Setting posts

[MH8675309]

Consider using round treated posts. We use ones that are 6'' in diameter and set them at least 42" down. 60" down for a corner post that will have stress from barbed wire or similar. For the corners you need bigger longer posts (old utility poles are the best) about 9 feet long. Put the same soil back in but use a tamper to pack it in tight. You want to make sure water isn't getting into the hole and freezing. This will cause the post to slowly inch up out of the hole as time goes by. Also,round posts don't warp like square ones sometimes do.

 

[Mace Canute]

Before you can make decisions about preventing rot you have to know what causes it. From What Causes Wood to Rot? - Professional Deck Builder Magazine

Wood rot is caused by several kinds of fungi. Mold and stain fungi primarily discolor wood and doesn't cause any significant loss in strength. Decay fungi, on the other hand, actually break down the cellular structure of wood, which does cause significant strength loss. They do this by secreting enzymes or producing chemical reactions that dissolve some of the constituents of wood cell walls. The activity of decay fungi is apparent when the wood becomes either darker or lighter than surrounding wood, develops checks and cracks in the discolored area, and is obviously softer or more brittle than solid wood.

Decay fungi are primitive plants, and like most other organisms, they require four basic conditions to survive. In some respects, they need the same things that people need to live:

Oxygen. In most cases, the air needs to contain at least 20 percent oxygen for decay fungi to operate.

Water, but not too much. Water is essential for all living things, and decay fungi are no exception. Wood is porous and can hold water, much like a sponge. If there is only a little water present in the wood, the fungi cannot survive. If there is too much, it can deprive the fungi of the oxygen it needs as in the case of the logs in your question, which were completely submerged under water that had a low oxygen content. A moisture content of 20 percent to 30 percent provides sufficient water for fungi while allowing oxygen to be present within the wood cells.

Moderate temperatures. The ideal temperature for decay fungi is between 70 degrees F and 90 degrees F. Most decay fungi die when exposed to temperatures above 130 degrees F and become dormant at temperatures below 40 degrees F.

Food. In this case, the food for the fungi is the wood itself. In addition to being a food source, wood shelters the fungi, insulating it from temperature extremes and providing a reserve of oxygen and water.

All of the above conditions must be met in order for decay fungi to thrive if even one is removed from the equation, fungi cannot attack the wood. Although we can control moisture to some extent, it is difficult to completely keep water, oxygen, or favorable temperatures from affecting wood used outdoors.

Depriving the fungi of its food source by using chemical wood preservatives that make wood inedible to decay fungi is the traditional method of wood protection. The pressure-treatment process drives such preservatives deep into the wood fiber. New methods being developed seek to modify the wood fiber itself with heat or by creating a barrier that decay fungi cannot penetrate.

I used to build power lines and preventing pole rot was a prime concern of the electric company. The best method was using a pressure treated pole and tamping it in solidly to ground level (and a tad more) to prevent water from pooling around the bottom of the pole. Using clay from the hole as filler (and not any of the top soil) allowed us to get good compaction without any voids from the very bottom of the hole all the way up which was quite important, especially in the top foot of the hole. Most rotted poles I saw were rotted at ground level down to about 6 inches below.

Whenever I plant a post I always make it a point to apply a few extra coats of additional wood preservative to the portion that is buried in the ground. Cheap to do and seems to help extend the life of the posts. If it actually doesn't I'm not out much, just a few $ and a little time. The 4x4 posts from the lumber yards aren't what you would call over treated. I had to replace my 4x6 gate post last year and had to trim it somewhat to fit and had to cut a half inch off the 6 inch dimension top to bottom. It was quite disappointing to see the very shallow penetration of the factory wood treat.

 

[whistlepig]

I have fence posts set in concrete and fence posts that are set in tamped earth. The ones set in tamped earth lean quickly and easily. The ones set in concrete stay forever straight and solid. With good quality treated posts I have never had an issue with them rotting. Some posts set in concrete over twenty years. When the state builds fence they use concrete on their posts. I dig the post hole, line and level the post, dump a 60# bag of Sakrete in the hole, then pour about 5 gallons of water on top of the Sakrete. I let the Sakrete harden two days then finish filling the hole with dirt tamped with a spud bar.

