We are installing a platform/dock on a small freshwater pond. The property has a great amount of red cedar available for our use. How long could we expect red cedar posts to last if used as pilings? How much longer would black locust last?
Cedar fence posts work about as well as pressure treated ones, 25 years or so. I think I would derate that somewhat due to constant circulation of water around them.
Estimate of 15 years.
- Warmer temps will shorten life.
- Fungi are aerobic: They are typically most active on a fence post in the 3" just below the top of the soil. Moisture + air. A fluctuating water level during the warm season will spread the damage done by the fungi somewhat. (Has to be long enough cycle that the wood dries out.)
If you do this, plant some posts that are smaller in diameter (2" smaller at least) at a spot you can check them. When they are getting weak, it's time to rebuild the dock. Park a bird feeder on top.
Larger timbers will last longer.