Misted up Aluminium UPVC PVCU Windows - misty, misted, glass, aluminium, frames, replacement windows, double glazing, double glazing forum, fensa, uk,

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Glass:
Misting in PVC-U & Aluminium frames

Double-glazed sealed units and the premature failure of sealed units in plastic and aluminium frames

Actually, it was a lovely, clear and bright sunny day when I took this picture!

This misted-up sealed unit is in a famous make, the name of which I cannot mention, just in case I get in trouble from a great height, say around the height of a well-known mountain!

Some causes of premature failure of sealed units in PVC-U and aluminium frames (Wooden frames have their own, different problems.) PVC-U and aluminium frames share similar frame arrangements:
•	The double-glazed sealed unit should sit on glazing blocks, not directly on the frame itself, and both panes should be supported equally to prevent ‘slippage’. These glazing blocks should not just be flat frame packers, but should be of the 'bridge' type, which means that water getting past the outer gaskets (as it does) will have a route to escape
•	The bottom of the framework should be drained, either through holes ‘hidden’ from view, where any water runs out on to the sill, or visible ‘face’ drainage.
•	The perimeter of the double-glazing glass should be well ventilated within the framework, as air enters and circulates from the drainage holes.
•	Clip-in beads hold the double-glazed sealed unit in the frame, preventing most water ingress, with a gasket or double-sided tape the other side

Some Variations exists in the above, but these are the common principles. In a year, there are different times in which there will be different amounts of moisture in the atmosphere, and also in hot summer days the atmosphere that we breath has a moisture content humidity. With the 'sealed' unit is subjected to changes in sonic and atmospheric pressure, moisture will be drawn in to mix with the otherwise dry interior of the unit through this breach. As temperature changes the moisture will compress in to liquid and this will go up and up, as the liquid cannot escape anywhere as easily as the moisture that is being drawn in. There are sealed units that have several inches of water lying at the bottom because the unit acts like a tank. Sealed units are not designed to be taken apart again in the future, hence, practically they cannot be cleaned and put back together. Whenever sealed units fails it requires replacements and the old glass is usually thrown away.

The most common causes of premature failure in this type of frame are:
1) Not sealed correctly during manufacture
	If a sealed unit is not fully sealed all the way round or not sealed properly, the unit is likely to fail within a relatively short time, normally within a year or so
2) Not seated correctly on glazing blocks
	It is difficult to be exact about the extent to which this will contribute to premature failure, as each case will vary. Worst case would be if drainage was blocked altogether with even a small amount water getting in, which could reduce the life of a 'good' unit by around 50% in terms of its otherwise fair life expectancy; see below
3) Exterior seals not fitting correctly, letting water in
	Similar to above, but if some of the water getting in contains washing-up liquid or similar, then this will attack and degrade the perimeter seal, usually along the bottom edge. Anything stuck together will come apart more quickly if immersed in water, and even more so if that water contains a solvent or any oil-based contaminants
4) Flexing of the framework
	Very difficult to quantify, but any pressures put upon the sealed unit will not do it any good at all. Installations most at risk are those of the PVC-U frames that go to make up the structure of a conservatory, which should always be fully reinforced to help reduce flexing caused by wind loads.

MOST IMPORTANT:
One of the BIGGEST mistakes a window supplier or the fitter on site can make is to use solid 'flat' packers to sit the glass unit on. All sealed units MUST be sitting on 'bridge' packers, so that any water that gets in will have ready egress through the drainage system of the frame. The use of solid 'flat' packers blocking drainage may well be the biggest single cause of premature sealed-unit failure that we see today.

In old aluminium frames the often-used glazing block had a soft packer, and very often was not fitted properly at 90 degrees to the unit. This proved to be a disaster, as the unit inevitably failed prematurely as a result of the soft glazing packer pressing into the edge seal.

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Glass: Misting in PVC-U & Aluminium frames

Glass:
Misting in PVC-U & Aluminium frames