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I am trying to build (extend maybe a better word) the back patio like thisenter image description here

where the red box is where I want to add a new slab of cement. Like shown in the picture, the dimension is 18ft by 5ft-5in. This extension will be connected to the existing porch as well as one side of the house. I have watched a couple of YouTube videos on how to add a patio, but every video seems to provide a different sets of instructions. So far, the general steps are seem to be as follow:

1) Dig out the existing ground by 6 inches deep.

2) Use stakes and 2x4's to make a frame.

3) Fill the area with gravel (some videos use sand and some just fill the area with mixed cement).

4) Since the new slab is right next to the house and an existing porch, I need to put in some joint, so that the new slab will not move in case of flooding.

5) Put in rebar grid

6) Mix cement and pour it in.

7) Use another 2x4 to smooth out the top

So, my first question is, for that big of an area, should I divide it up into smaller sections (may be 3 sections of 6ft by 5ft-5in) and add in each slab individually? Next, I know that my guide is probably incorrect and/or incomplete, so can someone provide me or point me to a better guide?

Thank you.

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    You do not "mix and pour" enough concrete for a patio ; serious work . A wheel barrow makes about a cubic foot of concrete , enough for 1' X 4' area , takes about 1/2 hour. You get a concrete truck to your location or make it with paver stones. Even with truck delivery it requires 2 strong people ( minimum) to work the concrete. – blacksmith37 Mar 10 at 2:00
  • Hello, and welcome to Home Improvement. Unfortunately, this is too broad a question for our Q&A format. Please take our tour to learn more. – Daniel Griscom Mar 10 at 2:24
  • To further blacksmith's comment, if the concrete isn't poured relative to each other the curing process could have issues. Meaning for a decent size patio you might be able to break it up into 3 batches spaced 30 mins apart - 1 hour isn't terrible (still not optimal). Meaning you could need 8-12 wheel barrows and doing it in 30 mins means about the same amount of people. (Back in the day neighbors did this and I remember 15 dads helping pour a slab next to my pool as a kid) – DMoore Mar 10 at 3:21
  • Going with a depth of 6" you might need 2x8 boards unless you are not digging out completely, even still, to use 2x4's you would need to back fill so that the concrete doesn't seep under and up the back side of the form. Using 2x6's will give you a 5.5" thickness. – Jeff Cates Mar 11 at 2:18
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Okay so you're looking at 2 cubic yards of concrete (cement is a component of concrete). That is a hellovalotta concrete. If you have no experience with it, that is too big of a project to start with. Secure some experienced help for the pour. This is not optional seriously concrete is not hard to do, but you do not give it a try fingers crossed. Even if you have to pay a general laborer with some experience it will likely save you from having to rent a large breaker and a 10 yard bin.

Preparing it is a different story. Excavation of the work area is not too difficult, takes a bit of time and elbow grease and needs to be done fully before the truck arrives. They bill by time and material usually.

Also have your experienced ringer come an hour or two before the truck to ensure it's ready.

You will almost certainly not be able to match the finish or colour of the existing pad but if that's a problem, jewel stone or some other finish across both can correct that. An expansion joint is recommended. It's available at hardware stores and building suppliers. At the seam drilling rebar dowels into the side of the existing pad will help mitigate any uneven heaving. For a pad that size I'd recommend renting a power tamper and tamp the soil before laying a good 4" minimum of 3/4 run gravel. Then tamp the gravel. Your form will need to be nearly perfect and free of movement. Concrete is much heavier than water and the pressure 5-6" high concrete will make is enough to distort a poorly secured 2x4. Any defects in the wood will transfer to the finished product.

For the rebar grid you can use wire mesh, it's a 4x8' sheet with 6x6" squares. These need to be laid down on stand-offs so the mesh is approximately center of the slab. You can tie it together with zip ties if you can't find the hook loop wire ties that are made for tying rebar.

For the difference in price and the additional strength use 2x6's or even 2x8's you only need four 8' lengths be careful to get very straight pieces free of cupping and bowing.

Finishing with a 2x4 is difficult for a pro to do. You may want to look into a pole trowel.

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