concrete slab no rebar?

[ManCave]

we are pouring a 5,000 sq ft slab for a tent wedding venue

our concrete guy says the fiber mesh in the concrete is all you need and you don't need rebar or wore mesh in the slab. he says no one uses it any more

the concrete plant suggests still using rebar even with the fiber mesh. rebar is another $2,000

any concrete pros here that can weigh in?

 

[The Cobbler]

rebar/ wire mesh is used all the time still. get another contractor

 

[doublearon98]

[emoji23][emoji23][emoji23][emoji23][emoji23]

Put rebar. Wire mesh is about like not using anything. The fiber is good but isn't good enough to hold on its own.

Like The Cobbler said get a new contractor, sounds like the one you have doesn't to deal with doing it proper imho

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[Kaizen]

My guy did rebar around thickened edge and just mesh in the middle. Mine is 1000 sq ft. Two years and two New England winters and I don’t even have cracks at the expansion joints. I did 6 inches 4k psi.



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[Musicinabottle]

They still use rebar. In fact rebar is used far more than fiber mesh here.

 

[LXCam]

It really depends on your soil condition. If you have expansive soil, I'd want rebar or at least mesh.

 

[southalabama]

Mine was rebar around edges and wire mesh in middle

 

[Toolfool]

I usually only see wire mesh used in sidewalks and patios. Slabs and driveways are always rebar. And most concrete contractors have gone away from fiber because customers end up complaining about the "hairs".

 

[crf731]

I poured a pad yesterday. It had rebar in it..

My dad has a 2 car garage that he built on his farm back in the 70's.

For some reason he didn't put rebar in the concrete. He has a 2" wide crack in the concrete right down the center of his garage now.

I'd tell your contractor that he is putting rebar or wire mesh in it, or he can pack up his equipment and go home.

 

[Musicinabottle]

I usually only see wire mesh used in sidewalks and patios. Slabs and driveways are always rebar. And most concrete contractors have gone away from fiber because customers end up complaining about the "hairs".

City sidewalks don't use any rebar or remesh and I think they do that so they can tear up a section without having to cut it.

 

[lakelandcat]

Mine was rebar around edges and wire mesh in middle

Ditto, My slab was 16x20 rebar wire mesh and fiber.tied to a 8x20 screened in porch and patio which is 10x40. porch and patio are P gravel. Didn't want cracks, thats why the overkill. Whole slab is on a harder than hell clay. It was a creek at one time. My driveway is 21 years old and cracking 4" with rebar only, shop slab is 4-6 with 12 footer. its 4 years old and not a hint of cracks. Better to have it and not need it than need it and not have it.

 

[matt_i]

There are many possible shortcuts. One can, or can-not: remove organic material and topsoil, compact disturbed soil, add crushed stone base, compact stone base, add vapor barrier, add reinforcing steel, saw cut the slab the next day after the pour, wet-cure for 1-4 weeks or use curing sealer. In my mind, the more of these one checks off as "do" the directionally better the job.

Also: don't fall into the trap of paying for the rebar, then show up the day of the pour to find it untied and sitting on the ground with cats saying they reach down into the wet concrete, hook it with little wire hooks and pull it into position in the wet concrete. It needs to be wire-tied and sitting on dobies or rebar chairs.....

 

[Prospecter]

I've done two garages in Maine. The one with fibers only cracked. The next one with rebar and mesh did not.

 

[acer66]

I usually only see wire mesh used in sidewalks and patios. Slabs and driveways are always rebar. And most concrete contractors have gone away from fiber because customers end up complaining about the "hairs".

A builder just had a walkway, small slap and a 2 car driveway/parking spaces poured all connected across the road and they did not use anything.

 

[DpSyChO]

City sidewalks don't use any rebar or remesh and I think they do that so they can tear up a section without having to cut it.

And a lot of the city sidewalks around here they end up going around every so often to "grind" one section of sidewalk to blend it to a section that has settled or pushed up by roots in order to keep people from tripping (lawsuits).

In my head rebar in the sidewalks would prevent this but then again it may cause a crack mid section instead of the section raising/settling.

Back to my pad: It is 30x40 and I went with rebar on 2' centers and fiber. I had to leave for work as they were putting the rebar into place that morning and tying it together. I ask if they were going to raise it as I had specified and was told "yes". The wife said they did raise it but did not use rebar chairs, they took some brick that was on the truck, broke into 1/3's and put pcs of brick under the joints. WTF.....even if it was left over brick from another job it was more work than using chairs. I specified I wanted it raised, but did not specifically tell them I wanted chairs so I guess I was partly to blame on that one. This was from a highly regarded mason in the area whom I do not recommended to anyone due to some other issues we had.

