I was trying to sand down my bathroom walls before painting. I have a fiberglass bathtub/shower that transitions to the wall with a piece of thin aluminum in between. There was an L-shaped piece of painted wood molding covering the strip-wall transition (pictured leaning against tub) which I removed in order to be able to get my sander to fit in the gap. But the thin layer of plaster on the strip is starting to crumble in places.
Edit: it's not just a side strip, it appears to extend to the whole wall above the shower.