When I had my interior worked on, I was told this was not stain due to water, but adhesive that had not been cleaned properly at the factory..? Anyone know how I should clean this? I have it in a few places and would like to take care of it in the spring.
This ceiling material seems somewhat porous. I would be very careful before using anything that may be absorbed and make matters worse. Maybe you should first test whatever you decide on inside a cabinet.
To mirror what Ruben said, two coats of "Kilz" the real stuff, NOT the acrylic stain killer. Yes, the smell is terrible, but use the original Kilz and it will do the trick.