Wire Mesh Gauge

[Tompet]

I've read and talked to a couple concrete people I know locally and the amount of opinions on concrete is more varied than most construction areas. Anyway, based on conversations for a 30' x46', 4"-4.5" thick slab I am thinking of using a combination of flat mesh panels and perimeter rebar for the thickened edge.

My question is if anyone has used one of the heavier gauge panels, 8 or 6, rather than the typical 10ga. mesh panels. The choice is 10ga. (1.4), 8ga. (2.1), and 6ga. (2.9).

It will be placed on chairs/supports.

 

[EddieWalker]

There is a rebar type panel that is sold at the hardware store that is probably half the thickness of #3 or 3/8's rebar that looks like rebar, but it's welded together into a panel. I've never used it since I prefer regular rebar. For a flat pad, your strength is more in making sure the rebar, or wire, is in the bottom third to middle of the concrete. The problem with wire and panels is the spacing is too small to walk around without pushing it to the bottom of the pad and making it worthless. Chairs are needed to keep it up because it's impossible to pull it up while walking on it and expect it to stay there. In every pour that I've seen where they say they are going to do this, they will for pictures at the beginning of the pour, but quit as soon as the real work begins. Then it's all walked on into the bottom of the pad.

Rebar hold the concrete together when it cracks. It doesn't actually make it all that much stronger, adding portland cement to the mix does that more then anything.

All concrete cracks. The reason it cracks is because of the water. You increase the volume of the concrete with water. The more water you add, the more volume you create. Then when the water evaporates away, you are left with a mass that is now smaller and the cracks are from that void. Almost all cracking you see in concrete is from too much water. Cracking from the soil not being compacted well enough takes years to happen, and most of the time, you just end up with a void or empty space under the concrete and never even know about it unless you cut into it. In really bad situations, it will break off and drop down to the lower soil. This is pretty rare. Too much water is your enemy.

The reason the finish guys add more and more water to the mix is because it's faster and easier for them to spread it. The challenge is in limiting them from doing this, and knowing that they will be trying to do this regardless of what you say.

On commercial and government jobs they do a slump test. Basically, you put some concrete in a small bucket and then dump it upside down like you would building a sand castle on the beach. If it holds it's shape, it's perfect. Guess how many houses pass this test? Almost none!!!

 

[Oldoak]

Commercial jobs and particularly government jobs are very specific as to what is called for. As a do it yourselfer, when we poured our concrete slab, yes we walked on the wire in front of the pour. As we moved with the pour, we hooked the wire grids with our rakes and pulled it up into the concrete as we moved along. Worked good enough for me and my 30' x 48' pole building, using 10 ga. wire mesh, 4,000# concrete, 5.5" thick. 40 years later, still holding up fine.
Accept for a few areas on the surface where us armatures flubbed the concrete finishing using all hand tools.

 

[sandman2234]

Hey Eddie,
Even on commercial jobs where a slump test is done, water is still added by the finishers, which isn't good for the concrete, but beats the heck out of turning the guy pouring it loose with a fire hose!
When I poured a slab at my house years ago (a commercial shop), I filled up two five gallon water buckets and put the garden hose in the garage, and took the handles off of my outside spigots. During the pour, I went into the house for five minutes and when I came back out, I saw one of the workers coming back from next door with two five gallon buckets full of water. I politely told him to put them down and get off of my property. The job foreman came over to me, saying they needed the help, and I couldn't fire him. I told him if he needed help, he better get on the phone because I wasn't going to have a thief on my property, much less someone going behind my back doing stuff against my will. I told him that they guaranteed me 3500 psi concrete, and if he added another drop of water to that pour, I would have a sample cored and tested, and his company could fight the concrete company for his settlement when it showed up below strength. (The next door neighbor had no idea they were using his water, which made him a thief)
David from jax

 

[topbuilder]

Like so many construction methods, they vary by region. For our region, wire mesh is not spec'ed in any kind of an engineered pour. The consensus being, all it does is displace concrete.
In pole barn pours I use rebar run through metal keyway expansion joints run between major support columns. I use solid bricks broke in half for chairs. They tend to stay in place better when walked on.

