The fire box and pot chamber wall are built up. the latter with no.26 insulating bricks.
Some used insulation brick are used in the lower layers of the pot chamber but new ones make up the upper parts of the walls and the front of the chamber where the wicket or door will be. The door will be cut once the ironwork is in place and the door bricks have been numbered with iron oxide wash. The upright post in the foreground is a roof support for the shelter, not part of the kiln.
The the corners are checked to ensure the structure is square and diagonals are frequently checked to ensure they are the same. Once the walls are at the desired height the whole structure will have an ironwork support added.