Mesh Or Rebar?

[powerhound]

I did a search and was unable to find what I needed. My question is now that I'm lining things up for my new/first pour, should I use rebar or mesh? Both would/will be put on 2" chairs with the pex underneath, but I have to assume that the weight of people walking on the mesh while pouring and the weight of the mud will push the mesh down and not let it come back to the center of the slab, and the chairs will get pushed into the foam board. Rebar on the other hand will let people step over and hold against mud weight better. Just asking because I can get mesh cheaper. 40 X 40 4" thick slab with 2" foam board underneath.

 

[A_Pmech]

Mesh is for keeping chickens in the barn.

Rebar is for concrete reinforcement.

 

[dirttracker18]

Mesh is for keeping chickens in the barn.

Rebar is for concrete reinforcement.

Save the mesh for the sidewalk or patio.

Many will tell you it's fine, for my money (lots of it to pour a pad) I will have the rebar, thank you.

30 X 36 mono slab, with rebar, in a deep frost area, no cuts, coming up on 5 years old, no cracks.

 

[bobadame]

How much is it worth to you to not have cracks in the concrete? The re-bar is a stronger system than the mesh. Compare the cost of each system and decide for yourself. I chose wire mesh and I expected a few cracks. For the difference in cost, I don't care about a few cracks. The floor works just fine either way. Now if you have ground water problems, expansive soil or bad drainage around the building, you will have problems either way.

 

[KPSquared]

Re-bar, unless you'd rather use re-bar, then in that case I would suggest re-bar or maybe re-bar.

 

[powerhound]

Rebar it is. I talked to a few guys who have actually sprung for overkill and done both. Mainly for keeping the pex tube from floating and running into issues when cutting. Off to get my steel.

 

[red]

I did both. Rebar on 2' squares with the mesh. No problems going on 12yrs!

 

[gatchel]

Rebar here too...mesh is for wussies...

 

[bobadame]

You guys want to kick in for the re-bar?

 

[Highbeam]

No reinforcement will eliminate all cracks. What it will do is prevent those cracks from opening up into canyons.

What is the guarantee on a slab? Nobody will steal it, it won't catch on fire, and it will crack.

 

[RangerDaleXp]

My dad did concrete and has always said mesh is for the birds

 

[ConCretin]

I agree with most of the comments. Go with rebar. #4's at 12" centers.

You don't really need the extra steel rebar provides- it's just difficult to keep mesh in the floor. Rebar is rigid enough to stay in position.

 

[dirttracker18]

You guys want to kick in for the re-bar?

No, it's your garage do what you want. If you are that cheap with your $20 000 plus garage then why put anything in there at all. Why even spend the money on preping the ground.

Just dump some concrete and when it sets start building.

Seriously, did you just say that?

 

[gpn911]

Hi everyone,
Just found this forum, I'am in the planning stage to build a garage and just talked to a concrete contractor yesterday. I asked about rebar and he said he would do anything I wanted but he said when you cross the rebar the top strand now is only 1.5 inch deep in the concrete. He said he has seen it crack along the rebar.
My orginal plan was to use rebar, now I'm thinking mesh.

 

[powerhound]

Run a lower rebar chair and lower the overall height.

 

[5wndwcpe]

When I did my floor I used slab bolsters, re-bar on 12" centers and mesh on top so the concrete guys wouldn't be trampling all over the pex.

http://www.vimcoinc.com/images/docs/22-23.pdf


Here's a link to the build, floor is on page 4.
http://www.garagejournal.com/forum/showthread.php?t=13286&page=4

 

[ConCretin]

Hi everyone,
Just found this forum, I'am in the planning stage to build a garage and just talked to a concrete contractor yesterday. I asked about rebar and he said he would do anything I wanted but he said when you cross the rebar the top strand now is only 1.5 inch deep in the concrete. He said he has seen it crack along the rebar.
My orginal plan was to use rebar, now I'm thinking mesh.

