ABSTRACT
It should be remembered that bricks, tiles and pipes are manufactured objects, and that brick clay is a raw material in an industrial process. As such, its blended properties are altered to suit the process and product, unlike other quarried materials, which are only crushed and screened. Consequently, there is no such thing as a brick clay specification, and brickmaking has as much in common with baking as with quarrying. A wide variety of fine-grained mineral compositions, ranging from slurries to lithified mudrocks, can be used for the purpose. The general requirements for brick-making materials, however, are as follows: • When moistened, the clay will behave plastically-meaning that it can be
extruded, shaped and pressed into a mould. • This formed clay ‘body’ will not shrink or crack excessively on drying, or
during firing. • The clay body will have sufficient ‘green strength’ to be handled after
drying, and adequate fired strength. In practice, these requirements are fairly easily met, either by mixing and modifying natural clays, or by manipulating kiln conditions. The three main products are: facing bricks, for which appearance is the most important characteristic; commons, which are cheaper and are used for interior walls or where looks are unimportant; and load-bearing or engineering bricks. Of the three categories, facing bricks are nowadays the most important in terms
of numbers produced; commons have largely disappeared, along with double-brick house walls, replaced by brick veneer construction and concrete blocks. Reinforced concrete has long replaced engineering bricks in most load-bearing applications. In this regard, developments in brick technology have paralleled those in dimension stone, changing it from a structural material to a decorative cladding.
