Glazing distortion

Postby andypandy » Mon Jan 28, 2008 3:57 pm

I have seen many double glazing installations with distorted reflections. This seems very commonplace, but rather odd. Does anyone know what causes this? is it a fault in the manufacturering process?
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Postby GrahamBennett » Fri Feb 01, 2008 11:33 am

I don't think so. I think it's an artifact of the two panes of glass being in close proximity, causing two slightly different reflections.
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Postby andypandy » Fri Feb 08, 2008 4:42 pm

Thanks for your post, but why doesn't all double glazing have wonky reflections if its to do with using two panes of glass so close? I currently have double glazing and my glass is not like it and I want to make sure any replacements match.
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Postby roger196 » Sun Feb 10, 2008 8:16 pm

A long time since i did physics, but the explanation goes something like this.
You get a reflection off both the front and back surface of a pane of glass. Part of the light which falls on the front face of the glass is reflected and part passes thru. The light which passes thru is then refracted ( bent) and the reaches the rear face. Again part is reflected and part passes thru. With double glazing this process is then repeated. In total there are four reflected beams of light which have taken slightly different paths. Hence the distortion. The distortion will be worse if float glass is not used. This is near flat as you can get.
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Postby xjr328 » Mon Feb 11, 2008 8:40 pm

Glass distortion:
Negative distortion is caused in double glazed units due to low temperatures. a sealed unit is not pressure equalised and is reacting to temperature changes. In cold weather the unit will have negative deflection and will distort any reflections, the same unit on a hot day will have positve deflection. units can now be pressure equalised by the fitting of a patented valve system.
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Postby andypandy » Wed Feb 20, 2008 5:12 pm

Patented valve system - sounds good and makes sense. I will mention this when speaking to the double glazing company.

Speaking to a glazing company recently they mentioned it could be the amount of dessicant used in the manufacturing process, as this should be measured out to in relation to the size of glazing unit being made. Never heard of this before, but I will go back to them to discuss about the possibility of a patented valve system to see what reaction I get.

Thanks for your help
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Postby rj » Tue Mar 11, 2008 11:45 pm

[quote]Glass distortion:
Negative distortion is caused in double glazed units due to low temperatures. a sealed unit is not pressure equalised and is reacting to temperature changes. In cold weather the unit will have negative deflection and will distort any reflections, the same unit on a hot day will have positve deflection.[/quote]

this is spot on but what i wold like to know is where can i get [quote]patented valve system[/quote]
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Postby andypandy » Fri May 09, 2008 3:01 pm

I understand do the patented valve system, which is mentioned above. I am not sure if this will cure the disorted reflection problem, but is meant to clear misty double glazing units.
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Postby andypandy » Tue May 27, 2008 2:52 pm

I have been trying without any sucess to try and establish why we get wonky reflections on some double glazing units. I fully understand that all double glazed windows will have double reflections, because of the two panes of glass used. But not why some have wonky double reflections and others smooth double reflections? I have been told by a glazing manufacturer that this affect is normally caused by the use of toughened glass, as this process does distort the glass somewhat and the effect is made much worse if the windows are large or if any other coating has been applied, say self cleaning coatings etc.

However I cannot believe that the hundreds of houses with wonky reflections all have toughened or coated glass. I have recently purchased some replacement windows, specifically stating that I did not want wonky double reflections from the windows, but this is precisely what I have got. This does not match in with the existing double glazed windows in the house, dispite being the same frames with small glazed panes to match etc. It makes my new horribly expensive windows look awful, cheap and nasty. The glazing will have to be ripped out.

Cost is not an issue and I just want to buy double glazing with smooth double reflections. All the glass manufacturers I have spoken to indicate that no wonky reflections should exist, if the window manufacturer has done their job correctly. All the double glazing companies I have spoken to seem to be in denial about this subject or are very touchy about it, stating that it is impossible to get away from. This cannot be the case or my existing windows would give the same problem and all new houses would have this effect, but they don't.

I cannot source new windows from the previous company I used, as they have gone out of business. Is there anyone out there with any ideas or suggestions on how I can get round this problem?
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Postby andypandy » Tue Dec 09, 2008 4:03 pm

I am still no further forward in trying to resolve the problem. I was advised to use a laminated double glazed unit, as this should be flatter. No so. The units arrived and they are worse than anything else we had before. The reflections look crazy. When you sit down in the evening to watch the TV the windows appear like mirrors when it gets dark (no street lights) and the reflections of whatever is in the room is weird. My internal door reflection appears concave and the reflection of the window on the opposite side of the room is duplicated but at roughly 30degree angles (prism effect). It looks like a crazy hall of mirrors at night. In the daylight looking out through the windows is fine, but looking outside in, the reflections are weird, weird, weird. The glass just looks wonky.
Someone must still make conventional, ordinary, flat double glazing.
Anyone out there with any suggestions?
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Postby daveo138 » Tue May 19, 2009 2:01 pm


Have you made any progress yet?

