How to reglaze windows

Reglazing is an occasional household maintenance job that you can easily do yourself if the need ever arises. And with the number of decorative forms of sheet glass available, it is a novel way of changing appearances.

Apart from the danger of exposed broken glass, a smashed window in the home is an open invitation to an intruder. You can reduce both risks by reglazing the window yourself. The job requires care but is straightforward and quick.

If you are reglazing a downstairs window it should not be necessary to remove the window from its frame. But if the window is upstairs, you need an extension ladder to reach the outside of the window. In this case, the job will take longer and you may find it more convenient to take the window out of its frame and reglaze it on a workbench at groundlevel.

A hinged sash can be removed from its window frame by unscrewing the hinges. Use a bradawl to scrape out paint from the screw heads. To remove a sash from a double-hung window means removing woodwork, so in the case of an upstairs window, it may be better to work from a ladder.

If you decide to work from the ladder, secure it at the top by looping a safety rope through the rungs and around a suitable anchor point. Additionally, make sure the feet of the ladder are well anchored.

A useful tip is to wear an apron or workman’s overall which has large tool pockets so that you can carry everything likely to be needed for the job. This will save countless trips up and down the ladder during the course of the installation.

Removing old glass

Take particular care when you are removing old glass from its frame. Always use heavy-duty gloves to pull out loose pieces.

Uncracked sections and stubborn slivers must be smashed out with a hammer. But before you do this, cover both sides of the glass with thick cloth or blanket to prevent chips flying through the air. For additional safety, wear spectacles, or old sunglasses at all times.

If you have removed the window from the main frame, cover it and lay it on several sheets of newspaper before you knock out the glass. This will make it easier to gather up the splinters afterwards.

After you have hammered out the glass, carefully remove the covering cloth and work loose fragments left in the frame. You should be able to prise out the glass quite easily, but if the putty is very old and hard and the glass refuses to be teased loose, cover the window with a cloth again and smash the fragments down to the level of the putty. Then, wearing eye protection, use a hammer and chisel to knock out the remaining putty with the glass embedded in it.

The old putty can be removed with a hacking knife—a tool specifically designed for this job—but a chisel will do the job nearly as well. Make sure that the chisel is an old one, well past its useful life, as it will become quite blunt when used in this way. Remove all the putty, including the back or bedding layer and take care not to damage the wood with whatever tools you use.

Measuring up the pane

When measuring up for the new pane of glass, always take the measurements twice: a mistake of only a few millimetres can make the pane unusable. Also, measure each opening within the main frame separately as small size differences between any two can go unnoticed until it comes to reglazing. When you have determined the final height and width measurements, subtract about 3mm from each to allow sufficient clearance in the frame— increase this to 6mm in the case of slightly warped frames.

When giving measurements to the glass merchant, it is customary to give the height before the width. This way, if you are buying frosted or patterned glass, the pattern will be the correct way up when you install it.

The glass

Glass is now graded by thickness in millimetres—it was formerly graded by weight per square foot—and for most applications 4mm is adequate, although 3mm is sufficient for smaller windows. Float glass is now the most commonly used for general purpose work but cheaper horticultural glass may be used where viewing distortion is no problem—such as in a greenhouse.

For help and advice on the choice and safe use of glass, do not be afraid to consult your local glass supplier. Several types of glass can be used around the house and it is important to use a strengthened form where there is risk of breakage. For example, UK recommendations state that only toughened or laminated glass should be used for balustrades which protect a difference in floor levels or which are used for shower screens.

Wired and laminated glass can both be used for floor-level windows, and those near to stairs can also benefit from these types.

A wide variety of decorative glass is available in addition to standard frosted patterns; using these in place of clear glass for extra privacy is well worth considering.

Before you install the glass, place and check it for fit in the frame and, if necessary, get the supplier to make small adjustments. You can sometimes accommodate very small irregularities by turning the sheet upside down or around in relation to the frame and then trying it again.

Using putty

Putty needs to be of the right consistency if it is to hold the glass in place and form a watertight seal. And when first taken from the tin it is inclined to be too wet, rather sticky and consequently difficult to handle. Knead it gently between the palms of your hands or place it between folds of newspaper to remove excess moisture and oil.

