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Brick clay: Geology and mineral planning factsheets for Scotland

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Brick clay is the term used to describe 'clay and shale' used in the manufacture of structural clay products, such as facing and engineering bricks, pavers, clay tiles for roofing and cladding, and vitrified clay pipes. Brick manufacture is the largest tonnage use. Fireclay is also used in the manufacture of these products, particularly facing bricks. The term 'fireclay' was derived from their ability to resist heat and their original use in the manufacture of refractories for lining furnaces. ' Fireclay' is currently used to describe seatearths of economic interest, irrespective of their refractory properties.

Brick clays and fireclays are essentially sedimentary mudstones of different geological ages, sources and compositions. These range from relatively soft, plastic clays to hard mudstones. Their chemical properties, which are related to their mineralogical composition, and physical properties, particularly grain size, are critical to determining their suitability for the manufacture of structural clay products. These properties affect the forming behaviour of the clay (the process prior to firing in which the ware is shaped), its behaviour during drying and firing, and also the final properties of the fired product. These latter properties include strength, water absorption (porosity) and frost resistance, and thus durability and performance in service. Importantly, they also affect aesthetic appearance, such as colour and texture, providing greater choice and style for architects and developers.

Fireclays are sedimentary mudstones which occur as 'seatearths' underlying almost all coal seams. Seatearths represent the fossil soils on which coal-forming vegetation once grew and are distinguished from associated sediments by the presence of rootlets and the absence of bedding. Fireclays are, therefore, mainly confined to coal-bearing strata and are commonly named after the overlying coal seam. The production is closely related to opencast coal extraction.Fireclays are typically thin (normally <1 m, although rarely >3m) and are composed of the clay minerals kaolinite and hydrous mica (illite), together with fine-grained quartz in varying proportions; kaolinite is the key component. Typically these three minerals make up some 90% of the rock and their relative proportions, together with the amount and type of impurities present (carbon, sulphur and iron), greatly influences their ceramic properties. In contrast to most brick clays, which are red firing, fireclays produce buff/cream coloured bricks because of their lower iron contents.

Clay bricks (and tiles) are versatile and durable construction materials and, along with building stone, one of the most visible components of the built environment in Scotland. In addition to their functional use, they make a major contribution to local architectural styles in our cities, towns and villages. The variety of clay used can give rise to distinctive regional variations in the appearance of the built environment. Some handmade brick and tile products are manufactured in Scotland for the repair of historic buildings.

Fireclay extraction at Greenburn opencast coal site, Ayrshire, Kier Mining Ltd. Picture courtesy of © Kier Mining Ltd.
Fireclay extraction at Greenburn opencast coal site,
Ayrshire, Kier Mining Ltd.
Picture courtesy of © Kier Mining Ltd.

Some clay and shale is also used for cement manufacture, engineering purposes, such as lining and capping landfill sites, lining canals and ponds and for general construction purposes (fill).

Most bricks and related clay-based building products are manufactured in automated factories. These represent a high capital investment in plant and are increasingly dependent, therefore, on raw materials with predictable and consistent firing characteristics in order to achieve high yields of saleable products. Blending different clays to achieve improved durability and to provide a range of fired colours and textures is an increasingly common feature of the brick industry. Continuity of supply of consistent raw materials is of paramount importance. Whilst in the past brick clay was usually consumed in brickworks adjacent to the quarry, today increasing tonnages are transported to other brickworks for blending purposes or to serve plants with no associated clay reserves.

Demand

'Facing' bricks for use in the domestic housing market account for the largest portion of demand for bricks in Scotland. These are bricks produced to high technical standards, so that they are resistant to the weather, and also have an attractive external appearance. The combination of cold and wet in the Scottish climate presents a particular challenge to brickmakers. The introduction of new, and more demanding, EU durability standards for bricks is placing greater constraints on the types of clays that can be used. Most brick clays are red firing, but there is a particular demand in Scotland for durable buff/cream coloured bricks manufactured from fireclays. Brick clays are also used to make 'engineering' bricks, which are high strength, low porosity bricks used in load-bearing structures and in other technically-demanding situations.

