How can the primer be removed from an earthen wall?

We deliberately chose traditional clay walls for our home, not least because of the beautiful texture. Unfortunately, an uninformed painter applied plaster primer from "Preludio" onto the clay and thereby ruined the beautiful appearance. How can we remove that stuff without destroying the clay texture? Does the primer possibly have negative effects on the natural material properties of clay?

"Preludio is a mineral, slightly gritty primer for subsequent clay decorative plasters. It compensates for different absorption behaviors in the substrate and ensures sufficient mechanical adhesion with the clay plaster."

I got this information from the manufacturer. Why did the painter apply this primer, was he contracted to do so - what was his assignment? In any case, this was the wrong product. Preludio is suitable as a substrate for clay decorative plasters - not as a medium on clay plaster. The primer must be sanded off: orbital sander with extraction.