Commercial NHL-containing mortars for the preservation of historical architecture. Part 2: Durability to salt decay

•Evaluation of salt decay susceptibility of NHL binders and ready mixed mortars.•Cubic mortar specimens and wallettes are tested against Na2SO4 crystallization.•PCA analysis is conducted to identify the main factors affecting durability.•Pore-size distribution is an important factor driving the decay.•Differential behaviour of supposedly similar materials under salt stress conditions.

The evaluation of the salt decay susceptibility of commercial NHL-based binders and pre-mixed mortars is reported. These products were chosen due to their increasing use not only in the field of restoration of built heritage. Mortar cubic specimens and simplified masonry systems were tested against sodium sulphate crystallization. Results were elaborated by Principal Component Analysis to identify the main factors influencing the durability. The microstructural features and pore size distribution represent risk factors for the damage in salt stress conditions; the results also confirm that testing is necessary to assess the differential behaviour of similar materials in specific environmental conditions.

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