Damp on internal stair wall

[Kennyb2013]

I'm currently renovating a 1920s house. I was aware that there was damp on an internal wall adjacent to the stairs, as there was a leak in what was the bathroom, which backs on to the stairs. My builder assured me that the damp would go once the walls dried out.

The wall has since been replastered and the heating has been on. It did appear to dry out but the damp has returned, now that the heating has been off for a week or so. The photos show the stairs before and after, with the damp remaining. The damp also shows in the lounge which can also be seen in one of the photos next to the socket. The old bathroom can also be seen after it was stripped back to the bare brick (this has since been dry lined for a utility room).

The floor in the stairs and hall is concrete. The floor in the adjacent lounge is suspended timber and the floor on what was the old bathroom is concrete. The latter was at one time an outhouse but has since been incorporated into the main house many years ago.

It's been about 3 months since replastering, with the heating on constantly for most of that time until recently. I'm reluctant to start hacking off plaster, now that it is carpeted, so any answers would be appreciated.

Damp on stairs before

• Kennyb2013
• 19 Mar 2013
• 1

Damp on stairs after

• Kennyb2013
• 19 Mar 2013
• 1

Damp in lounge adjacent

• Kennyb2013
• 19 Mar 2013
• 1

Adjacent bathroom

• Kennyb2013
• 19 Mar 2013
• 1

 

[noseall]

It's funny how the tide mark follows a parallel line with the stair string....?

Where is the damp coming from?

 

[Kennyb2013]

Yes it's strange. The damp originally came from the bathroom behind but it spread a fair distance and seemed to follow the stair. I'm hoping it just needs to dry out more but it's taking ages. Very puzzling.