Ben-

I believe the problem you are experiencing is due to having a very
thick (~5/8") layer of low density material. I have "cheated" & filled
a rather deep uneven suface with the regular density prmixed compound.


I was lazy & just kept putting extra coats day after day. Covering one
dried / crakced layer with another that would dry & crack. Finally the
layers became thinner (just enough to cover the previous layer's
cracks).

I never did the finger nail check so I'm not sure if was very hard
but it probably was since this is just an extreme example of th typical
corner method.

So the question is now...what should you do? (or what would I do in
your situtaion?

The problem is the lightweight is rather soft material so putting a
very thin layer of hard over soft may not help very much. Kinda like
putting a thin concret slab over a soft subgrade; might work depending
on the loading.

The "correct" way was to add some supporting framing so that
reasonable sized peieces of drywall could have been placed, taped &
mudded.

Or you could have jammed in & secured some 1/4" x 1/4" "hardware cloth"
(very coarse screen material) to act as reinforcement & then used
plaster, stucco or concrete "fixall"...That is some sort of water mix
cementious material.

The benefit of light weight is that is sands very easily.


It's you call at this point.........can you live with the current
result? If so forget about it.

It not remove it all & start over (it will go much faster the second
time)

cheers
Bob
).