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Removing Graffiti from Historic
Masonry
Martin E. Weaver
Removing graffiti as soon
as it appears is the key to its elimination-and
recurrence.
Thus, the intent of this
Preservation Brief is to help owners and managers of historic
masonry structures find the best way to remove exterior,
surface-applied graffiti* quickly, effectively, and safely.
The Brief will discuss the variety of materials used to apply
graffiti, and offer guidance on how to remove graffiti from
all types of historic masonry without harming either the
surface or the substrate. Suggestions will also be given
regarding the use of physical barriers to protect masonry
surfaces from graffiti, and the application of barrier
coatings to facilitate graffiti removal. Building managers
and owners of historic properties will be advised on the
importance of being prepared for rapid graffiti removal by
testing different cleaning techniques in advance in order to
select the most appropriate and sensitive cleaning technique.
Health and safety and environmental concerns are addressed,
as well as regulatory matters. Removing graffiti without
causing damage to historic masonry is a job for trained
maintenance crews, and in some cases, professional
conservators, and generally should not be attempted by
untrained workers, property owners or building managers.
Although the focus of this Preservation Brief is on
historic masonry, the same guidance may be applied
equally to removing graffiti from non-historic
masonry.
Identifying
the Graffiti and the Masonry
Successful graffiti
removal from historic masonry depends on achieving a balance
between breaking the bond between the graffiti and the
masonry surface without damaging the masonry. This generally
requires knowledge both of the materials used to make the
graffiti and the masonry on which the graffiti has been
executed, as well as knowledge of cleaning methods and
materials (Fig. 1). Without this, masonry surfaces can be
badly disfigured or damaged during graffiti removal.
*The word graffito
(graffiti, plural) -- is derived from the old Italian
diminutive of graffio-to scratch, and the Latin
graphire-to write. Graffiti in contemporary
usage has come to mean an inscription, drawings, or markings.
Except in very formal or technical applications,
graffiti is generally considered a "mass" noun and
paired with a singular verb.
Graffiti. Most
graffiti is made with spray paints. Although a number of
solvents and paint strippers are capable of dissolving or
breaking down these paints, some may permanently discolor or
stain the masonry surface if not used correctly. As a result,
the remaining paint may become more difficult, or even
impossible, to remove. Poorly thought-out and generally hasty
attempts to remove graffiti using harsh chemicals or
abrasives can also cause permanent damage to the masonry that
may be worse than the graffiti (Fig. 2).
The ability to identify
the graffiti material is an important step in successful
removal. Numerous kinds of spray paint (polyurethanes,
lacquers, and enamels), and brush-applied paints (oils and
synthetic resins such as vinyls, acrylics, acetates,
methacrylates, or alkyds), as well as permanent felt markers
are the materials most often used to make graffiti. But other
materials are also used for graffiti, including water-soluble
felt markers, ballpoint pens, chalk, graphite and colored
pencils, pastels, wax and oil crayons, liquid shoe polish,
and lipstick (Fig. 3). The range of materials adopted by
graffitists continues to expand.
Paints are composed of
pigments that provide color and hiding power; binder that
holds the pigments together and to the substrate; and a
solvent that allows the pigment/binder mixture to flow. Some
spray paints and markers may contain dyes instead of
pigments. Paints are applied wet. Generally, as the solvent
evaporates, the binder solidifies. The greater the solvent
content of the paint, the greater the flow rate, and thus,
the greater the ability of the paint to penetrate into
masonry pores.
The two primary
components contained in most graffiti materials-pigment or
dye, and binder-may simply remain on the masonry surface, or
penetrate into the masonry to varying depths depending on a
number of factors, including the surface tension of the
substrate and viscosity of the solvent or vehicle. Thus, even
the total removal of the pigment or the binder may leave
residues of the other component actually in, or below, the
surface of the stone. Residual stains, or graffiti "ghosts,"
such as those from any kind of red paint or the fine black
pigments used in spray paints, may be particularly difficult
to remove (Fig. 4). With painted graffiti, it is helpful to
establish how long it has been on the surface. For most
paints that have been on the surface for several weeks or
months, hardening processes are likely to be complete or
well-advanced; the solubility of the paint is proportionately
reduced and it will be more difficult to remove.
