I’m using examples from a job I carried out at the end of summer/start of autumn of 2018 near Barnoldswick or Barrowford in the Pendle area of Lancashire. The job was carried out for another contractor as part of a barn conversion project. The boundary dry stone walls were in a state of dis-repair and needed fixing.
The above photo shows how i’ve dismantled the wall to reveal the sagging and uneven foundation stones. There’s no point building the wall up from poor foundations, so they have to be dug out and re-bedded firmly and in a straight line. A string line is set up and fastened either to the existing wall from which I am extending or to a set of fencing pins.
After this the new foundation stones are laid. It is best to try to use the largest flat-bottomed stones available and it is good technique to lay the length of the stone going into the wall rather than lengthways along the face.