New wooden window frames The increasing use of sealed double glazing units has led to most manufacturers supplying new wooden frames with glazing rebates of sufficient depth to take standard sealed units up to a maximum thickness of about 20mm. By choosing your supplier carefully you will be able to order both frames and glazed units at the same time.

You won’t need to measure for the glass if the frame is one of the many standard sizes available. If you need to have frames made, you should make it clear to the carpenters & joiners that you will befitting sealed double glazing units. He will then make allowance for this when making up the frames Normally, the glass is fitted using wooden glazing beads to hold it in place and putty or a similar glazing mastic to provide a seal between the unit and the frame. Acrylic putty is coming into use now and is ideal for double glazing units.

There are several factors you should consider in deciding whether or not to replace single panes of glass with sealed double glazing units. Your existing window frames must be in excellent condition as there is little point in fitting sealed units into frames which may themselves have to be replaced within a few years.

If the frames are more than 60 years old they are not likely to be of a standard size and so they would need specially-made sealed units. These would not be reusable in a new standard replacement frame and so this would have to be made specially, too. Standard size sealed units are, in effect, mass-produced and so are cheaper than specially made ones. They are obtainable virtually ‘off the shelf from many suppliers, particularly for use in wooden-frame windows.

The rebate in the existing frames must be deep enough to accommodate the thickness of the sealed units and still allow them to be puttied in place or fixed with a glazing bead. You are likely to be changing from a single glazing thickness of 3 or 4mm to at least 12mm, rising to 18mm if you want units with a 12mm gap. For the latter, therefore, you would need a rebate measuring some 30mm from front to back, and not all old frames have this.

It is possible, however, to overcome the problem of too narrow a glazing rebate by using what are known as ‘stepped’ sealed units. These have one sheet of glass smaller than the other, the larger pane being fitted exactly in the same position as the original single pane with the smaller one on the inside, overlapping the back of the glazing rebate. Such stepped units are readily available to fit standard modern window sizes, or they can be made specially. They can be used in wooden frames but not in steel, which are generally unsuitable for sealed unit double glazing. The same can be said of any windows incorporating a large number of small panes, such as Georgian styles.

The cost of replacing all the individual panes with sealed units would be extremely high, even if the glazing bars were of a suitable size. However, if you wish to keep this appearance, complete sealed units are available that reproduce the Georgian or leaded-light look quite effectively.

If you are quite satisfied that sealed units can be fitted to your existing frames, the first step is to measure the rebate so you can order the correct size. Take great care to get the correct dimensions because, once made, the size of the sealed unit cannot be altered. With standard sizes this is not so much of a problem, but if you are having the units specially made it could prove to be an expensive mistake if you get it wrong. The height and width of the rebate should each be measured in at least two places. If there is a difference between any of the measurements, work with the smaller size.

Deduct a further 3mm from both the selected height and width to allow for clearance around the unit, and this will be the size you should order. Once you have the new sealed units, remove the putty from the window frame using an old chisel or similar tool and taking care not to damage the wood. Pull out the glazing sprigs with a pair of pincers and carefully lever the glass from the frame. Wear thick gloves or wrap a towel round the edge of the pane to prevent cuts as you lift it clear. If the glass is stuck fast to the old bedding putty, you may find that it can be tapped out from inside by a helper.

Only gentle taps should be used to avoid breaking the glass accidentally. If all else fails, break the glass from the inside with a hammer (making sure there is no-one outside who might be injured by the flying fragments) and pull out any remaining glass with a gloved hand or pair of pliers. Clean out the remains of the putty and brush any dust or dirt from the rebate. Reprime any areas of exposed wood and allow the primer to dry before fitting the new unit. Line the rebate with a bedding layer of fresh putty, inserting rubber spacing blocks at intervals along the bottom and at each side.

These should be cut to a thickness that will centralise and square the double glazing unit in the frame. Offer up the new unit bottom edge first and gently press it into place with the palms of your hands so that the bedding putty oozes out round the inside edges of the sealed unit. Apply pressure only to the edges of the unit to prevent the glass breaking where it is unsupported in the middle. Check inside that there is about 3mm of putty between the inner face of the glazing unit and the rebate. Next, very carefully tap in the glazing sprigs, using a cross-pein hammer. Use at least two sprigs per side and slide the head of the hammer across the glass to avoid breaking it.

