What’s causing this damp?!

[Holls81]

We have a real head scratcher.

There’s a small patch of paint that peels off in the top corner of our chimney breast. (Original patch was a couple of cm.)
(downstairs in the lounge.)

I sanded the paint round the area right back to where it stops flaking off.

The plaster underneath looks darker and the metal beading down the edge is rusty in a small patch.

Now, we asked a roofer to check the flashing and he said that if it was a problem with the flashing then the problem would also be evident upstairs (which it doesn’t seem to be.)
Structural engineer came out for something else and while he was here I asked his opinion. He too had no idea other than that it could possible be a flashing issue.

We’ve had a lot of rain over the past couple of weeks and the patch doesn’t seem to have changed (ie looking wetter or drier.)

when I sanded the area, down the side in a small gap in between the cupboard and the side of the chimney breast, some wall paper came off which seemed a little damp but not mouldy. (This is not a cavity wall)

Is it possible that condensation could be causing it where the air can’t get in to the little gap and the wet wall paper, that has seemingly always been in there (we’ve lived here 10 years and haven’t ever had wallpaper) might have been holding the water and not allowing the plaster around it to dry?

I’ve heard @pigletjohn might be able
to shed some light?!

not sure what else to try!

*I should also add that the dark patch on the plaster is my greasy finger print from the other day 😫

@PigletJohn also, any thoughts on how to ventilate it? Do you have to ventilate the used flue as well as the unused one please?

If that wall the meter is on is external, then I would say moisture is coming through from outside somehow , ( penetrating) ?

I wonder where the meter is.

And the supply cable.

We have not seen the outside yet.

Still not back for external pic.

meter is on external wall. There is a fairly large cable that comes through the wall to the meter but it’s the other side of the meter (not near the fireplace or chimney breast) and the wall behind meter seems bone dry

Does the cable go down to the hole, or up to it?

Up

On the outside, I mean?

Yes. Up, on the outside

**I wouldn't rule out the flashing, just because the damp doesn't appear upstairs.

You can maybe rule out the flashing by inspecting it. If it's been done with cement, expect it to let water in eventually.

Oh really. That’s interesting too. Do you think it’s possible to only see signs downstairs*

Water can get onto the inside of your outer wall stones or bricks and run down (and across a bit too) before finding something it can cross onto your lath and plaster. At lower levels, there are more buildups of plaster and mortar droppings that can bridge the air space.

If your wall is plastered on the hard stone or brick, ignore the above.

Have you tried a damp meter on the other side of the chimney breast? It may all be getting slightly damp, but the cupboard very close beside is stopping the damp just evaporating into the room at that point. How does the electricity cable get into the cupboard could that be causing a water path?