Proper way to set fence posts?

[Fordguy64]

So one of the first projects at our new house will be putting up a fence for our dogs. We are planning on doing a split rail type of fence with a mesh to fill the gaps. My questions is how to set the posts? I've seen things from just a 10" hole with a post In it with gravel filling the rest of it. This would allow water to drain off and hopefully prolong the life of the post. I've also seen a hole filled completely with concrete. Also even a few inches of gravel on the bottom and the rest with concrete..

What's everyone's thoughts?

[philb]

Are you planning on using pressure treated wooden posts? Or metal ones? What type of soil do you have?

IMHO, wooden ones are better tamp them in. That is, dig the hole large enough to compress the earth around the post. If you use concrete around them, the expansion and contraction of the wood will usually cause the concrete to crack.

Concrete works well around metal posts.

[Fordguy64]

Treated wood posts. I honestly don't know much about the soil yet. I don't own the property as of yet.

[stevehull]

I have literally placed thousands of wooden posts. Treated is essential, but know there are different treatment levels.

The key is to have drainage below the post. I like a minimum of a 30 inch hole with 6 inches of gravel at the base. This allows water to drain away from the wood post into the gravel. Extends post life about 100%.

Do not use concrete for wooden posts - it just traps water and promotes rotting.

But the most expensive line posts you can. Many of the cheap posts at big box stores only have a very superficial rot treatment. FAR better to pay twice that big box price and get a post that will last 20 years. Expect the big box posts to last only 5-7 years and then you do the job all over again. What is your time worth . . . .

Remember, the posts need to be all in registry and this is hard to do, so use a string 6 inches above the ground and set each post about 1 inch away.

I like to pack the bottom 10-12 inches with soil and then lit rain on it to compact that soil. Then, a couple weeks later, I add another 6 inches and wait a few weeks for that to compact. Then a final fill. Lazy man's way to do superb compaction around each post!

You simply cannot tamp a 24 inch hole column of dirt with a tamper and get deep compaction, no matter HOW strong you are! You will only compact the top 6-10 inches of soil around the post. Then the bottom soil is loose and the post wobbles - fills with water, rots and fails.

Good luck!

Steve
ps be careful with gas powered augers, especially in rocky soils or where roots are. One "got away" from me once and broke a couple ribs. Caveat emptor!

[natethebrown]

I am just finishing up replacing my wooden privacy fence now, and I will tell you what I did and why. Now, I will say soil conditions may change how you do things but down here in the South our soil is mostly red clay.

First, my old fence was about 8 years old, with all the posts cemented into the ground. When I was pulling up all of the old fence posts, I noticed the wood encased inside the concrete was not rotten and in pretty good shape. Also, the very bottom of the post, exposed to the subsoil (if it was protruding from the concrete), was in pretty good shape. The old posts that were in the worst shape where the ones where the top of the concrete was below the soil surface and top soil was allowed to pile up next to the post. I had a couple of posts that were nearly completely rotted away right at their base, right where they met the concrete.

Seeing this lead me to believe subsoil contact and concrete encasement don't matter. The real issue is top soil contact for the wooden posts.

Here is what I did to install my new fence:
1) Auger-ed out ~24" deep holes.
2) Placed the post into the hole.
3) Poured concrete around the posts, but still keeping the base firm against the bottom of the hole and maintaining direct contact with the subsoil. I read somewhere that this helps the post dry out.
4) Mounded the concrete up around the base of the post to keep as much soil and water away.
5) Painted the bottom 6" of every post with Roofing Tar, sealing it off from any potential top soil contact (which I already have even after step 4).

[jeff5may]

What these two said.

When I was doing satellite installs, I learned a whole lot more about setting strong posts than most (including me) would ever want to know. With the advent of HD programming, a stable and steady dish is very important. The old SD dishes have a little "wiggle 'n wobble" room designed into them, but the new generation must be rock solid to have quality reception. An unstable pole mount equals a free return visit in most cases. DIRTFT is built into the business model on both ends.

Like Steve said, for best results, go at least 30" deep and put some gravel at the bottom, before the post goes in. This will eliminate frost heaving and up to a 6 foot fence. For an 8 foot fence, go at least 36" deep. ALWAYS dig your end and corner posts deeper than your line posts. You can get away with as little as 2" worth of drain bed below the post, but only in dry climate zones. 3 to 6 inches is the norm.

Like Nate said: if you use concrete, apply sealer to the bottom end of the wood post and mix the concrete up before it goes down the hole! Filling with water, then pouring dry concrete mix on top only ensures a shoddy job! Either way (concrete or dirt fill), the stuff still has to be compacted to make the footer rigid. Air or water in the hole is a bad thing. For easy extra strength, taper the holes so they are larger at the bottom than at ground level.

The rest of the job will be dictated by the size and scope of the project. If you have less than 6 or 8 post holes to dig, a common post hole digger will do. Any more than that, go rent an auger or somebody will be sore for the rest of the event, and it will probably not all happen in one day. Measure everything more than twice, then triple check as you lay out the job. Support all posts with temporary legs and buy a couple or more post levels. That way, your helper will have one rather than stealing yours constantly.

There is a new method of installing poles and posts to consider. Instead of using dirt, gravel or concrete to fill the hole, expanding foam is used. At first, it may seem silly, but it works very well. The main advantages to this method are related to reduction of time, material and labor. I have seen contractors finish some pretty behemoth fences in only one day using this method. In the morning, the crew shows up, lays out and drills holes, puts posts in holes with temporary supports, and pours foam. They go to lunch. After lunch, they start removing supports and assembling fence panels. By mid afternoon, trim and finishing touches go on. Customer gets home from work to inspect with foreman after crew has cleaned up and left.

[Fordguy64]

Good info guys

[DEnd]

Originally Posted by natethebrown

Seeing this lead me to believe subsoil contact and concrete encasement don't matter. The real issue is top soil contact for the wooden posts.

Here is what I did to install my new fence:
1) Auger-ed out ~24" deep holes.
2) Placed the post into the hole.
3) Poured concrete around the posts, but still keeping the base firm against the bottom of the hole and maintaining direct contact with the subsoil. I read somewhere that this helps the post dry out.
4) Mounded the concrete up around the base of the post to keep as much soil and water away.
5) Painted the bottom 6" of every post with Roofing Tar, sealing it off from any potential top soil contact (which I already have even after step 4).

Subsoil wood contact with concrete matters (sort of). Wood will only rot in the presence of oxygen, and the further you are in the soil the lower the oxygen content, especially when you have an effective air seal around the post. In other words wood rot is most likely to occur in the first 1' or so of soil anyway. Creating an air barrier moves the rot to where there is ready moisture and oxygen. The contact with the concrete allows capillary action to happen. If the soil stays wet enough you would still see rot where air can get to the wood.

For maximum life of a fence post you would ideally wrap it in a moisture and air barrier plastic, that goes above the soil and under a metal collar (galvanized steel, stainless steel, aluminum etc...) that goes about 4-6" above grade. The Post hole would be cone shaped (larger at the bottom than top) to prevent frost heave and likely filled with concrete.