Cement for Fence Posts

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Old 03-23-15, 06:19 AM
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Cement for Fence Posts

I was curious on everyone's thoughts on techniques for pouting concrete for fence posts. I live in the Chicago area and will be isntalling a fence. I am digging down 48 inches, adding 6 inches of gravel and then will be cementing the 4x4 post in the ground. I have seen this done two ways:

1) Pre-mixing concrete in wheel barrow then pouring it into the hole

2) Use quick set cement where you pour the bag of dry cement in the hole then add water

Is one way better that the other?

Thanks,
Tom
 
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Old 03-23-15, 06:49 AM
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While pouring a dry mix in the hole and adding water works, premixing and pouring in wet cement does a better job. You can never mix the mud as well in the hole as you can in a bucket or barrow.
 
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Old 03-23-15, 07:18 AM
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Premix the concrete and then put it in the hole. The other way will work, but you have no way of being sure the entire mix is getting enough water to set properly.
 
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Old 03-23-15, 08:05 AM
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Thanks guys! Any reason to seal or coat the part of the post that will be underground even if I am using ground contact pressure treated 4x4?
 
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Old 03-23-15, 08:17 AM
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Anything you can do to prolong the life of the wood will help, but most times, you will find the posts rot right at the point they come out of the concrete, so concentrate your efforts there.
 
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Old 03-23-15, 08:42 AM
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question. Some TV DIY shows insist you should use gravel not concrete. They claim the concrete traps moisture and entourages rot where as the gravel allows the post to dry.

My personal opinion is this is something (BS) commercial fence companies came up with to save time and money not the wood.

Pros what is your opinion?
 
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Old 03-23-15, 08:45 AM
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... and I like to fill the bottom portion with gravel and just use concrete at the top. I believe that keeps the core of the 4x4 drier = longer life.
 
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Old 03-23-15, 09:05 AM
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We tell people not to put wood on bare concrete inside the house since concrete moves water into the wood - seems to me the same would apply underground as well.

That said, seems like the gravel would be nowhere near as strong, so I don't think I'd do it for a fence.
 
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Old 03-23-15, 09:10 AM
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A lot depends on the ground. I've installed fence posts with no concrete that were very stout and others that needed the cement to make them stable. Over the years I've come to the conclusion that if you need to concrete them in, the post fares best if the concrete is at the top and that also makes the post easier to remove if/when that day comes.
 
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Old 03-23-15, 10:00 AM
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One thing not asked...what is the diameter of your holes? I don't have any posts to check, but the formula says point to point (opposite corners) on a typical 4x4 is about 5". So a 6" dia hole (typical when using a manual post hole digger) only gives 1/2" at the corners. You need to go at least 8" (10" would be better) and ideally it should widen some at the bottom. Pretty tough to do at 48" depth.
Just something else to think about.

I haven't installed many, but depending on soil, one suggestion I remember was to put 6" of large gravel in the bottom, place your posts, then fill with crusher run in layers, slightly wetting and tamping well after each layer. Sets up hard and strong, but still allows good drainage. A lot more labor intensive though.
 
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Old 03-24-15, 04:57 AM
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The rigidity of any post is only as good as the compaction of the surrounding soil.
 
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Old 03-24-15, 08:36 PM
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I worked on a fencing crew in Wisconsin as a teenager. We never set any posts (agricultural fences, for cattle containment) in concrete, and they were all pretty stable, for many years. Used either native soil or crusher run to compact around the posts.
 
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Old 03-25-15, 08:42 AM
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I agree with Bridgeman! In WNY I dig a hole 2X the diameter of the post and 4' deep (frost level). I pour ~6" to 8" of concrete in the bottom of the hole and let it sit overnight. Place the post into the hole and back fill with crusher run gravel and compact every 6" to 8". I have an old pick ax handle I use and compact the gravel to the point it won't compact anymore. The post I have placed in this manner have not heaved or moved.
 
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Old 03-25-15, 01:00 PM
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Soil conditions and fence height and composition are the determining factors for concrete vs no concrete.
 
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