Masonry. The
historic masonry substrate must also be identified. As used
here, the term masonry encompasses all types of
natural stones; manufactured clay materials, including brick
and terra cotta; and cementitious materials, such as cast
stone, concrete and mortar. The common factor among masonry
materials is that they are porous, to a greater or lesser
extent, and sensitive to abrasion. After identifying the
masonry, its condition, including fragility, porosity and
permeability, must also be assessed prior to beginning
graffiti removal. For example, a smooth, newly-polished
granite surface is comparatively easy to clean because it is
relatively impermeable and paint vehicles tend to stay on the
surface rather than penetrate into microscopic pores. A very
smooth, polished surface also has no pits or crevices that
will retain
particles of pigment or
binder. In contrast, weathered marble or limestone may be
extremely porous and permeable, with a rough surface on which
particles of pigment can easily lodge. The fragility of such
a surface can make it impossible to clean the surface even
with a bristle brush without risking severe surface loss. A
difference in surface texture or finish may also be the
reason that a particular cleaning agent will work in one
situation but not another.
Some types of masonry may
react adversely to contact with the various cleaning agents
required to break or dissolve the bond between the graffiti
and the masonry surface. Thus, for purposes of cleaning,
masonry types are often categorized according to whether they
are acid-sensitive, non-acid sensitive, or alkali-sensitive.
Acid-sensitive stones consisting of carbonate
materials may be damaged or even destroyed by contact with
acids. Although, in many instances, acidic cleaning compounds
are not effective for graffiti removal and generally should
not be used for this purpose, it is useful to know that some
acid-sensitive materials include: stones such as limestone,
marble, travertine, calcareous sandstones and shales; most
polished stones; and glazed architectural terra cotta and
glazed brick. Non-acid sensitive masonry materials
include slate, granite, unglazed architectural terra cotta
and unglazed brick. Alkali-sensitive stones may
contain silicates, or ferrous, soluble iron compounds that
can react with alkalis or water to form severe staining.
Alkali-sensitive stones include some granites, Indiana
limestone, and many types of sandstone, especially those that
are green or grey in color. Glazed and polished surfaces tend
to be damaged by both strong acids and strong alkalis.
Graffiti Removal
Methods and Materials
A variety of treatments
are available from which to choose the most appropriate
method of graffiti removal that will not damage the surface
of historic masonry. Removal techniques, which are chosen
according to the type of graffiti and the masonry, range from
simply erasing pencilled graffiti with soft erasers, or
removing chalked graffiti with soft brushes, to poulticing
with water (with or without detergents), poulticing with
organic solvents or alkali-based paint removers, or applying
bleach to remove painted graffiti. In very limited
situations, it may mean using very delicate and controlled
abrasive means. Successful graffiti removal often requires a
combination of cleaning materials and methods.
Poulticing. The
most effective method of removing graffiti from masonry
usually involves the use of a poultice. A poultice consists
of an absorbent material or powder-inert clays such as kaolin
or sepiolite, diatomaceous earth (fuller's earth); or
cellulose products such as fluff pulp cellulose or shredded
paper-mixed with a cleaning solution (a liquid reagent such
as water, organic solvent, paint stripper or bleach) to form
a paste or slurry. The purpose of a poultice is twofold: it
enables a cleaning solution to be kept in contact with the
stained area as long as possible, while allowing the cleaning
solution to pull the staining material out of the substrate
via the poultice without redepositing it in, or restaining,
the masonry. A poultice is often covered with a plastic sheet
to retard evaporation (Fig. 5). With some extremely porous
types of stone, such as marble, although a poultice may
remove a stain from one side of the stone, stains can pass
completely through the stone and be redeposited on the other
side of the masonry slab. Thus, caution should always be
exercised in stain and graffiti removal.
Water and
Detergent. Graffiti removal from historic masonry should
always begin with the gentlest means possible. In some
instances, this means low-pressure water washing. Fresh
graffiti-one or two days old-made with water-soluble markers
may sometimes be removed with water, possibly aided by a
neutral or non-ionic detergent. (Non-ionic detergents which
do not ionize in solution, do not deposit a solid, visible
residue.) Ammonia can also be effective in removing fresh
graffiti. Any detergent should be approached with caution and
tested before using because most commercial laundry
detergents are not neutral and contain substances which may
leave undesirable residues on masonry materials. Usually, the
water and detergent should be mixed with an absorbent
material and applied in the form of a poultice. Although
water washing is often likely to be the gentlest cleaning
method for historic masonry, it may not be as effective for
removing graffiti because many graffiti materials are not
soluble in water.
