I have a portion of my deck that's a 4' square connecting stairs that go up and down from it. One of the corner posts (green post in the pic) has sunk between 1/2 and 1 inch and I'd like to raise it and pour a new deck piling to stabilize it. I don't think it's still sinking and has been stable in its current position for at least a few years. The wood seems all in good shape.
I'm a total newbie at this and am evaluating whether to even try this myself. I thought about using a jack to raise the corner, but I don't know where I can place the jack such that it won't interfere with my ability to dig the hole for the new concrete. When I tried to place it anywhere a foot or more from the post, it basically tries to lift the entire platform rather than the corner I'm concerned about. How could I effectively and safely raise the deck here while still leaving enough space to dig a hole around the offending post? Or is there another technique that might be better?
Approximate design below. Posts are 4×4 and platform is 4' x 4'.
To respond to @Ecnerwal's question about the screws versus nails attaching the framing to the post: lots and lots of nails, sunk deep into the wood.
Best Answer
I get the issue with the nails. I think you need to try to take them out.
I would start with a sledge hammer and try to tap one of the sides inward. When demo'ing a deck you are taking full swings to do the same thing but I would go really light. All you need is a slight gap. Once you get a tiny gap get a crow bar in their and try to get it popped out maybe to a 1/2" - I would not go further.
This only works if you can work it out without the rest of the deck moving and getting angles jacked up. So either you need to tap softer or just back out of this or try the other side and start over.
Once you get around a 1/2" (doesn't have to be that far) cut the nails with a reciprocating saw.
I would support this corner while you do this by either jack it up or throwing up something like a 2x6 which should be plenty with no load on deck. Now follow the same procedures for the other side and this side should be easier.
From there you need to raise the jack or 2x6 to level. Then drill a hole in each side for a lag bolt. Get your bolts in at level and then try to get one more hole on each side for another lag bolt.
Option 2... Dig post out really really good . Raise it up with jack and framing. Note that you must have this secure well to get the concrete raised (this could be easier if they didn't go very deep hence the sinking). Pour a couple more bags in or go down to the appropriate depth for your region. Let dry then take supports out.
Either of these options could be a 1 day deal. If you are dismantling a lot of the deck to get to post top (remember you have to saw those nails out) then I would try option 2 first. Digging this thing out in a muddy yard might take 30-40 mins and will give you an easy view of how hard it will be. This would be my choice if deck looked nice minus the tilt.