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How to prepare soil for a concrete patio?
I am planning to have a concrete patio poured at my new house. How can I be sure the contractor is properly preparing the "underlayment" before pouring the concrete? I know that a certain amount of dirt should be removed (about 8"), that 3/4" gravel and fine gravel should add back about 4" when compacted, and that there should be a pre-soil treatment as well as a vapor barrier installed before the rebar goes down, but what else should I be sure gets done before the 4" thick concrete gets poured?
Also, what PSI rating should the concrete be for this type of application?
I am in the Southern California area, in case weather is a concern.
Answer:
The newly updated standards for ground-supported monolithic concrete flooring is to ONLY use vapor barrior when it is an area that is air-conditioned. So, if your patio is "open-air" like a porch and garage, and will not have conditioned air above it, then do not use any vapor-barrior.
Stand firm on this, as vapor barrior pushes too much water to the surface during concrete curing and can cause more cracks then needed.
Dampen the ground before placing the concrete so that the dirt does not wick moisture away from the fresh concrete. This will also help in cracking.
Vibrate the concrete, if you can, by tapping on the form-boards with a hammer. Place #4 rebar at a minimum of 12 inches on center, and tied at intersections with wire-ties. Sufficient chairs will support the steel if placed one-chair per each 4 square feet.
Consider "control joints" if the longest deminsion is longer then 10 feet in length. These will help the cracking.
Do not pour in the heat of the day, if possible. Early morning is best.
Good luck.
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