PROTECTION & REMEDIAL TREATMENT 4.1 131 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 MASONRY CLEANING Practical Solutions – Professional, Technical Expertise and Project Support Restorative Techniques is an innovative supplier and manufacturer of surface cleaning systems and restoration products, with a high level of technical expertise, based on professional knowledge and significant, long experience in the field. The company is far more than simply a supplier. It provides technical support, training, CPDs and consultancy services to practitioners, architects and specifiers, involved with demanding conservation and restoration contracts, to help attain successful project results. Being experts in the use of safe and effective cleaning and coating removal techniques, the company can be engaged to test and produce on-site trials, reports and aid decision making in specification and implementation. Those using, or specifying the Restorative Techniques range of equipment and products, are supported with full technical expertise, from members within its team. Purchasers of machinery are supported and provided with periodical, free update training, to ensure their operators are kept informed of changes in regulations, best practice and to assist them in continuing to sensitively achieve, the appropriate and desired standards. www.restorativetechniques.co.uk T: 0044 (0) 1454 417831 info@restorativetechniques.co.uk ® RIBA rps no. 27199 Safe and cost effective removal of soiling and staining from historic masonry and acetates (> 6°C), but are best avoided for health and environmental reasons. Furthermore, if they are unsuccessful, the residual binder may be more difficult to rejuvenate subsequently. Hand tools include paint brushes, ‘lamb-chop’ fine filament stainless brushes, and nylon/natural bristle scrub brushes. Water may be applied as a fine spray from a hand-held spray bottle, as dry-steam (water vapour at 135–145°C), as a pressure wash (cold or warm water), or as a spray of superheated water (liquid water at c 150°C) system. Hot invariably works better than cold but high pressure is more likely to cause damage. Chemical reagents can be used in liquid form, in a gel, in a poultice or in impregnated cloths (graffiti wipes). Usually the organic binder of a paint is first dissolved with a solvent gel, those of which posing the lower hazard typically contain alcohol-esters. ‘Ghost’ removers include sodium or calcium hypochlorite (bleach), acetic or formic acid and sodium hydroxide and are generally a higher pollution and substrate risk. Regular use of even a mild acid on limestone will cause etching and dissolution, while sodium hydroxide is a high crystallisation risk if retained in the pore structure. Some commercial products combine the binder and ghost removal functions which may be convenient, or not! Abrasive cleaning, using air- or waterdriven soft abrasives, is suitable for brittle surface coatings only, such as oxidised bitumen. Laser cleaning is suited to the removal of dark surface coatings from light coloured substrates. The work area must be safetyscreened. Whichever system is used, consideration must also be given to containment, as no reagents or particulate, theoretically including tap water, can be discharged to a watercourse, groundwater or coastal water. Vacuum recovery can be used but this increases the equipment and time required. For small areas handworking (with graffiti wipes for example), is easier to contain than aqueous reagents and pressure washing. MITIGATION Occupied, lit and well-maintained buildings are less likely to be targeted. Clean buildings do not appear especially vulnerable but clean or plain patches of masonry often attract graffiti. Anti-graffiti coatings may help to protect high risk areas. ‘Permanent’ types are available but should not be used for historic substrates due to their tough and impermeable formulation. ‘Sacrificial’ types include waterborne microcrystalline wax and polysaccharides. These do not repel the paint but makes it easier to remove using hot water or solvents, although some further treatment is often necessary for pigment left in the substrate pores. These sacrificial coatings can be applied by pump sprayer or paint brush, avoiding wet or cold conditions. Untouched, the wax has a lifespan of 1–4 years but as they are removed with hot water or solvents, the coating must be reapplied after every cleaning. Some may have a sheen but are normally matt and turn milky during damp weather. JAMIE FAIRCHILD is managing director of Restorative Techniques Limited (see below) and provides training and consultancy including tuition for the Masonry Cleaning Master Class at West Dean College, Chichester. Recommended reading Graffiti on Historic Buildings, Historic England Advice and Guidance, 2021; http://bc-url.com/he-graffiti-guide An Investigation of Sacrificial Graffiti Barriers for Historic Masonry. English Heritage Research Transactions Vol 2 (2002). TAN 18, The Treatment of Graffiti on Historic Surfaces, Historic Scotland, 1999; http://bc-url.com/hes-graffiti-guide Archive of BCD cleaning articles; www.buildingconservation.com/articles/articles. htm#cleaning.
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