How and what can I loosen up stucco or popcorn ceiling paint with?
That's a messy job, use a profession. Be sure to get furniture and items out of each room being done as they spray stuff on it to soften it up and then scrape it off the ceiling (there might be other ways, but that's how the professionals do it in Fla, were there are TONS of popcorn ceilings!).
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