| Our bricks are made from clay, which is dug from adjoining land. It is a condition of the extraction of this clay that the land is restored to agriculture when extraction is complete. This is achieved by filling with inert waste, and then returning the topsoil. As can be seen from the picture below, its hard to tell that this was once a pit over 10m deep. |
Clay is a complicated mineral. The clay at Selborne is known as "gault clay". It was deposited some 60 million years ago as our part of Hampshire rose from the water. We frequently find ammonites in the clay.
Essentially clay is a combination of oxides and hydroxides of aluminium, silicon and iron, with a few other trace elements and impurities. It was made by the action of water on rocks. In the case of our gault clay this produced particularly fine particles, which pack together closely thereby imparting impressive strength to the bricks that we make. |
Essentially we are reversing the process of time, and recombining the particles into a strong, rock like substance. To do this we have to remove water and then heat the clay to high temperatures to allow the minerals to recombine.
The first step is to get the clay workable. It is loaded into a series of mechanical grinders, rollers and cutters. These break up the lumps of clay (which may be over one foot across) into smaller pieces about 3mm wide. |
These small particles are then fed by conveyor belt into an extruder, which squeezes them into a single, homogenous column of clay. This column is then cut into bricklike shapes. Our craftsmen take these shapes, sand them by hand and press them. The press increases their density, and thus strength, and puts in a frog [which is the indentation in a brick that improves its grip to mortar in the wall.
This wet brick is then loaded onto a pallet and sent to a drier. |
Special shapes are made in a similar manner, right up to the extruder. If the special is brick size or smaller, the pressed brick is taken to a template, where our craftsmen cut it by hand to the required shape. It then goes on a pallet and into the dryers with standard bricks.
If the special is larger than a normal brick a large piece of clay is taken from the extruder column. It is then shaped by craftsmen and, because it is so large, it is then dried specially and carefully. |
Bricks set for drying |
Drying
A press brick is about 35% water by weight - each brick containing almost one litre. We have to remove this water in two phases, and gently. Applying too much heat causes faults in the brick that will then crack it when it dries.
The first step is in the dryers. Here the temperature and humidity are carefully controlled to remove about half of the water in the brick. The temperature rises to a maximum of 90 degrees C over a period of a week. Initially we keep the humidity high to slow the rate at which water escapes. |
Gas fired brick kiln |
Firing
Once the brick is dried it is taken to a kiln. At the moment we use a shuttle kiln. The dry bricks are loaded onto the kiln cars. The cars are then pushed into the kiln, the doors shut and the kiln turned on. Natural gas is burnt, raising the temperature gently to about 600C. At this temperature the balance of the water is removed.
The bricks are then heated to over 1000C, and held at that temperature for some 12 hours. At the end of this 12 hours additional fuel may be introduced to produce a reducing atmosphere. This changes some of the iron oxides from red to blue, producing our popular multi-red brick. |
| The gas is then turned off, and the hot air removed. When the temperature is lowered to about 400C the doors are opened, and the cars pushed out. New cars are pushed in, the doors shut and the process restarts. |
When the bricks have cooled to a low enough temperature to be handled they are removed from the cars by forklift and sorted by hand for colour and quality. They are then packed on pallets, wrapped in plastic and are ready for shipping.
The entire firing process takes about 2½ days. |
Clay & Sand in Feeder |
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Clay entering the mill |
Sanded bricks going to brick press |
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Pressed bricks |
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