1 1/2" of cover is more than adequate. The concrete will not crack as a result of this. It may crack for a number of other reasons but not this.

 

[5lima30]

Buiding code here requires re-bar. You may want to check.

 

[pop pop]

Depends on how thick your slab.

 

[tdkkart]

If for some reason your base grade shifts or sinks your concrete will crack, it'll crack anyway, but the difference between mesh and rebar is that when the crack gets bad enough and starts shifting vertically the wire mesh will shear, the rebar will not.

You're spending thousands on a building, skimping for $200 worth of rebar is like buying a new 'vette and running recycled oil in it. If you can't afford the rebar you might want to re-think your project.

 

[Beaumont67]

I combined thick mesh (over standard) and rebar...on my floating slab, poured over 1" foam.
- that slab (24x30 ft.) was polished & saw cut 3 times / zero cracks still, some +20 years later

 

[ksj9393]

Both would/will be put on 2" chairs with the pex underneath

The question of rebar vs. mesh has been hotly debated during the planning stages for my build too, and is unsolved. I am strongly leaning towards rebar, especially after reading responses here. (Great build, by the way, LLWillysfan. With your credentials, I think I would believe anything you told me with respect to concrete questions!)

I am concerned about your idea of putting PEX "underneath", however. I am no expert, but believe it is advised that PEX tubing for radiant heat be buried no deeper than 2" from surface of slab. Am investigating same questions as you, and have picked design like this (well... except for the 10 ga. WWF):

 

[bobadame]

No, it's your garage do what you want. If you are that cheap with your $20 000 plus garage then why put anything in there at all. Why even spend the money on preping the ground.

Just dump some concrete and when it sets start building.

Seriously, did you just say that?

Actually I have about $50,000 in materials and concrete in my shop. None of that was for labor, I built it pretty much by my self. I didn't "over build" it. My neighbor hired out his concrete, 30' by 100" slab with rebar ala chingada to the tune of $25,000. I did my own excavation, set the forms, the re-bar around the perimiter top and bottom, the 8 pillar footings, the 6x6 welded wire mesh pulled tight. My cost for the concrete and a crew to place it was about $9,600. My place is a bit smaller, 40' by 64'. With the roughly 15K difference in cost for the concrete I was able to put in a shitload of insulation and a few nice windows and good quality insulated doors. My floor has a few hairline cracks. I don't care. I can heat mine for about $60.00/month. He can't afford to heat his and it's like an oven in there in the summer. He has no cracks in his floor. So what I'm saying is that sometimes you have to make a compromise. The last shop I built in '94 was done exactly the same way. It has a few small cracks as well. They have not been a problem in either building.

You are welcome to come and visit and check out either of my buildings. I'd be proud to give you the nickel tour anytime.

 

[kert]

Ask me in 20 yrs. Just had my slab poured Friday with wire and nylon fiber. I asked my contractor what he would do if it were his building and that's what he recommended. I figure I'm paying for his experience, so I might as well take advantage.

 

[1grnlwn]

No reinforcement will eliminate all cracks. What it will do is prevent those cracks from opening up into canyons.

What is the guarantee on a slab? Nobody will steal it, it won't catch on fire, and it will crack.

Sorry to contradict you but if poured on top of a landfill a concrete floor can catch fire.

 

[Highbeam]

Sorry to contradict you but if poured on top of a landfill a concrete floor can catch fire.

Show us! You can heat concrete to failure and the subgrade can burn but the concrete floor won't combust. Are you saying the concrete will burn or that something under the concrete will burn?

 

[50cal]

Ask me in 20 yrs. Just had my slab poured Friday with wire and nylon fiber. I asked my contractor what he would do if it were his building and that's what he recommended. I figure I'm paying for his experience, so I might as well take advantage.

I think, know some contractors will recomend whats easiest for them. I tried fiber mesh in a dog kennel aplication. Load was 85 pound GSD. Musta been something in his pee that caused the cracks.

