Concrete - No mixing necessary?


Old 08-14-11, 07:48 AM
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Concrete - No mixing necessary?

Got a huge, huge fence project planned. I've got all the materials, just need the time and some help to put it up in a timely manner. Still got a lot of planning to do.

My dad and I were discussing the fence with my uncle yesterday and I told him I planned on renting a skid-steer with an auger to drill the fence post holes and a gasoline concrete mixer for mixing the concrete, rather than mixing it laboriously in a wheel-barrow.

My uncle said save the money on renting a mixer and the huge amount of time it'll take to mix it and simply dump the bags of concrete powder into the holes and forget about it.

Now, I've seen this done before with a 36" sewer main that had collapsed and a guy dumped five or six bags of concrete mix into the sink hole (temporarily, of course) and said that it would cure without mixing. I just figured he was lazy and joking around. A, "I dunno, I just work here." sorta' thing. The sink hole was where I worked and it wasn't costing me any money, time, or was a danger to me or anything like that, so I didn't care what he did. lol

Anyhow, my uncle said that the concrete will draw moisture from the ground and it'll cure on its own. This makes sense! I did a little bit of research on the subject and it's actually what quite a few professional fence companies, etc. practice. Dump the concrete into the hole and move on. However, I also saw that it's recommended that some water be poured into the hole before and after the concrete is dumped in. That's no problem whatsoever. I wouldn't feel comfortable just relying on the moisture in the ground, 'cause we're in the worst drought in years here in southwest Oklahoma. lol

Anyhow, I just wanted to consult ya'll about this first. Any fist hand experience(s)? Pros? Cons?

By the way, this is a wooden privacy fence. 6' tall x 8' wide pre-built non-treated panels. I'm staining them with solid stain from Sherwin Williams. Nearly $50/gallon!!! Color is Ember. The fence posts are 8' tall, 2.5" diameter, and .095 wall thickness -stainless steel. Technically, the posts aren't quite 8' tall. They're actually gonna' be 6' from the top of the ground to the top of the post (in other words, 6' exposed) and roughly 18" will be in the ground.

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Old 08-14-11, 11:19 AM
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I never mix post hole concrete, although others may. One thing to remember, is not to dump the entire bag in the hole. Put in 1/4, then a little water and use a heavy tamper to force out air holes. Keep doing it until you reach the top. Doing it in increments will help you adjust your plumb on the post as you go. Dumping a whole bag in will pretty well set it without forgiveness.
Figure the volume of each hole, less the volume of displacement of the post. You may find buying concrete, sand and gravel, mixing it ahead in a mixer would be more economical. If you drill a 9" hole, it will probably take 1 1/2 to 2 bags per hole. That's about $8. Can you buy loose concrete, sand and gravel cheaper? Just look into it.
Old 08-14-11, 11:30 AM
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Originally Posted by ITSANSS View Post
my uncle said that the concrete will draw moisture from the ground and it'll cure on its own. This makes sense!
That method will eventually work, but will result in a VERY weak cement mix. Since fences need to be strong enough to stand up to wind loads, I would not recommend you just pour dry mix into your holes. A weak mix will split open at the corners of the post. Mixed concrete is always the strongest when mix it either by hand or machine and are careful not to use too much water.
Old 08-14-11, 01:56 PM
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Thanks for the replies, guys.


I probably could've saved some money by buying the kinda' concrete that needs gravel and sand to be put in and mixed. That's what we use where I work, Duracal is the brand. I tell ya' what, that is a LOT of work. lol At work we put some water into the mixer, then forty (40) shovel scoops full of gravel/sand mix (50/50) and then two bags of Duracal, then some more water. However, I've already got four full pallets of concrete that simply needs to be mixed with water and it's ready to set.

By the way, we figured two bags of concrete per hole. I'm not sure exactly how wide the holes will be.

Also, I had read that putting in a little water into the hole first, then some concrete, poking at it a while to work the air out, adding some more concrete, poking some more, maybe some more water, and repeating is about the best way to do it. Which basically is what I think you're saying and will likely be the way I go.


Yeah, being weak is a concern I had. I know there is a very fine line between not enough water and too much. I think if I take a little time to put water into the hole and in stages add concrete while poking and churning that it'll be strong enough for what I need.

More than half of the fence I'm putting up runs north and south. The wind here blows 360 days of the year and 355 of those days the wind is out of the north or out of the south, which will be "with" the fence. I'm thinkin' if we're careful, we can make the "hole mix" method work for us.
Old 08-14-11, 02:28 PM
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I am not an expert on fences, but if you are using panels, you will still need to adjust somewhere along the line to make of the accumulated length difference/tolerance.

It you are dealing with property lines, set the ends and corners first with a mixed concrete mix. Then go to filling in and making minor adjustments. The corners/ends will be properly anchored and be references for future spacing and alignment. The intermediate posts can be set with layers of premixed and water, with some mixing for consolidation.

There is nothing wrong with a little water in the holes for pre-wetting before the post installation. After the initial set (a day or so), the more water that gets dumped in the area, the better the concrete will be. Dry soil can suck the necessary water out of the concrete instead of providing moisture in the short run.

Old 08-15-11, 06:06 AM
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I'm not quite sure what you're gettin' at with your first sentence. I think what you're saying is that if I have a 20' run I'll have to cut the last panel to fit...?

20' run, three panels = 24', cut one panel in half. Right?

If so, I had already planned on that. There'll be several places that I'll have to cut a panel to make up the difference. Shouldn't be a problem. Put the circular saw blade in between two pickets on the non-runner side and cut the runners. My dad and I have done it before and seems to work well enough.

The biggest run of fence we're putting up IS between two properties. There is already a fence there, two fences actually, so knowing where the line is shouldn't be a problem if we take down the old stuff and put up the new not long after. We should be able to tell where the old stuff was pretty easily I think.

Yeah, the previous owner put up an 8' wooden fence next to the existing 4' chain link. I'm sure it was nice for them not to have to take anything down and not have to worry about animals getting out or in, but it sure does look like crap! lol I'm hoping to have a few hundred bucks worth of scrap metal out of the deal. Maybe more if there is a market for used chain link. Haven't looked into that yet....

After the posts and concrete get dumped into the holes, depending on whether we get rain or not (likely NOT), I may go around each post and water the ground some with a hose to help promote moisture to be seeped into the concrete.


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