wire mesh vs fiber?

[Innovate1]

GCs working up quotes for house, attached garage (2 car) and detached 30 x 40. One just ask about using fiber, stating that's his standard. Plans call for wire mesh. Plan to do some sort of stain in the basement - no tile. I can see fiber being a problem there but don't know much about the details. Wire is a bit more is my guess.

 

[Leaflessshadetree]

I like using both. IMO they address different possible issues.

 

[1953mercury]

#4 rebar on an 18" grid for garage and shop. Fiber if you like, wire mesh, I wouldn't waste my time. Concrete, once you do it wrong, you can't make it right. Use rebar. Mike

 

[Northerndave]

I'm not a fiber fan. The fiber fan boys will beat me up over it but I think you could just as well pour an assload of dry oatmeal in your mix.
If they give you a good strong mix you are good to go. I'm also a rebar fan, that's my preference, hold the fiber, give me enough powder in the mix and plenty of rebar.

 

[Walter_TA]

Fiber is use to hold the concrete together until it gains strength not to crack. Wire and rebar are used to hold the parts together once it cracks. Use both and pour at a slump of 4. Do not let them add water to the mix. Keep the top wet for a week.

 

[Northerndave]

I've had 3 pours done with fiber with crews that boast about the best finishing practices with laser screed etc and I've had 3 done with no fiber but more focus on a strong mix with enough portland, not too wet, nice sand and aggregate mix. They set pipes off stakes to carry the screed in the middle of the pour, all old school, no fiber and laser BS. Those are the best slabs I've had. My newest building was done this way just last fall, the one I work in right now was done by the fiber/laser junkies and it's garbage. I literally have hills and valleys, I could make a topo map for my shop floor and you would think I was in the black hills or something. That's of course not to do with the fiber but the screeding prior to power trowling. But the fiber does effect the finish as well, Not as nice. And I have formed the opinion that the guys that use fiber in the mix, they lean on that fiber like it's some kind of magic pixie dust that's going to make up for a lot of shortcomings here and there through the rest of the job.

Hey, that rebar spacing is a little wide isn't it? "yeah, but we use fiber"

Hey, the mix is pretty loose isn't it? "yeah, fiber tho, she'll be ok"

Hey I just washed some of this off my hands and it just didn't seem like there's much portland in it, can I see the mix design? "it's cool bro, we got fiber"

Hey, is the guy running the screed, is he stoned right now? "yeah, but we use lots of fiber"

Hey, your truck is on fire.... "fiber"

 

[Plump]

Well played, Northerndave!

 

[EdT]

I'd put in some metal wire mesh or rebar. I got the fiber bum's rush on my slab and it has lots of cracks. Further research (too late) indicates that fiber does improve the green strength to reduce shrink cracks while curing, but does little for the long term strength. The guys who do the slab work love it because it means less work for them than putting in metal.

 

[Toomanytools?]

Fiber isn't a substitute for WWM or rebar, it's to help reduce the small stress cracks at the initial stages of shrinkage. This may help:
http://www.chicagolandconcrete.com/fiber-mesh-vs-rebar-or-w-w-f

WWM and rebar debate goes on forever, this gives some light on the subject but a lot to digest. https://www.concrete.org/portals/0/files/pdf/fe2-00.pdf

Thing with mesh is it needs to be positioned in the slab properly, some will say 2" below surface or within the upper 1/3 of slab thickness. Others ....welded wire reinforcement shall be placed and maintained in the upper 1/2 of the slab depth with a min cover of 3/4" for interior applications and 1-1/2" for exterior."

For mesh you really need to chair it up so the workers can walk on it.

 

[Armorpoxy]

Our comments is that if you use fiber and plan to epoxy these stick up on epoxy and require grinding/sanding after you prime (what we call the hair gel effect). Better way to handle them is to burn them off with landscaping torch.

Or..don't use fiber if you plan to epoxy.

 

[ConCretin]

Well at least Northerndave brought some humor to this well worn debate. I'll just add that it's all about the cracks. Use fiber to delay em, control joints to hide em and/or reinforcing to hold em together. You can give my Guide to Floor Slabs (below) a read for some additional thoughts. Good luck with your placement!

 

[MrSurly]

I'm with Northerndave. I view fiber as just the latest trendy hokum like memory foam or essential oils. The first time I saw "hairy concrete" I swore I'd never do fiber. Rebar for me, or rebar AND mesh for some applications. Concrete will always crack, but it doesn't have to shift or separate just because it has surface cracks.

 

[Northerndave]

I can totally follow what the apparently experienced and educated folks are saying about the fiber being for the green stages. That makes total sense to me. I've got rebar and saw cuts in both of my current business buildings, one has the county fair fun house finish with it's roley hills.... Sometimes when I lose a 10mm socket I climb to the top of one of these hills in my shop so I can see far down into the valleys, searching for snap rings and 10mm sockets. The valleys often hold glacial melt off my drippy plow truck in the winter seasons. This is also the slab with the dog hair in the mix. The new building is hair free and rather lacking in terrain features. I guess we'll see if I can notice any any pros or cons going forward, fiber or no fiber. lol

 

[diesel_dan]

I too am a rebar fan, #4 @ 18" OC square pattern is overkill, but why not? I usually do 24" and its been fine. Same problem with rebar as what was stated above for mesh: if it isn't well into the mud, it does zero to support it - watch them pour and make sure the pull the grid up into the slab. Definitely skip fiber where you will be staining. I always thought it was nice to have the extra support otherwise, but don't feel strongly one way or the other. A high strength mix is a must have and too wet is a lousy contractor (he shouldn't accept it)...

 

[tff]

I went with wire mesh because some 2-post lifts require it in their installation instructions (but most don't). Fiber doesn't help hold the slab together structurally.
One note... my slab was done the sloppy way... they did not support the wire mesh to the middle of the thickness. Even though I complained as they were pouring that as they walked on just poured concrete they were just shoving the wire mesh to the bottom. Fortunately I have large areas where the lift will go that were much deeper, and so the wire mesh effectively is actually in the middle of those sections - lucked out there.

 

[Slowgsr]

I always put in rebar, and if you do mesh it usually ends up on the bottom of the pour anyways after its stepped on

 

[ConCretin]

Thing with mesh is it needs to be positioned in the slab properly, some will say 2" below surface or within the upper 1/3 of slab thickness. Others ....welded wire reinforcement shall be placed and maintained in the upper 1/2 of the slab depth with a min cover of 3/4" for interior applications and 1-1/2" for exterior."

You are so right about all the conflicting advice you'll get regarding placement of steel reinforcing. ACI recommends positioning the bar high in the slab to maximize its ability to keep cracks tight. Then there is the crowd that mistakenly tells you to place the reinforcing low in the slab because that's where the slab is in tension under load.

In reality it's a moot point. You want inch and a half of cover above and below your reinforcing. Any less eliminates any margin for error and risks not getting concrete under the reinforcing or having it poke through the surface when people start walking all over it. Then there is the issue of running your saw thru all that steel when you cut your control joints....

In a 4" slab, that leaves you an inch in the middle to place your reinforcing. Barely enough to cross your bars or accommodate two or three layers of mesh at the overlaps (end to end and side to side). In the average slab you really don't have a lot of flexibility. Shoot for the middle third and you'll be fine.