Here is what I was told...Keep in mind, I am checking stuff out over
the internet until I can get back to Va.

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I'm a licensed home builder & foundation contractor in Alabama and I've
got an hour at kill, so here's your own D-I-Y manual. To answer the
question directly at face value, assuming you just want someone to pour
& finish a slab, I pay my slab finishers appx $1/sf to $1.50/sf for
labor-only to dig any grade beams in the backfill (assuming sand is
your backfill material), install poly, WWM, rebar, any keyway, then
pouring and finishing the slab using a trowel machine & then cutting
control joints in the slab. They provide all tools & equipment,
including trowel machine, rebar cutter/bender, floats, walk-behind
concrete saw, etc. I would make my dirt contractor tamp the backfill,
but my particular slab guy does it all for me since I provide the
backhoe loader, otherwise I do my own dirt work since I own the
equipment and know what I'm doing. This price varies depending on the
size of the slab, and with fuel costs now, going more than 20 miles, he
would hit me with a fuel surcharge, maybe $1/mi one-way as he might be
bringing 2 vehicles. Alabama is cheap comparatively --- slab finishers
in other states may get double or triple that.

But let's assume you need the entire foundation done. Before you
attempt to do your own foundation work, I would pay the money for a
geotechnical engineer to do borings and prepare a soil report to
recommend the proper foundation to use, and I wouldn't D-I-Y any
foundation work if you don't have proper experience as the foundation
IS the workshop and it can't be fixed if you do it wrong. A soil
report in my area costs appx $1,800 and takes about 2 to 4 weeks to
schedule & prepare for you from the day you call to the day it's ready.
You have to have plans or at least the area staked out so they know
where the building corners will be. Here's what you're getting into
and what must be done to insure a proper foundation and what to watch
for if you sub it out:

To do a 28x32 slab-on-grade or built-up with block, assuming excellent
soil, no trees to remove and assuming the soil report doesn't say
otherwise, I would set the building corners and mark them with stakes
and set up batter boards to find them later after you remove the
stakes, then remove topsoil/grass to 6", build a small 12" compacted
pad at least 5' outside the footprint of the slab to replace the
scratched-out topsoil/grass for the slab to bear upon, then excavating
& pouring an 18"-square reinforced concrete exterior footing (you have
to set the tops of your footings below the frost line by code) and
reinforced with 4 rods of #5 rebar stacked 2+2 with #3 stirrups to box
them together in a caged format and wet-setting #4 vertical rebar to
extend through the stem wall & 2' into the eventual slab every 48" OC
after pouring, then my choice is to lay on top of that a course of 8"
concrete block + a course of 8" header block to level out and form the
slab (as opposed to forming the slab & stem wall with lumber and
pouring the footings monolithically as I don't personally like
monolithic slabs), then backfilling with "zero" sand & tamping,
assuming I have to dig out a couple of grade beams (interior footings)
into the sand appx 12"W x 8"D for interior roof support walls and
assuming no more than 40/lf, then termite spraying & covering with a
6-mil polyethelene moisture barrier, adding 2 rods of #5 rebar on 3"
foundation chairs in the grade beams, adding any keyway needed
(assuming no more than a couple of sticks but probably none needed in
this case since the whole slab can all be sawed with control joints
after pouring), adding 6"x6" 10-gauge WWM reinforcement, adding grade
pins, turning down the vertical rebar to extend 2' into the slab area
and in the center of it, then pouring 3,000psi concrete with fibers (we
have a lot of expansive clay here and need all the help we can get, so
I use both WWM & fibers) and filling the block stem wall & grade beams
at the same time, finishing the slab with a trowel machine (assuming
you'd want a smooth finish), then cutting control joints that afternoon
after we get done + hauling off all excavated soil we don't use for
backfilling and creating positive grade away from the slab.

I would typically charge about $17,500 for that job, which is about
$19.50/sf, lock & key with all materials, equipment, labor,
engineering, compaction testing & permit included. Note that in
Alabama, everything is cheaper and you could spend twice that and more
elsewhere, and in some areas around here, depending on soil conditions,
you would need a 5' compacted pad (about $15,000 for that size area is
what I would charge, installed) or a mud sill exterior footing, which
is usually a trench about 18"W x 36"D filled with concrete and no
reinforcement, then you add the 18"W x 18"D reinforced footing on top
of that, and I would charge an additional $3,500 to add the mud sill.
A post-tensioned slab would be expensive also. I buy concrete for
$78/sy with fibers & 10% sales tax included. My block work usually
costs me about $3.50 per block for all materials & labor. To do a
compacted pad like that (38' x 42' - remember you have to go at least
5' outside the footprint) would cost me about $875 for 5 loads of
"select fill" + $100 diesel fuel in my equipment + labor for 2
operators, and I'd place it in 3 "lifts" of 6" each and compact at each
lift to insure compaction. I usually sub out minor dirt work to my
slab sub-contractor only because he has a good backhoe operator and I
own the backhoe, so I only pay him enough to cover the labor for the
operator and a stick man using the transit, with me building the pad
myself & hiring a block mason to do the block work & calling my pest
control service for the termite spraying. My slab sub costs me
anywhere from $1.70/sf to $3/sf for labor only depending on the size of
the slab with him doing the excavation of exterior footings & backfill
the slab after the block is laid. This doesn't include plumbing or
electrical rough-in (floor plugs, conduit, etc) as you would typically
contract that work separately with the plumber & electrician. My slab
guy inserts the grounding electrode, which is nothing more than a full
20' piece of rebar that runs into the slab 18' and sticks out 2' at the
place where the electrical panel (a/k/a breaker box) will be and paints
it green as the inspector requires so he knows what/where it is.

There are a lot of variables to all this --- the virgin soil may be
weak or expansive, ground water may be high, a heavy sloping terrain, a
lot of trees which have to be removed root & all --- any trees whose
canopy may eventually hang over the footprint have to be removed as
that means their roots may eventually invade and upset the slab ---
hardwoods are bad about this and can reach twice as far as their canopy
sometimes, then there's the possibility the dirt company brings you
soil that doesn't meet engineering guidelines, and unless you know how
to spot it (proof-rolling by the dump truck after compacting a lift is
a great, low-tech field-measuring device), weather is a strong factor,
you have to allow for curing of the concrete & block mortar (3 to 5
days on mortar depending on weather and size of wall) and a lot more.
Most subs are lazy and can't be trusted to do it right and many
contractors are just brokers out to make a buck, and if you don't know
what's right, you could be in for a problem. Make sure they work the
edges and smooth them out, especially if you use a block stem wall as
the framing will be easily and will be much more level & sound if the
substrate (in this case, the edges of the slab) are as smooth & level
as possible.

In other words, use this as primer and what to watch for, then hire a
contractor to do it all, then watch and learn. Make sure you tell them
what specs you want when they give you a bid and give them a copy of
the soil report also.
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