Resetting A Post In Concrete
You’ve probably seen it before: A post is embedded in concrete, the concrete breaks, and then the post and whatever its holding up wiggles all over the place. Well, several months ago I got a call about just such a problem at a rental. And, since it was at a rental property, it wasn’t something the owner could simply “let develop”.
I took some pictures as I did the job so I could make this post for you. I’m finally getting the time to do it!
As you can see, the post held up a banister in the middle of a concrete porch. It’s held by two mounting brackets. One is fastened to the concrete stem-wall below the banister, the other holds the post from below. (Click on the images to enlarge them.)
The problem, in this case, turned out to be not broken concrete, but the use of the wrong type anchor. See the lag bolt hanging out of the middle of the anchor in the picture to the left? That is all that was holding these post anchors to the concrete. This particular post anchor was made to fasten a post to a wooden girder, not to concrete. As it aged, the torque of people swinging around the post wore on the metal (and the concrete), loosening it. So, it started to “wobble”.
The anchor at right is but one style designed for embedding in concrete that could have been chosen. It’s also the one we’ll be using for this repair; it will replace both of the old anchors, and will hold the post more securely than both of the originals combined. The bottom shows the tangs that will be embedded in the concrete. The upper ears will grip the post. Lag bolts will go in the two holes the manufacturer drilled into either side — a total of four bolts in all.
But before we can set the new post anchor we have to make a hole in the concrete large enough to receive it. The easiest way to do this is with a jack hammer, of course. In this case I’m using a miniature version. I could have sliced a nice neat square with a masonry saw, but that would have made a bigger cut that I needed, so I didn’t.
Don’t forget to wear eye protection during this phase! As you can see in the picture, there are chips and concrete dust all around the hole I’m breaking. It can, and probably will, get in your eyes too if you don’t protect them.
Once the hole is big enough — with a bit extra around the edges to make sure the concrete patch can get a good grip on the anchor — it’s time to soak it down and mix up the patch. For this job I chose a product called “Rockite” because it’s designed to bond to existing concrete without scoring and washing the old concrete with acid, and it hardens in less than thirty minutes.
That also means you have to work it fast! Make sure you mix up enough! Too much isn’t a bad thing. But with Rockite you have to do the entire job in one pour, so to little can be a disaster! Mix it up to a thick batter consistency, making sure to mix thoroughly. You don’t want any dry clumps running around in the mix. When it’s thoroughly mixed it should be like a thick batter, but thin enough not to form air pockets in the hole.
Just pour it in and let it spread out. Pour it just a little shy of completely full because, remember, you’ve got to push your post anchor down into the new concrete. If, after doing so it still looks a little shy of full, pull the post anchor up just a bit, pour a bit more of the Rockite into the hole, let it settle for a second or two, then push the anchor back down.
Now you get to take a break while you wait for the Rockite to harden. As it does it will become very hot, so be careful if you go over to touch it. The anchor can get quite warm.
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Anyway, you’ll have about enough time for lunch before you can put things back together again. If the Rockite is ready, it’ll be — well, as hard as concrete when you tap on it, though it might still be a bit warm.
At right are the before and after pictures. The “before” picture shows the original post anchor setup after I’ve removed the lag bolts. The bottom picture shows the banister back in place, attached to the new post anchor. Don’t be confused by the discolored spot on the front of the post. That’s just bare wood that was hidden beneath the old anchor. The owner didn’t want me to repaint because the entire building was going to be repainted anyway.
Good luck with you next embedded post repair!
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