Glazing repairs

Glazing repairs seem to fall into the category of ‘tasks that are put off until tomorrow’- many people simply do not know where to begin. Both timber and metal framed windows are easy to repair, however, with a few techniques. Warm weather is the time to tackle those external glazing repairs needed around the house, such as replacing cracked panes of glass, renewing crumbling old putty, and repairing leaking skylights or lean-to roofs.

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Improvements can also be made, such as installing wholly or partially glazed doors in a hallway or on a landing to give better illumination to these areas. Or, you might want to insert plastic circular, cord operated, ventilators in kitchen or bathroom windows to improve ventilation and reduce condensation. Whatever your plans, warm weather is the best time to handle glass, since it may be brittle to handle in cold weather, and more apt to crack or leave jagged cutting edges

Removing broken glass

Removing broken glass requires care at all times, but especially when working above ground level. If doing so, place obstructions around the area below and warn others to keep children and pets away from the area. Whenever possible remove sashes and frames and work on ground level.

Putty glazing to wooden frames windows & doors

In a wooden door or window frame, the glass is held in the rebate with putty and special nails called sprigs, or occasionally with panel pins. To remove the broken glass, first loosen all putty and fixings around the outside edge, in front of the glass. A glazier’s hacking knife is useful to use here or an old screwdriver and chisel. Remove panel pins or glazing sprigs, or drive them well below the wood surface with a hammer. Now, wearing thick gloves of some sort, such as gardening gloves, remove the old pane of glass; be careful that the glass does not fall out of the rebate. Broken or loose pieces can be pried out and detached with pliers, working always from the top so that loose bits do not fall on to your hands. Once this is done, clear out about 3.17mm of putty around and behind the glass; you should now be down to bare wood. With the glass removed, smooth the rebate with glasspaper, and give it a good coat of primer. Allow this to dry before proceeding -about four hours usually.

Reglazing

Begin by measuring the rebate-each side, top and bottom separately-and the two diagonals. Use a steel tape and take the measurement from the inside edge of each rebate. Deduct 1.6mm off each side or 3.17mm all round if the pane is more than 0.37sqm to allow for glass expansion within the rebate. Now, cut the glass. Avoid using old or weathered glass for reglazing, as it may be brittle and difficult to cut accurately. After cutting, any sharp edges can be smoothed down with an oil-stone which has been wet with turpentine, water or oil.

Once the piece is ready, mark the glass top on the outside face so that it is ready to offer up correctly into the rebate. Roll a lump of putty in your hands until it is soft and easy to work. If the putty is too oily, wrap it first in newspaper to absorb some of the oiliness. With your thumb, lay a continuous strip of bedding putty about 3mm thick all round the back of the rebate against which the glass will be placed. With sprigs or panel pins to hand, place the glass in the rebate, bottom first, leaving an equal space all round the edges and press it gently against the back putty. Never press from the centre. Squeeze out the surplus putty until a thickness of about l.6mm remains between the back ,cf the glass and the rebate. To fix the glass in place, tack the sprigs or panel pins into the side of the rebate, against the face of the glass.

Fix one close to each corner and space the others equally-about l50mm apart-around the pane. Use a small hammer to knock the sprigs in and keep it touching the glass as you work, so that you do not knock the glass and break it. Cut off the excess back putty around the rebate with the putty knife. A strip of weathering putty must now be placed around the outside of the pane. Knead the putty in the hands as before and lay a thick continuous strip into the angle of the rebate against the lace of the glass. Lubricate the knife with water to keep the putty from sticking to it. Hold the putty knife in one corner of the window with the blade against the rebate and the tip resting on the glass at an angle of 45″. Cut the excess putty off all round the pane in one clean stroke, so that a slope is formed to allow the rainwater to run off, and tidy the corners with a square-ended filling knife to form a mitre.

Finally, all the putty surfaces may be brushed over with a damp, soft brush. After two to three weeks, the putty may be painted over, using an oil undercoat and finishing coat to match the existing paintwork. Allow the brush to run over the putty onto the face of the glass about 3mm to seal the joint.

Putty glazing to metal frames

The procedure is the same as described for wooden sashes with three important differences:
1. A special putty for glazing to metal frames is necessary.
2. Small bits of plastic strips are needed to set in the bottom of the rebate to allow for expansion.
3. Sprigs are not used; the glass is held in position by spring clips which look like a bent’S’. These are hooked into the rebate and press onto the face of the glass. It is important to retain these for re-use.

When all the glass and old putty has been removed from a metal frame, there may be rust present in the rebate. No matter how little, this must be removed and bare metal exposed with wire wool or emery paper. Treat the bare metal areas with a rust inhibitor as soon as they have been exposed and, when dry, prime the whole rebate with a metal primer. If this is not done, the expansion of the rust in the rebate will eventually crack the glass. Steel windows may tend to distort and twist in shape from the effects of heat and cold. In such instances they will not shut properly and the glass will crack. Do not attempt to reglaze if this appears to be the situation, since you will first need to consult a blacksmith to straighten and square the sashes. Some steel and aluminium windows have metal glazing beads fixed to the exterior with grub screws. Before attempting removal of a glass pane, lubricate these with a drop of penetrating oil; it will make the job much easier.

In some cases the glass in windows is still sound, but the putty on the face has rotted away. To repair this simply chisel out all the remaining putty, rub the rebate smooth up to the glass, prime it and when dry, proceed as described in the section on apptying weathering putty under Reglazing.