A temporary skeleton of timber arches or ribs  is built and covered with a sheet of canvas.  Several layers of concrete are then painted onto the canvas.  The fabric will sag between the timber ribs under the weight, so that the finished structure looks corrugated and these buildings often resemble a 'jelly mould'.

Once the concrete has dried, the timber skeleton can be removed (and reused) leaving a concrete shell.   Waller's arched shape was inspired by the great  Ctesiphon arch in Baghdad, built of brick over 1,600 years ago.