Double glazing - why do some windows look 'wobbly'?

[Mosaic]

I've noticed over the years and being a nosey sort that some double glazed windows look wobbly - the glass, that is, looks almost jelly-like. Reflections are distorted and, well, wobbly. Can anyone explain why this is?

[tonyav]

Glass is probably slightly convex or concave I think.

[Mosaic]

But...won't that lead to it breaking? like, if a strong wind caught it?

[tonyav]

I wouldn't think so, not a sealed unit.

[The Builder]

This should never occur with modern "float" glass. Molten glass is "floated" on a bed of liquid, so it should be perfectly flat and uniform. It sounds as though lower quality glass has been used.

[hc4361]

I've noticed it a lot in modern double glazed units.

[Mosaic]

Coo! That would be a really carp advert for a double glazing firm then .....

So, given that Pilkington's is churning out float glass a a gazillion miles a minute where on earth are they getting inferior not-float-glass from?

[tonyav]

Cheap stuff from abroad, i would say Mosaic.

[ChuckFickens]

<waits for the inevitable glass is a liquid urban myth to raise it's head>

[tonyav]

Glass is a liquid, chuck ?

[douglas9401]

You had to ask.

[tonyav]

Afraid so, douglas lol.

[Mosaic]

If glass was a liquid then it would be served in a glass, surely, not loaded onto trucks.

[bazwillrun]

If the floor to the bottom of the glass is 300mm or less then a particular BS standard of toughened glass has to be used. Over 300mm then standard strength.

this warping is a product of the manafacturing process, rolling and heating and cannot be eliminated. some batches will have more and some less warping

I had a major to do with a double glazing firm over this exact problem a year ago.
I had a house re-glazed and it looked awful from the outside and when I called them they told me about all the regs, 300mm etc etc.

I then called Pilkington who maufactured the glass and spoke to their technical dept who confirmed all that the DG firm had said and more.

Anyway I wasnt happy about it so re-measured and made it 305mm, the DG firm sent their bloke around to remeasure and he had to agree it was 305mm, so they took out the panes and replaced them with another type of toughened glass that didnt have the warping effect, but from outside it does appear as if it has a slight dark tint to it, so you cant have everything.

[Graham-W]

You couldn't serve it in a glass. It's a liquid.
If the units are under partial vacuum, to increase their effectiveness, this would cause them to be slightly concave, hence the distorion.

[Mosaic]

Thanks Baz - you sound as persistent as me.

[marden40]

sorry to be a little off topic here.....but Baz's information on the regs is slightly wrong.........

in line with Building regs BS 6262 part 4 (1994)

Any glazing or part of that glazing, which is between the finished floor level and a height of 800mm above the floor level, is in a 'critical location'. (This includes any glass that can slide, tilt or move into the ‘critical location’)

Any glazing or part of that glazing, which is within 300mm of either side of a door edge and which is between the finished floor level and a height of 1500mm above the floor level, is in a 'critical location'.

glass in a 'critical location' must be safety glass

[bazwillrun]

I couldnt remember all the regs, i just recall roughly the 300mm and the floor bit and that i knew I was within the measurements required in the areas that had the problem with "warped" glass.

anyway, I have nice flat looking glass, thats all i was bothered about