Organic Solvents and
Paint Removers. Most graffiti can be removed without
damaging the masonry with proprietary graffiti-removal
products and commercial paint strippers containing organic
solvents. But, these products should always be tested and
used in accordance with manufacturer's instructions included
in the product literature. Normally, solvents should be used
in a poultice form to prevent them from penetrating into the
substrate, and permanently discoloring or staining the
masonry. A number of paint-removers are manufactured as thick
gels or pastes that cling to the surface, and some commercial
paint-removal products include a tough fiber-reinforced paper
or cloth backing that retards evaporation and also
facilitates neat and clean removal of the used stripper. The
advantage of using organic solvents is that they evaporate
completely, leaving no residual material in the masonry.
However, organic solvents may present a severe health hazard,
and workers using them must wear adequate protection.
"Off-the-shelf" aerosol graffiti removers generally should
not be used because the dissolved paint being removed may run
down the wall "staining" a previously clean area; or pigments
may also be redistributed by the rinsing and scrubbing
recommended by the product manufacturer (Fig. 6).
Alkaline
Compounds. Alkaline compounds may be used to remove some
oils and greases, and waxes from non-alkali sensitive
masonry. Like organic solvents, alkaline compounds should
generally be used in conjunction with a poultice when
removing graffiti. The use of alkaline compounds should
always be followed by a weak acid wash and a water rinse in
order to neutralize-or remove-all the alkaline residues from
the masonry. Strong alkalies (pH13-14), such as sodium
hydroxide-based paint removers (caustic soda or lye),
generally should not be used as they can cause efflorescence
and staining on masonry surfaces, if not properly
neutralized. Potassium and other hydroxide paint removers may
react with iron compounds in some masonry, particularly
Indiana limestone, to form dark brown (rust-colored), or
black ferric hydroxide stains, which are very difficult to
remove.
Bleaches.
Alkali-based bleaches such as calcium hypochlorite can
sometimes be used very successfully in a poultice to bleach
or decolorize certain dyes contained in some paints and inks
that cannot readily be removed by other means.
Mechanical or Abrasive
Methods. Mechanical treatments include dry or wet
blasting, using abrasive grits, such as sand, dolomite
powder, aluminum oxide, ground-walnut shells, sodium
bicarbonate (baking soda), and others; high-pressure water
washing; and mechanical sanding or grinding. All of these
abrasive methods will cause damage to masonry and, in most
instances, should never be considered as a method of removing
graffiti from historic masonry. Abrasive methods used
mistakenly by untrained workers to remove graffiti usually
result in etching the outline of the graffiti permanently
into the masonry (Fig. 7). Some historic masonry materials
can be easily damaged by pressure washing even at low or
moderate pressures (100-400 psi). Occasionally, however,
under very controlled circumstances, a micro-abrasive
technique may be appropriate for removing graffiti from
delicate masonry surfaces, if used at low pressures of 35-40
psi with fine abrasives. This treatment, which must be done
very slowly and carefully to avoid damaging the masonry,
should be tested first, and undertaken only by a professional
conservator. Another exception, even though it is not
strictly an abrasive treatment, is using a razor blade as a
first step to remove spray paint or felt-tip marker from
polished granite. However, this too, should be undertaken
only by a professional conservator, and only on
polished granite, which is very hard and generally
impervious to scratches.
Laser Cleaning.
Although not in general use as a cleaning technique, laser
technology offers great promise in the future as a
non-damaging method of graffiti removal.
Testing
Before selecting a
removal method, all cleaning materials and techniques for
removing graffiti from a historic masonry building should be
tested on mock-ups or areas of the resource that are not
highly visible, but which are representative of typical
conditions. Visual observation should be supplemented by the
use of a magnifying glass, and spot tests should be carried
out with various solvents to help identify the specific
graffiti medium, which will aid in its removal. More complex
testing using laboratory equipment and more scientific
analytical processes may sometimes be necessary in complex
situations. Sample areas that represent the desired degree of
"cleanliness" should be approved in writing by client,
architect, conservator or other appropriate authority. The
materials and all the other data necessary to reproduce the
desired cleaning results should be meticulously recorded and
the accepted sample area preserved for reference until the
end of the job. The existence of a "clean" sample for
comparison and a signed agreement can avoid unpleasant
surprises, misunderstandings, and perhaps
legal actions.
