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Discussion Starter · #1 ·
Hello, we're building a garage and need some advice. We're in the midwest and the pad is 40x50x6" thick. We took out topsoil and added 18" of compacted stone. We then dug a 12" wide x 36" deep trench all the way around. We plan for this to be monolithic with rebar. We were told that it would be good to have an isolation joint down the middle. I don't think I've seen any pads this size with anything more than control joints. Has anyone done this, or have any advice?

Thanks! Jason
 

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At that width that might be good advice. I did 20x30 same method control joints only. But some of the large retail warehouse places do seem to have control joints.
 

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When I had my shop poured (24x24) the concrete guy suggested control joints crossing in the middle to the edge. He said it will certainly crack, and he would guarantee it, BUT the control joints tell it WHERE to crack. 20 years later, no spiders, just the control joints.
 

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Hello, we're building a garage and need some advice. We're in the midwest and the pad is 40x50x6" thick. We took out topsoil and added 18" of compacted stone. We then dug a 12" wide x 36" deep trench all the way around. We plan for this to be monolithic with rebar. We were told that it would be good to have an isolation joint down the middle. I don't think I've seen any pads this size with anything more than control joints. Has anyone done this, or have any advice?

Thanks! Jason
Isolation, expansion and control joints in a monolithic pour usually don't work. Joints really depend on a uniform thickness. If cracks bother you, switch to a traditional foundation with a separate slab. (More money)

Also, if you do end up doing it, one joint is not enough. On a 6 inch slab ACI (American Concrete Instatute) says control joints should be place 2 to 3 times the thickness of the slab in ft. So that equals out to 12 to 18 ft spacings in a square pattern.

I always told clients, good concrete, lots of steel and just pour it. Small hairline cracks are fine and way easier to clean/sweep than big old control joints.

That's my 2 cents.
 

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Discussion Starter · #5 ·
Thanks everyone, really appreciate the advice! Unfortunately I'm starting to second guess the monolithic design but we're so far along I hate to change now. My concrete guy planned to cut control joints in a 10x10 grid but that might limit where I can put machinery. Maybe we'll pour the trench footing as is and put the slab on after. I can work around control joints, but a big isolation joint I don't care for.
 

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Thanks everyone, really appreciate the advice! Unfortunately I'm starting to second guess the monolithic design but we're so far along I hate to change now. My concrete guy planned to cut control joints in a 10x10 grid but that might limit where I can put machinery. Maybe we'll pour the trench footing as is and put the slab on after. I can work around control joints, but a big isolation joint I don't care for.
You can research putting polyurea inside your control cuts. Again, I would just put in lots of steel and do nothing. By the way, I have acid stained radiant floors in my house with no control joints.
 

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Concrete shrinks as it cures and cracking generally happens. Indoors you can saw cut control joints then later fill them with elastomeric filler. If you don’t mind hairline cracks, skip the control joints.
 
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