Fence Posts - What are your thoughts on using gravel, concrete, dirt or some combo to put in fence posts?

Question

We've just finished installing our first three panels of our first phase of our fence project. We decided to put a couple inches of gravel in followed by fast setting concrete with our PT posts. I'm curious to know what others' thoughts are on which to use - gravel, concrete, dirt or some combo? Also, we tried renting an auger but it was a big fail - manual digging was easier - this happening to anyone else?
http://29ruehouse.blogspot.com/2012/04/fence-progress.html

Post 2 Post Fence, Inc · Answer

Yes, you need to cement the posts. But, to make them sturdy, they must be in the ground at least 24 inches and have the hole filled with cement.  Personally, I don't like the fast drying cement, because it dries too fast and there is a tendency that it will crack.
We have had issues in the past with augers and, unless it is a large or rural  job, we manually dig the posts, too. There are too many irrigation lines along the property lines that are never marked. You have more control by hand digging. And, remember, you are required to call 811 before you dig.

3po3 · Answer

Agree with P2P on both the cement counts. Use regular cement and go down 2 feet. I used a shallow footing of quick-drying cement for a clothesline pole in my yard, and it cracked, then frost-heaved out of the ground. It's back to square one, and I am definitely going in 2 feet this time.

Jeff C · Answer

It's already been mentioned, but whenever you put something in the ground, you need to go a tad deeper than the frost line if possible. This will ensure that your cemented footing will not be surrounded by frozen soil which could push your post out of place and screw up the look of the fence. I tried just using gravel and digging down 20 inches or so for a mailbox post and that sure didn't last long. I used quick setting cement and that's been holding the post in quite nicely.

KMS Woodworks · Answer

I just replaced a run of two fence sections for a client here a couple of weeks ago.  A wind storm had blown them over. The failure point was just above the concrete were the lower portion of wood was in contact with soil.  Over time this soil wood contact zone rotted away.

My repair involved digging out the old post bases...concrete and all.  New cedar posts were installed in the holes and new (mixed) concrete was added.  I have never been a fan of the practice of adding dry mix to the holes then flooding...just get some quick crete and mix it in a tray or wheel barrow...it only adds about 15 minutes and makes for a much stronger pour.   I like beefy bases so I tend to dig 10' dia holes or so (with a shovel)  I use a hoe to lift dirt out of the deeper hole,  fence post digging tools only work for very shallow work in sandy or wimpy soils.

when the hole is about 2' deep an 8 foot post will give you a good 6' above ground. In my recent repair I filled the hole to about 2' of grade and shaped the concrete into a 'dome' shape this will allow water to drain away from the post.  To keep the soil from rotting away the post base I then added some coarse crushed stone ( 1' monzonite) this also limits plant growth at the post base.

Nichter's Home Services Corp · Answer

Never set fence posts in Crete!!!

Water gets in and is held tight in the post to cause it to rot faster.
That same water freezes and expands, so the crete will break apart in a few years if there is no re-inforcing wire tying it.

Frost can grab the rough edges of the crete poured in a raw unlined hole and lift it out easier than it can lift a post  alone with smooth sides.

I learn from old timers ( almost one myself now) and from demo work and repairs on older jobs.
The ones in crete do NOT last as long.

3po3 · Answer

So what should you use, Nichter?

Crystal - 29 Rue House · Answer

Thanks everyone for your input. Since we're only 3 panels in of our 8 panel job for the first phase (just the back side of our property for now), you're definitely giving us something to think about! We're going about 24' for each post but didn't realize the frost line had anything to do with it. From what I'm finding online the frost line is around 36' deep which makes 8' posts too short so I don't quite see how that could work.

What is crete? Is that a brand name?

Post 2 Post Fence, Inc · Answer

crete is a shortened term for concrete

Post 2 Post Fence, Inc · Answer

the bottom of the post should set on either the ground or gravel, not encased in concrete. When you cement the post, leave the bottom open so the post (and surrounding area) will drain.  If you use pressure treated lumber, it will not rot for at least 25 years or until it dries out.  We put up fences 20 years ago and they are still standing strong.

