Lumber rated for subterranean use?

[swampratt]

I get tired or replacing quite new pressure treated posts on fences.
All junk if you want to keep it for a long time.

I have had ants and termites nest in the pressure treated and cedar wood.
They may not eat the stuff but they nest in it.
Only thing I found that keeps ants off wood is used Transmission fluid.
Used oil works also but does not seem to last as long.


Concrete it.
I have set pressure treated posts with gravel in the bottom of the hole and poured concrete to set the post.
They will rot at the base where dirt touches the post.
Keep dirt off the post and it will last longer.

 

[dennishoddy]

Built my 20’X20’ deck about 30 years ago. Still solid as a rock with direct burial of 4X4 treated posts 3’ deep in concrete.
A building contractor gave us some tips that appear to work. His advice was to seal the 4X4 in roofing tar being especially heavy on the end grain. The tar extends a couple of inches above the concrete line.
Another critical issue is to make sure the concrete is domed on top so water runs away from the 4X4’s. After the concrete sets, use RTV sealer around the post so water can’t run inside if the concrete pulls away from the post.
Almost 30 years later we can still see the roofing tar line above the concrete and the posts are solid. We taped it off before applying the tar so there would be a cut line and not be an eyesore.

 

[Glock 40]

Another critical issue is to make sure the concrete is domed on top so water runs away from the 4X4’s.

A good friend ran a fence company for a long time. That was his #1 piece of advice get concrete above ground level so the water moved away from the post. If you are jamming 3 inches of dirt on top of your post. Your asking to replace it in half the time when the panel blows over post attached snapped off at ground.