The aim of this research was to modelize the colonization of mortar surface by green algae using Avrami's law. The resistance of mortars, with different intrinsic characteristics (porosity, roughness, carbonation state), to the biofouling was studied by means of an accelerated lab-scale test. A suspension of green alga Klebsormidium flaccidum, was performed to periodically sprinkle the mortar surfaces. The covered surface rate followed a sigmoidal type curve versus time. Moreover, in order to apply Avrami's law, the algal colonization has been described by two processes: attachment and growth of algal cells. The image analysis showed that both the roughness and the carbonation influenced the algal attachment, unlike the porosity. The attachment specific rate increased linearly with time. For the algal growth process, it's difficult to conclude on the influence of mortar characteristics due to a high dispersion of experimental results. However, the assumption of a constant growth rate was acceptable. A good agreement between the simulation and the experimental results was obtained.