How to Pour a Concrete Slab

Pouring Concrete
Gajus / Getty Images
Overview
  • Working Time: 2 hrs
  • Total Time: 48 hrs
  • Yield: 9 square foot slab, 4-inch thick
  • Skill Level: Intermediate
  • Estimated Cost: $50 to $75

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 all of your needs.

Working With Ready-Mix Concrete

For most do-it-yourselfers, the best material for building a concrete slab is ready-mix crack-resistant concrete mix. 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 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-foot by 3-foot 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 degrees F or higher for five days after pouring. You can pour the slab in colder temperatures (50 to 70 degrees F), but the curing time is extended to seven days.

Safety Considerations

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.

What You'll Need

Equipment / Tools

  • Hammer
  • Level
  • Electric miter saw or circular saw
  • Margin trowel
  • Finishing broom
  • Mixing hoe
  • Wheelbarrow
  • Measuring tape
  • Shovel
  • Tamper
  • Eye and breathing protection
  • Latex or nitrile gloves

Materials

  • 3 80-pound bags of ready-mix crack-resistant concrete
  • 8 50-pound bags of all-purpose gravel
  • 3 two-by-fours, each 8-foot
  • 4 wood stakes
  • Deck screws
  • Twine or mason's line
  • 16d galvanized nails, 3 1/2-inch
  • Vegetable oil (for cooking)

Instructions

  1. Roughly Outline the Slab Location

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

  2. 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.

  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. Build and Set the Concrete Slab Form

    Mark off four 3-foot, 3-inch long sections of the two-by-fours 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 the form.

  6. Coat the Concrete Form

    Coat the inside of the form with vegetable oil or a concrete form release agent.

  7. Wet the Sub-Base

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

  8. Mix and Pour the Concrete

    With the wheelbarrow, hoe, and hose, mix the ready-mix concrete according to 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.

  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 screed back and forth in a sawing motion to level the concrete and to 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.

  10. Float the Wet Concrete

    With the trowel and broom, float out the concrete to smooth it out and to provide texture.

  11. Let the Concrete Cure

    Let the concrete cure for about 48 hours. Keep the slab continually wet by misting with the garden hose. Keep the slab covered with plastic. Full strength is typically achieved after 28 days, though it can be used before then.

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.