Key Questions to Ask When Ordering Slab Mesh Factory

tomsteve
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Joined: Jan i am going to be building a 12' by 16' shed for my niece in may. thinking about the slab, which will be concrete. main concern? she has an 8' by 8' wood shed with wood floor that the #*& woodchucks have been digging under and the shed now has a nice lean to it. im wondering if i should put a ratwall around the perimeter to deter them buggers from digging under the slab and if so, how deep i should go. 

im also wondering if i should add some reinforcement in the slab.

concrete work isnt something ive done much of so could use some advise here. MstrCarpenter
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Joined: Feb In my experience it is not necessarily the depth, but how far out it goes. They start digging where grade meets the wall. If they can't go down, they move sideways. 

Yes to reinforcement, and air entrained concrete if subjected to freeze thaw conditions. Just tell the dispatcher at the plant what you're doing and they'll recommend the right mix. Fiberglass reinforced works but it's tougher for a DIY to get a good finish. I would do a 4-5" slab with thickened edges (Google "monolithic slab") with 6" x 6" mesh or 12" grid of #3 re-bar 1-1/2" - 2" from the bottom. If you use mesh, it's also good insurance to tie 2' lengths of re-bar to it spaced every foot where the control joints will be cut. Sign at N.E. Vocational School Cabinetmaking Shop , "Free knowledge given daily... Bring your own container" lift mechanic
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Location: Trout Creek, Montana Around my chicken coop I buried chicken wire about 12" deep to keep the varmints out. It has been 6 years now and nothing has dug under the coop. I had a small slab poured last year, 12' x 14'. The concrete finisher told me to have the plant to add stainless steel shards to the mix. He said he does not use wire mesh in the concrete with the SS pieces any more. I tried to break up a thin piece of the concrete with the SS in it. It was quite difficult to break with a sledge hammer. You can not see the pieces if SS once it is finished, I had a broomed finish and still could not see any SS pieces. Treat others as you want to be treated.

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srv
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(03-19-, 08:29 AM)tomsteve Wrote: ....
concrete work isnt something ive done much of so could use some advise here.

12x16 is not a huge project, but anything concrete deserves having a few friends over.  My uncle was a brick and concrete man.  When helping him as a kid he told me working concrete was a leisure activity; if you were working up a sweat you don't have enough people. EdL
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Location: Front seat on the Struggle Bus Wire mesh in the slab....freeze/thaw cycles will break a fibermesh pour in short order.

Flatwork guys like any reinforcment that can be mixed in....that way they don't have to mess with it.

Ed Snipe Hunter
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Location: Merryland I have a wood shed on a slab. The knucklehead who poured the slab and built the shed left the slab surface too close to grade. One end has actually settled below grade. Hoping to fix this next spring. The wood (pressure treated) is rotten and molded. The plan is to leave the slab. Jack up the shed about a foot (10x14) and lay 8" block around the slab perimeter. Cut 8" off the bottom of the shed and nail on a new sill plate and set the shed back down on the block. Generally, the rule of thumb is to have the sill plate, sheathing and siding at least 6 inches above grade. Neil Summers Home Inspections




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fixtureman
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(03-19-, 03:45 PM)EdL Wrote: Wire mesh in the slab....freeze/thaw cycles will break a fibermesh pour in short order.

Flatwork guys like any reinforcment that can be mixed in....that way they don't have to mess with it.

Ed

Our concrete company poured their drive using fiber mesh about 30 years ago and it still is holding up.  This is in northern Ohio Willyou
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Location: Mobile, Alabama For a slab that size I question if the steel mesh is necessary. If you are in an area where freeze/thaw is a problem, then maybe. However, there are a couple of things you need to know if you decide to add it to the slab. First, steel mesh is not for strength but for temperature/shrinkage crack control. Steel reinforcing for strength would be much more extensive and expensive and you don't need it. As such, the steel mesh needs to be as close to the center of the slab as possible. Probably the best way to do that is to use some bricks or something similar to block it up off of the ground before you do the pour. You can also do it by pouring the slab half way up, lay the mesh on top of what you poured, and then pour the rest. By doing it this way you risk having the two pours not properly bond and you end up with a weak slab. If you can, get the mesh in flat sheets. If it arrives in rolls, it is very difficult to get it to lie flat and you risk it popping up to the surface. If you hire someone to pour the slab, you need to have that understanding ahead of time and watch them very closely while they are doing it. Don't ask me how I know.
I would be inclined to ask a local engineer or reputable contractor if the steel is even needed. Snipe Hunter
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Location: Merryland If I were pouring the slab,I'd be more concerned about the underside than a mesh. A good tamped down pit in undisturbed soil with a rubble bed. Good sized, crushed aggregate. Not round stone. If you do a mesh, use large flat "remesh" sheets in the concrete isle. It's cheap and a lot easier to deal with than the rolled. But like said above... you really probably don't need mesh or rebar for a shed assuming it's on a good bed of rubble. If you do use mesh, you can use plastic Rebar Chairs to hold up your mesh. You don't really want to use anything metal exposed or touching the soil because metal will rust, swell and crack the concrete. Neil Summers Home Inspections




