Effect of adding agar to DAP solutions for protection and consolidation of limestone

Abstract In this article, the effects of adding a small amount of agar to the diammonium hydrogen phosphate (DAP) solution were investigated in order to increase the ability of limestone to resist acid. The results of FTIR, XRD, BET and SEM showed that the structure of calcium phosphate phases remained almost unchanged, except that its crystallinity was affected as a consequence of the agar addition. Compositional and morphological analyses show that reacted limestone surfaces develop calcium phosphate phases with a plate-like structure. A double application (as both coupling agent and consolidant) was also investigated, in which the samples were treated with DAP followed by a TEOS-based consolidant product. Resistance to acid rain on limestone treated with the DAP/agar and consolidant resulted in a decreased deterioration rate.