How to Replace a Rotted Fence Post
Posts are the Achilles’ heel of wood fencing. If one or two of the posts are rotted -- typically right below the ground surface -- the fence may still look invincible, but really it’s a house of cards that can easily topple in a stiff breeze. So, the time to replace that rotted fence post is now. In all honesty, it's not a fun job to replace a rotted fence post, but it’s not too technical, either -- a good “strong back, weak mind” kind of project. If you share the fence with your neighbor, hopefully he can at least contribute a strong back.
Step 1: Deal with the Fence Panels
If possible, completely remove the fence panel at either side of the post. Support the panels from below with blocks (concrete blocks, bricks, stacks of lumber, etc.) to keep them level, then remove the fasteners securing the panels to the posts. If the joints have nails that are hard to get out, simply cut through them with a reciprocating saw and a metal-cutting blade. Set the panels aside to gain unrestricted access to replace the rotted fence post.
If it’s not practical to remove the panels, add blocking below the panels on either side of the rotten post. Brace the tops of the panels, too, if there’s any chance they’ll lean once they’re free from the post. Make a simple cross brace by setting a 2x4 at an angle and screwing its top end to the top stringer (horizontal rail) of the panel and its bottom end to a stake in the ground.
Step 2: Deal with the Old Post
Extracting a post end that’s stuck in the ground can make you feel like a Lilliputian trying to pull one of Gulliver’s teeth. The good news is you have a few options. If there’s still some post sticking out of the ground, you can wiggle it for awhile to loosen it up. But chances are the post has broken just below ground level. If it’s buried in concrete, dig out around one side of the concrete footing, then beat the footing with a sledgehammer to break it up, or at least to get one side to slough off, making the remaining footing lighter and looser in the ground.
You can also take a mechanical approach with a buried post end: Set a long 2x4 across the hole. Make a lasso on one end of a cable or strong rope and cinch it around the post. Tie the other end to the board near its middle. Prop up one end of the board on top of a block, then grab the other end of the board and pull upward, using the board as a lever to yank the post free. Have a bad back? Use a bumper-type car jack to pull up the end of the board.
Step 3: Install the New Post
With the old post out of the way, hopefully you’re left with a nicely shaped hole for the new post. Clean up and enlarge the hole, as needed, using a posthole digger and/or a shovel. As a rule, the hole should be about 3 feet deep, or at least ½ the length of the aboveground portion of the post (3 feet for a 6-foot-tall fence). Add about 6 inches of pea gravel or bank-run gravel to the hole and tamp it thoroughly. Set the post in place and brace it with 2x4 cross braces so it’s plumb (perfectly vertical).
TIP: Since you have to replace only one rotted fence post at a time, it’s easy to cut the post to length before setting it; just add or remove gravel in the hole to fine-tune the installed height. Alternatively, you can trim off the top after the post is anchored in place (with new fences, cutting after setting is much easier).
Add a couple more inches of gravel, surrounding the bottom end of the post. Now the post is ready for your choice of backfill: concrete or tamped soil and gravel. If you go with concrete, overfill the hole and shape the concrete into a mound that sheds water down and away from the post (it’s also a good idea to caulk where the post enters the concrete to keep water out of this joint).
For tamped soil and gravel, start with 4 inches or so of soil, tamp it thoroughly, then add a layer of gravel, and tamp. Repeat with alternating layers, finishing with a mound of tamped soil at the top, shaped to shed water away from the post. Use a 2x4 or a digging bar with a tamping head to tamp the layers, and check the post periodically with a level to make sure it stays plumb.
Reattach the fence panels to the post using the same method as before. If the ends of the stringers aren’t in great shape, you can reinforce the connections with any number of metal framing connectors (look in the deck-supply section of any hardware store or home center). Ideally, concreted posts should be undisturbed for two or three days before reattaching the panels, giving the concrete more curing time for greater strength.
The best way to avoid spending a lot of money, as well as the need to replace rotted fence posts in the future, is to use pressure-treated (PT) lumber for the new post, and make sure it’s rated for ground contact. PT posts are stronger and more rot-resistant than cedar and redwood. They’re also cheaper. If you really want cedar or redwood to match the existing posts, choose heartwood lumber (often designated “all-heart” or “all heartwood”), which is far more decay-resistant than lower grades cut primarily or entirely from sapwood. Be sure to use hot-dipped galvanized or stainless steel fasteners to secure the fence panels to the post. Most other fastener materials can corrode in PT lumber, even if they’re rated for outdoor use.
For professional help with fence installation or repair, find a reliable fencing contractor in your area.
Philip Schmidt writes for Networx.com.
Updated April 16, 2018.
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