hello rick...i'm so grateful to hear back from you!
Its a free-standing wall. the wall was about 15 ft in height. it separates me from the neighbour and was very precarious. i thought it had just been the header stones which were loose. on bringing down the top stones it is obvious the weakness is lower still.
it had been abutted by an old outdoor lavatory...but i got rid of that immediately without even taking a photo or really taking much note but possibly the roof was protecting that part of the wall. Either side is surprisingly sound. To the left there is a concrete filet and top stones on top, to the right just a single skin infill, in stone - to raise the height from about 6ft of rendered poss double width stone to (slightly less than the section removed) about 14ft(?) but that layer is solid with a good strong mix. I think the problem with the unstable section, about 3ft in width, which was in between two pillars - an extra height above the 6ft base being finished with single skin brick - was that the mortar mix was very sandy.
As we removed the top we have had to keep going down removing more and more....we re at about waist height now. It would be easy to take the whole thing down...not so easy to put it back up!
Given the gaps between the stone as well as the sandy mix...if we poured a strong concrete mix into the holes would the slurry run down far enough before setting to hold the wall do you think ....so we can do the job ourselves?
Or is your concern that it might run out at the bottom or cause a bulge somewhere and force the wall apart?
What if we made it really runny so enough passes through to reach the bottom but just in small amounts til setting time has passed before pouring a little more down..or might it not pass through and than bulge as an accumulation somewhere?
Am I going to have to take this wall down and start again? Goodness knows what the foundations are like? How deep should the footings be for a wall?
We did successfully rebuild another section...its still standing! (But its lower).