Mesh Or Rebar?

I agree with justanoldguy about one thing, there are a lot of misconceptions and myths when it comes to concrete.

There is not a significant difference between rebar and mesh when it comes to stopping or controlling cracks. Neither helps much in stopping them and both can control them after they form. The major advantage to rebar is that it is more rigid, which allows for fewer supports to keep it off the ground.

It's perfectly possible to place a typical residential slab without cracks. It depends on a few basic factors. The first is to minimize shrinkage with larger aggregate, minimal water and proper curing. The second is to ensure that slab is not restrained from shrinking by the subgrade, rebar or penetrations. One final point is to avoid reentrant corners.

Lastly, Neither rebar or mesh does much to improve the structural strength of a slab. Its the subgrade that actually supports the loads placed on a slab. A slab isn't deep enough for rebar to form a 'beam' and support weight. The slab just transfers the load to what's underneath.

If you are worried about cracking from loads placed on your slab - put in a strong stable base.

If you want a crack free floor - pay attention to your construction details, slump and curing.

If a random crack will ruin your day - cut some control joints immediately after you place.

(Might as well bring fiber into the discussion. About all it's good for is to buy you some time to cut your joints by resisting early age plastic shrinkage cracks while the concrete has very little tensile strength of its own)

If you want to ensure that you won't trip over your cracks/control joints - install some properly supported rebar or WWF.

Like any good structure, the foundation is the key to success.
In the case of a slab, the ground below it is the foundation.
Get that right and chances are greatly diminished to getting cracks.
But, as said earlier, it WILL crack. So cut your concrete asap.

I see a good base mentioned a few times. Can someone please expand on that and how to verify if a base is good.

Yes the 3 Cs. COMPACTION, COMPACTION and COMPACTION of good stable material.

^^^^^^^ What he said

A few points to mention, control cracks are not necessary if the foundation is done correctly and/or you have access to good quality base. If your area is shifty or soft then it might be worth your while.

My contractor told me, I cannot gaurantee you will have no cracks, but you won't have any cracks. I have no control cuts, nor cracks. He spent a lot of time on my base. He went down until he hit good solid material, then compacted granular A every six inches to get back up to where my slab would be. That meant nearly 3 feet of material to bring in. It cost a little more but it worked out great and yes, no cracks.

So how to verify, dig down to a solid base, no deeper, no less. No more than about 6" of good gravel at a time, lots of water, compact well. Repeat until you reach your correct height.

Just did this pour with fiber mesh,,,24x28 slab 11 yards,,very easy pour,,now,,,two weeks old,,,,

Justanoldguy said:

A very wrong and unresearched amateur answer.
Getting good useable advise on this board is like a lottery.

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My copies of "Design of Concrete Structures" and "Designing Floor Slabs on Grade" are well read and I've built a few reinforced concrete structures with several more planned. Maybe the way I presented it, as a humorous saying of the trade, was not the correct way to state it.

Maybe it is different in NZ, but in most of America, when talking about "mesh" in the context of a residential slab, we're not talking about 2ga deformed and welded mesh panels. The building supplies have never heard of such stuff and wouldn't know where to order it. What we're invariably talking about is rolls of 10ga hog fencing sold by the lumber yards and used by many residential concrete finishers as "concrete reinforcement". It certainly isn't "reinforcement" and it's up in the air as to whether it controls cracks - maybe they mean it will hold together a pulverized floor. "Sooee Screen" is the derogatory name for such stuff in my circle.

Putting such stuff in a concrete floor is an exercise in pounding salt. For one, the resulting steel fraction in the slab is so minimal it's benefit is a rounding error. Second, the wire is of such a small gage that it is quickly trampled to the bottom of the pour. Many concrete contractors say they "hook it" into the concrete during the pour, but research has shown that to be of negligible value. The mesh largely does not end up in the lower 1/3rd of the slab where it will do the most good - what little good it will do. Rebar, on the other hand, does not get trampled down.

