I’m gearing up to start another round of fencing. I do add concrete my fence post holes, because in the floodplain, the flotation forces of full-submersion flooding can cause whole fence lines to float- or so I’m told by a neighbor who learned this the hard way! So the question I’m pondering this year is, pour the concrete in the hole dry and let it cure on its own, or pre-mix the concrete first?
Last year, we did a few posts with dry concrete, then I started to worry about this, and did the rest of them with wet concrete. At the time, I convinced myself that the wet concrete flowed better around the posts. And I wanted it to cure as fast as possible, since I’d be stretching the fence sometimes within days of setting the posts.
The downside is, hand-mixing the concrete adds a tremendous amount of labor and time to post setting. Since I’d do the posts little by little, renting a concrete mixer wasn’t practical. Instead, I’d mix one bag at a time in a plastic bin, pour it in the hole, tamp it, then do another bag. I often did 3-4 sixty pound bags in each hole (and I’m now thinking maybe that was more than I really needed). It was back-breaking!
So this year, I have been feeling tempted to dump dry concrete in there, add a little water, mix and tamp a little, and call it good. This is apparently called “in situ” curing. For one, the concrete manufacturers even recommend doing this, so it can’t be all that horrible to do! I searched the web on the subject and found a lot of good debate on either side of the issue, especially here. Many people feel strongly that a wet pour is far superior.
The con’s: possible compromised concrete strength, possible pockets of uncured concrete in the hole, longer cure time (though we have such wet soil, that may not be an issue here).
The pro’s: I found the abstract of an actual study done by engineers, (Paper number 034003, 2003 ASAE Annual Meeting; authors David R Bohnhoff, Zachary D. Hartjes, David W. Kammel, Nathan P. Ryan) that says this:
Hydration of a dry concrete mix after the mix has been covered with soil is herein referred to as in-situ hydration. In this study, a series of dry concrete mix footings were hydrated in-situ by burying them in sand and subjecting them to different water treatments. Footings were removed and cored at 4, 12 and 24 weeks. Compression tests on these cores showed that in-situ hydration could produce concrete with strength comparable to a normally hydrated mix. Additional research is needed to determine how in-situ hydrated concrete strength is affected by aggregate properties, initial compaction, confinement pressure, dry mix uniformity after placement, as well as conditions related to water movement into the confined mix.
I’m liking this idea, I think it will really speed up my fence building, and save my back! As I’ve mentioned in other posts, I think in our region, the first and biggest failure point of fencing is posts rotting. So, as long as my posts have enough decently cured concrete to keep them in the ground during a flood, and to help resist wire sagging, dry-cure concrete may be good enough for me!
While it is a good thing to limit the amount of water used in concrete its important to remember that a water to cement ratio below .25 will not be enough water to hydratethe cement in the concrete mix. i would suggest to minimize this you always use wet cureing proceedures.
Mike, thanks for the input. I would imagine for people who have dry soil, this could definitely be a concern and rationale for choosing wet cure. But, alas, we live north of Seattle, our pasture is in river bottom land, and I suspect there is never a day when the soil is too dry to cure concrete all on its own. We have the opposite problem, where concrete bags often cure while we are storing them in a garage or whatever, there is just so much moisture here! 😛 So far, my posts seem to be staying put, but the ultimate test will be in the next flood, when the flotation forces on the will really test how well their concrete feet hold them in the ground!
Michelle
Hi Michelle,
How did your posts hold up? I am putting in a fence near Seattle as well and considering the dry method (as recommended by a couple friends).
Thanks,
Jason
Jason, as far as I can tell, the wet and dry cure methods worked about the same here! I haven’t noticed any difference in the fields I did differently.
Michelle
I am a Fence Contractor located in Haymarket, VA. I rarely use wet concrete to build fences. I only wet pour when the homeowner insists. When this happens, I inform them there is a higher labor cost for installation. It is standard practice for most of the fence contractors in my area to Dry Pack the concrete around the posts. Standard practice is to use 40# per line post and a full bag (80#) for gate posts. We set the post in the hole, pour the concrete, tamp with a digging bar, finish filling the hole with dirt and tamp. Just make sure the holes are the right depth to accomodate the height of the fence. I have never had any issues with posts rising or leaning. When installing Farm Fencing I use a Wheatheart brand Post Driver and use no concrete.
Clyde, thanks for the input- it’s nice to know that it works well for someone in the business! So far, I have not noticed any difference in performance between posts I did wet versus dry!
Keep in mind that, while dry pouring may result in a somewhat weaker concrete than wet mixed, does it really matter for such an application?
