Clay Bricks in Manufacture

More information about how bricks are made.

Wienerberger Ltd clay brick plants in the UK bring together the latest production technologies and a high degree of awareness of environmental issues and all aspects of Sustainable Manufacturing.

Extraction of Clay

As a first step, the assessment of the quality of raw material is done by experienced geologists.  After that the excavated clay is laid in layers in a stockpile to achieve consistency of the mix and in order to ensure that the maximum amount of extracted mineral is beneficially used in manufacture. Extraction of clay takes place in accordance with the British Ceramic Confederation Code of Practice for mineral extraction and in accordance with all prevailing planning permissions which control working hours and the potential adverse impacts of quarrying such as noise and dust emissions. Wherever possible the clay is transported to the production plant without use of transport on the public highway.  

The great majority of clay raw materials come from Wienerberger’s own source quarries. All sites operate Environmental Management Systems meeting the requirements of BS EN ISO 14001. Appropriate restoration plans are in place for all quarries and at the end of a quarry’s working life it is often developed to create natural habitats where wildlife can flourish. Some quarries are required by the planning permission to be restored by import of waste materials. In this case it is normal for the landfill gas evolved to be used for the generation of green electricity

Processing of Clay
 
At the start of the manufacturing process clay is collected from the stockpile and loaded into box feeders. Water, sand and other additives are added to the clay and mixed in accordance with the recipe for a particular product type. The clay mixture is then fed into the clay preparation plant where it is ground and homogenized. 
Many of our products contain recycled materials as part of an industry initiative known as MARSS (Materials from Alternative, Recycled and Secondary Sources). On average this is in excess of 13.5% of the raw material requirement although this varies between product types and manufacturing locations. All raw materials where possible are recycled within the manufacturing process to minimise waste.  Wienerberger UK MARSS usage in 2009 was an impressive 19.2%

Brick forming

The majority of bricks are formed by the extrusion method. During this process the prepared clay mix is extruded through a die and then automatically cut into individual bricks. The front face of the bricks will often be textured at this stage and may be coloured by the use of various sands and liquid and powder pigments. Other bricks are formed by soft mud pressing which is an automated version of traditional hand brick making where a much softer clay mix – higher moisture content -  is pressed into a mould and then turned out on to a pallet. Normally sand is used as a release agent as the brick is removed from the mould although a small amount of bricks are released from the mould without use of sand – these are termed “slop moulded” bricks and have a characteristic soft texture.  

Drying

Extruded bricks may be dried on pallets or stacked on a kiln car for both drying and firing. Soft mud bricks will always be dried on pallets due to the lack of rigidity in the product immediately after forming. Depending on the drying method used this can take typically between 1 to 3 days. In most cases the heat energy for drying is waste heat transferred from the firing process. After the process of drying the bricks are grouped and set on kiln cars and transferred to the kiln. In a clamp kiln the dried bricks are stacked by hand into the body of the clamp kiln.

Firing 

After drying, the bricks are then fired for typically 48 hours in a kiln which is usually heated by natural gas and achieves a maximum temperature in the range 1000 to 1100°C. Through firing the clay achieves strength and durability by the mineralogical processes which take place forming “glass” from the clay minerals present. The nature of the firing process also gives the basic colouration to the products. Most clays give a red based brick although use of some clays such as fireclays give buff and cream bricks. In some cases the firing process uses a deficiency of oxygen to give a “reduction” process which is used for the manufacture of Staffordshire Blue bricks or London Yellow stock bricks. 

Packaging, Storage & Delivery  
 
After removal from kiln cars the bricks are inspected for quality and then packed and made ready for despatch. The packaged bricks are then taken outside the plant by forklifts and placed for storage and delivery.  All our products are packaged using the minimum quantity of material necessary to protect the product during storage and transportation. Wooden pallets are generally only used at specific customer request or for some higher value products. We are continually reviewing and reducing the amount of packaging materials used in conjunction with packaging waste regulations.   Wienerberger also operates a Transport Strategy whereby our brick delivery vehicles employ the latest technology to minimise CO2 emissions and noise pollution with new vehicles having the highest possible rated Euro cap engines/lowest CO2 emission levels.   

Environmental aspects of the brick manufacturing process

Many of our manufacturing sites use recycled water collected in adjacent quarries or harvested from rain water. Projects are in place to increase the amount of recycled water used. It is the Company objective to work towards use of 100% non mains water in the manufacturing process.  

Some of our sites use green electricity generated from renewable sources such as landfill gas. It is the objective of Wienerberger Ltd to achieve a situation where the Company is a net exporter of electricity to the National Grid from the variety of renewable generation facilities created on the Company’s manufacturing sites.  

All our UK manufacturing sites require an Environmental Permit to operate from the Local Authority under the Pollution Prevention and Control Regulations. These permits require regular monitoring and inspection to ensure that pollution is not caused by our manufacturing operations. Close links are maintained with the Local Authority Environmental Health Departments and the Environment Agency who are involved in other environmental aspects of the process such as water discharge and waste management.  

All manufacturing sites work closely with the local communities within which they operate in order to ensure that environmental issues such as dust, noise and traffic issues are managed so as to cause minimum disturbance. In the event that complaints are received from neighbouring residents then these are dealt with as part of the site Environmental Management System. Many sites operate properly constituted Liaison Committees in order to maintain close communication with local residents, Parish Councils etc.  

At all our manufacturing sites in the UK we work closely with the local Wildlife Trusts with respect to habitat protection and creation. At sites where protected species exist (eg badgers or Great Crested Newts) we obtain all necessary licences from Natural England to ensure habitats are preserved. A number of our sites contain areas of land which are classified as “Sites of Special Scientific Interest” or have other nature conservancy designations. In all such cases we work closely with Natural England and the Local Authority conservation officers to manage the land in an appropriate manner.  

Wienerberger Ltd are active members of the Brick Development Association and supply information which is published annually as part of the Key Performance Indicators in the Brick Development Association Sustainability Strategy. This includes the Environmental aspects of manufacturing activities such as water use, emissions of Carbon Dioxide and disposal of waste materials in addition to the wider Social and Economic aspects of clay brick manufacture.  

Wienerberger products have been assessed by the Building Research Establishment (BRE) as part of a study to identify the Environmental Profiles of building products. These profiles are then used to create environmental ratings for different forms of masonry construction in the BRE Green Guide. When used with suitable partner materials and construction methods these products satisfy the A+ Rating in the Green Guide.  

When used as part of an appropriate masonry design, clay bricks are entirely satisfactory to meet the “Materials” requirements of the Code for Sustainable Homes. Traditional clay brick masonry is compatible with the requirements of the Code at all levels although to meet Levels 5 and 6 requires particular attention to be paid to wider aspects of the Code such as the air tightness of the building and the overall energy management system.  

All operating sites in the UK have an Environmental Management System independently certified to BS EN ISO 14001 by CICS Ltd. The first such certification was achieved at the Denton factory in 1996 and this has progressively been extended to cover all sites. Good environmental practice and the concept of sustainable manufacturing is therefore nothing new to the Wienerberger factories in the UK.