The Building Conservation Directory 2022

86 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 2 2 C AT H E D R A L COMMU N I C AT I ON S craft practice during the 18th and 19th centuries of ‘ snapping ’ headers leading to a wall of largely two separate skins instead of one mass 5. Inadequate or even non-existent tying-in of brickwork at the junctions between walls, particularly where front and rear walls are insufficiently tied to cross walls 6 . ‘ Corbelling’ and ‘oversailing’ brickwork as projecting elements are especially prone to being insufficiently tailed-in to the main walling 7. Poorly designed parapet copings without damp-proof courses, leadwork, inadequate overhangs or weathering, and poor jointing techniques, all of which encourage damp penetration: and all skyward-facing surfaces, such as copings can be vulnerable. Induced Decay Alterations and ill-considered repair techniques can cause deterioration. All remedial works to historic brickwork must be carefully selected after expert analysis and should always be kept to an absolute minimum. Pointing with hard mortars is one of the most common causes of failure in historic brickwork, leading to a failure of the mortar and of the brickwork itself. Mortars should never be harder than the brickwork itself and should always be permeable to avoid trapping moisture. For these two reasons all repair mortars should be lime-based, and modern OPC- rich mortars which are dense, rigid and impermeable should never be used. Consolidants should only be applied to decaying brickwork as a last resort. Although predictably effective on soft porous bricks, their use is still in its infancy, and the long term effects of new techniques are less certain. The consolidated brick face may behave in a different manner from the base through thermal movement, resulting in eventual separation. Sealants may induce similar problems. By sealing the surface they are likely to inhibit or reduce surface evaporation leading to a build-up of moisture within the masonry, including condensing water vapour passing through from within the property. This can result in concentrating evaporation in other areas where crystallisation and frost damage may be exacerbated. Sealants should only be used in localised areas to prevent problems such as the staining which occurs from water run-off from limestone dressings, where it may be used after removal of the deposits. Inappropriate cleaning methods may cause substantial damage by removing not only the dirt but also the fireskin, leaving a pitted face. Rotary carborundum heads again, destroy the surface as well as dishing and scouring the ‘arrises’. Such methods are not cleaning, but surface removal, and will accelerate re-soiling and rate of decay by producing a more textured surface. Vegetation although often attractive, can be harmful to older brick walls of traditional construction. Many types of ivy and wisteria can cause serious damage to brickwork, particularly if in poor repair, or constructed of soft, possibly spalling bricks bedded in soft lime mortar where the pointing is defective. If not completely removed, these climbers should at least be heavily controlled and never allowed to reach eaves level where they might block gutters and downpipes. In a strong wind, vegetation can also transfer additional wind load, pulling out guttering, parapets, and even toppling a chimney stack. Pigeons can also present problems, especially in city centres. They can block up gutters and downpipes with feathers, detritus and excrement, causing water penetration and consequent decay. Their faeces rapidly deface the external (as well as internal) fabric, and may damage porous brickwork. Removal is difficult and expensive. Control is therefore imperative, and can involve bird nets, repellent gels, contraceptive corn pellets, poisons, traps and even shooting. Our historic environment contains a vast variety of magnificent historic brick structures, many hundreds of years old. They may appear to be built to last for centuries, but they do need to be well maintained on a regular basis and carefully repaired when deemed necessary. Recommended Reading RW Brunskill, Brick Building In Britain , Victor Gollancz Ltd, London, 1990 Historic England, Practical Building Conservation Earth, Brick and Terracotta , Ashgate, 2015 M Jenkins, Traditional Scottish Brickwork , Historic Environment Scotland, 2014 G Lynch, Tudor Brickwork, The Building Conservation Directory , Cathedral Communications, 2012 G Lynch, Joint Finishes on Historic Brickwork, The Building Conservation Directory, Cathedral Communications, 2016 G Lynch, Hot-mixed lime mortars and traditionally constructed brickwork, The Journal of The Building Limes Forum , 2017 G Lynch, Brickwork History, Technology and Practice , Routledge, 1994 G Lynch, The Colour Washing and Pencilling of Historic English Brickwork, Journal of Architectural Conservation , Donhead Publishing, 2006 G Lynch, The History of Gauged Brickwork , Elsevier, 2007 N Lloyd, A History of English Brickwork , H Greville Montgomery, London, 1925 GERARD C J LYNCH PhD , is an acknowledged master brickmason, historic brickwork consultant, educator and author of several books, numerous papers and articles on historic brickwork (see www.theredmason.co.uk ). He trained through the apprenticeship system and at Bedford College where he later became head of trowel trades. He is internationally recognised for his extensive specialist knowledge and authentic period skills in the conservation, repair and re-pointing of traditional and historic brickwork. This article is a revised and updated version of one which was originally published in The Building Conservation Directory 1993. Frost damage brickwork following saturation: the moisture expands as it freezes, causing the surface to disintegrate Fine brickwork on Salisbury station, roughly repaired following corrosion damage Late 19th century corbelled brick chimney in Bedfordshire