The question of rebar vs. mesh has been hotly debated during the planning stages for my build too, and is unsolved. I am strongly leaning towards rebar, especially after reading responses here. (Great build, by the way, LLWillysfan. With your credentials, I think I would believe anything you told me with respect to concrete questions!)

I am concerned about your idea of putting PEX "underneath", however. I am no expert, but believe it is advised that PEX tubing for radiant heat be buried no deeper than 2" from surface of slab. Am investigating same questions as you, and have picked design like this (well... except for the 10 ga. WWF):

My PEX is buried as below. No more than a 10 degree difference between supply and return. My radiant advisor said use that whole slab for storage.

I combined thick mesh (over standard) and rebar...on my floating slab, poured over 1" foam.
- that slab (24x30 ft.) was polished & saw cut 3 times / zero cracks still, some +20 years later

I thought maybe I had gone to far with 6 inch base, 15 mil vapor barrier, 2 inch foam,pex stapled to the foam, heavy remesh on top of the pex, 5/8 rebar on 1 foot centers, then another layer of heavy remesh, topped with a 4 inch floor of 5000 psi concrete. Sawed apprpriately, still waiting for the first crack.

 

[Kevin C]

Based on my reading, the location of the PEX is a factor only in transient operation. When you first turn a system on, the conduction distance allows for a faster warm-up.

However, since concrete will conduct heat within the slab pretty well ( compared to the insulation under it and the air above it), once under a steady state condition PEX location is not a big factor.

If you dont have insulation under your slab and you are relying on the insulating properties of concrete to isolate your thermal energy, then location would be more important. But at that point, you have a bigger problem (a very lossy heating system).

I also went with a 6" slab over R10 foam. Compared to the conductance of the concrete, the foam should isolate the energy. My goal is to use a solar heat source and use the thermal mass of the floor to store the heat. For me , this is not meant to be a primary heat source, just a way to reduce temperature swings and reduce how much heat is needed from other sources.

That's the plan....

 

[kert]

I think, know some contractors will recomend whats easiest for them. I tried fiber mesh in a dog kennel aplication. Load was 85 pound GSD. Musta been something in his pee that caused the cracks.

Well I laid the wire mesh, so not really any difference for him.

 

[50cal]

Well I laid the wire mesh, so not really any difference for him.

I guess what I am saying is your contractor and his help didnt have to step over,trip over rebar. Hard to wheel over rebar also. Remesh just lays there on the bottom out of the way. Unless you went to a great deal of trouble to hold it up, like with concrete bricks. I love remesh when applied above rebar it is a little added insurance to stop CRACKS.

 

[ksj9393]

For others researching this and like questions, I learned from the PEX "experts" (Plastic Pipe Institute, et al) that PEX tubing should be placed below rebar or re-mesh in slab on grad installations.

Source:
http://www.huduser.org/portal/publications/pex_design_guide.pdf

Now, with rebar being placed no closer than 1.5" below surface, plus 0.5" for diameter of #4 rebar, plus 1" OD of PEX tube - it would seem that a 4" slab would nominally place the bottom of the PEX a mere one inch above earth. Does this really even matter? I am guessing that once the room temperature reaches steady state, the slab likewise is at steady state with essentially a uniform temperature gradient throughout (except a bit cooler at the walls). Anyone affirm this?

 

[50cal]

For others researching this and like questions, I learned from the PEX "experts" (Plastic Pipe Institute, et al) that PEX tubing should be placed below rebar or re-mesh in slab on grad installations.

Source:
http://www.huduser.org/portal/publications/pex_design_guide.pdf

Now, with rebar being placed no closer than 1.5" below surface, plus 0.5" for diameter of #4 rebar, plus 1" OD of PEX tube - it would seem that a 4" slab would nominally place the bottom of the PEX a mere one inch above earth. Does this really even matter? I am guessing that once the room temperature reaches steady state, the slab likewise is at steady state with essentially a uniform temperature gradient throughout (except a bit cooler at the walls). Anyone affirm this?

