Graffiti on Historic Surfaces

Stephen Gordon

Incised historic graffiti on a timber door at Edinburgh Castle carried out by French prisoners during the Napoleonic wars

The term graffiti derives from the Italian graffio meaning 'scratching' and can be defined as uninvited markings or writing scratched or applied to objects, built structures and natural features. It is not a new phenomenon: examples can be found on ancient structures around the world, in some cases predating the Greeks and Romans. In such circumstances it has acquired invaluable historical and archaeological significance, providing a social history of life and events at that time. There are also examples which have been elevated from acts of vandalism to works of art. In April 2007, a mural by Banksy near Old Street Station in central London, was valued at £200,000 when it was painted over in error. However, such examples are extremely rare. Graffiti is now a problem that has become pervasive, particularly over the last 50 years, as a result of the availability of cheap and quick means of mark-making. These include biros, felt and marker pens, correcting fluid, stickers as well as the ubiquitous spray paints.

It is usually considered a priority to remove graffiti as quickly as possible after it appears. This is for several reasons. The first is to prevent 'copy-cat' emulation which can occur rapidly once a clean surface is defaced. It may also be of a racist or otherwise offensive nature and many companies and councils have a policy of removing this type of graffiti within an hour or two of it being reported. Also, as paints, glues and inks dry out over time they can become increasingly difficult to remove and are usually best dealt with as soon as possible after the incident. Graffiti can also lead to more serious forms of vandalism and, ultimately, the deterioration of an area, contributing to social decline.

Although graffiti may be regarded as an eyesore, any proposal to remove it from sensitive historic surfaces should be carefully considered: techniques designed for more robust or utilitarian surfaces may result in considerable damage.

In the event of graffiti incidents, it is important that the owners of buildings or other structures and their consultants are aware of the approach they should take in dealing with the problem. Some owners may wish to attempt their own treatment. Others may prefer to appoint a suitable specialist contractor to deal with the incident. Whichever course is chosen, it is important that all those involved follow as far as possible a systematic approach which includes such considerations as putting in place preventive measures. The following course of action is recommended when a graffiti incident is encountered:

• Record details of the graffiti (the type of media used, the area affected, the type and condition of the surface it is on) and the time and manner of its execution, if known.
• Photographs are useful to record graffiti incidents and may assist the police in bringing a prosecution. Such images are also required for insurance claims, and can be helpful to cleaning operatives, allowing them to see the problem area before arriving on site.
• The police should be informed as there may be other related attacks occurring locally. An incidence pattern can identify possible culprits, as can stylised signatures or nicknames, known as 'tags', which may already be familiar to local police.
• Owners of listed or scheduled buildings or monuments must contact the relevant heritage body or their local authority planning office, and inform cleaning contractors of its status before any trials take place.
• Having established that cleaning can take place, do the owners feel confident in carrying out the work themselves or should they seek professional help? This question is dependent on the individuals, the scale of the graffiti, and the type and condition of the surface it is applied to.
• The next step is to carry out cleaning trials. These usually involve testing a range of treatments, and are carried out on a small unobtrusive area, if possible. Cleaning trials should always start with the least aggressive method, usually water, and stop once a successful method has been found. Test results and methodology should be noted for future reference.
• Treatment of the area should begin once the cleaning trials have established the most effective method. Care should be taken to comply with health and safety legislation with regard to the protection of both passers-by and any person carrying out the cleaning. Operatives should follow product guidelines in terms of application and removal, and wear the appropriate protective equipment. Measures must be taken to ensure that run-off, aerial mists, drips and splashes do not threaten unprotected members of the public.
• If graffiti is expected to be repeated in a particular location it is wise to consider a removable, sacrificial, barrier-coating system as a form of preventive measure. This will not stop graffiti being applied but will make its removal much more effective and straightforward. Other preventive measures include Neighbourhood Watch schemes, improved lighting, CCTV, physical barriers such as gates and fences, and hard and soft landscaping.

GRAFFITI REMOVAL CONSIDERATIONS

An example of early graffiti carved by the Vikings into the walls of the Neolithic tomb at Maes Howe on Orkney

The type of cleaning required is dependent on two main factors: the media used (spray-paint, felt pen or enamel paint, for example); and the type of material that has been defaced (such as stone, metal, wood or plastic). The interaction of these factors must be considered when selecting the best cleaning method. For instance, solvents that will remove particular paints or inks from historic masonry may damage paintwork or plaster.

