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.