The primary reason for concrete in a post hole is to effectively make the portion of the post that is underground effectively bigger so that there is more surface area in contact with the surrounding soil. In such an application it is under compression, never tension. It would have to be amazingly weak to crack and crumble under compression. I would think the post would snap first.
Yes, the concrete can also add weight to hold the post down in the hole, but adding weight does not require a heck of a lot of strength either.
My fields are mostly clay, so I am lucky enough that I can get usually an “H” end-brace of a long tension fence to stay put in only 2 feet of soil with no need for concrete at all.
Once in a while I will find the need for concrete however. I dig my hole – trying for straight or even a bit wider at the bottom, drop in my post (asphalted on the portion going under ground), pour in dry concrete up to about 6 inches below the surface, pour 3-4 gallons of water into the remaining cavity, wait for the water to disappear, and fill the remainder of the hole with dirt to a level that is a little higher than the surrounding surface, and tamp it down with my foot. It will all settle out eventually. Make sure it is level when you are done, and keep an eye on it for a few hours to make sure nothing stupid happens. After a few hours it really isn’t going anywhere just standing there.
My water table is pretty high year round, so the soil is never dry around here. If it was a dry period, you can always pour some more water around the post every day for 3-4 days. By then you will have reached roughly the 50% of final cure strength. If you were building an elevated concrete bridge you might want more than that, but this is just a fence post putting the concrete under compression. Heck, even if the concrete did develop a crack or two, what real difference would it make? It would still resist forces applied under compression.
I see in your picture that you use “T-Posts” . Be careful with them, especially around horses or llamas (primarily the intact male kind of llama). They play rough (if you call a llama fight “playing”)… really rough.
A T-post can kill.
My vet told me that he pays for a new big dually pickup every 3-4 years on what he makes off T-Post injuries. I use mostly 5 wire tension fences with support posts every 100 feet or so if the run is straight enough and level enough to permit it. That is probably about 1/10th as many posts as you are using in the picture, and I only use PT 6×6’s now a days. The cost isn’t much different than a T-post (rough cut PT 6×6 is about 10 bucks right now). They are stronger, will last longer, and are safer. The part I like is there is only 1 post every 100 feet or so to plant and maintain. Less insulators to install and replace as well.
Fences… a fascination, a perpetual learning experience. We will all grow old and be dead before we figure it all out. 😉
Rick
Good points, Rick. I’m not very good at civil engineering principles; but it seems to me that the concrete does suffer some tensile forces- because the H brace post is experiencing torque from the pull of the top wire, the post wants to “flip” at the fulcrum point of its entry into the dirt. So it’s encouraging the concrete to crack apart. But even if that happens, there is still a lump of concrete on the upward side of the post that makes it harder for it to keep migrating. I think that creates the “dead man” affect that some people achieve instead by burying a big rock or a horizontal bit of wood on the side of the post that wants to flip. For cases where the concrete is only being used to stabilize an H-brace, I imagine putting most of the concrete on the flipping side of the post would be useful.
For me, since my fences are in the flood plain, the concrete feet serve two purposes- to discourage the H brace from leaning, and also to keep the posts from popping out of the soil when they are under water. I put bolts sticking halfway out of the posts, so it embeds in the concrete. So in theory, despite the posts wanting to float under 6′ of water, they’d have to take their concrete feet with them… So far, so good!
Re: T-posts, indeed, horse people don’t like them. No horses here, and only one guard llama. I am tempted by hi tensile wire for the points you raise, but several of my friends have found that it’s not as good for keeping dogs in our out as woven wire. Well-contained guardian dogs and deterred coyotes are a principle function here, so for now, it’s woven wire for us!
IN THE PAST WE HAVE ALWAYS WET SET POSTS BUT I THINK DRY SETTING WORKS IF THERE IS ENOUGH MOISTURE PRESENT.
Outstanding posts by all here.
I am building a fence in Lake Stevens and was wondering about dry or wet concrete. I see this article has answered my questions.. My concern is how long do I need to let the concrete cure before i start putting the panels on? I like the idea of 24 hr minimum. My contractor friend is telling me that you dig the hole, pour your dry concrete, wiggle your post, build your 8′ panel, and up it goes. I’m thinking that I am asking for problems if I do that.. I am thinking more like posts on weekend and the panels next weekend. It’s only going to be about 130′ total but I am in a development with a HOA and my property is next to the park. I am going to rent a 10″ auger. Am I overdoing it or is this about right?
