Interactions on site between powdering porous limestone, natural salt mixtures and applied ammonium oxalate

Abstract The consolidation of powdering porous limestone with ammonium oxalate treatment is hereby being examined through its performance in the field. The literature to date reports this treatment’s potential use for consolidation and protection (from acid attack), while still retaining the water transport properties and supporting compatibility. This inspired a long-term research project which started in the laboratory and progressed to real buildings with a specific focus on the interactions in the stone taking place between the treatment and salt mixtures that may be present on site. This study focuses on the outcomes following a 24-h application of a 5% ammonium oxalate poultice on a historical soil-retaining wall located in a seventeenth century garden. In this case, besides calcium oxalate, the by-product formation of ammonium magnesium chloride was detected through X-Ray Diffraction (XRD). This is a first-time reported finding, which is important to consider within the environmental context of built heritage and ammonium oxalate treatment