Damp on extension wall

[Richard326]

My house had an extension build well before I moved in. I'm currently decorating in the extension but have found a damp patch on the old external wall and the wall joining it from the extension.
I think it was caused by a leaking radiator pipe which I have now fixed. The wall has been left to dry for a number of weeks now but there just seems to be this one area that wont dry out.

Am I just being too impatient or could there be another cause?

Thanks

 

[noseall]

sounds like something more sinister to me.

masonry built in the rain soon dries out when the roof goes on.