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Alternative Methods for Filling a Break in the Windshield

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Sometimes a stone-break will not easily fill with just the tools vacuum and pressure. This is mainly because of two forces. (1) The glasses own cohesive strength and (2) the 3,000 psi PVB bond to the glass. The 3,000 psi PVB bond is the main reason that many stone-break do not crack-out for years. You can also have some comfort in knowing that your resin has a 3,000 psi head start by this pvb bond as long as your resin gets the tips of the cracks (legs) and the perimeter of the bullseye. The most basic function of the resin is to prevent a crack-out caused by thermal forces. Glass also breaks on the opposite side of impact which is why stone-breaks are sub-surfaced i.e. on the back side of the outerlite and above/against the PVB and for this reason you flex from the outside surface downward.

Almost all of these alternative methods are available to those with a piston-cylinder system.

Watch a video we created showcasing these methods,
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100-0029.jpgFlexing by the Holding Structure –remember the two forces that are holding the break together are the two forces your tool needs to overcome in order to get the resin to the tips and perimeter of the break. This is where a piston-cylinder that is just larger than the impact point does well as it pushes down on the (un-surfaced) break and flexes the break open. Having control of this pressure is a must so you can increase the flex on the glass when the break is not filing. This type of tool will also allow you to use a higher viscosity resin which in and of itself has more durability due to increase oligomer. Attempting to automate chip repair by a machine and eliminate the technician ends up with disastrous results. Not having control of this pressure can cause a crack–out on a hot windshield by your tool having uncontrollable pressure.

Increasing Pressure on the Resin – pressure on the resin actually comes from the holding structure and more precisely the opposing force on the suction cup(s). Increasing the flex by raising the structure by turning the injector and or leveling bolt(s) increases both the flex on the glass and the pressure on the resin. A threaded piston also fine-tunes this pressure.

flexing-thumb.jpgFlexing with a probe - this method of pushing down on a leg with a pointed metal tool flexes open the sub-surfaced leg. A tool must not cover the legs or when there is a stubborn leg you will end up needing to drill and in essence end up doing two repairs instead of just flexing a leg. Knowingly leaving a leg unfilled is an incomplete repair.

Flexing with a Star Flexor – a Star Flexor tool takes the place of manual flexing a leg with your hand and a probe. This flexes the leg for you and holds it for as long as is needed while you do something else.

Manual Pressure Pushing - Cold glass ONLY – When glass is cold the atoms are closer together which makes the glass more dense and the PVB is hard instead of soft. This allows you to use more force without the fear of a crack-out or flowering of the PVB. Place your hand or thumb on top of the injector, carefully and slowly push down and hold it. You will see the break and legs flex open and the resin start to flow.

Heat the Injector- Heating the injector will in turn heat the resin and drop its viscosity which will increase flow.

Drilling – Last but certainly not least is the good ole trusty drill. When all else fails then you drill. Not drilling or leaving a leg unfilled is an incomplete repair and, in my opinion, fraud.

You may have noticed that I did not mention putting a flame on the glass. That is because heat expands the glass which will close the leg. This also softens the PVB which can then cause flowering. So you are closing the leg, not opening it like flexing does. You are hoping that when the glass cools and the leg opens it is going to suck the resin up the leg (wishful thinking). That is about as efficient as trying to fill a break with only vacuum. It will cause under-filling of the break and legs. The rule of thumb with an adhesive application is to overfill.

These alternative methods are available to any piston-cylinder system. Any tool that covers the entire circumference of the break and beyond only allows for one alternative method to fill. The only alternative method for these systems is to Drill.

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   Before/After Photos
   Incorrect Resin Photos
   Correct Resin Photos
   Fundamentals of Windshield Repair Adhesives
   Repairable Windshield Damage
   Windshields are Made to Crack
   Windshields Repair Standard (ROLAGS)

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