# Forum Home Renovation Fences & Screens  Best Way to Set 100 x 100 Steel Posts in Concrete?

## Ed22

Hi guys, as the title says, I've got two 100 x 100 3mm thick gal steel posts that will be concreted in holes on either side of my driveway to hang gates off. Each gate is approximately 60kgs, nothing massive. 
My question is, what's the best method to set these in place? I've looked around online, but still am not confident with the proper process.  
Is it best to compact dirt at base, pour in some gravel, drop the post in and concrete up and around. Or should I pour in 6 inches of concrete, let it set, and then place my post on top of that and then pour concrete up and around the post? 
I've also seen people mention dropping the post in after the concrete is in the hole so that it fills up inside the post. Is this completely necessary?  
I do have rubber end caps, will definitely use on the top however I considered banging one on the base and siliconing around any gap to try and prevent water ingress into the post once it's in the ground.  
Sorry for all the questions/info. I really want to avoid going to all this work, and then having one of the posts sink/move once it's in 900 of concrete.  
Any suggestions welcome.  
Cheers
Ed

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## droog

All my fence posts I set in the wet concrete.
Putting gravel in the bottom of the hole is usually when setting timber posts to allow water to drain, are you intending to leave the top of the RHS open and that is your concern for future water ingress ? I would just cap the top of the post.

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## Whitey66

The way I do it is to place some concrete into the bottom of the hole, place the post into the wet concrete but don't force it down. It is important to have the end of the post fully surrounded by concrete to prevent corrosion.  Then fill in around the post and prop it in place ensuring it is plumb, use a length of timber or similar to tamp the concrete around the post to remove any trapped air and to settle the concrete mix into the hole and around the post. Leave your posts longer than what you need them and cut the tops off at the correct height and level once the concrete has set. Knock on some post caps and job done.

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## Ed22

> All my fence posts I set in the wet concrete.
> Putting gravel in the bottom of the hole is usually when setting timber posts to allow water to drain, are you intending to leave the top of the RHS open and that is your concern for future water ingress ? I would just cap the top of the post.

  Thanks Droog. I'll give the gravel a miss then. Yep will be capping top off. Was more worried about bottom in the concrete rusting out. People seem to suggest it's commonplace with gal if not treated right. Saying that, I walk around the neighbourhood and see plenty of gal posts sunk straight into concrete with no treatment. Hopefully a few coats of rust guard should help give it a few more years.    

> The way I do it is to place some concrete into the bottom of the hole, place the post into the wet concrete but don't force it down. It is important to have the end of the post fully surrounded by concrete to prevent corrosion.  Then fill in around the post and prop it in place ensuring it is plumb, use a length of timber or similar to tamp the concrete around the post to remove any trapped air and to settle the concrete mix into the hole and around the post. Leave your posts longer than what you need them and cut the tops off at the correct height and level once the concrete has set. Knock on some post caps and job done.

  Good to know, might go this route. Would it be worth capping the bottom off to to potentially help the post not sink into the mix? Unfortunately I have already got my posts cut. With that said I have a little bit of room to play with.

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## johnc

If you are worried about the post sinking, toss in some concrete, drop in half a brick and let the post settle on the brick, that is quite effective and simple.

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## Marc

If you set SHS in wet concrete and the edge of the steel is away from the bottom of the hole some 100 mm or more, the post has no chance to sink anywhere. The edge of the SHS will be on solid concrete. Try sinking the steel post into a concrete slab. 
What kills steel post in concrete is cracks, especially when they are in a small post hole. Be generous with the size of the footing. The larger and deeper the better. If you can bend a couple of rings of reo and drop around the post as you fill the concrete, even better. 
I wouldn't put any brick under it. The brick will retain water and encourage rust.
Pre painting with a good primer for galvo, like Luxepoxy4, at least the section that goes in the concrete is a good idea. The times I did it, I used this primer and then top coated with bituminous paint, 100 mm above ground, to prevent corrosion especially with a male dog in the house. Concrete eats into galvo, dog urine even more.  https://cornellengineers.com.au/stee...gal-vs-hdgalv/  There’s a couple of issues you should be aware of:  It is well known in the construction industry that DuraGal steel and the chemicals in concrete react and fail the thin galvanised coating on DuraGal steel prematurely. Duragal steel in contact with the ground will corrode If you are casting DuraGal steel into a concrete footing, ask your structural engineer to document the precaution you need to take specific to your situation. Yes, we’re talking about keeping your galvanised steel posts out of contact with the ground, uric acid and some other chemicals. Check with your structural engineer for your project.  Also, for the structural engineers and builders, don’t forget the requirements of National Construction Code NCC2019 Clause 3.4.4.4. Duragal has to be painted if it is in an external location (ie under a house). Check out the NCC for more information.

