# concrete questions

Discussion in 'Homesteading Questions' started by pcdreams, Jul 20, 2005.

1. ### pcdreamsWell-Known Member

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I'm looking for either an online calculator or the formulas to calculate how much concrete I need

I'm pouring footings 24"x24" at 8" thick.

I'm also pouring 8" piers that will be around 7' (max I hope)

and I need to figure out how much concrete to get.

how much water per 80lb bag should I figure on? We'll be hauling the water.

does anyone know where I can find sonotubes that long? I've found them only in 4' lengths locally.

2. ### Cabin FeverLife NRA Member since 1976Supporter

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Footings
2â (length) x 2â (width) x 0.67â (depth) = 2.67 cubic feet

Piers
0.33â (radius) x 0.33â radius x 3.14 (pi) x 7â length = 2.39 cubic feet

One 80 pound bag of Sakrete Contractors mix yields 0.60 cubic feet of concrete. You'll need about 8.5 bags of Sacrete for each footing/pier combination.

3. ### Nature_LoverWell-Known Member

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Here are two recent threads on the shop talk board:
Concrete calculators:

costs of concrete:

I also read somewhere around these boards that there is a compression factor when converting dry cubic yards to wet, regarding compacting out the air space in the sand. I think s/he said something like you will need approx. 11% more than actual finished size.
That's a new concept for me, but I've never done flatwork, either.

4. ### pcdreamsWell-Known Member

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Thanks CF.

Wow Thats a lot of concrete

I got 8 of these to do over vacation

5. ### mysticokraWell-Known Member

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Pre-mixed Concrete is sold by the cubic yard and a truck will usually hold up to 13 yards.

Cubic yard = 3' by3' by 3' = 27 cubic '
1 Cubic ' = 1728 cubic " (12x12x12)

Your footings 24"x24" at 8" thick. =4608 cu" or 2.66 cu'
You didn't say how many you were pouring.
Google has an on-line calculator for this.

I'm also pouring 8" piers that will be around 7' (max I hope)
and I need to figure out how much concrete to get.

The volume of a cylinder equals the (area of the base)*height = &#960; r2 h
Pi times the radius squared(in other words the area of the base)
times the height

So, 3.12 * 16 (radius is 1/2 diameter, square it)* 96"=4792 cu" or 2.77 cu'
each.

You may find in considerably cheaper and easier to order the concrete pre-mixed than to buy the bags and mix your own.
Sand cost at \$20/ton
Premixed contrete here was \$54.00/yard.

Don't take any crap off the delivery guy about how he has to get back.
Just tell the concrete company this is going to be a slow pour and they will stay there all day, if they have to.

By the way, for about \$8.00/yard you can have them add a retardent that keeps the concrete from setting up too fast. Takes about 24 hours to set up with that added.

how much water per 80lb bag should I figure on? We'll be hauling the water.

does anyone know where I can find sonotubes that long? I've found them only in 4' lengths locally.

6. ### ibcnyaWell-Known Member

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