how do you finish o.s.b. to have a finish like gyproc?

Question

o.s.b. (WAFERBOARD) when painted the wafers show through the paint.

Answer 1

Use a textured paint, or use a real good primer and then a coat of regular paint

Answer 2

You'd have to apply a skim coat of drywall mud to the whole wall and then sand it smooth---probably easier to texture paint the wall to hide the wafers. Or drywall with 1/4 inch drywall real quick over the OSB.