Effect of Trans-Cinnamaldehyde on Moisture-Related Properties of Lime–Cement Plaster

In the present study, the effects of trans-cinnamaldehyde (TCA) addition on selected properties of lime–cement plaster were investigated. The algicidal effect of TCA on natural biofilm isolated from lime–cement plaster was investigated in the first experiment. Concentrations of 200 mg/L or higher caused complete inhibition of algal growth. Two TCA solutions (0.02% and 1.5% w/w relative to binders) were then used for the preparation of plaster according to the results of biological testing and previous research. The results did not indicate any practically relevant statistically significant effect of TCA on compressive and bending strength, while the total porosity increased with higher aldehyde concentration in the matrix and the matrix and bulk density decreased. Samples with 1.5% TCA showed reduced moisture uptake, indicating improved moisture-related behavior under high-humidity conditions. The occurrence of micropores in the structure compared to the reference was revealed by scanning electron microscopy. The main conclusions of the study are that TCA can be considered for the improvement of algicidal formulations in the form of protective coatings and as an additive influencing the moisture-related behavior of plaster, with beneficial effects observed at a TCA content of 1.5% w/w.