concrete block size

[Thrashsmith]

Hi all,
I'm quoting for a pair of small but weighty solid gates approx 1m x 1m each (around 50kg each) that are going to be hung off new 100mm hollow posts that will also be part of the installation. I was given a good idea a while ago by a local fabrication firm to weld plate squares to the bottoms of the posts so that the posts can get bolted to concrete blocks 500mm below ground level, that gives flexibility in the installation as the posts can be shimmed about to get them level rather than just concreteing them in.

I know naff all about groundworks. What sort of size concrete block would you image each gate would need for the hanging post to be bolted to? Merci buckets!

 

[Shedendman]

I wouldn't put them on blocks at all,chances are you'll crack/split them while drilling,but if its 500mm below ground level and its to be concreted in then a bit of paving slab cut to the size of the hole placed at the bottom will do,that trick is mainly done to stop the posts sinking down.
OH,so your not back filling with concrete,not wise IMHO

 

[Thrashsmith]

Thanks for the raised concern. From their description it seemed like a very tried and tested method for them - they're a firm of about 20 guys, all coded welders & do large architectural jobs so I didn't interpret it as a "bodge it & scarper" method from a bunch of chancers.
Maybe they concrete threaded bolt in to the blocks rather than drill them after it's set?

 

[thinfourth]

Are we having a communication failure?

As you might be thinking sinking pre made blocks into the ground?

Where as they might be talking about digging some holes and filling them with concrete

 

[fixerupper]

Yes I think there was a communication failure about the term concrete block...I think the op was thinking a hole with concrete in it and maybe 4 rag bolts set in to the wet concrete , when the concrete is set the gate post can be adjusted for uprightness with washers and fastend down, then the hole can be back filled with earth , leanmix, or whatever ...have I got this right Thrashsmith?

 

[Fazerruss]

Yes this is the method they will have been referring to. This is a job I did a while ago. the hole was dug then the frame with the thread bar is concreted in to create a concrete "block"





I can't find any other photos but when the poured concrete was set I fitted the post and adjusted it millimetre perfect then poured another concrete mix allowing it to run under the base plate of the steel post which locked it in place.

 

[Thrashsmith]

Yes I think a miscommunication. Those pics seem to have the jist.
So...can anyone help with an approx "block" size? For the record it ain't gunna be me doing the groundworks, there will be a groundworks contractor, I'm just trying to put together a game plan to send to the architect.

 

[bigegg]

I always dig them at least 50% bigger than I think they'll possibly need.
The only thing I hate more than digging holes for footings, is digging em up cos they're not big enough!

I'd go for something about 18" cubed, and undercut the hole if possible.
It does depend upon the soil you're going into tho.
Round here, I go 12-24" into the clay layer, and about 12" diameter - for 6ft out of the ground fence posts with heavy wind load on the fence.

The soil can be anything from 8" to 36" deep - garden was levelled when my dad dug out for the garage - so potentially a hole nearly 5ft/1.8m deep. (That was a LONG day!)
You might need bigger footings on sand/gravel?

.

 

[Welderpaul]

Yes this is the method they will have been referring to. This is a job I did a while ago. the hole was dug then the frame with the thread bar is concreted in to create a concrete "block"


View attachment 127405 View attachment 127406


I can't find any other photos but when the poured concrete was set I fitted the post and adjusted it millimetre perfect then poured another concrete mix allowing it to run under the base plate of the steel post which locked it in place.

Did you mill those post holes?

 

[Fazerruss]

Dug out by hand 2 ton of soil

What can I say, I'm a perfectionist

Don't like messy uneven holes

 

[Thrashsmith]

Cheers me dears.
Like I say, I know nuffink about groundworks but guessed a 24" cube might do the trick. I'm kinda working backwards because I wanted to establish that an off the shelf 300 x 300 x 10mm or even a 400 x 400 x 10mm pre drilled base plate would be suitably paired to the block size so I don't have to spend time making bespoke base plates.

