# how much concrete can you mix



## tikicarver (Jan 24, 2008)

I need to pour a footing for a small addition. It is not big enough to need for a truck load of ready mix plus there is no access for a truck.
I was planning on renting a small mixer and mix a few bags at a time.
I was wondering how much time do I have between loads so I don't get a cold joint.
Also, would you start on one side of the forms and fill to the top and work your way across or just pour it in and keep adding til 
the forms are full?


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## Chris Johnson (Oct 31, 2007)

You will get cold joints if you are mixing by the bag...I promise...you can mix and mix and you will still get them. If you need more than 60 bags it's time for a ready mix truck and some wheel barrows if access is tight.

What does the building inspector or engineer think of this idea? are you planning rebar? That will help hold it together if you insist on doing the bag idea, but bags are not my first choice.


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## concretemasonry (Oct 10, 2006)

tikicarver -

You did not mention where you are (construction temperature), what a "small" addition is or what the footing dimensions are (width, thickness).

In many areas. narrow strip footings do not require longitudinal rebars and they are optional.

You can always plan for a cold joint and break up the job into reasonable if you create/form a cold joint with a shear key (2x4 vertically) and rebars embedded into each section of concrete.


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## tikicarver (Jan 24, 2008)

I'm in Hawaii. Temp never goes below 65 were I live.
The size of the addition is 13 X17. The footing is for a stem wall that will only be on two sides of the addition. There is also a slight incline of the area and we haven't decided if the one wall will have a step in it or not. If we do it with the step then I assume we can do two separate pours. 
So footing will be 16" wide x 8".


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## Chris Johnson (Oct 31, 2007)

Sorry Tiki

I'm in California, I have a habit of thinking California ways, ConcreteMasonry is good enough to recognize this and looks beyond my state lines.

Your 16"x8" footing is not a footing to me, it's a curb :laughing: 

The fact you are doing 30 l/f is not much, go ahead, use bags it's a little over 2 yds of concrete so expect it to take a while mixing but I'm sure you'll be fine.

If you have a step that is a good break point, have some #4 bar handy to wet set so a positive connection can be made if you choose to do the balance another time/day.

If you need help...it's only a 5 hour flight...arrange it on a weekend :yes:


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## tikicarver (Jan 24, 2008)

Thanks for the info.

You know, I work for the airlines and I could get you a ticket. 
Then I can sit by and watch you mix the concrete for me. :laughing:

PS, you have a formula for figuring out how many bags I need?


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## Chris Johnson (Oct 31, 2007)

You buy the ticket, I'll mix the mud...I'm serious, haven't made it to the island yet but would like to go.

Not sure on quantity, I haven't used bags in forever, memory tells me 60 bags is a yard. Next time you are by the home centers stop in and see, it tells you on the backs of the bags.

You want to send me an e-ticket or mail me a paper ticket?


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## amakarevic (Apr 12, 2007)

*how about the nation's capital ?*

chris - i got some mud mixing left to be done too and i'd be happy to fly you over to washington DC so you can visit all the museums and stuff. who wants to go to hawaii next to DC ? plus, there is hawaii avenue i'll be happy to drive you through (make sure you don't exit the truck).


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## Tscarborough (Mar 31, 2006)

42-43 80# bags to a CuYd. 3 guys with a small elec. mixer can mix and place 2 bags per 6 minutes or 20 bags per hour working hard.


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## amakarevic (Apr 12, 2007)

i would strongly discourage mixing two bags at a time in a small mixer.

reasons being is that the benefit of volume is offset by more mixing time and it is just plain easier and CLEANER to mix smaller loads at a time.


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## Tscarborough (Mar 31, 2006)

You have never mixed large volumes of concrete in bags, have you, Amakerevic?


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## amakarevic (Apr 12, 2007)

the most i've ever done in one shot was about 40.

i started with 2 at a time but figured out it was just plain easier to do 1.

took me about 5 hrs.


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## Tscarborough (Mar 31, 2006)

Here is how you do it:

Charge the mixer with enough water to a do bag and a half. Turn the mixer on, of course. Cut the top off a bag and add it to the mixer. Let mix for about 30 seconds. Cut the top off another bag and add it to the mixer. Add water if needed and mix for another 5 minutes. Dump and start over.

A 3 CuFt Mixer is plenty big enough for 2 bags, and one bag at a time is too slow to pour and too small an amount to bother placing.

The most important thing is mixer and concrete mix placement. I am left-handed, so I stack the bags to the right of the mixer waist high and move bags to the stack from the pallet as I use them. As an aside, when you empty the bags, wet them with the hose and use them as a ground cloth under the mixer. Unless you stop for more than 15 minutes, never turn the mixer off and never leave it without water or concrete mix churning.

Ideally, you have one mixer, one wheelbarrow/finisher and one bag stacker. The most I have ever done was 4 pallets in 8 hours with 5 people, grouting 12" CMU walls with buckets, but 20-60 bags is no big deal with 2 or 3 guys drinking beer on a Saturday morning.


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## comp (Jan 14, 2008)

Tscarborough said:


> Here is how you do it:
> 
> Charge the mixer with enough water to a do bag and a half. Turn the mixer on, of course. Cut the top off a bag and add it to the mixer. Let mix for about 30 seconds. Cut the top off another bag and add it to the mixer. Add water if needed and mix for another 5 minutes. Dump and start over.
> 
> ...


how was the back the next day :laughing:


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## amakarevic (Apr 12, 2007)

i have a husky portable mixer that i got at HD for $300.

dunno how many cu. ft. it is but 2 bags were doable but were also taking probably twice as long to mix, so there was no economies of scale type of a benefit.

the above described method seems too complicated. lowering half a bag of concrete and making sure it is cut so that it doesn't spill seems more attention requiring than i want to pay.

for me, mixing and pouring concrete is an exercise of routine and relaxation, kind of like yoga. i like to do it with minimal mental efforts (since physical effort is plenty), i.e. act like a robot.

one nice thing about the mixer that i have is that the braces inside ALWAYS rip a bag open themselves so i do not need to worry about busting it open as a side effort.

the machines that we have nowadays are both beauties and beasts. beauties because they eliminate so much drudge, beasts because they contribute to the alienation enabling one to do all himself without needing anyone else.


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## Tscarborough (Mar 31, 2006)

Yeah, my church is my backyard. Anyway, for less than 6 or 8 bags, I just mix it in a wheelbarrow. 2 bags at a time with a hoe and a lot more zen than I care for.


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## comp (Jan 14, 2008)

where is the thread on pouring a 4" slab ???


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