The article discusses the fabrication of sandwich steel and geopolymer structures using spray technology without the need for formwork. In the article, the effects of high temperatures on geopolymer materials are analyzed and their mechanical properties and durability are examined. The importance of geopolymer coatings for steel protection is also highlighted, and specific features such as the setting time, application process, attachment strength, fire testing, and production costs are analyzed. The materials and methods used in the study are described, including the composition of geopolymer binders and the process of applying geopolymer coatings to steel plates. The research includes test methods such as strength tests, density tests, thermal conductivity tests, accelerated aging tests, microstructure analyses, pore size analyses, and fire resistance tests. The research section concludes with a summary of the chemical and phase composition of the materials and a discussion of the fire resistance of the geopolymer composites (GCs). The results show that GC foams offer excellent thermal insulation, providing up to 75 min of fire resistance with a 6 mm coating, reducing temperatures by 150 °C compared to uncoated steel. GC foams have a density of 670 kg/m3, a thermal conductivity of 0.153 W/m∙K, and a cost effectiveness of USD 250 per cubic meter.