On Sat, 13 Apr 2019 08:35:25 GMT, 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?)

Captain Tollys Creeping Crack Cure is really for sealing "cracks"
that are no more than break in non absorbant materials that still
have capillary action.

Personally I follow the line of the crack with the point of a trowel,
making the crack wider and a few mm deep. Mix up some ordinary powder
filler, fairly stiff, spray the raked out crack with water to reduce
the suction, apply filler to crack with a flexible spatula filling
knife/blade, making sure the crack is fully filled. Leave very
slightly proud, layer of filler on surrounding plaster translucent
thin but not critical if there are some thicker lines from the edge
of the knife. Wait 10 mins, until the filler is partially set, wet
the flexible filling knife and smooth the the lot leaving just a
residue around. Leave to dry fully wipe of residue with damp cloth.

If the crack was caused by known movement that can't be sorted out
rather than just a random crack I'd be tempted to use decorators
caulk. Normally reserve that for timber/wall gaps, though more
recently have used powder filler as above and again fairly stiff for
that and it's not cracked,
yet...

--
Cheers
Dave.