People here in Portland and elsewhere (Sun Ray Kelly in Washington) have
used a small tractor, piling up the materials in the street or driveway
and running over it, scooping it up with a loader bucket if there is
one, and driving over it again while water is mixed in. Works very well
for large batches, but, obviously, the ERoEI is poor compared to hand
mixed cob. It makes us all grateful (again) for cheap oil.