What size earth auger bit do you use for a 4x4 fence post?

[SmallChange]

I've augured big holes, suspended the post in the hole with room below, and poured concrete to slightly above grade with a rounded top surface, with great results. Mine are now almost 40 years old and look fine.

It matters how you are attaching to the posts. If you are using prefabbed panels, and you need the post to be accurately placed (like an inch or better), your hole has to be big enough to not just fit the post but also provide you clearance within which you align the post. That belongs in your radius budget.

It also matters what the soil is like. If you have roots and rocks to deal with, they can put the auger off course. You also need to budget radius for that. Of course, you can also do more with hand tools to fix that, but it's labor intensive, so your choices for placing one post might be different than for placing 100.

 

[blehmann]

In our country, as small as the post will fit into. We normally hit rock at about a foot to a foot and a half under the surface. Three feet down, packed with the dirt and chips that came out of the hole and you will have a post that will stay straight until your grandsons are old men.

 

[Boss 302]

I didn't realize sitting a fence post could be so technical, drill a hole and sink that baby.

 

[EddieWalker]

I have a 9 inch and a 12 inch auger for my post hole digger. I bought the 9 inch because I thought it would dig faster on a project that I was using metal pile for posts. It dug too fast and I was spending more time pulling it out of the ground then anything else, so I took it off after a dozen holes and haven't used it again. The 12 inch works out great for everything I've need to do. If you are going to do a long fence line, and you want it really straight, you'll also need a good clamshell digger to adjust most of the holes after you've dug them with the auger. It's amazing how crooked those holes are after drill a bunch of them!!!!

I hate modern treated 4x4's because most of them will twist on you as they dry out. To save the environment, or whatever official reason the government came up with, the modern method requires a huge amount of water to be forced into the lumber. With 4x4's, the wood isn't large enough to withstand this and remain straight after drying six months after installing them. 4x6's do better, but if you want something to remain straight, you have to buy 6x6's or round posts.

Wood posts rot at the surface. A totally rotted out post will look brand new just six to 12 inches down. The cycle of getting wet, drying out, then getting wet and drying out again, over and over, is what rots out a treated post. The best way to keep a post dry at ground level is to create a slope next to the post. If backfilling with dirt, it need to come up the post and slope away. Over time, this usually washes away and you end up with a low spot next to the post that holds water. With concrete, build it up above grade so water runs away from the post. For those who are worried about the concrete leaving a small gap between the post as the post shrinks over time as the water leaves the post, the amount of water that gets into that space is insignificant and doesn't cause any issues.

I have no experience with foam. When it first came out, I looked at the cost and thought it was too expensive to bother with.

 

[blehmann]

2 3/8" used oilfield pipe is the way to go. One every hundred feet with t-posts in between every ten to twelve feet. I will never put another wooden post in the ground again after the wildfire of 2011 taught me a painful lesson.

 

[M59]

2 3/8" used oilfield pipe is the way to go. One every hundred feet with t-posts in between every ten to twelve feet. I will never put another wooden post in the ground again after the wildfire of 2011 taught me a painful lesson.

Please ship me 528 pieces at 10 feet per piece of oil field pipe to NC. No need to dig a hole, just drive them in.

 

[blehmann]

Please ship me 528 pieces at 10 feet per piece of oil field pipe to NC. No need to dig a hole, just drive them in.

That is exactly how my neighbor does it. I don't have the equipment for driving them and work solo, so it is not an option. If I thought you were serious, I know a guy that can supply the pipe. About $12 each plus a small freight charge.

 

[5030]

Been reading along and not commenting but... I just pulled 50 .40 retention PT posts that I set 10 years ago in 6" augered holes, 5 feet deep with 2 bags of Quick Crete in each and not one of them was rotted off and the Quick Crete came out with them and a quick wack with a sledge hammer broke off the hardened concrete which went back in the hole. Posts are still pristine and stacked behind the barn so from first hand experience I don't buy into the rotting or anything else. Didn't happen here and our water table is pretty high. Since then (now), I drive posts with my Shaver post driver instead of augering holes. Much easier and quicker.

 

[MAX-24-Dean]

I'm sure you're the first person invited to parties

Yea, but he's still right!

 

[sea2summit]

Yea, but he's still right!

But I wasn't wrong, so I'm still counting it as a win.