I have been doing it this way for decades. And I have had many folks ask me to come to their place to show them this method.

 

[tjse9006]

I'm getting ready to put up some fence for horses, should I use the 12 inch auger or he six inch auger. My initial thoughts were to use the six because it seemed like it would be stronger. After reading these replies I'm thinking it may be better to use the 12. What do you guys think?

 

[tman1020]

The size of the post determines the size of the hole. If you are setting them in concrete generally you go three times the diameter of the post. A 3 inch post =9 inch hole. If you are just setting them in dirt I would use the smallest hole that you can still compact dirt around. Remember you're not going to get your holes perfectly straight so a slightly larger hole also helps give you some room when you string line your posts to get them straight. Plus you can always dig the hole larger if it's too small or not quite lined up where you want it.

 

[EddieWalker]

should I use the 12 inch auger or he six inch auger

The smaller the hole, the less fill you will need. Of course, you have to be able to tamp the dirt down around the post after it's in the hole, so if you are filling with dirt, that might be a problem. If you are filling with concrete, it wont matter.

I've found that the real trick to doing fence posts is getting them lined up. With a three point post hole digger, there is a tendency for the auger to go in at an angle. There is also the problem of hitting a rock or a root while going down and having the auger change directions. And for me, it just seems that even when running a string line and marking where I want the holes with orange paint, I still seem to mess up and not have it where I want it once it's dug. I have a 12 inch auger and half the time, I have to adjust the hole with a clam shell digger to get the post lined up perfectly. There is no way that I would ever consider owning a smaller auger.

Eddie

 

[Gary Fowler]

I have put up board fences that the post were still solid after 20 year and the fence boards had rotted to the point of having to rebuild the fence but the post were still solid. I always use 4x4 treated and 6x6 treated for corners and gate post. I dig the hole at least 2" larger on all sides than the post and backfill with all concrete. I put in 2-3" of dry concrete fill first so the post is not setting on dirt, then set the post, square and plumb and then fill about half full with dry mix Sakrete. At this point, I add about a gallon of water to the hole and then finish filling with dry mix. The concrete mix will force out all the excess water and leave enough to hydrate the bottom half of dry mix while allowing enough water to mix with the top half to have a mud mix as it is filled. I mound up the top at least 2 inches above ground level with the concrete and slope it off each corner of the post. I have never had a post rot off from any place. This is in pure clay soil in Houston Texas area.

 

[texasjohn]

Well said, I have the same problems and comments.

The smaller the hole, the less fill you will need. Of course, you have to be able to tamp the dirt down around the post after it's in the hole, so if you are filling with dirt, that might be a problem. If you are filling with concrete, it wont matter.

I've found that the real trick to doing fence posts is getting them lined up. With a three point post hole digger, there is a tendency for the auger to go in at an angle. There is also the problem of hitting a rock or a root while going down and having the auger change directions. And for me, it just seems that even when running a string line and marking where I want the holes with orange paint, I still seem to mess up and not have it where I want it once it's dug. I have a 12 inch auger and half the time, I have to adjust the hole with a clam shell digger to get the post lined up perfectly. There is no way that I would ever consider owning a smaller auger.

Eddie

 

[texasjohn]

Gary's technique is new to me. But his 20 year experience in Houston black clay and Houston rainfall speaks for itself.

I have put up board fences that the post were still solid after 20 year and the fence boards had rotted to the point of having to rebuild the fence but the post were still solid. I always use 4x4 treated and 6x6 treated for corners and gate post. I dig the hole at least 2" larger on all sides than the post and backfill with all concrete. I put in 2-3" of dry concrete fill first so the post is not setting on dirt, then set the post, square and plumb and then fill about half full with dry mix Sakrete. At this point, I add about a gallon of water to the hole and then finish filling with dry mix. The concrete mix will force out all the excess water and leave enough to hydrate the bottom half of dry mix while allowing enough water to mix with the top half to have a mud mix as it is filled. I mound up the top at least 2 inches above ground level with the concrete and slope it off each corner of the post. I have never had a post rot off from any place. This is in pure clay soil in Houston Texas area.

 

[Rio_Grande]

Got rained out this week, maybe next.