Leaded light glass replacement.

Replacing a broken glass pane in a leaded light window.

Leaded light glass replacement.

How to replace a broken or cracked pane of glass in a leaded light window.

If you live in a listed building, be it a grade 1 or grade 2 listed and need Leaded light glass replacement here is a simple easy way to renovate a leaded light window and replace a broken glass pane without causing any damage to existing glazed units, frames or surrounds, and without needing to pay a fortune to get them done professionally.

This method of Leaded light glass replacement is exactly the same as the professionals do it. Having been in the building trade and having renovated many properties I've seen it done many times.
It works, as I have used it myself on my own windows shown in the picture above. I live in a grade II listed building and during the renovation project several broken glazing units needed replacing. Having been quoted at the time it would have cost nearly £750.00 to have them all replaced professionally.

Materials needed.

For this simple project you will need:

Waterproof Clear/grey silicone or glazing putty.

Measure around the edges of the broken glazing units to work out how much silicone or putty you will need. Depending on how many glazing units you are replacing. An average 310ml silicone cartridge with a bead depth of 4mm and bead width of 3mm will give approximately 25 linear metres bead of silicone. Based on that 1 silicone cartridge would be more than enough for most jobs or 1 small tub of glaziing putty.

Silicone gun. If you do not already own one you will also need a silicone gun to dispense the silicone. You can usually obtain a fairly cheap one where you buy your silicone cartridges.

Replacement glass units.
You'll first need to measure the size of each glazed pane including its thickness as depending on the age of your property it will vary. Earlier properties tended to have the thinner glass, usually about 3mm depending on whether the units are original. Later properties tend to have thicker glass so always check first.

Important: Also Do not assume the glass pane sizes will be all the same. Old leaded light windows can and do vary in size so once you have cut all the panes you'll not be able to trim them easily if they don't fit. Also you will not be able to fit them securely and make them watertight if they are a little small.

Glass choices.

When carrying out a Leaded light glass replacement your glazing choices will matter.

My property is early 1800c and the closest I could find to match the thickness without paying a fortune for period glass was to use old picture glass. The other alternative is to visit a glass supplier, or as I did a local glass artist who may be able to order authentic glass to match the age of your property. They will most likely cut the units for you also. (Listed buildings will expect this option but it will come at a price.) Your supplier will first have to order a full sheet of period glass, regardless of how much you require. You may get lucky and find they have a few suitable offcuts lying around their studio which can work out cheaper. However it's really up to you and your budget.
Note: Modern requirements are that you use safety glass when replacing glazing units. With that said, be aware that most glass suppliers will not cut picture glass for this purpose. However, at the time I explained my situation and told my local supplier that I was renovating a leaded light window with less than 3mm glass so he was happy do it. I needed 8 panes of glass at approx 185mm x 135mm which cost me £5-00 in total including cutting. Iater I needed 2 more units for my upstairs windows which I got for free. Luckily he had 2 offcuts that were just the right size for the job.

Tools required.

A sharp woodwork chisel. I used a 22mm wide chisel which was ideal for the job but you can use whatever you have to hand. Try to use the widest blade you have as this will make the job much easier. If you don't have a chisel then perhaps you can use just a Stanley knife blade.
A putty or filling knife/paint scraper
This is instead of using a woodwork chisel as not all of us have chisel's but most have a filling knife hanging around somewhere. Also if you do not have a filling knife or putty knife one can be purchased quite cheaply.
A sharp Stanley knife.
A flat bladed screwdriver.
Paint or dusting brush.
A damp cloth.
Goggles/eye protection.
Gloves for glass removal.

Leaded light glass replacement

Stage 1: Cutting the lead.

The first thing to do when replacing Leaded light glass is to remove the broken glass panel. This will need to be done from the outside because the internal saddle bars can cause problems.

Cutting marks.
1) Put on your eye protection then take your sharp knife and carefully cut a 45-degree angle in the lead on the top corners of the unit. This must be done at the top to prevent the risk of leaking. It will also need to be done from the outside because the saddle bars on the inside of the window usually get in the way. Make sure that you only cut to the edge of the existing glass panel. You should be able to locate the with the tip of the knife blade. Also make sure that you cut all the way through the lead, and as I have already said, only cut enough to get to the edge of the existing glass panel. Which can also sometimes be located by a slight ridge in the lead as shown below. This requires patience and care.

Stage 2: Lifting the lead

Now, take your sharp chisel/filling knife or even a Stanley knife blade and carefully lift the edge of the lead. Do this by sliding your chisel or knife blade between the glass and the lead making sure that you only lift enough to free the glass pane. Do this down each side also until you feel the panel is loose enough for removal.

