I can't identify the material that was on the layout that we are restoring for an Eagle Scout project and museum display.
You can get a glimpse in some of the photos in this thread.
I can pinch a piece off of an edge. It crumbles, but seems to have a fibers in it. The layout was built in 2003. I don't think Fusion Fiber was available then. It's too soft for straight plaster. It was applied over brown paper shopping bags about 1/4"-3/8" thick. It will rub to powder between the fingers and has some flex to it.
Is this perhaps the actual plaster cloth used for casting limbs that has succumbed to age and dampness?
We have a lot to replace or refresh, so any thoughts are appreciated.