 

[knighty]

how deep all depends on the ground conditions... if the ground is soft you need to go deeper

but... for things like post/beam foundations wide is more important than deep (as long as you've dun down under the soft stuff)

base plate is an easy bit - it's going to be under concrete so doesn't really matter what it's like ? - it's only really there to stop the post from sinking

gates at 1mx1m and 50kg each aren't going to need much

2ft cube, put base with threaded bar in hole, then 6inch concrete, post on top, adjust it, 1ft concrete on top of that

gives you room for 6inch of soil ontop

 

[8ob]

how deep all depends on the ground conditions... if the ground is soft you need to go deeper

but... for things like post/beam foundations wide is more important than deep (as long as you've dun down under the soft stuff)

Our landscape lads install a lot of heavy gates on some of these bigger estates, they now dig in a trench between the two posts connecting the two bases. a couple of bits of reo in the concrete and cast it all in one, this stops the two separate footings moving about and playing havoc with the shut gaps. Not always possible but worth it if you can.

Bob

 

[Thrashsmith]

Ah, maybe another miscommunication.
I'm imagined welding the base plate to the bottom of the hanging post, then bolting that to the pre-laid concrete block/cube.

The fitting of the gates & adjoining railings wouldn't happen in one go. The plan is to check the fit on site before being sent off for finishing.

 

[wyn]

Ah, maybe another miscommunication.
I'm imagined welding the base plate to the bottom of the hanging post, then bolting that to the pre-laid concrete block/cube.

Yes that's how it works.
That second pic might give the impression you concrete the whole lot in one go.
You do it like the first pic, then concrete up to where the nuts are on the threaded bar.
Once it's gone off bolt down the post

 

[Thrashsmith]

Yes that's how it works.
That second pic might give the impression you concrete the whole lot in one go.
You do it like the first pic, then concrete up to where the nuts are on the threaded bar.
Once it's gone off bolt down the post

Thanks for the clarification.
Is there anything wrong with pouring the cube (weeks in advance of the dummy run install) without the rod cast in, and instead drilling the holes & resining in the rod during a dummy run install?
There's going to be railings joining the hanging posts at funny angles either side so on a dummy run install I'd rather the concrete be set. The idea being come the day of install it only takes a fraction of the time & the expensive paint job isn't get scuffed half as much as it'll all just drop into place.

 

[GW8IZR]

Thanks for the clarification.
Is there anything wrong with pouring the cube (weeks in advance of the dummy run install) without the rod cast in, and instead drilling the holes & resining in the rod during a dummy run install?
There's going to be railings joining the hanging posts at funny angles either side so on a dummy run install I'd rather the concrete be set. The idea being come the day of install it only takes a fraction of the time & the expensive paint job isn't get scuffed half as much as it'll all just drop into place.

I have poured about a third of the hole, resined in studs when its set. Put nuts on the studs and then the plate / post .. put nuts on top and use the nuts under the plate to true it up, nuts on top to clamp. When your happy pour the rest and let it set.

I use a bit of plywood to hold the studs true while the resin cures

 

[Thrashsmith]

That sounds like a neat system for setting the posts, but doesn't sound like it would also carry the weight of the gates without flexing the rod which is only half secured - or am I wrong?

I need to test the swing of both gates during a dummy run install as they have to catch back onto the railings either side. I normally mock up installs in my workshop to find faults but in this situation I don't have enough space as each railing panel is 3m long.

 

[Thrashsmith]

Maybe my lack of concrete knowledge is confusing the issue. I have it in my head that a suitable lump of concrete will take days to set to a hardness that it can be bolted to, right? So I'm assuming that the above pictured system of pouring & testing the gates swing can't happen on the same day.

 

[GW8IZR]

That sounds like a neat system for setting the posts, but doesn't sound like it would also carry the weight of the gates without flexing the rod which is only half secured - or am I wrong?

I need to test the swing of both gates during a dummy run install as they have to catch back onto the railings either side. I normally mock up installs in my workshop to find faults but in this situation I don't have enough space as each railing panel is 3m long.

No cos the bolts just hold it in place while you pour - the plate and bottom of the post ends up cast in a lump of concrete that you have determined is big enough.