Generally speaking, the more porous the material onto which the graffiti is applied the more difficult it will be to remove without causing damage. In the case of a material such as stone, pigments are carried by the solvent in which they are suspended through capillary action well into the body of the material where they are hard to get at. This is particularly true in the case of aerosol paints.

In this situation a solvent/poultice-based treatment is about the only method that can be used if damage to the surface is to be avoided. Abrasive and other mechanical systems will only ever successfully remove the graffiti from a porous substrate by first removing a layer of the substrate material.

The type and condition of a stone, brick, concrete, wood or metal substrate may also determine what form of cleaning is possible. In some cases it may be advisable not to clean off, but to cover over, particularly where the substrate already has a covering of paint.

Removing graffiti from stone or other building surfaces may also remove the patina of surface grime and pollution products on the rest of the stone surface. This can result in a patchy appearance, although in some cases the cleaned area can be graded into the surrounding masonry to give a more subtle tonal transition. Alternatively, in extreme cases, it may be preferable to clean an entire wall or elevation so that the finish is consistent.

It is important to be aware of other historic finishes that may be present on top of the stone, such as plaster and pigments, as these may be damaged by attempts to remove any graffiti.

TYPES OF CLEANING AVAILABLE

Damage caused by repeated and inappropriate removal treatments

There are a variety of methods that are used to remove graffiti. Broadly these divide between chemical and mechanical systems.

Chemical preparations are based on dissolving the media; these solvents can range from water to potentially hazardous chemical 'cocktails'. Many companies produce proprietary graffiti-removal products, most of which will be based on similar solvents. The final choice should be based on small site trials. Certain chemicals can be used in conjunction with an inert poultice material, in which case the chemical is usually applied first to dissolve the pigment, followed by the poultice to draw the pigment in solution out of the substrate. Repeated applications of the poultice and solvent may be necessary to reduce the concentration of pigment in the substrate to an acceptable level.

Mechanical systems such as wire-brushing and grit-blasting attempt to abrade or chip the media from the surface. These include a variety of wet or dry air-abrasion systems using a broad range of abrasive media, from very coarse materials such as aluminium oxide through to fine talc. However, even at low pressure these air-abrasive systems can easily damage the surface beneath, particularly brick and stonework, so they are usually used by conservators to remove superficial dirt only. Air abrasives and other mechanical techniques used on their own are unlikely to be suitable for removing graffiti from masonry.

Lasers of the Nd:YAG wavelength have also been used with some success, particularly for the removal of graffiti from light-coloured substrates. This is because the light is absorbed by the pigmented layer of the graffiti, causing rapid expansion and ejection. As very little energy is absorbed by the substrate itself, controlled use of a laser by a specialist is less likely to have a significant effect on the substrate than conventional methods. The advantage is that there is no direct mechanical contact with the surface, allowing very fragile surfaces to be cleaned. However, its high cost means that use of this technology is largely confined to the most important monuments.

When examining a graffiti incident it is important to assess the ability of the substrate to withstand the prescribed treatment. If there is any doubt regarding this, then small trial areas should be undertaken to assess the impact of more extensive treatment.

As with any treatment, the success or otherwise of graffiti removal, and its potential to cause damage, always rests with the skills of the person undertaking the work. A reputable graffiti removal company will have well-trained staff who understand the importance of not damaging the substrate. It will also have a range of cleaning methods at its disposal so that the correct treatment can be selected for each circumstance. In the case of very sensitive historic surfaces, a conservator with a background in the material from which the graffiti is being removed should be consulted for specialist guidance.

Owners of historic buildings may wish to consider tackling the graffiti themselves and if this is the case there are free guides available to assist in the process.

Personal protective equipment is required for most graffiti-removal treatments. This may vary from the use of rubber gloves to full protective gear, including full hand and face protection in case of splash-back, and solvent mask to prevent inhalation. Reading the manufacturer's instructions or, better still, the pertinent 'technical data sheet' for the product (available free on request from all chemical manufacturers) will enable the correct protection to be used.

More often than not, the products developed for paint removal are hazardous to the environment and the resultant post-cleaning residues or run-off are required to be disposed of in a specific way. In particular, where there is a possibility of chemical residues getting into water or drainage systems, proper control and disposal is essential. The technical data sheet for the product will give the recommended means of disposal. Alternatively contact the manufacturer directly for advice on this subject. Local authorities will also be able to provide guidance on the safe disposal of waste products.

