The hydrophobicity of renovation plaster in manufacturing technology optimized by statistical methods

In this paper, the influence of cement and some selected admixtures: redispersible polymer powder, air-entraining and hydrophobing agents, on the hydrophobicity of cured renovation plaster was analysed. The results were obtained experimentally. The result of capillary action (H) over a given period of time was used to evaluate the hydrophobicity of these materials. Statistical methods based on multiple regressions were employed to evaluate the influence of particular factors on this parameter. The analysis of the results showed that the suggested statistical models can be considered as very useful tools in optimizing the plaster composition thereby allowing for considerably shortening the time of preparation of production formulas for renovation plasters, thus lowering the costs of production. The analysis of the research results showed that the hydrophobicity of renovation plaster is mostly influenced by the weight amount of such ingredients as: cement, redispersible polymer powder, air-entraining and hydrophobing agents known also as water repellents. As expected, water repellent admixtures based on silicone show the greatest influence on the hydrophobicity of renovation plasters. An addition of only 0.6% of that admixture, at a relatively low content of cement in the mix design, accounted for a ca. 10% reduction in the capillary rise. Such a ratio ensures meeting the requirements of EN-998-1: 2012 [EN-998-1: 2012 Specification for mortar for masonry – Part 1: Rendering and plastering mortar] as for CS II resistance category.