On Thu, 27 Jan 2005, Tom Bott wrote:
> Thanks to all of you who jumped in with ideas, suggestions, etc. concerning
> my idea for a wood shop floor over gravel. I would prefer concrete but I have
> never attempted a concrete slab project. Yes, the base cost of concrete is
> only slightly more than wood, but I know I can deal with the wood myself. The
> added cost of someone else finishing the slab including the fact that the
> concrete would have to be buggyed 100+ feet does make wood considerably less.
> I believe it was Keith who said I wouldn't be happy with anything other than
> concrete and I respect that. I also did a quick web search for "soil cement"
> and found a number of hits on the subject. May want to research it further.
The "Buggied 100'" part would stink.
However, presuming you're talking about a reasonable size slab, doing
concrete yourself just isn't that hard.
I'm _far_ from an expert. In fact, I probably know just enough to be
dangerous. That said...
There are three or four main steps in pouring a slab.
1) Prep. You need forms, packed gravel, rebar or mesh (unless you use the
fiber concrete) perhaps those interlocking metal slab dividers (if you're
doing a larger area, etc. You can take your time with this, so its an
excellent idea for doing it yourself. Ask questions here. I'm no expert,
but I sure bet some people here are.
2) The initial pour. Dump the cement in there. Use garden rakes to shove
it around as well as to hook the mesh/rebar to pull it up into the middle
of the concrete. We found it easier to put down a 2" or so layer of
concrete, pull the mesh onto that, then pour the rest. Pulling the mesh
up through the full thickness sucked. Remember to wash the concrete off
your hands fairly soon after you get it on there.
3) Skreeding. Take a 2x6, set it on the forms on end, and pull across the
top of everything. Your goal is to get the cement smooth and level. If,
as you're going along, there's a low spot, throw in spadefulls of concrete
until its not low. If there's a very high spot, you may well want to back
up and go over that area again (since, if the board gets an angle from
verticle, it'll bend and bow a bit, leaving a high spot). Btw, if your
skreed board won't hit a form on both sides... This is when you wanted
those metal interlocking forms above.
4) Floating. Buy a float. They're not that expensive. Get enough handle
on there to reach the other end and adjust the angle so that you can drop
the handle down when you're pushing out and raise it when you're pushing
back. You want the leading edge (in the direction you're moving) to be
higher than the back by a little so that the float doesn't dig in. It
really will feel like its floating, and this is way easier to do/feel than
to explain. Doing this will help smooth the surface and knock down the
rocks in the concrete. It won't, in my limited experience, do anything
about leveling, etc.
5) Power troweling. Wait until the concrete is fairly well set up.
Pushing on it with a finger should barely leave a mark, you should be able
to walk on it with just a bit of a footprint on the surface, etc. Lift
the power trowel up on there and start it up. If the trowel is smearing
the concrete vs. smoothing it, stop and let it setup up more. Work the
trowel back and forth, smoothing everything out. Btw, you control the
trowel by shifting the weight forward, back, to one side, or the other
side. Its just like a floor polisher (I knew being a janitor's helper
would come in handy! :-). Shifting the weight around makes the spinning
blades get a little more traction on one of the quadrants and the polisher
will move in that direction. Brute force doesn't work.
* You want four or five strong friends. Concrete is heavy. You'll want
two or three folks on the skreed board and at least one guy working the
concrete around behind you. If you've got to wheelbarrow it in there, I'd
add a couple more.
* You can just stand in the concrete you haven't skreeded yet. This
sounds dumb, but I was worried about it. :-)
I'd never done this prior to a few months ago and was _very_
nervous/tentative. So I went over to help a buddy pour his floor (who
also hadn't done it) and practice. :-) After just skreeding the floor,
we had a surface that was better than many I've seen and used and would
certainly beat the hell outta wood. After floating it was something I'd
have expected from someone who I was paying, but maybe wasn't an expert.
After power trowelling the floor looked as good as anything else I've
I'm quite sure that a pro could have done it faster, wouldn't have made
the mistake of trying to power trowel too soon, wouldn't have been as
nervous, and maybe could have made it look even better (particularly at
the edges... If you don't get concrete in the edges when you're skreeding,
you kinda screw yourself for later on). I know for sure that I wouldn't
have been as tired. :-) However the floor we poured, all of us as our
first time, was _much_ better than any of us were expecting it to be.
While I'm quite sure there's a _ton_ of stuff I don't know and mistakes
I'll make when I do my floor, I now see concrete as something that's not
too hard to do a decent job with.
Sorta like if you're a normal person who can do carpentry vs. a
professional carpenter... :-)