This is a c1915 2 storey house made of concrete located in Nova Scotia. The walls are about 8" thick solid poured concrete on the ground floor, and 4" on the second floor. Both stories have had an exterior skin added by applying bi-sected hollow blocks which gives a few inches of air gap. Interior was plaster and lathe, then strapping and gyproc was added. Over the years the inner walls have moisture damage.
For the past 20 years it has served as a museum and is closed for the winters. The past 15 years it has been unheated in the winters, but we have been advised to maintain at least a baseline temperature well above freezing. We are planning a "rehabilitation" project which will include replacing the interior walls. We are wondering what to use, and if it might be helpful to blow in rockwool or flax wool to the cavity under the outer skin? The concrete needs to breath, and we dont want to introduce condensation moisture problems when we start heating again. Any advice (short of destruction!) would be appreciated.