Proline Decorative Concrete Systems RS500 72" x 72" Grand Sandstone 1/4" Grout Joint Concrete Stamp. This piece will surely make a statement in any area of your home. One of our "Signature" pieces, this large natural stone pattern will give a very life-like rock with the durability of concrete. With an average size stone of 2 ft, this pattern will make a "Grand" impression. This pattern comes in 2 versions, see our Grand Sandstone Groutable for a wider and groutable grout line.