## 2 Materials and Methods
### Experiment 1: Selection of Methods Used for Assessing Photoautotrophic Growth on Plaster Coatings
#### 2.4.8 Correlation Analysis  
The acquired data were subjected to correlation analysis. To determine the degree of the linear relationship between the results, the correlation coefficient of determination (R\({}^{2}\)) was used. Based on calculated factors, the correlations between the tested methods for assessing photoautotrophic growth on plaster substrates were determined according to the following scale, based on [PERSON] [29]:  
R\({}^{2}\) = 0.00--0.19 = very weak correlation;  
R\({}^{2}\) = 0.20--0.39 = weak correlation;  
R\({}^{2}\) = 0.40--0.59 = moderate correlation;  
R\({}^{2}\) = 0.60--0.79 = strong correlation;  
R\({}^{2}\) = 0.80--1.00 = very strong correlation.  
Experiment 2: Assessment of the Inoculation and Incubation Conditions of Samples Tested for Resistance against Photoautotrophic Growth  
In accordance with the experimental design of the study, described in Section 2.1, the main goal of Experiment 2 was to develop a sample preparation, inoculation, and incubation procedure aimed at simulating the use of building materials, considering the simulation of environmental conditions, inter alia precipitation, temperature, the presence of dust particles, and UV radiation impacting tested substrates. Trials were performed based on the results acquired from previous stages of the described studies. During the experiment, two different methods of sample inoculation and incubation were tested.  
For the first method, hereinafter referred to as method 1 (M1), 6 samples of each coating type (see Section 2.2) were placed individually in the sterile Petri dishes containing previously poured and solidified 3N-BBM medium. An amount of 1 mL of inoculation mixture prepared in accordance with the methodology described in Section 2.4.1, substituting liquid BBM with the 3N-BBM modified medium, was added onto the surface of each of 4 samples and spread evenly with a sterile plastic spreader. Two samples were left as control samples, without inoculating suspension and only 1 mL of sterile, 3N-BBM medium was applied to the surface. The use of a solid 3N-BBM substrate poured onto the surface of a Petri dish was intended to protect the tested material from excessive drying and to increase the availability of water in the microenvironment, a key parameter determining the growth of algae on the materials.  
As a reference, a method hereinafter referred to as method 2 (M2) was used. An amount of 1 mL of sterile, non-solidified BBM medium with 1.5% agar additive was applied to the surface of each sample and spread with a sterile pad. Afterward, 1 mL of the algal inoculum prepared in accordance with Section 2.3 was introduced onto the surface of each of 4 samples. For two control samples, an inoculation mixture was not applied. A microbial medium solidified with 1.5% agar, applied to the surface of technical samples, was used to simulate the effect of dirt and fouling potentially influencing photoautotrophic growth.  
Prepared and inoculated samples were placed in a climatic chamber and incubated for 28 days under artificial lightning of 1200 Lux in a 16 h/8 h day/night cycle with a temperature of 22.0 \({}^{\circ}\)C \(\pm\) 0.2 \({}^{\circ}\)C and air humidity of 50% \(\pm\) 5%. After 28 days of incubation, the degree of photoautotrophic growth was examined using visual assessment and the spectrophotometric method (Sections 2.4.6 and 2.4.7 respectively) selected as the most suitable in the previous experiment.