Jim Manthei is vice president of Manthei Development Corp., a ready-mixed concrete producer, aggregate supplier, and site-preparation contractor in Charlevoix, Mich. Manthei's creation, American Redi-Block, uses a hinged and cam-locked form machine with which producers can cast top, middle, bottom, and even half-blocks by changing a 3/8-inch steel insert. A form set yields three blocks. Both of Manthei's plants have three forms, so the company produces nine blocks per plant in a typical day.
In addition to the easy forming operation, the design allows producers to create blocks with different front-face textures. Drivers insert a custom-made rubber liner on the bottom form and place enough concrete from the first load to cover the entire liner surface. Potential cold joints from additional concrete returns show up only on the block's sides and thus are hidden during field placement. Currently Manthei uses a pattern that simulates large quarried stones, and contractors often stain and seal the units in the field.
The blocks are shaped with an interlocking keyway design. As the blocks are stacked, each course is slightly recessed. The top block's shape includes a 5-inch step that allows backfilling, which eliminates the need for capstones.