ground flat under sidewalk

(Please, don't tell me to have me or a contractor put in a new sidewalk unless you're willing to pay for it. Anyhow, this is more an intellectual** question than it is a search for construction advice )
**Dirt is as intellectual as I get.
When a quality cement/sidewalk pourer puts a sidewalk in, does he make a real effort to have the ground underneath flat and horizontal?
The ground underneath my sidewalk was and is very uneven and the two squares I've lifted up vary in thickness from 2" to 4", sometimes in the space of 8 inches.
It looks like the paver made almost no effort to have the ground flat.
About 10 years ago a root had made one square heave up. I lifted up the square and moved it to the side -- got very good at that so that I could do it alone in from 5 to 10 minutes, and I could put it back in 5 minutes also -- and I cut out that root and others, but in doing so disturbed the height of the soil. Then when I put the square back, it rocked, or it was too high somewhere else, or too low.
If the ground had been flat in the first place, almost all I'd have to do is make it flat again.
I got it right on the 3rd of 4th try, but now I'm 10 years older, 40 pounds heavier, don't want to work so hard, and I hoped I'd get lucky, or be able to use what I learned the last time, and get it the first time. But I didn't. I can live with that, but I'm curious as to how it's supposed to be done.
I haven't found many flaws in my house, but this seems like one of them. depending on what you all say.
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Not exactly. Paved or poured sidewalks do not lie directly on the ground underneath. The contractor has to prepare a foundation for the sidewalk, usually done by digging out the dirt and replacing it by gravel of a planned size (to enable drainage, to prevent the sidewalk's cracking in future years etc.) which must be tamped down and levelled before paving or pouring.
--
Don Phillipson
Carlsbad Springs
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On Saturday, October 25, 2014 4:47:21 PM UTC-4, micky wrote:

The base doesn't have to be perfectly flat, some small variation is normal, but 2" to 4" is a lot more than normal. One obvious problem, you use a lot more concrete in the 4" thicker sections, but still wind up with only 2" in other places, which are going to be the weak links.
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Try a layer of sand.
nb
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Micky:
If a concrete contractor is doing a sidewalk, he probably won't care if the ground he pours the cement onto is flat or not since even the thinnest section of the sidewalk (say, 2 inches thick) is sufficient to support the traffic.
BUT, for that sidewalk slab to have been poured properly, the contractor should have both:
1. laid a bed of crushed limestone (or sand, but limestone compacts better) down first, and
2. compacted that crushed limestone with a plate compactor, or in larger jobs, a paving roller.
Doing that provides a sturdy base on which to pour cement and finish it.
If you didn't find a bed of either sand or limestone under your concrete, then the contractor was making that sidewalk the fastest easiest cheapest and worst way possible.
--
nestork


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The four of you have convinced me that I didn't get a very good sidewalk. No gravel, nothing below the sidewalk but dirt. It's probably too late this year (not enough warm days left) but next year I'll try a layer of sand.
Of course that means digging out some dirt, or the square will be higher than it was, and if I dig out more than the sand I put in, it will be lower.
But I need the exercise. I need the exercise now too, but not too many warm days left.
Thanks everyone.
On Sun, 26 Oct 2014 01:12:41 +0200, nestork

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If you're going to be doing this over, then you really should have a layer of landscaping fabric under the crushed limestone or sand. That landscaping fabric prevents the sand or limestone from dissipating into the ground below it so that the base of the concrete doesn't get weaker with time. So, from bottom up it's ground, landscaping fabric, compacted crused limestone (or sand) and then concrete.
Phone any company that does paving and see if they use something other than landscaping fabric. The stuff I saw looked like landscaping fabric, and serves the same purpose, but it might have been a heavier gauge of landscaping fabric used in construction. For a small job like this, though, it might be more economic to fold landscaping fabric over to get double or triple the thickness rather than buy the stuff the construction companies use.
--
nestork


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On Sun, 26 Oct 2014 04:51:11 +0100, nestork

I don't see the point to the landscaping fabric in this case, it's just one square out of many,... if he simply levels the dirt and compacts it some he's already miles ahead of what's under the other 90% of the squares.
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On Sunday, October 26, 2014 8:37:38 PM UTC-4, Ashton Crusher wrote:

I agree that I don't see the point in landscape fabric under concrete either. But you do need a stabil base, which isn't compacted typically just compacted dirt/soil. Typically you have to dig down to something that is solid, eg gravel layer, then fill with a stabilized base material, eg more gravel, crushed rock, etc.
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