Stone window jambs

Redecorating a room and the paint on the jambs on the window had started to flake, beneath it is a solid stone finish. Previously the paint covered up all the texture of the stone and it had a smooth finish but I now have a partially smooth partially masonry surface.

I want to get an even finish be it smooth or masonry however the previous paint wont budge, tried 40grit sand paper and a scraper. I've tried one of the sandex smooth masonry testers pots but this is still leaving a stone texture and it looks awful, is there a product that you could recommend to get a smooth finish to the masonry?

Do you mean the jambs or masonry returns. Are we talking about the outside?

If yes, you can use two pack styrene filler (for a very smooth finish) or Murex or Touprelith F for a slightly less smooth finish.

Touprelith F is the easiest to sand but the least smooth.