BCD 2019

95 C AT H E D R A L COMMU N I C AT I O N S T H E B U I L D I N G CON S E R VAT I ON D I R E C TO R Y 2 0 1 9 MASONRY 3.2 Bricks of different sizes used in the same building, five courses of the thinner facing bricks are the same height as three courses of the larger common bricks. A batch of wood fired bricks ready for use in repair work (Photo by courtesy of HG Matthews) Specially shaped bricks can be custom made to match. (Photo by courtesy of HG Matthews) It is important that when brickwork is being repaired, the replacement bricks should match the colour of those used originally to minimise visual impact. Many brick manufacturers will offer a colour matching service. It is best practice to try wherever possible to find bricks which are naturally the colour required rather than artificially tinting bricks to give a match. SHAPE Bricks in their standard form are rectangular with parallel sides. However, there are often situations where bricks of a nonstandard shape are required for both practical and decorative reasons. The two principal methods of producing a nonstandard shape are to cut a brick to the form required or to mould it to shape prior to firing, creating what is commonly referred to as a special. The use of moulded brick ornament parallels the history of terracotta, and after a brief appearance in the 15th century it largely fell out of use until the terracotta revival which emerged in the mid 19th century. Georgian decoratively shaped brickwork is predominantly carved, with simple shapes being cut using a brick axe. There is an incredible range of specials which may be found used in traditional buildings; one Scottish firm produced over 1,000 different shapes in the 1890s. When repairing brickwork which uses special bricks these should always be matched to ensure the structural and visual integrity of the brickwork. Generally, if a brick making company can supply matching standard shaped bricks then it will also be able to supply specials. Many brick makers will be able to form a purpose-made mould and supply specials to a customer’s requirements. This may take time, however, and sufficient leeway should be allowed in the planning of a project which requires special bricks to be formed. SURFACE TEXTURE The surface texture of replacement bricks should also match that of the originals, this being largely dependent on the method of manufacture and the raw materials used. Extruded bricks, for example, are likely to have drag marks on the face of the brick; common bricks are likely to have a granular appearance; pressed facing bricks a smoother more homogenous feel to surface texture. Sand moulded handmade bricks often have characteristic creases in their surface known as the brickmaker’s smile. The nature and type of inclusions found in the clay used to manufacture bricks can also influence surface appearance. If the brick type is matched the texture will normally be similar. FROST RESISTANCE The ability of a new brick to resist the actions of frost is defined under the relevant standard shown below. It is important to ensure that any bricks which are being matched for use in an existing wall have an appropriate frost resistance rating to ensure they will form a durable and long lasting repair. DURABILITY AGAINST FREEZE-THAW RATING OF NEW BRICKS Frost rating Description of rating F0 suitable for passive exposure F1 suitable for normal exposure F2 suitable for severe exposure It is likely that in repair situations of an external wall an F2 brick will be the most appropriate. F1 and F0 bricks are more likely to be appropriate for internal uses or in areas