 

[ConCretin]

Sooo, the short answer is no, steel reinforcing isn't an absolute requirement. If the sub grade is good and you control shrinkage, you can get by without it. Millions of square feet of commercial slabs are placed without steel reinforcing.

Steel reinforcing doesn't prevent cracks or make a slab on grade stronger, it simply holds any cracks that form together - including the cracks you can't see in the bottom of your control joints.

It's also true that fibermesh isn't a direct replacement for steel reinforcing. It prevents early age shrinkage cracks long enough for you to relieve the tension caused by drying shrinkage with saw cut control joints. It won't prevent cracks long term or hold cracks together after they form.

 

[ezover]

the comment that strikes me is, "he says no one uses it any more" sounds like some one trying to get in and out making a quick buck, or a hack.


I would get advice from a few other contractors in the area.

 

[ddawg16]

At the end of the day....it's about $$

Consider this....adding rebar has NO negative effects.

When you consider the additional cost?

It just means both you and the contractor do without a few more beers

 

[doublearon98]

And a lot of the city sidewalks around here they end up going around every so often to "grind" one section of sidewalk to blend it to a section that has settled or pushed up by roots in order to keep people from tripping (lawsuits).

In my head rebar in the sidewalks would prevent this but then again it may cause a crack mid section instead of the section raising/settling.

Back to my pad: It is 30x40 and I went with rebar on 2' centers and fiber. I had to leave for work as they were putting the rebar into place that morning and tying it together. I ask if they were going to raise it as I had specified and was told "yes". The wife said they did raise it but did not use rebar chairs, they took some brick that was on the truck, broke into 1/3's and put pcs of brick under the joints. WTF.....even if it was left over brick from another job it was more work than using chairs. I specified I wanted it raised, but did not specifically tell them I wanted chairs so I guess I was partly to blame on that one. This was from a highly regarded mason in the area whom I do not recommended to anyone due to some other issues we had.

Fyi broken chunks of brick is easier than those chairs. When pouring if someone steps on the rebar close to or on a chair they will break and float to the surface, brick doesn't so that. When we set the slab up for our new concrete guy we do use the chairs at his request

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[driz]

City sidewalks don't use any rebar or remesh and I think they do that so they can tear up a section without having to cut it.

Strange though. Cutting concrete with the demo saw is about like cutting wood so I can’t see why they would worry about that. I’m thinking more along the lines of cheap[emoji214] Being a motive


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[Walter_TA]

Rebar holds the concrete together after it breaks. The fiber holds the concrete together while it cures. Most concrete cracks are shrinkage cracks. They happen when concrete has to much water when it is poured and does not cure properly(it need to to wet to cure). Use Fiber and super P, then pour at a slump of 4. Make sure there is a vapor barrier under the concrete and make sure the top stays wet for five days. If the forms are stay in place they will also keep moisture in. If concrete stays wet for five days it will gain 30% in strength. There are cases where you need rebar, a slab is not one. If done right.

 

[Milton Shaw]

I had a neighbor that poured his basement floor. About two wheelbarrow loads from finishing he saw the roll of mesh he forgot to put down. Too late of course. He did have some cracks but nothing major as the basement dirt had not been disturbed for 20 year before he decided to pour.

 

[Musicinabottle]

Actually, I set up a pour once, for an on grade slab for a house, and hired a concrete finisher that I had worked with for years, likely now deceased. I remember compacting the sand top layer, then putting down plastic. then my rebar. He was quick to point out that the plastic trapped the moisture and that the plastic should have been down below the sand. In later years, every single concrete slab for a house I ever worked on had the plastic below the sand, and no plastic if it wasn't living space. I remember doing a series of concrete pours for the Army Corps of Engineers and they spec'ed for a 3 inch slump pour. We tail gated all the pours and right off, on the first project, we bumped it up to the typical 5 inch slump or possibly even more so that we could muck the concrete without dying!

Rebar holds the concrete together after it breaks. The fiber holds the concrete together while it cures. Most concrete cracks are shrinkage cracks. They happen when concrete has to much water when it is poured and does not cure properly(it need to to wet to cure). Use Fiber and super P, then pour at a slump of 4. Make sure there is a vapor barrier under the concrete and make sure the top stays wet for five days. If the forms are stay in place they will also keep moisture in. If concrete stays wet for five days it will gain 30% in strength. There are cases where you need rebar, a slab is not one. If done right.

 

[34kw]

I have a 40' x 80' shop floor that I poured over 20 years ago with fiber only. No cracks at all and I've had excavators and cats and lots of loaded semi's on it. It's 7 inches deep in the middle and slopes up to 4" about 2 feet from the wall. At he time, the cost was about the same as rebar, but lots easier.

