Is it damp, is it condensation, is it old, is it new?

[maxitone]

My daughter has bought a 1930s ex-council house. We've been stripping the walls ready for skimming and came across these marks under the bedroom window sills.

Untitled

• maxitone
• 31 Oct 2013
• 1

Untitled

• maxitone
• 31 Oct 2013
• 1

Untitled

• maxitone
• 31 Oct 2013
• 1

I'm hoping they were caused by the old windows the previous owners replaced.
The walls feel cold (they're external walls after all with no cavity insulation) but not damp (to my untrained hands).
I'm thinking: cut out all the old plaster, check for signs of damage and re-plaster (by a pro).
I'd really like some advice before we end up doing something now that we'll regret later.
MTIA
Andy

 

[Burnerman]

Thats probably just historic condensation - maybe the previous owners weren't too particular about mopping it up?
So long as the new windows are well sealed, there shouldn't be any water ingress or condensation in the future.
If the plaster is loose, chop it out until its firm, and then patch up......if its secure, then just keep an eye on that area.
John

 

[JohnD]

draw a pencil mark round the damp patch. See if it gets bigger or smaller. Look at it again during or after wet weather. New windows are sometimes not well sealed.

 

[Micilin]

Wipe Dry and tape a piece of plastic or tin foil on to the wall, sealing the edges. If after a time the moisture is on the wall side, it's damp. If on the room side, condensation

 

[maxitone]

Thanks to you all!
It's been nearly a week now and no signs of any dampness or condensation which is great.
The plasters are due to cut out the worst of it and make good
Thanks again