I'm sure there's a more authentic material that could be used but generally that kind of problem is patched using Toupret Rock Solid filler. There is also the Masonry Repair filler. To strip the paint off you can use a mixture of scraping and IR stripper for the bits that are really stuck a sharp chisel is very effective although it takes a bit of feel to chip it off quickly.
Interesting comment ‘just need the time’. If you have any ideas where I could get some time, it would be appreciated. It seems it’s a valuable commodity and hard to find. Screw fix and local hard ware shops don’t have in stock currently.
I'm sure there's a more authentic material that could be used but generally that kind of problem is patched using Toupret Rock Solid filler. There is also the Masonry Repair filler. To strip the paint off you can use a mixture of scraping and IR stripper for the bits that are really stuck a sharp chisel is very effective although it takes a bit of feel to chip it off quickly.