## 3 Results
### Experiment 1: Selection of Methods Used for Assessing Photoautotrophic Growth on Plaster Coatings
The largest average color change after 14 days was observed for the sample of material marked MP and the smallest for material S. After 28 days of incubation, depending on the tested material, the color change compared to the control samples was in the range of \(\Delta\)E = 1.20 \(\times\) 10\({}^{1}\)\(\pm\) 2.93 \(\times\) 10\({}^{0}\) (SSS)-2.65 \(\times\) 10\({}^{1}\)\(\pm\) 3.08 \(\times\) 10\({}^{0}\) (MP). Finally, after 28 days of incubation, a greater average color change was observed for the MP and MPGS substrates and lower overall discoloration was affecting S and SGS. Relatively high standard deviation values, visible especially for measurements performed  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Time (d)** & **MP** & **MPGS** & **S** & **SGS** \\ \hline \multirow{4}{*}{Cell density (cfu/cm\({}^{2}\))} & \multirow{2}{*}{0} & 0.00 \(\times\) 10\({}^{0}\) & 0.00 \(\times\) 10\({}^{0}\) & 0.00 \(\times\) 10\({}^{0}\) & 0.00 \(\times\) 10\({}^{0}\) \\  & & \(\pm\) 0.00 \(\times\) 10\({}^{0}\) & \(\pm\) 0.00 \(\times\) 10\({}^{0}\) & \(\pm\) 0.00 \(\times\) 10\({}^{0}\) & \(\pm\) 0.00 \(\times\) 10\({}^{0}\) \\ \cline{2-6}  & \multirow{2}{*}{14} & 3.33 \(\times\) 10\({}^{7}\) & 3.67 \(\times\) 10\({}^{7}\) & 2.00 \(\times\) 10\({}^{7}\) & 2.67 \(\times\) 10\({}^{7}\) \\  & & \(\pm\) 9.43 \(\times\) 10\({}^{6}\) & \(\pm\) 4.71 \(\times\) 10\({}^{6}\) & \(\pm\) 9.43 \(\times\) 10\after 14 days of incubation, may result from the intrinsic properties of tested materials, mainly low homogeneity of surface and high porosity. The change in the color components is illustrated in Figures 1 and 2. Overall, the surface of the tested samples became progressively darker, greener, and more yellow. Slight differences were observed between inoculated material types. After 28 days of incubation, samples representing S and SGS coatings showed discoloration towards more yellow (average a = \(-\)0.19 \(\pm\) 0.66, b = 10.88 \(\pm\) 0.68, and a = \(-\)0.80 \(\pm\) 0.35, b = 16.48 \(\pm\) 1.99, respectively) while MP (average a = \(-\)3.50 \(\pm\) 0.88, b = 12.04 \(\pm\) 2.33) and MPGS (average a = \(-\)6.20 \(\pm\) 1.05, b = 7.71 \(\pm\) 4.74) showed discoloration towards greener shades. The results of the abovementioned tests were subjected to correlation analysis and the indicators (R\({}^{2}\)) are presented in Table 2.  
With a minor exception of the test performed for the MPGS substrate, all tested methods showed a strong (R\({}^{2}\) = 0.60-0.79) or very strong (R\({}^{2}\) = 0.80-1.00) linear relationship to the change in cell density during the 28-day incubation. For the method of luminometric measurement of ATP, a significantly lower correlation coefficient, differing from the other substrates, was observed for the material designated as MPGS (R\({}^{2}\) = 0.342; weak linear dependence). This phenomenon corresponds to a much higher ATP value determined in the MPGS material after 14 days of incubation. For the M1 method, the first signs of biofilm formation were observed macroscopically after 14 days of incubation. Simultaneously, samples inoculated and incubated in accordance with the M2 method did not show any signs of photoautotrophic growth almost until the 28 th day of incubation. Regardless of the method used for incubation, all samples exhibited colonization after 28 days of incubation. However, samples incubated with the M1 method manifested a significantly higher degree of biofilm growth both in terms of covered surface and mean values of discoloration. Additionally, for less  
Figure 1: Color change measured for mineral plasters. (**A**)—mineral plaster (MP) measured after inoculation; (**B**)—mineral plaster (MP) measured after 14 days of incubation; (**C**)—mineral plaster (MP) measured after 28 days of incubation; (**D**)—mineral plaster with primer and silicone paint (MPGS) after inoculation; (**E**)—mineral plaster with primer and silicone paint after 14 days of incubation; (**F**)—mineral plaster with primer and silicone paint after 28 days of incubation.