BCD 2019

94 T H E B U I L D I N G CO N S E R VAT I O N D I R E C TO R Y 2 0 1 9 C AT H E D R A L COMMU N I C AT I ON S for. Many brick making companies will supply reference panels to allow comparison of features such as texture and colour. When the search for a match has been narrowed sufficiently, samples of full bricks should be obtained and these should be compared on site to existing bricks. If several different types or sizes are required, this process will need to be repeated for each type. Sufficient time should be allowed for this process to be undertaken with care and to allow for the extra time that may be required for delivery. BRICK TYPE Bricks of many different types are found throughout the UK and identifying which is used within an area of brickwork being repaired is critical to ensuring that replacement bricks are aesthetically and technically compatible with the wall into which they will form a part. Broadly the following brick types are likely to be found: COMMON BRICK TYPES IN BRITAIN AND THEIR CHARACTERISTICS Each of these brick types has its own appearance characteristics which can be used to visually identify the type of brick present in a wall. Some buildings will use bricks of different types in different parts of the structure. For example, facing bricks may be used for the principal facade of a building with common bricks for the rear and side elevations. Likewise, rubbing bricks may be used to form gauged arches and other enrichments in walls formed of bricks of a different type. For some types such as handmade bricks there may be several different manufacturers who can supply replacements. However, matching other brick types can be a challenge. Common bricks, manufactured from colliery shale are very hard to match and a close match in terms of appearance from a company which manufactures using a different method or raw material may be the best available. SIZE The size of bricks within a wall is generally related to the type of brick and the time period in which it was produced. For example, facing bricks were commonly made thinner than common bricks, while glazed bricks were typically produced larger and laid with finer joints. During the period of the brick tax (1784 to 1850) some works produced larger bricks in order to reduce the amount of duty paid. There is evidence for regional variation in the size of bricks used related to the gauge (the height of four courses of bricks and mortar joints) to which the brickwork was to be built. In the north of England what is termed ‘northern gauge’ is commonly found in four vertical courses rising to 13.5 inches in height and in Scotland ‘Scottish gauge’ of between 12 to 15 inches is commonly found. Ascertaining the size of bricks and sourcing replacements to match is critical to ensuring both the aesthetic and structural integrity of brickwork. Generally the average size of 12 bricks over several courses is taken to give an accurate indication of the size of the bricks throughout. The length, breadth and height of the bricks will need to be established, therefore both headers and stretchers will need to be measured. As with brick type, however, bricks of different sizes can be found in the same building. COLOUR Brick colour typically ranges from dark red to orange, with white, cream or yellow bricks also common. The colour of bricks comes from a combination of the minerology of the raw materials employed in their manufacture, the temperature reached during firing and the atmosphere within the kiln. For example, the clay used for London Stock Bricks, along with alluvial and boulder clay tends to fire to a red or yellow colour. Jurassic clay of the type found in the Oxford clay formation fires to a red or light red colour. Carboniferous deposits of the type in the Midlands, Scotland and the north of England fire to red, brown or buff. Where calcium carbonate is present within brick clay this will burn to a yellow or buff colour, as will bricks formed of fireclay. Today, some manufacturers will use clays from different sources to achieve the colour required. The other way to impart colour to bricks is to glaze them, with glazed bricks coming into common use from the mid 19th century onwards. The use of bricks of differing colours for decorative effect can be seen in various contexts. Until the 17th century diaper patterned brickwork could be found contrasting darker, more thoroughly fired bricks with red brick facings. From the mid 19th century bricks of different colours (commonly lighter colours but sometimes darker) were used to form patterns. This was often seen in the formation of arches, reveals and quoins around openings. Incredibly intricate decorative patterns could be formed using such polychromatic brickwork. Where bricks are significantly decayed suitable replacements will be required to carry out an effective repair. Poor matching of bricks has a significant impact in terms of appearance and performance. Brick manufacturers will often supply reference panels to allow visual comparison with existing brickwork. Testing a full-sized brick in situ ahead of ordering a batch of replacements