Department of Mineralogy, Petrology and Geochemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic, e-mail: mirka@sci.muni.cz

Department of Geotechnics, Faculty of Civil Engineering, Brno University of Technology, Veveří 95, 662 37 Brno, Czech Republic, e-mail: pospisil.p@fce.vutbr.cz

Abstract:
The presented paper summarizes results of historical plasters and mortars research of the Church of Saint Wenceslas in Ostrava, the Church of the Translation of Virgin Mary in Brantice and from archaeological survey of the basement of the Church of Saint Catherine in Kelč.

The relative dating of particular building stages of said churches is based on micropetrographic identification of the sandy fraction of mortars (in each stage, a different sand was used) and on the degree of re-crystallization (ageing) of the original micritic carbonate. The assessment of plasters and mortars relates to the localization (inner, outer plaster) and the height level of the sampling site above ground and position of the mortar in the wall (plaster, bedding mortar). The azimuthal orientation of the sampled wall has been also documented.

Micropetrographic analysis of sandy fraction of mortars and plasters, together with the assessment of the degree of matrix re-crystallization, can in almost 95% cases confirm or exclude the assumed age of the particular construction phases.

Key words: plasters, mortars, durability, degradation, re-crystallization