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Wire Mesh for Reinforcing a Slab on Grade

Alderwiser | Posted in GBA Pro Help on

I am soon to pour a 756 sq. ft. mono slab on grade with turned down footings in PNW 4C.

Sturdy subsoil but will be adding compacted crushed rock, Poly barrier, 4″ EPS, then a 4″ slab. However, the slab will not be the finish floor – 3/4″ T&G cdx with wood floor finish. Footings are to seismic code here with two #4 rebar at top and bottom of 12″ wide footing.

My main question is do I need to worry myself with welded wire mesh or even the fiber mesh additive if i won’t be seeing any cracks that form? ie. is it structurally sound enough to not mess with flooring above?

I have gleaned info from similar threads and plan to compact base well and wet concrete after pour to help prevent cracking.

Thanks!

Kevin

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Replies

  1. Expert Member
    Zephyr7 | | #1

    Wire mesh is always nice to have -- it helps to reduce cracking and generally reinforces the slab. I always spec wire mesh for any of my projects (mostly commercial stuff). I'd look at it as a relatively cheap upgrade.

    If you decide to go with wire mesh, make sure it's placed on chairs or similar to keep it elevated so that it will be in the approx middle of the finished slab. I've seen plenty of times where the mesh isn't supported properly, so it gets pushed to the bottom of the slab during the pour where it isn't really doing any good.

    Bill

  2. Andrew C | | #2

    RE order of layers - you probably just typed them out, but just to be clear the poly should go on top of the insulation and be directly in contact with the concrete.

    1. Alderwiser | | #5

      Andrew,
      Correct I mistyped, but thanks for the heads up!

  3. BloedelBuilders | | #3

    Reinforcement is always well worth it. It may cost a little more initially, but it is really easy to include before, and really painful and expensive to add later. Talk to a concrete professional or your ready-mix supplier - they can spec a level of fiber that will help with both shrinkage cracking as well as slab curl. Your situation is ideal for the fibers, as sometimes they will be visible on the finished surface, with no welded wire to trip on.

  4. Expert Member
    Malcolm Taylor | | #4

    Kevin,

    As long as you do a good job on the substrate I wouldn't worry about mesh or fibres, as cosmetic cracking has no consequence on your build - and won't make much difference for how your slab will perform in a seismic event. If you want to address that you will need to add rebar, and for it to be useful you should get it engineered.

  5. Alderwiser | | #6

    Thanks everyone for the responses! Funny, all three recommendations are pulling for the three different options I wanted to get clear on. All good information, I just need to figure out where I stand between cost, quality and time for the foundation.

    1. Expert Member
      Malcolm Taylor | | #7

      Kevin,

      The differing answers you have received are partly are due to some confusion around what issue the reinforcing is trying to address. I think there is a clear consensus some form of reinforcing is necessary.

      The design of load-bearing slabs are considered complex en0ugh that they move the foundation from the prescriptive part of our building code here in BC to part 4, which requires engineering. That's where I'd start.

  6. Daniel Allen | | #8

    Is your soil expansive/clay? In Los Angeles the standard is #4 @ 16" o.c. each way unless you can confirm soil is non-expansive.

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