Misted Double Glazing

Can misted double glazing units be repaired?

Double glazing is a great way to make your home more energy efficient, and modern frames can look attractive as well as keeping draughts out and heat in. Everyone has seen misted double glazed windows that are covered with foggy condensation between the two panes of glass; this is not only unattractive but will make your windows less efficient. So, is there anything you can do to repair misted double glazing?

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Why do double glazing units get misted up?

Double glazing units are made up of two panes of glass with an air gap in between them. They work because air is very bad at conducting heat compared to glass, and so the gap between the panes stops the heat in your home simply being passed across a pane of glass to the outside. The misting occurs when water gets into the sealed gap and causes condensation because of the difference in temperature of the panes of glass on either side of it.

What causes misted double glazing?

The root cause of your misted double glazing is that the seal between the panes of glass is compromised which can be caused by a few things

  • The drainage around the window is not sufficient; well-fitted windows will have a good drainage system that lets any water that gathers around the frame, particularly at the bottom, drain away easily. If the bottom edge of the double glazing unit is sitting in a pool of water the seal will be damaged quickly, even more so if the water has cleaning fluids in it
  • The window frame is flexing and putting pressure on the seal around the glass unit; this could be due to weather conditions or changes in temperature depending on the type of frames that are used
  • The seal was faulty when the unit left the manufacturer, and this is only becoming evident once water has got in.

Misted Double Glazing

Can a misted double glazing unit be repaired?

There is actually some debate about this, with some sources saying that the only fix is to replace the whole double glazing unit with a new one that has an intact seal, but this is obviously an expensive option, and there are some other suggestions out there.

The first thing to do is contact the original installer or manufacturer; if your windows are under warranty then they should be replaced as misting is a clear sign that the unit is either defective or not properly installed. If the installer suggests a fix it is up to you whether to let them try this, but make sure they will replace the units if the fix does not work.

If your misted double glazing windows are out of warranty, then there are tradespeople that offer to fix them for you, as well as ‘how to’ guides online that will tell you how to fix them yourself. The basic method in both cases is to drill a small hole in the unit, suck out the water, add a desiccant to absorb any further leaks, and then reseal the unit. There are obvious issues with this; drilling a hole in a glazing unit will affect its structure, and you have to be very careful that the whole thing is properly sealed afterwards. It is also important to find the original source of the problem or the condensation will just return.

Prevention is always better than cure, so make sure that your window is properly installed and certified, then take care of them, especially if they are wooden frames. There are reports of misted up double glazing being successfully repaired, just be aware that if you choose this option it takes a certain level of skill to do it yourself, and even if you do get someone in to do it for you, you may still have to replace the units in the end.

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