Eastern Red Cedar vs Black Locust -- post size

[hardrain]

Hey all, have a small plot of hop posts, I was able to acquire black locust and did 16' long, with 2-4" diameter tops. They're sturdy and work very well in my particular design/setup.

I'm looking to do the exact same design and setup, and was able to aquire eastern red cedar posts, however I'm finding that anything under ~3" in top side diameter seems more "rubbery". The posts are 24 hours old, so very fresh. Is this something different about red cedar vs black locust fundamental to the wood, or just a result of the fresh wood?

Anyone used red cedar in the past and stuck to a minimum top-side diameter?

Thanks!

 

[HollywoodTK]

Well, eastern red cedar has about 70% of the density that Black Locust has, and less than half/about half of the average elastic modulus and hardness, so it will be a bit "wobbly" in comparison. It's also a softwood, where Black Locust is a hardwood. That said, Black Locust is among the hardest/strongest of standard woods.

That said, Cedar generally a really good wood to use for exterior applications without any pretreating.

 

[hardrain]

Is it bad science to shoot for a diameter 30%-40% larger on red cedar vs what I know works for me in black locust in terms of stability, or does density not really work that way? Any adjustments for using soft wood instead of hard wood?

Thanks for the reply!

 

[HollywoodTK]

That'd be fine. All other things being equal, increasing the diameter by 30% should increase your second area moment of inertia by something like 300%. Considering the bending modulus of black locust is about 250% of the cedar's, this is about right.

A 4 inch or 5 inch mast of cedar should act similarly to a 3 inch mast of locust, more or less.

 

[hardrain]

I just thought I'd follow up here. Cedar posts are definitely more 'rubbery' than BL in transit but settle and hold nicely. Obviously haven't tested at 'full sail' yet but now that they're cut and grounded, Holywood's rule of thumb seems to work, and I wouldn't go less than 4" top-side (ie small-side) diameter.

 

[Wesmando]

Im running into the same questions. Have you carred or treated the ends?

 

[JohnSand]

Locust doesn't need any treatment, it is very rot resistant.

 

[Wesmando]

Im using cedar however, most of my poles are not huge. Some are 4-6" on the small end, making the butts 9-10". The amount of work going into setting and wiring them makes me want to do it right and get the most life out of them as i can.

 

[JohnSand]

Cedar is generally fairly durable, even in contact with soil. It has been used for utility poles (treated) and fence posts (often untreated). I think I would refrain from treating it for fear that any chemical applied might leach into the soil and affect my plants. You might find more information on agriculture sites or cooperative extensions.

 

[hardrain]

Im running into the same questions. Have you carred or treated the ends?

No treatment. That's the idea behind black locust & eastern red cedar, because of their rot resistance. I've seen people tar the ends before setting them, but that (1) defeats the point of using this kind of wood, (2) IS adding those chemicals to your soil, and (3) is more expensive & labor intensive, and (4) isn't based on any study/experiment I've seen suggesting that ground rot is the weakest link in the chain.

What I'm seeing in my existing 4-year old yard (black locust) is that the TOPs of the poles, with the holes, eye hooks & wiring, is the first thing to go, along with heavy rust on the supposedly galvanized cables & clamps. I'm not seeing any issue at all with ground rot.