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tomsteve
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(03-20-, 08:39 PM)Snipe Hunter Wrote:  A good tamped down pit in undisturbed soil with a rubble bed. Good sized, crushed aggregate. Not round stone. If you do a mesh, use large flat "remesh" sheets in the concrete isle. It's cheap and a lot easier to deal with than the rolled. But like said above... you really probably don't need mesh or rebar for a shed assuming it's on a good bed of rubble. If you do use mesh, you can use plastic Rebar Chairs to hold up your mesh. You don't really want to use anything metal exposed or touching the soil because metal will rust, swell and crack the concrete.

i was out lookin at the spot the shed is going yesterday. since we have 1- woodchucks that dug under the shed, and 2- moles that have trenched everywhere, i have some leveling and packing to do.thinking of leveling out, packing the soil, then raise elevation with crushed limestone or ??

I know we've beaten this topic to death but I thought I might revisit it one more time. The questions that are still nagging are:

1.) Best placement of the mesh in the slab, centered, 2 in. from top, or stomped on by construction workers until it is in the bottom.
2.) Should the mesh size extend to the perimeter of the slab? Ground clearance from edge and from bottom? If its a 4" slab isn't the 3" rule for reinforcement violated?
3.) Most typical mesh size I've seen is 6x6-W2.9xW2.9 but I've also seen 6x6-W1.4xW1.4, any thoughts on what mesh size is best for a typical 4" and 6" slab (residential work).
4.) I've seen dobie blocks and wire chairs used to keep up slab bars, what should be used for mesh? Won't the workers step on the mesh and bend it out of shape or push it to the bottom?
5.) #3 Bar, Mesh, or Fiber? What do you use and why?

For reference the image below shows a typical or proposed SOG with mesh reinforcement.



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My opinion, presently:

medeek said: 1.) Best placement of the mesh in the slab, centered, 2 in. from top, or stomped on by construction workers until it is in the bottom.

If it's a residential, 4" slab I put the mesh at mid-depth. If you're going to dodge the saw-cuts and get a modicum of cover, putting it in the upper third as some recommend is pretty tough. As I see it, the placement comes down to two issues as far as cracking goes. Firstly, the reinforcement helps with axial strains and cracking across the slab. For this purpose, position isn't all that important and mid-depth makes sense. Secondly, the reinforcement helps with flexural strain and cracking at the top of the slab where local hard spots may result in hogging moments. I say to heck with latter. In a 4" slab with saw-cuts, I doubt you'll ever get the reinforcing high enough in the section to be effective flexural reinforcement.

medeek said: 2.) Should the mesh size extend to the perimeter of the slab? Ground clearance from edge and from bottom? If its a 4" slab isn't the 3" rule for reinforcement violated?

I'd extend it to the perimeter or at least the last saw-cut joint if there is one near the perimeter. Cover is routinely violated in thin slabs on grade, both on the ground side and below the saw-cut joints. That's what's done and, at least for common interior applications, reinforcement rusting doesn't seem to come to pass or cause any problems. Slab on grade is, technically, not structural concrete.

medeek said: 3.) Most typical mesh size I've seen is 6x6-W2.9xW2.9 but I've also seen 6x6-W1.4xW1.4, any thoughts on what mesh size is best for a typical 4" and 6" slab (residential work).

I've been using W1.4 for thing residential slabs. Frankly, I consider the reinforcing in these slabs to pretty much just be nominal rather than seriously purposeful. Where I'm doing non-calculated token detailing, I lean towards light.

medeek said: 4.) I've seen dobie blocks and wire chairs used to keep up slab bars, what should be used for mesh? Won't the workers step on the mesh and bend it out of shape or push it to the bottom?

This. And yeah, it's a perpetual QC problem that routinely causes engineers to doubt the use of WWF for anything important.

medeek said: 5.) #3 Bar, Mesh, or Fiber? What do you use and why?

I like bars, fibers, or nothing from a performance/QC perspective as long as jointing is done properly. In my area it's almost always wire mesh because that's what contractors continue to prefer and expect.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it. If you are looking to get flexural reinforcement ratios for a 4" S.O.G., then good luck - especially with wire mesh. All we ever use mesh for in the South is for typical T&S steel. If you truly need flexural capacity, then use bars. If you do though, move up to a 6"-thick slab: its more practical, more workable, and more forgiving of slight reinforcement depth displacement. Space the bars at 16" o.c., so workmen can walk without stepping on the bars. And never, ever, let the workmen "hook and lift" ANY reinforcing - ever. As KootK suggested, if you want to keep the 4" slab thickness, opt for fiber reinforcing instead - it more than pays for itself in saved labor, and headaches about big shrinkage cracks forming because the wire was lying on the ground at the bottom of the slab, and working to exacerbate the cracking. The old joke around here is to use a "standard #6 slab": 6"-thick, #6 wire mesh, with 6" x 6" spacing. ;-)
Dave

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