In the cab of loco BB18 1/4 1037 Damien is passing the last brick, the keystone brick for the second of the two rows to Andrew and Oliver who are in the firebox installing the arch. Mouse over for the PiP to see Oliver on the left and Andrew on the right installing the first row, the one against the front of the firebox. Short lengths of timber support the bricks until the keystone brick is added. Then some wiggling and adjusting is done to get them into their final position. The same is repeated for the second row.