Instructions on Building a Concrete Slab Foundation

Written by james j. siegel
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Instructions on Building a Concrete Slab Foundation
Building a concrete slab is ideal for building patios or other outdoor spaces. (concrete backgrond image by Alison Bowden from

Whether you are looking to build a new patio or need a place to park a vehicle, a concrete slab foundation will do the trick. Installing a concrete slab can be fairly simple if you know how to work with concrete. The most important detail of the project is to make sure that you take everything into proper consideration. This includes the dimensions of the space and the depth required for the concrete slab. Check with your local building department for important guidelines before you take on the project.

Skill level:

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Things you need

  • Tape measure
  • Twine
  • Wooden stakes
  • Shovel
  • Wood 2x4s
  • Gravel
  • Cement
  • Trowel

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  1. 1

    With a tape measure, plot out the desired dimensions of the concrete slab. Mark the corners of the proposed concrete slab by driving a wooden stake in the ground. Tie each wooden stake together with twine. You will work exclusively within this area that has been tied off.

    Instructions on Building a Concrete Slab Foundation
    Use twine to tie the wood stakes together. (twine image by pdtnc from
  2. 2

    Begin digging the hole for the concrete slab. The depth of the hole will be larger than the actual thickness of the concrete. If you are laying a 6-inch concrete slab, make sure that the hole is 10 inches deep. This will need to be done because the hole must first be covered with 4 inches of gravel.

  3. 3

    Block off the dimensions of the concrete slab with wooden two-by-fours. The two-by-fours will run along the inside perimeter of the hole and will give the concrete slab its exact shape and dimension. To keep the two-by-fours in place, drill small wooden stakes into the two-by-fours. The wooden stakes will be drilled into the outside portion of the two-by-fours facing the soil line. Drill a new wooden stake every 2 feet.

  4. 4

    Pour in the 4 inches of gravel to the excavated area. Make sure to pack it down with a shovel so the area is level. If required by local code, add mesh or metal screening over the gravel. Depending on the soil and structure being built, some municipalities will require an interior reinforcement. If so, make sure the entire area of gravel is covered with mesh or metal screening.

    Instructions on Building a Concrete Slab Foundation
    Check your local codes to find out if your concrete slab will need a mesh or metal screening for interior reinforcement. (roll of mesh image by jimcox40 from
  5. 5

    Mix a batch of concrete. Follow the manufacturer's directions on mixing the concrete and how much is needed to cover the dimensions for the slab. Once the concrete is mixed, shovel clumps in various spots over the area. Smooth out the clumps with a trowel and then add additional wet concrete to any low spaces. Do not cover the wood two-by-fours. Only fill the concrete to the top of the two-by-fours. Let the concrete dry for 24 hours.

  6. 6

    After the concrete has hardened, remove the wood stakes and two-by-fours surrounding the slab. Mix another batch of concrete and fill the empty spaces left behind by the two-by-fours. Fill these spaces until they reach the top of the existing concrete slab. Smooth out the new concrete so that it blends with the existing concrete. Let the concrete on the edges harden for another 24 hours.

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