Chuck, it seems to me that if you are just attaching panels to the posts, there may be so little load on them that you’d be fine doing it right away. Because with those, most of the load is straight downward, the fence posts are mostly just bearing the weight of the panels hanging between them, so the forces on them are mostly just gravity (unless there is a windstorm pushing them sideways on the day you install! :-D). If you were worried, I think at most giving the corner/end posts an extra temporary support would help so they don’t inch towards the weight on one side, but all of the middle posts should have equal tension on both sides?
With farm fencing, where you are stretching wire between the posts, then they are under a little or a lot of tension which is encouraging them to “flip” sideways. So it could cause them to break their concrete footing if it wasn’t yet cured.
If it were me, I would wait a week between setting posts and applying pressure. Dry, uncured concrete is fairy slippery stuff… much slipperier than tamped dirt. You would be unhappy if the posts moved in he middle of the night due to a wind storm and you found the concrete had already set up as well.
Of course you do need moisture in there to make it set up. If the ground is damp already, or if it rains a fair amount you will be all set. If not, you will have to pour water in there … maybe a 5 gallon pail full per post every day for 3-4 days. Take it easy with water the first day as you don’t want to make mud out of the concrete. It might not fully saturate with water the first day, but at least some to most of it will stiffen up enough that it the post isn’t going to fall over on it’s own. Once it is somewhat stiff you can go with more water to make sure it is well saturated. It takes 30 days or so for damp concrete to reach its near-full strength, but it reaches roughly 50# of it’s ultimate strength after the first 3 days (depending on temperature). It needs to be kept moist the whole time. The water does not have to go directly into the concrete, just into the soil near the concrete to saturate the soil. Once the soil is wet, it will make it’s way thru the concrete.
Don’t forget of course that you are not pouring footings to support a high -rise skyscraper. As long as the concrete is a fairly solid chunk it will do it’s job just fine.
I recently pulled up a couple of PT 4×4 posts that I dry-set in 1994 and the concrete came up in one solid chunk still attached to the post. I recall at the time that I poured them the ground was fairly damp so I just poured the dry concrete in and walked away for a few days.
we dry set post yesterday into a 20 inch hole…is this deep enough for Pennsylvania..the post are for a hammock?
Tracy, I don’t know, I’m far away from you on the west coast, so I don’t know much about your soils. I guess since you already did it, you’ll find out soon enough! 🙂 I suppose you could always run a beam between the two posts at the top, to brace them against leaning inwards?
“Run a Beam” ……. Sigh….. Great idea. I am now building trapezoid for a gate. Although I am not building a gate very well.
With havin so much content do you ever run into any issues of plagorism or copyright violation?
My site has a lot of completely unique content I’ve either written myself or outsourced but it seems a lot of it is popping it up all over the web without my agreement. Do you know any ways to help stop content from being stolen? I’d truly
appreciate it.
David, I haven’t looked much to see if my content gets stolen, but I think it’s a fact of life on the web. Of course labeling things with copyrights and putting watermarks on images may help, but I still think a lot of people disregard it, and scraper sites are horrible about mirroring content. I suspect the only recourse is the same as what corporations do to protect intellectual property- spend a lot of resources looking for instances of violation, then taking action. I’m sure most violators will take the content down if you demand it, but some probably won’t without a lawsuit. So we’re stuck deciding how much energy, time and money we want to invest in self-protection- it’s a bummer indeed!
I wonder if WordPress has any articles on this topic? Since they are one of the largest blogging platforms, they may have some resources there, I just haven’t looked.
Thanks for the info!
A lot of them advocate a water-in-hole method where you dig the hole, get your post level, fill the hole 1/3rd with water, then dump the concrete on top of the water, mix it up a bit, then add some more water to the dry top, then more crete. I used this method for a major heavy-duty gatepost (6’X6’X8′ timber, four 50# bags and a 10′ steel tube gate) and its held up perfectly fine under heavy, daily use. For something as low stress as a fencepost, I’d have NO hesitation whatsoever to use this method.
If you put ideas on here, I would think that you are doing it to help , other wise dont do it.LOL if you voluntarily post some thing to help, why worry about some one using your idea, I thought that was the reason you posted it, so that some one could use it????
I had a chain link fence co put in about 200 feet of 4 foot chain link and they dry poured all the post.
