deckpost
I have a small deck that needs care. The top side is in really bad shape (rails, floors, lattice, stairs) need to be replaced. The deck is above a brick patio and I think that the posts are set in concrete buried under the patio bed.
I am trying to decide if I need to replace the posts as well. I am not very charmed by the idea of having to dig out the posts, the concrete and to pour concrete footing (quicrete and quicktube like here-not sure if quckrete is OK for this)
Burying the wood post will cause it to rot prematurely. Even ground-contact rated Pressure Treated lumber won't last forever.
The only benefit of burying the post (besides it being easier to do) is lateral stability. i.e. you can sometimes neglect lateral bracing this way.
Best practice for wood-post decks is to have the concrete extend above grade and use a stand-off post anchor to hold the wood post to concrete.
Here is an example of this with some knee-braces for lateral bracing.
The braces don't match so I find this somewhat ugly, but the image is clear and easy to understand.
Footings here don't need to be deep so I often form my own square ones but sometimes I use bigfoot forms and I really like those. Although Shirlock's "mushroom" method is more than adequate if you are only required 8" wide.
Without seeing the plans and what kind of precast piers you have - I would say that I'd pour more concrete, with some rebar drilled and epoxied into the precast piers and the new concrete poured over to join them both.
Then set stand-off post bases into the new concrete for the PT posts.
Best Answer
Hit them with a hammer to hear if they are solid. If the are rotting they will sound flat or hollow, if they are solid you can hear it.
You could also power wash them to get a better look at their condition.
From here they look fine. But then looks can be deceiving.
Good luck!