screwing a gate post into concrete

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13684 posts

Uber Geek

#1652415 17-Oct-2016 17:11

I'm a fan of concrete screws these days - they're easy to remove and replace if you need to, but presumably if they're going to have to be 12mm and long enough to do that job (perhaps 150mm), you'll need an impact wrench to drive them in. The top of the concrete you'll need to pour will have to be dead flat and level, or you wont get the post plumb unless you pack it under the base flange - which is another reason I'd use concrete screws - then set it up and tighten, check it's plumb, remove the post and grind concrete to adjust as needed - rather than try to pack it. If it's wonky and you've used chemset anchors, epoxy and threaded rod, or dynabolts that won't come out easily, then it sound like there's plenty of potential to stuff it up and make it very hard to correct, as the bolt threads will be in the way.

It's going to have to be a very solid concrete base based on description of the size and weight of the gate - it's hard to believe that the supplier hasn't specified what's needed.

hattrick123

71 posts

Master Geek

#1652537 17-Oct-2016 21:33

Firstly thank u all! Alot of this is new to me, so excuse my level of detail. Bought of trademe so no spec on install provided(hindsight).

here are some pics
https://www.dropbox.com/sh/7a81qw4bbnrqqga/AACIrep_6Jauj2UADYT-dIzqa?dl=0

Gate size is:
length:3.210m
height:~1m
thick:0.040m

post plate
length:0.25m
width:0.2m
thinkness:

post
length:1m
width:0.090m
thinkness:0.090m

post hole:
From a comment somewhere else, hole size should be 600mm x 600mm x 500mm would take about 10 40kg bags of ready mix. 10 bags seems alot, but if it does the job?

weight kgs:
180kgs as a min (my best guess)

@Bung "600mm x 600mm x 500mm would take about 10 40kg bags of ready mix." taht seems like alot of cement? Does 600mm x 600mm x 500mm not equal 0.18 meters cubed. How many cement bags do I need to achive this. I have donce some calculations and I think I need 20bags. That's a bit of a shock to be, was not expecting that much. will have to borrow a cement mixer, or what's the minimum order for a cement?

my calculation to achieve 600mm x 600mm x 500mm=0.18m cubed
https://www.bunnings.co.nz/cemix-maxcrete-20kg_p00291728
CoverageSlab equivalent to 800 x 300 x 40mm ( 0.0096 cubic metres)
> .6*.6*.5
0.18
> .8*.3*.04
0.0096
> .8*.3*.04*10
0.09599999999999999
> .8*.3*.04*20 ---------------------------------20bags@20kg to get 0.19m cubed
0.19199999999999998
>

@mikeAqua "A flared hole of a decent size filled with cement will hold quite a lot." care to quantify the hole size. maybe

@gzt - bought it off trademe so no spec sheet

some other Q's:
is the ground level - level enough - I will check.
The gate will swing over cobbles.

elpenguino

3424 posts

Uber Geek

#1652584 17-Oct-2016 23:15

Minimum order is usually 1m3, i have found. fine if you have other jobs at the same time or can waste some. A heck of a lot easier than mixing and not much more expensive unless you are wasting it....

BTW as mentioned i would also recommend to set studs into the slab - ensure the studs cannot rotate but attaching/welding something to them so they catch on the concrete.

Make a template out of plywood and you can just plop the thing down vertically after the concrete is in the hole. Keep threads clean.

You can adjust the post for vertical with spacers under the post as required.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

hattrick123

71 posts

Master Geek

#1652638 18-Oct-2016 08:06

elpenguino:

Minimum order is usually 1m3, i have found. fine if you have other jobs at the same time or can waste some. A heck of a lot easier than mixing and not much more expensive unless you are wasting it....

BTW as mentioned i would also recommend to set studs into the slab - ensure the studs cannot rotate but attaching/welding something to them so they catch on the concrete.

Make a template out of plywood and you can just plop the thing down vertically after the concrete is in the hole. Keep threads clean.

