My brother in-law is putting up a row of fairly heavy, 15ft gates on galvanised posts which he's concreting into the ground. The posts are slightly over 4inches square and will be set 2ft into a hole approximately 8inches square which will then be filled with concrete. How soon after pouring the concrete will the concrete have 'gone off' enough to be able to take the weight of hanging these gates on the posts?
How long does it take for concrete to 'cure'?
- Thread starter AndrewSchofield
- Start date
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after 2 weeks it will have reached 50% of its ultimate strength
it must be kept damp all this time. Once it dries it will stop gaining strength and will not start again.
the strength and hardness gaining gets slower and slower as time extends. The hardest and strongest concrete is usually underground where it has stayed damp and continued curing for 20 years or more.
BTW 2ft deep is not enough for a 15ft gatepost
it must be kept damp all this time. Once it dries it will stop gaining strength and will not start again.
the strength and hardness gaining gets slower and slower as time extends. The hardest and strongest concrete is usually underground where it has stayed damp and continued curing for 20 years or more.
BTW 2ft deep is not enough for a 15ft gatepost
Thanks for your reply John,
He's been provided the gateposts, gates and all accessories he needs by one company having told them what he wants to do - they've provided a 2ft 'shoe' to cast into concrete so presumably they think 2ft is OK? The gateposts are 7ft high (5ft will be above ground) and the gates are about 15ft long by 4ft 6in high?
So you're saying the concrete wont be strong enough to hang the gates on the posts for at least two weeks??
He's been provided the gateposts, gates and all accessories he needs by one company having told them what he wants to do - they've provided a 2ft 'shoe' to cast into concrete so presumably they think 2ft is OK? The gateposts are 7ft high (5ft will be above ground) and the gates are about 15ft long by 4ft 6in high?
So you're saying the concrete wont be strong enough to hang the gates on the posts for at least two weeks??
R
RedHerring2
When I did mine I poured concrete down the posts as well before putting the caps on. I used pea gravel in the concrete, not the usual gravel in ballast to ease the pouring and filling.
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I would be looking at digging a much bigger hole.
8" square is paltry and (as John D says) 2' deep is probably on the limit too.
A 15' long gate will have a hell of a lot of force when swinging. I would be thinking a minimum of 12-18" square with another 6-12" in the ground.
Cheers for the replies guys. I did think when I typed it that 8inches sqaure didn't sound a lot, on reflection the hole he started yesterday was probably more like 10inches square but i'll suggest to him he ought to make it bigger.
As for the depth, he can't go any deeper though without buying different 'shoes' and longer posts and as he's bought them as a 'kit' from a reputable company that have been recommended to him by friends and who's gates he's seen 'in action' - surely they should have provided equipment adequate to do what they say it will?? I totally understand what you mean, we carried the gates yesterday between the two of us and they were b****y heavy - when they're hung at one end that's gonna be a hell of a force acting on the top of the post. As I said though, he's bought gates, posts and shoes from the same company so they should be OK, shouldn't they??
As for the depth, he can't go any deeper though without buying different 'shoes' and longer posts and as he's bought them as a 'kit' from a reputable company that have been recommended to him by friends and who's gates he's seen 'in action' - surely they should have provided equipment adequate to do what they say it will?? I totally understand what you mean, we carried the gates yesterday between the two of us and they were b****y heavy - when they're hung at one end that's gonna be a hell of a force acting on the top of the post. As I said though, he's bought gates, posts and shoes from the same company so they should be OK, shouldn't they??
It won't matter that concrete goes below the post bottom, it just means you will have to sit the post on some half bricks.
At least you will have a mass of concrete below, stabilizing all the force above.
At least you will have a mass of concrete below, stabilizing all the force above.
Assuming we're still talking about concrete here, are you saying, Woody, that 2ft would be ok, so long as he makes the hole wider?
I don't know if it makes a difference but this is in a yard formed with a 4-6inch concete slab so its not just 10inches of concrete around the post base and 'beyond' that just soil - the whole yard surrounding the gates will be 6inches deep in concrete - I assume this will help support the posts?
Does that make sense??
The main issues here are the bearing pressure onto the soil below from the loads onto the footing, and the overturning moment from the self weight of the gate and any vertical loads applied to it (imagine a child - or worse, an adult - swinging on the end of a 15 foot gate, the forces at the foundation will be pretty big).
Even 2ft^3 of concrete won't be enough alone to prevent overturning. You would need to rely on passive pressures from the surrounding soil, and if you did that you would probably find that over time everything would rotate and the end of your gate would be dragging along the ground.
I was going to suggest spanning a beam between both posts, and casting it into concrete footings each end to stiffen everything up, but as you've told us that there is an existing slab in the yard, if you can be sure that the existing concrete is strong enough, it should cope with the forces applied to it. You'll still need plenty of concrete at the base though.
Even 2ft^3 of concrete won't be enough alone to prevent overturning. You would need to rely on passive pressures from the surrounding soil, and if you did that you would probably find that over time everything would rotate and the end of your gate would be dragging along the ground.
I was going to suggest spanning a beam between both posts, and casting it into concrete footings each end to stiffen everything up, but as you've told us that there is an existing slab in the yard, if you can be sure that the existing concrete is strong enough, it should cope with the forces applied to it. You'll still need plenty of concrete at the base though.
Wouldn't help when the gate was open though...
Thinking about it, gates of this length often have a wheel at the end opposite to the post, to reduce the forces on the foundation. Does your gate have this?
G
geraint
i disagree..... concrete can take up to 40 years to cure... so reaching 50 per cent in two weeks is not quite right...... but in most installations it is strong enough the next day....
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