Rebar Chairs
A rebar chair (image right) is a small spacer or stand that holds reinforcing steel at the correct height inside a concrete pour so the rebar ends up embedded where the engineer designed it to be. Chairs keep the rebar off the ground or formwork and maintain the required concrete cover. Rebar chairs also prevent the grid from sagging or getting pushed down during the pour.
Chairs are often made of plastic (very common for slabs), wire/steel (often used in heavier structural work) or concrete (dobies) in some specs
Chairs are used for slab-on-grade rebar or welded wire mesh or elevated mats in suspended slabs. Rebar chairs are also used in footings and foundations.
Example: if plans call for rebar to sit 2 inches above the subgrade, rebar chairs
are spaced under the grid so the steel stays exactly there while concrete is placed.
Where you can buy rebar chairs: