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concrete patio


Re: concrete patio

20 X 15 at 6" thickness would be 5.55 cubic yards of concrete.
Not a do it yourself job unless you have a mixer and lots of help.
Don't forget rebar suspended midway up. Also I would do it in sections, say 5 x 10 with expansion joints between each section.

Re: concrete patio

I would agree as to the difficulty of the job & the calculations.

A patio could perhaps be poured at 4" thick if steel reinforcement was used---the formula is the length X width X depth in inches, divided by 324.

Thus, a 4" thick patio would require 3.71 cu.yd, or rounded off to 4.0 cu.yd.

Since there is a shade less than 1/2 cu.ft. in each 80 lb bag of ready mix concrete, this would take over 200 bags of concrete.

Consider calling local ready mix companies who can deliver the concrete by pump hose if the patio is to be located in the back of the house--it would probaby cost less to do so.

Since this is "flatwork", a simple trench the depth of the pour would contain the wet concrete--but even at that it's a lot of work & several people would be required.

Re: concrete patio

I agree with DOBBS, there is 80 square feet of concrete in a yard of concrete 4" thick. You require 3.71`yards of concrete so order 4 yards to cover the voids in the sub base. For a patio 4" is thick enough. Also, you can use # 10 or # 6 wire reinforcement instead of re-bar, it will save a few pennies. I would suggest getting a good cement contractor to do the work, he will use redi mix concrete and do it all at once. Also, ask the contractor to use a concrete saw to cut the expansion joints. You will get a much better looking job, rather than using regular expansion strips and trying to keep them straight. He will cut the patio into segements a few days after the patio is poured. Hope this helps.
Calcats ;)

A. Spruce
Re: concrete patio

I'll toss another opinion in for a 4" slab, for a patio, that's plenty. I'd also like to add that I've poured a lot of patio and sidewalk slabs at 4" and have never used reinforcing wire or rebar, it just isn't necessary for a non stressed piece of concrete. If this were a driveway, then the story would be completely different (minimum of 6" thick with wire mesh ). Expansion joints are important, however you don't have to use any type of separation material to do them, a simple seaming tool will do the trick. If you don't like that look, then pour the patio in smaller segments, allowing each segment to cure before pouring the next. Expansion joints give the slab a place to crack so that it doesn't crack throughout the field.

The calculation is width times length times thickness to determine the number of cubic yards of concrete you'll need. To make this very simple, 4" is 1/3 or .34 of a foot, so it would be 15x20x.34 = 102 cubic feet. There are 27 cubic feet in a yard of concrete so you divide 102 by 27 and you come up with 3.78 yards. If you're doing this yourself, I agree with the others about getting it truck delivered and rounding the quantity up to take care of any thickness variations in the pour. Personally, I like to have a redi-mix truck come that mixes the concrete on site rather than a batch truck that brings a single load to you. The reason for this is that a redi-mix truck will only charge you for what you use and there will be no leftovers, whereas the batch truck will charge you for any overage and you'll run short if you miscalculate. This could also be done with a U-cart hopper IF you've got help, IF the supplier isn't too far away, and IF you've built your forms properly.

I also agree that a 4 yard pour is a pretty daunting task that is not suited to an inexperienced DIY'r without the proper tools. That is not to say that a DIY'r can't pour concrete, just that you'll want to learn how to do it on a much smaller pour, say 1/4 to 1/2 yard to get the feel for working the concrete with the proper tools. Your four yard patio will require at least two people, preferably four or more with at least one experienced person on site to orchestrate and oversee the work. That experienced person can also check that the forms are properly set and the area is ready for concrete before the truck arrives. If you have much distance to go, then hiring a pump may be in order, however you can move a lot of concrete with a couple contractor sized wheelbarrows in short order.

And to end this long message, be sure that you've set your forms so that the patio slab is at least 1" below any doorway and has an absolute minimum of 1/8" per foot of fall away from the house, a 1/4" would be much better.

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