Sash Windows Glass

Hi all,

We are looking to get our original sash windows repaired and made serviceable again. They seem to all contain the old-style "wobbly" glass which appears to be prohibitively expensive these days. Unfortunately quite a number of the existing panes are cracked and so need replacing.

My question is... is it worth keeping any of the glass which is still intact, or will a mixture of new glass and wobbly glass look strange? Would it therefore be best to replace it all?

Thanks for any advice,
Matt

I'd keep as much old glass as I could.
It gives character to the property.
Most old houses have a mixture of glass.

Remember that the modern glass is likely to be heavier than the old and the sash balance weights will need to be increased in size.

Hi Matt
We have a mixture of both, and you only notice the wobbly when you look closely. I wouldn't rush to replace any glass that you don't have to, but that's just me.

Horticultural grade glass is said to be a passable match, and also available in thinner section.

We have used agricultural glass to replace some damaged (modern) glass in our house - the agricultural glass has distortions and irregularities and so it does, in my opinion, look more appropriate than smooth modern glass in an old house. It isn't quite as charming as the old 'wobbly' glass but it does the trick and is very affordable. Cherish any original glass that you have.

Lime said:

I'd keep as much old glass as I could.
It gives character to the property.
Most old houses have a mixture of glass.

Remember that the modern glass is likely to be heavier than the old and the sash balance weights will need to be increased in size.

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Agree with that. The crown glass gives character and life. Modern float glass make the house look dead, like a face with no eyes. If the old glass has, for instance, a crack in one corner, I'd keep it in preference to new.

The wobbly glass is available from Tatra. Not cheap, but not a lot either compared to the overall cost if you're paying someone to do the work.

Agricultural glass might be OK, but not all of it has flaws, you might be unlucky and get a flat bit.

Glass now is supposed to be a min of 4mm, your glass might be 1/8" (3mm). Nothing wrong with 1/8" glass, depends whether you employ fusspots who insist on keeping to the regs.
If you use heavier glass, as has been said your sash weights need to be heavier. You can get 'makeweights' or use add-ons of lead.
The rule is Pound under Pound over - the weights for the top sashes need to be (cumulatively) a pound heavier than the sash, the weights for the bottom sashes must be a pound lighter.
Glass used to be sold by weight rather than thickness, for this reason.

Ivor

I have original sashes and when I had them restored a couple of years ago some panes had to be replaced with modern glass. I was given the choice of having it all replaced but decided to keep the "wobbly" panes that were OK. I like them. They give even more character to the cotswold stone of the houses built opposite me .

Is agricultural glass made by a different process than modern float glass or is it the case that it's just rejected/'lower quality' float glass?

It reminds me of old carbon resistors, which were normally available with a 5% or 10% tolerance. My understanding is that they were all made by the same process but that, when tested, those that were found to be within 5% of the target number of ohms were labelled as 5% parts (using a gold band as part of the colour code) and those within 10% were labelled as 10% parts (with a silver band).

Even though the production process was identical, the 5% resistors were slightly more expensive. Furthermore, if you bought 10% resistors you could be sure that they were at least 5% in error!

But I don't think anyone uses carbon resistors any more, not in these days of laser-trimmed metal-film resistors. The old stuff is not always the best stuff.

Flyfisher said:

Is agricultural glass made by a different process than modern float glass or is it the case that it's just rejected/'lower quality' float glass?

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Different process. I don't think float gets a lower quality - it's always optically flat. Horticultural glass is probably drawn and rolled - the way all glass used to be before float was invented by Pilkington in 1956. I think we import it from Russia.

Flyfisher said:

Is agricultural glass made by a different process than modern float glass or is it the case that it's just rejected/'lower quality' float glass?

It reminds me of old carbon resistors, which were normally available with a 5% or 10% tolerance. My understanding is that they were all made by the same process but that, when tested, those that were found to be within 5% of the target number of ohms were labelled as 5% parts (using a gold band as part of the colour code) and those within 10% were labelled as 10% parts (with a silver band).

Even though the production process was identical, the 5% resistors were slightly more expensive. Furthermore, if you bought 10% resistors you could be sure that they were at least 5% in error!

But I don't think anyone uses carbon resistors any more, not in these days of laser-trimmed metal-film resistors. The old stuff is not always the best stuff.

Click to expand...

I don't see the logic of that comment at all.

Never mind. Biff's already answered the question.