What's under my tiles?

[jshailes]

Before undertaking the tiling in the main bathroom I thought I'd try to get some practice by retiling around the sink in the downstairs wc. Having removed the tiles I'm unsure of what layers I've removed (in addition to grout) and how to prepare the walls for retiling.

It seems like the tiles were affixed to a thin, but hard, layer of concrete-like material with either grout (mostly) or a flexible white substance (for tiles directly around the sink). What would the flexible white stuff likely be? Photo below:
[GALLERY=media, 97986]Flexible white layer by jshailes posted 5 Jul 2016 at 7:43 PM[/GALLERY]

The hard concrete material (photo below), which reminds me of a skim of plaster but thicker, has come off as I've removed the tiles. I assume this will need replacing?
[GALLERY=media, 97985]Hard concrete layer by jshailes posted 5 Jul 2016 at 7:40 PM[/GALLERY]

Under this hard concrete layer is a much more powdery concrete which looks to have been set in a, now rusty, metal frame:
[GALLERY=media, 97984]Base Layer by jshailes posted 5 Jul 2016 at 7:39 PM[/GALLERY]

Any advice on what these layers are and how I need to prepare for retiling would be gratefully received.

 

[PrenticeBoyofDerry]

You likely have tile adhesive, plaster skim and render on the walls.
The tile adhesive can be removed softening up, warm soapy water or heat gun then scrape off.
The over surfaces can be repaired by using one coat plaster.
Once dry the area to be tiled will likely need priming. But check the tile adhesive manufacturer's instruction you use for best process of priming before you start.

The rusty frame is an angle bead, commonly used on external angles of walls and windows.