Measuring glass.

[Dave Plowman (News)]

I have a wood Victorian front door. At some time, the top panels were changed to glass - and that horrible ribbed stuff. The top of the panel is a semi-circle.

I'm going to change them to 'etched' glass with a thin clear border. Same as I've done with the fanlight which now includes the house number, and looks very nice.

But because of the curve the glass place wants a template.

Obviously I can measure the outside wood running round the glass easily - but the rebate is more difficult.

So what is the minimum overlap of the glass behind the wood into the rebate? 3mm? 5mm? (per side) If it is too small I could adjust the position. If too big, more of a problem. It will be laminated glass.

Rather obviously, I don't want to remove the old glass until the new is made.

[Adrian Brentnall]

Hi Dave If the glass is retained by a beading (probably on the inside) you should be able to see where the beading ends and the rebate begins. My usual method for creating templates for 'odd-shaped' (stained-)glass panels is to masking-tape some thinnish paper over the hole, and use a wax crayon rubbed on the paper (a la Brass Rubbing) to pick up the outline of the rebate. If you want to get posh, then go over it afterwards with a Sharpie.

Then mark the template 'shows size of rebate' - and your friendly local glass-merchant should be able to subtract the necessary 3 - 4 mm total (left-right and up/down) to give you some wiggle-room.

If the beading's on the inside, then you could pry that out without dislodging the glass (perhaps!), and then you could see the actual size / edge of the rebate. Tack the beading back in place until the new glass is delivered. Depending on how enthusiastic they were fitting the beading - you may or may not be able to re-use it.

Adrian

[Dave Plowman (News)]

There's no beading as such. Just the original moulding on the outside from when there was a wood panel. The inside appears to be putty. But not easy to get and accurate measurement of the full size including rebate without hacking out the putty. But can measure the size of the glass that shows easily. And it's the clear border which will need to be positioned neatly relative to the moulding/beading.

(Had it been 'square' I'd have used beading on the inside too, rather than just putty)

I've not got much confidence in my glass place - the fanlight is just a rectangle, and that was cut 4mm off square. Which meant hacking into the woodwork to make it fit. But they are convenient.

I'm going to give them a template made from ply - so no question if the glass isn't the same.

Obviously it would be better to remove the glass and make sure the ply templet fits - but the glass will take a few days to be made.

[The Nomad]

Dumb idea but - make two templates and use one to close the hole for the couple of days it takes to make a new glass one?

Avpx

[Dave Plowman (News)]

Think I've missed a bit out. Looking at the way the door was constructed, the panel openings to the inside are a lot bigger to the inside than outside of the door. So to avoid seeing through the glass to the putty on the outside moulding, a wood strip appears to have been added to cover that up - with just a fillet of putty round the outside of it. That wood strip runs up to the original mouldings inside the door. And the top bit is a semi-circle which I've no wish to try and make again - as it is bound to break if I removed it.

But what I dunno until the glass is removed is whether it goes behind this strip of wood.

[Adrian Brentnall]

I was about the say exactly the same thing!

I've done this for people who want stained-glass panels, but also want to install the door or window 'immediately'..

Watch out for the old putty - it tends to set like rock. If it won't hack out easily then the best thing I've found is a 'round' carbide tile-cutter in a Multitool - but the dust is pretty horrible..

Certainly, if you give the glass shop a template then it reduces the potential for them cocking it up! Adrian

[Adrian Brentnall]

Having trouble visualising that... can you post a photo? Adrian

[Brian Gaff]

Assuming the used the beading at all, as a friend of mine found when he tried to remove it, it was hard putty. Brian

[Dave Plowman (News)]

Does no one have a guess as to the minimum the glass needs beyond the edge of the outside beading to be secure? If it helps, the size to the edge of the beading - ie the glass that shows - is 912 x 172mm.

I expect to have some wiggle room to get the border lined up with the beading by eye as best as possible. Since nothing this age is ever perfectly square.

[Andy Burns]

It's been a while since I replaced any puttied glass, I'd guess it was about 8mm

[newshound]

If you warm up old hard putty with a hot air gun or a gas torch, it will soften and become much easier to remove. Even if it is very old.

[Robin]

How about centenarian putty that was not repainted regularly so the linseed oil has buggered off leaving stuff like mortar?

[charles]

but, unless you are very lucky, you'll crack the glass.

[Huge]

I consider this to be unlikely. The linseed oil will either have evaporated or oxidised, and heat is not going to make any difference to that.

[newshound]

I originally thought so too. Except that the linseed oil does *not* evaporate, it hardens by cross-linking.

Try it and you will find that it works. You don't need to get it particularly warm, evidently the linseed oil polymer is a thermoplastic. You don't need to heat it up to decomposition temperatures.

There is of course always a risk of the glass cracking. But in the OP's case, he wanted to *replace* the glass, so cracking would not matter.

[Huge]

Well, knock me down with a kipper. Hopefully, I shall remember this the next time I have to remove some elderly putty.

[Adrian Brentnall]

Well - it's easy enough to guess - for example - 'minimum 1/4 inch /

6mm' - but you've actually got the door-panel there, so you could measure it, rather than you or us guessing

Wiggle-room 'left-to-right' is fine, don't forget that the top-to-bottom wiggle room will need to take account of gravity, as (for simplest installation) the glass will want to sit flat on the bottom of the rebate - so you could argue that you only need half the up/down wiggle room.

Not sure what 'border' it is that you're mentioning?

Unless there's some added complication that we don't know about - wouldn't the simplest solution be to take out the existing glass, and cut two identical plywood templates that are a good fit (with 'wiggle-room' allowance) - temporarily fit one of the templates and get the glass cut to the size of the other? Takes out all the guesswork, doesn't it?

Adrian

[newshound]

This is when you will find you have the wrong sort of putty!

:-)

[Dave Plowman (News)]

Not really - as I explained earlier. The mouldings on the outside of the door are for a smaller opening than those on the inside of the door. Didn't matter when there were wood panels there - but does with glass. As round the edge you'd see through to the putty on the other side.

[Dave Plowman (News)]

I'll certainly give it a try. Removing old putty is always a pain - even when you've broken the glass out.