I recently got an older house(1907), and one room had paneling on the walls where they had removed the wall between a closet and another bedroom(to make it larger). So behind the paneling is rock solid rough coat plaster, and then paint is on the rest of the walls. I’m going to skim coat the walls with gypsum plaster to give it a more historic feel. The plan is to have plain white plaster on the top half of the walls, and tinted plaster on the lower half. One of the pigments I’m using is pricey, so I’d like to get only what I need. But to calculate that, I need to know an average of how much plaster I’ll use. Any recommendations on how to estimate that? Also, will more plaster probably be needed for the rough coat wall?