around a month ago i plastered a kitcken wall for my folks. the wall
was uneven so i used thistle hardwall as an undercoat after sealing the
wall with pva, then applied the plaster after another wet pva coat.
Left this to dry over night then the next day again i sealed the wall
with pva again and skimmed the wall with multfinish over another coat
of wet pva.

came back after a few days and noticed a few hairline cracks. i damped
the cracks with a wet sponge and the cracks have shrunk. going to apply
a little filler and sand, should look ok.

came back after a month to do some more work on the room and after
inspection of my previous work. ive noticed that alot of the wall
sounds hollow when i tap on it. mainly the part of the wall i plastered
last. the parts where the cracks were sound fine.

i am wondering if the tacky pva i used before skimming/scratch coat
dryed before i got to that part of the wall?

i wished i used thistle bonding instead of hardwall, is this right?

should i have not sealed the scratch coat with pva?

should i leave this wall as it is and paint it. or ive heard that it is
possible to drill a small hole in the plaster and inject some pva into
it to bond the plaster.

any advice on this whould be great!! i have three more walls to do
round there.