Whether you have had your house newly double glazed, or the units have been in situ for a period of time, the most common problem encountered is misting of individual units.

Misted double glazing replacement is one of the most common problems that Cheltenham Glass and Glazing are called on to rectify. Invariably a factory replacement is called for.

The cause of misting units:

Basically, the seal between the glass and the frame has broken down. Between the two sheets of glass are spacers, top, bottom and sides. These spacers contain a desiccant, which soaks up the miniscule amount of water which will normally permeate through a properly sealed unit.

Small drainage holes are drilled out of sight, which allow small droplets of water out and air circulation between the two panes of glass.

If the seal is damaged or badly fitted, more water seeps in, and the desiccant can’t cope with it. Condensation, the misting you see, then starts to form on the inside of the glass.

Various reasons can cause this ‘blown’ unit. A badly sealed unit; flexing of the unit, especially large units such as conservatory panels, poorly fitted exterior rubber seals, and the unit being incorrectly seated on the glazing blocks are all prime causes.

One of the most common causes is fitters using the wrong type of packers. The use of solid, flat packers, which invariably block the small drainage holes, instead of using bridge packers, which leave space to allow the all important air circulation.

Can the windows be de-misted?

Windows can be demisted. The process requires drilling of the glass, and fitting plastic valves to allow the additional water to drain. It is not considered to be a particularly effective or long term solution, and misted double glazing replacement should be considered. Having the unit stripped and replaced with a new one by Cheltenham Glass and Glazing, although the more expensive option, will be the cheapest long term. Under normal circumstances, correctly sealed double glazed units should have an effective life of 20 years.