Concrete slabs are multi-purpose surfaces for homes and gardens. Used for walkways, patios, and floors, concrete slabs are inexpensive to install and durable enough to last for years. When you pour your own concrete slab, you're giving yourself a design material that is adaptive to many of your outdoor design needs, while saving money that would have been spent on a contractor.
Working With Ready-Mix Concrete
For most do-it-yourselfers, the best material for building a concrete slab is a ready-mix crack-resistant concrete product. The wet mix is poured into a prepared wood form, then left to cure. After the concrete has hardened, the sides of the form are knocked off and the slab is ready to use.
Ready-mix concrete is a blend of gravel, sand, cement, and other additives. Bagged and available in most home centers, ready-mix concrete contains all of the materials to make concrete, except for the water.
To avoid setting a reinforcing bar (rebar) for strength, buy crack-resistant ready-mix. Its synthetic fibers eliminate the need for rebar on small-scale concrete slabs.
Working concrete by hand in a wheelbarrow requires strength, organization, and speed. For this 3-ft x 3-ft slab, you will need two assistants. Two people will mix the concrete in the wheelbarrow, while the third person spreads out the mixed concrete in the form.
When to Pour a Concrete Slab
Wait for dry, warm conditions to pour your concrete slab. For most ready-mixes, the temperature should be 70° F or higher for five days after pouring. You can pour the slab in colder temperatures (50—70° F), but the curing time will be extended to seven days.
Always use breathing protection when working with dry concrete mix since it is an irritant to breathing passages and lungs. Eighty-pound bags of concrete are very heavy, so have help when moving them to protect your back. Most home centers and hardware stores also carry sixty pound bags of concrete.
Equipment / Tools
- Electric miter saw or circular saw
- Concrete hand float
- Mixing hoe
- Measuring tape
- Eye and breathing protection
- Latex or nitrile gloves
- Speed square or carpenter's square
- 3 80-pound bags of ready-mix crack-resistant concrete
- 8 50-pound bags of all-purpose gravel
- 3 2 x 4s, 8-ft each
- 4 Wood stakes
- Deck screws
- Twine or mason's line
- 16d galvanized nails, 3 1/2 in
- Vegetable oil or release agent
Roughly Outline the Slab Location
Stake the Location
With the hammer, drive the four stakes in the ground at each of the four corners of the intended slab. Run the twine tightly between the stakes to define the slab area.
Remove the Turf
Use a shovel or a turf-cutting tool to remove turf, or lawn, about 6 inches beyond your marked area. The intent is to provide yourself with extra working room on all sides.
Lay the Sub-Base
Open the bags of all-purpose gravel and pour them into the slab construction site. Use the tamper tool to compact and flatten the gravel.
Set the Concrete Slab Form
If you're building the slab forms yourself, mark off four sections of the two-by-fours each measuring 3 feet, 3 inches, and use the circular saw or electric miter saw to cut them. Drive the 16d galvanized nails into the boards to build the form. Place the form on the sub-base.
Cut four scrap pieces of two-by-four to about 12 inches long and sharpen each one to a point (one end only). Pound each stake into the ground near a corner of the form. With the cordless drill, screw each stake into a side of the form to help stabilize it.
Depending on the price of wood, renting slab forms can be less expensive than building your own, and renting can also save you time.
Coat the Concrete Form
Coat the inside of the form with vegetable oil or a concrete-form release agent, such as Kleen Kote's water-based release agent.
Wet the Sub-Base
With the garden hose, lightly wet down the sub-base.
Mix and Pour the Concrete
With the wheelbarrow, hoe, and hose, mix the ready-mix concrete according to the manufacturer's specifications. When it has a peanut-butter-like consistency, pour it into the form. Push the concrete around the form with the hoe and with gloved hands.
Using slightly more water than specified makes the concrete easier to work. Too much water will reduce the cured strength of the concrete. Only add more water if absolutely necessary. Add the water in 2 ounce increments; a little goes a long way.
Screed the Wet Concrete
With a scrap 4-foot-long piece of two-by-four, screed the top of the concrete slab. This is done by moving the piece of lumber (the screed) back and forth in a sawing motion to level the concrete and remove excess. Let the excess drop off the side for later removal.
After screeding, tap all around the outside of the form with a hammer. This will remove air and spaces on the edges that would give a "honeycomb" look.
Float the Wet Concrete
Let the concrete settle until the surface water evaporates. Then, using a concrete hand float, smooth and compact the surface of the slab.
A metal concrete trowel can be used 10 to 20 minutes after floating for a smoother finish. It can be left smooth or textured by lightly dragging a broom across the surface. An edging trowel can be used for rounding the perimeter edges for a stronger and more finished look.
Let the Concrete Cure
Let the concrete cure for about 48 hours. Keep the slab continually wet by misting with the garden hose and keep it covered with plastic during this period. Full strength is typically achieved after 28 days, though it can be walked on after the two-day period. It's best to wait 7–10 days before putting any patio furniture on the slab.
Tips For Pouring a Concrete Slab
- Be mindful of the concrete hardening time and work quickly.
- Adjacent concrete slabs can be laid—even using the same forms—to build an overall larger slab.
- Letting the concrete dry out too fast is the main cause of cracking, so be sure to keep it moist.
- Be sure to clean your tools quickly after use to keep the concrete from ruining them.
Zeleke ZK, Moen BE, Bråtveit M. Cement Dust Exposure and Acute Lung Function: A Cross Shift Study. BMC Pulm Med. 2010;10:19. doi:10.1186/1471-2466-10-19