Bitumen paint removal from flagstones

[photogav]

I hope this is in the right place.

In the past (prob 10 years ago) someone painted the side wall of a covered passageway at the side of my house with a bitumen paint (Before I bough it).

I am prepping for a entire house paint and want to remove the bitumen. The trouble is, at the bottom the bitumen goes over the edge of the stone flagstones.

Id like to remove it. Obviously a bit of elbow grease, a scrapper and time will get to top layer off, but what can I use on the stubborn stuff that is bound to be left. I don't want to damage the stone. Is there a house hold product (I have used caustic soda and wallpaper paste on wood before with great success) or a bought chemical that will remove the bitumen and leave the stone undamaged?

Thanks for your advice as always it is greatly appreciated

 

[Tigercubrider]

Try proper white spirit
I removed bitumen from parquet using it and a paint scraper

It melts the tar and dilutes it so you need to mop it up