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I set an 9"x 8' creosote post in a 2' deep hole that is about 30" wide. I know the hole should be deeper but too much rock below that depth. I dumped 80 lb of Quick Crete in and added 2 gallons of water. It was still soft after 4 hours. I removed one of the three braces to see if it was tight. Big mistake. I wobbled the post when removing the brace and the pressure loosened the post slightly.

8 hrs later the cement has finally hardened but the post still wobbles slightly--about 1/2 inch at the top. How can I make it solid? I still have about a foot of hole left so should I just add another bag of QuickCrete? I could easily drive some three or four 8" nails in the crack between post and hole to firm it up before adding the QuickCrete. I may hang a gate on it so it needs to be solid. Any ideas?

isherwood
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Hard Head
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  • "dumped 80 lb of Quick Crete in and added 2 gallons of water" I could be reading into this but you didn't literally dump dry concrete into the hole and then put water on it, right? – JimmyJames May 18 '18 at 19:20
  • @JimmyJames While it's not recommended practice to do it that way, i've seen many different "professionals" do it this way with success. I do not recommend this practice either, however, if he did do it this way, it wouldn't be the worst thing in the world. Damage is already done, but I wouldn't suggest digging it up and "doing it right". – dberm22 May 18 '18 at 20:46
  • @JimmyJames that is how the manufacturer says to use their product https://www.quikrete.com/ – rogerdeuce May 18 '18 at 20:52
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    @rogerdeuce Well, I learned something today. Having pulled posts set in concrete, I'm a little dubious that the concrete does much. It's the earth that holds the post in place, not the concrete. I once built a pergola and used packed gravel instead. Of course it had structure in two directions so the posts weren't going to lean regardless of what they were set in. I'm not convinced that concrete really holds things in that much better in soil and it holds water against the wood. – JimmyJames May 18 '18 at 21:53

2 Answers2

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"How can I make it solid?"

Something isn't right in your post. An 80lb sack mixes up 2/3 cubic foot.

Spec sheet: https://www.quikrete.com/PDFs/DATA_SHEET-Fast%20Setting%20Concrete%20Mix%201004-50.pdf

The volume of your 2' deep, 30" dia hole, minus the 9" post volume, is 9 cubic feet.

Here is the volume calculation

Short answer is at 2' deep it'll never be a solid 6' tall gate post on it's own. Sp personally, I'd pull it all out, dig the post hole deeper and pack it with 1/4-minus.

Dig four 2' long trenches 15" deep, extending from the 9" post at right angles to each other. One pair parallel to your gate, the other pair perpendicular. Sandwich the 9" post with a pair of 5' long PT 2x6's laid in the trenches that are parallel to the gate. Bolt together. Do the same with another pair of 5' 2x6's in the perpendicular trench. Fill with concrete. Per Isherwood, add some rebar.

Alice
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  • The trouble with the underground bracing is that it relies on absolute rigidity at the connection. Typically I'd expect movement similar to what's described now. It's even more challenging with the post being round. – isherwood May 18 '18 at 15:01
  • It's all encased in concrete. – Alice May 18 '18 at 15:03
  • Sure, but narrow runs of premix like that tend to crack, leaving the post-to-brace joint as a critical factor. – isherwood May 18 '18 at 15:24
  • So, a 15" x15" x24" chunk is going to crack? If you think so, you're welcome to down vote my answer. – Alice May 18 '18 at 16:41
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Mix up some anchoring cement and pour it into the gap you created when you got impatient. You could probably also use epoxy. Brace the post if it's breezy and let it alone for a day.

If the gap is too thin to get anything into, try some treated wood shims.

isherwood
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    I would also add to the gap, since you still have some depth I would put a few wood screws in the post 1/2 of the screw in the post 1/2 left out then add additional sackcrete the screws will help secure the post in the concrete kinda like rebar in a slab. – Ed Beal May 18 '18 at 18:22
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    Yes, 3/8" lags would do well. – isherwood May 18 '18 at 18:23