Durability of stone-repair mortars used in historic buildings from Paris

Abstract

Stone-mortar specimens manufactured with limestone and commercial stone-repair hydraulic mortars have been exposed to accelerated ageing tests, salt crystallisation (mixture of sodium chloride, sodium sulphate, calcium sulphate and potassium nitrate) and acid vapours exposure (sulphurous and nitric acid) besides, their corresponding control specimens were exposed to deionized water imbibition cycles and water vapour, respectively. Large amounts of soluble nitrates and minor amounts of sulphates precipitate on the surface of both stone and mortar materials after the acid test. This mainly affects the surface of the specimens rather than the stone-mortar interface. Whereas parallel fissures to the interface show up due to salt mixture crystals precipitation after the salt crystallisation test. A remarkable yellowing of the stone takes place after both tests. The mortar with closest properties to Euville limestone, with no phyllosilicates is the most resistant. It shows good mechanical properties but bad hydric interactions with the stone that could prove damaging in the long run. The mortar with the highest porosity and better hydric behavior but poor mechanical interaction with the stone is highly affected by the ageing tests, acting more as a sacrificial mortar rather than as a repair mortar.