I'm currently replacing some fence posts that have rotted out. All of them were destroyed at the bottom, where the post met the dirt, above the concrete setting.
Seems pretty obvious that excess moisture is causing the issue. The soil and grade of the land doesn't really drain water well.


What's the best preservative or coating to use on the few inches of wood not in concrete and in contact with the soil?

I was bouncing around the idea of asphalt/driveway sealer (have some leftover). Is this a terrible idea?






An inch or two of gravel will be used for drainage as well, but it can be damn near a swamp, at times, on that part of the property.

 The house I bought has 4" wooden fence posts on the property, from talking to the neighbors the posts were put in about ten years ago.  



What I noticed was that ones put in directly into the ground are rotted, the ones with the base wrapped in 3 ml. black plastic to ground level are still firm and not rotted.



When I put new ones in, if not pressure treated, I'll wrap the base in plastic as he did.  

Can you use metal fence posts, or would they rust equally badly?



We replaced our fence out of necessity, but did it with metal posts and metal-to-wood brackets in order to still have a wood fence.

This seems promising, but a fair amount have already been set in concrete.

Thanks for the responses so far.

Set several posts in a 55 gallon drum.  Add a 50/50 mixture of used motor oil and diesel fuel to the drum.  Let soak a few days then remove and add more posts and mixture.

This is the way that I did mine 12 years ago.  On most of them I just drove the metal posts straight into the ground. But where the gate hangs, I set them in concrete and also filled the post with concrete. Its solid. I had to move 1 of the regular posts a couple months ago (because of other construction). There was very very little rust on the post. Should be good for another 15-20 years easy. I figure ill have to replace the wood slats, stringers, etc in another 8-10 years . But with a 20 year lifespan on wood and a 30+ year lifespan on the posts, I'm happy with it.

Metal posts. If you are insistent on wood posts I would look into possibly fiberglassing over that part of the post and up a few inches above ground level.  Even just the resin alone might be enough. But those posts better be pretty dang dry and you'll want to seal the wood.

If you want to stick with wood, try to find Osage Orange (a.k.a. hedge, horse apple...) posts.  I've got posts that have been in the ground 50 years and are still as solid as the day they went in... possibly more so.  Can be tough to find nice, straight posts, but it's worth the hunt.

Osage orange is about $20 to $25/bd-ft.  A four foot long 4X4 fence post would cost well over $110 each.  


For applications like this, it seems to me a metal insert in the ground would be best.  You can use a wooden post above the soil level.

Maybe dip them in black tar foundation waterproofing with the coating extending above the ground a few inches ?

That traps water in them. Not good



Oil is the best thing I have ever seen.





 

At home (WV) we used locust posts.  Dad put some in around the garden before he went in the US Air Force in 1953 and they had to replace most of them in the late 1980's and early 1990's.  Some lasted longer.

Dad said, after a few more years experience with fences/posts that he though the best time to cut the trees for posts was in the winter time when the sap was down in the roots/ground.

Don't know if you have locust trees in your area or not, or if you can cut some if you find them.  It's all we use at home.

The ones we put in along the fence in front of the house in the mid to late 70's were still there when dad passed away a couple years ago.  Mom had them cut off and had a chain link fence put up along the road (dad was about what works best, mom wanted pretty).

Even treated posts are not consistent.  I put up a 3 rail fence of treated posts/rails in front of my house (for looks) about 10 years ago.  One of them rotted out last year.  Right at the top of the ground is were it was broke but it was rotted all the way to the bottom of the hole.  I checked the rest and they all seemed solid, still, but that one just fell over on its own and broke the tips off a couple of the rails.

Yeah, if you're buying furniture-grade, milled wood.  A 6-8" fence post is about ten bucks here.

Mostly just depends on local availability, though.  I burn oak and black walnut for firewood, which makes some people cry.  On the other hand, I spend about $5/bag to buy little mesquite shavings for my smoker... after spending a good chunk of my adolescent years flagging for an aerial spraying company spraying Tordon over half of Texas to try and wipe it out.

Cedar's not a bad alternative, and it grows pretty much everywhere.  Won't last as long as Osage Orange, though.

Use a petroleum based sealer/stain on the cedar post, before setting it in the hole make sure the ends of the post has been saturated.

Pour a couple inches of 3/4-1 inch river gravel into the bottom of the belled out hole for drainage.

Set the post and pour your mix making sure that the concrete level will be higher than the finish grade line.
I use a 12" square form I made out of 1x2 for this. It insures that what is seen from above looks good.
Make sure the post stays above the gravel and does not push it aside.
The raised concrete will protect the post from weed eater damage.

Over time I reseal/stain the post and make sure that the connection between the wood and concrete is saturated.

Driven in steel bases and wood bolted on them.

ANYTHING you do to try and 'seal' the bottom of the post is going to allow water from teh above grade to penetrate down (end grain iis a bunch opf 'soda strays' in a bindle) and be trapped.
It than rots.

Burial grade treated wood is NOT the same as 'ground contact.'

The other thing to consider is the actual cost over time of having to replace the posts at X year intervals.

How much money do you want to spend NOW to extend the X years?

Wow! , yes we live in different worlds.  The only cedar you can buy here is partially/mostly sapwood which rots as fast as pine.  Heartwood cedar is BIG bucks, too.  

Honestly, I have never even seen osage orange except in specialty, exotic wood suppliers.  Do termites eat osage orange?  There are lots of termites here.

IMO, metal bases in the ground with treated posts above is the way to go.

Do you not have any farm supply stores?

I can buy two types of fence posts from the local farm supply, one is green and the other is black creosote.

The green treated one is not the same treatment as pressure treated at the hardware store, this is much better, made for ground contact.

I prefer the creosote though and you better ware gloves.  Don't get that shit on your bare skin cause it burns.  the creosote posts will outlive you an me both.

Back on the farm (MO), I searched all over our properties to find good hedge to use as posts (they rarely grow straight).

Locust trees are just as good, just watch out for the thorns.

Burial grade is even higher than "ground contact."

Soak the post in in antifreeze, it works. google it