Harled masonry is a popular vernacular building style in Scotland which means that there has been a demand for 'common' bricks (bricks for general construction whose appearance is unimportant), although concrete blocks are making serious inroads into this market.

Although not currently manufactured in Scotland, brick clays can also be used for 'paving' bricks which are designed for hard wear, low porosity and resistance to frost, as well as other types of structural clayware, such as pipes for drainage and sewerage, and roof tiles.

Figure 1 Sales of clay and shale in Scotland, 1996 - 2005. Source: AMRI, Office for National Statistics.

Figure 1 Sales of clay and shale in Scotland, 1996 - 2005. Source: AMRI, Office for National Statistics.

Supply

Extractors' sales of 'clay and shale' for the manufacture of bricks, pipes and tiles are not separately recorded for Scotland by the Annual Minerals Raised Inquiry. Sales shown in Figure 1 are for total 'clay and shale' and included is some years substantial tonnage probably for construction fill. Clay and shale production for brick manufacture is estimated to be in the range 200-300 000 t/y. In addition, some 35 000 t/y of fireclay is also used in brick manufacture.

In 2005, Scotland accounted for just less than 4% of UK production of clay bricks. Whilst output of engineering bricks has remained fairly static in Scotland in recent years, production of both common and facing bricks has declined substantially (Figure 2). The decline in output of common bricks reflects a UK-wide trend in the substitution of these bricks by concrete blocks in internal walls and harled masonry. Overall UK output of facing bricks has been relatively steady since 2000, whereas Scottish production has declined by over 30%. The reasons for this are unclear, although the steep drop in output from 2000 to 2001 may be due in part to the closure of Wemyss Brick at Methil in Fife in 2001.

Figure 2 Brick Production in Scotland 1999-2005. Source: DTI Monthly statistics of building materials and components.

Figure 2 Brick Production in Scotland 1999-2005. Source: DTI Monthly statistics of building materials and components.

Consumption

House building is the main consumer of bricks (and therefore brick clay). Across the UK there is a reasonably close positive correlation between brick production and house building. However, in Scotland, this connection is not well defined. In contrast to the downward trend in brick production, new dwelling starts have been on the increase in Scotland since the late 1990s (Figure 3). The reasons for this contradiction are unclear. Contributing factors probably include:

  • Trend toward higher density housing. Smaller houses and flats consume fewer bricks per unit. This trend is having an impact on the brick industry across the UK. In addition, Scottish cities have a higher proportion of their population living in flats when compared to cities in the rest of the UK.
  • A preference for harled masonry. Housing constructed in this style reduces demand for facing bricks and increasingly utilises concrete blocks rather than common bricks.
  • Imports from England. Although some Scottish bricks are exported to England and Ireland, it is likely that Scotland is a considerable net importer of bricks, mainly from manufacturing sites in England.

Despite relatively high levels of new housing starts, this combination of factors makes future brick consumption patterns in Scotland difficult to predict.

Economic importance

Clay and shale used in the manufacture of bricks are not generally sold on the open market but are consumed by the brick manufacturers themselves. The principal exception to this is fireclay, although it is becoming more common for brick clays to be traded. Objective evaluation of importance to the Scottish economy is difficult because of a lack of specific statistical information. Brick clay has a very low unit value ( ex-quarry about £2.3/t) and the total value of clay and shale production in the UK is placed at only £24 million in 2004. Although brick clay is a relatively low priced raw material, it supports a manufacturing industry of some considerable importance with a high value-added component. The total value of sales of clay-based construction products in UK as a whole was £632 million in 2004, with brick sales accounting for over 80% of the total. Bricks are themselves important building materials for the construction industry, which is a major sector of the Scottish economy. In 2004, the total value of the work done in the construction sector in Scotland was £8.61 billion; £5.71 billion of new work and £2.90 billion repair and maintenance.

