Windshield Repair Forum

Last week, I had a problem with a repair. The damage was a 5 leg "Star" on a VW Golf, approximately 4" from the " A " post edge on the drivers side. Everything seemed fine, all the legs were flexing, glass temperature was good, but as soon as I applied my repair equipment, a crack shot straight to the edge of the screen!. I was able to repair the damage successfully, but what puzzled me was the speed at which the crack happened. When I got home I did some research on windscreen manufacture, focussing on stress problems. During the process the edge of a laminated screen must be cooled quicker than the rest of the screen to give it "Edge Compression", this essentially seals the stresses within the glass, preventing premature cracking during manufacture and fitting, something that is known within the business as "Stress Cracking". If the cooling process is faulty it leaves intermittent stress gaps at the edge of the glass which will allow any tensile stress to cause a break very easily. I think this was the cause of the rapid break out. Unfortunately there are no visible indicators, prior to repairing, of this weakness in the glass. The only advice I can give is to be wary of this happening with a Star break, close to an edge where there has been a high degree of curvature( bending) done to the glass during manufacture. This will usually be along the "A" post edges.

Many thanks for a very imformative post,