redoing 145 year old plaster over limestone interior walls

[retiredalexanders]

hi, i am attempting to redo a bedroom in a 145 year old stone home. 2 layers of wallpaper over what seems to be a concrete plaster mix applied directly on the stone. there are large areas where the plaster has broken down, leaving bare stone. the morter between the limestone can be scraped off with a screwdriver very easily. some areas sound hollow when knocked. there is no lath in the entire room. there are huge gaps around the window trim and doorjams. there was even a lot of cloth pieces shoved in the gaps and plaster applied but it was falling off and left 1-2 inch gaps. i only want to do this once, so i need advice so i do it right.

 

[wozza56]

The mortar between the stone should be quite soft as lime mortar is the best thing used on stone buildings as this allows the stone to breath
Im not too sure what materials are available in the usa but i would give people 2 options based on price really ,1 you could buy a lime render from a specialist supplier and use as directed or 2 you could use a sand and cement render but with added hydrated lime in the mix at 1 part hydrated lime 1 part cement and 6 parts sharp sand
The second option usually works out the cheaper and is not really any worse than the first its just that some people want to do it all as original as possible