A cracked pane lets in drafts and rain, and broken glass is a safety hazard. Replacing glass in an old single-pane wooden window is a classic DIY repair. Double-pane windows are different: the sealed glass unit is usually replaced as a whole, often by a glass shop.
Safety first
Wear thick gloves, safety glasses, long sleeves and closed shoes. Put a drop cloth on both sides of the window. If you need a quick temporary fix, cover the crack with clear packing tape or tape a sheet of plastic over the frame.
Many houses built before 1978 have lead-based paint, including on window sashes and in old putty. Scraping it creates dangerous dust. Read the EPA’s guidance on lead-safe renovation before you start in an older home.
Removing the broken glass
- If possible, remove the sash and lay it flat on a workbench.
- Crisscross the glass with masking tape so it does not shatter, then lift out the pieces, starting at the top.
- Soften the old putty (glazing compound) with a heat gun on a low setting and scrape it out with a putty knife.
- Pull out the small metal glazing points that held the glass.
- Clean the rabbet (the groove where the glass sits) and brush on a coat of primer or boiled linseed oil so the wood does not suck the oil out of the new putty.
Measuring and buying the glass
Measure the opening in both directions and subtract about 1/8 inch so the glass fits with a little play. A hardware store or glass shop will cut single-strength or double-strength glass to size. In doors or near the floor, building codes often require tempered or safety glass.
Installing the new pane
- Lay a thin bead of glazing compound in the rabbet to bed the glass.
- Press the glass in gently.
- Push in new glazing points every 6 to 8 inches.
- Roll glazing compound into a rope and press it along the edges, then smooth it at an angle with a putty knife.
- Let it cure as directed (often a week or more) before painting. Overlap the paint slightly onto the glass to seal it.
Double-pane windows
If condensation appears between the two panes, the seal has failed and the unit must be replaced. Glass shops make new units to order. For a broader look at window choices, see the different types of windows and their benefits. Drafty windows also affect your bills, as covered in the best ways to protect your home from the elements.
