Repointing an old stone wall.

[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?

[Fewetime]

Such repointing should be done with pure lime mortar. Portland cement should not be used in any way. Cement is not compatible with the fieldstones because it's too hard and traps moisture.

Bagged hydrated lime found at masonry yards is intended for mixing with portland cement and is not the best material for making pure lime mortar. Instead, look for slaked lime putty (which you mix with your own sand) or a hydraulic lime mortar mix, which is premixed with sand.

Slaked lime putty produces a nonhydraulic mortar that may be too soft for locations exposed to severe weather.

Hydraulic lime mortar becomes harder and may be better for exposed locations. It may be too hard, however, for old soft bricks.

The following publications are useful and reliable:
http://www.doeni.gov.uk/niea/tn37_repoi ... rick-2.pdf
http://www.dumgal.gov.uk/CHttpHandler.ashx?id=1492&p=0
http://www.heritage.nsw.gov.au/docs/rep ... update.pdf

[BML]

Many thanks for the advice. I served an apprenticeship as a Bricklayer in the early 1950s when Lime Mortar had stopped being used being replaced by bagged lime mixed with cement and sand. However, I was lucky enough to see the construction of Nuffield College Oxford as a boy and I watched them actually slake lime to create lime mortar.
I will now be able to advise my son to tell the chancers who suggested repointing the building in sand and cement to take a walk and if necessary I will dig my tools out and do the job myself hoping to avoid the Scottish Midge season.