KMS Woodworks · Answer

This also depends a bit on your climate.  The posts I replaced last week were 16 years old.  Where the post had failed was were the soil was in contact with the wood ABOVE the concrete.  The wood inside the concrete was still very sound.  In the two short sections I replaced, where the old concrete bases were taller...and not topped with soil the post were also sound.  Concrete is only wet until it cures...then it can wick moisture a bit like a sponge...the exposure to moisture is more of a problem.  If the crete is rounded on top it will shed nearly all the water that may fall on it.  I have seen posts set this way that are well over 20 years old with out any trouble at all.  The trick is to keep the soil away from the wood.

Cindy M · Answer

We set ours in 2 ft and  dug with post hole diggers, set with concrete.

Cindy M · Answer

and of course you have to put some gravel in first, then the post then concrete.

Nichter's Home Services Corp · Answer

It definitely is a regional thing. The clay soils in the NE hold water that encourages rot and frost heaves. I compact mineral soil in around my posts. That lets water drain thru. The soils in FL are sandy and it never freezes there. The extreme cold in CO and the drier climate means less rot organisms to attack.

When I see bare naked cedar posts rot off after 30-40  years, it is always in the top 8' of soil. There you have moisture and oxygen. In damp clay soils there is not enough O2 to feed the microbes down deeper.

I set posts four feet deep. That fights strong wind better than only two feet deep too.

When you only set them to the expected frost depth, the frost can still grip the sides of the post and lift it up and out of the ground over time. Set them much deeper or use a technique some do - nail or bolt a cross member onto it at the bottom to make a reverse T and wrap the PT post in plastic like saran wrap - several plies. This makes it slippery so the frost cannot get a grip on it. 
Personally I dislike anything like this that can hold water TO the wood and trap it there.
Crystal, You mentioned you are using Cedar posts, but the photo shows it green, making it seem like a pressure treated. Is it possible that the post is PT but the fence sections are cedar?

How much frost acts on a post depends a lot on how well the site and the soils drain. Wet soils will do a lot of heaving while dry places will turn cold without ever heaving up.

This is art as much as science

Crystal - 29 Rue House · Answer

Nice catch Nichter - you are right they are PT and not cedar. We also recently planted a raised garden bed made from cedar and I must have had that on the brain when I typed this. Just fixed this in the original question/post. Thanks for all your input!

Nancy Rhodes C · Answer

I like the idea of doing a few sections at a time.  I have one post to my wooden dog pen that is loose at one of the gates.  Guess the only thing to do is dig out some space and pour more concrete around the post without disturbing the remainder of the fence?  We used all concrete to a comfortably high point then finished with filling in some dirt.  The posts set overnight.  After the contractor left I tested that post to see if it had set so I know I am the one who messed it up.  Why did I do such a stupid thing?  I really thought it would be set already.

KMS Woodworks · Answer

One problem with back filling soil over the concrete is it creates a biologically active 'rot' zone above the concrete...this continual exposure will lead to a more rapid fail.  I like to use a bit more concrete and fill all the way up or cover the top of the concrete with a very coarse (1 inch) crushed stone to keep it well drained. In both cases tooling the concrete into a slight dome shape to allow water to shed naturally.

Rich M · Answer

I've done 2 decks, and both locations had local building codes that required me to pour a concrete 'footer' (12' diameter, depth to 6' below frost line).  I embedded an L bolt in that at the time of pour, then bolted on a galvanized post bracket.  The 4x4 was then screwed into the bracket.  Both decks over 20 years in place, no failure.

Thanks to Nichter....
I see that I misread the request - you are right, fence post application is entirely different.  For fencing, I've used a gravel base at the bottom of the hole, and dry-packed concrete to fill in the hole around the post.

Nichter's Home Services Corp · Answer

Rich a deck post has to bear the vertical load of the deck, the occupants, and snow that lands on it, so it must have footings to support that.

The only load a fence post has to handle is a horizontal load applied by wind. The two different situations call for two different approaches

KMS Woodworks · Answer

If deck post base brackets were used in a fence application the fence would blow over in the first wind storm. I most of these cases the only lateral resistance are a few short 8d hanger nails driven in the 1 1/2' sheet metal tab...its not going to survive any real lateral loads.

Nancy Rhodes C · Answer

I see! our fence posts should have been filled to the top with cement.  Nichter's Home Services C... Contractor, how many deck posts (footings) would you place under a 9X21 deck supporting a pitched roof?

