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How to Set Fence Posts That Won’t Rot

Keep moisture and insects from destroying your cedar fence posts

wooden fence posts wooden fence postFamily Handyman
Did your fence posts rot at the bottom? Here's how to install new ones—and avoid the problems that made your old posts rot.

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How to install cedar fence posts that last

Anatomy of a long-lasting fence post

This photo shows the five ways to make your wooden fence posts last a long time when your setting posts in concrete.

“Please see an enlargement in additional information below.”

Pick the right posts

Don’t use posts that contain sapwood. Instead, use heartwood, because it’s denser and more insect-resistant.

Treat the post with preservatives

Soak the bottom of the wooden fence posts in a wood preservative containing copper napthanate, such as Cuprinol.

Caulk around the fence post base

Apply high-quality exterior acrylic caulk, or silicone specifically designed to adhere to concrete, at the base of the post.

If your cedar wooden fence posts are rotting at the bottom, you need to replace them. The rot probably developed because the posts were installed improperly. So if you install your new posts the same way the old posts were installed, you’ll just have to do the whole thing over again a few years down the line.

Cedar has a reputation for durability, but unless a few guidelines are followed, cedar posts can fail in as few as five years. Three factors contribute to this early failure: poor drainage, low-quality wood and poor protection against insect damage. To get the most out of your new posts, here are five things you can do:

1. Soak the bottom of the posts in a wood preservative containing copper napthanate, such as Cuprinol. Available at some paint stores and home centers, this wood treatment is specifically designed for in-ground applications.

2. Place about 6 in. of aggregate in the bottom of the posthole to allow for drainage. The bottom of the post should extend a few inches into the aggregate as shown.

3. Pour the concrete so that it’s above the soil level. Trowel the top smooth and slope it so that water runs away from the post.

4. Apply high-quality exterior acrylic latex caulk, or silicone specifically designed to adhere to concrete, at the base of the post. This will seal the gap between the concrete and post that’s caused by freeze/thaw cycles.

5. Don’t use posts that contain sapwood. Sapwood is lighter in color (usually yellow) than heartwood, which is dark. Instead, use heartwood, because it’s denser and more insect-resistant.

These handy hints make everything in the great outdoors easier:

Additional Information

Required Tools for this Project

Have the necessary tools for this DIY wooden fence post project lined up before you start—you’ll save time and frustration.

  • Bucket
  • Caulk gun
  • Paintbrush
  • Posthole digger
  • Shovel
  • Trowel
  • Wheelbarrow

Required Materials for this Wooden Fence Post Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

  • Acrylic caulk
  • Aggregate
  • Cement
  • Wood preservative