PREVENTIVE STRATEGIES

Graffiti on rubble masonry

For sites where there is a recurring problem of graffiti attacks, local authorities and estate managers will find preparing a policy or strategy to deal with future incidents well worthwhile. This will help individuals who are responsible for dealing with the problem by providing them with a clear set of guidelines.

In dealing with the graffiti problem, a combination of detection through regular inspections and deterrence through the use of preventive strategies should form the basis for a coordinated response to the problem.

A variety of preventive strategies can be adopted to combat a recurring problem of graffiti at a given site. It is also clear that preventive measures will ultimately be cheaper, more effective and less damaging than multiple removal treatments.

It is worth undertaking a site audit to look at where the vulnerable surfaces are located and where past graffiti attacks have occurred. Often these are readily accessible flat surfaces where the graffiti will have most impact, but this is not always the case and graffitists may scale walls or bridges for example to give their work greater impact.

As no two sites are the same, no one set of protection measures will be suitable for all situations. Each site must be looked at individually. Typical site protection measures may include a combination of the following:

• Floodlighting or improved lighting to illuminate dark areas may act as a deterrent.
• Surveillance systems such as closed circuit television may also help. In cities and towns around the country, prominently placed cameras have been shown to reduce anti-social behaviour of all types including graffiti.
• Security patrols will also act as a deterrent to prevent recurring attacks. However, the cost of this may be too high for most situations.
• Physical barriers such as a wall, railings, doors or gates can be introduced to discourage unauthorised access to a vulnerable site. However, consideration has to be given to the impact measures have on the structure being protected. In the worst cases, they can be almost as damaging to the quality of the environment as the graffiti they prevent. In others, they might simply provide a new surface for graffiti.
• Soft and hard landscaping can form an important feature of any anti-graffiti strategy. These features can be used to prevent easy access and may include fastgrowing thorn bushes or large planters.
• The location of new fixtures may affect an adjacent structure. For instance the positioning of a bus shelter or telephone box next to an ashlar stone wall may encourage graffiti, so alternative locations should be considered.

ANTI-GRAFFITI COATINGS

Modern graffiti on painted timber panelling

One of the most significant problems associated with graffiti removal is the need to remove it from surfaces that are repeatedly attacked. Under these circumstances the repeated removal of graffiti using even the most gentle methods will ultimately cause damage to the surface material.

There may be situations where the preventive strategies mentioned above do not work or are not a viable proposition at a given site.

Anti-graffiti coatings are usually applied by brush or spray leaving a thin veneer that essentially serves to isolate the graffiti from the surface. Removal of graffiti from a surface that has been treated in this way is much easier, usually using low-pressure water which reduces the possibility of damage. Depending on the type of barrier selected it may be necessary to reapply the coating after each graffiti removal exercise.

A range of barriers is available, some of which are designed for more utilitarian surfaces and others which may be more applicable to sensitive surfaces such as masonry.

In the case of porous materials such as natural stone there are several issues to be addressed before selecting a barrier system:

• The coating should ideally be permeable to water vapour, allowing the stone to behave as it would in its natural state.
• Ideally, there should not be any change in the appearance of the treated surface. Many coatings cause a darkening of the surface or sheen. The coating should perform in the same way in wet or dry conditions.
• The coating should remain stable as it ages and should not discolour or be vulnerable to washing away through natural weathering cycles.
• The coating should be easy to remove from the surface. Some coatings require hot, high-pressure water to remove them which can damage a sensitive substrate.
• The coating should not be toxic to people, animals or plant life.
• The process must be reversible so that the coating can be completely removed should this be necessary. Some coatings are permanent while others are designed to be washed away each time any graffiti is applied. It should not produce a cumulative adverse effect if repeated applications are necessary.

Small trial applications should be made on a given surface before committing to more extensive treatment. This would include applying and removing the barrier to check the ease of removal, as well as any adverse effects that might result. This will ensure that the product is suitable for the surface being protected.

Modern graffiti in a medieval chapel

Barriers based on aqueous solutions produced from vegetable polysaccharides are perhaps the most suitable for historic surfaces. Such barriers are fully reversible and do not restrict the diffusion of water through a porous substrate. Some slight colour change of the surface is possible, but the effect is likely to be minimal.

There is no prescription for dealing with every graffiti incident, but by taking all the above into consideration a satisfactory strategy can usually be adopted.