Thanks guys. Before we started tearing stuff out to see what was behind it, the walls had what I'm told is Marlite fiberglass reinforced paneling on them. It was really hard to clean and looked pretty ugly we thought. Under the Marlite FRP we found some plywood, some lathe and plaster. I think the plywood areas are covering lathe and plaster. I'm assuming the prudent thing would be to remove the plywood and lathe and plaster and get down to the studs?