Test 1 — size
Put a quarter over the damage. If the chip disappears underneath it, it is almost certainly repairable. For a crack rather than a chip, the working limit is about six inches — roughly the length of a dollar bill.
Beyond those sizes, resin can still fill the break, but it cannot restore enough strength across that much glass, and the repair tends to fail.
Test 2 — location
Sit in the driver’s seat and look straight ahead. Anything inside that primary viewing area — roughly the area swept by the driver’s wiper, at eye level — should be replaced, not repaired. A repair leaves a small distortion, and a distortion directly in the driver’s sightline is both a safety problem and a possible ticket.
The other disqualifying location is the edge. If the damage touches or nearly touches the black frit border, replace it. The edge is where the windshield carries structural load, and a repair there is holding together the one part of the glass that must not fail.
Test 3 — depth
A windshield is two layers of glass with a plastic interlayer between them. If the damage has only broken the outer layer, it repairs. If you can catch a fingernail on damage on the inside of the glass, both layers are broken and it has to be replaced.
Test 4 — age
A fresh chip is a clean void. A chip that has been open for a month is full of dust, road film and water, and resin will not bond into contamination — you get a cloudy, weak repair that looks worse than the chip did.
This is the test people fail. The other three are about the damage; this one is entirely about how long you waited. Put a piece of clear tape over any chip the day you notice it, and call within the week.
The Sacramento factor
Valley summers are unusually hard on damaged glass. A car sitting in 100°F sun all afternoon has a windshield well above air temperature; blast the air conditioning at it on full when you get in, and the sudden contraction across a weakened area is exactly the load that turns a repairable star into a crack running the width of the glass.
If you have a chip and it is August, park in shade where you can, and cool the cabin with the windows down for the first minute rather than aiming cold air straight at the windshield.
Need this done rather than explained? There is no shop to drive to. We come to wherever your car already is — your driveway, your workplace car park, an apartment lot, or the side of the road it stopped on — anywhere in greater Sacramento, with no call-out fee and no mileage charge. Give us the year, make and model and you will have a firm price before the call ends.