15 Years of Ammonium Phosphate (DAP) for Heritage Conservation: A Review of the Treatment Performance in Laboratory Studies and Field Applications

The use of aqueous solutions of diammonium hydrogen phosphate (DAP) to induce formation of calcium phosphates on the surface and inside the pores of carbonate stones was proposed in 2011 to consolidate and protect her- itage substrates. Given the very promising results provided by the DAP- treatment in the first exploratory studies performed in the laboratory, in the fol- lowing years research on DAP has expanded to progressively move from sim- plified systems to more representative and more complex ones. The present pa- per aims to provide a review of various aspects investigated through the years, namely (i) the type of substrate on which the treatment has been tested, (ii) its deterioration level, (iii) the application method and (iv) the properties investi- gated (effectiveness, compatibility, durability, sustainability). Overall, the tech- nical performance and the sustainability of the DAP-treatment can be regarded as very high, also in comparison with the available commercial alternatives, which has led to DAP application on several real moments in the last few years.