## 2 Materials and Methods
### Gypsum Plasters  
The following materials were used in order to generate the different gypsum mixtures:  
* _Gypsum_. The gypsum used was a controlled B1 gypsum cast (gypsum for construction), also known as YG/L (its traditional name), according to standard UNE-EN 13279-1 [29]. Its main characteristics are presented in Table 2.
* _Water_. In order to obtain an appropriate workability for the plasters, and to favor the comparison of results, the quantity of water used was the same for all the mixtures. Thus, four different mixtures were prepared. Three of them with a different percentage of biocercamics, called GBC-0.3, GBC-0.65 and GBC-1, as well as the reference sample (R). The percentages of biocercamics were 0.3, 0.65 and 1% (percentage by the weight of gypsum). A constant water/gypsum ratio of 0.55 was used in all the mixtures. As it was mentioned, the biocercamics used was in powder form. To ensure a homogeneous distribution of the biocercamics in the mixtures and, therefore, in the subsequent composition of the specimens produced, the product was previously dissolved in the gypsum mixing water until it was completely dissolved. The quantities used were accurately calculated to guarantee the established percentages of biocercamics. Table 3 summarizes the composition of all mixtures per kilogram of gypsum powder used. Each sample was composed of twelve specimens of a size of 160 \(\times\) 40 \(\times\) 40 mm\({}^{3}\), according to the UNE-EN 13279-2 standard [30], for their physical and mechanical characterization. After the specimen preparation, the samples were cured at a temperature of 24 \(\pm\) 1 \({}^{\circ}\)C and a relative humidity level of 50 \(\pm\) 1% for 7 days [30]. They were then dried in an oven at 40 \(\pm\) 2 \({}^{\circ}\)C for approximately 48 h, until they reach a constant mass. They were then cooled to air temperature before being tested. For all of the mixtures, the following tests methods were carried out:  
* _Dry State Density_. Measuring the weight and dimensions of each sample, their dry state density was obtained following the procedure defined by UNE-EN 13279-2 standard [30]; \begin{table}
\begin{tabular}{c c} \hline
**Composition** & **[\%]** \\ \hline Silica (SiO\({}_{2}\)) & 62.72 \\ Alumina (Al\({}_{2}\)O\({}_{3}\)) & 25.88 \\ Sodium oxide (Na\({}_{2}\)O) & 2.30 \\ Ferric oxide (Fe\({}_{2}\)O\({}_{3}\)) & 0.47 \\ Potassium oxide (K\({}_{2}\)O) & 1.16 \\ Calcium oxide (CaO) & 0.42 \\ \hline \end{tabular}
\end{table} 
Table 1: Bioceramics chemical composition. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Purity** & **Particle Size** & **Surface Hardness** & **Performance** & **Flexural Strength** & **Compressive Strength** & **Adherence** & **Ph** \\
**[\%]** & **[mm]** & **(Shore C)** & **[kg/mm\({}^{2}\)/cm Thickness]** & **[N/mm\({}^{2}\)]** & **[N/mm\({}^{2}\)]** & **[N/mm\({}^{2}\)]** & **Ph** \\ \hline \(>\)75 & 0–1 & \(>\)45 & 10–12 & \(>\)2 & \(>\)2 & \(>\)0.1 & \(>\)6 \\ \hline \end{tabular}
\end{table} 
Table 2: Characteristics of gypsum powder used as base material. \begin{table}
\begin{tabular}{c c c c c} \hline
**Samples** & **Gypsum [g]** & **Water [g] or [mL]** & **W/G Ratio** & **Bioceramics [g]** \\ \hline
**Reference (R)** & 1000 & 550 & 0.55 & - \\
**GBC-0.3** & 1000 & 550 & 0.55 & 3 \\
**GBC-0.65** & 1000 & 550 & 0.55 & 6.5 \\
**GBC-1** & 1000 & 550 & 0.55 & 10 \\ \hline \end{tabular}
\end{table} 
Table 3: Gypsum plasters composition (per kilogram of powder used). * _Mechanical Properties_. To calculate the mechanical behavior of the samples, flexural and compressive strength tests were carried out, in accordance with the procedure described in the UNE-EN 13279-2 standard [30]. A universal Suzpecar multi-test press was used. This press has a load capacity of 20 tons and its precision depends on the type of control. In the control per round, the precision is 0.01 mm/min, whereas in the load control the precision is 0.1 Kg/s (Figure 3a);
* _Scanning Electron Microscopy (SEM)_.