Mould problem

[NT]

Hi

What do you reckon the cause of this mouldy damp patch is?

rest of the room is perfectly dry. Its a bedroom, and the window gets left open right by the damp patch. The window itself is also mouldy, but the wooden cill between the 2 mouldy thing in the picture is totally free of it.

If it were due to rain splash, I'd expect a) the window frame and cill would be affected. Yet neither is b) the window itself would not be affected, yet it is, equally badly.

I've checked outside, and no visible source of water.

NT

[John Rumm]

What is the wall construction? Is it insulated?

[Dave]

I can't make out what the widow frame is made of, but my initial thoughts were that the window is chilling the wall just underneath and the damp is caused by condensation on the wall. No water ingress at all, in my oppinion.

Dave

[The Natural Philosopher]

Yep. Thats my take too.

Cavity wall, but bridged under the window hence cold. Frames also cold= mould. But cill is not conductive, so a bit warmer.

Another possibility is plant pots on the cill at some time.

[Rod]

I wondered whether there is just space under the cill - allowing cold air onto the back of the plaster(-board?) wall?

[The Medway Handyman]

And mine. Classic condensation scenario.

[Phil L]

My money's on the exterior cill being sandstone, which is one solid block about 12 inches wide and 6 inches thick, to cover two complete courses of brick in height and to cover the entire thickness of the wall plus a few inches overhang. This is plastered inside, but instead of using render, they have used browning or bonding, neither of which is suitable for this application.

To the OP; stick a screwdriver or similar in the wall where it's mouldy - if it's like damp chalk, you'll need to take it off where the sandstone cill is, allow to dry for a week or two, then render and skim.

As far as the rest of your post goes WRT the frame being mouldy, I can't understand it, you say the window itself is mouldy, then a second later say that neither the cill nor the window are mouldy.

[NT]

The wall is 9" brick & plaster, no insulation. Whether it has a cavity is currently unknown. The window sash, window frame and interior cill are timber. The exterior cill is concrete. I'm reasonably confident there havent been any plants there.

Rod wrote:

Fraid I don't understand what you mean there. There's no PB and no gap that shouldnt exist.

Phil L wrote:

spot on, though concrete.

I believe the interior plastering, bar the final layer, is cement mortar, for some reason.

Its solid, no deterioration.

Window is very mouldy, frame is clean, cill is clean, then the wall is very mouldy.

I have to agree its condensation, but not sure the best way to tackle the problem yet.

NT