The freezing process in a NaCl eutectic solution is discussed taking into account both a non-constant specific heat and a nonconstant thermal conductivity as potential functions of temperature. The non-linearity of the problem is introduced in the heat diffusion equation and in its boundary conditions. A strictly exact solution is used to solve it. By considering only conduction heat transfer mechanisms with phase-change, the simple analytical solutions common to these types of substances are obtained. Different characteristic parameters related to the freezing process are included, such as the movement of the interface boundary and the freezing time. Furthermore, some experiments were carried out for comparison with the theoretical model.