I'm boarding my staircase in. I was going to use plasterboard /skim across the newell posts but it's already a narrow staircase. I'm considering using plywood instead as it could save me a bit of space, but I want it to look like plaster when it's done, so does/would plywood painted with emulsion look like plaster. I suppose MDF is an option as well but I don't find thin sheets particularly strong.