Teak Fence-Post Durability
From contributor B:
Here in SW Florida I have seen 4x4 PT fence posts rot out at the base in 4 years because they were set in concrete. I have also seen 25 year old cypress 4x4 posts with no visable signs of rot, rot because they were set in a sand backfill with a stone base. The combination of ground contact and constant moisture will rot anything, steel included.
The key to a long lasting post is to dig the hole 12" deeper than the post with a 6" minimum all around the posts diameter. Layer gravel on the bottom, stone dust or coarse sand for the backfill and a bitimus based coating on the sides only of the post will all contribute to a long lasting post by allowing any moisture to drain away from the wood.
If strength is needed by setting the post in concrete, try wrapping foundation wall type drainage plane material and add a weep hole straight down through the bottom of the footing. The idea to longevity is not to prevent water from coming in contact with the wood but to provide adequate drainage to allow the water and moisture to exit.
From contributor C:
I've never seen teak actually rot (meaning dry rot, fungus or even termites). I have seen it dry-out and crack. It's my understanding that teak is the most weather/insect resistant wood on the planet. Teak comes from tropical rain forests and is unaffected my water or moisture. Ancient teak logs are actually dredged from the bottom of bogs and rivers and sold for lumber.
I read once that a prehistoric dug-out canoe was discovered by a local native fisherman. It had been underwater for thousands of years. Government authorities (who wanted to place it in a museum) had a hard time talking the fisherman out of his new-old boat which he had been using for quite some time.
At more than $15 BF, please tell me you're not really going to use it for fence posts?
From the original questioner:
It is expensive, but if that's what the client wants... The actual application is for signage, and the post would be the support. They wanted an estimated warranty, like 10, 25, or 50 years? I may suggest it will last "X" amount of time, but my contract will not extend to cover it for the duration.
From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Old growth teak does indeed have very good natural decay resistance. Younger growth and plantation grown does not do so well. There are other species with similar natural decay resistance. Treated wood will usually have better resistance than natural decay resistance species but only if the preservative used is correct for ground contact (including the type and amount of preservative and depth of penetration) and the species is a good species for receiving such a treatment. In other words, not all preservative treated wood is the same.
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