Study on physical and chemical properties of external lime–sand plasters of some historical buildings

• Analysis of physico-chemical properties of external sand lime plasters to find the reason of low and great hardness.
• The knowledge about physical properties and chemical compounds of plasters after the influence of atmospheric agents.
• Determination of the chemical composition of the original external facade plasters of historical buildings.
• Suggests for the reconstruction of the damaged facade plasters during the restoration works of historical buildings.

The article presents the results of laboratory tests of facade plasters from two selected sacred objects from the fourteenth and eighteenth centuries. In both buildings lime plaster was used, both internal and external facades. Plasters have different strength depending on the destination. In spite of the use of lime binders only, some of plasters, i.e. on plinths, are of considerable hardness and high resistance against weathering agents in comparison to other ones. In order to identify differences in the internal structure of different strengths plaster, samples were collected from different places and tests on physico-chemical characteristics were carried out. Due to the limited size and shape of the samples, physical properties such as absorbability, density and total porosity and granulometric analysis of the aggregate were marked. In addition, studies were made of mineral composition by differential thermal analysis and X-ray diffraction and chemical tests. The results obtained have allowed to clearly identify the nature of the binder and the mineral composition of the original plaster existing hikes, as well as reasons for the high hardness of some plaster. These results are of cognitive importance, as well as in the practical work of the revaluation of historical objects.