Drive each sprig in squarely so that it does not pinch the glass until only 6mm (1/4in) remains visible. If you can’t obtain proper glazing sprigs, you can use 19mm panel pins with their heads nipped off

Apply a finishing fillet of putty all round the rebate, pressing it into place with your thumb so that it covers all the edges of the glass. Smooth this off to an angle with a putty knife, making sure it does not project above the level of the rebate otherwise it will be visible from inside the room. Mitre the corners carefully and clean off any excess putty from both inner and outer panes of the unit.

Leave the putty to harden for two weeks before applying a coat of primer and finally a finishing coat of paint. The latter should overlap onto the glass by 3mm to ensure a watertight seal. If stepped double glazing units are to be fitted, a rebate for the stepped portion of the unit can be made by pinning lengths of beading around the inside of the window frame. Extra putty will be needed around this stepped rebate to provide a bed and surround for the inner pane of glass.

London Carpenters

Fitting sealed double glazing units will provide good heat and sound insulation as well as reducing draughts. They are easy to install in either existing or replacement window frames.

It is well known that double glazing offers considerable benefits for the homeowner. It can considerably reduce draughts from around the window area, not only those which enter through badly fitting frames but also down-draughts caused by warm air close to a cold, single pane of glass being quickly cooled and so falling.

Eliminating these down-draughts makes for a more comfortable environment and prevents that ‘chilly’ feeling even though the room is heated. Some forms of double glazing can, to some extent, also reduce the penetration of noise from outside the building, but the major advantage is that the use of two panes instead of one can help reduce heat losses through glazed areas, providing a potential for saving energy and, hence, cutting fuel costs.

By far the most efficient method of achieving such thermal insulation is by the fitting of sealed double glazing units in place of single panes of glass in the window frame. This is known as primary double glazing.

Each sealed unit comprises two sheets of glass separated by a metal, glass or rigid plastic spacer which is fitted around the edges. The air between the two panes is dehydrated so that it contains no moisture, and the entire unit is sealed hermetically so that none can enter. As long as the seal remains unbroken condensation cannot form between the two sheets of glass. The space between the panes normally varies between 6 and 12mm (1A and 1/2in), the wider gap providing the best thermal insulation properties.

The glass itself will vary in thickness from 3mm upwards depending on the size of the pane and the position of the window, many different types being available including float, laminated, toughened, standard sheet, tinted and obscured. All sealed double glazing units are factory made by specialist companies and cannot be assembled at home. However, they can be fitted by the non-professional glazier in much the same way as normal replacement panes of glass either to existing window frames or into completely new replacement windows.

Local glass merchants and double glazing manufactures are involved in the supply of sealed double glazing units in a wide range of standard sizes or in made-to-measure form to suit individual requirements, and it is now common practice for complete replacement windows, made from wood, aluminium or UPVC, to be supplied with sealed glazing units fitted as standard.

Criss-cross the pane with brown sticky tape so that when you tap the glass out it won’t fragment.

TOOLS FOR REGLAZING

Hacking knife: has a flat back for tapping in glazing sprigs.
Cross-pein hammer: light, has a wedgeshaped pein opposite the striking face.
Putty knife: can have square-ended blade, or flat and curved edges to the blade.

Buying new glass

It’s important to choose the right type of glass, but don’t try to cut it to size yourself. Your local glazier will do a much better job, and is less likely to break the pane in the process. There’s also no financial advantage to doing the job yourself for you’ll be left with unusable off-cuts. And don’t think you can use up that odd piece of glass you may have lying about.

Old glass does not cut well at all, and tends to break in the wrong place even when you’ve scored it with a carbide – diamond tipped glasscutter. So measure the width and height of the rebate into which the glass must fit; double check the measurements to be sure, and order the glass to be cut 3mm smaller on each dimension. This allows for any slight inaccuracy in your measurements, and avoids the risk of the glass cracking due to expansion or contraction of the frame. If you need patterned glass, make a note of which way the pattern runs.

The fixing process

First you must line the rebate with putty. You can either take a ball of putty in the palm of your hand and squeeze it out between thumb and forefinger using your thumb to press it in; or you can roll the putty into fingerthick sausages and press these into place. Wet your hands before handling putty to prevent it sticking to your fingers, and knead it until it is pliable and any surface oils are thoroughly mixed in.

