Most wood fence posts don't fail because the wood was bad. They fail because of how they were set. One of the most common culprits is something we call teacupping, and you usually can't see it until the fence starts to lean.
What is teacupping?
Teacupping is a shortcut some installers take to save time. Instead of setting the post at the bottom of the hole and cutting it to height later, they:
- Pour dry concrete mix into the bottom of the hole first.
- Set the post on top of that concrete, raising it until the top lines up at the right height, so they never have to cut the posts.
- Fill around the post and add water.
It looks fine on install day. But the bottom of the post is now sitting in a cup of concrete, with concrete underneath and all around it. When it rains, water runs down the post and into the gap between the wood and the concrete. The concrete cup has no drain, so the water just sits there against the bottom of the post. The wood stays wet and rots out quickly, often within a few years instead of the many years a properly set post should last. On Front Range clay, which already drains slowly, it's even worse.
The problem gets worse with a flat or dished top on the concrete, or concrete finished below the dirt line, because even more water funnels down along the post.
Signs your posts may be teacupped
- Posts that are soft, dark or spongy right at the ground line.
- Water standing around the base of posts after rain or sprinklers.
- A fence that's only a few years old but already leaning or wobbling.
- Posts that snap off at ground level in a windstorm, leaving the stump in the concrete.
How posts should be set
- Dig deep enough. We set posts about 3 feet deep in concrete. See fence posts in Colorado clay and rock.
- Put dirt in the bottom of the hole first. Never start with a layer of concrete.
- Set the post down into the dirt, at least a couple of inches deep.
- Pack the dirt tight around the post. Tamp it down firm so the post is solid before any concrete goes in. Because the post sits in dirt instead of concrete, there's no cup underneath for water to pool in.
- Then add the concrete around the sides to hold the post firmly.
- Cut posts to height after they're set, instead of propping them up on concrete to line up the tops.
- Crown the top of the concrete. Slope it up toward the post, finished slightly above the soil, so water runs away from the post instead of pooling.
- Keep dirt, mulch and sprinklers away from the base after the job is done. See how to make a cedar fence last.
For the longest life, skip the wood post altogether. We install PostMaster steel posts that won't rot at the ground line. See building a fence for Colorado wind.
Keep an eye on your contractor
Post setting is the part of the job that's buried and hard to check later, so it's where shortcuts happen. Questions to ask before you hire anyone:
- How deep will the posts be set?
- What does the post sit on at the bottom: packed dirt, or concrete?
- Do you cut posts to height after setting them?
- How do you finish the top of the concrete?
- Do you offer steel posts?
If you're home during the install, it's fair to watch a few posts go in. If you see dry concrete going into the hole before the post, ask about it. A good crew won't mind.
Already have teacupped posts?
If only a few posts are soft or leaning, they can often be replaced without tearing out the whole fence. Catching it early is much cheaper than waiting for a section to blow over. See our fence repair page, or ask for a free estimate and we'll take a look.