"Crying" Walls

[Shippy]

Hello All,
Moved in on friday to a Georgian townhouse (built 1740, probably extending previous dwelling). The survey did mention some damp, but nothing too bad. The property has been extensively re-plastered (not sure if lime), but no signs of major cracks.
The property is end-terraced. In the ground-floor room on the end, the front and back walls appear to be "weeping" on the inside. Little streaks of damp, ending in a brownish drop. Wiping removes this, leaving a shiny glimmer. Can't see any other signs in other rooms. I'm assuming this is the damp and understand that we can address it hopefully with the various measures covered on this (excellent) forum. But, is this manifestation normal?? I was expecting some dis-colouration and dark patches (of which I've spotted a couple in the ceiling of the same room), but was surprised to see liquid. The ground floor was concreted in 1970 when and there was a chemical damp course done in 1980.
Thanks,
Neil

 

[Mark]

If these are the external walls I would be checking the render or pointing and the gutters.

Also check the rooms above looking for any leaks. esp where the visible damp patches are.

recent relastering ? Any pipes in this wall ?

Could you confirm where abouts on the walls (high /low / proximity to windows/doors/gutters/chimneys etc)

 

[Shippy]

These areas are not near a chimney, but reasonably close to sash windows (front) and french doors (rear). I think the plastering was done in 1980 when there was a lot of rot treatment done. It is possible that it's been re-done more recently.

Room above appears dry. All heating pipes run proud of the walls with no sign of leaks.

Front wall has been re-pointed, but probably with cement rich mortar.

Rear wall has hanging tiles so can't see!

I've had a thought (after more reading..) - could this be condensation rather than damp? (and how do you determine which it is?!)

 

[Penners]

The property has been extensively re-plastered

If this replastering was done recently, then there's every possibility that what you're seeing is condensation, particularly if there's a considerable temperature difference between the walls and the air. For example if you've switched on central heating to dry the place out.

Plastering uses very large quantities of water, and can take some weeks to dry out fully. Has the plaster been painted or not? If not (and assuming it's gypsum) is its pink colour a bit patchy - i.e. some darker and lighter patches? This would indicate that the plaster is still drying out.