How much concrete do I need?


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Old 06-22-07, 07:58 AM
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Talking How much concrete do I need?

I am going to use 12" diameter carboard tubing to build deck foundation.
The tubing is 4 feet long, I'm planning to put 3 feet below the ground and leave half foot above ground, cut the remaining half foot off.

For 80 pound concrete bags, how many bags do I need for each tubing?

Thank you.
 
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Old 06-22-07, 10:33 AM
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The formula for the volume of a cylinder is: pi x [radius(squared)] x height.

That turns out to be 3.14 cu ft per cylinder. If you are buying redi-mix (cement, sand and gravel all combined) and each 60 lb bag makes .5 cubic feet, you'd need roughly 7 bags to fill each cylinder. I'd get 8 or 9 each just to be safe. It seems those bags never make as much as you think.

If you get 80 lb bags (.66 cubic feet), you'd need 5 or 6.
 
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Old 06-22-07, 11:24 AM
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Thank you, it is a little bit more than I thought.
 
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Old 06-22-07, 12:08 PM
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But I just feel a 12" diameter with 3.5' high cylinder should have more cubic feet.
 
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Old 06-22-07, 01:17 PM
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How much concrete do I need?

Each 12" diameter x 42" long cylinder will take 2.75 cubic feet (3.14*6*6*42/1728) to fill. You can deduct the volume of the post, which is about .4 cubic feet if you stick a 4x4 post in. If you use brackets instead, do not deduct. Add for waste. - It is till a lot less than if you tried to fill a rough sided post form.

Xsleeper is right about not it not going quite as far as they claim it will .

Dick
 
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Old 06-22-07, 01:17 PM
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Volume

Sleeper,

He says he will cut off 6" of the tube. That would reduce the volume to 2.75 cubic feet per cylinder.
 
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Old 06-22-07, 03:06 PM
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Oh yeah, guess I should have read more carefully.

Maybe he won't be short that way. I swear, every time that I fill sonotubes with bags of redi-mix I always am short a couple bags.
 
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Old 06-22-07, 06:08 PM
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OK -- 2.75 cu. ft. per tube. The 60# bags are 1/2 ft. and the 80/90# bags are 2/3 ft.

Use embedded post bases (Simpson PB, CB, CBSQ, etc.) rather than embedding the post directly in the concrete. The steel and the concrete are going to be pretty much eternal. The wood IS going to rot at some point. Make it easy to replace.
 
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Old 06-25-07, 07:35 AM
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Thank you all for your input.

When I look at the CBSQ site. http://www.strongtie.com/products/connectors/CBSQ.html

I'm going to use this kind of connector.

I feel I do not necessary need such a thick concrete tube as foundation.
Can I use 10" diameter cylinder for a 4x4 post?
 
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Old 06-25-07, 08:59 AM
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10" should be adequate, but best check the local building codes before going either way...
 
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Old 06-25-07, 04:51 PM
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lzhang,

If you are going 3' deep with your footings, I'm guessing that frost is an issue. (You haven't told us where you're at.) If that's the case, what the footing SHOULD look like is a hole 4' deep, with the bottom of the hole being 15" to 18" square. You fill the bottom 12" of the hole, then set your 4' sonotube on that (while the concrete is still wet!), then fill the sonotube with concrete to a level 6" above grade, filling around the outside of the sonotube with dirt as you go. Once you have the tube as full as you want, set the CBSQ. After the concrete is set (give it a day), cut the top 6" of the tube off.

Just the sonotube itself won't be a large enough footing for your deck.
 
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Old 06-25-07, 07:12 PM
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Thumbs up

Ooops,

Lefty, thank you for your infor. I'm in NJ. The 3 feet is most people use here.
I did not know I should dig a square block under the sonotube. This will involve a lot of digging and burying afterwards. I will check with the code office to see if they will give me some direction.

Thank you all again.
 
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Old 06-17-12, 02:11 PM
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help!

hey all
what if i want to order a cement truck how much sq metre should i order ?
i have 24 sonotube 18 10" dia and 6 12" all 4' length
 
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Old 06-17-12, 07:59 PM
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razik,

Unless things are vastly different up there than down here, you'll need to order your mud in Cubic Metres, not Square Metres. My cheapo calculator says you'll need a total of 2.14 C.Y. or 1.64 C.M. Just order 2 C.M. to hopefully avoid a small load charge--maybe you could use the extra to fill your neighbor's empty garbage cans as payback for his barking dog keeping you up all night.

OK, just kidding. But it wouldn't hurt to have something else formed up to take the excess, like a sidewalk widening or extension, downspout extensions, etc.
 
 

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