I had some DG fitted about 7 months ago and have bad distortion on most of the units.

The supplier initially agreed that there was an issue and offered to replace it. After changing two units and not improving matters, they are now saying there is nothing wrong with them.

The worst thing is, out of all of the units fitted, only one of them gives a perfect reflection. They are now saying that this one must be faulty!
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Postby xjr328 » Thu Aug 13, 2009 10:26 pm

Pressure equalisation of sealed units is a achieved by drilling into the units either through the glass or through the spacer bar, the holes are then screened using a micro screen that allows air to enter the unit and filter out water droplets and dust etc, to understabd why a sealed unit distorts is very simple, the air molocules trapped between the two panes of glass react to temperature changes (atmospheric pressure (AP)), the air molocules vibrate on a hot day and rise this causes the pressure inside the unit to rise and the glass unit will start to swell in the centre causing the visual distortion. the opposite happens in cold weather when the air molocules cool down and shrink causing the centre of the unit to pull inward.
Pressure equalising the unit stops this thermal pumping, thermal pumping is the main reason all sealed units fail, it is this constant expansion and contraction of the glass that causes the primary and secondary seals on IGU's (Insulated Glass Units) to fail, so you would have thought that is it then a simple solution to a massive problem, not so. what you have now done is allowed the unit to draw air in instead of going into negative deflection, the air that is entering the unit will contain moisture, the air passing through the unit will not condensate untill the AP changes and the Dew Point is achieved at this stage the moisture in the air passing through the unit (Vapour) will condense on the glass at the top of the unit and begin to run down the glass and build up in the bottom spacer bar, the following day when the temperature rises the water trapped in the bottom spacer bar turns to vapour and the cycles starts all over again. the only difference is that if the air passing through the unit and has a low moisture level (Low humidity) the unit appears to have been cured, unfortunatley this is only a temporary repair and will not prevent the unit condensating in high humidity areas and times of the year(Spring).
There is a solution to the problem Crystal Clear Window Works Uk and its network of dealers not only pressure equalise the units they also apply a Super-hydrophilic coating to the unit that prevents the moisture in the air passing through the unit showing up as fog or consensation on the glass, similar coating are used on mirrors in bathrooms to prevent them from steaming up whilst taking a shower etc.
The long term problem of sealed unit failure by the application of the patented coating is changing the double glazing industry.

However be aware of individuals and companies offering to remove the moisture by simply installing valves or sieves IT DOES NOT WORK and can not work, a very basic understanding of the physics inside the unit and understanding dew points, moisture vapour and atmospheric pressure
affecting the unit is all that is needed to discredit these individuals.

The savings made from having the units re-engineered is massive and the enviromental savings made are impressive reducing landfill waste and carbon footprints. is the website to check out.
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Postby daveo138 » Sun Sep 06, 2009 10:52 am

All very interesting, but that doesn't explain why some units are distorted and others are perfect.
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Postby Jays Diamond » Fri Oct 09, 2009 11:53 am

I've had the same problem. I had some glazed unit fitted earlier this year with 6mm exterior/4mm interior glass and the reflections were fine. A builder fitted some new glazed units to an extension a couple of months ago and we ended up with distorted units - the units looked as if the air had been drawn out of the middle of the units. I checked with the original supplier and he informed me that the 6mm exterior glass will have helped with his units but that there are two manufacturing methods used for manufacturing glazed panels:
1. Hot Melt: Glazed units are assembled horizontally on a bench, the hot bonding agent/sealing material is applied in a continuous bead around the outside of the unit. The weight of the glass and the cooling of the air inside the unit following the manufacturing process leads to a partial vacuum/lower pressures inside the glazed unit.
2. Cold Cure: Glazed units are assembled on a bench with a cold curing sealing agent around all but the last 10mm of the unit. The unit is then lifted onto a 'toaster rack' to stop any effects from the weight of the top pane of glass. The last 10mm is then sealed. A company called System 3 Ltd in Manchester utilise this method and I think this process is covered by a British Standard.
Jays Diamond
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