Concrete expands and contracts with moisture and temperature changes, and these are known as volume changes. Volume changes produce cracks in hardened concrete unless they are controlled. With Mar-flex Concrete Control Joints at predetermined locations, you can prevent a concentration of crack-producing forces. The Mar-flex Control Joint System is designed to ensure optimum protection, with a watertight outside control joint which is created when filled with Mar-flex Waterstop Elastomeric Sealant and protected by Mar-flex Fiberglass Fabric Reinforcement. This system is an economical, easy-to-use system for eliminating cracks, which are typically unavoidable unless properly planned for with control joints.