ᐅ How to Remove Tar Patina from a Granite Ledge?

Hello,

I have 40 granite kerbstones from road construction that I would like to use for building.

Unfortunately, over the years, a very thin layer of tar from traffic has formed in some areas. How can I remove it?

The surface of the stone is very rough. Solvents and scrubbing don’t work for me.

Thanks in advance

I don't have practical experience, but try using hot margarine. In theory, it should work.

And then? Scrub like that? But then I end up with a huge grease stain that soaks into the stone.

Yes, scrub it off.
Well, the grease might end up more evenly distributed and less noticeable, and sooner or later it will wash out anyway... I don’t know what you plan to do with the stones.
You could also try using mineral spirits and warm the stones first with a heat gun.
Your "tar" (I assume it is bitumen, as tar has not been allowed in road construction for a very long time) is a hydrocarbon that was heated during processing. So, to remove it, you ideally need heat and another hydrocarbon, preferably one that is not sticky. That’s the theoretical basis I came up with.
Maybe try it on one stone first...

Ah, okay. How about using gasoline and a brush then?

My approach would be sanding – however, the rough texture will not be preserved.