Problem with wall in an old stone cottage

[Johnla]

I have an old stone cottage possibly built at the turn of the last century. I have lived there for almost 25 years and have always had to heat the wall at the back of my living room. I assumed it was because it was an old building and stone. I was checking the outside of the cottage last week and found that the outside of this wall seems to have gaps in the stone. You cant see it looking at it directly,you have to really hunker down and find these gaps .
I checked as far as I could inside these gaps no more than a couple of inches wide and it seems damp in there.
Now my problem is do I fill in these gaps with stone or could I be walling these damp conditions into the wall?. There is not outward sign of the damp on the internal wall no salt deposits are visible.
Any ideas on the best way to tackle this?
Any help would be appreciated

 

[bernardgreen]

Re-pointing the with lime mortar may be the best way to improve the situation.

A local stone mason who has experience of the local stone would be the best person to ask for advice