Ammonium oxalate treatment application in the presence of soluble salts: laboratory results on soft limestone

Abstract

Ammonium oxalate treatment of calcareous stone has, in recent years, emerged as a conservation treatment with both consolidating and protective properties through the surface conversion from calcium carbonate to calcium oxalate. This treatment on Maltese Globigerina Limestone has also produced positive results, increasing the acid resistance while retaining the water transport properties of the stone. Furthermore, treatment in the presence of sodium chloride did not impede the conversion. This paper focuses on ammonium oxalate treatment application in the presence of sodium chloride as well as sodium sulphate and sodium nitrate, in a comparative study where the treatment was applied to quarry samples of this soft Limestone under laboratory conditions. The resistance to salt crystallisation and the water absorption properties were subsequently studied. This stage in the understanding of ammonium oxalate treatment of calcareous stone under different soluble salt content conditions is an important step towards carrying this treatment forwards to real site conditions where soluble salts are naturally present in the stone and where desalination may prove to be difficult or impossible. Results obtained were positive in all respects and show that ammonium oxalate treatment may be relevant in the treatment of this stone type.