Penetrating damp around window (s)

[AndersonC]

Thanks to the torrential rain of the last few days I have a damp internal wall adjacent to a window frame. I immediately sensed that something was allowing moisture to penetrate from the outside leaf around the window and into the cavity.

The house is a terraced built in about 1920 by the way.

So I remove one length of architrave from the edge of the internal frame and the sash weights from the old windows are still in there (place has been UPVC'd obviously without removing all the old sash mechanisms). So I pull these out and notice that the cavity appears completely blocked under the window frame. So I remove the internal sill and there is a load of mortar sitting between the sandstone outer sill and the internal brickwork. Is the only proper solution to remove this mortar and thus ensure that the cavity is not bridged?

There are no guarantees for the windows as the previous owner apparently got her son to fit them (I use the word 'fit' in it's loosest possible sense here). From what I am finding out he's done a diabolical job and doesn't appear to know the slightest about damp.

This is going to be a messy job but I would like it sorted properly. Any advice whatsoever would be gladly appreciated. Thanks.

 

[^woody^]

Strictly, a cavity should be clear, or have a barrier to prevent water bridging it.

However it this was a one off, it may be worth just applying water sealant (Thompsons) the external wall and cill in this area, and ensuring that the frame to wall joint is sealed with mastic.