PROTECTION & REMEDIAL TREATMENT 4.1 129 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 but they often penetrate more deeply than paint and require poulticing techniques to draw them out. Products containing egg or milk protein can bind strongly and may also develop black mould if not fully removed. A recent phenomena has been the use of hydrofluoric acid based paints on the glass frontage of retail premises. The acid is extremely hazardous when fresh and is able to etch or dissolve silica, including terracotta and faience. It cannot be removed from glass conventionally but rather by specialist polishing. Paint – This is an opaque mixture of pigment, filler, binder and modifiers borne in an aqueous (water) or organic solvent carrier that forms a film on drying. Paints are normally categorised by purpose but for removal the primary factor is the binder type. Organic binders (primarily natural and synthetic resins) are normally flexible, thermoplastic, solvent susceptible, abrasion and acid resistant. Conversely inorganic (mineral) paints are brittle, highly heat and solvent resistant but susceptible to removal by abrasion and perhaps acid. The majority of paint graffiti will have an organic binder. It is unusual to find an inorganic type used but chalk paint is an example (see ‘craft’, below). While polyurethane, alkyd, cellulose and acrylic resins are carried in organic solvent, acrylics and more recently alkyds can be suspended in water using surfactants. There is a brief opportunity to hose away a waterborne paint before it dries, or to pressure wash it semi-dry, before the surfactant itself disperses. Automotive – Most aerosol body paint will be solvent borne acrylic or alkyd-acrylic, the alkyd constituent adding toughness. Polyurethane (transport polyurethane or coach enamel) or cellulose formulations are also available in aerosol form though normally supplied in conventional tins. Bitumen is used in car body under-seal: black and thermoplastic, it embrittles in time (months) and may become increasingly heat and solvent resistant. Craft – These paints range from aerosols to poster paints. Solid colour aerosols are normally water or solvent borne acrylic. Metallic fleck paints contain large particulate and are therefore less penetrating and easier to remove. Chalk paint is a craft/furniture paint with an exceptionally high filler content, insoluble pigment and little or a weak binder. It is comparatively easy to remove and might be chosen for this reason. Poster paints are also typically chalk and fine ground bright organic pigments or with mineral pigments for darker colours, traditionally bound with a little egg protein. Household – Modern flexible masonry paints and interior emulsions are usually waterborne acrylic. Gloss oil paints (with a binder of polyurethane, alkyd resin or, traditionally, linseed oil) are carried in white spirit but are increasingly available in waterborne alkyd. Household paints used for graffiti are usually brushed or poured. They are formulated to be higher build and slower to dry. Dye – This is a soluble, often translucent pigment in a water or solvent carrier. These might be synthetic or plant based commercial dyes designed for fabric and paper products, or alternatively vegetable derived food products and colorants. Lacking filler and binder they rely on substrate porosity, where they will be more penetrating than a paint. If the dye acts as a mordant it will cross-link or fix with the substrate on drying, preventing water or solvent carrier alone from removing it. Marker pen – Like a dye, the carrier here is water- or solvent-based, with little or no filler or binder. Thin and highly penetrating, the soluble pigments fade in strong sunlight. Food colouring – The liquid colour is typically mixed with a filler such as flour and applied as a paste using a glove or template. Wax – Lipstick and crayon are the most common sources. Lipstick normally contains an organic oil carrier such as castor, while crayon is a hard wax, only fluid when heated. Virtually all categories of wax will melt at or well below 100°C. Automotive paints, marker pen, roadmarker spray and correction fluid all need to be fast drying and so contain volatile organic solvents such as alcohols, acetone and xylene. REPORTING AND ASSESSMENT Swift removal or covering with a drape or temporary screen is the most effective discouragement for repetition and necessary if the graffiti is directly offensive. The task is also easier in the first few hours or days. Painting over graffiti is normally only an option where the substrate itself was already painted. On finding graffiti, photograph the damage, check CCTV and any witnesses, look for discarded paint tins or other evidence, inform the police/crime prevention officer, obtain a crime number and inform the insurance company. For a listed building an application for consent (LBC) is made to the local authority conservation officer. Initially verbal, it may then require a formal draft by the conservation or architectural agent working for the building owner or guardian, with advice from a specialist graffiti consultant or contractor. If the site is within or adjacent to a Site of Special Scientific Interest (SSSI), the statutory conservation agency should also be informed. Graffiti on a grade 1 listed limestone aqueduct; (top left) before removal; (top right), after brushing with a conservator’s lamb-chop brush and water; and (bottom) after the application of an alcohol based graffiti-gel remover, washed off after 10 minutes by sponge and cold water. To minimise removal of organic growth (which had acted as a natural anti-graffiti barrier) the chosen graffiti remover was pH neutral, and was rinsed with cold water alone. The ghosting was left as ghost removers are more toxic to organic growth.
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