You can adjust the post for vertical with spacers under the post as required.

tks elpenguino

"studs into the slab" is that for the holes for the bolts to save me drilling? sorry this is lost on me abit. Or is it to save me drilling and I can use the studs to place the plate on and then put the nuts on to hold the post plate in place?

MikeAqua

7785 posts

Uber Geek

#1652644 18-Oct-2016 08:36

The studs are lengths of threaded rod that your set into the wet concrete - an alternative to dynabolts.

You make up a plywood template to line up with the holes in your post's base plate, and use that to position the studs correctly (and dead vertical) while the concrete cures. One the outside of the concrete hardens you remove the ply gently. When the concrete is set you slide the post onto the studs and secure it with nuts and washers.

It's important to: -

Use masking tape or similar to cover the threads above the concrete to keep them clean. Coat the underside of the ply in something to aid release e.g. brown packing tape and screw a couple of little screws into the top side to act as handles when you pull it off later.

Sorry I can't be more quantitative about how much concrete you need. As I said I tend to just do these things by intuition. I would just dig hole I thought was right and pour the concrete.

Mike

GregF

52 posts

Master Geek

#1652650 18-Oct-2016 08:44

hattrick123:

Or is it to save me drilling and I can use the studs to place the plate on and then put the nuts on to hold the post plate in place?

Yep - I reckon you've got it spot on. Take a bit of timber, and trace out the bottom plate of the gate post. Mark and drill holes in the timber. Then fix your bolts to the timber, and press them down into the wet concrete. This way, the bolts are poking up in the right place for you to pop the gate post onto once the concrete is set.

The only consideration would be the finishing / smoothing of the concrete with the timber there - if you pressed it down into the concrete you'd end up with an indentation which would trap water etc - so I reckon you'd want to have pondered that before pouring the concrete. Maybe use a square of timber that would be the total size of your concrete hole?

Cheers, Greg.

ps - saw the pictures - that gate sure ain't going to blow away!

MikeAqua

7785 posts

Uber Geek

#1652651 18-Oct-2016 08:44

Keeping stuff level

As others have mentioned it's important that your concrete pad is level to keep your post plumb, so that your (long) gate swings correctly.

The usual way to do this is to make some boxing for the edge of the concrete pad you are making, get the boxing dead level in both directions and skim the concrete to the top edge of the boxing.

Mike

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GregF

52 posts

Master Geek

#1652655 18-Oct-2016 08:49

Grin - Mike was too quick! Snap!

Just another thought - I used stainless rod when I made up some of these in the past - you can buy 1m lengths from Bunnings and cut to suit. I did mine quite long - to spread the load throughout the concrete as much as possible.

+1 for the screws in the top of the timber to aid in lifting it off - good idea!

Fred99

13684 posts

Uber Geek

#1652657 18-Oct-2016 08:52

You can also only guess how much concrete is needed, as it makes a big difference - to the size and depth you'll need - whether the hole is going in hard clay, soft puggy topsoil, or loose sand etc.

I wouldn't embed rod with the pour - the concrete screws I posted an image of above will work perfectly and save a lot of hassle setting it up.

Ordering a minimum drop of concrete will cost $$$ - there's a minimum charge on top of M3 rate - so count on cost being several hundred $$$. A concrete supplier might do a deal for 1/2 metre or whatever, left over from a larger job they're doing in the area, but you need to have the hole dug and be on site and be ready to go at short notice.

ETA - if the ready-mix delivery proves to be too much hassle, most landscape supply places sell builders mix by the scoop (1/3 metre small scoops), have free trailer hire, and have concrete mixers for hire.

elpenguino

3424 posts

Uber Geek

#1652695 18-Oct-2016 09:34

Gents (ladies?) , all good replies with good detail.

In answer to the query - how do you finish the concrete under the plywood? What you do is elevate the plywood template off the concrete surface. use 2 nuts on each hole to lift the wood off the ground, then you can trowel underneath the wood, to some degree at least.

I suggest it is easier to accurately mount studs with a template than it is to drill 4 holes in exactly the right place. Do you have a large masonry drill?

