We have found that repairing cracks with chip repair resin (low viscosity)—a shortcut many shops use—will almost always fail.
We have tested several different repair systems and Crackmaster is the first one we found that could properly restore a cracked windshield. Cracks almost always start from the edge of the windshield and they vary in openness or tightness as they move away from the edge. At the edge they are open and you can usually feel them with your fingernail but as you move toward the end of the crack it becomes very tight and hard to feel. We also know that when a crack repair fails it usually reopens at the (open) edge.
We us several different resins that vary in viscosity (thickness). The high viscosity (thick) resin—the strongest resin—fills the edge where the most strength is needed and as we move toward the end of the crack where it is tight we step down in viscosity (thinner) so that the tighter crack will still fill.