Tanking suggestions

Could anybody help with any suggestions of what to use or where might help, what I have is a stone building which I am converting into a house, the rooms are quite small and on some of the walls building control have asked for bituthene against the stone and then block, but this is taking up valuable space. Somebody mentioned something about slurry, what is this? and would building control accept it? and what is the correct name for it? and how is it fitted? Thanks in anticipation.