Preventing Cedar-Post Rot
You can’t completely stop wood from rotting, but you can delay the decay.
I’m replacing the posts on a 20-year-old cedar fence. The fence panels are fine, but the posts were buried directly into the soil and have decayed to the point that the fence is falling over. Pressure-treated posts won’t match the fence panels, so I have to use cedar. How can I prevent new cedar posts from rotting?
Lonny Wiles, Ashville, Ky.
Editorial adviser Mike Guertin replies: You can’t stop the cedar from rotting, but you can delay the decay. Start by overdigging the depth of the hole by at least 6 in., and backfill with crushed stone. After you position the post, backfill with more stone rather than the soil you dug out. The water will drain more freely through the stone and help the post stay drier.
Because water wicks up through the cut end grain of the post much more readily than it does through the sides of the post, either soak the end of the post in a preservative solution (copper naphthenate), or coat it with a waxy end sealer such as Anchorseal.
Finally, wrap the buried portion of the post with self-adhering membrane as a barrier to moisture. I use plastic-surfaced window flashing tape or self-adhering roof underlayment. Wrap the post from a couple of inches above the grade line down to the bottom. Do your best to get the membrane tight, and then warm it with a heat gun. The membrane will shrink a little for a tight seal around the post. Incorporate all three methods on the posts for a belt-and-suspenders approach that will extend the life of the posts by many years.