On Sat, 28 Apr 2012 03:38:47 -0700 (PDT), Hank
wrote:


Many times gravel is used to bring the grade up to a 4 inch pour.
Gravel is cheaper than concrete. Sand may wash away from under the
concrete. I advise against using sand unless you are sure it won't
wash away.

Rule of thumb is figure 1 yard will do 80 sq.ft. at 4 inches. So, your
math is correct.

One more thing to think about is to drop the concrete approx. 1 inch
below the entrance of the garage floor. This will serve 2 purposes.
One is that water won't enter under the garage door if you get a
sudden wind driven down-pour of rain. The other is if there is a cold
snap and the outside concrete heaves up a little.

Since the pour is only 20x12, I wouldn't worry about the gravel for
drainage too much if you have a good slope to the pour ( 1 inch in 10
ft ).

I wouldn't drive on it for at least a week, 3 weeks is recommneded. Do
not let anything heavy, like a car, sit in one spot very long. Even
after a year of curing, a heavy object will cause the concrete to
develop low spots ( puddles).

Good luck.

Hank

Thanks for all the replies

I'll look up those plastic rebar chairs.

I plan to order 3.5 yards to make sure I have enough. I have a barn
with a small feed room, and want to put concrete in there too. What ever
excess concrete is left over will go in there. The room is only 6 ft
wide, so I'll just have a 6 foot 2x4 that I can move to accomodate
whatever is left over. Whatever part of that room is not covered, I can
do later with bagged concrete, since I have a concrete mixer. But 3
yards is too much to mix by hand.

I'm assuming that when I use rebar, in both directions, that I skip the
place where there is a joint. In a 20ft run, that should only be one
joint.

Thanks