Disclosed is a casting resin based on acrylic acid esters having a high content of finely dispersed fillers and containing a mixture of organosilicon compounds having functional groups and metallic acid esters of metals of Groups IVB and VB of the Periodic Table of the Elements. The functional group of the organosilicon compound is ethylenically unsaturated and bound to the silicon atom either directly or through alkylene groups. The addition of this mixture to the casing resins produces a desirable reduction of the viscosity of these resins, which are used, for example, for the manufacture of sanitary articles.The filler content is at least 20% and can be as high as 95% with the proviso that when the filler content is in excess of 80 wt. -%, the filler contains 10 to 30 wt. -%, based on the total weight of filler, of fines having a particle size less than 0.1 mm and the remainder of the filler being coarse up to 4 mm.