Proline Decorative Concrete Systems RS100 34" x 36" Random Sandstone Groutable Concrete Stamp. Looking for a natural stone look with the durability of concrete? Our Random Sandstone comes in 3 versions-including this groutable rendition. This variation of our Random Sandstone can be grouted for a more natural look. Each stamp contains 6 natural looking stones ranging in size from approx. 8' x 10" to 13" to 17.5". See RS120 & RS130 for other versions of this pattern.