In concept these practices would seem to block some moisture transfer into the wood but there isn t any research to suggest that it increases longevity.
Roof sealnt fence post.
Coating the post base with asphalt roofing cement driveway sealer tar or a bituminous self adhesive flashing tape are fairly common practices.
They would reuse or as we say today re purpose old motor oil.
In this video i show how the old timers use to treat protect fence posts from rotting.
Of aggregate in the bottom of the posthole to allow for drainage.
Brush the bottom third or bottom half of the fence post with waterborne copper naphthenate a wood preservative that is free of arsenic and chromium.
The posts are about 10 years with tops sawn at an angle and nothing was ever applied per the installer.
They are being sealed to preserve against decomposing.
Available at some paint stores and home centers this wood treatment is specifically designed for in ground applications.
Sealing tops of treated fence posts.
Soak the bottom of the posts in a wood preservative containing copper napthanate such as cuprinol.
Prepping to apply sealer to the tops fence posts hoping we will get a day over 50 degrees i went around with straight bleach over the tops today.