When a type of graffiti
appears for the first time that was executed with a material
not immediately recognizable and for which no countermeasures
have been developed, tests may need to be carried out by an
architectural conservator to identify the material and to
determine effective removal treatments. Agencies with large
inventories of graffiti-prone buildings and structures should
watch for graffiti made with new materials and experiment
with different cleaning methods in order to be prepared when
it appears. Such early action can save large sums of money in
the long term. (See "Development of a Treatment
Plan.")
Health and Safety
Considerations
Most of the chemicals
used for graffiti removal are dangerous to workers, as well
as to others who may be in the vicinity. Organic solvents are
toxic by ingestion, inhalation, and skin contact. Material
Safety Data Sheets (MSDS), available from the product
manufacturer for all paint-removal products, should always be
consulted and followed. Identification of hazardous
components and checking with chemical reference works will
help assure that the least hazardous, but most effective,
products are selected.
Generally speaking, it is
a sensible policy to carry out all graffiti removal in
well-ventilated conditions. Some solvents can be used only
outdoors, and sometimes forced ventilation may be necessary
even there, requiring workers to use air-fed respiratory
equipment to avoid wind-blown fumes. Smoking, eating or
drinking must not be allowed when cleaning is in
progress.
Some materials used for
graffiti removal are so corrosive that accidental contact can
cause serious, permanent scarring and painful injuries.
Wearing appropriate protective clothing must be strictly
enforced. Mandatory personal protective equipment (PPE)
normally includes face shields or safety glasses; long,
chemical-resistant gloves; face masks with respirators for
organic solvents; and possibly, full protective clothing with
an independent air supply.
All smoking and open
flames should be rigorously excluded from work areas; many
solvents are flammable or highly explosive in vapor or liquid
form when mixed with air. Solvent residue, used swabs,
cloths, overalls and all other solvent-contaminated items
should be safely and legally disposed of, or properly
stored-even overnight-away from potential sources of fire.
Electrical equipment may require explosion-proof fittings
when used with certain solvents.
When electric pumps and
pressure-spraying equipment are used, it is especially
important that all necessary precautions be taken to avoid
electric shock. Water sprays and puddles on the ground
present a potentially dangerous situation, if they come into
contact with temporary wiring at worksites where graffiti is
being removed. Such hazards must be carefully monitored and
controlled.
As with any construction
project, attention should always be directed toward the
general safety of the workers and passers-by, but also toward
possible damage to the resource itself that might result from
careless placement of ladders, or scaffolding. Chemicals used
for masonry cleaning can also damage adjacent metals, glass,
and painted surfaces, as well as vegetation (Fig. 8). Product
manufacturers' instructions should always be closely followed
to avoid such inadvertent "collateral" damage.
Environmental
Considerations
To protect against
environmental contamination, including the formation of
unwanted ozone at ground level and damage to the ozone layer
in the earth's outer atmosphere, legislation has been enacted
in some states making it illegal to use even moderate
quantities of some solvents-
volatile organic
compounds (VOCs) contained in paint removers. In response
to this legislation, many new products are being developed
that do not contain VOCs.
After completing graffiti
removal, the disposal of chemical products and rinsing
effluent must be taken into account. Arrangement for disposal
of the cleaning waste should be made prior to
beginning graffiti removal, especially if it is a project of
considerable size. In many places it is illegal to discharge
solvents and/or paint residues into sewers or storm drains.
The owner or manager of a historic property, or in some cases
the individual or firm doing the cleaning or graffiti
removal, is responsible for being informed of, and complying
with, relevant laws and regulations. Under provisions of the
National Historic Preservation Act of 1966, as amended,
approval may be required from a state or federal preservation
agency before any work can be undertaken on buildings or
structures listed in or eligible for listing in the National
Register of Historic Places, if such a project involves
federal funding or licensing. Many state and local historic
district commissions and review boards have their own
regulations that require approval for cleaning or graffiti
removal work that is undertaken on landmarks or properties in
locally designated historic districts.
Barrier Coatings
Anti-graffiti or barrier
coatings are intended to facilitate the removal of graffiti
from porous as well as non-porous surfaces. These coatings
are most commonly transparent, but may also be pigmented.
They are available in a variety of formulations designed to
serve different needs. The use of barrier coatings to protect
graffiti-prone historic masonry surfaces may seem to be an
easy preventive solution to a persistent graffiti problem.
However, for the most part, these coatings are not the
panacea that some advertising might suggest. Some of them
simply do not work, and others may cause physical or
aesthetic changes or damage to the masonry.
