The efficiency of protective treaments against damage to monuments by acid particulate

The fly ashes produced by the burning of heavy oil) have been identified as carriers of strong primary acidity (SPA) into the atmosphere. Oil fly ash SPA is acidity which is strong from the moment of its emission; it is transmitted to water on impact resulting in highly acid pH values (0-2) and high total acidity (2-3 mmoles/g) as well as significant concentrations of metals that are dangerous to the environment (especially vanadium and nickel). It has been demonstrated that SPA is typical of ash obtained by burning oil and its derivates and not from other fossil fuels. Its dry deposition on marble and calcarenite (common types of calcareous materials used in the building of monuments) causes hard alterations at relative humidity (RH) above 40% over brief periods of time, whereas no alterations are observed at RH < 40% over longer periods of time (up to a year). It is therefore very useful to attempt to establish whether the common protective products proposed for the surface treatment of stone are an efficient means of stopping or delaying the decay deriving from acid agents (SPA, S02, etc.). The objective of this paper was to verify the effects produced by dry ash deposition on the surface of calcareous materials treated with protective commercial products designed to preserve monuments from decay.