Spreadsheet (.xlsx) containing research data supporting "Fresh state stability of vertical layers of concrete". The following data are provided: • Mix composition of the mortars used in the experiments. • Densities of the mix constituents. • Experimental measurements for the mixes under investigations: density, spread length, yield stress, difference in yield stresses, sum of the yield stresses, stability coefficient, ratio between lower and higher yield stress, and maximum horizontal displacement of the interface between the two vertical layers of concrete. • Relationship between sum of the yield stresses, difference in densities of the materials, and average horizontal displacement obtained for each test. • Maximum horizontal displacement d as a function of the stability coefficient. • Analytical bound solutions and experimentally measured relationship between sum of the yield stresses, difference in densities of the materials, and average horizontal displacement obtained for each test. • Analytical bound solutions and experimentally measured maximum horizontal displacement as a function of the stability coefficient.