The 'studs in the concrete' technique is used on extremely large civil structures so there must be something in it. Only disadvantage I can see is that if the gate is removed, you are left with studs sticking out.

BTW I remembered - if you want an easy way to stop the stud rotating later on, you can bend a small portion at one end into an 'L' shape. This 'L' end goes into the concrete and then wont turn.

Also, stainless is nice and shiny but is less ductile than carbon steel so it has less 'give' in it. If your studs are not under sized you should be OK with stainless but get a similar/same metal which matches your gate post to reduce galvanic corrosion.

You can calculate the required concrete volume by measuring your hole size WxLxH.

Going off the size of your gate I would be looking to the manufacturer to provide a recommended foundation plan.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

Fred99

13684 posts

Uber Geek

#1652703 18-Oct-2016 09:51

elpenguino:

The 'studs in the concrete' technique is used on extremely large civil structures so there must be something in it. Only disadvantage I can see is that if the gate is removed, you are left with studs sticking out.

Think you'll find that when there's precision needed in placement (ie to match up with pre-drilled flanges etc), they'll drill the concrete then anchor rod with epoxy.

Drilling those holes accurately would take only a few minutes with a rotary hammer drill - very easy. I'd only think about embedding rod if lacking the gear to use concrete screws in that case - ie the rotary hammer, and a high-torque impact wrench. Once the concrete was there, I'd have the job done in minutes.

trig42

5814 posts

Uber Geek

ID Verified

#1652715 18-Oct-2016 09:54

How does the gate attach to the pole?

Could you not just do away with the galv. pole, and sink a wooden retaining post a 500-750mm into the ground, and attach the gate to that? Most gates have hingels that will just drop down over 'L' shaped stays on a pole. Your photos don't show how the gate attaches to the pole though, so yours may be different.

Or, if you must use the pole, attach it (drill through the pole and bolt it) to a wooden post sunk into the ground? That way you wont have the weak point being the poles connection to a large concrete pad, and you concrete needs will be a lot less.

Coil

6614 posts

Uber Geek
Inactive user

#1652717 18-Oct-2016 09:59

Avoid using dyna bolts as they will pull out over time and you will be left with a big block of useless concrete in the ground. The concrete screws are also a little dodgy looking but i assume they are strong if you get your concrete mix right. From what you have explained i personally would set a sleeve into the ground, So you can slide the post down into it like a bollard if you could make a little extension for it.

Otherwise do like they do with lamp posts and traffic lights, Set a post flange into the concrete that you can bolt the post to.

Fred99

13684 posts

Uber Geek

#1652725 18-Oct-2016 10:17

TimA:

Avoid using dyna bolts as they will pull out over time and you will be left with a big block of useless concrete in the ground.

From what you have explained i personally would set a sleeve into the ground, So you can slide the post down into it like a bollard.

Otherwise do like they do with lamp posts and traffic lights, Set a mount into the concrete flush with the ground you can bolt the post to.

The OP posted photos - there's a pre-drilled flat plate flange welded to the bottom of the 90x90 RHS post, and it's a (3m?) long heavy-looking gate (two people needed to lift it).

Coil

6614 posts

Uber Geek
Inactive user

#1652726 18-Oct-2016 10:19

Fred99:

TimA:

Avoid using dyna bolts as they will pull out over time and you will be left with a big block of useless concrete in the ground.

From what you have explained i personally would set a sleeve into the ground, So you can slide the post down into it like a bollard.

Otherwise do like they do with lamp posts and traffic lights, Set a mount into the concrete flush with the ground you can bolt the post to.

The OP posted photos - there's a pre-drilled flat plate flange welded to the bottom of the 90x90 RHS post, and it's a (3m?) long heavy-looking gate (two people needed to lift it).

Yeah i updated the post just as you replied haha, I had a real good look through and saw the flange hence why i think its best to mount a flange into the slab or block.
As soon as that gate comes under load it will rip out of the concrete for sure. Kids climbing it or how ever.

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