Historically we've had a leak from our shower in our bathroom which has leaked into the neighbour below's bathroom and kitchen (this has gone though the bathroom wall to the kitchen which is adjacent). This caused staining on the ceiling and dividing wall of the neighbours kitchen / bathroom.
Was fixed in Feb this year and the neighbour reported no further problems. We decided to wait a long time for everything to dry out - the building is an old 120 year old tenement flat with a large amount of deadening material (soil, rubble, stone, sand) between the floors so a lot of water could be absorbed and need time to dry out.
About mid July this year we had a leak from our kitchen sink into our neighbour kitchen. This found a path through the interfloor material quite quickly so we are not sure how much water was absorbed. I'm told it leaked through the ceiling although I suspect water would have been absorbed everywhere behind the ceiling plaster, including going down the wall against the brickwork. Anyway, leak fixed.
Now neighbour is telling me that they are getting further marks / stains on their walls and wants me to take down my shower and pull up my kitchen floor to investigate. They have been away for three weeks so I am not sure how much of this has suddenly appeared and how much of this happened while they were on holiday.
To make matters worse, I am away from home at the moment and have let my flat out. I won't be back for about 7 weeks without making an unplanned flight home.
I think this might be residual marking as the wall dries out / water comes to the surface - plaster on these walls is about 30-50mm thick, but I'm no expert. I'm not able to actually see any of this other than some photos so it's difficult to tell if this is actually a further leak.
We've contacted a firm who say they can do a thermal image of the wall to show the temperature differences along with actual damp meter readings which will indicate how damp the wall is (cost ~£100).
Anyone have any suggestions? Are stains appearing 2 months after the initial escape likely to be the wall drying out?
Any suggestions on ways to find the leak if there is one?
(sorry for the long explanation and perhaps incorrect keywords - there's no "damp" keyword)