On Sunday, July 10, 2016 at 9:44:21 AM UTC-4, John G wrote:
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?

Perce

I couldn't say for sure, but perhaps the joint compound needed to be primed first before applying any other coating to it. Try contacting the manufacturer.

Except that he says it's the drywall compound that is apparently lifting
off the drywall board at the tapered edges, not the paint lifting off.
Plus I thought Shieldz was a primer. IDK, I've never seen this happen.
If you don't remove all the dust from sanding, that could affect the
paint not sticking, but if it's actual pieces of drywall compound coming
off, IDK. What kind of drywall compound was used?