inches close to the edge are normally wide enough to accept resin through capillary action and without injector pressure assuming that the resin is of proper viscosity and contains the requisite amount of surfactant to allow it to "wick". If there is a star or bullseye present it's virtually impossible to control this method of resin application from spreading partially into the damage that caused the crack - which ultimately makes the damage more difficult if not impossible to repair. Also, it's extremely difficult to control the flow of resin if applied straight from the bottle - it's easy to use literally ten-to-twenty times the resin necessary and wasting that much resin ultimately costs more money and makes an unprofessional-looking mess. When I use this technique, I use a syringe, find the top of the crack with the needle tip and run the needle along the crack. It takes very little pressure on the needle - oftentimes the resin will almost "draw" itself out of the needle and into the crack - but obviously this takes a bit of practice to get right. On average it should take no more than one drop of resin to fill one inch of crack no matter which method is used.

Cheers;

Puka Pau

[Brent Deines]

Well it's not quite as simple as dribbling resin along a crack, but the method that has been the most successful for me does not involve placing bridges on both ends or sliding bridges, does not result in air being trapped in the center, and rarely requires the use of a crack expander, flexing the glass or drilling a bunch of holes.

I do however agree that whatever method you prefer, it does take practice to get good at long crack repair, and even the best crack repair technicians will sometimes find it impossible to remove all the air from a crack. There are a lot of variables that come into play such as the age of the glass, the age of the crack, the condition of the PVB, etc.

Now back to the original question. If you get all the air out, a properly filled crack can be nearly invisible from some angles, but will almost always show (a faint, clear line) from others. What you should see is the black air disappearing all along the break as the crack fills. Always look the crack over carefully before you start and as it begins to fill find the angle where you can best observe the progress.

I typically try not to flex the crack as it fills because doing so can draw air in from the surface, but if you find it necessary to do so you can minimize the introduction of air from the surface by covering with curing film as the crack fills. There are lots of little tricks to getting the best possible results when repairing cracks and obviously a lot of different methods used by experienced windshield repair technicians. Don't rule any of them out until you have tried them as instructed by someone who has successfully used the technique, and don't experiment on a customer's car. Get a practice windshield and practice, practice, practice.

Be sure the crack is clean and dry before you start or you will not have success.

[clearquest]

Brent, would you mind sharing your tecnique for filling cracks with us, I've used a slider bridge myself but would love to hear another alternative. What do you feel is the best way to fill long cracks? How do you do it?

[Brent Deines]

I have done so many times on this forum and elsewhere, so I would ask that if you want a real discussion on the matter that you give me a call. I will however give you the abbreviated version.

If the crack is over 3" long and radiates from an impact point I first warm or cool the glass as necessary and dry out the crack, then drill the end and pop a bullseye, making sure to blow out any dust or loose glass from the drill hole. I then set up my bridge at the impact point and start injecting resin just as I would with any other repair. There are a number of factors that determine how far the resin will travel from the impact point but in some cases it can travel 6" or more without touching a thing. I then cover the crack nearly up to where the resin stops, but leaving at least 1/8" of the filled crack extending beyond the curing film. Where the resin stops I use an eye dropper to place a tiny drop of resin just "behind" the point at which the resin stopped (not over the unfilled crack). How much resin is dispensed from the dropper is easily controlled by placing the tip of the dropper against the glass as the resin is applied. From the point where the resin is applied at the surface it is wicked into the crack. With every drop the crack will fill from .25in to 1" or more. As the crack fills I cover it with curing film a few inches at a time. When the resin reaches the end of the crack it will sometimes fill the mini bullseye that I created without any further interaction. If it does not fill I place a straight pin in the hols and run a little resin down the pin to fill the bullseye and drill hole. If there is any air still remaining I will attach a bridge at this point and inject resin into the mini bullseye, but I prefer not to if I can help it. Cure, scrap, polish, done.

Why don't I slide a bridge? In my experience sliding a bridge applies pressure and partially closes the crack. As that pressure is released the crack opens back up and sucks in surface air. Using this method you can fill a crack from side to side, top to bottom and bottom to top. Most people are surprised when I tell them I prefer to fill a crack from the bottom up rather than the top down as it is easier to control the flow of resin.

Why don't I use an injector on each end? As puka pau said, that often leave a bit of air trapped at the point where the resin meets in the middle. Also, some cracks are prone to run even after being drilled and popped so I'd rather not put any extra pressure on that volatile point.

Why don't I use crack expanders (crack jacks)? Normally they are not necessary to fill the break, but I will use them if I have a particularly stubborn crack. If I do have to use one I put it on and leave it on until I have the crack filled and covered with curing film, removing it just before I'm ready to cure.

Why don't I flex the glass as I'm filling? This often introduces air bubbles into the crack that are very difficult to remove.

Filling from one end to the other without any other manipulation pushes the air out of the crack and provides the best results for me. Some think this is nothing more than "dribbling" resin across the surface of the crack, but in reality I am using the pressure from the injector to displace the air in the crack with resin. If I don't get in a hurry and get ahead of where the resin stops as I apply additional resin to the surface there are no real limitations to the length of crack I can fill. (That does not mean that I recommend repairing a crack that runs from one end of the windshield to the other.)

Over the years I've had many, many technicians tell me that after practicing this method a bit they get better results than with their previous methods, but only you can decide which method works best for you and which method that is may be in part determined by the injector and resin used. I also only use one viscosity of resin where some technicians prefer to use several. People sometimes think their way is the only way, but I have an endless supply of glass to practice on so after 24 years of repairing glass I find I'm still learning all the time. To each his own as long as you get the crack properly filled and it does not crack out after it is cured.