The search of reduction for the permeability of concrete structures, and consequently, increase in the durability of the structural elements has led to develop products for this purpose. One of the options is the use of crystalline waterproofing admixture (CWA). This research evaluated the influence of the use of crystalized admixture for waterproofing on the Portland cement concrete porosity. Water absorption and compressive strength of concretes with crystalline waterproofing admixture at the dosage recommended by the supplier were evaluated and the results were compared with regular concrete, without addition of admixture. The results show a reduction of porosity with reduction of absorption from 3.30% to 0.32% at 56 days of age after specimens molding. A reduction of compressive strength by 7.89% in concrete with admixture was also observed.