Brick Manufacture

The vast majority of bricks used in construction are made from the naturally occurring raw material of clay. A small proportion are made from calcium silicate (in other words, sand/lime) or concrete, but this chapter will focus on those manufactured from clay.

Подпись: Brick Terms A variety of terms and terminology will be used here; see Fig 29 for some definition and clarity. The question of what constitutes a ‘solid' brick as opposed to a ‘perforated' brick is not clear-cut. A ‘solid' brick can still be defined as such, even when it has holes or voids, provided they do not exceed 25 per cent of the brick's total volume. Where holes exceed 25 per cent of the total volume of the brick, and where the holes are considered to be small, the brick is defined as ‘perforated'. Where the holes exceed 25 per cent of the total volume of the brick and are large, the brick is defined as ‘hollow'. Finally, ‘cellular' bricks have holes that are only open at one end and exceed 20 per cent of the

In the manufacture of bricks, selected clays are prepared, moulded into shape and burnt under a variety of manufacturing processes, each of which will produce a brick that possesses certain qualities or properties. Various colours of brick can be made by using iron oxides, iron sulphides, and other additives. The mineral content of the clay raw material will also have an effect on the physical properties, colour and hardness of the finished brick.

Подпись: total volume of the brick. A ‘frogged' brick where the frog is very deep could well be considered to be a cellular brick.
Подпись: 'Arris' - the edges 'Stretcher face’ 'Header face’ of a brick | МІЩрй | 'bedding face' 'Perforations' - small holes 'Frog' - a shallow through a brick sinking in a brick
Подпись: Fig. 29 Brick terms and terminology. Despite these ‘grey areas' in definition, for the purposes of this book, reference to ‘solid' is intended to mean bricks with no holes at all (Fig 27), while ‘perforated' refers to bricks or blocks with any holes, regardless of size, that pass all the way through (Fig 28). Any ‘frogged' brick will be referred to as such, regardless of the depth of the indentation (Fig 30).

All clays used for brick manufacture have one common characteristic: they must be capable of being finely ground by machine and then mixed with water, so that they may be moulded, or ‘pugged’.

After excavation from clay pits, the clay must first be ‘weathered’ to wash out all of the impurities and soluble salts, which could later lead to efflorescence on the face of the finished brickwork. The most basic method is to leave piles of clay outdoors and open to the elements during the winter so that the rain simply washes out the soluble salts. Other clays are passed through a wash-mill first before being stored in large open storage areas.

The washed clay then undergoes a number of grinding processes (usually three) until the raw material is reduced to a particle size of 1-2mm, at which point water is added in order to enable the clay to be moulded into brick shapes by one of the following three basic methods.