Mike Dobony wrote:
"Wpg Man" wrote in message
om...
Does anybody have any thoughts about using straw bales as a "void
form" for a concrete garage pad?

Typical garage pads in my area are made on top of a gravel base that
is deeper around the edge. This gives a one-piece concrete pad that
is "thickened" around the edge for strength. These pads are pretty
good, but they are only "thickened" around the edge and can still
crack.

I want to dispense with the gravel completely, and use hay bales as a
"void" form as follows:

Place bales in a series of solid 8ft x 8ft squares on the ground.
Between each set of 8ft squares would be an 8 inch gap. If you can
imagine, the concrete is poured over the while thing. The concrete
would go down into the 8" gaps, giving an integral concrete "beam"
every 8 feet. So instead of a "thickened" edge beam only, this pad
would have a matrix of beams every 8 feet. Of course there would be
rebar also.

The hay bales are basically there to "save money" on concrete
(instead of pouring a 2 foot thick floor). I think this floor would
be so strong that you could lift one corner and the whole thing
would stay together (no cracking due to frost etc).

I am wondering about these hay bales though. I really don't care if
they rot after the concrete sets. Does anybody see any problems? I
would probably put plastic on top of the bales to seperate them from
the concrete. Do you think I should also put plastic underneath them
so they stay dry forever?

I think the cost would be less also. Typically, you need 2 feet of
gravel under the floor to raise the grade of the garage floor. With
the bales, I automatically get a 2 foot raise in the grade, as well
as the extra strength from the beams.

Also, if you really want to go nuts, the beams can be made deeper (or
the grade can be raised) with very little cost by stacking bales on
top of each other. If you were to stack 2 bales (instead of one),
the beams are deeper and it would not take much extra concrete.

I also like the fact that the beams (both in the middle and around
the edge) are nice and "square". The "thickened edge" garage pad
has a beam around the edge that is formed by the sloping gravel
beneath it, giving a "not so pretty" beam.

Thanks.

What you are describing is a bad way of making a structural concrete
garage pad like a parking ramp construction. Bare in mind that these
structures are heavily reinforced with pre-tensioned rebar and high
strength concrete. It takes special knowledge and skill to do this.
you risk having your car drop 2 feet into a hole when, not if, your
floor fails. Stick with gravel and go with a 6" pour instead of the
standard 4" and go a good 10" around the perimeter for an integrated
footing.

I've seen it used for walls but not floors.
If you want to save just backfill with old material.