How to replace a broken windowpane

There's no need to call a specialist when a windowpane breaks. It's quicker and much cheaper to replace it yourself.


What you'll need
  • Leather gloves
  • Safety goggles
  • Glass cutter
  • Hammer
  • Hacking knife or old chisel
  • Pincers
  • Dustpan and brush
  • Paintbrush
  • Putty knife
  • Primer paint
  • Putty
  • Glazing sprigs
  • Glass to fit the window
Before you start

When buying glass, tell the supplier the size of the panes. He'll advise on the thickness of glass you should use and will cut them to fit.

Use 3mm glass in very small panes, such as Georgian-style windows. For windows up to about 1m square use 4mm glass. For anything larger, use 6mm glass.

When glass is to be used over a very large area such as a picture window, or where it may be mistaken for an opening, as in a patio door, or where it'll be fitted within 800mm of the floor, use safety glass.

For wooden windows use linseed oil, universal or acrylic putty; for metal windows use metal casement, universal or acrylic putty. You'll need about 1kg of putty for 3.5m of frame. Brown putty is available for windows that are to be finished with preservative stain.

Broken glass in doors is replaced in the same way as for wooden windows, unless the door has been glazed with beads that are replaced as for square-edged double glazing units.

Removing the broken glass

1. Lay a dustsheet on the ground on both sides of the window to catch the fragments of old glass.

2. Put on leather gloves and safety goggles. Also wear thick leather shoes in case jagged pieces of glass fall to the ground.

cutting glass

3. Using a glass cutter, score the glass all round the window, close to the putty.

tapping glass with hammer

4. Working from the outside, tap the glass with a hammer to break it, starting from the top. Try to keep the pieces as large as possible.

5. After breaking out as much old glass as possible, remove remaining putty and glass with a hacking knife or old chisel. Hold a hacking knife in one hand with the point against the putty and tap it on the blunt edge with a hammer.

Look out for glazing sprigs embedded in the putty, or metal clips in metal frames. Pull them out with pincers. Leave the rebate in the window as clean as possible, before putting in new glass.

6. Brush all dust from the frame and paint a wooden frame with primer, which should be allowed to dry. This is not necessary on a metal window unless it's rusty. If the window has to be left overnight, cover it with a sheet of polythene or a piece of plywood.

Putting in the new glass

1. Mould the putty in your hands to get it soft and pliable. If it sticks to your hands, try wetting them, or take some of the oil out by rolling the putty on kitchen paper.

applying puty

2. Hold the pliable putty in the palm of your hand and squeeze it out between the thumb and forefinger to form a layer about 3mm thick in the rebate all the way round the window.

3. Press the glass carefully into the rebate so it's well bedded on the putty. Press it round the edges only, taking care not to push too hard in one place—and never in the middle of the glass. It could break and cause injury.

trim excess putty

4. Fix the glass in place with glazing sprigs inserted into the window about 250mm apart. Knock them in with the edge of the chisel or with the back of the hacking knife, sliding it along the face of the glass.

The heads of the sprigs should protrude about 5mm from the frame. Trim off excess bedding putty on the inside of the pane.

5. Apply more putty to the front of the glass to fill the rebate, and smooth it off with a putty knife to form a neat triangular line of putty that covers the heads of the sprigs and lines up with the putty on the inside edge. Make neat mitres at corners.

6. Leave the putty for about 2 weeks to harden slightly before painting it. When you paint it, allow the paint to spread onto the glass by 3mm to keep out the rain.

Emergency cover for a broken window

It's often impossible to repair a broken window immediately, so carry out an emergency repair to keep out weather while you arrange to get the new glass. A cracked pane can be temporarily sealed with waterproof glazing tape, which is transparent.

If the panel is smashed, cover the window with heavy-gauge polythene, secured with timber battens nailed around the edge of the frame. The battens will prevent the sheet from tearing. If security is important, cut a sheet of plywood to cover the window frame and fix it with either nails or screws.

Helpful tip

Disposing of broken glass can be difficult. The best way is to take it to your local bottle bank. Otherwise, wrap it thickly in newspaper and put it either beside or in your dustbin, clearly labelled "broken glass".

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