Toughened glass - a few thoughts
Posted: 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.
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.
The downside, it still takes ten days. Will report back on how it goes.
BJ
BJ
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.
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.
The downside, it still takes ten days. Will report back on how it goes.
BJ
BJ