damp & mould on plaster around windows

[Robbox]

Old stone house, timber windows (fitted around 2001).

The windows were all fitted with minimal recess into the stone facings. There is a membrane around the perimeter of the windows and the gap between the timber and the wall has been rendered in (the edge of the membrane is visible). Someone has also put a clear silicone seal over the membrane edge.

So on most of the windows there is mould and damp appearing in the bottom corners on the plaster. Some condensation does appear on the inside on the d/g units, when it's cold outside. No condensation in the airgaps though.

Could it be a failure of the membrane/seal or just plain simple internal condensation? I did wonder if wind and rain could force moisture past any barriers.

 

[foxhole]

Bottom corner of window tends to indicate condensation due to lack of adequate ventilation, does not rule out penetrating damp though.

 

[^woody^]

This is an area prone to condensation mould or even water penetration

Water penetration would tend to have a lot of staining and be worse after rain, so aas you have mould it most likely condensation related and ventialtion will not help in these corners

If you wipe the condensation water up regularly as it appears then that should deal with the mould. But you may need to sanitise the plaster with a fungicide first

Or line the reveals with some thin polystrene and re-plasterboard

 

[Robbox]

I think now it may be lack of ventilation, now. Since there is little sign of staining.
The plaster in the reveals does need a re-finish, so maybe the polystyrene/plaster board trick can be employed.
Have to say that's a new one on me and not something I would have thought of immediately.

 

[HERTS P&D]

Do a test. Dry up the moisture and then leave the top window open over night. But close the room door. (saves the rest of the house getting cold)

Andy

 

[Robbox]

If I decide to replace the windows in the future, what would be the best way to counteract the condensation and also make water penetration less of a problem. The side of the house is very exposed to wind and rain, there is evidence of past water ingress....

I wonder how difficult it would be to cut a reveal into the stonework and sit the frame behind that, sealed on the outside and foamed in place. The walls are 500mm thick. Would creating a reveal make a better weatherproof job? I also imagine that the further back the frame sits into the wall, will make the frame and finish less prone to weathering.