Your not insulating? You will be heating a huge chunk of dirt under the slab. Anyway I thought this was about remesh, which is great for holding the sawn chunks of demowed slab together until the loader gets it into the dump truck.

 

[ksj9393]

Sorry... you're right. I should start a separate thread for the PEX dialogue. Mea culpa. And yes, I am insulating with 3" extruded polystyrene over 10mil vapor barrier (radon gas issue here).

So, getting back to rebar vs. remesh - what nominal spacing is indicated for rebar? Do most go with #4 in 24" square grid? I've been advised 18", even 12", but that really seems like overkill. Would then 5" pour be overkill too? My garage is 24'x66', with a 6'x32' jut front and center. Sits on sand deposited by Mississippi centuries ago. 3000psf rated soil.

http://www.garagejournal.com/forum/showthread.php?t=146713

 

[tlmartin84]

Concrete cracks period, unless you are lucky...and luck is all it is. Most of the "uncracked" stuff has hairlines in it you can't see.

I have done bridge decks with rebar on 6" centers that develop cracks. I have designed floor systems for commercial buildings some with rebar and some with mesh. Biggest thing is is subgrade prep getting everything compacted. Minimum of 2" clearance, and 3" anywhere concrete is in contact with ground.

A lot of guys use #4 or #5 rebar on 2' centers. This is good unless you have concentrated point loads, so I prefer mesh.

Also let me point out that by mesh I mean #4 or #6 ga. 5' x 10' welded mats, tied together overlapping a minimum of 6".

You can also reduce chances of cracking placing control joints every 15' and then sealing them with silicone, I recommend DOW 888.

 

[37ford4dr]

i used rebar and tied the pex tubing to the rebar with cable ties....i over reinforced the areas in the garage with additional rebar in the areas that a 4 post lift would go. the builder still used the wire mesh over everything i think for county regulations. i did sweat the idea of the laborers walking over the Pex tubing and damaging it , but the funny thing is i have yet to hook up the radiant floor heating....the 2x6 construction and insulated doors and windows make it easy to heat with the cieling mounted 240v Dayton heater. i just cant justify the initial cost of the manifold and water heating set up.

 

[50cal]

Concrete cracks period, unless you are lucky...and luck is all it is. Most of the "uncracked" stuff has hairlines in it you can't see.

I have done bridge decks with rebar on 6" centers that develop cracks. I have designed floor systems for commercial buildings some with rebar and some with mesh. Biggest thing is is subgrade prep getting everything compacted. Minimum of 2" clearance, and 3" anywhere concrete is in contact with ground.

A lot of guys use #4 or #5 rebar on 2' centers. This is good unless you have concentrated point loads, so I prefer mesh.

Also let me point out that by mesh I mean #4 or #6 ga. 5' x 10' welded mats, tied together overlapping a minimum of 6".

You can also reduce chances of cracking placing control joints every 15' and then sealing them with silicone, I recommend DOW 888.

Now thats the kind of remesh I am talking about. The rest is just chicken wire.

 

[BadgerBoilerMN]

Controlling cracks is the best you can hope for. Failures due to poor substrate prep can not be made up for with rebar. l

Putting wire down to "keep the tube from floating" is not necessary. In most of these smaller garages no reinforcement is needed since the fiber "controls" cracking and the loads are usually modest.

Staple the tube down and set #3 on top to get it in the slab where it will some good. For flat work on grade, 3/4" is the minimum cover required.

I would spend my money on ground prep, insulation and radiant floor controls where real benefits are proven.

 

[Shocker]

Exactly. My slab is 24x32x6" and uses rebar for the perimeter footing and the #4 5x10 welded mats. Overlapping and 2 layers.

4 years now and no cracks at all.

 

[mrobins297aaa]

if your planning on putting in a car lift at a later date make sure your re-bar is clear of the anchor locations because you can't drill threw the rebar

 

[Justanoldguy]

Mesh is for keeping chickens in the barn.

Rebar is for concrete reinforcement.

A very wrong and unresearched amateur answer.
Getting good useable advise on this board is like a lottery.