How to Fix Hairline Cracks in Car Windows

Reviewed by Jason Shackelford

Last Updated: January 9, 2025

Like windshields, car windows are highly susceptible to nicks, scratches, and hairline cracks. It can be tedious to repair a car window yourself, but it’s easy enough with the right gear and a few hours. Read on to learn everything you’ll need to do to get your windshield back into tiptop shape.

1

Check your windows.

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There may be additional cracks that require your attention.

2

Buy a bridge kit.

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Bridge kits have suction cups at each end of the bridge that latch onto the window and are the best option for hairline cracks on vertical car windows. These kits are available at various auto supply, hardware, or retail stores.^{[1]
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3

Clean the crack.

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A metal probe works best for the cleaning process.

4

Add end cracks.

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Gently tap the metal probe so that the inner plastic layer of the glass is not damaged. This prevents further widening or spreading of the crack.^{[2]
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5

Put resin in the injector.

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Load the specified amount of resin into the injector as instructed on the bridge-kit packaging.

6

Put the apparatus over the crack.

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Secure the suction cups in place. Add resin into the crack using the injector or use the pressure and vacuum controls of the injector to suck air out of the crack while forcing the resin in. When the crack has been filled with resin, remove the bridge from the window.^{[3]
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7

Wait for the resin to harden.

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Windshield repair kit resin does not air-dry; it requires UV light from the sun or an artificial UV lamp to adequately dry.^{[4]
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8

Apply resurfacing resin.

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Use a cellophane patch, and cover the area that you just applied resurfacing resin to. Expose to direct sunlight or UV lamp, and allow the area to dry. After it is dry, remove the cellophane patch and gently scrape off the excess resurfacing resin with a razor blade to make it level with the surrounding glass to complete the car window hairline crack repair.^{[5]
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9

Clean the window.

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Once the resin is dry, cleanup should be a breeze.^{[6]
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Community Q&A

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Question

How do I fix an improper repair on a windshield crack?

Community Answer

If bigger than a quarter in diameter you're supposed to take it to a shop for replacement. I've tried the crack repair stuff before on longer cracks, and used some at each end to hopefully stop the spreading. It didn't last too long for me.

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Question

My car windshield got a crack on my way to work by a truck loaded with sand and stones; the stone fell on my window and it cracked. How can I remove it (an easier and cheaper way)?

Community Answer

If it's bigger than a quarter, you have to get it replaced, because the "filler" stuff doesn't usually work, and it usually spreads too. If smaller in diameter than a quarter, there are some kits at auto parts stores, Amazon, even Walmart had one a while back. It takes a try or two to get it right if you've never done these before, but you can do it.

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Tips

Even though the repair kit is meant for windshields, it will work just as well on car windows as the glass is the same.

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Do the hairline crack repair as soon as you see it. The sooner you repair it, the better the results of the repair will be.

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Do the repair on a sunny day if you plan to do it outside. This allows the resin to dry faster and better.

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Warnings

Professional resin injection methods usually provide better results than a do-it-yourself kit.

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If the crack on your window is longer than 3 inches (7.6 cm) then a windshield repair kit will likely not work for you. In this case, it is best to contact a professional.^{[7]
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