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  1. #1
    Silver Member
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    Nov 2007
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    Mobile, Al
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    1974 MF135

    Default Post frame building slab.....

    I am building a post frame metal building.30'x40' with a 10' leanto off the back. This will make the slab part 40'x40'. I have only had one estimate and waiting to get more. But not sure what to look for or what i need. I live in South Alabama. The concrete guy said 4" thick slab with 6" footers, using fiber mesh and no rebar. I will use this as a work shop and to house my "toys" ie; lawn mower, tractor, 4 wheelers etc....

    Would you guys mind pointing me in the right direction?

    Thanks in advance.

  2. #2
    Gold Member
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    Jul 2011
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    SE Louisiana

    Default Re: Post frame building slab.....

    That is what I did on my barn (4", fiber, no wire, footers). I have not had any cracks from tractors, trucks, loaded trailers or anything else. The only crack that happenned was in the tack room with nothing heavier than me going in there. I guess it must have settled there or somehting.

  3. #3
    Platinum Member DutchHenryBrown's Avatar
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    Aug 2009
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    Tombstone, AT
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    Mahindra 5010

    Default Re: Post frame building slab.....

    I have had 2 30x40 pole barns built 1 w/fiber no footings 1 w/rebar no footings and a 20x20 garage w/wire and footings. They all cracked but using stress cuts or what ever they are called help to control that some what. The only thing with the fiber and not sure if it was not finished right but the fibers came to the surface in some spots? Seems like all concrete cracks some time or other in its life or I just was not lucky enough to get it done right? Oh and all were in the 4" range of thickness. Good luck.

  4. #4
    Veteran Member
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    May 2005
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    N. E. Florida

    Default Re: Post frame building slab.....

    I graded formed and had a 40' X 65' slab poured. I got the "With fiber you don't need rebar" sales pitch.
    WELL obviously they never go back and look at the slab 11 years later!
    I've got areas that have heaved up or dropped an inch and cracks! And these are areas that I scraped down to level, no fill what so ever!
    I think fiber is BS just so the concrete co can get $4. more a yard and the drop and finish crew doesn't have to work around rebar or wire! With rebar and or mesh there is no guessing if will it crack and lift later.

  5. #5
    Silver Member
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    Nov 2007
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    Mobile, Al
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    1974 MF135

    Default Re: Post frame building slab.....

    Talked with the concrete guy again. He does use wire mesh. So will thise be adequate? And the footers are 8 inches deep.

  6. #6
    Platinum Member ustmd's Avatar
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    May 2009
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    557
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    Manor, TX (outside of Austin)
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    Kioti CK25

    Default Re: Post frame building slab.....

    Where I live (Central TX), every reputable concrete guy will say you need wire mesh, rebar, grade beams and you can add the fiber if you want to avoid hireline cracks.

    Now, I also live on the Blackland Prarrie and the soild has a very high plasticity rating--it moves a loT. During the high summer, we have crack open up that you cannot see the bottom of.

  7. #7
    Platinum Member familyman's Avatar
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    May 2004
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    Perkiomenville, Pa
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    Kubota L2800DT

    Default Re: Post frame building slab.....

    The ground beneath the slab must be adequately compacted. If it's undisturbed soil, running a heavy piece of machinery back and forth over the area should do it. Just don't tear it up.

    3" of clean, washed 3/4" gravel should be next, followed by a layer of 6 mil. poly sheeting.

    Mesh is good, don't omit it no matter what concrete you use. Be sure the mesh is supported on wire or brick "chairs", to keep it suspended in the concrete. It does no good down at the bottom.

    Wet concrete is weak concrete. Be sure that the compressive strength is what you want (3,500lb?) and that they don't add water to make it easier to spread. You would need special tools to check the slump; the concrete should appear fairly stiff and not at all soupy. Plenty of aggregate (gravel) is good.

    Be sure that they provide relief cuts every 10 feet. This will help reduce cracking.

