Prefab concrete retaining walls are made to be strong enough to stand alone, but when the ground is not even or the foundation is not level, they are at serious risk of sinking. They need to be replaced or repaired immediately. Concrete walls do not have a layer of cement on top that helps retain it’s shape during times of heavy movement. They are normally placed on the ground and poured into place to make an impermeable barrier. In most cases, they will be made out of concrete, but can also be made out of stone, granite or other materials.