On Wed, 12 Apr 2006 10:53:41 -0400, "Don Phillipson"
wrote:

Problem: deck surrounding an above-ground pool
(deck standing on wood posts into sand without
appropriate foundations) has sunk badly at one
corner, has sunk 9 inches at the pool edge, and
17 inches at the outermost corner. Thus the corner
post has sunk about 17 inches and two or more
intermediate posts about half that.

(This deck & pool are about 19 years old and
I contemplate repacing both whenever the
pool collapses . . . I.e. repairs should last two
or three years.)

I plan to raise the deck and support it by
a new joist of doubled 2x6" cedar (i.e. 4x6" total)
diagonally under the corner, and supported at each
end by new posts (4x4" lumber) on 2ft concrete slabs
atop the ground (sandy soil). The deck must first be
raised by one or two auto jacks, placed atop 12" drums
cut from a large poplar tree (2 ft. diameter.)

Questions remain:
1. Should I raise the deck with a single jack
under the deck (lifting the new diagonal joist)
or a pair of jacks outside the deck footprint?

Why not a single jack outside, or a pair inside? That is, I don't
understand why these are the two choices. Oh I get it, now.

I've done this but on a much smaller scale, a 6 foot by 12 foot deck
that had only sunk 8 to 10 inches.

I used a floor jack and I thought it worked great. That's the one
that looks like an lizard, with a lever one end, a platform that goes
up on the other end, and 4 wheels on the part in the middle. I put
the "platform" just aabout 6 inches to the side of the post that had
rotted away. (26 year old deck) That way there was room to put in
another post beside the first post. I plan to enlarge and replace the
thing this summer.

This would require having the diagonal joist
extend at least 3 ft. beyond the deck footprint
at both ends (and cutting off the surplus when
the job was finished.)

Like I say, my plan worked fine. I jacked up one side and put another
piece of 4x4 in to hold it up. Then went to the other side 12 feet
away, and jacked that up.

2. How fast should I try to raise the deck?
I.e. if it seems to stick at (say) 3 inches, should

I don't think it will stick and i don't think waiting overnight will
change much. Why do you think it will stick?

I just leave it overnight and try to raise it another
3 inches next day? Or should I use two jacks,
crank one end up 3 inches, then raise the other
end 3 inches, and repeat at the first end?

Despite the fact that the other edge of the deck stayed attached to
the house, and the near eadge was only 6, or 5, feet from the house,
each corner seemed not to care what the other corner was doing.
Lifting up one corner didn't make the other one, 12 feet away, move at
all. But I only went up 8 to 10 inces.

3. Two new pillars (resting on concrete slabs
on the ground) will be hangered to the new
2x2x6 diagonal joist, the pillars placed under
the edge of the deck like the others. But just
how far from the corner post should I fit this
diagonal, e.g. 2 or 3 or 4 ft. from the corner?

4. If I can raise the deck and insert new
supporting posts as planned, would there be
any point in digging below the old corner post,
with a view to filling the empty hole below it
(probably 17 inches deep)?

How deep is the whole hole. That is how much above the soon to be
empty part. I don't think it would take much effort to open a channel
from the side of the post to the hole and fill it with rocks, stones,
soil, more rocks, stone, soil. Or something more permanent, if
permanence isn't a problem. Then there would be that much more for
the deck to rest on. (although the horizontal beam at ground level
someone else suggested would solve that.)