I am trying to work out what the inner walls of my house are made out of. I want to attach some shelves but have no clue what anchor to use.

I've attached a photo of the area around a light switch, it looks like breeze block ? ( *I have a faint memory of someone telling me that it was many years ago but can't remember for sure* ). 

In some places, although not around this light switch for example, tapping the wall sounds very hollow.

It's an old barn conversion from the mid 20th century, if that helps!

Cheers in advance !

[![d](https://i.stack.imgur.com/CPDpN.jpg)](https://i.stack.imgur.com/CPDpN.jpg)