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Toughened glass - a few thoughts

Does what it says on the tin
bungeejumper
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Toughened glass - a few thoughts

#402007

Postby bungeejumper » April 6th, 2021, 1:16 pm

Bit of a shock the other day to find that a large pane of toughened (tempered) glass on our greenhouse had turned itself into a pile of granulated sugar without any obvious reason. Nice sunny day, no violent winds, no obvious missiles chucked over the wall, and no feathers that might have indicated a bird strike. Indeed, what was also interesting was that 99.99% of the broken glass had landed outside the greenhouse, not inside it. :|

A quick Google dispensed with the bird strike theory. Apparently toughened glass is six to eight times more impact-resistant than normal window glass. And the usual cause for (non-impact) shattering is either that the glass has become tight in its frame, or that there was some tiny scratch or nick in one of the edges when the glass was first delivered. I'm pretty sure that there were no tensions in the frame, because the glass was foam-cushioned all the way, and clipped in with plastic strip mountings, not metal.

But I digress. (What's new?) When I went looking for replacement glass, neither the greenhouse supplier nor any other g/h outfit wanted to even quote for a replacement panel. Everywhere I looked, it was "out of stock" or "not currently offering toughened glass", and the leading local supplier would have wanted £60 plus £40 delivery for a single five foot sheet. Apparently, you don't cut toughened glass to size - you cut standard glass and then toughen it afterwards. Which can take weeks to arrange. I hadn't thought of that.

It also explained why the big outfits need to charge so much. They subcontract the job out to a specialist and then double the number they first thought of. :lol:

To cut a long story short, I eventually tracked down a local toughened glass outfit who weren't going to charge me silly money. £22 including VAT for a 1500 x 610mm pane (60 x 24 inches) in a 4mm thickness, but I have to collect it myself. (Not a problem in the estate car.) Would have been thirty quid if I'd wanted the Pilkington Optiwhite (ultra-clear), but heck, this was a greenhouse. :lol:

The downside, it still takes ten days. Will report back on how it goes. :)

BJ

BJ

pompeygazza
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Re: Toughened glass - a few thoughts

#402049

Postby pompeygazza » April 6th, 2021, 2:48 pm

could you not have replaced it with perspex?

bungeejumper
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Re: Toughened glass - a few thoughts

#402056

Postby bungeejumper » April 6th, 2021, 3:13 pm

pompeygazza wrote:could you not have replaced it with perspex?

Certainly, at greater cost! But would I want glass, glass, glass, perspex, glass on my greenhouse? Prolly not. ;)

BJ

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Re: Toughened glass - a few thoughts

#402059

Postby mike » April 6th, 2021, 3:40 pm

Just out of interest as it is now too late, but is there any reason you went for toughened as opposed to laminated ?

Laminated will stay in place when cracked, doesn't end up like confetti, and you can buy pieces cut to size, rather than cut to size and then treat.

bungeejumper
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Re: Toughened glass - a few thoughts

#402061

Postby bungeejumper » April 6th, 2021, 3:52 pm

mike wrote:Laminated will stay in place when cracked, doesn't end up like confetti, and you can buy pieces cut to size, rather than cut to size and then treat.

I haven't looked into it, TBH, but I believe laminated is a fair bit thicker than toughened? And if so it would presumably need a different kind of fixing strips to mount it into the frames. As with perspex, there's a disadvantage to doing just one pane with something different from all the others. But thanks for the thought.

BJ

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Re: Toughened glass - a few thoughts

#402082

Postby tjh290633 » April 6th, 2021, 4:43 pm

The source of the fracture would be interesting, but probably impossible to locate. To break a toughened pane of glass you need a point inpact, or a high stress on the edge somewhere. I have seen one or two where the origin was at the frame edge, due to something in the groove exerting pressure on the glass at one point. With a greenhouse, slight movement of the frame due to thermal effects or wind pressure could be the cause.

Before you insert the new pane, make a very close examination of the frame to ensure nothing is there which might exert a point load on the new pane.

TJH

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Re: Toughened glass - a few thoughts

#402107

Postby Stompa » April 6th, 2021, 6:14 pm

bungeejumper wrote:Bit of a shock the other day to find that a large pane of toughened (tempered) glass on our greenhouse had turned itself into a pile of granulated sugar without any obvious reason.

