How to prevent wood posts from rotting in concrete

Written by carson barrett
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How to prevent wood posts from rotting in concrete
Age and moisture can cause wood to rot. (Jupiterimages/liquidlibrary/Getty Images)

Wood is often used in outdoor projects such as building a fence or a deck because it's inexpensive and easy to use, and it provides a natural look that fits in with your yard. The posts for fences and decks are often encased in concrete when they are in the ground, as the concrete provides a stronger, more stable base for the fence or deck than placing the wood directly in the ground can provide. One problem with wooden posts is that they can rot due to exposure to moisture, even when they're set in a concrete foundation.

Skill level:

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Things you need

  • Pressure-treated 4-inch by 4-inch boards
  • Circular saw
  • Safety goggles
  • Mask
  • Gloves
  • Wood preservative
  • Paint can
  • Paintbrush
  • Gravel
  • Wooden post sleeves
  • Concrete
  • Level
  • 6-inch J-bolt threads
  • Soap
  • Petroleum jelly
  • Brackets

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  1. 1

    Cut the pressure-treated 4-inch by 4-inch boards to fit your needs. The standard rule of thumb is to make the fence posts long enough that one-third is buried in the ground.

  2. 2

    Apply a wood preservative designed for pressure-treated lumber to the bottom of the post where it's being installed in the ground. Ideally, you would pour the preservative into an old paint can and place the end of the post into the can and allow it to soak up the preservative overnight, but if time is a factor, you can apply the preservative to the end of the post, using a paintbrush.

  3. 3

    Pour 6 inches of gravel into the bottom of the hole for the base.

  4. 4

    Place a wooden post sleeve in the centre of the hole, and fill the hole partway with concrete.

  5. 5

    Check the sleeve for plumb and level, and finish filling the hole with concrete. Slope the concrete at the top of the hole down away from the sleeve to help water drain away from post.

  6. 6

    Place the post in the sleeve with the treated end going into the ground.


  1. 1

    Pour the concrete into the holes for the piers.

  2. 2

    Coat 6-inch J-bolt threads with soap or petroleum jelly to prevent the concrete from sticking to them.

  3. 3

    Sink the J-bolts into the centre of the concrete piers before the concrete hardens. Leave approximately 1 inch sticking above the concrete. Allow the concrete to cure for the time specified on the packaging.

  4. 4

    Install the brackets on the J-bolts, following the manufacturer's instructions.

  5. 5

    Place the pressure-treated beams for the deck in the brackets. Keeping the wood off the concrete can help prevent it from rotting.

Tips and warnings

  • Wear gloves when handling the pressure-treated boards, and gloves, a mask and safety goggles when sawing the wood. The chemicals in the wood that protect it from rot can be hazardous.

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