Setting posts

[Rio_Grande]

I have a troubled privacy fence. The posts seem to lean no matter what I do. They were tamped in with dirt and have started to break at ground level. I am going to replace 17 of them this weekend. I have set a few in sack Crete, but many folks say not to do that as it will rot them. I was thinking about using gravel with lime in it, same as we use for road base but smaller.

What is the best way to set these 4x4 pressure treated posts? Have to stay put and prefer long life out of them.

 

[Sysop]

Dig your holes a foot deeper than you need, fill and pack the hole with stone allowing someplace for the water around the post to drain into. That keeps water from settling against the post and rotting it off. If you really want to get the most time out of them, line the hole with drainfield cloth so the stone doesn't mix with the surrounding soils and maintains the highest capacity possible. Then wrap the ends of the posts with drainfield cloth. That prevents the soil from making direct contact with the wood and provides a drainage pathway around the post down into the stone below.

 

[s219]

The building inspector here actually recommends some posts be backfilled with pea gravel or fine crushed gravel (#78 or #8). It will hold the post just fine and let water drain away (as long as the soil below drains; may not work with heavy clay soil).

Concrete would be OK if you can slope or dome the top of it so that water cannot collect next to the pole. My neighbor's gate posts -- untreated pine logs -- have been in the ground for decades with no rot. He actually set them right after sawing, when the wood was still green! Used dry mix, no water, then went back a few weeks later and put a cone of concrete around the post at ground level.

I copied him almost exactly, since I had some big pines to drop and needed gate posts. I dry set the posts with sacks of quickcrete and then put a sloped "hat" around the post with dry mix and watered it in gently. It set in place. No sign of problems, though it's only been 2 years. Check back with me in 10-20!

 

[Rio_Grande]

We have about 6 set in sack Crete. They broke off when it was wet and we couldn't tamp them in tight so I put a bag of quick creat in the holes tamped it in and they haven't moved. Just don't know how long they will last.

 

[AGRIMAN]

The best thing I have used is just dry sand. I don't use any of the dirt dug from the hole. Layer the sand in and pack as you go. If the ground is wet or the sand damp, I will add in some concrete.

 

[tman1020]

Make sure u use treated wood that is rated for ground contact not just standard treated there is a difference. Dig hole 3 times size of post set post in concrete. Trowl top of concrete to a dome. This was most common method in commercial application. additionally I would wrap post with roofing tar paper or something similar. Using the gravel pack or dry set concrete in my opinion is also a good option. I have had good luck with setting 4x4 posts in 9 inch holes backfilling bottom of post with existing dirt and toping off with 1 or 2 bags of dry concrete.

 

[EddieWalker]

The worse thing you can do it put gravel in the hole with the post. All this does is give water a place to sit.

Posts rot from the process of standing water slowly drying, then getting wet again and slowly drying. You want to keep the post as dry as possible and not create a place for water to stay any longer then possible.

If you have good clay soil, you don't need concrete. If your soil freezes, you need to be deep enough to be below the freeze line where you get frost heave. What happens is the ground gets saturated with water, then that moisture in the ground freezes and it either moves the post or pushes them up. Concrete works good in poor soil, loamy soil and sand.

Dig your hole, clean it out so it's all virgin soil on the sides and bottom. Put your posts in the hole, and get it level. Then fill with concrete so there is a mound at the top that allows the water to drain away. Just about every rotten post that I've ever seen is at the base of the post, where water sat after a rain or from sprinklers. If you fill with clay, compact it as it goes in and build it up to keep the water away from it.

With the new treatment methods of treating posts, 4x4's now twist and turn pretty bad. It might be worthwhile buying 50% more then you need, and let them dry out before starting. That should give you enough straight ones to proceed. Maybe.

Eddie

 

[texasjohn]

I have given up on treated wood posts...all methods of tamping in have resulted in rot and breaking off, over time. Your lean problem exists because the soil is moving as a plastic, slowly over time. The deeper you dig, the less it will move. To solve both problems, I recommend using metal posts and sinking them at least 3 feet. I suspect that the ones you are replacing were only 1.5 foot deep to start with. Use big U bolts to attach the posts to the wood fence.

Nothing else, IMHO, will last beyond a few years, like 5 to 10. Metal posts well sunk will last 30+ years.

 

[two_bit_score]

I have a troubled privacy fence. The posts seem to lean no matter what I do. They were tamped in with dirt and have started to break at ground level. I am going to replace 17 of them this weekend. I have set a few in sack Crete, but many folks say not to do that as it will rot them. I was thinking about using gravel with lime in it, same as we use for road base but smaller.

What is the best way to set these 4x4 pressure treated posts? Have to stay put and prefer long life out of them.

Try to get creosote treated posts if you can find some. Last bunch I found was in Seguin.

Looks lie there are two distinct schools of thought on the 'gravel at the bottom' theory. I never thought it was that great of an idea myself.

If you are going with typical treated posts try to buy them at a locally owned farm & ranch supply or lumberyard that knows what people have had good luck with over the years in your area.

Square posts do warp more than round posts.

Good luck on your project and let us know where you are located.

 

[Rio_Grande]

I am in southeastern Indiana. We have clay loam but this area has been back filled witch makes it layered odd.

The ones that are coming out are pressure treated, but they did not hold up, a couple broke off the winter after they were put in. The new posts are 4x4 rated for ground contact and purchased locally from a mom and pop hardware. I even asked what I needed even though I had a decent idea.

The old ones were put in by tamping the dirt removed from the hole back in. In the springs we have heavy rains that cause part of the ground to lay wet. When replacing one this spring there was about 2 foot of water in the hole. These that we are replacing are on higher ground and shouldn't lay that wet.

These are 8 foot post we set them 3 feet 6 in in the ground. That brings them out an inch or so taller than the nail rail on the fence.

When the ground was wet I have pushed these replacement 4x4 posts in the holes the old posts came out of and they have stood for a long time. The only reason I don't try that here is the existing holes are not straight. So I figure we will auger the holes.

 

[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.