1920 House - ceiling question.

Hi all,
We have a 1920 cape in NJ. Only lived here 3 years. The previous owners finished the attic to a master bedroom with a shower. A few weeks ago I noticed bubbling in the paint in the ceiling downstairs where the shower is. Got a plumber in and he said the seal around the shower pipedrain was probably leaking water and he sealed it. However, the paint downstairs seems to be coming away from the ceiling faster and in a wider area.
Today I climbed on a ladder and chipped a big piece of the paint from the ceiling. It doesn't seem most. There's literally about an 1/8th or more of an inch worth of paint so the paint layer is heavy. The ceiling seems to be made of something like concrete. I don't know what else to call it. It's rough and not like plaster (which is what I expected to find). It doesn't feel particularly most to the touch. I'm wondering a few things...
1) What might this material on the ceiling be? Can it be concrete? 2) Could the continued sagging paint and cracking be what's left from the original moisture that got into the ceiling and the paint is just falling down with gravity cuz now it's loose??? 3) How do I find out if there might be wet beams between the shower stall and the ceiling? I'm concerned I could have water damage in there.
At NO POINT was there a noticeable leak or water. Just bubbling paint that seemed like a sign of moisture, but no obvious water.
Not sure if that was all clear but I'll clear up anything that I can.
Thanks.
Girly Girl :)
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(1) It sounds like the ceiling is made of plaster, and you are getting layer separation. The plaster was applied in two layers. The base coat is the concrete-looking stuff (really, it's not too different from cement), tan or grayish stuff with visible sand and perhaps fibers as well. Then the thin white topcoat was put on. What is coming off is not super thick paint, but rather that top coat of plaster (plus paint).
(2) Yes it could be that what's happening now is just the continuation of problems caused by the leak, even though it is no longer leaking. If you are lucky.
(3) It would be good to investigate whether it is still leaking and whether there is other damage in there, although the latter is not that likely. Is there an access panel? Often a shower or bath will have an access panel in the wall behind it (which might be the back wall of a closet or something) that gives a look at the plumbing. If so you can open that and maybe investigate if things are wet in there. If not, you might have to bite the bullet and cut out a piece of ceiling below. Or just wait and see what else happens.
(4) There are a lot of ways a shower can leak; from the drain, or the seal between the wall and the pan, or through small cracks in the grout between the tile. If it wasn't put in right you can wind up ripping a lot out and redoing it.
Good luck --- H
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Wow, that was such a thorough and informative answer. I'm really grateful for that. Thanks for taking the time!
Girly Girl :)
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