"Percival P. Cassidy" wrote in message
...
I repaired some holes in a wall that is to be wallpapered, and then started
applying "Shieldz" to provide the proper surface for the wallpaper -- and
now, an hour or so later, I find that the drywall compound is lifting up
and falling off at the nicely tapered edges. The dry-wall compound has had
a couple of days to dry.

What have I done wrong?

My guess is that the water base Shieldz transmitted enough water to the thin
areas of compound to turn it back into its original state. If that is so, I
wouldn't expect it to fall off though, just stay where it is and dry again.

A coat of shellac before Shieldz would solve the problem.