Pergola wooden post

[john2k]

I have a wooden pergola with 4 100x100 wooden posts. It’s about 1.8m post to post one side and the long side is about 3.5m post to post. The pergola has been up for 12 years. Two of the posts are postcreted to the ground and the other two are bolted to the ground slab with the metal brackets. The wooden beams on top have aged but still seem ok and I was planning to put a polycarbonate sheet onto it. But just discovered that one of the posts that is postcreted has some rot where it goes into the ground. So my dilemma is do I change both posts that are postcreted before putting the polycarbonate sheet or just change the one that rotten. Is there any other suggestions of what I can possibly do? I’m assuming there’s no long term way to save the post?

Do I need to remove all the supporting beams taking the load off before changing the post or can a temporarily support that corner somehow then remove old post and put new post?

I’m trying to revive this on budget too don’t so any advice would be really appreciated

Or could I leave it for now and add some extra safety to it? It’s literally just rotting around the edge a little but not sure how deep the rot goes but there’s not wobble

 

[Wayners]

I bought a new post.
Propped up the pergola with some CLS timber as cheap.
Removed post and concrete.
Places new post in group with a bag of type one gravel under.
A few bits of broken concrete to jam it in place.
Poured concrete around.
I also run some masking tape around wood prior to fitting, and coated the wood that's underground with liquid rubber roof coating stuff I bought for DIY store.

 

[john2k]

I have a two pieces of 45x70mm c16 timber 2.4m long could prop up that corner with one of these in each side and place a concrete slab at the bottom so the timber is resting in solid surface then when replacing the post I’m thinking to use 750mm galvanised spike for 100x100post so the new post isn’t actually inside the ground that way in the future repalcing posts becomes easier

 

[john2k]

the pictured 750mm spike can this be installed by postcreting instead of the hammering them in method? Because my current post is postcreted in so when I remove it could I just attached the new post first to this and bolt it together then place this with the spike and the metal bit sticking above ground level and then pouring postcrete in to secure it then giving the spike a solid foundation similar to concreting a post into the ground?

 

[Wayners]

Better off with https://ebay.io/m/lYLYL0

 

[john2k]

Better off with https://ebay.io/m/lYLYL0

Thank you. The Problem with this is I’d have to make the ground concrete then secure that down. Having inspected the rotting post the rot basically is just from about 10 to 20mm above ground level. I can actually poke screwdriver into the wood it just goes in but the rest of the post is still rock solid and in good condition as I kept it treated yearly too. So instead of getting a completely new post what I’m thinking is using that spike which is 75cm long basically temporarily remove the post and cut off about 30 to 50mm above the rot area that essentially should give me enough space to put the spike and because the spike is 750mm should be able to allow for that excess that I cut off. Then can pour postcrete in around the spike. This keeps the job a bit smaller and cheaper too. Thinking to paint the cut end of the post as it enters the spike with Bitumen paint maybe. Is there anything else I can do to make sure the metal spike is rock solid in the ground? Then after that I can just do the poly roof and keep an eye on the remaining posts and deal with any other posts as and when the need arises rather than replace the ok post too