Generally there are 5 things I look at when evaluating whether a chip can or can not be repaired.

Overall Size - If the chip or damage is much larger than the size of a quarter the quality of the repair and the safety of it would be in question.

This Chip Was Over Twice The Repairable Size.

Surface Cracks - If there are too many surface cracks, leakage would be too great, resulting in an incomplete fill with resin.

A Close Up Of The First Picture Shown Above Reveals Excessive Surface Cracks.

Pit Size - If the impact point is extremely large, the repaired chip will look like a bubble in the center when viewed from the inside looking out. Further on large pits the tendency is for the pit filler to fall out over time.

Generally I prefer to work on damage with a pit smaller than the diameter of the eraser on a number 2 pencil.

Age - A chip that hasn't been repaired for several months will pick up contaminates that will render the repair weak, plus when mixed with the injected resin may cause discoloration.

Location - While I'll perform a repair on almost any location on the windshield, if I believe it will create an unsafe distortion in front of the driver I'll recommend replacement.

The above close up of a chip repair that was performed by another company. The result was due to the damage being much larger than recommended. The impact point being too large and when combined with what I believe to be a poor quality resin.

The owner asked if anything could be done to improve the appearance? When I told them that nothing could be done, they chose to replace the windshield.

Finally here's a chart to help show what can be repaired.