How to Pour a Concrete Slab

1. Outline the Slab Location

   In the desired location, use the tape measure and a rope or hose to lay out the general area of the concrete slab. Use the speed square or a carpenter's square to set the perpendicular lines.

2. Stake Out the Location

   With the hammer, drive the four stakes into the ground at each of the four corners of the intended slab. Run the twine tightly between the stakes to define the slab area.

3. 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.

4. 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.

   Tip

   After it is first poured out, the gravel sub-base will be about 1 inch too high. However, tamping will bring down the level to its correct height.

5. Set the Concrete Slab Form

   Make concrete forms from two-by-fours. Or, depending on the price of wood, you may find that renting slab forms can be less expensive than building your own.

   • Mark off four sections of the two-by-fours, each measuring 3 feet, 3 inches.
   • Use the circular saw or electric miter saw to cut the wood.
   • 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-fours 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.
   • Use a cordless drill to screw each stake into a side of the form to help stabilize it.

6. 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.

7. Wet the Sub-Base

   With the garden hose, lightly wet down the sub-base.

8. Mix and Pour the Concrete

   Mix the ready-mix concrete according to the manufacturer's specifications with the wheelbarrow, hoe, and hose. 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.

   Tip

   Using slightly more water than specified makes the concrete easier to work with. However, too much water will reduce the concrete's cured strength. Add the water in 2-ounce increments.

9. 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.

   Tap all around the outside of the form with a hammer to settle the concrete.

10. Float the Wet Concrete

    Let the concrete settle until the surface water evaporates. Then, using a concrete hand float, smooth and compact the slab's surface.

    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.

11. Let the Concrete Cure

    Let the concrete cure for about 48 hours. Keep the slab continually wet by misting it 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 two days. It's best to wait 7 to 10 days before putting patio furniture on the slab.

Concrete Slab Costs

To calculate the materials for your concrete slab, you must determine the length and width of space and thickness of the slab. This table provides an average of the costs that you can expect.

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.
• Clean your tools quickly after use to keep the concrete from ruining them.

When to Call a Professional

Large concrete slabs are difficult for do-it-yourselfers to pour. When the concrete slab exceeds 25 to 40 square feet, it's probably time to call a concrete professional.