We are renovating an old stone farmhouse and have built a wrap around extension around most of it so that the majority of the original walls are internal. However one side elevation will be behind a lean to glass conservatory to act as thermal mass heat collector and will not be rendered but repointed.Obviously this side will breathe, so do we have to be particular about how we finish the internal side of this wall i.e. use a breathable finish e.g lime plaster? The stone wall is 700mm thick in very good structural condition except that the inside has been hacked about over the years and would not make an attractive bare wall. As the house was very damp when we bought it is now very dry after we hacked off the external pepple dash cement render the internal cement render with plaster finish.and dug up the floor and laid concrete over a DPM.