Tech Tip – Terminating Long Cracks

Recently, there has been some debate on the forum about how to terminate long cracks and if they are worth the attempt to repair. Delta Kits follows ROLAGS (Repair of Laminated Auto Glass Standards) in all areas of windshield repair repairing damage, which recommends that any piece of glass with damage longer than six inches (the size of a dollar bill) should be replaced and not repaired. ROLAGS is a set of standards and guidelines, not a set of laws or rules that require obedience. With that said, cracks over six inches can be repaired, but most insurance companies only cover cracks up to six inches.

What are the benefits to doing long crack repair? Many technicians are afraid of attempting to fix long cracks; therefore, there is a market for doing these types of repairs. However, there are a couple of things to be aware of when fixing long cracks. The crack will never completely disappear though many times the customer expects it to. It cannot be stressed enough that expectations need to be established with the customer before the repair is started. Fixing cracks takes more resin and more time, which means that most technicians need to charge more for long crack repair. Check with your customer’s insurance company to make sure they will cover the cost. If they do not, then your customer will need to pay out of pocket. Be sure to thoroughly explain your payment policy and cosmetic expectations prior to performing any long crack repair.

When terminating a long crack, first make sure the windshield is between 70-100 degrees; this step is very important because long cracks are volatile and unpredictable. Check for moisture and clean out the pit using your scribe. The end of the crack is not always where it appears to be, so it is very important to find where the crack actually ends. Do this is by using your scribe to gently flex the glass while watching carefully for any movement that will help you locate the very end. Often you will find that the crack is longer than it appears when you are not flexing the glass; take a marker and make a mark about one thirty-second of an inch past the ending point of the crack. Next, using a Delta Kits 26020 tapered tip bur, drill a 0.042″ deep hole (approximately 2/3rds through the first layer of glass). If you drill too shallow you will not get a good mini-bullseye and if you drill too deep you will drill into the laminate, so use the depth gauge included with the Delta Kits 22001 Spring Hammer to verify the correct depth before proceeding. If the crack has not already run into the bulls-eye, carefully flex the glass to force the crack into the bulls-eye. This process is meant to anchor the crack and stop it from spreading any further.

After you have completed the first part of the process, mount your bridge on the glass and line up the injector over the impact point. Set up the bridge like you would for any other repair. Once your bridge is properly situated on the glass, proceed to inject resin into the impact point following Delta Kits standard windshield repair procedures.

The resin will fill the crack from one to several inches. Once you see the resin stop flowing, fill a dropper with resin and place a small drop behind the stopping point. This will force the resin to continue moving through the crack. Do not drop resin in front of the stopping point; this will create air pockets. After every couple inches place curing tape over the filled area of the crack. Continue this process until you get to the end of the crack. If you cover your bridge and injector with a Delta Kits 23005 UV Sun Shield, you can cure the crack which you have already laid curing tape on, with the bridge still in pressure cycle. Be sure to leave at least a ¼” of the crack uncured at each end of the crack if there is still air in the impact point or in the mini bulls-eye at the opposite end. Covering the bridge is very important to keep the resin from curing inside and directly under the injector.

After the crack portion of the break is cured, you may then go into your normal vacuum and pressure cycles with the bridge over the impact point. Once all of the air has been successfully replaced with resin, remove the bridge, place curing tape or a curing tab over the impact point and cure for five minutes with a suitable UV lamp. If your mini bulls-eye has not filled completely, mount your bridge over the mini bulls-eye and perform a normal repair with your pressure and vacuum cycles. Cure as you did over the impact point.

Using a new razor blade at a 45 degree angle, remove the tape and scrape the cured resin off the glass, again leaving about ¼” of cured resin at each end of the crack untouched. Scrape the pit and mini bulls-eye at a 90 degree angle and polish according to Delta Kits standard procedures.

Yes, it is a more involved process to fix long cracks, but it can be done and there is a market for it. If fixing long cracks is something that you are considering, get some practice glass and spend some time learning the process before you work on a customer’s vehicle. The crack described above is a general case and there are many different scenarios that you may run into. If you find yourself up against a difficult repair and don’t know what to do, contact Delta Kits for free tech support at (800) 548-8332 or take a look at our very helpful online how-to videos at

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