Colin Richards is Conservation Officer for South Shropshire and an experienced practitioner in intermediate technology. His work for the Mihai Eminescu Trust has been invaluable. The following is his account of the construction of a wood-fired brick kiln in Viscri, Romania.
The Transylvanian Saxons constructed their buildings from readily available local materials namely timber and river washed stone, as well as bricks and tiles fired from local clay. Limestone was burnt to provide mortar and the vital render for masonry affording protection to structures, which were exposed to seasonal extremes of heat and cold. Such an aggressive climate demanded a regular cycle of maintenance to avoid water penetration of vulnerable building elements. The Saxon’s organised their working lives to include repair and upkeep of their property and ensured continued survival of ancient fabric over many hundreds of years.
In 1989, after the fall of Nicolae Ceauscesceau and the resulting mass migration of the Saxon population to Germany, the outstanding architectural heritage of the Siebenburgen was left suspended in time with whole villages denied the care which had guaranteed their very existence. For many abandoned farmsteads, successive hot summers and bitterly cold winters have taken their toll. Water and frost damage in many properties has resulted in the need for extensive repair and consequently the skills and materials to undertake such work.
The Mihai Eminescu Trust began by organising a series of building workshops in the villages and a programme of repair was undertaken which has prevented the ruination of many fine buildings. However, to achieve a repair which is both technically and aesthetically true to the original, requires work which consumes large quantities of traditional raw materials.
Lime pits were re-established in each village where the Trust worked and replenished each year for the season ahead. However, there were scarcely any indigenous kilns still in existence and the great difficulty was sourcing bricks and tiles of a quality and appearance consistent with the original items. The Trust thus decided to construct its own kiln and then lease it out to local workers to establish a dedicated small-scale clay based industry.
A survey of eight sites in villages in and around Viscri was undertaken. The criteria for identifying the optimum location for a kiln was as follows:
1) A good source of clay suited to the making of bricks and tiles.
2) Good vehicular access to the site for the import and export of heavy material.
3) Access to a water supply.
4) A ready source of wood for the firing of the kiln.
5) Community support and permits for the enterprise.
Analysis was carried out at each site to identify suitable material, which requires approximately 50% clay, and 50% sand, ideal for both bricks and thin traditional tiles. Viscri was chosen as the preferred site. The actual location for the kiln, set on higher ground to the west of the village, was also the original ancient Saxon site of brick and tile production, further reinforcing its appropriateness for supplying closely matched material to the existing buildings.
The site, set on the edge of a coniferous plantation, is sloping and it was decided to place the different aspects of production in sequence down the hillside to minimise the amount of lifting.
A small reservoir was excavated at the top of the bank to collect surface water. An underground pipe was laid from the reservoir to the clay preparation area where soaking pits were excavated. From here material could be loaded into the horse-powered clay-pugging machine and finally delivered to the workbenches in the combined brick and tile workshop and drying shed.
The process of making bricks and tiles is as follows: the wet clay is thrown into a mould for bricks or into an iron frame for tiles, constructed approximately 10% larger than the desired finished product to allow for shrinkage. The “green” bricks and tiles are laid on drying racks to harden up through evaporation prior to loading into the kiln. With tiles it is critical to avoid a rapid drying out as this will create structural tension across the material and lead to cracking. The drying shed is thus timber clad with very narrow gaps between the boards to create minimal air movement.
The kiln is established on the lowest part of the site. It is an open chamber whose dimensions are 5 metres long, 3 metres wide and 3 metres high, with a loading door facing the drying shed. It is constructed of hand made bricks with a clay mortar to minimise movement and cracking during the firing process. A shelter has been constructed over the kiln to protect it from the elements particularly during firing when water penetration would ruin the contents.
Three fire holes are located on either side and fires are alternated every 24 hours with the opposite side then temporarily blocked with dry bricks and sealed with clay. This process allows for a gentle and even build up of heat during the firing period. Within the kiln the first vertical metre close to the fires is stacked with bricks set approximately a finger width apart. Fire tunnels are created to the same dimension as the fire surrounds on the kiln and these continue through the stack. The remainder of the kiln volume is either filled with bricks or tiles depending on need up to some 2.7 metres in height. Two layers of fired bricks are then laid on top.
For some two days gentle fires gradually warm the kiln and contents until all residual moisture is driven off. At this point a layer of soil is placed over two thirds of the area of fired bricks and the heat intensified. The one third open area is alternated from side to side opposite the side being fired, to exhaust the fire and draw the heat through all of the stack. This process continues day and night for a further four days until the last 48 hours when the entire stack is covered in soil apart from approximately 300 mm squares in each corner. This final heat soak should result in an even firing of the kiln, which at the end of six to seven days should be 950-1000 degrees centigrade.
The kiln is allowed to cool slowly for some 4-5 days after which the contents may be unloaded and distributed for use.
Colin Richards September 2006