Treating buried PT fence posts?

Mike in Arkansas

I'm getting ready to build a fence later this year and am planning on using PT posts. At my age they will probably outlive me but I was just wondering if coating the portion of the post that goes in the ground with roofing cement might add to their longetivity. I am visualizing just dipping the ends that go into the ground into a 5 gallon bucket of the cement. Is there a better material to use?

Bondo

Ayuh,... Sounds like you want to add an Unneccessary step...

Carpenter

If you're that worried about your posts rotting underground while encased in concrete, try either wrapping the post in 6mm plastic (wrap the plastic around the post to 1' above the post-hole, and shove the concrete into the hole) After the concrete's cured, just cut off the excess plastic with a utility knife.
And if that's not hardcore enough for you, you can also treat the underground part of the post with a chemical available at any hardware store called End-Cut Preservative. Makes your green wood even greener. Neon-green, for that matter.

If that is still not enough, then I'm sure you're planning on living another 80 years with those fence posts.

Ron6519

I would just set the posts in an angularly shaped gravel. Put 6" of gravel in the hole bottom. Set the posts and pour in gravel around the post. Every 12" compact it. The gravel will allow the water to drain and keep the post from sitting in wet soil. You can keep the soil out of the gravel with the use of landscape fabric.
Ron

Mike in Arkansas

Thanks for the replies and suggestions. I want this to be a fence for the ages. Right now the plans are for a formal looking traditional white picket fence for a two story built in 1925.

Termite

Coating the buried portion of the post in roofing cement or wrapping it in plastic as suggested are two things that will have the opposite of the intended effect. The posts will always have moisture inside them. It is critical that they be able to expel that moisture, and that is done through their end grain. Even when buried in concrete they can do this to some degree due to the pearmeability of the concrete. Sealing them as suggested will keep the bottom ends perpetually wet, accellerating their degradation.

Gravel in the bottom of the hole is the single best thing you can do to prolong the life of the posts. Set them on the gravel and then concrete around them.

ARI001

I treat the end grain with copper napothrene (sp?) in addition to what KC just stated.

Termite

Good idea, an extra measure of protection that won't hurt the wood!

Scuba_Dave

My fence is starting to get wobbly
Neighbor said its not that old, I doubt they put gravel in the bottom
Its rotting around the ground level and possibly deeper around the post
I keep using rocks/gravel to make the posts sturdier

diy'er on LI

no experience with fence posts, but I do with wood mail box posts...

When I was a teen (almost 20 years ago), I replaced our mail box post. All I did was dig a hole, pour concrete into the hole, and insert the post into the concrete. It's still totally fine. No rot what so ever, even though it's in partial shade. From my limited knowledge, I believe the post will remain rot free as long as 1) the cement is not poured into a plastic bucket in the ground and 2) the post is not wrapped in plastic. I think the reason is that each case, moisture in the concrete and wood won't be able to escape, and instead will encourage rotting.

tgm1024

I've bumped into a fierce argument about this every time I've searched about it. (Show of hands: anyone surprised?) Let's hear the opposing view on this for a sec:

Turns out that one of the things you're doing when you water-proof seal a PT post is actually lock in the preservative used in treating it. CCA, or what-have-you. Yes, before the screaming starts, the treatment is on the exterior, so the interior is at risk.

However, in the case of PT, it's not the interior moisture that destroys the wood quite so fast as it is the exterior water leaching out the preservative (which then allows any moisture, internal or otherwise, to accelerate the rot).

IOW, absolutely no full consensus is available on this. That said however, it's not the same deal as the vapor escaping a house through the siding. This is treated wood, accelerated by its preservative leaching out, and further, if the preservative is not leached out, the internal moisture can stay there for a much much longer time without any degradable growth destroying the wood.

It seems to me though that something that is often overlooked in all this though is that regardless of any kind of plastic/latex/tar water proofing that goes on, the posts will sooner or later crack, or shift sizes, or something that allows moisture in and out under the sealing compound. This is where things get even MORE sketchy for me.

Larryh86GT

I put in 40 4x4 PT fence posts set in concrete with gravel on the bottom 19 years ago and the wood is still solid. They will outlast me.