strange damp problem

[dazwalsh]

In one of my rentals I have a bedroom wall which has some strange damp patches on it, a photo will show it best.



Its a solid block single skin internal wall with no pipes or anything near it. Roof is in good nick. And no other damp in the whole house.

Any ideas?

For reference the biggest patch is about the size of a large dinner plate.

[dazwalsh]

HootersGsy said:

What's on the outside wall?

The landing.

[dazwalsh]

Defcon5 said:

Could it be something spilt on the wall that isn't drying out? Massage oil/lube or something.

Yes it was being used as a brothel, if you were wondering

You could be on to something there, tenant had a real knobhead child who I just wanted to slap, might have sprayed wd40 on the wall or something.