How to replace a broken window pane

A cracked or smashed window is dangerous and an invitation to intruders, so replace the broken pane as soon as possible. Only tackle small to medium sections that you can handle easily and don't try to replace glazing in UPVC frames - leave this to a professional. Make note of the telephone number of a local glazier just in case you need to call in help.

How to replace a broken window pane

You will need:

  • Hammer
  • Old chisel
  • Sheet
  • Replacement glass
  • Linseed Oil Putty
  • Tape measure
  • Glazing sprigs
  • Pliers
  • Thick gloves
  • Wood filler
  • Primer

Time to complete job: Half a day.
Approximate budget: Around £25 for a small to medium pane of glass.

Metal window frames
Glass is held into metal window frames with small spring clips. If the clips that hold the glass in place are broken or missing, call in a glazier repair the window and add new clips. Otherwise, repair in the same way as for a timber frame.

For more information please see the Glass and Glazing Federation.

  • Step 1: Preparation

    Step 1: Preparation

    Wear safety goggles, thick gloves, boots and thick clothing for protection when removing the old glass.

    Lay an old sheet outside the window to catch the remaining glass and take out the largest fragments of glass. You may need to use a hammer and old chisel to knock out the smaller fragments.
    Break up the pieces and wrap in newspaper. Dispose of the bits carefully at your local tip.

    Measure the window frame rebate (the groove that holds the glass in place). You should take a couple of measurements at different points along the frame in case the wood is warped. Subtract 2-3mm (0.08-0.12in) from the height and width measurement so that the glass will fit easily into the rebate.

    Tip: If you can't repair the window on the same day, cut a piece of flakeboard or plywood to the size of the window frame and screw into place.

  • Step 2: Sanding & filling

    Step 2: Sanding & filling

    Chip out the remaining putty with the hammer and chisel and prise out any old glazing sprigs with pliers.

    Sand smooth any rough patches and treat any bare areas of wood with an external primer. Fill any holes and cracks.

  • Step 3: Applying the putty

    Step 3: Applying the putty

    Knead some of the new putty into a thin 20mm diameter roll and squeeze it into the frame rebate.

    Tip: If the putty is wet and sticky, take a handful and roll it on some newspaper to absorb some of the linseed oil.

  • Step 4: Inserting the glass

    Step 4: Inserting the glass

    Carefully lower the bottom edge of the pane onto the lower part of the frame and gently push into place. The putty should squash out of the rebate to form a weatherproof seal.

    Tap new glazing sprigs into the sides of the rebate to hold the glass firmly in position. Space these at around 150mm (6in) intervals around the frame.

    Tip: To reduce the chances of accidentally breaking the new pane, always slide your hammer across the face of the glass as you tap in the sprigs.

  • Step 5: Finishing

    Step 5: Finishing

    Use a putty knife to press more putty all along the outer edge of the glass to complete the weatherproof seal. Try and form the putty into a uniform slope away from the glass so that rainwater will run off.

    Carefully trim off all the remaining putty from the edges of the rebate with the putty knife. Leave the putty to harden for about 14 days before painting.