I have a job coming up to apply Clone Stone (cast concrete stone) for a fireplace surround.  The problem:  there is already existing Malapais stone (natural basalt stone) in place.  The Malapais is securely attached and removing it before applying the Clone Stone would damage original plaster and probably the existing framing besides the demolition and removal of the material in a finished house.  The question:  can the reveal be floated out, lathed and the new stone applied; or am I better off furring out the reveal and applying the stone over cement board?