How to Fix a Window That Has Cracked Glass

A cracked window pane lets in drafts, reduces security, and will eventually shatter completely. Here's how to assess the damage, apply a temporary fix, and replace the glass properly.

Types of Window Cracks

• Stress crack: Starts at the edge of the glass and spreads inward; caused by temperature stress or frame pressure
• Impact crack: Spider-web pattern radiating from a central impact point
• Pressure crack: Curved crack caused by the frame warping and putting pressure on the glass
• Thermal crack: Straight crack from edge to edge caused by extreme temperature differential

Step 1: Assess the Damage

Is the crack in a single pane or a double-pane unit? For double-pane windows, if only the outer pane is cracked and the inner pane is intact, the window still provides some insulation. If both panes are cracked, replace immediately.

Temporary Fix: Glass Adhesive

For a small crack that hasn't spread, clear glass adhesive can stabilize it temporarily and prevent it from spreading further. Clean the crack thoroughly, apply the adhesive, and let cure.

• Glass Glue Ultra Strong Clear 100g — waterproof, fast-curing adhesive for glass repair; stabilizes cracks and prevents spreading

Note: This is a temporary measure only. Cracked glass should be replaced as soon as possible.

Temporary Fix: Clear Tape

Apply clear packing tape over the crack on both sides to hold the glass together and reduce drafts. This is a very short-term fix only — arrange for replacement promptly.

Permanent Fix: Replace the Glass Pane

For single-pane windows, replacing the glass is a DIY-friendly repair:

1. Measure the opening carefully (height and width)
2. Order replacement glass cut to size from a hardware store or glazier (subtract 1/8" from each dimension for clearance)
3. Remove the old glazing compound with a putty knife and heat gun
4. Remove the broken glass carefully wearing heavy gloves
5. Apply a thin bed of glazing compound to the frame rabbet
6. Set the new glass and press firmly into the compound
7. Apply glazing compound around all four edges and smooth with a putty knife
8. Let cure, then prime and paint the glazing

• DAP '33' Window Glazing White 32oz — professional-grade glazing compound for bedding and sealing single-pane glass

For Double-Pane Windows

Double-pane IGUs cannot be repaired — the entire sealed unit must be replaced. A glazier can install a new IGU in the existing frame. This is not a DIY job as it requires specialized equipment to handle the sealed unit.

Safety First

• Always wear heavy leather gloves when handling broken glass
• Wear safety glasses
• Score and snap glass rather than breaking it randomly
• Wrap broken glass in newspaper before disposing