Doug Fir Fence posts

[flyingparks]

I think this is the right place to on the forum post. I'm going to be building a privacy fence and will use 4x4 rough sawn posts. I refuse to use pressure treated posts for many reasons. The best deal I can find are for some rough sawn Doug Fir 4x4s. They will be ten feet long and three feet in the ground. The ground is hard Colorado mountain dirt. Lots of granite. My question is what is the best product to seal the under ground portion of the posts. Penofin? some type of poly? just paint? I'm curious to read what all you knowledgable people here think. Thanks.

[barbender]

I'd probably just leave them natural. Probably the best thing you could do to preserve them is backfill with crushed rock. The mountain West is pretty forgiving on posts, imo. I see old pine posts out there that are weathered and look 40 years old. They wouldn't last but a year or two in Minnesota. Seems up in the mountains out there you go from frozen, to a brief thaw and moist period, to dry and then back to frozen. I think there's only about 3 weeks where it's both moist enough and thawed to rot anything😁

[Don P]

The problem with things that seal is if water gets in the vapor can't get out, the moisture content rises into the rot zone. The seal is rarely perfect. I prefer things that repel the water but let the wood dry back out. If there is a preservative under that water repellant finish so much the better.

A friend came by a couple of days ago needing a 6x6 locust post for an equipment shed repair. We poked around for a couple of minutes and I pulled one out and remembered it immediately. I was working on posts for a barn repair and was dipping them in a trough of borate. This one was in the trough when I finished and I forgot about it for a week or two. I expect it will be the last stick standing on that farm :D. 

[flyingparks]

So maybe a combo of gravel, borate on the post. Maybe some anchor seal on the end grain. I really worry about rot stemming from the end grain.I really like the idea of gravel. Should be good for drainage. Thanks for the suggestions.

[Don P]

The bottom of a post never rots, when you remove a post the decay zone is in the foot around grade. There is no oxygen in the bottom of the hole.

[flyingparks]

Interesting. Like how a wooden bridge only has corrosion around water line. More knowledge.  8)

[flyingparks]

I couldn't shake the nightmares of rotting fence posts from my mind. I knew I had seen post rotting from the end grain which was exposed to the earth...mycelium being the culprit. Guessing it can absorb oxygen from water...a moist environment. 

[Don P]

Deny it moisture, oxygen, temperature, or food. Typically indoors we deny it moisture and outside we poison the food.