mix it or pre-mix concrete?

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  #1  
Old 04-11-09, 01:08 AM
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mix it or pre-mix concrete?

I want to add a 4", 90sf slab to an existing patio in my backyard and I'm thinking of mixing the concrete myself, since I was told that it was the cheaper way to go, but I dont know how much cement, sand and gravel I would need for the project. Or should i just take the "easier" route and buy the pre-mix 90lb bags of concrete? Also, would I need rebar or expansion joint since two of the sides will be connected to the existing concrete patio?

I'll appreciate any answers I recieve. Thanks.
 
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Old 04-11-09, 05:06 AM
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How much help will you have?

Bud
 
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Old 04-11-09, 08:26 AM
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According to two different concrete calculators it will take approx 40 or so 90 lb bags.the calculators vary a bit but range around 3500 lbs.

So yeah how much help do you have? A 80-90 lb bag of concrete(varies by brand) makes 2/3 of a cubic foot.I have concrete calculators from both sakrete and quikrete that say you need that many bags.(Don't doubt them they are probably older than you are) and I've sold this stuff for many years.

Obviously premixed would be easier and faster but I assume cost more.I've never dealt with premixed.

Bagged would allow you to sort of do it on your own time a few bags at a time etc.If you go with bagged see if you can find a supplier that will work with you on a pallet.The pallet will have more than you need but the price break might work out better.Pallet quantity is probably close to what you need.
 
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Old 04-11-09, 08:34 AM
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No concrete pro, but I think thats just over one cubic yard. No way you will be able to mix that by hand and have one solid homogeneous slab. There may also be surface texture and color variations.

Either try and find one of the small load companies, or find a neighbor who also needs some.

One of the Concrete experts will be around later, I'm sure.
 
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Old 04-11-09, 10:07 AM
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Thanks for the posts guys. Im actually going to have at least 3 other guys giving me a hand. The local store carries quikrete products and if I go with the premix I'm gonna go with that brand. I'm really insterested in finding out how much of each individual material I would need if I try making my own concrete though.
Thanks,
Dad2b
 
  #6  
Old 04-11-09, 11:34 AM
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Mixing

This page may be helpful:

Creative Homeowner - Dream ~ Design ~ Create.

The paragraph below the tool list gives estimates of materials needed. Hope this helps. I would buy premixed concrete rather than mix by hand.
 
  #7  
Old 04-11-09, 01:36 PM
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90 sq ft at 4 inches thick is 1.1 cubic yards. That is a LOT of mixing. I don't know if you are just trying to save some money or just want to do this yourself, but it would be infinitely easier to call a ready mix concrete company and have them bring it to you already mixed in a truck. Then all you have to do is move it by wheelbarrow to where you need it. Believe me, it's so much easier than mixing it yourself!
When you add up the cost of individual bags, the hassle of transporting them and handling them a few times each, renting a mixer, and the labor of doing all the mixing, you'd probably be about even if you just ordered it out. Not to mention that the quality and consistency of ready mix concrete far surpasses that which you mix yourself. If you are in a freeze/thaw climate, your concrete also needs to be air-entrained, which it won't be if you mix it yourself.
 
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Old 04-14-09, 12:01 AM
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i dunno, pecos. i've had some pretty lousy ready-mix show up at job sites. the guys - or women - who run the big clamshell cranes at the concrete plants sometimes dig a little too deep and wet, or get big batches of dry sand or gravel and it takes more than the allowable water to get the desired slump.

if d2b has that many hands, they can mix it themselves. if he really is a dad to be, i'm guessing he's young enough to handle the work. just make sure you have one patient old guy for doing the finish while you clean up and hand him everything he asks for.

a ready-mix truck will carry concrete that is 6- or 7-sack per yard (a sack is a 94-pound bag of portland cement.) 6 bags of portland is plenty, 7-sack is highway strength. (and get an extra bag to practice with before game time.) you will need 1 cubic yard of sand/gravel mix. if you're getting that bagged also, that's about a full pallet, or 35 100-pound bags; so use 5 or 6 of those per sack of portland, depending on your ratio. if you're having it dumped or picking it up loose, count out 25 or 30 round-point shovels of sand/gravel per sack of portland. keep your shovels consistent.