Transparent
Coatings. Transparent coatings serve as a barrier between
the masonry surface and graffiti, preventing graffiti from
penetrating into the masonry. They are also intended to make
graffiti removal easier since most graffiti does not adhere
well to them. Generally, graffiti applied over transparent
barrier coatings can be removed with low-pressure water and a
detergent, or with a solvent.
There are basically two
kinds of transparent barrier coatings: temporary and
permanent. Temporary, or "sacrificial" coatings are removed
when graffiti is removed and then must be reapplied.
Permanent transparent barrier coatings are more resistant to
the water or solvents used to remove graffiti, and remain on
the masonry surface when graffiti is removed (although this
type of coating also must usually be reapplied after several
cleanings). A third type of transparent barrier coating
combines temporary and permanent coatings, based on a
two-part system. A water-based acrylic sealer is first
applied to the masonry surface, after which a sacrificial
layer consisting of a polyethylene wax emulsion or dispersion
coat is applied over the sealer. When graffiti is removed,
the sealer coat remains on the masonry, but the
sacrificial
coat dissolves and is
removed with the graffiti, and thus must be reapplied. (With
this two-part system, even the first coat will eventually
wear off after multiple cleanings, and must also be
reapplied.)
Unfortunately, in
application, there are a number of negative aspects of
transparent barrier coatings that generally prevent their
being recommended for use on historic masonry. First,
clear coatings may alter
the color of the masonry surface and add a gloss that may be
highly visible, or apparent only in certain lighting
conditions or when it rains. Second, clear coatings may
reduce the water-vapor permeability of the masonry, thereby
contributing to possible water-related deterioration. Third,
the coating may discolor and change over time. Exposure to
ultra-violet light can cause a coating to yellow; dirt
build-up may darken the treated surface; and some coatings
acquire a sheen when rubbed or brushed against. Such changes
are especially noticeable when only a portion of the building
has been coated. Furthermore, if coatings are not maintained
on a regular basis, usually through periodic removal and
reapplication, many coatings tend to fail. What often results
is an uneven, "patchy" look to the masonry that can have a
very negative impact on the character of the historic
building (Fig. 9).
Despite these potential
drawbacks, there may be some instances in which the graffiti
problem or frequency of occurrence is so severe that
application of a transparent barrier coating on historic
masonry may be worth considering. Some water-base
polysaccharide coatings, and silicone and silicone-base
coatings have been used with success on masonry structures.
They are essentially invisible, and do not change the natural
appearance of the masonry. Although less durable than
solvent-borne coatings, they are water-vapor permeable
(breathable), and may be reapplied to the masonry surface
immediately after removing graffiti, while the surface is
still damp.
However, extreme caution
must be exercised before applying a transparent barrier
coating. Experimental test applications should always be
tried first on discrete areas that are not highly visible,
and the treated areas evaluated over a period of time.
Laboratory test results on the performance of coatings
applied to samples of like masonry types may be useful to
some extent. But because the tests are carried out in a
controlled environment, they may not be as accurate or
reliable as tests actually carried out on-site where the
factors of weather and pollution are the same as those at the
location where the coating will be used. If circumstances
warrant, and the use of a barrier coating is determined
necessary, an architectural conservator should evaluate the
test performance of a variety of coatings before selecting
one to be applied to historic masonry. Because of the
potential for disfigurement, owners of landmark-designated
buildings are required by some preservation review boards and
landmark commissions to obtain approval before they apply a
barrier coating.
Pigmented
Coatings. A pigmented barrier coating may be used on
masonry as a permanent, preventive barrier coating, or
as a temporary means of concealing graffiti until it
can be removed.
Like a transparent
barrier coating, a pigmented barrier coating facilitates the
removal of graffiti because graffiti does not adhere well to
it. Pigmented barrier coatings that are water-vapor permeable
may sometimes be used as a permanent barrier coating
on non-historic masonry where there is frequent recurrence of
graffiti, and when constant surveillance is not possible
(Fig. 10). Although there are some instances in which
pigmented barrier coatings may be appropriate on painted
historic masonry, they are not recommended for
unpainted historic masonry because they will change the
appearance of the masonry. There is also another kind of
pigmented coating that is specially formulated to be used as
a temporary measure to conceal graffiti that cannot be
removed right away. This temporary, vapor-permeable paint is
removed when the graffiti is removed.
