Stepped double glazing sealed units

[JZMosalski]

I have read about misting problems on double glazing units fitted in wooden frames. Can someone clarify is it the fact that the sealed units come into contact with damp from condensation that causes the misting.

My limited research suggests that the units should be placed on some sort of plastic packing blocks which I assume are designed to allow air to circulate around the units that prevents or at least slows the misting effect.

Also my existing units are bedded in normal putty should a butyl based putty have been used.

In summary can someone explain how the glazed unit can be bedded in putty and at the same time be rested on plastic blocks which prevent the unit form resting on the wooden window frame. Surely by the very fact that putty is used then there cannot be a clear area around the sealed unit which allows air flow. If someone can clarify this situation or better still can point me in the direction of a site which illustrates the process I'd be very grateful.

Regards,

Jan

[masona]

JZMosalski wrote:

I have read about misting problems on double glazing units fitted in wooden frames. Can someone clarify is it the fact that the sealed units come into contact with damp from condensation that causes the misting.

Are you talking about the misting inside the double glazing unit, if so, then the seal has gone so it's cheaper & quicker to renew the unit.

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[The-brickie]

I never use an aggressive type of 'sticky' bedding compound, which by its nature sticks to the glass and the wood.

We all know that wood moves, so what happens is that the sealed unit is actually pulled apart by the movement of the wood, sitting in a non drained rebate doesn't help either.

I tend to use double sided foam, aka security foam at least on one side which will allow for the movement and, as the op said, plastic packers under the unit and if possible some drainage at the bottom.

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