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Joining Two Slabs, Help

 
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Old 03-30-2010, 01:49 PM   #1
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Joining Two Slabs, Help


I recently poured one side of my wifes barn floor for office, feed room, wash stall, etc. Now I am forming the isle way to pour it. The question I have is:

Do I need to put some form of expansion joint up against the previously poured slab, and should I pin the two slabs together by drilling rebar into the existing slab?? I'm worried when the new slab contract/shrinks back I'm going to have a troublesome gap between the slabs which might create a problem in the area of the wash stall.

The barn is on a compacted subsoil, I have 4-5" of 57's down with plastic vapor barrier, wire mesh and rebar (will be driving tractor and skidloader down the isle). The stall side of the barn will remain unpoured. No heat in the floor.

I've read differing opinions on the web but none matching my exact project. So any help would be appreciated.
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Old 03-30-2010, 04:10 PM   #2
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Re: Joining Two Slabs, Help


You will be fine if you dowel 36" x 1/2 rebar every 24" OC. Embed them at-least 8-12" in the exsisting slab. I'm a commercial contractor and we encounter this alot. No Problem at all.

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Old 03-31-2010, 09:03 AM   #3
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Re: Joining Two Slabs, Help


Kevin,

First thank you for the reply, but what is your suggestion on the expansion joint, or since I'm pinning them it really doesn't need it??

Thanks,
Kenny
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Old 03-31-2010, 10:25 AM   #4
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Re: Joining Two Slabs, Help


You will not need the expansion joint. Just pour the new slab directly up to the existing one. I only use the expansion material when pouring up against a separate element, like a block wall that is sitting on a footing or a steel column that is also sitting on a footing. This allows those two members two expand & contract independently of each other. Your new slab once 100% cured and properly doweled should move with the old one. Just make sure your pouring atleast 4" thick 3000 psi on good compacted ground and allow it to cure properly.

Oyeah - make sure when pouring the concrete to pull up on your wire mesh so it gets completely embedded (atleast 1 1/2" from bottom) into the concrete. I've seen alot of guys jusy pour directly on top of mesh and it ends up at the bottom of the concrete not doing it's job. You didn't mention how big this slab is but you might want to cut some control joints.

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Old 03-31-2010, 12:10 PM   #5
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Re: Joining Two Slabs, Help


Yeah I'm pouring an area 12'x60', it'll be 5" 3000 psi w/fiber. I set the rebar on feet and tied wire on top the rebar. I thickened it up at each end where I'll be driving up on it. With all the steel do you feel I need to put control joints in 15' sections?? Thank you for your help.
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Old 03-31-2010, 12:15 PM   #6
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Re: Joining Two Slabs, Help


Sounds like you've got it figured out! 15 or 20' control joints will be fine.

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Old 03-31-2010, 07:37 PM   #7
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Re: Joining Two Slabs, Help


Control joints need to be much closer. If it's 60 foot long go every 10 foot saw 1inch deep. Better to saw them now or it will crack later
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Old 03-31-2010, 07:59 PM   #8
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Re: Joining Two Slabs, Help


I agree that you should have saw joints every 12 feet minimum. Every 8 feet wouldn't hurt. It's no big deal for the finish. I just caulk them later.

As for the dowelled joint, I have poured a lot with no expansion joint and will continue to do so. No problems ever. However, I was at a concrete seminar and it was recommended to have an expansion joint there. Noone, including me, asked why. I don't think an expansion joint (1/2" foam) is necessary and time has proven it isn't. Pouring one pour against another acts as a control joint anyway, but we don't want it to move (that's why we dowel it together).

