The Building Conservation Directory 2022

85 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 2 2 MASONRY 3.2 cut and rubbed, and ‘gauged’ brickwork which was popularised by Wren. This used a facade of fine, colour-matched bricks cut and rubbed to exact units, laid with thin joints of lime putty and silver sand. After 1730 however, this was considered too expensive for complete facades and was generally reserved for window arches, aprons, niches and other architectural ornamentation only. VICTORIAN BRICKWORK 1830–1914 The 19th century introduced a period of revivalism in domestic architecture and industrial building. The former, led by architects, ultimately turned to ‘medievalism’ and other exotic building forms as a relief from the un-spirituality of the Machine Age. The latter, led by engineers, was largely met through the cheap use of bricks for the more utilitarian infrastructure such as factories, warehouses and railway bridges. During this period, more bricks were made and laid than during all the previous periods. Brick manufacturing methods had improved in all areas including quality, accuracy and regularity, and in a larger range of colours available. From the mid- 19th century onwards, the manufacturing process, like many others, was becoming mechanised. This enabled deeper clays to be used for pressing into dense bricks for use on civil engineering works. With improvements in travel and communications, bricks could be transported over wide areas which removed the traditional local variations in building materials, particularly in cities and towns with rail connections. Portland cement continued to develop in quality and strength, and by the second half of the 19th century this binder increasingly took a premier position over natural cements. A particular factor in its rise was its highly successful use in the construction of the new brick-built sewers in London. Brickwork joints reduced to 0.3 inches (8mm) due to the accuracy of the machine pressed bricks, and continued to be finished in various profiles. These were popular from the 17th century, although the new ‘ weather-struck’ and ‘cut’ style of joint became particularly popular. A variety of face bonds were now used, although in the main, Flemish bond predominated domestically, while English bond was favoured industrially. In all matters of brickwork, the Victorian desire for enrichment was readily achieved by the use of often garish multi- coloured or ‘polychromatic’ work, and the lavishing of ornamentation by detailing mass-produced, purpose moulded ‘special- shaped bricks’ or by gauged brickwork. DECAY, CONSERVATION AND REPAIR Before considering the most appropriate method of repairing brickwork, correct diagnosis of the cause of failure is vital. Manufacturing defects in bricks can be the result of under-firing or impurities in the clay used. These bricks decay more rapidly than better burnt bricks, especially with frost action. They can also act as a point of entry for moisture, which in turn will affect the whole wall, leaving it open to damage from frost and chemical action. Free standing walls, parapets and retaining walls are particularly vulnerable, and some judicious replacement may be necessary. Sulphate attack can occur when water is present with OP cement-based mortars, producing slow steady expansion of sulphate crystals within the mortar or the bricks as the water evaporates. It is a terminal condition in OPC mortars, and can result in damage and even failure of the masonry. This is particularly common in unlined chimney stacks, where sulphates have been introduced by the burning of sulphur-rich fossil fuels. Where chimneys have been designed without bends, allowing rain straight down the flue, damp may appear on the chimney breast with a possible resultant salt problem. This can especially occur when the air is humid, or where the fireplace has been sealed without proper ventilation. Victorian carved and gauged brick pilaster in South Kensington, London with fine joints of lime putty and silver sand, and (below) a similarly gauged brickwork crest carved in situ by the author Construction Defects Poor detailing can also contribute to failure through construction defects such as: 1. The decay of timbers which have been embedded or built into the masonry: these may include bond timbers, joists, timber lintels, plates or bearers 2. The expansion of rust on corroding iron and steel structural members, wall ties or reinforcement embedded in the brickwork 3. The failure of arches and lintels from inadequate bearings, or abutments 4. Poor bonding between brickwork skins or leaves, often due to a bad