10ga. Sooee Screen in a floor before pouring, taken from the internet:



For entertainment, here's a nomograph from Army Technical Manual 5-809-12 "Concrete Floor Slabs on Grade Subjected to Heavy Loads" August 1987. This nomograph allows comparison between unreinforced concrete slabs on grade to reinforced concrete slabs on grade by reinforcing steel fraction.

While it is correct and true that the vast majority of residential floor slabs do not require reinforcement of any kind so long as the subgrade is properly prepared, if you're going to put something in the slab put something in there that will do some good. Rebar will do that, barnyard fencing material won't.

Another reason to watch your base - you may "think" about it, but not really think about it. My 24x40 has 16 yards of 5 sack mix. Some Googling says that comes to about 61,000 lbs on the ground.

This is what we use in NZ

http://www.wireplus.co.nz/categories/119/665-mesh/

It comes in large 12'x 6'sheets

There seems to be some confusion in some of the replies regarding the causes and inevitability of cracks.

Structural cracks caused by loads placed on the slab can only be avoided by installing a well compacted granular base.

Shrinkage cracks occur early in curing process as the slab 'dries'. You can either design and construct a slab to minimize the possibility of cracking or just saw cut control joints to hide the crack.

These are two completely different issues with their own causes and effects. The use of reinforcing doesn't have much to do with either. It's only there to hold a crack or control joint together.

A_Pmech said:

My copies of "Design of Concrete Structures" and "Designing Floor Slabs on Grade" are well read and I've built a few reinforced concrete structures with several more planned. Maybe the way I presented it, as a humorous saying of the trade, was not the correct way to state it.

Maybe it is different in NZ, but in most of America, when talking about "mesh" in the context of a residential slab, we're not talking about 2ga deformed and welded mesh panels. The building supplies have never heard of such stuff and wouldn't know where to order it. What we're invariably talking about is rolls of 10ga hog fencing sold by the lumber yards and used by many residential concrete finishers as "concrete reinforcement". It certainly isn't "reinforcement" and it's up in the air as to whether it controls cracks - maybe they mean it will hold together a pulverized floor. "Sooee Screen" is the derogatory name for such stuff in my circle.

Putting such stuff in a concrete floor is an exercise in pounding salt. For one, the resulting steel fraction in the slab is so minimal it's benefit is a rounding error. Second, the wire is of such a small gage that it is quickly trampled to the bottom of the pour. Many concrete contractors say they "hook it" into the concrete during the pour, but research has shown that to be of negligible value. The mesh largely does not end up in the lower 1/3rd of the slab where it will do the most good - what little good it will do. Rebar, on the other hand, does not get trampled down.

10ga. Sooee Screen in a floor before pouring, taken from the internet:

For entertainment, here's a nomograph from Army Technical Manual 5-809-12 "Concrete Floor Slabs on Grade Subjected to Heavy Loads" August 1987. This nomograph allows comparison between unreinforced concrete slabs on grade to reinforced concrete slabs on grade by reinforcing steel fraction.

While it is correct and true that the vast majority of residential floor slabs do not require reinforcement of any kind so long as the subgrade is properly prepared, if you're going to put something in the slab put something in there that will do some good. Rebar will do that, barnyard fencing material won't.

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Most of the lumber yards and cement plants around here carry the 4 and 6 gauage welded mats, the "wire rolls" are junk. Like others have said the only benefit I see to it is for seperation if you do have a crack.

Actually after tearing down several old bridge abutments and piers down built in the 1930-40's it makes me wonder why we use so much reinforcement these days. I'd venture to say that in those old structures I may have seen 1 piece of steel per 50cy of concrete and I think that was just tossed in for the heck of it. Most were poured using what ever they had laying around for filler, creek rocks, bricks, wood (now petrified), railroad rails. Most of these 70-80 year old structures are fine today, everything thing that I have seen messed up is do to a base failure.