Presumably nobody had recently been mowing a lawn nearby?

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Re: Toughened glass - a few thoughts

#402284

Postby fisher » April 7th, 2021, 1:01 pm

There can a delay between the impact occuring and the toughened glass shattering. A few years ago I heard a very strange noise coming from my en suite bathroom. It turned out the shower door had completely shattered - it was fitted years earlier. Nobody had been in that room for hours. A week or so before I had a plumber round doing work in that room. The door into the en suite opened towards the shower door and the door handle could hit it if the door was pushed far enough open. We were always careful but my theory is that the plumber may have pushed it open hard when carrying a radiator, the handle probably struck the shower door causing a weakness which took a week to take full effect.

There is now a door stop to prevent the same happening again.

So, your greenhouse pane may have been hit some days before it collapsed.

Dod101
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Re: Toughened glass - a few thoughts

#402289

Postby Dod101 » April 7th, 2021, 1:13 pm

I think I would probably have just used ordinary glass.

Dod

bungeejumper
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Re: Toughened glass - a few thoughts

#402296

Postby bungeejumper » April 7th, 2021, 1:38 pm

fisher wrote:There can a delay between the impact occuring and the toughened glass shattering. A few years ago I heard a very strange noise coming from my en suite bathroom. It turned out the shower door had completely shattered - it was fitted years earlier. Nobody had been in that room for hours.

Aye, it's weird stuff. I once had a toughened glass windscreen go while doing seventy up a dual carriageway in Kent. I saw the stone that pinged off the lorry in front of me, and then came the bang and the first split. Followed about twenty seconds later by the second crack, and then the first proper spider's web started to develop quite slowly after another thirty seconds.

All in all, it took fully ten minutes for the screen to craze up completely. Result, I was able to drive on for nearly a mile until I came to a suitable layby. With a telephone box! Result! :lol:

BJ

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Re: Toughened glass - a few thoughts

#402533

Postby sg31 » April 8th, 2021, 10:08 am

Dod101 wrote:I think I would probably have just used ordinary glass.

Dod


If it is situated at low level it must be safety glass. All glass within 800mm of the ground and within 300mm of a door (from memory). That's according to building regs. I'm not sure building regs apply to greenhouses but it would be sensible to stick to the rules purely for safety reasons.

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Re: Toughened glass - a few thoughts

#402555

Postby bungeejumper » April 8th, 2021, 11:12 am

sg31 wrote:All glass within 800mm of the ground and within 300mm of a door (from memory). That's according to building regs. I'm not sure building regs apply to greenhouses but it would be sensible to stick to the rules purely for safety reasons.

I'm still seeing greenhouses being advertised with standard glass, so I suppose it must still be legal. But the more modern designs feature a 5 foot glass side panel, which is both more attractive and more stable if a single piece of strong glass is used than two smaller pieces of standard glass. (I don't know why they don't use a 5 foot sheet of standard glass, but I assume it's because it isn't rigid enough?)

But all that's by the by. When my granddaughter hurtles up the path on her bike, I'm glad that it's toughened safety glass in the greenhouse. :)

Incidentally, I forgot to say. my trusty wet and dry vacuum cleaner made short work of my mountain of shattered glass. As used by windscreen repairers the world over.

BJ

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Re: Toughened glass - a few thoughts

#402559

Postby Dod101 » April 8th, 2021, 11:15 am

sg31 wrote:
Dod101 wrote:I think I would probably have just used ordinary glass.

Dod


If it is situated at low level it must be safety glass. All glass within 800mm of the ground and within 300mm of a door (from memory). That's according to building regs. I'm not sure building regs apply to greenhouses but it would be sensible to stick to the rules purely for safety reasons.


I understand for houses and so on but it is a long time since I had a greenhouse. When I did I simply used ordinary glass.

So called safety glass, I assume the stuff that shatters into a thousand pieces, seems to be what is used in say showers. It is actually anything but safe. My wife was in the shower one evening and slipped and fell onto the glass wall of the shower which shattered and caused her to look as if she had shrapnel wounds. Safer no doubt than had it been ordinary glass but not very safe. In fact the shower was a so called walk in shower with no door and very little support but that is another story.

Dod


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