Diary of a Pool Project Pt. 2: The Rebar Chronicles

In addition to the installation of rebar, the drain is hollowed-out in the center of the pool floor. You can see the cage-like form of the built-in spa, which will be raised above the pool's surface and will have a separate access. Those square blocks on the floor are spacers, which keep the rebar the required distance away from the edge of the concrete and soil. Spacers are usually made of hard plastic, steel, brick or concrete -- materials that won't expand.