Hi I have an early 1900's 4 square kit home. We moved in 4 years ago and started removing wallpaper and painting one room at a time. All the rooms we've done so far had the typical white plaster over lathe walls. I just stripped the wallpaper in the living room and have encountered something that has me stumped. It started with one of my twins pulling off a piece of wallpaper and the plaster came with it so I opened the hole up a bit and patched in a piece of drywall. Since the room needed it anyway I stripped off all the paper planning on painting. The plaster though is pretty fragile and very gritty. It is spalling in spots and almost looks like poorly mixed concrete.It's also primed (?) in blue and green stripes with an outline like a grid for hanging wallpaper and a border. I thought at first that it was a concrete board that I was taking the paper off of but there are no joints and where it has holed you can see that the substance is keyed into wooden lathes. I've also discovered that someone has had loose cellulose insulation blown into the exterior walls between the outside wall and the lathe so removing the plaster and lathe is not an option. What kind of plaster is this and can I skim coat over it? What with, patching plaster,joint compound? I'm kinda stumped on what to do to repair this, if I can.