Something else for you guys, all of the concrete highways around here 12" thick and have NO reinforcement. 40' slabs x 12' wide with 18" x 1-1/4" dowls placed at the contraction joints. Just got finished replacing several hundred base failures on these (which is minimal considering thats on a 6 mile stretch of highway).

SwampCat said:

Yes the 3 Cs. COMPACTION, COMPACTION and COMPACTION of good stable material.

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And 3/8" rebar grid 2 foot on center. By the way, when you think it is compacted enough, it is not- keep going. Small loads compacted as you go. Your base should be as strong as the finished product. Also making sure that the substrate is good clean material will help in making sure that things do not settle. A lot of cracks are due to settling underneath and unstable soils are usually the culprit.

I have put down 2 slabs both almost 1000 sq ft

1986: done in 2 pours, no foam under. Ran a machine shop on it for 6 years, vibratory tumbler. Some undermining of base along back wall, you could here it was hollow. One fine crack that I would have to search for, but I recall it being near an interior post support.

2003: radiant slab 2 inches of foam under. It had an inside corner that developed a fine crack.

Both were done with mesh. Both used bar in a few places for point reinforcement.
[edit] both were allowed to sit open for months before the floor was poured. Rain is a great compactor.

If you use your shop like a normal human, bar is a waste of money. If you like to waste money, go for it.

If you like overkill, go ahead, just understand it is overkill

I agree that Bar is generally a waste of money and overkill when pouring your basic job. If your design is more dynamic, or not level, then I would have to think that bar may be a better choice for you.

Which mesh do you guys usually use in this scenario? I am going to be pouring a small foundation in the next few weeks, if it ever stops raining, and not sure what size and alloy mesh to use. Does stainless steel work? How bi of openings for the wire mesh?

Would you buy from a manufacturer like http://www.bwire.com/ or something more of a Home Depot or a Lowe's for this job? Any advice helps, thanks a lot guys.

tlmartin84 said:

Something else for you guys, all of the concrete highways around here 12" thick and have NO reinforcement. 40' slabs x 12' wide with 18" x 1-1/4" dowls placed at the contraction joints. Just got finished replacing several hundred base failures on these (which is minimal considering thats on a 6 mile stretch of highway).

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FWIW - The miles concrete road they are putting down on I-20 west is 12" with a ton of rebar in it. Miles of bar tied in a grid, on chairs, on a packed base covered with what looks like a pretty decent drivable road bed of asphalt. It's 180 miles to Fort Worth and every section I've seen poured over the last several years is built the same way.

So, I ended up going with both. I found that for my tubing lay out, I needed the mesh to tie off to and went ahead and put the rebar in for extra support since I had already paid for it. The bar is on 18" centers and the mesh is 6". Should be plenty stout for what I'm doing.

This is why Geotechs were born.

To tell you what type of soil you're on, and how to adequately prep for the intended building.

pics?????

cj7365 said:

pics?????

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http://www.garagejournal.com/forum/showthread.php?p=2809796#post2809796

Rebar and wire mesh does two different jobs, they are not design to counteract the others job. Rebar is for load factors. it doesnt do anything till a load is applied. as in weight of house. That why sidewalks, patios, general house slabs doesnt not have rebar. they no load applied. In general an everyday garage has no load, general.

Wire mesh and fibers are to control micro cracking till the concrete creates enough strength to do this itself. thiis can also be controlled with the cement water ratio. Usually after 7 days, the wire mesh and fiber has no purpose. 90% of cracking will be in the first 24 hours, most will occur while you still placing the concrete. This has to do with weather and the procedure. Cracking can be controlled also with control joints being cut as soon as you can walk on it. not the next day

OK back to rebar. rebar does nothing till the concrete generates enough strength, usually after seven days. when a load is applied to concrete, the concrete slab will bend or curl. this is where the cracking starts. by having rebar it counteract the cracking by acting like a large spring. Rebar will bend in the middle by the forces are pulling on the ends of the rebar, as the concrete bend the forces are on the ends.

