Abstract: Metal shims are positioned within intersecting slots of a lower mold member, normally employed in the molding of an open grid fiberglass reinforced molded resin grating with the shims being of a height less than the vertical height of the slots. The grating is repositioned in the slots such that the upper ends of the grating bars project above the upper surface of the lower mold member. The upper mold member bearing projecting grids corresponding to the slots is covered with a solid checker plate. An impregnated glass sheet formed of the same molding compound as the open grid molded resin grating is interposed between the checker plate and the grating. A further shim defining the extent of compression of the molding compound sheet is interposed between the lower mold member and the checker plate.