splurge and rent a big tow-behind mixer from a big box store or a tool rental outlet - maybe one that will hold a bag of portland and 25-30 shovels of sand/mix (about 1/6 yard.) if you have the access to get it next to your form work, this is a way better tool than those little portable electric ones, 'cause you can adjust the mixer speed.

use plenty of water to start the load. mix with the mixer at as low an angle as possible, with the throttle closed to a slow speed. this lets the ingredients fall through the fins on the mixer instead of allowing centrifugal force to stick them to the bottom.

don't let it rip your arm off by catching loose clothing when you're putting half-bags of portland in there: they don't stop for meat.

make a practice batch, so you can see where the dry goods will want to stick to the mixer, and practice hosing those lumps down without getting too much water in the batch. trust me; i've mixed enough concrete by various methods to know that the first time or three you'll get dried turds that fall off of the bottom of the mixer when you dump it. put 5 gallons of water and 5-10 shovels sand/mix in first, add half yer portland, water as necessary, other half portland, finish with mix and water to consistency. let it mix for a good 10-15 minutes; there will be plenty of screed work to do while you're waiting.

so now, if you do decide to get a small ready-mix "light load," you'll know to ask for:

"6-sack, 60/40, 5/8 aggregate, 6-inch slump." 60/40 is the ratio of sand/aggregate, 5/8 (of an inch) is the size of the aggregate, slump is a test of how stiff the mix is and lets the batch plant operator know how much water to add. 6-inch slump is kind of stiff, but 8-inch slump you might be waiting all night to put the finish on it.

and remember that some dumb blue collar guy told you how.
 
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Old 04-14-09, 08:31 AM
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Buy 97 bags of quickcrete(80lbs) and several 90 lb bags of portland cement. Use a 32 oz cup to measure portland cement per bag of concrete. That'll cost you about $350.00, and a back ache for a good month. You only need 1.25 cubic yards. You can get 4 yards for the same price, from your concrete supplier pre-mixed. Less than 4 yards, they'll charge you $75-100 to deliver. 4 yards or more, no delivery charge!
 
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Old 04-14-09, 01:55 PM
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Originally Posted by Brick Guy View Post
Buy 97 bags of quickcrete(80lbs) and several 90 lb bags of portland cement. Use a 32 oz cup to measure portland cement per bag of concrete. That'll cost you about $350.00, and a back ache for a good month. You only need 1.25 cubic yards. You can get 4 yards for the same price, from your concrete supplier pre-mixed. Less than 4 yards, they'll charge you $75-100 to deliver. 4 yards or more, no delivery charge!
the o.p. wanted to know ratios for mixing concrete, so i shared my knowledge. i also helped him - and anyone else reading - understand how to order ready-mix if he wanted to go that way.

that's why they call it "skilled labor."

then again, one sack of portland per 25-30 shovels of sand/mix is kind of a difficult equation...

good point, though: warm-up and calisthenics are important if you're not used to labor.

if you choose to take "brick guy's" advice, some suppliers take exception to having to eat 3 yards of concrete. their drivers aren't stupid, and you might get a clean-up charge that would equal or exceed the less-than-load charge.
 
  #11  
Old 05-02-09, 02:09 PM
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hey guys i, i really appreciate all the advice i got.
i've actually finished my slab, along with 3 of my buddys. all it took was a yard of sand/gravel mix, 6 bags of 94 portland, three shovels and a wheel barrow. we knocked it out in a few a hours. luckily one of my buddys was really familiar with concrete so he was the brains of all of it.
oh yeah, sleeper, my wife is now 9 weeks pregnant and should be due in early december.
thanks again ya'll!
 
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Old 05-02-09, 02:26 PM
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Congratulations on both accounts.

Bud
 
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Old 05-04-09, 07:10 AM
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yeah, congratulations.

so how does it look? got a link to some pictures?

the patio, i mean.
 
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