How to Pour a Concrete Slab or Foundation Like a Pro Home Builder

Start by clearing the site of any trees, shrubs, underbrush, stumps, large rocks, or pieces from any former construction. Position the slab site parallel to the lot line, then drive four stakes into the ground to roughly indicate the site’s corners.

"Be extra careful to remove all the stumps and large roots. Over time, they will decompose and cause sinkholes if not carefully removed and properly filled in with new compacted material," says Matt DiBara, Angi Expert Review Board member and owner of DiBara Masonry.

Next, you’ll create forms for the foundation's footings, which are wooden frames used to hold the concrete in a particular shape when poured. Anywhere from 16- to 20-inch-wide footings are enough to handle the weight of a typical home. You may need larger footings and forms if you live on volatile ground or your home is expansive.

Cut boards of forming lumber to the length of each side of the site and nail them to your wooden stakes. Brace the forms with additional vertical wooden stakes and kickers angled into the ground every 2 feet around the outside. Measure carefully to ensure that you set each board at 90 degrees from the ones it’s nailed to. Save the straightest boards for the top form so the edge is nice and straight.

Using a line level and string or a builder’s level, measure down in multiple spots to see whether the site is sloped. Hire a professional excavator or use a skid loader to add or remove soil, build up low sides, or dig out high sides. Add a solid layer of gravel fill on top of your soil for the slab to sit on.

Pack the fill down solidly using your plate compactor, sloping it down in a 12-inch deep by 12-inch wide trench along the perimeter so the edges of your slab will be thicker. Cover the fill with the plastic sheeting.

Depending on the slab’s thickness, you may need rebar to reinforce the concrete. With your fill in place, set metal stakes around the perimeter of your wooden forms, about 4 inches in. This will form a second perimeter for two rebar bands, strengthening your slab.

Cut the rebar using a metal-cutting blade, bend it, and splice lengths together using tie wire until you’ve created two rebar perimeters set on top of each other. Next, lay a grid of rebar to partition the slab. Space the rebar 4 feet apart over the plastic sheeting, running the length and width of your site. Connect the intersections with tie wire.

Arrange to have concrete delivered on a day with a mild forecast. Avoid hot days, high winds, and rain. Check again to ensure that your forms are square, level, and well-braced, and have a few strong friends or contractors on-site to help with the pour. Concrete will be poured directly into your forms, which should keep it contained.

Drag a long, straight 2-by-4 screed board across the top of your forms to level the concrete, also known as screeding. It’s best to check your screed board using a string line to ensure it’s completely straight. Simply hold the spring line from end to end to verify. Make multiple passes until the concrete is flat. 

Have one of your friends or contractors add or remove concrete in front of the screed board as needed as you pull it. Next, push a bull float across the screeded concrete to flatten it, keeping the leading edge slightly elevated. 

Pull the float back across when you reach the far side of the form. Do this up to three or four times across the entire surface. Water may bleed out onto the surface, so wait for it to disappear and for the slab to harden slightly before rounding off the slab edges with an edging tool. Work the tool between the slab and the forms until all edges are smooth.

Wait until the concrete can support your weight to finish the surface. Kneeling on squares of foam insulation, use a magnesium float to smooth out bumps, dips, and pebbles left by edging and leveling. You may need to put some pressure on the float if your concrete starts to harden.

To achieve a smooth finish, follow up hand floating by troweling with a steel trowel. For a rougher, nonslip finish, skip troweling and drag a push broom over the surface for a broom finish.

Your concrete slab should take between three and 10 days to cure, during which time you’ll want to keep it moist. This will allow it to cure slowly and develop maximum strength. Spray your finished slab with a curing compound in a regular garden sprayer, following your product’s instructions on the label. Once the curing process is complete, you can carefully strip off the forms.

Finally, you can waterproof the slab by adding a sticky rubber substance called an elastomer.

This substance retracts water so it can't seep into your walls or foundation and cause damage. Apply the elastomer with a roller or brush.