To Mix Or Not To Mix

croatan

123

Meetre

I've always mixed it before dumping it in the hole. I don't think you'll get the right amount of water to all the concrete if you just dump it in the hole. Could cause troubles down the road.

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neolitic

Gee, I don't want to put gas
in my truck either....
Do an experiment, buy a bag,
dump it in a sonotube,
"hose it down."
Wait 7 days and take it to
a lab for testing.
Don't experiment with the
customer's property.

Answer is, it will never break
to design strength.

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shanekw1

Not to question your design but that sounds like an extreme amount of concrete to me.

9 big foot footings and 3 feet of 10" sono tube on each is not even 1.5 yds.

75 60 lb bags, my ex-partner and I mixed and poured that in 2.5 hrs.

And yes, mix first.

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croatan

...yeah prolly going to have it pre-mixed and trucked in. for a 4x4 fence post it wouldn't be a big deal but to support this deck is another story. I was just interested in what thoughts were there.

The 'extreme' amount of concrete is due to the 'uplift' parameters we have here. In other words hurricanes will blow the thing away if not for the amount of concrete. Or at least that's the reasoning behind it all.

BuiltByMAC

The labor/material expense to do this should've been considered when creating the bid. Don't shortchange your customer because "you don't 'wanna' do it"

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I couldn't begin to imagine handling that many bags of concrete - are you aware of pump services? For that amount of concrete, a pump truck would be the fastest, easiest, least invasive to landscaping way to go.

But...if you're dead set on using bags of concrete, please, please mix it before dropping in the hole. The difference between a fence and a deck is no one is gonna hold a graduation party on the top of a fence.
L I A B I L I T Y.

Mac

Tom R

Do it right = Do it once

A code to live by.

redwood

Definately mix the concrete. A fence post does not exert pressure down on the concrete like a deck.

A pump is a good way to go, if it is in your budget. You would be done in a hour or so.

I have a little electric mixer that works really well and have mixed that much concrete many times, unfortunately. The hardest part is moving the concrete from the street or driveway to the deck site.

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SLSTech

I can't believe this is even a question. Then you go into uplift requirements, hurricanes, etc... & you want to shortchange the build? Get the site ready & call in the concrete truck which would probably be cheaper than all the bags you are going to have to buy

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deck king

Have it delivered premixed, you can also verify the mix and slump, this way if there is ever a question about how you installed the project you have documentation!

croatan

Seriously..?
what does shortchanging the build have to do with anything?
My question was about the science of concrete.
I was questioning whether the concrete would harden over time just the same without premixing it.
But it doesn't matter as I've decided to bring it in premixed.

I do think that over time a bag of dry concrete mix left in a wet hole will harden. But I'm not about to test this theory on a customer's project.
Thanks for the replies

SLSTech

Sorry after reading your post & the reply - I forgot the second part about using the premix truck - me bad

I would either use the premix truck with a pump or use a mixer in the backyard

I have seen some of those fence posts in similar ground & they came out in chunks - it never mixes & hardens together properly

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croatan

SLS, no worries man...

Yeah, I wouldn't be able to sleep at night wondering about it ...

I admit: prolly a stupid idea to begin with

RobertCDF

It will fully harden yes... eventually... HOWEVER it will not have the same PSI rating. You likely will have failure.

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Warren

I'm no expert on this but I have always mixed. Seems to me that you would probably have pockets of air and such which would mean you would have places that wouldn't fully bond to each other. I also agree that the amount of water could have some adverse affect as well.

deck king

To answer your question yes, the concrete will harden and will probably harden structurally intact. Problems could arise if there is any movement of the ground ao the structure. Most of the villages ( around here) use the bag in the ground method ( they don't even add water ) for their street signs.

John Hyatt

Its a far far better thing I do today,than I have ever done before.

J.

RobertCDF

http://www.structural.net/Article/ta...5/Default.aspx
Take a look at this... should tell you what has already been said just with the proof to back it up.

Deck hack probably does not believe this report and will continue to just dump bags in the holes dry.

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neolitic

I'm sure he uses petroleum additives....
Like olive oil, and KoolAid.

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deck king

No, the correct mixture would have hydrogen in it. Petroleum would interfere with the curing process.. oh wait, in which universe are you in!