In article .com,
" says...
Some respondents imply that steam or water will only remove tiles that
were stuck on with wallpaper paste or something similar.

My house had some poly tiles stuck to one ceiling. I removed the bulk
of them mechanically with a paint scraper. Each tile was stuck to the
ceiling with five blobs of glue. The type of glue was unknown, but I
would assume it was something sold as a poly tile adhesive.

I was delighted to discover that a steam wallpaper stripper rapidly
softened the adhesive and it was possible to entirely remove it with a
paint scraper.

Obviously not the stuff they used in my dining room then - scraping
pulled off chunks of plaster, steaming didn't touch it. I eventually
attached a hot air gun and a scraper to a length of 2x1, which did
the job but the fumes were nasty and wearing a respirator made it
really uncomfortable even at a distance - I needed to get quite a lot
of heat into the plaster and it soon got too hot to be comfortable
working near it. Maybe I'll try using a big fan to keep the air
clear, and finish it off when the weather cools down.