Proline Decorative Concrete Systems AS400A 36" x 36" Large New England Slate Groutable A Concrete Stamp. Looking for a pattern that makes a real statement? Proline's Large Ashlar New England Slate Groutable offers the popularity of both Slate and Ashlar Stones with a larger, bolder size stone. This stamp is also groutable, for a true natural stone appearance. This pattern is made to work in conjunction with AS400B.