Concrete Masonry Directory For more information on Concrete Masonry or Retaining Wall Units, contact the following industry association: National Concrete Masonry Association 2302 Horse Pen Road Herndon, VA 22071 T: (703) 713-1900 F: (703) 713-1910 Web: http://www.ncma.org/ We welcome questions or comments. Or call:   West: 800-356-4848   East: 800-638-4444