 

[Redlands Okie]

Concrete and the results you get have little to do with opinions. It's a science and that's why there are recipes for concrete for different types of work. Also why there are concrete engineers that have all this stuff figured out. Types of sand, gravel, cement, and chemicals added and their ratios. In some areas you can have fly ash (coal plant left over product) added to help slow down the curing of the concrete. Their are other chemicals that can be added. Talk to your plant. Concrete finishing is a bit of a art and experience is hard to beat.

Do some reading up on MANUFACTURES web sites. Also read up on concrete specs from code books, manufactures sites etc. The fiber mesh now available to add to the concrete mix at the mixing plant replaces the old style wire mesh in general. Rebar is used to add structural strength to the slab in general. Wire / mesh and rebar do separate jobs. They are not interchangeable for what they do. Some wire is better than nothing but its far from the ideal product.

In warm weather start the pour EARLY in the day, not at 10 am or noon. You should be done with the slab by then. Make sure the concrete plant your using keeps the gravel cool. All you have to do is drive by the plant and look for water sprinklers running on top of the gravel pile in many areas. Hot materials causes all kinds of complications and problems. That's why commercial jobs check the concrete temperature when it comes out of the truck.

Less water means more work but stronger concrete in the end. You have to decide what the balance of water versus workability you need for your project. Keep in mind for a small amount of money extra you can have smaller rock used in the mix, 3/4 inch max for example and it helps with the handling of the concrete.

Proper curing of the concrete in hot weather or freezing weather has its effects also. In warm weather keep the slab cool. After it hardens up and you have power trowled it (or could have) run sprinklers on it, or cover it with a product similar to gunny sack material thats kept damp or some such idea. A few dollars in water for a couple days is cheap compared to what you have invested in your slab.

Saw cuts are best done as soon as possible if your going to do them. As in same day or next morning. Not a few days later.

 

[RNeumann]

By the time you fiddle fart with wire mesh panels the cost savings is lost- plus it's an inferior product to good old rebar. I'd take #3 rebar 24" OC over mesh. But in my area it's hard to even find the mesh.

 

[Tompet]

There is a rebar type panel that is sold at the hardware store that is probably half the thickness of #3 or 3/8's rebar that looks like rebar, but it's welded together into a panel. I've never used it since I prefer regular rebar. For a flat pad, your strength is more in making sure the rebar, or wire, is in the bottom third to middle of the concrete.

Thanks, for picking up on the question. that is the mesh type I was referring. It is a #6 (2.9) and that is size that starts to look like mini rebar on 6" squares. And from there you can get some pretty heavy duty mesh panels. I did find a two part engineering firm video and (frost heave region) stating and illustrating why rebar should be place in Top Half of slab.

Redlands Oakie, yes it is science with a lot of variables but opinions even with seasoned installers come in play. Engineers have varying opinions, no difference.

Oldoak....good summary on typical slab and success without over thinking it.

Rneumann...Lol...you are probably right...though it seems recommendations is #3 should be placed 18" spacing.

Thanks all for responses...

 

[Stimw]

Here was the rebar/wire in my 40 X 60 building.

 

[AGRIMAN]

Proper compaction also plays an important part. Most of the issues we get called about are related to settling/ cracking concrete are due to poor compaction and they are more common than you might think.

When I built my new shop (50x50 red iron) we spent the extra time to ensure we got good compaction under the pad. I did the dirt work myself, but hired an experienced crew to pour and finish the floor.

They used control joints which dividend the floor into 6 sections. The floor is 6 inches with 24x24 footers under each door and at the post. There is no rebar or mesh wire in my floor, its only concrete reinforced with fiber.

After 7 years of heavy use ( driven on my tractors, combines, backhoes and semi trucks) there's no cracks it my floor anywhere.