Nichter's Home Services Corp · Answer

Nancy, the answer to that is variable.
If you are framing with 2x8 you need loser spacing than if you frame with 2x12 for instance.

And it depends as well on the soils in your area and their bearing capacity and the width of each footer spreads the load over a greater soil area.

Again, if you attach one side directly to the house, then half the load is borne by the house footer, but it is becoming increasingly ( with very good reasons) more common to build decks freestanding with its own foundation support, which doubles the number of posts and footing pads

But in general, since you have no snow load to speak of bearing on this, I would space those posts ~9'OC

Home improvement specialties · Answer

generally, if you have ground heaves, shifts or your posts are going behind a wall that might contract and expand, putting them in gravel is the best. But if you use just gravel, the post hole should be twice the depth of concrete. Never, ever dirt, especially for privacy fences with some weight - rain or other water sources will make them fail quickly. Looks great, by the way :)

TRD Designs Ltd. · Answer

3/4 inch gravel 6's below and around post so the drain.  concrete or mortar mixed into posts with gates.

Nancy Rhodes C · Answer

Are you talking to me Tom Dieck/TRD Designs L?  Are you saying I should have my dog pen post dug out entirely with old cement removed with 3/4 inch gravel put below and around post with total of 6 inches for drain.  Then pour the concrete mix to top on top of the gravel?  This would have to be a big hole around that very important post but if that is what to do, it will be done.  This is the post that the gate locks into.  The other gate is perfect and all else is perfect except for this one post.  It wobbles.

TRD Designs Ltd. · Answer

No, that is not what I am saying.  If you were building a new fence, I would place the line post (pressure treated or cedar) in a base with gravel.  No cement.  Only the gates should have concrete for the fact that they move and will stronger with a concrete base.  It never pays to redu something unless its not working.

Nancy Rhodes C · Answer

Well Tom,the post is working by holding the lock in place but so much pressure is put on it that I actually feel sorry for it.  I walk all the way around the pen to use the other door to keep from disturbing this one wobbly post.  I do so want it secure and strong like the rest of the perfect and beautiful fence.

Sheryl J. Wykes · Answer

I put in a 6' farm fence about 20 years ago and I just now have to the replace the double gate leading into the back yard. About 5 of my horizontal boards have had to be replaced mostly due to damage by weather. The posts are still fine! All together I hand dug 31 post holes, my son tried to rent an auger and after digging approx. 10 holes that weren't in the area of my giant maple tree he gave up! I dug 2 foot holes with the old post hole digger, added 6' of gravel, then quikrette, of course using the post leveling tool. This worked for me, but it took me a while to finish by myselr and working full time, but it was worth it!

La Habra Fence Company · Answer

Agreed. These material could be good for creating a fence. It will be less expensive also.

Nun32489822 · Answer

there is a bag of post fix you can buy from the DIY shops or super garden centers eric

Tom wilson · Answer

If you want to build a fence for adding a definition to your yard, it is essential to ensure your wall is fully functional by setting the fence posts correctly. Deciding what material you will use for setting the fence posts is necessary for your stability before digging a post hole. My thoughts on using gravel, concrete, or dirt to put in your fence posts!

Setting Fence Posts in Concrete

Whether you want to leave the fence in place for a long time or have very loose, sandy soil, It is essential to set fence posts in concrete. Pour 6 in. of gravel around the fence post and then top with concrete. If the concrete is too loose, use braces to keep the seat upright. Make sure the concrete is hard before attaching anything that puts weight on the posts.

Setting Fence Posts in Gravel

Gravel is less untidy than concrete, but it can be less durable. Stone is best for fencing in heavier than soils and allows water drainage around the fence posts, making the posts less susceptible to frost heaves. Dig the holes the same way as you would set posts in concrete. Pour 5 in. of gravel in the gap around the poles and tamp it down. If you want to grow grass around the fence post, leave 2 in. of space between the top of the gravel and the soil line around it. Unlike concrete, the stone doesn't need to set. Setting fence posts right the first time is the best way to ensure that your fence is sturdy and wind- or animal-resistant.

Fence Posts - What are your thoughts on using gravel, concrete, dirt or some combo to put in fence posts?

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