Filler, plaster, or use something else?

[Dandal88]

Hello, I've removed the old beading off my staircase skirting, as I plan to sand it all and paint it matte, leaving it as a square finish. Annoyingly, this was all an afterthought, AFTER we had all the walls skimmed with multifinsh.

With the 10mm gap I've been with, I think most areas i think ill get away with using filler then sanding, but some gaps are actually quite deep, like in the photos.

For the larger gaps, with not much behind them, would I get away with just using filler and then sanding square?

thanks

 

[Wayners]

Could you cut to allow for plasterboard?
PVA board edges of the new and existing plasterboard.
Stick board in with Stixall or other polymer.
Fill joints with toupret when you fit board so it all becomes one.
Sand and paint.

Maybe a think trim along edges of stringer. You will always have some movement to deal with....