I recently saw a concrete parking lot being made. This was after hours,
so no one was around to ask. They had the forms made, and had rebar
placed about every 2 feet in both directions. Under the rebar they had
small plastic "stands" to keep it off the ground.
What are these things called, and where does someone buy them? Also,
what did they use before they made these plastic things? I plan to pour
a pad of concrete in front of my garage soon, and think rebar should be
used, but I was just going to use rocks under the rebar. Actually the
thought was to buy some of those cheap patio blocks, which are about 1.5
inches thick and bust them up into pieces for this. That way the rebar
would all be about the same space off the ground, and those patio blocks
are pretty low cost. Possibly cheaper than those plastic things.
On the other hand, I was wondering if using that metal mesh material
which is sold in rolls would work just as well as rebar and which would
be cheaper to buy.
Any concrete experts out here?
On Friday, July 19, 2013 4:02:05 AM UTC-5, firstname.lastname@example.org wrote:
Google is your friend http://www.globalindustrial.com/p/building-materials/
On Fri, 19 Jul 2013 04:02:05 -0500, email@example.com wrote:
When commercially made chairs are not available, installers use pieces
of brick, concrete block or whatever they can find. Worst case is when
they use wood, foam or a coffee cup which weaken the pour.,
A responsible contractor will provide real chairs so their workers can
build a better product at a faster pace. These things are dirt cheap
in contractor qualities anyway. That is peanuts compared to the time a
crew wastes looking for something to use on the site and try to make
What you should do is excavate and then:
1. put down landscaping fabric. This is a tight weave material that
won't rot due to exposure to moisture in the ground. It's purpose is to
prevent the limestone from dissipating into the soil to prevent soft
spots in either the asphalt or concrete you put over top.
2. Spread crushed limestone over the area you intend to pave or place
concrete over. Typically, the limestone will be anywhere from 3 to 4
inches thick and will be compacted down to 2 1/2 to 3 inches thick with
a plate compactor you can rent.
3. Put your rebar in. Ideally, it's best to put in TWO layers of rebar;
one layer near the top of the slab and one near the bottom. That way,
for the slab to bend far enough to break, the rebar has to stretch.
Since steel is very strong in tension, it's the rebar's resistance to
stretching that makes the slab more rigid and resistant to bending.
Where you only see one layer of rebar supported in the middle of the
slab, it's not there to strengthen the concrete, it's only there to
prevent the pieces of concrete slab from spreading apart when (not if)
the slab breaks. You can buy supports for rebar at any place that sells
rebar. Look under "Steel" or "Concrete" in your yellow pages phone
4. HIRE someone to finish your concrete for you. You can save 90
percent of the cost of the job by doing all the bullwork yourself, but
placing concrete and finishing it is a skill that takes a lot of
experience to master. And, with concrete, any screw ups are permanent
screw ups. Do all the bull work yourself, and then hire a concrete
contractor to actually place the concrete for you, and you'll end up
paying less for a professional looking job.
Can you make your slab thicker, say 6 inches?
And, can you squeeze that cover down to 1 1/2 inches so that you have
your two layers 1 1/2 inches from the top and bottom of the slab
If it's only going to be a patio slab, and you're not going to be
putting anything heavy on it, then stick with the 4 inch thickness and
put the rebar in the middle just to hold the slab together if it breaks.
While this does sound like the top of the line method, it seems rather
excessive, not to mention costly, for a home driveway. This sounds more
suited to a highway. My plan is to just pour the concrete over some
gravel, and add either the rebar or that rolled steel material that
looks like fencing. My only modification is on one side of the
driveway, the soil tapers down a little bit, so I intend to make it a
little thicker on that side to prevent washing out under it. So, while
the slab is 4 inches, that edge will be about 6 inches. I plan to
finish it myself. I've done it several times in the past and it's
always been smooth enough for my needs. The surface will just be a
broomed finish. A little roughness is desired to prevent slipping when
On Fri, 19 Jul 2013 11:57:10 -0400, firstname.lastname@example.org wrote:
I would actually think that the brick or concrete block pieces, would
make the best slab because it's the same material, and becomes part of
the concrete. I do agree that wood or foam would be a bad choice. But
I do wonder if plastic "chairs" would also weaken the slab to a small
degree. Plastic is not a very solid material, but I suppose it wont
decay under a slab. Wood would definately rot, and I would not evne
consider using it.
replying to mancave, Derek Lindstrom wrote:
Yeah they're called Dobies! We use them for keeping the steel or rebar off the
ground and in a central location so the it's ready for the concrete and wont
need any extra work lifting or placing the rebar in the center of the slab
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