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What you need:
  • Shovel
  • Sand
  • Concrete mix
  • Wheelbarrow
  • 2 x 4's
  • Spirit level
  • Stakes or rebar
  • Chicken wire, metal hardware cloth, or remesh
  • Sealer/curing compound (optional)
A concrete slab provides a long-lasting foundation for an outdoor generator, garden machinery, woodpile, etc. Laying a concrete slab is easy. Once you have decided on size and placement, excavate an area a few inches wider and longer than the future slab's shape, and 4" to 5" deeper than the finished grade.
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Fill the hole with sand to serve as a firm base for your slab. If the finished grade is to be at ground level, fill to 3 " from the top of the hole. If the grade is to be higher, you can fill the hole to the top. Smooth out the surface using a spirit level and a straight board to make it flat and level.
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Next, compact the sand. If you are pouring a large slab, such as for a walkway or patio, rent a plate compactor for this job. For smaller slabs as shown, just spray the sand with water (Sand packs down about 90% when wet, which is sufficient for a slab of this size).
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Construct a form for the concrete. 2" x 4" lumber works great for this, since the average concrete slab is 3" to 4" thick. Set the form over the compacted sand. Check that the form is level, and adjust as necessary.
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With the form in position, drive rebar or stakes into the ground around the outside to keep it from moving or bowing out when filled.
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Mix concrete in a wheelbarrow and fill the form halfway. Place chicken wire, metal hardware cloth, or remesh on top of the poured concrete to reinforce the slab and keep it from breaking apart in the future.
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Now fill the form the rest of the way up with concrete. You want to slightly overfill the form.
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Use a 2" x 4" that is wider than the form to settle the concrete by chopping downward onto the form. This will disrupt air pockets and cause the aggregate material in the concrete to sink to the bottom, leaving a smoother surface on top. Use the same 2" x 4" to further smooth the surface by sliding it back and forth across the form. This action is called screeding.
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Fill any holes or low spots that develop from the settling and screeding process using fresh concrete. Smooth the surface again using a magnesium float.
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If desired, apply a beveled edge as the concrete is starting to set by going around the sides of the form with a concrete edger. Cure the concrete so it will continue to gain strength. You can spray the slab with an acrylic curing product, or cover with wet sand.
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After the concrete has set for two days, you can remove the form. Be careful when doing so, as the concrete will be very soft for the first week or so. Wet the sand covering for up to 28 days for maximum strength.