Getting ready to have new garage slab poured and have a question about the Fibermesh concrete. My Concrete guy says you don't need rebar or mesh in the floor?Going to pour 4 Inch 4000psi concrete.(old school thinking) you need rebar in concrete? what do you guys think? Cost about 400-500 extra to put rebar in the floor.
Concrete question/Help
- Thread starter Tofast4U
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Doug B
Well-known member
I would use wire mesh throughout,and I like to add 2 #2 re-bars across each garage door.
gussteve
Well-known member
yes,the more the merrier and make sure you go deep all around the edge of your forms.also pitch the floor so the water/snow will melt or naturally drain toward and out the door . i just built mine and even with hardly any pitch at all you will love that no puddles are just hangin out on you floor.
54FordPanel
Well-known member
I would pay extra for the rebar.
Not sure of your location but in Vermont I put in both rebar and fibermesh, maybe overkill but my excavator recomended it before the concrete guy did as insurance against cracks etc. especiaaly in the harsh swings of the winters here..... much easier to do than retrofit LOL 
Cost is minimal on the whole project! have fun bobbycoke
Cost is minimal on the whole project! have fun bobbycokeGrumpy365
Well-known member
x 2 ^^^^^
tmars
Active member
I am getting ready to pour as soon as it stops raining, I am going with 5 inch fibermesh and no steel, they say it is better than steel
Junkman
Well-known member
I have fiber mesh and wire in my slab, and I went with a 6" slab, since it was going to cost almost as much to truck in fill to raise the height. Back then concrete was inexpensive, and so was fill, but the trucking and compacting was the expensive part. I found that the best thing that you can do to make sure that your floor doesn't develop cracks later on, it to slow the curing process once the concrete hardens up. To do this, I kept the concrete wet for the first 30 days, by spraying water from a hose on it. This was the advise of an old concrete worker, and it worked well for my floors. When I had the cellar floor poured, I didn't have water at the time, so I put a clear sealer on the concrete 24 hours after it was poured. That floor never cracked either. My garage floors are 4500 or 600 PSI .. don't remember, but I know it was an extra cost. Just watch that the contractor doesn't water down the concrete to make it easier to spread. This weakens the concrete ultimately.
ConCretin
Well-known member
Fibermesh is designed to control plastic shrinkage cracking in the early stages of strength gain, which does provide some value. It does not however replace properly positioned steel reinforcement - rebar or mesh. Fibermesh will not provide structural reinforcement or keep a crack from 'opening up'.
I would use wire mesh or #3-4 bar at 12" centers. Most importantly I would position the reinforcement in the center of the slab with continuous slab bolster or some similar method. Do not depend on you finishers to pull up the reinforcement during placement. I would use saw cut control joints to manage cracking. If you want to add fibermesh for a little extra insurance you can but I wouldn't use it in lieu of traditional reinforcement.
Junkman is right with regard to water. Keep the slab continuously moist for at least seven days - do not let it dry out. Do not let your finishers apply water during finishing.
I would use wire mesh or #3-4 bar at 12" centers. Most importantly I would position the reinforcement in the center of the slab with continuous slab bolster or some similar method. Do not depend on you finishers to pull up the reinforcement during placement. I would use saw cut control joints to manage cracking. If you want to add fibermesh for a little extra insurance you can but I wouldn't use it in lieu of traditional reinforcement.
Junkman is right with regard to water. Keep the slab continuously moist for at least seven days - do not let it dry out. Do not let your finishers apply water during finishing.
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We have a winner. This is the way I built. (Retired Engineer, if that means anything)
tyjoja
Well-known member
I used just the fiber meshed in my shop, and seem to have lots of cracks. But I believe almost all slabs will crack, good luck bob
70redbee
Well-known member
Go with a least 4000# concrete,rebar and wire mesh. It's cheaper now than to try and repair it later.As said, don't add water to the mix when pouring. If you are on any kind of fill, even if compacted, it is wise to add grade beams with rebar to help strengthen the floor.
I don't know about you but i'm doing 24x32 6" thick with 12 inch thickened edge and a hip wall tied in with stirrups and i will have 1/2 rebar 16 in on center on the whole thing. i dont want it to move on me at all. the extra 5 or 600 bucks is worth it in my opinion. and thats 35 mpa with air probably.
Falcon67
Well-known member
That sure happens - just remember, if the slab is done well, anything set on top will have a long and happy life. Worth the extra effort.
Oldtymeflyr
Well-known member
One of the issues that comes up is where the steel goes.
My steel is on a 2 foot grid #3 bars, we also used the fiber reinforced concrete, its a pretty cheap option. Plenty strong.
If you are going to put in a 2 post lift, figure out spacing before you pour because steel rebar can be a problem in placing the lift. A steel cutting drill bit may have to be used.
Also, go easy on the joints in the lift area, that can raise questions. We have 8-9 inches of concrete in the lift area and managed to miss the steel when the lift was installed. One of the issues that did come up during the install was that one control joint was about 4 inches away from a bolt, but with 8-9 inches of concrete it worked out.
Have fun!
Rick
My steel is on a 2 foot grid #3 bars, we also used the fiber reinforced concrete, its a pretty cheap option. Plenty strong.
If you are going to put in a 2 post lift, figure out spacing before you pour because steel rebar can be a problem in placing the lift. A steel cutting drill bit may have to be used.
Also, go easy on the joints in the lift area, that can raise questions. We have 8-9 inches of concrete in the lift area and managed to miss the steel when the lift was installed. One of the issues that did come up during the install was that one control joint was about 4 inches away from a bolt, but with 8-9 inches of concrete it worked out.
