Unpopular opinion: I think using a 4x4 for every corner post is overkill in some soils.

I was putting up a basic privacy fence for a neighbor in a new subdivision here in Springfield. The soil was that heavy, dense clay they have out by the new park. I figured it was tough stuff, so for the first two corner posts, I went with the standard 8-foot 4x4s and set them in concrete like always. On a whim for the third corner, I used a 6x6 post instead, thinking more mass would be even better. When we came back after the concrete cured, that 6x6 post had actually shifted slightly, while the 4x4s were rock solid. I think in that wet clay, the bigger hole I had to dig for the 6x6 just never packed as tightly, and the concrete didn't bond as well to the wider post. It made me wonder if the standard advice needs a soil check first. Has anyone else found that bigger isn't always better for post stability depending on the ground?

3 comments

3 Comments

leebrown27d ago

You're not wrong about sand, concrete can be a mess in that stuff. But I gotta push back on the clay thing a little. I've put up fences in heavy clay around here for years, and a 4x4 with concrete has never let me down if you give it time to set. That 6x6 shifting sounds like the hole was too big and the concrete didn't grip the wider post right, not that bigger posts are worse. The real trick is digging a clean hole and tamping the concrete down good, not mixing in gravel or dirt which just makes a weak base. I've seen too many fences lean after a few seasons because people try those fancy fixes instead of sticking with what works. Clay is strong and holds concrete fine, you just have to work with it instead of against it.

charles_henderson3mo ago

Remember reading about a guy who lost a whole garden fence in sandy soil because he used concrete. The water just drained away and left a brittle shell that cracked. Sometimes the standard fix fights the ground you're working with.

amy3023mo ago

Yeah, that "standard fix fights the ground" thing is so true. I had the same problem with a post in pure sand. I ended up using a mix of gravel and dirt to pack around the base, almost like making a really solid dry pack. It lets the water drain but still locks everything in place. That post hasn't moved an inch in three years, even with some wild storms.