Sealing slurries used to modify the subsoil should meet a number of requirements, including: rheological properties, setting time, appropriate mechanical strength and durability. The study determined the technological properties of sealing slurries prepared with ordinary Portland cement and blended binders containing appropriately selected mineral additives. The tests used granulated blast furnace slag, silica fly ash and ash obtained in the fluidized bed combustion of coal. The assessment of the technological properties of fresh slurries included the selection of an appropriate rheological model and the assessment of the rheological properties of the sealing slurry, such as: plastic viscosity, apparent viscosity and yield point. The research determined the factors causing improvement of the technological properties of fresh slurry. The use of supplementary cementitious materials, also in systems with fluidizing admixtures, allowed for a significant modification of the rheology of the tested sealing slurries. The obtained results indicate their beneficial effect on the functional properties of slurries, enabling their use as binder components replacing Portland cement, while limiting or even eliminating the addition of superplasticizers.