What type of damp is this?

[Christmascookiesmmmm]

I thiiiink this has been here a few weeks/months and I’ve mistaken it for shadows in the past 🤦‍♀️ Only noticed that it was actual damp last week.. it’s on either side of French door/window (which we’ve never actually opened since moving in last December as we don’t have the key.. we’ve put a dehumidifier in, thinking it’s probably condensation due to the room not being very ventilated.. no damp came up on our homebuyers survey however they did say the outdoor patio is too high meaning there’s no space for an airbrick (we haven’t rectified this yet so maybe we should..)
The damp patches don’t seem any smaller than last week despite having dehumidifier on 24/7- don’t suppose it could be something more sinister? Or does it just take a while to dry out with condensation ?

Paint isn’t peeling or anything (painted walls last October, masking tape is because I finally got round to doing wood now!)

Cant see anything. Where is the damp

Thanks so much for reply! Sorry it’s really hard to photograph , the photo is pretty dark anyway but the damp is where it’s just a bit darker

You may need to describe where the damp is. Up high, down low. Damp comes from somewhere. Could be condensation. But would have thought the dehumidifier would have sorted that. Try and find out where the damp would be coming from. Sort that and problem solved.

I think I can see a darker patch on the dark patch! Is that an outside wall, have you looked to see if the brickwork is ok, nothing getting in there. Does that patch actually feel damp when you touch it, has it been raining?

Thanks both! It’s an exterior wall yes, and it wasn’t raining particularly bad last week... it’s on either side of the Patio doors.. it seems to be worse at the bottom on one side but not the other.. I’ll try and do a diagram later to better explain! Thanks again for help!

I wonder if its the seal and frames around the patio doors. Are they new. Is it brickwork outside. Have you checked the mortar.

If the patio is too high that will suck up water due to the high ground level and cause a problem like this. I had similar patches of damp on a wall at a low level above the skirting board, I looked outside and saw the ground level was quite high...luckily it was only earth on a driveway verge and I was able to dig it up and lower the level easily. It too some time but the damp went away. Not sure how you would achieve this with the patio however.

It makes you think - was this section painted black to deliberately disguise this!? I have another wee patch of similar looking damp but it's on an internal wall and no way can I get access to see what is happening underneath. That said it doesn't cause any problems, is very stable and not spreading so I've just left it.