The freezing of water-salt solutions on a horizontal wall is investigated experimentally and theoretically. The growth of the two-phase solid-liquid region is observed for NaCl-H₂O and NH₄C1-H₂O systems under different temperature and concentration conditions. A unidirectional mathematical model is developed to predict the temperature distribution in a semi-infinite medium based on the assumption that a local thermodynamic equilibrium exists between the solid and the liquid in the two-phase region. The transport of heat is by diffusion, and convection in the liquid is absent. The mass diffusion is neglected and the growth of the crystals is governed by the transport of heat. In all experiments the salt concentration in the solution is smaller than the eutectic composition, and the wall temperature is higher than the eutectic temperature. The predicted temperature profiles agree well with experimental data. The local solid fractions as well as the salt concentrations are shown as a function of the position.