4x4 POSTS IN CONCRETE – HOW DO I SET THEM SECURELY?
Apr 15, 2024Railing posts that are seated in concrete below ground level are notorious for working themselves loose over time. This type of post also holds mailboxes and fences. If you secure them well, they won’t move for years!
This article shows you a great trick for making your ground posts as strong as possible. I include a short video tutorial as well.
(The ground post I strengthened in this project happens to be holding up the lower end of a handrail. But, note that this trick works for any post who’s bottom end is in the ground.)
TOOL LIST:
MATERIAL LIST:
4×4 Treated Post
50 lb. Bag Concrete
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WHY RAILING POSTS WOBBLE
Often, when I grab a handrail leading down a flight of exterior steps, it shakes in my hand. This is because their wood posts are poorly anchored into the ground. They have less support than posts attached to structural elements of a deck, porch, or house.
Generally, these railing posts are at least partially anchored in concrete. Unfortunately, the posts shrink as they dry. When that happens, they are smaller than the concrete hole that surrounds them. To make things worse, they experience a lot of leverage from people leaning on them. These effects only worsens as both concrete and post continue to degrade over time.
The technique I show below is a really great trick for preventing this problem. And it only requires a handful of exterior screws!
STEPS TO AVOID THESE PROBLEMS
MARK GROUND LEVEL ON RAILING POSTS
I assume that the hole for your post has already been dug. And that the post has been cut to length. (As a general rule, you want up to 1/3 of the post length to be below ground level. I make mine at least 20″ deep.)
Temporarily drop the post into the hole and make sure it’s standing vertically. With a pencil, draw a line on all four faces of the post, at ground level. Then, lift the post back out and find a good place to lay it down, preferably on a work table.
PARTIALLY DRILL SCREWS INTO THE POSTS
With the post lying horizontally, begin embedding your 3″ exterior screws into the wall of the post below your ground level mark. To do this, use a drill or impact driver. Only sink the screws about halfway. Ideally, drive them at a bit of an angle.
Use two or three screws for each side of the post. Will your post sit up against brick stairs, or wooden stair stringers? If so, don’t embed any screws on that side of the post. They will prevent it from sitting flush to the structure.
Are your posts free-standing? Maybe in the yard, like fence posts? In that case, embed screws into all faces of the post.
I call this process creating a “screw tree.” Of course, the tree is upside down :) ! Each exposed screw provides an anchoring point for the post when concrete is poured around it.
SET AND PLUMB THE RAILING POST
Drop your screw tree back into the post hole. Make sure nothing is obstructing it from sitting where it needs to sit. Roots, rocks, and bits of masonry should be dug out or broken off to provide ample clearance.
Position the post upright, and check it for plumb. I like to use a post level to do this. (This L-shaped tool has three spirit gauges. You just rubber band it to the post, and check the two bubbles that indicate plumb.)
When your post is where you want it, make sure it doesn’t move. If needed, tack a couple pieces of scrap lumber to it as braces. Use trim nails to hold it in place. (Later, you can easily remove them with a claw hammer.)
POUR CONCRETE AROUND YOUR RAILING POSTS
I use 50 lb bags of quikrete or sakrete for my post holes. These smaller bags are much easier to maneuver than their 80 lb cousins! Cut a gash in the top, then dump the rocky powder straight into the hole. Again, be sure your post hasn’t moved!
A lot of fence builders don’t even wet their concrete powder. They just pour it dry and let ground water slowly seep into it over the next day or two. I speed up the process by pouring some water directly into the hole first. Then I dump them mixture down into it.
You can use a long pry bar to mix the two parts down in the hole. This also helps force concrete down into little voids, making sure it is well compacted. Do about half the needed amount at first. Add more, until you’ve covered all the exposed screws.
Leave the surface of the concrete just below ground level. That way, you can hide it with dirt, bark, or mulch. (Nobody likes unsightly blobs of concrete right at the entrance to their home.)
IMPORTANT POINT:
Use a margin trowel to slope the top edge of the concrete boot downward to form a cone. This will shed water away from the post, preventing rot over time.
RAILING POSTS WRAP-UP
Repeat this process for any posts anchored into the ground. Let the concrete mixtures set up for at least a day. When the posts are ready, remove any temporary supports and test the railing for sturdiness.
I’m always amazed at how much stronger posts are with screw trees in place! And, as the post slowly dries out and shrinks, the screws will continue to ensure that the railing doesn’t lose its rigidity.
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