Plaster falling off wall


New Member
A month ago, I primed a ceiling and a sloping wall with 4:1 water / PVA. A few days later, using multifinish, I applied the 1st skim coat then I applied the 2nd skim coat to the ceiling only (I ran out of time to finish the sloping wall). The ceiling has come out okay and is fully dry. The first coat on the wall had obviously dried too.

Today I intended to do another two coats on the sloping wall and finish the job. I applied the same water/PVA mix and about an hour later I noticed the plaster was coming away from the wall.
The wall was previously like the ceiling, painted (not flaky) skimmed plasterboard.

About a quarter of my skim on the wall has come off, and other places may be a bit loose. The skim was about 1-2mm thick (should have been 4mm I know). The ceiling seems fine - firm and no hollow sound when I knock it etc.

What has caused this ?
What can I do to rectify it ?
Was it because the coat was thin and I made it wet with the water/PVA after it dried ?
Should I hack off unsound plaster, apply a stronger pva to the original wall and wait for it to get tacky, then apply two proper coats ?

Really would appreciate some help


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