Cracked glazing to patio doors - why have they cracked ?

[oggi998]

I would be most grateful if someone could suggest why the inner pane of glass may have cracked in these two patio doors (in separate adjoining rooms). There is no cracking to the external pane.

My inital concern was that there may be movement in the property but the doors slide open quite easily and there is no external evidence of any movement in the property.

A couple of photos attached showing the cracks.

Many thanks for any clues.

Untitled

• oggi998
• 3 Mar 2011
• 1

Untitled

• oggi998
• 3 Mar 2011
• 1

 

[crank39]

Thermal stress......

http://www.thewindowman.co.uk/explode.htm

 

[Mw Roofline]

Crank i've never seen a toughened unit show lines like that. Should the whole thing have popped?

 

[Richard C]

Crank i've never seen a toughened unit show lines like that. Should the whole thing have popped?

No neither have I; only glass I've seen go like that is laminated but I was not aware anyone used laminated glass on DG; slightly better for security but rather more expensive I would think.

Thermal shock as said; the external glass pane temperature dropped (or rose) far more than the inner one & “pop”; sometimes poor fitting can help it along. Get your wallet out as you probably won’t be covered on insurance unless you tell lies about how it happened!

 

[God]

Does them there look like laminated units to me

 

[crank39]

Crank i've never seen a toughened unit show lines like that. Should the whole thing have popped?

Toughened units obviously are a lot stronger than float and maybe even laminated so would be able to withstand this thermal stress better but if it were to break then you are quite correct, one pane would pop and shatter and if your really unlucky would fall to the ground and give you months upon months of finding shards in your feet

 

[keveljay]

Unless i'm mistaken these look like Magnet or John Carr sliders circa 1986 ~ 1993, in which case theyve done well to last this long. Doubt laminated was used at the original installation, but may have been retrofitted. The thing about the toughening process is you never will know whether a broken pane will shatter or shard - its impossible to tell. All your knowledge and instincts tell you tough should shatter, but, and i've had it once, a kitemarked unit (both leaves) was dropped and one side shattered and the other sharded not from a sh**te manufacturer either

 

[crank39]

Unless i'm mistaken these look like Magnet or John Carr sliders circa 1986 ~ 1993, in which case theyve done well to last this long. Doubt laminated was used at the original installation, but may have been retrofitted. The thing about the toughening process is you never will know whether a broken pane will shatter or shard - its impossible to tell. All your knowledge and instincts tell you tough should shatter, but, and i've had it once, a kitemarked unit (both leaves) was dropped and one side shattered and the other sharded not from a sh**te manufacturer either

When you say sharded do you mean it broke into long lengths like 6" long? If so then its s*** quality toughening, likely cause is it wasn't cooled quickly enough at the end of the heat cycle and its normally european toughened that does it, stuff you find in old wooden John Carr/Boulton & Paul patios.

As for the patio in the pics then lets have a cyber bet, looking at the style of the handle and the threshold strip i reckon its a Monarch. There should be an 'M' on the barrel and the locking strip if it is.