Stage 3: Removing the broken glass panel

Tip: Apply some tape over the broken glass pane. This will help prevent the broken glass shards from falling all over the floor.
The next thing to do, with goggles and gloves on of course, is to carefully remove the broken glass pane. Make sure that you do not over bend the lead as it will be very fragile. This again requires patience and care. Try to lift the panel up toward the top sliding it out of the lead surround. You may need to ease the bottom corners slightly with your chisel but try not to over distort, split or tear the lead. The less damage caused during removal will make the new Leaded light glass replacement so much easier.

Stage 4: Cleaning the lead rebate.

Next, with the glass removed you'll see that there is a slight rebate between the inside and outside lead surrounds. Take the flat bladed screwdriver and carefully remove any old putty/cement from around all the edges and faces of the lead where the glazing panel was seated. gain take care not to damage or distort the lead.
Tip: If the lead distorts, use a narrow flat piece of timber that you can easily place along the length of the lead and gently ease the lead back into shape by carefully tapping or pressing it back into shape.

With this done now take your dusting brush and remove any dust, dirt or debris from the lead.

Stage 5: Checking the fit of the Leaded light glass replacement.

With all dust, dirt and debris removed you are now offer your new piece of glass into the lead frame. Important: Do not apply the putty or silicone yet. This is the point when you will know if you have got your measurements correct.

Stage 6: Applying the silicone or putty seal.

If your glass panel fits correctly, remove it, as it is now time to apply the silicone or glazing putty to the lead.

NB: Standard practice will normally require you use putty but from experience I have found that.

1. The putty makes a thicker bed than silicone making it harder to redress and seal the Leaded light glass replacement.
2. Putty dries hard and holds the glass rigid thus making it more succeptable to crack again under vibration. This is usually always the case if you live in a heavy traffic area or near a main road.
3. Putty is also noticable once you have reglazed the unit.

Silicone application.

Tip: I always use silicone as like I have stated above putty dries hard and holds the units firm allowing any vibration. Especially if like me you live near to the main road to potentially re-crack the glass. Silicone's alot more flexible and acts like a shock absorber reducing the risk of the glass re-cracking. This has been proven as both my next door neighbour and I have restored our windows. He had his repaired professionally using putty and mine were done by myself using silicone. Most of his have re-cracked whereas none of mine have.

The other main advantage using silicone is that you can get a good invisible sealed joint between the Leaded light glass replacement and the lead making it completely water tight.

Apply a thin bead of silicone, lead sealent or putty to the back edge of the lead first, making sure you apply a continuous bead. You can apply the putty with the flat of the chisel, your filling knife/putty knife or knife blade.
Tip: If you're using glazing putty make sure you knead it well before applying it as the softer and more malleable it is the easier it will be to fit the replacement glass panel.

Stage 7: Refitting the new Leaded light glass replacement.

Take your glass pane and carefully refit it into place.
You may need to offer the glass in from the top then gently ease it down to the bottom of the lead and into the rebate.
From the top down apply even pressure around all the edges to get a good seal. A good way to check is if you can see a thin line of putty or silicone around all the edges of the lead.

Tip. If you see any slight gaps around the edges fill them by carefully pushing the excess putty or silicone into them with the flat of the chisel. filling/putty knife or knife blade until you have a continuous bead around all the edges.

Stage 8: Resealing the glass and dressing the lead surround.

With that done apply another thin bead of silicone or putty under the raised lead on the outer edge of the glass, then using the top of the chisel handle or the screwdriver handle carefully push the lead back into place onto the glass. Apply gentle even pressure until the lead is seated evenly onto the glass and there is a continuous fine line of silicone or putty visible around all its edges.
Tip. If you see any slight gaps around the edges fill them by carefully pushing the excess putty/silicone into them. Use the flat of the chisel/putty/filling knife or knife blade until you have a continuous bead around all the edges.

Remove any excess silicone or putty by carefully running your chisel blade around the edges of the glass and then wiping them with a damp cloth. You'll also need to repeat this on the inside of the glass pane.
Tip: If you 're using silicone and find it does'nt come off satisfactorily when running a chisel blade around the edges of the lead you can remove the excess with a drop of white spirit or turpentine. Alternatively, allow the silicone to dry first then using the knife blade carefully run it around all the edges of the lead to free it up. Next, carefully slide the blade around the unit until all the excess silicones removed. DO NOT press hard or scrape the glass as it may scratch.

Stage 9: Blending and resealing the cut edges of the lead.

The next thing to do is to blend the cuts in the corners.
To do this you will need to again use the handle of your chisel or screwdriver. Always work from the outside edge to the inside. Gently rub it across the cut until the lead blends into itself, hiding the cut. You may find some silicone or putty spews from the joint but this is ok as it means the joint is sealed. Any excess can be removed with the cloth, or you can wait for it to dry and then carefully remove it with a chisel or sharp knife blade.