In the face of dwindling natural resources, manufacturers of building materials are increasingly turning to solutions that reduce their environmental impact, whilst ensuring high product quality and the conservation of natural resources. A natural consequence of this situation is the search for alternative non-clinker components that could take over the role previously fulfilled by traditional additives. The aim of this study was to determine the feasibility of using waste materials, namely chalcedonite and diatomite, at levels of 10% and 20%, as well as a combined proportion of diatomite and chalcedonite (total cement substitution levels of 10% and 20%). The study utilised additives naturally occurring in Poland in mine tailings. The aim of the research was to determine the rheological properties and parameters of the hardened mortar curing under laboratory conditions. The following properties were tested: setting time, bulk density, consistency, compressive and flexural strength, water absorption and capillary rise, as well as the microstructure of the mortars. The reference mortar achieved the highest increases in compressive and flexural strength after 7, 28 and 56 days of curing. The bulk density of the mortar containing 10% diatomite showed the greatest decrease in this parameter compared with the reference series. However, after 28 days of curing, the results recorded for the series containing 10% and 20% diatomite were similar to those of the reference series.