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Due to the lime inclusions, the RM mortar can be classified as a dry slaked mortar, that is known due to its sandwich-like preparation (Wedekind 2014). The RM mortar was made in a traditional way, but its durability is limited and not comparable with a hot mixed mortar by using amorphous aggregates, like the two described historical mortars. However, 142the RM mortar from the 1941 restoration work was still preserved in huge amounts. The RM mortar does not show any harmful side effects unlike the modern, cement-containing mortars used for the main restoration works in Zvartnots.

Figure 5: Damage mapping of a wall at the Zvartnots Cathedral ruin.

The two different historical mortars can be classified as hot-prepared mortars. In this case, the burned lime was probably mixed and slaked together with the amorphous siliceous aggregate. This could be the reason why no visible lime accumulation is visible. It is known, that the solubility of amorphous silicate increases sharply at a high pH in combination with heat (Iler 1979). All conditions are present during the mortar preparation, heat, a high pH of 14 and a lot of amorphous silicate material used as aggregate.

The high temperature reached by the exothermic reaction of the burned lime slaked with water and the high pH (14) seems to soften and chemically desolve the fine amorphous silicious particles within the aggregate and to form calicite-silica compounds. These cement-like, but salt-free and highly porous mortars seem to be the main reason, why very large parts of the Armenian cultural heritage is still preserved. These mortars also show a perfect compatibility with the highly porous building stones (Tab. 1). The tuff material has a high water uptake capacity and shows a comparably high resistance agains salt weathering (Pötzl et. al 2018).