Advice needed for repairing a damp internal brick wall pleas

[littleapple]

I'd really appreciate some advice here. I have a damp problem in the upstairs bedroom of my 1881 Victorian mid terrace house. Having redecorated, I realised I had a repetitive damp area on the inside of the weather wall so I hacked back the very damp, crumbly old plaster and fill (more like soil!)to the brick work, which is quite wet at about 5 - 6 feet above floor level. Will this be the inner layer of a double cavity wall or is this THE wall? There appears to be a tiny damp patch just where the wall meets the ceiling above and to the left, although I had the roof repaired last year after some little toerag nicked all my lead flashing, so i'm wondering if the damp is more likely to be penetrating from outside? The exterior wall is rendered (sort of pebble dash) and painted so it's impossible to tell what's going on underneath. No cracks evident. It looks in good nick.

Am I best stripping back the whole wall, waiting for the brick to dry out (will it ever? and how long might that take?)and then applying some kind of waterproof sealant or membrane (Oldroyd 'P' Plaster Membrane anybody?!) followed by replastering or plaster board? Or will this just cover up the problem without dealing with it?

All help greatly appreciated!

 

[marshman]

The bricks will dry out in time.
It sounds more like the rain is getting in the top of the brick wall and making its way down through the brick joints,
have you a leaking gutter, gutter blocked and overflowing ?,
is there old felt under your tiles, slate, this may have rotted back and if the rain is getting under the tiles, slate it will run the water on to the bricks,
this is the problem I have here and the rain water comes out from under the skirting in the kitchen. but only when the rain and wind is from the northeast.

 

[littleapple]

Thank you Marshman, I think that's exactly what's happening. On closer inspection I have detected some fine cracks in the parapet above the windows (it's a London roof) that match pretty much where the little damp patches are, so I guess the wet bricks are the result of prolongued leaking water from above. Looks like it's another roofing job that's needed!