The calcareous deposit formation on a marine structure under cathodic protection is depending on a large number of parameters. The influence of clay in suspension in artificial sea water has been mostly studied with montmorillonite, but some results with kaolinite are also presented. For both types of clays, the chronoamperometric curves show a delay for the calcareous deposit with respect to the situation without sediments and the deposition kinetics themselves are not modified whatever the clay concentration. This delay is proportional to the clay concentration in the particular case of montmorillonite. Conversely, the clay effect is negligible on the deposition kinetics of the Ca-based film in the absence of Mg2+ and small for the Mg-based film in the absence of Ca2+. A qualitative model is proposed to explain the role of clay suspension.