REBAR VS. WIRE MESH FOR CONCRETE DECK

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FISHOUTOFWATER

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Jun 18, 2011
32
Northern Middle Tennessee
We are gettting ready to pour our concrete deck around our pool . We understand concrete cracks but we want to minimize this as much as possible.

Is there one method that is preferred over another when considering rebar laid and tied together every 18 inches around the circumference of the pool or would wire mesh elevated to the middle of the pour around the circumference be better? In either situation it is going to be 4000psi w/fiber mesh in the mix.

Has anyone had experience with either method?
 
Fiber mesh isn't worth the extra $. Don't waste your time with wire mesh either. If you want the concrete to hold together, use rebar. What are the dimensions of the deck you are pouring? 18" centers is propbably overkill.
 
I think that you could use rebar or wire mesh, but rebar would be stronger. There are several other things that will make a difference in the longevity of the concrete.

1) The preparation of the ground, making sure that everything is compacted properly.
2) The thickness of the concrete.
3) The proper placement of expansion/control joints.
 
Of course, proper compaction of the substrate is the SINGLE most important factor to reduce cracking.....by far.

What does your concrete contractor say? Does he make sense? I'd take his advice unless you feel uncomfortable with him.

Here in NC, Fiber mesh is considered a valid, important additive for strength. most of the contractors I have worked with do not prefer rebar over mesh.....they say it's a toss-up.

Control joints placed properly, are probably more important than the type of reinforcement but neither count NEARLY as much as proper compaction of the substrate.
 
I can't remember, but I think there are 3 rules of concrete:

#1 - It Cracks
#2 - It's very hard to steal
#3 - ?

The only metal in my decking is the bonding grid. The cracks in my decking go right through the area of the bonding grid, just like the rest of the decking.

The only other metal in my concrete us inside the RV pad. The pad is 6" thick with rebar in the middle.

Someone (maybe my PB) talked to an engineer a while back and was convinced that the rebar or mesh will not prevent any cracks. It will just hold it together a little better WHEN it cracks. He also mentioned something about a minumum of 3" between the metal and end of the concrete to prevent Rust / Deterioration of the metal (Rebar or Wire). If that is the case, you need a minumum of 6" thickness for the concrete (3" above the metal and 3" below).
 

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As far as the compaction issue I should have added the concrete is going on top of #57 rock base , if this makes a difference.......
Click to expand...
Absolutely.....That's about the best substrate available. How deep will it be? What's under that?

It seems you know a bit about this stuff to begin with......how do you feel about your contractor?
 
The proper placement of control joints depends on the specifics of the job. In any case, I would recommend that they not be placed more than 12 feet apart.

One issue that sometimes gets overlooked is the design aesthetics of the joints. You should consider how the joints will affect the overall look of the concrete.

Another issue I would recommend you consider is the width of the concrete. My preference is at least 5 feet wide around the pool. That might not work for you, but it's something to consider.
 
4" think concrete isn't thick enough for #4 rebar, you should have at least 2" clear on all faces of the concrete, 5" thick min concrete, 6" is MUCH better. Rebar needs to be at least 3" from the end of the concrete.

All the structural engineers I work with say the mesh isn't worth it. It doesn't help like people think it does, but do what you feel is right. Do make sure the compaction is done right, subgrade needs to be prepared properly and the gravel is also compacted.

Most 3 ksi concrete will cure close to 3.3-3.5 ksi as long as you don't add too much water when pouring it. Getting 4 ksi concrete might be overkill, but I know a guy that poured a slab for a garage at 8" thick, #4 rebar 12" OC EW and 4 ksi concrete <g>
Control joints, 10' - 12' apart max. As nightmare said, the rebar won't prevent it from cracking, but it helps hold it together when it cracks. The control joints are there so if it does crack, it will crack at the joint.
 
The third guarantee of concrete is that it gets hard.

In regards to the 57s substrate, unless the 57s go all the way down to virgin soil, they will do little to prevent cracking or settlement. 57s on top of uncompacted backfill material still leaves you with uncompacted backfill material that will settle and leave voids under the concrete. The concrete then has three options--
1) bridge over the settled soil area (somewhat likely with 4' wide slabs if the outside edge sits on virgin soil, but more likely than with 3' wide slabs),
2) crack and settle, or
3) settle without cracking.

Reinforcement, such as welded wire mesh or rebar can help promote options 1 and 3, and discourage number 2. If the concrete does crack (which is most likely will, to some degree), rebar or mesh can help to keep the pieces on either side of the crack from sliding apart of settling differentially (one side settles more than the other, creating a trip hazard). Proper control joints can help discourage randomized cracking (they are called control joints in that they control where the concrete cracks).

In regards the strength of the concrete, unless you're planning on driving vehicles on your pool deck, the crushing strength of it is unlikely to come into play. The tensile strength is what drives its ability to avoid cracking due to inadequate support from below. Embedded fiber can help when there are tiny, localized voids under the concrete, but the settlement of backfill material will cause larger voids than fiber is designed to assist the concrete in bridging.

Uniform thickness is absolutely crucial. If you think of a graham cracker, it cracks easiest at the thin lines in it. Those lines are similar to the control joints that are either cast into, cut into or tooled into the concrete. Areas where the underlying material is not uniform in elevation prior to placement cause thin spots in the concrete which act the same way as an expansion joint, in that they are a weak spot in the concrete. Therefore it is unbelievably important to ensure that the substrate material is uniform in elevation in relation to what will be the surface profile of the concrete slab. 57s do provide an advantage in this area in that they're easy to rake and smooth out to ensure a uniform thickness of the slab.

Concrete of all thicknesses cracks and deteriorates, from 18 inch thick bridge approaches down to three inch thick pool decks. Proper preparation of the material below, particularly compaction of backfill, is the most important preventative measure.
 
The wire mesh or rebar is also an important part of the equipotential bonding grid of the pool. Some builders only want to use the fiber and no metal, but that adversely affects the bonding grid.
 
People need to stop using wire mesh. When I had one of our structural engineers check the rebar equilivent of 6x6x10x10 WWF, it is what I got back.... A 10 gage wire has an area of 0.0082in^2, which is 13.5 times smaller than the area of a #3 bar (0.1104in^2). This means that the WWF is more equivalent to #3’s at 6.5’ to 7’. Very, very, very, very little steel.
 
Here's what I did in the spring, and it looks perfect, no cracks yet, see what the winter does. Wish I had a pic to share.
- 8" gravel base (3/4" stone process); compacted multiple times and days; uniform surface & thickness; also compacted the dirt first
- 12yds. of concrete, 3500lb mix, medium aggregate stone, 4" thick, on wire mesh
- cut control joints about one week later with a demo saw (no cold joints during the pour)
- two coats of sealer w/ gator grip; I'd recomend using more than the instructions BTW

I'd agree the prep and base are most important vs. the mesh/rebar. Lots of other factors involved for a good job overall (tempertaure, weather forecast, not over working the concrete, etc.)
 
Likes stated before the most important aspect with concrete on grade is going to be prep along with properly positioned reinforcing. It its on the bottom it will do nothing for you. Cutting CJ after the concrete is placed will help relieve stresses once the concrete starts to cure as well as provides relief when the concrete moves with temp differential .

During the curing process keep the concrete moist, best bet is burlene and soaker hoses for 7 days after placement.
 

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