Greetings and Salutations....
Thanks for the details...it really clarifies things.

On Tue, 31 Aug 2004 09:12:51 -0300, "jtaylor"
wrote:
*snip*

Well, there are places where it has a nice troweled finish, that I'm happy
with.

Yep, it is always nice to see that!

There are places where the surface will sort of flake off and it looks sandy
underneath.
There are some areas where it seems like water marks.
There are places where you can see footprints, and marks from the
kneeboards.

Nothing deeper than about 1/8 inch.

I told the ready-mix place what I was doing and the fellow said I'd need
4000 psi mix; the truck driver was very helpful but I think he put some
extra water in on the way - it was very soupy - the pictures of "slump" in
the concrete books I had read _all_ looked stiffer, even the ones the books
said were too wet.

It made for easy pouring and screeding, but I did notice that there was a
large amount, a bulge, of sandy water in the middle after I floated it the
first time, with a 4 foot piece of wood on a 12 foot handle. The slab was
beside an existing building, so there was a bit of difficulty getting to one
side, and with screeding, As well, the last part of it was in the sun, so
it seems to me that the first and last parts set before the middle; that's
where I left footprints, anyway...


Yea...that sounds as if someone screwed up. Probably not the
driver, as they typically don't do anything to the mix between the
time it gets dumped into the truck and the time it reaches your site.
I would suspect that something got set wrong at the concrete yard,
and, no one noticed it.
No use crying over spilled milk, but, I suspect it would be
a GOOD thing to get one of the supervisors from the company to come
out and take a look at your pour. It might not get YOU anything
but, it probably will make a mixing operator's life uncomfortable
for a little while. On the other hand, it might get you some
compensation, and, certainly would be good to have a professional
eye look at the slab.
Now...it does sound as if you started out with a WAY too
soupy mix. this is bad for several reasons, not the least of
which is that concrete consists of a mixtures of glue (the cement)
and matrix (rocks, sand, etc). It gets its strength from the EVEN
distribution of that matrix through the entire slab. If it is too
wet, as you work (or overwork) the concrete, all the matrix will
work its way to the bottom, leaving a fairly low-strength layer
of sand and cement on top. It may work ok for as long as you
live there. It may start spalling off and falling apart in a
year... I would be inclined to drill a test core someplace, to see
what the distribution looks like.
Your comment about the flaky, sandy areas make me think
that it is REALLY separated out, and, for me, that is a bad thing.
If it is flaking now, there is an excellent chance it will flake
even worse when you start moving heavy machines across it. Also,
if the matrix has really settled out, there is an increased chance
of cracking and other problems. Which reminds me... I forgot to
ask if there is any steel in this slab? Rebar or grid to keep
it from breaking up? Also, what about expansion joints?
As for the footprints, etc, those will have to be filled
in and levelled out, or your life is going to get WAY too exciting
later on. There is nothing like moving a 1000 lb, top-heavy lathe
(for example) and having a wheel on the dolly catch in an imperfection
in the floor! DAMHIKT *smile*.
Now...what to do to "fix" the whole thing. I can see a few
of ways out of this.
1) Jack hammer it all up and pour a new slab, with the RIGHT
mix this time. THis is kind of the worst-case scenario, and would
not be one that I would take unless a pro said the slab was crap.
(hence the reason for getting one out to look at YOUR slab). If it
were me, I would also look at some serious help from the concrete
company on this, if it was their fault that the concrete did not
meet specs.
2) put forms back on the slab, and, pour another couple
inches of the RIGHT mix on top. You will probably want to pin
re-enforcing mesh to the existings slab for this, to ensure
good bonding and stability.
I don't know if you tried flattening the concrete on your
own, but, if you did...this time see if you can wave a six-pack
in the direction of a couple of buddies to help spread the mix and
screed it off. Also, be sure to rent a big bull float to do the
"final" topping. They come with long enough handles that you
should NEVER have to actually walk on the concrete itself.
The good news is that you are a lot more educated about
pouring concrete now, and, the NEXT slab will be a lot better
(cold comfort, I know).
3) you could take a hybrid approach. Fill in the holes
with patching compound and knock down the ridges with a sander,
to get it as smooth as possible. Then, there are a number of
epoxy based floor coatings that one can put down that will
provide an excellent surface. I don't recall any names just
off the bat, but, a quick poke through the yellow pages under
floor treatments should get you some names. Also, I am sure
that the concrete company would have a clue about this too
(which is a good reason to try and stay on friendly terms with
them...) In any case, the deal is that you spread this thick
layer of epoxy on the floor, then, sprinkle on these flakes
of material..sometimes coarse sand, sometimes little flakes
of plastic. It then gets rolled down flat. Once it sets up
it will be a nearly indestructable floor treatment. We had
this done to the concrete floor of the fellowship hall in my
church back in the mid-70s or so, and, it STILL looks just
as good as it did then (and it has had a LOT of use, too).
I would be a little concerned about the areas you
mention as spalling off...that does not bode well for a good
surface, but, perhaps the epoxy will stabilize it enough that
all will be well. Or...at the worst...the areas that are really
bad are JUST where you will put a workbench or some large,
stationary tool (*smile*).
Regards
Dave Mundt