Fence posts in wet, clay soil?

I want to install a wood privacy fence in my backyard. Soil is clay, with the additional bonus of being very wet. In some parts of the yard the soil is completely saturated after the snow melt, and this will remain until late spring.

I've dug a test post hole and it filled up with water once I got about a foot down. I'll wait to do this until the soil is not quite as wet.

What's the best thing to do in this situation? Set the 4x4 wood post in concrete? I've read if you do this, you should allow for drainage at the bottom of the post, but in my case, I would think I would have constant pocket of water there. Or do I use galvanized steel posts?

 

Is the water table always that high or will it dry out later in the year? I like using gravel under the posts. Better for the water to go to the gravel than surrounding the post.

 

I compact gravel/crushed stone into the hole around posts. There is no waiting for concrete to harden and it drains to help prevent the post from rotting.

 

The water table is pretty high throughout the year in this section of the yard. I wouldn't be surprised if the bottom half of the posts would constantly be wet.

 

Is it feasible to provide some sort of drainage for that section of the yard? It's hard to keep a post stable in wet conditions and it will lead to rot or rust of whatever post you use.

 

Yeah that's the problem -- its the lowest point in this area. I've got a drainage easement directly behind my lot.

Is this just in general a bad idea with these types of soil conditions? I don't want to put up a fence that isn't going to last very long.

 

While I've put up a half dozen or so fences, I'm a painter not a fence guy. I'm sure a fence can be made to work in those conditions but I'm not sure how. The moderator of this forum is a pro fence installer, he stays pretty busy and doesn't check in everyday but hopefully when he does he'll have better info for you.

 

We put in a PVC fence around our office.

 

Don't the PVC privacy fences still use a PT 4x4 with a vinyl sleeve slipped over it ??

 

I've lived in a farmhouse with a split rail fence in heavy clay since I was a little kid.

First, wood posts rot just below ground where you have soil + oxygen + humid air. When a post rots, you are often left with an intact 18" section of post at the bottom of the hole
If a post is waterlogged, actually underwater, it won't rot because there's no oxygen.

That being said, whether any particular post will rot, or not is really hit and miss.
I've got some 40 year old posts that are fine, while the post beside it has rotted out.
Same for the 20 year old posts

I've found that the biggest issue about whether a post lasts comes down to the grain.

If you have a circular post that is dead-center on the grain,
so that the outermost ring is a complete "O", it will last for decades.

If you have a circular post that is off center on the grain, or has a split
so that the outermost rings are incomplete "C" shapes, the posts seem to rot faster.
Seems like rot gets into the gap between rings, or follows a split.

If I were you, I'd just get regular posts, but check the grain carefully.

I guess you could pre-treat the 12" that will be at/under ground with roofing tar or several application of a penetrating water repellent stain.

 

Yeah I had thought about doing that, I read somewhere that advocated for sealing the bottom of the posts with driveway tar.

Still a good idea to set the posts in concrete? Given how wet the soil is, I was planning to just dump the dry mix in.

 

You could put a 4x4 inside the posts we used, I suppose, but we did not. FWIW, it was a split rail type fence, so maybe the 4x4 would be needed for something in the privacy type of fence due to the considerably heavier weight borne by the posts.

 

Eh, not a fan of concrete for wood posts.
Add concrete when the post is wet, then the post dries out in winter is shrinks and leaves a gap where water gets in, the water either rots the post or freezes and splits the concrete.
Add concrete when the post is dry, then the post swells in spring and splits the concrete in spring.

One thing that seemed to work, is leftover whitewashing mix; stone dust and slaked lime.
I had some mix left over after whitewashing a masonry wall, dumped the excess into the
hollows around the nearest fence posts, I've noticed those seemed to last quite a bit longer.

Part of it seems to be that stone dust, or grit, seems to pack down tightly, as a result of freeze-thaw, and the slake lime stays "sticky" and soaks into the posts.

 

I am elderly and have experience of some of the wettest soil conditions here in Co. Leitrim. I have had success with posts by soaking for 24 hours, the bottoms of the posts in creosote, then wrapping in black plastic , placing in the hole and surrounding with concrete with a COLLAR of CONCRETE up to about 3 or 4 ins. above ground level, then when dry, sealing between the post and the concrete with linseed oil putty to prevent water ingress from rain etc.I usually placed the 4 x 4 posts about 2ft. deep in the soil.

 

I've replaced half my posts with these. Z-post Inc. Go in easy, easy to attached rails to. Have a 2x6 top cap installed over 1x6 board on board pickets. Oldest ones installed about 7 years ago and are as solid as can be (of course my old 4x4 posts lasted about 14 years so...)

Some of the things I like are the rails don't work themselves out of attachment to a wood post due to expansion/movement. (They use screws to attach). During install, I don't need to brace posts as concrete is thick enough to maintain plumb. When I've done wood posts they can catch the wind during install and lean requiring support until concrete has set.

All I'll have to do when time come to replace is disconnect rails from post and reinstall. They make different kinds, some are U shaped. I like the Z-post because they have a larger flange to attach the rail to.

I also trim out the metal post with a picket so you can't tell it's metal. So aesthetically it looks fine.

 

y Here in the USA creosote is pretty much banned [25-30 yrs ago] and isn't an option for diyers.