The behaviour of water-repellent mortars with regards to salt crystallization: from mortar specimens to masonry/render systems

This study is specifically concerned with the behaviour of water-repellent mortar specimens and masonry–render systems upon the penetration and crystallization of salt solutions. Portland limestone cement, natural hydraulic lime and Pozzolana lime were admixed with siloxanes and calcium stearates to obtain water-repellent mortars and renders. In order to select the most suitable water-repellent mixtures in the presence of salt solutions, investigations were carried out upon mono-material mortar specimens and macro-samples (masonry–render systems). Alongside pore structure characterization, the behaviour in connection with water and mechanical properties were determined. In addition, a non-invasive diagnostic methodology is proposed for the study of masonry macrosamples, including thermal imaging, water absorption at low pressure, and sclerometric measurments. The results revealed the difference between the behaviour of the mortar specimens in comparison to the masonry/render systems. Among the mortar specimens, Portland limestone cement mixtures demonstrated better resistance to salt crystallization, whilst those of natural hydraulic lime showed a longer service life, when applied as renders to masonry subjected to rising damp of sodium sulphate solution.