Next, press the pane into the puttied rebate with the palms of your hands, so that putty oozes out, around and behind the glass. Apply pressure around the edges rather than in the centre of the pane and check that, when you’ve finished, the glass is separated from the frame on the inside by a bed of putty which is 2mm to 3mm (up to 1/8in) thick.

Now for the unnerving part – nailing the glass in place.

It’s best to use glazing sprigs, but you could make do with 19mm panel pins that have had their heads nipped off with pliers. You’ll need at least two per side, spaced no more than 230mm (9in) apart, and you must be sure to drive them squarely into the wood so they don’t pinch and crack the glass. When you’ve finished, just over 6mm (1/4in) of pin should be showing. The final stage is to fill the rest of the rebate with a triangular fillet of putty that neatly covers the pins.

Apply the putty in the same way as when lining the rebate, and use a putty knife or an ordinary filling knife to do the shaping, mitring the corners of the fillet as neatly as possible. Wet the knife blade to prevent the putty sticking to it as you draw it over the fillet. Clean off the excess putty – including any that oozed out inside the pane earlier – and allow to dry hard before painting. When you need to reglaze a window that isn’t at ground level, you’ll have to work from a ladder. Obviously you’ll have to be organised when working at a height. Tap out most of the glass first from inside-and make sure there’s no one standing below as you do so. Put all the tools and equipment in a bucket which you can hang on a hook attached to the ladder at the top. Don’t try to carry the glass – it’s best to get someone to pass it through the window.

Modern windows

Conventional steel-framed windows are reglazed in almost the same way as wooden ones, except that the glass is fixed with wire clips fitting into holes in the frame, rather than with glazing sprigs. Remove these and re-use them to fix the new pane – along with the right type of putty – after priming with a metal primer. Because putty needs paint to protect it, and because modern aluminium and plastic windows aren’t meant to be painted, a different method is used to hold the glass. Normally, it’s a variation on the rubber gasket system used to keep the windows fixed in a car. Just how easy these windows are to reglaze depends on the design; different manufacturers have their own systems and unless it is obvious how the glass fits in, all you can do is ask the window manufacturer for his advice. In some cases, he will prefer to do the repair himself.

Replacing double glazing

There are few problems where secondary double glazing is involved. This system uses a completely separate window frame to hold the extra pane of glass. All you do is treat each element of the system as a single glazed window. One complication you may come up against is where a do-it-yourself double glazing kit has been used.

In this case the extra ‘frame’ may be no more than plastic channelling clipped over the edge of the glass, so it’s more a case of remaking this frame than reglazing it. Replacing double glazing where both panes are mounted in the same frame is more involved, and how you approach it depends on whether factory-made sealed units or two ordinary panes of glass have been used. In the latter case, you merely fix two new panes in the same way as if reglazing an ordinary window. Just be sure you don’t get marks on the panes facing into the double glazing’s air gap – you can’t clean them off once the second pane is in place.

Factory-made sealed units are also sometimes fitted like a single pane of glass but, more often, you’ll have a modern gasket system to contend with. In any case, the most important thing is to order the new sealed units to exactly the right size. They cannot be trimmed if you make a mistake. Dealing with leaded lights Strictly speaking, to reglaze a leaded light, you must remove the putty and glazing sprigs from the main window frame and lift out the entire glass and lead latticework, so it can be worked on flat.

You may, however, get away with working in situ if you get a helper to hold a sheet of hardboard or something similar against the other side of the pane, to keep it flat while you carry out the repair. Whichever approach you adopt, you must lever away the lip of lead (called the ‘came’) holding the glass in place by using an old chisel. Cut the lead near the comers of the pane with a knife to make this easier. Remove the broken glass, clean out the putty from the channel in the lead, apply new putty and then fit the new pane-this should be cut to fit the dimensions of the rebate exactly. Finally, smooth back the lead with the handle of the chisel to hold it in place. To finish, make good the knife cuts with solder, or with a proprietary plastic repair compound.
There’s more about this type of repair in another section.

Why glass?

You may be wondering why nobody has come up with a glass or glass substitute that never breaks. Well, they have. Leaving aside bullet-proof glass and the like, there are a host of plastic glazing materials on the market ranging from the familiar Perspex to compounds with complicated chemical names. But they all have two major drawbacks – they are comparatively expensive to buy, and they scratch so easily that they lose their transparency.