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AndrewF 07-08-2009 10:29 PM

Concrete Slab Pour - 35 Yards
I am prepping my barn to have the floor poured.

I am going to have 4000 psi concrete poured to a depth of approximately 4".

The size of the floor is 40' x 68'

My question is wether to pay the extra $210 for fiber and not utilize any wire mesh OR; forgo the fiber and do wire mesh.

My thought is to go with wire mesh as it will help keep the concrete together should (when) a crack develops.

While the fiber does increase the holding strength, it does no good after a crack has formed as there is nothing to hold the two pieces together.

Also, for a barn floor, is it necessary to put down vapor barrier.

jomama45 07-08-2009 11:35 PM

Andrew, as a contractor, I do utilize the cost effectiveness of fibers quite often, but NEVER rely on them completly. I personally hate rolled mesh, & the tetanous shots that would come with it regularily. The only time I will use mesh is when it is clearly speced, & then I will only use sheet mesh, which is about 8' by 15'. Far easier/faster to handel, but a real PITA to haul/pick-up on a daily basis. I have run the numbers many times, & always find that installing 3/8" rebar on 4' centers each way saves us time & money, & when used w/ fibers, offers a far superior re-enforcement in the long run. In short, fibers alone wont be sufficient IMO. Remember, with concrete, you have one opportunity to get it right. As for the vapor barrier, it depends on the use of the barn. It should cost about the same as the fiber cost for the material. In humid weather, it should cut most, if not all floor "sweating", which may be a big plus depending on the use of the barn.

Just Bill 07-09-2009 07:06 AM

And don't forget control joints. Concrete will crack, but you can usually tell it where to crack. And I would use a moisture barrier, might even consider some foam insulation.

AndrewF 07-09-2009 02:20 PM

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I was going to use the wire mesh sheets. I used them in my last barn.

The barn is mostly to be used to store equipment, park my truck in at night and a workshop for repairs and other projects that are too dirty for the house garage.

Unfortunately, cost is a concern, like most projects. I don't mind doing it right, but I still have to manage the costs.

Yes, control joints will be done.

SNC 07-09-2009 03:47 PM

I do not believe in doing any concrete without using steel or wire or both :no:

Gary in WA 07-09-2009 06:16 PM

Don't forget underground conduit for wiring, looks like you don't have it yet. And plumbing supply to keep that truck clean. lol
Be safe, G

Wildie 07-09-2009 08:26 PM

Moisture in frozen concrete can/will cause cracking!
I would lay plastic down before the pour.
I did this with my garage back in 1978. The garage is unheated and sometime the temp goes down to 10F. It has never cracked anywhere. I used 4" mat reinforcing, with rebar around the perimeter.

RippySkippy 07-10-2009 08:33 AM

I second the vapor will virtually stop the sweating in the spring...for the few $, I never pour any concrete except exterior, with out it.

Termite 07-10-2009 09:45 AM

Fiber's great, but treat it as a supplement to mesh or rebar reinforcement. It just isn't an alternative to it. I think I'd opt for 6" welded wire mesh and call it good.

As Rippy said, vapor barrier is a very good idea even though the barn isn't habitable. It'll help reduce moisture transmission.

Daniel Holzman 07-10-2009 11:13 AM

This is a 4 inch thick slab, as such you cannot achieve even the minimum recommended cover over rebar. Further, the rebar would have to be placed at the center, which is useless from a structural standpoint, i.e. the rebar is at the neutral axis of the concrete, hence adds no strength to the slab. At best, rebar would act as minimal temperature reinforcing, and might reduce cracking somewhat.

I agree that mesh is a PITA, further no contractor ever supports it properly, so it winds up at the bottom of the pour, doing absolutely nothing except costing money and time.

I happen to like fiber reinforced concrete, for a relatively small premium, you get a mix that is more likely to resist cracking, but no concrete pour is crack free.

The most important considerations are proper preparation of the base, it must drain correctly, and be adequately compacted to support the slab. Also, you need control joints correctly installed. They do not stop cracking, they simply concentrate the cracks inside the joint, where the cracking is not objectionable. I also agree that a vapor barrier under the slab is a good idea, 6 mil polyethylene is typical, but there are alternatives.

For my money, the most important concerns should be foundation preparation, vapor barrier, high quality concrete, proper curing and finishing. I would not include any steel in the concrete, I would use fibers, for the reasons noted above. For a four inch slab, steel adds nothing, only costs money.

AndrewF 07-10-2009 12:16 PM

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Thanks for the input.

The floor will have drains over each bay (4), over where the freeze proof faucet is, and a stub up for a future wash sink near the water faucet. I put a 6" PVC pipe around the freeze proof faucet so that if(when) I ever have to repair or replace it, I can without jack hammering the cement around it up. It sits about 6" from the outside wall, so I can dig outside down to it.

I already ran the 1 1/2" conduit in for the electrical service as well as ran a spare 1 1/4" to the house for future and then also buried two cat5e (outdoor) and 2 RG6 cables from the house to the barn and stubbed them up in PVC as well.

On my last barn, I used 6"x"6 mesh. We used j hooks and pulled it up as we did the pour, being careful to not walk on it too much and push it back down. Yes, I am sure some of it sunk back to the bottom. I did NOT order fiber for this pour.

The first two photos are for this project.

The last photos are from the barn I built in 2006 at my old house.

AndrewF 07-10-2009 12:19 PM

Also, should I have them apply a curing agent to it at the time of the pour?

I plan on armosealing it about a month later and I didnt know if the acid I have to use to clean the floor would not work well with the curing agent.

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