Proline Decorative Concrete Systems ST1240F 24" x 36" Sandstone Tile 12" x 12" Concrete Stamp. Sandstone is a sedimentary rock that is formed as pieces of earth have eroded and settled into the bottom of rivers, lakes and oceans. Cast from real stone, Proline has duplicated the look of natural sandstone with a 12 Inch x 12 Inch square tile. This pattern has a thin grout line with straight-edge tiles. Check out the many other background textures Proline offers in a 12 Inch x 12 Inch square tile.