The presented paper summarizes the result of the research of historical plasters and mortars from the Church of Saint Venceslas in Moravská Ostrava, the Church of the Transition 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 the mentioned churches is based on micropetrographic identification of the sand fraction of mortars (in each stage, a different sand was used) and on the degree of recrystallization (ageing) of the original micritic carbonate. The assessment of the plasters and mortars has to take into account the localization (inner, outer plaster) and the altitude of the sampling site and position of the mortar in the wall (plaster, cast mortar, bedding mortar). The orientation of the sampled wall with respect to cardinal points has also to be documented.