INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Goto Heyou to know more.

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!

• Talk With Other Members
• Be Notified Of Responses
  To Your Posts
• Keyword Search
• One-Click Access To Your
  Favorite Forums
• Automated Signatures
  On Your Posts
• Best Of All, It's Free!

Join Us!

*Eng-Tips's functionality depends on members receiving . By joining you are opting in to receive .

Posting Guidelines

Students Click Here

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Eng-Tips Posting Policies

Contact US

Rebar vs. Wire Mesh

thread507- Forum Search FAQs Links MVPs

• Forum

• Search

• FAQs

• Links

• MVPs

Rebar vs. Wire Mesh

Rebar vs. Wire Mesh

medeek

(Structural)

(OP)

13 Aug 15 17:32

Perhaps a better option would be #3 bars at 18" o/c or #4 bars at 24" o/c, at least workers can step around the bars.

For residential work (slab-on-grade foundations, garage slabs etc...) I usually call out a 4" or 6" thick slab reinforced with 6x6-W2.9xW2.9 WWM. However, after some recent reading I'm beginning to think that rebar slab reinf. may be better for a number of reasons. One of which is how do you actually get out on a mesh reinf. slab without stepping all over the mesh, bending it and pushing it to the bottom of the slab even it is supported by chairs or dobies?Perhaps a better option would be #3 bars at 18" o/c or #4 bars at 24" o/c, at least workers can step around the bars.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Rebar vs. Wire Mesh

cvg

(Civil/Environmental)

13 Aug 15 17:40

don't do any residential work, however I never allow mesh except for shotcrete. contractors belly ache, but the results are far superior. light weight mesh at the bottom of the slab is a total waste of time and money. always use #4 minimum. I don't see that you save much by going with #3's

RE: Rebar vs. Wire Mesh

DBuker

(Structural)

13 Aug 15 17:44

I almost always spec rebar in residential slab on grade applications. #3 @ 12"oc meets the minimum temperature reinforcing requirement of 0.002 * Area for grade 60 bar. I also leave a note for wire mesh specs in my general notes so that when the contractor calls and requests a substitute there's already a basic spec for the product in the plans.

I prefer rebar for all of the reasons that you mentioned. Wire mesh just doesn't produce as nice of a finished product most of the time. But really, there's so much more to a good concrete slab than the reinforcing. W/C ratio, concrete strength, curing conditions, etc, all have a big impact on the final product...

RE: Rebar vs. Wire Mesh

medeek

(Structural)

(OP)

13 Aug 15 17:59

Other than material cost and setup labor and time what are the advantage of mesh over the rebar?

Has anyone ever used wire mesh with rebar combined? For example #4 bars @ 48" with WWM to help support the mesh from being trampled?

There are a number of threads on this same topic but I kind of want to get some current thinking.Other than material cost and setup labor and time what are the advantage of mesh over the rebar?Has anyone ever used wire mesh with rebar combined? For example #4 bars @ 48" with WWM to help support the mesh from being trampled?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Rebar vs. Wire Mesh

RM87

(Structural)

13 Aug 15 18:10

I would go with #4 @ 16" O.C. each way. Specify GR60 bars, but keep in mind that your contractors may try to cut corners with GR40.

In my experience, if any corrosive elements are exposed to #3 rebar, they won't survive long. Make sure to specify the required base rock, the compaction of the area, and appropriate waterproofing measures, because if the slab starts cracking, things aren't going to be so fun.

RE: Rebar vs. Wire Mesh

manstrom

(Structural)

13 Aug 15 18:34

If I was building my dream home (and not paying for it), #3 bars @ 12" o.c. so that I know is will be in the right location and will actually do something. There is a good cost associated with this though.

