The Building Conservation Directory 2022

132 T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 2 2 C AT H E D R A L C O MM U N I C AT I O N S and residual staining (and ‘ghosting’) is likely to remain after cleaning. Conversely, hard, dense, non-absorbent/ non-porous masonry surfaces, such as polished granite, glazed brick and terracotta, glass, and smooth textured concrete are relatively impermeable, non- porous and resistant to penetration of graffiti media. Such surfaces are therefore typically easier to clean. However, these surfaces can be damaged by etching using strong chemical cleaning agents or abraded by mechanical cleaning using excessively high pressures. EFFECTIVE GRAFFITI REMOVAL There is considerable variability in the type of graffiti medium employed, and in the type of surface (material) that may be targeted, as well as the surface condition. Consequently, the cleaning (removal) method must be tailored to fit – a generic ‘one size fits all’ approach is very unlikely to be effective. In most urban areas local planning authorities (LPAs – councils) offer a removal service, which can be accessed online. However, this typically comes with a caveat and a damage waiver, absolving the LPA and their cleaning subcontractor of responsibility for damage, including any surface damage that may occur during cleaning. In this context, cleaning services are offered as part of environmental services and street cleaning, often falling into the same general category as removal of chewing gum, flyposting, dog fouling and dead animals! In general, cleaning services offered in this way cater for relatively robust (hard/ resistant) surfaces, such as pavement and concrete, and consequently often employ high pressure methods (normally water, sometimes pressurised air and abrasive). This kind of standard approach (designed/ intended for modern buildings and street materials and finishes) is likely to be damaging to historic building surfaces. Selection of cleaning method should always be subject to a small-scale removal trial in a pre-agreed area. A trial is essential to determine the optimal cleaning method, which might include several stages or processes and might potentially include more than one cleaning agent (proprietary product). The trial area should be inspected after the surface has dried and the cleaned section should be free of residual staining and marks. A suitably skilled and experienced contractor should be able to demonstrate their understanding and skills by providing examples of graffiti removal work from historic building surfaces, including ‘before and after’ photographs to illustrate these. There are many proprietary cleaning products (chemical cleaners) designed to target specific graffiti media and binder types, some of which are designed specifically for historic buildings. This latter group of specialist cleaning products and systems is preferable, and includes chemical cleaners designed to be easier to apply and less hazardous for the user, the surface, and the wider environment. Among these are clear gel poultices which are easier to apply and control than liquid cleaners and can be left in place for the optimal duration (dwell time), provided they are not allowed to dry out. In general, all chemical cleaning residues need to be rinsed from surfaces and this is most effectively achieved using a hot water pressure washer, subject to a site trial to ensure the minimal pressure setting is used to achieve effective cleaning without surface damage. Further information on suitable cleaning methods can be found in the Historic England guidance document Graffiti on Historic Buildings: Removal and Prevention (Historic England 2021, co-authored with Jamie Fairchild) under the headings Mechanical, Water and Chemical cleaning. This document includes case studies and covers graffiti prevention, from physical barriers such as anti-graffiti coatings on masonry to social measures, education, building local engagement and appreciation of the historic environment. Recommended Reading GRAFFITI REMOVAL Graffiti on Historic Buildings: Removal and Prevention, Historic England , Swindon 2021 Technical Advice Note (TAN) 18, The Treatment of Graffiti on Historic Surfaces , Historic Scotland, Edinburgh, 1999 M J Whitford, Getting Rid of Graffiti: A practical guide to graffiti removal and anti-graffiti protection , Routledge, London, 2016 HISTORIC GRAFFITI AND PROTECTIVE (WITCHES) MARKS Matthew Champion, Medieval Graffiti: The Lost Voices of England’s Churches , Ebury Press, 2015 Professor Ronald Hutton, Physical Evidence for Ritual Acts, Sorcery and Witchcraft in Christian Britain , Palgrave Macmillan, London 2016 Brian Hoggard, 2021, Magical House Protection: The Archaeology of Counter- Witchcraft , Berghahn Books, 2021 RakingLightweb sitehttps://rakinglight.co.uk/ Found Folk Art on Instagram: @foundfolkart CATHERINE WOOLFITT (catherine@ cwoolfittassociates.co.uk ) is a buildings archaeologist and conservator specialising in porous building materials and historic masonry (see page 31). She is also Subject Leader in Historic Building Conservation and Repair at West Dean College (www.westdean.org.uk/study/ tutors/catherine-woolfitt). Spray painted graffiti on glazed terracotta: the paint runs illustrate the relatively impermeable (smooth and non-porous) nature of the glazed surface Above: before graffiti removal Below: after graffiti removal