Fence Posts

[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.