Remove plaster residues from sandstone

Hello everyone!

How can hard, dry plaster residues be removed from sandstone? These are sandstone blocks of a garden wall.

By the way, I find it difficult to come up with more lines (to reach 200 characters), although I have already asked my quite simple question. Thank you very much!

Regards
Mike

Without having tried it myself, I would take a hard brush. In the worst case, a softer wire brush.

Without damaging the surface, probably not at all.

Chipping off large chunks, sandstone will come away. Possibly wire brush

If you have time, frost might cause a detachment.

Ok, thank you very much for the previous answers. Is there perhaps a liquid agent for that? Acetone?

Not attempted. Sandstone is very soft. I would not dare to use chemical solvents.