Damp patch after bathroom re-fit

Just finished a bathroom refit for a relative but have noticed a small damp patch that keeps re-appearing on the bare plaster half way up the window reveal where it meets the window.It starts at the window frame and spreads out over an area about 4 x 2" square. As part of the refit I hacked off the plaster back to brick in the whole room and re-plastered . The wall concerned is a brick cavity wall. Window is upvc.
The damp patch appears after rain and I noticed that whoever fitted the window had sealed the gap outside between window and brickwork with silicone sealant which was fair enough but the gap was about 3/8" inch wide so asking a bit much. I took the silcone out and filled the gap with expanding foam then fitted a piece of cloaking profile over the gap and sealed all round the edge with silicone sealant. I also spent half a day repointing the brickwork outside over quite a large area as it was pretty bad in this general area. It was a decent job and I felt confident the damp patch would not re-appear.

But it has.

I'm now thinking back to the plastering stage and I remember that the brickwork around the window at the point where the damp patch is was in a poor state and I gobbed some bonding plaster in first which probably bridged the gap between the inner and outer wall over a small area but from memory over roughly the same area where the damp patch keeps appearing.

I suspect i've answered my own question but I'll ask it anyway:

Have I made a basic error in bridging the cavity with plaster?

And would that in itself be enough to allow the ingress of damp even though the area outside was weatherproof?

Thanks

Yes, water will run down cavity face of external brickwork, seep across the bridge and aborb into the inner wall. Sounds like the simplest reason for the damp

Can't you try waterproofing the brick on the outside. may be a much easier solution than hacking out what you've already finished.

I admit the best solution is to hack it out, but its gutty ripping out whats already been done.

Go on, hack it out, you know you ought to. but also, get someone to squirt a hose round the window and see if you can tell where it's getting in.

Thanks for the replies.

One question's just occurred to me tho'

How do you normally plaster a window reveal- I mean if there's a cavity between the bricks that mustn't be bridged what does the plaster stick to in this 'middle bit'?
Or should you normally insert some sort of damp proof membrane across the cavity and plaster on to that?

Get an old length of plasterboard,dab some bonding on the inner cavity wall , cut the plasterboard to suit the reveal , stick it to the bonding dabs and plumb up. Sin e ! I would also check that your dpc under the cill has been returned(turned up inside the cill) if your problem keeps recurring.G'luc.

JMC, do you mean plasterboard the whole span but only dot and dab on the inner wall?

Sorry 4 the delay in getting back to you.Yes thats exactly what i mean , the rigidity of the board when the bonding goes off will allow you to skim it no problem.Probably done by now ! G'luc

Thanks. No, I haven't done it yet. Will try as you suggest any day soon. Might even get the rest of the measly pitttance I'm owed for the job then.

measly pittance , that is the joys of working for family , avoid at all costs ...they are the worst customer