Misted glass (broken down sealed units) These pictures show the results of having broken down sealed units. The sealed unit is the two panes of glass sealed together before going into the window. Normally there should be water drainage slots underneath the sealed units within the frame. If water gets into the frame and can’t drain away then the sealed unit ends up sitting in water and this eventually breaks down the seal. The water then gets between the two panes of glass and the only practical way to remedy this is to have a new sealed unit made. In my experience, in almost every case either bad drainage or the way the sealed unit was put in originally leads to them failing: they don’t usually just go for no reason. Where the glass is beaded externally it is quite common for the bead to be blocking the drainage slots. The units also need to sit on packers. This gives them a gap underneath where any water can drain away without touching the seal. A common reason for excessive water getting into the frames is shrinkage of the rubber gaskets around the glass. The bad news is that if you get one or two misted windows and this is due to bad frames or bad fitting, then it is very likely that others will eventually go as well. The good news is that replacing the glass is a lot cheaper than new windows and if done properly they shouldn’t go again.People sometimes ask if we can just ‘suck the water out’ or ‘split the unit, clean the glass and re-seal it’. The answer to the first is simple – no we can’t suck the water out. The units could, in theory, be split apart and the glass cleaned and re-sealed. The problems with this are: the possibility of the glass breaking, they would have to be taken away and sealed in a factory so the window would have to be boarded up in the meantime, it would be a lot more time consuming and mean two visits and therefore would be more expensive than just having a new one made in the first place. On very rare occasions we have done this but only when there has been a design or a glass pattern that cannot be matched.When we replace sealed units we don’t just take the old one out and put the new one in as the new one would just mist up for the same reasons. We identify the problem and make necessary repairs before inserting the new glass. The drainage is inspected and new or wider slots drilled, the bead has channels cut into it (underneath and not seen when re-fitted) the glass is correctly sat down on glazing blocks and new gaskets supplied and fitted if required. (All of this is done as standard and is included in our original fixed quote.)We also issue a new guarantee on our sealed units against them misting up.