 

[tom3]

I suppose most of you guys have a tractor hitched auger but for anyone reading this from a search: I put in a property line split rail fence last year, number one son helped me with this. He's used a rental two man auger before so we went out to get one, old friend works there and said to get the self propelled wheeled machine, better for an old guy like me and not much more money. That machine is a jewel. Son was really surprised at how easy that machine bores the holes, especially in the pretty rugged area, no real lifting too. And I was thinking about hand digging? Might even be handier than the tractor hitch digger, and safer too I suspect. Highly recommended.

 

[grsthegreat]

You surely do not want concrete on fence posts. It will trap moisture and either rot the post, freeze and split the concrete, or both.

Well, tell that to my 30 yo fence posts. Still solid. But i mound concrete at top to displace water

 

[zzvyb6]

What do you think about using a 4" auger for the initial hole and then driving the 4x4 post with a bucket or forks ? I've been using my forks to press steel posts into virgin ground and lashing them to broken off wood posts. I can even pound them with a good amount of force by cycling the loader.
Could a wood post be driven into a pilot hole ? I hate using a 6" or 8" auger because I always need extra fill dirt or gravel, with tamping, to complete the installation.

 

[nybirdman]

In northern NY;I found if you surround with concrete;the frost will jack the post up.We just built two pole barns with6x6's in the ground.
concrete pad on the bottom,4' plastic sleeve(Home Depot) around the post 1ft.above ground level,back fill with dirt.Looks good so far.

 

[M59]

In northern NY;I found if you surround with concrete;the frost will jack the post up.We just built two pole barns with6x6's in the ground.
concrete pad on the bottom,4' plastic sleeve(Home Depot) around the post 1ft.above ground level,back fill with dirt.Looks good so far.

nybirdman,

Perhaps your posts, or at least the concrete surrounding the posts were above the frost line. Northern NY in a cold winter with ground clear of snow possibly/ probably freezes to 3-4 feet. I know one year in lower NH the ground froze to 6-8 feet on open field, free of snow, and we didn't have running water till August because water line froze.

 

[Wolfy]

The problem depends on where you live. Many people do not get frost heaves. The other thing is the copper preservative used in Pressure treated lumber since 2003, certainly is better for humans but does not last like pre 2003 wood. Ive seen pressure treated wood rot in 8 years. Its unreal.

 

[nyone]

For the past five years local utility is using foam when setting poles. They are not having poles fall over

They also use the fill the dirt back in method here. We have a 4ft frost line and none have fallen over.

I put up a firewood/tractor shed about 2yrs ago useing telephone poles and just used the pack the dirt back in method. I have even hit a few poles with my tractor with no issues.

 

[rScotty]

Streetcar,

Several huge differences in what the power company is probably using for urethane foam and what guys walking into the local hardware are going to be able to purchase. I spent 20+ years in advanced elastomers and there are many grades of urethane for many different applications. I could bore ( pun intended ) your with the details but finished cured urethane can range from glass like to foamy elastic stretchy sponge just by changing the polymerization components/ ratios.
Power company is also sinking that power pole a min of 10 feet and probably closer to 15-18 feet into the ground and they are probably using a very small overbore tolerance which all produces a tight fit and very little foam gets used.

The power company doesn't go nearly that deep. I was surprised at how shallow that power poles are set into the ground and how loose the fit. Not at all what I expected. Check it out with your local utility. None in our area are anywhere near ten feet.
I agree on the elastomers. There are lots of types, and the epoxy foam that the power company uses probably isn't available retail.
rScotty

 

[EarPlug]

Streetcar,

Now if one wants to purchase the commercial grade utility pole setting product from then I might consider running a trial of the foam on a few posts to monitor its performance. Sika does not appear to sell a commercial line of foams for setting utility poles.

Pole Setting Foam - Rainbow Technology

A hydrophobic, two-part polyurethane, expanding foam, designed to rapidly provide intermediate backfill for setting utility poles. It forms a low-density, high-strength foam that can structurally support the pole and maintain its upright positions. Hardware may be strung after 15 minutes. Serves...

rainbowtech.net

I have used the Rainbowtech products for gate posts. No sag after years. We also use the Rainbowtech products at our Sign Shop to install Post & Panel signs and they hold very will in our Colorado high wind zone.

 

[bigtiller]

Utility poles are typically 10% of the length + 2ft. So a 40' pole would be set 6', a 60' pole would be 8' in the ground.

I believe you're correct.

That's what a lineman told me after replacing all the power poles in a 6 mile stretch after the derecho in 2020 blew them all down.

10% plus 2 feet.

The new poles along highway 17 were 80 ft. long.