# Lightweight Insulating Geopolymer/Phase-Change Materials Applied Using an Innovative Spray Method
## 3 Results and Discussion
This indicates that the tested coating not only adheres effectively to various substrates but may also potentially withstand deformation, mechanical stress, and cyclic weather fluctuations during service. Furthermore, the strong adhesion of the functional layer enhances the overall integrity of the material system, reducing the risk of delamination, cracking, or spalling. Thus, using the described material as an insulating, protective, or thermal storage layer is well justified from both technological and functional perspectives. The research and development of the spraying method aimed to identify a simple application technique enabling the use of foamed insulating geopolymers containing PCMs. Therefore, the measurements of specific heat and thermal conductivity were crucial in confirming the results' effectiveness. In order to assess the thermal conductivity of the insulation layers produced by the spraying method, a series of samples were prepared by spraying the geopolymer into moulds with dimensions of 20 \(\times\) 20 \(\times\) 3 cm\({}^{3}\). The samples were fabricated using the developed spraying system and subjected to infrared heating for 30 min. The distance between the IR emitter and the sample surface was maintained at 45 cm, which ensured a surface temperature of approximately 80 \({}^{\circ}\)C. Measurements of thermal conductivity (\(\lambda\)) and specific heat capacity (C\({}_{\text{p}}\)) were carried out using the HFM 446 heat flow meter (Netzsch, Hanau, Germany), under standards including ASTM C1784 [54],  
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**Visual Representation** & **Type of Substrate** & **Average Pull-Off Strength [N/mm\({}^{2}\)]** \\ \hline  & &  
ASTM C518 [55], ISO 8301 [56], and EN 12664 [57]. Temperature regulation and control were verified using the Peltier system. The measurement accuracy was \(\pm\)1-2%, repeatability was \(\pm\)0.25%, and reproducibility was \(\pm\)0.5%. The thermal properties were determined using the hot-and-cold plate method. The thermal conductivity was measured in the temperature range typical for standard insulation materials (e.g., expanded polystyrene), i.e., 0-20 \({}^{\circ}\)C. The specific heat capacity was determined in the temperature range of 27.5-32.5 \({}^{\circ}\)C.  
Figure 10 shows an example of a fabricated sample and its initial placement in the testing device. The average thermal conductivity of the produced samples (based on three measurements for each of the three samples) was 0.0776 W/m-K, while the specific heat capacity reached 1.398 J/g-K. The density of the tested samples, as determined using the measuring device, averaged 356.95 kg/m\({}^{3}\). Samples without the addition of the PCM exhibited approximately 15% lower average specific heat values (mean value: 1.214 J/g-K). The increase in thermal storage capacity resulted from the incorporation of 10 wt.% of PCM GR42. Geopolymer compositions containing the PCM ensured good thermal insulation, non-flammability, and high heat storage capacity, making them attractive solutions for the construction industry. Although foamed geopolymers generally exhibit slightly lower thermal insulation properties than traditional insulation materials, their thermal conductivity coefficient, averaging around 0.07 W/m-K, is considered reliable and has been confirmed by multiple independent studies [58; 59; 60; 61]. The earlier literature occasionally reported much lower values, such as 0.037 W/m-K [61], but those results have not been consistently replicated and are not considered representative for practical applications. A number of potential performance and technological advantages were identified based on process observation and analysis of operating parameters. Compared to manual methods of applying foams or geopolymers, the spraying technique allowed for uniform coverage of large areas in a short time. The estimated spraying rate using the designed system was about 0.4-0.5 m\({}^{2}\)/min for a layer thickness of approximately 20 mm, while limiting material losses to less than 7%.