damp inside fireplace

laxeylady

We plan on replastering our sitting room using a membrane to protect from penetrating damp - the house is built into a bank and the sitting room is the worst affected room. We don't know how to proceed when it comes to our fireplace though. At the moment it has a stove (we will replace with another) but the back of the fireplace itself is very damp. We are assuming a membrane in there would be impossible so what can we do? We toyed with the idea of buying slate slabs/flags and making/tiling a 'box' inside the fireplace. But would they stay up?