Eco-innovation in the conservation of built heritage: Two-steps protocol of Di-ammonium phosphate application

Abstract

A new protocol for the application of the consolidating di-ammonium phosphate (DAP) has been designed and verified, to contain the decay of carbonate substrates occurring in cultural heritage. DAP reacts with carbonate substrate to produce calcium phosphate phases, generally insoluble and liable to re-establish the cohesion of the stone. The Finale and Lecce Stones have undergone the consolidation treatment by applying consecutively-two solutions with different concentrations. The first solution (0.5 wt% DAP in water) is meant to build a porous network with hardened walls, reacting with calcium carbonate substrate and producing Ca-phosphates on the pore walls without occluding them. The second solution (4 wt% DAP in water) can flow into the Ca-phosphate-coated pores, without reacting and thus reaching carbonates deeper in the substrate. The samples were characterized by multiple physical and chemical investigation techniques to detect Ca phosphates and tested for treatment effectiveness. The results showed that DAP solution attains up to 1 mm in depth, even under low concentration; the nature of Ca-phosphates is undetectable due to instrumental detection limits and to heterogeneity of the investigated substrates.