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Old April 27th 12, 05:55 AM posted to alt.home.repair
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Default How necessary is gravel under concrete?

I'm wanting to put a 20 foot concrete pad in front of my garage. Right
now, the garage floor is concrete, but the driveway in front is just
dirt. However, under that dirt, there is a bed of 2" to 3" rock, which
I put there about 6 years ago. What I want to do is just make forms and
have a just have a few yards of concrete delivered, to trowel myself.
The base dirt is well packed and solid from years of driving on it.

To add gravel, I will have to disturb this well packed dirt with the
rock underneath. (or the drive will be higher than the garage floor).
Not only will this disturb the well packed base, but will double the
cost of this job, because of the cost of the gravel, and the cost to
rent some sort of machinery to dig up this dirt and rock base, since I
already tried a shovel and with that rock base, the shovel wont even go
in the ground unless it's after a rain when it's muddy, and even then
the rock base could not be dug up with just a shovel.

My plan was to simply make forms, remove the small wooden ramp I made at
the front edge of the concrete garage floor (I left the dirt about 4
inches lower than the garage floor intending to pour concrete, but made
that ramp out of stacked 2x8's to drive in and out of the garage). Add
a few bricks with some rebar on top, And pour/finish the concrete.
A fairly simple job. However, someone told me I must put dravel under
it first. Is this gravel really needed? If it is, why? After all, I
already have the rock base, which is very solid, and rock is like
gravel. It's just that dirt has filled in around the rock so it just
looks like dirt now.

One other thing. For a 20 foot long by 12 foot wide strip of concrete,
how many joints should I cut in the concrete? I'm thinking just one, so
each section is 10ft. I plan to place one of those black fiber strips
where it meets the garage slab. I'll probably just trowel the joint in
the middle, to avoid having to rent a concrete saw.

Finally, did I figure this correctly?

20 X 12 = 240 sq ft. At 4 inches think, I estimated that I need
roughly 3 cubic yards of concrete. (Actually 2.96 cu yd). Is this
right? (I'm not the best at math).

Thanks



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Old April 27th 12, 06:58 AM posted to alt.home.repair
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Default How necessary is gravel under concrete?

A fairly simple job. However, someone told me I must put dravel under
it first. Is this gravel really needed? If it is, why? After all, I
already have the rock base, which is very solid, and rock is like
gravel. It's just that dirt has filled in around the rock so it just
looks like dirt now.


You say nothing about your climate or location. Do you have freeze thaw
cycles? Gravel base helps keep the water away from the concrete. Do you
have seasons? Dry, wet cycles? Soil expands when it gets wet and shrinks
when it dries. Rock helps isolate the concrete from soil movement. When
the soil is wet its load carrying capacity is diminished. Concrete corners
may not have good support and break. Generally rock under concrete is
essential. Especially under driveways where there is loading from vehicles.

A thin layer of sand under the concrete allows up to 10 feet between joints.
The joints control where the concrete cracks. If the joints are too far
apart then a crack forms before the joint is reached. The sand allows a
little slippage so the joints can be stretched a little.

I figure 2.7 yards.


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Old April 27th 12, 08:05 AM posted to alt.home.repair
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Default How necessary is gravel under concrete?



Pat wrote:
A fairly simple job. However, someone told me I must put dravel under
it first. Is this gravel really needed? If it is, why? After all, I
already have the rock base, which is very solid, and rock is like
gravel. It's just that dirt has filled in around the rock so it just
looks like dirt now.


You say nothing about your climate or location. Do you have freeze thaw
cycles? Gravel base helps keep the water away from the concrete. Do you
have seasons? Dry, wet cycles? Soil expands when it gets wet and shrinks
when it dries. Rock helps isolate the concrete from soil movement. When
the soil is wet its load carrying capacity is diminished. Concrete corners
may not have good support and break. Generally rock under concrete is
essential. Especially under driveways where there is loading from vehicles.

A thin layer of sand under the concrete allows up to 10 feet between joints.
The joints control where the concrete cracks. If the joints are too far
apart then a crack forms before the joint is reached. The sand allows a
little slippage so the joints can be stretched a little.

I figure 2.7 yards.



And no rebar?
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Old April 27th 12, 02:20 PM posted to alt.home.repair
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Default How necessary is gravel under concrete?

I would recommend putting a 1'X1' footing adjacent to your garage slab
and one at the end of your new slab, also. Put an expansion joint at
the center of your pour by placing a physical divider there. Just
cutting a kerf in the concrete (after it sets up well?) is not a
proper expansion joint and may likely not work to prevent the slab
from cracking somewhere else.

Order 3000psi concrete. Costs the same as 2500 psi.
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Old April 27th 12, 02:21 PM posted to alt.home.repair
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Default How necessary is gravel under concrete?

On Apr 27, 1:05*am, Tony Hwang wrote:
Pat wrote:
A fairly simple job. *However, someone told me I must put dravel under
it first. *Is this gravel really needed? *If it is, why? *After all, I
already have the rock base, which is very solid, and rock is like
gravel. *It's just that dirt has filled in around the rock so it just
looks like dirt now.


