Windshield Chip vs Crack: When to Repair or Replace

Chip, star, or crack — what are you actually looking at?

Glass shops sort damage by shape, because shape predicts whether resin will hold. A chip is a contained impact point. A crack is a line traveling through the glass, and lines want to keep traveling.

Your windshield is laminated: two panes of glass with a plastic layer bonded between them. Almost all repairable damage lives in the outer pane only.

• Surface pit — a tiny nick with no legs. Cosmetic, and no repair needed unless it sits right in your view.
• Bullseye — a round, dark cone with a clean circle. The easiest break to fill and the most likely to nearly disappear.
• Star break — a center point with short legs radiating out. Repairable, but those legs run when the glass flexes or heats up fast.
• Half-moon — a bullseye cut off on one side. Usually repairable.
• Combination break — a bullseye with star legs. Repairable if it is small and tight, borderline once the legs pass an inch.
• Floater crack — a line that starts mid-glass and touches no edge. Sometimes repairable if it is short and fresh.
• Edge crack — a line that reaches or starts within about two inches of the glass perimeter. This one means replacement, because the edge carries structural load and those cracks grow.
• Stress crack — a line with no impact point at all, from a flaw, a pinched install, or thermal shock. Not repairable.

The quarter rule and the dollar-bill rule

Two field tests have survived because they actually work. Cover the chip with a quarter — if the quarter hides all of it, including the legs, most shops will repair it. Lay a dollar bill along a crack — if the bill covers the length, you are inside the range most technicians will attempt.

A dollar bill is about 6.1 inches, which is where the common six-inch cutoff comes from. Some shops with long-crack resin equipment go to 12 or even 14 inches. A few conservative ones stop at three. Call two places before you assume you need glass.

Does location matter more than size?

Yes, and this is the part drivers miss. A tiny chip in the wrong spot is a replacement, and a bigger one behind the mirror might not matter at all.

California Vehicle Code 26710 makes it unlawful to drive with a windshield defective enough to impair the driver's vision. That is what turns a crack into a fix-it ticket, and officers look at the wiper-swept area directly in front of the steering wheel.

• Driver's primary sight line — repairs are never invisible, and a faint blemish sits there permanently. Most shops recommend replacement here even for a small chip.
• Within two inches of any edge — replacement, no argument.
• Over the camera window behind the rearview mirror — even a good repair can distort what your driver-assist camera sees.
• Over a rain sensor or an embedded heating element — same distortion problem, plus the sensor may misread.
• Up in the black dotted border at the top — often a non-issue, since it is out of your view and out of the swept area.

How does resin injection repair actually work?

A technician cleans the pit, sometimes opens the impact point with a fine drill to create a path, then mounts a bridge with a vacuum-and-pressure injector over it. The vacuum pulls air out of the break, pressure forces acrylic resin in, a UV lamp cures it, and the surface gets scraped flush and polished. Twenty to forty minutes for a single chip.

Honest expectations: a good repair restores most of the structural integrity and takes the damage from obvious to a faint blemish you have to hunt for at the right angle. It does not vanish. Bullseyes clean up best. Star legs often stay visible as thin gray lines. Anyone promising invisible is overselling.

Glass pricing swings hard by vehicle and shop, so treat these as ballpark and get two quotes.

• Single chip repair: roughly $60 to $150 in the Bay Area, often nothing out of pocket if your insurer covers repairs
• Extra chips on the same visit: usually $20 to $40 each
• Standard replacement, older car with no cameras: roughly $300 to $500
• Replacement with an ADAS camera and recalibration: commonly $800 to $1,500 and up, higher for heated, acoustic, or heads-up-display glass

Why do chips spread so fast in San Francisco?

Because this city runs a temperature and vibration cycle on your glass every single day, and most cars here live on the street where they cannot escape it.

Fog rolls in overnight and your windshield sits at 50 degrees in the Sunset. You get in at 7 a.m., blast the defroster on high, and the inner pane expands while the outer pane stays cold. That differential is what turns a quarter-inch star into a ten-inch crack in about 90 seconds. The reverse works too: a windshield baking in Bernal Heights sun, then a cold hose or a sudden shower.

