Efficiency and counter effects of cleaning treatment on limestone surfaces - investigation on the Corfu Venetian Fortress

Surface alterations of the original limestone and the efficiency of several cleaning methods were investigated on the Corfu Venetian Fortress facade. Black crusts of gypsum dendrites and loose depositions or black-grey calcareous encrustations in combination with biological decay were identified as main decay processes. The cleaning treatments, chosen according to their acting on the stone surface, were: sepiolite for solvent action, ammonium bicarbonate for exchange action, EDTA for the chemical chelating action, hydrogen peroxide for chemical action on biological species and nylon brushes for physical action. Each cleaning method's efficiency and counteractions were evaluated by laboratory examinations concerning the morphology and the composition of the surface with SEM observations and X-ray microanalysis, before and after treatment and during ageing tests in sulphur dioxide and humidity atmosphere. The used methodology creates a sound basis for the evaluation and proper selection of a cleaning method, which should be highly efficient and with limited counteractions to the stone. (C) 2002 Published by Elsevier Science Ltd.