Figure 3 Housing starts in Scotland 1999-2004. Source: Scottish Executive.

Figure 3 Housing starts in Scotland 1999-2004. Source: Scottish Executive.

Structure of the industry

There are four companies manufacturing bricks in Scotland. The location of the industry mainly reflects the distribution of clay resources. These companies operate 5 brickworks with a combined capacity to produce 120 million bricks per year (Table 1). Plants operating currently have individual capacities ranging from 10 to 50 million bricks per year.

Company

Brickworks

Kiln

Capacity/year

Type

Caradale Traditional Brick Ltd

Mayfield Works, Carluke

Hoffman

14 million

Pressed

Caradale Traditional Brick Ltd

Etna Works, Armadale

1 x Hoffman

1 x Intermediate

21 million

Extruded

Errol Brick

Errol

Tunnel

10 million

Extruded

Ibstock Scottish Brick

Uddingston

Tunnel

50 million

Extruded

Raeburn Brick Ltd

Blantyre

2 x Tunnel one operational

25 million

Extruded

Snowie Heritage Brick

Fired at Raeburn Blantyre

4 million (Fired at Raeburn Blantyre

Extruded

Table 1 Brick making companies in Scotland.

The brick industry has undergone major rationalisation over the last two decades through mergers, acquisitions and brick plant closures.

The largest producer in Scotland, with a production share of over 40%, is Ibstock Brick Ltd (owned by the CRH Group based in the Irish Republic). Although Ibstock operates a relatively large number of manufacturing operations concentrated in England, it has only one site in Scotland. This company also imports bricks from its factories in Northern England. Remaining production share is taken by 3 smaller companies which are indigenous to Scotland. Although it has no production units in Scotland, Hanson Brick UK (the UK's largest manufacturer) imports some 29 million bricks yearly from its plants in England. Although figures are unavailable, other companies with manufacturing units in England also import bricks into Scotland.

Gas fired Hoffmann kiln, Etna Brickworks, Caradale Brick Ltd, Armadale, West Lothian.
Gas fired Hoffmann kiln, Etna Brickworks, Caradale Brick Ltd, Armadale, West Lothian.

The British Ceramic Confederation is the trade association for the ceramic manufacturing industry and deals with, amongst other topics, issues related to raw materials supply. The Brick Development Association is the trade association for the brick sector and deals primarily with technical standards, marketing and bricks in use. The interests of the clay pipes and roof tiles sectors are dealt with by the Clay Pipe Development Association and the Clay Roof Tile Council respectively.

Figure 4 Scotland: Distribution of the principal brick clay resources.
Figure 4 Scotland: Distribution of the principal brick clay resources.

Resources

A wide range of clays (including clay or shale waste from other mineral extraction operations such as coal mining) have been used in the past in the manufacture of structural clay products. Clays are relatively common in many parts of Scotland and resources are, therefore, potentially very large. However, many clays are unsuitable for brickmaking. The extent of the principal brick clay resources is shown in Figure 4, although not all the areas shown will be suitable for the manufacture of structural clay products. The presence of other rock types, such as siltstone and sandstone, which may predominate in some areas, high overburden thicknesses and excessive amounts of impurities, such as carbon and sulphur, will also preclude working in some areas (see below).