Pigmented coatings are
also not generally recommended as a permanent measure to
cover up graffiti. Some graffiti materials, particularly felt
markers, bleed through the coating; and repeated applications
of the coating or paint can result in a heavy paint build-up
on a masonry surface. Another disadvantage of using paint or
a pigmented coating to hide graffiti is that it usually
appears as an obvious patch on unpainted masonry and tends to
attract more graffiti unless the paint can be applied in a
discrete, and well-defined area (Fig. 11). If incompatible
with either the masonry or the graffiti, such a coating may
peel off the masonry surface in an unsightly manner. Like
transparent coatings, pigmented coatings may be difficult or
impossible to remove completely once their performance or
appearance is no longer satisfactory (Fig. 12).
Preventing and
Controlling Graffiti
Experience shows that
prompt removal of graffiti is one of the most effective
measures against its recurrence. Graffiti that is not removed
quickly tends to attract more graffiti. Often motivated by a
need to have their work seen, graffitists tend to be
discouraged from repeating their efforts in a location where
their work is quickly removed.
Apart from removal,
effective graffiti-prevention measures can be considered
under two headings. The first consists of physical measures
involving maintenance, lighting, security and the erection of
barriers on or around the property itself. The second focuses
on community awareness programs that include neighborhood
patrols, community service programs and educational programs
in the schools.
Maintenance and
Security. Neglect invites vandalism, whereas a
well-maintained property encourages civic pride. Thus,
careful attention should be given to establishing regular
maintenance programs which do not allow properties to reach a
point of obvious deterioration or abandonment. Cyclical
maintenance also makes good sense economically.
Graffiti is less likely
to occur if graffitists can be clearly seen. It is often
recommended that accessible, graffiti-prone areas be
illuminated with floodlighting or spotlights. Graffiti may
also be reduced or prevented by the presence of security
guards, park rangers or police officers, or by the visible
presence of surveillance cameras. Publicity about arrests and
punitive measures against the graffitists, and the general
vigilance of the security system may also reduce
graffiti.
If they are historically
appropriate and compatible with the historic property, soft
barriers in the form of low, possibly thorny, shrubs and
bushes or other forms of landscaping and planting may be
effective deterrents. Such plantings can make it difficult to
reach the property by any route other than the approved
secure one. Hard barriers provided by fences and transparent
screens or shields, such as clear acrylic or other
polycarbonate sheets, may also afford some degree of
protection. But these can have a negative aesthetic impact on
the property's appearance, particularly if the barriers
themselves become disfigured by graffiti.
Community
Awareness. Community action and education often play an
important role in a successful anti-graffiti program.
Neighborhood watches can effectively deter graffitists, and
can help police and other security agencies in the detection
and prevention of graffiti. Intensive public campaigns
against graffiti, including presentations in schools,
developing programs to foster community pride, and sentencing
offenders to remove graffiti in their own community can also
be useful. Publicity concerning arrests of graffitists can be
a useful preventive tool. (But, on the other hand, frequent
newspaper coverage of graffiti outbreaks or even of new
community efforts at deterring graffiti can sometimes have
the opposite effect by challenging the "creativity" of
graffitists.) Community groups trained in proper cleaning
techniques can also assist property owners in prompt and
non-damaging graffiti removal.
Summary
Although rapid graffiti
removal is the most effective weapon in eliminating graffiti
and preventing its recurrence in the same location, hasty,
untested removal attempts can disfigure and cause harm to
historic masonry. Thus, it is important that the owner or
manager of a historic masonry building or structure be
prepared with a plan to ensure the prompt removal of graffiti
when it occurs. Regularly scheduled maintenance and cleaning
programs to eliminate graffiti from historic masonry
properties may be assisted by the installation of physical
barriers, security systems and lighting, as well as increased
community involvement. Successful graffiti removal from
historic masonry requires knowledge of a variety of cleaning
methods and materials, and an awareness that what works to
remove graffiti from one kind of masonry surface may not
remove it from another. By testing different cleaning methods
in advance, treatment plans will be available, when needed,
to provide guidance for safe and sensitive graffiti removal
from historic masonry.
Selected Reading
American Geological
Institute. AGI Glossary of Geology and Related
Sciences. Washington, D.C.: American Geological
Institute, 1960.
Ashurst, Nicola.
Cleaning Historic Buildings. Vol. I: Substrates, Soiling and
Investigations; Vol. II: Cleaning Materials and
Processes. London: Donhead Publishing Ltd., 1994.
"Chemistry Leaves Its
Mark on Graffiti." Chemical Marketing Reporter.
November 14, 1993.
