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Chad, I have a friend who is an engineer with lots of good sense. He was the one who suggested to use the rebar instead of mesh. I tied mine with some leftover stainless electric fence wire that was left in the shed by the previous owner. I blocked it up 2" off the bottom on piece of brick, cinderblock, rocks and whatever was handy. Rebar or mesh does no good if it goes to the top or bottom of the slab. Mesh floats, sinks, or gets walked down to the bottom during the pour. Rebar stays where you put it. 16" centers is just fine... but here's an even better way. Concrete cracks at the edge. If you can keep the edges from cracking, it's probably not going to crack. This means your rebar needs to be biased towards the edges. Out on the edge of the slab, my first two courses of rebar are on about 6" centers. The next couple are on about 9" centers, then 12" centers, then 16" centers, then 18" centers and so on until the middle of the slab where it's about 24" centers over about 6 or 8 squares. I also put a bunch of leftover 5ft pieces in the doorway of the bay, where I pull my cars, trucks, (and eventually tractor or whatever) in and also where I unload my machine tools. It's about 10" centers over a 10x10ft area there. The cure was slow and, being inside, was nice and damp the entire time. The finisher did a marvelous job, leaning a glassy smooth floor, but one that is not even the slightest bit powdery. After he finished, he told me to go buy some curing sealer and mop it on, which I did. No weight other than my feet touched the surface until after 30 days. After the cure, i beagn moving stuff back in. I have a 6000lb lathe, a 6000lb radial drill, a 4000lb mill and a couple of other small machines on one 12x30ft end of the 30x36ft slab. All came in through the big doors and were rolled across the floor on pipe rollers. No cracks whatsoever after two years. However you pour your sab, DO NOT cut corners to save money. I did my own grading and forming, which saved a lot of money, but I spent the money on rebar, 4000lb mix, fiber, and a professional finisher. You might screed off your driveway solo, but a nice level shop floor is no place to learn the fine art of smooth finishing concrete. As for thickness, I went with 5" (I think I mistakenly said 4", but it's 5). I was looking for info for how thick a slab should be on the net and hit an Army site that suggested a 7" slab for a TANK SHOP. Not planning on working on 120,000lb tracked vehicles, I decided that 6" would be waaaayyy plenty at that point and figured 4 would probably suffice. I then hit another site on driveways that said a 5" slab was a really great compromise. Apparently from 4-6", there isn't a lot of difference in strength and 5" is not that much more expensive than 4" while yeilding nearly the stregth of a 6" slab... a difference that is made up with 4000lb mix, rebar and fiber at far less cost. So far, so good.
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