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Setting wood fence post---I've heard to set wood fence posts using quikrete dry, allowing it get moisture from the ground. Is this a good idea?

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Consider that avoiding concrete altogether has strong merit. See this question diy.stackexchange.com/questions/243/… – Dean MacGregor Mar 31 at 14:04

No. Unless you live in a swamp, there won't be enough moisture, and even if you do it won't be mixed with the cement properly. The concrete will be dry, crumbly, and have no strength. Just mix it like the directions say.

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This isn't true. If it was, concrete that sits in bags for a time also wouldn't cure. Concrete cures as water is available, and while it may not be the best approach due to the possibility of interim movement, the concrete will absorb soil moisture and cure just fine over time. – isherwood Mar 30 at 19:26
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The concrete that cures in a bag is dry, crumbly, and weak, like I said. It's hard enough to be useless, but not good enough to be the foundation for anything. – iLikeDirt Mar 30 at 20:10
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I think you and I are the only people in the world that wait those ten minutes and then mix it again. RTFM. ;) – Mazura Mar 30 at 21:29
    
@isherwood when concrete cures with a water/cement ratio between 0.38 and 0.44 it is completely waterproof. If there are uncured layers trapped within a layer that cured at that ratio, it will never cure, because water will not become available to it. This not only can happen with dry concrete left in soil, it is quite likely to. – Jules Mar 31 at 13:31
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@isherwood It's possible for a fence with no concrete around the posts to last a long time. So the fact that some fences have survived with nothing more than dumping dry concrete into the hole, is far from conclusive. – stannius Apr 1 at 23:26

Many vendors do recommend pouring the concrete in dry, but then they advise to pour a specific amount of water on top to immediately set, not to allow rain and ground moisture to cure the concrete. This lets you skip mixing in the wheelbarrow or bucket and then shoveling the wet concrete in with a lot more cleanup of the tools required. For strength, the latter method of mixing first and pouring in wet should give you a stronger result over the dry pour method since the moisture and aggregate will be more thoroughly mixed.

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Personally I don't like concreting in wooden posts, because eventually they will rot and have to be replaced. Getting the old concrete out is then difficult.

Ideally, concrete in a short concrete fence post and use coach screws to fix your wooden posts to these. The concrete will never rot, your wooden posts can be set off the ground, so will last almost indefinitely.

If you must concrete in wooden posts, make sure you buy them properly pressure treated and at least 4" square to survive rot longer.

Like someone else said, put a rock in the bottom of the hole. This helps keep everything level. I also jam small rocks either side of the post to get it square, leaving plenty of space for the dry concrete to pass.

In the UK, we have a product called Postcrete. Having looked at Quikrete, it seems almost identical. Both are specifically designed to be used without mixing, but do require water.

Someone else mentioned putting water in the hole first. This is how Postcrete is used.

A video and instructions for Quikrete is at: https://www.quikrete.com/athome/video-setting-posts.asp

Instructions for Postcrete are at: http://www.tarmac.com/media/756324/postcrete-product-data-sheet.pdf

I imagine following either instructions for either product will produce good results. Neither of them are as strong as mixing proper concrete from scratch.

Particularly note the limitations quoted for Postcrete: "for the purposes of fixing domestic posts, for fixing decking posts, rotary washing lines and small/medium sized gateposts (less than 1.0m width gate). Postcrete may not be used for general concreting, screeds, mortar, grout or render. If a particular compressive strength is required, Postcrete should not be used.

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+1 for addressing rot. This will definitely happen as the bottom of the hole is likely sealed (mostly at least) by the concrete and the post is then sitting in a puddle until it evaporates back out through the wood again. My parents are in the process of fixing their deck for exactly this reason, and it's no longer code where they live. – AaronD Mar 31 at 17:27

Using dry concrete is very helpful in places where a hose is not available and where tool cleanup is not going to occur within the next few hours.

I have set hundreds (maybe thousands) of wooden fence posts with dry concrete with satisfactory results (0 fails). I've only done this in an areas with moist soil though, so this method might not work everywhere (desert?).

I also like to put a large stone on the bottom first, if it's handy; and if I have a little water, I add it to the hole before pouring dry contrete (although it may not make any difference). For larger holes (or for cable anchors) I sometimes add concrete, then water, mix/tamp with a stick, then add more contrete and water.

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It is a good idea if heavy mixing and shoveling aren't in your best interest.

Moisture is absorbed and distributed very well by capillary action and other mechanisms, and the concrete will eventually cure as well as if you had mixed it yourself.

It will take a while in some cases, so the drawback is that the post may move in the meantime.

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Capillary action cannot be relied upon to allow concrete to cure over time, as capillaries only form when the water/cement ratio is over 0.44. This means that enough water for the cement in the concrete to cure must be supplied before any of it cures, otherwise sections may never cure. This is likely to be substantially less water than the manufacturer of the mix recommends, but in order to ensure a correct cure it is required. – Jules Mar 31 at 13:45
    
Yeah, that doesn't happen. I'm not only educated, but I have extensive time in the trenches, so to speak. Conditions in a post hole are far too varying for this to occur with any likelihood. The concrete will cure to adequate strength. Period. – isherwood Mar 31 at 14:09

Do what the bag says. Some products, such as this one recommend you pour the concrete into the hole dry.

Optionally this foam-based product is lighter-weight and will be easier to remove when the wood invariably rots away.

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You heard 2 pieces of very bad advice. 1st, concrete is not needed nor beneficial. It's extra work, it delays the installation, it doesn't compact itself into the hole & therefore isn't as solid, it absorbs water, it retains water & it's a chore to remove in future replacements.

2nd, no, your posts will not remain plumb in both directions. You need to pour in at least 1/3rd of the amount of water for the amount of concrete you put in & wait at least 2-hours, to lock the posts quite anemically into position.

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Concrete may be essential to keeping the fense up. It depends on the soil and region, as well as the specific application (e.g. adjecent to the gate). – JDługosz Mar 31 at 13:35
    
So I'm told by the industry. Loose soil just means go deeper. A gate I might agree with, if it's over 3' wide. But, I did 3 fences over a decade ago without concrete & those along with their gates are still perfect. Concrete didn't become "trendy" until just 20-yrs ago & no fence before then was falling down or blowing across the street. Done some way doesn't mean done right. They botch fences, hang drywall the wrong way, use a crap-load of nails instead of a few screws, install the "builders grade" garbage everywhere & put up particleboard cabinets. Why not question & doubt the "Pro way". – Iggy Mar 31 at 13:53
    
Here I have clay soil. Extrodiarily hard to dig. If deep enough in principle, it would be a problem to refill the void with the original tailings. Pouring slurry is easier than compacting sand or whatnot around the post in a hole 3 feet deep. – JDługosz Mar 31 at 17:30
    
No, don't use sand unless your soil is sand. Water will get in & then take forever to drain back out, especially in your soil. Tamping the removed soil back in at 6" or so lifts with a 2x2 or 2x4 is much better & cheaper. – Iggy Mar 31 at 22:29
    
Easy for you to say! Digging is more akin to slicing up old tires than anything you've seen on "Ground Force". As I said, the workability depends on the region and conditions. You only took away from that "loose" as being less optimal. different beyond your experience. – JDługosz Apr 1 at 0:18

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