Concrete fence post depth and concrete strength

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Karlitob
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Concrete fence post depth and concrete strength

Post by Karlitob »

Hi all

I’m installing concrete h posts and wooden fences over 40m (140ft) [Metric for Ireland]

Post Length:
I’m getting caught up in knots as to the length and depth required. I want 2.1m above ground (1.8m fence and .3m gravel board) but I’ll stuck on whether to get a 2.7m or 3m. I know that 2.7m is the norm with .6m underground, but I wondered would it be better to go with the .9m so that it’ll be more secure. I’m worried that the length of the run needs a deeper hole. I think I read that it’s not the concrete that gives the post it’s strength against lateral movement but rather the depth. I have a petrol auger and no problem hitting the .9m

Concrete
I know that the recommended is 1:6 cement:ballast but again, for belt and braces I have read that I should go to 1:4.

Any comments appreciated. I don’t just want to do it, I want to do it right and make sure it’s lasts a long time.
dewaltdisney
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Concrete fence post depth and concrete strength

Post by dewaltdisney »

The issue is really how much wind force is the fence likely to take? If normal the shorter posts should be fine. The posts are made with four reinforcing rods which provide the strength. I have seen badly damaged posts with concrete missing still doing their job. The way I do a post is to ram rubble around the foot of the post and make a concrete donut around the post. If you ever have to chop it out in the future you only need to break out one side and you have a housing still there for the replacement. I think that a row of tallish shrubs helps to diffuse wind force somewhat also. Just a few thoughts :thumbright:

DWD
Karlitob
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Concrete fence post depth and concrete strength

Post by Karlitob »

Thank you.
Since I’m using closed board fencing I’m worried about the force.
dewaltdisney
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Concrete fence post depth and concrete strength

Post by dewaltdisney »

I have close board panels in concrete. They are very strong and although, like all fences, they take the wind it largely depends on the prevailing wind direction, usually the west, as to their vulnerability. I have Laurels that are quite tall and they tend to take the wind rather than the fence. Another idea is to lessen the panel size using trellis for the topmost foot. You have to have consideration as to how much of a threat is it to fence people out as regards height. So the equation might be (wind + scrotes) = ( height + post depth) :lol:

DWD
Bob225
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Concrete fence post depth and concrete strength

Post by Bob225 »

it depends on the wind loading and ground type if your on sand/clay or gravel, deeper the better

As for the mix 5:1 is a good universal mix
Karlitob
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Concrete fence post depth and concrete strength

Post by Karlitob »

Thanks for reply.

It’s in an estate with house all around but the length will now be quite open. I’m clearing the land to get the fence in. I’m sure there’ll be trees and shrubs in time.

Soil is good quality loamy soil. Clumps easily, breaks easily. No sand, no clay.

Thanks for advice on 5:1. There’s so much advice out there.

Would you add an additive? Some suggestion same - but not sure what to add?
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