 

[LXCam]

I have a 40' x 80' shop floor that I poured over 20 years ago with fiber only. No cracks at all and I've had excavators and cats and lots of loaded semi's on it. It's 7 inches deep in the middle and slopes up to 4" about 2 feet from the wall. At he time, the cost was about the same as rebar, but lots easier.

Amazing huh. I've got over 12ksqft of driveway and walk paths without so much as a single stick of rebar in it. I poured all this in 03 and other then a couple cracks created by bad judgement on my saw cutters part all looks nice and healthy. Originally I planned on using bar but rebar doubled in price right before I was ready to start so I switched to a simple 7 sack mix and stayed with my original thickness choice of 6". Been lots of heavy **** all over this thing without issue including loaded concrete trucks.

 

[Moose97]

rebar/ wire mesh is used all the time still. Get another contractor

^^^^^this!!!^^^^^

 

[Moose97]

City sidewalks don't use any rebar or remesh and I think they do that so they can tear up a section without having to cut it.

They do in Texas. #3 @ 18" OCEW

 

[JUNK-MAN]

A pad that big? Yes rebar and yes mesh. The only time I've ever not used rebar is side walks.. one thing to remember also, an old guy old me once on a concrete job, that there are only two sure things in concrete, its gonna be a pain in the *** to pour and its gonna crack.

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[Musicinabottle]

They do in Texas. #3 @ 18" OCEW

Texas is kind of a different planet.

 

[Moose97]

Texas is kind of a different planet.

 

[6768rogues]

Fiber mesh helps to keep it together when it cracks, and it helps keep those cracks tight. It does not add structural strength. Rebar adds structural strength. Concrete is strong in compression and weak in tension. Steel is strong in tension and weak in compression. Putting steel bars on the tension side of the slab will make a stronger slab. For a tent venue, you probably do not need additional strength, so rebar might be overkill.
Sidewalks don't have rebar because they don't need additional structural strength. Steel bars are used when the load being placed on the concrete requires additional strength on the tension side.

 

[Lelandwelds]

Life is too short to teach a contractor how not to do a shoddy job. Find another contractor.


Make certain the steel is in the center or bottom third of the concrete. The oversized macro fiber with the waves in it is far stronger than cat whiskers. Having a compacted in layers rock base is very important. Mesh is ok. I have used it on top of rebar that's tied in a larger than normal spacing.

 

[ConCretin]

It's a common misconception that rebar increases the load bearing capacity of a slab on grade. The reality is that a 4 or 5" slab isn't deep enough to take advantage of rebar's tensile strength and make the slab act like a beam and span between supports.

Firstly, by the time you allow an 1 1/2" of cover under the mat, it's essentially in the middle of the slab where there isn't any tension to resist. Secondly, even if this theory is correct, what happens around the perimeter where the slab cantilevers and the top is in tension.

The reality is that a slab on grade is not structural and simply bends and transfers the loads placed on it to the soils below. If those soils give, your slab is going to crack. You need to get into much thicker sections before you get a true structural slab.

For a slab on grade placed on a solid base constrained by perimeter walls, there is no absolute need for rebar. I have placed many hundreds of thousands of square feet of such slabs on engineered commercial and industrial projects over the last 30 years. Now a free floating mono slab is another matter. Rebar would be helpful here, not to prevent cracks but to hold everything together if the slab experiences some movement.

Rebar's only function in a slab on grade is to keep cracks from opening up. In fact rebar actually increases the likelihood of shrinkage cracks by restraining the slab from shrinking inward as it drys. Think of rebar as crack control not crack prevention.

Finally, to say that the absence of rebar somehow implies a contractor is inept is a ridiculous statement. There a many reasons including the owners specifications and budget that could determine whether rebar is installed.

I realize this flies in the face of conventional wisdom and our dearly held belief in overkill but we might as well pass on accurate information to those who come looking.

 

[850xpeps]

Put the rebar in. If nothing else it helps with the errors and mistakes made as builders during the process. May it be unevenly compacted bass or whatever. It helps at a small cost in the end. You are laying down 5000 sq ft and $2000 is an issue?

 

[Jason280]

Where are you located and what type soil?

Locally, very few slabs are poured with rebar (but these are all residential sized slabs). In fact, I can't remember the last time I saw a residential slab with rebar. We have poured around 2k square feet in three different slabs at my house, and none of it has rebar. Its all 3-4k psi with fiber, with screener base and expansion joints, and haven't had a single issue with any of the pours (the oldest is 8-9 years old, most recent was 2-3 years ago).

