Fence Posts

[Furu]

Not quite sure where to put this so here it is.

I have always mixed concrete for fence posts the old fashion way. Yes I know there is an argument to not concrete posts but in some instances it is is the right thing.

My question is: There is a technique that some contractors are using in which instead of mixing concrete the normal way they merely dump the mix in the hole dry. Tamp it in and then let it absorb water and harden slowly over time with the leaching of moisture. Who has done it that way and what are the pros and cons as you see them. My house fence has three posts needing replacement and I am trying to figure out how I want to concrete them in. Old style or new style.

 

[jaxs]

The new posts will decay and be replaced again and you will never know the difference. I have miles of fence built over half a century ago without concrete around posts.

 

[oosik]

The two corner posts and four gate posts on a 1/4 mile run here - we used the "new style". That was five years ago. Seems to have worked just fine. Note - I live in what is called a semi-arid climate. So ......it could be many months between putting a dry concrete mix around a post and the first rain. The "new style" sure saves a whole lot of sweat and bother.

 

[Frankenkubota]

I've done it many times. Seems i used about 3/4 bag per post, dry, tamped it down and put an inch or so of water on top. Next day and forever on, solid as a rock.

 

[Redlands Okie]

Pack the dry concrete mix in tight and your good to go. I have done so for years and unknown number of hundreds of posts. Put the mix in layers about 8 inches or so and pack, then another layer. If easily available will put in splash of water every 6 or 8 inches of powder so that it packs tighter and easier but the water is not required. By a splash I mean about a measuring cup or two. Have used the dry mix in dry sand areas in New Mexico and a week or so later its hard. Was quite surprised since I figured it would be months or a few rains. Keep in mind that concrete attracts water and not a lot is actually needed.

Pro part is that you can build fence that day with out worrying about cracking the material around the post into separate sections. No bracing is needed to keep post plumb. No water to haul. Less mess.

Keep in mind that once you wet up the concrete it is supposed to take about 3 weeks to cure. Since it seems most people start building the fence the next day or so, the movement and vibration of the post actually crack the concrete in the hole. Reduces the effectiveness of the whole process.

 

[s219]

I almost exclusively use dry mix to set posts for pole barns and decks, and it works great. I dump in a little, then poke it good with rebar or a skinny stick to settle and pack the mix, then add more and repeat. Probably do about 6" at a time.

It's very important to do the packing carefully as that is what makes it so firm and strong right away, and will keep it from moving as it absorbs moisture from the ground.

I know some people just dump the mix in then walk away. That might be OK for certain fence posts, but for pole barns and decks I need to keep working and will be putting loads and impacts on the posts soon after they go in the ground. Properly packed, they do not budge. It's amazing how tight it holds.

 

[Diggin It]

Recently I've pulled up a half dozen or so treated 4x4s that I used dry mix on. They've been down 15 years or so and only needed to come up because I'm reworking those areas and taking the fences out. None show any rot, all concrete is solid and firmly attached to the posts. Only one post has some insect damaged (some kind of wood boring ant) and I'm not sure if they came in below ground or above.

I may put the posts back down in new locations with the concrete still attached.

 

[Deere Dude]

I don't want to stray much from posts but I just thought of something else.

I think I may have put a lot of work in for nothing if the put in dry method works.
I had a couple pallets of concrete mix for a bridge footings spanning a creek. I formed up a a couple 12' x 4 or 5' pads a few years ago and had my wife mix premixed using a HF mixer. Put a bag in and add water, then I would dump and drive it over to formed area, and repeat, and trowel off.

Could I have just dumped premix dry in the footing until almost full and maybe put an inch of mixed on to and trowel down.

 

[Redlands Okie]

Some also think its best to not have the post touch the soil at the bottom of the hole. A few inches of gravel or concrete to set the post on, then fill and tamp in layers. Wood post will last longer usually this way.

 

[Furu]

Some also think its best to not have the post touch the soil at the bottom of the hole. A few inches of gravel or concrete to set the post on, then fill and tamp in layers. Wood post will last longer usually this way.

True whether you are using old style or new style or even if you are just tamping in clay without any concrete.
It seems like a fair number of you have had very good luck with this new method. I will give it a try and just tamp in the concrete mix like a normal field fence.

 

[jaxs]

I don't want to stray much from posts but I just thought of something else.

I think I may have put a lot of work in for nothing if the put in dry method works.
I had a couple pallets of concrete mix for a bridge footings spanning a creek. I formed up a a couple 12' x 4 or 5' pads a few years ago and had my wife mix premixed using a HF mixer. Put a bag in and add water, then I would dump and drive it over to formed area, and repeat, and trowel off.

Could I have just dumped premix dry in the footing until almost full and maybe put an inch of mixed on to and trowel down.

I also would like to hear the answer to this. 100% of companies who manufacture concrete products say proper ratio of water to material is extremly important. If this dump and done method work's as well as folks are saying here it would be far less labor when pouring pads. I'm a little too old to believe fairies come at night and add correct amount of water to concrete .

