How to prepare the ground for a concrete slab

Written by brenda ingram-christian
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How to prepare the ground for a concrete slab
You can't just pour concrete on unprepared ground. (Roman Antonov/iStock/Getty Images)

Pouring your own concrete slab is not such a difficult task with the right tools. But, if the work site is not properly prepared, your project can be a disaster. Not only should you understand the steps to properly mixing, pouring and levelling concrete, but you should take just as much care when preparing the ground before pouring to lengthen the life span of the slab and prevent cracking.

Skill level:
Easy

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Things you need

  • Gloves
  • Measuring tape
  • T square
  • Level
  • Stakes
  • Twine
  • Rake
  • Shovel
  • All-purpose gravel
  • Wheelbarrow
  • Hammer
  • Nails

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Instructions

  1. 1

    Gather your materials to prepare for the start of your project. Advance planning will save you the headache of having to stop your project and make another trip to the hardware shop.

  2. 2

    Measure and mark off the area where you want to make a concrete slab. Add 5 cm (2 inches) on each side to account for your 5 cm (2 inch) frame. This can be done using a measuring tape, a right angle, twine, and four or more sticks, depending on the size of the area. Use a T square to help create perfect right angles in the corners to ensure that your corners are square.

  3. 3

    Rake the area free of stones and debris.

  4. 4

    Dig out all grass and sod. Sakrete.com recommends digging a minimum depth of 5 cm (2 inches) -- a minimum 10 cm (4 inches) if the slab will be used for a drive or path. In an area of poor drainage, the ground should be dug deep enough to be able to add 10 or 12.5 (4 or 5 inches) of all-purpose gravel so that the concrete is not sitting in water.

  5. 5

    Level the ground using a rake and a shovel and by filling in any pockets or soft spots with the all-purpose gravel.

  6. 6

    Frame the area using 5 by 10 cm (2 by 4 inch) timber, with the narrow edge facing up. Nail the sides of the frame together for stability.

Tips and warnings

  • With any project, it is always best to measure twice, particularly when you are about to pour something permanent like concrete.
  • Slabs must be at least 5 cm (2 inches) thick or they will be more likely to break under pressure from above and below, such as when the ground swells during cold winter months.
  • Don't pour one slab against another -- use a cushion between the slabs to prevent rubbing and cracking. Sakrete.com recommends placing polythene or building paper in between adjacent slabs.

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