Hi,

Please excuse the newbie question, but I've spent about two hours
Googling for an answer to this, and I'm none the wiser...

I'm trying to fix some shelves to my kitchen wall. Should be simple?
Possibly not -- I can't for the life of me figure out the wall construction.

My property is a flat, in the UK, built somewhere around 2000. Most of
the interior walls in the flat are stud walls (plasterboard over metal
studs, as far as I can tell). But the kitchen wall, whilst interior in
terms of the building itself, forms a separating wall between my flat
and my neighbour's flat. And this wall appears to have a different
construction.

I initially assumed it would be a plasterboard stud wall, the same as
the rest. But I got nowhere fast when trying to drive a plasterboard
screw into it -- it went about 1/2in, then hit something hard, and would
go in no further (and made a bit of a mess of the wall).

I investigated the wall's construction by taking the cover off a power
outlet in that wall and having a look. From what I can tell, the wall is
constructed of:

a) a thin layer of what I assume must be plaster
b) behind that, a 1/2in layer of something that resembles plasterboard
(and is soft enough to screw into easily enough)
c) behind that, a 1/2in layer of something that *looks* the same as the
plasterboard, but is much harder (and cannot easily be screwed into)
d) behind that, there appears to be a gap/cavity

So, what I can't work out is: what the hell is layer (c)? And, more
importantly, what sort of fixings can/should I use to fix shelves to
this wall?

Any advice would be appreciated.

Cheers,

Dave