 

[Diggin It]

You can do a small space around a post that way when you want weight to hold the post down and stable. You can't do anything where structural strength or surface integrity matters.

 

[EarPlug]

Have you ever tried setting them with Foam? I have used it with 8x8 post hanging a 16 foot gate. Easy and fast.

Pole Setting Foam - Rainbow Technology

 

[bcp]

The premix I've had harden in a bag by absorbing moisture is far weaker than properly mixed concrete.

Bruce

 

[RalphVa]

Not quite sure where to put this so here it is.

I have always mixed concrete for fence posts the old fashion way. Yes I know there is an argument to not concrete posts but in some instances it is is the right thing.

My question is: There is a technique that some contractors are using in which instead of mixing concrete the normal way they merely dump the mix in the hole dry. Tamp it in and then let it absorb water and harden slowly over time with the leaching of moisture. Who has done it that way and what are the pros and cons as you see them. My house fence has three posts needing replacement and I am trying to figure out how I want to concrete them in. Old style or new style.

That's what I've always done. I'll supply some water on top.

Ralph

 

[ultrarunner]

40 years ago I did a lot of fences with the Green Pressure treated and mixed the concrete and set it.

Not a one has gone bad... some have the Brown Pressure treated not nearly as long and bad.

I don't know what the answer is..

 

[Redlands Okie]

The premix I've had harden in a bag by absorbing moisture is far weaker than properly mixed concrete.

Bruce

More than likely because they have not had enough water to allow the complete processing of the chemicals in the bag. To much water weakens the finish result. To little water does the same. The post in the ground are going to eventually absorb all the water they need to complete the reaction.

 

[Redlands Okie]

40 years ago I did a lot of fences with the Green Pressure treated and mixed the concrete and set it.

Not a one has gone bad... some have the Brown Pressure treated not nearly as long and bad.

I don't know what the answer is..

The treated post of recent years do not hold up near as well as the old formulas used on post. Environmental regulations are not always useful or well thought out. Put in one arsenic treated post like we used 30 years ago and typically expected to last a life time. Today’s post in central northern Oklahoma will often times last 5 to 7 years. Lot more chemicals, resources, and money being used and wasted as a result in the long term.

 

[Redlands Okie]

I also would like to hear the answer to this. 100% of companies who manufacture concrete products say proper ratio of water to material is extremly important. If this dump and done method work's as well as folks are saying here it would be far less labor when pouring pads. I'm a little too old to believe fairies come at night and add correct amount of water to concrete .

If enough water and time was available for the complete chemical reaction to take place it would probably do better than many think. Concrete typically is like a sponge. Concrete attracts water. Always. To much water in the beginning weakens the end result.



“These chemical reactions form calcium silicate hydrate which then grow into crystalline fibers which bind to each other and quite literally, cement the entire mixture together. These fibers bind to each other and also to the inert materials, like sand and gravel.”

Why Concrete Doesn't Actually Dry Out


“Increased space between cement grains: Higher water-to-cement ratios result in greater spacing between the aggregates in cement, which affects compaction. Similarly, increased moisture levels reduce the concrete’s compressive strength and durability. As concrete’s surface area increases, particularly with the addition of fine aggregates, so does the demand for water. The increased water leads to a higher water-to-cement ratio.

When excess water creates greater spaces between aggregate materials, the voids fill with air after the moisture evaporates. The resulting inadequate compaction reduces the concrete’s strength. Concrete with trapped air levels as little as 10 percent experience reductions in strength of up to 40 percent.”

3 Ways Moisture Affects Concrete Strength - Polygon Group

 

[EddieWalker]

As a contractor, I sometimes get jobs to replace rotten out fence posts. In every case, the wood post is rotten at ground level, and then going up a little, or a lot, depending on how long the rot has been going on. In every case, there is a low spot next to the post where the water sits for periods of time. In every case, when I get the post out of the ground, it's in pristine condition. Some still have the green color from being treated. In my opinion, the most important thing for a fence post to last is that the water is forced to go away from the post.

When concrete is poured around a post, it locks it in better then compacted dirt. Compacted dirt will absorb moisture and hold it more then the undisturbed soil. For line posts, and posts that do not have to hold back livestock, compacting soil around the post is fine. Just be sure to ramp up the dirt.

When pouring in concrete dry, it will harden around the post better then compacted soil. For line posts with livestock, this works pretty good.

Mixed concrete that is poured into the hole around the post will be the strongest because the Portland Cement is well mixed through all and and aggregate. When pulling a post, it is very obvious to tell if the concrete was poured in dry, or mixed. The mixed concrete does not break off of the post, but the dry concrete usually falls apart when removing the post, and it breaks off pretty easily.

For corner posts and gate posts, mixing the concrete first will make for a much stronger post.