Effect of ultraviolet light on the removal of red acrylic paint from limestone

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Biggio, Elizabet T.
Daas, Mahesh
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Thesis (M.S.H.P.)
Department of Architecture
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Graffiti is a near constant problem for historic structures and monuments, particularly in urban environments. Currently available non-destructive techniques are not always adequate for graffiti removal. Acrylic spray paints, the most common graffiti material, are composed of polymers which are subject to degradation by ultraviolet light. The feasibility of using this mechanism as a tool for graffiti removal was explored through practical experiments. Red acrylic paint was sprayed onto samples Indiana limestone which were then exposed to UV-B light sources for two, four, and six weeks. Following exposure, samples were scrubbed with acetone, a common solvent used in graffiti removal. Relative differences in the paint removal on the treated and untreated sides were observed, with more paint being removed from the treated sides in some cases. Additional samples were coated with titanium dioxide and exposed to ultraviolet light, yielded a greater level of overall paint removal. It was concluded that this mechanism offers promise and warrants further study.