*3.3. Mechanical Tests*

The results obtained in the mechanical tests display differences for the different mixes, in terms of both compressive and flexural strength, during the test period (120 days). The results obtained from the mechanical tests are set out in Table 6 (samples without added pigments) and Table 7 and Figure 5 (binders and samples after 120 days).

**Table 6.** Results of the mechanical tests (120 days) and standard deviation for the different pastes tested.


**Table 7.** Results for mechanical tests and standard deviation for the different pastes containing added pigments tested after 120 days.



**Table 7.** *Cont.*

**Figure 5.** Mechanical strength values (MPa) of binders at 120 days and their corresponding pigmentcolored pastes (PPS, PALS, PHLS and PWGS). Blue bar plot corresponds to compressive strength. Line plot with red circles corresponds to flexural strength.

#### 3.3.1. Compressive Strength

#### PPS + Pigment Samples

In the plaster paste samples containing added pigment (PPS + PIGMENT), the maximum compressive strength after 120 days was 5.52 MPa ± 0.02 for the PPS + PGE (Green Earth pigment) sample. The minimum value was 5.3 MPa ± 0.05 for the PPS + PZY (Zinc yellow pigment) pigment sample.

In percentage terms, the variation among the pastes containing added pigment was 3.98%, and the difference among the pastes without added pigment was 2.17%. This shows full compatibility between the pastes and the pigments used.

### PALS + Pigment Samples

The compressive strength of the plaster + lime pastes exhibits a slight increase in the results, compared to the previous group. In this case, the values range between 5.74 MPa ± 0.05 for the PALS + PGE (Green Earth pigment) samples and 5.56 MPa ± 0.03 for the PALS + PCG (chromium green pigment) samples. This represents an average increase of 3.74% compared to the pure plaster samples.

#### PWGS + Pigment Samples

The compressive strength levels of the plaster + sodium silicate pastes were higher compared to the previous groups. In this case, the values range between 8.72 MPa ± 0.01 for the PWGS + PGE (Green Earth pigment) samples and 8.62 MPa ± 0.01 for the PWGS + PUB (Ultramarine Blue pigment) samples. This represents average increases of 37.6% compared to the pure plaster samples and 35.2% compared to the plaster and air lime samples.
