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Old 11-30-2008, 06:57 PM   #1
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control joints--do i need them?


Here are the details thus far:
Monolithic slab, footers 18" below surface to put it below frost line, footers 12" wide, slab portion to lay on undisturbed soil with 4" of gravel, vapor barrier, #3 rebar grid 16" on center going down into the footers and connected to rebar running around footers perimeter, 4000 psi concrete. (This is going to be a music room/workshop, not a garage)

So, do I need control joints? If so, where should they be placed?

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Old 11-30-2008, 07:16 PM   #2
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control joints--do i need them?


You didn't mention how large the slab will be - what are the dimensions? If its over 200 square feet, you are probalby going to want to install control joints. Since this appears to be an interior slab, I would recommend sawing in the joints. It's a smaller joint and easier to install flooring over than a tooled joint.

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Old 11-30-2008, 07:24 PM   #3
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control joints--do i need them?


Agreed, unless it is very small I'd suggest sawing some joints in the slab. Don't saw all the way through, just deep enough that you don't hit your rebar.
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Old 11-30-2008, 07:28 PM   #4
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control joints--do i need them?


wow, i didn't even mention the dimensions. It is going to be 16' by 20'.
How would I determine how many and where to put them?
Why saw afterwards?
What would the risk of not having them be?
Thanks for your help.
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Old 11-30-2008, 09:14 PM   #5
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control joints--do i need them?


That's a good sized slab. As others have suggested, have the joints sawed - much better than doing them when wet and hand tooled.

http://www.concretenetwork.com/concr...troljoints.htm
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Old 11-30-2008, 10:41 PM   #6
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control joints--do i need them?


Cut one joint each way and you should be good to go. Cut the joints right after the concrete is hard enough to walk on...Don't wait more than a day or two.
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Old 12-01-2008, 06:48 AM   #7
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control joints--do i need them?


Quote:
What would the risk of not having them be?
Ayuh,...

The difference is,... Without joints,.. It'll Crack wherever it wants too...
With the joints, it'll crack In the joints....

I'd do Atleast 1 in each direction,... Maybe 2,...
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Old 12-01-2008, 06:13 PM   #8
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control joints--do i need them?


Thanks everyone.
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Old 12-02-2008, 06:25 AM   #9
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control joints--do i need them?


for a 16' x 20' slab, we'd saw 2 jnts long ( 20' - 6'8" o/c ) & 2 crosswise ( 5'4" ),,, didn't mention slab thickness & its a controlling factor to aci ( american concrete institute ),,, IF the slab's 4", cut thickness/3 ( current spec'd be 1.33" or 1 1/4" nominal )

ps - you don't NEED them but, without 'em, the random cracking might not be appealing in appearance OR structural integrity


Last edited by yesitsconcrete; 12-02-2008 at 06:29 AM.
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