How would you set 4x4” Pergola posts to last ?

[paddypower]

In concrete they seem to rot at the concrete/soil interface and then be a pain to replace. Met-posts can be unsightly and rust away. Toying with the idea of a buried block of concrete with a bolt down met-post fitting on top (just below soil level), then which ever rust/rots can be replaced.
Any other way or will concrete out last me and be simpler?

 

[ColJack]

try standing the bottom of the post in old engine oil for a few days prior to use..
or give it several coats of fence stain and varnish up to the top of the soil level..

alternatively, glue some cardboard onto the outside of the post before you concrete it in and then when it rots you can drill out the wood, pull out the cardboard and you'll have a socket a few mm larger than the post..
slot in a new post and pack it with shims to solidify it..

 

[freddiemercurystwin]

What happens when your cardboard rots away to nothing after about 3 weeks Col?

 

[ColJack]

then you use metal or plastic shims to solidify it in place... didn't I already say that above?

 

[freddiemercurystwin]

Yea but then what's the point of the cardboard then? Besides if you've ever had a slightly wobbly post in a concrete footing you can barely stick something about 2 inches down the side let alone all the way down the length of the hole. Your idea of shims and ultimately drilling out the duff post is madness. It'd be quicker and easier to just replace the footing than drill 18" of timber post out of a hole!

 

[HERTS P&D]

Soak the posts in an old barrel, 18" deep, take them out to dry then paint the bottom 2 feet with bitumen and wrap polythene around them but don't cover the bases of the posts. Put gravel in the bottom of the post holes, ram the posts into it then pour the concrete. You are trying to leave a clear path at the bottom of the post for water to drain out rather than get trapped. Cap the posts to shed water, if you don't want to cap them cut them at an angle so the water runs off. Lasts ages.

Andy

 

[paddypower]

Thanks for the input, I’ll be back in 10 years to let you know how they’re going !!

 

[Deluks]

You are trying to leave a clear path at the bottom of the post for water to drain out rather than get trapped.

Not so good in clay though.

Me, use a bolted connection between post and the rest of the structure, that way the pergola can be temp propped, post cut away and unbolted, and a new one put in its place.
Soaking in preserver and the shingle thing also good idea though. Easy on the concrete, or just ram stones down the post hole. Pergs depending on design don't strictly need concreting in, much the same way a table doesn't need concreting to your dining room floor.