**5. Conclusions**

Two fired bricks (Vysoké Mýto sample and Holešov-Žopy sample) were cut and their layers were studied in a diffusion experiment with calcium or in a biodegradation experiment. The results indicated that the structure of bricks' layers and especially their specific surface area affected the rate of calcium diffusion through the brick layers and probably also the density of colonization by biofilm (algae, cyanobacteria).

**Author Contributions:** Conceptualization, K.K and I.M. and R.C.; methodology, K.K. and J.N. and ˇ M.K. and I.M..; investigation, K.K.; writing—original draft preparation, K.K. and M.K. and Z.S. and R.C.; writing—review and editing, K.K. and Z.S. and R. ˇ C.; supervision, R. ˇ C. All authors have read ˇ and agreed to the published version of the manuscript.

**Funding:** This research was funded by Czech Technical University, grants No. SGS19/143/OHK1/3T/11, SGS22/137/OHK1/3T/11, by Technological Agency of Czech Republic, grant No. FW03010422 and by the Ministry of Education, Science, Research and Sport of the Slovak Republic, project VEGA No. 1/0682/19.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data supporting the reported results can be found with the authors.

**Acknowledgments:** The authors would like to thank Magdaléna Doleželová for measuring of bricks' properties, native speaker Marek Procházka for correction of English and two anonymous reviewers for their valuable advice. Publication cost of this paper was covered with founds of the Polish National Agency for Academic Exchange (NAWA): "MATBUD'2023—Developing international scientific cooperation in the field of building materials engineering" BPI/WTP/2021/1/00002, MATBUD'2023.

**Conflicts of Interest:** The authors declare no conflict of interest.
