Soft-Mud Moulded Bricks
In ‘soft-mud moulding’ the clay is mixed with water to a fairly soft consistency and a ‘clot’ of the soft clay is thrown by hand into a mould box. The mould is oversized to allow for shrinkage of the brick during the later drying and firing processes. The clay is prevented from sticking to the inside of the mould by way of a releasing agent such as sand, oil or water. The excess clay is struck off from the top of the mould box and the bricks are then turned out. Using sand as a releasing agent will produce a brick with a ‘sandy’ texture, whereas using oil or water will produce a smooth finish. Making bricks by hand in this way is clearly slow and labour-intensive and they are, therefore, expensive to make in large quantities.
For large quantities of standard-sized bricks the process of ‘soft-mud moulding’ by hand can be replicated much faster and on a grander scale using large automated machines. These employ banks of mould boxes on a continuous circuit, with the boxes being washed, sanded, filled with clots of clay and struck off level, and the formed bricks being turned out in a matter of seconds. Again, using oil or water as a releasing agent will result in a smoother finish.
Soft-mud moulded bricks are either solid or have an indentation called a frog. They are characterized by having edges that are not sharp, being somewhat irregular in shape and lacking uniformity of size. These characteristics tend to be more noticeable in the hand-made varieties. In addition, the action of throwing by hand or mechanically dropping the clay into the moulds means a crease is achieved in the face of the brick, which creates a decorative effect that varies from brick to brick.