How to Fix Cracks in Windows: DIY Guide

This guide shows you how to repair cracks in glass windows, whether it’s a small chip, a hairline crack, or a longer fracture. You’ll learn which cracks you can fix yourself, the exact steps for both temporary and permanent repairs, and when it’s safer to call a professional. Before you start, assess the damage: if the crack is longer than a few inches, spreads across the pane, or is in a double-glazed unit, replacement is often the only safe option. For small chips and cracks, a glass repair kit and a steady hand can restore the window’s integrity and appearance.

What You’ll Need

Glass crack repair kit (includes resin, applicator, and curing film)
Glass cleaner or rubbing alcohol
Clean, lint-free cloths
Scissors
Clear packing tape (for temporary fixes)
Razor blade or utility knife (for cleanup)
UV flashlight or direct sunlight (to cure resin)
Safety glasses and gloves

Step-by-Step

Clean the damaged area. Use glass cleaner or rubbing alcohol and a lint-free cloth to thoroughly clean the crack and the surrounding glass. Remove all dirt, dust, and moisture. Let the area dry completely.
Apply a temporary patch (if needed). If the crack is large or you need to wait before repairing, place a piece of clear packing tape over the crack on both sides of the glass. This prevents dirt and moisture from entering and keeps the crack from spreading.
Prepare the repair kit. Read the instructions that came with your glass repair kit. Typically, you’ll attach the applicator’s adhesive base directly over the crack. Make sure the crack is centered in the opening.
Inject the resin. Follow the kit’s instructions to fill the syringe or applicator with the resin. Attach the syringe to the base and gently inject the resin into the crack. The resin should fill the entire crack; you may need to move the syringe slightly to work the resin in.
Remove air bubbles. Most kits include a plunger or vacuum to pull air out of the crack before injecting resin. If your kit has this, use it. If not, gently tap the glass near the crack to help bubbles rise to the surface.
Apply the curing film. Once the crack is filled with resin, apply the small curing film (provided in the kit) over the top of the crack and the applicator base. This film helps the resin cure properly.
Cure the resin. Expose the repair to direct sunlight or a UV flashlight for the time specified in your kit (usually 5-10 minutes). The resin will harden and become clear.
Remove the film and applicator. After curing, peel off the curing film. Use a razor blade or utility knife to carefully scrape off any excess resin from the surface of the glass.
Clean and polish. Wipe the area with glass cleaner to remove any residue. The crack should now be filled and much less visible.

Common Mistakes

Attempting to repair a crack that’s too large. Cracks longer than 3-4 inches, or those that reach the edge of the pane, are not safe to repair. The structural integrity is compromised, and the crack will likely spread.
Repairing in cold or damp conditions. Resin doesn’t cure well in cold or humid weather. Always repair in a dry, warm environment.
Skipping the cleaning step. Dirt and moisture inside the crack will prevent the resin from bonding properly, leaving a visible line and weakening the repair.
Not removing air bubbles. Air bubbles in the resin will create a cloudy spot and reduce the strength of the repair. Take your time to work them out.
Using too much resin. Excess resin can overflow and create a mess. Apply it slowly and use only as much as needed to fill the crack.

Tips

For a temporary fix that lasts a few days, cover the crack with clear tape on both sides. This prevents dirt and moisture from entering and keeps the crack from spreading.
If the crack is in a double-glazed (insulated) window, a repair kit will not fix the seal. Moisture between the panes indicates a broken seal, and the unit must be replaced.
Always wear safety glasses and gloves when handling glass and resin.
If the crack is in a car windshield, use a windshield-specific repair kit. The process is similar, but the resin is specially formulated for automotive glass.
Repair as soon as possible. The longer you wait, the more dirt and moisture that gets in, and the more likely the crack will spread.

Troubleshooting

The resin won’t fill the crack completely. This usually happens when the crack is too thin or has dirt inside. Try cleaning the crack again with a needle or compressed air. If the crack is still too thin, you may need to widen it slightly with a glass cutter, but this is risky and may worsen the crack. If you can’t get the resin to fill, the crack is likely not repairable.

The repair looks cloudy or has bubbles. This is often caused by moisture or air trapped in the crack. You can try re-injecting resin over the cloudy area and curing again. If it remains cloudy, it’s a cosmetic issue but the crack is sealed.

The crack spreads after repair. This indicates the crack was too large or the repair wasn’t strong enough. The glass is now compromised and needs to be replaced. Do not attempt another repair.

The resin doesn’t cure. The resin requires UV light to harden. If you’re not in direct sunlight, use a UV flashlight. Check the kit’s instructions for curing time and make sure the film is applied correctly.

Frequently Asked Questions

Can I fix a crack in a window myself?

Yes, if the crack is small (under 3 inches) and doesn’t spread to the edges. Use a glass repair kit. For larger cracks or double-glazed units, call a professional.

How long does a resin repair last?

A properly done resin repair can last for years, but it’s not as strong as the original glass. It will prevent the crack from spreading and restore some structural integrity.

Will the crack be invisible after repair?

It will be much less visible, but not completely invisible. The resin fills the crack and makes it clear, but a faint line may remain, especially if the crack was long or had dirt in it.

Can I use nail polish or super glue instead of a repair kit?

These are not recommended. They don’t have the same optical clarity or bonding strength as glass repair resin, and they can damage the glass. Use a proper kit.

Is it safe to drive with a cracked windshield?

It depends on the size and location. A small chip or crack outside the driver’s line of sight may be legal, but any crack that obstructs vision or is larger than a dollar bill is unsafe and may be illegal. Check local laws and get it repaired or replaced.

How much does professional window crack repair cost?

Professional repair is often covered by insurance and can be cheaper than replacement. The cost varies by location and the extent of damage. A DIY kit costs around $15-30.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

More in this bed

The whole Tech How-To bed →