    Several hours after the pour, cover the slab with 6 mil. poly. Staring the following day, each morning lift the plastic and sprinkle lightly with water. Keep covered for 3 days.

    Use a good sealer, and you're done.

    Best of luck!
    Kubota L3800HST, LA 463 FEL, Woods BH80-X backhoe, Befco 6' BB, Woods RM59, Woods LR72
    I work, therefore I am.

  8. #8
    Member
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    Jun 2004
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    45
    Location
    N.W. Alabama
    Tractor
    Kubota L2800

    Default Re: Post frame building slab.....

    I live North of you in Alabama, I had a 30x50 slab poured in a pole barn. The fella that poured mine didn't recommend fiber his response was,"we all thought it was a great idea, but since I've been using it I've decided that it doesn't replace the wire or rebar". My floor has mesh and rebar. I think the rebar was only on 24" center. In the doorway where I pull my tractor and other equipment in, the slab is a full 6" thick 10ft wide and about 24ft long, was very easy to reinforce that area prior to the pour. During the pour, Steve(contracted with crew to pour and finish) said that "it's probably the strongest floor in the county". My advise is to make sure it's a little overbuilt because it would be a sad sick day to have it done and then a crack across the floor. I have crack control joints sawcut and thus far after about 5 years no visible cracks.

  9. #9
    New Member
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    Feb 2014
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    Location
    Eleva, WI
    Tractor
    IHC

    Default Re: Post frame building slab.....

    I plan to build a 36x48 shop (studded walls) on a floating slab with heated floor here in Wisconsin. That's not a problem. Now, we decided we would like a 12ft open canopy/lean-to on one side. If the canopy is pole type construction(poles down four ft. below frost level) and the slab is always heated, will this work? What if the slab is not heated for a season? Will the slab shift and pole part not? Is there a better way to add the canopy?

  10. #10
    Veteran Member
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    Feb 2007
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    easten Colorado
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    JD 4020

    Default Re: Post frame building slab.....

    most ever awning on a pole barn or steel building, is done much the same way,

    one could always pour a concrete column in the earth, and bolt a pipe/tube on it to support the awning

    If your planning on heating the floor one should put a thermo break (insulation board) between the floor and the out side any way,

    and many around here use a trencher to make a "stem wall" when pouring a slab like that, kinda of a cross between a stem wall footer system and a floating slab,

    in our country very little water will come up from under the building, thus there is nothing to freeze in the soil to make it expand, if you go under a building it is very dry and dusty, and or if you up a slab if there is a edge at all, it is dry,
    some also depends on your soils, if there expansive, and if they are it could be good to dig down and remove and bring in some type of fill that is not expansive,


    the fiber mesh does not replace wire or rebar, but IMO makes a better floor, and when welding or cutting less popping of the slab occurs,
    you still need to run your rebar, (never was big believer in the wire) besides making it much harder take up a slab if it needs replaced, out side I think wire if placed correctly is good, but one gets it placed properly so seldom, most of the time it is on the bottom of the slab 1/2 in the grade and just on he bottom of the concrete most of the time.

    If your jack hammering concrete out, the fiber offers very little restance to the process of breaking up the slab,



    I would pour 6" in the drive way areas at least, on the edges where the benches and storage is 4 is fine,

    I would ring the slab with rebar,1/2" at lest one if not two, and lap the ends, if some thing does crack it will not move away, as easily.

    concrete by it nature will basically crack about ever 10-12 foot so cut joints or grove it to have straight cracks. try to not have cold joints where there is a large time lag between trucks and the concrete starts to set before the other truck gets there, if a know time is a have to one could be wise to set a tempory form board and make it nice and straight and when the other truck gets there pull it and continue at least the break will be straight if it does break at the meeting of the two loads

    if possible try not to have sharp in side corners like around a pillar or footer, if you have to have a control joint in line with the footer/pillar.




    my two cents

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