You say nothing about your climate or location. *Do you have freeze thaw
cycles? *Gravel base helps keep the water away from the concrete. *Do you
have seasons? *Dry, wet cycles? *Soil expands when it gets wet and shrinks
when it dries. *Rock helps isolate the concrete from soil movement. *When
the soil is wet its load carrying capacity is diminished. *Concrete corners
may not have good support and break. *Generally rock under concrete is
essential. *Especially under driveways where there is loading from vehicles.


A thin layer of sand under the concrete allows up to 10 feet between joints.
The joints control where the concrete cracks. *If the joints are too far
apart then a crack forms before the joint is reached. *The sand allows a
little slippage so the joints can be stretched a little.


I figure 2.7 yards.


And no rebar?- Hide quoted text -

- Show quoted text -




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Old April 27th 12, 02:29 PM posted to alt.home.repair
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Default How necessary is gravel under concrete?

On Apr 27, 1:05*am, Tony Hwang wrote:

And no rebar?-


Rebar for footings, yes. It's also a good idea to use reinforcement
wire on any large slab.
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Old April 27th 12, 02:39 PM posted to alt.home.repair
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Default How necessary is gravel under concrete?

On Fri, 27 Apr 2012 00:05:55 -0600, Tony Hwang
wrote:



Pat wrote:
A fairly simple job. However, someone told me I must put dravel under
it first. Is this gravel really needed? If it is, why? After all, I
already have the rock base, which is very solid, and rock is like
gravel. It's just that dirt has filled in around the rock so it just
looks like dirt now.


You say nothing about your climate or location. Do you have freeze thaw
cycles? Gravel base helps keep the water away from the concrete. Do you
have seasons? Dry, wet cycles? Soil expands when it gets wet and shrinks
when it dries. Rock helps isolate the concrete from soil movement. When
the soil is wet its load carrying capacity is diminished. Concrete corners
may not have good support and break. Generally rock under concrete is
essential. Especially under driveways where there is loading from vehicles.

A thin layer of sand under the concrete allows up to 10 feet between joints.
The joints control where the concrete cracks. If the joints are too far
apart then a crack forms before the joint is reached. The sand allows a
little slippage so the joints can be stretched a little.

I figure 2.7 yards.



And no rebar?



I like the idea of rebar (or even mesh) in residential driveways but
I've yet to see it in the dozen or so driveways under construction
I've come across on Long Island or in Houston. All were poured on
just sand without any gravel. Personally I like the idea of sand,
gravel and rebar but that's not what I've seen so far. Of course one
reason is probably to keep costs down.
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Old April 27th 12, 03:22 PM posted to alt.home.repair
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Default How necessary is gravel under concrete?

"Doug" wrote:


And no rebar?



I like the idea of rebar (or even mesh) in residential driveways but
I've yet to see it in the dozen or so driveways under construction
I've come across on Long Island or in Houston. All were poured on
just sand without any gravel. Personally I like the idea of sand,
gravel and rebar but that's not what I've seen so far. Of course one
reason is probably to keep costs down.


I like some iron in there, too-- but I keep hearing folks who know a
lot more about it than I do say that the fiberglass right in the mix
is a better binder. To a casual observer it looks like there is
*no* reinforcement, but it is in the mix.

Jim
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Old April 27th 12, 05:25 PM posted to alt.home.repair
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Default How necessary is gravel under concrete?

On 4/27/2012 8:22 AM, Jim Elbrecht wrote:
wrote:


And no rebar?



I like the idea of rebar (or even mesh) in residential driveways but
I've yet to see it in the dozen or so driveways under construction
I've come across on Long Island or in Houston. All were poured on
just sand without any gravel. Personally I like the idea of sand,
gravel and rebar but that's not what I've seen so far. Of course one
reason is probably to keep costs down.


I like some iron in there, too-- but I keep hearing folks who know a
lot more about it than I do say that the fiberglass right in the mix
is a better binder. To a casual observer it looks like there is
*no* reinforcement, but it is in the mix.

Jim


There'll be 1/2" rebar on two foot centers in any slab i own. No steel
in concrete is just stupid.

--
Steve Barker
remove the "not" from my address to email
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Old April 27th 12, 05:57 PM posted to alt.home.repair
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Default How necessary is gravel under concrete?

On Apr 27, 6:22*am, Jim Elbrecht wrote:
"Doug" wrote:

And no rebar?


I like the idea of rebar (or even mesh) in residential driveways but
I've yet to see it in the dozen or so driveways under construction
I've come across on Long Island or in Houston. *All were poured on
just sand without any gravel. *Personally I like the idea of sand,
gravel and rebar but that's not what I've seen so far. *Of course one
reason is probably to keep costs down.


I like some iron in there, too-- * but I keep hearing folks who know a
lot more about it than I do say that the fiberglass right in the mix
is a better binder. * *To a casual observer it looks like there is
*no* reinforcement, but it is in the mix.

Jim


Been told also that rebar and wire are an 'old wive's tale' and not
necessary today. And, worse, a huge nuisance if you try to break it up
and remove later.


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