It has been awhile since I wrote about fence posts, but a buddy asked about replacing some a few weeks ago, so I decided it was time again.
His dilemma is that he’s replacing posts that were replacements for previous posts, and those replacements were set in concrete. Apparently, removing the original posts left very large holes, which the previous fence builder filled with concrete.
So my buddy is dealing with a lot of concrete.
First rule, gang: Do not set wooden posts in concrete.
Look, no matter what preventative steps you take (and I’ll get to those), eventually wooden posts rot, and eventually you’ll have to set new ones. Not only does burying them in concrete make for more work down the line, it actually can speed up the rotting.
The concrete creates a collar around the post, and because different materials expand and contract with mosture and temperature at different rates, inevitably a little space develops around the post.
Water loves to seep into little spaces.
But it doesn’t seep out because the concrete is not just a collar; it’s also a cup.
And cups hold water.
If you have a post sitting in a cup of water, is it any wonder that the post eventually rots?
This is how to set a post:
1. Dig a hole as close in diameter as you can to the diameter of the post. You
want as little wiggle room
as possible. It should come as no surprise that a standard clam-shell posthole digger or hand auger bores a perfectly sized hole for
a standard 4-by-4-inch post.
2. Dig deep. Measure the post and plan on burying at least a third of it. For a 5-foot fence, you’d want an 8-foot post and you’d need a 3-foot hole. Don’t cheat by cutting the post shorter.
3. Before you set the post in the hole, place a rock or broken chunk of concrete in the bottom — pointy end up if possible. That little footing will give the post something to stand on instead of damp soil.
4. Set the post in the hole and brace it plumb (or put a helper on the job) and in line and level with the posts you’ve already set.
If you remember to set the corner posts first, it makes it easy to run string lines between them.
5. Slowly shovel in equal parts crushed rock or sharp gravel and soil, tamping between layers, until you get to ground level. For years I’ve been using an oddly curved length of 2-by-2 to tamp with. Many use an upended shovel. All that’s needed is something long and fairly narrow.
6. When you get to ground level, pour enough of your dirt and rock mix around the post to tromp it down and make a little hill so rain will run away from the post.
7. End-grain is the enemy, which was the reason for installing that little rock “foundation” under the post. It holds that end-grain above whatever moisture might collect at the bottom of the post hole.
But you have to deal with end-grain at the top of the post, too.
You can bevel the top with a chop saw set at 45 degrees; you can buy both wooden and metal post caps at the home center; or you can make your own caps from shop scrap.
I find that pieces of 2-by-6 (actually 5 1/2-inch squares) make perfect caps. I designed a special jig so I can bevel them at 10 degrees on my table saw to create a squat pyramid, then I soak them in wood preservative for several days before tacking them to the tops of the posts.
They last about four years, but it would be longer if the squirrels didn’t chew on them.
How to defend the garden against squirrels, of course, would be a whole ‘nother column.
Send your questions to HouseWorks, P.O. Box 81609, Lincoln, NE 68501, or email email@example.com.
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