If a pressure washer is going to damage the ceiling, it's not a structurally sound ceiling.
If you want to remove all the paint, you can also use a dry ice blaster. Think sand blasting, but without the cleanup of all the sand.
It's a no less than 4-inch poured slab and the damage is only in the interior surface as I described above.
I have seen the dry ice thing at work where they used it to decontaminate some machines (pharmaceutical packaging) from some nasty stuff before they were used for a different product but that's just too expensive. I think some elbow grease will be the solution after all.
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