If you have a garage with heavy equipment, large vehicle. yes have rebar.
Most cracking is cause by the concrete crew pouring too wet or a weak concrete mix.

Sub base compaction, this is another item that will cause cracking. all bldg foundation settle. but you have to control the settlement to a minimum and in a uniform settlement. If you whole bldg settled 1/4 inch, this is not a problem but if one corner settles four inches that the problem, you want uniform settlement. it might take years for a site to quit settling, it might not settle at all if the loads are light and compaction is good.

Also wrong base material will cause cracking by swelling, some clays will swell and pick up a garage or bldg, creating cracking.

Concrete thickness will also crete cracking, if the rebar, wire, heat tubing is too close to top surface.

There are many varable that will cause cracking, all concrete cracks is a pour excuse for sloppy workmanship. if I can convinct use all concrete cracks I can do a sloppy job and you will love it. all concrete doesnt crack

Cracking that happen due to wire mess or fiber is usually not structural and just ugly.

Cracking that happen depending on rebar placement is a foundation failure and could be damaging to structural and occupants.

Hopefully any cracking that does take place will be hidden by the epoxy floor cover.

I know this is an old thread but if you want the mesh ( perferably road mesh) 5’ x 10’ to stay in the middle of the pour like it should. You need a mucker ( a person whos only job is to muck the pour). This person stays right with the laborers, the driver will give you roughly 2 or 3, 5 gal piles of concrete. The mucker has a rod with a hook & pulls the mesh up though the piles of concrete, then you get started. Although people will be standing on the mesh the muckers job is to pull the mesh up right when it comes out of the chute. That’s how it’s done on commerical jobs. I’m not talking about little concrete outfits.

i did not read the entire thread but whats the word on the fiber mesh i was told
if i used long fiber it would be the same as rebar
a friend used it on his driveway 8" thick no cracks yet he has had a rig with an excavator on it a few times i am pouring this spring and am using rebar 6" thick floor
i may use fiber and rebar any ideas is it worth it

He78ather said:

take place will be hidden by the epoxy floor cover.

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And this means what in english?

curly8888 said:

i did not read the entire thread but whats the word on the fiber mesh i was told
if i used long fiber it would be the same as rebar...

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And many of us know experts who will tell you fiber mesh is worthless. When I did my slab (rebar) the contractor would not even consider fiber mesh (no, I didn't suggest it, he almost started out his description of what he wanted to do with "no fiber mesh".

fiber mesh is not worthless, as a concrete quality tech, i can assure you fibers are one of the best product to come along in years, but fiber does nor replace rebar. rebar is for load factors. fiber replace the wire mesh, and since most wire mesh is sitting on the bottom, fiber does an oustanding job in the replacement. also the labor factor of rolling and cutting the wire mesh is elimnated, so fiber is also cheaper than a wire mesh job.

I did rebar and fiber mesh on 24" spacings and in 6" concrete floating slab(12" thick outer 1 ft. edge) back in 2008. Sawed control cuts every 6-8'. Infloor heat turned on 2011, and NOT A SINGLE crack anywhere. located in central WIS. My Brother operates a small construction company and did all the foundation work. He said the foundation under the concrete will make or break your concrete. Make sure to remove ALL topsoil, I had 3-4ft to be removed and then hauled in 1 inch breaker run About 18"thick, then the top remainder road gravel,and I think topped off with screenings. Then compact compact, compact, he owns one you sit on.(Had to be careful not to crack drywall in house from vibration) Best situation is to let foundation sit through rain, frost and time to settle naturally. Ideally 1 yr but most people dont have the luxery of all that time. PS went with a pretty high cement bag mix,but dont recall how many bags I went with , but said it was on the high side for a car garage. Now Back to your Question, Rebar or (fiber) mesh :YES

