Bricks, Masonry, Asphalt and Concrete - layers for basement slab pour?

I have removed my old basement floor and want to repour. It will be on top of hard packed clay. I have seen several different variations: plastic- gravel- concrete, gravel -plastic -concrete, no plastic, no gravel etc.

Is there a standard method for the misdwest, for example, plastic, 6 inches of 3/4 hard-packed gravel, four inches of concrete (fiberglass additive)? The dimensions are 20 X 30 feet.

Thanks,
Bill

The last way you described is the way to go, the plastic will act as a vapor barrior and keep moisture out of the basement.

You do not want to place concrete directly on plastic because it will hold in the moisture at the bottom, slowing down the curing time considerably. If the clay is hard, then plastic, two inches of sand, then concrete would work. A 4,000 psi mix with fiber mesh added is fine, unless the clay tends to heave. Then steel wire mesh reinforcing is needed (at a minimum, maybe actual bars in extreme cases). Check with your local building department for the details if that is the case.

Definately put the sand over the plastic like bungalow jeff said, then 3-1/2" to 4" of concrete. In addition to slowing curing, if concrete is placed directly on plastic, it has a tendency to "curl" (ie, it turns up) at the edges due to different rates of curing at bottom and top of slab. Engineers have told me of extreme cases where the edges curled 1-1/2" at edges! Be sure to slightly moisten the sand just before you pour to keep it from sucking all the water out of the concrete. And, yes, use Fibermesh; we specify Fibermesh for slabs almost exclusively for projects we design now. Good luck with your project.

Bruce

Thanks for teh information.

as these guys are saying, I can understand why they want to put the sand on top of the poly. But you dont need to. when we do new houses, we just get the excavator to dump gravel (we used to use 1/4 to 1/2 inch, but apparently the gravel pits are out of it). now we use a sand/gravel mix.

to get ready for pouring after the plumbing is installed in the ground, we level off the gravel, lay the poly, and pour. We havn't had any problems yet.

SO id say whatever is easier.