Replacing wooden fence posts.

April 24, 2011 8:02 AM

I need some advice for DIY replacement of a wooden fence.

I've got a 6' tall, old wooden fence that has started to weaken in places. In particular, some of the fence posts have rotted at ground level. Unfortunately for me, they are sunk about 2' in concrete. I've managed to dig one up completely and now have a big hole there.

1) Do non-corner posts need to be sunk in concrete?
2) The hole from the previous post is pretty wide right now. What's the best way to get it back to the right size (and compact enough) for concrete if that's the suggestion?
3) I have at least two more posts that need to be replaced. Should I dig up the concrete or just shift the positions of the new posts?
4) If the new wood is already pressure-treated, do I need to apply anything else, above ground or below?

I'm in central Texas, so not much of a frost line to worry about. Also, I don't have a post hold digger, just a shovel. Will I need to spend $50 on one just for three posts?

posted by Durin's Bane to home & garden (4 answers total)

I don't have answers to all of those questions, but here's some ideas:

2. You could get a round concrete form from your local home improvement place. It's a big cardboard tube. Put the tube in place, set the post in it & brace it upright, then pour concrete into the form around the post. When the concrete is set, tear off the form and pack dirt back in around the concrete. Make sure to pack it down well or it'll tip over.

4. Pressure-treated wood will hold up fine by itself. You may want to paint it for looks, of course. The pressure-treating doesn't get all the way into the wood, though, so if you cut the ends you'll expose untreated wood. You'll need to seal off the end with a brush-on preservative like copper naphthenate.
posted by echo target at 8:13 AM on April 24, 2011

1) I would not put the wood into the concrete, but secure the post with a Simpson Stong-tie anchor. Some don't need to be set into concrete.
2) you could use a cardboard tube to hold the concrete.
3) If you don't want to dig up the old post, and the wood above ground is solid you could 'splint' a new post adjacent to the old one.
4) Yes, I'd use treated wood.
posted by TDIpod at 8:18 AM on April 24, 2011

I'd suggest metal fence posts instead of wood -- they are lighter and easier to set in place, and they last a lot longer. The round ones are ok, but I like these (available at most big-box stores) better. If you have the option of shifting posts to the side rather than having to dig out the old concrete, that's what I'd suggest, because digging out concrete by hand is a miserable and thankless task.
posted by Forktine at 8:51 AM on April 24, 2011

The postmaster posts are OK (they're also called T-posts), but you really want to sink things into concrete or someone who comes along later will be really peeved at you when their dog knocks the entire fence over with one push on a post after the ground's been wet for a few days... or when the wind knocks the entire thing over during a thunderstorm.

We had the same problem with my fence (in College Station, incidentally... although I am not an Aggie.) You could literally push the fence over at the ground level because the base of all the posts was rotten.

The proper way to build a privacy fence in our climate is to dig a 2.5' to 3' foot hole into the ground, DO NOT clear away the auger debris around the base of the hole, put about 2' of sharp gravel in the bottom, put your post in, and fill the hole with relatively firm (not soupy) concrete until it is mounded at the top. Do not bounce the post up and down or you lose the draining effect of the gravel at the bottom; if you need to agitate the concrete after pouring it to remove bubbles (good idea) then use a wood scrap or a metal rod of some sort. When the concrete has fully set, you remove the dirt that is around the concrete plug and you have something that water/dirt will not rest on, and therefore will not rot the base. To keep the base of the pickets from rotting, the first thing you put on the 'good' side of the fence is a "rot sill", which is a 2x6 or 2x8 that the bottom of the pickets rest on. (The pickets are expensive, a 2x6 is not. Pickets are about $1.30 each; a 2x6 to go across the bottom is $8 at the most.) Attach everything with deck screws (Tan or green colored) instead of drywall or galvanized screws, or worse, nails. The screws will let you make repairs later if you need to, where nails will ruin the wood.

If your soil is anything like mine (river bottom clay), you will want to dig the hole with a gas powered auger. One can be rented for less than a hundred bucks a day from Home Depot or Redtail or whomever. You do not want to try using a post hole digger; you'll get about five feet in and want to kill yourself.

I'll be replacing my hastily erected year-old fence this coming winter with a properly built one, and I will rent a bobcat when I do it in order to pull the old concrete out of the ground and to auger the new holes to the right depth.

Note that building a fence over 6' in most cities in Texas will require a permit.

Also note: That's the proper way to do it. How you actually do it is up to you, because doing it right is a lot of work, and if you're a poor grad student living in a rental you don't need to do it right. Email/mefimail me if you need more help or info.
posted by SpecialK at 1:21 PM on April 25, 2011