A flexible filler like toupret fibacryl is widely used for cracks up to 1 cm, which are then overpainted. But further movement can always reopen cracks particularly from a first floor room that is walked on.
I'd sand away any rough edges to begin with. I'd then use a MS polymer such as Sikaflex or CT1. They are like silicone sealants but can be overpainted.
Standard caulk may, or may not crack. Either way, caulk will shrink back, potentially leaving you able to see where the crack is/was.
Try to make sure that the concave section isn't too big when you apply/smooth the MS polymer, otherwise cutting in will be more difficult. It is always easier to cut in when you have a true right angle.
Use decorators' wipes to clean up afterwards. The sealant are very sticky.
A flexible filler like toupret fibacryl is widely used for cracks up to 1 cm, which are then overpainted. But further movement can always reopen cracks particularly from a first floor room that is walked on.
Fibacryl is great stuff but difficult to smooth off cleanly. Additionally, like other caulks, it will shrink back.
Although I too recommend it, I recently had to visit a house with crack in the suspended ceiling plasterboard join. Unfortunately the electrician fitted two recessed lights bang on the join. I didn't want to cut through the plasterer's tape and so simply dug through the top layer of skim and then applied the Fibacryl and then filled over the top of that.
It cracked again within two days. I guess that the crack wasn't deep enough for the fibacryl to work properly. The fact that I didn't allow it to cure fully before over filling didn't help either. I now have to go back and do an Easy Fill tape and fill...
Fibacryl isn't that good, I've seen it fail a number of times, it's impossible to sand as it's like chewing gum, it shrinks too. If you use it fill below the surface and then when dry over fill with red devil or similar.
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