Gypsum panels and blocks represent a good economical method for the manufacture of partitions and walls, since the raw material cost as well as the labor cost are cheap, besides the ease of decoration. Their main drawbacks are the high-water permeability and their poor mechanical strength. In the present paper, polypropylene (PP) fibers were blended with plaster in an attempt to improve the properties of these products. It was found that the addition of PP fibers reduces the porosity, decreases the setting time and enhances the mechanical strength. The optimum composition was found to consist of plaster blended with 50% water, 10% sand and 500 g/m³ PP fibers of length 30 – 50 mm.