If I had to pay for it, 6x6 W1.4 WWM all day. It is pretty standard and produces a reasonable slab. Keep in mind, these things can be poured without any steel at all. The mesh just restrains cracks.If I was building my dream home (and not paying for it), #3 bars @ 12" o.c. so that I know is will be in the right location and will actually do something. There is a good cost associated with this though.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Rebar vs. Wire Mesh

medeek

(Structural)

(OP)

13 Aug 15 18:44

Wow, everyone is all over the board with the spacing on the rebar. I just got off the with a local contractor after picking his brain a bit and he typically will use a #4 bar @ 48" o/c. He says he stays away from the mesh though, too much trouble and he can't get good quality, flat material anymore.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Rebar vs. Wire Mesh

IRstuff

(Aerospace)

13 Aug 15 18:47

I've not seen any construction recently that uses mesh. Our housing development is only about 3 yr old, and everything was rebar'd and post-tensioned.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: Rebar vs. Wire Mesh

Lomarandil

(Structural)

13 Aug 15 19:27

This is just a gut feel thing, but I'd have trouble convincing myself that anything at 48" would do a great job restraining cracks.

RE: Rebar vs. Wire Mesh

medeek

(Structural)

(OP)

13 Aug 15 19:34

.002 for GR40 or GR50
. for GR60

Also spacing should not be farther apart than five times slab thickness or 18 in. For a 6" slab the 18" requirement controls.

This section deals specifically with structural slabs. Are SOG applicable?

How does the WWM meet this requirement? For residential work it seems like we are constantly breaking all of the rules but no one seems to care.

For a 6" thick slab with GR60 bar per the ACI318 I get the following max. spacings:

#4 bar = 18.17 inches (18" controls)
#3 bar = 10.23 inches

For a 4" thick slab with GR60 bars I get the following max. spacings:

#4 bar = 27.26 inches (18" controls)
#3 bar = 15.33 inches

The min. reinf. requirements for shrinkage and temp. (ACI318-11, Section 7.12.2.1) specify the following ratios for slabs:.002 for GR40 or GR50. for GR60Also spacing should not be farther apart than five times slab thickness or 18 in. For a 6" slab the 18" requirement controls.This section deals specifically with structural slabs. Are SOG applicable?How does the WWM meet this requirement? For residential work it seems like we are constantly breaking all of the rules but no one seems to care.For a 6" thick slab with GR60 bar per the ACI318 I get the following max. spacings:#4 bar = 18.17 inches (18" controls)#3 bar = 10.23 inchesFor a 4" thick slab with GR60 bars I get the following max. spacings:#4 bar = 27.26 inches (18" controls)#3 bar = 15.33 inches

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Rebar vs. Wire Mesh

medeek

(Structural)

(OP)

13 Aug 15 19:50

I would strongly agree, might as well forego the reinforcement entirely. Funny thing is I just talked with another contractor in the area and his suggestion was to place the bar @ 48" o/c as well. He also avoids the wire mesh entirely and prefers fiber reinf. which he thinks takes the place of the wire. However, once the concrete cracks the fiber is useless and will not hold the crack together so that line of reasoning seems a bit flawed in my opinion.

@LomarandilI would strongly agree, might as well forego the reinforcement entirely. Funny thing is I just talked with another contractor in the area and his suggestion was to place the bar @ 48" o/c as well. He also avoids the wire mesh entirely and prefers fiber reinf. which he thinks takes the place of the wire. However, once the concrete cracks the fiber is useless and will not hold the crack together so that line of reasoning seems a bit flawed in my opinion.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Rebar vs. Wire Mesh

DBuker

(Structural)

13 Aug 15 20:19

I don't think a 4" slab on grade in a residential unit is really considered "structural" and therefore it probably doesn't actually have any reinforcing requirements. Since a slab on grade is continuously supported by soil, the plain concrete chapter in ACI 318 could be referenced but again, if it's not structural then why use the "structural plain concrete" code. A quick check of the IRC didn't turn up any requirements but I rarely look at the IRC, so maybe there are requirements that I'm not aware of.

I know that ACI 302.1 has a lot of information about slab on grade design for various different performance requirements but I don't have a copy of it...

As far as putting a bar at 48" oc, why bother?

