Some folks are just too independent to have a partner. We like to call all the shots and do not answer to nobody. In fact most self employed business owners are those types, including myself. We will take a silent partner any day though, one that drums up business but says nothing and does not even take a pay check. The silent partner of your auto glass business is the Frit.
As the warmer months approach we all see business pick up as consumers windshields begin cracking. Just what roll does the Frit play in drumming up business for you? It adds heat and thermal stress in an area of the windshield that is already stressed with two other stresses (residual and induced) plus the atoms of the glass are further apart when glass is warm and the warmer the glass is the less dense it is and it takes less energy to fracture. In comes the Frit heating the glass at its weakest spot and causing thermal stress too. The image below shows a small impact point that caused a crack becuase it was in the Frit.
Thermal stress occurs when there is temperature variance in different parts of the glass. If the stress caused by the temperature difference is greater than the strength of the glass, thermal stress glass breakage will result. A glass fracture can be identified as thermal stress breakage if the start of the crack is 90 degrees to both the edge and face of the glass. You will call this one a stress crack as it will have no impact point but surface pits in the Frit area will cause an edge crack also from thermal stress and this will be the pinhead size surface chip that those ethical auto glass shops that tell consumer the truth as to repairable damage see when they repair an edge crack. I say ethic because those that repair per the ROLAGS standard know that over 50% of edge cracks have an impact the size of pin head or even as small as a grain of sand instead of one the common stone-break types of breaks. This is also much easier to repair than when the impact is a star or combination break.
How to Repair -
With the pin-head impact point you can just ignore it and inject the crack. However when the impact is a star or combination break you must separate it and seal it off. Using 2400 CPS repair resin, inject both sides of the break, but do not get too close to the break , you do not want resin to bleed into the bullseye of the break. Then finish the rest of the crack and when you are ready to cure cover and tab the impact and break area with 2400 which should not bleed into the break and then cure it. After curing remove the tab and leave the resin on the glass. You have sealed it of and are now going to repair it like you would a normal break. Sealing it off will allow you to use vacuum and pressure to fill the break. Drill through the resin at the impact point. You can either go to the PVB or try to tap a bullseye, it will not matter because you are more times than not in the Frit area.
Don't forget to check out our videos to see a live windshield repair.