it isn't terribly important, but i'm wondering what the heck this stuff is.

i removed some wallpaper from a wall in my stairwell and found some typical plaster damage underneath. what was atypical were the previous repairs. in one section, an area about the size of a horizontal piece of paper was missing the original plaster. you wouldn't know at first glance, because the area was completely patched.

but as i poked at it, i found that from the surface of the wall all the way to the lath (this stuff was keyed into the lath) was a patching material that was almost like styrofoam. you could stick a fork in it if you wanted to.

any idea what the heck this might be? my plan is to remove it all and fix the plaster properly -- just curious about this oddball material.