Sedimentary clays consist essentially of clay minerals and quartz, although other minerals may occur in accessory amounts. These other minerals may have a considerable affect on the suitability of clay for brick manufacture. In a brick clay, there must be sufficient clay minerals present to make it plastic to mould and to retain its shape prior to firing. 'Fluxing' materials (usually potassium, sodium and/or iron) must also be present to allow the clay to vitrify (partially fuse to form a glass to give the product strength) when fired. An adequate proportion of non-plastic constituents, usually quartz, is also required to prevent excessive shrinkage and deformation during drying and firing. In good quality brick clays, the predominate clay minerals are kaolinite and illite. These impart desirable properties which are important in forming and firing the brick. Carbon and sulphur can have a major influence on firing performance and emissions, and low levels are preferred (< 1.5% and 01% respectively). The familiar red/ brown colour of most bricks is due to the presence of iron minerals in almost all clays. However, the presence of carbonate minerals, such as calcite and dolomite, can produce paler-coloured bricks. Carbonate minerals must be in fine-grained form as coarse carbonate leads to a problem known as 'lime-blowing' (falling away of the surface of a brick due to expansion, following hydration of nodules of lime). Production of very pale buff/ cream 'through-colour' bricks is presently only made possible by using fireclays with low iron contents. In the manufacture of bricks and other structural clay products, the term 'clay' is used relatively loosely, since the clay mineral content of the raw materials may vary from 20% to 80%.

With the reduction in the number of brick and pipe works, clay production has become concentrated on a much more limited range of clay resources. Modern brickmaking technology requires a high capital investment and is increasingly dependent, therefore, on raw materials with predictable and consistent firing characteristics in order to achieve high yields of saleable products. This ensures that raw materials (both clay and energy) are used optimally, an important objective of sustainable development. Blending different clays to achieve improved durability and to provide a range of fired colours and aesthetic qualities is a common feature of the brick industry.

Current production is confined to North and South Lanarkshire, West Lothian and Perth and Kinross. Although other clays are used on a small-scale, the location of the industry tends to reflect the distribution of the principal brick clay resources. In approximate order of tonnage used in brickmaking these are:

  • Carboniferous mudstones in central Scotland: variable in quality, with only a small proportion suitable for brick manufacture (most are too high in carbon and sulphur). Despite this, they are the most important resource, accounting for almost 92% of consumption.
  • Fireclays (from Carboniferous coalfields): associated with coal seams and produced mainly as a by-product of opencast coal extraction. Although a minor component of total consumption, they are important clays used extensively in high-value, highly durable extruded buff bricks which are manufactured in Scotland.

Important brick clay resources are located close to the major population centres of the Midland Valley of Scotland. These are: mudstones ('blaes') including fireclays in the extensive but largely drift (Quaternary) covered Carboniferous outcrop and virgin clay and silt in Quaternary deposits. The Scottish brick industry also utilises waste (secondary) blaes from tips ('bings') produced by past coal and oil shale mining activities (see section below on 'alternatives and recycling').

Scottish Carboniferous sedimentary rocks, including mudstones and fireclays, are generally low in pyrites (this is also true for the associated coal seams) except where oil shale is present or the mudstones are of marine origin. With the exception of oil shale horizons (such as the West Lothian Oil Shale Formation) and some thin canneloid (coaly) shales, Scottish Carboniferous mudstones in the Midland Valley of Scotland are also relatively low in carbon.

Subsystem

Lithostratigraphical Units

Formations

Groups

Central Coalfield

Fife Coalfield

West Lothian

East Lothian

Upper Carboniferous

Upper Coal Measures

Coal Measures

Middle Coal Measures

Lower Coal Measures

Passage Formation

Clackmannan Group

Upper Limestone Formation

Limestone Coal Formation

Lower Limestone Formation

Lower Carboniferous

Lawmuir Formation

Pathhead Formation

West Lothian Oil Shale Formation

Aberlady Formation

Strathclyde Group

Kirkwood Formation

Sandy Craig Formation

Gullane Formation

Clyde Plateau Volcanic Formation

Pittenweem Formation

Anstruther Formation

Fife Ness Formation

Arthur's Seat Volcanic Formation

Garleton Hills Volcanic Formation

Clyde Sandstone Formation

Inverclyde Group

Ballagan Formation

Kinnesswood Formation

Table 2 Classification of the Carboniferous strata in the Midland Valley of Scotland. Names in bold currently worked for brick manufacture; italicised formations unlikely to be of interest.

