How much concrete per fence post?

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Jan 30, 2007
Clovis, CA
Me and the neighbors that own the house behind me are splitting the cost of a fence. They insist on using their own contractor. The other contractors that I've talked to say they use 1-1/2 bags of concrete per 4x4 fence post. The guy my neighbors are insisting on hiring only uses a 1/2 bag per post. He says the reason for that is "because you want to disturb the least amount of soil as possible." He says if you use more concrete, then you have to dig a larger hole around the post. The larger the hole he says, the more loose soil you're gonna have around each post. So what he's doing is using a post hole digger and going down 2ft. He then pours the concrete dry around the post and packs it in - then adds water. I don't buy it. I'm thinking the more concrete the better. What are your thoughts?
IMO their contractor is trying to do stuff on the cheap and not the right way. For the strongest concrete mix, you'll want to premix the concrete with the proper about of water, before you pour it in the hole. The lazy way is the way he wants to do it and you will not get the strongest mix. Also 1-1/2 bags per hole is about right for a 4x4 fence post. Also remember, the depth of the post hole should be one-half of the above-ground post height. (Example: For a 6' above ground post, use a post with an overall height of 9 feet and place 3 feet in the ground). If it was me I'd not go with the contractor that wants to do it the cheap and lazy way. How's the rest of his work going to turn out? That's my 2cents.
Also, I think the best way and most costly, but for a long lasting fence and fence post. Is to pour the concrete into the holes then set post anchors in the concrete before in sets. Then you set the post in the metal post anchors and bolt them up using lags screws. That way the post can't rot off at the concrete. So if you ever have to replace a post you just unscrew the post from the anchor and replace. Without having to dig up a concrete base too.
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Pay the extra for treated lumber 4x4 posts. I have removed rotted 4x4 fence posts from the concrete and shop vac'd out the holes, only to find dirt at the bottom. So the end grain of the 4x4 was sucking up water and rotted out that much earlier. Whoever installed it just put the post in the hole, plummed it up and poured in concrete. I like to use treated lumber, and prime the whole thing before re inserting it into the concrete, but double and triple up the primer on the endgrain so it cannot suck up any water from the ground. I'll be doing this tomorrow, because the clients never want to have to have this done again. Contractors working on an estimate would never go this far. Time = money, and if it falls over in 5 years, it equals job security too.
Here's a pic of the 2 ways for 4x4 post. Note the gravel at the bottom of the post that's set in concrete to help with water. The pic on the left is the way I was talking about. As with anything you get what you pay for.
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strongt, what's the distance from the bottom of the post to the bottom of the gravel? It looks like it might be 1ft.
It looks like it is, but UBC codes only calls for 3in of gravel. That gravel and post may not be to scale. (They don't give a scale for the gravel in the pic) I just put the pic up to show you the different options for putting the post up.
I helped put up a farm pavilion about 10 years ago with 4x4's We used about 1-1.5 bag per hole we also filled 6" of gravel on the bottom.. premixed the concrete in a large wheelbarrow and it worked pretty good. sounds like their guy wants to make a buck the cheap way.
I have a large property with 1200 feet of fence. I chose not to pre-mix the concrete, but rather, to place 1 dry bag of cheap concrete per pole. I set the poles with a level and watered a few of them. Finally, I gave up and left the rest for the rain to work it's magic. Years later, the county removed my fence for me. I was surprised to see that all the concrete stuck to the poles perfectly. The county guy really had to work to pull the poles up with his backhoe. The fence held up well in all 3 hurricanes, so it was plenty strong. I would do it the same way again.
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