Author Topic: Galvanized steel fence posts in existing concrete  (Read 1555 times)


  • Stubble
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Galvanized steel fence posts in existing concrete
« on: February 03, 2018, 01:18:39 PM »
Hi all - Looking for some advice from some frugal DIY-ers on how to set our backyard fence posts properly. Someone who might have advice other than "hire contractors to do it and throw money at the problem" :)

The fence was installed by whoever flipped the house ages ago and is...let's just say... every kind of wrong.

Long story short, I have looked at a number of post materials to support our 6' high wood picket fence, which stands on a 5-6" thick exposed aggregate concrete pad, and the 12' (yes I do mean 12 *feet*) wide gate.

Wood posts have too much bend to support the gate - learned from experience. Concrete posts are too fragile under tension of a gate that heavy, and crack - learned from experience too. That's how the right and the left gate posts are installed now.

So I'm going with galvanized steel, I think. But not chain-link, ew, something like this:

All the information I'm finding online either assumes your yard is dirt or is on how to take galvanized steel (chain link) fences *out* of existing pads. But I need to set the posts where there *is* existing exposed aggregate concrete. What is the best way to do this?

1. How do I demo the existing concrete to get the posts in? Can I just create a hole slightly larger than the posts? What tools do this? Or do I have to demo a larger area and re-fill with the post set in it?

2. What kind of concrete should I use to ensure that a) I don't end up with cracks where it meets the existing concrete due to freezing and b) is strong enough to hold the posts especially for the extra-wide gate.

3. How far into the concrete should I get these posts, assuming that the fence is 6 feet tall at it's highest?

4. Or am I totally off with the galvanized steel idea? Is there something better?


  • Stubble
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Re: Galvanized steel fence posts in existing concrete
« Reply #1 on: February 03, 2018, 01:52:41 PM »
Hah, the second I post this, I find an answer.

This might work. I just need to find a drill strong enough to do it and a masonry drill bit strong enough to make multiple holes in exposed aggregate.

I've used a (rented) hammer drill before on our exposed aggregate in order to put our cane bolt into an actual hole (not just hanging out on the ground. It basically did not work. It took about-5 hours to drill one 4 inch deep hole using a hammer drill+masonry drill bit. The masonry bit got fried and was flattened and un-usable after that. I'm not sure if it was the drill itself or how DH was using it. But whatever we were doing, it wouldn't work for drilling 40+ holes.

Once I figure that one, I just have to find a place where I can buy the kind of galvanized steel fence posts I want - square, 8' tall, and thick enough to support this massive gate. Home depot and Lowes are disappointing me here...


  • Handlebar Stache
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Re: Galvanized steel fence posts in existing concrete
« Reply #2 on: February 04, 2018, 11:25:56 AM »
I would core drill a 12" round hole thru the slab, then auger excavate at least 48" down, then encase the full depth post in concrete.
Even at this, a hinged gate like that may still sag some.   If you have room, I'd consider a sliding gate that has a wheels on bottom to support it.


  • Handlebar Stache
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Re: Galvanized steel fence posts in existing concrete
« Reply #3 on: February 05, 2018, 10:41:57 AM »
The reason your fence post sagged is probably because there wasn't any cross bracing. I've hung longer than 12 feet gates on wooden posts with someone jumping on the end with no sag as long as it has cross bracing. This is easily done with some cable and some cable tensioner to tighten it that you can find in just about any hardware stores. These can easily be added after the fact to fence sagging fence posts/gates.

You do need to remove more concrete that just a hole big enough for the post because you need concrete all around the post all the way down below frost depth in your particular area. For a neat job, rent a concrete saw and cut a large square around the old fence post and then a jackhammer to remove all the concrete inside the area. One of the easiest ways to pour concrete is to get an earth tube the size of your auger and slide it down right after you make the hole and trim it to seize height wise. This prevents dirt/debris from falling back into the hole while you mix and pour the concrete.

After you pour the post hole and are ready to fill in the area that you cut out with the concrete saw and jackhammer, apply expansion joint material made specifically for that application around the smooth cut area of your existing slab. This allows for expansion and contraction of the slab without pushing against the new concrete you poured. This too can be found in most hardware stores that sell concrete supplies. It is usually a dense black fiber/foam material.

Link to show correct bracing for gate supporting posts:

Nate R

  • Bristles
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Re: Galvanized steel fence posts in existing concrete
« Reply #4 on: February 05, 2018, 11:28:12 AM »
Does the gate HAVE to be 12' wide? Could you get away with 9 and fill in the extra?

Just wondering if you're making it harder on yourself with that gate size, and no increase in utility for you.