Significant resources of mudstone and fireclay suitable for the manufacture of bricks exist throughout the Midland Valley of Scotland in the Carboniferous succession (Table 2) that cumulatively (but in no one area) amounts to a thickness of over 7 km of strata. The five remaining operating brick works are currently geographically restricted to the areas of occurrence of Upper Carboniferous rocks of the Central and Fife coalfields. Only one of these works has its' own on-site captive clay pit, the remainder rely on imported materials, largely from opencast coal sites.

Upper Carboniferous mudstone resources are available in the Lower Limestone, Limestone Coal and Upper Limestone formations in the Clackmannan Group and from the Lower and Middle Coal Measures. The Upper Coal Measures are of limited extent in central Scotland but locally (near Hamilton) are worked for mudstone and fireclay. The Passage Formation at the top of the Clackmannan Group was formerly an important source of high alumina fireclay for manufacture of refractory bricks. This formation also hosts nationally important resources of silica sand.

The Limestone Coal Formation is host to numerous coal opencast sites and at some, such as Climpy OCCS near Forth in South Lanarkshire, mudstone is stockpiled to feed the Mayfield Brickworks at Carluke. The Coal Measures are also worked extensively for opencast coal and at some sites, mudstone, and fireclay for brickmaking are or have been worked alongside coal (such as Laigh Riggend OCCS, Airdrie and Northrigg OCCS, Bathgate). The Upper Limestone Formation produced mudstone for the defunct and now demolished Niddrie Brickworks, Edinburgh.

Mudstones in the Lower Carboniferous rocks of the Midland Valley of Scotland may have some potential as brick clays, although none are worked currently.

The Quaternary deposits of central Scotland include considerable resources of both late Devensian and Flandrian raised marine and lacustrine silts and clays that have been worked for common and facing bricks etc. Relatively small quantities of late Devensian marine clay are worked in the Perth area for specialist products including red facing brick. These raised marine clays are quite extensive in distribution in the Clyde, Forth, Earn and Tay valleys. Plans existed during the 1970s for a major red facing brick development at Linwood in the Clyde valley. In the past, glacial till was also used when the manpower was available to cheaply pick out the included stones and boulders. At Avondale Sand and Gravel Pit near Linlithgow, Golday Ltd work glacial till for low porosity canal construction clay and landfill liner.

Large quantities of red brown sandy and silty mudstones occur in the Lower Devonian sedimentary rocks of the Strathmore area of the northern Midland Valley of Scotland. These particularly occur in the Cromlix Mudstone Formation. Their brick making character is unknown.

Reserves

In mineral planning, the terms 'reserves,' 'mineral reserves' or 'permitted reserves' refer to the tonnage of mineral that has a valid planning permission for mineral extraction. Without a valid planning permission no mineral working can legally take place and the inherent value of a resource cannot be released. There has been no definitive survey of the size (tonnage) of permitted reserves of brick clay in Scotland (or elsewhere in Britain). However, in the course of preparing their development plans, planning authorities may gather this information for their areas.

Figure 5 Relationship of Scottish clay resources to major environmental designations. National Parks-pale green; International designations- blue; SSSIs-green; Remaining colours and symbols as in Figure 4.
Figure 5 Relationship of Scottish clay resources to major environmental designations. National Parks-pale green; International designations- blue; SSSIs-green; Remaining colours and symbols as in Figure 4.

Relationship to environmental designations

Scottish brick clay resources are largely unaffected by national landscape designations, although some are coincident with national nature conservation designations.

Extraction and processing

The brickmaking process consists of several different stages; clay extraction; clay preparation, in which the raw material is reduced to a workable consistency for forming or shaping; forming; drying to remove moisture and to give the brick strength to retain its shape, and finally firing.

Brick clays are worked entirely by open pit methods. A range of equipment and working methods have evolved to meet the very differing demands of deep or shallow quarries, uniform or heterogeneous deposits, soft clays or hard shales.

