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How to pour a small concrete slab

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Overview

Whether you’re creating a space for an outdoor alfresco area or putting down the foundations for a new shed, pouring a concrete slab can be a simple D.I.Y. project. We’re sharing a step-by-step guide to walk you through the basics.

Safety tip: Always wear the appropriate safety equipment (safety glasses, gloves, ear muffs and a mask, for example) and always follow the instructions for the product or equipment.

Steps

  1. 1

    Work out the location and size

    First, decide where you want the slab to go and how big you need it to be. (The size will depend on what you’ll be using it for.)
    Green Bunnings hammer
    Tip: Choosing a level location will make the job easier.
    Work out location and size.
  2. 2

    Mark the area using paint spray

    Measure out the slab and mark it down using brightly coloured spray paint. This will help you get a visual on how big the slab will be and its placement.
    Mark out using spray paint
  3. 3

    Prepare the area

    Prepare your space for the concrete by removing anything unstable or unlevel – topsoil, grass, dirt, or rocks, for example
    Scrape out the base of the slab.
  4. 4

    Cut timber to length

    Construct a frame with four pieces of timber. The inside of the box will be the slab size, so cut it longer than your spray line. (For example, 2m plus the thickness of your timber.)
    Cut the timber to length
  5. 5

    Screw the box together

    Once you’ve cut the timber, screw the corners of it together, creating a border for your slab. To ensure your box is square, measure diagonally and check that both measurements are the same. If they are, your box is squared and you’re all set!
    Cut the timber to length
  6. 6

    Place steel pickets to brace the timber

    Once your timber box is in place, remove the diagonal timber braces – you won’t need these anymore.

    Using a sledge hammer, hammer in some steel posts until they sit flush with the top of the timber. Double-check your timber box is level and square, then screw the steel posts to your timber.

    Place steel pickets to brace the timber
  7. 7

    Lay crushed rock

    Lay down crushed rock and compact it down with a tamper. The crushed rock must be at least 50mm thick once compacted.
    Green Bunnings hammer
    Tip: For bigger projects, hire a compactor in-store.
    Lay crushed rock
  8. 8

    Install the steel

    To reinforce your concrete, install some steel mesh reinforcement. Use bolt cutters or a grinder to cut it to size, making it 40mm smaller than the timber box on each edge. Place the steel into your timber box and use bar chairs to keep it off the ground.

    Install the steel.
  9. 9

    Pour the slab

    Mix up the concrete in a wheelbarrow and pour it into place. Make sure you pour at least 40mm of concrete on top of the steel mesh.

    To remove any air holes from the fresh concrete, give each side of the box a few good taps with a hammer.

    Pour the slab
  10. 10

    Screed the concrete

    Use a screed to flatten the concrete to the level and height of the box.

    Screed the concrete.
  11. 11

    Smooth the concrete off

    Use a bull float to smooth it all off. While the concrete is still partially damp, use a finishing trowel to smooth over the whole surface. Leave it to dry for at least 24 hours.
    Smooth the concrete off
  12. 12

    Edge the corners

    Use an edger to smooth off the corners so that, when the box is removed, you won’t have sharp edges. Allow the concrete to dry partially until it’s firm enough so that you can’t push your finger in, but you can see a fingerprint.

    Edge the corners
  13. 13

    Watch the full episode

    For more renovation inspiration, watch Episode 7: Backyard and Alfresco renovation in our Make It Happen: The House Project series.

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Health & Safety

Asbestos, lead-based paints and copper chromium arsenic (CCA) treated timber are health hazards you need to look out for when renovating older homes. These substances can easily be disturbed when renovating and exposure to them can cause a range of life-threatening diseases and conditions including cancer. For information on the dangers of asbestos, lead-based paint and CCA treated timber and tips for dealing with these materials contact your local council's Environmental Health Officer or visit our Health & Safety page.

When following our advice in our D.I.Y. videos, make sure you use all equipment, including PPE, safely by following the manufacturer’s instructions. Check that the equipment is suitable for the task and that PPE fits properly. If you are unsure, hire an expert to do the job or talk to a Bunnings Team Member.