Slate tiling, preferred surface to tile on?...

[shorn]

Hi all,

Im about to start tiling a bathroom in slate. Now the walls had a thin plaster skim, and that started coming off, so I stripped it back to a sandy cement render that has been applied to the (breeze block) wall. The surface is quite sandy and can do dusted off, but im guessing it would need to be sealed first before tiling?
The wetroom side consists of two walls in aqua panel, bt i was thinking about d&d'ing some plasterboard up on the two other walls and tiling on that. What would be the best to tile on? Obviously the plasterboard will be a tad easier as it will be a nice flat surface however the there is the added hassle of getting the plasterboard up.

Just wondered what peoples opinions were?

 

[DHTiling]

If it can be dusted off easily then i would suggest it is a backing coat and not render.

How thick is the slate..?

 

[The Legend; Phil Hobson RIP]

As Dave, any pics?

 

[shorn]

Pics as requested.....

What you think? Plasterboard over?

 

[DHTiling]

Hardibacker 250 glued and screwed.. that will hold the slate..

 

[White Room]

If it is render I would scrape off the remaining finish, prime with thinned sbr and tile on that.

It's difficult to tell if it's a gypsum or render though