Knackered bathroom wall - suggestions for repair?

You are approaching it the wrong way. "Strong smell of damp". What about curing this first?

It's not concrete, it's plaster...just a different plaster to the surface plaster.

Render and skim.

Bare bricks? - as a feature you mean?

Is it a 'wet' wall? - is there a shower or bath against it? - if there is then you don't have many options...personally, if it were my house I would hack the lot off, allow it to dry (the water has probably been getting behind it for years), PVA, two coats of render, then tile over

Thanks for your suggestions, but...

...do I need to take off all of the plaster first then, or only the loose stuff?

One part of the wall will be a wet wall which needs tiling and I don't fancy tiling over manky plaster. The other part of the wall joined via an L shape will just be tiled

If it's damp (and it sounds to me like you've had water running on it for it to be damp, unless the bathroom is downstairs in which case it could be rising damp, or possibly an outside source - leacky gutter, downspout etc) then it will probably all be loose (another IF here - if it's oldish plaster that is, if it's less than say 30 years old plaster than you may get away with just taking the loose off and skimming over it all)

Anything that you are tiling will need a solid base, the general rule of thumb is: if you think it /might/ be loose, even just a little bit, whip it off, either down to bare brick or just the top coat of plaster, apply 2 coats of PVA and replaster.

Many thanks - it is an exterior wall with no guttering above. The plaster is around 25 years old as this part of the house was renovated in 1981 (I think) - and hasn't been re-decorated since!

There's no reason (other than it being an exterior wall) for it too be damp as it has not been in constant (or even semi-constant) contact with water; I can only think the damp has stemmed from the humidity in the bathroom

Bear :-)

Um. How old is the house? Is it a cavity wall or not (look for air bricks)? How thick is it?

If it's an exterior wall, I would take a closer look at the outside brickwork, maybe it needs re-pointing, 25 year old plaster shouldn't deteriorate so much without a fairly substansial amount of water penetration over a prolonged period....humidity from the bathroom shouldn't affect it, after all, the plaster in our kitchen is 60 years old and that has had pots, pans and kettles boiled in it thousands of times

Worrying thought...the house was built in 1901!

Sounds like you have 9" solid wall

Is the bathroom upstairs or downstairs?

If downstairs - can you see the slate damp-proof course outside the house, or has someone put a path or garden above the level of it?

Charlie