To your original question, I think rebar is more likely to provides a better end product than mesh but it's undoubtedly more expensive so one must balance the cost with the desired end product.

RE: Rebar vs. Wire Mesh

KootK

(Structural)

The company is the world’s best Concrete Structures Welded Steel Mesh supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

13 Aug 15 20:21

Interior = 3.5" with no reinforcing. Really easy to walk through.
Garage = 4" with 10M@ (1/2 x 0.2%). That's easy to walk through and provides a bit more durability. Not sure if it's required.

SE's in my market are stodgy and going with an unreinforced slab on grade makes me look like a fool / ballsy maverick. Contractors eat it up. I use the un-conservative tack here in exchange for credibility that I spend elsewhere on issues that are more important to me. I usually have a chat with the client regarding expectations and the fact that they're not buying the main floor slab of the Guggenheim.

I don' believe that either the 0.2% or the 5X apply to slabs on grade. Slabs on grade are not generally reinforced as flexural members and the restraint condition for SOG is much different than it is for suspended slabs (it's worse actually).

Some related ACI info:

I've been going pretty liberal for my residential slabs on grade.Interior = 3.5" with no reinforcing. Really easy to walk through.Garage = 4" with 10M@ (1/2 x 0.2%). That's easy to walk through and provides a bit more durability. Not sure if it's required.SE's in my market are stodgy and going with an unreinforced slab on grade makes me look like a fool / ballsy maverick. Contractors eat it up. I use the un-conservative tack here in exchange for credibility that I spend elsewhere on issues that are more important to me. I usually have a chat with the client regarding expectations and the fact that they're not buying the main floor slab of the Guggenheim.I don' believe that either the 0.2% or the 5X apply to slabs on grade. Slabs on grade are not generally reinforced as flexural members and the restraint condition for SOG is much different than it is for suspended slabs (it's worse actually).Some related ACI info:

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.

RE: Rebar vs. Wire Mesh

medeek

(Structural)

(OP)

14 Aug 15 03:31

My only qualm with this line of thought is that when the concrete cracks it will have a tendency to separate and even worse the two edges may settle slightly differently creating an edge that juts up. My own garage has a large crack line running down the center with this exact problem. The mesh or bar would prevent this. Additionally if there are voids beneath the slab the added reinf. should help the concrete bridge these voids. In my opinion a good quality slab should have some reinforcement.

Realistically though I don't think a residential slab needs to comply with the .002 or . ratio, this is probably overkill unless the client has an open check book or has some serious load requirements.

My thinking is mesh is garbage and an outdated method, too hard to place properly and for that reason too easy to mess up. Mesh at the bottom of the slab may be slightly better than no mesh at all but how do you quantify this and why design a defective product from the start.

#3 rebar @ 24" o/c for a 4" residential slab and #4 rebar @ 24" o/c for a 5" or 6" residential slab would probably be my recommendation. Bars need to be placed on chairs or dobie blocks prior to the pour, none of this lifting things up or hooking I've read about. For 4" slab I would place the bar in the center of the slab. For 5" or 6" slab place the bar about 2" from the top. Fiber reinf. conc. with low moisture content, psi min., use a 6 mil vapor barrier on all interior slabs (living space,garages etc...) In a hot dry environment make sure the concrete stays wet as it cures (ie. burlap).

The consensus seems to be that SOG for residential work is non-structural and no requirement exists for reinforcement.My only qualm with this line of thought is that when the concrete cracks it will have a tendency to separate and even worse the two edges may settle slightly differently creating an edge that juts up. My own garage has a large crack line running down the center with this exact problem. The mesh or bar would prevent this. Additionally if there are voids beneath the slab the added reinf. should help the concrete bridge these voids. In my opinion a good quality slab should have some reinforcement.Realistically though I don't think a residential slab needs to comply with the .002 or . ratio, this is probably overkill unless the client has an open check book or has some serious load requirements.My thinking is mesh is garbage and an outdated method, too hard to place properly and for that reason too easy to mess up. Mesh at the bottom of the slab may be slightly better than no mesh at all but how do you quantify this and why design a defective product from the start.#3 rebar @ 24" o/c for a 4" residential slab and #4 rebar @ 24" o/c for a 5" or 6" residential slab would probably be my recommendation. Bars need to be placed on chairs or dobie blocks prior to the pour, none of this lifting things up or hooking I've read about. For 4" slab I would place the bar in the center of the slab. For 5" or 6" slab place the bar about 2" from the top. Fiber reinf. conc. with low moisture content, psi min., use a 6 mil vapor barrier on all interior slabs (living space,garages etc...) In a hot dry environment make sure the concrete stays wet as it cures (ie. burlap).

