|3 hole perforated and 5 slot hollow|
Most of the name bricks in Victoria are soft mud sand-stock moulded or semi-dry pressed. In each case a reverse of the frog, with the negative of the name impression, is screwed down to the bottom of the mould. The other main method of forming bricks is extrusion, where a screw forces the clay through a die.
While dry-pressed bricks were the norm in 19th and early 20th century Melbourne, extruded bricks, often involving repressing, were common in Sydney. Modern brickmakers are more likely to use extruders due to the speed of manufacture.
Such machines have been available since the earlier 19th century, and extruded bricks have featured holes through the body for as long. Problems with even burning slow drying and distorting of solid extruded bricks (which require a larger water volume in the clay) led to the use of dies which left holes in the finished brick. Three hole and ten hole bricks have been common in the past, but a diverse pattern of perforations have been employed.
However, perforated extruded bricks did not become common in Victoria until the second half of the twentieth century.