If I use white oak milled posts or unmilled logs, how long can I expect them to last in direct contact with the soil? And, how can I optimize their longevity? This would be for posts for a shed to store farm implements, etc. Thanks.
I am not a forester, but why not use a post hole filled with concrete, put some steel pieces in it to run bolts through to bolt the post to the concrete? Menards is selling some plates that bolt to poles that attach to anchor bolts in concrete. Think they use 2 anchor bolts per plate. I have put angle iron in concrete, one on each side of the post, drilled holes through the angle and used short pieces of rebar to help the angle anchor to the concrete, with holes drilled through the center of the angle so both edges contact the post. Welded mine, to make it easier to set in the concrete. They must be plumb, so used a form and then put a piece of wood across the top of the form to fasten to the angle iron, to help hold it in place till the concrete was set. Morton buildings uses some 5" wide plates about 4 or 5' long to repair posts that rot off. They dig out the old wood, then fill the hole with concrete, and then bolt the post to the plates to hold the rotted off post. Several years ago, maybe a different method now.
8 years. Maybe. I used white oak 8" by 12" off the mill to build a 3 step flight inset up into the yard from our driveway. They looked pretty good up until the day one didn't. 8 years later. They were now just an outer shell, the rest of the wood was almost compost.
I've got some white oak barn posts going on 17 years but they are set in the round cardboard concrete forms so are fully encased in Quickcrete to a little above grade.
I have done the same with pt pine and they've been good for 20 ish years.
Any chance you've got some black locust around you can use for posts? They'll last longer.
One thing you can try: Spread roofing tar on your post from about a foot or so above ground level down to about a foot or more blow ground level. That's usually the area that rots first.
EDIT: The tar thing won't completely stop the rot, it just buys you more time. We needed a post to hold up one corner of a tree house when we were building it 10+ years ago. We used a 6"x6" PT post. The problem was that the only post we had available was only rated for "above ground" use. We could not find "ground contact" or "in ground" treated posts, so we tried the roofing tar trick. The post has been in the ground for over 10 years and is still in very good shape. The real answer is to keep the wood up off the ground as others have noted in this thread. We just wanted to get it done, and figured it would last until our kids lost interest, and was easy to replace if problems developed.
When you dig your holes throw the topsoil to the side and don't use it to refill around the post, topsoil holds the bad stuff that rots the post the quickest.
Quote from: Oddman on April 06, 2020, 06:22:55 AM
When you dig your holes throw the topsoil to the side and don't use it to refill around the post, topsoil holds the bad stuff that rots the post the quickest.
Yeah, it's the topsoil that is "active" biologically speaking. The problem is that almost anything you fill with will eventually become bio-active (well, unless you are filling with cement)
Quote from: graysearch on January 17, 2020, 07:07:38 PM
If I use white oak milled posts or unmilled logs, how long can I expect them to last in direct contact with the soil? And, how can I optimize their longevity? This would be for posts for a shed to store farm implements, etc. Thanks.
Dont do it unless you like jacking up barns with your future time.
(https://forestryforum.com/gallery/albums/userpics/43722/Resized_20200524_181409.jpg?easyrotate_cache=1590464891)
Pour a cement footing of some sort. Even just a 4" thick blob in a hand dug spot for each post. pop in a vertical pin. Can be rebar or a bolt or a redhead wedge anchor, whatever. Now pop an asphalt shingle over that, gravels down. Then set your post over the pin, with a predrilled hole in the center of course. If you keep that dry itll outlast you.
White oak sapwood rots pretty quick. If you leave the bark on itll be powder in 3yrs. Whole tree hillbilly leanto's are pretty common in TN. You need to keep the butt out of the dirt entirely and a generous roof overhang if you want it to last
Sourwood is the only rot free wood ive encountered. But its always small, twisty and it splits open in the sun. I use it for garden fences. Black locust is obsolete here unfortunately.
Whats your soil like?
I was in a 250 yr old barn in upstate NY last year. stacked flagstone on the ground about knee high, could see lihjt through every spot you looked. then a thick timber sill and everything built ontop that. Perfect condition because the airflow prevents moisture and microbial activity.
My father built a really stout house 30 yrs ago. But laid the sill right on block with no asphalt barrier. Turned triple 2x12 pine lumber to powder. 2 yrs of jacking up to replace. The pic is my brothers 200ish yr old barn. Was moved there mid 90s by prior owner, and set in dirt. Been rotted to nothing atleast 10 yrs. The siding boards held the frame up and bowed out, broke windows etc.
Wood and dirt make a better garden than they do a shed.