James, if you are referring to the commenter approval process, I have it in place to prevent spammers (sometimes people try to post porn, or advertisements ). So WordPress flags anyone new, and the comment waits in a queue until I ok it. Once you make it through the process the first time, WordPress less you comment freely after that. I almost never have to remove a comment, as my commenters are pretty well behaved! 🙂 Usually I do it the same day, but was on vacation, sorry I was so slow! Thanks for your comment on the dry cure, interesting to know that a professional company uses it for chain link!
Well an update from my June 2012 posting. I have noticed a twist in my gate post and a lean. Bad enough that I redid the whole panel and the gate. As I look back on the reply from my post. I think I might have stressed the concrete too soon…..like I was warned about.
I dumped it in dry on a hot July 4th day. Then let the hose run on each post and sprinklers for about a few hours. Started around noon the next day. It might have cracked from still being green. I knew their was a chance but my time was limited. Good lesson for my first fence project ever.
Good to see the blog still Truckin.
Thanks for the update Chuck! I think I would be inclined to let concrete cure at least a week. I’m trying to remember the advice from the concrete guy who poured the foundation under our house, which was moved to this location. I think he also said wait a week before setting the house down on the foundation, to be safe. And that is with mixed concrete- I would think dry-cure, you’d have to be conservative, since it may take some time for the powder to pull in enough moisture to finish curing all the way through?
I crappy concrete guy will claim it is “cured” in one or two days so he can remove his forms and move on to the next job. A friend of mine had to do a very expensive repair job to the foundation of a house that he had built just because of this. It cracked within hours of the guy pulling out of the yard with the forms on the back of his truck. A more responsible guy will leave his forms in place for at least 3 days (pour on a Friday and take the forms down on a Monday).
Rule of thumb is that it reaches 50% of it’s cured strength in 3 days at 60-70 degrees F if you keep it damp. If it is colder or allowed to dry out all bets are off.
30 days 60-70F and damp should bring it to around 90% of it’s ultimate strength, which is typically more than one should need for a fence post hole.
For me, I dry pour concrete one weekend, start adding load to it the next weekend, and during that week that it is curing I try to dump at least a few gallons of water over it at least once around mid week to keep the area damp. If I am lucky, it will rain and I wont need to do that.
Good advice Rick, thanks!
Drive nails un post below ground level. About3 or 4 in each side of square posts ..it holds concrete to posts, doesn’t crack and come loose, my posts were 18 to 20 ins deep, a bag or less per posts and make the hole a bell shape..bigger at bottom..havevt had a y problems so far…and dry pour…works for me
Thanks for the comment Larry. I have often used galvanized lag bolts to the same purpose and it has worked well for me too!
Last year, we did a few posts with dry concrete, then I started to worry about this, and did the rest of them with wet concrete. At the time, I convinced myself that the wet concrete flowed better around the posts. And I wanted it to cure as fast as possible, since I d be stretching the fence sometimes within days of setting the posts.
Mike, thanks for the input. I would imagine for people who have dry soil, this could definitely be a concern and rationale for choosing wet cure. But, alas, we live north of Seattle, our pasture is in river bottom land, and I suspect there is never a day when the soil is too dry to cure concrete all on its own. We have the opposite problem, where concrete bags often cure while we are storing them in a garage or whatever, there is just so much moisture here! ?? So far, my posts seem to be staying put, but the ultimate test will be in the next flood, when the flotation forces on the will really test how well their concrete feet hold them in the ground! Michelle
Drive nails un post below ground level. About3 or 4 in each side of square posts ..it holds concrete to posts, doesn t crack and come loose, my posts were 18 to 20 ins deep, a bag or less per posts and make the hole a bell shape..bigger at bottom..havevt had a y problems so far and dry pour works for me
Mike, thanks for the input. I would imagine for people who have dry soil, this could definitely be a concern and rationale for choosing wet cure. But, alas, we live north of Seattle, our pasture is in river bottom land, and I suspect there is never a day when the soil is too dry to cure concrete all on its own. We have the opposite problem, where concrete bags often cure while we are storing them in a garage or whatever, there is just so much moisture here! ?? So far, my posts seem to be staying put, but the ultimate test will be in the next flood, when the flotation forces on the will really test how well their concrete feet hold them in the ground!
Well an update from my June 2012 posting. I have noticed a twist in my gate post and a lean. Bad enough that I redid the whole panel and the gate. As I look back on the reply from my post. I think I might have stressed the concrete too soon ..like I was warned about. I dumped it in dry on a hot July h day. Then let the hose run on each post and sprinklers for about a few hours. Started around noon the next day. It might have cracked from still being green. I knew their was a chance but my time was limited. Good lesson for my first fence project ever.
Thanks for the followup bmwmarine! 🙂