Is that clear?
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Old 04-01-2010, 01:15 PM   #9
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Re: Joining Two Slabs, Help


Just troweled it, waiting for it to set up for final finish and a broom. I ended up using 4000psi and put the joints ever 17' since it actually measured out to 51' long. Picked a great day as it's sunny and about 80 degrees. The wife can't wait to use it. Thanks again for everyone's help, I build houses when not working at the fire house. Poured lots of footers not have done very little slab work so all of you have helped me out a great deal. Thanks again.
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Old 04-01-2010, 02:50 PM   #10
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Re: Joining Two Slabs, Help


Quote:
Originally Posted by beretta13 View Post
Control joints need to be much closer. If it's 60 foot long go every 10 foot saw 1inch deep. Better to saw them now or it will crack later
Every 10x 10 no more than 100 sf
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Old 04-01-2010, 06:46 PM   #11
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Re: Joining Two Slabs, Help


Control joints should be 2-3 times (no bigger) the thickness of the slab, in feet, in this case, a 5" slab should have them at no more than 15'.
Good Luck!
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Old 04-01-2010, 08:24 PM   #12
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Re: Joining Two Slabs, Help


I personally think you guys are pushing it with your 15 ft control joints. Portland Cement wants to crack every 10 foot. If your ever in dought when sawing, split it. For example 24 foot, yea you could cut at 12 but why chance it split them and cut into 8ft then you have no question about proper joint placement. Just my opinion, homeowners don't like cracks......
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Old 04-02-2010, 06:32 AM   #13
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Re: Joining Two Slabs, Help


With the fiber, mesh, & 4000 psi, your gonna be fine at 17'.

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Old 04-02-2010, 11:59 AM   #14
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Re: Joining Two Slabs, Help


Sorry I just totally disagree with you. 17 f
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Old 04-02-2010, 12:00 PM   #15
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Re: Joining Two Slabs, Help


17ft is just way to much
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Old 04-02-2010, 05:58 PM   #16
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Re: Joining Two Slabs, Help


Quote:
Originally Posted by beretta13 View Post
17ft is just way to much

Agreed, I'd stick to 10-12' to play it safe. Being his own property, it may not matter as much to him. With extremely slow & wet curing, you could probably get by with the 17' inside, but not with 80 degree weather.
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Old 04-02-2010, 07:36 PM   #17
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Re: Joining Two Slabs, Help


Quote:
Originally Posted by Gett'n it done View Post
I recently poured one side of my wifes barn floor for office, feed room, wash stall, etc. Now I am forming the isle way to pour it. The question I have is:

Do I need to put some form of expansion joint up against the previously poured slab, and should I pin the two slabs together by drilling rebar into the existing slab?? I'm worried when the new slab contract/shrinks back I'm going to have a troublesome gap between the slabs which might create a problem in the area of the wash stall.

The barn is on a compacted subsoil, I have 4-5" of 57's down with plastic vapor barrier, wire mesh and rebar (will be driving tractor and skidloader down the isle). The stall side of the barn will remain unpoured. No heat in the floor.

I've read differing opinions on the web but none matching my exact project. So any help would be appreciated.
I would like to give you just a little advice...you can add expansion joints if it is a large pour but not necessary if you have a minimum 95% compacted soil, with that compaction if done correctly should not settle.I would dowel in #4 (1/2") rebar into the existing edged of the slab that your pouring against, if you feel like you need to, not going to hurt.The poly should be a minimum 6mils, wire mesh in our area is not needed if you use fiber mesh but will not hurt if you still want to use re-wire the minimum you should use is 6"x6"x10".The rebar is not needed on 95% compacted soil but will not hurt if you want to install it because it will make the tinsel strength of the concrete stronger
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Old 02-23-2012, 11:41 PM   #18
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Re: Joining Two Slabs, Help


Well now that it's been almost two years... Did you get any cracks in the slab?

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Old 02-26-2012, 10:44 PM   #19
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Re: Joining Two Slabs, Help


Hobgood,

It worked beautifully, no cracks what so ever and I drive a 43hp compact tractor up and down it all the time even with a ton of feed on the forks. I pinned it as you advised, but in wire and rebar plus used 4000psi with fiber @ 5" and the control joints with a jointer at 17'. A friend of mine said I could probably drive a tank down it.

Thank you for all the advice.
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Old 02-28-2012, 12:30 PM   #20
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Re: Joining Two Slabs, Help


in commercial work, the standard is control joints not to exceed 200 sq ft.

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