If you own or are responsible for an old building made of stone or brick with solid walls the chances are it was constructed with lime mortar. Cement is to solid and impermeable to use with these buildings. It cracks when the building flexes and lets quite a lot of moisture in through those cracks but not out again. The answer is to use lime, it works similarly to Gortex and breathes.
There are 2 types of lime you should consider, Lime Putty or Natural Hydraulic Lime. Lime Putty has to be tended to more than hydraulic lime but is more breathable. Hydraulic lime is far better than cement and more controlable than putty and still retains a lot of flexibility and breathability which putty lime does with less tending time.
Also when used for internal plastering it has antiseptic qualities.
So all in all drier walls means warmer and healthier walls.
Talk to the conservation department at your local council or SPAB, the society for the protection of ancient buildings.