I have a 1957 California Ranch house with vaulted beamed ceilings. The ceiling between the beams is formed from the underside of the roof decking/sheathing material. It is a fiber board covered with thin paper skin but you can see raw beveled fiberboard edges between deck sheets. I have attached a photo of the material. Over time the surface of the ceiling has gotten dingy, stained and needs attention. Painting it would be the cheapest, easiest option but I am unsure if the material can stand up to painting?

Perhaps I should mention I also thought about using a peel and stick paintable vinyl wallpaper between the beams but was unsure if the adhesive would adhere to the sheathing without damaging it.

I also considered enclosing the ceiling with plywood, drywall etc… but am concerned about sag, adding that much extra weight to those rib beams…