The impracticability and cost of removing impurities is such that brick clays undergo little processing other than grinding and screening to remove any hard or coarse components. It is, therefore, important to extract the clay selectively, avoiding any contaminating material and to ensure subsequent homogenisation of the clay raw material so that the feed to the plant has consistent and predictable firing characteristics. Clays with different properties are laid down as superimposed layers in stockpiles, which are later removed vertically to ensure a consistent mix. Many stockpiles are allowed to 'sour', a process of weathering over several months to increase plasticity. Primary crushing and stone removal are sometimes necessary at the quarry site. Blending different clays to achieve improved durability and to provide a range of fired colours and textures is an increasingly common feature of the brick industry.

Most bricks manufactured in Scotland are formed or shaped principally by extrusion, although one producer does produce hand-made bricks using the 'soft-mud' process. Another producer uses pressing to manufacture bricks. Extrusion involves forming a column of clay by pushing the material through a die at high pressure. The rectangular section column is then cut into bricks (known as 'wirecut'). In the soft-mud process, individual bricks are formed in a sand-lined mould from clay with a relatively high moisture content (known as 'stock' bricks). This process produces bricks with an irregular outline, often showing surface creases and sanded on all surfaces. The aesthetic properties of these bricks have resulted in a resurgence in their popularity. Although soft-mud bricks can be machine made, hand-made bricks are popular, particularly in producing bricks for conservation projects and awkwardly-shaped 'specials'.

The bricks are then dried prior to firing. Most are fired using natural gas in a linear kiln known as a 'tunnel kiln', which allows the process to proceed continuously and in which a line of cars loaded with bricks is pushed through a stationary firing zone. Traditional semi-continuous Hoffman kilns are also still used in one brick making operation in Scotland. The important changes relating to the development of brick properties result from the breakdown of the original clay mineral and the formation of new crystalline material and glass phases. The temperature at which vitrification (glass formation) occurs depends on the mineralogy of the clay. Vitrification usually begins at 900 oC and is complete by 1050 oC-(or up to 1100°C in the case of more refractory fireclays). Vitrification gives the brick the strength and durability it requires to perform in service, as well as an attractive appearance. 'Facing' bricks are used in external walls where architectural appearance is important - they can be wirecut or stock bricks. Wirecut 'engineering' bricks are made to meet strict technical specifications for use in demanding situations where strength and durability are critical. Conventional tunnel kilns normally require a 2-3 day firing cycle.

The EU Integrated Pollution and Prevention Control Directive has been implemented in the UK by the Pollution Prevention Control Regulations. All facilities for the manufacture structural clay products require a permit from the Planning Authority or SEPA as appropriate. Permits are site specific and take into account amongst other factors the raw materials used. Permits cover plant operating conditions and emissions such as fluorine and sulphur dioxide.

Working Clay Stockpiles at Edge Farm, East Kilbride; Raeburn Brick Ltd, Snowie Heritage Brick Ltd. Brick clay for the Snowie Bricks is imported from an initial stockpile at Brotus pit, Cults, Fife then stored under the cover shown until ready for fir
Working Clay Stockpiles at Edge Farm, East Kilbride; Raeburn Brick Ltd,
Snowie Heritage Brick Ltd. Brick clay for the Snowie Bricks is imported
from an initial stockpile at Brotus pit, Cults, Fife then stored under the
cover shown until ready for firing at Raeburns Brickworks.

Alternatives/recycling

Some secondary materials and waste types can, in some circumstances, be used as a partial substitute for primary clay in the manufacture of bricks, although not currently in Scotland.

Colliery spoils, together with waste burnt oil shale form a secondary source of brick shale and continue to be important to the operating industry. With the closure of all the Scottish deep mines, these materials are a finite resource. This resource is also being depleted by the continuing use of these materials as fill. Reservation of coal-rich ('fiery') waste shale bings for brick manufacture may be considered because of the reduction in fuel costs in processing perhaps partly taking account of sustainable use of minerals. The use of pulverised flue ash for brick manufacture as well as currently for building blocks may also be a possibility.

