Abstract Polymer-cement-concrete (PCC) is made by the addition of a polymer admixture, in the form of an aqueous dispersion to a cementitious mix. The dispersion is usually stabilized with surfactants and colloidal stabilizers. These surface active agents cause the formation of a large number of air bubbles in the fresh and hardened mix. Electron microscopy studies have shown that the inner surfaces of these cavities are covered by a dense growth of calcium-hydroxide crystals in the form of well shaped fine platelets which stick out perpendicular to the surface with the crystalline a-axis in the main dimension. The question is raised, and is unanswered, regarding the origin of the growth of these platelets-crystals. Keywords: air-bubbles, polymer-cement-concrete (PCC), Portlandite.