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Rebar vs. Wire Mesh

XR250

(Structural)

14 Aug 15 12:15

Many times I will specify, "Slab per code. Optionally add #4 @ 24" o.c. each way for greater crack control". Passing the buck to the client :>

RE: Rebar vs. Wire Mesh

JStructsteel

(Structural)

14 Aug 15 18:23

I have seen alot of 6" slabs installed with no reinforcing at all, with proper saw joints ,cracks are controlled.

If putting in mesh, have it about 2" from the top. Your right, trampled down at the bottom does no good. goto a 12x12 mesh that the workers can step between.

RE: Rebar vs. Wire Mesh

shaneelliss

(Structural)

14 Aug 15 18:46

The commentary on section 7.12.1 in the ACI specifically states that slabs on grade are not structural slabs and that the provisions for minimum steel don't apply to them. Many homes around here don't use any for slabs on grade. I like to specify #3 @ 18" to provide some crack control.

RE: Rebar vs. Wire Mesh

medeek

(Structural)

(OP)

26 Sep 15 11:30

A local contractor says he would like to replace the mesh and/or rebar with fiber reinf. concrete.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Rebar vs. Wire Mesh

MacGruber22

(Structural)

26 Sep 15 14:31

medeek - that is an acceptable way to control crack widths from shrinkage and mitigate cracks from temperature changes. Clients of huge warehouses often like to go this route, and it works fine when it is spec'd properly. But, they still need to provide contraction joints.

"It is imperative Cunth doesn't get his hands on those codes."

RE: Rebar vs. Wire Mesh

XR250

(Structural)

26 Sep 15 17:06

My concrete engineer says you have to spec the fiber at about three times what is normally added for it to do anything. I never count on it.

RE: Rebar vs. Wire Mesh

bridgebuster

(Civil)

26 Sep 15 17:34

NYCDOT standard sidewalk is 4" unreinforced concrete on 6" of gravel, broken stone, or sand. Driveways are 7" unreinforced concrete on 6" base. Bus stops are 12" concrete with WWF4x4-W4-W4 with 4" of cover. Dummy joints are 1/8" wide by 1/2" deep or 3/4" deep if saw cut.

I just figured I'd muddy up the water a little more.

RE: Rebar vs. Wire Mesh

MacGruber22

(Structural)

26 Sep 15 17:41

Quote (XR)

My concrete engineer says you have to spec the fiber at about three times what is normally added for it to do anything. I never count on it.

It sounds like you are talking about using fibers for primary reinforcement - no one that I am aware of does that.

It sounds like you are talking about using fibers for primary reinforcement - no one that I am aware of does that.

"It is imperative Cunth doesn't get his hands on those codes."

RE: Rebar vs. Wire Mesh

BUGGAR

(Structural)

26 Sep 15 21:45

Yoda speaks: "Proper and thorough curing. That is the Way."

RE: Rebar vs. Wire Mesh

RPMG

(Structural)

27 Sep 15 01:35

I realize that I'm opening myself up for insult. We use wire mesh as temperature reinforcement, and I have yet to receive any performance problems or contractor complaints. Also, wire mesh is used very commonly with metal decks (elevated floor slabs).

