Ceramics-Silikáty 62, (4) 311 - 324 (2018)

The effect of 5% water solution of the sodium sulphate and the reference environment of distilled water on changes in mechanical resistance of the commercial dry render mixes was researched in the paper. The prism-shaped specimens cured 28 days in humid and stable conditions were immersed in water or sodium sulphate water solution. At chosen time, the particular specimens were collected, dried to constant mass, and subjected to tests. The maximum time of specimen exposure to moisture or salt action was 168 days. Within the performed experiments, length changes, mass gain, mechanical and basic properties were measured in order to reveal the effect of sulphate corrosion on researched materials. Additionally, pore size distribution measurement and X-Ray CT analysis for the most damaged render were done, in order to characterize the disruptive impact of sulphate solution on porous microstructure of lime-metakaolin-based render. The obtained data revealed the high capacity of porous space of the tested renders for salt storage. For shorter times of exposure to salt action, most of the studied renders exhibited improvement in mechanical resistance. On the other hand, after the full filling of the porous space, the evoked crystallization pressures led to the decrease in mechanical resistance and materials damage. However, one type of studied renders originally designed for restoration of salt laden masonry maintained its excellent mechanical properties even after 168 days of sulphate exposure