On one of the walls in a room I'm renovating, there are some kind of large boards, not sure what but it might be masonite? They have bulged in some places. I'm thinking of removing them and putting OSB boards instead. I've seen that many install drywall over the OSB boards. Why should one do that? Is drywall necessary or can you wallpaper directly on OSB?
Or maybe it's enough to just nail down the masonite where it's bulging?
Or maybe it's enough to just nail down the masonite where it's bulging?
OSB is quite uneven on the surface. Applying a smooth wallpaper to it would not be recommended without carefully plastering first. The reason for using OSB is for several reasons, it's sound insulating, and because drywall does not have enough load-bearing capacity if you, for example, want to hang up grandma's large mirror. 
The best result is likely to first install OSB and then cover it with drywall. Plaster the seams and screw heads. Then, it's just a matter of wallpapering!
The best result is likely to first install OSB and then cover it with drywall. Plaster the seams and screw heads. Then, it's just a matter of wallpapering!