I asked this question on the NG some time ago but the suggested solution of rebuilding in the same fashion does not appeal.
Would it be feasible to use "casing" or a couple of wood sheets nailed approx 750mm apart, then fill thes with a gravel/ cement mix along with most of the original stone.
My thoughts are that the more stone that goes in the stronger the final wall.
Or might there be problems with the ingredients expanding and contracting at different rates?
Regards
HN