How can I repair old plaster (wall tiles removed)

[alexeix]

Hi,

I'm replacing my bathroom suite and have decided to renovate the whole room while I'm at it.
The bathroom walls were tiled up to approximately 1000mm from the floor and when I removed the tiling, quite a bit of plaster came off the wall as well. This is old plaster (grey, crumbly when you scratch it), possibly original - and the house is about 100 years old.

Now, I want to put up tongue and groove (T&G) panelling up to the same height all round, so I'm not concerned about how the bottom half of the walls look; I just need a surface good enough to fix the T&G panels onto.

Does anyone have any advice on how to do this?
How should I treat the surface in order to be able to fix T&G panels onto it?
Obviously I need to remove any existing plaster which is loose, but what then? I don't really want to have to remove ALL the old plaster, especially since their may be lathes underneath.

Thanks in advance for any advice!

[welsh brickie]

If the wall is uneven its best to cut out the plaster and drill and fix battens to the wall.Fix the battens straight and level Then nail the T&g to the battens