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## Whitey66

The OP didn't say he was using DuraGal did he?
H.D (hot dipped) galvanised is the way to go for fence posts that are concreted into the ground. DuraGal just coats the outside surface with a thin zinc coating, the inside is usually only painted. DuraGal Plus has a zinc coating inside and out but it is a lot thinner coating than hot dipped galvanising.

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## droog

> The OP didn't say he was using DuraGal did he?
> H.D (hot dipped) galvanised is the way to go for fence posts that are concreted into the ground. DuraGal just coats the outside surface with a thin zinc coating, the inside is usually only painted. DuraGal Plus has a zinc coating inside and out but it is a lot thinner coating than hot dipped galvanising.

  
With the statement from the OP “I've got two 100 x 100 3mm thick gal steel posts” my assumption is that they are duragal not HDG.
Hopefully the OP will confirm.

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## r3nov8or

I painted the post inside and out with Kill Rust or something similar up to 100 above the desired depth. Filled the hole with most of the wet concrete, extra cement to the mix for strength, and made it just a little wetter than usual, so the hollow post would settle into it at the right depth with a little encouragement. Painted with exterior acrylic. i think I went down 800mm for the hole for 600mm embedment. First time with steel posts.. Happy so far... 
By the way 60 kgs sounds like a heavy gate to me. How high and wide, and what materials?

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## cyclic

> I painted the post inside and out with Kill Rust or something similar up to 100 above the desired depth. Filled the hole with most of the wet concrete, extra cement to the mix for strength, and made it just a little wetter than usual, so the hollow post would settle into it at the right depth with a little encouragement. Painted with exterior acrylic. i think I went down 800mm for the hole for 600mm embedment. First time with steel posts.. Happy so far... 
> By the way 60 kgs sounds like a heavy gate to me. How high and wide, and what materials?

  Yes I would be concerned with the posts leaning with 60 kg hanging off them 
As the Professor said, hold  weight at arms length and it is heavier than it is by your side. 
The posts should not bend ? but they will move in the hole as the concrete shrinks away from the dirt. 
Maybe ? look at over levelling 15-20 mm at the top as a counter to the weight. 
Another way with heavy gates is a wheel under each gate.

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## Ed22

Thanks for the replies guys.  
So the steel was purchased from Steel Solutions here https://www.steelsolutions.com.au/st...gr7#anchor_224 
I had a look, can't see exactly what Galvanised it is.  
So from everything you guys have said, I'll go out and get some bitumen paint and go over the rust guard with a coat or two of that.  
I'll pour a decent, healthy footing. I'll also buy some rebar and bend some squares to drop around.   
The gates are made from 50 x 50 x 2 steel tube. They have hardwood timber fastened to the face. They might not have been 60kg sorry, possibly high 40's. I did the calculations a while back and now can't remember.  
Either way the posts will be sunk over half their depth into a 300mm hole with a larger width at base of hole to keep them anchored. Should be fine. 
Thankyou for all the help!

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## r3nov8or

That all sounded great, until "300mm hole". 
Diameter?, that's good. 
Depth?, nowhere near deep enough

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## droog

> That all sounded great, until "300mm hole". 
> Diameter?, that's good. 
> Depth?, nowhere near deep enough

  
From the OP "then having one of the posts sink/move once it's in 900 of concrete."

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## r3nov8or

> From the OP "then having one of the posts sink/move once it's in 900 of concrete."

  Ah. Ok. Good. Maybe I didn't quite get to the end of #1.  :Smilie:  Cheers

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## Ed22

Ha yep, 300 diameter, should have said. 
Thanks again for the help!

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