Before slab preparation can begin, all the underground
utilities such as main electrical feed, conduit for any
electrical floor outlets, PVC drain lines, etc must have
been installed. The soil must have been re-compacted
properly (to re-achieve sub-grade level) so to ensure that
no uneven settling, resulting in subsequent cracking will
Slabs can be poured monolithically (ie: at the same time
as) footings if the footings are standard 12 inches wide 18
inches deep. In larger structures, or in unfavorable soil
conditions, where the footings are wider and/or deeper or
consist of caissons or piles or CMU block, the footings
were constructed in a prior step.
Slab preparation typically consists of a 10 mil visqueen
vapor barrier placed on the sub-grade (to prevent any
moisture penetrating up through the slab), upon which is
placed 4 inches of sand.
Next comes rebar, in a grid pattern with "dobies" to
ensure it is in the middle of the slab (vs resting on the
visqueen). Thereafter, if called for, such as in the photo
below, red "pex" piping for radiant floor heating is
installed and fastened to the rebar.
After passing inspection, the concrete can be ordered. In
the Orange County climate, morning pours tend to be
favorable, not only because the cooler temperatures allow
a slower cure (minimizing the potential of cracks as much
as possible), but also it leaves lots of time for screeding
and application of water to keep the slab temperature
moderate as the concrete sets. It is important that any
water piping (ie: radiant floor heating) be under pressure
during the entire pour and a repair kit be standing by, so
that any accidental puncture can be immediately repaired
and will not lead to a slab leak in the future.