Matthew Reed wrote:
More on my fence building subject. I live in Oregon, Lebanon, near Salem.
Rains all year. Lots and lots of rain. I'm using pressure treated ground
contact rated 4x4x8' posts. I plan on setting them 2 feet deep in concrete.
Would it be worthwhile to apply any additional waterproofing coating to the
posts before setting them in concrete? What kind of life expentancy can I
expect from these posts set in concrete? Assuming I take reasonable care to
taper the concrete, cap the top, and keep it painted. If they rot out in 5
years, I'll be stuck with rotted posts in concrete that will need to be dug
up, and I'll have several dozen big chunks of concrete that I won't know
what to do with.

Just make sure you use enough gravel and keep the posts clean from
debri.
I put PT posts in my house near Portland 20 years ago and there is no
sign of rot at all,
except for one post near a fir tree that was always covered at the base
with pin needles and rotted out after about 15 years. If you install
them so they can dry out after getting wet, the'll last a lot longer
than 20 years.