The Brick Directory Blog. Articles mentioning 'bricks' - brick making, Articles and Words taken from news agencies and newspapers, magazines and books about brick and other building materials including reference ('how to') and sometimes amusing 'brick related' stories. The blog is linked with helping you get in contact with every brick, paver, tile and stone manufacturer in the UK and Ireland.

Wednesday, 21 April 2010

Brickmaking History

For centuries bricks were moulded by hand in wooden moulds. These were four sided and rectangular in shape with no base or lid. Moulds were placed either directly on the ground or on a roughly made brickmakers table. Bricks made on the ground are generally pre 19th cent. They were known as 'place' bricks and often contain grass impressions. From the 19th cent rectangular block of wood, smaller than the mould dimensions, would be screwed on the table which created the brick's 'frog'. Sometimes letters were carved in the frog to identify the brickyard owner. With the advent of steam power brickmaking became mechanized wherever volume justified it. Steam driven extrusion plants with nine overhead wire cutters produced ten bricks every few minutes.One of the oldest methods of firing is by clamp. A clamp is a temporary construction of unfired or green bricks which is dismantled after firing and could be erected near the clay source. Clamps varied from yard to yard but there were general rules which most followed. The floor had to be level and was made of burnt brick. Channels were often made in the floor and filled with fuel, usually breeze (crushed coke) but any fuel would suffice and wood, furze, charcoal were also used. Next came three or four layers of green bricks which were placed on edge and then another layer of fuel was added. After this, green bricks were packed closely together to a height of 14 or 15 feet. The bricks were 'dished' or tilted inward to prevent injury to workmen during firing. Sometimes the outside was sealed with wet pug. Most clamp bricks had a small percentage of breeze added to the clay during manufacture. This helped to 'self fire' them and ensured that a good temperature was reached. Clamps contained 30,000 to 150,000 bricks. An average size would take two or three weeks to burn out, although larger ones could take as much as ten or twelve weeks. Updraught kilns may be as old as clamps. These were known as Scotch kilns and were permanent structures with one or more firing chambers.The kilns were built of burnt brick. Flues ran under the perforated floor from one end to the other. Green bricks were stacked on the chamber floor with small gaps between them to allow the heat to circulate. The open top was covered with old burnt bricks and turf or pug to help conserve the heat and prevent draughts that would cause uneven firing. The kilns had to be stoked regularly day and night for at least three or four days. It was quite common to see flames rising from the top of these kilns when firing. The death knell sounded for many small yards in 1939 when Blackout Regulations were brought into force. A later development came to be known as a Suffolk kiln. These were fired on the same principle but smaller and set into a bank. One reason for this was to provide ease of access for loading or setting, another was for insulation. The downdraught kiln was far more efficient than the Scotch or Suffolk. Firing was much easier to control. They were often circular in structure with about eight fire holes. Inside the fireholes were baffles or 'bag' of firebricks. It had a domed roof and a perforated floor under which ran a flue leading to the chimney stack. The circular or 'beehive' kiln had a capacity of about 12,000 green bricks. Coal was lit inside the firehole grates and hot gases were directed upward from the baffles and then downwards from the underside of the dome and through the stacked bricks by the draught from the chimney. Altogether it took fourteen days or so to operate, with two days for loading or setting, three days for 'curing', two days for heating to full temperature, one day at full heat, then another three or four days to cool down and a further day to unload or draw.

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