Stone wall renovation and repointing

Cat amongst the pigeons?

We have a very large stone barn in Normandy of two storey and 200m2 ground floor footprint.

I agree the arguments for a hydrated lime based mortar for the external pointing in order that the stone walling may breath. However due to the rather small stone pieces and very slim joints …some are only quarter inch in width…I fear that a pnupoint pointing system will no be compatible here? Any knowledge of this?

My other cat is that I am very drawn…singly by expense I admit…that my treatment for the INTERNAL stonework…where it is not attractive enough to expose…will be to rake out the millions of small thin joints and render with two coats of sand and cement render with a Sika1 damp proofing additive to tank the inside of the building in preparation for…dot n dab Gypsum plasterboard with back insulation with taped joints for plaster skim coat finish. Your feedback would be most appreciated.

I appreciate that my stone wall will still breath albeit to the outside where I want it to be. My rendered tanking will let me bind the internal stonework and level it to accept my Gypsum insulated boarding. It will be dry and easily marry with my two coats Synthaprufe Dom over the existing concrete over site…laid by others. Newtonite lath was considered as although I was advised that this breaths on the inside where exactly would this discharge to? The wall thickness is 750mm thick so hardly a companion for weep holes? Please do not advise me to provide a chemical dpc as I find the logic of this only applicable to brickwork rather than possible mid wall rubble pockets.

I have thought this through but I am very open to crucifixion and or advice. Yes I know about the fibre boarded lime finished sustainable options but I really cannot afford them.

Anyone there?