Should I remove plaster (browning)

[what]

Could someone help me with this?
I need to re-tile our bathroom which entirely covered floor to ceiling with 6" ceramic tiles.
There a two external walls covered in some sort of browning and the other walls are ordinary plaster board.
The browning is detached from the wall where the existing shower/bath is over a large area (sounds hollow when tapped) and only the tiles are holding it up at the moment, other areas which are not subjected to water ingress from the shower are sound.
My question(1) is given that this is a bathroom which is subject to condensation, should I should I remove ALL the browning, not just he damaged area and replace it with a cement mix plaster.
My other question(2) is should I remove all the plaster board also and replace it with cement board.
To save time time and effort I am tempted to just tackle the damaged area and just tile over the existing tiles where it appears sound.
I don't wish to do anything that is totally unnecessary, but I don't want do something I would regret later.

 

[widler]

Knock it all off and reboard it all.
Dot and dab solid walls and screw partition walls.
If you are tiling it all no need to skim.
Tank the shower area before tiling , then tile away.
For the sake of a few quid its better boarding it all

 

[One Day]

^^What he said^^

 

[what]

Thanks for the replies
But what do I re-board with - Is it cement board not plaster?
What do you mean by tanking - best method?

 

[widler]

Just everyday half inch plasterboard ,8x4 sheets , or 6x3 if you want to make it easier .
For tanking kit I use tilemaster tanking kit, there's loads of different ones though, look about ont nett

 

[what]

Just everyday half inch plasterboard ,8x4 sheets , or 6x3 if you want to make it easier .
For tanking kit I use tilemaster tanking kit, there's loads of different ones though, look about ont nett

Hi widler / impish
I looked at the tilemaster tanking and paste kit instructions PDF, it seems straight forward. How much tape is included?

Thanks for the help and great advice, I shall proceed as directed.

 

[widler]

Think its a 10m roll , plenty for a shower area

 

[what]

Thanks
BTW--
What's the most civilised way to remove previously tiled plaster board without bashing through and damaging the the plaster board on the the other side of the stud wall.
In my situation the the other side is above the stairs,just newly decorated and difficult to access.
Is there some technique that is generally used, or is it just careful brute force.
It occurred to me that I should remove more or less all the tiles first, maybe with an sds hammer drill (on rotation stop) using a tile removal chisel then prise the boards off the studs.
What's the usual way?

 

[widler]

Personally id just make a hole inbetween the studs and yank away , carefully you shouldnt danage the otherside , its quite tough

 

[what]

Personally id just make a hole inbetween the studs and yank away , carefully you shouldnt danage the otherside , its quite tough

careful brute force!
Thanks