Chairs are extremely important in helping keep the rebar in their correct positions during construction. Once the mat has been established, the chairs will hold the rebar in place as the concrete covers it completely.
Rebar chairs are specially designed components made for supporting rebars, which are embedded metal bars used to reinforce newly-poured concrete. Rebars are laid out in a crisscross grid pattern and are locked together with the rebar chairs before the fresh concrete is poured over them.
If rebar spacing is greater than 12", place chair at every rebar crossing. If rebar spacing is 12" or less, place chair at every other rebar crossing.