Pulverised Fuel Ash ( PFA) is a glassy, silt-grade material which is a by-product of coal incineration in thermal power stations. This material is finding increasing usage in the manufacture of both pressed and soft-mud bricks where it typically replaces between 10 and 20% of the clay. Other furnace ashes such as Municipal Incinerator Bottom Ash might also be used in a similar way by the brick industry.

Granular blast furnace slag can be used in extruded bricks. This material reduces emissions by dilution and by reaction with gases emitted by the clays. Research and production trials carried out elsewhere in the UK have demonstrated that addition of ground recycled glass to certain brick clays can have some modest benefits in reducing firing temperatures and emissions from kilns.

Carefully controlled amounts of waste organic materials such as sawdust, chopped straw or foamed polystyrene can be added to the clay mix, along with paper mill waste and, after incineration, water treatment sludge and sewage sludge.

Concrete blocks, bricks, pipes and tiles are the main alternatives to clay products. Concrete blocks are replacing 'common' bricks in building interior and harled exterior walls. Plasterboard and stud walling is replacing both clay and concrete products in internal walls. Other building materials such as steel, timber, glass, and natural and reconstituted building stone compete directly with clay-based products. Block pavers and roof tiles made from concrete compete with those made from fired clay. Fired clay drainage pipes compete with those made from plastic (smaller diameters) and concrete (larger diameters).

Re-use of bricks for matching style in conservation and other building work is common practice. Recovery of bricks, for re-use as bricks, is generally limited to those buildings which are more than 60 years old where lime mortars were used. Bricks of that age and older can, subject to careful selection and cleaning, have an appreciable 'new' life in new construction projects. This is due to the lower strength of these mortars making them easier to separate from bricks. However, re-use may cause environmental and economic costs arising from the operation itself, as well as storage and transport. Problems may also arise due to the mismatch between imperial components in metric structures. Technical properties, such as frost resistance, may be uncertain.

Brick buildings less than 60 years of age were normally constructed using Portland cement based mortars. These mortars have superior setting and bonding strength. The removal of cement mortar to enable bricks to be reused is not practical. However, subject to the quality of the brick, the material can be recycled to produce low quality aggregate such as capping layers and sub-base in road construction, and drainage blankets in civil engineering.

Effect of economic instruments

'Clay' and 'shale' are exempt from the Aggregates Levy and these materials may be used as sources of bulk fill where they are unsuitable for brick manufacture. However, problems have arisen with the precise definition of these terms and the BGS has produced a report to describe them in more detail (see Further information). Sandstone occurs as overburden at some sites and may be sold as a low quality aggregate. Increasing competition from alternative aggregates that are exempt for the Aggregate Levy may, however, locally have had an impact on sales of this material resulting in increased overburden removal costs.

The UK Government introduced the Climate Change Levy ( CCL) on the 1 st April 2001, which applies to some fuels used by energy intensive industries including the brick industry. In exchange for an 80% rebate on the Levy the brick industry has agreed challenging energy reduction targets through energy saving measures.

The EU Emissions Trading Scheme ( EUETS) came into effect in 2005 with the objective of reducing the EU's carbon dioxide emissions. The brick industry is eligible for EUETS and an allowance on carbon dioxide emissions has been allocated for almost all brickworks in Britain, although, in common with other energy intensive industry, as low CO 2 emitters most brickworks have been given a temporary exclusion from the Scheme until 1 st January 2008. Allowances can be traded if they are not reached or exceeded. In the brick industry carbon dioxide is derived from two sources; the fuel used to manufacture the product and from the body itself where this contains carbonate minerals. For some products with high carbonate contents, carbon dioxide emissions from the clay body may be as much as from the fuel used for firing.

The extent to which both CCL and ETS will have on raw materials requirements is difficult to judge at this stage. For example, increasing the volume of perforations in a brick will reduce the amount of clay used and consequently save fuel when firing. However, a change to using lower carbonate bodies would have major implications for the colour and appearance of the product and thus on the very properties for which it is marketed.

Transport issues

There is an increasing trend towards the import of clays and other raw materials from off-site into brickworks which, in the past, would have relied entirely on raw material from a 'captive', on-site pit. This trend is generally driven by the need to improve locally sourced clays to allow manufacture of bricks which both meet the highest technical specifications, and give the consumer maximum choice of colours and textures. This tendency is likely to increase, as product specifications get tighter. It is highly unlikely that this movement of clay will be by any other method than road. However, compared to movements of some other minerals (particularly aggregates), the volumes involved are small. The manufactured products are almost always transported to the market by road.

Planning issues

Planning issues centre on the environmental acceptability of the quarry and the manufacturing plant in any proposed location. However, a number of other issues are relevant.

The important role that bricks and related products play in determining the appearance and quality of our built environment is widely recognised. The variety of brick products contributes to the rich regional and local architectural heritage of Scotland as well as the repair of traditional brick built structures.

Clays used in the manufacture of bricks have a major influence on their technical performance and appearance, and consumers are likely to continue to demand a wide choice of high quality, affordable bricks. In order to satisfy this demand, remain competitive and meet increasingly stringent environmental controls, industry requires continued access to a range of clay resources, including premium quality clays, such as Carboniferous age fireclays.

The levels of capital investment required to build and maintain automated manufacturing plant, with associated environmental engineering, are large and require security of supply for brick clay to allow operators to secure and justify that investment. This could, in some cases, be as much as 20 or more years. Technical innovation in brick, tile and pipe products, together with the implementation of more stringent European technical standards, increasing use of automated manufacturing and tighter controls on kiln emissions has led to more blending of clays, and therefore a trend away from using clay from a captive pit toward increased transport of material from other sites. The supply of brick clays to individual brickworks is increasingly from more than one source.

The key planning issue concerning fireclay is that supply is mainly an ancillary operation to the extraction of opencast coal. It is, therefore, future planning permissions for opencast coal extraction that will essentially govern future fireclay supply. The associated recovery of fireclay may provide additional support for an opencast coal proposal on the grounds of making the best possible use of the resource, in line with the principles of sustainable development. However, it is also likely to generate some additional impacts, such as increased lorry movements, adjustments to the restoration programme and, perhaps, some uncertainty about the actual timing and rate of working of individual extractive operations. Unlike brick clay extraction, opencast coal operations tend to be rapid and short lived such that fireclay is made available over concentrated periods. There is invariably a mismatch between potential fireclay supply and the requirements of the market, raising the issue of stockpiling on or off site. Stockpiling ensures that fireclay reserves can be made available rather than lost, but creates the potential for further impacts and the development of a stocking site that may be used over a long period.

Further information

Scottish Planning Policy 4. Planning for Minerals

Scottish Planning Policy 16. Opencast Coal

Brick Clays: Issues for Planning. A J Bloodworth, J F Cowley, D E Highley and G K Bowler. British Geological Survey Commissioned Report, CR/01/117N.

Definition and characteristics of very-fine grained sedimentary rocks: clay, mudstone, shale and slate. R J Merriman, D E Highley and D G Cameron. British Geological Survey Commissioned Report, CR/03/281N.

Elliot, R W. 1985. Central Scotland Mineral Portfolio: Resources of Clay and Mudstone for Brickmaking. Open-file report of the British Geological Survey, Edinburgh.

Authorship and acknowledgements

This factsheet was produced by the British Geological Survey for the Scottish Executive .

It was compiled by Don Cameron and Mike Browne (British Geological Survey) based on previous work by Andrew Bloodworth and David Highley (British Geological Survey) and John Cowley (Mineral & Resource Planning Associates), with the assistance of Deborah Rayner.

The advice and assistance of the brick industry is gratefully acknowledged.

© Crown Copyright 2007

Unless otherwise stated all illustrations and photographs used in this factsheet are BGS© NERC. All rights reserved.