Help filling hairline cracks in newly skimmed walls!

[handyman11]

I have just had a bedroom skimmed and have noticed a couple of hairline cracks in the corners of the room, about three or four foot down from the ceiling that sort of run diagonally up the wall towards the ceiling.

Its a Victorian terraced house so I presume this is not uncommon?

Anyway, I bought some Ronseal Smooth finish filler (quick dry) and ran that over it with my finger. As soon as I had done it, it looked like the hairline crack had gone, but a few minutes later, as the filler started to dry I could see the crack again, showing through the filler. It seems like a good filler and certainly it dries quite smooth, but it does not seem to be working. I want to avoid opening the crack up, as I will simply make it worse!

Any advice really appreciated. I heard polycell do a brush on filler specifically for hairline cracks, is it worth me buying this? Or do Ronseal have something more appropriate?
Thanks a lot.

 

[Bosswhite]

Filler shrinks when it dries out, it needs several fillings and rubbing down.

 

[Pigeon85]

When you give the new plaster a mist coat before painting you may find that will fill the crack. Personally I would advise to open the crack up then fill and sand twice, I know you don't want to go down that route but it always does the job for me.