 

[Dirtydan69]

They poured my driveway extension 3 years ago. 12x35. No rebar, no mesh and no fiber, standard concrete. The only thing done was pinning it with rebar to the existing driveway, at my insistence. I park my Express 2500 work van with at least1500lbs of tools in it every day. No cracks and no issues whatsoever. I’m told they rarely, if ever, use mesh here let alone rebar, in driveways. House slabs/foundations they use post tension.

 

[Radix2]

I just tore out my driveway due to heaving from tree roots. It was at least 50 years old, about 4 in thick. No rebar, no fiber, no mesh.

Not a single crack, even with some sections raised 2" from the next.

Driven over by fully loaded concrete trucks, and all sort of equipment.

When prying it up with a backhoe for removal, the slabs had to dropped to break them.

Soil below is a sand dune.

It's all about the base. Before rebar, make sure you get good prep and compaction underneath. Many times, contractors pour on loose soil full of backfilled spots....

Since the trees are still there, I am putting in brick. Hopefully I don't regret not just leaving it crushed limestone.

 

[rustyjames]

I just tore out my driveway due to heaving from tree roots. It was at least 50 years old, about 4 in thick. No rebar, no fiber, no mesh.

Not a single crack, even with some sections raised 2" from the next.

Driven over by fully loaded concrete trucks, and all sort of equipment.

When prying it up with a backhoe for removal, the slabs had to dropped to break them.

Soil below is a sand dune.

It's all about the base. Before rebar, make sure you get good prep and compaction underneath. Many times, contractors pour on loose soil full of backfilled spots....

Since the trees are still there, I am putting in brick. Hopefully I don't regret not just leaving it crushed limestone.

You hit the nail on the head, I laugh to myself every time I read these threads about the requirement of rebar. Soil conditions, prep and proper installation are everything. I've never used rebar in any slab, welded wire, but never rebar. Never had any cracking either.

 

[wssix99]

It's a common misconception that rebar increases the load bearing capacity of a slab on grade. The reality is that a 4 or 5" slab isn't deep enough to take advantage of rebar's tensile strength and make the slab act like a beam and span between supports.

Firstly, by the time you allow an 1 1/2" of cover under the mat, it's essentially in the middle of the slab where there isn't any tension to resist. Secondly, even if this theory is correct, what happens around the perimeter where the slab cantilevers and the top is in tension.

The reality is that a slab on grade is not structural and simply bends and transfers the loads placed on it to the soils below. If those soils give, your slab is going to crack. You need to get into much thicker sections before you get a true structural slab.

For a slab on grade placed on a solid base constrained by perimeter walls, there is no absolute need for rebar. I have placed many hundreds of thousands of square feet of such slabs on engineered commercial and industrial projects over the last 30 years. Now a free floating mono slab is another matter. Rebar would be helpful here, not to prevent cracks but to hold everything together if the slab experiences some movement.

Rebar's only function in a slab on grade is to keep cracks from opening up. In fact rebar actually increases the likelihood of shrinkage cracks by restraining the slab from shrinking inward as it drys. Think of rebar as crack control not crack prevention.

Finally, to say that the absence of rebar somehow implies a contractor is inept is a ridiculous statement. There a many reasons including the owners specifications and budget that could determine whether rebar is installed.

I realize this flies in the face of conventional wisdom and our dearly held belief in overkill but we might as well pass on accurate information to those who come looking.

^ Lot's of wisdom and good direction here.

our concrete guy says the fiber mesh in the concrete is all you need and you don't need rebar or wore mesh in the slab. he says no one uses it any more

the concrete plant suggests still using rebar even with the fiber mesh.

Fiber mesh may not even be the right thing for you...

It sounds like you may have gotten some lazy or uninformed advice from your sources. The fact that your contractor placing the concrete and your concrete supplier may not have concrete slab design skills should not be a concern. (although, their insistence in an alternative without having these skills might be)

Please share with us your:
- geographical location
- slab specs (size, depth, base details, etc.)
- goals (are control/saw cut joints OK?, do you need a particular finish or smoothness?)
- use (what kind of equipment and loads will be placed on it? forklifts moving equipment under the tent? just people?)

and the folks here can give you some good design advice with rationale.

 

[Pluribus]

Watching this one with interest, as one of the local contractors here recommends slabs with fiber only. At first I was skeptical, but now I'm seeing some professional concrete people weighing in on lack of need for steel mesh or rebar in a lot of cases. To not hijack the OP's thread, I'll stick with general questions. Should there be any different materials/techniques be used in prep for a fiber-only slab? Would it be preferable to go slightly thicker than 4" for a garage/shop slab?