Page 136 - Handbook of Surface Improvement and Modification

8.1 Methods and mechanisms of surface cleaning 131

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ture. The paint removal by the cleaning product from the protected concrete was always
incomplete and concrete surface was permanently damaged if concrete was not pro-
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tected. The permanent protection coating (water-based formulation containing fluori-
nated alkyl moieties that reduced the substrate surface energy making it hydrophobic and
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oleophobic) had advantage over sacrificial coating (a water-based wax dispersion). Per-
manent anti-graffiti product (AGS1) partially fills the concrete pores (diameters of pores
on concrete surface varied in the range of 59–258 μm) and forms a protective hydrophobic
and oleophobic layer on concrete surface, but does not completely prevent the paint pene-
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tration. Sacrificial anti-graffiti protection (AGS2) formed a coating (protective coherent
layer), and adhered relatively uniformly to the concrete surface (Figure 8.13) but it did not
cover the entire pore surface, thus did not prevent the ink penetration into the pores. 28
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After the paint removal, some paint residues were still observed on the porous surface.
A coating for marble stone surfaces based on the fluorosurfactant (Capstone FS-63)
has been optimized for spray application by adjustment of solvent composition, giving an
effective penetration depth of the hydrophobic properties to 0.5 mm, ensuring a long-term
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protection against water uptake. Ethylene glycol was beneficial due to the prolonged
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functionalization time as a consequence of the slow evaporation rate. The coating bene-
fited anti-graffiti properties which was easily washed away with a standard pressure
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washer repeatedly 3-4 times.
Graffiti paintings, as an act of vandalism, are one of the most severe threats to stones
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preserved as cultural heritage. The review paper discusses composition of individual
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anti-graffiti formulations and their protective effectiveness. Anti-graffiti coatings facili-
tate the removal of graffiti compared to untreated surfaces, however their efficacy may be
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compromised on more porous substrates.
The cleaning effectiveness of limestone and lime-based mortar substrates protected
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with anti-graffiti product have been evaluated. Four commercial anti-graffiti products
(two sacrificial and two permanent) applied on three types of substrates (limestone and
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lime-based mortar with or without a finishing paint layer) were compared. A high-pres-
sure water washing and commercial chemical graffiti removers were used in graffiti
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removal. The anti-graffiti products facilitated cleaning, especially on the porous sub-
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strates such as mortar. The cleaning effectiveness of surfaces protected with anti-graffiti
products depended on the type of graffiti paint used (its color and application method). 31
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A grey paint was easier to remove than blue paints but still it has left yellowish stains.
The review paper analyses types of graffiti and their components, graffiti removal
methods (chemical and physical) including modern techniques such as ultrasonic/megas-
onic agitation, plasma spray, arc or thermal spray, dry ice blasting (CO -based), soda
2
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blasting, laser, and biological methods, and graffiti-substrate interaction. None of the
tested methods was capable of removing the graffiti from substrates without affecting the
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underlying material.