I recently bought a Victorian-era house. We had wallpaper removed in several rooms and found horsehair walls that are for the most part in remarkable shape. In several areas, the surface is a chalky white though. At first I though it was calcimine, but now I'm not sure. It seems to have been used as a patch in a couple of small (2-3 inch round areas) and in one large area. The large area butts up against a piece of drywall (I think some plaster had to be removed at some point to work on the heating ducts in the wall) and the white chalky material is covering the mesh joint tape.
Any idea what this is? Can I paint over it? In some areas it is covered with a thin layer of what looks like paint that has bubbled and peeled. We were considering covering a small area with a heavy-duty oil primer and letting it sit for a few days to see what happens.