Proline Decorative Concrete Systems SL400 20" x 50" Running Bond New England Slate Concrete Stamp. Proline Decorative Concrete Systems SL400 20" x 50" Running Bond New England Slate Concrete Stamp. This pattern offers 10 Inch x 20 Inch stones with a New England Slate background texture in a Running Bond, or offset, pattern. If you love the New England Slate look, take a look at our Opa Locka or our Ashlar New England Slate for the same background texture.