The description of the wearing course depends on the size of the aggregate and the density used in its make up. The size varies from 20mm normal size to 3mm nominal size. The most common ones are 6mm and 10mm. The density is either open textured, medium textured or dense. 6mm dense wearing course is commonly used on drives, playgrounds and footpaths. 10mm open textured wearing course on a surface that requires porosity. The open textured materials are generally less strong then the dense materials. The wearing course can be either black or red. The red being 2½ to 3 times the cost.