Properly Setting Fence Posts
Contributed by: John Wilder
In all of the how-to magazines and how-to books in all the home improvement stores across the land, you find erroneous information about setting fence posts. People have the mistaken notion that if it is in print, then it must be right. Other construction writers who usually don’t have any “real world experience” copy and re-write the same erroneous information.
I have worked for years repairing fences as a fencing contractor. That involves replacing rotted fence posts. I am if you will a fence post archeologist. I have replaced hundreds of fence posts and the rot pattern is always the same. It occurs from the ground level down about 6 inches. There has never been any rotting below that 6 inch line.
One of the most common fallacies in print is to put gravel in the bottom of the hole for drainage. That simply does not work because the water does not drain anywhere. You would have to install drain tile to carry water away. It further does not matter because water does not rot wood. We have submerged posts holding up docks and piers for more than 50 years without rotting. We are bringing up logs from the bottom of Lake Superior which have been submerged for 100 years with no rotting. That sort of blows the claims of Thompson’s Water Seal about water damage.
When you set a fence post, you must encase it in concrete. This helps to anchor the post, but also protects it from rotting. You need to set at two feet in depth but you really don’t need any more than that.
Now some writers have actually claimed that concrete rots fence posts. They believe this because while the posts were set in concrete, they allowed soil above the concrete to touch the post. The ground contact is what rots the posts. If you have one inch of soil above the concrete, that post will rot off in that one inch. This is due to the bacterial enzyme found in soil called: cellulase. This is Mother Nature’s all purpose chemical. It is aerobic in nature meaning that it requires oxygen to work. That is why the rotting pattern only goes 6 inches deep, below that there is no oxygen. That is why seed packets warn not to plant the seed any lower than 4 inches. The cellulase also causes the seed to sprout. Cellulase also causes fallen limbs to rot in a relatively short period. It is for this reason that you must encase the post in concrete slightly above the soil line so as to protect it from soil contact.
If you have a lot of fence posts to set, I recommend that you go to the rental store and rent what is called a mini skid steer. It is easy to operate and will hydraulically dig your holes in less than 30 seconds each. You get the side benefit of saving your back and shoulders. DO NOT RENT A TWO MAN POST HOLE DIGGER! They are very dangerous. This is because there is no safety clutch. If you hit a root or a rock, which is common, all of that torque from the machine goes into your back, shoulders, arms and wrists risking injury. It is also common to get the augur stuck which is a real bear to get unstuck. The mini skid steer avoids all of that because it is hydraulically driven.
It is also imperative to check with your utilities company to have them inspect the property first for underground utilities which is always free. If you avoid getting the check and damage an underground utility, you will be on the hook for several hundred dollars worth of repair. Additionally, you want to make sure that your posts sit inside your property line. If you don’t locate the property stakes, your neighbor can force you to tear down the fence and move it.
When you set those posts in concrete, make sure that the concrete is on the soupy side. This is because the ground will commonly absorb water from the concrete. This prevents the concrete from curing properly and you will have weak easily broken concrete if you mix it stiff. You also do not want to use the mix where you pour in concrete and add water after. This is because the water does not properly mix all the way through and you will have weak concrete. This kind of concrete is also expensive, almost triple in price of conventional sack mix.
It should go without saying that you set the two end posts and run a string line between them to set the other posts to. I recommend, nailing the 2X4’s that you are going to use as stringers for the fence to be used as temporary braces to keep the posts plumb. This also keeps them from moving while the concrete is setting. You use two 2X4’s tacked in a diagonal brace fashion from the top of the post down to the ground. You do one first and then another at a 90 degree angle from the first.
You then need to let the concrete set for at least 24 hours before building your fence. If you follow my directions, your fence posts will easily last 30 years or more. Good luck on your project.
John Wilder is a Cool Old Guy from New Castle, IN who contributes regularly to helping other COG’s in many areas of life.