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Would 3 or 4 yards of concrete cover a 12x20 garage?

25432 Views 33 Replies 9 Participants Last post by  CJIII
I am wondering would 3 or 4 yards of concrete cover a 12x20 garage foundation with a 12''x12'' footing?
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Ayuh,... Do the math,... a yard of concrete is 27 cu. ft....

12'x 20'x how many inches,..??
For the footing, each linear foot requires 1 cubic foot of concrete. You have 60 linear feet of footer, hence 60 cubic feet required there. The slab is 240 square feet, so for a 4 inch thick slab you would need an additional 80 cubic feet of concrete, for a total of 140 cubic feet, which is a little over 5 cubic yards. Due to spillage and waste, best to order 6 yards of concrete. Unless of course your slab is not 4 inches thick, in which case you need to modify the computations.
Yes the slab is 4'' thick.
I personaly would never suggest anyone DIY there own slab. Seems ike a simple job, but it's not.
It's a one shot deal, once that truck pulls in there is not do over or just make it work.
Even the lay out, footings, height of the slab, the slope toward the front can be tricky.
Have you taken into consideration that the bottom row of siding needs to be at least 6" off of grade?
Have you concidered using stem wall constrution?
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4" slab on a 12 x20 works out to .3333x12x20 / 27 +10%= 3.256 yrds round up to 3.5 yrds if you can get 1/2 yrd ordered otherwise get 4
Better to order too much since concrete is not that costly once you reach the minimum delivery amount. Nothing is worse than coming up short if you did not have base under the slab graded as accurately as you want you pencil will be in figuring costs in advance.

Plan ahead and make sure you have something formed in advance that you ultimately need - sidewalk, apron, etc. to use up any excess. Much better than just dumping it in the wrong place.

the biggest mistake with concrete pours is to not have enough (poor concrete job with cold joints) or enough help to place it quckly if the weather turns. - Also have protection for rain or snow.

I understand that pour concrete is not a DIY job, thats why I thought about doing a wooden floor.
I figure it was 4 yards.
I figure it was 4 yards.
CJ, It would be a little over 3.5 yds for just the slab, but you said you were pouring 12X12 footings so you will need at least 6 yds like Daniel said.
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Are you pouring that with a totally flat floor? No stem wall?

For reference, my floor is took 20 yards of concrete.....oh, the footing is 18"w x 24" deep and has an 8"h x 6"w stem wall all the way around. I love that gets my walls at least 8" above the ground and on the inside....all my cabinets sit on the lip of the stem wall anchord to studs....nothing touches the floor....makes it easy to wash out the floor.

If you want to see on the garage build link in my signature.
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The reason I wont concrete is that I will be using the garage as a woodworking shop!
Going to be tight in that small an area trying to use it for a wood working shop.
Have you done a simple lay out on some graft paper to see how it's going to look.
Just been there far to many times. Built the garage, moved eveything in, find out it's to small and have to go back to working outside.
I know its small but my current shop is 10x12 shed.
CJ---I'm not a concrete guy--But I've helped a few times---you will want to cut your stakes down so the top of the form is clear----then use a 14 or 16 foot 2x6 as a screed board --

this will get you somewhat flat and smooth--

Rent a 'bull float' to get it smooth----you may be happy with that---for a good surface you will want a 'pool trowel'---that is a hand held trowel with round ends---waiting for the concrete to reach a trowel able firmness will make you nervous----do the pour on a cool day ,in the morning if possible,

Kneeling boards will be needed---
The first shed I built for myself was a 12 X 16. Once it was built I added a work bench on one side and a radial arm saw on the other plus all my other tools.
It was less then useless, and ended up using it for nothing but storage.
Something as simple as trying to lay a door flat for sanding and painting was a nightmare. Just not enough room to work around it without bumping into it.
Everytime I wanted to plane, rip a sheet of plywood, cut some 2 X 's to length I ended up outside rough cutting it.
Thanks Mike, I understand that Joe, my old shed is the sameway? Mike do I use 2x6's for form work?
You will want 2X material for the forms-------wet concrete really pushed hard--so stake it well and have a few extra stakes waiting in case something moves while you are pouring--

I hope one of the finishers chimes in ---concrete needs to set up just a bit before the troweling begins if you want a smooth finish---it's hard to describe---the one finisher I knew sat next to the freshly floated stab and ate his lunch and tested the surface with his trowel--

when the cement was 'just right' lunch was over and he laid his board onto the wet concrete and started troweling.
I hear you have to let a slab sit before troweling.
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