• Thermal shock — cold glass plus hot defroster, or hot glass plus cold water. The number one crack starter in this city.
• Body flex — the hills, the steep driveway aprons, and the pothole seams on Van Ness and Cesar Chavez twist the body shell, and your windshield is a stressed panel bonded into it.
• Gravel and construction — 101, 280, and the Bay Bridge approaches throw rock, and there is always a repaving zone somewhere.
• No garage — street parking means your car takes the full fog-to-sun swing daily, plus tree sap and branch drops in Noe Valley and around the Presidio.
• Salt air — corrosion at the pinch weld under old glass makes replacements more involved on cars that have lived here a decade.
• Playa dust — Burning Man returns come back with abrasive alkaline dust in every gap, and dry-wiping that glass grinds fresh pits into it.

How do you stop a chip from spreading before the shop visit?

You cannot make it heal, but you can absolutely keep it from running. These are the things I tell customers when I spot a fresh chip during a walkaround.

• Cover it with a small square of clear packing tape on the outside only, to keep dirt and water out of the cone. Not duct tape — the adhesive residue is its own problem.
• Warm the car gradually. Defroster on low, aimed low, then step it up over a few minutes.
• Never pour warm water on a frosty windshield. That is the fastest way to turn a chip into a crack.
• Skip the automated car wash and the pressure washer until it is repaired. High-pressure water and spinning brushes both load the break.
• Close doors gently, or leave a window cracked. Slamming a sealed cabin pressurizes it and flexes the glass.
• Take the hills, the potholes, and the curb drops slowly.
• Get it looked at within a week. A chip is a repair. A crack is a windshield.

What happens to your cameras after a replacement?

If your car has lane-keeping, adaptive cruise, automatic emergency braking, or a full driver-assist suite, a camera is looking through your windshield from behind the mirror. Pull the glass out and that camera's aim shifts by fractions of a degree, which becomes meters of error a hundred feet down the road.

Recalibration is not optional and it is not a checkbox. Static calibration uses printed targets at measured distances on a level floor. Dynamic calibration requires driving at a steady speed on well-marked roads, which is genuinely hard in SF traffic — that is why some shops road-test out on 280 or down the Peninsula. Plenty of cars need both.

• Ask whether the shop calibrates in-house or sublets it, and ask for the calibration report in writing.
• Ask what glass they are installing. You want OEM or true OE-equivalent with the correct camera bracket and clean optics in the camera window. Cheap glass with slight distortion can throw a camera off even after a proper calibration.
• Teslas, Subarus with EyeSight, Hondas with Sensing, and most 2018-and-newer cars all need this. If a shop tells you yours does not, verify it against your owner's manual.
• Drive it and pay attention. Warning lights, lane-keeping that tugs the wrong direction, or cruise control braking for nothing all mean go straight back.

Does insurance pay, and where does detailing fit in?

Glass damage falls under comprehensive coverage, not liability or collision. Many carriers will waive or reduce the deductible for a chip repair specifically, because filling a $100 chip saves them a $1,200 windshield. That is worth one phone call before you pay out of pocket. Replacement usually runs against your full comprehensive deductible, so if that deductible is $1,000 and the glass is $700, you are paying either way. California does not force insurers to cover glass with a zero deductible, so read your policy instead of assuming.

Now the honest part about my end of it. Detailing does not repair glass. No polish, coating, or compound fixes a chip, and any detailer who tells you otherwise is guessing. What I can do is make damage visible and keep your glass from hiding it.

• Decontaminating and clay-barring the outside of the windshield pulls off road film, wiper smear, and bonded grit that hide small pits
• Removing hard-water spots — the mineral rings left when sprinklers and fog dry on glass — so you can actually see the pit underneath
• Cleaning the inside, which in SF is a haze of vinyl off-gassing and hand oils that turns oncoming headlights into a wall of glare
• Applying a hydrophobic glass sealant, so your wipers scrape less and you run them less often
• Telling you what I find. I walk every car before I touch it, and glass damage goes on the list I hand back

Frequently Asked Questions