The Mar-flex Control Joint Extrusion .750″ System is designed to eliminate “Random Shrinkage Cracks” by creating vertical control-joints on both sides of the foundation walls. To ensure further protection. The Mar-flex Control-Joint System provides an economical, easy to use system for eliminating “Random Shrinkage Cracks” which are generally unavoidable, uncontrollable, unsightly and will leak water if not planned for ahead of time.