Ehrenkrantz & Eckstut
Architects, P.C. Technical Tips: Removing Graffiti.
New York: New York Landmarks Conservancy, n.d. (1994).
Graffiti Removal
Manual. Providence, RI: Keep Providence Beautiful,
September 1986.
Grimmer, Anne E.
Keeping it Clean: Removing Exterior Dirt, Paint, Stains and
Graffiti from Historic Masonry Buildings. Washington,
D.C.: Preservation Assistance Division, National Park
Service, U.S. Department of the Interior, 1988.
Lewis, Richard J.
Hazardous Chemicals Desk Reference. Second Edition.
New York: Van Nostrand Reinhold, 1991.
NIOSH Pocket Guide to
Chemical Hazards. Washington, D.C.: National Institute
for Occupational Safety and Health, Centers for Disease
Control and Prevention, Public Health Service, U.S.
Department of Health and Human Services, June 1994.
Reisner, Robert.
Graffiti: Two Thousand Years of Wall Writing. Chicago: Cowles
Book Company, 1971.
Science for
Conservators: Conservation Teaching Series. The
Conservation Unit of the Museums and Galleries Commission. 3
volumes. New York: Routledge, A Division of Routledge,
Chapman and Hall, Inc., 1992.
Torraca, Giorgio.
Porous Building Materials. Rome: ICCROM, 1988.
Torraca, Giorgio.
Solubility and Solvents for Conservation Problems. Rome:
ICCROM, 1990.
Weaver, Martin E.
Conserving Buildings: A Guide to Techniques and
Materials. New York: John Wiley & Sons, Inc.,
1993.
Whitford, Maurice J.
Getting Rid of Graffiti: A practical guide to graffiti
removal and anti-graffiti protection. New York: Van Nostrand
Reinhold, Inc., 1992.
Wollbrinck, Thomas. "The
Composition of Proprietary Paint Strippers." Journal of the
American Institute for Conservation. Vol. 32 (1993), pp.
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Development of a
Treatment Plan.
For managers or owners of
historic masonry buildings, or agencies responsible for large
inventories of graffiti-prone properties, including parks,
highway and railroad bridges and viaducts, bus, train and
subway stations, and cemeteries, the development of a
treatment plan may be the first step toward an effective
graffiti-removal program. It is becoming increasingly common
for large or important historic properties to have regular
maintenance and disaster plans that include
graffiti removal.
When feasible, a separate
treatment plan should be prepared for each structure.
However, if this is not possible, it is advisable to prepare
a variety of treatment plans for specific masonry types.
Plans should be prepared to cover all types of masonry that
fall under one jurisdiction, management or ownership that are
potential targets for graffiti.
Guidance contained in
treatment plans should be based on the results of carefully
controlled testing to remove a wide variety of common
graffiti materials safely, and without damaging the various
types of masonry. Individual treatment plans should address
all parts of the building or structure that could be
disfigured by graffiti, and any features too fragile to be
cleaned by anyone other than a conservator should be noted on
the plan.
A treatment plan is
essentially a cleaning specification, but it should also
include information on the following:
-
the types and
conditions of masonry likely to be targeted by
graffiti;
-
methods, materials and
techniques known to work most successfully in the removal
of specific types of graffiti from the surface of each
type of masonry;
-
sources for
materials;
-
a list of contractors
with expertise in graffiti removal, including names,
telephone numbers, information on emergency access to the
property, and storage location of materials;
-
graffiti-removal
methods which may be harmful to the masonry
surface;
-
contractors or
consultants who are not acceptable and should not
be considered for graffiti removal;
-
scaffolding, pumps, or
safety equipment that might be required, where it is
available, and costs involved; and
-
health and safety
concerns regarding specific removal treatments, product
literature and Material Safety Data Sheets (MSDS).
Criteria
to Consider Before Selecting a Barrier Coating as the Primary
Protective Means of Combating Graffiti
What to look for in a
Barrier Coating:
-
Water-vapor permeable,
or "breathable".
-
"Invisible" without
gloss or sheen, when applied to masonry.
-
No change in
appearance from uncoated areas when masonry is wet.
-
Does not discolor or
attract dirt.
-
Weathers
evenly.
Questions to Ask:
-
Will the coating last
long enough to offset its cost?
-
Will the application
and reapplication of the coating be cost effective?
-
Will the coating be
effective against more than one type of graffiti?
-
Can the coating be
completely and thoroughly removed, so that, if necessary,
paint, or another coating will adhere to the masonry
surface?
