Pouring a Concrete Slab

Concrete slabs are found virtually everywhere. They are widely used for house and commercial building foundations. Other applications include shed floors, patios, and the deck surrounding a backyard pool. Pouring a concrete slab is just one aspect of installing a slab.

Remember the phrase “It's not set in concrete?” Well, with a slab, many things are. Everything should be accounted for in advance. Any plumbing should be stubbed out in advance. Any electrical conduit should be set prior to pouring the slab.

If any of these details are not taken care of in advance, the slab will need to be at least partially broken up to install these components. Then that section of the slab must be re-poured, a laborious process to say the least!

Map Out Your Slab

Figure out where your slab will be situated and how big it will be. Lay out the corners with stakes. Connecting the stakes with string. This will define the boundary of the slab. Make sure that boundary is true and square. You can apply the 3-4-5 method to each corner, working your way around.

Set the Footings and Steel Mesh

Take up all of the grass and other plant matter within the string lines. Smooth out the dirt and get it reasonably level. Trench around the inside of the string line. Make this trench ten inches wide and at least four inches in depth. This is called the footing of the slab. It lends strength and stability to the concrete slab.

Do you need a vapor barrier under the slab? Check your local building code. You may not need one.

Lay steel mesh in the footing and wire it together at all corners. If this is a large project like home construction, reinforcing bar (or rebar) should be used. For a patio or shed slab, lighter steel mesh is just fine. This mesh gives holds the concrete together where the pressure is.

Construct Your Form

All concrete slabs require a form. A form is basically a mold. It supports your wet concrete while it dries and cures. Use 1” X 4” boards to build your form. The perimeter string you ran before is the guide for the form.

Nail the ends of the form together. Drive wooden stakes into the ground every sixteen inches on the outside of your form to keep it straightly aligned. This will hold the pressure exerted by the concrete as it is poured.

It's critical for the top of the form to be level on all sides. Make adjustments to make this happen. Nail your stakes to the form to keep it level while you pour and finish the concrete.

Pouring the Slab

Your best bet is to use a portable cement mixer. For a very small project the concrete can be mixed in a wheelbarrow but this is usually not practical. Get the mixer in position so that the chute can dispense the concrete into the form. Start slowly pouring the concrete and work it into all areas areas of the form.

After the form is full, level it off using the edge of a 2” X 4”, working it across the top of the form in a sawing motion from one end to the other.
For a smoother finish, use a concrete float and trowel.