Castable is a type of concrete product. A variety of additives is applied to improve the construction ability and water content during construction. A variety of products is used depending on the applications such as float, inflow, and gunning construction. The most common binder used in castables is HAC (high alumina cement). Other binders that are often used include hydratable aluminas and colloidal silica. Castables are mixed with water and then installed by either pouring or pumping. Placement of the material then requires vibration.