On Saturday, 13 April 2019 09:35:27 UTC+1, DerbyBorn wrote:
What is the easiest way to seal with a hairline crack in the overskim of a
plasterbaord covered wall.

Do I need to rake it out or can I apply something that will penetrate and
fill it (Creeping Crack Cure?)

Probably a joint with no scrim.
If so, it will come back whatever you do.