Recommended materials: Common Clay / Block Paviers (40 N/mm), Clay roofing tiles, common facing brick (50N/mm), Granolithic Screeds, Granite Concrete, Solid concrete blocks (35 N/mm), dense Yorkshire stone, vibrated concrete products, common facing brick (35 N/mm), limestone / whinstone concrete and slate For occasional use only: River Gravel Concrete, Flint Concrete, Terrazo, Mica,