Zec© and SemiFlexible Grinding Discs for Concrete/Masonry. Zec© Disc16 grit silicon carbide, minimal loading, ideal for grinding concrete, masonry and stone along with adhesives from concrete. SemiFlex Disc16, 24, 36, 60, 80 120 grit silicon carbidea lower cost alternative to plasticbacked Zec wheels. 41/2 In. x 7/8 In.