We should all understand that there is a huge difference between wire mesh and fiber mesh. Fiber mesh (actually pieces of fiber) is added at concrete plant,part of the total mix of concrete (cement, water stone,calcium, etc...before it is put in concrete truck.Wire mesh is layed down @ job site before concrete is poured. This wire mesh needs to be pulled up into the middle during the pour to be effective,because the mesh laying on the bottom is absolutely worthless!!!

fyi, i have notice in the past couple years that architect are making the wire mesh be tied to concrete chairs, they feel that the pulling of the wire mesh is creating air voids. I dont know how serious that is, just the story they tell me.

ketas47 said:

We should all understand that there is a huge difference between wire mesh and fiber mesh. Fiber mesh (actually pieces of fiber) is added at concrete plant,part of the total mix of concrete (cement, water stone,calcium, etc...before it is put in concrete truck.Wire mesh is layed down @ job site before concrete is poured. This wire mesh needs to be pulled up into the middle during the pour to be effective,because the mesh laying on the bottom is absolutely worthless!!!

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I didn't realize that none of us didn't know this?

They've been tieing mesh to chairs for longer then I've been an Ironworker (33yrs) and there's still is a mucker on every job.

HAY YOU said:

They've been tieing mesh to chairs for longer then I've been an Ironworker (33yrs) and there's still is a mucker on every job.

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True. That was one of my jobs as an apprentice carpenter way back in the '60's.

Hello,
I am also confused regarding Mesh or Reber,
However, I am thinking to buy rebar chairs

I built my first garage back in the late 1970's and used wire mesh. It was probably built all wrong, just a slab with no footings, no stress cuts and on questionable base (pit run gravel, just packed down with a tractor.) That being said, other than the inevitable shrinkage cracks (only a couple small ones) it is still standing and as solid as it ever was.
My new garage was built with proper foundation, well packed base, foam, pex for heating and wire mesh on top of the pex. It was cut for stress relief. It was only installed last year, but has no cracks and, I'm sure, will be there longer than I will.
IMHO, if your base is solid wire mesh is certainly adequate for most use. Perhaps, if you are parking loaded semi's on it, then rebar might be a better option.

Jasmine11 said:

Hello,
I am also confused regarding Mesh or Reber,
However, I am thinking to buy rebar chairs

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I poured my garage floor about 25 years ago and it has held up very well. It was on 6-8 feet of well compacted fill (weird grading on the lot). The engineer at the time explained it to me this way. the Rebar and Mesh - or welded wire fabric WWF - serve different purposes and are placed within the slab differently. The Rebar should be suspended in the LOWER third of the pour (held up with small pieces of concrete or brick during the pour). This adds strength to the slab and prevents large structural cracks and separation but doesn't do much to prevent small surface cracks.

The WWF, on the other hand, prevents surface cracking when suspended in the UPPER third of the pour. It takes some effort during the pour to maintain the position of the steel.

As I recall, we used 1/2' Rebar in a 2' grid pattern and 6" X 6" 10 gauge WWF. then poured 3500lb concrete 6" thick - it might have been overkill but not a single crack in 25 years.

Once it was set I made expansion cuts separating each bay of the 3 car garage.

lineman88 said:

The WWF, on the other hand, prevents surface cracking when suspended in the UPPER third of the pour.

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He sure put you crook with his thinking there.
It will not prevent surface cracking.
That is a myth.

It may reduce the likelihood a bit though.

Here's my 2 cents: prepare the base of the slab by removing all organic matter and placing stone. Compact the stone. Your concrete contractor and your building inspector can advise how thick and what kind of stone you use in your region.

As for rebar or mesh, I would go with rebar for a garage. I have personally poured garage slabs with both. Mesh is more difficult to work with, especially if it comes in a role. Don't laugh. I've seen this on jobs and have had to deal with it. Rebar is easier to keep in the center of the pour and still allow for workers to move around easily on the jobsite.

Rebar is better but if your not driving farm equipment in and out of the garage you will be fine with mesh.