-
Will the building ever
need to be repointed or patched? A barrier coating may
make this difficult or even impossible.
Before
Application:
-
Seek advice of an
architectural conservator.
-
Test coating on an
inconspicuous area of masonry, or study the
success/failure of the coating in other locations where it
has been used.
Tips for
Successful Graffiti Removal
-
It is important to
pre-wet the masonry surface when using an alkaline paint
remover; it is also advisable to pre-wet the masonry
surrounding a graffitied area to dilute the effect of any
cleaning agents that might be inadvertently splashed or
spilled on the unsoiled surface. Do not wet the area to
be cleaned if the cleaning agent is solvent-based or
incompatible with water.
-
Always rinse the
cleaning agent off the masonry surface starting at the
bottom and moving up. This prevents the cleaning agent
from running down and staining a lower surface.
-
Air temperature can be
a factor in graffiti removal. Most paint removers do not
work when the air temperature is either very cold or very
hot. This may sometimes explain why a method that worked
in one instance may not be effective again in another,
similar situation.
-
Variations within the
same type of stone, such as bedding planes, density,
finish, or degree of weathering, may explain why some
areas of the same stone sometimes clean better that
others.
-
Even if advance
testing has been done and a treatment plan exists, at
least some on-the-spot testing will probably be
necessary.
-
Mortar joints react
differently from masonry units, and may require a
different cleaning material and/or method to be cleaned
effectively.
-
Graffiti removal may
result in an obviously "clean" spot. Always clean the
entire masonry unit that is bounded by mortar joints (but
not the joints themselves, unless necessary). The
prominence of the clean spot may be minimized by fanning
the cleaning out from the spot, and "feathering" it by
gradually reducing the strength or thoroughness of the
cleaning.
-
If it is not possible
to completely remove all traces of graffiti without
removing some of the masonry surface, it may be preferable
to leave the masonry alone. Some graffiti ghosts become
less noticeable with time due to fading of the dyes used
in paints and markers. Sometimes it may be possible to
conceal more obvious graffiti ghosts with
carefully-matched paint.
-
After graffiti
removal, the masonry surface should always be tested with
Ph strips to make sure all the cleaning materials have
been completely removed. Non-staining Ph strips, available
from chemical supply companies, will indicate whether
acids or alkalis remain on the masonry surface.
-
Although alkaline
paint removers are sometimes ineffective on modern
formulations of aerosol paints, they can work well in
removing multi-layered graffiti because they last
longer.
-
What removes graffiti
in one instance may not always work again even in what
appears to be an identical situation.
-
More than one cleaning
material and technique may be required to clean a heavily
graffitied area if different materials were used to make
the graffiti. For example, shapes are often outlined with
broad-tipped felt markers and then filled in with spray
paint.
-
Effective graffiti
removal often depends on trial-and-error testing, as well
as a knowledge of masonry materials, graffiti materials
and cleaning techniques.
Acknowledgements
This Preservation Brief
was developed under a cooperative agreement between the New
York Landmarks Conservancy and the National Park Service.
Mark A. Weber, Director, Technical Services Center,
served as project coordinator for the Conservancy. The
author, Martin E. Weaver, is the Director of the
Center for Preservation Research at Columbia University. He
is an internationally recognized expert in the conservation
of architectural and cultural resources, a noted lecturer,
and author of Conserving Buildings: A Guide to Techniques
and Materials, as well as numerous articles on the
subject.
Anne E. Grimmer,
Senior Architectural Historian, Technical Preservation
Services, Preservation Assistance Division, National Park
Service, coordinated the development of this Preservation
Brief and served as Technical Editor. Technical review of
this publication by the following is gratefully acknowledged:
Frances Gale, Training Coordinator, National Center for
Preservation Technology and Training, National Park Service,
Natchitoches, LA; Judith M. Jacob, Architectural Conservator,
Building Conservation Branch, Northeast Cultural Resources
Center, National Park Service, NY, NY; Andrea Mones-O'Hara,
Regional Historic Preservation Officer, National Capital
Region, General Services Administration, Washington, DC;
Nicolas F. Veloz, Conservator of Outdoor Sculpture and
Monuments, National Capital Area Office, National Park
Service, Washington, DC; and Michael J. Auer, Timothy
Buehner, Charles E. Fisher, and especially Kay D. Weeks,
Preservation Assistance Division, National Park
Service.
Washington, DC. October,
1995
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