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Getting plaster off tiles isn't complicated however, if you don't know what you're doing, you could damage the tiles or the plaster on the walls!

Are we talking plaster that sprayed onto the tiles or plaster on the walls that came up onto the tiles? I'm hoping the former but fear that it's the latter.

Please answer and we'll see what's tha safest way for you to correct your issue. (I'll tell you that the bond of the plaster to the tiles is far weaker than that of the plaster to the walls, so no power tools should be required)