Ceiling crack

crack repair tape from Brewers, then fill over the top.

 

If the crack is reappearing, then you've got movement - either the plaster boards or the ceiling joists or both

If you push on the PB either side of the crack, do the boards move slightly

Do you know if the PB joint lines up on a joist or noggin. Can try knocking a thin nail through the PB either side of the crack to see if you hit timber, or if the nail just disappears right through the board

If you have movement in the boards and if there is timber under the join, then happy days indeed

Add PB screws either side of the crack to firm up the boards. Drive heads just below surface but not tearing the face paper (can get PB screw bits that stop screw going in too deep)

Rack out crack, brush out loose bits. I would then brush PVA diluted 1-5 into the crack and let it soak in to edges of PB and dry, then repeat (maybe) dont get PVA all over the ceiling as may cause an issue when you paint ceiling. So, small artists brush or similiar to apply PVA, wipe ceiling either side of crack with damp cloth to remove excess

Then fill, sand, mist coat, emulsion, should be all good

If no timber to screw into, then PVA, scrim tape (will need to remove plaster just wider than tape from either side of crack) then filler, sand, mist coat, emulsion

Any quality filler I guess, Toupret interior is very good, SF sell it. Any thing branded 'flexible' will only put up with so much abuse and flexing though before it fails- it won't perform miracles. Always best to sort the problem first instead of relying on secondary methods and 'snake oil' !

If loose joists ...... dunno, much bigger problem