Damp Proofing a random stone wall built with lime mortor.

[BML]

My son has a cottage in Scotland about 150 years old which he is bringing back to life. The structure is a solid wall built about 24 inches thick built with what I would refer to as, random stone and lime mortar. Many of the joints have fallen out over the years and it is allowing water to work its way through it. His local builder has suggested raking the joints out, pointing the gaps with sand and cement and then pebble dashing the walls with a sand and cement mortar.
I looked up some solutions offered for this problem and found suggestions such as repointing the wall with a natural lime mortar because sand and cement mortar may not adhere to the original lime mortar.
I have a number of questions:
1. Would sand and cement with plasticiser work as a pointing agent and not conflict with the original natural lime mortar?
2. I remember seeing bags of lime back in the 1950s which was used with cement and sand to create mortar. Is that sort of lime the sort that one uses to make lime mortar?

[stoneyboy]

BML,
The walls were built with lime mortar because this tolerates movement well. If you repointed with a cement based mortar this will crack in time as wiil a coat of rendering on the blocks. Repoint using lime mortar, in the south we use hydraulic lime but it may be called something different in scotland. Do not use hydrated lime.
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