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Do I need rebar for a small slab?

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  • Do I need rebar for a small slab?

    I am going to pour a couple of pads to place the steps for my deck onto. The slabs will be 5'w x 4'd x 4"to6" thick (6" at edges, 4" in centre). I was going to place 3/8" rebar in a foot square grid, but .... am I wasting the $40 of rebar for that size of a slab? All the slab will hold is a set of steps, the steps are wood, two steps high, approx 48" x 32" and weigh almost nothing.
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  • #2

    Re: Do I need rebar for a small slab?

    rebar isnt just fir strength but crack control.
    depends on soil capacity as well as loads.
    based on your post I'd be more inclined to do the following.
    12" base well draining granular fill
    8 inch compacted grade 'A' gravel compacted to 95 % Proctor
    and have your steps sit on that.
    if you want concrete just use a 6x6x10ga WWF instead of the rebar. might be cheaper.
    p

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    • #3

      Re: Do I need rebar for a small slab?

      $40 well spent, wire or rebar.And as Paolo said the base is the most important.
      • “The greatest lesson in life is to know that even fools are right sometimes.”Winston Churchill

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      • #4

        Re: Do I need rebar for a small slab?

        I would add some rods to keep it together if it cracks, but more importantly I would make a very rich cement. One extra bag of cement for a small pour like that will make a real nice slab. I have a vibrator so would definitely use that.
        Rob
        nnieman and Mike in Waubaushene like this.

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        • #5

          Re: Do I need rebar for a small slab?

          A 4 foot by 5 foot slab of concrete would roll down a hill upside down and backwards and never break unless there was a few tons on one end and more tonnage on the other end trying to pick it up. Save your re bar money for a meal after your done.

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          • #6

            Re: Do I need rebar for a small slab?

            Concrete has great compressive strength but has little flexural strength. Rebar's main purpose is to provide flexural strength to the concrete. As for shrinkage cracking 48" x 32" is in little danger of cracking of cracking .... it's simply too small. In any case rebar or mesh won't stop shrinkage cracking. It only keeps the cracks tight but it won't stop them from occuring ..... nothing will stop concrete from cracking all you can do is cut control joints so concrete cracks where you want it to. A 48" x 32" slab is too small to experience cracking .... unless you have a combination of really poor compaction and really wet concrete.

            When we built the Formet plant in St. Thomas the loading yard, which takes the load of heavy forklift traffic carrying truck frames as well as tractor trailers, was 8" thick unreinforced concrete. Control joints were cut in the slab but there was no steel and no wire mesh. The reason was properly placed concrete could easily carry the load and water seeping into the control joints causing corrosion to the wire mesh would only cause more cracking and damage than leaving it out. The requirement for steel mesh for crack control in concrete comes mainly from the USA ...... it works in places like Nevada and California but not in Canada where it's wet and we salt the roads.

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            • #7

              Re: Do I need rebar for a small slab?

              Thank you for all the replies. I should have responded sooner.

              After thinking about it for a bit, I pretty much came to the conclusion that rebar or wire will not stop the cracking. It only keeps the pieces together after the cracking has happened (as was well stated above). So, I poured a 48" x 60" x 6" thick pad without rebar or mesh and let it cure for 24 hours before removing the form. All went well.

              What did I learn ::

              1) I am not a concrete guru .... my concrete work is acceptably strong, square and level ... not pretty
              2) I need to schedule my pours so that the "curing" happens during the day, not at midnight .... so that I can do the trim troweling properly
              3) there is a balance between too thick (won't flow) and too thin (runs all over), and learning that balance takes more than three mixer loads ... but the next pad should go better

              (Ignore the steps please ... they're temporary)

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              Last edited by John Bartley; 09-11-2018, 07:12 AM.
              nnieman and beachburl like this.

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              • #8

                Re: Do I need rebar for a small slab?

                I’m assuming you mixed your own concrete?
                Egon
                from
                The South Shore, Nova Scotia

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                • #9

                  Re: Do I need rebar for a small slab?

                  Originally posted by Egon View Post
                  I’m assuming you mixed your own concrete?
                  I did. I have a bag mixer on the back of my tractor. The next slab is being poured today.

                  I am a much, much better small engine mechanic than I am a concrete guy. Fortunately the top looks pretty good and nobody will ever see beneath the landscaping ...

                  cheers

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                  • #10

                    Re: Do I need rebar for a small slab?

                    With your own mix you can add a little extra Portland and boost the strength. Also the amount of water can be regulated to get a nice stiff slump.

                    nnieman likes this.
                    Egon
                    from
                    The South Shore, Nova Scotia

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                    • #11

                      Re: Do I need rebar for a small slab?

                      Originally posted by Egon View Post
                      With your own mix you can add a little extra Portland and boost the strength. Also the amount of water can be regulated to get a nice stiff slump.
                      Ive found that can make a big difference to the final surface.

                      Nathan

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                      • #12

                        Re: Do I need rebar for a small slab?

                        Originally posted by nnieman View Post

                        Ive found that can make a big difference to the final surface.

                        Nathan
                        One can even sprinkle a little Portland on the top when finishing but doing that can be touchy.
                        Egon
                        from
                        The South Shore, Nova Scotia

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                        • #13

                          Re: Do I need rebar for a small slab?

                          So, I was using a 4:1 mix of gravel to Portland instead of the 5:1 recommended because that is what seems to work best with the granular A that is made in this area. I had forgotten until you mentioned changing the mix, but years ago I had done some pouring and I was advised to mix a shovel of Mortar Mix into each tub of concrete. It makes the edge troweling much easier. It turned out ok anyway without it.

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                          • #14

                            Re: Do I need rebar for a small slab?

                            When I suggested making it richer that meant more than one bag (cubic foot)cement to two sand and three crushed stone. Do I understand you are using pit run gravel that includes stone and sand?
                            Rob

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                            • #15

                              Re: Do I need rebar for a small slab?

                              Originally posted by iamtooler View Post
                              When I suggested making it richer that meant more than one bag (cubic foot)cement to two sand and three crushed stone. Do I understand you are using pit run gravel that includes stone and sand?
                              Rob
                              Yes, everyone here uses crushed stone (not pit run), instead of clear stone and sand for home jobs. So your suggestion is exactly what I did anyway ... slightly more Portland than recommended. Your mix is 5:1 and I used 4:1 (four sand/stone to 1 portland).

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