Have fun!
Rick
highland512
Well-known member
In a 4" slab for a car garage you would only need 6"x6" welded wire mats placed in the CENTER of the slab. Way to often we have taken old slabs out that where all busted up and cracked and the dam wire is laying on the ground below the concrete. 4000psi fibermesh with wire reinforcement and good placement of control joints should produce a quality long life slab.
TOOL MASTER
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rebar rusts...when it does it expands...thats why most bridges ect. are falling apart...
just go thicker
just go thicker
ddawg16
Well-known member
Rust needs 3 things to happen....Steal, water, and Oxygen. If the oxygen is not getting in there....it won't rust.
To the OP.....
Concrete is not one of those things you can go back to and 'add' something to make it better. Once its poured....your done....
Based on what I have learned....the information on fiber vs rebar is correct. Go rebar....the contractor wants to use fiber because its a lot easier....and any potential cracks won't likely show up until well after any kind of warranty.
Additionally, I have heard that fiber will give your floor finish a 'hairy' feel to it....
Falcon67
Well-known member
They just poured a big house slab next door - all bar on 24" centers, no mesh, no fiber. Crew and builder been in the business a long time.
ConCretin
Well-known member
Concrete IS prone to cracking because it is brittle i.e. weak in tension. Hard to crush - easy to pull apart. Shrinkage that occurs during hydration or subsequent temp. changes is enough to create cracks.
Good design and construction - including steel reinforcing, which adds tensile strength - is a good start. Control joints will help ensure that the slab cracks in a uniform and visually acceptable manner. Above a certain size, all slabs are likely to crack.
ConCretin
Well-known member
Sorry for the double post and the highjack but I gotta comment on Highland512's avatar. For those who don't know ABC is a fantastic business association especially if you are a believer in free enterprise. Nice to see a brother in arms on the GJ.
highland512
Well-known member
The key to preventing cracks is having a good base. Bare minimum you should have 6" of compacted stone. But none the less ALLconcrete will crack eventually, thats why you need to have control joints cut to prevent the unsightly cracks that run diagonally or in a spider like fashion. With a 4" slab rebar seems to be a little over kill, I haven't looked at a set of plans or specs that called for 3 or 4 bar in a 4" slab for years. The wire mats give you the same abilities of 3 bar at a much smaller material and labor cost.
I didn't use any rebar (it did have fiber) in my garage pour other than at the door/footer area. I poured over the old floor, up against the old footer. I felt that the new floor was going nowhere. I did use some 6x6 wire when I poured the apron, along with some rebar.
ConCretin
Well-known member
Wire mesh or fibermesh for that matter is fine for most slabs if they are supported on a properly compacted base such as you have suggested. If settlement or frost is a concern, I'd use rebar. It is easier to support and ensure it ends up in the middle of the slab. You can spend more on supports for wire mesh than the up-charge to use rebar and get a stronger slab to boot. Cheap insurance in my opinion.
jumbo61
Well-known member
LLWillysfan. "It is easier to support and ensure it ends up in the middle of the slab. You can spend more on supports for wire mesh than the up-charge to use rebar and get a stronger slab to boot". How do you support the rebar to assure it's in the middle of the slab? May be doing that in the near future. Thanks.
Bruce4310TX
Well-known member
Fiber mesh sole purpose is to help stop surface cracks during the cure right after the pore once it sets up there is no structural strength from the fiber yes it helps the initial setup but remember all concrete cracks fiber will not hold it together. only rebar wire mesh is better than than fiber but it usually ends up on the bottom of the pore spend the money on rebar best money spent. money saved on fiber can be spent on your friends when they come over to help feed them. i have pored a couple hundred slabs im not perfect but rebar is the way to go if your contractor tells you fiber is the way to go get a new contractor.
I would also add a vapor barrier- not to keep moisture from coming up, but to keep the water in the concrete longer as it cures instead of be absorbed by the ground. I had my 25'x 17' aprons done this way- with fiber mesh- and the contractor doing the job was amazed how long it took the material to set up so it could be finished. He was used to the time it took a basement floor to set, but hadn't made the correlation between an inside pour and an outside pour and the set times.
tmars
Active member
Is a 6mil vapor barrier adequate? It is awsome that there is so much inforation provided by everyone. Thanks
ConCretin
Well-known member
Slab reinforcement is only effective if it ends up in the middle third of a slab. Wire mesh is less rigid than rebar so it must be supported more thoroughly to avoid sags, which greatly reduce its effectiveness.
If you are going to use wire mesh, I would suggest 'continuous slab bolster' at no more than 4' on center. Depending on the gauge and stiffness of the wire, you may need to place it closer together. Rebar mats can be supported on individual chairs or cement bricks.
Most construction supply house will carry a variety of products. Just keep in mind that your finishing crew will be walking all over your reinforcing so it needs to be rugged.
Some finishers will lay the wire on the sub grade and try to pull the wire up as they place but this is not an effective or consistent method. When they walk back into the concrete to screed it level, they will inevitably push it back down.
While I don't believe it is as effective as properly installed rebar, fibermesh is probably better than rebar or wire that ends up in the dirt on the bottom of your slab.
ConCretin
Well-known member
It depends on whether you intend to install a floor covering. If not, a 6 mil vapor barrier is adequate. If you intend to install something like an epoxy floor, I would invest in a 35 mil product with taped seams. It is a difference of about 25 cents a square foot, which is cheap insurance given the time an effort involved with most floor coverings.