Investigations of the efficacy of Di-Ammonium Hydrogen Phosphate treatment on globigerina limestone

Abstract

The aim of this study was to examine the efficacy of diammonium hydrogen phosphate ((NH4}2HP04) as a consolidant on Globigerina Limestone, a stone widely used in architecture and heritage within the Maltese Islands. The choice of the recently introduced consolidating product, which chemically reacts with calcite leading to the formation of hydroxyapatite (HAP), stems from reporting on its promising application in recent literature. Treatment performance was investigated through a number of parameters, including: mode of application (brushing and polluting) and treatment concentrations (O.SM and 1.0M). The efficacy of the treatment was evaluated through a planned testing, regime, comprising: colorimetry, water absorption by capillarity, water vapour permeability Drilling resistance Measurement System (DRMS) and resistance to salt crystallisation. Results indicated an improvement in the stones' mechanical properties post treatment, without significant alteration in aesthetics and water transport properties, for both liquid and vapour phases. Furthermore, results showed a dependency on both application method and treatment concentration, necessitating also a thorough understanding of environmental factors and stone pathology, for the most effective choice of parameter combination. As this is one of the first stages in treating with this product, future work to evaluate better is suggested.