My friend has a mesh floor and all he does is drive his 70s hot rod and 95 chevy in the garage. No issues and was a lot cheaper then rebar (and easier)

With that said my other friend has a rebar floor and has had zero issues as well.

Im going for a mesh floor in my garage. $100 does my entire floor vs $500-$600 I believe for rebar.

Im on a budget and since the heaviest thing I will ever have in my barn is a explorer I think it will be fine.

Now i might throw some rebar in where I want my 2 post lift...that we will see.

ffjosh said:

Now i might throw some rebar in where I want my 2 post lift...that we will see.

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Just don't " throw" it in where the bolts may go..

If you don't have a good compacted base, you will get cracks. Fiber mesh in the concrete DOES NOT STOP CRACKS. If you have wire mesh as reinforcement, wire mesh DOES NOT STOP CRACKS, If you have rebar, rebar DOES NOT STOP CRACKS.

You mix of concrete, your curing of concrete, and above all, the compaction of the base materials will all help to stop cracking. A cut control joint may or may not crack, but if it does, it did it's job.

For the ones that are saying that the concrete guy talked them out of rebar. You have a lazy concrete guy, period. He doesn't want to have to mess around stepping over rebar and hooking it with his tools while pulling the 'crete around. He wants wire mesh, so he can tell you he pulls it up as he goes along, and while your back is turned he's walking on top of it. For the ones that said there is only 1 1/2" of 'crete on top of the rebar, I can almost guarantee you that you have 4" or so of 'crete on top of the wire.

Again, rebar, fiber mesh will not stop cracks. That is determined by your base prep. Fiber mesh will HELP, but not stop it. Rebar, will not stop it, but what does is that eliminates a trip hazard. How many times have you walked down a sidewalk, and then stubbed your toe on one of the joints?

How many times have you heard where they are tearing down an old building, or a viaduct, and the concrete is so tough they can't hardly get it broke up. That wasn't wire, that wasn't fiber mesh, and it wasn't the rebar. It was damn good concrete.

Todays concrete is not as strong, but what you want to do is take reasonable steps to avoid problems in the future. A very tight compacted base. Rent a tamper for a day, or even two. Pound that shit down so tight that it would almost take a jack hammer to loosen it back up. If you think you have it compacted enough, wet it down and go over it for another two hours. If you say to yourself, "that's good enough" take a break and fire the compactor up again just for good measure.

Rebar!!!! Spend the money. If you don't want to spend the money, spend half the money. Some people will pour directly over a compacted base using only fiber mesh in the concrete. That's fine if your base is in great shape for the pour. But you want rebar at least in the areas of a control joint. You want rebar from the floor to the apron. If you have any sidewalks out of the building, you want rebar.

When I poured my sidewalk from the house to my garage, I had rebar in it. Two places, one on each side of the center. The rebar was tied to the next rebar at every control joint. I had already specified where I wanted the joints put in. THe base material was down for a year before I poured the sidewalk. The sidewalk has been down for 14 years now, and at every control joint, there is not the first crack. I did forget to pin the sidewalk to the concrete at the overhang on my garage though. The concrete at that area will raise an inch in the winter, and back down flush in the warm weather due to frost heave when it gets cold. We put sidewalks completely around our house, and I specified two runs of rebar all through the sidewalks.

One reason I specified that, is that the older a person gets, they can't lift their legs up high enough and often trip. My parents were like that and had a hell of a time getting up one step. And they had a hell of a time walking out through a yard. Someday my wife and I will be that age, and we'll probably still live here. I don't want someone falling and breaking a hip. We can go almost anyplace except all the way out in the backyard, and never step in the grass. When we get older and sell the place, the next couple may have parents that have the same issues. It may also be someone in a wheelchair. They will be able to enjoy the house flower beds all the way around. And there will be no trip hazards.

Rebar is the cheapest insurance that you can have to avoid injuries.