How to Replace Window Glass

Updated: Aug. 16, 2023

Here are the steps involved in replacing and re-glazing a broken glass pane in an old window.

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Here are the steps involved in replacing and re-glazing a broken glass pane in an old window.

Tools Required

  • Carbide scraper or chisel
  • Putty knife
  • Screwdriver
  • Utility knife

Materials Required

  • Cloth
  • Glazing compound
  • Glazing points
  • Gloves
  • Mineral spirits
  • Replacement antique glass pane
  • Safety glasses

Replacing glass in windows can sometimes be challenging, especially if you’re working on one in an old home.

You can pick up a new glass pane replacement from your local hardware store, cut it yourself or have them cut it for you. If your window contains antique glass and you need the replacement pane to match it, reach out to a local window repair store.

Norbert Rodriguez, owner of Quaint Milwaukee Window Restoration, said it’s important for the replacement pane to match the thickness of the original pane to keep the weight of the sash balanced properly. With that in mind, here’s how to replace glass on old windows:

Project step-by-step (9)

Step 1

Clean off old glazing compound

Chip out the old glazing compound carefully with a window zipper deglazing tool or putty knife. A heat gun or torch can soften the putty for easy removal.

Fhmvs23 Mf 06 23 Replacingglass Step1TMB Studio

Step 2

Remove broken glass

Use a putty knife or pliers to remove the glazing points that hold the glass in place. Carefully remove the glass shards from the cracked window pane.

Remove broken glassTMB Studio

Step 3

Clean out the rabbet

Clean any remaining glazing compound on the glass rabbets with a carbide scraper, chisel or utility knife, making sure not to damage or scrape the wood.

Fhmvs23 Mf 06 23 Replacingglass Step3TMB Studio

Step 4

Size the replacement glass

Measure the glass opening and subtract about 1/8-in. to 1/4-in. for replacement glass. If you don’t feel comfortable cutting the glass yourself, bring your measurements a local window repair shop or hardware store and they’ll cut it for you.

Once you’ve returned to your shop, ensure the replacement is clean and free of cracks or flaws before proceeding.

Step 5

Apply glazing putty to rabbets

Apply glazing putty with a putty knife to the glass rabbets the pane will rest on. Norbert recommends Sarco Linseed oil-based glazing compound, but it can be expensive. Cheaper options include Dap Glazing Compound.

Step 6

Replace the window pane

Carefully tilt the new pane into place, verifying that it fits and it’s completely flat against the glass rabbets. Apply small amount of pressure around the perimeter where putty touches the glass to make sure there’s complete contact. Allow the excess putty to ooze out under the glass and carefully scrape it off.

Fhmvs23 Mf 06 23 Replacingglass Step4TMB Studio

Step 7

Add glazing points

Install the glazing points with a putty knife to secure the glass pane. This adds extra support to hold everything in place while it dries. Depending on size of pane, two or three on each side should be enough.

Add glazing pointsTMB Studio

Step 8

Re-glaze the window

Glaze the window around the new pane with whichever glazing compound you choose.

Mead and roll the putty with your hands, then place it around the perimeter of the glass with a heavy layer of compound. Press the putty down and be sure not to leave any gaps or hollow spots.

Use the putty knife to create beveled profile and smooth out the glazing compound. Remove excess by dragging the glazing putty knife away from finished joint without harming smoothed beveled putty.

Pro tip: Spray the putty knife with silicone to allow smooth application and prevent compound from sticking.

Re-glaze the windowTMB Studio

Step 9

Clean and paint

Continue cleaning up the edges with the glazing putty knife. Remove putty oils from the glass window with a microfiber cloth and mineral spirits, or paint thinner if it’s really messy. If you wait a few hours for the putty to dry and skin before cleaning, it may be easier to remove.

Prime and paint the putty after it completely skins over; it takes about a week depending on temperature. (Norbert recommends using primer before you paint, and avoiding “primer and paint in one” products.) You must paint the putty or it won’t be effective.