This paper highlights the results and interpretations of experiments conducted to analyze the effect of sea water on conventional precast cement mortar (OPC) and polymer impregnated mortars (PIC). The precast cement mortars were impregnated with a mixture of methyl methacrylate and 2, 2'-Azobisisobutyronitrile (AIBN) initiator and polymerized using two different procedures: by microwaves and by conventional hot water method. The OPC and PIC specimens were immersed in sea water separately for 7, 14, 21 and 28 days and their strength parameters were calculated. The changes in the microstructure indicated movement of ions into the cement matrix and the presence of fan-like crystals on the surface of cement mortar. The protective polymer coating in the PIC prevented contact of sea water with cement concrete, thereby increasing the durability of the composite.