RE: Rebar vs. Wire Mesh

emmgjld

(Geotechnical)

27 Sep 15 02:22

In my world, Much depends on the subgrade conditions & preparations.
My father disliked wwf, at least since about . Installation was always a problem & performance in near vicinity to expansive clays was usually poor.
His 2 comments :
1) Very little benefit if not a very heavy wire & the wwf will double the cost of removal when failure occurs.
2) He NEVER observed a concrete worker with 6 inch feet.
My comments for residential use:
a) I specify either #3 @ 18"c/c or #4 @24"c/c for 4" to 5" slabs. The #3 is preferred as the @4 has been associated with reflective cracking on the slab surface.
b) If curling may be an issue, I keep the rebar at the upper 1/3 zone (hence part of the reflective cracking problem).
c) A light wwf may be used with the rebar matte to support in-floor heat tubing.

RE: Rebar vs. Wire Mesh

TehMightyEngineer

(Structural)

27 Sep 15 03:19

XR250, yeah I've done a lot of investigation into research on using macrofibers for strengthening concrete without rebar, it can be done but requires very large dose rates and probably isn't worth it.

Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com

RE: Rebar vs. Wire Mesh

medeek

(Structural)

(OP)

27 Sep 15 08:23

I've been doing a good bit of reading on the subject and a #4 bar in a 4" slab may be a potential problem because of the reflective cracking. A number of other comments by contractors and others lead me to believe that WWM may be the best solution for a typical 4" residential slab because of this particular problem. However, I really would like to get away from calling out the mesh since all of the local contractors seriously dislike the stuff and they probably aren't installing it correctly anyways.

Lately I've had a lot of clients who want large RV garages and many of these have 6" slabs which naturally lend themselves toward rebar reinforcment. For these going to a #4 bar @ 24" o/c is a no brainer.

What is the thinking on fiber (poly) reinforced concrete combined with mesh or bar?

@ emmgjldI've been doing a good bit of reading on the subject and a #4 bar in a 4" slab may be a potential problem because of the reflective cracking. A number of other comments by contractors and others lead me to believe that WWM may be the best solution for a typical 4" residential slab because of this particular problem. However, I really would like to get away from calling out the mesh since all of the local contractors seriously dislike the stuff and they probably aren't installing it correctly anyways.Lately I've had a lot of clients who want large RV garages and many of these have 6" slabs which naturally lend themselves toward rebar reinforcment. For these going to a #4 bar @ 24" o/c is a no brainer.What is the thinking on fiber (poly) reinforced concrete combined with mesh or bar?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Rebar vs. Wire Mesh

XR250

(Structural)

27 Sep 15 12:27

Quote (MacGruber)

t sounds like you are talking about using fibers for primary reinforcement - no one that I am aware of does that.

I was referring to it for temp. and shrinkage reinforcement. I used #4 @ 24" O.C. in my house in the basement and first floor and have seen no reflective cracking.
I do have some super small hairline cracks in the basement as they used a pump mix. The first story was done with wheelbarrows and has zero cracks anywhere.

I was referring to it for temp. and shrinkage reinforcement. I used #4 @ 24" O.C. in my house in the basement and first floor and have seen no reflective cracking.I do have some super small hairline cracks in the basement as they used a pump mix. The first story was done with wheelbarrows and has zero cracks anywhere.

RE: Rebar vs. Wire Mesh

TLHS

(Structural)

28 Sep 15 12:23

You certainly don't need to reinforce a slab on grade if it isn't critical to control cracks and you've followed common practice for crack control joints. For more critical applications, the ACI document on slabs on grade recommends half a percent of reinforcement in each direction at either two inches from the top or two thirds from the bottom (it suggests that both are common).

RE: Rebar vs. Wire Mesh

emmgjld

(Geotechnical)

29 Sep 15 02:30

@ medeek

As a whole, most of my work with typical 4" residential slabs has been using the #3 bar matte. A lot of the finishers also use fiber, they seem to think the added expense is offset by some improvement of slab surfaces & a little less raveling at cut & tooled joints.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

News

For more Concrete Structures Welded Meshinformation, please contact us. We will provide professional answers.