When we had an extension on our kitchen, my partner Cari felt inspired to make a leaded-glass window to fit a window that looked over the bins and a fence. We asked the builder to install a plain non-opening double-glazed window in a white aluminium frame in that position. The frame had the inner rebate about 1cm deep and 95 by 75 cm height by width.
Traditional window-leading
The window was made using traditional leading (not copper foil). The coloured glass shapes that make up the pattern are each surrounded by lead H-shaped strips all designed to interlock and to fit into a rectangular H-frame about 1.5 cm smaller in height and width than the recess of the window where it is to be fitted. The glass pieces all held into the leadwork, which is then soldered together. The glass is sealed to the leadwork with window cement to keep it stiff and water-tight. Nevertheless, like anything made of glass, it must not be bent, otherwise the glass will crack.
We really had no idea how to fit this onto the existing window! Obviously we sought advice from the stained-glass tutor, but in the end we had to use our craft skills and YouTube!
A supplier of leaded-glass windows showed how they fitted a rather smaller window against a wood-framed window using double-sided tape. What? Then they sealed around it with mastic to fix it in place.
Materials
But they didn’t say what materials they used. Hence the purpose of this blog. After research, we settled on Scotch Fix Double-face Exterior Mounting Tape, 19 mm wide on 5 m rolls. This tape is black, very flexible and very sticky, on a plastic backing. We put this all round the face of the frame holding the existing double-window and since the tape is slightly wider than the face of the frame, we folded the edge over the frame towards the glass. This hid the white edges of the frame.
The leaded window has knobs of solder at each joint, so would not be able to make full contact all round the edge. Obviously we were worried that the adhesion may be inadequate, so we stuck double-sided tape onto the flat parts of the outer lead of the H-frame. Since the tape is about a millimetre thick, this ensured a much greater contact area.
Trial fitting
The tape is extremely sticky, so as soon as the new leadwork makes contact, it is immovable without tearing the adhesive.
This meant that we had to dry-test it before putting on the sticky tape, to check that the gap between the glass frame and the window-frame was correct, and to get some practice at how best to offer up the window. We were only going to get one chance to do this.
The gap was about 6 mm all round, so the measurements and making were excellent! Also the window wasn’t too heavy and yet it was stiff and strong enough to survive being lifted and tilted into place.
The bottom-edge gap
We realised that the secret of fitting it correctly was to ensure that the bottom-edge gap was correct and held firmly. We found a strip of 6 mm plywood that just fitted, and we rested this on the bottom edge of the rebate, with some small off-cuts underneath to hold it level. The double-sided tape grabbed the edge and kept it there.
We then applied masking tape all round the outer face of the window and the frame, to protect them from the sealant we were going to use to seal the gap later.
Having made sure everything was spotlessly clean, we offered up the window, resting the bottom edge on the strip of plywood, then tilting the window vertical without touching the sticky tape. There was just room to get our fingers in. Then, checking that we had a 6 mm gap on each side and keeping it vertical, we slide the glass against the sticky tape on the window frame. It stuck immediately, and after checking the position again, we carefully pressed the lead frame against the sticky tape all the way round. It was firmly fixed.
Sealing the window in place
Now it was time to seal the lead frame in place. This is to prevent moisture and insects getting into the space behind the glass, although it does mean that it’s probably not possible to remove the window without damaging it.
We used White CT-1 sealant-adhesive. This isn’t silicone and doesn’t use solvents. Moreover, it remains pliable, which is important for a window that will be subject to considerable temperature changes – this should mean that it allows for expansion but doesn’t shrink or crack over time. Interestingly, this product was recommended to us by our cleaning lady whose husband is a builder who uses this all the time.
After squeezing enough sealant to fill each of the edges, we smoothed it straight away. We used thin plastic gloves, wetted the gloved index finger with plain water and carefully ran it along each edge. As soon as this was done, we vary carefully removed the masking tape, taking care not to get any excess onto the frame or window. It’s important to do this immediately so that the sealant hasn’t started to skin over. It is very sticky and messy. We needed 1½ tubes of sealant.
CT-1 is fairly slow to cure so we left the plywood strip at the bottom for a couple of days until the adhesive had set. The reason is that when we did a test fitting, I removed the bottom support before putting in any sealant and over a period of days, the sticky tape stretched more at one side than the other, letting the window twist out of vertical. It was very slight, but my eagle-eyed partner was understandably most dissatisfied.
It is now quite magnificent and we couldn’t be happier with it.