There are two types of putty: linseed oil putty for wooden-framed windows, and metal casement putty for use with metal frames. The latter should also be used as a bedding seal if metal-framed glass—such as insulating glass —is fixed into a wooden frame. In this case, linseed oil putty is used to finish off the outside seal.

In Canada, a glazing compound is widely used instead of putty—you apply it to the window frame in much the same way.

Installing the glass

Once you have checked the glass for fit, lay a strip of back putty around the window frame. Where hacking off the old putty has exposed areas of bare wood, prime these and let them dry before you apply putty over them. Use the heel of your hand to smear the nodules of putty around the insides of the rebates. Place the glass in the frame and push it gently but firmly against the bedding putty. Push around the outside of the frame—not the middle—with a pad of cloth to protect you against any slivers of old glass left in the frame. As you do this, the putty will ooze out on the other side.

The bedding putty is necessary not only for providing a good watertight seal, but because it also takes up small irregularities in the trueness of the backing frame. A final depth of up to about 5mm is recommended, and you can ensure an even depth around the frame by locating small wooden spacers such as match wood.

The sheet of glass must be centred within the frame—you should already have had it cut to measurements slightly smaller than the frame’s inner dimensions. The best way of doing this is to stick matchsticks between the glass edge and frame at odd points around the window; or use folds of thin wood or card to build up greater depths. Spacers should not be necessary if you can work on the window flat.

When the sheet of glass is properly bedded, by which time it should remain in position by itself, secure the glass on each side of the frame by tapping home a couple of glazing sprigs These are small, headless nails, buried by the face putty when the glazing is completed. On larger windows, use more sprigs at 150mm spacings around the frame. Start with the bottom edge and then deal with the top and side edges.

To avoid breaking the glass, if you choose a hammer, hold the sprig next to the glass and then slide the hammer head along the glass to tap the sprig down and below the level of the facing putty later added. Never lift the hammer from the glass surface, nor try to force a sprig home.

When this is done, you can apply the final putty. Start where you like and feed in little nodules of putty as you proceed around the edge, using the heel of your hand to press it fully home. The finished height of the facing putty must be no higher than the inside level of the frame, and therefore not visible from inside.

Finish the job by trimming off waste putty with a putty knife. Hold the flat edge against the pane of glass and run the knife along the edge of putty, pressing firmly downwards as you go . If the knife sticks, wet the blade with water. Should the putty become unstuck as you drag the knife over it, push it back in firmly and continue trimming with the knife.

Finally, rake off the putty that has oozed out at the back of the glass level with the frame. When trimming be careful of small splinters which may still be left in the putty.

Wooden beading

Some windows use wooden beading in place of facing putty and you can usually use this again when you set the new pane. Remove the side beading first—because it is longer and therefore more flexible—by bowing the ends towards you.

Then remove the small fixing nails afterwards by pulling them right through the beading—do not try to knock them back through the beading as this may split the wood. When you have removed all the nails, clean the beading with a medium grade of glass-paper. Any old putty-on the back must be removed, as must the jagged edge left by the broken paint line where the bead joins the frame.

If the old beading is damaged and needs replacing, ask your supplier for staff beading in the length required. It is normally available in two sizes, so take along a piece of the old beading.

The mitred joints at the ends of glazing beads are most easily cut on a mitre block. If you do not have one, lay the new length beside the old one and use the latter as a cutting guide. It helps if both are taped or clamped together before cutting.

Beading is positioned as the sheet of glass is pushed home on the bedding putty. Fix the shorter lengths first, using nails at 100mm intervals. For a really professional finish, punch in the glazing pins first so that the heads will not be visible when the beading itself is later decorated.

Use the point of a putty knife to remove bedding putty that has oozed out of the back and sides.


Leave the freshly-bedded putty to mature for about four weeks before you paint it. But do not delay this final job for too long or the putty will shrink and crack, causing all sorts of problems later. When painting, carry the paint layer just beyond the edges of the putty and on to the glass in order to provide a better waterproof seal and to keep the putty moist. Allow for this overlap when gauging the depth of putty required.

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